Highly efficient Co/NC catalyst derived from ZIF-67 for hydrogen generation through ammonia decomposition

Small-size cobalt nanoparticles (NPs) distributed on nitrogen doped carbon support (Co/NC-X) were prepared by pyrolysis of ZIF-67 at various temperatures (X = 500, 600,700 and 800 °C) in nitrogen atmosphere and utilized as catalysts for hydrogen production through ammonia decomposition. Characterizations of the catalysts including XRD, HRTEM, XPS, H₂-TPR, CO₂-TPD, etc., were conducted for structure analysis. The N–C plate obtained from pyrolysis was coated with Co NPs to hinder its aggregation, which made the Co NPs dispersed evenly and increased their dispersion. The calcination temperature and the strong base of the support can adjust the strength of Co–N bond. The activity of the Co/NC-X catalysts is attributed to the high content of Co⁰ and the moderate Co–N bond strength. The ammonia decomposition activity of Co/NC-X catalysts in this paper is higher than many reported Co-based catalysts. Co/NC-600 catalyst demonstrates an ammonia conversion of 80% at 500 °C with a space velocity of 30,000 ml g_cat^?1 h^?1, corresponding to a hydrogen production rate of 26.8 mmol H₂ g_cat^?1 min^?1. The work provides insight for the development of highly active cobalt-based catalysts for hydrogen production through ammonia decomposition.     

The effect of annealing temperature,reaction time,and cobalt precursor on the structural properties and catalytic performance of CoS2 for hydrogen evolution reaction

In this study, cobalt disulfide (CoS₂) nanostructures are synthesized using a simple hydrothermal method. The effects of experimental parameters including cobalt precursor, reaction times, and reaction temperatures are investigated on the structure, morphology and electrocatalytic properties of CoS₂ for hydrogen evolution reaction (HER). The characterization of as-prepared catalysts is performed using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS). The HER efficiency of the catalysts is examined using linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) methods in 0.5 M H₂SO₄ solution. Furthermore, chronoamperometry (CA) is used for stability evaluation. The catalyst obtained from cobalt acetate precursor, within 24 h at 200 °C exhibits superior electrocatalytic activity with a low onset potential (139.3 mV), low overpotential (197.3 mV) at 10 mA. cm^?2 and a small Tafel slope of 29.9 mV dec^?1. This study is a step toward understanding the effect of experimental parameters of the hydrothermal method on HER performance and developing optimal design approaches for the synthesis of CoS₂ as a common electrocatalyst.     

Comparative study on the resistance of different catalysts to electrochemical damage of fuel cells

This paper studies the catalytic performance and resistance to electrochemical damage of different catalysts in fuel cells by DFT calculations. The most commonly used platinum particle catalysts (Pt (111) surface) and three kinds of graphene-based platinum single-atom catalysts (G-N1-Pt, G-N2-Pt and G-N4-Pt) are selected as research objects. Based on Norskov's classical electrochemical theory, the step diagrams of hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) under the standard reaction conditions and the interference with the addition of SO₃⁻ groups are calculated. Combined with the actual adsorption situation in the intermediate steps of the reaction, the catalytic performance of the standard reaction and the catalytic performance under the interference of SO₃⁻ groups are compared. For HOR reaction and ORR reaction, the catalysts with the best catalytic ability and anti-interference ability are G-N1-Pt catalyst and G-N2-Pt catalyst, respectively. A catalyst selection principle that balances activation performance and anti-interference performance in fuel cells is proposed.     

