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.     

Defect‐Rich Copper‐doped Ruthenium Hollow Nanoparticles for Efficient Hydrogen Evolution Electrocatalysis in Alkaline Electrolyte

It is of great importance to develop highly e?cient and stable Pt‐free catalysts for electrochemical hydrogen generation from water electrolysis. Here, monodisperse 7.5 nm copper‐doped ruthenium hollow nanoparticles (NPs) with abundant defects and amorphous/crystalline hetero‐phases were prepared and employed as efficient hydrogen evolution electrocatalysts in alkaline electrolyte. Specifically, these NPs only require a low overpotential of 25 mV to achieve a current density of 10 mA cm^?2 in 1.0 M KOH and show acceptable stability after 2000 potential cycles, which represents one of the best Ru‐based electrocatalysts for hydrogen evolution. Mechanism analysis indicates that Cu incorporation can modify the electronic structure of Ru shell, thereby optimizing the energy barrier for water adsorption and dissociation processes or H adsorption/desorption. Cu doping paired with the defect‐rich and highly open hollow structure of the NPs greatly enhances hydrogen evolution activity.     

Nickel Foam Supported NiO@Ru Heterostructure Towards High-Efficiency Overall Water Splitting

Electrocatalytic water splitting for hydrogen production from renewable energy requires the innovation of electrocatalysts with high activity and low cost. In this work, densely packed NiO@Ru nanosheets were fabricated on the surface of Ni foam through a two-step method of Ni(OH)₂ growth followed by Ru deposition. Through pair distribution function analysis from selected-area electron diffraction and X-ray photoelectron spectroscopy, the interface structure feature is revealed as a thin layer of perovskite NiRuO₃ sandwiched between NiO and Ru. The electrode exhibits high activity and durability for HER and OER, delivering a current density of 10 mA cm⁻² at a voltage of 1.55 V for overall water splitting in 1 M KOH. The excellent performance can be attributed to the intimate interface contact of NiO and Ru in addition to low charge transfer resistance and super-hydrophilic surface structure, as verified by the electrochemical impedance spectroscopy and contact-angle measurement.     

Blending Cr2O3 into a NiO–Ni Electrocatalyst for Sustained Water Splitting

The rising H₂ economy demands active and durable electrocatalysts based on low‐cost, earth‐abundant materials for water electrolysis/photolysis. Here we report nanoscale Ni metal cores over‐coated by a Cr₂O₃‐blended NiO layer synthesized on metallic foam substrates. The Ni@NiO/Cr₂O₃ triphase material exhibits superior activity and stability similar to Pt for the hydrogen‐evolution reaction in basic solutions. The chemically stable Cr₂O₃ is crucial for preventing oxidation of the Ni core, maintaining abundant NiO/Ni interfaces as catalytically active sites in the heterostructure and thus imparting high stability to the hydrogen‐evolution catalyst. The highly active and stable electrocatalyst enables an alkaline electrolyzer operating at 20 mA cm^?2 at a voltage lower than 1.5 V, lasting longer than 3 weeks without decay. The non‐precious metal catalysts afford a high efficiency of about 15 % for light‐driven water splitting using GaAs solar cells.     

Multifunctional Active-Center-Transferable Platinum/Lithium Cobalt Oxide Heterostructured Electrocatalysts towards Superior Water Splitting

Designing cost-effective and efficient electrocatalysts plays a pivotal role in advancing the development of electrochemical water splitting for hydrogen generation. Herein, multifunctional active-center-transferable heterostructured electrocatalysts, platinum/lithium cobalt oxide (Pt/LiCoO₂) composites with Pt nanoparticles (Pt NPs) anchored on LiCoO₂ nanosheets, are designed towards highly efficient water splitting. In this electrocatalyst system, the active center can be alternatively switched between Pt species and LiCoO₂ for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Specifically, Pt species are the active centers and LiCoO₂ acts as the co-catalyst for HER, whereas the active center transfers to LiCoO₂ and Pt turns into the co-catalyst for OER. The unique architecture of Pt/LiCoO₂ heterostructure provides abundant interfaces with favorable electronic structure and coordination environment towards optimal adsorption behavior of reaction intermediates. The 30 % Pt/LiCoO₂ heterostructured electrocatalyst delivers low overpotentials of 61 and 285 mV to achieve 10 mA cm⁻² for HER and OER in alkaline medium, respectively.     

