•l-glutamic acid is a new carbon precursor with nitrogen functionality.•Pyrolysis of a complex from l-glutamic acid and ZnCl2 leads to carbon formation.•Carbon is highly microporous due to the evaporation of zinc species.•Carbon as electrode for EDLC possesses stable cycle life and low leakage current.The selection of carbon precursor is an important factor when designing carbon materials. In this study, a complex derived from l-glutamic acid and zinc chloride was used to prepare highly microporous carbons via facile pyrolysis. l-glutamic acid, a new carbon precursor with nitrogen functionality, coordinated with zinc chloride resulted in a homogeneous distribution of Zn2+ on the molecular level. During pyrolysis, the evaporation of the in situ formed zinc species creates an abundance of micropores together with the inert gases. The obtained carbons exhibit high specific surface area (SBET: 1203 m2 g−1) and a rich nitrogen content (4.52 wt%). In excess of 89% of the pore volume consists of micropores with pore size ranging from 0.5 to 1.2 nm. These carbons have been shown to be suitable for use as supercapacitor electrodes, and have been tested in 6 M KOH where a capacitance of 217 F g−1 was achieved at a current density of 0.5 A g−1. A long cycling life of 30 000 cycles was achieved at a current density of 1 A g−1, with only a 9% loss in capacity. The leakage current through a two-electrode device was measured as 2.3 μA per mg of electrode and the self-discharge characteristics were minimal.

At the operating temperature (80–120 °C) of a proton exchange membrane fuel cell (PEMFC), high-efficiency elimination of CO while minimizing the H2 consumption processes is highly desired but still remains a challenge. In the present manuscript, one novel potassium-treated Au–Cu/Al2O3 catalyst was synthesized via a two step deposition–precipitation (DP) method with excellent catalytic performance for preferential oxidation of CO (CO-PROX) in a H2-rich stream. This catalyst exhibits 100% CO conversion over a wide temperature window of 60–110 °C and ≥50% selectivity of CO2 under the PEMFC operating temperature. Furthermore, the as-prepared potassium-treated Au–Cu/Al2O3 catalysts were also characterized by N2 adsorption analysis, scanning transmission electron microscopy (STEM)-energy dispersive X-ray spectroscopy (EDX), and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS), and the reasons for enhanced catalytic activity of the potassium-treated sample were elucidated. The introduction of copper could strengthen the CO adsorption on the Au–Cu/Al2O3 catalyst and potassium treatment could significantly increase the stability of active Cu+ species that contribute to enhanced catalytic performance.

Asphaltene supermolecules extracted from coal consist of highly condensed polyaromatic units and peripheral aliphatic chains, which is a natural source with high carbon content. In this study, we demonstrate that the asphaltene can be used as an ideal supermolecular carbon precursor for the fabrication of carbon nanosheets by self-assembly via π–π and hydrogen bonding interactions with a sheet-structure-directing agent of graphene oxide. The overall thickness of the obtained asphaltene based carbon nanosheets can be tuned from 13 ± 3 to 41 ± 5 nm. These carbon nanosheets show an electrical conductivity of ca. 450 S m–1. When they are used as electrode materials for supercapacitors, the carbon nanosheets demonstrate a specific capacitance of 163 F g–1 even at a current density of 30 A g–1 tested in a three-electrode system, due to high electrically conductive networks and short diffusive paths. The maximum specific gravimetric capacitance and surface area-normalized capacitance in two-electrode system are 191 F g–1 and 43 μF cm–2, respectively, indicating very high utilization of the available surface area. These results prove that asphaltene is a promising molecular precursor for the preparation of energy materials, further displaying an efficient route for staged conversion of coal that is abundant in nature.