Constructing rod-shaped Co2C/MoN as efficient bifunctional electrocatalyst towards overall urea-water electrolysis

In this paper, Co₂C/MoN/NF at different calcination temperatures (T = 500, 550, 600, 650, 700 °C) was prepared in situ on 3D foam nickel (NF) by hydrothermal treatment and high-temperature calcination. The experimental results show that the sample synthesized at 600 °C (Co₂C/MoN-600/NF) has the best catalytic capacity and the maximum electrochemical active area. For the hydrogen evolution reaction (HER), the potential is only ?176 mV at 100 mA cm^?2, meanwhile, only 1.42 V is needed for urea oxidation reaction (UOR). Furthermore, a two-electrode electrolyze cell of Co₂C/MoN-600/NF6Co₂C/MoN-600/NF was constructed. And the voltage required for overall urea splitting (OUS) is 1.507 V at 50 mA cm^?2, which is 171 mV lower than that of overall water splitting (OWS, 1.678 V). Moreover, the prepared catalyst not only can treat urea in wastewater but also catalyze the production of hydrogen. Therefore, it will be a promising green electrocatalyst.     

Electrochemical performance and distribution of relaxation times analysis of tungsten stabilized La0·5Sr0·5Fe0·9W0·1O3-δ electrode for symmetric solid oxide fuel cells

W-doped La_0·5Sr_0·5Fe_0·9W_0·1O_3-δ (LSFW) was prepared and evaluated as a symmetric electrode for solid oxide fuel cells (SSOFCs). Phase and structural stability of LSFW under both reducing and oxidizing atmospheres was studied. The oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) mechanisms were investigated by using electrochemical impedance spectra (EIS) and distribution of relaxation times (DRT). Electrode polarization resistance (R_p) of LSFW are 0.08 and 0.16 Ω cm² in air and wet hydrogen at 800 °C, respectively. DRT results indicate that the rate-limiting step of LSFW at 800 °C in cathodic conditions and anodic conditions are related to oxygen diffusion and hydrogen adsorption/diffusion, respectively. A La_0·8Sr_0.2Ga_0.8Mg_0·2O_3-δ (LSGM) electrolyte-supported single cell using LSFW electrodes shows a maximum power density of 617.3 mW cm⁻² at 800 °C with considerable stability and reversibility, which enables LSFW a promising SOFCs symmetric electrode material.     

Hierarchical porous spinel MFe2O4 (M=Fe,Zn, Ni and Co) nanoparticles: Facile synthesis approach and their superb stability and catalytic performance in Fischer-Tropsch synthesis

The environmental pollution problem and the dwindling in the crude oil resources have been driving considerable researches into alternative routes for the production of clean and low cost liquid fuels. Fischer-Tropsch synthesis (FTS) is a key-technology and a clean alternative for the production of valuable organic chemicals and high standard liquid fuels through the reaction of syngas (CO/H₂). In this study, one-pot hydrothermal reaction was adopted for the synthesis of robust MFe₂O₄ (M = Fe, Zn, Ni and Co) nanoparticles (NPs) with hierarchical porous-structured. The as-synthesized NPs and without the reported necessary pre-calcination step were appointed as robust catalysts in FTS at various reaction temperature (240–290 °C). The obtained catalytic results have demonstrated that CoFe₂O₄ NPs catalyst with its inversed spinel structure exhibited the optimum catalytic activity compared with the type of normal spinel structure of ZnFe₂O₄ catalyst. More precisely, CoFe₂O₄ NPs catalyst showed the best CO conversion ratio of 96% at 290 °C and the highest light-olefin (C₂–C₄) selectivity value of 63%. However, Fe₃O₄ NPs catalyst displayed the highest selectivity toward long chain hydrocarbon product (C₅₊) of 50 wt%, and the lowest CH₄ selectivity value of 12% at 260 °C. Notably, the obtained results from X-ray diffraction and N₂-physisorption characterization for the spent ferrite catalysts demonstrated that the co-existence of the active sites of Hägg iron carbide (χ-Fe₅C₂) and metallic Co phases and along with the high surface area and pore diameter plays the key role for the obtained high catalytic activity in CoFe₂O₄ NPs. Moreover, the produced catalysts in this study exhibited good stability performance within maintained high catalytic activity for a period of at least 700 h of industrial-relevant FTS conditions.     

