One step synthesis of Fe4.4Ni17.6Se16 coupled NiSe foam as self-supported,highly efficient and durable oxygen evolution electrode

The development of cost-effective, durable and high-efficient oxygen evolution reaction (OER) electrocatalysts is an extremely critical technology for the large-scale industrial water electrolysis. Here, a new strategy is proposed to significantly enhance the electrocatalytic activity by forming a hybrid electrode of NiSe and Fe_4.4Ni_17.6Se₁₆ through direct selenization of porous iron-nickel (FeNi) alloy foam via thermal selenization process. The obtained self-supported Fe_4.4Ni_17.6Se₁₆/NiSe hybrid (FNS/NiSe) foam displays outstanding durability and remarkable catalytic activity in 1.0 M KOH with low overpotentials of 242 and 282 mV to achieve the current densities of 100 and 500 mA cm^?2, respectively. To the best of our knowledge, it exceeds most of the reported OER electrocatalysts in alkaline electrolytes.     

A Surface-Oxide-Rich Activation Layer (SOAL) on Ni2Mo3N for a Rapid and Durable Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is key to renewable energy technologies such as water electrolysis and metal–air batteries. However, the multiple steps associated with proton-coupled electron transfer result in sluggish OER kinetics and catalysts are required. Here we demonstrate that a novel nitride, Ni₂Mo₃N, is a highly active OER catalyst that outperforms the benchmark material RuO₂. Ni₂Mo₃N exhibits a current density of 10 mA cm⁻² at a nominal overpotential of 270 mV in 0.1 m KOH with outstanding catalytic cyclability and durability. Structural characterization and computational studies reveal that the excellent activity stems from the formation of a surface-oxide-rich activation layer (SOAL). Secondary Mo atoms on the surface act as electron pumps that stabilize oxygen-containing species and facilitate the continuity of the reactions. This discovery will stimulate the further development of ternary nitrides with oxide surface layers as efficient OER catalysts for electrochemical energy devices.     

Phosphate-induced interfacial electronic engineering in VPO4-Ni2P heterostructure for improved electrochemical water oxidation

Anodic oxygen evolution reaction（OER） is the key bottleneck for water electrolysis technique owing to its sluggish reaction kinetics. Interfacial engineering on the rationally designed heterostructure can regulate the electronic states efficiently for intrinsic activity improvement. Here, we report a co-phosphorization approach to construct a VPO₄-Ni₂P heterostructure on nickel foam with strongly chemical binding,wherein phosphate acts as electronic modifier for Ni₂     

A Surface‐Oxide‐Rich Activation Layer (SOAL) on Ni2Mo3N for a Rapid and Durable Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is key to renewable energy technologies such as water electrolysis and metal–air batteries. However, the multiple steps associated with proton‐coupled electron transfer result in sluggish OER kinetics and catalysts are required. Here we demonstrate that a novel nitride, Ni₂Mo₃N, is a highly active OER catalyst that outperforms the benchmark material RuO₂. Ni₂Mo₃N exhibits a current density of 10 mA cm^?2 at a nominal overpotential of 270 mV in 0.1 m KOH with outstanding catalytic cyclability and durability. Structural characterization and computational studies reveal that the excellent activity stems from the formation of a surface‐oxide‐rich activation layer (SOAL). Secondary Mo atoms on the surface act as electron pumps that stabilize oxygen‐containing species and facilitate the continuity of the reactions. This discovery will stimulate the further development of ternary nitrides with oxide surface layers as efficient OER catalysts for electrochemical energy devices.     

Dynamically Restructuring NixCryO Electrocatalyst for Stable Oxygen Evolution Reaction in Real Seawater

In the pursuit of long-term stability for oxygen evolution reaction (OER) in seawater, retaining the intrinsic catalytic activity is essential but has remained challenging. Herein, we developed a Ni_xCr_yO electrocatalyst that manifested exceptional OER stability in alkaline condition while improving the activity over time by dynamic self-restructuring. In 1 M KOH, Ni_xCr_yO required overpotentials of only 270 and 320 mV to achieve current densities of 100 and 500 mA cm⁻², respectively, with excellent long-term stability exceeding 475 h at 100 mA cm⁻² and 280 h at 500 mA cm⁻². The combination of electrochemical measurements and in situ studies revealed that leaching and redistribution of Cr during the prolonged electrolysis resulted in increased electrochemically active surface area. This eventually enhanced the catalyst porosity and improved OER activity. Ni_xCr_yO was further applied in real seawater from the Red Sea (without purification, 1 M KOH added), envisaging that the dynamically evolving porosity can offset the adverse active site-blocking effect posed by the seawater impurities. Remarkably, Ni_xCr_yO exhibited stable operation for 2000, 275 and 100 h in seawater at 10, 100 and 500 mA cm⁻², respectively. The proposed catalyst and the mechanistic insights represented a step towards realization of non-noble metal-based direct seawater splitting.     

