Ni2P Interlayer and Mn Doping Synergistically Expedite the Hydrogen Evolution Reaction Kinetics of Co2P

Transition metal phosphide is regarded as one of the most promising candidates to replace noble-metal hydrogen evolution reaction (HER) electrocatalysts. Nevertheless, the controllable design and synthesis of transition metal phosphide electrocatalysts with efficient and stable electrochemical performance are still very challenging. Herein, a novel hierarchical HER electrocatalyst consisting of three-dimensional (3D) coral-like Mn-doped Co₂P@an intermediate layer of Ni₂P generated in situ by phosphorization on Ni foam (MnCoP/NiP/NF) is reported. Notably, both the incorporation of Mn and introduction of the Ni₂P interlayer promote Co atoms to carry more electrons, which is beneficial to reduce the force of the Co−H bond and optimize the adsorption energy of hydrogen intermediate (|ΔG_H*|), thereby making MnCoP/NiP/NF exhibit outstanding HER performance with onset overpotential and Tafel slope as low as 31.2 mV and 61 mV dec⁻¹, respectively, in 1 m KOH electrolyte.     

Enhancing Hydrogen Evolution by Optimizing the Hydrogen Adsorption on Titanium Monoxide Nanodot-Decorated Cobalt Sulfide Nanosheets

Modulating the local electronic state of metal compounds through interfacial interaction has become a key method for manufacturing high-performance hydrogen evolution reaction (HER) electrocatalysts. The electron-rich active sites can promote the adsorption of hydrogen, which accelerates the Volmer step and thereby enhances the electrocatalytic performance of HER. Here, we found that the strong interfacial interaction between TiO nanodots (TiO/Co−S) and Co−S nanosheets could advantageously improve the performance toward HER of electrocatalyst. Meanwhile, XPS results showed that modulating the local electronic structure of the TiO nanodots produces electron-rich regions on Co. As a result, the overpotential of the TiO/Co−S nanocomposite at 10 mA cm⁻² was 107 mV, and the Tafel slope was 83.3 mV dec⁻¹. This study focused on the effect of the solid-solid interface on the local electronic structure of the catalytic metal active sites and successfully improved the catalytic activity of transition metal materials in HER catalysis.     

Ligand Modulation of Active Sites to Promote Cobalt-Doped 1T-MoS2 Electrocatalytic Hydrogen Evolution in Alkaline Media

Highly efficient hydrogen evolution reaction (HER) electrocatalyst will determine the mass distributions of hydrogen-powered clean technologies, while still faces grand challenges. In this work, a synergistic ligand modulation plus Co doping strategy is applied to 1T−MoS₂ catalyst via CoMo-metal-organic frameworks precursors, boosting the HER catalytic activity and durability of 1T−MoS₂. Confirmed by Cs corrected transmission electron microscope and X-ray absorption spectroscopy, the polydentate 1,2-bis(4-pyridyl)ethane ligand can stably link with two-dimensional 1T−MoS₂ layers through cobalt sites to expand interlayer spacing of MoS₂ (Co−1T−MoS₂-bpe), which promotes active site exposure, accelerates water dissociation, and optimizes the adsorption and desorption of H in alkaline HER processes. Theoretical calculations indicate the promotions in the electronic structure of 1T−MoS₂ originate in the formation of three-dimensional metal-organic constructs by linking π-conjugated ligand, which weakens the hybridization between Mo-3d and S-2p orbitals, and in turn makes S-2p orbital more suitable for hybridization with H-1s orbital. Therefore, Co−1T−MoS₂-bpe exhibits excellent stability and exceedingly low overpotential for alkaline HER (118 mV at 10 mA cm⁻²). In addition, integrated into an anion-exchange membrane water electrolyzer, Co−1T−MoS₂-bpe is much superior to the Pt/C catalyst at the large current densities. This study provides a feasible ligand modulation strategy for designs of two-dimensional catalysts.     