Electrocatalytic hydrogen evolution on metallic and bimetallic Pd–Co alloy nanoparticles

Increasing world energy demands and crises led to alternative energy production methods, such as fuel cells using hydrogen gas which is the half electrochemical reaction of water splitting process. Herein, we synthesize polyvinylpyrrolidone coated Pd, Co and Pd_xCo_1-x (x: 0.5, 0.12, 0.23, 0.49, 0.55, 0.62) metallic and bimetallic nanoparticles (NPs) via polyol process alternative to Pt-based catalysts for hydrogen evolution reaction (HER). Detailed structural analyses of Pd, Co and Pd_xCo_1-x NPs revealed that fcc-Pd, fcc/hcp-Co and fcc-PdCo NPs crystal structures, and the lattice parameters were calculated as 3.5358 Å for Co NPs and 3.9777 Å for Pd NPs. The average size confirmed below 9 nm via TEM imaging and XPS data confirmed the formation of a bimetallic PdCo structure. Although Pd catalyst is mostly responsible for HER process, Pd₆₂Co₃₈ catalysts reduced the onset potential to about 197 mV and provided greater current density. Although E_a values were slightly higher against the Pt/C (20 wt %) benchmark which is reported as 16 kJ mol⁻¹, PdCo NPs provided considerably reduced activation energy (E_a) values compared to Pd/C catalyst of 31 kJ mol⁻¹. The best onset potential was recorded for Pd₆₂Co₃₈ catalysts for HER activity which is 16 mV higher compared to commercially available Pt/C catalyst.     

Different alkaline earth metals doped Sm0.5A0.5Fe0.9Ni0.1O3-δ (A=Ca,Sr and Ba) for symmetric solid oxide fuel cells

Symmetric solid oxide fuel cells have gained increasingly attention due to their characteristics of simple fabrication and low cost. Due to the same anode and cathode used, the oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) of the electrodes are very demanding. In this work, Sm_0.5 × _0.5Fe_0.9Ni_0.1O_3-δ (X = Ca, Sr, Ba, SCFN, SSFN, SBFN) were synthesized, and the physico-chemical properties of three materials and their electrochemical performance as electrodes were systematically studied. They all maintain stable phase structures under oxidizing and reducing atmospheres below 750 °C. X-ray photoelectron spectroscopy (XPS) results showed that metal nanoparticles was exsolved and oxygen vacancies were increased after the treatment in reducing atmosphere at 750 °C. For electrochemical performance test, the peak power densities of symmetrical cells with SCFN-GDC, SSFN-GDC and SBFN-GDC electrodes can reach 26.7, 186.78, and 138.8 mWcm^?2 at 750 °C, respectively. Moreover, SSFN-GDC cell showed better long-term stability than the other two.     

CoSe2@NiSe2 nanoarray as better and efficient electrocatalyst for overall water splitting

Electrocatalytic water splitting is identified as one of the most promising solutions to energy crisis. The CoSe₂@NiSe₂ materials were first prepared and in situ grown on nickel foam by typical hydrothermal and selenification process at 120 °C. The results show that the CoSe₂@NiSe₂ material used as the 3D substrates electrode can maximize the synergy between the CoSe₂ and NiSe₂, and also exhibits high efficiency of water splitting reaction. The lower overpotential of only 235 mV is presented to attain 20 mA cm⁻² compared to the benchmark of RuO₂ electrodes (270 mV @ 20 mA cm⁻²). Besides, the CoSe₂@NiSe₂ material also shows a remarkable improved hydrogen evolution reaction activity compared to NiSe₂ (192 mV@10 mA cm⁻²) and Co precursor catalysts (208 mV@10 mA cm⁻²) individually, which a low overpotential of only 162 mV is achieved at 10 mA cm⁻². The CoSe₂@NiSe₂ catalysts exhibit excellent water splitting performance (cell voltage of 1.50 V@ 10 mA cm⁻²) under alkaline conditions. It was proved that the high water splitting performance of the catalyst is attributed to high electrochemical activity area and synergistic effect. The work offers new ideas for the exploitation of synergistic catalysis of composite catalysts and adds new examples for the exploitation of efficient, better and relatively non-toxic electrocatalysts.     