Nanostructured mesoporous α-MnO2 nanorods were synthesized via a simple hydrothermal process using MnSO4·H2O and KMnO4 as precursors. A series of Au/MnO2 catalysts were prepared by a colloidal deposition (CD) method and were characterized by X-ray diffraction (XRD), nitrogen adsorption, scanning electron microscopy (SEM) and temperature programmed reduction of hydrogen (H2-TPR) analysis. The influence of the preparation conditions of the supports on the catalytic performance of Au/MnO2 catalysts in CO oxidation has been investigated. The results show that the structure and properties of MnO2 products were strongly dependent on the hydrothermal time. One can distinguish the aspect ratio of MnO2 nanorods from SEM images. The obtained Au/MnO2 catalysts with 1 wt% Au exhibits excellent performance with a complete CO conversion at 20 °C (T100% = 20 °C) and 50% CO conversion at −25 °C (T50% = −25 °C). Furthermore, H2-TPR studies reveal the superior activities have been attributed to the support unique reducibility and the interaction between Au and support. However, the U-shaped activity curves show a significant drop in CO conversion at low-temperature. With the help of temperature programmed desorption (CO2-TPD) and CO2 static adsorption studies, it confirms that the deactivation of catalytic activity was attributed to the adsorbed CO2 taking up the active sites, which can be desorbed by increasing the reaction temperature.

Rod-like alumina materials were synthesized via a template-free hydrothermal method by using aluminum nitrate as precursor and urea as precipitating agent. The resulting alumina has a high specific surface area (up to 773 m2 g−1) and an abundance of hydroxyl groups, giving it a good Cr(VI) removal efficiency. External factors were investigated, including contact time, adsorbent dose, initial concentration of adsorbate and pH. The maximum adsorption capacity for Cr(VI) was 39.1 mg g−1, which is superior to most of the reported alumina adsorbents. The Al2O3 samples before and after Cr(VI) adsorption were also characterized by FT-IR and XPS analysis. The results show that the adsorption can be mainly ascribed to the ion exchange between the abundant hydroxyl groups on the alumina surface and chromium anions. Together with an outstanding adsorption–regeneration performance, it is anticipated that the as-synthesized alumina materials are an attractive adsorbent for the removal of heavy metal ions from water.

•The confinement effect of porous carbon allows controllable nano-sized LiFePO4.•The interconnected carbon offers fast and continuous electrons transfer path.•LiFePO4 with smaller size and suitable loading exhibits good rate performance.•Small nanospheres confined in open-mesopore carbon leads to fast Li-ion diffusion.LiFePO4/C composites with tunable particle size and loading content have been prepared using the porous carbon with large pore volume and controllable pore size as an interconnected conductive framework and rigid nano-confinement matrix. The large pore volume of carbon provides sufficient space for LiFePO4 hosting and the controllable pore size of carbon restricts the growth of LiFePO4 crystals to further improve the rate performance. When used as the cathode materials for lithium-ion batteries, they exhibit a stable and high reversible capacity of 161 mA h g−1 at 0.1 C, 106 mA h g−1 at 20 C and 50 mA h g−1 at 50 C. The cell retains 94% of its initial capacity at 20 C over 200 cycles with an ultrahigh specific power of 10,446 W kg−1. The high rate performance and good cycle stability can be ascribed to the small nano-sized LiFePO4 confined in the nanopores of the carbon matrix with suitable loading content and good contact between LiFePO4 and the continuous conductive carbon framework, thus allowing fast lithium-ion diffusion and electrons transfer. This structure model may be valid for better understanding the rate performance and might be extended for fabrication of other high power electrode materials.Graphical abstract

Lithium ion capacitors (LICs), bridging supercapacitors and lithium ion batteries (LIBs), have recently drawn considerable attention. In this report, a non-aqueous LIC was fabricated using tubular mesoporous carbon as a cathode and a SnO2–C hybrid (ultrafine SnO2 encapsulated in the tubular mesoporous carbon) as an anode. Such a LIC can achieve a maximum energy density of 110 W h kg−1 and a maximum power density of 2960 W kg−1. The capacitance retention is fairly stable and retains 80% of its initial value after 2000 cycles. This unique performance arises because of the highly conductive tubular mesoporous carbon matrix and fast charge/ion diffusion in the SnO2–C hybrid anode. It is shown that the SnO2 loading in the anode has a great influence on the stability of the SnO2 nano-structure and the kinetics of lithium ion transfer. Electrochemical impedance spectroscopy (EIS) was used to evaluate the charge transfer resistance and the ionic diffusion resistance before and after long-term cycling. The diffusion coefficient was also calculated to verify the good rate and cycling capability.

