N-doped graphene supported W2C/WC as efficient electrocatalyst for hydrogen evolution reaction

Tungsten carbides (W₂C and WC) materials, as promising non-precious electrocatalysts, possess highly efficient activity for HER. Herein, N-doped graphene supported tungsten carbide (N–W₂C/WC) nanocomposite is synthesized by spray drying process followed with a two-step pyrolysis treatment, which exhibits a remarkable hydrogen evolution reaction (HER) activity and excellent stability in acidic solution and alkaline solution. N–W₂C/WC displays low overpotentials of 166 mV and 125 mV to achieve a current density of 10 mA cm^?2 and small Tafel slopes of 60.97 and 62.66 mV dec^?1 in 0.5 M H₂SO₄ and 1.0 M KOH, respectively. After 1000 cycles, the electrocatalytic activity of N–W₂C/WC is almost no change in acidic media but slightly decreases in alkaline media. This work might provide a new way to explore high comprehensive performance tungsten-based electrocatalyst for HER.     

NiMo/Cu-nanosheets/Ni-foam composite as a high performance electrocatalyst for hydrogen evolution over a wide pH range

We designed and fabricated non-precious and highly efficient electrocatalysts of nickelmolybdenum/copper-nanosheets/nickel-foam composites (NiMo/Cu-NS/NF) by step electrodepositions, combining with chemical oxidation method. The catalysts were charaterized by means of SEM, XRD and XPS spectra. Their electrocatalytic activities were assessed by hydrogen evolution reactions (HER) over a wide pH range, where acidic, neutral and alkaline electrolytes were used, respectively. Benefiting from the unique midlayer Cu nanosheets (NS) architecture and optimum Mo–Ni composition at the surface layer which led to high electronic conductivity and large electrochemically active surface area (ECSA), the NiMo/Cu-NS/NF-2 catalyst displayed superior electrocatalytic activities with low overpotentials of η₁₀ = 43, 86 and 89 mV in 0.5 M H₂SO₄, 1.0 M PBS and 1.0 M KOH electrolyte, respectively. Especially in the acidic condition, it exhibited the best electrocatalytic activity with smaller Tafel slope of 54 mV dec^?1 and higher exchange current density of 1.93 mA cm^?2.     

Self-supported N-Doped Carbon@NiXCo2-XP core-shell nanorod arrays on 3D Ni foam for boosted hydrogen evolution reaction

The development of highly efficient and low-cost electrocatalysts for large-scale hydrogen evolution reaction (HER) is great important but remains a significant challenge. Transition-metal phosphides (TMPs) have attracted intense attention as promising non-noble-metal HER electrocatalysts due to their unique electronic properties and high intrinsic catalytic activities. Herein, we directly grew Ni_XCo_2-XP nanorod wrapped with N-doped carbon shell on 3D Ni foam to fabricate a self-supported electrode with core-shell nanorod array morphology. The obtained hybrid electrode exhibits remarkable electrocatalytic HER activity over a wide pH range with low overpotentials of 121 mV and 181 mV to obtain the current density of 200 mA cm⁻² in 0.5 M H₂SO₄ and 1 M KOH electrolytes, respectively, which is comparable to that of the current state-of-the-art Pt/C electrocatalyst. The experimental results indicate that the elaborate architectural superiority and compositional synergy of this hybrid electrode give rise to the boosted HER performance.     

Overall noble metal free Ni and Fe doped Cu2ZnSnS4 (CZTS) bifunctional electrocatalytic systems for enhanced water splitting reactions

Herein, we report an inexpensive synthesis of sonochemical nickel and iron (M = Ni, Fe) doped Cu₂ZnSnS₄ (CZTS) and their utility as a nanoelectrodes for improved electrocatalytic water splitting performance. The as-synthesized electrode materials were characterized further by Transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman and X-ray photoelectron (XP) spectroscopic studies. Significantly, Ni doped CZTS electrocatalyst exhibits low overpotential approximately 214 and 400 mV for the hydrogen evolution reactions (HER) in 0.5 M H₂SO₄ and 1 M KOH electrolyte solutions respectively, and 1.29 V vs RHE for the oxygen evolution reactions (OER) in 1 M KOH at 10 mA/cm² current density. Small Tafel slopes and tested durability for longer time i.e. upto 500 min for water splitting, demonstrates that Ni doped CZTS is efficient bifunctional electrocatalyst having high activity along with extraordinary current/potential stability. Moreover, Fe doped CZTS electrocatalyst shows relatively poor response, i.e. overpotential 300 mV in 0.5 M H₂SO₄ and 445 mV in 1.0 M KOH towards HER and overpotential 1.54 V for the OER in 1 M KOH reaches at 10 mA/cm². This highly efficient bifunctional electrocatalysts that can meet the existing energy anxiety.     