Devisable POM/Ni Foam Composite: Precisely Control Synthesis toward Enhanced Hydrogen Evolution Reaction at High pH

Polyoxometalates (POMs) are promising catalysts for the electrochemical hydrogen production from water owing to their high intrinsic catalytic activity and chemical tunability. However, poor electrical conductivity and easy detachment of the POMs from the electrode cause significant challenges under operating condition. Herein, a simple one-step hydrothermal method is reported to synthesize a series of Dexter–Silverton POM/Ni foam composites (denoted as Ni M -POM/Ni; M =Co, Zn, Mn), in which the stable linkage between the POM catalysts and the Ni foam electrodes lead to high activity for the hydrogen evolution reaction (HER). Among them, the highest HER performance can be observed in the NiCo-POM/Ni, featuring an overpotential of 64 mV (at 10 mA cm⁻², vs. reversible hydrogen electrode), and a Tafel slope of 75 mV dec⁻¹ in 1.0 m aqueous KOH. Moreover, the NiCo-POM/Ni catalyst showed a high faradaic efficiency ≈97 % for HER. Post-catalytic of NiCo-POM/Ni analyses showed virtually no mechanical or chemical degradation. The findings propose a facile and inexpensive method to design stable and effective POM-based catalysts for HER in alkaline water electrolysis.     

High Valence State Sites as Favorable Reductive Centers for High-Current-Density Water Splitting

Electrochemical water splitting is a promising approach for producing sustainable and clean hydrogen. Typically, high valence state sites are favorable for oxidation evolution reaction (OER), while low valence states can facilitate hydrogen evolution reaction (HER). However, here we proposed a high valence state of Co³⁺ in Ni_9.5Co_0.5−S−FeO_x hybrid as the favorable center for efficient and stable HER, while structural analogues with low chemical states showed much worse performance. As a result, the Ni_9.5Co_0.5−S−FeO_x catalyst could drive alkaline HER with an ultra-low overpotential of 22 mV for 10 mA cm⁻², and 175 mV for 1000 mA cm⁻² at the industrial temperature of 60 °C, with an excellent stability over 300 h. Moreover, this material could work for both OER and HER, with a low cell voltage being 1.730 V to achieve 1000 mA cm⁻² for overall water splitting at 60 °C. X-ray absorption spectroscopy (XAS) clearly identified the high valence Co³⁺ sites, while in situ XAS during HER and theoretical calculations revealed the favorable electron capture at Co³⁺ and suitable H adsorption/desorption energy around Co³⁺, which could accelerate the HER. The understanding of high valence states to drive reductive reactions may pave the way for the rational design of energy-related catalysts.     

Cooperative Ni(Co)-Ru-P Sites Activate Dehydrogenation for Hydrazine Oxidation Assisting Self-powered H2 Production

Water electrolysis for H₂ production is restricted by the sluggish oxygen evolution reaction (OER). Using the thermodynamically more favorable hydrazine oxidation reaction (HzOR) to replace OER has attracted ever-growing attention. Herein, we report a twisted NiCoP nanowire array immobilized with Ru single atoms (Ru₁−NiCoP) as superior bifunctional electrocatalyst toward both HzOR and hydrogen evolution reaction (HER), realizing an ultralow working potential of −60 mV and overpotential of 32 mV for a current density of 10 mA cm⁻², respectively. Inspiringly, two-electrode electrolyzer based on overall hydrazine splitting (OHzS) demonstrates outstanding activity with a record-high current density of 522 mA cm⁻² at cell voltage of 0.3 V. DFT calculations elucidate the cooperative Ni(Co)−Ru−P sites in Ru₁−NiCoP optimize H* adsorption, and enhance adsorption of *N₂H₂ to significantly lower the energy barrier for hydrazine dehydrogenation. Moreover, a self-powered H₂ production system utilizing OHzS device driven by direct hydrazine fuel cell (DHzFC) achieve a satisfactory rate of 24.0 mol h⁻¹ m⁻².     

