Hydrogen Evolution Reaction Overpotential Research Articles

Cu3p/N-Doped Carbon Catalyst with One-Step Synthesis Method for Hydrogen Evolution Reaction of Alkaline Water Electrolysis

Hydrogen energy is in the spotlight to resolve the imbalance in the supply and demand for renewable energy. Water electrolysis is an eco-friendly method of producing hydrogen, and it is necessary to develop a high-efficiency, low-cost hydrogen evolution reaction (HER) catalyst. This study presents a copper phosphide/N-doped carbon (Cu3P/N-C) catalyst with relatively abundant reserves and low cost. This catalyst is synthesized in a one-step process involving phosphorization of copper and cyclization of polyacrylonitrile (PAN). By adding PAN to the phosphorus precursor, the Cu3P particles are electrically and physically connected, providing improved electrical conductivity and structural integrity of the Cu3P electrode. The disordered N-doped carbon structure formed under the influence of the phosphorus source induces a synergistic effect with the extended electrochemically active surface area (ECSA), increasing HER activity. The P to PAN ratio is optimized to achieve the best HER activity, and Cu3P/N-C prepared in copper foam exhibits HER overpotentials of 211.1 and 301.8 mV at 10 and 50 mA cm-2 current densities in 1 M KOH solution. At a current density of 10 mA cm-2, the HER overvoltage remained stable between 211.1 and 222.1 mV for 24 hours.

Facile electrochemical synthesis of Ni-Co-B film on Cu sheet for dual-electrocatalysis of hydrogen and oxygen evolution reactions

Fabricating efficient and affordable electrocatalysts is essential to make electrochemical water splitting more feasible. However, to minimize the electrocatalysts' fabrication costs, developing bifunctional electrocatalysts has been proposed as a profitable strategy. Herein, the Ni-Co-B film was fabricated on a Cu sheet surface by a one-step and facile electrodeposition method. The optimized sample showed noticeable electrocatalytic activity for total water splitting. The required overpotential for hydrogen evolution reaction (HER) at -10 mA cm−2 current density was recorded to be -145 mV, and in the case of oxygen evolution reaction (OER), this value was 276 mV at 10 mA cm−2. The unique morphology of the optimized Ni-Co-B sample with a high number of spherical micro-nodules was proposed to be responsible for this high HER and OER catalytic activity. Moreover, the optimized value of the B, Ni, and Co in the coating was highly important in facilitating the electrochemical reactions. Density functional theory (DFT) calculations indicated that the better electrocatalytic activity of the Ni-Co-B electrode is due to the regulate the electronic structure and new active catalytic sites which are created by Co incorporation. Finally, the binder-free approach of fabricating the coating resulted in the long-time high stability of the fabricated Ni-Co-B/Cu electrode at high current densities.

Oxidized single nickel atoms embedded in Ru matrix for highly efficient hydrogen evolution reaction

It is desirable but challenging to fine adjust the electronic structure of single atom to enhance the activity of single atom catalysts (SACs). Herein, we embedded an oxidized single nickel atom into pure ruthenium (Ru) metal (NiRu SAC), thereby constructing an atomic-level interface with high catalytic activity. NiRu SAC exhibits a long-term durability and an extremely low overpotential for hydrogen evolution reaction (optimal value reaches 17 mV) at 10 mA cm−2 which is superior to that of the commercial Pt/C catalyst and most reported Ru-based catalysts. NiRu-0.2 SAC also shows a remarkable oxygen evolution reaction (OER) performance of 210 mV at 10 mA cm−2, and a resulted excellent water splitting property (1.5 V vs. RHE @ 10 mA cm−2). Density functional theory (DFT) calculations demonstrate the fabricated oxidized single-nickel-atomic interface (between single nickel atom and neighboring Ru/O atom) not only lowers the energy barrier for water dissociation but also optimizes the H adsorption through the interaction between the interfacial Ru and O atoms. The single-atomic tailoring provides a new idea to further enhance the performance of single atom catalysts to satisfy the industrial applications.