Urchin-like Co0.8-Mn0.2-P/CC nanowires array: a high-performance and cost-effective hydrogen evolution electrocatalyst

Using cost-effective materials to replace precious Pt-based hydrogen evolution reaction (HER) catalysts holds great foreground for energy saving and environmental protection. In this work, we successfully prepared an urchin-like Co_0.8-Mn_0.2-P nanowires array supported on carbon cloth (CC) through a hydrothermal-phosphatization strategy and we also systematically studied its electrocatalytic HER performance. Electrochemical tests demonstrate that our urchin-like Co_0.8-Mn_0.2-P/CC possesses outstanding HER activity in acidic and alkaline media. In 0.5 M H₂SO₄, this urchin-like Co_0.8-Mn_0.2-P/CC only requires an overpotential of 55 mV to drive a current density of 10 mA cm⁻², with the Tafel slope of 55.9 mV dec⁻¹. Similarly, when reaching the same current density, just a particularly low overpotential of 61 mV is required with a corresponding Tafel slope of 41.7 mV dec⁻¹ in 1 M KOH. Furthermore, this electrocatalyst exhibits superior stability with 1000 cycles of cyclic voltammetry and 24 h in the I-T test. Such excellent HER catalytic performance can be attributed to the synergistic effect between Co and Mn atoms and high electrochemical active surface area (ECSA). Our work provides a valuable synthesis strategy of non-precious and high HER performance catalytic material.     

Accessible active sites activated by nano cobalt antimony oxide @ carbon nanotube composite electrocatalyst for highly enhanced hydrogen evolution reaction

The electrochemical hydrogen evolution reaction (HER) was one of new energy development strategies with clean, efficient and renewable characteristics, and electrocatalysts play a crucial role in HER technology. Herein, a composite material (CSO@0.5CNT) derived from the combination of nano cobalt antimony oxide (CSO) with carbon nanotubes (CNT) through hydrothermal reaction, in which the nanoparticles of CSO were closely compounded on the surface of CNT, could be a highly efficient electrocatalyst for HER in 1 M KOH. The binary composite electrocatalyst of CSO and CNT reduced the internal resistance, promoted the charge transfer, exhibited a large electrochemical active area, and obtained the lower overpotential, with 155 mV at 10 mA/cm² current density. Moreover, such a CSO@0.5CNT electrocatalyst displayed a small Tafel slope of 86.5 mV dec^?1, excellent catalytic activity and extraordinary long-term structural stability after 30 h and 3000 CV cycles. Furthermore, the electrocatalytic mechanism revealed by Density Functional Theory (DFT) calculation proved that, the decomposition of H₂O molecules was the control step of the whole HER, and the superior electron transport ability of CNT was favorable to the improvement of electrocatalytic performance. Benefitting from accessible active sites on carbon nanotube (C atom) and CSO (Co atom), the composite electrocatalyst of CSO@0.5CNT displayed synergistic effect for electrocatalytic HER properties, and that was the main mechanism for significantly improving the electrocatalytic activities. Our work provides a novel strategy towards high-efficiency electrocatalysts for hydrogen evolution reaction.     

Transition metal chalcogenides based nanocomposites as efficient electrocatalyst for hydrogen evolution reaction over the entire pH range