Effect of metal particle size and Nafion content on performance of MEA using Ir-V/C as anode catalyst

Ir and Ir-V nanoparticles were synthesized in ethylene glycol using IrCl₃ and NH₄VO₃ as the Ir and V precursors, respectively. These nanoparticles were evaluated as anode catalysts in proton exchange membrane fuel cells (PEMFCs). A thermal treatment of the catalysts at 200 °C in a reducing atmosphere leads to very high electrocatalytic activity for the hydrogen oxidation reaction. The fuel cell performance reveals an optimal Nafion ionomer content of 25% in the catalyst layer used for the MEA fabrication. The electrocatalytic effects related to the change in the electrocatalyst structure are discussed based on the data obtained by X-ray diffraction (XRD) and transmission electron microscopy (TEM). In addition, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques are used in-situ to assess the kinetics of hydrogen oxidation on the surface of these catalysts. A maximum power density of 1016.6 mW cm⁻² was obtained at 0.598 V and 70 °C with an anode catalyst loading of 0.4 mg (Ir) cm⁻². This performance is 50.7% higher than that for commercially available Pt/C catalysts under the same conditions. In addition, we also tested the anode catalyst with a low loading of 0.1 mg (Ir) cm⁻², the maximum power density is 33.8% higher than that of the commercial Pt/C catalyst with a loading of 0.4 mg (Pt) cm⁻².     

Design of electrocatalysts with reduced Pt content supported on mesoporous NiWO4 and NiWO4-graphene nanoplatelets composite for oxygen reduction and hydrogen oxidation in acidic medium

Herein, a new direct synthesis route leading to a mesoporous NiWO₄ with crystalline framework and NiWO₄ - graphene nanoplatelets (GNP) composite is reported. Ni and W assembled into a mesoporous tungstate type of symmetry by co-precipitation synthesis route and its composite with GNP were used as supports for electrocatalysts, with reduced Pt content (8 wt.%), in oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) in acidic medium. A comprehensive assessment of the modifications related to the crystalline and porous structures, morphological aspects as well as the surface chemistry aiming to explain the electrochemical properties was performed. It was found that the presence of GNP during the synthesis process leads, mainly, to the enhanced growth of NiWO₄ nanocrystallites, as well as induces changes in the surface chemistry. The electrochemical results show that the introduction of GNPs into the NiWO₄ composite support leads to a significant improvement in the activity of the Pt electrocatalyst in ORR and HOR compared to both initial NiWO₄ and Pt/NiWO₄ samples, as well as mechanical mixtures of these catalysts with carbon. Mass activity for hydrogen oxidation, determined in a mixed kinetic-diffusion controlled region, obtained on the 8 wt.% Pt/NiWO₄-GNP catalyst was significantly higher compared to the commercial 20 wt.% Pt/C Quintech catalyst. Our comprehensive structural and surface chemistry assessments indicate this composite material as a viable electrocatalyst for PEMFCs using a broader type of fuels.     

Activity and stability optimization of RuxIr1-xO2 nanocatalyst for the oxygen evolution reaction by tuning the synthetic process

