Co-reporter:Shanke Liu, Linhu Li, Liejin Guo, Hui Jin, Jiajing Kou, and Guoliang Li
Energy & Fuels November 16, 2017 Volume 31(Issue 11) pp:12046-12046
Publication Date(Web):October 19, 2017
DOI:10.1021/acs.energyfuels.7b02505
Coal supercritical water gasification (SCWG) is famous for generating clean gas without SOx pollutant. Study of sulfur transformation characteristics can provide the basis of sulfur removal during hydrogen production by coal gasification in supercritical water (SCW) at the source. In this work, two coals produced from Linfen and Zhangjiamao in China (hereinafter to be referred as L-coal and Z-coal), were chosen as experimental feedstocks to investigate sulfur transformation characteristics during hydrogen production by coal gasification in SCW (550–750 °C, 20 min, 25 MPa). Sulfur transformation pathway and sulfur forms in the products were complex but detected comprehensively. H2S was the only gaseous product instead of SOx, whereas SO42– was the main liquid–sulfur product. Inorganic and organic sulfur compounds were used to investigate sulfur transformation mechanisms. H2S had three sources as follows. First, among inorganic sulfur of raw coal, FeS2 (Pyrite) was chemically stable in SCW lacking of hydrogen. When FeS2 was in hydrogen atmosphere, H2S was generated and FeS2 was converted to Fe1–xS and Fe3O4 under SCW. Second, H2S came from unstable sulfate minerals such as FeSO4 which may decompose and be converted to Fe3O4. Third, organic sulfur, especially thiophene sulfur transformed to H2S. The two sulfur products H2S and SO42– depend on H or OH free radical in SCW. More H free radical provided a reducing environment of SCW to generate H2S at higher temperatures, whereas more OH radical provided an oxidizing environment of SCW to generate SO42– at lower temperatures, but the final trend was generating H2S when coal gasified completely at a higher temperature. The results of this study may provide an experimental basis of solving the SOx emission from coal at the source and demonstrate a promising clean utilization way of coal.
Co-reporter:Qiang Xu, Liejin Guo, Liang Chang
International Journal of Heat and Mass Transfer 2017 Volume 110(Volume 110) pp:
Publication Date(Web):1 July 2017
DOI:10.1016/j.ijheatmasstransfer.2017.03.017
•Condensation regime diagram is developed to describe the four condensation regimes.•Mechanisms of pressure oscillation in the four regimes are explored.•Probability Distribution Function of pressure signal under varies regimes is studied.•Deviation and maximum of pressure signal could identify four condensation regimes.Pressure oscillation associated with direct contact condensation of steam jet in water pipe flow is of high significance for industrial processes. In this paper, experimental study is conducted to reveal the mechanisms of the pressure oscillation in steam jet condensation in water flow in a vertical pipe. The interfacial characteristics of the jet plume are acquired by high speed camera, and the pressure oscillation due to condensing jet are captured by using high frequency pressure transducers. Four main types, including Chugging, Oscil-I, Oscil-II and Stable condensation regimes, are identified visually based on the interfacial behavior of the jet plume, and their distribution is described in a three-dimensional condensation regime diagram based on steam mass flux, water temperature, and Reynolds number of water flow. In the Chugging regime, the high-amplitude pressure oscillation appears at low frequency, and the unimodal PDF demonstrates that the pressure oscillation is only dominated by steam mass flux. In the Oscil-I regime, the pressure oscillation is approximately sinusoidal and its intensity is the highest among the four condensation regimes, whereas the intensity of the pressure oscillation remains at a low level and varies little in the Stable regime. In both the Oscil-I and Stable regimes, with increase of water temperature and Reynolds number of water, the unimodal PDF spreads out over a wider range, and finally the bimodal and symmetrical PDF appears for the Oscil-I regime. The statistical analysis shows that both the deviation and maximum of pressure signals could identify the four condensation regimes well, while both the skewness and kurtosis of pressure signals could easily distinguish the Chugging and Oscil-II regimes.
Co-reporter:Wensheng Li, Liejin Guo, Xiangdong Xie
Chemical Engineering Science 2017 Volume 171(Volume 171) pp:
Publication Date(Web):2 November 2017
DOI:10.1016/j.ces.2017.05.017
•Experiments on air-water flow in a long pipeline with an S-shaped riser were made.•Effects of a long pipeline on severe slugging properties and region were analyzed.•A modified stability criterion for severe slugging was derived.•A stability criterion for unstable flow in pipeline/riser systems was derived.Severe slugging is an undesired multiphase phenomenon in offshore pipeline/riser systems. Previous experimental studies have been limited to relatively short pipelines (no more than 400 m) compared with the subsea fluid transportation system. Here, a much longer pipeline/riser system (46 mm ID) was built to investigate severe slugging. The test loop consists of a 1657 m long horizontal pipeline; 30 m long, 7-degree downward inclined pipeline; and 11.2 m high S-shaped riser. Based on the pressure cycling characteristics, the flow patterns were classified into three broad categories. It was found that the long pipeline resulted in a longer slug production stage during severe slugging flow, eventually leading to longer liquid slugs. The critical gas velocities for the severe slugging region were larger compared with short pipeline/riser systems, while the critical liquid velocities were barely influenced by the long pipeline. The main factors that influenced the flow pattern transitions on the critical gas and liquid velocities for the severe slugging region were different. Based on the existing models, two criteria for severe slugging and unstable flows were developed, and more accurate predictions were obtained when compared with experimental results in the present study and the literature.
Co-reporter:Yupeng Yang, Xu Zhang, Liejin Guo, Hongtan Liu
International Journal of Hydrogen Energy 2017 Volume 42, Issue 38(Volume 42, Issue 38) pp:
Publication Date(Web):21 September 2017
DOI:10.1016/j.ijhydene.2017.07.223
•Anode pressure swing significantly mitigates degradation in PEM fuel cell with DEA.•Anode pressure swing supply reduces electrolyte membrane degradation.•Anode pressure swing has no significant effect on cathode catalyst degradation.High cost remains to be one of the primary obstacles for the commercialization of proton exchange membrane fuel cells (PEMFCs). To simplify the fuel cell system and reduce cost, dead-ended anode (DEA) is widely used. However, water and nitrogen can accumulate in the dead-ended anode, resulting in cell performance decrease and severe cell degradation. Anode pressure swing supply is a new technology which has been shown to be effective in reducing local water and nitrogen accumulation in the anode channel. In this work, the effects of pressure swing supply on fuel cell degradation have been experimentally studied. Two sets of experiments on the same fuel cell are conducted, one under conventional constant pressure operation and the other under pressure swing operation. Polarization curves show that pressure swing supply can significantly mitigate cell degradation during DEA operations. Electrochemical characterizations are performed to study the mechanisms of mitigations in cell degradation. The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) results show that pressure swing supply can significantly reduce electrolyte membrane degradation, but has no significant mitigation effect on the cathode catalyst degradation during DEA operation. Further examinations of the membrane-electrode-assembly (MEA) by scanning electron microscope (SEM) confirm the significant difference in membrane degradations since there is a very large difference in average thickness of the membranes after the degradation tests.
Co-reporter:Kai He, Liejin Guo
International Journal of Hydrogen Energy 2017 Volume 42, Issue 38(Volume 42, Issue 38) pp:
Publication Date(Web):21 September 2017
DOI:10.1016/j.ijhydene.2017.06.234
•The NiS/CdS was successfully synthesized via a new one-step-ammonia method.•The NiS/CdS showed an extremely high apparent quantum yield (74.6%) at 420 nm.•The NiS/CdS showed a perfect photocatalytic stability maintaining for 120 h.•Two barriers promoting the separation of photo-generated charges was proposed.NiS modified three-dimensional pyramidic CdS with stacking fault structures were successfully synthesized by using the one-step method and an ammonia aqueous solvent as the hydrothermal solvent. Thus, CdS showed superior photocatalytic activities for hydrogen evolution from water under visible light irradiation (λ ≥ 420 nm), which could achieve a hydrogen evolution rate of 49.2 mmol g−1 h−1, with an extremely high apparent quantum yield (AQY = 74.6%) at 420 nm. To our knowledge, this value is the highest reported efficiency value for NiSx modified CdS photocatalysts. CdS exhibited a three-dimensional pyramid structure with large specific surface areas, which may provide more active sites for the photocatalytic reaction. Stacking fault structures were observed in CdS by transmission electron microscopy (TEM). P-type NiS nanoparticles were highly dispersed on the surface of n-type CdS pyramids, forming p-n junctions at the interface. The stacking fault structures and junctions strengthened the separation of photo-carriers near the interface, which may greatly enhance the activity of photocatalytic hydrogen production for CdS. The catalyst also showed perfect stability, and the photoactivity showed no significant degradation during continuous hydrogen production over nearly 120 h, which has not been reported in the literature.The CdS particles formed pyramid structures, and the NiS particles attached to the plane of pyramid structure (red circled portion), showed in Fig. a. The clear stacking fault structures can be obviously observed within pyramid CdS shown in TEM images (b). The activity of hydrogen production for NiS/CdS with different concentration of lactic acid was showed in Fig. c. When the concentration of lactic acid was enhanced to 50%, The average rate reached maximum of 49.2 mmol g−1 h−1 with an extremely high apparent quantum yield (AQY = 74.6 %) at 420 nm. To our knowledge, this value was the highest efficiency for NiSx modified CdS photocatalysts. The catalyst also showed a perfect stability for photocatalytic reaction of continuous long time, and the photoactivity had no significant degradation after photocatalytic reaction for 120 h under visible light irradiation, which had not been reported in the literatures.Download high-res image (333KB)Download full-size image
Co-reporter:Zhixiao Qin;Yubin Chen;Zhenxiong Huang;Jinzhan Su;Liejin Guo
Journal of Materials Chemistry A 2017 vol. 5(Issue 36) pp:19025-19035
Publication Date(Web):2017/09/19
DOI:10.1039/C7TA04434H
Developing suitable cocatalysts is crucial to promoting photocatalytic hydrogen and oxygen generation using solar energy. Herein, non-precious NiCoP-based cocatalysts were synthesized by a facile solid-state phosphorization reaction, and coupled with metal-free graphitic carbon nitride (g-C3N4) for photocatalytic reactions. It was revealed that NiCoP-based nanoparticles exhibited a core/shell structure, where the NiCoP core was surrounded by amorphous-like nickel cobalt phosphate (NiCo–Pi) shell. The detailed spectroscopic and electrochemical studies demonstrated that NiCoP cores behaved as the active sites for the photocatalytic reductive half-reaction, and NiCo–Pi shells could serve as the active sites for the photocatalytic oxidative half-reaction. As a consequence, the improved surface reaction rate through the bifunctional NiCoP-based cocatalyst, as well as the enhanced charge separation efficiency, cooperatively boosted the separate photocatalytic hydrogen and oxygen generation in the presence of appropriate sacrificial reagents. The apparent quantum efficiency for hydrogen generation over the NiCoP@NiCo–Pi/g-C3N4 photocatalyst can reach 9.4% at 420 nm, which is one of the best values for noble-metal-free g-C3N4-based photocatalysts. To our knowledge, this is the first demonstration of the NiCoP-based cocatalyst to promote both photocatalytic hydrogen and oxygen generation, which is expected to pave a new way to exploit efficient bifunctional cocatalysts for overall water splitting.
Co-reporter:Yupeng Yang, Xu Zhang, Liejin Guo, Hongtan Liu
International Journal of Hydrogen Energy 2017 Volume 42, Issue 47(Volume 42, Issue 47) pp:
Publication Date(Web):23 November 2017
DOI:10.1016/j.ijhydene.2017.09.103
•Anode pressure swing supply can cause voltage spikes during DEA operation.•The voltage spikes are caused by the backflow of liquid water and nitrogen.•An anode exit reservoir can effectively eliminate/minimized the voltage spikes.•There is a threshold amplitude for effective pressure pulsation.In proton exchange membrane fuel cells with dead-ended anode, water and nitrogen can accumulate in the anode, causing cell performance decrease and cell degradation. The anode pressure swing operation can reduce the local accumulation of water and nitrogen by generating an oscillatory flow in the anode channel. However, sharp spikes are observed in cell voltage and these spikes are especially large near the end of a purge period. Thus the mechanisms of these voltage spikes are studied through dynamic voltage and local current measurements. The measurement results show that even though the average current density is maintained constant, local current densities also experience sharp spikes and these spikes occur at exactly the same time as the voltage spikes. By examining the spikes in local current densities, it is found that in the upstream the spikes are upward and in the downstream downward. Further detailed study show that the periodical spikes of cell voltage and local current densities are due to the backflow of liquid water and nitrogen in the anode channel from the outlet tube. Based on the mechanism, a novel approach to alleviate the cell voltage spikes is proposed – adding an anode exit reservoir. The experimental results with the anode exit reservoir show that it is very effective in reducing the spikes of cell voltage and local current densities by storing accumulated liquid water and nitrogen and enhancing the backflow of hydrogen. With the anode exit reservoir, the effect of the pressure pulsation amplitude on the cell performance is also studied. The experimental results show that there is a threshold of the pressure pulsation amplitude for a specific fuel cell system and the threshold for the experimental fuel cell is around 0.05 bar.
Co-reporter:Wen Cao, Changqing Cao, Liejin Guo, Hui Jin, ... Xiangdong Yao
International Journal of Hydrogen Energy 2017 Volume 42, Issue 15(Volume 42, Issue 15) pp:
Publication Date(Web):13 April 2017
DOI:10.1016/j.ijhydene.2017.03.115
•SCWG of diosgenin solid waste for hydrogen production was firstly studied in a fluidized-bed reactor.•K2CO3 was used to catalyze the SCWG of diosgenin solid waste.•Black liquor was firstly used as a substitute of alkalis source to catalyze the SCWG of diosgenin solid waste.•K2CO3 was found to migrate into the residue char during the SCWG process by SEM analysis.The potential of diosgenin solid waste (DSW) to be a proper feedstock for hydrogen production from supercritical water gasification was assessed through thermodynamic analysis and experimental study. The thermodynamic analysis of DSW gasification in SCW was performed by Aspen Plus software based on the principle of minimum Gibbs free energy. The effects of temperature (500–650 °C), flow ratio of feedstock slurry to preheated water on the gasification were studied. K2CO3 and black liquor were used to catalyze the gasification of DSW. The morphological structures of DSW and residue char were characterized by SEM. The results showed that DSW was almost completely gasified at 650 °C without catalyst and the carbon gasification efficiency reached up to 98.55%. K2CO3 could significantly promote the gasification reactivity of DSW at a lower temperature. H2 yield was remarkably improved by adding black liquor. The SEM analysis indicated that parts of the organic matters reacted to form gases and liquid products, and K2CO3 was found to migrate into the residue char during the reactions.
Co-reporter:Zhiwei Ge, Liejin Guo, Hui Jin
International Journal of Hydrogen Energy 2017 Volume 42, Issue 15(Volume 42, Issue 15) pp:
Publication Date(Web):13 April 2017
DOI:10.1016/j.ijhydene.2017.02.018
•A kinetic model for non-catalytic partial oxidation of coal in SCW is developed.•Steam reforming of fixed carbon is the rate-determining step for coal gasification.•CH4 is the rate-determining step for directional hydrogen production.•The SCWG process of coal in reactor could be simulated by using the kinetic model.Supercritical water gasification (SCWG) has attracted great attention for efficient and clean coal conversion recently. A novel kinetic model of non-catalytic partial oxidation of coal in supercritical water (SCW) that describes formation and consumption of gas products (H2, CO, CH4 and CO2) is reported in this paper. The model comprises 7 reactions, and the reaction rate constants are obtained by fitting the experimental data. Activation energy analysis indicates that steam reforming of fixed carbon (FC) is the rate-determining step for the complete gasification of coal. Once CH4 is produced by pyrolysis of coal, steam reforming of CH4 will be the rate-determining step for directional hydrogen production.
Co-reporter:Kai Zhang, Yawen Dai, Zhaohui Zhou, Saad Ullah Jan, Liejin Guo, Jian Ru Gong
Nano Energy 2017 Volume 41(Volume 41) pp:
Publication Date(Web):1 November 2017
DOI:10.1016/j.nanoen.2017.09.021
•Nanocrystals with zincblende-wurtzite (ZB-WZ) superlattice show an excellent quantum efficiency of 48.7% at 425 nm.•DFT simulation elucidates that saw-tooth-like potential distribution in ZB-WZ superlattice dominates charge separation.•The potential distribution in ZB-WZ superlattice could be tuned by changing its specific configuration.•It opens a new pathway for the design of efficient photocatalyst.Hydrogen production from solar water splitting over semiconductors shows great potential in solving the urgent energy and environmental issues, but its energy conversion efficiency is always restricted by the insufficient utilization of photogenerated charge carriers. Introducing built-in electric fields is a promising strategy for achieving efficient charge utilization in photocatalysts. However, the representative examples of built-in electric fields reported to date all have their own insurmountable shortcomings. Herein, we demonstrated that the zincblende-wurtzite (ZB-WZ) superlattice structure which widely spreads in II-VI and III-V group semiconductors is a promising candidate for the sufficient utilization of photogenerated charge carriers. We developed the ZB-WZ superlattice structures in a model semiconductor photocatalyst, Cd1−xZnxS, by employing the oriented-attachment growth mechanism, and realized highly efficient photocatalytic hydrogen production under visible light irradiation with an excellent apparent quantum yield of 48.7% at 425 nm. Then the huge impact of the ZB-WZ superlattice structure on the photocatalytic performance was proved by the strong reciprocal relationships between the percentage of the nanocrystals with superlattice structures and the photoluminescence intensity, as well as that between the photoluminescence intensity and the photocatalytic activity. Moreover, theoretical simulation demonstrated that the spatial separation and alternate accumulation of electrons and holes around ZB/WZ interfaces is dominated by the polarization-induced saw-tooth potential distribution in the ZB-WZ superlattice rather than the staggered band alignment, and the intensities of built-in electric fields in adjacent ZB and WZ segments can be tuned by changing the specific configuration of the ZB-WZ superlattice. These findings open a new pathway for the development of novel and efficient semiconductor photocatalysts by tuning the superlattice structure with atomic precision, which will greatly benefit the solar water splitting area.Download high-res image (176KB)Download full-size image
Co-reporter:Changqing Cao, Liejin Guo, Hui Jin, Wen Cao, Yi Jia, Xiangdong Yao
Energy 2017 Volume 132(Volume 132) pp:
Publication Date(Web):1 August 2017
DOI:10.1016/j.energy.2017.05.104
•The integrated system of pulping process and SCWG of black liquor was simulated.•The separator parameters were optimized by calculating the phase equilibrium.•Both process using air and oxygen as oxidant in gas combustion were compared.•The mass and energy flow of the integrated system was obtained.•The total energy consumption of pulp production in the form of kgce was obtained.Supercritical water gasification is an innovative black liquor treatment method for hydrogen production. In the present study, an integrated system of pulping and SCWG of black liquor was simulated. Combined hydrogen, power, MP and LP steam are produced for pulping process. The gas product after H2 extraction was burned with imported natural gas to supply more heat. For a reference pulp mill producing 1000 ADt pulp/day, potentially 37126 Nm3/h hydrogen can be produced. The generated MP and LP steam can fully meet the requirement of pulping process. Using air as oxidant in gas combustion is more energy-efficient than using oxygen for being free of oxygen production process. In the case of using air, 22604 kW power can be exported after balancing the consumptions and 219 kgce energy can be produced with 1t pulp production. While using oxygen, 10723 kW power needs be imported and 288 kgce energy can be consumed to produce 1t pulp. However, using air as oxidant may bring N2 and NOx in the exhaust gas, posing a challenge to the subsequent processing. Scaling-up of the system improved the energy efficiency, but the influence is very small when the capacity is above 250ADt/day.
Co-reporter:Qiang Xu, Liejin Guo
Applied Thermal Engineering 2017 Volume 117(Volume 117) pp:
Publication Date(Web):5 May 2017
DOI:10.1016/j.applthermaleng.2017.02.024
•Massive experimental data on steam jet condensation in water pipe flow system.•Clear interrelations between condensation regimes and features of pressure signal.•Method of extraction features and their ability evaluation of regimes classification.•Support vector machine is adopted to the clusters for construction of classifiers.•Satisfactory recognition rate of condensation regimes by pressure signal is gained.Recognition of unstable and harmful condensation regimes in liquid pipe flow system can promote a higher level of flow assurance in liquid propellant rocket engine. However, challenges are encountered in extracting distinguishable characteristics from pressure oscillation signals which commonly contains plentiful information strongly associated with various condensation regimes. This article attempts to set up a simple and practical approach of recognizing the steam jet condensation regime in water pipe flow system based on statistical features of pressure oscillation. The recognition procedure was performed in three major steps. Initially, twelve statistical features of pressure oscillation in time-domain (probability density function) and frequency-domain (power spectrum density) were chose. Subsequently, principal component analysis was implemented to obtain the clear interrelations between condensation regimes and statistical features of pressure oscillation signal, and then to extract useful features for establishing condensation regimes clusters for classification in the selected features space. Finally, least squares support vector machine was adopted to the clusters for construction of classifiers to forecast the condensation regimes automatically. The experimental results showed that the proposed approach is feasible and effective for recognizing the steam jet condensation regime in water pipe flow system by statistical features of pressure oscillation.
Co-reporter:Zhixiao Qin, Yubin Chen, Xixi Wang, Xu Guo, and Liejin Guo
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 2) pp:1264
Publication Date(Web):December 29, 2015
DOI:10.1021/acsami.5b09943
In the field of photocatalytic hydrogen generation, cocatalysts play a vital role in enhanced properties. Delicate control of the physicochemical properties of cocatalysts and systematic optimization of the coupling between cocatalysts and host photocatalysts are essential. Herein, a simple one-step hydrothermal method was proposed to synthesize noble-metal-free NiSx/CdS photocatalysts for the first time. Time-dependent growth studies revealed that NiSx cocatalysts and CdS host photocatalysts were intergrown with each other in the one-step hydrothermal process. Compared with NiSx@CdS photocatalysts prepared by the common two-step method, the intergrowth effect induced close contact between NiSx and CdS, as well as smaller size and better dispersity of NiSx nanoparticles. These specific characters of NiSx/CdS finally resulted in efficient charge separation and rapid surface reaction, giving rise to significantly improved photocatalytic activity with the apparent quantum efficiency at 420 nm as high as 60.4%. To our knowledge, this value is the highest efficiency for NiSx modified CdS photocatalysts and is among the best efficiencies for visible-light-driven photocatalysts. It is believed that the present work can provide a general guidance to develop an efficient heterostructured cocatalyst/photocatalyst system for hydrogen generation.Keywords: cocatalyst; hydrogen generation; intergrowth; one-step; photocatalyst
Co-reporter:Xiaoyang Feng, Yubin Chen, Zhixiao Qin, Menglong Wang, and Liejin Guo
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 28) pp:18089-18096
Publication Date(Web):June 27, 2016
DOI:10.1021/acsami.6b04887
Herein, sandwich structured tungsten trioxide (WO3) nanoplate arrays were first synthesized for photoelectrochemical (PEC) water splitting via a facile hydrothermal method followed by an annealing treatment. It was demonstrated that the annealing temperature played an important role in determining the morphology and crystal phase of the WO3 film. Only when the hydrothermally prepared precursor was annealed at 500 °C could the sandwich structured WO3 nanoplates be achieved, probably due to the crystalline phase transition and increased thermal stress during the annealing process. The sandwich structured WO3 photoanode exhibited a photocurrent density of 1.88 mA cm–2 and an incident photon-to-current conversion efficiency (IPCE) as high as 65% at 400 nm in neutral Na2SO4 solution under AM 1.5G illumination. To our knowledge, this value is one of the best PEC performances for WO3 photoanodes. Meanwhile, simultaneous hydrogen and oxygen evolution was demonstrated for the PEC water splitting. It was concluded that the high PEC performance should be attributed to the large electrochemically active surface area and active monoclinic phase. The present study can provide guidance to develop highly efficient nanostructured photoelectrodes with the favorable morphology.
Co-reporter:Xiaowei Hu, Zhenshan Cao, Yechun Wang, Shaohua Shen, Liejin Guo, Juanwen Chen
Electrochimica Acta 2016 Volume 202() pp:175-185
Publication Date(Web):1 June 2016
DOI:10.1016/j.electacta.2016.04.028
This paper presents a study on single bubble photogenerated by 376 nm laser light at TiO2 nanorod-array electrode during photoelectrochemical (PEC) conversion. The surface properties of TiO2 nanorod-array electrode were investigated at first for a better understanding of the three-phase contact line behavior. The results indicate the light-induced hydrophilic effect of TiO2 nanorod-array electrode under illumination, which makes bubble tend to be pseudo-sphere shape during attaching on electrode. The experimental investigation on photogenerated bubble at TiO2 nanorod-array electrode shows that there is a linear relationship between cubic root of time and bubble radius, demonstrating the gas products from the surface reaction transferring into bubble through bubble bottom according to the analysis of the relative size between bubble and effective solid surface. Furthermore, the coupling effects between bubble and irradiance were discussed. The bubble scatter effect on light causes a local light intensity increase at electrode surface area on both sides of bubble, and leads to photocurrent increase especially at small bubble size. While the increase of irradiance causes the parameters of bubble evolution period, dissolved gas concentration for nucleation and departure diameter increase, but leads to bubble evolution rate and incident photon conversion efficiency (IPCE) decrease. These results suggest a lower irradiance is preferred for a higher PEC conversion efficiency from the aspects of IPCE and bubble evolution rate.
Co-reporter:Tao Zhang, Jinzhan Su and Liejin Guo
CrystEngComm 2016 vol. 18(Issue 5) pp:665-669
Publication Date(Web):24 Sep 2015
DOI:10.1039/C5CE01484K
We reported a facile solvothermal strategy for fabricating hierarchical architectures of WO3 nanosheets with WO3 nanorod branches standing orderly on the nanosheets. An enhanced photoelectrochemical activity is achieved, attributable to the high porosity provided by the hierarchical architecture. The novel 3D nanostructure holds great potential in photocatalysis, concurrent filtration, water purification and chemical sensing.
Co-reporter:Jinwen Shi, Yazhou Zhang, Yuchao Hu, Xiangjiu Guan, Zhaohui Zhou, Liejin Guo
Journal of Alloys and Compounds 2016 Volume 688(Part A) pp:368-375
Publication Date(Web):15 December 2016
DOI:10.1016/j.jallcom.2016.07.053
•Novel MoS2-based photocatalysts developed by high-temperature NH3 treatment on MoS2 nanosheets.•First report on NH3-treated MoS2 as effective host photocatalyst rather than cocatalyst for photocatalytic H2 evolution.•An effective route to explore new H2-evolution photocatalysts by modifying traditional cocatalysts.MoS2 is widely applied in photocatalytic H2 evolution to function as an efficient cocatalyst, whereas it is not yet reported that this material acted as an effective host photocatalyst in this field. Herein, MoS2 nanosheets were prepared by a general hydrothermal process at first, and then treated with flowing NH3 at temperatures from 400 to 900 °C to develop a series of novel MoS2-based photocatalysts, which showed considerable photocatalytic activities for H2 evolution under visible-light irradiation. It was deduced from different instrumental characterizations on the physicochemical properties of photocatalysts that the enhancement of photocatalytic activity by high-temperature NH3 treatment could be mainly attributed to the modification of surface properties (such as electric property and acid-base properties) by N, which promoted the adsorption of reactants and further accelerated photocatalytic reaction. This work presented an effective route to explore new H2-evolution photocatalysts by modifying the appropriate materials that were commonly employed as cocatalysts.Figure optionsDownload full-size imageDownload as PowerPoint slide
Co-reporter:Fei Xue, Wenlong Fu, Maochang Liu, Xixi Wang, Bin Wang, Liejin Guo
International Journal of Hydrogen Energy 2016 Volume 41(Issue 45) pp:20455-20464
Publication Date(Web):7 December 2016
DOI:10.1016/j.ijhydene.2016.07.233
•Cd0.9Zn0.1S solid solution with tetrapod structure was fabricated by a simple one-step hydrothermal method.•The formation of Cd0.9Zn0.1S tetrapod was based on temperature-determined nucleation and diffusion mechanism.•Cd0.9Zn0.1S tetrapod photocatalysts exhibited the highest photocatalytic activity among those with various morphologies.•This work demonstrated the important role of polymorphism in constructing photocatalysts.Shape-controlled synthesis of semiconductor nanocrystals enables fine manipulation over their physicochemical properties. In this paper, unique Cd0.9Zn0.1S tetrapod nanostructures consisting of two different polymorphisms, i.e., wurtzite and zinc blende, were successfully synthesized via a simple ethylenediamine-assisted solvothermal route. It is found that the temperature determines the formation of the zinc blende-structured seeds, while the ethylenediamine facilitates the subsequent preferential growth of the wurtzite phase arms. Furthermore, the tetrapods, characterized by a type-II staggered band alignment, have shown enhanced photocatalytic performance for H2 generation from an aqueous solution containing electron donors under visible light irradiation, in comparison to the nanocrystals with distinct morphologies. Our results indicate that coupling different polymorphisms in a nanocrystal may be advantageous for photocatalytic proton reduction over single-crystal photocatalyst.
