Developing high-performance bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is of vital importance in energy storage and conversion systems. Herein, we demonstrate a facile hydrothermal synthesis of highly dispersed Co3O4 nanoparticles (NPs) anchored on cattle-bone-derived nitrogen-doped hierarchically porous carbon (NHPC) networks as an efficient ORR/OER bifunctional electrocatalyst. The as-prepared Co3O4/NHPC exhibits a remarkable catalytic activity toward both ORR (outperforming the commercial Pt/C) and OER (comparable with the commercial RuO2 catalyst) in alkaline electrolyte. The superior bifunctional catalytic activity can be ascribed to the large specific surface area (1070 m2 g–1), the well-defined hierarchically porous structure, and the high content of nitrogen doping (4.93 wt %), which synergistically contribute to the homogeneous dispersion of Co3O4 NPs and the enhanced mass transport capability. Moreover, the primary Zn–air battery using the Co3O4/NHPC cathode demonstrates a superior performance with an open-circuit potential of 1.39 V, a specific capacity of 795 mA h gZn–1 (at 2 mA cm–2), and a peak power density of 80 mW cm–2. This work delivers a new insight into the design and synthesis of high-performance bifunctional nonprecious metal electrocatalysts for Zn–air battery and other electrochemical devices.Keywords: cattle bone; Co3O4 nanoparticles; electrocatalysts; nitrogen-doped hierarchically porous carbon; oxygen reduction and evolution reactions;

Lattice contraction has been regarded as an important factor influencing oxygen reduction reaction (ORR) activity of Pt-based alloys. However, the relationship between quantitative lattice contraction and ORR activity has rarely been reported. Herein, using Pt–Cu alloy nanoparticles (NPs) with similar particle sizes but different compositions as examples, we investigated the relationship between quantitative lattice contraction and ORR activity by defining the shrinking percentage of Pt–Pt bond distance as lattice contraction percentage. The results show that the ORR activities of Pt–Cu alloy NPs exhibit a well-defined volcano-type dependent relationship toward the lattice contraction percentage. The dependent correlation can be explained by the Sabatier principle. This study not only proposes a valid descriptor to bridge the activity and atomic composition but also provides a reference for understanding the composition–structure–activity relationship of Pt-based alloys.Keywords: dependent relationship; lattice contraction percentage; oxygen reduction reaction; Pt-based alloy; X-ray absorption spectroscopy;

To replace high-cost platinum group metal (PGM) electrocatalysts for oxygen reduction reaction (ORR) that is the crucial cathode reaction in fuel cell technology and metal–air battery, the development of low-cost and high-efficiency non-PGM catalysts for ORR has attracted much attention during the past decades. As one of the promising candidates, N-doped carbon is highly desirable for its strong designability and outstanding catalytic activity and stability. In this work, a facile and rational strategy is demonstrated for preparation of N,P-codoped mesoporous carbon (N,P-MC) for ORR by the direct pyrolysis treatment of polypyrrole with phytic acid as P-dopant and polystyrene sphere as template. The resultant N,P-MC exhibits a mesoporous structure with the optimized ORR active sites originating from the N,P-codoping. Owing to these features, N,P-MC exhibits excellent ORR activity, remarkable electrochemical stability, and superior methanol tolerance, comparable or even better than that of commercial Pt/C catalyst. The origin of enhanced ORR performance can be attributed to both the increased active sites and the mesoporous structure, which is expected to guide the future preparation of more capable carbon-based electrocatalysts for oxygen reduction and other electrocatalytic application.Keywords: carbon-based materials; electrocatalysts; mesoporous carbon; metal-free; nitrogen and phosphorus codoped; oxygen reduction reaction;

Rational design of porous structure is an effective way to fabricate the nonprecious metal electrocatalysts (NPMCs) toward oxygen reduction reaction (ORR) with high activity comparable or even superior to Pt-based electrocatalysts. Herein, we demonstrate a facile synthetic route to fabricate cobalt and nitrogen codoped carbon nanopolyhedra with hierarchically porous structure (Co,N-HCNP) by one-step carbonization of core–shell structured ZIF-8@ZIF-67 crystals. The resultant Co,N-HCNP electrocatalyst possesses a unique hierarchically micro/mesoporous structure with internal micropores and external mesopores, of which sufficient exposure and accessibility of ORR active sites can be achieved due to the large specific surface area and efficient transport pathway. More importantly, the existence of ZIF-8 core in the core–shell structured ZIF-8@ZIF-67 can promote the homogeneous pyrolysis of ZIF-67 shell, leading to a uniform distribution of Co–Nx active sites for Co,N-HCNP. As a result, the well-designed Co,N-HCNP electrocatalyst exhibits remarkable ORR activity with a high onset potential comparable to the commercial Pt/C, a half-wave potential of 0.855 V (9 mV more positive than that of Pt/C), and a kinetic current density of 63.84 mA cm–2 at 0.8 V (2.3-fold enhancement compared with that of Pt/C) in alkaline electrolyte. Furthermore, the Co,N-HCNP electrocatalyst also presents outstanding electrochemical durability and methanol tolerance in comparison with Pt/C. The unique hierarchically porous structure of Co,N-HCNP achieved in this work provides a new insight into the design and synthesis of nanoarchitecture with targeted pore structure and opens a new avenue for the synthesis of highly efficient NPMCs for ORR.Keywords: cobalt and nitrogen codoped carbon nanopolyhedra; core−shell metal−organic framework materials; electrocatalysts; hierarchically porous structure; one-step carbonization; oxygen reduction reaction;

Understanding exact electronic configurations of carbon atoms bonded by nitrogen (N) functionalities at atomic-level may literally open a door to advance metal-free carbon materials as efficient catalysts for the oxygen reduction reaction (ORR). In this paper, a set of well-defined carbon nanotubes with controlled doping of various N species, such as pyrrolic, pyridinic and graphitic N, have been achieved by in-situ pyrolysis of polyaniline (PANI) nanotubes at different temperatures. Among these synthesized samples, the carbon nanotubes fabricated at 700 °C exhibit the highest electro-catalytic ORR activity, long-standing stability and good tolerance against methanol in alkaline medium. The improved activity is mainly attributed to the high nitrogen level of the active pyridinic and graphitic N. But, the pyridinic N possesses higher activity than the graphitic N because of their different sp2 electronic structures. Pyridinic N, after bonding with two carbon(C) atoms, has two distorting N−C orbitals and one dangling orbital occupied by a lone electron pairs which are exposed, as the N sits at the edge of the carbon planes. Such unique electronic configuration makes the nitrogen and surrounding carbon atoms, bonded in the CN bonds, can serve host of active sites or work as active sites for the ORR.

The development of highly efficient metal-free electrocatalysts towards the oxygen reduction reaction (ORR) is of vital importance for the large-scale application of fuel cell technologies. Herein, we demonstrate a facile and effective strategy for the controllable synthesis of nitrogen and phosphorus co-doped hierarchically porous carbon (N,P-HPC) electrocatalysts by pyrolyzing phytic acid (PA) and dicyandiamide (DCDA) with nitrogen-doped hierarchically porous carbon (NHPC) derived from cattle bones. The results show that optimal N and P co-doping plays an important role in enhancing the ORR catalytic activity of carbon-based electrocatalysts. The optimized N,P-HPC with a high content of N (3.2 at%) and P (4.0 at%) exhibits remarkable ORR activity with an onset potential of 0.924 V (comparable to commercial Pt/C), a half-wave potential of 0.853 V (12 mV higher than that of Pt/C) and a kinetic current density of 38.2 mA cm−2 at 0.8 V (1.9-times that of Pt/C) in alkaline electrolyte. Furthermore, the N,P-HPC electrocatalyst also demonstrates superior electrochemical stability and methanol tolerance in comparison with Pt/C. The excellent ORR performance of N,P-HPC can be attributed to the increased number of active sites, the favorable three-dimensional hierarchically porous structure and the large specific surface area (1516 m2 g−1). This attractive strategy opens a new avenue for the synthesis of highly efficient metal-free electrocatalysts for the ORR.

AbstractThe achievement of crystal-lattice tuning along low Miller index planes to decrease the bandgap of spinel transition-metal oxides may be an effective way to enhance their electrocatalytic activity for the oxygen reduction reaction (ORR). Herein, we have prepared spherical Co3O4 nanoparticles with a preferred orientation along the (111) plane by direct nucleation and growth of the oxide on graphitized carbon black (GCB). The formation of the preferred (111) oxide is attributed to a unique chemical interaction at the interface between Co3O4 and carbon, which results in covalent C-O-Co bonds in the hybrid. Electrocatalysis experiments in an alkaline environment revealed that the electrocatalytic activity for ORR on the preferred (111) oxide increased as a function of the degree of crystal-lattice orientation, which implies a closely intrinsic correlation between the predominant (111) plane and the catalytic activity. Because Co2+ cations are enriched in this plane, they possess a narrow bandgap and unfilled conduction bands at low energy with respect to Co3+ ions in the preferred (111) Co3O4, which can contribute to the absorption and activation of active oxygen and lead to improved ORR activity

The development of pure-phase semi-conducting buffering materials as the substitution of conventional cadmium sulfide (CdS) is extremely important for the large-scale application of solar cells. Herein, we demonstrated a facile approach to deposit pure-phase indium sulfide (In2S3) thin films on the indium tin oxide (ITO) substrates by sulfurizing the co-electrodeposited In2S3 films. The effect of sulfurization temperatures (200–550 °C) on the surface morphologies, crystal structures, optical and electrical properties of In2S3 films was investigated. The results showed that the highly-oriented pure β-In2S3 thin films were obtained as the sulfurization temperature exceeded 250 °C. The obtained β-In2S3 films possessed a relatively ideal S/In atomic ratio and a continuous and densely packed surface feature. The optical band gaps of the β-In2S3 films have been determined in the range of 1.93 ± 0.01–2.06 ± 0.01 eV, which can be controlled by adjusting the sulfurization temperature. The electrical properties tests demonstrated that the pure β-In2S3 films obtained by sulfurizing at 550 °C exhibited the characteristic n-type semiconductors with a low electrical resistivity of 38.8 Ω cm, a carrier concentration of 3.8 × 1015 cm−3 and a carrier mobility of 42.3 cm2 V−1 s−1. This facile synthetic route is promising for the preparation of pure-phase In2S3 films, and then gives the guidance for future design and synthesis of other metal sulfide films for high-performance solar cells.

