NiWO3 Nanoparticles Grown on Graphitic Carbon Nitride (g‐C3N4) Supported Toray Carbon as an Efficient Bifunctional Electrocatalyst for Oxygen and Hydrogen Evolution Reactions

Catalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are at the heart of water oxidation reactions. Despite continuous efforts, the development of OER/HER electrocatalysts with high activity at low cost remains a big challenge. Herein, a composite material consisting of TC@WO₃@g‐C₃N₄@Ni‐NiO complex matrix as a bifunctional electrocatalyst for the OER and HER is described. Though the catalyst has modest activity for HER, it exhibits high OER activity thereby making it a better nonprecious electrocatalyst for both OER and HER and is further improved by g‐C₃N₄. The catalytic activity arises from the synergetic effects between WO₃, Ni‐NiO, and g‐C₃N₄. A Ni‐NiO alloy and WO₃ nanoparticles decorated on the g‐C₃N₄ surface supported toray carbon (TC) matrix (TC@WO₃@g‐C₃N₄@Ni‐NiO) by a facile route that show an excellent and durable bifunctional catalytic activity for OER and HER in the alkaline medium are developed. This carbon nitride with binary metal/metal‐oxide matrix supported with TC exhibit an overpotential of 0.385 and 0.535 V versus RHE at a current density of 10 mA cm^?2 (Tafel slopes of 0.057 and 0.246 V dec^?1 for OER and HER, respectively), in 0.1 m NaOH . The catalyst is tested in water electrolysis for 17 h.     

Ultrasound assisted synthesis of highly active nanoflower-like CoMoS4 electrocatalyst for oxygen and hydrogen evolution reactions

Rapid technological development requires sustainable, pure, and clean energy systems, such as hydrogen energy. It is difficult to fabricate efficient, highly active, and inexpensive electrocatalysts for the overall water splitting reaction: the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The present research work deals with a simple hydrothermal synthesis route assisted with ultrasound that was used to fabricate a 3D nanoflower-like porous CoMoS₄ electrocatalyst. A symmetric electrolyzer cell was fabricated using a CoMoS₄ electrode as both the anode and cathode, with a cell voltage of 1.51 V, to obtain a current density of 10 mA/cm². Low overpotentials were observed for the CoMoS₄ electrode (250 mV for OER and 141 mV for HER) at a current density of 10 mA/cm².     

Bifunctional oxygen electrocatalysts for rechargeable zinc−air battery based on MXene and beyond

Oxygen electrocatalysts are of great importance for the air electrode in zinc–air batteries (ZABs). Owing to large surface area, high electrical conductivity and ease of modification, two-dimensional (2D) materials have been widely studied as oxygen electrocatalysts for the rechargable ZABs. The elaborately modified 2D materials-based electrocatalysts, usually exhibit excellent performance toward the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which have attracted extensive interests of worldwide researchers. Given the rapid development of bifunctional electrocatalysts toward ORR and OER, the latest progress of non-noble electrocatalysts based on layered double hydroxides (LDHs), graphene, and MXenes are intensively reviewed. The discussion ranges from fundamental structure, synthesis, electrocatalytic performance of these catalysts, as well as their applications in the rechargeable ZABs. Finally, the challenges and outlook are provided for further advancing the commercialization of rechargeable ZABs.     

Co3O4 Hollow Polyhedrons as Bifunctional Electrocatalysts for Reduction and Evolution Reactions of Oxygen

It is very important to exploit low‐cost and efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts for the development of renewable‐energy conversion and storage techniques. Although much attention has been made to develop efficient catalysts for ORR and OER, it is still highly desired to create new bifunctional catalysts. In this study, Co₃O₄ hollow polyhedrons are synthesized as efficient bifunctional electrocatalysts for ORR and OER by simple one‐step annealing Co‐centered metal–organic frameworks (ZIF‐67). Due to the large specific surface areas and high porosity, the as‐prepared Co₃O₄ hollow polyhedrons exhibit excellent electrocatalytic activities for ORR and OER in alkaline media. Co₃O₄ hollow polyhedrons show higher peak current density (0.61 mA cm^?2) with four‐electron pathway than Co₃O₄ particles (0.39 mA cm^?2), better methanol tolerance and superior durability (82.6%) than commercial Pt/C electrocatalyst (58.6%) for ORR after 25 000 s. In addition, Co₃O₄ hollow polyhedrons also display excellent OER performances with smaller overpotential (536 mV) for 10 mA cm^?2 than Co₃O₄ particles (593 mV) and superior stability (86.5%) after 25 000 s. This facile one‐step strategy based on metal–organic frameworks self‐sacrificed templates can be used to develop the promising well‐defined porous hollow metal oxides electrode materials for energy conversion and storage technologies.     