Co-reporter:Xu Guo, Yubin Chen, Zhixiao Qin, Menglong Wang, Liejin Guo
International Journal of Hydrogen Energy 2016 Volume 41(Issue 34) pp:15208-15217
Publication Date(Web):14 September 2016
DOI:10.1016/j.ijhydene.2016.05.218
•ZnxCd1−xS/ZnO heterostructures are fabricated by a one-step hydrothermal method.•The composition, structure, and morphology of ZnxCd1−xS/ZnO can be tuned.•ZnxCd1−xS/ZnO photocatalyst exhibits an apparent quantum yield of 26.0% at 420 nm.•Balancing the band gap and band offset in heterostructured photocatalysts is crucial.Photocatalytic hydrogen generation from water is an appealing strategy for solar energy conversion, and fabricating heterostructured photocatalysts is demonstrated to be an effective way to improve the photocatalytic performance. Herein, we applied a facile one-step hydrothermal method to construct ZnxCd1−xS/ZnO heterostructures for photocatalytic hydrogen production. By varying the initial S2−/Cd2+ molar ratio, the composition, structure, and morphology of ZnxCd1−xS/ZnO heterostructures could be gradually tuned. It was demonstrated that the photocatalytic activity of ZnxCd1−xS/ZnO first increased and then underwent a decrease with the increased S2−/Cd2+ molar ratio. ZnxCd1−xS/ZnO sample showed a highest photocatalytic hydrogen production rate of 1.89 mmol/h with an apparent quantum yield of 26.0% at 420 nm. To our knowledge, this value was the highest for the reported ZnxCd1−xS/ZnO composite photocatalysts. The excellent performance could be attributed to the balance of the light absorption and conduction band offset of ZnxCd1−xS/ZnO heterostructures, as well as the intimate contact of two components at the interface. This work not only provided a facile one-step route to fabricate efficient composite photocatalysts, but also demonstrated the importance of balancing the band-gap and band offset of heterostructured photocatalysts for the improved hydrogen production.Table of contents entry.Download high-res image (157KB)Download full-size image
Co-reporter:Shanke Liu, Hui Jin, Wenwen Wei, Liejin Guo
International Journal of Hydrogen Energy 2016 Volume 41(Issue 36) pp:15985-15997
Publication Date(Web):28 September 2016
DOI:10.1016/j.ijhydene.2016.04.219
•The experiments of indole gasification in supercritical water (SCW) were carried out.•Products of indole gasification in SCW were measured.•A nitrogen transformation pathway of indole gasification in SCW was proposed.•A quantitative kinetic model for describing indole gasification in SCW was developed.Nitrogen is an important element related to coal conversion process due to its considerable impact on the environment. In this study, indole, a nitrogen-containing compound of coal, was utilized to explore nitrogen transformation during supercritical water gasification. Experiments were conducted with K2CO3 as catalyst under temperature conditions from 650 °C to 750 °C, pressure of 25 MPa, and residence time from 1 min to 30 min with feedstock concentration of 2 wt%; products and nitrogen transformation characteristics were then investigated in detail. First, we found that carbon gasification efficiency of 95.89% was obtained under conditions of 750 °C, 25 MPa for 30 min, and that gaseous products mainly contained H2, CO, CO2 and CH4. Nitrogen-containing products were not detected in gaseous products. Second, the main liquid intermediate organic products were phenol, aniline, and other nitrogen-containing compounds, and the liquid inorganic product was ammonia. Then a reaction pathway of indole gasification in supercritical water was proposed. The quantitative kinetic model for describing the gaseous products and nitrogen transformation mechanisms of indole was developed. The activation energy of carbon gasification reaction with K2CO3 as catalyst was 209.1 ± 33.2 kJ/mol.
Co-reporter:Chao Zhu, Runyu Wang, Hui Jin, Xiaoyan Lian, Liejin Guo, Jianbing Huang
International Journal of Hydrogen Energy 2016 Volume 41(Issue 36) pp:16002-16008
Publication Date(Web):28 September 2016
DOI:10.1016/j.ijhydene.2016.06.085
Co-reporter:Chao Zhu, Liejin Guo, Hui Jin, Jianbing Huang, Sha Li, Xiaoyan Lian
International Journal of Hydrogen Energy 2016 Volume 41(Issue 16) pp:6630-6639
Publication Date(Web):4 May 2016
DOI:10.1016/j.ijhydene.2016.03.035
•The organic compounds in residual liquid were extracted using liquid–liquid microextraction method.•A degradation pathway of glucose in supercritical water was discussed.•Ru/Al2O3 catalyst promoted the degradation of phenols and inhibited the formation of char.Supercritical water gasification of glucose as a model compound for biomass was conducted in quartz reactors at 500 °C. The concentration of glucose solution was 5 wt.% and the reaction time was adjusted within the range of 10–1800 s. The effects of reaction time and catalyst on the product distribution were investigated and the formation and degradation pathways of intermediate products with and without catalyst were discussed. The results show that the gas yields increased while the yields of organic intermediates in residual liquid decreased with the reaction time. The organic intermediates in residual liquid were mainly composed of phenols, furans, organic acids, alcohols, arenes and ketones. The Ru/Al2O3 catalyst had a significant influence on the gasification of glucose, which promoted the degradation of intermediates to gaseous products, increased the yield of hydrogen and inhibited the formation of char.
Co-reporter:Fei Jia, Fengfeng Liu, Liejin Guo, Hongtan Liu
International Journal of Hydrogen Energy 2016 Volume 41(Issue 15) pp:6469-6475
Publication Date(Web):27 April 2016
DOI:10.1016/j.ijhydene.2016.03.037
•Reverse startup current with N2 purging is due to charging EDL on the cathode side.•Reverse current occurs only when open circuit voltage is lower than startup voltage.•Reverse current is proportional to difference between startup and open circuit voltages.•Pre-filling air before startup can eliminate reverse current.•Linear startup strategy is effective in reducing or eliminating reverse current.Understanding the dynamic behaviors of proton exchange membrane (PEM) fuel cells during startups is crucial for their proper operations to minimizing the detrimental effects of reverse current. In this study, the fuel cell is initially filled with nitrogen at both sides, and then reactants are supplied to the cell and the load is imposed simultaneously. Experimental results show that reverse current still occurs even though nitrogen purging is employed before the startup and hydrogen/air boundary is eliminated at the anode. The magnitude of reverse current density increases with the startup voltage. Analysis shows that the reverse current is proportional to the difference between the startup voltage and the open circuit voltage, and it occurs only when the open circuit voltage is lower than the startup voltage, which is due to the charging of the electrical double-layer on the cathode. Thus a startup strategy of air pre-filling is devised and the experimental results show that reverse current can be completely avoided or significantly reduced by pre-filling the cathode with air before startups. Another startup strategy, a linear startup mode, is also tested and the results show that it is effective in reducing the reverse current.
Co-reporter:Guiyin Chen, Guangsheng Zhang, Liejin Guo, Hongtan Liu
International Journal of Hydrogen Energy 2016 Volume 41(Issue 9) pp:5063-5073
Publication Date(Web):9 March 2016
DOI:10.1016/j.ijhydene.2016.01.074
•MPL has distinct functions under different local water conditions.•MPL can prevent flooding under high humidification and low temperature.•MPL can also enhance membrane hydration under dry condition.•Under high temperature, effect of MPL is not significant.Though it is well known that adding micro porous layers (MPL) in proton exchange membrane fuel cells (PEMFC) can improve fuel cell performance, durability and stability, their functions and mechanisms on water transport are still not fully understood. To determine the functions and the mechanisms of MPL on water transport, systematic experiments have been conducted on fuel cells with and without MPL under wide range of operating conditions. Besides overall cell performance, current density distribution along gas channel and electrochemical impedance spectroscopy are used in the analyses. The experimental results show that the functions and mechanisms of MPL depend on the humidity level and operating temperature. At low and medium temperature, MPL can significantly enhance cell performance under both high and low humidity conditions. Under high humidity conditions, adding an MPL can effectively reduce flooding of the catalyst layer by preventing the formation of liquid water in its much smaller pores than in the GDL. Under low humidity conditions, MPL reduces the loss of water to the gas channels as well as enhances back diffusion, thus reduces membrane dehydration. MPL also reduces Joule heating and further reduce membrane dehydration. At high temperature, the effectiveness of MPL is much reduced under both high and low humidity conditions due to the different mechanism of water transfer.
Co-reporter:Shuanglin Shen, Liejin Guo, Hongtan Liu
International Journal of Hydrogen Energy 2016 Volume 41(Issue 5) pp:3646-3654
Publication Date(Web):9 February 2016
DOI:10.1016/j.ijhydene.2015.12.162
•A polarization model for a bi-layer electrolyte SOFC is developed.•Modeling results compared well with the experimental data.•OCV and output characteristics increase with cathode exchange current density.•Modeling results confirm optimal relative thickness from simplified models.A polarization model for a solid oxide fuel cell (SOFC) with a bi-layer electrolyte is developed and a set of explicit expressions for output current, maximum power and thickness ratio of bi-layer electrolyte are obtained. In the model, two dominating polarizations, activation polarization and ohmic polarization, are considered and the concentration polarization is neglected. The activation polarization at the electrodes is described by the Butler–Volmer equation. The ohmic polarization is represented by the charge transport equation, and this equation is solved with the assumption of constant ionic conductivity. To close the model equations, a supplemental relation is introduced by the energy conservation analysis. The modeling results compare well with the experimental data. The model is further used to study the effect of cathode exchange current density on the working characteristics of a solid oxide fuel cell with a bi-layer electrolyte.
Co-reporter:Yang Zhang, Honghui Yang, Liejin Guo
International Journal of Hydrogen Energy 2016 Volume 41(Issue 1) pp:190-197
Publication Date(Web):5 January 2016
DOI:10.1016/j.ijhydene.2015.09.122
•Transponson mutagensis was employed to create high H2 production mutants.•Mutation on mmsA gene results in lower PHB and Bchl a content.•Mutation on mmsA gene enhanced H2 production rate and yield clearly.The effects of mmsA disruption in Rhodobacter capsulatus SB1003 on the pigment content, poly-β-hydroxybutyrate (PHB) content and photo-fermentative hydrogen production were studied. A transposon mutant assigned ZY29 with mutation on mmsA and an mmsA partially deleted mutant assigned ZYDM9 (mmsA−) were obtained. The mutants showed reduced pigment and PHB content, and improved photo-fermentative hydrogen production performance. The hydrogen yield and maximum hydrogen production rate of ZYDM9 were 4675 ± 76 mL/L and 92.4 ± 2.6 mL/(Lh), which increased by 22.8% and 20% compared with that of the WT, respectively. In the meantime, its pigment and PHB content were 20.7 ± 0.1 nmol/mg and 54.5 ± 2.6 mg/g-dcw, which reduced by 34.2% and 43.4% compared with that of WT, respectively. The optimum parameters for hydrogen production were initial pH 7.0, carbon nitrogen ratio (g/g) 3.0:0.5, and light intensity 800 ± 35 W/m2.
Co-reporter:Zening Cheng, Hui Jin, Shanke Liu, Liejin Guo, Jialing Xu, Di Su
International Journal of Hydrogen Energy 2016 Volume 41(Issue 36) pp:16055-16063
Publication Date(Web):28 September 2016
DOI:10.1016/j.ijhydene.2016.06.075
•This was the first time supercritical water was applied to gasify semicoke.•Semicoke-water slurry of 30 wt% was continuously transported into the reactor.•600 °C might be the trigger temperature for fixed carbon complete gasification.•Carbon gasification efficiency of more than 95% was obtained.Semicoke powders with particle size less than 6 mm are by-products during the pyrolysis of coal. Direct combustion of semicoke powders is difficult due to the low volatile content. Supercritical water gasification might provide an efficient conversion method for semicoke powders. In order to determine the optimum conditions of gasification of semicoke with the supercritical water fluidized bed reactor, the influences of the main operating parameters including temperature (540–660 °C), feedstock concentration (10–30 wt%), flow rate of preheated water (40–80 g/min) and alkali catalysts (K2CO3, KOH, Na2CO3 and NaOH) were systematically investigated in this study. The results showed that semicoke-water slurry of 30 wt% was continuously transported into the reactor and stably gasified without plugging problems. Hydrogen yield of 85.90 mol/kg was obtained with the hydrogen molar fraction of 61.02%. In particular, carbon gasification efficiency of more than 95% was obtained under the conditions of 660 °C, 60 g/min flow rate of preheated water and 10 wt% feedstock concentration with 5 wt% K2CO3.
Co-reporter:Dongsheng Wen, Jin Y. Ooi, Liejin Guo
Powder Technology 2016 Volume 304() pp:1
Publication Date(Web):December 2016
DOI:10.1016/j.powtec.2016.10.052
Co-reporter:Xiaohui Su, Liejin Guo, and Hui Jin
Energy & Fuels 2016 Volume 30(Issue 11) pp:9028
Publication Date(Web):September 30, 2016
DOI:10.1021/acs.energyfuels.6b01557
Supercritical water gasification of coal is a newly clean coal technology. In this study, we established a quantitative model for the reaction kinetics of coal gasification in supercritical water. The large number of real intermediates formed during gasification were lumped using volatile and fixed carbon, and mass balance was also ensured in kinetic equation which would facilitate access to a comprehensive model considering flow and heat transfer. The model focused on the formation of the individual gaseous species (H2, CO2, CH4, CO). Then the model was applied to fit the experimental data and kinetic parameters were estimated. It was found that predicted results of the model were in accordance with experiments. The model predicted that volatile completely converted into gas quickly when temperature reached above 650 °C, and the reforming reaction of fixed carbon became the control step of gasification. Hydrogen was mainly from volatile decomposition in the initial short stage and water gas shift reaction then contributed to the hydrogen production. Carbon reforming reaction dominated hydrogen generation after about 5 min. Methane generated from the direct decomposition of volatile and the effect of methanation reaction was negligible. Carbon monoxide was generated during the volatile decomposition and it was consumed simultaneously in water gas shift reaction with substantial carbon dioxide produced. As a result, carbon monoxide content accounted for a small percentage and hydrogen and carbon dioxide dominated the gas products of gasification.
Co-reporter:Yechun Wang, Xiaowei Hu, Zhenshan Cao, Liejin Guo
Colloids and Surfaces A: Physicochemical and Engineering Aspects 2016 Volume 505() pp:86-92
Publication Date(Web):20 September 2016
DOI:10.1016/j.colsurfa.2016.01.004
•A reaction cell for photoelectrochemical and electrochemical conversions were set up for gas-evolving investigation.•Bubble grows as R ∼ t0.3 in photoelectrochemical conversion due to the small effective solid surface engaged.•Bubble grows as R ∼ t0.5 in the electrochemical conversion due to the big effective solid surface participating.•Mathematical models for the two growth mechanisms were established.Bubbles evolving from electrode surface are the results of the multi-processes, interfacial mass transfer, chemical reaction, micro fluid flow, etc. In this paper, the investigations on the bubble growth mechanism during photoelectrochemical and electrochemical conversions are carried out. The experimental results show two different growth laws during photoelectrochemical and electrochemical conversions, which are chemical reaction and diffusion controlled respectively, caused by the difference in the effective surface area of the electrode. And mathematical models for bubble growth describing the two effects are established.
Co-reporter:Zhixiao Qin
The Journal of Physical Chemistry C 2016 Volume 120(Issue 27) pp:14581-14589
Publication Date(Web):June 27, 2016
DOI:10.1021/acs.jpcc.6b05230
The development of efficient noble-metal-free hydrogen evolution catalysts is quite appealing with the aim of providing cost-competitive hydrogen. Herein, nickel sulfides (NiSx) with tunable NiS/Ni3S4 molar ratios were synthesized via a simple hydrothermal method. Detailed electrochemical studies under neutral conditions indicated that the electrocatalytic property of NiSx catalysts was determined by the composition. Notably, the NiSx sample with the NiS/Ni3S4 molar ratio of 1.0 exhibited the lowest overpotential and charge-transfer resistance. As analyzed from the Tafel plots, the rate-determining step of NiSx catalysts for hydrogen generation was the Volmer step, in which the proton adsorption played a key role. Theoretical calculation revealed that NiS and Ni3S4 exhibited the metallic behaviors with different work functions. Consequently, the NiSx sample with the NiS/Ni3S4 molar ratio of 1.0 owned the most adsorbed protons, which led to the highest electrocatalytic property. Meanwhile, NiSx was demonstrated to be efficient cocatalysts to promote photocatalytic hydrogen generation. NiSx/CdS with the NiS/Ni3S4 molar ratio of 1.0 showed the best photocatalytic activity with the apparent quantum efficiency of 56.5% at 420 nm. This result was in good agreement with the electrocatalytic activities of NiSx samples, indicating the intrinsic property for efficient hydrogen generation.
Co-reporter:Jie Chen, Shaohua Shen, Po Wu and Liejin Guo
Green Chemistry 2015 vol. 17(Issue 1) pp:509-517
Publication Date(Web):18 Sep 2014
DOI:10.1039/C4GC01683A
Nitrogen-doped CeOx nanoparticles (N-CeOx NPs) were directly formed on graphitic carbon nitride (g-C3N4) via a facile one-pot method by annealing a mixture of Ce(NO3)3 and melamine as CeOx and g-C3N4 precursors, respectively. Nitrogen was in situ doped into CeOx under NH3 atmosphere released by the decomposition of melamine during the annealing process. The physical and photophysical properties of N-CeOx NPs modified g-C3N4 photocatalysts were investigated to reveal the effects of N-CeOx NPs on the photocatalytic activities of g-C3N4. It was found that the one-pot annealing method was favorable for forming intimate interfacial contact between N-CeOx and g-C3N4. The visible light photocatalytic hydrogen production activity over g-C3N4 was enhanced by ca. 1.2 times with the N-CeOx NPs modification. The significant enhancement in photocatalytic performance for the N-CeOx/g-C3N4 heterojunction should be mainly because of the promoted charge transfer and charge separation between N-CeOx NPs and g-C3N4 resulting from the intimate interfacial contact and Type II band alignment. In addition, the improved visible light absorption of N-CeOx NPs induced by nitrogen doping could be another reason for the enhanced photocatalytic activity of the N-CeOx/g-C3N4 heterojunction.
Co-reporter:Lijing Ma, Maochang Liu, Dengwei Jing and Liejin Guo
Journal of Materials Chemistry A 2015 vol. 3(Issue 10) pp:5701-5707
Publication Date(Web):28 Jan 2015
DOI:10.1039/C4TA06577H
CdS is a well-known and efficient photocatalyst for photocatalytic hydrogen production. However, CdS is prone to photocorrosion in the photocatalytic reaction, in which CdS itself is oxidized by the photogenerated holes. Most of the work reported, to date, has focused only on the structure of CdS. However, less attention was paid to the kinetic changes of CdS during the photocatalytic reaction, which, in our opinion, is a crucial step for its practical utilization. In this report, we have developed a facile in situ Raman analysis, aiming to clarify the microstructural changes of CdS during the photocatalytic reaction process. In this study, photocatalytic hydrogen production over CdS in an Ar or air atmosphere was studied using various techniques in addition to in situ Raman spectroscopy. With Raman spectroscopy, a significant increase in the surface lattice strain of CdS was only observed when it was exposed to air, while the electron–phonon interactions remained the same regardless of the atmosphere. A direct correlation between the interfacial crystal lattice and photocorrosion of the CdS photocatalyst during photocatalytic hydrogen production was found based on our in situ Raman investigation. Finding the photocorrosion of the CdS photocatalyst at its very early stage using our in situ Raman technique is expected to provide meaningful guidance for the design of active and stable chalcogenide photocatalysts, which, however, cannot be achieved using traditional characterization techniques.
Co-reporter:Meng Wang, Myeongwhun Pyeon, Yakup Gönüllü, Ali Kaouk, Shaohua Shen, Liejin Guo and Sanjay Mathur
Nanoscale 2015 vol. 7(Issue 22) pp:10094-10100
Publication Date(Web):05 May 2015
DOI:10.1039/C5NR01493J
In this study, plasma enhanced chemical vapor deposition (PECVD) was utilized to co-axially modify hydrothermally grown Fe2O3 nanorod arrays by depositing a TiO2 overlayer to create Fe2O3/TiO2 core–shell photoelectrodes. Comprehensive structural (XRD, SEM, TEM) and compositional (XPS) analyses were performed to understand the effects of the TiO2 shell on the PEC activities of the Fe2O3 core. It was revealed that the heterojunction structure formed between TiO2 and Fe2O3, significantly improved the separation efficiency of photo-induced charge carriers and the oxygen evolution kinetics. A maximum photocurrent density of ∼900 μA cm−2 at 0.6 V vs. saturated calomel electrode (SCE) was obtained for the Fe2O3/TiO2 photoelectrodes, which was 5 and 18 times higher when compared to that of hydrothermally synthesized Fe2O3 and PECVD synthesized TiO2 electrodes, respectively. Moreover, the Fe2O3/TiO2 core–shell nanorod arrays displayed superior stability for PEC water splitting. During 5000 s PEC measurements, a steady decrease of the photocurrent was observed, mainly attributed to the evolution of oxygen bubbles adsorbed on the working electrodes. This observation was verified by the complete recovery of the PEC performance demonstrated for a second 5000 s PEC measurement carried out after a brief time interval (10 min) that allowed the electrode surface to regenerate.
Co-reporter:Bin Wang;Maochang Liu;Zhaohui Zhou ;Liejin Guo
Advanced Science 2015 Volume 2( Issue 11) pp:
Publication Date(Web):
DOI:10.1002/advs.201500153
Co-reporter:Xu Zhang, Liejin Guo, Hongtan Liu
Journal of Power Sources 2015 Volume 296() pp:327-334
Publication Date(Web):20 November 2015
DOI:10.1016/j.jpowsour.2015.07.063
•Both kinetic and mass transport losses after AST can be partially recovered.•Kinetic recovery is due to platinum oxide reduction and platinum re-attachment.•Mass transport recovery is due to removal of oxide groups on carbon surface.•AST without recovery significantly over-estimates true degradation in PEMFCs.The mechanisms of performance recovery after accelerated stress test (AST) in proton exchange membrane fuel cells (PEMFCs) are systematically studied. Experiments are carried out by incorporating a well-designed performance recovery procedure right after the AST protocol. The experiment results show that the cell performance recovers significantly from the degraded state after the AST procedure. The results from cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements further show that the performance recovery can be divided into kinetic and mass transport recoveries. It is further determined that the kinetic recovery, i.e. the recovery of electrochemical active area (ECA), is due to two distinct mechanisms: the reduction of platinum oxide and the re-attachment of detached platinum nanoparticles onto the carbon surface. The mass transport resistance is probably due to reduction of hydrophilic oxide groups on the carbon surface and the microstructure change that alleviates flooding. Performance comparisons show that the recovery procedure is highly effective, indicating the results of AST significantly over-estimate the true degradation in a PEM fuel cell. Therefore, a recovery procedure is highly recommended when an AST protocol is used to evaluate cell degradations to avoid over-estimating true performance degradations in PEMFCs.
Co-reporter:Ning Zhang, Jinwen Shi, Fujun Niu, Jian Wang and Liejin Guo
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 33) pp:21397-21400
Publication Date(Web):20 Jul 2015
DOI:10.1039/C5CP02983J
Owing to the effect of energy band bending, p-type Co3O4 quantum dots sensitized by Eosin Y showed a high and stable photocatalytic activity (∼13440 μmol h−1 g−1cat) for water reduction and hydrogen production under visible-light irradiation without any cocatalyst.
Co-reporter:Sha Li, Chao Zhu, Simao Guo and Liejin Guo
RSC Advances 2015 vol. 5(Issue 100) pp:81905-81914
Publication Date(Web):07 Sep 2015
DOI:10.1039/C5RA12025J
Hydrothermal gasification (HTG) is a promising technique for the utilization of wet biomass or organic wastes. This study reports a highly dispersed rutile-TiO2-supported Ni nanoparticle synthesized by a sol–gel method and its catalytic performance for gas production (H2 and CH4) from HTG of glucose as a model compound of biomass. NiTiO3 formation of the gel precursor during the calcination process demonstrated the enhanced interaction of Ni and TiO2, and highly dispersive nickel crystallites were obtained after the reduction activation. Increase of the calcination temperature decreased the catalytic activity due to the sintering of nickel crystals. The supported Ni nanoparticle greatly promoted the carbon gasification efficiency of HTG of 10 wt% glucose (glucose:Ni = 1:0.11) from 27.1% to 68.7% at 400 °C and from 48.2% to 96.4% at 600 °C in supercritical water. A highly active temperature region (400–500 °C) of nickel catalyzed methanation reaction for CH4 formation was particularly confirmed. As the gasification was prolonged in supercritical water, the rutile-TiO2-supported Ni nanoparticle showed stable crystalline structures and part of the deposited carbon was gasified. The regenerated catalysts also showed significant activities.
Co-reporter:Yubin Chen, Zhixiao Qin, Xixi Wang, Xu Guo and Liejin Guo
RSC Advances 2015 vol. 5(Issue 23) pp:18159-18166
Publication Date(Web):04 Feb 2015
DOI:10.1039/C5RA00091B
Developing efficient noble-metal-free photocatalysts is of great importance for the large-scale application of photocatalytic hydrogen production. Herein, low-cost and environment-friendly p-type Cu2S was successfully loaded on n-type CdS photocatalyst by an in situ method to achieve efficient Cu2S/CdS hybrid photocatalysts. Cu2S nanoparticles of ca. 50 nm were intimately assembled on the surface of polyhedral CdS nanocrystals, giving rise to the formation of numerous nanoscale p–n junctions between p-type Cu2S and n-type CdS. Compared to single CdS, Cu2S/CdS exhibited increased photocatalytic hydrogen production under visible light irradiation. The generated nanoscale p–n junctions in Cu2S/CdS, leading to the enhanced charge separation efficiency and better utilization of visible light, were crucial to the improved photocatalytic activity. During the photocatalytic reaction, Cu2S nanoparticles captured the photogenerated holes in CdS and served as the active sites for the surface oxidation reaction. The photocatalytic property of Cu2S/CdS photocatalysts was influenced by the Cu/Cd molar ratio, with the optimal one of 0.05. P-type Cu2S could also be utilized for improving the photocatalytic activities of n-type ZnIn2S4 and n-type TiO2 by forming efficient p–n junctions, indicating the general applicability of p-type Cu2S. This work demonstrates that forming p–n junction structure was a useful strategy for developing efficient noble-metal-free hybrid photocatalysts.
Co-reporter:Chao Zhang, Chao Wang, Shaojun Zhang, and Liejin Guo
Industrial & Engineering Chemistry Research 2015 Volume 54(Issue 36) pp:8883-8892
Publication Date(Web):August 31, 2015
DOI:10.1021/acs.iecr.5b01830
In this paper, a new efficient one-step technical method was first developed for the production of magnesium in the industry. The one-step method could combine the two processes of dolomite decomposition and magnesium reduction in the magnesium reduction retort. Thus, the high-temperature carbon dioxide produced by the dolomite decomposition process could be collected in a timely manner instead of being emitted into the atmosphere, and excessive heat loss caused by the two separate processes also could be almost completely avoided. This paper presents an experimental study on the intrinsic chemical kinetics mechanisms of this new efficient one-step technology. By applying each of the most likely solid-state kinetic models, the kinetic parameters of the two reactions that reacted during the dolomite decomposition stage and magnesium reduction stage were evaluated, and the kinetic models that best verify the experimental data were attempted. For the dolomite decomposition stage of the one-step technology, the equation of the chemical kinetic model can be represented by α2/2 = kD1τ in the temperature range of 1173–1473 K, and the apparent activation energy was determined to be 160.6 kJ mol–1. For the magnesium reduction stage of the one-step technology, the surface reaction chemical kinetic model 1 – (1 – β)1/3= kSτ described very satisfactorily the experimental values for the different reduction temperature. Then, a one-step model incorporating the chemical reaction kinetics of the dolomite decomposition stage and the magnesium reduction stage and heat conduction was first developed. The simulations of the impact of heating temperature on the dolomite decomposition stage and magnesium reduction stage were carried out in the reduction retorts of the furnace utilizing this model. The distribution of dolomite decomposition extent in the retorts, the total extent of dolomite decomposition with time, the distribution of magnesium reduction extent in the retorts, and the total extent of magnesium reduction with time were studied in detail. The analysis showed that the one-step technology is effective in not only reducing the cycle time of dolomite decomposition stage and magnesium reduction stage but also saving energy.
Co-reporter:Changqing Cao, Liejin Guo, Jiarong Yin, Hui Jin, Wen Cao, Yi Jia, and Xiangdong Yao
Energy & Fuels 2015 Volume 29(Issue 1) pp:384-391
Publication Date(Web):December 2, 2014
DOI:10.1021/ef502110d
Black liquor is a major wastewater generated from the pulping process that has a detrimental impact on the environment. This work assessed the potential of black liquor to be an inexpensive resource of alkali catalyst in supercritical water gasification of coal through thermodynamic analysis and experimental study. The experiments were performed in a fluidized-bed reactor at 550 °C and 25 MPa, and the products were characterized by gas chromatography, X-ray fluorescence, X-ray diffraction, and gas chromatography-mass spectrometry. In the gasification of coal and black liquor mixtures, the presence of coal can improve the H2 production under the equilibrium state. Both the inherent alkalis and lignin in black liquor played a role of improving the gasification efficiency of coal. The alkalis also accelerated the water–gas shift reaction and increased the H2 fraction. The high total mixture concentration inhibited the gasification, and the reactor was plugged with a concentration of 25 wt %. The presence of black liquor fixed more sulfur in the solid residues, but it aggravated the corrosion of the 316 SS reactor. The aqueous product mainly contained alkylphenols, cyclopentanone, and their derivatives. A simple influencing mechanism of lignin on coal gasification was proposed: the decomposition of lignin prior to coal can generate some phenolic compounds, which can promote the extraction of the substances coated outside the coal particle and favor the further reaction between the coal and water.
Co-reporter:Fei Jia, Liejin Guo, Hongtan Liu
International Journal of Hydrogen Energy 2015 Volume 40(Issue 24) pp:7754-7761
Publication Date(Web):29 June 2015
DOI:10.1016/j.ijhydene.2015.01.051
•Current overshoots occur in the entire cell during startups.•Patterns of local current overshoot are very different under different humidification.•Current overshoot increases along the channel with under-humidified condition.•Current overshoot decreases along the channel with fully-humidified condition.•The linear startup mode is effective in reducing current overshoot during startupsCurrent overshoot resulting from a sudden decrease in the cell voltage during start-up process could cause performance fluctuation and reduced durability in proton exchange membrane (PEM) fuel cells. In this study, transient responses of local current densities and high frequency resistance (HFR) of the cell are measured in situ. The experimental results show that when the cell starts up under potentiostatic mode, both the magnitude of current overshoot and the fluctuation of HFR decrease with the increase of anode humidity. A dimensionless current overshoot is defined to describe the magnitude of current overshoot during start-ups. Experimental results show that dimensionless current overshoots are very different at different locations along the flow direction under different anode humidification. When unsaturated hydrogen is fed into the cell, dimensionless current overshoot increases along the flow direction; while as anode gas is fully- or over-humidified, the dimensionless current overshoot decreases along the flow direction. Further experimental results show that the magnitudes of current overshoot are significantly reduced when a linear start-up strategy is used, indicating that the linear start-up strategy is effective in alleviating current density overshoots in PEM fuel cells during start-ups.