In the present investigation, a series of noble metal-free, earth-abundant, inexpensive, efficient, and long-term stable electrocatalysts have been developed for hydrogen evolution reaction at different pH values. Transition metal chalcogenides nanocomposites, namely, CoTe₂@CuTe, FeTe₂@CuTe, CoSe₂@CuSe₂, and FeSe₂@CuSe₂ have been synthesized via hydrothermal method and their electrocatalytic activity towards hydrogen evolution reaction at different pH values have been studied using different techniques. All the four investigated electrocatalysts are efficient towards the hydrogen evolution reaction. Out of these electrocatalysts, the sphere-like shaped CoTe₂@CuTe nanocomposite exhibits outstanding electrocatalytic activity towards hydrogen evolution reaction at different pH values. The novelty of the designed catalyst is its specific shape, low cost and high activity towards HER. The overpotential of CoTe₂@CuTe nanocomposite electrocatalyst to achieve current density of 10 mA/cm² has been found as 68, 106, and 125.8 mV in 0.5 M H₂SO₄ (pH < 0), 1.0 M KOH (pH ≈ 14) and 1.0 M PBS (pH ≈ 7), respectively and corresponding Tafel slope as 59.94, 67.6 and 69.53 mV/decade, respectively. Thus, CoTe₂@CuTe nanocomposite exhibits good electrocatalytic activity in acidic, basic, and neutral medium. It possesses significant Brunauer-Emmett-Teller surface area, synergic effect, small charge transfer resistance, good conductivity, considerable electrochemically surface area (ECSA) value, and higher number of active sites.     

Cobalt phosphide nanoparticles embedded in 3D N-doped porous carbon for efficient hydrogen and oxygen evolution reactions

An electrocatalyst based on a unique three-dimensional (3D) N-doped porous carbon sheet networks embedded with CoP₂ nanoparticles (CoP₂@3D-NPC) was synthesized by a facile pyrolysis process as well as an in-situ phosphatization method. The improved CoP₂@3D-NPC hybrid materials show excellent electrocatalytic activity toward HER and OER. This material provides a low overpotential of 126 mV at 10 mA cm⁻² in 0.5 M H₂SO₄ and 167 mV at 20 mA cm⁻² in 1.0 M KOH for HER with a small Tafel slope value of 59 mV dec⁻¹, respectively. Besides, it is also active for the OER under alkaline conditions. Such a prominent property of the CoP₂@3D-NPC electrocatalyst could be attributed to its excellent electrical conductivity of 3D carbon substrate, strong synergistic effect between CoP₂ nanoparticles and carbon nanosheet as well as extra active sites created by the N-doped structure.     

Heterostructured CoP/MoO2 as high efficient electrocatalysts for hydrogen evolution reaction over all pH values

Delicate design and rapid development of low-cost, highly active, and perdurable pH-universal heterogenveous hydrogen evolution reaction (HER) electrocatalysts are demanding challenge in energy-conversion technologies. Herein, heterostructured CoP/MoO₂ electrocatalyst was synthesized by employing MoO₂ nanorods as framework for the growth of CoP nanoparticles. Owing to the fact that the effective interface of heterostructure can enhance electron transfer/mass diffusion and expose ample active sites, the CoP/MoO₂ reveals eminent HER activities with favorable long-term stability in all pH electrolytes, overpotentials of 69, 78, and 165 mV in 0.5 M H₂SO₄, 1.0 M KOH, and 1.0 M PBS (phosphate-buffered solution) electrolytes were required for CoP/MoO₂ to reach the current density of 10 mA cm^?2. This work emphasizes that strategy of electronic structure engineering holds great promises in pH-universal HER electrocatalysts for energy storage and conversion.     

One-step synthesis of Co2P/N-P co-doped porous carbon composites derived from soybean derivatives as acidic and alkaline HER electrocatalysts

Developing inexpensive and efficient electrocatalysts for hydrogen evolution reaction (HER) in both acidic and alkaline mediums is of great significance to the hydrogen energy industry. Hereby, we prepared a mixture of precursors with homogeneous composition by using the chelating ability of soybean protein isolate (C and N source) and phytic acid (dopant and phosphating agent) with cobalt ions, and achieved one-step synthesis and construction of Co₂P/N–P co-doped porous carbon composite by carbonization at 800 °C. The as-synthesized Co₂P/NPPC-800 electrocatalyst exhibits low HER overpotentials of 121 and 125 mV at 10 mA cm^?2 in 0.5 M H₂SO₄ and 1.0 M KOH, which are close to those of the commercial Pt/C catalyst. Additionally, the NPPC substrate surrounding the Co₂P could diminish the corrosion during the HER, and Co₂P/NPPC-800 displays good stability and durability. Furthermore, this work offers a convenient synthesis strategy for phosphide/doped porous carbon composites in other electrochemical energy technologies.     