Preparation of a porous bulk copper ferrite spinel with high performance in the electrolysis of water

Copper ferrite spinels (CFOs) show potential application for use in the field of water electrolysis. However, CFOs are prepared using traditional fabrication methods and as a result always exist in powder form, making them difficult to utilise in applications. In this work, a porous bulk CFO material was fabricated via the milling and sintering of metal oxides, which can be used directly as an electrode. This CFO shows excellent oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activities. The results show that preparing the CFO under an argon (Ar) atmosphere, at high temperature and with a milling pretreatment improves the density of oxygen vacancies (OVs) in the material, thereby enhancing its ability to electrolyse water. The CFO shows high OER and HER performance when sintered at 1000°C under an Ar atmosphere and milled. In 6 M KOH solution at 10 mA cm−2, the OER and HER overpotentials of CFO are as low as 290 and 241 mV, with OER and HER Tafel slopes of 75.5 and 114 mV dec−1. The synthesis route developed in this study is versatile, with the CFO electrode produced exhibiting high performance in water electrolysis.

Metal doped layered MgB2 nanoparticles as novel electrocatalysts for water splitting

Growing environmental problems along with the galloping rate of population growth have raised an unprecedented challenge to look for an ever-lasting alternative source of energy for fossil fuels. The eternal quest for sustainable energy production strategies has culminated in the electrocatalytic water splitting process integrated with renewable energy resources. The successful accomplishment of this process is thoroughly subject to competent, earth-abundant, and low-cost electrocatalysts to drive the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), preferably, in the same electrolyte. The present contribution has been dedicated to studying the synthesis, characterization, and electrochemical properties of newfangled electrocatalysts with the formal composition of Mg1−xTMxB2 (x = 0.025, 0.05, and 0.1; TM (transition metal) = Fe and Co) primarily in HER as well as OER under 1 M KOH medium. The electrochemical tests revealed that among all the metal-doped MgB2 catalysts, Mg0.95Co0.05B2 has the best HER performance showing an overpotential of 470 mV at − 10 mA cm−2 and a Tafel slope of 80 mV dec−1 on account of its high purity and fast electron transport. Further investigation shed some light on the fact that Fe concentration and overpotential for HER have adverse relation meaning that the highest amount of Fe doping (x = 0.1) displayed the lowest overpotential. This contribution introduces not only highly competent electrocatalysts composed of low-cost precursors for the water-splitting process but also a facile scalable method for the assembly of highly porous electrodes paving the way for further stunning developments in the field.

Metal–Organic Framework-Derived CuS Nanocages for Selective CO 2 Electroreduction to Formate

Electroreduction of CO2 to target products with high activity and selectivity has techno-economic importance for renewable energy storage and CO2 utilization. Herein, we report a hierarchical CuS h...

In-situ growth of Fe–Co Prussian-blue-analog nanocages on Ni(OH)2/NF and the derivative electrocatalysts with hierarchical cage-on-sheet architectures for efficient water splitting

To design an efficient and cost-effective electrocatalyst based on Prussian blue and its analogs are a promising choice to realize energy transformation and storage via water-splitting. Herein, a facile and practical method is developed to in-situ grow Fe–Co Prussian-blue-analog (PBA) nanocages with an open hole in each face center on Ni(OH)2/NF substrate to form the hierarchical cage-on-plate structure. Furthermore, the Fe–Co PBA nanocages attached to Ni(OH)2/NF plates are hydrogenated and nitrogenized into FeCoNi/NF and FeCoNiN/NF electrodes, respectively. As-prepared electrodes successfully retain the 3D hierarchical micro-nano structures of Fe–Co PBA@Ni(OH)2/NF precursor and can be used as a bifunctional water-splitting catalyst for overall water splitting. Compared to FeCoNi/NF, FeCoNiN/NF shows more efficiency and durability in the electrolytic water splitting tests in alkaline media. For the FeCoNiN/NF electrocatalyst, ultralow overpotentials for hydrogen evolution reaction (HER) are only 56 and 290 mV at current densities of 10 and 500 mA cm−2. Meanwhile, overpotentials for oxygen evolution reaction (OER) are 267 and 374 mV at current densities of 50 and 500 mA cm−2. The FeCoNiN/NF electrode can act both the cathode and the anode for overall water splitting, this electrolyzer only requires a cell voltage of 1.492 V to afford a current density of 10 mA cm−2. This electrolyzer can stably deliver a viable high current density of 625 mA cm−2 for 40 h to meet the condition of industrial application.