Co-reporter:Xixi Wang, Jie Chen, Xiangjiu Guan, Liejin Guo
International Journal of Hydrogen Energy 2015 Volume 40(Issue 24) pp:7546-7552
Publication Date(Web):29 June 2015
DOI:10.1016/j.ijhydene.2014.11.055
•A series of Cd0.5Zn0.5S/g-C3N4 photocatalysts were successfully prepared by a two-step solvothermal method.•The two semiconductors were proved could form a type II band alignment.•Both photocatalytic efficiency and photocatalytic stability have been improved.Controlling the behavior of charge transfer is central to semiconductor based photocatalytic reactions. While a myriad of methods have been developed, successful approaches towards enhanced activity and stability but low cost have been elusive. Herein, we report a robust two-step solvothermal method for the synthesis of a novel Cd0.5Zn0.5S/g-C3N4 composite. The composite possesses a type II staggered band alignment and intimately contacted interfaces, directing the rapid charge separation upon visible light irradiation and thus a remarkable enhancement of the photocatalytic efficiency. Comparing to pure Cd0.5Zn0.5S, the initial hydrogen production rate was improved from 13.6 mL/h to 20.8 mL/h without any co-catalyst loading, companied with a high apparent quantum efficiency of 37% at 425 nm. Significantly, photoexcited holes on Cd0.5Zn0.5S transferred to photocorrosion-resisted g-C3N4, leading to a more stable photocatalytic performance. The photocatalytic activity was kept over 95% in a three-circle hydrogen production test. Our work thus offers a promising route to the low-cost fabrication of novel photocatalyst in terms of both superior photoreactivity and stability.
Co-reporter:Xiaohui Su, Hui Jin, Liejin Guo, Simao Guo, Zhiwei Ge
International Journal of Hydrogen Energy 2015 Volume 40(Issue 24) pp:7424-7432
Publication Date(Web):29 June 2015
DOI:10.1016/j.ijhydene.2015.02.110
•Zhundong coal was gasified completely in SCW with a quartz reactor.•Reaction kinetic data of coal gasification in SCW were obtained.•An adequate kinetics model for carbon gasification efficiency was established.•A simplified conversion pathway was claimed and discussed.China has fairly rich reserves of Zhundong coal but the utilization of it is limited due to the high alkali metal content which can cause great troubles in a traditional boiler. Supercritical water gasification is a novel thermochemical conversion technique to convert wet feedstock into hydrogen-rich gas product with near zero emission. Reaction kinetics of Zhundong coal gasification in supercritical water was investigated with a quartz reactor in this study. The effects of reaction temperature (650–850 °C) and coal concentration (5–15 wt%) on the gasification behavior were investigated in a wide range of residence time (0–30 min). Experimental results showed that the experimental method employed presents good performance in revealing the continuous change of gas formation with residence time. Carbon gasification efficiency can reach nearly 100% at 850 °C with the residence time of 15 min and the mole fraction of hydrogen was more than 50%. A simplified gasification reaction pathway was also claimed at the end. The results show a promising prospect of Zhundong coal conversion in supercritical water and provide some useful information for reaction kinetics model establishment of coal gasification in supercritical water.
Co-reporter:Hui Jin, Liejin Guo, Jian Guo, Zhiwei Ge, Changqing Cao, Youjun Lu
International Journal of Hydrogen Energy 2015 Volume 40(Issue 24) pp:7523-7529
Publication Date(Web):29 June 2015
DOI:10.1016/j.ijhydene.2014.12.095
•A novel gasification kinetics model focusing on the gas products was established.•Gas fraction can be predicted by the gasification kinetics model.•Gas formation and consumption pathways can be simulated.•Lignite gasification in supercritical water was experimentally investigated.Supercritical water gasification provides a clean and efficient way to produce hydrogen from high-moisture lignite. The development of kinetic model is a demanding task for the understanding of the reaction pathway and the reactor optimization. A novel gasification kinetics model mainly concentrating on the gas products (H2, CO, CH4 and CO2) was established to omit the unimportant reactions and intermediates owing to the complexity of the gasification process. Seven reactions were selected as the main routes of lignite gasification in supercritical water based on the present gasification mechanisms. The kinetics model was used to fit the experimental data obtained from the tubular reactor for continuous lignite gasification in supercritical water (operating in 560 °C, 25 MPa, lignite slurry concentration 5%, residence time 4.66 s–12.41 s). Rate constants were determined through minimizing the sum of the square of prediction errors. The gas product concentration as a function of time can be predicted by the model and it indicates that the concentrations of CO and CH4 increased first and then decreased to be negligible after 30 min. The concentrations of H2 and CO2 increased and remained unchanged and the fractions of H2 and CO2 were 65.62% and 34.29% respectively. The predictions agreed well with the thermodynamic results by minimizing Gibbs free energy. Gas formation and consumption pathways can also be predicted. Most hydrogen was produced by steam reforming reaction and consumed by methanation reaction.Hydrogen formation/consumption reaction pathway is deduced by a novel kinetics model.
Co-reporter:LieJin Guo;Hui Jin;ZhiWei Ge;YouJun Lu
Science China Technological Sciences 2015 Volume 58( Issue 12) pp:1989-2002
Publication Date(Web):2015 December
DOI:10.1007/s11431-015-5967-0
Energy conversion and utilization, particularly carbon-based fuel burning in air phase, have caused great environmental pollution and serious problems to society. The reactions in water phase may have the potential to realize clean and efficient energy conversion and utilization. Coal gasification in supercritical water is a typical carbon-based fuel conversion process in water phase, and it takes the advantages of the unique chemical and physical properties of supercritical water to convert organic matter in coal to H2 and CO2. N, S, P, Hg and other elements are deposited as inorganic salts to avoid pollution emission. The State Key Laboratory of Multiphase Flow in Power Engineering has obtained extensive experimental and theoretical results based on coal gasification in supercritical water. Supercritical water fluidized bed reactor was developed for coal gasification and seven kinds of typical feedstock were selected. The hydrogen yield covers from 0.67 to 1.74 Nm3/kg and the carbon gasification efficiency is no less than 97%. This technology has a bright future in industrialization not only in electricity generation but also in hydrogen production and high value-added chemicals. Given the gas yield obtained in laboratory-scale unit, the hydrogen production cost is U.S.$ 0.111 Nm3 when the throughput capacity is 2000 t/d. A novel thermodynamic cycle power generation system based on coal gasification in supercritical water was proposed with the obvious advantages of high coal-electricity conversion efficiency and zero pollutant emission. The cost of U.S.$ 3.69 billion for desulfuration, denitration and dust removal in China in 2013 would have been saved with this technology. Five kinds of heat supply methods are analyzed and the rates of return of investment are roughly estimated. An integrated cooperative innovation center called a new type of high-efficient coal gasification technology and its large-scale utilization was founded to enhance the industrialization of the technology vigorously.
Co-reporter:Liejin Guo, Hui Jin, Youjun Lu
The Journal of Supercritical Fluids 2015 Volume 96() pp:144-150
Publication Date(Web):January 2015
DOI:10.1016/j.supflu.2014.09.023
•Coal is gasified in supercritical water with carbon gasification efficiency of 100%;•A novel thermodynamics cycle is proposed based on SCWG of coal with zero emission;•Research and development of supercritical water gasification in China are reviewed.Supercritical water gasification is a promising technology to convert coal/biomass/organic wastes to hydrogen cleanly and efficiently. Extensive investigations on supercritical water gasification were conducted in China. State Key Laboratory of Multiphase Flow in Power Engineering (SKLMFPE) together with other universities/institutes established experimental device with the reactor type of quartz tube reaction system, tubular reactor and fluidized bed reactor. The fluidized bed reactor system solved the blocking problems to guarantee continuous and stable gasification. Typically Hongliulin coal as a typical coal in China was completely gasified in supercritical water fluidized bed system and the hydrogen yield was 77.5 mol per kg of coal. A pilot scale demonstration plant for supercritical water gasification driven by solar concentration system was established with a handling capacity of 1 t/h and it proves the feasibility of the system scale up. A novel thermodynamics cycle power generation system based on coal gasification in supercritical water was proposed with the obvious advantages of high coal-electricity efficiency and zero pollutant emission. An Integrated Cooperative Innovation Center with the name of A New Type of High-efficient Coal Gasification Technology and its Large-scale Utilization was founded in order to vigorously enhance the industrialization of the technology.
Co-reporter:Yuchao Hu ;Dr. Liejin Guo
ChemCatChem 2015 Volume 7( Issue 4) pp:584-587
Publication Date(Web):
DOI:10.1002/cctc.201402924
Abstract
Ultrathin perovskite lead niobate nanosheets, (TBA/H)Pb2Nb3O10, were rapidly prepared by novel high-power ultrasonic exfoliation of layered HPb2Nb3O10, and were used as a photocatalyst for hydrogen production from methanol solution under visible light irradiation (λ>415 nm) for the first time. When compared with bulk HPb2Nb3O10, the nanosheets showed same tetragonal crystal structure, but dramatic decrease in thickness and two times higher photocatalytic hydrogen evolution activity. Enhanced photocatalytic performance resulted from the fact that the photoexcited electrons were more efficiently separated and utilized for H2 production on the nanosheets, owing to shorter migration distance of photoexcited electrons.
Co-reporter:Xixi Wang
The Journal of Physical Chemistry C 2015 Volume 119(Issue 35) pp:20555-20560
Publication Date(Web):August 19, 2015
DOI:10.1021/acs.jpcc.5b07370
Controlling the shape or morphology of semiconductor nanocrystals is central to their enhanced physical and chemical properties. Herein, using CdS as a model photocatalyst, we demonstrate that the crystal habit of a visible-light-active semiconductor can be quantitatively controlled through synthesis kinetics. Growth rate control of {0001} facets (r1) and {101̅1} facets (r1′) of CdS nanocrystals was achieved by simply employing a syringe pump, which enables us to finely tune the crystal shape from nanocones, to nanofrustums, and further to nanoplates. These shape-controlled samples, showing altered proportions of {0001} to {101̅1} facets, were used to investigate the crystal-facet dependence of solar hydrogen production. The results indicate that CdS nanoplates with the largest {0001} facets showed the highest photocatalytic activity. This work not only advances our knowledge on the growth mechanism of semiconductor crystals but also illustrates a robust method to targeted crystal design of semiconductors toward optimizing their associated catalytic activities.
Co-reporter:Xiangjiu Guan and Liejin Guo
ACS Catalysis 2014 Volume 4(Issue 9) pp:3020
Publication Date(Web):July 29, 2014
DOI:10.1021/cs5005079
Ag3PO4 has been reported to be an excellent photocatalyst for O2 evolution from aqueous solution, which makes it a promising candidate for designing a Z-scheme water-splitting system. In this work, in order to further improve the photocatalytic activity, a series of SrTiO3/Ag3PO4 composite photocatalysts was constructed by introducing SrTiO3 (with a less positive valence band minimum) to Ag3PO4 and was synthesized by two consecutive hydrothermal processes. The obtained photocatalysts were systematically characterized by XRD, SEM, BET, UV–vis, etc., showing that SrTiO3/Ag3PO4 composites were formed by coating SrTiO3 onto a Ag3PO4 polyhedron. Photocatalytic O2 evolution results demonstrated that a small amount of SrTiO3 brought about significant enhancement of photocatalytic activity of Ag3PO4 and that the apparent quantum yield at 420 nm reached 16.2% with a molar ratio of SrTiO3 to Ag3PO4 equal to 1/20, which led to the fact that SrTiO3 could serve as cocatalyst for water oxidation providing both accelerated electron–hole separation by band gap alignment and more active sites by enlarged surface area.Keywords: Ag3PO4; cocatalysis; O2 evolution; photocatalysis; SrTiO3
Co-reporter:Naixu Li, Maochang Liu, Zhaohui Zhou, Jiancheng Zhou, Yueming Sun and Liejin Guo
Nanoscale 2014 vol. 6(Issue 16) pp:9695-9702
Publication Date(Web):10 Jun 2014
DOI:10.1039/C4NR02068E
Finding active sites for photocatalytic reduction and oxidation allows the mechanistic understanding of a given reaction, ensuring the rational design and fabrication of an efficient photocatalyst. Herein, using well-shaped Cu2WS4 decahedra as model photocatalysts, we demonstrated that photoinduced oxidative etching could be considered as an indication of the photooxidation reaction sites of chalcogenide photocatalyst as it only occurred on {101} facets of Cu2WS4 during photocatalytic hydrogen production. The photocatalytic reduction reaction, in contrast, was confined on its {001} facets. Based on this finding, the photocatalytic activity of Cu2WS4 decahedra could be further tailored by controlling the ratio of {001}/{101} facets. Thus, this work provides a general route to the determination of reactive sites on shaped chalcogenide photocatalysts.
Co-reporter:Jie Chen, Shaohua Shen, Penghui Guo, Po Wu and Liejin Guo
Journal of Materials Chemistry A 2014 vol. 2(Issue 13) pp:4605-4612
Publication Date(Web):08 Jan 2014
DOI:10.1039/C3TA14811D
ZnFe2O4 modified g-C3N4 was successfully synthesized by a simple one-pot method. The visible-light-driven photocatalytic hydrogen production activity of g-C3N4 was significantly enhanced due to spatial engineering of the photo-active sites via ZnFe2O4 modification and Pt loading. It is proposed that ZnFe2O4 does not function as visible light sensitizer but as oxidation active sites. In the present ZnFe2O4/g-C3N4 photocatalysts, the photo-induced holes in g-C3N4 tend to transfer to ZnFe2O4 due to the straddling band structures (Type I band alignment), while the photo-induced electrons in g-C3N4 prefer to transfer to the loaded Pt cocatalysts, which can function as reduction active sites for hydrogen production. As a result, the photoinduced electrons and holes in g-C3N4 are efficiently separated by spatial engineering of the photo-active sites, and hence enhanced photocatalytic hydrogen generation activity is obtained.
Co-reporter:Po Wu, Jiarui Wang, Jing Zhao, Liejin Guo and Frank E. Osterloh
Journal of Materials Chemistry A 2014 vol. 2(Issue 47) pp:20338-20344
Publication Date(Web):16 Oct 2014
DOI:10.1039/C4TA04100C
Graphitic carbon nitride (g-C3N4) is a promising visible-light-responsive photocatalyst for hydrogen generation from water. As we show here, the photocatalytic activity of g-C3N4 is limited by structure defects generated during the calcination process. Specifically we find that the photocatalytic hydrogen production rate from aqueous methanol is inversely related to the calcination temperature (520–640 °C). The highest activity of 0.301 mmol h−1 g−1 is observed for the sample prepared at the lowest processing temperature. Surface photovoltage (SPV) spectroscopy shows that the maximum photovoltage is reduced (from 1.29 V to 0.62 V) as the processing temperature is increased, in accordance with higher defect concentrations and faster electron–hole recombination. The defects also produce additional optical absorption in the visible spectra and cause a red shifted, weakened photoluminescence (PL). Based on the sub-gap signal in the SPV and PL spectra, defect energy levels are +0.97 V and −0.38 V (vs. NHE) in the band gap of the material. According to Fourier transform infrared (FTIR) spectra, the defects are due to amino/imino groups in the g-C3N4 lattice.
Co-reporter:Ning Zhang, Jinwen Shi, Samuel S. Mao and Liejin Guo
Chemical Communications 2014 vol. 50(Issue 16) pp:2002-2004
Publication Date(Web):13 Jan 2014
DOI:10.1039/C3CC48026G
Co3O4 quantum dots were synthesized by a facile reverse micelle method for the first time, and were capable of splitting pure water into O2 and H2 stoichiometrically under visible-light irradiation (λ > 420 nm) without any cocatalyst.
Co-reporter:Po Wu, Jiarui Wang, Jing Zhao, Liejin Guo and Frank E. Osterloh
Chemical Communications 2014 vol. 50(Issue 98) pp:15521-15524
Publication Date(Web):20 Oct 2014
DOI:10.1039/C4CC08063G
A high rate of 2.23 mmol h−1 g−1 (quantum efficiency of 6.67% at 400 nm) for visible light driven photocatalytic H2 evolution can be achieved with g-C3N4 by alkalization of the solution to a pH of 13.3, due to accelerated transfer of photoholes to the sacrificial donor.
Co-reporter:Shuanglin Shen, Yupeng Yang, Liejin Guo, Hongtan Liu
Journal of Power Sources 2014 Volume 256() pp:43-51
Publication Date(Web):15 June 2014
DOI:10.1016/j.jpowsour.2014.01.041
•SOFC model with a mixed ionic–electronic conductor electrolyte is developed.•The modeling results agree well with experimental data.•Effects of various parameters are studied.•The distribution of oxygen partial pressure in the MIEC electrolyte is obtained.A polarization model for a solid oxide fuel cell (SOFC) with a mixed ionic and electronic conductor (MIEC) electrolyte is developed based on charge transport equation and a constant ionic conductivity assumption. The electrochemical reaction at the electrode is described by the Butler–Volmer equation and the energy conservation equation is included as an additional condition to complete the model. The modeling results agree well with experimental data. Utilizing this model the effects of key parameters, including conductivities of electrolyte, electrolyte thickness and cathode exchange current density on the performance of the SOFC are analyzed. The distribution of oxygen partial pressure in the electrolyte is also obtained.
Co-reporter:Longzhou Zhang, Dengwei Jing, Liejin Guo, and Xiangdong Yao
ACS Sustainable Chemistry & Engineering 2014 Volume 2(Issue 6) pp:1446
Publication Date(Web):April 21, 2014
DOI:10.1021/sc500045e
Traditionally, Cu ion-based oxide materials are considered not functional as photocatalysts owing to their instability in the photoelectrochemical processes. Here, we report on the light-induced photochemical synthesis of Cu2O microcubes utilizing CuWO4 as the precursor. It was found that under light irradiation and in the presence of glucose CuWO4 could be reduced in situ into Cu2O with its morphology reassembled from irregular bulk particles to hollow microcubes. Similar morphology transformation could not be observed when CuO or Cu(NO3)2 were used as precursors. More importantly, the in situ photochemical-synthesized Cu2O naoncubes showed both high activity and excellent stability for glucose reforming under visible light, which overcame the general barrier of Cu2O instability in photochemical processes. The activity could be remarkably enhanced when 0.1 wt % Zn was doped into the Cu2O. The excellent performances of the material were related to the existence of hollow microcubes and the modified band structure due to Zn doping.Keywords: Cu2O; H2 evolution; Hollow microcubes; In situ synthesis; Photocatalysis
Co-reporter:Rihua Lan, Hui Jin, Liejin Guo, Zhiwei Ge, Simao Guo, and Ximin Zhang
Energy & Fuels 2014 Volume 28(Issue 11) pp:6911-6917
Publication Date(Web):October 16, 2014
DOI:10.1021/ef502050p
A high-throughput batch reactor system was designed for hydrogen production by catalytic gasification of bituminous coal in supercritical water. The experimental system was made up of six subsystems with the same parameters, which was designed with a maximum temperature and pressure of 750 °C and 30 MPa, respectively. The system ensures that a maximum of six series experiments are conducted at the same time, which promotes the efficiency of the experimental work. In this study, the experiments were conducted under different operational conditions: temperature of 600–750 °C, pressure of 23–25 MPa, feed concentration of 5–20 wt %, reaction time of 4–15 min, and K2CO3 addition rate of 0–200 wt %. The effects of operational conditions were examined. The results obtained show that the carbon gasification efficiency (CE) and gasification efficiency (GE) increased with decreasing feed concentration and increasing temperature, reaction time, and K2CO3 addition rate. The addition of K2CO3 promoted the gasification reactivity significantly. CE and GE in the catalytic case were about 1.7 and 2 times that in the non-catalytic case, respectively. Kinetic information on catalytic gasification of coal in supercritical water was experimentally investigated. The activation energy and pre-exponential factor obtained were 59.47 ± 4.87 kJ/mol and 43.89 ± 1.82 min–1, respectively.
Co-reporter:Zhiwei Ge, Hui Jin, Liejin Guo
International Journal of Hydrogen Energy 2014 Volume 39(Issue 34) pp:19583-19592
Publication Date(Web):20 November 2014
DOI:10.1016/j.ijhydene.2014.09.119
•Coal was gasified completely with K2CO3 at 700 °C in a micro batch reactor.•Raw coal was converted into white residual.•Some pits or micropores were found on the coal substrate with alkali metal catalysts.•A reaction mechanism was used to understand catalytic coal gasification in SCW.Supercritical water gasification (SCWG) of coal is a promising technology for clean coal utilization. In this paper, hydrogen production by catalytic gasification of coal in supercritical water (SCW) was carried out in a micro batch reactor with various alkaline catalysts: Na2CO3, K2CO3, Ca(OH)2, NaOH and KOH. H2 yield in relation to the alkaline catalyst was in the following order: K2CO3 ≈ KOH ≈ NaOH > Na2CO3 > Ca(OH)2. Then, hydrogen production by catalytic gasification of coal with K2CO3 was systematically investigated in supercritical water. The influences of the main operating parameters including feed concentration, catalyst loading and reaction temperature on the gasification characteristics of coal were investigated. The experimental results showed that carbon gasification efficiency (CE, mass of carbon in gaseous product/mass of carbon in coal × 100%) and H2 yield increased with increasing catalyst loading, increasing temperature, and decreasing coal concentration. In particular, coal was completely gasified at 700 °C when the weight ratio of K2CO3 to coal was 1, and it was encouraging that raw coal was converted into white residual. At last, a reaction mechanism based on oxygen transfer and intermediate hybrid mechanism was proposed to understand coal gasification in supercritical water.
Co-reporter:Rui Xie, Jinzhan Su, Ya Liu, Liejin Guo
International Journal of Hydrogen Energy 2014 Volume 39(Issue 7) pp:3517-3527
Publication Date(Web):25 February 2014
DOI:10.1016/j.ijhydene.2013.12.088
•The solid solutions of CdS1−xSex thin films were prepared.•The growth mechanism of CdS1−xSex thin films was investigated.•The band gap can be adjusted successively via changing the S/Se ratio.•The photocurrents were greatly depended on the absorption of thin films.•The annealed CdSe film got the highest photo-to-current efficiency.A series of CdS1−xSex thin films have been deposited on fluorine doped tin oxide (FTO) coated glass substrates by chemical bath deposition. The influences of S/Se ratio in the precursor solution and annealing treatment on the structural, morphological, compositional, optical, and photoelectrochemical properties of the films were investigated. X-ray diffraction patterns revealed that the hexagonal cadmium cyanamide and the solid solutions of CdS1−xSex were formed. The morphological and compositional studies indicated that the thin film was composed of cadmium cyanamide sheets in the upper layer and CdS1−xSex spherical grains in the underlying layer. The optical absorption studies revealed that the band gap of unannealed and annealed films varied from 2.4 eV to 1.94 eV and from 2.35 eV to 1.67 eV as x increased from 0 to 1, respectively. The photo responses well agreed with the optical absorption of these films. The annealed CdSe shows the best photoresponse with a photon-to-current efficiency of 1.69% at 0.27 V (versus SCE).
Co-reporter:Xueqing Wang, Honghui Yang, Yang Zhang, Liejin Guo
International Journal of Hydrogen Energy 2014 Volume 39(Issue 27) pp:14633-14641
Publication Date(Web):12 September 2014
DOI:10.1016/j.ijhydene.2014.07.061
•The first study on the effect of spbA disruption to H2 production in Rhodobacter sphaeroides.•Disruption of spbA could partially derepress NH4+ inhibition on nitrogenase activity.•The gene spbA could be an activator of nitrogenase expression.•WSH10 (spbA−, hupSL−) showed remarkably enhancement on H2 production.The redox balance and bacteriochlorophyll (Bchl) synthesis are both significant to hydrogen generation in photosynthetic bacteria. In this study, spbA and hupSL genes were knocked out from the genome of Rhodobacter sphaeroides HY01. The UV–vis spectra showed that the Bchl contents of spbA mutants were enhanced under photosynthetic conditions. The hydrogen yields of WH04 (hupSL−) and WSH10 (spbA−, hupSL−) mutants increased by 19.4%, 21.8%, and the maximum hydrogen evolution rates increased by 29.9% and 55.0% respectively using glutamate as sole nitrogen source. The maximum hydrogen production rate of WSH10 was up to 141.9 mL/(L·h). The nifH expression levels of the mutants and the wild type supported the correlation between hydrogen production and nitrogenase activity. The results demonstrate that disruption of spbA in R. sphaeroides can partially derepress the ammonium inhibition in nitrogenase activity, and indicate that spbA is a negative regulator in nitrogenase synthesis in the presence of ammonium.
Co-reporter:Dan An, Qing Li, Xueqing Wang, Honghui Yang, Liejin Guo
International Journal of Hydrogen Energy 2014 Volume 39(Issue 35) pp:19928-19936
Publication Date(Web):3 December 2014
DOI:10.1016/j.ijhydene.2014.10.014
•A new bacterium Clostridium beijerinckii YA001 was isolated.•A H2 yield of 2.31 mol-H2/mol xylose was obtained with YA001.•The H2 production parameters for YA001 in batch tests were optimized.•YA001 is able to digest a series of carbon sources.A mesophilic bacterium was isolated from cow manure, and identified as Clostridium beijerinckii YA001 based on 16S rRNA gene sequence calculation using MEGA 5.0 and biochemical tests. This strain showed the ability to digest a wide range of carbon and nitrogen sources for hydrogen production, and it showed high hydrogen production performance using xylose as substrate. The optimum parameters for bio-hydrogen production in batch tests were pH 8.0, 1% substrate concentration, 40 °C and yeast extract as nitrogen source. The maximum hydrogen yield and the hydrogen production rate were obtained at 2.31 mol/mol xylose and 311.3 mL H2/(Lh), respectively. These results indicate that C. beijerinckii YA001 is an ideal candidate for fermentative hydrogen production.
Co-reporter:Fei Jia, Liejin Guo, Hongtan Liu
International Journal of Hydrogen Energy 2014 Volume 39(Issue 24) pp:12835-12841
Publication Date(Web):13 August 2014
DOI:10.1016/j.ijhydene.2014.06.061
•Current density near cell exit maintains non-zero during hydrogen starvation.•An exit hydrogen reservoir is effective in alleviating hydrogen starvation.•CVC increases sharply along the channel under potentiostatic hydrogen starvation.•CVC decreases along the channel under galvanostatic hydrogen starvation.Hydrogen starvation during a start-up process in proton exchange membrane (PEM) fuel cells could result in drastic local current density variations, reverse cell voltage and irreversible cell damages. In this work, variations of local current densities and temperatures are measured in situ under both potentiostatic and galvanostatic modes. Experimental results show that when the cell starts up under potentiostatic mode with hydrogen starvation, current density undershoots occur in the downstream; while under the galvanostatic mode, local current density in the downstream almost drops to zero, but the current density near the outlet remains almost constant. The phenomenon of near constant current density near the outlet leads to a novel approach to alleviate hydrogen starvations - a hydrogen reservoir is added at the anode outlet. Experimental results show that the exit hydrogen reservoir can significantly reduce the zero current region and alleviate hydrogen starvations. A non-dimensional current-density variation coefficient is proposed to measure the magnitude of local current density changes during starvations. Experimental results show that the exit hydrogen reservoir can significantly reduce the current-density variations coefficient over the entire flow channel, indicating that adding an exit reservoir is an effective approach in mitigating hydrogen starvations.
Co-reporter:Xueqing Wang, Honghui Yang, Chao Ma, Liejin Guo
International Journal of Hydrogen Energy 2014 Volume 39(Issue 7) pp:3176-3184
Publication Date(Web):25 February 2014
DOI:10.1016/j.ijhydene.2013.12.098
•Wb301 (ΔccoNOQP), Wbp02 (ΔcbbP) and W3p03 (ΔcbbP, ΔccoNOQP) were constructed.•The nifH expression levels were enhanced clearly when ccoNOQP was deleted.•Hydrogen production was conducted in two reactors with different optical path.•The hydrogen yields and hydrogen production rates of the mutants were enhanced.The effect of redox balance on photosynthetic bacteria growth and hydrogen generation is significant since it affects the distribution of electron flow. In this study, cbbP encoding the key enzymes in CO2 fixation cycle, and ccoNOQP encoding cyt cbb3 oxidase in cytochrome respiratory chain, were knocked out from the genome of Rhodobacter capsulatus SB1003 to obtain the mutants Wb301 (ΔccoNOQP), Wbp02 (ΔcbbP) and W3p03 (ΔcbbP, ΔccoNOQP). The transcriptional and translational level of nifH gene showed that the nifH expression levels in Wb301 and W3p03 were enhanced by 93.5% and 62.5%, and the activities of nitrogenase of Wb301 and W3p03 were enhanced by 30% and 10%, compared with those of wild type strain, respectively. In 60 mL reactors, the hydrogen yields of Wb301 and W3p03 increased by 44.8% and 36.0%, and the maximum hydrogen evolution rates increased by 15.8% and 41.7% compared with that of the wild type, respectively. The mechanisms of CBB and cytochrome c oxidase deactivation on the growth and hydrogen production performance were discussed.
Co-reporter:Dr. Zhaohui Zhou;Dr. Jinwen Shi;Dr. Po Wu ; Dr. Liejin Guo
ChemPhysChem 2014 Volume 15( Issue 14) pp:3125-3132
Publication Date(Web):
DOI:10.1002/cphc.201402164
Abstract
The structural, energetic, and electronic properties of zincblende and wurtzite phase Cd1−xZnxS (0≤x≤1) solid solutions were investigated by first-principles calculations. It was revealed that the trend of atom distribution in configurations with the same x value can be quantitatively characterized by the average length of the ZnS bonds. The origin of this trend was attributed to the strong interaction of the ZnS bonds, which acted against the aggregation of Zn atoms in this solid solution. By using a configuration-averaged method, structural and energetic properties were estimated as a function of Zn content at the level of the generalized gradient approximation, whereas electronic properties were corrected by using a hybrid functional. Phase diagrams of both solid solutions were established. An optimal x value of approximately 0.5 for photocatalytic hydrogen production was determined by taking both the band edges and band gaps into consideration; this conclusion was supported by the results of a variety of experiments.