Consisted of closely packed nanoflakes, γ-Al2O3 hollow microspheres with ca. 4–6 μm in diameter, and 500–700 nm in shell thickness have been hydrothermally synthesized through utilizing Al(NO3)3·9H2O as precursor, urea as precipitant agent and sulfate K2SO4, (NH4)2SO4, or KAl(SO4)2·12H2O as additive, followed by a calcination step. The samples were further characterized by thermogravimetric analysis, scanning electron microscope, x-ray powder diffraction, nitrogen adsorption, and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of adsorbed CO etc. The morphology of alumina products was strongly dependent on the presence of SO42−. Then via a deposition–precipitation method, 3 wt.% Au nanoparticles supported on γ-Al2O3 hollow microspheres exhibit excellent performance with a complete CO conversion at 0 °C (T100% = 0 °C) and 50 % conversion at −25 °C (T50% = −25 °C). The good catalytic activity is associated with the special hollow microsphere structures assembled by nanoflakes of γ-Al2O3 support. The DRIFTS confirms the presence of Auδ+ and Au0 on the surface of γ-Al2O3 hollow microspheres. As a contrast, Au catalyst prepared using alumina support with undefined morphology shows low activity under the same catalytic test conditions (T100% = 190 °C, T50% = 80 °C).

Hierarchically organized γ-Al2O3 hollow microspheres were prepared via a hydrothermal method using potassium aluminum sulfate and urea as reactants. The corresponding Au/Al2O3 catalysts were obtained using a deposition-precipitation (DP) method. The effect of the pretreatment under different atmospheres (N2, air, and H2) on the activity and stability of the Au/Al2O3 catalysts in CO oxidation was investigated. The results showed that the pretreatment under H2 atmosphere improved the low-temperature CO oxidation activity. Furthermore, a 50 h long-term test at 30 °C showed no significant deactivation for the H2-pretreated catalyst. Moreover, the catalytic activity was promoted by H2O vapor in all cases, and the H2-pretreated catalyst exhibited a good tolerance in the co-presence of CO2 and H2O. Finally, oxygen temperature-programmed desorption (O2-TPD) and in situ diffuse reflectance infrared Fourier transform spectra (DRIFTS) revealed that the reductive atmosphere pretreatment greatly improved the CO adsorption capacity and facilitated the oxygen activation.

Porous carbon nanofibers (CNFs) are regarded as essential components of high-performance energy storage devices in the development of renewable and sustainable resources, due to their high surface areas, tunable structures, and good conductivities. Herein, we report new synthesis methods and applications of two types of porous carbon nanofibers, i.e., colloidal mesoporous carbon nanofibers as electrode materials for supercapacitors, and microporous carbon nanofibers as substrate media for lithium–sulfur (Li-S) batteries. These carbon nanofibers can be synthesized either by confined nanospace pyrolysis or conventional pyrolysis of their polymeric precursors. The supercapacitor electrodes which are fabricated via a simple dipping and rinsing approach exhibit a reversible specific capacitance of 206 F g−1 at the current density of 5 A g−1 in 6.0 mol L−1 aqueous KOH electrolyte. Meanwhile, the Li-S batteries composed of microporous carbon nanofiber-encapsulated sulfur structures exhibit unprecedented electrochemical performance with high specific capacity and good cycling stability, i.e., 950 mA h g−1 after 50 cycles of charge–discharge. The excellent electrochemical performance of CNFs is attributed to their high-quality fiber morphology, controlled porous structure, large surface area, and good electrical conductivity. The results show that the carbon nanofibers represent an alternative promising candidate for an efficient electrode material for energy storage and conversion.