IrO₂ and RuO₂ are known as two of the best catalysts for the oxygen evolution reaction (OER) in acidic electrolyte. It is reported that RuO₂ has higher OER catalytic activity, while IrO₂ possesses better electrochemical stability during the OER process in acid. Therefore, many combined strategies have been proposed to utilize the advantages of both IrO₂ and RuO₂ catalysts in water electrolysis applications. In this article we describe how, by tuning the wet-chemical synthesis process in which the Ir precursor is added after the synthesis of RuO₂ nanoparticles (NPs) (two-step), the Ru_0.5Ir_0.5O₂ NPs have been synthesized to improve the OER catalytic activity in both acidic and alkaline media. In detail, the specific OER activity of the Ru_0.5Ir_0.5O₂ NPs (with a particle size of ca. 10 nm) is 48.9 μA cm⁻² at an overpotential ŋ = 0.22 V (vs. RHE) and 21.7 μA cm⁻² at ŋ = 0.27 V (vs. RHE) in 0.1 M HClO₄ and 0.1 M KOH, respectively. These values are higher than those for the one-step (Ir_0.5+Ru_0.5)O₂ NPs (obtained by contemporaneously adding both Ru and Ir precursors), which are 19.5 and 15.5 μA cm⁻² at the same measuring conditions, respectively. Additionally, with more IrO₂ component distributed on the particle surface, the two-step Ru_0.5Ir_0.5O₂ NPs show better OER catalytic stability than RuO₂ NPs.     

TiO2–CdS supported CuNi nanoparticles as a highly efficient catalyst for hydrolysis of ammonia borane under visible-light irradiation

TiO₂–CdS nanotubes (NTs) were used for the first time as a support to load metal nanoparticles (NPs) for the hydrolysis of ammonia borane (AB) which is a new strategy. The TiO₂–CdS NTs support was first synthesized using a hydrothermal method, and then the CuNi NPs were loaded using a liquid-phase reduction method. The synthesized samples were characterized by XRD, SEM-EDS, TEM, XPS, ICP, UV–Vis, and PL analyses. The characterization results show that the CuNi NPs existed in the form of an alloy with a size of ~1.2 nm and uniformly dispersed on the support. Compared with their single metal counterparts, the bimetallic CuNi-supported catalysts showed a higher catalytic activity in the hydrolysis of AB under visible-light irradiation: Cu_0·45Ni_0·55/TiO₂–CdS catalyst had the fastest hydrogen evolution rate with a high conversion frequency (TOF) of 25.9 mol_H2·mol_cat⁻¹ min⁻¹ at 25 °C and low activation energy of 32.8 kJ mol⁻¹. Cu_0.45Ni_0.55/TiO₂–CdS catalyst showed good recycle performance, maintaining 99.3% and 85.6% of the original hydrogen evolution rate even after five and ten recycles, respectively. Strong absorption of visible light, improved electron–hole separation efficiency, and metal synergy between Cu and Ni elements played a crucial role in improving the catalytic hydrolysis performance of AB. The catalyst prepared in this study provides a new strategy for the application of photocatalysts.     

Fine interface contact and high activity of nickel-based anode modified by gadolinium for hydrogen and methane fuel

In this work, gadolinium is used to modify nickel catalyst, which can improve the properties of nickel oxide particle and inhibit its sintering and grain growth. Interface contact between nickel catalyst and YSZ is significantly improved and fine anode microstructure can be obtained when gadolinium is used to modify Ni-YSZ anode. Fine interface contact of GdNi-YSZ anode can accelerate charge transfer process and steam formation process, which leads to high activity for electrochemical oxidation of hydrogen and low impedance resistance. The remarkable characteristic of GdNi-YSZ anode cell is that the cell performance for humidified methane fuel is greatly improved due to the high anode activity for methane reforming and electrochemical oxidation of hydrogen. The maximum power density of GdNi-YSZ anode cell with humidified methane as fuel can reach 1.59 W/cm² at 800 °C and 0.46 W/cm² at 650 °C. High performance of GdNi-YSZ anode cell with humidified methane as fuel leads to much H₂O produced during the electrochemical oxidation process, which can depress carbon deposition and improve the cell stability for humidified methane fuel.     