Co-reporter:Meng Wang, Jiangang Jiang, Jinwen Shi, and Liejin Guo
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 10) pp:4021
Publication Date(Web):April 22, 2013
DOI:10.1021/am400851q
Novel CdS/CdSe core–shell nanorod arrays were fabricated by a chemical bath deposition of CdSe on hydrothermally synthesized CdS nanorods. The CdS rods were hexagonal phase faced and the top of the rod was subulate. After the chemical bath deposition approach, CdS nanorod arrays were encapsulated by a uniform CdSe layer resulting enhanced absorbance and extended absorption edges of the films. A tandem structure of the energy bands of CdS/CdSe was also formed as a result of the Fermi level alignment, which is a benefit to the efficient separation of photogenerated charges. CdS/CdSe core–shell arrays gave a maximum photocurrent of 5.3 mA/cm2, which was 4 and 11 times as large as bare CdS and CdSe, respectively.Keywords: CdS; CdSe; core−shell; Fermi level alignment; photoelectrochemistry;
Co-reporter:Kai Zhang and Liejin Guo
Catalysis Science & Technology 2013 vol. 3(Issue 7) pp:1672-1690
Publication Date(Web):19 Feb 2013
DOI:10.1039/C3CY00018D
Photocatalytic hydrogen production using semiconductor materials is one of the ideal processes for direct solar energy conversion. Sulphide semiconductor photocatalysts have attracted much attention due to their excellent solar spectrum responses and high photocatalytic activities. This article presents recent research progress in the development of visible light driven sulphide photocatalysts, focusing on the expansion of solar spectrum response and enhancement of charge separation efficiency. As is known, the ultimate goal of photocatalytic hydrogen production is to meet the practical energy demand of human beings. Thus, design of highly efficient and low cost sulphide photocatalysts with excellent sunlight response is highly desired. So we also highlight the crucial issues in the development of highly efficient sulphide photocatalysts without noble metal cocatalysts. The present paper is expected to provide important scientific reference for future works. Finally, the challenges and perspectives in this area are also discussed.
Co-reporter:Dengwei Jing, Li Jing, Huan Liu, Song Yao, and Liejin Guo
Industrial & Engineering Chemistry Research 2013 Volume 52(Issue 5) pp:1992-1999
Publication Date(Web):January 9, 2013
DOI:10.1021/ie302315g
Based on the numerical simulation results in our previous article, experimental studies were conducted. Under our reaction conditions, the selected nano-Cd0.5Zn0.5S photocatalyst could be homogenously suspended by 40 ± 5 mL/min H2S bubbling, as predicted. A homogenous distribution of photocatalyst ensured efficient absorption of the incident light. Hydrogen production with Na2S/Na2SO3 solution in a batch photocatalytic reactor (BPR) and in a fluidized-bed photocatalytic reactor with H2S bubbling (FBPR) were compared. The activity of the FBPR was obviously higher than that of the BPR. The reaction rate constant was 1.12 for the FBPR, whereas it was only 0.083 for the BPR case. The similar hydrogen productions and significant difference in reaction rate constants for the two reactors indicates that an increase in the effective initial reactant concentration in FBPR is essential. In this regard, a circulating fluidized bed with recycling use of H2S gas is preferred. Our study is expected to provide useful guidance for the development of a direct photocatalytic H2S decomposition technology.
Co-reporter:Xianghui Zhang, Mao Yang, Jianguo Zhao, Liejin Guo
International Journal of Hydrogen Energy 2013 Volume 38(Issue 36) pp:15985-15991
Publication Date(Web):13 December 2013
DOI:10.1016/j.ijhydene.2013.10.014
•Hydrogen can be produced from organic agent solutions over (CuIn)0.2Zn1.6S2.•Formic acid is the most efficient sacrificial agent due to its simple structure.•The possible mechanism of the photocatalytic reaction was discussed preliminary.Using various organics as electron donor, (CuIn)0.2Zn1.6S2 microsphere solid solution prepared via hydrothermal method as photocatalyst, hydrogen production by anaerobic photocatalytic reforming organics were researched. The photocatalytic hydrogen production activity was notably enhanced in the presence of the organic electron donors. Formic acid was found to be the most efficient sacrificial agent among methanol, glucose, triethanolamine and formic acid. The effects of initial formic acid concentration on hydrogen generation were investigated. When the initial formic acid concentration was 10 vol%, the photocatalytic activity reached the highest. The average activity in initial 10 h can amount to 144 μmol h−1. The possible mechanism of photocatalytic reaction for hydrogen production with simultaneous formic acid degradation was discussed preliminary.
Co-reporter:Peng Xiao, Liejin Guo, Ximin Zhang, Chao Zhu, Shaohua Ma
International Journal of Hydrogen Energy 2013 Volume 38(Issue 29) pp:12927-12937
Publication Date(Web):30 September 2013
DOI:10.1016/j.ijhydene.2013.04.139
•A solar hydrogen production system using molten-salts-stored solar energy was built.•The performance of molten salts reactor was evaluated by a non-dimensionless parameter NTU.•Model compound and real biomass are successfully gasified in the molten salts reactor.•Increasing NTU number leads to higher hydrogen yield and gasification efficiency.•Glycerol is more suitable as feedstock to be gasified in nitrate molten salts reactor.Hydrogen production by biomass gasification using solar energy is a promising approach for overcoming the drawbacks of fossil fuel utilization, but the storage of discontinuous solar flux is a critical issue for continuous solar hydrogen production. A continuous hydrogen production system by biomass gasification in supercritical water using molten-salts-stored solar energy was proposed and constructed. A novel double tube helical heat exchanger was designed to be molten salts reactor for hydrogen production. Model compounds (glycerol/glucose) and real biomass (corn cob) were successfully gasified in this molten salts reactor for producing hydrogen-rich gas. The unique temperature profiles of biomass slurry in the reactor were observed and compared with that of conventional electrical heating and direct solar heating approaches. Product gases yield, gasification efficiency and exergy conversion efficiency of the reactor were analyzed. The results showed that the performances of reactor were determined by feedstock style, biomass concentration, residence time and biomass slurry temperature profiles.
Co-reporter:Bo Liao, Liejin Guo, Youjun Lu, Ximin Zhang
International Journal of Hydrogen Energy 2013 Volume 38(Issue 29) pp:13038-13044
Publication Date(Web):30 September 2013
DOI:10.1016/j.ijhydene.2013.03.113
•A novel solar-H2 receiver/reactor for SCWG of biomass was developed.•SCWG of biomass driven by concentrating solar energy was conducted successfully.•Heat recovery by heat exchanger was realized in solar receiver/reactor.•DNI and feed concentration have significant effects on hydrogen production.A novel receiver/reactor driven by concentrating solar energy for hydrogen production by supercritical water gasification (SCWG) of biomass was designed, constructed and tested. Model compound (glucose) and real biomass (corncob) were successfully gasified under SCW conditions to generate hydrogen-rich fuel gas in the apparatus. It is found that the receiver/reactor temperature increased with the increment of the direct normal solar irradiation (DNI). Effects of the DNI, the flow rates and concentration of the feedstocks as well as alkali catalysts addition were investigated. The results showed that DNI and flow rates of reactants have prominent effects on the temperature of reactor wall and gasification results. Higher DNI and lower feed concentrations favor the biomass gasification for hydrogen production. The encouraging results indicate a promising approach for hydrogen production with biomass gasification in supercritical water using concentrated solar energy.
Co-reporter:Xixi Wang, Maochang Liu, Qingyun Chen, Kai Zhang, Jie Chen, Meng Wang, Penghui Guo, Liejin Guo
International Journal of Hydrogen Energy 2013 Volume 38(Issue 29) pp:13091-13096
Publication Date(Web):30 September 2013
DOI:10.1016/j.ijhydene.2013.03.016
•A series of CdS and CdS/CNTs photocatalysts were successfully prepared by hydrothermal method.•We got the optimal condition to synthesize CdS/CNTs photocatalysts with the highest photoactivity.•The hydrogen production rate was further improved by loading co-catalyst NiS.A series of CdS and CdS/CNTs photocatalysts were successfully prepared by hydrothermal method and they were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), UV–visible optical absorption spectra (UV–Vis), etc. By studying their photocatalytic properties, it is found that, for CdS, photocatalysts prepared in appropriate alkaline environment presented higher hydrogen production activity, reaching 794.6 μmol h−1 g−1; the photocatalytic activity of CdS was obviously enhanced by combining it with CNTs via a special two-step hydrothermal method, and the corresponding hydrogen production rate reached 1.771 mmol h−1 g−1; the photocatalytic activity was further improved by loading co-catalyst NiS, achieving 12.13 mmol h−1 g−1.
Co-reporter:Xiaokang Wan, Mingtao Li, Liejin Guo
International Journal of Hydrogen Energy 2013 Volume 38(Issue 27) pp:11720-11726
Publication Date(Web):10 September 2013
DOI:10.1016/j.ijhydene.2013.06.135
•BiWxV1−xO4+x/2 films were synthesized by a polymer-assisted method.•The films showed porous properties and the optical absorption blue-shifted monotonically as x increased.•The highest photocurrent and IPCE were achieved by BiW0.1V0.9O4.05.A series of BiWxV1−xO4+x/2 films were coated on fluorine-doped tin oxide (FTO) glass by a polymer-assisted method and examined as photoelectrodes for photoelectrochemical measurements under Xe lamp light irradiation in a 0.5 M Na2SO4 solution. The compositions, structural, optical and morphologic properties of the films were characterized by XPS, XRD, UV–vis and SEM. The results showed the successfully synthesized films and their photoelectrochemical activities, revealing that the amount of tungsten had an important effect on the photoelectrochemical activities of BiWxV1−xO4+x/2 films and the highest incident photon to current conversion efficiency (IPCE) was obtained when x equaled 0.1.
Co-reporter:Sha Li, Liejin Guo, Chao Zhu, Youjun Lu
International Journal of Hydrogen Energy 2013 Volume 38(Issue 23) pp:9688-9700
Publication Date(Web):6 August 2013
DOI:10.1016/j.ijhydene.2013.05.002
•Highly dispersive Ni–Al and Ni–Mg–Al catalysts were prepared for SCWG.•Mg promotes the anti-carbon ability and hydrothermal stability of Ni–Al catalyst.•Co-precipitated Ni–Mg catalyst is confirmed not suitable for SCWG.Supercritical water gasification (SCWG) is a promising process for hydrogen production from biomass. In this study, a series of Ni–Mg–Al catalysts with different Mg/Al molar ratios has been synthesized by a co-precipitation method for hydrogen production by SCWG of glucose. Effects of Mg addition on the catalytic activity, hydrothermal stability and anti-carbon performance of alumina supported nickel catalyst were investigated. The highly dispersed nickel catalysts prepared by co-precipitation could greatly enhance the gasification efficiency of glucose in supercritical water. Among the tested Ni–Mg–Al catalysts, NiMg0.6Al1.9 showed the highest catalytic activity with the hydrogen yield of 11.77 mmol/g (912% as that of non-catalytic test). NiMg0.6Al1.9 also showed the best hydrothermal stability probably due to the formation of MgAl2O4. Mg could efficiently improve the anti-carbon ability of Ni–Al catalyst by inhibiting the formation of graphite carbon. It is also confirmed that MgO supported nickel catalyst is not suitable for SCWG process owing to the difficulty on nickel oxides reduction in the precursors and the phase change of MgO to Mg(OH)2 under the hydrothermal condition.
Co-reporter:Xiangjiu Guan, Jinwen Shi, Liejin Guo
International Journal of Hydrogen Energy 2013 Volume 38(Issue 27) pp:11870-11877
Publication Date(Web):10 September 2013
DOI:10.1016/j.ijhydene.2013.07.017
•Ag3PO4 photocatalysts were synthesized by optimized hydrothermal method.•Photocatalytic O2 evolution activity was doubled due to hydrothermal treatment.•Better visible-light absorption and more regulated morphology were key factors.Visible-light-driven semiconducting photocatalysts of Ag3PO4 were prepared by a hydrothermal method, and were optimized by adjusting reaction conditions, i.e., temperature, pH of reaction solution, concentration of feedstock, and time of hydrothermal process. The obtained photocatalysts were then systematically characterized by different instruments, such as XRD, UV–vis, FESEM, and BET, to reveal the physicochemical properties. Furthermore, activities of photocatalysts for visible-light-driven O2 evolution were evaluated, demonstrating that the photocatalytic activity of Ag3PO4 prepared by hydrothermal reaction (initial rate of O2 evolution, 1156 μmol g−1 h−1) was more than two times as that of sample prepared by room-temperature reaction (initial rate of O2 evolution, 533 μmol g−1 h−1), which could be attributed to its better ability to utilize visible light and more regulated morphology.
Co-reporter:Liejin Guo
International Journal of Hydrogen Energy 2013 Volume 38(Issue 29) pp:12878
Publication Date(Web):30 September 2013
DOI:10.1016/j.ijhydene.2013.09.007
Co-reporter:Yunan Chen, Liejin Guo, Hui Jin, Jiarong Yin, Youjun Lu, Ximin Zhang
International Journal of Hydrogen Energy 2013 Volume 38(Issue 29) pp:12912-12920
Publication Date(Web):30 September 2013
DOI:10.1016/j.ijhydene.2013.05.076
•Near and super-critical water gasification of sewage sludge was studied.•Temperature was more important than residence time for the gas formation.•Characteristics of solid and liquid product varied by temperature were studied.•Relationship among gas, solid and liquid product varied by temperature was studied.The gasification of sewage sludge in near and super-critical water was investigated in a batch reactor. Results showed that the formation of gaseous products could be intensively affected by temperature. In order to understand the effect of temperature on the development of reaction process and the formation of gaseous products better, the detailed characteristics of solid and liquid products were analyzed by SEM, N2 adsorption–desorption technique, FTIR, TOC, Ammonia–nitrogen analysis and SPE-GC/MS. The changes in the yield distribution of products and the characteristics of solid and liquid products indicated that organic matters in sewage sludge were almost completely dissolved and hydrolyzed in water at 425 °C. The dissolution and hydrolysis products were gasified by reforming and other reactions. The polymerization and dehydrogenation also occurred in dissolution and hydrolysis products, and the Diels–Alder reaction mechanism could be used to explain the phenomenon.
Co-reporter:Yunan Chen, Liejin Guo, Wen Cao, Hui Jin, Simao Guo, Ximin Zhang
International Journal of Hydrogen Energy 2013 Volume 38(Issue 29) pp:12991-12999
Publication Date(Web):30 September 2013
DOI:10.1016/j.ijhydene.2013.03.165
•Sewage sludge supercritical water gasification in fluidized bed reactor was studied.•Effect of temperature, concentration, alkali catalyst type and loading was studied.•High temperature and low concentration enhanced the gasification.•Addition of alkali catalyst enhanced the formation of hydrogen.•Alkali catalyst promoted the water-gas shift reaction rather than steam reforming.In this work, gasification of sewage sludge in supercritical water was investigated in a fluidized bed reactor. Effect of operating parameters such as temperature, concentration of the feedstock, alkali catalysts and catalyst loading on gaseous products and carbon distribution were systematically studied. The results showed that the increase of temperature and the decrease of feedstock concentration were both favorable for gasification, and the addition of catalyst enhanced the formation of hydrogen better. The K2CO3 catalyst could better enhance gasification efficiency and the catalytic activity of different catalysts for hydrogen production was in the following order: KOH > K2CO3 > NaOH > Na2CO3. The maximum molar fraction and yield of hydrogen reached to 55.96% and 15.49 mol/kg respectively with KOH at 540 °C. Most carbon in feedstock existed in gaseous and liquid products, and alkali catalysts mainly promoted the water-gas shift reaction rather than steam reforming.
Co-reporter:Chao Ma, Honghui Yang, Yang Zhang, Liejin Guo
International Journal of Hydrogen Energy 2013 Volume 38(Issue 29) pp:13031-13037
Publication Date(Web):30 September 2013
DOI:10.1016/j.ijhydene.2013.03.116
•A mutant of Rhodobacter capsulatus was created by transposon.•MdtB mutant showed higher hydrogen production ability.•Pigment content of R. capsulatus may be influenced by mdtB gene.Rhodobacter capsulatus (R. capsulatus), which is a typical purple nonsulfur photosynthetic bacterium, is able to produce hydrogen under photosynthetic condition. A mutant of R. capsulatus named MC122 was obtained by Tn5 transposon mutagenesis. The transposon mutant had improved photoheterotrophic hydrogen production performance using acetic acid as substrate and its mutation site was located by sequencing the rescued plasmid containing the transposon insertion from the genome of the mutant. It was found for the first time that disruption of the multidrug resistance protein (mdtB) gene resulted in improved hydrogen production.
Co-reporter:Shuanglin Shen, Liejin Guo, Hongtan Liu
International Journal of Hydrogen Energy 2013 Volume 38(Issue 4) pp:1967-1975
Publication Date(Web):12 February 2013
DOI:10.1016/j.ijhydene.2012.11.084
A theoretical model for a solid oxide fuel cell (SOFC) with a bi-layer electrolyte is developed and analytical solutions of various important relationships, such as I–V relationship, distribution of oxygen partial pressure in the bi-layer electrolyte, leakage current density etc. are obtained. Based on the assumptions of constant ionic conductivity and reversible electrodes, the model takes into considerations of transports of both ions and electrons in the electrolyte. The modeling results are compared with both experimental data and results from other models in the literature and very good agreements are obtained.Highlights► An analytical model for a SOFC with a bi-layer electrolyte is developed. ► A set of analytical expressions for various relationships are obtained. ► Such relations include leakage current density, I–V relationship, open circuit voltage and oxygen partial pressure. ► The modeling results are compared with both experimental data and other models. ► Very good agreements are obtained.
Co-reporter:Changqing Cao, Liejin Guo, Hui Jin, Simao Guo, Youjun Lu, Ximin Zhang
International Journal of Hydrogen Energy 2013 Volume 38(Issue 30) pp:13293-13299
Publication Date(Web):8 October 2013
DOI:10.1016/j.ijhydene.2013.07.068
•The precipitated alkali in SCW still had catalytic effect.•Alkali accumulation improved the catalytic effect in the earlier gasification stage.•The results from SCWG with different NaOH content at steady state were similar.•Above 81% Na fed in the reactor was recovered after gasification.•Fluidized-bed reactor was beneficial for alkali recovery.The inorganic substances precipitate in the reactor for its low solubility in supercritical water, which may influence the performance of supercritical water gasification (SCWG). In the present study, we studied the influence of alkali precipitation on the gasification of glucose with NaOH as catalyst at 500 °C, 25 MPa in a fluidized-bed reactor. The presence of NaOH increased H2 fraction by accelerating water–gas shift reaction and also increased the gas yield. The catalytic effect was further improved with longer reaction time due to the alkali accumulation in the reactor. The precipitated alkali in the reactor still showed high catalytic effect on the subsequent gasification of glucose without further addition of alkali. The catalytic activity was slightly reduced for the transformation of NaOH to Na2CO3 and NaHCO3. The precipitated alkali flowed out of the reactor with water when the temperature in the reactor decreased to near the critical temperature because of the increasing solubility. Most of the sodium fed into the system (81.07%) was recovered in this process.
Co-reporter:Zhiwei Ge, Simao Guo, Liejin Guo, Changqing Cao, Xiaohui Su, Hui Jin
International Journal of Hydrogen Energy 2013 Volume 38(Issue 29) pp:12786-12794
Publication Date(Web):30 September 2013
DOI:10.1016/j.ijhydene.2013.06.092
•Coal is gasified completely in quartz reactors for the first time.•High temperature is a key factor for complete gasification of coal.•Oxidant facilitates complete gasification of coal.•Mass transfer has an important effect on complete gasification of coal.•The chemical equilibrium is difficult to be reached without catalyst.Supercritical water gasification (SCWG) of coal is a promising technology for clean coal utilization. In this paper, hydrogen production by non-catalytic partial oxidation of coal was systematically investigated in supercritical water (SCW) with quartz batch reactors for the first time. The influences of the main operating parameters including residence time, temperature, oxidant equivalent ratio (ER) and feed concentration on the gasification characteristics of coal were investigated. The experimental results showed that H2 yield and carbon gasification efficiency (CE) increased with increasing temperature and decreasing feed concentration. CE increased with increasing ER, and H2 yield peaked when ER equaled 0.1. CE increased quickly within 1 min and then tended to be stable between 2 and 3 min. In particular, complete gasification of lignite was obtained at 950 °C when ER equaled 0.1, as for bituminous coal, at a higher temperature of 980 °C when ER equaled 0.2.
Co-reporter:Liejin Guo, Hui Jin
International Journal of Hydrogen Energy 2013 Volume 38(Issue 29) pp:12953-12967
Publication Date(Web):30 September 2013
DOI:10.1016/j.ijhydene.2013.04.089
•A novel thermodynamics cycle power generation system is proposed.•The novel cycle is based on coal and supercritical water gasification.•The novel cycle has multi-staged steam turbine reheated by hydrogen combustion.•The novel cycle has high coal-electricity efficiency and no pollutants.•Developments of coal and supercritical water gasification in SKLMFPE are reviewed.Coal is the single most important fuel for power generation today. Nowadays, most coal is consumed by means of “burning coal in air” and pollutants such as NOx, SOx, CO2, PM2.5 etc. are inevitably formed and mixed with excessive amount of inner gases, so the pollutant emission reduction system is complicated and the cost is high. IGCC is promising because coal is gasified before utilization. However, the coal gasifier mostly operates in gas environments, so special equipments are needed for the purification of the raw gas and CO2 emission reduction. Coal and supercritical water gasification process is another promising way to convert coal efficiently and cleanly to H2 and pure CO2. The gasification process is referred to as “boiling coal in water” and pollutants containing S and N deposit as solid residual and can be discharged from the gasifier. A novel thermodynamics cycle power generation system was proposed by us in State Key Laboratory of Multiphase Flow in Power Engineering (SKLMFPE) of Xi'an jiaotong University (XJTU), which is based on coal and supercritical water gasification and multi-staged steam turbine reheated by hydrogen combustion. It is characterized by its high coal-electricity efficiency, zero net CO2 emission and no pollutants. A series of experimental devices from quartz tube system to a pilot scale have been established to realize the complete gasification of coal in SKLMFPE. It proved the prospects of coal and supercritical water gasification process and the novel thermodynamics cycle power generation system.
Co-reporter:Jiangang Jiang, Meng Wang, Lijing Ma, Qingyun Chen, Liejin Guo
International Journal of Hydrogen Energy 2013 Volume 38(Issue 29) pp:13077-13083
Publication Date(Web):30 September 2013
DOI:10.1016/j.ijhydene.2013.03.056
•The uniform ZnO/ZnS/CdS nanorod films were first synthesized.•The CdS content in films can be adjusted easily by changing the reaction temperature.•The intimate contact between core and shell was observed, which facilitated the charges transfer.The uniform ZnO/ZnS/CdS core–shell nanorod film was synthesized by a two-step ion-exchange method. The crystal structure, morphology, composition and optical property of as-prepared films were characterized by X-ray diffraction (XRD), Raman, Scanning electron microscope (SEM), Transmission electron microscope (TEM), Energy dispersive X-ray Detector (EDX) and UV–vis techniques. The results showed that the ZnO nanorod arrays can be used as sacrificial templates to synthesize uniform ZnS layer and further transform into CdS by simple ion-exchange approach. The CdS content in the films can be adjusted easily by changing the reaction temperature. The intimate contact between core and shell can be observed by high-resolution TEM image, which decrease the crystal boundary potential barrier and then facilitate the photogenerated charges transfer between the different phases. In this experiment, the ZnO/ZnS/CdS nanorod films were used in the photoelectrochemical (PEC) hydrogen production. And it is found that the film prepared at 70 °C (first step) and 100 °C (second step) gives a maximum photocurrent density and photo conversion efficiency.
Co-reporter:Shuanglin Shen, Liejin Guo, Hongtan Liu
International Journal of Hydrogen Energy 2013 Volume 38(Issue 29) pp:13084-13090
Publication Date(Web):30 September 2013
DOI:10.1016/j.ijhydene.2013.03.035
•An analytical expression of the relative thickness ratio of a bi-layer electrolyte SOFC as a function of the OCV is derived.•The SOFC characteristics are analyzed for two types of bi-layer electrolyte configurations.•The blocking layer on the cathode side is more effective in blocking the electronic current.•The blocking layer on the anode side is more effective in protecting electrolyte from reduction.From the analytical model derived earlier [17], analytical expressions for the relative thickness ratio rs of a bi-layer electrolyte and the maximum power density of a fuel cell are developed. Using these expressions, together with the other relationships from the analytical model, the characteristics of solid oxide fuel cells (SOFCs) with a bi-layer electrolyte are analyzed and theoretical analysis of the effect of the configuration of a bi-layer electrolyte on the SOFC performance is performed. The results show that the effectiveness of the bi-layer electrolyte depends strongly on its configuration. In the analyses, the variations of open circuit voltage and the maximum power density with the thickness ratio at different total electrolyte thicknesses and different operating temperatures are obtained. Furthermore, by taking into considerations of the oxygen partial pressure at the interface between the two layers of electrolytes, an analytical expression for the critical relative thickness ratio, above which, the electrolyte is stable, is obtained.
Co-reporter:Jiangang Jiang, Meng Wang, Rong Li, Lijing Ma, Liejin Guo
International Journal of Hydrogen Energy 2013 Volume 38(Issue 29) pp:13069-13076
Publication Date(Web):30 September 2013
DOI:10.1016/j.ijhydene.2013.03.057
•Two type of heterostructured film electrodes (BiVO4/CdS and CdS/BiVO4) were studied.•The CdS/BiVO4 film electrode showed the high IPCE values, 65% at 480 nm.•The possible charge transfer mechanism was proposed.The photoelectrochemical (PEC) properties of heterostructured CdS/BiVO4 and BiVO4/CdS film electrodes on conducting glass for hydrogen production under visible light were investigated. These two types heterostructured film electrodes were prepared using spin coating method and ultrasonic spray pyrolysis method. The structural analyses of the prepared films were determined by using XRD, SEM, EDX and UV–vis. Photoelectrochemical measurements were carried out in a convenient three electrodes cell with 0.5 M Na2SO3 aqueous solution. In order to investigate band gap influence of electrode PEC property, a series ITO/Cd1−xZnxS/BiVO4 and ITO/BiVO4/Cd1−xZnxS (x = 0 ∼ 1) film electrodes were also synthesized. After PEC test, a maximum photocurrent density from ITO/CdS/BiVO4 film electrode was confirmed. The maximum photocurrent density, 3 times and 113 times as that of single CdS film electrode and single BiVO4 film electrode, respectively. Incident photon to current conversion (IPCE) of as prepared film electrodes were measured and the value were 65% (ITO/CdS/BiVO4), 22% (single CdS film) and 10% (ITO/BiVO4/CdS) at 480 nm with 0.3 V external bias. Comparison with ITO/BiVO4/CdS electrode and single Cd1−xZnxS electrodes, the heterostructured ITO/CdS/BiVO4 electrode can effectively suppress photogenerated electron-hole recombination and enhance light harvesting. Therefore, the ITO/CdS/BiVO4 electrode gave the maximum photocurrent density and IPCE value.
Co-reporter:Penghui Guo, Jiangang Jiang, Shaohua Shen, Liejin Guo
International Journal of Hydrogen Energy 2013 Volume 38(Issue 29) pp:13097-13103
Publication Date(Web):30 September 2013
DOI:10.1016/j.ijhydene.2013.01.184
Heterojunction structures are attracting lots of attention for enhancing the electron injection across the interface. The ZnS/ZnO one-dimensional heterojunction film was firstly prepared via a chemical sulfidization following hydrothermal reaction. The heterostructure was characterized as ZnS(blende)/ZnO(wurtzite) shell–core nanorods via XRD, SEM and TEM. A type II band alignment structure of ZnS/ZnO composite was synthesized via a temperate condition proved by PLS and XPS. The values for valence band offset (VBO) and conduction band offset (CBO) were calculated to be 0.96 eV and 1.25 eV, respectively. The special electron structure in the heterojunction helped reduce the energy barrier height at the interface and enhance the separation of photo-generated carriers. Thus, the photoelectrochemical performance was highly improved, and a photocurrent density of 380 μA/cm2 at 0.9 V (vs. Ag/AgCl) was obtained.Highlights► ZnS/ZnO shell/core nanorod arrays were prepared via sulfidization following hydrothermal process. ► The morphologies and structures of the composite heterojunction are characterized; especially the energy band alignment. ► The type II band alignment helps improve the PEC performance.
Co-reporter:Simao Guo, Liejin Guo, Jiarong Yin, Hui Jin
The Journal of Supercritical Fluids 2013 Volume 78() pp:95-102
Publication Date(Web):June 2013
DOI:10.1016/j.supflu.2013.03.025
•Quantitative kinetics model for gases production of glycerol SCWG was developed.•Reaction rates for formation/consumption of H2, CO, CH4 and CO2 were analyzed.•Temperature for completely SCWG of glycerol was estimated by kinetics model.•Sensitive analysis of WGSR rate constant was done based on the kinetics model.In this paper, the liquid products from supercritical water gasification (SCWG) of glycerol were analyzed and some intermediates were identified. A simplified reaction pathway for gases production from SCWG of glycerol was proposed. The first quantitative kinetics model for describing the gaseous products (H2, CO, CH4 and CO2) of SCWG of glycerol was developed. The model comprises seven reactions to describe the typical reactions in SCWG, and the reaction rate constant of each reaction was obtained by using the nonlinear least-square fitting method. The reaction rate analysis showed that the main sources of hydrogen yield were glycerol pyrolysis and steam reforming of intermediates, while the hydrogen yield from water–gas shift reaction (WGSR) was very small. The temperature estimated by the kinetics model for completely SCWG of glycerol solution was given. In addition, the sensitivity analysis of rate constant of WGSR was done based on the model.
Co-reporter:Yubin Chen and Liejin Guo
Journal of Materials Chemistry A 2012 vol. 22(Issue 15) pp:7507-7514
Publication Date(Web):2012/03/09
DOI:10.1039/C2JM16797B
Semiconductor based nanocomposites are quite promising in the areas of photocatalysis and photovoltaics due to their efficient charge separation. Herein, we demonstrated a simple and green one-step method to prepare novel Cd0.5Zn0.5S/TNTs (titanate nanotubes) nanocomposites with low-priced metallic elements. Transmission electron microscopy (TEM) images revealed that an enwrapped architecture was achieved for Cd0.5Zn0.5S/TNTs nanocomposites. Cd0.5Zn0.5S nanoparticles of ca. 90 nm were tightly surrounded by the network of titanate nanotubes, which led to the high dispersity of Cd0.5Zn0.5S nanoparticles and the intimate multipoint contacts between Cd0.5Zn0.5S and TNTs. Highly efficient charge separation was finally achieved in the hybrid Cd0.5Zn0.5S/TNTs through the enwrapped structure. Under visible light irradiation Cd0.5Zn0.5S/TNTs displayed improved activities compared to the single Cd0.5Zn0.5S for hydrogen evolution. The effect of sacrificial reagents on the photocatalytic activity of Cd0.5Zn0.5S/TNTs was discussed. The highest apparent quantum yield of 38.1% at 420 nm was achieved. This value is among the highest efficiencies for the noble-metal free photocatalysts ever reported. Meanwhile, Cd0.5Zn0.5S/TNTs showed good stability for hydrogen production, and the content of toxic cadmium was as low as 4.0 wt% of the nanocomposites. These factors are of great significance for their application in the field of solar energy conversion.