Porous carbon materials with large pore volume are crucial in loading insulated sulfur with the purpose of achieving high performance for lithium–sulfur batteries. In our study, peapodlike mesoporous carbon with interconnected pore channels and large pore volume (4.69 cm3 g–1) was synthesized and used as the matrix to fabricate carbon/sulfur (C/S) composite which served as attractive cathodes for lithium–sulfur batteries. Systematic investigation of the C/S composite reveals that the carbon matrix can hold a high but suitable sulfur loading of 84 wt %, which is beneficial for improving the bulk density in practical application. Such controllable sulfur-filling also effectively allows the volume expansion of active sulfur during Li+ insertion. Moreover, the thin carbon walls (3–4 nm) of carbon matrix not only are able to shorten the pathway of Li+ transfer and conduct electron to overcome the poor kinetics of sulfur cathode, but also are flexible to warrant structure stability. Importantly, the peapodlike carbon shell is beneficial to increase the electrical contact for improving electronic conductivity of active sulfur. Meanwhile, polymer modification with polypyrrole coating layer further restrains polysulfides dissolution and improves the cycle stability of carbon/sulfur composites.Keywords: carbon/sulfur composite; high sulfur loading cathode; large pore volume; lithium−sulfur battery; peapodlike mesoporous carbon;

A novel LiFePO4/C composite, including 85.4 wt% of spherical LiFePO4 nanocrystallites with the size of 22 nm is fabricated by using 3D coralloid nitrogen-containing carbon with large pore volume (4.68 cm3 g−1) and thin walls (2–3 nm) as interpenetrating conductive framework. Based on the whole composite, the LiFePO4/C cathode material exhibits a stable and high reversible capacity of 144.6 mA h g−1 at 0.1 C and 60.4 mA h g−1 at 20 C (based on the weight of LiFePO4, it can deliver a high capacity of 155.8 mA h g−1 at 0.1 C and 85.3 mA h g−1 at 20 C). The cell retains 96.7% of its initial capacity at 10 C over 1000 cycles with an ultrahigh specific power of 5114 W kg−1 and the coulombic efficiency is >99%. The excellent performance is ascribed to the facile lithium-ion diffusion within the LiFePO4 nanocrystallites and high conductivity through the 3D continuous network. This coralloid carbon not only provides sufficient space for LiFePO4 hosting to further assist in energy storage, but also acts as a rigid nano-confinement support that prevents agglomeration of LiFePO4 during calcinations, which might be extended for the fabrication of other nano-sized electrode materials.Graphical abstractA novel cathode LiFePO4/C composite with uniform nanosized LiFePO4 spheres (22 nm) and superior performance was fabricated using coral-like carbon with large pore volume (4.68 cm3 g−1) and thin walls (2–3 nm) as support.Highlights► Poly(benzoxazine-co-resol) based N-doped porous carbon using silica as template. ► Coralloid carbon with large pore volume provides high LiFePO4 loading. ► LiFePO4 nanospheres from the confinement of carbon lead to fast Li ion diffusion. ► Thin interpenetrated walls offer a fast and continuous electron transfer network. ► The obtained LiFePO4/C exhibit excellent rate and cycling performance.

•An easy synthesis of NH4Al(OH)2CO3 nanorods without templates is developed.•Decomposition of NH4Al(OH)2CO3 could create pores on the external surface of γ-Al2O3.•External mesopores can act as “holders” to stabilize Au nanoparticles efficiently.•The prepared catalyst exhibits excellent performance for CO oxidation (T100% = 18 °C).External mesoporous γ-Al2O3 nanorods with an aspect ratio of 2–4 has been hydrothermally synthesized using Al(NO3)3·9H2O as precursor and (NH4)2CO3 as precipitant without any templates and followed by a calcination step. The obtained samples were characterized by thermogravimetric analysis (TG), X-ray powder diffraction (XRD), nitrogen sorption, Fourier transform infrared spectrometry (FT-IR), and scanning transmission electron microscopy (STEM). It can be confirmed that the morphology of nanorods is formed in the low-temperature hydrothermal process of 100 °C. Through the thermal decomposition of intermediate product NH4Al(OH)2CO3, the prepared γ-Al2O3 possesses abundant external mesopores, which can act as “holders” to stabilize or anchor gold nanoparticles efficiently. Using CO oxidation as an probe reaction, the results demonstrated that Au catalyst exhibited excellent catalytic performance with the complete CO conversion at 18 °C (T50% = −11.2 °C) and reactive stability over 166 h under a space rate of 134,000 mL h−1 gcat−1.