Crystallinity-Modulated Electrocatalytic Activity of a Nickel(II) Borate Thin Layer on Ni3B for Efficient Water Oxidation

The exploration of new efficient OER electrocatalysts based on nonprecious metals and the understanding of the relationship between activity and structure of electrocatalysts are important to advance electrochemical water oxidation. Herein, we developed an efficient OER electrocatalyst with nickel boride (Ni₃B) nanoparticles as cores and nickel(II) borate (Ni-B_i) as shells (Ni-B_i@NB) via a very simple and facile aqueous reaction. This electrocatalyst exhibited a small overpotential of 302 mV at 10 mA cm⁻² and Tafel slope of 52 mV dec⁻¹. More interestingly, it was found that the OER activity of Ni-B_i@NB was closely dependent on the crystallinity of the Ni-B_i shells. The partially crystalline Ni-B_i catalyst exhibited much higher activity than the amorphous or crystalline analogues; this higher activity originated from the enhanced intrinsic activity of the catalytic sites. These findings open up opportunities to explore nickel(II) borates as a new class of efficient nonprecious metal OER electrocatalysts, and to improve the electrocatalyst performance by modulating their crystallinity.     

Interface‐Engineered Ni(OH)2/β‐like FeOOH Electrocatalysts for Highly Efficient and Stable Oxygen Evolution Reaction

Iron‐based (oxy)hydroxides are especially attractive electrocatalysts for the oxygen evolution reaction (OER) owing to their earth abundance, low cost, and nontoxicity. However, poor OER kinetics on the surface restricts the performance of the FeOOH electrocatalyst. Herein, a highly efficient and stable Ni(OH)₂/β‐like FeOOH electrocatalyst is obtained by facile electroactivation treatment. The activated Ni(OH)₂/β‐like FeOOH sample indicates an overpotential of 300 mV at 10 mA cm⁻² for the OER, and no clear current decay after 50 h of testing; this is comparable to the most efficient nickel‐ and cobalt‐based electrocatalysts on planar substrates. Furthermore, studies suggest that β‐like FeOOH plays a key role in remarkably enhancing the performance during the electroactivation process owing to its metastable tunnel structure with a lower barrier for interface diffusion of Ni²⁺ ions between the bilayer electrocatalyst. This study develops a new strategy to explore efficient and low‐cost electrocatalysts and deepens understanding of bilayer electrocatalysts for the OER.     

Laser-Ablation-Produced Cobalt Nickel Phosphate with High-Valence Nickel Ions as an Active Catalyst for the Oxygen Evolution Reaction

Cost-effective, highly efficient and stable non-noble metal-based catalysts for the oxygen evolution reaction (OER) are very crucial for energy storage and conversion. Here, an amorphous cobalt nickel phosphate (CoNiPO₄), containing a considerable amount of high-valence Ni³⁺ species as an efficient electrocatalyst for OER in alkaline solution, is reported. The catalyst was converted from Co-doped Ni₂P through pulsed laser ablation in liquid (PLAL) and exhibits a large specific surface area of 162.5 m² g⁻¹ and a low overpotential of 238 mV at 10 mA cm⁻² with a Tafel slope of 46 mV dec⁻¹, which is much lower than those of commercial RuO₂ and IrO₂. This work demonstrates that PLAL is a powerful technology for generating amorphous CoNiPO₄ with high-valence Ni³⁺, thus paving a new way towards highly effective OER catalysts.     

Fe‐Doped Ni3C Nanodots in N‐Doped Carbon Nanosheets for Efficient Hydrogen‐Evolution and Oxygen‐Evolution Electrocatalysis

Uniform Ni₃C nanodots dispersed in ultrathin N‐doped carbon nanosheets were successfully prepared by carburization of the two dimensional (2D) nickel cyanide coordination polymer precursors. The Ni₃C based nanosheets have lateral length of about 200 nm and thickness of 10 nm. When doped with Fe, the Ni₃C based nanosheets exhibited outstanding electrocatalytic properties for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). For example, 2 at % Fe (atomic percent) doped Ni₃C nanosheets depict a low overpotential (292 mV) and a small Tafel slope (41.3 mV dec⁻¹) for HER in KOH solution. An outstanding OER catalytic property is also achieved with a low overpotential of 275 mV and a small Tafel slope of 62 mV dec⁻¹ in KOH solution. Such nanodot‐incorporated 2D hybrid structures can serve as an efficient bifunctional electrocatalyst for overall water splitting.     