Co-reporter:Honghui Yang, Xueqing Wang, Lizhu Zhang, Liejin Guo
International Journal of Hydrogen Energy 2012 Volume 37(Issue 18) pp:13296-13303
Publication Date(Web):September 2012
DOI:10.1016/j.ijhydene.2012.06.101
A new isolated photosynthetic bacterium, Rubrivivax gelatinosus M002, can produce hydrogen with glucose or lactate as sole carbon source, and grow on butyrate and acetate without hydrogen evolution. Experiments on studying its hydrogen production performance from glucose mixed with acetate, butyrate or lactate were carried out. The results showed that the hydrogen yield increased significantly and the pH value of the photo-fermentations could retain around 7 in these mixed carbon sources cultures. A hydrogen yield of 9.9 mol H2/mol-glucose was observed when 20 mM acetate and 15 mM glucose was co-fed as substrate. The maximum hydrogen production rate was 44 mL/(L·h), which was 37.5% higher than the highest rate obtained with glucose as sole carbon source. The results suggest an alternative way for high-yield hydrogen production with mixed carbon source in one-step process instead of two-step fermentation process.Highlights► The photo-hydrogen production performance of Rubrivivax gelatinosus M002 was studied. ► Its H2 production property increased clearly when glucose and acetate were co-fed. ► The pH values were maintained around 7 automatically with the mixed carbon sources. ► The bacteria formed biofilm fast in hydrogen production process.
Co-reporter:Po Wu, Jinwen Shi, Zhaohui Zhou, Wendong Tang, Liejin Guo
International Journal of Hydrogen Energy 2012 Volume 37(Issue 18) pp:13704-13710
Publication Date(Web):September 2012
DOI:10.1016/j.ijhydene.2012.02.143
A series of CaTaxZr(1−x)O(3−x)Nx solid solutions were successfully synthesized through nitriding precursors prepared by the polymerized complex method. The physicochemical properties of these multicomponent semiconductors were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), N2 adsorption–desorption isotherms, UV–visible optical absorption spectra (UV–Vis) and density functional theory (DFT) calculations. The diffraction peaks in XRD patterns gradually shifted to higher angles as x increased, indicating that CaTaxZr(1−x)O(3−x)Nx solid solutions had been formed. The absorption edges in UV–Vis spectra red-shifted monotonically as x increased, demonstrating that the band gap of the prepared photocatalysts could be precisely controlled with the adjustment of compositions. The solid solutions rendered photocatalytic H2 evolution from a formic acid aqueous solution under visible-light irradiation. The narrow band gap, sufficient crystallization, enough pore volume and large specific surface area resulted in the best photocatalytic activity of CaTa0.8Zr0.2O2.2N0.8.Highlights► CaTaxZr(1−x)O(3−x)Nx solid solutions were synthesized by PC method. ► Absorption edges red-shifted monotonically as x increased. ► CaTa0.8Zr0.2O2.2N0.8 showed best H2 evolution. ► Band gap and specific surface area were both key factors.
Co-reporter:Ying Yang, Liejin Guo, Hongtan Liu
International Journal of Hydrogen Energy 2012 Volume 37(Issue 18) pp:13822-13828
Publication Date(Web):September 2012
DOI:10.1016/j.ijhydene.2012.04.026
Co-reporter:Chao Ma, Liejin Guo, Honghui Yang
International Journal of Hydrogen Energy 2012 Volume 37(Issue 17) pp:12229-12233
Publication Date(Web):September 2012
DOI:10.1016/j.ijhydene.2012.05.148
The light shielding effect of photosynthetic bacteria in photo fermentation process, which is caused by high content of pigment, hinders their hydrogen production rates under intense light irradiation. In order to mitigate this effect and improve hydrogen production efficiency, it is necessary to screen mutants that hold less pigment content. In this study, a mini-Tn5 transposon encoded plasmid pRL27 was employed for transposon mutagenesis of Rhodobacter capsulatus SB1003. A mutant named MC1417 showed significant lower light absorbance from 330 nm to 900 nm compared to its parental strain by UV–visible spectra, and its bacteriochlorophyll a content was reduced by 38%. The results showed that its photo fermentative hydrogen production was improved by 50.5% on the basis of BChl a content using acetate and butyrate as carbon source under intense light irradiation, indicating that it is effective on improving hydrogen production by repressing the pigment biosynthesis. DNA sequencing and BLAST in NCBI Genebank showed that the mutation occurred within its pucDE gene.Highlights► Transposon mutagenesis was used to screen pigment mutant of Rhodobacter capsulatus. ► A reduced pigment mutant of R. capsulatus was created by transposon. ► Mutant with less pigment showed higher hydrogen production ability.
Co-reporter:Youjun Lu, Liejin Guo, Ximin Zhang, Chengmeng Ji
International Journal of Hydrogen Energy 2012 Volume 37(Issue 4) pp:3177-3185
Publication Date(Web):February 2012
DOI:10.1016/j.ijhydene.2011.11.064
Supercritical water gasification (SCWG) is a promising technology for wet biomass utilization. In this paper, orthogonal experimental design method, which can minimize the number of experiments compared with the full factorial experiments, was used to optimize the operation parameters of SCWG with a tubular reactor system. Using this method, the influences of the main parameters including pressure, temperature, residence time and solution concentration on biomass gasification were also investigated. Simultaneously, in order to further improve the gasification efficiency of biomass, acid hydrolysis pretreatment of feedstock, oxidizers addition and increasing reaction temperature were employed. Results from the experiments show that in the range of experimental parameters, the order of the effects of the factors on H2 yield of corn cob gasification in SCW is temperature > pressure > feedstock concentration > residence time. Temperature and pressure have a significant and complicated effect on biomass gasification. Hydrogen yield increases by the acid hydrolysis pretreatment of feedstock, and oxidizer addition reduces the hydrogen yield but it promotes the increase in carbon gasification efficiency. Biomass feedstock with high concentration was gasified successfully at high reaction temperature.Highlights► Orthogonal experimental method was used to optimize the operation parameters. ► The optimum operation condition for H2 production was obtained using this method. ► The influences of the main parameters on SCWG were obtained using this method. ► High concentration feedstock was gasified completely at high temperature.
Co-reporter:Ying Yang, Liejin Guo, Hongtan Liu
International Journal of Hydrogen Energy 2012 Volume 37(Issue 2) pp:1875-1883
Publication Date(Web):January 2012
DOI:10.1016/j.ijhydene.2011.06.088
Corrosion performance of 316L stainless steel as a bipolar plate material in proton exchange membrane fuel cell (PEMFC) is studied under different simulated PEMFC anode conditions. Solutions of 1 × 10−5 M H2SO4 with a wide range of different F− concentrations at 70 °C bubbled with hydrogen gas are used to simulate the PEMFC anode environments. Electrochemical methods, both potentiodynamic and potentiostatic, are employed to study the corrosion behavior. Scanning electron microscope (SEM) and atomic force microscope (AFM) are used to examine the surface morphology of the specimen after it is potentiostatic polarized in simulated PEMFC anode environments. X-ray photoelectron spectroscopy (XPS) analysis is used to identify the compositions and the depth profile of the passive film formed on the 316L stainless steel surface after it is polarized in simulated PEMFC anode environments. Mott–Schottky measurements are used to characterize the semiconductor passive films. The results of potentiostatic analyses show that corrosion currents increase with F− concentrations. SEM examinations show that no localized corrosion occurs on the surface of 316L stainless steel and AFM measurement results indicate that the surface topography of 316L stainless steel becomes slightly rougher after polarized in solutions with higher concentration of F−. From the results of XPS analysis and Mott–Schottky measurements, it is determined that the passive film formed on 316L stainless steel is a single layer n-type semiconductor.Highlights► The effect of fluoride ions concentration on corrosion behavior of SS316L in PEMFC anode environments is studied. ► Corrosion current densities of SS316L at different fluoride ions concentration are all lower than US DOE 2015 target, 1 μA cm−2. ► No localized corrosion occurs for SS316L in all simulate PEMFC anode environments. ► A single layer n-type semiconductor passive film formed on SS316L indicates there is a potential risk of localized corrosion.
Co-reporter:Guangsheng Zhang, Shuanglin Shen, Liejin Guo, Hongtan Liu
International Journal of Hydrogen Energy 2012 Volume 37(Issue 2) pp:1884-1892
Publication Date(Web):January 2012
DOI:10.1016/j.ijhydene.2011.04.120
Reactant starvation during proton exchange membrane fuel cell (PEMFC) operation can cause serious irreversible damages. In order to study the detailed local characteristics of starvations, simultaneous measurements of the dynamic variation of local current densities and temperatures in an experimental PEMFC with single serpentine flow field have been performed during both air and hydrogen starvations. These studies have been performed under both current controlled and cell voltage controlled operations. It is found that under current controlled operations cell voltage can decrease very quickly during reactant starvation. Besides, even though the average current is kept constant, local current densities as well as local temperatures can change dramatically. Furthermore, the variation characteristics of local current density and temperature strongly depend on the locations along the flow channel. Local current densities and temperatures near the channel inlet can become very high, especially during hydrogen starvation, posing serious threats for the membrane and catalyst layers near the inlet. When operating in a constant voltage mode, no obvious damaging phenomena were observed except very low and unstable current densities and unstable temperatures near the channel outlet during hydrogen starvation. It is demonstrated that measuring local temperatures can be effective in exploring local dynamic performance of PEMFC and the thermal failure mechanism of MEA during reactants starvations.Highlights► Dynamic variations of local current densities and temperatures during starvations are measured simultaneously. ► During starvations, local current densities and temperatures can become very high, posing serious threats for the membrane and catalyst layers. ► Measuring local temperatures can be effective in exploring local dynamic performance of PEMFC and thermal failure mechanism of MEA during reactants starvations.
Co-reporter:Simao Guo, Liejin Guo, Changqing Cao, Jiarong Yin, Youjun Lu, Ximin Zhang
International Journal of Hydrogen Energy 2012 Volume 37(Issue 7) pp:5559-5568
Publication Date(Web):April 2012
DOI:10.1016/j.ijhydene.2011.12.135
In this work, glycerol was used for hydrogen production by supercritical water gasification. Experiments were conducted in a continuous flow tubular reactor at 445∼600 °C, 25 MPa, with a short residence time of 3.9∼9.0 s. The effects of reaction temperature, residence time, glycerol concentration and alkali catalysts on gasification were systematically studied. The results showed that the gasification efficiency increased sharply with increasing temperature above 487 °C. A short residence time of 7.0 s was enough for 10 wt% glycerol gasification at 567 °C. With the increase of glycerol concentration from 10 to 50 wt%, the gasification efficiency decreased from 88% to 71% at 567 °C. The alkali catalysts greatly enhanced water-gas shift reaction and the hydrogen yield in relation to catalysts was in the following order: NaOH > Na2CO3>KOH > K2CO3. The hydrogen yield of 4.93 mol/mol was achieved at 526 °C with 0.1 wt% NaOH. No char or tar was observed in all experiments. The apparent activation energy and apparent pre-exponential factor for glycerol carbon gasification were obtained by assuming pseudo first-order kinetics.Highlights► H2 production by supercritical water gasification (SCWG) of glycerol was studied. ► Effects of temperature, residence time and glycerol concentration were studied. ► H2 yield with alkali catalysts was in the following order: NaOH > Na2CO3>KOH > K2CO3. ► No tar or char was observed in all experiments. ► A pseudo first order kinetics for glycerol carbon gasification was proposed.
Co-reporter:Maochang Liu, Yuanchang Du, Lijng Ma, Dengwei Jing, Liejin Guo
International Journal of Hydrogen Energy 2012 Volume 37(Issue 1) pp:730-736
Publication Date(Web):January 2012
DOI:10.1016/j.ijhydene.2011.04.111
A series of Mn2+ doped CdS photocatalysts were prepared by a co-precipitation method and characterized by XRD, DRS, TEM, and XPS techniques. While the band gap, crystal phase and the morphology of CdS nanocrystal were not found to be affected noticeably by Mn2+ doping, there was an optimal Mn2+ doping content of wt 0.5% where the hydrogen production was more than doubled compared to pure CdS. Calculations of density functional theory (DFT) with plane waves and pseudopotentials were used to characterize the doping effect of Mn in cubic CdS. It is assumed that Mn2+ serving as shallow trapping sites can separate e−/h+ pairs at surface of nanosized CdS, so as to greatly reduce their surface recombination and which in turn leads to improved hydrogen yield.Highlights► Co-precipitating synthesis of mesoporous Mn doped CdS photocatalysts. ► Enhanced Photocatalytic activity on CdS by dopping Mn2+. ► Mn2+ in CdS induces shallow energy level certified by band calculation.
Co-reporter:Kai He, Mingtao Li, Liejin Guo
International Journal of Hydrogen Energy 2012 Volume 37(Issue 1) pp:755-759
Publication Date(Web):January 2012
DOI:10.1016/j.ijhydene.2011.04.065
In this paper, a series of PANI-CdS (PANI is the abbreviation of Polyaniline) composites were synthesized by changing the mass of PANI (molar ratio of PANI and CdS : 0.5, 0.7, 1, 1.5, 2). The PANI-CdS composites were characterized by XRD patterns, IR spectra and elemental analysis. The activities of as-prepared composites were also tested with regard to hydrogen evolution. It was found that PANI-CdS composites showed good activity for hydrogen evolution. With increment of PANI, the activity for hydrogen evolution of PANI-CdS reduced. But compared with pure CdS, PANI-CdS had a much higher activity for hydrogen evolution.Highlights► It was the first time to use PANI-CdS composite as a kind of photocatalyst. ► The activity of catalysts is much higher than that of pure CdS. ► The photocatalyst was stable enough during the reaction.
Co-reporter:Shu Zhang, Qingyun Chen, Dengwei Jing, Yunhai Wang, Liejin Guo
International Journal of Hydrogen Energy 2012 Volume 37(Issue 1) pp:791-796
Publication Date(Web):January 2012
DOI:10.1016/j.ijhydene.2011.04.060
PdS–CdS modified by polyaniline (PANI) as a novel photocatalyst was synthesized via a sonochemical approach for the first time. The as-prepared photocatalysts were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–vis absorption spectra, FT-IR spectra, and fluorescence spectra (PL). Under visible light, the photocatalysts showed excellent photocatalytic activity for hydrogen evolution in the absence of noble metal Pt and the antiphotocorrosion performance of the composite photocatalyst was also found to be significantly improved simultaneously compared to PdS–CdS without PANI modification. The highest rate for H2 evolution was 3.32 mmol/h with the concentration of 1 wt.%PANI and 1 wt.%PdS.Highlights► In this study we modified PdS–CdS photocatalysts with polyaniline. ► We found that the as-prepared photocatalysts were both efficient and stable for photocatalytic hydrogen production under visible light. ► We concluded that PANI was very ideal to be used to modify sulphide photocatalysts.
Co-reporter:Zheng Liu, Shaohua Shen, Liejin Guo
International Journal of Hydrogen Energy 2012 Volume 37(Issue 1) pp:816-821
Publication Date(Web):January 2012
DOI:10.1016/j.ijhydene.2011.04.052
A series of CdS/M(x)-MCM-41 (M = Zr, Ti, x stands for molar ratio of M/Si) photocatalysts were preprared by hydrotherm, ion-exchange and sulfidation process. The catalysts were characterized by X-ray diffraction, UV–vis spectra and N2 adsorption–desorption isotherm et al. The characterization results shown that Zr or Ti was successfully doped into the mesoporous of MCM-41, and CdS was also successfully incorporated into such modified mesoporous. The results of photocatalytic performance for hydrogen production shown that CdS/Zr(0.005)-MCM-41 and CdS/Ti(0.02)-MCM-41 had the highest hydrogen evolution activity in triethanolamine aqueous solution under visible light (λ > 430 nm) irradiation, which can be explained by the diffusion velocity of the reactants and resultants and the protection which MCM-41 provided for CdS.Highlights► CdS was successfully incorporated into M(x)-MCM-41. ► The photocorrosion of CdS had been solved availably. ► Photocatalytic activity was further enhanced by Zr and Ti doping. ► Hydrogen evolution and pollutant degradation were achieved at the same time.
Co-reporter:Shaohua Shen, Liang Zhao, Xiangjiu Guan, Liejin Guo
Journal of Physics and Chemistry of Solids 2012 Volume 73(Issue 1) pp:79-83
Publication Date(Web):January 2012
DOI:10.1016/j.jpcs.2011.09.027
A series of alkaline-earth metal doped ZnIn2S4 photocatalysts were prepared by the microwave-assisted hydrothermal method, and characterized using various analysis techniques, such as XRD, Raman, UV–vis spectra, photoluminescence spectra and SEM. The successful incorporation of Ca, Sr and Ba into the lattices of ZnIn2S4 was proved by Raman spectra. Photocatalytic results demonstrated that Ca doping could greatly enhance the activity of ZnIn2S4, with about two times higher than undoped ZnIn2S4, while Sr and Ba doping could not. The varied photocatalytic activities of doped ZnIn2S4 as a function of alkaline-earth metals as dopants were discussed on the basis of the sophisticated photoluminescence process.Highlights► Ca-, Sr- and Ba-doped ZnIn2S4 were synthesized by a microwave-assisted hydrothermal method. ► Ca doping could greatly enhance the activity of ZnIn2S4 as two times higher than undoped ZnIn2S4. ► Activities of doped ZnIn2S4 were related to the sophisticated photoluminescence process.
Co-reporter:Shaohua Shen, Jiangang Jiang, Penghui Guo, Coleman X. Kronawitter, Samuel S. Mao, Liejin Guo
Nano Energy 2012 Volume 1(Issue 5) pp:732-741
Publication Date(Web):September 2012
DOI:10.1016/j.nanoen.2012.05.013
Hematite (α-Fe2O3) nanorod arrays modified by surface doping of chromium (III) ions (Cr3+) for photoelectrochemical (PEC) water splitting are fabricated using a general process involving a combination of aqueous chemical growth and spin coating. The PEC activity of Cr-doped α-Fe2O3 nanorod films first increases then decreases with increasing dopant content. At the optimal content of Cr, Cr-doped α-Fe2O3 nanorod films exhibit about 3.5 and 6 times higher PEC activity than the undoped material under solar light (AM 1.5, 100 mW cm−2) and visible light (λ>430 nm) irradiation, respectively. A comprehensive characterization of the chemical, morphological, PEC, structural, and optical properties of the doped α-Fe2O3 films are presented to assess the mechanisms by which the dopants influence photoelectrode performance. The relationship between dopant content, photoluminescence intensity, and PEC performance suggests Cr doping alters charge transfer in the films under irradiation. At low Cr doping contents, Cr dopants act as electron (or hole) traps and retard photoinduced charge recombination, leading to enhanced PEC activity. Whereas, at high Cr doping contents, Cr dopants act as charge recombination sites and lower the charge separation efficiency, leading to decreased PEC activity. High temperature annealing proves to be effective for further improvement of the PEC activities of doped and undoped hematite films, by Sn diffusion.Graphical abstractHighlights► Surface composition of hematite nanorods was tuned by Cr3+ doping facilely. ► Doing of Cr3+ at a optimal concentration led to enhanced photoelectrochemical activity. ► Photoelectrochemical performances were promoted by altering photoinduced charge transfer ability.
Co-reporter:Jinwen Shi, Liejin Guo
Progress in Natural Science: Materials International 2012 Volume 22(Issue 6) pp:592-615
Publication Date(Web):December 2012
DOI:10.1016/j.pnsc.2012.12.002
ABO3-based photocatalysts for water splitting were systematically reviewed in this manuscript. Crystal structure and chemical composition characteristics of ABO3 materials were briefly introduced to guide the modification of ABO3-based photocatalysts. The ABO3-based photocatalysts were then reviewed in detail and divided into four groups based on the employed modification strategies, i.e., chemical component adjustment, micro-/nano-structure adjustment, local lattice structure adjustment, and application of the modification strategy of ABO3 photocatalysts in designing AxByOz photocatalysts. In this section, the recent research works on ABO3-based photocatalysts in our group were presented. Finally, application of ABO3 photocatalysts in Z-scheme systems for overall water splitting was introduced. This review summarized the development of ABO3-based photocatalysts and showed the values and possible direction of future research, thereby offering a guide for photocatalytic water splitting.
Co-reporter:Shaohua Shen;Coleman X. Kronawitter;Jiangang Jiang;Samuel S. Mao
Nano Research 2012 Volume 5( Issue 5) pp:327-336
Publication Date(Web):2012 May
DOI:10.1007/s12274-012-0213-6
Co-reporter:Jinwen Shi;Dr. Jinhua Ye;Dr. Qiuye Li;Zhaohui Zhou;Dr. Hua Tong;Dr. Guangcheng Xi;Dr. Liejin Guo
Chemistry - A European Journal 2012 Volume 18( Issue 11) pp:3157-3162
Publication Date(Web):
DOI:10.1002/chem.201102214
Co-reporter:Jinwen Shi;Dr. Jinhua Ye;Lijing Ma;Dr. Shuxin Ouyang;Dr. Dengwei Jing;Dr. Liejin Guo
Chemistry - A European Journal 2012 Volume 18( Issue 24) pp:7543-7551
Publication Date(Web):
DOI:10.1002/chem.201102807
Abstract
A series of upconversion luminescent erbium-doped SrTiO3 (ABO3-type) photocatalysts with different initial molar ratios of Sr/Ti have been prepared by a facile polymerized complex method. Er3+ ions, which were gradually transferred from the A to the B site with increasing Sr/Ti, enabled the absorption of visible light and the generation of high-energy excited states populated by upconversion processes. The local internal fields arising from the dipole moments of the distorted BO6 octahedra promoted energy transfer from the high-energy excited states of Er3+ with B-site occupancy to the host SrTiO3 and thus enhanced the band-to-band transition of the host SrTiO3. Consequently, the erbium-doped SrTiO3 species with B-site occupancy showed higher photocatalytic activity than those with A-site occupancy for visible-light-driven H2 or O2 evolution in the presence of the corresponding sacrificial reagents. The results generally suggest that the introduction of upconversion luminescent agents into host semiconductors is a promising approach to simultaneously harnessing low-energy photons and maintaining redox ability for photocatalytic H2 and O2 evolution and that the site occupancy of doped elements in ABO3-type perovskite oxides greatly determines the photocatalytic activity.
Co-reporter:Jinwen Shi;Lijing Ma;Po Wu;Zhaohui Zhou;Jiangang Jiang;Xiaokang Wan;Dr. Dengwei Jing ;Dr. Liejin Guo
ChemCatChem 2012 Volume 4( Issue 9) pp:1389-1396
Publication Date(Web):
DOI:10.1002/cctc.201200063
Abstract
A series of tin(II)–antimonate photocatalysts with varied Sn content were prepared by altering the ion-exchange time and reaction temperature to control their physicochemical properties, especially their band-gaps and nanostructures. Furthermore, the effect of these catalysts on visible-light-driven photocatalytic H2-evolution was also investigated. With an increase in Sn content, the narrowed band-gaps enhanced the absorption of photons to excite the photogenerated charge carriers. A decrease in nanocrystal size approaching stoichiometric compositions impeded the recombination of the photogenerated charge carriers; the increased surface areas and pore volumes, owing to the nanostructural transformation, accelerated the redox reactions. Consequently, the photocatalytic activities gradually improved and the highest rate was observed for stoichiometric Sn2Sb2O7. As a result, the as-prepared tin(II) antimonates—especially Sn2Sb2O7—were confirmed to be stable and efficient photocatalysts for visible-light-driven H2 evolution. Moreover, the activities of these photocatalysts could be improved by tuning their physicochemical properties to jointly optimize all of the processes in the photocatalytic reaction.
Co-reporter:Fengjun Xiao, Liejin Guo, Debiao Li, Yueshe Wang
Particuology 2012 Volume 10(Issue 2) pp:221-228
Publication Date(Web):April 2012
DOI:10.1016/j.partic.2011.10.004
An Eulerian/Lagrangian numerical simulation is performed on mixed sand transport. Volume averaged Navier–Stokes equations are solved to calculate gas motion, and particle motion is calculated using Newton's equation, involving a hard sphere model to describe particle-to-particle and particle-to-wall collisions. The influence of wall characteristics, size distribution of sand particles and boundary layer depth on vertical distribution of sand mass flux and particle mean horizontal velocity is analyzed, suggesting that all these three factors affect sand transport at different levels. In all cases, for small size groups, sand mass flux first increases with height and then decreases while for large size groups, it decreases exponentially with height and for middle size groups the behavior is in-between. The mean horizontal velocity for all size groups well fits experimental data, that is, increasing logarithmically with height in the middle height region. Wall characteristics greatly affects particle to wall collision and makes the flat bed similar to a Gobi surface and the rough bed similar to a sandy surface. Particle size distribution largely affects the sand mass flux and the highest heights they can reach especially for larger particles.Graphical abstractComparison of simulation results with experimental data.Highlights► Effects of wall characteristics, size distribution of sand particles and boundary layer depth on distributions of sand mass flux and particle velocity are simulated. ► The simulated mean horizontal velocity for all particle size groups well fits experimental data. ► Wall characteristics greatly affects particle to wall collision and makes the flat bed similar to a Gobi surface and the rough bed similar to a sandy surface.
Co-reporter:Jinwen Shi;Lijing Ma;Po Wu;Zhaohui Zhou;Penghui Guo;Shaohua Shen
Nano Research 2012 Volume 5( Issue 8) pp:576-583
Publication Date(Web):2012 August
DOI:10.1007/s12274-012-0243-0
Co-reporter:Maochang Liu, Lianzhou Wang, Gaoqing (Max) Lu, Xiangdong Yao and Liejin Guo
Energy & Environmental Science 2011 vol. 4(Issue 4) pp:1372-1378
Publication Date(Web):28 Feb 2011
DOI:10.1039/C0EE00604A
Cd1−xZnxS solid solution with nano-twin structures are synthesized and exhibit superior photocatalytic activities for H2 evolution from water under visible light irradiation (λ ≥ 430 nm) without noble metal co-catalysts. Such Cd0.5Zn0.5S nanocrystals show the highest activity for hydrogen evolution with an extremely high apparent quantum yield (AQY = 43%) at 425 nm, achieving a hydrogen evolution rate of 1.79 mmol h−1 without noble metals. The hydrogen evolution rate of 1.70 mmol h−1 was achieved under simulated sunlight conditions (without infrared light). The “back to back” potential formed by parallel nano-twins in the Cd1−xZnxS crystals can significantly improve the separation of the photo-generated electrons/holes (preventing their recombination) thus enhancing the photocatalytic activity. Photodeposition experiments of noble metals strongly support such a mechanism. It is found that noble metals were selectively photo-deposited at central regions between the twin boundaries. The concentration of free electrons at the central region of twins was markedly higher and the twins can effectively separate the H2 evolution sites (electrons) from oxidation reaction sites (holes).
Co-reporter:Jinzhan Su, Liejin Guo, Ningzhong Bao, and Craig A. Grimes
Nano Letters 2011 Volume 11(Issue 5) pp:1928-1933
Publication Date(Web):April 22, 2011
DOI:10.1021/nl2000743
We report on a novel heterojunction WO3/BiVO4 photoanode for photoelectrochemical water splitting. The heterojunction films are prepared by solvothermal deposition of a WO3 nanorod-array film onto fluorine-doped tin oxide (FTO) coated glass, with subsequent deposition of a low bandgap, 2.4 eV, visible light responding BiVO4 layer by spin-coating. The heterojunction structure offers enhanced photoconversion efficiency and increased photocorrosion stability. Compared to planar WO3/BiVO4 heterojunction films, the nanorod-array films show significantly improved photoelectrochemical properties due, we believe, to the high surface area and improved separation of the photogenerated charge at the WO3/BiVO4 interface. Synthesis details are discussed, with film morphologies and structures characterized by field emission scanning electron microscopy and X-ray diffraction.
Co-reporter:Yubin Chen, Lianzhou Wang, Gaoqing (Max) Lu, Xiangdong Yao and Liejin Guo
Journal of Materials Chemistry A 2011 vol. 21(Issue 13) pp:5134-5141
Publication Date(Web):22 Feb 2011
DOI:10.1039/C0JM03945D
CdS/titanate nanotubes (CdS/TNTs) photocatalysts with a unique morphology were successfully synthesized via a simple one-step hydrothermal method. Compared with traditional CdS@TNTs composite photocatalysts prepared by the common two-step method, CdS/TNTs exhibited much higher activity for photocatalytic hydrogen evolution under visible light irradiation. Transmission electron microscopy (TEM) revealed that the CdS nanoparticle was intimately enwrapped by the surrounding TNTs. This unique architecture resulted in the appropriate dispersion of CdS nanoparticles and the intimate multipoint contacts between the CdS nanoparticle and TNTs, which led to significant enhancement of charge separation in CdS/TNTs. Accordingly, the photoactivity was improved. Meanwhile, X-ray powder diffraction (XRD) demonstrated that the highly crystalline hexagonal CdS was obtained in CdS/TNTs, which was also essential for the enhanced photocatalytic performance. The unique morphology and photocatalytic activity of CdS/TNTs were influenced by the Cd/Ti molar ratio with an optimal value of 0.05. Under this condition, the CdS amount was only 6 wt% of the total photocatalyst, which was important from an environmental point of view. The influence of loaded Pt on the activity of CdS/TNTs had also been investigated. The hydrogen production rate of 2.0 wt% Pt-loaded CdS/TNTs reached 353.4 μmol h−1, with the apparent quantum yield of 25.5% at 420 nm. This study provides a potential way to synthesize highly efficient composite photocatalysts with a novel architecture.
