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.     

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.     

A Facile Strategy to Synthesize Cobalt‐Based Self‐Supported Material for Electrocatalytic Water Splitting

Designing and developing active, robust, and noble‐metal‐free catalysts with superior stability for electrocatalytic water splitting is of critical importance but remains a grand challenge. Here, a facile strategy is provided to synthesize a series of Co‐based self‐supported electrode materials by combining electrospinning and chemical vapor deposition (CVD) technologies. The Co, Co₃O₄, Co₉S₈ nanoparticles (NPs) are formed in situ simultaneously with the formation of carbon nanofibers (CNFs) during the CVD process, respectively. The Co‐based NPs are uniformly distributed through the CNFs and they can be directly used as the electrode materials for hydrogen evolution reaction (HER) in acid and oxygen evolution reaction (OER) in alkaline. The Co₉S₈/CNFs membrane exhibits the best HER activity with overpotential of 165 mV at j = 10 mA cm^?2 and Tafel slope of 83 mV dec^?1 and OER activity with overpotential of 230 mV at j = 10 mA cm^?2 and Tafel slope of 72 mV dec^?1. The onion‐like graphitic layers formed around the NPs not only improve the electrical conductivity of the electrode but also prevent the separation of the NPs from the carbon matrix as well as the aggregation.     

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.     

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.     

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.     

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.     

2D siloxene supported NiO/Co3O4 electrocatalyst for the stable and efficient hydrogen evolution reaction

The activity of NiO/Co₃O₄ for the hydrogen evolution reaction (HER) during water splitting was increased by depositing these metal oxides on siloxene multi-sheets. The improvement in active sites due to siloxene was used to increase the catalytic activity. The hierarchical structure of the composite with the synergistic effect of metal oxides helped enhance the catalytic activity to show a low overpotential of 110 mV at 10 mA/cm² in 1 M KOH and stability at 10 mA/cm² over 20 h without an obvious change in voltage. The as-prepared catalyst can be a promising electrocatalyst for the HER owing to the low cost of transition metal oxides, the abundance of silicon on Earth, and the simplicity of the synthesis process.     

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).     

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.     

Graphene‐Based Phosphorus‐Doped Carbon as Anode Material for High‐Performance Sodium‐Ion Batteries

Graphene‐based phosphorus‐doped carbon (GPC) is prepared through a facile and scalable thermal annealing method by triphenylphosphine and graphite oxide as precursor. The P atoms are successfully doped into few layer graphene with two forms of P–O and P–C bands. The GPC used as anode material for Na‐ion batteries delivers a high charge capacity 284.8 mAh g^?1 at a current density of 50 mA g^?1 after 60 cycles. Superior cycling performance is also shown at high charge?discharge rate: a stable charge capacity 145.6 mAh g^?1 can be achieved at the current density of 500 mA g^?1 after 600 cycles. The result demonstrates that the GPC electrode exhibits good electrochemical performance (higher reversible charge capacity, super rate capability, and long‐term cycling stability). The excellent electrochemical performance originated from the large interlayer distance, large amount of defects, vacancies, and active site caused by P atoms doping. The relationship of P atoms doping amount with the Na storage properties is also discussed. This superior sodium storage performance of GPC makes it as a promising alternative anode material for sodium‐ion batteries.     

Highly Dispersed ZnSe Nanoparticles Embedded in N‐Doped Porous Carbon Matrix as an Anode for Potassium Ion Batteries