V2O3-Decorated Spinel CoFe2O4 with Carbon-Encapsulated Mesoporous Nanosheets for Efficient Water Splitting

A lot of research has been going on to develop efficient nonprecious bifunctional catalysts for electrochemical water splitting. Here, we synthesize a V2O3-decorated spinel CoFe2O4 catalyst self-supported on nickel foam (NF) with a carbon-encapsulated mesoporous nanosheet structure [(V2O3–CoFe2O4)@C/NF] through a hydrothermal method and high-temperature annealing. It exhibits lower overpotentials for hydrogen evolution reaction (61 and 301 mV) and oxygen evolution reaction (226 and 310 mV) at ±10 and ±500 mA cm–2 and can hold at ±500 mA cm–2 for 80 h. As for overall water splitting, it needs 1.53 V to produce 10 mA cm–2 and maintains 80 h at 100 mA cm–2, suggesting good stability. This high performance originated from the V2O3-decorated spinel CoFe2O4, carbon-encapsulated structure and the self-supported mesoporous nanosheets. Therefore, this work provides a convenient, green, and promising method to design non-noble, low-cost, and high-efficient catalysts for water splitting.

Potential Visible-Light Driven PtO₂/GaN vdW Hetero-Bilayer Photocatalysts for Water Splitting Using First-Principles

Novel two-dimensional (2D) PtO2/GaN van der Waals (vdW) hetero-bilayers (HBL) are studied here for photocatalytic water splitting (PWS) application under first-principles density functional theory (DFT). We proposed six HBLs due to the atomic orientational variations and two of them are found dynamically stable confirmed by phonon dispersion curves. The two stable HBLs, HBL1, and HBL6 also show negative binding energy depicted by the interlayer distance-dependent binding energy curves. Among them, HBL1 has the lowest binding energy, suggesting the exothermic practicability of the material. Electronically both materials show a visible ranged indirect bandgap of ~2.65 (2.69) eV for HBL 1 (HBL6), lowered by ~2 times compared to their intrinsic constituents (2D PtO2, 2D GaN). The bandgaps also have type-II band orientation, which is highly required for efficient spatial carrier separation in photocatalytic water splitting (PWS) applications. The optical properties of the HBLs were also calculated, and it’s found that the HBLs have $\sim 2\times 10 ^{5}{\mathrm {cm}}^{-1} $ of perovskite material-like absorption coefficient in the visible spectrum, a key requirement for efficient photocatalysis. Reflectivity is as low as ~7% in the visible spectrum, suggesting the low-loss nature of the materials. Photocatalytic band-edges with type-II band alignments show sufficient kinetic overpotential for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in both HBLs, suggesting effective water-splitting capacity. Moreover, we have explored the biaxial strain-induced tunability of the electronic bandgap, absorption coefficients, and photocatalytic band edges. They all found responsive due to homogeneous biaxial strain and show bandgap-lowering, absorption coefficient visible shifting, and band-edges tuning from compressive to tensile strains in the −6 % to +6% range. These studies suggest that the novel PtO2/GaN vdW layered material can be a probable efficient material for visible-light-driven photocatalytic water-splitting technology.

Double MOF gradually activated S bond induced S defect rich MILN-based Co(z)-NiMoS for efficient electrocatalytic overall water splitting.