•Porous carbons were prepared by direct carbonization of cattle bones.•Mesopore-dominant carbon with a narrow PSD (~4 nm) was obtained at 1100 °C.•The porous carbon possessed high defect density and good electrical conductivity.•The porous carbon showed high performance as electrodes for LIBs and SCs.Porous carbons with high specific surface area and high defect density have been prepared through direct carbonization of cattle bones without any additional activators and templates. Benefiting from self-activation induced by hydroxyapatites within the cattle bones, the high-defect porous carbons obtained at 1100 °C (PC-1100) possess the high specific surface area (2096 m2 g−1), largest mesopore volume (1.829 cm3 g−1), a narrow mesopore size distribution centered at approximately 4.0 nm and good electrical conductivity (5141 S m−1). Due to the synergistic effect of the defects and pores, PC-1100 as the anode for Li-ion battery exhibits a high reversible capacity of 1488 mA h g−1 after 250 cycles at 1 A g−1 and 661 mA h g−1 after 1500 cycles at 10 A g−1. Even at 30 A g−1, PC-1100 can still deliver a high reversible capacity of 281 mA h g−1, showing superior lithium storage capability. Moreover, the symmetric supercapacitor based on the PC-1100 in neat EMIM-BF4 electrolyte delivers a high energy density of 109.9 W h kg−1 at a power density of 4.4 kW kg−1, and maintains an energy density of 65.0 W h kg−1 even at an ultrahigh power density of 81.5 kW kg−1, as well as a superior cycling performance (96.4% of the capacitance retention after 5000 cycles).High-defect mesopore-dominant porous carbons with large specific surface area have been prepared via direct carbonization of cattle bones, and showed outstanding rate capability and superior cycling performance as electrode materials for Li-ion batteries and supercapacitors.Download high-res image (263KB)Download full-size image

•Activated carbons are prepared by carbonization and KOH-activation of available biomass tremella.•The activated carbons possess ultrahigh specific surface area (3760 m2 g−1).•High specific capacitance (71 F g−1) detected in two-electrode systems.•High energy density: 65.6 W h kg−1 at the power density of 743 W kg−1.Activated carbons derived from sustainable biomass have attracted widespread attention as electrode materials for supercapacitors due to their economic value, tunable physical/chemical properties and environmental concern. Tremella, renewable and abundant biomass, has been explored as precursor to prepare hierarchical activated carbons by means of carbonization and KOH activation. The obtained sample possesses an ultrahigh BET specific surface area of 3760 m2 g−1 and very high mesopore volume ratio of 72%. So, the sample shows a superior specific capacitance 71 F g−1 at 1 A g−1; extraordinary rate performance with a capacitance of 53.5 F g−1 at 30 A g−1; outstanding cycle stability with 99% capacitance retention after 10,000 galvanostatic charge-discharge cycles at 5 A g−1 in a symmetric two-electrode supercapacitor with 6 M KOH solution as electrolyte. The assembled supercapacitor shows a superior energy density of 65.6 W h kg−1 in ionic liquid electrolyte system and 28 W h kg−1 is still maintained even at an ultrahigh power density 19,700 W kg−1.Download high-res image (303KB)Download full-size image

Nitrogen and oxygen co-doped hierarchical porous carbon (N,O-HPC) networks has been synthesized using cattle bones as precursors via pre-carbonization and carbonization combined with KOH activation. The effects of carbonization and activation temperature on the physiochemical and electrochemical performances of the N, O-HPCs were systematically studied. The N,O-HPC obtained at 850 °C (referred to as N,O-HPC-850) possesses a mesopore-dominant hierarchical porous network with a large specific surface area (2520 m2 g−1), a relatively high content of N (1.56%) and O (10.2%) and a good electrical conductivity (421.9 S m−1). As it is used as supercapacitor electrode material, N,O-HPC-850 exhibits a large specific capacity (444 F g−1 at a scan rate of 5 mV s−1 and 435 F g−1 at a current density of 0.1 A g−1, respectively) and good rate performance (252 F g−1 at a scan rate of 500 mV s−1 and 309 F g−1 at a current density of 20 A g−1, respectively) in 6 M KOH solution. Moreover, the assembled symmetric supercapacitor based on N,O-HPC-850 electrode delivers the energy density of 30.3 and 9.7 Wh kg−1 at the power density of 0.341 and 43.8 kW kg−1, respectively, and exhibits a good cycling stability with a capacitance retention of 97.5% after 20000 cycles in 1 M Na2SO4 solution.In-situ nitrogen and oxygen co-doped carbon networks with a mesopore-dominant hierarchical porosity were prepared from cattle bone and exhibited superior performance as electrode material for high energy and power density supercapacitor.Download high-res image (253KB)Download full-size image

Developing cost-effective porous carbon adsorbents with large adsorption capacity and superior recyclability over a wide pH range is critical for the efficient removal of toxic phenol from industrial wastewater. Herein, we demonstrate a facile and effective strategy for synthesis of a nitrogen-doped hierarchically porous carbon (NHPC) network derived from cattle bone as a highly efficient adsorbent for the removal of phenol from wastewater. The as-prepared NHPC possessed a high specific surface area (2687 m2 g−1), a unique three-dimensional (3D) hierarchical porous structure and high content of nitrogen doping (2.31 at%). As a result, NHPC exhibited a remarkable adsorption performance towards phenol with a significantly large adsorption capacity of 431 mg g−1 (3.56-fold that of the commercial adsorbent (Norit CGP)), a high adsorption rate of 4.57 g mg−1 h−1 (17-fold that of Norit CGP) and an outstanding recyclability with 98% of the initial adsorption capacity maintained after 5 cycles (75% for Norit CGP). More importantly, the NHPC held almost the identical maximum adsorption capacity over a wide pH range of 2–9, showing a good applicability in the removal of phenol from a variety of wastewaters. Thermodynamic and kinetics analyses indicated that the adsorption process was spontaneous and exothermic, which fitted well the Langmuir isotherm model and pseudo-second-order model. This biomass-based porous carbon with well-defined hierarchical porosity can be applied as a promising adsorbent for efficient removal of phenol from wastewater.

A hierarchical structure composed of vertically aligned ultrathin two dimensional (2D) MoS2/WS2 nanosheets is fabricated through a facile one-pot hydrothermal reaction. Scanning electron microscope (SEM), transmission electron microscope (TEM) and photoluminescence (PL) indicate that the MoS2/WS2 hybrid shows ultrathin nanoflakes with a thickness of 2–10 nm, and the as prepared heterostructure markedly enhances the separation of electro–hole pairs. Benefiting from the integrated W-doped MoS2, the vertically aligned nanostructure exhibits a moderate degree of disorder and increased active surface area. Electrochemical measurements (cyclic voltammetry (CV), linear sweep voltammetry (LSC) and electrochemical impedance spectroscope (EIS) under light illumination or in dark) indicated that the MoS2/WS2 hybrid (especially the hybrid with Mo : W of 1/1) exhibits much better photo-and electrochemical performance than its counterpart of pure MoS2 or WS2, which made it a promising photocathode for electrocatalytic hydrogen evolution reaction (HER) by photo-assistance.

The development of high-efficiency and low-cost electrocatalysts for the oxygen reduction reaction (ORR) is critical to allow large-scale application of fuel cell technologies. As promising candidates for the replacement of platinum-based electrocatalysts for the ORR, iron–nitrogen doped carbon (Fe–N–C) materials are appealing due to their outstanding ORR performances. To meet the requirements for commercial applications in fuel cells, the electrocatalytic activity and durability of the Fe–N–C electrocatalysts need to be further improved over a wide pH range. Herein, we report a facile and rational synthesis strategy for the preparation of a kind of Fe–N–C catalyst by low-temperature thermal treatment of iron phthalocyanine (FePc)-adsorbed nitrogen-doped hierarchically porous carbon (NHPC) derived from porphyra. The as-prepared electrocatalysts exhibit a superior ORR performance, even better than that of state-of-the-art Pt/C catalysts, in alkaline electrolyte (E1/2 = 0.88 V, n = 4.0, Tafel slope = 55 mV dec−1 and ca. 6 mV negative shift of E1/2, after 3000 cycles). This work develops a low-cost, but rational and efficient, methodology for the synthesis of high-performance Fe–N–C electrocatalysts for the ORR, and also provides an effective way to design and utilize hierarchically porous carbon for other electrocatalysts.

Lithium–sulfur (Li–S) batteries with high energy density are considered as promising for rechargeable energy storage. However, the shuttle effect hinders their practical application. Here, novel nitrogen-doped micro-/mesoporous carbon (N-MIMEC), derived from crab shells, was fabricated via a sustainable and cost-effective route. A modified separator coated with an N-MIMEC layer for Li–S batteries exhibits many advantages: (1) the micro-/mesopores provide enough surface area for sulfide adsorption, and accommodate the volume change; (2) the nitrogen in N-MIMEC enhances polysulfide adsorption and increases the electronic conductivity of the carbon framework; and (3) the conductive layer acts as an upper current collector, increasing the electrical conductivity. An enhanced Li–S battery with an N-MIMEC-coated separator was constructed, with an initial capacity of 1301 mA h g−1 and a high reversible capacity of 971.3 mA h g−1 after 100 cycles at 0.1C. Also, upon further increasing the sulfur loading from 63 wt% to 77 wt%, the corresponding Li–S batteries exhibit a high reversible capacity of 578 mA h g−1 after 500 cycles at 1C, with a decay rate of about 0.029% per cycle. Considering the green and sustainable source material, simple preparation and good electrochemical performance, the N-MIMEC-coated separator is promising for Li–S battery applications.

Porous carbons were obtained by chemical activation of hydrochar, prepared by hydrothermal carbonization using enzymatic hydrolysis lignin originated from the butanol fermentation of corn straw. The intermediate hydrochar was activated using different KOH/hydrochar weight ratios to evaluate the influence of these ratios on its electrochemical properties. The materials thus prepared exhibited high specific surface areas in the range 1290–1660 m2 g−1 mainly attributed to the three-dimensional hierarchical texture made up of abundant micropores, small mesopores and macropores, and high electrical conductivity in the 4.0–5.4 S cm−1 range. Consequently, the samples show high specific capacitance, superior rate performance and outstanding durability in three-electrode and two-electrode systems in 6 M KOH. The as-assembled symmetric supercapacitor in an ionic liquid electrolyte system exhibits a superior energy density of 46.8 W h kg−1 and a value of 22.9 W h kg−1 is maintained even at an ultrahigh power density of 25 400 W kg−1. These materials possessing excellent structural features are an ideal candidate for high performance supercapacitors.

The development of low-cost and structure-controlled precursors has become one of the crucial issues in the improvement of pyrolyzed carbonaceous materials for the oxygen reduction reaction. In this work, a facile and interchangeable cross-linking process has been developed to synthesize polyphthalocyanines with different cross-linking degrees. After the pyrolysis treatment, the cross-linked polyphthalocyanine generated N-doped carbon-encased metal nanoparticle materials. During the pyrolysis treatment, the cross-linked structure of polyphthalocyanine can effectively restrain the aggregation of the metal core and significantly increase the amount of active N species in the pyrolyzed carbon shell. Different from the pyrolyzed pure phthalocyanine, the pyrolyzed cross-linked polyphthalocyanine electrocatalyst shows excellent electroactivity via a 4-electron pathway along with remarkable stability and good methanol tolerance. In addition, the unraveling of the cross-linking degree effect also provides guidance for future design of more efficient non-precious metal catalysts for oxygen reduction and other electrochemical applications.

Exploring high-performance iron and nitrogen co-doped carbon (Fe–N–C) electrocatalysts with desirable active sites toward the oxygen reduction reaction (ORR) is extremely important for future applications of fuel cells and metal–air batteries. Herein, we demonstrate a facile and effective strategy for the synthesis of high-performance Fe–N–C electrocatalysts by pyrolyzing a physical mixture of conventional carbon black (Black Pearls 2000, BP2000) and Hemin followed by a post-treatment procedure including acid-washing and heat-treatment. The resultant Fe–N–C electrocatalysts possessed numerous out-of-plane FeII–N4 moieties (D1 sites) uniformly distributed in the porous carbon matrix, and a well-defined micro/mesoporous structure that is expected to significantly improve the ORR activity in both alkaline and acidic electrolytes. In an alkaline electrolyte, the Fe–N–C electrocatalyst exhibited a remarkable ORR activity with a high onset potential of 0.942 V and a half-wave potential of 0.848 V, which were 9 mV and 12 mV more positive than those of the commercial Pt/C, respectively, while its half-wave potential was 0.73 V, only 60 mV less than that of Pt/C in an acidic electrolyte. Furthermore, the Fe–N–C electrocatalyst also demonstrated better electrochemical durability and methanol tolerance in comparison with Pt/C in both alkaline and acidic electrolytes. This work opens a new avenue for the rational design and synthesis of highly active and durable TM–N–C electrocatalysts towards ORR.