Two-Dimensional NiIr@N-Doped Carbon Nanocomposites Supported on Ni Foam for Electrocatalytic Overall Water Splitting

Electrochemical water splitting can provide a promising avenue for sustainable hydrogen production. Highly efficient electrocatalysts toward the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are extremely important for the practical application of water splitting technology. Herein, a one-step annealing strategy is reported for the fabrication of a metal–organic framework-derived bifunctional self-supported electrocatalyst, which is composed of two-dimensional N-doped carbon-wrapped Ir-doped Ni nanoparticle composites supported on Ni foam (NiIr@N-C/NF). The resultant NiIr@N-C/NF displays excellent electrocatalytic performance in 1.0 m KOH, with low overpotentials of 32 mV at 10 mA cm⁻² for the HER and 329 mV at 50 mA cm⁻² for the OER. Particularly, the HER-OER bifunctional NiIr@N-C/NF needs only 1.50 V to yield 10 mA cm⁻² for overall water splitting.     

Ferricyanide Armed Anodes Enable Stable Water Oxidation in Saturated Saline Water at 2 A/cm2

The direct seawater electrolysis at high current density and low overpotential affords an effective strategy toward clean and renewable hydrogen fuel production. However, the severe corrosion of anode as a result of the saturation of Cl⁻ upon continuous seawater feeding seriously hamper the electrolytic process. Herein, cobalt ferricyanide / cobalt phosphide (CoFePBA/Co₂P) anodes with Cap/Pin structure are synthesized, which stably catalyze alkaline saturated saline water oxidation at 200–2000 mA cm⁻² over hundreds of hours without corrosion. Together with the experimental findings, the molecular dynamics simulations reveal that PO₄³⁻ and Fe(CN)₆³⁻ generated by the electrode play synergistic role in repelling Cl⁻ via electrostatic repulsion and dense coverage, which reduced Cl⁻ adsorption by nearly 5-fold. The novel anionic synergy endow superior corrosion protection for the electrode, and is expected to promote the practical application of saline water electrolysis.     

One-Step Template/Solvent-Free Pyrolysis for In Situ Immobilization of CoP Nanoparticles onto N and P Co-Doped Carbon Porous Nanosheets towards High-efficiency Electrocatalytic Hydrogen Evolution

The search for economical, active and stable electrocatalysts towards the hydrogen evolution reaction (HER) is highly imperative for the progression of water electrolysis technology and related sustainable energy conversion technologies. The delicate optimization of chemical composition and architectural configuration is paramount to design high-efficiency non-precious metal HER electrocatalysts. Herein, we report a one-step scalable template/solvent-free pyrolysis approach for in situ immobilizing uniform CoP nanoparticles onto N and P co-doped carbon porous nanosheets (denoted as CoP@N,P-CNSs hereafter). The simultaneous consideration of architectural design and nanocarbon hybridization renders the formed CoP@N,P-CNSs with plentiful well-dispersed anchored active sites, shortened pathway for mass diffusion, enhanced electric conductivity, and reinforced mechanical stability. As a consequence, the optimized CoP@N,P-CNSs exhibit an overpotential of 115 mV to afford a current density of 10 mA cm⁻², small Tafel slope of 74.2 mV dec⁻¹, high Faradaic efficiency of nearly 100 %, and superb long-term durability in an alkaline medium. Given the fabrication feasibility, mass production potential and outstanding HER performance, the CoP@N,P-CNSs may hold great promise for large-scale electrochemical water splitting. More importantly, the explored one-step template/solvent-free pyrolysis methodology offers a feasible and versatile route to fabricate carbon nanosheet-based nanocomposites for diverse energy conversation-related applications.     

MoSe2/Co-MOF/NF复合材料的制备及电催化产氧性能

设计高效的催化剂对于电解水制氢至关重要。基于过渡金属硒化物(TMSe)的高催化活性和金属有机骨架(MOFs)的灵活结构,我们提出了一种将MOFs与TMSe复合的策略,在导电基底泡沫镍(NF)上生长的复合材料不仅继承了2种单体的优点,还有效地改善了MOFs导电性差、TMSe易团聚的缺点。MoSe₂/Co-MOF/NF在碱性溶液中展示出优异的电催化产氧活性,在电流密度为10 mA·cm^-2时其过电位仅为242 mV,塔菲尔斜率仅为50.64 mV·dec^-1。此外,该材料在碱性溶液中经1 000圈循环伏安(CV)循环测试和30 h的恒电压电解测试均表现出良好的稳定性。     