Co-reporter:Shaohua Shen, Jie Chen, Xixi Wang, Liang Zhao, Liejin Guo
Journal of Power Sources 2011 Volume 196(Issue 23) pp:10112-10119
Publication Date(Web):1 December 2011
DOI:10.1016/j.jpowsour.2011.08.103
Aiming at the enhancement of photocatalytic activity for hydrogen evolution over ZnIn2S4, different transition metals (Cr, Mn, Fe, Co) are doped into the lattices of ZnIn2S4 to narrow the band gap. The doped ZnIn2S4 is characterized by XRD, Raman, UV–vis spectra, photoluminescence spectra, SEM and XPS techniques. The photocatalytic evaluation shows that Mn-doped ZnIn2S4 performs photocatalytic activity 20% higher than undoped ZnIn2S4, while Cr-, Fe-, and Co-doped ZnIn2S4 perform poorer activities in an order of Cr > Fe > Co. Based on the combined characterization results, the band structures of doped ZnIn2S4 are schematically depicted, which illustrates the different effects of transition-metal doping on the photocatalytic activity for hydrogen evolution. For Mn-doped ZnIn2S4, the enhancement of photocatalytic activity could be due to narrowed band gap induced by Mn doping. However, for Cr-, Fe-, and Co-doped ZnIn2S4, the suppressed photocatalytic activities should be attributed to the dopant-related impurity energy levels localizing the charge carriers or acting as non-radiative recombination centers for photoexcited electrons and holes. Hence, this study indicates that it is of great importance to make the in-depth investigation on the effects of band structures on the photocatalytic activity, especially for the doped semiconducting photocatalysts.Highlights► Transition-metal ions were doped into ZnIn2S4 by a microwave-assisted hydrothermal process. ► Mn doping could enhance the activity of ZnIn2S4, while Cr, Fe, Co doping would not. ► The various activities of doped ZnIn2S4 were related to their different band structures.
Co-reporter:Ying Yang, Liejin Guo, Hongtan Liu
Journal of Power Sources 2011 Volume 196(Issue 13) pp:5503-5510
Publication Date(Web):1 July 2011
DOI:10.1016/j.jpowsour.2011.02.070
The effect of temperature on the corrosion behavior of SS316L in simulated proton exchange membrane fuel cell (PEMFC) environments has been systematically studied. Electrochemical methods, both potentiodynamic and potentiostatic, are employed to characterize the corrosion behavior. Atomic force microscope (AFM) is used to examine the surface morphology and X-ray photoelectron spectroscopy (XPS) analysis is used to identify the composition and the depth profile of the passive film. Photo-electrochemical (PEC) measurements are also performed to determinate the band gap energy of the passive film semiconductor. Interfacial contact resistances (ICR) between polarized SS316L and carbon paper are also measured. The experimental results show that corrosion resistance decreases with temperatures even though the thickness of passive film increases with temperature, at a given cell potential, the corrosion behavior of SS316L can be significantly different at different temperatures in PEMFC cathode environments, and the band gap of passive films decrease with temperature. The results also show that within the temperature range studied (25–90 °C), after different passivation time, the corrosion current densities of SS316L are all lower than the US DOE 2015 target value of 1 μA cm−2, but the ICR between the carbon paper and polarized SS316L does not satisfy the US DOE 2015 target.Highlights► We systematically studied the effect of temperature on corrosion behavior of SS316L in PEMFC cathode environments. ► The corrosion behavior of SS316L can be significantly different at different temperatures. ► Corrosion current densities at different temperatures are all lower than US DOE 2015 target, 1 μA cm−2. ► At high temperature, the bi-layer structure of the passive film disappears.
Co-reporter:Changqing Cao, Liejin Guo, Yunan Chen, Simao Guo, Youjun Lu
International Journal of Hydrogen Energy 2011 Volume 36(Issue 21) pp:13528-13535
Publication Date(Web):October 2011
DOI:10.1016/j.ijhydene.2011.07.101
Supercritical water gasification of alkaline black liquor was investigated in a continuous flow system. The experiments were carried out at 400–600 °C, 25 MPa, with residence times ranging from 4.94 to 13.71 s. The results showed that the increase of temperature and residence time and the decrease of feeding concentration enhanced the gasification. The gaseous product contained high level of hydrogen (40.26–61.02%). Maximum COD removal efficiency (88.69%) was obtained at 600 °C. The alkalis in black liquor were found to be precipitated in the reactor during the gasification, which decreased the pH of the effluent to the neutral region (6.4–8.0). The precipitated alkalis were dissolved in the water when the fluid temperature in the reactor was cooled to about 360 °C which increased the pH of the effluent to 11.0. A simplified kinetic study for COD removal efficiency was done by the pseudo-first order reaction assumption. The apparent activated energy was 74.38 kJ/mol and the apparent pre-exponential factor was 104.05 s−1.Highlights► Supercritical water gasification (SCWG) of black liquor was studied in continuous system. ► SCWG decontaminated black liquor in COD, the color and the pH values. ► Influence of temperature, residence time and concentration were studied. ► Precipitation of alkali salts were found and verified. ► Simplified kinetic study was done and the reaction equation was achieved.
Co-reporter:Youjun Lu, Liang Zhao, Liejin Guo
International Journal of Hydrogen Energy 2011 Volume 36(Issue 22) pp:14349-14359
Publication Date(Web):November 2011
DOI:10.1016/j.ijhydene.2011.07.138
A novel thermochemical method for solar hydrogen production was proposed by state key laboratory of multiphase flow in power engineering (SKLMFPE) of Xi’an Jiaotong University. In this paper, a technical and economic evaluation of the new solar hydrogen production technology was conducted. Firstly, the advantages of this new solar hydrogen production process, compared with other processes, were assessed and thermodynamic analysis of the new process was carried out. The results show that biomass gasification in supercritical water driven by concentrating solar energy may be used to achieve high efficiency solar thermal decomposition of water and biomass for hydrogen production. Secondly, the hydrogen production cost was analyzed using the method of the total annual revenue requirement. The estimated hydrogen production cost was 38.46RMB/kg for the experimental demonstration system with a treatment capacity of 1 ton wet biomass per hour, and it would be decreased to 25.1 RMB/kg if the treatment capacity of wet biomass increased from 1 t/h to 10 t/h. A sensitivity analysis was also performed and influence of parameters on the hydrogen production cost was studied. The results from technical and economic evaluation show that supercritical water gasification of biomass driven by concentrated solar energy is a promising technology for hydrogen production and it is competitive compared to other solar hydrogen production technologies.Highlights► SCWG of Biomass driven by concentrating solar energy was proposed. ► A technical and economic evaluation of the new technology was conducted. ► It is a promising technology for solar hydrogen production. ► It can achieve high efficiency solar thermal decomposition of water and biomass. ► Its cost is competitive compared to that of other solar hydrogen production.
Co-reporter:Sha Li, Youjun Lu, Liejin Guo, Ximin Zhang
International Journal of Hydrogen Energy 2011 Volume 36(Issue 22) pp:14391-14400
Publication Date(Web):November 2011
DOI:10.1016/j.ijhydene.2011.07.144
Supercritical water gasification (SCWG) of wet biomass is a very promising technology for hydrogen energy and the utilization of biomass resources. Ni-based catalysts are effective in catalyzing SCWG of original biomass and organic compounds for hydrogen production. In this paper, hydrogen production by SCWG of glucose over alumina-supported nickel catalysts modified with Cu, Co and Sn was studied. The bimetallic Ni–M (M = Cu, Co and Sn) catalysts were prepared by a co-impregnation method and tested in an autoclave reactor at 673 K with a feedstock concentration of 9.09 wt.%. XRD, XRF, N2 adsorption/desorption, SEM and TGA were adopted to investigate the changes of chemical properties between Ni and Ni–M catalysts and the deactivation mechanism of catalysts. According to the experimental results, the hydrogen yield followed this order: Ni–Cu/γAl2O3 > Ni/γAl2O3 > Ni–Co/γAl2O3 > Ni–Sn/γAl2O3. The results show that Cu could improve the catalytic activity of Ni catalyst in reforming reaction of methane to produce hydrogen in SCWG. In addition, Cu can mitigate the sintering of alumina detected by SEM. Co was found to be an excellent promoter of Ni-based catalyst in relation to hydrogen selectivity.Highlights► Bimetallic Ni–Cu, Ni–Co and Ni–Sn carried on alumina as catalysts. ► Catalysts for supercritical water gasification of biomass. ► Cu could enhance the reforming reaction of methane to produce more hydrogen. ► Co greatly enhanced the hydrogen selectivity of Ni catalyst.
Co-reporter:Kai Zhang, Zhaohui Zhou, Liejin Guo
International Journal of Hydrogen Energy 2011 Volume 36(Issue 16) pp:9469-9478
Publication Date(Web):August 2011
DOI:10.1016/j.ijhydene.2011.05.058
Novel Ba(x)–Cd0.8Zn0.2S photocatalysts, which has not been reported yet, was synthesized for the first time by thermal sulfuration method. These samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, N2 absorption–desorption isotherm, ultraviolet visible diffuse reflectance spectroscopy, density functional theory calculation and photoluminescence spectroscopy. Results showed that Ba mainly existed on the surface of Cd1−xZnxS particles, because of the largest atom radius compared to Cd and Zn atoms, in the chemical form of Ba–S–Cd/Zn bonding. The successful surface doping finally induces the element gradient from bulk phase to surface, which efficiently promotes the photogenerated charges’ transition and separation. On the basis of various characterization results, the mechanism of this promotion effect is proposed. The element gradient efficiently enhances the transition of electrons, while the noticeable doping influence on valence band significantly promotes the holes’ migration. Thus, the bulk recombination of photoelectrons and holes was efficiently suppressed, and the hydrogen production was improved efficiently.Highlights► Novel Ba doping CdxZn1−xS photocatalysts were synthesized for the first time. ► These photocatalysts exhibited much higher photocatalytic activities than Cd0.8Zn0.2S. ► Ba mainly existed on the surface or near the surface of Cd0.8Zn0.2S particles. ► The enhanced DOS in valence band is favorable for photogenerated holes’ migration. ► Charge separation is also promoted by the driving force produced by element gradient.
Co-reporter:Ying Yang, Lie-jin Guo, Hongtan Liu
International Journal of Hydrogen Energy 2011 Volume 36(Issue 2) pp:1654-1663
Publication Date(Web):January 2011
DOI:10.1016/j.ijhydene.2010.10.067
The corrosion characteristics of SS316L in simulated proton exchange membrane fuel cell (PEMFC) environments with a wide range of H2SO4 concentrations have been systematically studied. Electrochemical methods, both potentiodynamic and potentiostatic, are employed to determine the corrosion parameters and the results show that corrosion resistance decreases with increasing H2SO4 concentrations. Scanning electron microscope (SEM) is used to examine the surface morphology of the specimens after potentiostatic polarized in simulated PEMFC cathode environments and the results indicate that local corrosion occurs under all the conditions studied and local corrosion is more severe with higher H2SO4 concentrations. Auger electron spectroscopy (AES) analysis is used to identify the composition and the depth profile of the passive film formed on the SS316L surface and the results show that the thickness of passive film decreases with increasing H2SO4 concentrations. Interfacial contact resistances (ICR) between SS316L polarized and carbon paper are measured and the results show that ICR decreases with increasing H2SO4 concentrations. The corrosion mechanisms of SS316L in PEMFC cathode environments are analysed and discussions on choosing simulated PEMFC cathode corrosion environments for accelerated tests are also provided.
Co-reporter:Shaohua Shen, Penghui Guo, Liang Zhao, Yuanchang Du, Liejin Guo
Journal of Solid State Chemistry 2011 Volume 184(Issue 8) pp:2250-2256
Publication Date(Web):August 2011
DOI:10.1016/j.jssc.2011.06.033
Cubic and rhombohedral ZnIn2S4 were synthesized by thermal sulfidation of Zn–In mixed oxide precursor in H2S atmosphere at different temperatures. Cubic ZnIn2S4 was obtained when Zn–In mixed oxide precursor was sulfurized at 400 °C. With sulfidation temperature increasing from 400 to 800 °C, the crystal phase of ZnIn2S4 gradually turned from cubic to rhombohedral, which was demonstrated by different analysis techniques such as XRD, Raman, SEM, etc. UV–vis absorption spectra indicated that cubic ZnIn2S4 displayed better light absorption property than rhombohedral ZnIn2S4, with band gaps calculated to be 2.0 and 2.5 eV, respectively. However, under visible light irradiation, rhombohedral ZnIn2S4 photocatalyzed H2 evolution from aqueous sodium sulfite/sulfide solution efficiently, whereas cubic ZnIn2S4 was not active for this reaction. The photoluminescence property revealed the different dynamics of photogenerated carriers, which made a predominant contribution to the increasing photocatalytic performances of ZnIn2S4 with crystal phase turning from cubic to rhombohedral.Graphical AbstractRhombohedral ZnIn2S4 showed a superior photocatalytic activity for H2 evolution than cubic ZnIn2S4, which was proved to be related with their different dynamics of photogenerated carriers.Highlights► Cubic and rhombohedral ZnIn2S4 were synthesized by thermal sulfidation. ► Rhombohedral ZnIn2S4 could photocatalyze H2 evolution efficiently. ► The dynamics of photogenerated carriers affected the photocatalytic activity.
Co-reporter:Zhaohui Zhou, Jinwen Shi, Po Wu, Mingtao Li, Liejin Guo
Chemical Physics Letters 2011 Volume 513(1–3) pp:72-76
Publication Date(Web):6 September 2011
DOI:10.1016/j.cplett.2011.07.065
Abstract
Using the first-principles method, the absolute band edge positions were calculated for the (1 1 0) surface of zinc-blende type II–VI semiconductors. The thickness of the slab which was used to model the (1 1 0) surface has significant effect on the band edge positions. The variation trend of Eg with the slab thickness is dominated by that of ECBM, while almost irrespective of EVBM. This phenomenon can be interpreted by the electron (at CBM) and hole (at VBM) effective masses. The absolute band edge alignments with different slab thickness can give reasonable interpretation for a series of photocatalytic experiments.
Co-reporter:Guanjie Liu, Zhaohui Zhou, Liejin Guo
Chemical Physics Letters 2011 Volume 509(1–3) pp:43-47
Publication Date(Web):3 June 2011
DOI:10.1016/j.cplett.2011.04.073
Abstract
CdxCuyZn1–x–yS photocatalysts which showed high photocatalytic performance under visible light irradiation (λ ≥ 420 nm) even without Pt cocatalysts were synthesized by a simple coprecipitation method. The diffuse reflection spectra proved that both Cu and Cd could narrow the band gap. The calculation result indicates that the conduction and valence bands were tuned separately and independently by controlling the content of Cu and Cd in the photocatalyst. The dependence of the photophysical and photocatalytic properties upon the elemental composition was mainly due to the change of the band structure.
Co-reporter:Jinwen Shi;Dr. Jinhua Ye;Zhaohui Zhou;Dr. Mingtao Li;Dr. Liejin Guo
Chemistry - A European Journal 2011 Volume 17( Issue 28) pp:7858-7867
Publication Date(Web):
DOI:10.1002/chem.201003755
Abstract
Cubic perovskite structure photocatalysts of Na0.5La0.5TiO3 and (Na0.5La0.5TiO3)1.00(LaCrO3)0.08 solid solution that consisted of well-defined single-crystal nanocubes were successfully prepared by means of facile and surfactant-free hydrothermal reactions for the first time. The results from different instrumental characterizations and theoretical calculations consistently confirmed the formation of nanocubic single-crystal solid solution of (Na0.5La0.5TiO3)1.00(LaCrO3)0.08, and clearly revealed the modification of its physicochemical properties compared with those of Na0.5La0.5TiO3. In particular, the effective narrowing of the bandgap (from 3.19 to 2.25 eV) by Cr3+ in the solid solution made it possible to utilize visible light. The solid-solution configuration maintained the charge balance to preserve the valence of Cr3+ rather than Cr6+, and accommodated Cr3+ with high content to form new energy bands instead of localized impurity levels. The hydrothermal preparation strategy ensured the formation of single crystals with high purity, few defects, and regulated morphology; it also guaranteed the valences of Ti4+ and Cr3+ in the solid solution. Consequently, the recombination of photogenerated carriers could be effectively suppressed to benefit photocatalytic H2 evolution. (Na0.5La0.5TiO3)1.00(LaCrO3)0.08 nanocubic single-crystal solid solution showed stable photocatalytic activity, and thus was proved to be a promising candidate for visible-light-driven photocatalytic H2 evolution.
Co-reporter:Xiaomin Wu, Honghui Yang, Liejin Guo
International Journal of Hydrogen Energy 2010 Volume 35(Issue 1) pp:46-51
Publication Date(Web):January 2010
DOI:10.1016/j.ijhydene.2009.10.039
Anaerobic fermentation by microorganisms is a promising method of hydrogen production for it can be conducted at mild conditions. In this paper, a series of tests were carried out to investigate the effect of pH, hydraulic retention time (HRT), temperature (T) and substrate concentration on anaerobic dark fermentation. Glucose was utilized as model substrate. The Taguchi orthogonal array was applied in the experimental design and a verification experiment was tested. The results showed the optimal parameters for hydrogen production were pH 5.0, HRT 8.34 h, T 33.5 °C and substrate concentration of 14 g/L, with hydrogen yield of 2.15 mol H2/mol glucose. Butyric-type fermentation occurred in most tests. According to the analysis of effluent contents, at pH 5.5, 5.0, 4.0, the effluent contained mostly butyric acid (43.1–56.6%), followed by acetic acid (24.6–29.8%); at HRT 4.17, 6.26, 8.34 h, the effluent contained mostly butyric acid (43.0–53.6%). Increasing temperature from 29 to 39.5 °C resulted in the decrease of butyric acid percentage but increase of ethanol percentage. Substrate concentration had little effect on product constitution.
Co-reporter:Jingwei Chen, Youjun Lu, Liejin Guo, Ximin Zhang, Peng Xiao
International Journal of Hydrogen Energy 2010 Volume 35(Issue 13) pp:7134-7141
Publication Date(Web):July 2010
DOI:10.1016/j.ijhydene.2010.02.023
A novel system of hydrogen production by biomass gasification in supercritical water using concentrated solar energy has been constructed, installed and tested at the State Key Laboratory of Multiphase Flow in Power Engineering (SKLMF). The “proof of concept” tests for solar-thermal gasification of biomass in supercritical water (SCW) were successfully carried out. Biomass model compounds (glucose) and real biomass (corn meal, wheat stalk) were gasified continuously with the novel system to produce hydrogen-rich gas. The effect of direct normal solar irradiation (DNI) and catalyst on gasification of biomass was also investigated. The results showed that the maximal gasification efficiency (the mass of product gas/the mass of feedstock) in excess of 110% were reached, hydrogen fraction in the gas product also approached to 50%. The experimental results confirmed the feasibility of the system and the advantage of the process, which supports future work to address the technical issues and develop the technology of solar-thermal hydrogen production by gasification of biomass in supercritical water.
Co-reporter:Hui Jin, Youjun Lu, Bo Liao, Liejin Guo, Ximin Zhang
International Journal of Hydrogen Energy 2010 Volume 35(Issue 13) pp:7151-7160
Publication Date(Web):July 2010
DOI:10.1016/j.ijhydene.2010.01.099
The technology of supercritical water gasification of coal can converse coal to hydrogen-rich gaseous products effectively and cleanly. However, the slugging problem in the tubular reactor is the bottleneck of the development of continuous large-scale hydrogen production from coal. The reaction of coal gasification in supercritical water was analyzed from the point of view of thermodynamics. A chemical equilibrium model based on Gibbs free energy minimization was adopted to predict the yield of gaseous products and their fractions. The gasification reaction was calculated to be complete. A supercritical water gasification system with a fluidized bed reactor was applied to investigate the gasification of coal in supercritical water. 24 wt% coal-water-slurry was continuously transported and stably gasified without plugging problems; a hydrogen yield of 32.26 mol/kg was obtained and the hydrogen fraction was 69.78%. The effects of operational parameters upon the gasification characteristics were investigated. The recycle of the liquid residual from the gasification system was also studied.
Co-reporter:Youjun Lu, Sha Li, Liejin Guo, Ximin Zhang
International Journal of Hydrogen Energy 2010 Volume 35(Issue 13) pp:7161-7168
Publication Date(Web):July 2010
DOI:10.1016/j.ijhydene.2009.12.047
Hydrogen production by supercritical water gasification (SCWG) is a promising technology for wet biomass utilization. Ni catalyst can realize the high gasification efficiency of biomass near the critical temperature of water. In this paper, Ni/γAl2O3 and Ni/CeO2-γAl2O3 catalysts were prepared by an impregnation method. The catalyst performance for glucose gasification in supercritical water was tested in autoclave reactor. All experiments were carried out in the autoclave at 673 K, 24.5 MPa, and the concentration of glucose was 9.09 wt.%. The catalysts before and after reaction were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), BET specific surface area measurements, X-ray fluorescence spectrum (XRF) and Thermo-gravimetric analyses (TGA) in order to investigate on the chemical property and catalytic mechanism. The experimental results showed that hydrogen yield and hydrogen selectivity increased sharply with addition of Ni/γAl2O3 and Ni/CeO2-γAl2O3 catalysts. The catalytic activity and H2 selectivity of Ni/CeO2-γAl2O3 was higher than that of Ni/γ-Al2O3 catalyst. The results revealed that carbon deposition and coking led to the deactivation of the catalysts. Ce in the Ni/CeO2-γAl2O3 catalyst had a certain role in the inhibition of carbon deposition and coking.
Co-reporter:Xiaomin Wu, Xueqing Wang, Honghui Yang, Liejin Guo
International Journal of Hydrogen Energy 2010 Volume 35(Issue 13) pp:7194-7199
Publication Date(Web):July 2010
DOI:10.1016/j.ijhydene.2009.12.141
The characteristics of hydrogen production from individual and mixed volatile fatty acids (VFAs) were compared among three photosynthetic bacterial strains, Rhodopseudomonas sp., Rhodopseudomonas palustirs W004 and Rubrivivax sp. Rhodopseudomonas sp. and R. palustirs W004 could convert both butyrate and acetate into hydrogen. Rubrivivax sp. could assimilate butyrate and acetate, but could not produce hydrogen from them when individual VFA was used as substrate. The highest hydrogen amount (2191.7 mL/L culture), COD reduction efficiency (85.3%) and H2 yield (468.3 mL H2/g COD) were achieved by Rhodopseudomonas sp. with butyrate as carbon source. All the three strains could produce hydrogen from mixed VFAs. Rhodopseudomonas sp. and R. palustirs W004 could digest the substrates completely. Hydrogen production from mixed VFAs by Rubrivivax sp. lasted for 3.7 days and only 38.8% of COD was reduced, for high pH value of the culture harmed hydrogen production.
Co-reporter:Shaohua Shen, Liang Zhao, Liejin Guo
International Journal of Hydrogen Energy 2010 Volume 35(Issue 19) pp:10148-10154
Publication Date(Web):October 2010
DOI:10.1016/j.ijhydene.2010.07.171
A new series of ZnmIn2S3+m (m = 1–5, integer) photocatalysts was synthesized via a simple hydrothermal method. X-ray diffraction (XRD), Raman spectra, UV–vis–near-IR diffuse reflectance spectra (UV–vis), X-ray fluorescence (XRF) and scanning electron microscope (FESEM) were used to characterize these photocatalysts. These ZnmIn2S3+m photocatalysts had a similar layered crystal structure. The absorption edge of ZnmIn2S3+m shifted to shorter wavelength as the atomic ratio of Zn/In in the synthetic solution was increased (i.e. m increased from 1 to 5). Additionally, the morphology of ZnmIn2S3+m greatly depended on the atomic ratio of Zn/In. The photocatalytic activity of ZnmIn2S3+m was evaluated by photocatalytic hydrogen production from water under visible light. The Zn2In2S5 product, with quantum yield at 420 nm determined to be 11.1%, had the highest photocatalytic activity among these ZnmIn2S3+m (m = 1–5, integer) photocatalysts.
Co-reporter:Dengwei Jing, Maochang Liu, Qinyun Chen, Liejin Guo
International Journal of Hydrogen Energy 2010 Volume 35(Issue 16) pp:8521-8527
Publication Date(Web):August 2010
DOI:10.1016/j.ijhydene.2010.04.170
Decahedral Cu2WS4 was synthesized by a facile hydrothermal method and employed as photocatalyst for photocatalytic hydrogen production for the first time. The hydrothermal method avoids the traditional use of H2S for the preparation of such chalcogenide, which guarantees an environmental-friendly process. The properties of the Cu2WS4 samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–Vis reflectance spectra, etc. The results showed that the decahedral Cu2WS4 possessed a band gap of ca. 2.1ev. The photocatalyst was demonstrated to be very active under visible light for hydrogen production. Especially, Cu2WS4 synthesized at 200 °C for 72 h showed the highest activity with the apparent quantum yield of 11% at 425 nm. The correlation between the preparation parameters and the photocatalytic properties were investigated. It was expected this first report of W-based chalcogenide photocatalyst would add to the photocatalyst group and lead to the finding of new photocatalyst with much higher activity.
Co-reporter:Xianghui Zhang, Yuanchang Du, Zhaohui Zhou, Liejin Guo
International Journal of Hydrogen Energy 2010 Volume 35(Issue 8) pp:3313-3321
Publication Date(Web):April 2010
DOI:10.1016/j.ijhydene.2010.01.111
(CuIn)xZn2(1-x)S2 (x = 0.01–0.5) microspheres were prepared by a simple hydrothermal method. They were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–Visible diffuse reflectance spectra (UV–Vis), Raman scattering spectra and Brunauer-Emmett-Teller (BET) surface area measurement. It was found that the (CuIn)xZn2(1-x)S2 samples formed solid solution only in the presence of surfactant cetyltrimethylammonium bromide (CTAB). CTAB enabled the increase of the surface area for the (CuIn)xZn2(1-x)S2 solid solutions. Diffuse reflection spectra of the solid solutions shifted monotonically to long wavelength side as the value of x increased. The photocatalytic H2 evolution activity under visible-light irradiation of the solid solutions was evaluated. The result showed that the activity depended on their corresponding compositions closely. Ru (1.5 wt%)-loaded (CuIn)0.2Zn1.6S2 showed the highest photocatalytic activity of 198.09 μmol h−1 under visible-light irradiation, and the apparent quantum yield amounted to 15.45% at 420 nm. Furthermore, the density functional theory (DFT) calculations showed that the solid solution with the ration of ZnS and CuInS2, 6:1, was a direct band gap semiconductor. The valence band consisted of the hybrid orbital of S 3p and Cu 3d and the conduction band consisted of In 5s5p orbital mixed with Zn 4s4p. The energy band structure resulted in the visible-light response of the solid solution, and affected its photocatalytic performance.
Co-reporter:Kai Zhang, Dengwei Jing, Qingyun Chen, Liejin Guo
International Journal of Hydrogen Energy 2010 Volume 35(Issue 5) pp:2048-2057
Publication Date(Web):March 2010
DOI:10.1016/j.ijhydene.2009.12.143
Alkaline earth metal Sr was successfully doped into CdS–ZnS solid solutions for the first time. The as-prepared photocatalysts were characterized by X-ray Diffraction (XRD), Brunauer–Emmett–Teller (BET) surface areas, UV–vis diffuse reflectance spectra (UV–vis), photoluminescence spectra (PL), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), etc. BET characterization indicated that all the prepared samples possessed mesoporous structures with large specific surface areas. Photocatalytic H2 evolution results showed that Sr-doping can efficiently improve the photocatalytic activities while the molar ratio of Zn was greater than 20% in the absence of noble metal as co-catalyst. The correlation between the Zn/Cd ratio of solid solution and the Sr-doping amount was investigated in detail. Results showed that the recombination of photoelectrons and holes could be efficiently suppressed by doping metal ions on the shallow surface of CdS–ZnS, which could become the centers of shallow electrons or holes traps, thus significantly improve the efficiency of charge separation.
Co-reporter:Hui Jin, Youjun Lu, Liejin Guo, Changqing Cao, Ximin Zhang
International Journal of Hydrogen Energy 2010 Volume 35(Issue 7) pp:3001-3010
Publication Date(Web):April 2010
DOI:10.1016/j.ijhydene.2009.06.059
Partial oxidative gasification in supercritical water is a new technology for hydrogen production from biomass. Firstly in this paper, supercritical water partial oxidative gasification process was analyzed from the perspective of theory and chemical equilibrium gaseous product was calculated using the thermodynamic model. Secondly, the influence of oxidant equivalent ratio on partial oxidative gasification of model compounds (glucose, lignin) and real biomass (corn cob) in supercritical water was investigated in a fluidized bed system. Experimental results show that oxidant can improve the gasification efficiency, and an appropriate addition of oxidant can improve the yield of hydrogen in certain reaction condition. When ER equaled 0.4, the gasification efficiency of lignin was 3.1 times of that without oxidant. When ER equaled 0.1, the yield of hydrogen from lignin increased by 25.8% compared with that without oxidant. Thirdly, the effects of operation parameters including temperature, pressure, concentration, and flow rate of feedstock on the gasification were investigated. The optimal operation parameters for supercritical water partial oxidative gasification were obtained.
Co-reporter:Yongliang Li, Liejin Guo, Ximin Zhang, Hui Jin, Youjun Lu
International Journal of Hydrogen Energy 2010 Volume 35(Issue 7) pp:3036-3045
Publication Date(Web):April 2010
DOI:10.1016/j.ijhydene.2009.07.023
The technology of supercritical water gasification can convert coal to hydrogen-rich gaseous product efficiently and cleanly. A novel continuous-flow system for coal gasification in supercritical water was developed successfully in State Key Laboratory of Multiphase Flow in Power Engineering (SKLMF). The experimental device was designed for the temperature up to 800 °C and the pressure up to 30 MPa. The gasification characteristics of coal were investigated within the experimental condition range of temperature at 650–800 °C, pressure at 23–27 MPa and flow rate from 3 kg h−1 to 7 kg h−1. K2CO3 and Raney-Ni were used as catalyst and H2O2 as oxidant. The effects of main operation parameters (temperature, pressure, flow rate, catalyst, oxidant, concentration of coal slurry) upon gasification were carried out. The slurry of 16 wt% coal + 1.5 wt% CMC was successfully transported into the reactor and continuously gasified in supercritical water in the system. The hydrogen fraction reached up to 72.85%. The experimental results demonstrate the bright future of efficient and clean conversion of coal.