•Hierarchically porous carbon nanosheets were prepared via hydroxyapatite/KOH-synergetic pyrolysis of cattle bone.•The obtained carbon material possessed rich heteroatoms and high defect density.•The resultant carbon anode for Na-ion storage exhibited obvious capacitive storage behavior.•Na-ion storage via reversible formation and decomposition of metallic Na was found.Tremella-like hierarchically porous carbon nanosheets (HPCNS) with a carbon interlayer distance of 0.41 nm have been simply prepared via hydroxyapatite/KOH-synergetic pyrolysis of low-cost cattle bone at 550 °C. The HPCNS possesses high surface heteroatom content (17.1 at% oxygen and 6.4 at% nitrogen) due to the low-temperature thermal treatment. The HPCNS that is tested in half-cell against metallic Na can deliver a high reversible capacity of 198.5 mAh g−1 after 1000 cycles at the current density of 0.7 A g−1, and maintains a capacity of 150.8 mAh g−1 even after 10,000 cycles at the current density of 7 A g−1. The further characterization shows that the superior rate performance and the unparalleled long-term cycling stability are attributed to the capacitive storage features of HPCNS and additional Na-ion storage via reversible formation and decomposition of metallic Na in HPCNS. Consequently, the Na-ion capacitor based on the HPCNS anode delivers integrated high energy and power densities (105.2 W h kg−1 at 0.07 kW kg−1, 32.5 W h kg−1 at an ultrahigh power density of 60.4 kW kg−1), as well as good long-term cycling stability (85.8% of the capacitance retention after 4000 cycles at the current density of 3.5 A g−1).N,O-codoped hierarchically porous carbon nanosheets were prepared and showed superior performance as anodes for Na-ion storage.Download high-res image (279KB)Download full-size image

•The modification approach for graphene is easier than typical oxidation methods.•The prepared Pt-Co/CA-G catalyst is proton conductive.•The Pt-Co/CA-G catalyst exhibits superior ORR activity and stability.•The enhanced proton transfer is responsible for excellent ORR performance.Designing highly efficient electro-catalysts for the oxygen reduction reaction (ORR) has been regarded as a demanding task in the development of renewable energy sources. However, little attention has been paid on improving Pt-based catalysts by promoting proton transfer from the electrolyte solutions to the catalyst layer at the cathode. Herein, we design proton conductive Pt-Co alloy nanoparticles anchoring on citric acid functionalized graphene (Pt-Co/CA-G) catalysts for efficient ORR. The facile modification approach for graphene can introduce oxygenated functional groups on the graphene surface to promote proton transfer as well as keeping the high electron conductivity without destroying the graphene original structure. The electrochemical results show that the Pt-Co/CA-G catalyst exhibits more excellent ORR activity and stability than the commercial Pt/C catalyst, which can be attributed to its improved proton transfer ability. The fast proton transfer comes from the hydrogen-bonding networks formed by the interaction between the oxygenated functional groups and water molecules. This work provides not only a novel and simple approach to modify graphene but also an effective strategy to improve Pt-based catalysts for the ORR.Download high-res image (396KB)Download full-size image

Here we propose amorphous CuPt alloy hollow nanotubes as efficient catalysts for the methanol oxidation reaction (MOR) prepared by Na2S2O3-assisted galvanic replacement reaction. The formation mechanism can be explained by the nanoscale Kirkendall-effect-induced hollowing process of the galvanic replacement reaction. The electrochemical tests suggest that the amorphous CuPt alloy exhibits better MOR activity and stability than the crystalline CuPt and commercial Pt/C catalysts, which can be ascribed to the enhanced CO tolerance ability of amorphous alloy. XPS measurements demonstrate that the enhanced anti-CO poison characteristic of amorphous CuPt alloy originates from the strong interaction between Pt and Cu atoms as a result of a unique crystallization state. This research not only provides a facile approach to synthesize amorphous alloy but also opens up an interesting way for amorphous Pt-based alloy to apply to the MOR.Keywords: amorphous alloy; bifunctional mechanism; CO tolerance; galvanic replacement reaction; methanol oxidation reaction

Through in-situ nucleation and growth of perovskite-type LaMnO3 nanocrystals on a modified carbon black, a set of LaMnO3/C hybrids with different LaMnO3 loadings (40 wt%, 80 wt%, 100 wt% and 140 wt%, relative to carbon) were facilely fabricated via hydrolysis and precipitation in an ethanol solution, followed by calcination at 700 °C. The obtained LaMnO3 nanoparticles feature perovskite-type structure and are dispersed uniformly on the carbon surface. The electrochemical experiments in 1 mol L−1 NaOH solution illustrate that the hybrid catalyst (100 wt% of LaMnO3) exhibits the highest ORR electrocatalytic activity and the lowest hydrogen peroxide yield. X-ray photoelectron spectroscopy (XPS) reveals that the catalyst with the best catalytic activity has the highest content of covalent COMn bonds formed at the interface between the LaMnO3 and carbon, which implies a close correlation between the loading and the covalent bond content within the hybrids. The synergy between the oxide and carbon, raised by the formed COMn bonds in their hybrid, is responsible for the remarkably improved ORR activity. This information is important to achieve synergy between non-noble metal oxides and carbon in their composites as efficient and economical ORR catalysts.

The Pt-Co-P ultrafine nanoparticles supported on carbon nanotubes (Pt-Co-P/CNT) have been successfully synthesized by a hypophosphite-assisted one-pot reduction strategy and used as the electrocatalysts for methanol oxidation reaction (MOR). Transmission electron microscope observation clearly indicates that the Pt-Co-P nanoparticles are highly dispersed onto the surface of CNT with a narrow particle size distribution. The average diameter of the Pt-Co-P nanoparticles with the different P contents can be controlled from 1.5 nm to 2.7 nm, probably by the assistance of in-situ phosphate capping agent for nanoparticle growth, which generated from simultaneous oxidation of sodium hypophosphite. The electrochemical measurement data indicate that the Pt-Co-P/CNT with the average particle diameter of 1.5 nm possesses superior electrocatalytic activity, outstanding tolerance against CO-like intermediates and excellent electrochemical stability, which is better than those of Pt-Co/CNT and commercial Pt/C. The improved electrochemical performance of Pt-Co-P/CNT can be attributed to the high electrochemical active surface area and rapid removal of CO-like intermediates arising from the ultrafine features of Pt-Co-P nanoparticles as well as the strong interaction among Pt, Co, and P. Therefore, the Pt-Co-P/CNT electrocatalysts prepared by a hypophosphite-assisted one-pot reduction strategy can be considered as a promising candidate for high performance MOR electrocatalyst.

Investigating the synergy in hybrids between rare earth (La, Ce, Y) oxides and carbon may be an effective way to develop new efficient and cheap catalysts for catalyzing the oxygen reduction reaction (ORR). In this work, a set of La2O3/C hybrids with different La2O3 loadings were prepared by chemical precipitation in alkaline solution, followed by calcination treatment. The prepared La2O3 nanoparticles with hexagonal structure covered uniformly on the carbon surface. X-ray photoelectron spectroscopy (XPS) indicated different contents of covalent C–O–La bonds at the interface between the La2O3 and carbon in these hybrids. The electrochemical experiments in alkaline solution show that the catalyst with 80 wt% of La2O3 exhibits the highest electrochemical activity in catalyzing ORR and the lowest production of hydrogen peroxide among the synthesized hybrids. The remarkably enhanced ORR activity is attributed to the maximum content of the C–O–La bonds formed in the hybrid. Interestingly, the above C–O–La covalent bonds can promote the electron transfer from the supported carbon (π electron) to the La2O3 phase, and the transferred electron can fill the unoccupied eg orbital splitted by the La 5d orbital of La2O3, which should be responsible for the improved ORR performance.

In this work, a facile approach is reported to prepare a series of transition-metal phthalocyanines (TMPc) supported on graphitized carbon black (TMPc/GCB, TM: Fe, Co, Ni and Cu) as oxygen reduction reaction (ORR) electrocatalysts, via π–π interaction self-assembly. Through transmission electron microscopy (TEM), Raman spectroscopy and UV spectroscopy, it was found that TMPc was coated on graphitized carbon black with non-aggregated morphology. The catalytic activity, both in terms of the onset potential (0.98 V to 0.76 V) and half-wave potential (0.90 V to 0.55 V) follows the trend of FePc/GCB > CoPc/GCB > CuPc/GCB > NiPc/GCB. However, the catalytic durability follows the decreasing order of NiPc/GCB > CoPc/GCB > FePc/GCB > CuPc/GCB. To better elucidate the ORR catalytic mechanism for TMPc/GCB, we employed density functional theory (DFT) calculations and drew the following conclusions: (i) the –O2 adsorption is the major step to determine the ORR catalytic activity; (ii) the way O2 is adsorbed on TMPc is the key point affecting the Tafel slope; (iii) the –H2O2 desorption determines the transfer electron number; and (iv) the –OH desorption and the central metal atom removal leads to the damage affecting catalytic durability.

Palladium (Pd) nanoparticles encapsulated by the vanadium–phosphorus–oxygen (V–P–O) compound were synthesized and decorated on carbon nanotubes (Pd@V–P–O/CNT) through an oleylamine-mediated method stabilized with trioctylphosphine. Electrochemical measurements indicated that the Pd@V–P–O/CNT exhibited comparative catalytic activity towards the oxygen reduction reaction (ORR) compared with commercial Pd/C and Pd nanoparticles supported on carbon nanotubes (Pd/CNT), but with a significantly enhanced methanol tolerance. The vanadium/phosphorus mixed oxide shell on the Pd nanoparticles could effectively block the active Pd sites from methanol oxidation without obviously decreasing the catalytic activity towards the ORR process, implying that Pd@V–P–O/CNT might be a promising alternative to the Pt electrocatalyst applied in direct methanol fuel cells.

The ability to precisely control the nanoscale phase structure of bimetallic catalysts is required to achieve a synergistic effect between two metals for the oxygen reduction reaction (ORR). In this work, we synthesized Pt–Ag bimetallic nanoparticles (NPs) with Ag@Pt core–shell, highly alloyed solid and hollow nanostructures respectively, via a galvanic replacement reaction by modifying H2PtCl6 concentration in an aqueous solution containing homemade Ag NPs as the sacrificial templates. The nanophase and corresponding electronic structures of the synthesized Pt–Ag NPs were characterized by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The formation of these Pt–Ag NPs with different nanophase structures is closely ascribed to a defect-induced Kirkendall effect that involves the accelerated interdiffusion of Ag and Pt atoms, triggered by the high density of defects along the Ag NP surface generated by the galvanic replacement reaction. The nanophase structure-dependent electrocatalytic activity of three Pt–Ag bimetallic NPs was determined in 0.5 M H2SO4 solution by using a rotating disk electrode (RDE). The results showed that the core–shell and hollow alloy NPs exhibit excellent ORR activity in acidic solution, which is remarkably higher than that of the commercial Pt/C (E-TEK). The physical origin of the enhancement in the ORR activity can be explained by a mutual ligand effect, raised by the substantial electronic transfer between Pt and Ag at the atomic level, which results from the downshift of the d-band center for Pt and the increased number of the unpaired electrons for Ag in these bimetallic catalysts. Thus two factors achieve a synergistic effect that dominates the remarkably improved electrocatalytic activity for the ORR.