Thin porous alumina sheets have been synthesized using a lysine-assisted hydrothermal approach resulting in an extraordinary catalyst support that can stabilize Au nanoparticles at annealing temperatures up to 900 °C. Remarkably, the unique architecture of such an alumina with thin sheets (average thickness ∼15 nm and length 680 nm) and rough surface is beneficial to prevent gold nanoparticles from sintering. HRTEM observations clearly showed that the epitaxial growth between Au nanoparticles and alumina support was due to strong interfacial interactions, further explaining the high sinter-stability of the obtained Au/Al2O3 catalyst. Consequently, despite calcination at 700 °C, the catalyst maintains its gold nanoparticles of size predominantly 2 ± 0.8 nm. Surprisingly, catalyst annealed at 900 °C retained the highly dispersed small gold nanoparticles. It was also observed that a few gold particles (6–25 nm) were encapsulated by an alumina layer (thickness less than 1 nm) to minimize the surface energy, revealing a surface restructuring of the gold/support interface. As a typical and size-dependent reaction, CO oxidation is used to evaluate the performance of Au/Al2O3 catalysts. The results obtained demonstrated Au/Al2O3 catalyst calcined at 700 °C exhibited excellent activity with a complete CO conversion at ∼30 °C (T100% = 30 °C), and even after calcination at 900 °C, the catalyst still achieved its T50% at 158 °C. In sharp contrast, Au catalyst prepared using conventional alumina support shows almost no activity under the same preparation and catalytic test conditions.Keywords: epitaxial growth; gold nanoparticles; high temperature; porous alumina sheet; strong interfacial interaction

High surface area mesoporous manganese dioxide (MnO2) with α-phase crystalline structure has been synthesized by the reduction of potassium permanganate with ethylene glycol under acidic conditions. Nitrogen sorption analyses show that MnO2 synthesized under acidic conditions exhibits a type IV isotherm, indicating a mesoporous character. Electrochemical performances of MnO2 samples as supercapacitor electrode materials have been studied in a three-electrode system. A hybrid supercapacitor based on using a composite material (MnO2&Activated Carbon) as the positive electrode and activated carbon as the negative electrode has been fabricated. The hybrid supercapacitor fabricated using MnO2 synthesized under acidic conditions has excellent large current charge–discharge performance, and shows a practical cell voltage of 1.8 V and a capacitance of 22.1 F g−1 after 1500 cycles even in the presence of the dissolved oxygen. MnO2 synthesized in the absence of acid shows poor cycle performance and a low capacitance.Graphical abstractHighlights► High surface area and mesoporous MnO2 has been synthesized under acidic conditions. ► Hybrid supercapacitors with MnO2&AC based positive electrodes have been fabricated. ► The practical cell capacitance is high up to 22.1 F g−1 with a lower IR. ► The cycle stability of mesoporous MnO2 based supercapacitors is obviously improved.

Porous silica with different nanostructures, namely two-dimensional hexagonal SBA-15, three-dimensional cubic KIT-6 and hierarchical monolith silica (HMS), were used as supports to fabricate gold catalysts using a liquid-phase deposition–precipitation method. Pre-loading of ceria on porous silica can significantly improve the dispersion of the subsequently introduced gold nanoparticles and the catalytic activity of the final composite (Au/CeO2/SiO2) catalysts in CO oxidation. The composite catalysts were characterized by N2 adsorption, X-ray diffraction. The results indicate that different nanostructures of silica imposed significant influence on the catalytic activity of Au/CeO2/SiO2 catalysts. Gold catalyst supported on HMS exhibited the highest activity for the conversion of CO to CO2 with a complete conversion (T100%) at a temperature of 60 °C and at a space velocity of 80,000 mL gcat−1 h−1, whereas T100% shifted to 120–130 °C for SBA-15 and KIT-6 supported gold catalysts.Graphical abstractHighlights► Various structured SiO2 modified with CeO2 were used to construct gold catalysts. ► Nanostructures of SiO2 had great effect on the catalytic activity for CO oxidation. ► Different structures of the supports exert great influence on the diffusion rate. ► Hierarchical monolith silica supported Au had the highest activity (T100% = 60 °C).