Multifunctional Active‐Center‐Transferable Platinum/Lithium Cobalt Oxide Heterostructured Electrocatalysts towards Superior Water Splitting

Designing cost‐effective and efficient electrocatalysts plays a pivotal role in advancing the development of electrochemical water splitting for hydrogen generation. Herein, multifunctional active‐center‐transferable heterostructured electrocatalysts, platinum/lithium cobalt oxide (Pt/LiCoO₂) composites with Pt nanoparticles (Pt NPs) anchored on LiCoO₂ nanosheets, are designed towards highly efficient water splitting. In this electrocatalyst system, the active center can be alternatively switched between Pt species and LiCoO₂ for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Specifically, Pt species are the active centers and LiCoO₂ acts as the co‐catalyst for HER, whereas the active center transfers to LiCoO₂ and Pt turns into the co‐catalyst for OER. The unique architecture of Pt/LiCoO₂ heterostructure provides abundant interfaces with favorable electronic structure and coordination environment towards optimal adsorption behavior of reaction intermediates. The 30 % Pt/LiCoO₂ heterostructured electrocatalyst delivers low overpotentials of 61 and 285 mV to achieve 10 mA cm^?2 for HER and OER in alkaline medium, respectively.     

General π‐Electron‐Assisted Strategy for Ir,Pt, Ru,Pd, Fe,Ni Single‐Atom Electrocatalysts with Bifunctional Active Sites for Highly Efficient Water Splitting

Both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) are crucial to water splitting, but require alternative active sites. Now, a general π‐electron‐assisted strategy to anchor single‐atom sites (M=Ir, Pt, Ru, Pd, Fe, Ni) on a heterogeneous support is reported. The M atoms can simultaneously anchor on two distinct domains of the hybrid support, four‐fold N/C atoms (M@NC), and centers of Co octahedra (M@Co), which are expected to serve as bifunctional electrocatalysts towards the HER and the OER. The Ir catalyst exhibits the best water‐splitting performance, showing a low applied potential of 1.603 V to achieve 10 mA cm^?2 in 1.0 m KOH solution with cycling over 5 h. DFT calculations indicate that the Ir@Co (Ir) sites can accelerate the OER, while the Ir@NC₃ sites are responsible for the enhanced HER, clarifying the unprecedented performance of this bifunctional catalyst towards full water splitting.     

General π‐Electron‐Assisted Strategy for Ir,Pt, Ru,Pd, Fe,Ni Single‐Atom Electrocatalysts with Bifunctional Active Sites for Highly Efficient Water Splitting

Both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) are crucial to water splitting, but require alternative active sites. Now, a general π‐electron‐assisted strategy to anchor single‐atom sites (M=Ir, Pt, Ru, Pd, Fe, Ni) on a heterogeneous support is reported. The M atoms can simultaneously anchor on two distinct domains of the hybrid support, four‐fold N/C atoms (M@NC), and centers of Co octahedra (M@Co), which are expected to serve as bifunctional electrocatalysts towards the HER and the OER. The Ir catalyst exhibits the best water‐splitting performance, showing a low applied potential of 1.603 V to achieve 10 mA cm^?2 in 1.0 m KOH solution with cycling over 5 h. DFT calculations indicate that the Ir@Co (Ir) sites can accelerate the OER, while the Ir@NC₃ sites are responsible for the enhanced HER, clarifying the unprecedented performance of this bifunctional catalyst towards full water splitting.     