Soybeans are extensively cultivated worldwide as human food. However, large quantities of soybean roots (SRs), which possess an abundant three-dimensional (3D) structure, remain unused and produce enormous pressure on the environment. Here, 3D hierarchical porous carbon was prepared by the facile carbonization of SRs followed by chemical activation. The as-prepared material, possessing large specific surface area (2143 m2 g–1), good electrical conductivity, and unique 3D hierarchical porosity, shows outstanding electrochemical performance as an electrode material for supercapacitors, such as a high capacitance (276 F g–1 at 0.5 A g–1), superior cycle stability (98% capacitance retention after 10,000 cycles at 5 A g–1), and good rate capability in a symmetric two-electrode supercapacitor in 6 M KOH. Furthermore, the maximum energy density of as-assembled symmetric supercapacitor can reach 100.5 Wh kg–1 in neat EMIM BF4. Moreover, a value of 40.7 Wh kg–1 is maintained at ultrahigh power density (63000 W kg–1). These results show that the as-assembled supercapacitor can simultaneously deliver superior energy and power density.Keywords: energy storage; hierarchical porous carbon; ionic liquid; soybean root; supercapacitor;

The present study demonstrates the effect on photovoltaic performance of regioregular poly (3-hexylthiophene)(rr-P3HT) grafted oxide graphene (GO) on in situ doping of cadmium sulfide (CdS) quantum dots (QDs) (GO-rr-P3HT-CdS). Firstly, CH2OH-terminated rr-P3HT of different molecular weights (MW) and distributions synthesized by Grignard metathesis (GRIM) method was grafted onto carboxylic groups of GO via esterification reaction. Then, the GO-rr-P3HT-CdS was prepared with an oleylamine solution composed of 1 mmol of cadmium and 1 mmol high pure sulfur in the presence of GO-rr-P3HT. The covalent linkage and the strong electronic interaction between the rr-P3HT and graphene moieties in GO-rr-P3HT were confirmed by spectroscopic analyses (XPS and FTIR). The photovoltaic properties of as prepared nanocomposites are evaluated by UV–Vis spectroscopy, photoluminescence, and electrochemical measurements, and are found to be strongly affected by MW, which influences the behavior of the bulk heterojunction organic solar cells based on this material. It is found that the optical and electrochemical properties of the resultant GO-rr-P3HT-CdS nanocomposite are relatively better than that of conventional composite, in which the pristine graphene, CdS, and rr-P3HT (or GO-rr-P3HT) are physically mixed together. The significant PL quenching is attributed to additional decaying paths of the excited electrons through the CdS. Bulk heterojunction photovoltaic devices with a thin film of GO-rr-P3HT-CdS containing higher molecular weights of rr-P3HT show an increase in the power conversion efficiency by about three times with respect to their counterparts based on GO-rr-P3HT/CdS and GO/rr-P3HT/CdS due to improvement in contact between GO-rr-P3HT and CdS and enhancement in the device parameters like fill factor and open-circuit voltage (VOC).

•A composite with a 3D stacked-up nanostructure composed by Mn3O4, Co3O4 and graphene.•The novel composite exhibits superior ORR activity to Co3O4/GO and Mn3O4/GO alone.•The enhanced synergy in this composite is responsible for the ORR activity.•There exists an interphase ligand effect between two spinel oxides and graphene.Constructing composite materials with a smart nanostructure, by using various transition metal oxides and carbon carriers as building blocks, is of great importance to develop highly active, economical noble metal-free catalysts for oxygen reduction reaction (ORR). We have synthesized a novel ternary composite with a special 3D stacked-up nanostructure, composed of Co3O4, Mn3O4 and graphene oxide (GO), via a facile two-step aqueous synthesis without adding any structure directing agent. The composite was characterized by X-ray diffraction, scanning transmission electron microscope, Raman spectroscopy, and X-ray photoelectron spectroscopy. The results revealed that Mn3O4 nanocrystals had been successfully epitaxially deposited onto the surface of Co3O4 nanoparticles to form Mn3O4-on-Co3O4 nanostructures on surface of the graphene. In an alkaline environment, the Co3O4-Mn3O4/GO composite exhibits much better electrocatalytic activity and durability towards ORR than individual Mn3O4/GO and Co3O4/GO catalysts. The recorded kinetic current density (JK) of O2 reduction for the composite is 2.078 mA/cm2, which is comparable to that of a commercial Pt/C (20%) but far exceeding the sum of that obtained from the Co3O4/GO and Mn3O4/GO. The remarkably improved ORR activity is closely attributed to the enhanced synergy between these two oxides and the graphene, raised by the 3D stacked-up structure in this composite. The oxide-on-oxide heterostructure comprising Co3O4 and Mn3O4 can promote covalent electron transfer from carbon support to the oxides as a result of the interphase ligand effect between them, which facilitate the ORR kinetics. Moreover, Mn3O4 phase acting as a co-catalyst, located at the top of Co3O4 phase, also favor the chemical disproportionation of H2O2 intermediates generated by the composite during the ORR.

A novel class of Pt–Co secondary solid solution catalysts with long-range ordered intermetallic CoPt3 as the solvent and Co as the solute for the oxygen reduction reaction (ORR) is proposed. The catalysts exhibit a volcano-type dependence on Co solid solubility in ORR activity and the optimum catalyst with 10% Co solid solubility shows remarkably enhanced catalytic activity and durability, which can be ascribed to the unique electronic structure of secondary solid solution catalysts.

Graphite with a large inter-planar distance (0.357 nm) was obtained from pig bone. It delivered an improving specific capacity which increased continuously to 538 mA h g−1 at 1 A g−1 after 1000 cycles. With microscopic characterization, it has been found that the pig-bone-based graphite was exfoliated to graphene during the charge–discharge process.

Constructing nanoscale hybrid materials with unique interfacial structures by using various metal oxides and carbon supports as building blocks are of great importance to develop highly active, economical hybrid catalysts for oxygen reduction reaction (ORR). In this work, La2O2CO3 encapsulated La2O3 nanoparticles on a carbon black (La2O2CO3@La2O3/C) were fabricated via chemical precipitation in an aqueous solution containing different concentrations of cetyltrimethyl ammonium bromide (CTAB), followed by calcination at 750 °C. At a given CTAB concentration 24.8 mmol/L, the obtained lanthanum compound nanoparticles reach the smallest particle size (7.1 nm) and are well-dispersed on the carbon surface. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results demonstrate the formation of La2O2CO3 located on the surface of La2O3 nanoparticles in the hybrid. The synthesized La2O2CO3@La2O3/C hybrid exhibits a significantly enhanced electrocatalytic activity in electrocatalysis experiments relative to pure La2O3, La2O2CO3, and carbon in an alkaline environment, by using the R(R)DE technique. Moreover, its long-term stability also outperforms that obtained by commercial Pt/C catalysts (E-TEK). The exact origin of the fast ORR kinetics is mainly ascribed to the La2O2CO3 layer sandwiched at the interface of carbon and La2O3, which contributes favorable surface-adsorbed hydroxide (—OH–ad) substitution and promotes active oxygen adsorption at the interfaces. The unique covalent —C—O—C(═O)—O—La—O— bonds, formed at the interfaces between La2O2CO3 and carbon, can act as active sites for the improved ORR kinetics over this hybrid catalyst. Therefore, the fabrication of lanthanum compound-based hybrid material with an unique interfacial structure maybe open a new way to develop carbon-supported metal oxides as next-generation of ORR catalysts.Keywords: carbon black; chemical bonds; interfacial structure; La2O2CO3 encapsulated La2O3; oxygen reduction reaction

Surface-functionalized multiwalled carbon nanotubes (MWCNTs) supported Pd100–xIrx binary alloy nanoparticles (Pd100–xIrx/MWCNT) with tunable Pd/Ir atomic ratios were synthesized by a thermolytic process at varied ratios of bis(acetylacetonate) palladium(II) and iridium(III) 2,4-pentanedionate precursors and then applied as the electrocatalyst for the formic acid electro-oxidation. The X-ray diffraction pattern (XRD) and transmission electron microscope (TEM) analysis showed that the Pd100–xIrx alloy nanoparticles with the average size of 6.2 nm were uniformly dispersed on the MWCNTs and exhibited a single solid solution phase with a face-centered cubic structure. The electrocatalytic properties were evaluated through the cyclic voltammetry and chronoamperometry tests, and the results indicated that both the activity and stability of Pd100–xIrx/MWCNT were strongly dependent on the Pd/Ir atomic ratios: the best electrocatalytic performance in terms of onset potential, current density, and stability against CO poisoning was obtained for the Pd79Ir21/MWCNT. Moreover, compared with pure Pd nanoparticles supported on MWCNTs (Pd/MWCNT), the Pd79Ir21/MWCNT exhibited enhanced steady-state current density and higher stability, as well as maintained excellent electrocatalytic activity in high concentrated formic acid solution, which was attributed to the bifunctional effect through alloying Pd with transition metal.Keywords: bifunctional effect; composition-dependent; formic acid electro-oxidation; palladium iridium alloy; stability;

Well-defined copper-platinum (Cu-Pt) nanotubes with a high degree of alloying were synthesized through a galvanic replacement reaction; this reaction utilized aqueous solutions containing H2PtCl6 and copper nanowires, which acted as the sacrificial templates, without other surfactants or organic solvents at room temperature. The size, morphology and alloy composition of the well-alloyed Cu-Pt nanotubes were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD) and inductively coupled plasma (ICP) mass spectrometry. The electrochemical replacement reaction generated a hollow one-dimensional (1D) structure and the high degree of alloying in the as-synthesized products. Compared to a commercial Pt/C catalyst (40 wt.%, E-TEK), the as-synthesized Cu-Pt alloy nanotubes exhibited superior electro-catalytic activity and stability during oxygen reduction reaction in acidic solutions due to their unique hollow 1D structure and the high alloying degree. In addition, the kinetic parameters of the oxygen reduction over the Cu-Pt alloy nanotubes were calculated based on ring-disk electrode, Tafel plot, and electrochemical impedance spectra (EIS) measurements.

A highly sensitive, reliable and reproducible sensor for the detection of hydrazine was fabricated using a porous Co3O4 nanowire (NW) electrode. Porous Co3O4 NWs constructed from interconnected nanorod units with a three-dimensional porous network were synthesized via a facile hydrothermal process. The hydrazine sensor based on the Co3O4 NW electrode demonstrated a relatively high sensitivity (28.63 μA mM−1) and a rather low detection limit (0.5 μM) due to the fast electro-oxidation of hydrazine catalyzed by Co3O4 NWs. The unique porous structure of Co3O4 NWs offers a promising probe candidate for efficient electrochemical sensors of hydrazine.