The Core/Shell Structure P Doped MoS2@Ni3S2 Nanorods Array for High Current Density Hydrogen Evolution in Alkaline and Acidic Electrolyte

Electrocatalysis is the most promising strategy to generate clean energy H₂, and the development of catalysts with excellent hydrogen evolution reaction (HER) performance at high current density that can resist strong alkaline and acidic electrolyte environment is of great significance for practical industrial application. Therefore, a P doped MoS₂@Ni₃S₂ nanorods array (named P-NiMoS) was successfully synthesized through successive sulfuration and phosphorization. P-NiMoS presents a core/shell structure with a heterojunction between MoS₂ (shell) and Ni₃S₂ (core). Furthermore, the doping of P modulates the electronic structure of the P-NiMoS; the electrons transfer from the t_2g orbital of Ni element to the e_g empty orbital of Mo element through the Ni−S−Mo bond at the Ni₃S₂ and MoS₂ heterojunction, facilitating the hydrogen evolution reaction. As a result, P-NiMoS exhibits excellent HER activity; the overpotential is 290 mV at high current density of 250 mA cm⁻² in alkaline electrolyte, which is close to Pt/C (282 mV@250 mA cm⁻²), and P-NiMoS can stably evolve hydrogen for 48 h.     

Heterostructured Inter-Doped Ruthenium–Cobalt Oxide Hollow Nanosheet Arrays for Highly Efficient Overall Water Splitting

The development of transition-metal-oxides (TMOs)-based bifunctional catalysts toward efficient overall water splitting through delicate control of composition and structure is a challenging task. Herein, the rational design and controllable fabrication of unique heterostructured inter-doped ruthenium–cobalt oxide [(Ru–Co)O_x] hollow nanosheet arrays on carbon cloth is reported. Benefiting from the desirable compositional and structural advantages of more exposed active sites, optimized electronic structure, and interfacial synergy effect, the (Ru–Co)O_x nanoarrays exhibited outstanding performance as a bifunctional catalyst. Particularly, the catalyst showed a remarkable hydrogen evolution reaction (HER) activity with an overpotential of 44.1 mV at 10 mA cm⁻² and a small Tafel slope of 23.5 mV dec⁻¹, as well as an excellent oxygen evolution reaction (OER) activity with an overpotential of 171.2 mV at 10 mA cm⁻². As a result, a very low cell voltage of 1.488 V was needed at 10 mA cm⁻² for alkaline overall water splitting.     

In situ electrochemical dehydrogenation of ultrathin Co(OH)2 nanosheets for enhanced hydrogen evolution

Transition metal hydroxides/oxyhydroxides have recently emerged as highly active electrocatalysts for oxygen evolution reaction in alkaline water electrolysis, while have not yet been widely investigated for hydrogen evolution electrocatalysts owing to their unfavorable H*-adsorption, making it difficult to construct an overall-water-splitting cell for hydrogen production. In this work, we proposed a straightforward and effective approach to develop an efficient in-plane heterostructured CoOOH/Co(OH)₂ catalyst via in-situ electrochemical dehydrogenation method, in which the dehydrogenated –CoOOH and Co(OH)₂ at the surface synergistically boost the hydrogen evolution reaction (HER) kinetics in base as confirmed by high-resolution transmission electron microscope, synchrotron X-ray absorption spectroscopy, and electron energy loss spectroscopy. Due to the in-situ dehydrogenation of ultrathin Co(OH)₂ nanosheets, the catalytic activity of the CoOOH/Co(OH)₂ heterostructures is progressively improved, which exhibit outstanding hydrogen-evolving activity in base requiring a low overpotential of 132 mV to afford 10 mA/cm² with very fast reaction kinetics after 60 h dehydrogenation. The gradually improved catalytic performance for the CoOOH/Co(OH)₂ is probably due to the enhanced H*-adsorption induced by the synergistic effect of heterostructures and better conductivity of CoOOH relative to electrically insulating Co(OH)₂. This work will open the opportunity for a new family of transition metal hydroxides/oxyhydroxides as active HER catalysts, and also highlight the importance of using in situ techniques to construct precious metal-free efficient catalysts for alkaline hydrogen evolution.     

