Metallic Intermediate Phase Inducing Morphological Transformation in Thermal Nitridation: Ni3FeN-Based Three-Dimensional Hierarchical Electrocatalyst for Water Splitting

Single-Atom Pt Embedded in Defective Layered Double Hydroxide for Efficient and Durable Hydrogen Evolution

Electrocatalysis in neutral conditions is appealing for hydrogen production by utilizing abundant wastewater or seawater resources. Single-atom catalysts (SACs) immobilized on supports are considered one of the most promising strategies for electrocatalysis research. While they have principally exhibited breakthrough activity and selectivity for the hydrogen evolution reaction (HER) electrocatalysis in alkaline or acidic conditions, few SACs were reported for HER in neutral media. Herein, we report a facile strategy to tailor the water dissociation active sites on the NiFe LDH by inducing Mo species and an ultralow single atomic Pt loading. The defected NiFeMo LDH (V-NiFeMo LDH) shows HER activity with an overpotential of 89 mV at 10 mA cm-2 in 1 M phosphate buffer solutions. The induced Mo species and the transformed NiO/Ni phases after etching significantly increase the electron conductivity and the catalytic active sites. A further enhancement can be achieved by modulating the ultralow single atom Pt anchored on the V-NiFeMo LDH by potentiostatic polarization. A potential as low as 37 mV is obtained at 10 mA cm-2 with a pronounced long-term durability over 110 h, surpassing its crystalline LDH materials and most of the HER catalysts in neutral medium. Experimental and density functional theory calculation results have demonstrated that the synergistic effects of Mo/SAs Pt and phase transformation into NiFe LDH reduce the kinetic energy barrier of the water dissociation process and promote the H* conversion for accelerating the neutral HER.

Ligand effect on switching the rate-determining step of water oxidation in atomically precise metal nanoclusters

The ligand effects of atomically precise metal nanoclusters on electrocatalysis kinetics have been rarely revealed. Herein, we employ atomically precise Au₂₅ nanoclusters with different ligands (i.e., para-mercaptobenzoic acid, 6-mercaptohexanoic acid, and homocysteine) as paradigm electrocatalysts to demonstrate oxygen evolution reaction rate-determining step switching through ligand engineering. Au₂₅ nanoclusters capped by para-mercaptobenzoic acid exhibit a better performance with nearly 4 times higher than that of Au₂₅ NCs capped by other two ligands. We deduce that para-mercaptobenzoic acid with a stronger electron-withdrawing ability establishes more partial positive charges on Au(I) (i.e., active sites) for facilitating feasible adsorption of OH^- in alkaline media. X-ray photo-electron spectroscopy and theoretical study indicate a profound electron transfer from Au(I) to para-mercaptobenzoic acid. The Tafel slope and in situ Raman spectroscopy suggest different ligands trigger different rate-determining step for these Au₂₅ nanoclusters. The mechanistic insights reported here can add to the acceptance of atomically precise metal nanoclusters as effective electrocatalysts.

Fast and Durable Alkaline Hydrogen Oxidation Reaction at the Electron-Deficient Ruthenium-Ruthenium Oxide Interface

The slow hydrogen oxidation reaction (HOR) kinetics under alkaline conditions remain a critical challenge for the practical application of alkaline exchange membrane fuel cells. Herein, Ru/RuO₂ in-plane heterostructures are designed with abundant active Ru-RuO₂ interface domains as efficient electrocatalysts for the HOR in alkaline media. The experimental and theoretical results demonstrate that interfacial Ru and RuO₂ domains at Ru-RuO₂ interfaces are the optimal H and OH adsorption sites, respectively, endowing the well-defined Ru(100)/RuO₂ (200) interface as the preferential region for fast alkaline hydrogen electrocatalysis. More importantly, the metallic Ru domains become electron deficient due to the strong interaction with RuO₂ domains and show substantially improved inoxidizability, which is vital to maintain durable HOR electrocatalytic activity. The optimal Ru/RuO₂ heterostructured electrocatalyst exhibits impressive alkaline HOR activity with an exchange current density of 8.86 mA cm^-2 and decent durability. The exceptional electrocatalytic performance of Ru/RuO₂ in-plane heterostructure can be attributed to the robust and multifunctional Ru-RuO₂ interfaces endowed by the unique metal-metal oxide domains.