Ultrathin Fe‐N‐C Nanosheets Coordinated Fe‐Doped CoNi Alloy Nanoparticles for Electrochemical Water Splitting

The development of highly active and cost‐effective catalyst materials toward electrochemical water splitting is of great importance for converting and storing the intermittent solar energy in the form of hydrogen. Herein, for the first time, an ultrathin Fe and N‐co‐doped carbon nanosheet encapsulated Fe‐doped CoNi alloy nanoparticle (FeCoNi@FeNC) composite is obtained and applied as a bifunctional catalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). This catalyst exhibits prominent catalytic performances for both HER and OER, which only requires overpotentials of 102 and 330 mV, respectively, to reach a current density of 10 mA cm^?2 in alkaline media. The high catalytic activity is intrinsically associated with the presence of Fe in both nanosheets and nanoparticles, which has triggered the occurrence of coordinative effects between Fe‐N‐C and FeCoNi that are beneficial for HER and OER, as revealed by electrochemical techniques. In an overall water splitting electrolyzer, FeCoNi@FeNC is employed as both the cathode and anode catalysts, achieving 12 mA cm^?2 at 1.63 V for a duration of more than 12 h.     

Direct pyrolysis and ultrasound assisted preparation of N,S co-doped graphene/Fe3C nanocomposite as an efficient electrocatalyst for oxygen reduction and oxygen evolution reactions

Bifunctional electrocatalysts to enable efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are essential for fabricating high performance metal–air batteries and fuel cells. Here, a defect rich nitrogen and sulfur co-doped graphene/iron carbide (NS-GR/Fe₃C) nanocomposite as an electrocatalyst for ORR and OER is demonstrated. An ink of NS-GR/Fe₃C is developed by homogeneously dispersing the catalyst in a Nafion containing solvent mixture using an ultrasonication bath (Model-DC150H; power − 150 W; frequency − 40 kHz). The ultrasonically prepared ink is used for preparing the electrode for electrochemical studies. In the case of ORR, the positive half-wave potential displayed by NS-GR/Fe₃C is 0.859 V (vs. RHE) and for the OER, onset potential is 1.489 V (vs. RHE) with enhanced current density. The optimized NS–GR/Fe₃C electrode exhibited excellent ORR/OER bifunctional activities, high methanol tolerance and excellent long-term cycling stability in an alkaline medium. The observed onset potential for NS–GR/Fe₃C electrocatalyst is comparable with the commercial noble metal catalyst, thereby revealing one of the best low-cost alternative air–cathode catalysts for the energy conversion and storage application.     

Three-dimensional flower-like NiS2/MoS2 assembly of randomly oriented nanoplate for enhanced hydrogen evolution reaction

The continually worsening energy crisis has stimulated research into energy conversion technology to produce pure hydrogen, H₂. Transition metal-based compounds have attracted great attention as electrocatalysts for hydrogen evolution reaction (HER) as alternatives to commercial, high-cost, and scarce noble metal-based catalysts. In this work, a 3D flower-like NiS₂/MoS₂ is synthesized with the advantages of a three-dimensional (3D) morphology and the compositing of different metal compounds, thus leading to enhanced electrocatalytic performance. The structure of 3D flower-like NiS₂/MoS₂ augments the specific surface areas resulting from nanoplate assemblies as well as the heterointerface ascribed to two different phases of NiS₂ and MoS₂. These characteristics are confirmed by electrocatalytic measurements of the lower overpotential of 165 mV at 10 mA/cm² with high charge transfer ability, thus demonstrating the structure's potential for advanced electrocatalysts for the HER.     

Composite Nanoarchitectonics with iron nickel bimetallic nanoparticles and carbon composite for efficient electrocatalysis in hydrogen evolution reaction

The poor efficiency and stability of cost-effective metal compounds are major hurdles to substitute expensive metal-based nanomaterials for the hydrogen evolution reaction (HER). As a result, new concepts and tactics for developing electrocatalysts based on earth-abundant elements must be developed. We present iron-nickel alloy nanoparticles that are supported with carbon (FeNi@C) to improve HER performance in alkaline conditions. FeNi particle was supported on Trimesic acid (TMA) based carbon. In particular, the high conductivity of the carbon and a large number of catalytically active sites in the FeNi demonstrated a synergistic effect, making the hybrid structure a good choice for HER catalyst. Moreover, the physicochemical interaction between the carbon and FeNi metal enhanced the electrocatalytic performance and resulted in achieving 10 mA/cm² current density at 190 mV overpotential with 15 h chronopotential cycling, proving the possibility for replacing costly Pt-based catalysts.     