•Bifunctional leaf-like CdS/MoS2 hybrids were prepared by electrodeposition.•The interactive influence of MoS2 and CdS on the catalytic activity was analyzed.•The CdS/MoS2 showed the improved photocatalytic activity due to the p–n junction.•The CdS/MoS2 has superior electrocatalytic activity for HER relative to the MoS2.•A Tafel slope of ∼42 mV/decade was measured for CdS/MoS2 hybrid in the HER.Bifunctional leaf-like CdS/MoS2 hybrids were successfully prepared by electrodeposition. The interactive influences between MoS2 and CdS on the photoelectrocatalytic activity for catalyst of CdS/MoS2 were characterized by analyzing the current density (J)–potential (V) curves of cathodic and anodic polarization. On the one hand, the CdS/MoS2 hybrid showed the improved photoelectrochemical performance which was attributed to the visible light absorption enhanced by MoS2 and the formation of p–n junction between CdS and MoS2. On the other hand, the CdS/MoS2 hybrid exhibited superior electrocatalytic activity in the hydrogen evolution reaction (HER) relative to the MoS2 catalyst. A Tafel slope of ∼42 mV/decade was measured for CdS/MoS2 hybrid in the HER, which exceeded by far the activity of previous MoS2 catalysts and resulted from the abundance of catalytic edge sites on the MoS2 nanoparticles. The Tafel slope of∼42 mV/decade suggested the Volmer_Heyrovsky mechanism for the CdS/MoS2-catalyzed HER, with electrochemical desorption of hydrogen as the rate-limiting step.

Through incorporation of other metal elements like Li, K and Cu into the Co3O4 lattice, tuning electronic structures of carbon-supported Co3O4 may be an effective way to improve electrochemical properties of the oxide as an efficient catalyst for the oxygen reduction reaction (ORR). In this paper, we have synthesized Li-doped Co3O4 (Li/Co = 0, 2.5%, 5%, 7.5%) solid solution nanocrystals through direct nucleation and growth of the lithium-cobalt oxide on a acid-treated carbon black. The carbon supports LixCo3−xO4 spinel nanocrystals with average particle size of approximately 4 nm, covered evenly on the surface of carbon in this hybrid. The electrocatalysis experiments in an alkaline solution reveal a close correlation between the ORR electrocatalytic activities and the doped Li contents of these LixCo3−xO4/C catalysts. Interestingly, the half-wave potential and the mass-specific activity of these catalysts show a typical volcano plot as a function of Li contents. Among all the synthesized Co3−xO4/C samples, the sample prepared at the Li/Co atomic ratio of 5% displays the most positive half-wave potential and the largest mass-specific activity respectively, which are 70 mV and 3.3 times higher than the undoped Co3O4/C. Compared with that of the undoped Co3O4/C, the remarkly increased content of covalent OC–O–CoIII–O bonds formed at the interfaces between Li-doped Co3O4 and carbon support is responsible for the improved electro-catalytic performances of the doped catalyst. Moreover, the covalent electron transfer from the CoIII species to the electron-withdrawing OC–O species through the OC–O–CoIII–O bonds can not only promote the oxidation of active sites CoIII into CoIV but also facilitate the surface hydroxide displacement, which can significantly contribute to the ORR kinetics. Therefore, the exact understanding of the unique interfacial electronic structures of the LixCo3−xO4/C hybrids is very important to develop the lithium-cobalt oxides on carbon as next-generation catalysts for ORR.

Carbon nanotubes supported PtFe@Pt core–shell nanoparticles with ordered L10 intermetallic PtFe cores and approximately three atomic layers of Pt shells have been successfully synthesized. As a result of the contracted lattice and the unique core–shell structure, PtFe@Pt/CNT exhibited superior catalytic activity and significantly improved durability towards the oxygen reduction reaction.

Poly(D,L-lactide-co-glycolide) (PLGA) microspheres were prepared by emulsion solvent evaporation method. The influences of inner aqueous phase, organic solvent, PLGA concentration on the morphology of microspheres were studied. The results showed that addition of porogen or surfactants to the inner aqueous phase, types of organic solvents and polymer concentration affected greatly the microsphere morphology. When dichloromethane was adopted as organic solvent, microspheres with porous structure were produced. When ethyl acetate served as organic solvent, two different morphologies were obtained. One was hollow microspheres with thin porous shell under a lower PLGA concentration, another was erythrocyte-like microspheres under a higher PLGA concentration. Three types of microspheres including porous, hollow core with thin porous shell (denoted by hollow in brief) and solid structures were finally selected for in vitro drug release tests. Bovine serum albumin (BSA) was chosen as model drug and encapsulated within the microspheres. The BSA encapsulation efficiency of porous, hollow and solid microspheres was respectively 90.4%, 79.8% and 0. And the ultimate accumulative release was respectively 74.5%, 58.9% and 0. The release rate of porous microspheres was much slower than that of hollow microspheres. The experiment results indicated that microspheres with different porous structures showed great potentials in controlling drug release behavior.

Achieving synergy between inexpensive metals and metal oxides is a key challenge for the development of highly active, economical composites as next-generation catalysts for oxygen reduction reaction (ORR). We have synthesized highly dispersed Ag and Mn3O4 nanocrystals covalently coupled with carbon black via a simple thermal decomposition of AgNO3 and Mn(NO3)2 precursors at elevated temperatures. The resulting Ag and Mn3O4 nanocrystals are located separately on the carbon, but in close proximity to each other. Electrocatalysis experiments in an alkaline solution reveal a remarkably improved electrocatalytic activity and prolonged long-term durability for the Ag–Mn3O4/C composite relative to the Ag/C (90 wt%). Moreover, X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) demonstrate that the unique electronic structures of the composite could be tuned by the substantial electron transfer between the two nanoparticles through the common carbon support, which highly correlates with the enhanced ORR performance. The exact origin of the improved ORR activity may be associated with the favorable formation of monolayer Ag2O film and promoted active oxygen adsorption on the Ag surfaces as a result of the particle-to-particle ligand and ensemble effects between Ag and Mn3O4 phases in this composite.

Novel hierarchical lamellar porous carbon (HLPC) with high BET specific surface area of 2730 m2 g–1 and doped by nitrogen atoms has been synthesized from the fish scale without any post-synthesis treatment, and applied to support the platinum (Pt) nanoparticle (NP) catalysts (Pt/HLPC). The Pt NPs could be highly dispersed on the porous surface of HLPC with a narrow size distribution centered at ca. 2.0 nm. The results of the electrochemical analysis reveal that the electrochemical active surface area (ECSA) of Pt/HLPC is larger than the Pt NP electrocatalyst supported on the carbon black (Pt/Vulcan XC-72). Compared with the Pt/Vulcan XC-72, the Pt/HLPC exhibits larger current density, lower overpotential, and enhanced catalytic activity toward the oxygen reduction reaction (ORR) through the direct four-electron pathway. The improved catalytic activity is mainly attributed to the high BET specific surface area, hierarchical porous structures and the nitrogen-doped surface property of HLPC, indicating the superiority of HLPC as a promising support material for the ORR electrocatalysts.Keywords: electrocatalyst; fish scale; hierarchical lamellar porous carbon; nanoparticle; oxygen reduction reaction;

Au nanoring@Ag core–shell nanostructures with controllable morphologies and tunable symmetries are synthesized via the seed-mediated growth of Ag onto a sole seed: a circular Au nanoring (AuNR). The 2D isotropic AuNR is prepared firstly by chemical etching, then by galvanic replacement with HAuCl4. By delicately altering the regrowth procedure and mixing the capping agents, different Ag triangular nanoplates with embedded AuNRs in different sizes and shapes can be obtained. Furthermore, by using a single capping agent, the growth of Ag on the AuNR can be preferentially confined to a lateral or vertical mode, to form eccentric nanoplates or nanocubes in both sequence sets at room temperature. Such nanostructures with precisely controllable shape evolution not only displayed unique optical properties, but also revealed the feasibility of breaking the original dimensions, and especially symmetry, at the nanoscale using seed-mediated growth. This paves the way for future applications including catalysis, diagnosis, plasmonics, and biological and chemical sensing.

The ability to precisely tune the chemical compositions and electronic structures of nanoalloy catalysts is essential to achieve the goals of high activity and selectivity for the oxygen reduction reaction (ORR) on the catalysts by design. In this work, we synthesized carbon-supported Pt–Co alloy nanoparticles with controlled bimetallic compositions (Pt/Co atomic ratio = 81:19, 76:24, 59:41, 48:52, 40:60 and 26:74) by regulating solution pH and the amount of Pt and Co precursor salts to elucidate the effect of catalyst composition on ORR activity. The obtained Pt–Co alloy nanoparticles have face-centred cubic (fcc) structures and are well-dispersed on the surface of the carbon support with a narrow particle size distribution (2–4 nm diameters). The electrocatalysis experiments in alkaline solution reveal a strong correlation between ORR activity and the alloy composition of the catalysts. Interestingly, the mass-specific activities of the catalysts manifest a typical double-volcano plot as a function of alloy composition. In this Pt–Co alloy series, the catalyst with a Pt:Co atomic ratio of 76:24 exhibits the best ORR performance, which is remarkably higher than that of the commercial Pt/C (E-TEK). X-ray photoelectron spectroscopy (XPS) measurements demonstrate that the electronic structures of these catalysts can be tuned by controlling their alloy compositions, which are highly correlated with the trends in ORR activity. The origin of the enhancement in ORR activity may be strongly related to the unique chemical surface structures of the catalysts.

A series of oxygen depolarized cathodes (ODC) with different gas diffusion layers (GDLs), determined by different carbon black fillers, PTFE contents, and pore-forming agents, were fabricated. The structure-sensitive activity for the oxygen reduction reaction (ORR) on these cathodes has been studied in alkaline solutions, with the aim of revealing the effect of pore structures in GDLs on the ORR activity. A linear-type gas permeability (K) dependence on the ORR activity is observed, indicating that K is one of the key parameters representative of the ability of gas diffusion through GDLs. The added PTFE as binder favors the formation of the secondary pores instead of the primary pores in GDLs. By introducing (NH4)2C2O4 as pore-forming agents in GDL, the best performance of the ODC was obtained. The resulting GDL possessed the average secondary pore diameter of 144 nm and the secondary pore volume of 0.3032 mL/g.

A novel strategy to prepare highly dispersed Pt nanocrystals supported on ultrasonic cavitation functionalized carbon nanotubes (CNTs) was developed. We started with a facile and environmentally friendly method of ultrasonic cavitation of CNTs in aqueous solution and subsequently synthesized Pt supported on the functionalized carbon nanotubes by using different reducing agents including citric acid, sodium citrate, and sodium borohydride. The morphological and electronic structures of the Pt/CNTs hybrid catalysts were characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. The results showed that the prepared Pt nanocrystals were uniformly dispersed on surfaces of the ultrasonic-functionalized CNT, and the average diameter of Pt nanocrystals was about 2.2 nm. The synthesized Pt/CNTs exhibits enhanced electrocatalytic activity and improved resistance to CO poisoning during methanol electrooxidation, compared to a commercial Pt/C (E-TEK). The enhanced catalytic performance could be explained by strong electronic interaction between Pt and CNTs in this hybrid.

•The silver nanostructures with various shapes have been successfully conducted.•The shape-controlled silver nanostructures can be yielded.•As-synthesized silver dendrites have occurred spontaneous evolution in morphology.•Dissolution–recrystallization process mechanism is proposed.The fabrications of the silver nanostructures with various shapes have been successfully conducted by using an ultrasound assisted galvanic replacement reaction (GRR) in aqueous solutions containing silver nitrate and copper sheet using PVP as stabilizer. Powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) have been used to characterize the as-synthesized silver products. The results show that a variety of silver nanostructures, such as silver dendrites, the triangular, hexagonal, disk nanoplates and spherical nanoparticles, can be yielded in large scale by facilely tuning the silver nitrate concentrations, temperature and concentration of PVP in aqueous solutions. The as-synthesized silver dendrites were deposited in ethanol without any field (UV or visible light irradiation) or thermally induced activation, a significantly spontaneous evolution in morphology occurred from the fractal structure to silver nanoparticles at room temperature. Moreover, the mechanisms of the architectural reconstruction of silver nanostructures in ethanol at room temperature by self-assemble were discussed. The proposed dissolution recrystallization process induced by ethanol may be responsible for the morphological reconstructure of the as-synthesized Ag dendrites.