Herein, cactus like nanorods with rich S defects and functional group MILN-based Co(z)-NiMoS are synthesized through a facile method. First, we prepared MIL-88B precursor to give a fairly dispersed frame structure, and then Con+ was doped into disulfides, which are rich in sulfur bonds, and the imidazole group was cleverly connected into graphitized carbon via self-etching of ZIF-67. The doping of Con+ and functional groups makes tiny changes in the sulfide lattice, which promotes the unsaturation degree of the S bond and activates it gradually. The prepared semi frame sulfide with a unique structure, on the one hand, ensures the hydrophilicity and multiple active specific surface area, which lays superior functions in morphology. On the other hand, coupling metals that have strong valence change ability and functional groups by active S bonds play an important role in the process of electrocatalytic reaction. Amazingly, disintegration and self-reconstruction of MILN-based Co(z)-NiMoS occurs during oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) due to the activation of the S bond, which provides a new perspective for the overall water splitting mechanism. The electrochemical results show that the MILN-based Co(z)-NiMoS electrocatalyst exhibits overpotentials of HER, OER, and overall water splitting (OWS) to be 169 mV, 170 mV, and 1.466 V, respectively, making it a promising electrode material for OWS applications.

CoS2 needle arrays induced a local pseudo-acidic environment for alkaline hydrogen evolution.

The alkaline electrocatalytic hydrogen evolution reaction (HER) is a potential way to realize industrial hydrogen production. However, the sluggish process of H2O dissociation, as well as the accumulation of OH- around the active sites, seriously limit the alkaline HER performance. In this work, we developed a unique CoS2 needle array grown on a carbon cloth (NAs@C) electrode as an alkaline HER catalyst. Finite-element simulations revealed that CoS2 needle arrays (NAs) induce stronger local electric field (LEF) than CoS2 disordered needles (DNs). This LEF can greatly repel the local OH- around the active sites, and then promote the forward H2O dissociation process. The local pH changes of the electrode surface confirmed the lower OH- concentration and stronger local pseudo-acidic environment of NAs@C compared to those of DNs@C. As a result, the NAs@C catalyst exhibited a low HER overpotential of 121 mV at a current density of 10 mA cm-2 in 1 M KOH, with the Tafel slope of 59.87 mV dec-1. This work provides a new insight into nanoneedle arrays for the alkaline HER by electric field-promoted H2O dissociation.

Electrochemically Exfoliating MoS2 into Atomically Thin Planar‐Stacking Through a Selective Lateral Reaction Pathway

AbstractThe production of atomically thin transition‐metal dichalcogenides (TMDs) has been investigated through various top‐to‐down exfoliation methods, such as mechanical and chemical exfoliation, while large‐scale chemical exfoliation is sluggish and needs over ten hours to achieve atomically thin TMDs. Herein, a new strategy is reported for exfoliating bulk MoS2 into two/three‐layer flakes within tens of seconds through a mild electrochemical treatment. This exfoliation method is driven by a lateral inward oxidation reaction starting from the typical layer edge with a rapid depth penetration, whereby a stacked few‐layer (two/three layers) structure is ultimately formed. This efficient reaction process is monitored based on an individual MoS2 on‐chip device combined with in situ Raman and cross‐sectional scanning transmission electron microscopy, and the uniformity of thickness is demonstrated. This preferentially initiated method can be also extended to produce few‐layer MoSe2 and the selective extraction mechanism is assumed to be related to intrinsic layer‐dependent energy band properties. Moreover, the special reassembled few‐layer MoS2 possesses great performance as functional materials in electrocatalysis (127 mV overpotential for hydrogen evolution reaction) and surface‐enhanced Raman spectroscopy (105 enhancement factor). These results illustrate the broad prospects of the reassembled few‐layer MoS2 for optics, catalysis, and sensors.