Understanding the Effects of Ultrasound (408 kHz) on the Hydrogen Evolution Reaction (HER) and the Oxygen Evolution Reaction (OER) on Raney-Ni in Alkaline Media

The hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) occurring at the Raney-Ni mesh electrode in 30 wt.-% aqueous KOH solution were studied in the absence (silent) and presence of ultrasound (408 kHz, ∼54 W, 100% acoustic amplitude) at different electrolyte temperatures (T = 25, 40 and 60 °C). Linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) experiments were performed to analyse the electrochemical behaviour of the Raney-Ni electrode under these conditions. Under silent conditions, it was found that the electrocatalytic activity of Raney-Ni towards the HER and the OER depends upon the electrolyte temperature, and higher current densities at lower overpotentials were achieved at elevated temperatures. It was also observed that the HER activity of Raney-Ni under ultrasonic conditions increased at low temperatures (e.g., 25 °C) while the ultrasonic effect on the OER was found to be insignificant. In addition, it was observed that the ultrasonic effect on both the HER and OER decreases by elevating the temperature. In our conditions, it is suggested that ultrasound enhances the electrocatalytic performance of Raney-Ni towards the HER due to principally the efficient gas bubble removal from the electrode surface and the dispersion of gas bubbles into the electrolyte, and this effect depends upon the behaviour of the hydrogen and oxygen gas bubbles in alkaline media.     

C_9N_4 as excellent dual electrocatalyst: A first principles study

We perform first principles calculations to investigate the catalytic behavior of C_9 N_4 nanosheet for water splitting.For the pristine C_9 N_4,we find that,at different hydrogen coverages,two H atoms adsorbed on the 12-membered ring and one H atom adsorbed on the 9-membered ring show excellent performance of hydrogen evolution reaction(HER).Tensile strain could improve the catalytic ability of C_9 N_4 and strain can be practically introduced by building C_9 N_4/BiN,and C_9 N_4/GaAs heterojunctions.We demonstrate that the HER performance of heterojunctions is indeed improved compared with that of C_9 N_4 nanosheet.Anchoring transition metal atoms on C_9 N_4 is another strategy to apply strain.It shows that Rh@C_9 N_4 exhibits superior HER property with very low Gibbs free energy change of-30 meV.Under tensile strain within ～2%,Rh@C_9 N_4 could catalyze HER readily.Moreover,the catalyst Rh_9 C_9 N_4 works well for oxygen evolution reaction(OER)with an overpotential of 0.58 V.Our results suggest that Rh@C_9 N_4 is favorable for both HER and OER because of its metallic conductivity,close-zero Gibbs free energy change,and low oneset overpotential.The outstanding performance of C_9 N_4 nanosheet could be attributed to the tunable porous structure and electronic structure compatibility.     

Biomass-Templated Preparation of Hierarchically Multi-Functional Ni/NiO@C Hollow-Fibers

Two series of hierarchically Ni/NiO@C hollow-fibers with magnetic, adsorptive, and electrocatalytic oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) properties are successfully prepared via a facile and green cotton fiber (CF)-templated dipping/adsorbing-calcining strategy. The effect of calcination temperature and CF amount on morphologies, components, and properties of the as-prepared materials is investigated. The results demonstrate that a proper CF template can endow the as-obtained materials with hierarchically hollow-fiber morphology and multi-components (Ni⁰, NiO, and C) at a certain calcination temperature, therefore providing excellent magnetic, adsorptive, and electrocatalytic OER and HER properties. Specifically, the unique hierarchical morphology and synergistic effect between Ni⁰ and NiO remarkably enhance OER and HER properties of as-prepared samples. This strategy is low-cost, simple, eco-friendly, and could be extended to prepare other composites with multi-components and functionalities.     

Shape-controlled synthesis of nickel phosphide nanocrystals and their application as hydrogen evolution reaction catalyst

Monodisperse nickel phosphide (Ni₂P) nanorods and nanoparticles were synthesized by one step solution-phase route, in which the mixture of trioctylphosphine oxide (TOPO) and trioctylphosphine (TOP) was used as solvent, capping agent and phosphor source. The morphologies of the Ni₂P nanocrystals were controlled simply by varying the dropping rate of metal source. The as-prepared Pt-free Ni₂P nanocrystals exhibit the enhanced electrocatalytic activity toward hydrogen evolution reaction (HER) compared to pure commercial Ni nanoparticles. Therefore, the obtained Ni₂P nanocrystals appear to be promising non precious metal electrocatalysts for HER.     