Interface Engineering of MoS2/Ni3S2 Heterostructures for Highly Enhanced Electrochemical Overall‐Water‐Splitting Activity

To achieve sustainable production of H₂ fuel through water splitting, low‐cost electrocatalysts for the hydrogen‐evolution reaction (HER) and the oxygen‐evolution reaction (OER) are required to replace Pt and IrO₂ catalysts. Herein, for the first time, we present the interface engineering of novel MoS₂/Ni₃S₂ heterostructures, in which abundant interfaces are formed. For OER, such MoS₂/Ni₃S₂ heterostructures show an extremely low overpotential of ca. 218 mV at 10 mA cm^?2, which is superior to that of the state‐of‐the‐art OER electrocatalysts. Using MoS₂/Ni₃S₂ heterostructures as bifunctional electrocatalysts, an alkali electrolyzer delivers a current density of 10 mA cm^?2 at a very low cell voltage of ca. 1.56 V. In combination with DFT calculations, this study demonstrates that the constructed interfaces synergistically favor the chemisorption of hydrogen and oxygen‐containing intermediates, thus accelerating the overall electrochemical water splitting.     

Self-supported ultrathin Co3O4 nanoarray enabling efficient paired electrolysis of 5-hydroxymethylfurfural for simultaneous dihydroxymethylfuran (DHMF) and furandicarboxylic acid (FDCA) production

Production of value-added chemicals and fuels from biomass via electrochemical methods has been of emerging interest in light of the increasing environmental, economic, and political challenges. Paired electrolysis, with anodic oxidation and cathodic reduction reactions pairing in a single electrochemical cell, offers an effective way to produce desired products in both electrodes, thus achieving complete electron economy. In this work, an efficient 5-hydroxymethylfurfural (HMF) paired electrolysis system is developed over a self-supported ultrathin Co₃O₄ nanoarray electrocatalyst for simultaneous production of value-added 2,5-dihydroxymethylfuran (DHMF) and 2,5-furandicarboxylic acid (FDCA). The as-designed paired electrolysis cell achieves a high HMF conversion and DHMF/FDCA selectivity at both anode and cathode without external hydrogen and oxygen input. A near-quantitative yield (95.7%) of FDCA and 78.8% yield of DHMF can be achieved in the paired electrolysis system, with a total Faradaic efficiency of 127%. This work will open up new opportunities in designing efficient electrochemical devices to simultaneously produce building-block chemicals from biomass-derived molecules in both anode and cathode.     

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.     

Efficient electrocatalytic oxygen evolution at ultra-high current densities over 3D Fe,N doped Ni(OH)2 nanosheets

Developing highly efficient nickel or iron based hydroxide electrocatalysts is primary essential but challenging for oxygen evolution reaction (OER) at ultra-high current densities. Herein, we developed a facile method to prepare nitrogen and iron doped nickel(II) hydroxide nanosheets on self-supported conductive nickel foam (denoted as Fe,N-Ni(OH)₂/NF) through ammonia hydrothermal and impregnation methods. Owing to the optimization of the electronic structure by nitrogen doping and the strong synergistic effect between Fe and Ni(OH)₂, the three-dimensional (3D) Fe,N-Ni(OH)₂/NF nanosheets delivered superior electrocatalytic OER performances in basic solution with low potentials of 1.57 V and 1.59 V under 500 mA/cm² and 1000 mA/cm² respectively and robust operation for 10 h with ignored activity decay, comparing well with the potentials of previously reported NiFe based electrocatalysts as well as the benchmark commercial Ir/C/NF. In-situ Raman spectroscopy revealed that the main active species were NiOOH during the OER process. The present results are expected to provide new insights into the study of OER process towards ultra-high current densities.     