The Advanced Multi‐functional Electrocatalyst Efficiently Built from Multi‐integrated Sites for Overall Water Splitting and Rechargeable Zinc‐air Battery

Exploration of cost‐effective, high‐performance and durable multifunctional electrocatalysts is of significant importance for renewable energy conversion and storage. In this work, a simple strategy is developed to tailor the nickel metal with the collaboration of nitrogen‐doped graphene and single‐walled carbon nanotubes. The resulted nickel catalyst exhibits superior trifunctional activities for oxygen evolution, hydrogen evolution and oxygen reduction reactions in the same electrolyte, even comparable to commercial Pt/C and RuO₂ respectively, which can be attributed to the synergistic advantages between nickel, nitrogen and carbon, mainly including abundant integrated active sites achieved by the irregular charge distribution among C?N and Ni?N coupling centers. Such remarkable effects on trifunctional catalysis elicit the efficient overall water splitting, and endow the assembled zinc‐air battery with a good performance. These highlight the metallic nickel as an advanced multifunctional electrocatalysts with integrated sites developed from the collaboration of two different carbon nanomaterials.     

Designed Single Atom Bifunctional Electrocatalysts for Overall Water Splitting: 3d Transition Metal Atoms Doped Borophene Nanosheets

Single atom catalysts (SAC) for water splitting hold the promise of producing H₂ in a highly efficient and economical way. As the performance of SACs depends on the interaction between the adsorbate atom and supporting substrate, developing more efficient SACs with suitable substrates is of significance. In this work, inspired by the successful fabrications of borophene in experiments, we systematically study the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) activities of a series of 3d transition metal-based SACs supported by various borophene monolayers (BMs=α_sheet, α₁_sheet, and β₁_sheet borophene), TM/BMs, using density functional theory calculations and kinetic simulations. All of the TM/BMs systems exhibit superior HER performance compared to Pt with close to zero thermoneutral Gibbs free energy (ΔG_H*) of H adsorption. Furthermore, three Ni-deposited systems, namely, Ni/α_BM, Ni/α₁_BM and Ni/β₁_BM, were identified to be superior OER catalysts with remarkably reduced overpotentials. Based on these results, Ni/BMs can be expected to serve as stunning bifunctional electrocatalysts for water splitting. This work provides a guideline for developing efficient bifunctional electrocatalysts.     

Core–Shell NiO@Ni‐P Hybrid Nanosheet Array for Synergistically Enhanced Oxygen Evolution Electrocatalysis: Experimental and Theoretical Insights

Cost‐effective and highly‐efficient electrocatalysts for the oxygen evolution reaction are crucial for electrolytic hydrogen production. Here, we report core–shell NiO@Ni‐P nanosheet arrays as a high‐performance 3D catalyst for water oxidation electrocatalysis. Such nanoarrays demand overpotentials of 292 and 350 mV to drive geometrical catalytic current densities of 10 and 100 mA cm^?2, respectively, with an activity superior to its NiO and Ni‐P counterparts. Notably, this catalyst also shows a high long‐term electrochemical durability with a Faradaic efficiency of 98.1 %. Density functional theory calculation reveals that the superior activity benefits from the synergistic effect between NiO and Ni‐P.     