Ultrasmall Mo2C in N-doped carbon material from bimetallic ZnMo-MOF for efficient hydrogen evolution

The exploration and development of cost-effective and highly stable electrocatalysts with the highest possible energy efficiency remain a constant pursuit in the catalyst design and synthesis for electrocatalytic hydrogen evolution reaction (HER). In this work, a convenient approach is proposed to synthesize a type of ultrafine Mo₂C nanoparticles in average sizes of 3–4 nm embedded in hierarchically porous N-doped carbon material calcined from bimetallic ZnMo-MI (MI = 2-methylimidazole) is obtained at 1000 °C, denoted as ZnMo-MI-1000. First of all, the crystalline hybrid metal-organic framework of ZnMo-MI is fabricated from zeolitic imidazolate framework of Zn-MI precursors via solvothermal reaction, in which the conversion from Zn-MI to ZnMo-MI occurs gradually over time. After calcination, the as-obtained ZnMo-MI-1000 sample shows a satisfying HER performance with the small overpotential of 83.0 mV in 0.5 M H₂SO₄ and 100.1 mV in 1.0 M KOH to reach a current density of 10 mA cm^?2, which is attributed to ultrasmall Mo₂C, Mo and N-doped graphitic carbon matrix. The multiporous network of ZnMo-MI-1000 can provide continuous mass transportation with a minimal diffusion resistance that produce effective electrocatalytic kinetics in both acidic and alkaline media, which is utilized as a highly active and durable nonprecious metal electrocatalyst for HER.     

Low loading of P modified Rh nanoparticles encapsulated in N,P-doped carbon for boosted and pH-universal hydrogen evolution reaction

Searching for highly efficient and Pt-free electrocatalysts with comparable hydrogen evolution reaction (HER) activities to the benchmark Pt/C catalyst is highly demanded for developing renewable water electrolysis system but still remains challenging. In the current work, low loading of P modified ultrafine Rh nanoparticles encapsulated in N, P dual-doped carbon layers (Rh–P@NPC) have been prepared through a facile polymerization-impregnation followed by high-temperature pyrolysis process. Benefiting from the unique core-shell structural advantages and synergistic effect of Rh–P and NPC components, the resulting Rh–P@NPC catalyst not only exhibits remarkable electrocatalytic activity for HER in the whole pH range with a low overpotential of 31 mV, 65 mV, and 130 mV to drive a current density of 10 mA cm^?2 in 0.5 M H₂SO₄, 1.0 M KOH, and 1.0 M PBS, respectively, but also demonstrates high durability. It is worth to note that all these HER performances are on a par with commercial Pt/C catalysts for HER. This synthetic strategy provides possibility for the fabrication of carbon-based heterostructures with high catalytic activity and durability in harsh environments.     

Ni modified ultrafine MoxC (x = 1, 2) wrapped by nitrogen-doped carbon for efficient hydrogen evolution reaction in acid and alkaline electrolytes

Hydrogen production is of significance in solving urgent energy and environmental issues, so it is necessary to develop superior electrocatalysts to catalyze the sustainable hydrogen evolution process efficiently. This study reports the synthesis of the Ni modified ultrafine Mo_xC (x = 1, 2) wrapped by nitrogen-doped carbon through a facile one-pot strategy, which can be applied for catalyzing the hydrogen evolution reaction (HER) in both acid and alkaline conditions. Benefiting from the regulating effect of Ni towards Mo_xC (x = 1, 2) and the synergistic mechanism among Ni, Mo₂C and MoC, Ni/Mo_xC-NC exhibits superior electrocatalytic activity, displaying a low overpotential of 141 mV in 0.5 M H₂SO₄ and 110 mV in 1 M KOH at a current density of 10 mA cm⁻² for HER, as well as long-term durability for 20 h.     