One-Step Approach for Constructing High-Density Single-Atom Catalysts toward Overall Water Splitting at Industrial Current Densities

The construction of highly active, durable, and cost-effective catalysts is urgently needed for green hydrogen production. Herein, catalysts consisting of high-density Pt (24 atoms nm⁻²) and Ir (32 atoms nm⁻²) single atoms anchored on Co(OH)₂ were constructed by a facile one-step approach. Remarkably, Pt₁/Co(OH)₂ and Ir₁/Co(OH)₂ only required 4 and 178 mV at 10 mA cm⁻² for hydrogen evolution reaction and oxygen evolution reaction, respectively. Moreover, the assembled Pt₁/Co(OH)₂//Ir₁/Co(OH)₂ system showed mass activity of 4.9 A mg_{noble metal}⁻¹ at 2.0 V in an alkaline water electrolyzer, which is 316.1 times higher than that of Pt/C//IrO₂. Mechanistic studies revealed that reconstructed Ir−O₆ single atoms and remodeled Pt triple-atom sites enhanced the occupancy of Ir−O bonding orbitals and improved the occupation of Pt−H antibonding orbital, respectively, contributing to the formation of the O−O bond and the desorption of hydrogen. This one-step approach was also generalized to fabricate other 20 single-atom catalysts.     

A Nickel Dithiolate Water Reduction Catalyst Providing Ligand‐Based Proton‐Coupled Electron‐Transfer Pathways

A nickel pyrazinedithiolate ([Ni(dcpdt)₂]²⁻; dcpdt=5,6‐dicyanopyrazine‐2,3‐dithiolate), bearing a NiS₄ core similar to the active center of [NiFe] hydrogenase, is shown to serve as an efficient molecular catalyst for the hydrogen evolution reaction (HER). This catalyst shows effectively low overpotentials for HER (330–400 mV at pH 4–6). Moreover, the turnover number of catalysis reaches 20 000 over the 24 h electrolysis with a high Faradaic efficiency, 92–100 %. The electrochemical and DFT studies reveal that diprotonated one‐electron‐reduced species (i.e., [Ni^II(dcpdt)(dcpdtH₂)]⁻ or [Ni^II(dcpdtH)₂]⁻) forms at pH<6.4 via ligand‐based proton‐coupled electron‐transfer (PCET) pathways, leading to electrocatalytic HER without applying the highly negative potential required to generate low‐valent nickel intermediates. This is the first example of catalysts exhibiting such behavior.     

Electrodeposition at Highly Negative Potentials of an Iron-Cobalt Oxide Catalyst for Use in Electrochemical Water Splitting

Earth-abundant transition metal-based catalysts have been extensively investigated for their applicability in water electrolysers to enable overall water splitting to produce clean hydrogen and oxygen. In this study a Fe−Co based catalyst is electrodeposited in 30 seconds under vigorous hydrogen evolution conditions to produce a high surface area material that is active for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). This catalyst can achieve high current densities of 600 mAcm⁻² at an applied potential of 1.6 V (vs RHE) in 1 M NaOH with a Tafel slope value of 48 mV dec⁻¹ for the OER. In addition, the HER can be facilitated at current densities as high as 400 mA cm⁻² due to the large surface area of the material. The materials were found to be predominantly amorphous but did contain crystalline regions of CoFe₂O₄ which became more evident after the OER indicating interesting compositional and structural changes that occur to the catalyst after an electrocatalytic reaction. This rapid method of creating a bimetallic oxide electrode for both the HER and OER could possibly be adopted to other bimetallic oxide systems suitable for electrochemical water splitting.     