Granular micro/mesoporous carbon with a ratio of mesopore to total pore volume (Vmeso/Vtotal) greater than 75% was prepared using coconut shells as a precursor by a one-step thermal treatment, i.e., combined pyrolysis and steam activation process. The process variables, such as final activation temperature, time, and water flow rate were studied. The N2 adsorption isotherms of the samples were of type IV, indicating mesoporous characteristics. The mesoporosity of the resultant porous carbons prepared by this method is greater than the one of those prepared by the conventional two separate pyrolysis and activation processes. Experimental results showed that the yield of porous carbon was proportional to the final pyrolysis temperature and activation time. Additionally, with the increase of activation time and water flow rate, the mesoporosity increased considerably. When the activation time and water flow rate were kept constant, the mesoporosity also increased with a rise in the final pyrolysis temperature. Electrochemical tests indicate that with the increase of Vmeso/Vtotal of the porous carbons, the equivalent series resistance (ESR) decreases and the capacitance retention is of 93% at a high current density of 5 A g–1. Thereinto, the carbon electrode made from sample CS-800-0.12-60 with the highest Vmeso/Vtotal have a high capacitance of 228 F g–1 in 6.0 mol L–1 KOH electrolyte at 5 mV s–1 and the energy density of 38.5 Wh kg–1 with an ESR of 1.9 Ω at 0.5 A g–1.

A series of hierarchically multimodal (micro-, meso-/macro-) porous carbon monoliths with tunable crystallinity and architecture have been designedly prepared through a simple and effective gelation through a dual phase separation process and subsequent pyrolysis. Because of the magnificent structural characteristics, such as highly interconnected three-dimensional (3D) crystalline carbon framework with hierarchical pore channels, which ensure a fast electron transfer network and lithium-ion transport, the carbon anodes exhibit a good cycle performance and rate capability in lithium-ion cells. Importantly, a correlation between the electrochemical performances and their structural features of crystalline and textural parameters has been established for the first time, which may be of valid for better understanding of their rate performance and cycle stability.

Utilizing the dual functions of activated carbon (AC) both as a conductive agent and an active substance of a positive electrode, a hybrid supercapacitor (AC-MnO2&AC) with a composite of manganese dioxide (MnO2) and activated carbon as the positive electrode (MnO2&AC) and AC as the negative electrode is fabricated, which integrates approximate symmetric and asymmetric behaviors in the distinct parts of 2 V operating windows. MnO2 in the positive electrode and AC in the negative electrode together form a pure asymmetric structure, which extends the operating voltage to 2 V due to the compensatory effect of opposite over-potentials. In the range of 0–1.1 V, both AC in the positive and negative electrode assemble as a symmetric structure via a parallel connection which offers more capacitance and less internal resistance. The optimal mass proportions of electrodes are calculated though a mathematical process. In a stable operating window of 2 V, the capacitance of AC-MnO2&AC can reach 33.2 F g−1. After 2500 cycles, maximum energy density is 18.2 Wh kg−1 with a 4% loss compared to the initial cycle. The power density is 10.1 kW kg−1 with an 8% loss.Research highlights▶ In this study we model a hybrid supercapacitor with a MnO2&Carbon composite-based positive electrode. ▶ The supercapacitor integrated approximate symmetric and asymmetric behaviors in the range of 0–1.1 V and 1.1–2.0 V. ▶ The AC introduced in positive electrode increases capacitance and decreases internal resistance. ▶ The dual functions of AC as the conductive and capacitive substance of positive electrode were indicated. ▶ The maximum capacitance was calculated, and thus an optimal mass proportion can be achieved through a mathematic process.