Co-reporter:Mingtao Li, Jiangang Jiang, Liejin Guo
International Journal of Hydrogen Energy 2010 Volume 35(Issue 13) pp:7036-7042
Publication Date(Web):July 2010
DOI:10.1016/j.ijhydene.2009.12.090
A series of Cd1−xZnxS thin films were deposited onto indium-doped tin oxide (ITO) coated glass substrates by ultrasonic spray pyrolysis CdCl2, ZnCl2, and CS(NH2)2 aqueous solutions. The XRD patterns revealed that these films processed a wurtzite structure and a series of solid solutions of CdS and ZnS formed. The lattice constants decreased as the x value increased. From the transmittance and reflectance, the optical band gap was estimated to be between 2.45 eV and 3.72 eV, and the band gap increased as the x value increased according to a near linear relationship with the x value. The Mott-Schottky tests revealed that the flat potential shifted negatively as the x value increased. The photo responses agreed with the optical absorption of these films quite well. The current–potential measurements under chopped Xe lamp light irradiation show that the CdS deposited at 300 °C had best photoresponse. Its photoelectrochemical efficiency was estimated to be about 0.95% under 0.73 V bias from two electrodes current–potential tests.
Co-reporter:Xianghui Zhang, Dengwei Jing, Liejin Guo
International Journal of Hydrogen Energy 2010 Volume 35(Issue 13) pp:7051-7057
Publication Date(Web):July 2010
DOI:10.1016/j.ijhydene.2009.12.132
A series of Ni2+ doped Cd0.1Zn0.9S photocatalysts were prepared with different salt by hydrothermal method. The prepared photocatalysts were characterized by XRD, UV–Vis, BET and SEM. The effects of SO42−, CH3COO−, Cl− and NO3− anions on the photocatalytic hydrogen production performance of these photocatalysts were examined. Experimental results showed that the photocatalysts prepared with acetates and chlorides have the highest hydrogen production activity, and their initial hydrogen production rate reaches to 76.52 μmol/h and 80.75 μmol/h under visible-light irradiation with the apparent quantum yield of 12.30% and 14.36% at 420 nm without any noble metal loading, respectively. The absence of noble metal is propitious to reduce the cost of photocatalyst preparation.
Co-reporter:Maochang Liu, Dengwei Jing, Liang Zhao, Liejin Guo
International Journal of Hydrogen Energy 2010 Volume 35(Issue 13) pp:7058-7064
Publication Date(Web):July 2010
DOI:10.1016/j.ijhydene.2009.12.140
A novel catalyst-fixed way is present. And two series of novel CdS-incorporated special glass composite photocatalysts working under visible light were successfully prepared in this way by a two-step thermal sulfidation procedure for the use of catalyst-fixed system. One was by a high temperature way, and the other was by a low temperature way. The composite photocatalysts with different content of CdS prepared by the methods were found to show a good activity for the decomposition of water under visible light. The highest rate of H2 revolution is 1549 μmol/(hgCdS) with wt1%-Pt loaded. The composites prepared by high and low temperature were characterized by X-ray diffraction (XRD), diffuse reflectance UV–vis spectra and scanning electron microscopy (SEM). The as-prepared photocatalysts exhibited different photochemical and photophysical properties for the combined way between glass-base and CdS. The photochemical and photophysical properties were very important in the catalyst-fixed system used for large-scale hydrogen production.
Co-reporter:Hu XiaoWei, Guo LieJin
International Journal of Hydrogen Energy 2010 Volume 35(Issue 13) pp:7065-7072
Publication Date(Web):July 2010
DOI:10.1016/j.ijhydene.2009.12.162
A new device of photocatalytic reactor with solar concentrator for hydrogen production was introduced in this paper. In order to investigate the effects of the slurry flow and catalyst distributions in the reactor on photocatalysis for hydrogen production, an algebraic slip mixture model (ASM) was used to simulate the dynamics of the catalyst–water slurry flow. A block-structured non-uniform grid was applied to discretize the entire domain and an algebraic multi-grid (AMG) method was used to solve the pressure field. The mean slurry pressure gradients obtained by the model were in agreement with the experimental data in former literature. Based on this verification, catalyst particle distributions, slurry velocity distributions and inter-phase slip velocity distributions in photocatalytic reactor pipe were investigated. The results show that the catalyst tends to distribute near the bottom of the pipe in the reactor, leading to a concentration gradient along the vertical direction of cross section. But due to the effects of turbulence force against the gravity, a heterogeneous suspending state will be achieved in a fully developed flow.
Co-reporter:Haipei Liu, Kai Zhang, Dengwei Jing, Guanjie Liu, Liejin Guo
International Journal of Hydrogen Energy 2010 Volume 35(Issue 13) pp:7080-7086
Publication Date(Web):July 2010
DOI:10.1016/j.ijhydene.2010.01.028
In this paper a novel SrS/CdS composite powders were prepared by coprecipitation method. The physicochemical properties of the photocatalysts were analyzed by XRD, UV–Vis, BET, PL and SEM. Photocatalytic hydrogen production results showed that these composite powders can work efficiently under visible light without loading noble metal, and it was found that the ratio of SrS/CdS equaling to 2/8 has the best performance among various SrS/CdS composite powders, and the hydrogen evolution rate amounted to 123 μmol/h under visible light irradiation. The apparent quantum yield for this photocalyst was calculated to be 2.85%, 4.59%, 9.63% at 420 nm, 440 nm and 480 nm respectively, and the apparent quantum yield under visible light was 5.83%. The reason for its high activity was analyzed.
Co-reporter:Dengwei Jing, Liejin Guo, Liang Zhao, Ximin Zhang, Huan Liu, Mingtao Li, Shaohua Shen, Guanjie Liu, Xiaowei Hu, Xianghui Zhang, Kai Zhang, Lijin Ma, Penghui Guo
International Journal of Hydrogen Energy 2010 Volume 35(Issue 13) pp:7087-7097
Publication Date(Web):July 2010
DOI:10.1016/j.ijhydene.2010.01.030
Photocatalytic water splitting with solar light is one of the most promising technologies for solar hydrogen production. From a systematic point of view, whether it is photocatalyst and reaction system development or the reactor-related design, the essentials could be summarized as: photon transfer limitations and mass transfer limitations (in the case of liquid phase reactions). Optimization of these two issues are therefore given special attention throughout our study. In this review, the state of the art for the research of photocatalytic hydrogen production, both outcomes and challenges in this field, were briefly reviewed. Research progress of our lab, from fundamental study of photocatalyst preparation to reactor configuration and pilot level demonstration, were introduced, showing the complete process of our effort for this technology to be economic viable in the near future. Our systematic and continuous study in this field lead to the development of a Compound Parabolic Concentrator (CPC) based photocatalytic hydrogen production solar rector for the first time. We have demonstrated the feasibility for efficient photocatalytic hydrogen production under direct solar light. The exiting challenges and difficulties for this technology to proceed from successful laboratory photocatalysis set-up up to an industrially relevant scale are also proposed. These issues have been the object of our research and would also be the direction of our study in future.
Co-reporter:Huirong Liang, Liejin Guo
International Journal of Hydrogen Energy 2010 Volume 35(Issue 13) pp:7104-7109
Publication Date(Web):July 2010
DOI:10.1016/j.ijhydene.2010.01.037
A novel visible-light-driven Cu2MoS4 photocatalyst was prepared by a facile hydrothermal method using Ammonium Tetrathiomolybdate reacting with cuprous chloride in aqua ammonia. The synthetic catalysts were characterized by XRD, UV–vis spectra, XRF and SEM techniques. The influence of the reaction temperature and time on the activities of the catalysts and the morphology of particles was investigated. The results showed that the catalysts exhibited strong absorption in visible light region. It was found that the photocatalyst prepared under hydrothermal condition at 140 °C for about 24 h showed good crystallinity with regular shape, and the highest activity for hydrogen production under visible light irradiation in an aqueous Na2S–Na2SO3 solution. The reason for its better performance has been discussed in detail.
Co-reporter:Shaohua Shen, Liejin Guo, Xiaobo Chen, Feng Ren, Samuel S. Mao
International Journal of Hydrogen Energy 2010 Volume 35(Issue 13) pp:7110-7115
Publication Date(Web):July 2010
DOI:10.1016/j.ijhydene.2010.02.013
Nanostructured Ag2S/CdS were synthesized by a two-step precipitation method, and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and UV–Vis absorption spectra. With Ag2S highly dispersed in the CdS nanostructures, the photoactivity was evaluated by hydrogen evolution from aqueous solution containing Na2S/Na2SO3 as a hole scavenger under simulated solar light (AM1.5). When the concentration of Ag2S was 5% by weight, Ag2S/CdS showed the highest photocatalytic activity for hydrogen evolution, with the solar-hydrogen energy conversion efficiency approximately 0.7%. We investigated the effect of highly dispersed Ag2S on the photoactivity.
Co-reporter:Mingtao Li, Liang Zhao, Liejin Guo
International Journal of Hydrogen Energy 2010 Volume 35(Issue 13) pp:7127-7133
Publication Date(Web):July 2010
DOI:10.1016/j.ijhydene.2010.02.026
Thin films of BiVO4 with monoclinic structure were deposited onto indium-doped tin oxide (ITO)-coated glass substrates by ultrasonic spray pyrolysis. The effects of tungsten doping and hydrogen reducing were investigated. The films were characterized with XRD, Raman spectra, SEM, UV–Vis transmittance spectra. Furthermore, the films were investigated by electrochemical and photoelectrochemical measurements with regard to splitting water for solar energy conversion. The films possessed a scheelite-monoclinic structure with good absorption to visible light. The optical band gaps were evaluated to be about 2.65 eV. The flat band potentials were estimated to be about −0.61 V vs. saturated calomel electrode (SCE) in 0.5 M Na2SO4 solution from Mott–Schottky plots. For non-doping samples, the incident photon to current conversion efficiency (IPCE) was relative low because of low density and activity of carriers. When treated with hydrogen reducing, the carrier density increased due to more oxygen vacancies, resulting in the increase of IPCE. In addition, substituting 1% vanadium with equal mole tungsten can increase IPCE remarkably, which achieved about 10% at 0.3 V vs. SCE potential under 400–450 nm wavelength photo irradiation.
Co-reporter:Zhaohui Zhou, Mingtao Li, Liejin Guo
Journal of Physics and Chemistry of Solids 2010 Volume 71(Issue 12) pp:1707-1712
Publication Date(Web):December 2010
DOI:10.1016/j.jpcs.2010.08.021
Co-reporter:Dengwei Jing;Maochang Liu;Liejin Guo
Catalysis Letters 2010 Volume 140( Issue 3-4) pp:167-171
Publication Date(Web):2010 December
DOI:10.1007/s10562-010-0442-9
Ni2+ doped ZnIn2S4 microsphere with flower-like nanoscale petals were prepared by a hydrothermal method. There was an optimal Ni doping content of 0.3 wt% where hydrogen production reached the maximum. Higher Ni2+ doping can hardly dope into the ZnIn2S4 lattice and just stay at ZnIn2S4 surface, leading to decreased activity. It was determined that Ni2+ entering the ZnIn2S4 lattice instead of surface NiS dominated the enhanced photocatalytic activity. The experimental results were rationalized by assuming Ni2+ serving as shallow trapping sites, greatly enhancing the activity of the photocatalyst.
Co-reporter:Shaohua Shen, Liang Zhao, Liejin Guo
Materials Research Bulletin 2009 44(1) pp: 100-105
Publication Date(Web):
DOI:10.1016/j.materresbull.2008.03.027
Co-reporter:Chanjuan Xing, Dengwei Jing, Maochang Liu, Liejin Guo
Materials Research Bulletin 2009 44(2) pp: 442-445
Publication Date(Web):
DOI:10.1016/j.materresbull.2008.04.016
Co-reporter:Shaohua Shen, Liang Zhao, Liejin Guo
International Journal of Hydrogen Energy 2008 Volume 33(Issue 17) pp:4501-4510
Publication Date(Web):September 2008
DOI:10.1016/j.ijhydene.2008.05.043
A series of ZnIn2S4 photocatalysts was synthesized via a cetyltrimethylammoniumbromide (CTAB)-assisted hydrothermal method. These ZnIn2S4 products were characterized by X-ray diffraction (XRD), UV–visible absorption spectra (UV–vis) and scanning electron microscopy (FESEM). The effects of hydrothermal time and CTAB on the crystal structures, morphologies and optical properties of ZnIn2S4 products were discussed in detail. The photocatalytic activities of the as-prepared samples were evaluated by photocatalytic hydrogen production from water under visible-light irradiation. It was found that the photocatalytic activities of these ZnIn2S4 products decreased with the hydrothermal time prolonging while increased with the amount of CTAB increasing. The highest quantum yield at 420 nm of ZnIn2S4 photocatalyst, which was prepared through the CTAB (9.6 mmol)-assisted hydrothermal procedure for 1 h, was determined to be 18.4%. The optimum amount of Pt loaded for the ZnIn2S4 photocatalyst was about 1.0 wt%, under the present photocatalytic system.
Co-reporter:Mingtao Li, Jinzhan Su, Liejin Guo
International Journal of Hydrogen Energy 2008 Volume 33(Issue 12) pp:2891-2896
Publication Date(Web):June 2008
DOI:10.1016/j.ijhydene.2008.04.008
Thin films of ZnIn2S4 were deposited onto indium-doped tin oxide (ITO)-coated glass substrates from a mixed aqueous solution of ZnCl2, InCl3 and (NH2)2CS by a simple and economical spray pyrolysis technique. Structural, morphologic and optical properties of the deposited films were characterized by XRD, SEM, and UV–vis spectra. Moreover, the electrochemical and photoelectrochemical properties were studied via Mott–Schottky method, current–voltage measurement, and photocurrent spectrum measurement. It was found that ZnIn2S4 films can be prepared by spray pyrolysis and the grain size obtained was about 120–200 nm in diameter. The deposited films have a cubic spinel structure and the optical band gap is about 2.1 eV. The results of electrochemical and photoelectrochemical characteristics show that ZnIn2S4 is a potential material for splitting water to produce hydrogen using solar energy.
Co-reporter:Y.J. Lu, H. Jin, L.J. Guo, X.M. Zhang, C.Q. Cao, X. Guo
International Journal of Hydrogen Energy 2008 Volume 33(Issue 21) pp:6066-6075
Publication Date(Web):November 2008
DOI:10.1016/j.ijhydene.2008.07.082
Hydrogen production by biomass gasification in supercritical water (SCW) is a promising technology for utilizing high moisture content biomass, but reactor plugging is a critical problem for biomass gasification in the tubular reactor. A novel SCW fluidized bed system for biomass gasification was developed successfully in State Key Laboratory of Multiphase Flow in Power Engineering (SKLMF) to prevent the plugging and it was designed for the temperature up to 923 K and the pressure up to 30 MPa. Model compound (glucose) and real biomass (corn cob) were gasified under SCW conditions to generate hydrogen-rich fuel gas and a performance testing of the new SCW fluidized bed system was conducted. The product gas composed of H2, CH4, CO2, CO and small amount of C2H4 and C2H6 was obtained. The effects of solution concentration, temperature, pressure and oxidant concentration on gasification were studied. 30 wt% glucose and 18 wt% corn cob feedstocks were continually and stably gasified and reactor plugging was not observed. The results showed that using fluidized bed reactor for biomass gasification in SCW has many advantages and good prospects.
Co-reporter:Shaohua Shen, Liang Zhao, Liejin Guo
Journal of Physics and Chemistry of Solids 2008 Volume 69(Issue 10) pp:2426-2432
Publication Date(Web):October 2008
DOI:10.1016/j.jpcs.2008.04.035
Hexagonal ZnIn2S4 photocatalysts with different morphology and crystallinity (micro-structures) were prepared in aqueous-, methanol- and ethylene glycol-mediated conditions via a solvothermal/hydrothermal method. The aqueous- and methanol-mediated ZnIn2S4 presented to be Flowering-Cherry-like microsphere, while the ethylene glycol-mediated ZnIn2S4 presented to be micro-cluster. In comparison with two other products, aqueous-mediated ZnIn2S4 possessed the best crystallinity (micro-structure), which resulted in the highest photocatalytic activity for hydrogen evolution under visible-light irradiation. Additionally, aqueous-mediated ZnIn2S4 was found to be more stable than the other two ZnIn2S4 photocatalysts while undergoing the photocatalytic process. During the photocatalytic reaction, the average rates for hydrogen production over aqueous-, methanol- and ethylene glycol-mediated ZnIn2S4 were determined to be 27.3, 12.4 and 9.1 μmol h–1, respectively, in the present photocatalytic systems.
Co-reporter:Yu Guan;Aixia Pei;Liejin Guo
Frontiers of Chemical Science and Engineering 2008 Volume 2( Issue 2) pp:176-180
Publication Date(Web):2008 June
DOI:10.1007/s11705-008-0026-z
Cellulose, one of the important components of biomass, was gasified in supercritical water to produce hydrogen-rich gas in an autoclave which was operated batch-wise under high-pressure. K2CO3 and Ca(OH)2 were selected as the catalysts (or promoters). The temperature was kept between 450°C and 500°C while pressure was maintained at 24–26 MPa. The reaction time was 20 min. Experimental results showed that the two catalysts had good catalytic effect and optimum amounts were observed for each catalyst. When 0.2 g K2CO3 was added, the hydrogen yield could reach 9.456 mol·kg−1 which was two times of the H2 amount produced without catalyst. When 1.6 g Ca(OH)2 was added, the H2 yield was 8.265 mol·kg−1 which is lower than that obtained using K2CO3 as catalyst but is still 1.7 times that achieved without catalyst. Comparing with the results obtained using K2CO3 or Ca(OH)2 alone, the use of a combination of K2CO3 and Ca(OH)2 could increase the H2 yield by up to 2.5 times that without catalyst and 25% and 45% more than that obtained using K2CO3 and Ca(OH)2 alone, respectively. It was found that methane was the dominant product at relatively low temperature. When the temperature was increased, the methane reacts with water and is converted to hydrogen and carbon dioxide.
Co-reporter:BoFeng Bai;ShaoJun Zhang;Liang Zhao
Science China Technological Sciences 2008 Volume 51( Issue 8) pp:1186-1194
Publication Date(Web):2008 August
DOI:10.1007/s11431-008-0160-3
The key reasons that the present method cannot be used to solve the industrial multiphase flow pattern recognition are clarified firstly. The prerequisite to realize the online recognition is proposed and recognition rules for partial flow pattern are obtained based on the massive experimental data. The standard templates for every flow regime feature are calculated with self-organization cluster algorithm. The multi-sensor data fusion method is proposed to realize the online recognition of multiphase flow regime with the pressure and differential pressure signals, which overcomes the severe influence of fluid flow velocity and the oil fraction on the recognition. The online recognition method is tested in the practice, which has less than 10 percent measurement error. The method takes advantages of high confidence, good fault tolerance and less requirement of single sensor performance.
Co-reporter:Kai Zhang, Dengwei Jing, Chanjuan Xing, Liejin Guo
International Journal of Hydrogen Energy 2007 Volume 32(Issue 18) pp:4685-4691
Publication Date(Web):December 2007
DOI:10.1016/j.ijhydene.2007.08.022
A series of Cd1-xZnxSCd1-xZnxS solid solution photocatalysts were prepared by thermal sulfuration of the corresponding mixed oxide precursors. The photocatalytic activity for H2 evolution under visible light irradiation over the prepared photocatalysts was evaluated. Results showed that the Cd1-xZnxSCd1-xZnxS solid solution with xx equaling to 0.2 exhibited the highest photocatalytic activity and amounted to a high apparent quantum yield of 10.23% at 420 nm without needing the deposition of noble metal cocatalyst. Cd0.8Zn0.2SCd0.8Zn0.2S solid solution was prepared by different methods. Comparative studies showed that the sulfide photocatalyst prepared by thermal sulfuration had much higher activity than that prepared by conventional methods. The reason for its high activity was analyzed.
Co-reporter:Aixia Pei;Liejin Guo;Hui Jin
Frontiers in Energy 2007 Volume 1( Issue 4) pp:451-456
Publication Date(Web):2007 October
DOI:10.1007/s11708-007-0066-2
Peanut shell, mixed with sodium carboxymethyl-cellulose, was gasified at a temperature of 450°C and a pressure range from 24 to 27 MPa with the presence of different catalysts, including K2CO3, ZnCl2 and Raney-Ni. The experimental results show that different catalysts have greatly different effects on the reaction. Gasification efficiency (GE), hydrogen gasification efficiency (GHE), carbon gasification efficiency (GCE), yield of hydrogen production \((Y_{H_2 } )\) and potential yield of hydrogen production \((Y_{PH_2 } )\) are applied to describe the catalytic efficiency. From the result of gaseous components, ZnCl2 has the highest hydrogen selectivity, K2CO3 is lower, and Raney-Ni is the lowest, but Raney-Ni is the most favorable to gasify biomass among the three catalysts, and its GE, GHE, GCE reach 126.84%, 185.71%, 94.24%, respectively. As expected, hydrogen selectivity increased and CH4 reduced rapidly when the mixture of ZnCl2 and Raney-Ni is used under the same condition. The optimization mixture appeared when 0.2 g of ZnCl2 was added to 1 g of Raney-Ni, 43.56 g·kg−1 of hydrogen production was obtained. In addition, the catalytic mechanisms of different catalysts were analyzed, and the possible reaction pathway was brought forward, which helped to explain the experiment phenomena and results correctly.
Co-reporter:Qiuhui Yan;Liejin Guo;Xing Liang
Frontiers in Energy 2007 Volume 1( Issue 3) pp:327-330
Publication Date(Web):2007 July
DOI:10.1007/s11708-007-0048-0
Hydrogen is a clean energy carrier. Converting abundant coal sources and green biomass energy into hydrogen effectively and without any pollution promotes environmental protection. The co-gasification performance of coal and a model compound of biomass, carboxymethylcellulose (CMC) in supercritical water (SCW), were investigated experimentally. The influences of temperature, pressure and concentration on hydrogen production from co-gasification of coal and CMC in SCW under the given conditions (20–25 MPa, 650°C, 15–30 s) are discussed in detail. The experimental results show that H2, CO2 and CH4 are the main gas products, and the molar fraction of hydrogen reaches in excess of 60%. The higher pressure and higher CMC content facilitate hydrogen production; production is decreased remarkably given a longer residence time.
Co-reporter:Zhengmeng Gu;Liejin Guo
Frontiers in Energy 2007 Volume 1( Issue 3) pp:336-340
Publication Date(Web):2007 July
DOI:10.1007/s11708-007-0050-6
Wavelike slug-flow is a representative flow type in horizontal pneumatic conveying. Kinetic theory was introduced to establish a 3D kinetic numerical model for wavelike slug gas-solid flow in this paper. Wavelike motion of particulate slugs in horizontal pipes was numerically investigated. The formation and motion process of slugs and settled layer were simulated. The characteristics of the flow, such as pressure drop, air velocity distribution, slug length and settled layer thickness, and the detailed changing characteristics of slug length and settled layer thickness with air velocity were obtained. The results indicate that kinetic theory can represent the physical characteristics of the non-suspension dense phase flow of wavelike slug pneumatic conveying. The experiment in this paper introduced a new idea for the numerical calculation of slug-flow pneumatic conveying.
Co-reporter:Chanjuan Xing, Yaojun Zhang, Wei Yan, Liejin Guo
International Journal of Hydrogen Energy 2006 Volume 31(Issue 14) pp:2018-2024
Publication Date(Web):November 2006
DOI:10.1016/j.ijhydene.2006.02.003
A series of Cd1-xZnxSCd1-xZnxS (x=0x=0–0.92) photocatalysts were prepared by coprecipitation method and were calcined at 723 K under N2N2 atmosphere. X-ray diffraction patterns results showed that the solid solution of Cd1-xZnxSCd1-xZnxS were formed between ZnS and CdS. UV–Vis spectra indicated that the absorption edges of Cd1-xZnxSCd1-xZnxS were red-shifted as the value of x decreased. The band gaps of the photocatalysts were estimated to be between 2.20–3.12 eV (x=0x=0–0.92) from the onsets of the absorption edges and almost showed linear variation with x increasing. The position of conduction band for solid solution is shifted towards more negative potential as compared to that of CdS. The hydrogen productions of Cd1-xZnxSCd1-xZnxS (x=0x=0–0.92) by splitting water photocatalytically under ultraviolet and visible light irradiation were carried out in an inner-irradiation type reactor. The results indicated that the photocatalyst of Cd0.62Zn0.16SCd0.62Zn0.16S has the highest rate of hydrogen evolution with the quantum efficiency of 2.17% and 0.60% under ultraviolet and visible light irradiation, respectively. It has been considered that the crystallite size, (1 0 1) plane and band gap for the Cd1-xZnxSCd1-xZnxS solid solutions have a strong influence on the efficiency of hydrogen production capability for water splitting.
Co-reporter:Y.J. Lu, L.J. Guo, C.M. Ji, X.M. Zhang, X.H. Hao, Q.H. Yan
International Journal of Hydrogen Energy 2006 Volume 31(Issue 7) pp:822-831
Publication Date(Web):June 2006
DOI:10.1016/j.ijhydene.2005.08.011
Hydrogen production by biomass gasification in supercritical water is a promising technology for utilizing high moisture content biomass, but reactor plugging is a critical problem when feedstocks with high biomass content are gasified. The objective of this paper is to prevent the plugging problem by studying the effects of the various parameters on biomass gasification in supercritical water. These parameters include pressure, temperature, residence time, reactor geometrical configuration, reactor types, heating rate, reactor wall properties, biomass types, biomass particle size, catalysts and solution concentration. Biomass model compounds (glucose, cellulose) and real biomass are used in this work. All the biomasses have been successfully gasified and the product gas is composed of hydrogen, carbon dioxide, methane, carbon monoxide and a small amount of ethane and ethylene. The results show that the gas yield of biomass gasification in supercritical water is sensitive to some of the parameters and the ways of reducing reactor plugging are obtained.
Co-reporter:Liqiang Kang, Liejin Guo
Powder Technology 2006 Volume 162(Issue 2) pp:111-120
Publication Date(Web):1 March 2006
DOI:10.1016/j.powtec.2005.12.002
A numerical investigation of aeolian sand transport is performed with an Eulerian–Lagrangian model. In this model, the gas phase is described by the volume-averaged Navier-Stokes equations of two-phase flow. The particle motion is obtained by solving Newton's second law of motion taking into account the inter-particle collisions, where a soft sphere model is used to describe inter-particle collisions. The dynamic process of aeolian sand transport is simulated. The simulation results show that the variation of mean horizontal velocity of the particles with height can be expressed by a logarithmical function or a power function at h > 0.02 m, and the power function can be described below 0.02 m. The sand mass flux decreases exponentially with height for h > 0.02 m, but there is a deviation from the exponential decay due to the creep grains in the near-bed region. It is also shown that the inter-particle collisions play an important role in sand saltation. Therefore the present numerical model is capable of being applied to the study of windblown sand movement.
Co-reporter:Shaohua Shen, Liejin Guo
Journal of Solid State Chemistry 2006 Volume 179(Issue 8) pp:2629-2635
Publication Date(Web):August 2006
DOI:10.1016/j.jssc.2006.05.010
In2S3 nanocrystallites were successfully encapsulated into the mesopores of Ti-MCM-41 by a two-step method involving ion-exchange and sulfidation. The X-ray diffraction (XRD) patterns, UV-vis absorption spectra (UV-Vis), high-resolution transmission electron microscopy (HRTEM) and N2 adsorption–desorption isotherms were used to characterize the structure of the composite materials. It is found that the diameter of most In2S3 nanocrystallites is about 2.5 nm, less than the pore size of Ti-MCM-41. The In2S3 nanocrystallites inside the Ti-MCM-41 host show a significant blue-shift in the UV-vis absorption spectra. Under irradiation of visible light (λ>430nm), the composite material has much higher photocatalytic activity for hydrogen evolution than bulk In2S3. It can be explained by the effective charge-separation in the quantum-sized In2S3-sensitized Ti-MCM-41.In2S3 nanoparticles are loaded into the mesopores of Ti-MCM-41 by ion-exchange and sulfidation methods, the obtained In2S3@Ti-MCM-41 has much higher activity for hydrogen evolution than bulk In2S3.
Co-reporter:X.H Hao, L.J Guo, X Mao, X.M Zhang, X.J Chen
International Journal of Hydrogen Energy 2003 Volume 28(Issue 1) pp:55-64
Publication Date(Web):January 2003
DOI:10.1016/S0360-3199(02)00056-3
Thermochemical gasification of biomass has been identified as a possible system for producing renewable hydrogen. A continuous tubular supercritical water gasification system is under development that can be used for solution or slurry materials gasification without drying. A unique feature of this system is its ability to realize the overall high-pressure continuous reaction by operating the valves. By the use of this system, designed for temperatures up to and pressures up to , glucose, as a model compound of biomass, was gasified in supercritical water at a series of temperature and pressure during different resident times to form a product gas composed of H2, CO, CH4, CO2, and a small amount of C2H4 and C2H6. Glucose at low concentrations (ca. ) can be completely gasified in , , and resident time and no char or tar was observed. Consequently, we adopted these conditions as baseline reaction conditions for the following glucose concentration, alkali addition and reactor tube diameter effect studies. The raw biomass feedstock of sawdust with some CMC was also gasified in this system, the gasification efficiency in excess of 95% was reached.
Co-reporter:Suifeng Zou, Liejin Guo, Chen Xie
International Journal of Multiphase Flow (January 2017) Volume 88() pp:222-237
Publication Date(Web):1 January 2017
DOI:10.1016/j.ijmultiphaseflow.2016.08.007
•Method on basis of relatively clear and intuitive physical meaning.•Avoidance of PSD or more complex feature extraction and feature reduction.•Recommendation of minimum sample length for regime recognition.•Effect of feature distribution on sensitivity to test sample length.•75%–92% reduction in recognition time.Fast recognition of unstable and harmful flow regimes in pipeline-risers can promote a higher level of flow assurance in offshore petroleum exploitation. However, challenges are encountered in extracting distinguishable characteristics from a short sample which usually covers much less than a fluctuation period. This article attempts to set up a fast recognition method through the interrelation of differential pressures representing phase distribution along different sections, by which the regime category can be highly decoupled from time, and eventually sample length can be reduced remarkably with less complicated signal and data processing. Based on a number of experiments under different pressure conditions, we established a method that combined conditional judgment with LS-SVM whose inputs were dimensionless means and amplitudes of differential pressure signals, and four global regimes were conveniently recognized. The results proved the feasibility of our method, and time consumption was significantly reduced compared with that in literature. The shortest limit of sample length for effective recognition was discussed, and the sensitivity of trained model to test sample length was also analyzed through the distribution of input features.