Advanced nanostructured functional materials obtained from the precursors of metal–organic frameworks show several unique advantages, including plentiful porous structures and large specific surface areas. Based on this, designed and constructed are highly dispersed ZnSe nanoparticles anchored in a N‐doped porous carbon rhombic dodecahedron (ZnSe@NDPC) by a sequential high‐temperature pyrolysis and selenization method. The specific synthesis process involves a two‐step heat treatment of the template‐engaged reaction between zinc‐based zeolitic imidazolate framework (ZIF‐8) and selenium power. By optimizing the calcination temperature, the as‐synthesized ZnSe@NDPC‐700 as an advanced anode of potassium ion batteries demonstrates the best electrochemical performance, including a high capacity (262.8 mA h g^?1 over 200 cycles at 100 mA g^?1) and a good rate capability (109.4 mA h g^?1 at 2000 mA g^?1 and 52.8 mA h g^?1 at 5000 mA g^?1). Moreover, the capacitance and diffusion mechanisms are also investigated by the qualitative and quantitate analysis, finally accounting for the superior K storage.     

Structure Dependence of Fe‐Co Hydroxides on Fe/Co Ratio and Their Application for Supercapacitors

Fe‐Co hydroxides with different Fe/Co atomic ratios grown on nickel foams are synthesized by one‐step electrochemical deposition. The prepared samples are characterized by X‐ray diffraction, X‐ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. It was found that the influence of initial Fe/Co ratios in the precursor solutions on the structure and electrochemical performance of electrodeposited products is significant. Fe(OH)₃ shows particle shape with average diameter of 200 nm. With addition of Co ions, frame‐like structure consisting of smaller particles is formed for Fe‐Co hydroxides. Based on the morphology of Co(OH)₂, it is deduced that Co(OH)₂ serves as a network former constructing a tridimensional frame network structure. Fe‐Co hydroxide with Fe/Co ratio of 1:1 exhibits two types of structure features: nanoflake‐like network structure overall and nanoparticle structure with numerous mesoporous microscopically. As the supercapacitor electrode materials, the as‐prepared Fe‐Co hydroxide electrode with Fe/Co ratio of 1:1 exhibits highest specific capacitance of 2255.6 F g^?1 at the current density of 1 A g^?1 and also shows good cycling performance of 73.5% capacity retention at current density of 10 A g^?1 after 2000 cycles. This work provides a facile method to produce promising Fe‐Co hydroxide electrode materials with high performance for supercapacitors.     

Cobalt Based Nanoparticles Embedded Reduced Graphene Oxide Aerogel for Hydrogen Evolution Electrocatalyst

Efficient water electrolysis catalyst is highly demanded for the production of hydrogen as a sustainable energy fuel. It is reported that cobalt derived nanoparticle (CoS₂, CoP, CoS|P) decorated reduced graphene oxide (rGO) composite aerogel catalysts for highly active and reliable hydrogen evolution reaction electrocatalysts. 7 nm level cobalt derived nanoparticles are synthesized over graphene aerogel surfaces with excellent surface coverage and maximal expose of active sites. CoS|P/rGO hybrid aerogel composites show an excellent catalytic activity with overpotential of ≈169 mV at a current density of ≈10 mA cm^?2. Accordingly, efficient charge transfer is attained with Tafel slope of ≈52 mV dec^?1 and a charge transfer resistance (R_ct) of ≈12 Ω. This work suggests a viable route toward ultrasmall, uniform nanoparticles decorated graphene surfaces with well‐controlled chemical compositions, which can be generally useful for various applications commonly requiring large exposure of active surface area as well as robust interparticle charger transfer.     

钴原子插层增强磷烯纳米片析氢反应活性

本文基于第一性原理计算,证明了钴插层磷烯的析氢催化活性可以显著增强.钴插层磷烯具有金属特性,电荷从钴原子向磷烯转移,增强了磷烯的催化活性.钴插层磷烯表面的氢吸附吉布斯自由能与铂(111)表面相当,与氢覆盖度无关.研究结果表明钴原子插层提供了一种有效的方法来增强磷烯的析氢反应催化活性.     