Two nitrogen-doped carbon monoliths with hierarchical porosity over a large size range were prepared by polymerization of resorcinol and formaldehyde in the presence of an organic amine, L-lysine, and an inorganic base, ammonium hydroxide under ambient conditions. Their physical and chemical features were characterized by N2 sorption, transmission and scanning electron microscopy, and elemental analysis. Their electrochemical properties as the electrodes of supercapacitors were evaluated under both a three-electrode system and a two-electrode system. Results show that the two types of nitrogen-doped carbon possess similar pore structures, but have distinct electrochemical performances. The L-lysine incorporated carbon monolith has a high nitrogen content, a high specific capacitance of 199 F·g−1, and a 1.6% loss in the specific capacitance after 1000 charge-discharge cycles, indicating a long-term cycling stability.

Various nanocast ordered mesoporous carbons (OMCs) were synthesized using mesoporous silicas such as SBA-15, SBA-16, KIT-6, SBA-3 and MCM-48 as templates via nanocasting pathway. The structures of OMCs were analyzed by X-ray diffraction, transmission electron microscope and nitrogen sorption technique. These OMCs with well-defined pore structure were used as model electrode materials for investigating the influence of pore structure on their double layer capacitances. The cyclic voltammetry and galvanostatic charge/discharge measurements were conducted to estimate the capacitive behaviour of OMCs. The results show that the mesopore structures of OMCs play an important role in improving surface utilization for the formation of electrical double layer. OMCs synthesized from SBA-15 and SBA-16 show great advantage over others because their micropores are being easy accessible through the mesopores, thus allowing rapid electrolyte ion diffusion. To achieve a higher specific capacitance (μF cm−2), the optimized amount ratio between micropore and mesopore needs to be controlled. In addition, great impact of the electrode disc thickness on the capacitive performance was demonstrated by a series of careful measurements.

Nanostructured mesoporous manganese oxides were easily prepared by mixing KMnO4 with ascorbic acid in an aqueous solution under ambient conditions. The obtained manganese oxides were identified as having an α-MnO2 tunnel structure composed of an edge-shared network of [MnO6] octahedra. TEM observations revealed that the obtained MnO2 materials had three-dimensional frameworks which consisted of homogeneous nanoparticles with sizes of ca. 5 nm. Nitrogen sorption analyses showed that these MnO2 nanoparticles exhibited a type IV isotherm, indicating a mesoporous character. Large surface areas up to 284 m2 g−1 were recorded. The electrochemical performances of the synthesized α-MnO2 nanoparticles as supercapacitor electrode materials were studied using cyclic voltammetry and galvanostatic charge−discharge cycling in a three-electrode system at a potential range from 0 to 1.0 V vs a saturated calomel electrode in 0.5 M sodium sulfate solution. The result showed that mesoporous MnO2 with three-dimensional frameworks exhibit a high capacitance up to ∼200 F g−1. Furthermore, a hybrid supercapacitor was assembled by using MnO2 mixed with a small amount of activated carbon as the positive electrode and activated carbon as the negative electrode in a 0.5 M Na2SO4 electrolyte. By balancing the mass of MnO2 and activated carbon, a practical cell voltage of 1.8 V could be obtained in aqueous medium with a capacitance of 23.1 F g−1. After 1200 cycles, the maximum energy density is 10.4 Wh kg−1 and power density is 14.7 kW kg−1. Thus, the obtained α-MnO2 nanoparticles are suitable for use as supercapacitor electrode materials.

A flake-like alumina with rough surface and small mesopores has been prepared by a hydrothermal method. Remarkably, such alumina was able to stabilize Au nanoparticles, predominantly ∼2.2 nm in size, even up to an annealing temperature of 700°C. The catalytic activity was tested using the CO oxidation model reaction where a complete conversion of 1% CO in air at 30°C was obtained.