NiO表面磁性对分子吸附的影响的第一性原理研究

过渡金属氧化物广泛应用在当今能源与环境相关的催化领域,理解其表面化学性质以及结构-反应活性之间的关系对于先进催化材料的进一步发展以至理性设计至关重要.3d后过渡系金属(Mn,Fe,Co,Ni)的氧化物以其中金属离子独特的自旋状态和由此产生的铁磁/反铁磁性为典型特征.研究过渡金属氧化物的自旋状态以及磁性对表面化学的影响将使我们更加完整了解这些材料的表面化学.以NiO为代表的后过渡系金属岩盐结构一元氧化物具有反铁磁性,被经常作为反铁磁研究的模型体系.尽管在低温(低于其Neel温度)下NiO体相的完整晶体具有确定的反铁磁序,但是一系列最新研究表明,在条件变化时NiO表面的Ni离子可以产生不同的磁序.以此为背景,本工作以NiO为模型体系,采用DFT+U的第一性原理方法研究了NiO表面磁序对表面的小分子吸附活性的影响,包括表面吸附活性对各磁性相的表面取向以及吸附物种磁性的依赖关系.我们考察了NiO的5种反铁磁相和一种铁磁相,两个晶面NiO(001)和NiO(011),顺磁性分子NO和非顺磁性分子CO.我们发现表面能受磁性的影响较轻微,NiO(001)面上从49到54 meV/?2,NiO(011)面上从162到172 meV/?2.在NiO(001)面上,CO与NO都倾向于在Ni离子的顶位吸附.对于不同的体相磁序与表面取向,CO吸附能的变化范围为-0.33~-0.37 eV,NO吸附能的变化范围为-0.42~-0.46 eV.在NiO(011)表面,两种分子都倾向于吸附在由两个Ni离子构成的桥位.我们发现相对于NiO不同磁性相的体相长程磁序,吸附位点处构成桥位的两个Ni离子的局部磁矩相对取向对于分子的吸附具有更加显著的影响.计算得到NO在局部磁矩相对取向反平行(↑↓)吸附位点处的吸附能为-0.99~-1.05 eV,在局部磁矩相对取向平行(↑↑)吸附位点处吸附会增强,吸附能为-1.21~-1.30 eV.对于CO,尽管计算的吸附能在(↑↓)吸附位点(-0.73~-0.75 eV)与在(↑↑)吸附位点(-0.71~-0.72 eV)非常接近,两种吸附位点处的CO吸附时分子轨道杂化方式以及吸附后CO的局域电子态密度却具有明显不同的特征.本工作突出揭示了分子在过渡金属氧化物表面的多重吸附位点上吸附时吸附位点的局域磁矩相对取向对吸附性能的影响.     

三维百合花状的CoNi2S4作为先进的双功能电催化剂用于氢析出和氧析出反应

为简化电解水催化剂的合成过程和优化电解水操作系统, 双功能电解水催化剂的研究, 特别是在碱性条件下同时具有优异催化氢析出和氧析出反应性能的双功能电催化剂的研究尤为重要. 其中, 过渡金属硫化物, 特别是 CoNi 硫化物, 被报道有与氢化酶类似的催化活性中心, 从而具有优异的催化氢析出和催化氧析出反应性能. 虽然有关对过渡金属硫化物的研究很多, 但主要集中在具有一维纳米线和二维纳米片形貌结构的过渡金属硫化物. 不幸的是, 这些形貌结构的过渡金属硫化物在电催化过程中容易聚集和受限于电荷传输能力. 三维纳米结构的材料具有较大的比表面积以分布更多的活性位点和拥有良好的电子传输能力, 所以, 开发三维纳米结构的过渡金属硫化物材料可能是改进其催化电解水性能的一个好途径. 本文采用简单的两步水热法, 通过硫化合成的 CoNi 前体得到了长于泡沫镍上的三维百合花状的 CoNi2S4(Co-Ni2S4/Ni). 它只需要 54 mV 的过电位即可获得 10 mA cm-2的催化氢析出反应电流, 是最好的碱性催化氢析出反应电极材料之一. 它在驱动 100 mA cm-2的催化氧析出反应电流时也只需要 328 mV 的过电位. 另外, 把 CoNi2S4/Ni 分别作为阴极和阳极组装成双电极碱性水电解槽时, 它只需要 1.56 V 的电压即可获取 10 mA cm-2的催化全电解水电流并具有良好的催化全电解水稳定性.扫描电子显微镜、透射电子显微镜和 N2吸脱附曲线测试结果表明, 该三维百合花状的 CoNi2S4/Ni 的表面粗糙度高和拥有多孔特性. 多孔结构的 CoNi2S4/Ni 可提供更多可接触的催化活性位点, 也有利于催化过程中的电解质和生成的气体的扩散与传递. 交流阻抗图谱测试结果表明, CoNi2S4/Ni 具有良好的电子传输能力. 另外, 不同于前期对尖晶石结构的硫化物 AB2S4的研究结果, XPS 结果表明, CoNi2S4/Ni 中含有 Niб+和 Sб-活性物种, 表明 CoNi2S4具有与活性氢化酶类似的活 性中心. Niδ+和 Sδ-可分别作为氢氧根和质子的接收体, 协助促进吸附的水分子的分离, 从而提高材料的催化性能. 所以, Niδ+和 Sδ-活性物种的出现, 大比表面积的三维百合花状多孔结构和良好的电荷传输能力等特性集合于 CoNi2S4/Ni 上使得CoNi2S4/Ni 具有优异的催化氢析出和催化氧析出反应性能.     