•Polyacrylate/silica core-shell particles were formed without pretreatment of SiO2.•The effect of silica on the polymer in growth was investigated.•A formation mechanism in the presence of an electrostatic repulsion was proposed.•The polyacrylic precursors absorbed SiO2 particles to lower the interfacial free energy.•The core-shell composite particles formed at early polymerization.Polyacrylate/silica nanocomposite particles are synthesized by soap-free emulsion polymerization using negatively charged silica particles, where the anionic initiator, potassium peroxydisulfate (KPS), is used. The influence of the content of hydrophilic silica particles on the composite particle growth and conversion is investigated. Nucleation process of unmodified silica-stabilized emulsion polymerization is studied by characterizing the structures of composite particles forming at different polymerization stages with transmittance electron microscope (TEM) and laser light scattering (DLS). The results show that the presence of silica particles on latex particles reinforces the barrier to radical absorption and retards the polymerization rate and therefore the growth of the latex particles. However, the composite particle size does not decrease much when the content of silica sol is increased to more than 5 wt%. A mechanism is proposed to explain the formation of the core-shell structured particles when an electrostatic repulsive force between the silica and polyacrylate particles is present. The polyacrylate precursors forming in the early stage of the soap-free emulsion polymerization are unstable and tend to aggregate and absorb silica particles to lower their interfacial free energy, thus forming the composite particles. In contrast to the monomer droplets dispersed in the sole acrylic soap free emulsion polymerization, the monomer droplets dispersed in the aqueous system containing silica sol can work as polymerization loci due to their relatively small size and the large quantity (or the large specific surface areas), hence enhancing the ability to capture radicals.

A novel porous sulfur/carbon nanocomposite was prepared as the cathode material for lithium–sulfur batteries. The porous nanostructure of the composite is beneficial for enhancing the cycle life by accommodating the volume expansion of sulfur particles and adsorbing the polysulfide produced during the electrochemical reaction. The resulting nanocomposite shows a high capacity of 1039 mA h g−1 at 1C (1C = 1675 mA g−1) in the first cycle and the reversible capacity remains high at up to 1023 mA h g−1 even after 70 cycles.

Sulfosalicylic acid (C7H6O6S) as a special additive was applied to favor the deposition of pure zinc sulfide (ZnS) nanocrystal thin films on ITO substrates from acidic solutions by potentiostatic technique with subsequent annealing. XRD, EDX, Raman, SEM and UV–vis–NIR analyses demonstrate that a proper concentration of C7H6O6S additive (0.2 mM) in the electrolyte containing 20 mM Zn2+, 20 mM S2O32−, 0.375 mM SO32− and 200 mM LiCl can greatly contribute to the controllable growth of pure cubic ZnS film along (2 0 0) orientation at potential of −1.1 V vs. SCE. The film possesses a uniform surface with an average crystallite size ca. 40.9 nm, and a band gap ca. 3.68 eV. Electrochemical studies indicate that C7H6O6S could adsorb on ITO surface and act as a hydrogen bond donor for free Cl−. The adsorption of C7H6O6S blocks some active sites used for the deposition of S, while the role of hydrogen bond donor promotes the deposition of Zn element by decreasing the concentration of [ZnCl4]2− and increasing the concentration and mobility of Zn2+ in electrochemical double layer. Consequently, the addition of C7H6O6S narrows the deposition potential gap of S and Zn elements in the range of −1.0 to −1.2 V, thus resulting in their co-deposition to form pure ZnS.

Highly graphitic carbon black (GCB) was synthesized by heat-treating commercial carbon black (CB, Vulcan XC-72) at 2800 °C. The resulting GCB with a high degree of graphitization was analyzed by X-ray diffraction patterns (XRD), Raman spectroscopy and high-resolution transmission electron microscopy (HR-TEM) and was then used as the support material for synthesizing a platinum–GCB (Pt/GCB) hybrid catalyst. This catalyst was obtained through a simple chemical reduction using ethylene glycol as the reducing agent, which is amenable to large-scale production. The results show that the Pt nanoparticles are highly dispersed on the GCB with an average diameter of 3.6 nm and a narrow particle size distribution. The electrochemical results obtained using cyclic voltammetry (CV), linear sweep voltammetry (LSV) utilizing a rotating disk electrode (RDE) and electrochemical impedance spectroscopy (EIS) show that the Pt/GCB electrocatalyst exhibits higher conductivity, stability, and electrocatalytic activity for the oxygen reduction reaction. The ORR proceeds through a four-electron process and when compared with Pt nanoparticles supported on Vulcan XC-72 (Pt/Vulcan XC-72) prepared under the same conditions, the Pt/GCB exhibits a significant enhancement for the ORR reaction.Highlights► Highly graphitized GCB was obtained by heat-treatment of Vulcan XC-72 at 2800 °C. ► GCB exhibited higher resistance against oxidation than Vulcan XC-72 did. ► Pt/GCB showed superior catalytic activity for the ORR compared to the Pt/Vulcan XC-72.

Carbon black supported ultra-high loading silver nanoparticle catalyst (Ag/C) was prepared by a modified ethylene glycol reduction method. The thermogravimetry analysis showed that the Ag mass loading of this catalyst reached up to 392 wt.%. The X-ray diffraction and scanning electron microscopy characterizations showed that the Ag nanoparticles were ca. 10 nm diameter of fine spheres with a face-centered cubic crystal structure, and were densely stacked but not aggregated on the carbon black surface in spite of such ultra-high loading and small size. The chronoamperometry and polarization studies utilizing rotating disk electrode (RDE) or rotating ring disk electrode (RRDE) revealed that this ultra-high loading 392 wt.% Ag/C catalyst exhibited higher electrocatalytic activity for oxygen reduction reaction (ORR) in alkaline medium. The ORR proceeded a four-electron process when compared with the low loading 40 wt.% Ag/C catalyst. Furthermore, the chronopotentiometry test on gas-diffusion electrode containing the 392 wt.% Ag/C catalyst implied that this catalyst had a considerably stable ORR activity for application in brine electrolysis.Highlights► This work developed a facile method to synthesize ultra-high loading Ag/C catalyst. ► The Ag nanoparticles are densely loaded on carbon black surface without aggregation. ► The loaded Ag nanoparticles are ca. 10 nm diameter of fine spheres. ► The catalyst owns high electrocatalytic activity and stability for four-electron ORR.

Carbon black supported ultra-high loading silver nanoparticle catalyst (Ag/CB) was prepared by a modified ethylene glycol reduction method, using ethylene glycol as the reducing agent and sodium hydroxide as the pH adjusting agent. The X-ray diffraction, thermogravimetry and scanning electron microscopy characterizations showed that the Ag nanoparticles crystallized with a face-centered cubic structure and were densely stacked on the CB surface without aggregation, despite such a small average size (ca. 10 nm) and an ultra-high loading mass (392 wt.%). The electrochemical evaluation based on cyclic voltammetry, chronoamperometry and polarization tests revealed that the ultra-high loading Ag/CB catalyst possessed a superior electrocatalytic activity for the oxidation of hydrazine, via a diffusion-limited process and a 4-electron transfer pathway. Moreover, the chronoamperometry response on an electrode modified with this ultra-high loading Ag/CB catalyst exhibited a promising application for determination of hydrazine, due to a broad linear calibration ranging from 50 to 800 μM, a high sensitivity of 0.03795 μA/μM and a low detection limit of 3.47 μM.

Iron titanium oxide (Fe1.5Ti0.5O3) nanoparticles with the diameter of about 150 nm were prepared by hydrothermal process and further heat treatment at 300 °C for 2 h. The morphology, structure and electrochemical performance of Fe1.5Ti0.5O3 nanoparticles as anode material for lithium-ion batteries were investigated by scanning electron microscopy, X-ray diffraction and a variety of electrochemical testing techniques. It was found that, compared with TiO2 and Fe2O3, the iron titanium oxide electrode exhibited higher specific capacity of 734.9 mAh g−1 after 50 cycles at the current density of 50 mA g−1, good cycle stability and high-rate performance, suggesting that the Fe1.5Ti0.5O3 nanoparticle synthesized by this method is a promising anode material for lithium-ion batteries.

TixSn1−xO3 solid solutions were prepared by a hydrothermal process. The morphologies and structures of TixSn1−xO3 solid solutions were investigated by scanning electron microscope, transmission electron microscope and X-ray diffraction measurements. The electrochemical properties of TixSn1−xO3 solid solution electrodes with different Sn/Ti ratios were examined by a variety of electrochemical testing methods. It was found that, the TixSn1−xO3 solid solution showed not only higher specific capacity of 506 mAh g−1 after 30 cycles but also better cycle performance, superior than the pure SnO2 electrode, which can be ascribed to the stable cyclability of TiO2 and the high reversible capacity of nanosized SnO2. The TixSn1−xO3 solid solutions would be a potential candidate as anode material for a new generation lithium ion batteries.

Zinc sulfide (ZnS) semiconductor nanocrystal films have been prepared on indium tin oxide coated glass substrates by sulfosalicylic acid (C7H6O6S)-assisted galvanostatic deposition with subsequent annealing. The deposition was performed at 10 mA cm− 2 in acidic electrolytes containing 15–30 mM Zn(CH3COO)2, 20 mM Na2S2O3, 200 mM LiCl, 0.375 mM Na2SO3, and 0 or 0.2 mM C7H6O6S. Results show that the presence of C7H6O6S can suppress the precipitation of Zn and S impurity phases during the ZnS deposition process. As the [C7H6O6S] = 0.2 mM and [Zn2 +] = 20 mM, the deposited ZnS film exhibits only hexagonal structure with an ideal Zn/S atomic ratio of 1.03 and a close-packed granular morphology. But its band gap about 2.86 eV is narrower than the common value of ZnS, probably due to the existence of some spurious acetate species and defect states. By annealing the film at 400 °C for 60 min, its band gap increased up to 3.70 eV, despite that its crystalline phase transformed into cubic structure which usually shows the narrower band gap than hexagonal ZnS. The significant band gap widening could be ascribed to the degradation of spurious acetate species and the reduction of various possible defect states in the annealing process.Highlights► Galvanostatic deposition of ZnS semiconductor nanocrystal films ► Assisted by sulfosalicylic acid additive with subsequent annealing ► Sulfosalicylic acid can improve the purities of ZnS nanocrystal films. ► Annealing can modify the film crystallinities and optical properties.

Nanostructured copper/multi-walled carbon nanotube (Cu/MWCNT) films have been fabricated by means of pulse electrodeposition in an acidic plating bath containing copper sulfate and purified MWCNTs. The influence of MWCNTs on copper electrochemical reduction behavior is studied by cathodic polarization and electrochemical impedance spectrums (EIS) analysis. Results show that the existence of the hydrochloric acid purified MWCNTs in the electrolytes shows the accelerating action toward Cu electrochemical reduction during the electrodeposition process, making the Cu films finely grow with the crystal growth toward the (1 1 1) orientation compared to the pure Cu electrodeposited film. The resulting Cu/MWCNT composite film is comprised of Cu matrix and the spatial network of MWCNTs with a considerable high MWCNT content.