FeNi Layered Double‐Hydroxide Nanosheets on a 3D Carbon Network as an Efficient Electrocatalyst for the Oxygen Evolution Reaction

An efficient electrocatalyst for oxygen evolution has been prepared via the deposition of iron–nickel layered double‐hydroxide (FeNi‐LDH) nanosheets on 3D carbon network as the building scaffold in a one‐step hydrothermal process. It is found that upon the assembling of FeNi‐LDH nanosheets with graphene into the 3D cross‐linked hybrid, the FeNi‐LDH/graphene hybrid features a well‐improved catalytic activity towards the oxygen evolution reaction (OER) with a good stability during the long‐term cycling experiment. Moreover, the hybrid catalyst is also active in the oxygen reduction reaction (ORR), qualifying it as a new type of bifunctional catalyst that can work in metal–air batteries.     

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.     

Co3O4 Hollow Nanoparticles and Co Organic Complexes Highly Dispersed on N‐Doped Graphene: An Efficient Cathode Catalyst for Li‐O2 Batteries

Rechargeable Li‐O₂ batteries are promising candidates for electric vehicles due to their high energy density. However, the current development of Li‐O₂ batteries demands highly efficient air cathode catalysts for high capacity, good rate capability, and long cycle life. In this work, a hydrothermal‐calcination method is presented to prepare a composite of Co₃O₄ hollow nanoparticles and Co organic complexes highly dispersed on N‐doped graphene (Co–NG), which acts as a bifunctional air cathode catalyst to optimize the electrochemical performances of Li‐O₂ batteries. Co–NG exhibits an outstanding initial discharge capacity up to 19 133 mAh g^?1 at a current density of 200 mA g^?1. In addition, the batteries could sustain 71 cycles at a cutoff capacity of 1000 mAh g^?1 with low overpotentials at the current density of 200 mA g^?1. Co–NG composites are attractive as air cathode catalysts for rechargeable Li‐O₂ batteries.     

Ni与Co掺杂Fe2O3（0001）表面增强析氧反应活性

Fe based oxides are considered as a promising catalyst for the oxygen evolution reaction (OER) due to their low cost and high stability. Here, based on density functional theory calculations, the electrocatalytic behaviors of pure and metal (Ni, Co) doped Fe-terminated Fe₂O₃(0001) are investigated. The potential-limiting step for OER is determined as the formation of O^* by dehydrogenating surface hydroxyl and it is suggested that the doping enhances the catalytic activity of Fe₂O₃(0001) by reducing the free energy change of rate limiting step on doped Ni or Co atom. Especially, the calculated over-potential of Co-doped Fe₂O₃ (0001) surface is about 0.63 eV on Co site, which is comparable with the theoretical over-potential of 0.56 eV for RuO₂.     

Selective Etching of N‐Doped Graphene Meshes as Metal‐Free Catalyst with Tunable Kinetics,High Activity and the Origin of New Catalytic Behaviors

New N‐doped reduced graphene oxide (N‐RGO) meshes are facile fabricated by selective etching of 3–5 nm nanopores, with controllable doping of N dopants at an ultrahigh N/C ratio up to 15.6 at%, from pristine graphene oxide sheets in one‐pot hydrothermal reaction. The N‐RGO meshes are illustrated to be an efficient metal‐free catalyst toward hydrogenation of 4‐nitrophenol, with new catalytic behaviors emerging in following three aspects: (i) tunable kinetics following pseudofirst order from commonly observed pseudozero order; (ii) strikingly improved activity with 26‐fold increased rate constant (1.0 s⁻¹ g⁻¹ L); (iii) no induction time required prior to reaction due to depressed back conversion, and dramatically decreased apparent activation energy (E_a) (17 kJ mol⁻¹). The origin of these new catalytic properties can be assigned to the synergetic effects between graphitic N doping and structural defects arising from nanopores. Deeper understanding unveils that the concentration of graphitic N is inverse proportion to E_a, while the pyrrolic N has no impact on this reaction, and oxygenate groups hampers it. The porous nature allows the N‐RGO meshes to conduct catalyze reactions in continuous flow fashion.