Highly Efficient Alkaline Water Splitting with Ru-Doped Co-V Layered Double Hydroxide Nanosheets as a Bifunctional Electrocatalyst.

Active electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are decisive for achieving efficient energy conversion from electricity to hydrogen fuel through water electrolysis. In this study, tremella-like Ru-doped Co-V layered double hydroxide nanosheets on Ni Foam (Ru-CoV-LDH@NF) was fabricated by a one-pot solvothermal reaction. As-prepared Ru-CoV-LDH@NF, with a nominal Ru loading of around 51.6 μg cm-2 exhibits excellent bifunctional catalytic activity towards HER and OER in alkaline media. To accomplish a current density of 10 mA cm-2 , it demands 32 mV and 230 mV overpotentials for HER and OER, respectively. The alkali electrolyzer utilizing Ru-CoV-LDH/NF as bifunctional electrocatalyst affords 10 mA cm-2 electrolytic current density at an extremely low cell voltage of 1.50 V, showing excellent performance compared to a Pt/C-RuO2 -based electrolyzer and many other bifunctional electrocatalyst-based ones. The incorporation of Ru changes the morphology of the resultant nanosheets to offer high electrochemical surface areas for electrocatalysis; at the same time, it significantly boosts the intrinsic HER/OER electrocatalytic activity. For HER, the energy barrier of the Volmer step is efficiently reduced upon Ru doping, whereas the Ru dopants optimize the absorption strength of *O intermediates to facilitate the OER process. This work offers a feasible means to optimize the Co-based hydroxide materials for improved electrocatalysis in overall water splitting.

Fabrication of porous Ni-Co catalytic electrode with high performance in hydrogen evolution reaction

Porous Ni-Co alloy with low overpotential for hydrogen evolution reaction (HER) were fabricated by dynamic hydrogen bubble template (DHBT) method, which has the potential of being used to obtain hydrogen energy efficiently and environmentally friendly. The porous Ni-Co alloy was prepared by one-step electrodeposition at different current density and electroplating time. Scanning electron microscopy (SEM) was used to observe the diverse morphology of the electrodes obtained by different conditions, while its catalytic activity for HER was investigated by electrochemical measurements. Results showed the positive correlation between active sites of micro-morphology of porous Ni-Co electrode and its catalytic performance for HER. Based on the results, current density of 250 A/dm2 and electroplating time of 120 s were chosen as the optimum conditions, with the overpotential of only 54 mV for HER. Additionally, the porous Ni-Co alloy electrode showed high catalytic stability with a small activity loss after 10 h chronopotentiometry stability test. With prominent electrochemical properties and facile preparation method, porous Ni-Co alloy electrode fabricated by DHBT has the potential of being widely applied in hydrogen evolution reaction.

Surface amorphized nickel hydroxy sulphide for efficient hydrogen evolution reaction in alkaline medium

Non-oxide/hydroxide hydrogen evolution reaction (HER) catalysts undergo hydroxylation to a significant extent even under reductive condition when exposed to alkali. Actual role of such hydroxylation in alkaline HER electrocatalysis is not previously given any significance. In this study, we report an intriguing finding that nickel sulfide a well-known HER electrocatalyst when subjected to anodic potential cycling covering Ni2+and Ni3+redox couple led to accelerated hydroxylation accompanying surface amorphization. As a result, improved electrochemical surface, better HER kinetics, and better charge transfer were achieved that lowering the HER overpotential by 110 mV at 100 mA cm2. This surface amorphized and hydroxylated nickel sulfide exhibited excellent stability upon both galvanostatic and potentiostatic electrolysis for over 50 h. Besides, it also showed a lower Tafel slope (120 mV dec-1), higher relative ECSA in terms of 2Cdl (3.85 µF cm−2), and higher electrochemical accessibility for Ni sites (3.7 × 1017 cm−2) which further advocate the superiority of our way of improving HER activity of a non-oxide/hydroxide catalyst. Thus, this study open up new avenues for re-examining other non-oxide/hydroxide catalysts in alkaline HER for benefiting the energy and cost-efficient hydrogen generation.