Nickel-iron borate coated nickel-iron boride hybrid for highly stable and active oxygen evolution electrocatalysis

The development of efficient and cost-effective electrocatalysts toward anodic oxygen evolution reaction (OER) is crucial for the commercial application of electrochemical water splitting. As the most promising electrocatalysts, the OER performances of nickel-iron-based materials can be further improved by introducing metalloid elements to modify their electron structures. Herein, we developed an efficient hybrid electrocatalyst with nickel-iron boride (NiFeB) as core and amorphous nickel-iron borate (NiFeB_i) as shell (NiFeB@NiFeB_i) via a simple aqueous reduction. The obtained NiFeB@NiFeB_i exhibits a small overpotential of 237 mV at 10 mA/cm² and Tafel slope of 57.65 mV/dec in 1.0 mol/L KOH, outperforming most of the documented precious-metal-free based electrocatalysts. Benefiting from the in situ formed amorphous NiFeBi layer, it shows excellent stability toward the oxygen evolution reaction (OER). These findings might provide a new way to design advanced precious-metal-free electrocatalysts for OER and the application of electrochemical water splitting.     

Boosting Electrocatalytic Oxygen Evolution over Ce−Co9S8 Core–Shell Nanoneedle Arrays by Electronic and Architectural Dual Engineering

An dual electronic and architectural engineering strategy is a good way to rationally design earth-abundant and highly efficient electrocatalysts of the oxygen evolution reaction (OER) for sustainable hydrogen-based energy devices. Here, a Ce-doped Co₉S₈ core–shell nanoneedle array (Ce−Co₉S₈@CC) supported on a carbon cloth has been designed and developed to accelerate the sluggish kinetics of the OER. Profiting from valance alternative Ce doping, a fine core–shell structure and vertically aligned nanoneedle arrayed architecture, Ce−Co₉S₈@CC integrates modulated electronic structure, highly exposed active sites, and multidimensional mass diffusion channels; together, these afford a favorable catalyzed OER. Ce−Co₉S₈@CC exhibits remarkable performance in the OER in an alkaline medium, where the overpotential requires only 242 mV to deliver a current density of 10 mA cm⁻² for the OER; this is 70 mV superior to that of Ce-free Co₉S₈ catalyst and other counterparts. Good stability and impressive selectivity (nearly 100 % Faradic efficiency) are also demonstrated. When integrated into a two-electrode OER//HER electrolyzer, the as-prepared Ce−Co₉S₈@CC displays a low operation potential of 1.54 V at 10 mA cm⁻² and long-term stability, thus demonstrating great potential for economical water electrolysis.     

Synergism of Interface and Electronic Effects: Bifunctional N-Doped Ni3S2/N-Doped MoS2 Hetero-Nanowires for Efficient Electrocatalytic Overall Water Splitting

The realization of water electrolysis on the basis of highly active, cost-effective electrocatalysts is significant yet challenging for achieving sustainable hydrogen production from water. Herein, N-doped Ni₃S₂/N-doped MoS₂ 1D hetero-nanowires supported by Ni foam (N-Ni₃S₂/N-MoS₂/NF) are readily synthesized through a chemical transformation strategy by using NiMoO₄ nanowire array growth on Ni foam (NiMoO₄/NF) as the starting material. With the in situ generation of Ni₃S₂/MoS₂ heterointerfaces within nanowires and the incorporation of N⁻ anions, an extraordinary hydrophilic nature with abundant, well-exposed active sites and optimal reaction dynamics for both oxidation and reduction of water are obtained. Attributed to these properties, as-converted N-Ni₃S₂/N-MoS₂/NF exhibits highly efficient electrocatalytic activities for both hydrogen and oxygen evolution reactions under alkaline conditions. The superior bifunctional properties of N-Ni₃S₂/N-MoS₂/NF enable it to effectively catalyze the overall water-splitting reaction.     

Preferential Co substitution on Ni sites in Ni–Fe oxide arrays enabling large-current-density alkaline oxygen evolution

Developing low-cost and high-activity transition metal oxide electrocatalysts for an efficient oxygen evolution reaction (OER) at a large current density is highly demanded for industrial application and remains a big challenge. Herein, we report vertically aligned cobalt doped Ni–Fe based oxide (Co–NiO/Fe₂O₃) arrays as a robust OER electrocatalyst via a simple method combining hydrothermal reaction with heat treatment. Density functional theory calculation and XRD Rietveld refinement reveal that Co preferentially occupies the Ni sites compared to Fe in the Ni–Fe based oxides. The electronic structures of the Co–NiO/Fe₂O₃ could be further optimized, leading to the improvement of the intrinsic electronic conductivity and d-band center energy level and the decrease in the reaction energy barrier of the rate-determining step for the OER, thus accelerating its OER electrocatalytic activity. The Co–NiO/Fe₂O₃ nanosheet arrays display state-of-the-art OER activities at a large current density for industrial demands among Fe–Co–Ni based oxide electrocatalysts, which only require an ultra-low overpotential of 230 mV at a high current density of 500 mA cm⁻², and exhibit superb durability at 500 mA cm⁻² for at least 300 h without obvious degradation. The Co–NiO/Fe₂O₃ nanosheet arrays also have a small Tafel slope of 33.9 mV dec⁻¹, demonstrating fast reaction kinetics. This work affords a simple and effective method to design and construct transition metal oxide based electrocatalysts for efficient water oxidation.