Three-dimensional (3D) nanostructured Sn2S3 semiconductor films have been prepared on ITO-coated glass substrates by potentiostatic electrodeposition at −0.80 V (vs. SCE) from a novel plating bath containing K4P2O3 as a complexing agent and Na2SO3 as a stabilizing agent and by subsequent annealing. Results showed that the annealing drove the as-deposited Sn2S3 films to grow from a granular structure into a nanorod network structure. The nanorods were around 50–100 nm in diameter and 1000 nm in length. The band gap of the annealed film was 1.65 eV and the conductivity was n type. The carrier mobility achieved up to 20.5 cm2 V−1 s−1 due to the direct electrical pathways provided by the nanorod network.

Multi-walled carbon nanotube (MWCNT) supported nickel (Ni) catalysts were chemically synthesized via a hydrazine reduction process with addition of cetyltrimethylammonium bromide (CTAB) as a special additive. As evidenced by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and high-revolution transmission electron microscope (HR-TEM), the Ni nanoparticles (NPs) deposited on the sidewalls of MWCNTs were found to be face-centric cubic (fcc) crystal structure, and dispersed homogenously with a sharp particle size distribution centered at around 20 nm of diameter. Electro-oxidation of ethanol on MWCNT/Ni catalysts was investigated by cyclic voltammetry (CV) measurement. The MWCNT/Ni catalysts showed excellent electro-catalytic activity for the oxidation of ethanol in alkaline solution.Highlights► Ni NPs were homogeneously dispersed on MWCNTs with an average size of 20 nm. ► Ni NPs were fcc polycrystalline structure. ► The catalysts showed high current response to ethanol oxidation in alkaline solution. ► The electro-oxidation process was controlled by the diffusion transport of ethanol.

Identifying the phase purity of CdS nanorods (NRs) is complicated by the serious overlap between the X-ray diffraction peaks of zinc blende and wurtzite phases as well as anisotropic growth, which might hide a mixed phase. Here we show that the density gradient ultracentrifugation rate separation method can be used to sort CdS NRs synthesized under nitrogen according to differences in particle size and morphology. Furthermore, it was found that the different sized NRs formed in a single batch synthesis had different phases: the thinner ones (<3.5 nm in diameter) were predominantly wurtzite phase, while the thicker ones (>5 nm in diameter) were mainly zinc blende phase. Dark-field transmission electron microscopy (TEM) and high-resolution TEM images indicated the presence of numerous stacking faults in the thick zinc blende rods, while the wurtzite thin rods were exclusively single crystals. As a result of the differences in phase and stacking faults, the NRs showed different photoluminescent properties. The development of an effective way of separating such NRs thus leads to further insight into the differences in phase, structure, and optical properties between individual colloidal particles synthesized in a single batch. A preliminary mathematical model of the separation process has been proposed.Keywords: aspect ratio; CdS; crystal phase; nanoseparation; quantum rods

The effect of potassium hydrogen phthalate (C8H5KO4) as a special additive on the one-step electrodeposition of single-phase CuInS2 thin films from acidic solution (pH 2.5) was investigated in detail. The XRD, SEM and UV–vis–NIR characterization confirms that the addition of an adequate concentration of C8H5KO4 (23 mM) to the electrolytic bath containing 12.5 mM Cu2+, 10 mM In3+, 40 mM S2O32− and 100 mM LiCl can contribute greatly to the controllable growth of pure chalcopyrite CuInS2 films with uniform surfaces and an ideal band gap of approximately 1.54 eV. Complexation studies of C8H5KO4 with Cu2+ and In3+ in electrolytic solutions indicated that C8H5KO4 can complex Cu2+ more strongly than In3+ and move the electrode potentials of Cu2+ and In3+ near each other as determined by polarization analysis. Furthermore, the potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) analysis performed in a series of solution systems revealed a three-step reaction mechanism for CuInS2 deposition and considerable adsorption of C8H5O4− and Cu(C8H5O4)+ to the cathode surface. This deposition shows that the synergetic effects of complexation and adsorption originated from the additive on the Cu2+ electro-reduction, thus promoting the co-deposition of copper, indium and sulfur in the form of single-phase CuInS2.

The highly ordered Ni–P alloy nanotube and nanowire arrays with high aspect-ratio have been successfully synthesized inside porous anodic aluminum oxide (AAO) membranes by self-assembly electrodeposition at different current densities. The as-synthesized Ni–P alloy arrays have the amorphous phase structure with nanograin of crystalline Ni. The length and outer diameter predominantly determined by the deposition time and pore diameter of the AAO membranes achieve 40 μm and 200 nm, respectively. The formation of nanotubes or nanowires during electrodeposition mainly depends on the current densities, deposition time and phosphorous acid concentration in the electroplating bath. The magnetic properties of these nanostructure arrays have also been studied. From the hysteresis loops, it is obtained that the nanotube and nanowire arrays have anisotropy with the easy magnetization along the direction of the arrays. Moreover, as the soft magnetic materials, the nanotube array is better than nanowire array in magnetic performance of saturation magnetization.

Tailoring of nickel–sulfur (Ni–S) intermetallic compound film electrodes for hydrogen evolution reaction in alkaline solutions was attempted by electrodeposition from a typical Watts bath containing sodium thiosulfate as sulfur source and sulfosalicylic acid as additive. The XRD analysis shows that the as-deposited Ni–S film electrode with fine morphological features comprised of intermetallic compound phase structure and amorphous phase structure. The intermetallic compound film electrodes generate a higher catalytic activity for the hydrogen evolution reaction in alkaline solution in comparison with Ni–S film electrodes comprised of amorphous phase structures, even with commercial Ni mesh or Ni/RuO2 composite electrode.

It is confirmed that a layer of vacuum-evaporated carbon on the surface of a preoriented ultrathin polymer film can lead to an oriented recrystallization of the polymer film. This has been attributed to a strong fixing effect of vacuum-evaporated carbon layer on the film surface of the polymer. To study the origin of the strong fixing effect of vacuum-evaporated carbon layer on the polymer films, the melting and recrystallization behaviors of the preoriented ultrathin PE film with a vacuum-evaporated carbon layer were studied by using atomic force microscopy, electron diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy. We found that there exists some extent of chain orientation of carbon-coated polyethylene (PE) preoriented ultrathin film above its melting temperature. These oriented PE chain sequences act as nucleation sites and induce the oriented recrystallization of preoriented PE film from melt. Raman spectroscopy results suggest that new carbon−carbon bonds between the carbon layer and the oriented PE film are created during the process of vacuum carbon evaporation. As a result, some of the PE chain stems are fixed to the coated carbon substrate via covalent bond. Such a bonding has retarded the relaxation of the PE chains at the spot and, therefore, preserves the original orientation of the PE stems at high temperature, which in turn derives the recrystallization of the PE chains in an oriented structure.

The ordered arrays of Fe–Pd binary alloy nanotubes were synthesized from the mixed metal-complex solution by a simple electrodeposition method with the assistance of nanoporous anodic alumina (AAO). The electrodeposition potentials of Fe2+ and Pd2+ can be controlled by complexing agents, which has allowed for the fabrication of the Fe–Pd nanotubes by the AAO-template-assisted electrodeposition. Furthermore, the adjustment of the cathodic current density has caused the variation of the inner diameters and Fe–Pd composition ratios of the alloy nanotubes. Although the as-prepared Fe–Pd nanotubes are comprised of f.c.c. crystal structures, the metastable phase structure has been converted to L12 supper-lattice structure by annealing. The results of this work have shown a potential applicability of AAO-template-assisted electrodeposition to the preparation of other new binary alloy nanotubes by selecting adequate complexing agents.

Multi-walled carbon nanotube/cadmium sulfide hybrid heterostructures were easily synthesized by employing a thermal decomposition of thioacetamide as a sulfide-ion source in an aqueous regime. The resulting cadmium-sulfide phase is comprised of a zinc-blende structure of spherical polycrystalline nanoparticles (cadmium-sulfide nanoclusters) with the subunits of ca. 15 nm, deposited on the nanotube surface. The formation of the cadmium-sulfide nanoparticles with zinc-blende structure (cubic crystal) suggests that the local concentrations of reacting ion species in the vicinity of the nanotube surface are different from those in the reaction solution. The cadmium-sulfide nanoparticles are comprised of a stoichiometrically ideal chemical-composition ratio (cadmium: sulfur=1:1.02) of cadmium and sulfur with the valence states of +2 and −2, respectively. The optical responses of the cadmium-sulfide phase for ultraviolet-visible light and photoluminescence spectroscopes show the proper size-effect and inherent optical properties of the cadmium-sulfide nanoparticles.Transmission electron micrograph observation and electron diffraction pattern analysis of MWCNT/CdS heterostructures, which show that CdS nanoparticles with cubic CdS phase are deposited on the surface of MWCNTs.

Carbon black–silver hybrid catalysts were easily synthesized by a mixing method of acid-oxidized carbon black and the colloidal dispersion of silver nanoparticles. The silver colloidal dispersion was pre-synthesized by a chemical reduction of silver nitrate by dimethyl sulfoxide in the presence of trisodium citrate dihydrate as capping agents. In the mixing method, approx. 6.0 nm diameters of silver nanoparticles with face-centered cubic crystal structures are highly dispersed on the acid-oxidized carbon blacks due to the surface reactivity resulting from the enhancement of oxygen-containing functional groups. The hybrid catalysts were examined for electro-catalytic activity towards oxidation of hydrazine. The results clearly show that the carbon black–silver hybrid catalysts are highly active for electro-catalytic oxidation of hydrazine.

Multi-walled carbon nanotube/silver nanoparticles hybrid materials were easily synthesized by a mixing method of acid-oxidized nanotubes and the colloidal dispersion of silver nanoparticles. The silver colloidal dispersion was pre-synthesized by a chemical reduction of silver nitrate by dimethyl sulfoxide in the presence of trisodium citrate dihydrate as capping agents. In the mixing method, approx 5.0 nm diameters of silver nanoparticles with face-centered cubic crystal structures are highly dispersed on the acid-oxidized nanotubes due to the surface reactivity resulting from the enhancement of oxygen-containing functional groups. The results emphasize that the anchoring effect of the functionalized nanotube surface on silver nanoparticles originates from electrostatic metal-support interactions.

•The Pc-FePc complex supported on the Mn-modified GCB as electrocatalyst for ORR.•The Pc group can tune the Fe atom coordination environment in FePc.•The Pc-FePc/Mn-GCB exhibits much better ORR performance than Pt/C.•The Pc-FePc structure plays a key role in improving ORR performance.Despite the superior electrocatalytic activity of iron (II) phthalocyanine (FePc) for oxygen reduction reaction (ORR) in alkaline media, the large-scale applications of these FePc-based materials are still greatly hindered by their rapidly declined activity. To overcome this obstacle, it is essential to enhance the catalytic durability of FePc-based electrocatalysts. Herein, we demonstrate a superior FePc-based catalyst by employing low-cost graphitized carbon black as carbon supports, and tuning the Fe coordination environment in FePc, via the delocalized π coordination. Owing to the excellent ORR catalytic activity (the specific activity of 2.26 mA cm−2, 3.6-fold enhancements compared with the commercial Pt/C catalyst), the remarkable durability (after 3000 potential cycles, 3-mV shifts for the half-wave potential, only 4.2% decreases from the initial specific activity) and the outstanding selectivity (good methanol tolerance, and free from interfering species effects, including NO3-, SO42-, PO43-, Br-, Cl- and SCN-), the novel FePc-based electrocatalyst is promising substitutes for Pt-based catalysts for ORR. Furthermore, to better elucidate the origin of the ORR performance, the density functional theory (DFT) calculation indicates that the unique structure of phthalocyanine tethered iron phthalocyanine (Pc-FePc) plays a key role in improving of both the catalytic activity and durability.A novel iron phthalocyanine based material, prepared by the phthalocyanine tethered iron phthalocyanine with the low-cost graphitized carbon black as carbon support, exhibits excellent ORR catalytic activity, remarkable durability and outstanding selectivity for oxygen reduction reaction.