Three-dimensional interconnected MoS2 nanosheets on industrial 316L stainless steel mesh as an efficient hydrogen evolution electrode

The development of inexpensive and competent electrocatalysts for high-efficiency hydrogen evolution reaction (HER) has been greatly significant to realize hydrogen production in large scale. In this paper, we selected the inexpensive and commercially accessible stainless steel as the conductive substrate for loading MoS₂ as a cathode for efficient HER under alkaline condition. Interconnected MoS₂ nanosheets were grown uniformly on 316-type stainless steel meshes with different mesh numbers via a facile hydrothermal way. And the optimized MoS₂/stainless steel electrocatalysts exhibited superior electrocatalytic performance for HER with a low overpotential of 160 mV at 10 mA cm⁻² and a small Tafel slope of 61 mV dec⁻¹ in 1 M KOH. Systematic study of the electrochemical properties was performed on the MoS₂/stainless steel electrocatalysts in comparison with the commonly used carbon cloth to better comprehend the origin of the superior HER performance as well as stability. By collaborative optimization of MoS₂ nanosheets and the cheap stainless steel substrate, the interconnected MoS₂ nanosheets on stainless steel provide an alternative strategy for the development of efficient and robust HER catalysts in strong alkaline environment.     

Ultra-fine Ru nanoparticles decorated V2O3 as a pH-universal electrocatalyst for efficient hydrogen evolution reaction

Developing high-efficiency electrocatalysts viable for pH-universal hydrogen evolution reaction (HER) has attracted great interest because hydrogen is a promising renewable energy carrier for replacing fossil fuels. Herein, we present a facile strategy for fabricating ultra-fine Ru nanoparticles (NPs) decorated V₂O₃ on the carbon cloth substrates as efficient and stable pH-universal catalysts for HER. Benefiting from the metallic property and electronic conductivity of V₂O₃ matrix, the optimized hybrid (Ru/V₂O₃-CC) exhibits excellent HER activities in a wide pH range, achieving lower overpotentials of 184, 219, and 221 mV at 100 mA cm⁻² in 0.5 M H₂SO₄, 1.0 M KOH and 1.0 M phosphate-buffered saline, respectively. Moreover, the electrode remains superior stability with negligible degradation after 5000 cyclic voltammetry scanning whether in acidic, alkaline or neutral media. Experimental results, combined with theoretical calculations, demonstrate that the interaction between Ru NPs and the support V₂O₃ induces the local electronic density diversity, allowing optimization of the adsorption energy of Ru towards hydrogen intermediate H1, thus favoring the HER process.     

Mixed-metal MOF-derived Co-doped Ni3C/Ni NPs embedded in carbon matrix as an efficient electrocatalyst for oxygen evolution reaction

The exploration of electrocatalysts with high oxygen evolution reaction (OER) activity is highly desirable and remains a significant challenge. Transition metal carbides (TMCs) have been investigated as remarkable hydrogen evolution reaction (HER) electrocatalysts but few used as oxygen evolution reaction (OER) electrocatalysts. Herein, a Co doped Ni₃C/Ni uniformly dispersed in a graphitic carbon matrix was prepared by pyrolysis of a metal organic framework (Co/Ni-MOF) under a flow of Ar/H₂ at 350 °C, and Ni₃C/Ni@C was also prepared for comparison. The various characterization techniques confirmed the successful preparation of the heteroatom doped TMCs-based catalysts by pyrolysis of MOFs. Co doped Ni₃C/Ni@C exhibited superior electrocatalytic properties for OER. For example, Co–Ni₃C/Ni@C depicts a lower overpotential and smaller Tafel slope than Ni₃C/Ni@C and IrO₂ during the OER in 1 M KOH solution, additionally, it shows a higher active surface area than Ni₃C/Ni@C. The outstanding electrocatalytic performance of Co-doped Ni₃C/Ni@C in the OER was mainly ascribed to the synergistic effect of the Co and Ni₃C/Ni active sites.     

Carbon supported Ni3N/Ni heterostructure for hydrogen evolution reaction in both acid and alkaline media

Hydrogen (H₂) is a carbon-free clean energy source and can be generated from water by electrolysis. The fabrication of highly sustainable electrode materials to replace expensive platinum is vital for the supportable production of molecular hydrogen via electrolysis of water. Nickel based electrode materials have attracted a great attention in the water splitting reaction. In this context, supporting material such as carbon is adopted to increase the catalytic activity. In this study, a special route was advanced to construct carbon supported Ni₃N/Ni, which was as an effective electrocatalyst for hydrogen evolution reaction (HER) in both 0.5 M H₂SO₄ and 1 M KOH electrolytes. We observed that the carbon support can effectively improve the electronic structure of Ni₃N/Ni by introducing intrinsic active sites. The optimized Ni₃N/Ni@C composite showed superior electrical conductivity and charge transfer rate. Consequently, the Ni₃N/Ni@C750 °C composite showed enhanced electrocatalytic behaviour with a small overpotential of 163 and 172 mV to attain an optimal current density of 10 mA cm⁻² and durability over 1000 cycles in acid and alkaline electrolytes towards HER application.     