Co-reporter:Pengfei Han, Liejin Guo
International Journal of Heat and Fluid Flow (December 2015) Volume 56() pp:355-366
Publication Date(Web):1 December 2015
DOI:10.1016/j.ijheatfluidflow.2015.10.005
•A hyperbolized two-fluid model is presented for a pipeline–riser system.•The coupling of severe slugging and hydrodynamic slugging is realized.•Accurate predictions are obtained with consideration of the coupling effect.•The effect of hydrodynamic slugs on severe slugging is addressed.A numerical study based on a one-dimensional two-fluid model is carried out to describe the transient hydrodynamic slugging and terrain-induced severe slugging in a pipeline–riser system. The system of equations is rendered well-posed by interfacial pressure model for the riser. The selected flow conditions are restricted in the well-posed region for the horizontal and the downward inclined pipes to ensure the hydrodynamic slug characteristics are predicted correctly. The validity of the model is examined by water faucet problem and horizontal slug flow experiments. Simulations with and without slug capturing are conducted to address the effect of hydrodynamic slugs on severe slugging. It has been found that more accurate predictions are obtained by taking hydrodynamic slugs into account. At low superficial gas velocity, the simulation without slug capturing tends to overestimate the severe slugging period. When hydrodynamic slugs are captured, the upstream gas expansion is suppressed by the hydrodynamic slugs. At relatively high superficial gas velocity, the simulation without slug capturing tends to underestimate the severe slugging period. When hydrodynamic slugs are captured, the upstream compressible volume is greatly enlarged by the blowout of the hydrodynamic slugs. In both situations, the influences of the hydrodynamic slugs can reduce the errors of the predicted severe slugging characteristics.
Co-reporter:Jinwen Shi, Liejin Guo
Progress in Natural Science: Materials International (December 2012) Volume 22(Issue 6) pp:592-615
Publication Date(Web):1 December 2012
DOI:10.1016/j.pnsc.2012.12.002
ABO3-based photocatalysts for water splitting were systematically reviewed in this manuscript. Crystal structure and chemical composition characteristics of ABO3 materials were briefly introduced to guide the modification of ABO3-based photocatalysts. The ABO3-based photocatalysts were then reviewed in detail and divided into four groups based on the employed modification strategies, i.e., chemical component adjustment, micro-/nano-structure adjustment, local lattice structure adjustment, and application of the modification strategy of ABO3 photocatalysts in designing AxByOz photocatalysts. In this section, the recent research works on ABO3-based photocatalysts in our group were presented. Finally, application of ABO3 photocatalysts in Z-scheme systems for overall water splitting was introduced. This review summarized the development of ABO3-based photocatalysts and showed the values and possible direction of future research, thereby offering a guide for photocatalytic water splitting.
Co-reporter:Wen Cao, Changqing Cao, Liejin Guo, Hui Jin, Matthew Dargusch, Debra Bernhardt, Xiangdong Yao
International Journal of Hydrogen Energy (28 December 2016) Volume 41(Issue 48) pp:22722-22731
Publication Date(Web):28 December 2016
DOI:10.1016/j.ijhydene.2016.09.031
Co-reporter:Senlin Chen, Liejin Guo
Chemical Engineering Science (19 April 2014) Volume 109() pp:1-16
Publication Date(Web):19 April 2014
DOI:10.1016/j.ces.2014.01.021
•Viscosity effect on regular bubble entrapment was presented.•Viscosity effect on critical cone angle, pressure and velocity was investigated.•Viscosity effect on regular bubble entrapment region was conducted.•A scaling model for limits of the regular bubble entrapment region was proposed.•Viscosity effect on bubble size distribution was studied.Viscosity plays an important role in regular bubble entrapment during drop impact into a deep pool. In this paper, the volume of fluid (VOF) model in conjunction with the continuum surface force (CSF) model is used to investigate the dynamics of regular bubble entrapment in fluids with a range of viscosities (η=0.1–10.0×10−3 Pa s). Time evolutions of the crater profiles and crater depths in different viscous fluids are compared. Numerical results show that the damping effect of the viscosity on capillary wave propagation leads to an increase in the lower limit of the regular bubble entrapment region, whereas the damping effect on crater cusp reversal dynamics leads to an increase in the upper limit. Based on the timing estimate, a scaling model for the effect of viscosity on the limits of the regular bubble entrapment region is provided. Finally, the distribution of bubble size as a function of the capillary number is investigated.
Co-reporter:Chen Xie, Liejin Guo, Wensheng Li, Hongliang Zhou, Suifeng Zou
Chemical Engineering Science (18 May 2017) Volume 163() pp:68-82
Publication Date(Web):18 May 2017
DOI:10.1016/j.ces.2017.01.028
•A new large-scale pipelines-riser experimental system for high pressures.•New experimental data, flow patterns and flow properties at various pressures.•Effects of gas compressibility and gas solubility on severe slugging properties.•A stability criterion for steady state operation under various backpressures.Severe slugging is a well-known instability in multiphase flow through a pipeline-riser system that is characterized by sharp pressure changes and violent flow fluctuations. This can cause safety and operational problems in the production of oil and gas. Particularly for deepwater risers, which can be up to 3000 m long, the operating pressure in the pipeline and riser can be high (that is a few hundreds of bar). Most lab experiments carried out so far for severe slugging were conducted at atmospheric pressure. The present study contains new experiments at elevated pressure. Thereto a new large-scale pipeline-riser system was established with 300 bar maximum pressure. To study the effect of the pressure at the riser top on severe slugging, experiments for the stability boundaries and for the amplitude and frequency of the slugging were carried out for pressures in the range of 0–50 barg. The results show that an increased backpressure gives a reduced region of severe slugging in the flow pattern map, whereas it also mitigates pressure fluctuations and decreases the slug frequency. Based on these experimental results, the existing prediction model for the stability of steady state operation and the transition to severe slugging was modified to incorporate the effect of the backpressure.
Co-reporter:Xu Zhang, Yupeng Yang, Liejin Guo, Hongtan Liu
International Journal of Hydrogen Energy (16 February 2017) Volume 42(Issue 7) pp:
Publication Date(Web):16 February 2017
DOI:10.1016/j.ijhydene.2016.08.223
•Carbon corrosion in PEMFC can cause large mass transfer losses.•Sharp voltage drop in degraded cell mainly is due to water flooding in MEA.•The mass transfer loss recovery phenomenon is due to enhanced PCI flows.•Low inlet humidity and high air flow rate can mitigate flooding in a degraded cell.Carbon corrosion in proton exchange membrane fuel cells (PEMFC) causes not only kinetic degradation, but also damages to electrode microstructure and hydrophobicity, which can lead to increases in mass transport resistance. While much attention has been paid to catalyst degradation and kinetic losses, the increases in mass transfer loss is also a very serious problem and thus it is the focus of this work. To induce carbon corrosion, accelerated stress test (AST) by holding the cell potential at 1.4 V is used. The AST procedure is interrupted periodically to record cell performance after each period of AST at three different current densities. Experiment results show that at low current density, the decrease in cell voltage is linear with time of AST, but the rate in cell voltage decrease accelerates after some period of AST at medium and high current densities. It is hypothesized that such an accelerated voltage decrease is from the increase in mass transfer loss due to water flooding in the MEA. Further experiments with either reduced inlet air humidification or reduce air flow rate confirm that water flooding in the MEA is the cause for the sharp decline in cell voltages. A phenomenon that the cell voltage increases, or the rate in cell voltage reduction decreases as cell degradation progresses is repeatedly observed. It is determined that such a phenomenon is mainly caused by the enhanced phase-change-induced flow (PCI) due to the higher heat generation rate in a more severely degraded cell. The experimental results also provide some insights on how to optimize operating conditions for degraded fuel cells.
Co-reporter:Yupeng Yang, Xu Zhang, Liejin Guo, Hongtan Liu
International Journal of Hydrogen Energy (16 February 2017) Volume 42(Issue 7) pp:
Publication Date(Web):16 February 2017
DOI:10.1016/j.ijhydene.2016.08.091
•Local current densities change very differently at different locations.•Impurities accumulate at the channel end first and progress gradually upstream.•Operating conditions have significant effects on water and nitrogen transfer.•The concentration gradient of impurities along the channel can be very steep.Nitrogen and water accumulations in fuel cells with dead-ended anode can cause severe cell performance decline and fluctuations. In this work, both overall and local effects of fuel cell operating parameters, i.e., cathode humidity, air stoichiometry, hydrogen pressure and operating current density, have been experimentally studied under galvanostatic mode. A purge at the anode is automatically triggered when the cell voltage has decreased by 0.1 V and the mean purge interval, defined as the average time between two purges, is recorded as a characteristic parameter. Local current densities are measured to study the local effects and detailed local characteristics of the fuel cell. The experimental results show that mean purge intervals decrease with cathode inlet humidity and operating current density, and increase with inlet hydrogen pressure and air stoichiometry. The experimental results also show that the local current densities change very differently at different locations and impurities first accumulate near the end of the anode channel and then gradually progress upstream.
Co-reporter:Jiarong Yin, Zening Cheng, Liejin Guo, Sha Li, Hui Jin
International Journal of Hydrogen Energy (16 February 2017) Volume 42(Issue 7) pp:
Publication Date(Web):16 February 2017
DOI:10.1016/j.ijhydene.2016.07.065
•Hydrothermal conversion of glucose was conducted in a stirred vessel.•Conversion conditions covered ambient, subcritical to supercritical parameter.•Ni/MgO can inhibit the formation of polymers and char.•Phenol's content kept increasing and proved difficult to degrade.•Ni/ZnO can promote the generation of 5-HMF and inhibit its condensation.Biomass hydrothermal decomposition is a clean and rapid way for hydrogen production. In order to reveal the conversion mechanism, glucose with a concentration of 10 wt. % was gasified from 473 K to 673 K in 25 K increments in a stirring vessel and both the gaseous and liquid products were analyzed. Nickel based catalysts with different supports were used to promote the production of hydrogen as well as reduce the char formation. The concentration of furfural, 5-hydroxylmethylfurfural (5-HMF), levulinic acid, cyclopentanone and phenol in the liquid products were detected by a Gas chromatography–Mass spectrometry detector (GC–MS). It came out that the contents of phenol increased as reaction temperature increased, while 5-HMF, furfural and levulinic acid was consumed successively soon after their contents reached the maximum. The concentration of levulinic acid decreased and that of cyclopentanone increased sharply when nickel catalysts were used especially for magnesia-supported catalyst. The concentration of furfural decreased with the adding of catalysts and nearly approached to zero other than alumina-supported catalyst.
Co-reporter:Dengwei Jing, Maochang Liu, Jinwen Shi, Wendong Tang, Liejin Guo
Catalysis Communications (15 December 2010) Volume 12(Issue 4) pp:264-267
Publication Date(Web):15 December 2010
DOI:10.1016/j.catcom.2010.09.031
Hydrogen production under visible light by photocatalytic reforming of glucose over an oxide solid solution photocatalyst BixY1 − xVO4 (BYV) was demonstrated for the first time. It was found that a certain amount of Y doping would promote the transition of BiVO4 from monoclinic to tetragonal phase and finally lead to the formation of tetragonal BYV solid solution. BYV with a B/Y ratio of 1:1 showed the highest activity for hydrogen production. The amount of photoproduced hydrogen lowered after several hours of reaction. However, when the gas product was replaced with N2 atmosphere, hydrogen production recovered. It is supposed that the generated CO2 might participate in the redox reaction and in some way inhibit the hydrogen production. Therefore, for photocatalytic reforming of glucose, removal of gas product in time is indispensable.Photocatalytic reforming of glucose under visible light over an oxide solid solution BixY1 − xVO4(BYV) was demonstrated for the first time. It was found that certain a amount of Y doping would promote the transition of BiVO4 from monoclinic to tetragonal phase and finally lead to the formation of tetragonal BYV solid solution. BYV solid solution with a B/Y ratio of 1:1 showed the highest activity for hydrogen production.Download full-size imageResearch Highlights►Y doping promotes the transition of BiVO4 from monoclinic to tetragonal phase. ► BYV solid solution with a B/Y ratio of 1:1 shows the highest activity. ► Removal of gas product in time is indispensable for photocatalytic reforming of glucose.
Co-reporter:Shaohua Shen, Liejin Guo
Catalysis Today (15 December 2007) Volume 129(Issues 3–4) pp:414-420
Publication Date(Web):15 December 2007
DOI:10.1016/j.cattod.2006.08.070
A series of Cr incorporated, and Cr and Ti co-incorporated MCM-41 photocatalysts were synthesized by hydrothermal method. X-ray diffraction (XRD), UV–vis diffuse reflectance spectra (UV–vis), Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence analysis (XRF), N2 adsorption–desorption isotherms and Raman spectra were used to investigate the effects of the incorporated elements on the structure of MCM-41. The experimental results for photocatalytic water splitting under visible light irradiation (λ > 430 nm) demonstrated that the photocatalytic activities of Cr-MCM-41 and Cr-Ti-MCM-41 catalysts for hydrogen production decreased with an increase in the amount of Cr incorporated. Compared with the Cr-MCM-41 which had the same amount of incorporated Cr, the Cr-Ti-MCM-41 exhibited much higher hydrogen evolution activities.
Co-reporter:L.J. Guo, Y.J. Lu, X.M. Zhang, C.M. Ji, Y. Guan, A.X. Pei
Catalysis Today (15 December 2007) Volume 129(Issues 3–4) pp:275-286
Publication Date(Web):15 December 2007
DOI:10.1016/j.cattod.2007.05.027
Hydrogen production from biomass gasification in supercritical water is a new technology, which was developed in last two decades. Biomass energy of low quality can be converted to hydrogen energy of high quality by supercritical water gasification. Particularly, supercritical water gasification is an elegant way of wet biomass utilization. Up to now, many important progresses have been made in supercritical water gasification technology by the studies of researchers around the world. Since 1997, supercritical water gasification, which include reaction system, rule of biomass gasification and theory, have been studied in State Key Laboratory of Multiphase Flow in Power Engineering of Xi’an Jiaotong University. In this paper, we summarize the results from systematic experimental and analytical study on biomass gasification in supercritical water in our laboratory. Also, the development status and future prospect on supercritical water gasification is evaluated.
Co-reporter:Jing Ye, Liejin Guo
Chemical Engineering Science (11 October 2013) Volume 102() pp:486-501
Publication Date(Web):11 October 2013
DOI:10.1016/j.ces.2013.08.048
•Massive experimental and field data on multiphase flow in pipeline–riser system.•Clear interrelations between flow patterns and statistical features of pressure signals.•Methods of extracting features and their ability evaluation of flow patterns classification.•Automatic recognition and objective prediction of flow pattern by pressure fluctuation signal.•Selected pressure signal and methods are found to be easily realized in industrial.In the offshore petroleum industry, it is important to recognize the severe slugging in multiphase flow patterns in oil and gas transportation through a pipeline–riser system. After analyzing the inadaptability of the existing methods, we proposed a simple and practical method of measuring the multiphase flow patterns based on pressure fluctuations. Our recognition was carried out in three steps. First, the outlet pressure signals were selected and processed because of their accessibility to practical applications in oil fields. Second, statistical and principal component analysis were performed on the sampled signals to obtain the clear interrelations between the signals and flow patterns and to extract useful features for forming flow pattern clusters for classification in the feature space. Finally, machine learning was applied to the clusters for constructing classifiers to predict the flow patterns automatically. The experimental results from a small-scale flow loop and an offshore petroleum field show that the proposed method is feasible and effective for recognizing the multiphase flow patterns in the pipeline–riser system.
Co-reporter:Chao Zhang, Chao Wang, Shaojun Zhang, Liejin Guo
International Journal of Mineral Processing (10 September 2015) Volume 142() pp:154-160
Publication Date(Web):10 September 2015
DOI:10.1016/j.minpro.2015.01.008
•Hydration activity of calcined dolomite affects the silicothermic reduction process.•The influence mechanism was studied by experiments.•A numerical model was first developed and verified by a series of experiments.•The hydration activity of calcined dolomite should not be lower than 25%.In this paper, the effects of hydration activity of calcined dolomite (HCD) on silicothermic reduction process were studied. A series of experiments were carried out on a single briquette to investigate the impact of different HCD on the chemical reaction kinetics of the silicothermic reduction process. This study was the first to experimentally show that HCD plays an important role in the intrinsic chemical reaction rate of the silicothermic reduction process, but has no impact on the final reduction rate. The chemical kinetic data of the silicothermic reduction process with different HCD was obtained at a temperature range from 1323–1473 K. And then, a numerical model considering both heat transfer by radiation and heat conduction and chemical kinetics was developed according to the experimental data, and was used to simulate the phenomenon of heat transfer occurring during the silicothermic reduction process. The model was verified by the experiments conducted on several briquettes which were loaded on a corundum crucible. The computed results show that the increase of HCD leads to a decrease in reduction cycle time and an increase in production capacities.
Co-reporter:Chao Wang, Chao Zhang, Shao Jun Zhang, Lie Jin Guo
International Journal of Mineral Processing (10 September 2015) Volume 142() pp:147-153
Publication Date(Web):10 September 2015
DOI:10.1016/j.minpro.2015.04.017
•A new method of experiment on the silicothermal reaction was proposed.•Accurate extents of magnesium reduction were obtained.•Box-Lucas fitting was given based on the kinetic equation of solid-state reaction.•The influence of CaF2 content on the silicothermal diffusion process was linear.Calcium fluoride (CaF2) was widely used in magnesium production as a surfactant. In this paper, the effect of CaF2 content on the silicothermal process was investigated. Experiments were carried out on briquettes made from mixture of calcined dolomite, ferrosilicon (Fe·Si) and CaF2. Briquettes with a thickness of about 2 mm were used to reduce the effect of heat transfer on the reaction. The extent of magnesium reduction with different experimental temperatures, CaF2 content and reaction time was proposed. The experimental temperature ranged from 1323 K to 1473 K, and the CaF2 content was 0%–3%. The results showed that the increase of CaF2 content leads to the decrease of reaction time and the increase of reaction rate. In addition, a Box-Lucas fitting of magnesium reduction was proposed in order to describe the influence factors of reduction extent, in which the temperature, CaF2 content and reaction time were independent variables. It was indicated that the CaF2 influenced the diffusion process instead of the reduction process, which could be explained with the mathematical expression reasonably.
Co-reporter:Xiaokang Wan, Fujun Niu, Jinzhan Su and Liejin Guo
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 46) pp:NaN31810-31810
Publication Date(Web):2016/11/03
DOI:10.1039/C6CP06233D
Nanoporous bismuth vanadate is modified simultaneously via tungsten doping and graphene surface modification for use as an efficient photoanode. The modified films were prepared on a FTO substrate by a drop-cast method followed by photoreduction of graphene oxide. SEM, XRD, Raman and XPS characterization was conducted to confirm the incorporation of tungsten and reduced graphene oxide (RGO), and to look into their influences on the structure and performance of BiVO4. Electrochemical impedance spectroscopy analysis clearly revealed enhanced carrier density and improved electronic conductivity, which are beneficial for the enhancement of PEC performance in comparison to either individually doped or RGO modified BiVO4. Our results indicated that the enhanced PEC performance can be attributed to the synergistic effect of bulk doping and surface modification that facilitates electron and hole transport and transfer in the bulk and at the semiconductor–electrolyte interface.
Co-reporter:Yubin Chen, Lianzhou Wang, Gaoqing (Max) Lu, Xiangdong Yao and Liejin Guo
Journal of Materials Chemistry A 2011 - vol. 21(Issue 13) pp:NaN5141-5141
Publication Date(Web):2011/02/22
DOI:10.1039/C0JM03945D
CdS/titanate nanotubes (CdS/TNTs) photocatalysts with a unique morphology were successfully synthesized via a simple one-step hydrothermal method. Compared with traditional CdS@TNTs composite photocatalysts prepared by the common two-step method, CdS/TNTs exhibited much higher activity for photocatalytic hydrogen evolution under visible light irradiation. Transmission electron microscopy (TEM) revealed that the CdS nanoparticle was intimately enwrapped by the surrounding TNTs. This unique architecture resulted in the appropriate dispersion of CdS nanoparticles and the intimate multipoint contacts between the CdS nanoparticle and TNTs, which led to significant enhancement of charge separation in CdS/TNTs. Accordingly, the photoactivity was improved. Meanwhile, X-ray powder diffraction (XRD) demonstrated that the highly crystalline hexagonal CdS was obtained in CdS/TNTs, which was also essential for the enhanced photocatalytic performance. The unique morphology and photocatalytic activity of CdS/TNTs were influenced by the Cd/Ti molar ratio with an optimal value of 0.05. Under this condition, the CdS amount was only 6 wt% of the total photocatalyst, which was important from an environmental point of view. The influence of loaded Pt on the activity of CdS/TNTs had also been investigated. The hydrogen production rate of 2.0 wt% Pt-loaded CdS/TNTs reached 353.4 μmol h−1, with the apparent quantum yield of 25.5% at 420 nm. This study provides a potential way to synthesize highly efficient composite photocatalysts with a novel architecture.
Co-reporter:Yubin Chen and Liejin Guo
Journal of Materials Chemistry A 2012 - vol. 22(Issue 15) pp:NaN7514-7514
Publication Date(Web):2012/03/09
DOI:10.1039/C2JM16797B
Semiconductor based nanocomposites are quite promising in the areas of photocatalysis and photovoltaics due to their efficient charge separation. Herein, we demonstrated a simple and green one-step method to prepare novel Cd0.5Zn0.5S/TNTs (titanate nanotubes) nanocomposites with low-priced metallic elements. Transmission electron microscopy (TEM) images revealed that an enwrapped architecture was achieved for Cd0.5Zn0.5S/TNTs nanocomposites. Cd0.5Zn0.5S nanoparticles of ca. 90 nm were tightly surrounded by the network of titanate nanotubes, which led to the high dispersity of Cd0.5Zn0.5S nanoparticles and the intimate multipoint contacts between Cd0.5Zn0.5S and TNTs. Highly efficient charge separation was finally achieved in the hybrid Cd0.5Zn0.5S/TNTs through the enwrapped structure. Under visible light irradiation Cd0.5Zn0.5S/TNTs displayed improved activities compared to the single Cd0.5Zn0.5S for hydrogen evolution. The effect of sacrificial reagents on the photocatalytic activity of Cd0.5Zn0.5S/TNTs was discussed. The highest apparent quantum yield of 38.1% at 420 nm was achieved. This value is among the highest efficiencies for the noble-metal free photocatalysts ever reported. Meanwhile, Cd0.5Zn0.5S/TNTs showed good stability for hydrogen production, and the content of toxic cadmium was as low as 4.0 wt% of the nanocomposites. These factors are of great significance for their application in the field of solar energy conversion.
Co-reporter:Jie Chen, Shaohua Shen, Penghui Guo, Po Wu and Liejin Guo
Journal of Materials Chemistry A 2014 - vol. 2(Issue 13) pp:NaN4612-4612
Publication Date(Web):2014/01/08
DOI:10.1039/C3TA14811D
ZnFe2O4 modified g-C3N4 was successfully synthesized by a simple one-pot method. The visible-light-driven photocatalytic hydrogen production activity of g-C3N4 was significantly enhanced due to spatial engineering of the photo-active sites via ZnFe2O4 modification and Pt loading. It is proposed that ZnFe2O4 does not function as visible light sensitizer but as oxidation active sites. In the present ZnFe2O4/g-C3N4 photocatalysts, the photo-induced holes in g-C3N4 tend to transfer to ZnFe2O4 due to the straddling band structures (Type I band alignment), while the photo-induced electrons in g-C3N4 prefer to transfer to the loaded Pt cocatalysts, which can function as reduction active sites for hydrogen production. As a result, the photoinduced electrons and holes in g-C3N4 are efficiently separated by spatial engineering of the photo-active sites, and hence enhanced photocatalytic hydrogen generation activity is obtained.
Co-reporter:Lijing Ma, Maochang Liu, Dengwei Jing and Liejin Guo
Journal of Materials Chemistry A 2015 - vol. 3(Issue 10) pp:NaN5707-5707
Publication Date(Web):2015/01/28
DOI:10.1039/C4TA06577H
CdS is a well-known and efficient photocatalyst for photocatalytic hydrogen production. However, CdS is prone to photocorrosion in the photocatalytic reaction, in which CdS itself is oxidized by the photogenerated holes. Most of the work reported, to date, has focused only on the structure of CdS. However, less attention was paid to the kinetic changes of CdS during the photocatalytic reaction, which, in our opinion, is a crucial step for its practical utilization. In this report, we have developed a facile in situ Raman analysis, aiming to clarify the microstructural changes of CdS during the photocatalytic reaction process. In this study, photocatalytic hydrogen production over CdS in an Ar or air atmosphere was studied using various techniques in addition to in situ Raman spectroscopy. With Raman spectroscopy, a significant increase in the surface lattice strain of CdS was only observed when it was exposed to air, while the electron–phonon interactions remained the same regardless of the atmosphere. A direct correlation between the interfacial crystal lattice and photocorrosion of the CdS photocatalyst during photocatalytic hydrogen production was found based on our in situ Raman investigation. Finding the photocorrosion of the CdS photocatalyst at its very early stage using our in situ Raman technique is expected to provide meaningful guidance for the design of active and stable chalcogenide photocatalysts, which, however, cannot be achieved using traditional characterization techniques.
Co-reporter:Po Wu, Jiarui Wang, Jing Zhao, Liejin Guo and Frank E. Osterloh
Chemical Communications 2014 - vol. 50(Issue 98) pp:NaN15524-15524
Publication Date(Web):2014/10/20
DOI:10.1039/C4CC08063G
A high rate of 2.23 mmol h−1 g−1 (quantum efficiency of 6.67% at 400 nm) for visible light driven photocatalytic H2 evolution can be achieved with g-C3N4 by alkalization of the solution to a pH of 13.3, due to accelerated transfer of photoholes to the sacrificial donor.
Co-reporter:Kai Zhang and Liejin Guo
Catalysis Science & Technology (2011-Present) 2013 - vol. 3(Issue 7) pp:NaN1690-1690
Publication Date(Web):2013/02/19
DOI:10.1039/C3CY00018D
Photocatalytic hydrogen production using semiconductor materials is one of the ideal processes for direct solar energy conversion. Sulphide semiconductor photocatalysts have attracted much attention due to their excellent solar spectrum responses and high photocatalytic activities. This article presents recent research progress in the development of visible light driven sulphide photocatalysts, focusing on the expansion of solar spectrum response and enhancement of charge separation efficiency. As is known, the ultimate goal of photocatalytic hydrogen production is to meet the practical energy demand of human beings. Thus, design of highly efficient and low cost sulphide photocatalysts with excellent sunlight response is highly desired. So we also highlight the crucial issues in the development of highly efficient sulphide photocatalysts without noble metal cocatalysts. The present paper is expected to provide important scientific reference for future works. Finally, the challenges and perspectives in this area are also discussed.
Co-reporter:Ning Zhang, Jinwen Shi, Samuel S. Mao and Liejin Guo
Chemical Communications 2014 - vol. 50(Issue 16) pp:NaN2004-2004
Publication Date(Web):2014/01/13
DOI:10.1039/C3CC48026G
Co3O4 quantum dots were synthesized by a facile reverse micelle method for the first time, and were capable of splitting pure water into O2 and H2 stoichiometrically under visible-light irradiation (λ > 420 nm) without any cocatalyst.
Co-reporter:Po Wu, Jiarui Wang, Jing Zhao, Liejin Guo and Frank E. Osterloh
Journal of Materials Chemistry A 2014 - vol. 2(Issue 47) pp:NaN20344-20344
Publication Date(Web):2014/10/16
DOI:10.1039/C4TA04100C
Graphitic carbon nitride (g-C3N4) is a promising visible-light-responsive photocatalyst for hydrogen generation from water. As we show here, the photocatalytic activity of g-C3N4 is limited by structure defects generated during the calcination process. Specifically we find that the photocatalytic hydrogen production rate from aqueous methanol is inversely related to the calcination temperature (520–640 °C). The highest activity of 0.301 mmol h−1 g−1 is observed for the sample prepared at the lowest processing temperature. Surface photovoltage (SPV) spectroscopy shows that the maximum photovoltage is reduced (from 1.29 V to 0.62 V) as the processing temperature is increased, in accordance with higher defect concentrations and faster electron–hole recombination. The defects also produce additional optical absorption in the visible spectra and cause a red shifted, weakened photoluminescence (PL). Based on the sub-gap signal in the SPV and PL spectra, defect energy levels are +0.97 V and −0.38 V (vs. NHE) in the band gap of the material. According to Fourier transform infrared (FTIR) spectra, the defects are due to amino/imino groups in the g-C3N4 lattice.
Co-reporter:Ning Zhang, Jinwen Shi, Fujun Niu, Jian Wang and Liejin Guo
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 33) pp:NaN21400-21400
Publication Date(Web):2015/07/20
DOI:10.1039/C5CP02983J
Owing to the effect of energy band bending, p-type Co3O4 quantum dots sensitized by Eosin Y showed a high and stable photocatalytic activity (∼13440 μmol h−1 g−1cat) for water reduction and hydrogen production under visible-light irradiation without any cocatalyst.
Co-reporter:Yubin Chen ; Chi-Hung Chuang ; Keng-Chu Lin ; Shaohua Shen ; Christopher McCleese ; Liejin Guo ;Clemens Burda
The Journal of Physical Chemistry C () pp:
Publication Date(Web):
DOI:10.1021/jp500270d
This work provides new routes for developing efficient photoelectrodes for photoelectrochemical (PEC) water splitting using a low-cost electrophoretic film preparation method. A series of (Cu2Sn)xZn3(1–x)S3 (0 ≤ x ≤ 0.75) quaternary nanocrystals (NCs) with tunable optical band gaps are synthesized. Morphologies including particles, rods, and wires are obtained by tuning the composition of the NCs. (Cu2Sn)0.75Zn0.75S3 (Cu2ZnSnS4) has a pure kesterite structure, but an increase in the Zn content results in a kesterite–wurtzite polytypism. (Cu2Sn)xZn3(1–x)S3 films are fabricated from their colloidal solutions via electrophoretic deposition, and the PEC properties of these films with p-type character have been examined under water-splitting conditions. It is shown that the photocurrent varies as a function of film thickness as well as chemical composition. The produced (Cu2Sn)0.45Zn1.65S3 (x = 0.45) film has the highest photocurrent, and the incident photon to current conversion efficiency is improved compared with previously reported results of Cu2ZnSnS4 photocathodes.