Mesoporous LiFePO4/C composites containing 80 wt% of highly dispersed LiFePO4 nanoparticles (4–6 nm) were fabricated using bimodal mesoporous carbon (BMC) as continuous conductive networks. The unique pore structure of BMC not only promises good particle connectivity for LiFePO4, but also acts as a rigid nano-confinement support that controls the particle size. Furthermore, the capacities were investigated respectively based on the weight of LiFePO4 and the whole composite. When calculated based on the weight of the whole composite, it is 120 mAh·g−1 at 0.1 C of the high loading electrode and 42 mAh·g−1 at 10 C of the low loading electrode. The electrochemical performance shows that high LiFePO4 loading benefits large tap density and contributes to the energy storage at low rates, while the electrode with low content of LiFePO4 displays superior high rate performance, which can mainly be due to the small particle size, good dispersion and high utilization of the active material, thus leading to a fast ion and electron diffusion.LiFePO4/C composites with 80% of uniform and dispersive LiFePO4 nanoparticles were fabricated using bimodal mesoporous carbon (BMC) with large pore volume (1.99 cm3·g−1) as conductive framework.Download full-size image

Microalgae biomass is a sustainable source with the potential to produce a range of products. However, there is currently a lack of practical and functional processes to enable the high-efficiency utilization of the microalgae. We report here a hydrothermal process to maximize the utilizability of microalgae biomass. Specifically, our concept involves the simultaneous conversion of microalgae to (i) hydrophilic and stable carbon quantum dots and (ii) porous carbon. The synthesis is easily scalable and eco-friendly. The microalgae-derived carbon quantum dots possess a strong two-photon fluorescence property, have a low cytotoxicity and an efficient cellular uptake, and show potential for high contrast bioimaging. The microalgae-based porous carbons show excellent CO2 capture capacities of 6.9 and 4.2 mmol g−1 at 0 and 25 °C respectively, primarily due to the high micropore volume (0.59 cm3 g−1) and large specific surface area (1396 m2 g−1).

Porous carbon nanofibers (CNFs) are regarded as essential components of high-performance energy storage devices in the development of renewable and sustainable resources, due to their high surface areas, tunable structures, and good conductivities. Herein, we report new synthesis methods and applications of two types of porous carbon nanofibers, i.e., colloidal mesoporous carbon nanofibers as electrode materials for supercapacitors, and microporous carbon nanofibers as substrate media for lithium–sulfur (Li-S) batteries. These carbon nanofibers can be synthesized either by confined nanospace pyrolysis or conventional pyrolysis of their polymeric precursors. The supercapacitor electrodes which are fabricated via a simple dipping and rinsing approach exhibit a reversible specific capacitance of 206 F g−1 at the current density of 5 A g−1 in 6.0 mol L−1 aqueous KOH electrolyte. Meanwhile, the Li-S batteries composed of microporous carbon nanofiber-encapsulated sulfur structures exhibit unprecedented electrochemical performance with high specific capacity and good cycling stability, i.e., 950 mA h g−1 after 50 cycles of charge–discharge. The excellent electrochemical performance of CNFs is attributed to their high-quality fiber morphology, controlled porous structure, large surface area, and good electrical conductivity. The results show that the carbon nanofibers represent an alternative promising candidate for an efficient electrode material for energy storage and conversion.

Lithium ion capacitors (LICs), bridging supercapacitors and lithium ion batteries (LIBs), have recently drawn considerable attention. In this report, a non-aqueous LIC was fabricated using tubular mesoporous carbon as a cathode and a SnO2–C hybrid (ultrafine SnO2 encapsulated in the tubular mesoporous carbon) as an anode. Such a LIC can achieve a maximum energy density of 110 W h kg−1 and a maximum power density of 2960 W kg−1. The capacitance retention is fairly stable and retains 80% of its initial value after 2000 cycles. This unique performance arises because of the highly conductive tubular mesoporous carbon matrix and fast charge/ion diffusion in the SnO2–C hybrid anode. It is shown that the SnO2 loading in the anode has a great influence on the stability of the SnO2 nano-structure and the kinetics of lithium ion transfer. Electrochemical impedance spectroscopy (EIS) was used to evaluate the charge transfer resistance and the ionic diffusion resistance before and after long-term cycling. The diffusion coefficient was also calculated to verify the good rate and cycling capability.