Interlaced rosette-like MoS2/Ni3S2/NiFe-LDH grown on nickel foam: A bifunctional electrocatalyst for hydrogen production by urea-assisted electrolysis

In targeting the most important energy and environmental issues in current society, the development of low-cost, bifunctional electrocatalysts for urea-assisted electrocatalytic hydrogen (H₂) production is an urgent and challenging task. In this work, interlaced rosette-like MoS₂/Ni₃S₂/NiFe-layered double hydroxide/nickel foam (LDH/NF) is successfully synthesized by a two-step hydrothermal reaction. Due to its unique interlaced heterostructure, MoS₂/Ni₃S₂/NiFe-LDH/NF exhibits excellent bifunctional catalytic activity towards the urea oxidation reaction (UOR) and the hydrogen evolution reaction (HER) in 1.0 M KOH with 0.5 M urea. In a concurrent two-electrode electrolyser (MoS₂/Ni₃S₂/NiFe-LDH/NF(+,-)), only voltage of 1.343 V is required to reach 50 mA cm⁻², which is 216 mV lower than for pure water splitting. Furthermore, after 16 h of urea electrolysis in 1.0 M KOH with 0.5 M urea, the current density remains at 98% of the original value. Thus, the catalyst is not only favorable for H₂ production, but also has great significance for the problem of urea-rich wastewater treatment.     

Ultrafine RuP2 nanoparticles supported on nitrogen-doped carbon based on coordination effect for efficient hydrogen evolution

It is still a challenge to develop the high-efficiency noble metal-based electrocatalyst with good dispersion and durability for hydrogen evolution reaction (HER) in wide pH range. Herein, we have successfully synthesized a nitrogen-doped carbon (NC) coated ultrafine ruthenium phosphides (RuP₂) nanoparticles catalyst with a facile method. With the help of ethylene diamine tetraacetic acid (EDTA), the uniform RuP₂ nanoparticles with ultrafine size of about 3 nm are well dispersed on the surface of the NC. The directed coordination between EDTA and Ru ion may be responsible for the excellent structure. Benefiting from the superior electrical conductivity of NC carrier and the reduced resistance of electrons to the active site, the prepared ultrafine RuP₂@NC demonstrates the obviously enhanced electrocatalytic activity for HER, which results in higher current density and lower overpotentials (99, 98 and 196 mV to reach 10 mA cm^?2 in 0.5 M H₂SO₄, 1 M KOH and 1 M PBS, respectively). The stability is also very good due to the close integration between ultrafine RuP₂ and NC. This work provides a new view to rationally design and synthesize the highly effective, stable and great dispersion of phosphide-based electrocatalysts for HER.     

Construction of Mo2C/W2C heterogeneous electrocatalyst for efficient hydrogen evolution reaction

Constructing high-performance catalyst for hydrogen evolution reaction (HER) is the effective way to eliminate energy crisis. Reasonable engineering of heterointerfaces can effectively create more active sites and promote electron transfer resulting in improvement in the catalytic activity. In this work, we synthesize the well-defined molybdenum carbides and tungsten carbides nano-heterostructure (Mo₂C/W₂C) by carbonization with CH₄/H₂ at 800 °C showing excellent HER activity, fast kinetics and electrochemical stability in both alkaline and acidic electrolytes. Mo₂C/W₂C requires only 140 and 132 mV overpotentials to reach catalytic current density of 10 mA cm^?2 in 0.5 M H₂SO₄ and 1 M KOH electrolyte, respectively. Tafel slope is as low as 51 and 76 mV dec^?1 in 0.5 M H₂SO₄ and 1 M KOH comparable to the benchmarked Pt/C. Moreover, Mo₂C/W₂C exhibits a superior stability with slight deterioration in HER performance after 5000 potential cycles. This work elucidates that the rational construction of heterointerfaces is favorable for design of efficient non-noble metal electrocatalyst for HER catalysis.