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.     

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.     

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.     

Metal phosphonate coordination networks and frameworks as precursors of electrocatalysts for the hydrogen and oxygen evolution reactions

The hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) play key roles in the conversion of energy derived from renewable energy sources into chemical energy. Efficient, robust, and inexpensive electrocatalysts are necessary for driving these reactions at high rates at low overpotentials and minimize energetic losses. Recently, electrocatalysts derived from hybrid metal phosphonate compounds have shown high activity for the HER or OER. We review here the utilization of metal phosphonate coordination networks and metal-organic frameworks as precursors/templates for transition-metal phosphides, phosphates, or oxyhydroxides generated in situ in alkaline solutions, and their electrocatalytic performance in HER or OER.     

Controlled synthesis of porous nickel oxide nanostructures and their electrochemical capacitive behaviors

Achieving precise control over the synthesis and properties of porous nanostructured materials has been garnering considerable recent research attention. In the work presented here, nickel oxalate nanostructures with controllable shapes were synthesized through a simple and facile wet-chemistry route without any surfactant. An interesting shape evolution process from 2D nanoflakes to 1D nanorods has been illustrated on the basis of time-dependent experimental studies. Subsequent calcination at 380 °C yielded porous NiO nanostructures that retained the morphologies of their predecessors. The phase composition, morphology, and structure of the as-obtained products were studied by various tools. Electrochemical properties of the NiO electrodes were carried out using cyclic voltammetry and galvanostatic charge–discharge measurements by a three-electrode system. Electrochemical studies reveal that the as-prepared mesoporous NiO nanostructures have good specific capacitance and exhibit excellent capacity retention for more than 1,000 cycles due to its porous character and morphology. The results suggest that mesoporous NiO nanostructures are a promising supercapacitor electrode material.     

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.     

The impact of ultrasonic parameters on the exfoliation of NiFe LDH nanosheets as electrocatalysts for the oxygen evolution reaction in alkaline media

The ultrasonic process has been examined to exfoliate layered materials and upgrade their properties for a variety of applications in different media. Our previous studies have shown that the ultra-sonication treatment in water without chemicals has a positive influence on the physical and electrochemical performance of layered materials and nanoparticles. In this work, we have probed the impact of ultrasonication on the physical properties and the oxygen evolution reaction (OER) of the NiFe LDH materials under various conditions, including suspension concentration (2.5–12.5 mg mL⁻¹), sonication times (3–20 min) and amplitudes (50–90%) in water, in particular, sonication times and amplitudes. We found that the concentration, amplitude and time play significant roles on the exfoliation of the NiFe LDH material. Firstly, the NiFe LDH nanosheets displayed the best OER performance under ultrasonic conditions with the concentration of 10 mg mL⁻¹ (50% amplitude and 15 min). Secondly, it was revealed that the exfoliation of the NiFe LDH nanosheets in a short time (<10 min) or a higher amplitudes (≥80%) has left a cutdown on the OER activity. Comprehensively, the optimum OER activity was displayed on the exfoliated NiFe LDH materials under ultrasonic condition of 60% (amplitude), 10 mg mL⁻¹ and 15 min. It demanded only 250 mV overpotentials to reach 10 mA cm⁻² in 1 M KOH, which was 100 mV less than the starting NiFe LDH material. It was revealed from the mechanism of sonochemistry and the OER reaction that, after exfoliation, the promoted OER performance is ascribed to the enriched Fe³⁺ at the active sites, easier oxidation of Ni²⁺ to Ni³⁺, and the strong electrical coupling of the Ni²⁺ and Fe³⁺ during the OER process. This work provides a green strategy to improve the intrinsic activity of layered materials.     

Template-free sonochemical synthesis of hierarchically porous NiO microsphere

A novel template-free sonochemical synthesis technique was used to prepare NiO microspheres combined with calcination of NiO_2.45C_0.74N_0.25H_2.90 precursor at 500 °C. The NiO microspheres samples were systematically investigated by the thermograviometric/differential scanning calorimetry (TG/DSC), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), fourier-transformed infrared spectroscopy (FT-IR), Brunnauer–Emmett–Teller (BET) nitrogen adsorption–desorption isotherms, laser particle size analyzer, and ultraviolet–visible spectroscopy (UV–Vis). The morphology of the precursor was retained even after the calcination process, and exhibited hierarchically porous sphericity. The morphology changed over the ultrasonic radiation time, and the shortest reaction time was 70 min, which was much less than 4 h for the mechanical stirring process. The mechanical stirring was difficult to form the complete hierarchically porous microsphere structure. The BET specific surface area and the median diameter of the hierarchically porous NiO microspheres were 103.20 m²/g and 3.436 μm, respectively. The synthesized NiO microspheres were mesoporous materials with a high fraction of macropores. The pores were resulted from the intergranular accumulation. The ultraviolet absorption spectrum showed a broad emission at the center of 475 nm, and the band gap energy was estimated to be 3.63 eV.     

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.     

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.     

紫外激光调控CoFe2O4表面氧空位以增强析氧反应催化活性

本文以尖晶石型材料CoFe₂O₄为模型催化剂,研究证实脉冲紫外激光辐照可以有效调控材料表面的氧空位含量,进而改变其析氧催化活性,得到了催化活性随辐照时间的火山型变化趋势. 这种激光辐照方法可用于定量研究过渡金属化合物的表面阳离子价态、阴离子空位和物化性质间的关联.     

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.     

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.     

The influence of NiO addition on the magnetic properties of polycrystalline yttrium iron garnet

The influence of NiO addition on the magnetic properties of polycrystalline Y₃Fe₅O₁₂ is studied for the saturation magnetization, Curie temperature, initial magnetic permeability and ferromagnetic resonance line width. Dependence of saturation magnetization on NiO addition suggest that Ni²⁺ ions enter octahedral sites of the garnet lattice. Real part of the complex initial permeability versus temperature curves reveal the single phase for samples with NiO content. The absence of any additional peak in these curves and the invariance of Curie temperature suggest that NiO addition cannot alter the magneto-crystalline anisotropy of the material. Variations of initial permeability with NiO content are due to change of saturation magnetization and grain size of the materials. The ferromagnetic resonance line width varies linearly with the porosity of samples with NiO showing no anisotropy contribution in it.     

Ferromagnetism of Ni cluster in Ni-doped ZnO by solid state reaction

Ni-doped ZnO samples with ferromagnetism at room temperature have been prepared by solid state reaction. It is found that the ferromagnetism originates from the nanosized Ni clusters formed from the decomposition of NiO during calcination. The magnetic properties can be explained by the microstructure of sparsely distributed, randomly oriented and magnetically saturated Ni clusters. Experiments show that the addition of Cu ions will block the decomposition of NiO because Cu²⁺ is more likely reduced to Cu⁺. Hall effect confirms the absence of exchange coupling between local spins and charge carriers.     

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.     

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.     

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.     

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.     

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.