Enhanced Metal-Support Interactions Boost the Electrocatalytic Water Splitting of Supported Ruthenium Nanoparticles on a Ni3N/NiO Heterojunction at Industrial Current Density

Developing highly efficient and stable hydrogen production catalysts for electrochemical water splitting (EWS) at industrial current densities remains a great challenge. Herein, we proposed a heterostructure-induced-strategy to optimize the metal-support interaction (MSI) and the EWS activity of Ru-Ni₃N/NiO. Density functional theory (DFT) calculations firstly predicted that the Ni₃N/NiO-heterostructures can improve the structural stability, electronic distributions, and orbital coupling of Ru-Ni₃N/NiO compared to Ru-Ni₃N and Ru-NiO, which accordingly decreases energy barriers and increases the electroactivity for EWS. As a proof-of-concept, the Ru-Ni₃N/NiO catalyst with a 2D Ni₃N/NiO-heterostructures nanosheet array, uniformly dispersed Ru nanoparticles, and strong MSI, was successfully constructed in the experiment, which exhibited excellent HER and OER activity with overpotentials of 190 mV and 385 mV at 1000 mA cm⁻², respectively. Furthermore, the Ru-Ni₃N/NiO-based EWS device can realize an industrial current density (1000 mA cm⁻²) at 1.74 V and 1.80 V under alkaline pure water and seawater conditions, respectively. Additionally, it also achieves a high durability of 1000 h (@ 500 mA cm⁻²) in alkaline pure water.     

NiSe Nanowire Film Supported on Nickel Foam: An Efficient and Stable 3D Bifunctional Electrode for Full Water Splitting

Active and stable electrocatalysts made from earth‐abundant elements are key to water splitting for hydrogen production through electrolysis. The growth of NiSe nanowire film on nickel foam (NiSe/NF) in situ by hydrothermal treatment of NF using NaHSe as Se source is presented. When used as a 3D oxygen evolution electrode, the NiSe/NF exhibits high activity with an overpotential of 270 mV required to achieve 20 mA cm^?2 and strong durability in 1.0 M KOH, and the NiOOH species formed at the NiSe surface serves as the actual catalytic site. The system is also highly efficient for catalyzing the hydrogen evolution reaction in basic media. This bifunctional electrode enables a high‐performance alkaline water electrolyzer with 10 mA cm^?2 at a cell voltage of 1.63 V.     

Cu@Cu3P Core–Shell Nanowires Attached to Nickel Foam as High-Performance Electrocatalysts for the Hydrogen Evolution Reaction

The development of highly efficient and inexpensive electrocatalysts is of great importance for generating renewable energy. In this work, Cu@Cu₃P core–shell nanowires grown on nickel foam (Cu@Cu₃P/NF) are prepared by a novel in situ reduction of CuSO₄ ⋅ 5 H₂O, which forms Cu, followed by surface oxidation and low-temperature phosphorization. The unique hierarchical architecture of Cu@Cu₃P/NF integrates the advantages of enlarged surface area, fast electron transport, numerous channels for gas rapid diffusion, non-polymer binder, and enhanced catalytic performance. Remarkably, Cu@Cu₃P/NF-50, with a molar ratio of Cu/Cu₃P of around 2.63, reveals a highly efficient catalytic performance for the hydrogen evolution reaction in alkaline solution with a Tafel slope of 59 mV dec⁻¹ and a long durability of 48 h. Overpotentials as low as 218 and 302 mV are required to reach current densities of 10 and 100 mA cm⁻², respectively. Furthermore, the scientific understanding and design principle of Cu@Cu₃P/NF with controlled performance will encourage more research into other high-performance, low-cost electrocatalysts for renewable energy.     

Folded nanosheet-like Co<Subscript>0.85</Subscript>Se array for overall water splitting

Active, stable, and earth-abundant bifunctional electrocatalyst for overall water splitting is pivotal to actualize large-scale water splitting via electrolysis. In this work, the hierarchical folded nanosheet-like Co_0.85Se array on Ni foam is constructed by liquid-phase chemical conversion with cobalt precursor nanorod array. It can serve as an efficient bifunctional electrocatalyst for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline electrolyte, with a current density of 10 mA cm^?2 at overpotential of 232 mV for OER and 129 mV for HER and Tafel slope of 78.9 mV dec^?1 for OER and 95.0 mV dec^?1 for HER, respectively. The two-electrode alkaline water electrolyzer utilizing this folded nanosheet-like Co_0.85Se array as both anode and cathode toward overall water splitting offered a current of 10 mA cm^?2 at a cell voltage of 1.60 V. This work explores an efficient and low-cost electrocatalyst for overall water splitting application in alkaline electrolytes.