Comprehensive facilitating of water oxidation reaction by ultrasonic attenuation of hydrogen-bonded structure of water

The balance between water-metal interactions and water-water hydrogen bonding (HBs) controls the process of water adsorption on metallic surfaces. In other hand, the yield of oxygen evolution reaction (OER) is dependent on the binding energy of H₂O at electrode surface. Therefore, on a specific metal substrate, attenuation of HBs may be a promising route for improving OER. In this study, the computational and experimental evidences indicate that the performance of ultrasonically irradiated deionized water (USI-DW), participated in water oxidation reaction (WOR), is different from its in the intact bulk water. To date, establishing of new electrocatalysts with lower overpotentials (η) and higher current densities (J) in OER have been mostly considered based on metals and oxide materials. Here, we ultrasonically agitated the water clusters formed by strong HBs, and as a sustainable improvement route explored its particular effects on the efficiency of OER. The molecular modeling (MM) of the (H₂O)_n clusters (n = 1–100 molecules), the corresponding IR spectra, the molecular orbitals energy levels and the adsorption of free and cluster confined H₂O molecules on the Pt surface were studied by the appropriate quantum mechanical (QM) methods. The result of deconvolution of FTIR spectra recorded for USI-DW in the –OH stretching region (∼2600–3900 cm⁻¹) properly confirmed the expected increase of the single water molecules. The reduction in overpotentials was 82 ± 8 mV and 158 ± 12 mV, to reach the J of 1 mA cm⁻¹ at the typical pHs 12.2 and 13.1, respectively.     

铜纳米阵列高效电解水产氧催化剂的制备

本文报道了一种利用简单的两步牺牲模板法,在泡沫铜基底表面完成了三维氧化铜纳米晶阵列的生长. 氧化铜纳米晶阵列具有良好的导电性,稳定性,在碱性溶液中有着优秀的电解水产氧催化性能. 氧化铜纳米晶阵列催化水的电化学氧化只需400 mV的过电势即可达到100 mA/cm²的电流密度,与其它铜基电解水产氧催化剂以及贵金属IrO₂相比都有着明显的优势. 氧化铜纳米晶阵列在270 mA/cm²左右的工作电流下连续工作10 h依然可以保持良好的稳定性,是相同的工作电压下IrO₂工作电流的10倍(约25 mA/cm²).     

Highly Efficient Bifunctional Catalyst of NiCo2O4@NiO@Ni Core/Shell Nanocone Array for Stable Overall Water Splitting

Electrochemical splitting of water is an efficient way to produce clean energy for energy storage and conversion devices. Herein, 3D hierarchical NiCo₂O₄@NiO@Ni core/shell nanocone arrays (NAs) are reported on Ni foam for stable overall water splitting with high efficiency. The architecture and composition of the 3D catalysts are particularly tuned. The outstanding structural and component features of the as‐prepared 3D catalysts are characterized by the vertically grown NiCo₂O₄ nanocone/NiO nanosheet core/shell structure and Ni decorated 3D‐conductive networks, which largely prompt the catalytic performance. The hybrid catalyst with core/shell nanocone array structures exhibits superior bifuncational activities for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) with an overpotential of 240 and 120 mV at a current density of 10 mA cm^?2, respectively. The Tafel slope of the optimal 3D electrode is about 43 and 58 mV dec^?1 in an alkaline electrolyte for OER and HER, respectively. An alkaline electrolyzer constructed by two symmetric NiCo₂O₄@NiO@Ni electrodes delivers splendid activity toward overall water splitting with a current of 10 mA cm^?2 at only ≈1.60 V and almost no deactivation after 10 h. This work provides a promising strategy to design ternary core/shell electrodes as high performance Janus catalysts for overall water splitting.     

Laser fragmentation in liquid synthesis of novel palladium-sulfur compound nanoparticles as efficient electrocatalysts for hydrogen evolution reaction

One promising way to tune the physicochemical properties of materials and optimize their performance in various potential applications is to engineer material structures at the atomic level. As is well known, the performance of Pd-based catalysts has long been constrained by surface contamination and their single structure. Here, we employed an unadulterated top-down synthesis method, known as laser fragmentation in liquid (LFL), to modify pristine PdPS crystals and obtained a kind of metastable palladium-sulfur compound nanoparticles (LFL-PdS NPs) as a highly efficient electrocatalyst for hydrogen evolution reaction (HER). Laser fragmentation of the layered PdPS crystal led to a structural reorganization at the atomic level and resulted in the formation of uniform metastable LFL-PdS NPs. Noteworthy, the LFL-PdS NPs show excellent electrocatalytic HER performance and stability in acidic media, with an overpotential of -66 mV at 10 mA· cm^-2, the Tafel slope of 42 mV· dec^-1. The combined catalytic performances of our LFL-PdS NPs are comparable to the Pt/C catalyst for HER. This work provides a top-down synthesis strategy as a promising approach to design highly active metastable metal composite electrocatalysts for sustainable energy applications.     