Electrocatalysts Based on Transition Metal Borides and Borates for the Oxygen Evolution Reaction

Electrochemical water splitting is a clean and sustainable process for hydrogen production on a large scale as the electrical power required can be obtained from various renewable energy resources. The key challenge in electrochemical water splitting process is to develop low-cost electrocatalysts with high catalytic activity for the hydrogen evolution reaction (HER) on the cathode and the oxygen evolution reaction (OER) on the anode. OER is the most important half-reaction involved in water splitting, which has been extensively studied since the last century and a large amount of electrocatalysts including noble and non-noble metal-based materials have been developed. Among them, transition metal borides and borates (TMBs)-based compounds with various structures have attracted increasing attention owing to their excellent OER performance. In recent years, many efforts have been devoted to exploring the OER mechanism of TMBs and to improving the OER activity and stability of TMBs. In this review, recent research progress made in TMBs as efficient electrocatalysts for OER is summarized. The chemical properties, synthetic methodologies, catalytic performance evaluation, and improvement strategy of TMBs as OER electrocatalysts are discussed. The electrochemistry fundamentals of OER are first introduced in brief, followed by a summary of the preparation and performance of TMBs-based OER electrocatalysts. Finally, current challenges and future directions for TMBs-based OER electrocatalysts are discussed.     

Enhanced Electrocatalytic Hydrogen Oxidation on Ni/NiO/C Derived from a Nickel‐Based Metal–Organic Framework

The sluggish hydrogen oxidation reaction (HOR) under alkaline conditions has hindered the commercialization of hydroxide‐exchange membrane hydrogen fuel cells. A low‐cost Ni/NiO/C catalyst with abundant Ni/NiO interfacial sites was developed as a competent HOR electrocatalyst in alkaline media. Ni/NiO/C exhibits an HOR activity one order of magnitude higher than that of its parent Ni/C counterpart. Moreover, Ni/NiO/C also shows better stability and CO tolerance than commercial Pt/C in alkaline media, which renders it a very promising HOR electrocatalyst for hydrogen fuel cell applications. Density functional theory (DFT) calculations were also performed to shed light on the enhanced HOR performance of Ni/NiO/C; the DFT results indicate that both hydrogen and hydroxide achieve optimal binding energies at the Ni/NiO interface, resulting from the balanced electronic and oxophilic effects at the Ni/NiO interface.     

Heteroatom‐doped MoSe2 Nanosheets with Enhanced Hydrogen Evolution Kinetics for Alkaline Water Splitting

Electrochemical water splitting for hydrogen generation is a vital part for the prospect of future energy systems, however, the practical utilization relies on the development of highly active and earth‐abundant catalysts to boost the energy conversion efficiency as well as reduce the cost. Molybdenum diselenide (MoSe₂) is a promising nonprecious metal‐based electrocatalyst for hydrogen evolution reaction (HER) in acidic media, but it exhibits inferior alkaline HER kinetics in great part due to the sluggish water adsorption/dissociation process. Herein, the alkaline HER kinetics of MoSe₂ is substantially accelerated by heteroatom doping with transition metal ions. Specifically, the Ni‐doped MoSe₂ nanosheets exhibit the most impressive catalytic activity in terms of lower overpotential and larger exchange current density. The density functional theory (DFT) calculation results reveal that Ni/Co doping plays a key role in facilitating water adsorption as well as optimizing hydrogen adsorption. The present work paves a new way to the development of low‐cost and efficient electrocatalysts towards alkaline HER.     