Effect of treatment temperature on the performance of RuO2 anode electrocatalyst for high temperature proton exchange membrane water electrolysers

Ruthenium oxide catalysts were prepared by a sol–gel technique and calcined at different temperatures e.g., 400 °C, 500 °C and 600 °C. The catalysts performance for the oxygen evolution reaction was studied using cyclic voltammetry and their performance in a high temperature proton exchange membrane water electrolyser (PEMWE) examined. Physio-chemical characterization was carried out to study the thermal stability, oxygen-metal bond formation, crystallinity phase and crystallite size, particle size and elemental analysis by TGA, FTIR, XRD, TEM and EDX respectively. The electrolyte used for electrochemical characterisation was 1.0 M H₃PO₄ and 0.5 M H₂SO₄. Additionally, the effect of calcination and electrolyte temperature on oxygen evolution reaction of RuO₂ catalysts was studied and the apparent activation energy was determined using chronoamperometry. The prepared RuO₂ were tested as anode catalyst in PEMWE in the temperature range of 120–150 °C using phosphoric acid doped polybenzimidazole membrane electrolyte. The physio-chemical and electrochemical characterization results indicate that RuO₂ calcined at 500 °C gave the best performance with a current density of 0.875 A cm⁻² at 1.8 V in a PEMWE operated at 150 °C.     

Tungsten(VI) oxide supported rhodium(0) nanoparticles; highly efficient catalyst for H2 production from dimethylamine borane

It reports the preparation and characterization of tungsten(VI) oxide supported rhodium(0) nanoparticles (Rh⁰/WO₃ NPs) being used as catalysts in releasing H₂ from dimethylamine borane (DMAB). The reducible nature of WO₃ plays a significant role in the catalytic efficiency of rhodium(0) nanoparticles in the dehydrogenation of DMAB. The Rh⁰/WO₃ NPs were in-situ generated from the reduction of Rh²⁺ ions on the surface of WO₃ during the catalytic dehydrogenation of dimethylamine borane in toluene and isolated from the reaction solution after the dehydrogenation to be characterized by using SEM, TEM, XPS, ATR-IR and XRD. The results reveal the formation of Rh⁰ NPs with a mean particle size of 1.92 ± 0.34 nm dispersed on the surface of tungsten(VI) oxide. Rh⁰/WO₃ NPs are found to be very active catalyst releasing 1.0 equiv. H₂ per mole of dimethylamine borane under ambient conditions. Among the various WO₃ supported Rh⁰ NPs with different metal loadings, the sample with 0.1% wt. Rh provide the record catalytic activity (TOF = 2816 h^?1) which is one of the highest value ever reported for rhodium-based catalysts in H₂ generation from DMAB at 60.0 ± 0.5 °C. Rh⁰/WO₃ NPs were also reusable catalyst in dehydrogenation of DMAB retaining 55% of their initial catalytic activity in the 3rd run of the dehydrogenation reaction. Control experiments were performed at various catalyst concentrations and temperatures to investigate the kinetics of dehydrogenation and to calculate the activation parameters for the reaction.     

Solid oxide cells with cermet of silver and gadolinium-doped-ceria symmetrical electrodes for high-performance power generation and water electrolysis

A cermet of silver and gadolinium-doped-ceria (Ag-GDC) is investigated as novel symmetrical electrode material for (ZrO₂)_0.92(Y₂O₃)_0.08 (YSZ) electrolyte-supported solid oxide cells (SOCs) operated in fuel cell (SOFC) and electrolysis (SOEC) modes. The electrochemical performances are evaluated by measuring the current density-voltage characteristics and impedance spectra of the SOCs. The activity of hydrogen and air electrodes is investigated by recording overpotential versus current density in symmetrical electrode cells, respectively in hydrogen and air, using a three-electrode method. Conventional hydrogen electrode, Ni-YSZ, and oxygen electrode, LSCF (La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ)-GDC, are tested as comparison. The results show that, as an oxygen electrode, Ag-GDC is more active than LSCF-GDC in catalyzing both oxygen reduction reaction (ORR) in an SOFC and oxygen evolution reaction (OER) in an SOEC. As a hydrogen electrode, Ag-GDC is more active than Ni-YSZ in catalyzing hydrogen oxidation reaction (HOR) in an SOFC and hydrogen evolution reaction (HER) in an SOEC, especially in high steam concentration. An SOC with symmetrical Ag-GDC electrodes operated in a fuel cell mode, with 3% H₂O humidified H₂ as the fuel, displays a peak power density of 395 mWcm^?2 at 800 °C. Its polarization resistance at open circuit voltage is 0.21 Ω cm². Ag-GDC electrode can be operated even at pure steam. An SOEC operated for electrolyzing 100% H₂O, the current density reaches 720 mA cm^?2 under 1.3 V at 800 °C.     