Co–NiO/Fe₂O₃ nanosheets featuring Co substitution on Ni sites can effectively regulate electronic structures and exhibit high OER activities with low overpotential (η₅₀₀ = 230 mV), small Tafel slope (33.9 mV dec⁻¹) and superb durability for 300 h.     

Fe/Co‐based Bimetallic MOF‐derived Co3Fe7@NCNTFs Bifunctional Electrocatalyst for High‐Efficiency Overall Water Splitting

Electrocatalytic water splitting to produce hydrogen and oxygen is regarded as one of the most promising methods to generate clean and sustainable energy for replacing fossil fuels. However, the design and development of an efficient bifunctional catalyst for simultaneous generation of hydrogen and oxygen remains extremely challenging yet is critical for the practical implementation of water electrolysis. Here, we report a facile method to fabricate novel N‐doped carbon nanotube frameworks (NCNTFs) by the pyrolysis of a bimetallic metal organic framework (MIL‐88‐Fe/Co). The resultant electrocatalyst, Co₃Fe₇@NCNTFs, exhibits excellent oxygen evolution reaction (OER) activity, achieving 10 mA/cm² at a low overpotential of just 264 mV in 1 M KOH solution, and 197 mV for the hydrogen evolution reaction. The high electrocatalytic activity arises from the synergistic effect between the chemistry of the Co₃Fe₇ and the NCNTs coupled to the novel framework structure. The remarkable electrocatalytic performance of our bifunctional electrocatalyst provides a promising pathway to high‐performance overall water splitting and electrochemical energy devices.     

Ir Nanoparticles Anchored on Metal-Organic Frameworks for Efficient Overall Water Splitting under pH-Universal Conditions

The construction of high-activity and low-cost electrocatalysts is critical for efficient hydrogen production by water electrolysis. Herein, we developed an advanced electrocatalyst by anchoring well-dispersed Ir nanoparticles on nickel metal-organic framework (MOF) Ni-NDC (NDC: 2,6-naphthalenedicarboxylic) nanosheets. Benefiting from the strong synergy between Ir and MOF through interfacial Ni−O−Ir bonds, the synthesized Ir@Ni-NDC showed exceptional electrocatalytic performance for hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and overall water splitting in a wide pH range, superior to commercial benchmarks and most reported electrocatalysts. Theoretical calculations revealed that the charge redistribution of Ni−O−Ir bridge induced the optimization of H₂O, OH* and H* adsorption, thus leading to the accelerated electrochemical kinetics for HER and OER. This work provides a new clue to exploit bifunctional electrocatalysts for pH-universal overall water splitting.     

Simultaneous H2 Generation and Biomass Upgrading in Water by an Efficient Noble‐Metal‐Free Bifunctional Electrocatalyst

As an environmentally friendly approach to generate H₂, electrocatalytic water splitting has attracted worldwide interest. However, its broad employment has been inhibited by costly catalysts and low energy conversion efficiency, mainly due to the sluggish anodic half reaction, the O₂ evolution reaction (OER), whose product O₂ is not of significant value. Herein, we report an efficient strategy to replace OER with a thermodynamically more favorable reaction, the oxidation of 5‐hydroxymethylfurfural (HMF) to 2,5‐furandicarboxylic acid (FDCA), catalyzed by 3D Ni₂P nanoparticle arrays on nickel foam (Ni₂P NPA/NF). HMF is one of the primary dehydration intermediates of raw biomass and FDCA is of many industrial applications. As a bifunctional electrocatalyst, Ni₂P NPA/NF is not only active for HMF oxidation but also competent for H₂ evolution. In fact, a two‐electrode electrolyzer employing Ni₂P NPA/NF for simultaneous H₂ and FDCA production required a voltage at least 200 mV smaller compared with pure water splitting to achieve the same current density, as well as exhibiting robust stability and nearly unity Faradaic efficiencies.