Theoretical investigation of CoTa2O6/graphene heterojunctions for oxygen evolution reaction

Water electrolysis is to split water into hydrogen and oxygen using electricity as the driving force. To obtain low-cost hydrogen in a large scale, it is critical to develop electrocatalysts based on earth abundant elements with a high efficiency. This computational work started with Cobalt on CoTa₂O₆ surface as the active site, CoTa₂O₆/Graphene heterojunctions have been explored as potential oxygen evolution reaction (OER) catalysts through density functional theory (DFT). We demonstrated that the electron transfer (δ) from CoTa₂O₆ to graphene substrate can be utilized to boost the reactivity of Co-site, leading to an OER overpotential as low as 0.30 V when N-doped graphene is employed. Our findings offer novel design of heterojunctions as high performance OER catalysts.     

Oxygen vacancies and V co-doped Co_3O_4 prepared by ion implantation boosts oxygen evolution catalysis

Introducing heteroatoms and defects is a significant strategy to improve oxygen evolution reaction(OER) performance of electrocatalysts. However, the synergistic interaction of the heteroatom and defect still needs further investigations. Herein, we demonstrated an oxygen vacancy-rich vanadium-doped Co_3O_4(V–O_v–Co_3O_4), fabricated by V-ion implantation, could be used for high-efficient OER catalysis. X-ray photoelectron spectra(XPS) and density functional theory(DFT) calculations show that the charge density of Co atom increased, and the reaction barrier of reaction pathway from O*to HOO*decreased. V–O_v–Co_3O_4 catalyst shows a low overpotential of 329 mV to maintain current density of 10 m A·cm~(-2), and a small Tafel slope of 74.5 m V·dec~(-1). This modification provides us with valuable perception for future design of heteroatom-doped and defect-based electrocatalysts.     

NiSb纳米颗粒的热液路线制备及电催化析氢性能研究

本文发展了一种简单经济的过渡金属锑化物热液合成路线,在160 oC的温和条件下,由商业易得的乙酰丙酮基镍和三苯基铋在油胺介质中还原制备出NiSb纳米颗粒. 反应中,还原剂甲硼烷-叔丁基胺络合物的使用能够有效促进金属源的快速还原,用以促进NiSb纳米颗粒的生成. 结构表征显示,所制备的NiSb产物为六方相(空间群P6₃/mmc)颗粒状纳米晶,其粒径约为10 nm. 该合成方法可拓展用于CoSb和Ag₃Sb等纳米颗粒的温和制备. 电催化析氢性能研究显示,NiSb纳米颗粒具有良好的电化学析氢反应性能. 结果显示,当阴极电流密度达到50 mA/cm²和10 mA/cm²时所需要的过电位分别为531和437 mV. 同时,NiSb纳米颗粒还具有较小的电荷转移阻抗和优良的循环稳定性能.     

A Highly Effective,Stable Oxygen Evolution Catalyst Derived from Transition Metal Selenides and Phosphides

Recently, transition metal chalcogenides and phosphides have been increasingly reported as efficient and stable oxygen evolution reaction (OER) catalysts in alkaline medium, despite the fact that they are thermodynamically unstable under highly oxidative potentials. Here the active forms of these materials are elucidated by synthesizing a hybrid catalyst, which has a metal chalcogenide in the form of CoSe₂ and metal phosphide in the form of CoP—CoSe₂|CoP. Both CoSe₂ and CoP in the as‐prepared catalyst are completely transformed into their respective oxyhydroxides and hydroxides, which are, in fact, the true OER‐active species in alkaline medium and not the selenide and phosphide themselves. The derived oxides from the hybrid catalyst deliver an excellent OER activity by reaching a current density of 10 mA cm⁻² at a low overpotential of 240 mV (vs reversible hydrogen electrode (RHE)) and a Tafel slope of 46.6 mV dec⁻¹. The stability of the derived oxyhydroxide/hydroxide catalyst shows no appreciable deactivation during 120 h of continuous electrolysis, displaying an extraordinary operational stability.