Atomic interface engineering: Strawberry-like RuO2/C hybrids for efficient hydrogen evolution from ammonia borane and water

Efficient hydrogen production plays a key role in establishing hydrogen economy in the current world. In this study, we fabricated ultrafine RuO₂ nanoparticles on carbon black to form a strawberry-like RuO₂/C hybrid, using by a solid-phase grinding and subsequent low-temperature annealing. The synthesized hybrid displays very low reaction activation energy (28.5 KJ mol^?1) for hydrogen evolution from ammonia borane. In case of hydrogen evolution from alkaline water, it also exhibits a remarkably improved electrocatalytic activity than a commercial Pt/C, with an ultra-low overpotential of 8 mV (at 10 mA cm^?2). For the above bifunctional catalyst, the formed C–Ru–C bonds between the ruthenium oxide and carbon result in the ultrahigh activity of the hybrid, as evidenced by DFT results. This work offers a guideline to synthesize efficient metal-based (Ru, Pd, Rh, Ir, Au, etc.) catalysts with smart structures for catalysis.     

Ru–RuO2/C as an efficient catalyst for the sodium borohydride hydrolysis to hydrogen

How to efficiently hydrolyze NaBH₄ to H₂ has been greatly concerned due to its theoretically high hydrogen storage capacity (10.8 wt. %). In this work, Ru–RuO₂/C catalyst is prepared by the galvanic replacement reaction of Ni based material. By evaluating the hydrolysis activity, analyzing the structure and component of the catalysts and exploring the possible reaction channels, we find that Ru–RuO₂/C has the excellent hydrolysis activity of 16.8 L H₂ min⁻¹ g_cat.⁻¹ in 5 wt. % NaBH₄ and 1 wt. % NaOH solution at 323 K, which is higher than most data in open literature. The more reducible RuO₂ (110) crystal at about 423 K plays an important role in the high hydrolysis activity of Ru–RuO₂/C. The ruthenium oxide facilitates the dissociation of water, a rate-determining step of NaBH₄ hydrolysis to H₂, while Ru acts as an active phase for NaBH₄ dissociation. A synergetic effect of RuO₂ and Ru on Ru–RuO₂/C is crucial to the high hydrolysis activity of sodium borohydride and it can also be kept in repeated experiments.     

Solvothermal synthesis of iron phosphides and their application for efficient electrocatalytic hydrogen evolution

In this paper, we present a solvothermal synthesis of iron phosphide electrocatalysts using a triphenylphosphine (TPP) precursor. The synthetic protocol generates Fe₂P phase at 300 °C and FeP phase at 350 °C. To enhance the catalytic activities of obtained iron phosphide particles heat-treatments were carried out at elevated temperatures. Annealing at 500 °C under reductive atmosphere induced structural changes in the samples: (i) Fe₂P provided a pure Fe₃P phase (Fe₃P−500 °C) and (ii) FeP transformed into a mixture of iron phosphide phases (Fe₂P/FeP−500 °C). Pure Fe₂P films was prepared under argon atmosphere at 450 °C (Fe₂P−450 °C). The electrocatalytic activities of heat-treated Fe₂P−450 °C, Fe₃P−500 °C, and Fe₂P/FeP−500 °C catalysts were studied for hydrogen evolution reaction (HER) in 0.5 M H₂SO₄. The HER activities of the iron phosphide catalyst were found to be phase dependent. The lowest electrode potential of 110 mV vs. a reversible hydrogen electrode (RHE) at 10 mA cm⁻² was achieved with Fe₂P/FeP−500 °C catalyst.