Abundant heterointerfaces in MOF-derived hollow CoS2–MoS2 nanosheet array electrocatalysts for overall water splitting

A MOF-etching strategy is reported to design hierarchical hollow CoS 2 –MoS 2 heteronanosheet arrays. Due to the controllable etching of MOF by MoO 4 2− , the obtained CoS 2 –MoS 2 catalyst has abundant heterointerfaces for efficient HER and OER. • Hierarchical hollow CoS 2 –MoS 2 heteronanosheet arrays is fabricated. • The selective etching of MOF by MoO 4 2− can generate abundant heterointerfaces. • The engineered heterostructure exhibits small overpotentials for HER, OER. • A cell voltage of 1.56 V at 10 mA cm −2 can boost overall water splitting. Rational coupling of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysts is extremely important for practical overall water splitting, but it is still challenging to construct such bifunctional heterostructures. Herein, we present a metal–organic framework (MOF)-etching strategy to design free-standing and hierarchical hollow CoS 2 –MoS 2 heteronanosheet arrays for both HER and OER. Resulting from the controllable etching of MOF by MoO 4 2− and in-situ sulfuration, the obtained CoS 2 –MoS 2 possesses abundant heterointerfaces with modulated local charge distribution, which promote water dissociation and rapid electrocatalytic kinetics. Moreover, the two-dimensional hollow array architecture can not only afford rich surface-active sites, but also facilitate the penetration of electrolytes and the release of evolved H 2 /O 2 bubbles. Consequently, the engineered CoS 2 –MoS 2 heterostructure exhibits small overpotentials of 82 mV for HER and 266 mV for OER at 10 mA cm −2 . The corresponding alkaline electrolyzer affords a cell voltage of 1.56 V at 10 mA cm −2 to boost overall water splitting, along with robust durability over 24 h, even surpassing the benchmark electrode couple composed of IrO 2 and Pt/C. The present work may provide valuable insights for developing MOF-derived heterogeneous electrocatalysts with tailored interface/surface structure for widespread application in catalysis and other energy-related areas.

Nanocrystalline Ni–Cu Electroplated Alloys Cathodes for Hydrogen Generation in Phosphate-Buffered Neutral Electrolytes

The use of hydrogen as a green fuel alongside an environmentally friendly electrolyte is the most promising technology required for the conversion and storage of renewable energies and the transition to a low carbon future. Nanocrystalline Ni–Cu alloys have been electroplated onto copper electrodes and characterized via scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. The electrocatalytic performance of the electroplated Ni–Cu alloys cathodes for the hydrogen evolution reaction (HER) was investigated using cyclic voltammetry, electrochemical impedance spectroscopy and cathodic polarization measurements in the PBNE. The results demonstrate that the nanocrystalline Ni–Cu alloys cathodes have high electrocatalytic efficiency for HER. The overpotential of HER required to reach a catalytic current density of 10.0 mA/cm2 was 284 mV vs. RHE. The most active cathode was a 30:70 (Atom ratio) Ni:Cu alloy in the PBNE and had 1.5 times higher than standard Pt/C which can be applied as a cathode for H2 production in the industrial water electrolyzer, potentially increasing the efficiency of devices and thus lowering the cost of green hydrogen production.