•CZTS thin film was successfully electrosynthesized in a novel green electrolyte.•Pure phase kesterite formed after sulfurization free annealing.•The electrolyte design was based on a synergetic effect from the additives.•Potassium pyrophosphate has complex effects with Cu2+ and Sn2+.•Sulfosalicylic acid promotes Zn2+ reduction by providing hydrogen bond.Cu2ZnSnS4 (CZTS) is a quaternary kesterite compound with suitable band gap for thin film solar cells. In most electrodeposition-anneal routes, sulfurization is inevitable because the as-deposited film is lack of S. In this work, a novel green electrolyte was designed for synthesizing CZTS thin films with high S content. In the one-step electrodeposition, K4P2O7 and C7H6O6S were added to form complex with metallic ions in the electrolyte, which could attribute to co-deposition. The as-deposited film obtained high S content satisfying stoichiometry. After a sulfurization free annealing, the continuous and uniform CZTS thin film was obtained, which had pure kesterite structure and a suitable band gap of 1.53 eV. Electrodeposition mechanism investigation revealed that the K4P2O7 prevented the excessive deposition of Cu2+ and Sn2+. The C7H6O6S promoted the reduction of Zn2+. So the additives narrowed the co-deposition potentials of the metallic elements through a synergetic effect. They also promoted the reduction of S2O32− to ensure the co-deposition of the four elements and the stoichiometry. The sulfurization free annealing process can promote the commercialization of CZTS films and the successful design principle of environmental friendly electrolytes could be applied in other electrodeposition systems.

•Bifunctional CdS@MoS2 nanorod array exhibit photoelectrocatalytic activity for HER.•Nanorod array shows better photoelectrochemical activity than bilayer structure.•The photoresponse of photocathode is structure-dependent.•Photocurrent derives of the photogenerated electrons in the vertical nanorods.•Reverse biased P type enhances the depletion region, reducing charge recombination.The structure design of hydrogen electrodes catalyst is important for the photoelectrocatalytic activity for hydrogen evolution reaction (HER). An oriented nanorod array on transparent conductive substrates would be the most desirable nanostructure in preparing photoelectrocatalytic cells (PECs) because of its efficient charge separation and transport properties as well as superior light harvesting efficiency. We report a bifunctional CdS@MoS2 core–shell nanorod arrays which exhibit both photo- and electrocatalytic activity for HER. The CdS@MoS2 core–shell nanorod arrays are prepared by a simple hydrothermal method and a followed electrodeposition. The characterization results indicate that CdS nanorods are covered by the MoS2 (∼30 nm), and the as prepared heterostructure markedly improves the separation and transfer of charge carriers. The photo- and electrocatalytic activity are characterized by cathodic polarization measurement. The results show that the nanorod array exhibits much better photo- and electrochemical performance than its counterpart of bilayer structure where no photocurrent is detected, suggesting that the photoresponse of photocathode is structure-dependent. Photocurrent derives of the hopping of photogenerated electrons in the vertical direction of CdS@MoS2 nanorods where p–n junction is probably reverse biased the P region, leading to the depletion region enhanced, and thus, suppresses charge recombination. This work proposes a new idea for designing the nanostructure of cathode with enhanced electrocatalytic activity by photo-assistance.

•Carbon materials as the excellent HER catalysts over wide pH range.•Co-NHPC by a sacrificial self-generated cobalt nanoparticle template synthesis.•Layered texture with inter-lamellar spacing and mesoporous structure.•Higher activity of Co–N–C complex than Co nanoparticle.To obtain clean and sustainable alternative energy, the development of low-cost, high efficient, wide pH range and durable non-precious metal electrocatalysts for hydrogen evolution reaction (HER) has become one of the crucial issues for the large-scale application of water splitting. We demonstrate a simple and efficient synthetic strategy for the preparation of cobalt-nitrogen codoped hierarchically porous carbon (Co-NHPC) electrocatalysts towards HER, by the direct carbonization followed by removing the Co nanoparticles. The resultant carbon-based materials were demonstrated to be three-dimensional porous graphitic structure with the highly active Co–N–C complex, leading to a high electrocatalytic activity and durability for HER in both of alkaline and acidic electrolyte. Considering the facial and rational preparation processes, the self-sacrificial nanoparticle templates synthetic strategy developed in this work is promising to design other carbon-based materials for other electrochemical applications.Figure optionsDownload full-size imageDownload high-quality image (454 K)Download as PowerPoint slide

The development of high-efficiency and low-cost electrocatalysts for the oxygen reduction reaction (ORR) is critical to allow large-scale application of fuel cell technologies. As promising candidates for the replacement of platinum-based electrocatalysts for the ORR, iron–nitrogen doped carbon (Fe–N–C) materials are appealing due to their outstanding ORR performances. To meet the requirements for commercial applications in fuel cells, the electrocatalytic activity and durability of the Fe–N–C electrocatalysts need to be further improved over a wide pH range. Herein, we report a facile and rational synthesis strategy for the preparation of a kind of Fe–N–C catalyst by low-temperature thermal treatment of iron phthalocyanine (FePc)-adsorbed nitrogen-doped hierarchically porous carbon (NHPC) derived from porphyra. The as-prepared electrocatalysts exhibit a superior ORR performance, even better than that of state-of-the-art Pt/C catalysts, in alkaline electrolyte (E1/2 = 0.88 V, n = 4.0, Tafel slope = 55 mV dec−1 and ca. 6 mV negative shift of E1/2, after 3000 cycles). This work develops a low-cost, but rational and efficient, methodology for the synthesis of high-performance Fe–N–C electrocatalysts for the ORR, and also provides an effective way to design and utilize hierarchically porous carbon for other electrocatalysts.

The development of low-cost and structure-controlled precursors has become one of the crucial issues in the improvement of pyrolyzed carbonaceous materials for the oxygen reduction reaction. In this work, a facile and interchangeable cross-linking process has been developed to synthesize polyphthalocyanines with different cross-linking degrees. After the pyrolysis treatment, the cross-linked polyphthalocyanine generated N-doped carbon-encased metal nanoparticle materials. During the pyrolysis treatment, the cross-linked structure of polyphthalocyanine can effectively restrain the aggregation of the metal core and significantly increase the amount of active N species in the pyrolyzed carbon shell. Different from the pyrolyzed pure phthalocyanine, the pyrolyzed cross-linked polyphthalocyanine electrocatalyst shows excellent electroactivity via a 4-electron pathway along with remarkable stability and good methanol tolerance. In addition, the unraveling of the cross-linking degree effect also provides guidance for future design of more efficient non-precious metal catalysts for oxygen reduction and other electrochemical applications.

Graphite with a large inter-planar distance (0.357 nm) was obtained from pig bone. It delivered an improving specific capacity which increased continuously to 538 mA h g−1 at 1 A g−1 after 1000 cycles. With microscopic characterization, it has been found that the pig-bone-based graphite was exfoliated to graphene during the charge–discharge process.

The ability to precisely tune the chemical compositions and electronic structures of nanoalloy catalysts is essential to achieve the goals of high activity and selectivity for the oxygen reduction reaction (ORR) on the catalysts by design. In this work, we synthesized carbon-supported Pt–Co alloy nanoparticles with controlled bimetallic compositions (Pt/Co atomic ratio = 81:19, 76:24, 59:41, 48:52, 40:60 and 26:74) by regulating solution pH and the amount of Pt and Co precursor salts to elucidate the effect of catalyst composition on ORR activity. The obtained Pt–Co alloy nanoparticles have face-centred cubic (fcc) structures and are well-dispersed on the surface of the carbon support with a narrow particle size distribution (2–4 nm diameters). The electrocatalysis experiments in alkaline solution reveal a strong correlation between ORR activity and the alloy composition of the catalysts. Interestingly, the mass-specific activities of the catalysts manifest a typical double-volcano plot as a function of alloy composition. In this Pt–Co alloy series, the catalyst with a Pt:Co atomic ratio of 76:24 exhibits the best ORR performance, which is remarkably higher than that of the commercial Pt/C (E-TEK). X-ray photoelectron spectroscopy (XPS) measurements demonstrate that the electronic structures of these catalysts can be tuned by controlling their alloy compositions, which are highly correlated with the trends in ORR activity. The origin of the enhancement in ORR activity may be strongly related to the unique chemical surface structures of the catalysts.

Achieving synergy between inexpensive metals and metal oxides is a key challenge for the development of highly active, economical composites as next-generation catalysts for oxygen reduction reaction (ORR). We have synthesized highly dispersed Ag and Mn3O4 nanocrystals covalently coupled with carbon black via a simple thermal decomposition of AgNO3 and Mn(NO3)2 precursors at elevated temperatures. The resulting Ag and Mn3O4 nanocrystals are located separately on the carbon, but in close proximity to each other. Electrocatalysis experiments in an alkaline solution reveal a remarkably improved electrocatalytic activity and prolonged long-term durability for the Ag–Mn3O4/C composite relative to the Ag/C (90 wt%). Moreover, X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) demonstrate that the unique electronic structures of the composite could be tuned by the substantial electron transfer between the two nanoparticles through the common carbon support, which highly correlates with the enhanced ORR performance. The exact origin of the improved ORR activity may be associated with the favorable formation of monolayer Ag2O film and promoted active oxygen adsorption on the Ag surfaces as a result of the particle-to-particle ligand and ensemble effects between Ag and Mn3O4 phases in this composite.

A novel porous sulfur/carbon nanocomposite was prepared as the cathode material for lithium–sulfur batteries. The porous nanostructure of the composite is beneficial for enhancing the cycle life by accommodating the volume expansion of sulfur particles and adsorbing the polysulfide produced during the electrochemical reaction. The resulting nanocomposite shows a high capacity of 1039 mA h g−1 at 1C (1C = 1675 mA g−1) in the first cycle and the reversible capacity remains high at up to 1023 mA h g−1 even after 70 cycles.

A novel class of Pt–Co secondary solid solution catalysts with long-range ordered intermetallic CoPt3 as the solvent and Co as the solute for the oxygen reduction reaction (ORR) is proposed. The catalysts exhibit a volcano-type dependence on Co solid solubility in ORR activity and the optimum catalyst with 10% Co solid solubility shows remarkably enhanced catalytic activity and durability, which can be ascribed to the unique electronic structure of secondary solid solution catalysts.

Au nanoring@Ag core–shell nanostructures with controllable morphologies and tunable symmetries are synthesized via the seed-mediated growth of Ag onto a sole seed: a circular Au nanoring (AuNR). The 2D isotropic AuNR is prepared firstly by chemical etching, then by galvanic replacement with HAuCl4. By delicately altering the regrowth procedure and mixing the capping agents, different Ag triangular nanoplates with embedded AuNRs in different sizes and shapes can be obtained. Furthermore, by using a single capping agent, the growth of Ag on the AuNR can be preferentially confined to a lateral or vertical mode, to form eccentric nanoplates or nanocubes in both sequence sets at room temperature. Such nanostructures with precisely controllable shape evolution not only displayed unique optical properties, but also revealed the feasibility of breaking the original dimensions, and especially symmetry, at the nanoscale using seed-mediated growth. This paves the way for future applications including catalysis, diagnosis, plasmonics, and biological and chemical sensing.