Constructing Built-in Electric Field in Heterogeneous Nanowire Arrays for Efficient Overall Water Electrolysis

Efficient bifunctional electrocatalysts for hydrogen and oxygen evolution reactions are key to water electrolysis. Herein, we report a built-in electric field (BEF) strategy to fabricate heterogeneous nickel phosphide-cobalt nanowire arrays grown on carbon fiber paper (Ni₂P-CoCH/CFP) with large work function difference (ΔΦ) as bifunctional electrocatalysts for overall water splitting. Impressively, Ni₂P-CoCH/CFP exhibits a remarkable catalytic activity for hydrogen and oxygen evolution reactions to obtain 10 mA cm⁻², respectively. Moreover, the assembled lab-scale electrolyzer driven by an AAA battery delivers excellent stability after 50 h electrocatalysis with a 100 % faradic efficiency. Computational calculations combining with experiments reveal the interface-induced electric field effect facilitates asymmetrical charge distributions, thereby regulating the adsorption/desorption of the intermediates during reactions. This work offers an avenue to rationally design high-performance heterogeneous electrocatalysts.     

The Co_3O_4 nanosheet array as support for MoS_2 as highly efficient electrocatalysts for hydrogen evolution reaction

The electrochemical hydrogen evolution reaction(HER) on a non-precious electrocatalyst in an alkaline environment is of essential importance for future renewable energy. The design of advanced electrocatalysts for HER is the most important part to reduce the cost and to enhance the efficiency of water splitting. MoS_2 is considered as one of the most promising electrocatalysts to replace the precious Pt catalyst.Herein, for the first time, we have successfully loaded MoS_2 electrocatalysts onto the Co_3O_4 nanosheet array to catalyze HER with a low onset potential of ~76 mV. The high hydrogen evolution activity of MoS_2 supported on the Co_3O_4 nanosheet array may be attributed to the increased active sites and the electronic interactions between MoS_2 and Co_3O_4.     

General synthesis of Pt and Ni co-doped porous carbon nanofibers to boost HER performance in both acidic and alkaline solutions

It is essential to develop efficient electrocatalysts to generate hydrogen from water electrolysis for hydrogen economy. In this work, platinum(Pt) and nickel(Ni) co-doped porous carbon nanofibers(Pt/NiPCNFs) with low Pt content were prepared via an electrospinning, carbonization and galvanic replacement reaction. Because of the high electrical conductivity, abundant electrochemical active sites and synergistic effect between Pt and Ni nanoparticles, the optimized Pt/Ni-PCNFs catalyst shows an e...     

Interfacial Coupling of Graphene with Nickel Nanoparticles for Water Splitting and Urea Oxidation: A Spectroelectrochemical Investigation

Nickel nanoparticle and graphene interfaces of various stoichiometries were created through electrodeposition techniques. The catalytic behavior of the electrodeposited films was investigated through spectro-electrochemical methodologies. UV-vis absorbance spectra of the electrodeposited films are significantly different in the air and alkaline medium. Furthermore, UV-vis and Raman spectroscopy confirmed the coupling of Ni nanoparticles (Ni-NP) with the graphene framework, along with NiO and Ni(OH)₂. A combination of Raman and impedance spectroscopy revealed that the surface adsorption and charge transfer properties of the electrodeposited films are entirely dependent on the defects on graphene structure as well as distribution of Ni-NP on graphene. The electrodeposited films possess heterogeneous catalytic properties with a low overpotential of 50 mV (10 mA/cm⁻²) for hydrogen evolution reaction, as well as 601 mV and 391 mV (at 50 mA/cm⁻²) for the oxygen evolution reaction and urea oxidation reaction, respectively. In addition, eelectrodeposited samples show extraordinary overall water splitting performance by achieving a current density of 10 mA/cm² at a very low applied potential of 1.38 V. This synergistic coupling of Ni and graphene renders the electrodeposited samples promising candidates as electrodes for overall water splitting in alkaline and urea-supplemented solutions.