In situ growth of NiSe@Co0.85Se heterointerface structure with electronic modulation on nickel foam for overall water splitting

Constructing heterointerface engineering has becoming an effective and general strategy for developing highly efficient and durable nonnoble electrocatalysts for catalyzing both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this work, we synthesized a self-supporting heterogeneous NiSe@Co0.85Se/NF electrocatalyst using a facile in situ selenization of transition metal precursors that coated on the nickel foam (NF) in polyol solution. The NF was used as both conductive substrate and nickel source, ensuring superior electronic conductivity for catalyzing. The NiSe@Co0.85Se/NF exhibited remarkable bifunctional electrocatalytic activities with HER overpotential of 168 mV and OER overpotential of 258 mV to achieve 10 mA·cm−2. The water splitting system using NiSe@Co0.85Se/NF as both anode and cathode electrodes achieved a current density of 10 mA·cm−2 at 1.61 V with nearly 100% faradaic efficiency and impressively long-term stability. The efficient bifunctional catalytic performance of NiSe@Co0.85Se/NF should be attributed to the electronic modulation and synergistic effect between NiSe and Co0.85Se, the intrinsic metallic conductivity and the enlarged active sites exposure. This work provides a facile method for developing heterogeneous bifunctional catalysts for advanced electrochemical energy conversion technologies.

Electrodeposition of α-Ni/β-Co composite coatings on the carbon felt: Structural features and electrochemical performance

Efficient hydrogen production by electrolysis of aqueous and aqueous-alcohol solutions is based on the use of electrode materials with a low overpotential of hydrogen evolution reaction (HER). Apart from materials containing noble metals (Pt, Pd, etc.), coatings consisting of the iron triad metals (Fe, Ni, Co) obtained by electroplating method on the substrate surface (nickel foam, carbon fibers) are used. However, there is a problem with the crystallites size and the coating degree of the substrate. The use of simple (non-complex) electrolytes doesn’t solve them. This article is devoted to the preparation of composite Ni–Co coatings from a complex citrate electrolyte by electrodeposition on carbon felt and their testing in an aqueous-alcoholic solution of KOH. The pH effect of the electrolyte on the morphology, structure, and electrochemical properties has been studied. The morphology and structure of synthesized coatings have been investigated using SEM and PXRD methods. The chemical composition of the samples has been determined by EDX spectroscopy. The electrochemical performance of the coatings has been evaluated by cyclic voltammetry and chronopotentiometry methods. The synthesized samples are carbon filaments with a submicron coating (300 nm) of the α-Ni/β-Co composite. The crystallite sizes are 15 ± 5 nm and depend on the pH value of the electrolyte used. It has been found that the use of nanocomposites reduced the overpotential of HER to -196 mV while maintaining their stability. Thus, the study shows that the use of a complex electrolyte based on citric acid allows obtaining nanoscale composite coatings of α-Ni/β-Co on a carbon substrate. Changing the pH of the electrolyte makes it possible to vary the coating degree of the substrate and the Ni:Co ratio in the composite. A more detailed study of the observed overpotential shift to the anodic side remains an interesting issue.

Synthesis of hollow CoSe2/MoSe2 nanospheres for efficient hydrazine-assisted hydrogen evolution

Hydrazine-assisted hydrogen evolution cell has been regarded as a promising route to replace conventional water splitting because of the lower thermodynamic oxidation potential. Therefore, the design and synthesis of highly efficient bifunctional electrocatalysts for anodic hydrazine oxidation reaction (HzOR) and cathodic hydrogen evolution reaction (HER) are crucial and highly desired. In this work, we report a facile synthesis strategy to prepare hollow CoSe2/MoSe2 nanospheres with abundant active interfaces for hydrazine-assisted hydrogen production. The homogeneous mixing of Co and Mo ions in the metal organic framework precursors ensures the formation of intimately contacted interfaces after selenization, leading to the “reinforced concrete” CoSe2/MoSe2 composites. Benefiting from the CoSe2/MoSe2 interfaces, the hollow CoSe2/MoSe2 nanosphere performs a low HER overpotential of 168 mV with an excellent stability over 12 h. Additionally, it also exhibits a low overpotential of 386 mV (vs. RHE) for HzOR and an ultralow cell voltage (1 mA cm−2) of 160 mV, which are among the best reported performance of powdered electrocatalysts. The present work develops a promising bifunctional electrocatalyst with active interfaces for energy-saving electrolytic hydrogen production.