A Unique NiOOH@FeOOH Heteroarchitecture for Enhanced Oxygen Evolution in Saline Water

The development of highly efficient non-precious metal electrocatalysts for the oxygen evolution reaction (OER) in low-grade or saline water is currently of great importance for the large-scale production of hydrogen. In this study, by using an electrochemical activation pretreatment, metal oxy(hydroxide) nanosheet structures derived from self-supported nickel-iron phosphide and nitride nanoarrays grown on Ni foam are successfully fabricated for OER catalysis in saline water. It is demonstrated that the different NiOOH and NiOOH@FeOOH (NiOOH grown on FeOOH) structures are generated from nickel-iron nitride and phosphide, respectively, after electrochemical activation. In particular, the NiOOH@FeOOH heteroarchitecture shows outstanding electrocatalytic performance with an ultralow overpotential of 292 mV to drive the current density of 500 mA cm^-2 . An unconventional dual-sites mechanism (UDSM) is proposed to address the OER process on NiOOH@FeOOH and show that the FeOOH underlayer plays a critical role regarding the enhanced OER activity of NiOOH. The new possible UDSM involving two reaction sites presents a different understanding of the OER process on multi-OH layer complexes, which is expected to guide the design of heteroarchitecture electrocatalysts.

NiO nanobelts with exposed {110} crystal planes as an efficient electrocatalyst for the oxygen evolution reaction

The electrocatalytic oxygen evolution reaction (OER) is necessary and challenging for converting renewable electricity into clean fuels, because of its complex proton coupled multielectron transfer process. Herein, we investigated the crystal plane effects of NiO on the electrocatalytic OER activity through combining experimental studies and theoretical calculations. The experimental results reveal that NiO nanobelts with exposed {110} crystal planes show much higher OER activity than NiO nanoplates with exposed {111} planes. The efficient OER activity of the {110} crystal planes comes from their intrinsically high catalytic ability and fast charge transfer kinetics. Density functional theory (DFT) shows that the {110} crystal planes possess a lower theoretical overpotential value for the OER, leading to a high electrocatalytic performance. This research broadens our vision to design efficient OER electrocatalysts by the selective exposure of specific crystal planes.

The controlled synthesis of nitrogen and iron co-doped Ni3S2@NiP2 heterostructures for the oxygen evolution reaction and urea oxidation reaction

At present, global resources are nearly exhausted and environmental pollution is becoming more and more serious, so it is urgent to develop efficient catalysts for hydrogen production. Herein, nitrogen and iron co-doped Ni₃S₂ and NiP₂ heterostructures with high efficiency oxygen evolution reaction (OER) and urea oxidation reaction (UOR) performances were firstly successfully prepared on nickel foam by hydrothermal and high-temperature calcination methods. Benefiting from the hierarchical structure, the exposure of more active sites and the doping effect of N and Fe, the N-Fe-Ni₃S₂@NiP₂/NF material showed excellent electrocatalytic activity for the OER and UOR. The N-Fe-Ni₃S₂@NiP₂/NF material displays excellent catalytic OER performance; the overpotential is only 251 mV to drive 100 mA cm^-2 current density, while for the UOR, the potential is only 1.353 V to drive 100 mA cm^-2 current density, which is one of the best catalytic activities reported so far. It is worth noting that scanning electron microscopy showed that the surface of N-Fe-Ni₃S₂@NiP₂/NF is rough and has some mesopores, which may have resulted in an increase of active sites during the electrocatalytic process. The N-Fe-Ni₃S₂@NiP₂/NF electrode couple also has relatively long-term durability in alkaline solutions, maintaining a stable current density for 15 h at 1.35 V. The density functional theory (DFT) calculation shows that the in situ generated Fe doped nanooxides exhibit strong water adsorption energy, which may be one of the reasons for the good catalytic activity. Our work is conducive to the rational design of electrocatalysts for efficient hydrogen production from water splitting and wastewater treatment.

CoTe2–NiTe2 heterojunction directly grown on CoNi alloy foam for efficient oxygen evolution reaction

One-step fabrication of a self-supported CoTe2–NiTe2 heterojunction electrocatalyst directly grown on CoNi foam for efficient and durable oxygen evolution reactions.

Cobalt, iron co-incorporated Ni(OH)2 multiphase for superior multifunctional electrocatalytic oxidation

The cobalt, iron co-incorporated Ni(OH)₂ multiphase displays superior catalytic activity and stability for multifunctional electrocatalytic oxidation, ascribed to the multiphase synergy, enhanced charge transfer and well-exposed active sites.

General fabrication of RuM (M = Ni and Co) nanoclusters for boosting hydrogen evolution reaction electrocatalysis

Rational design and fabrication of highly active electrocatalysts toward the hydrogen evolution reaction (HER) are of paramount significance in industrial hydrogen production via water electrolysis. Herein, by taking advantage of the high surface-to-volume ratio, maximized atom-utilization efficiency, and quantum size effect, we have successfully fabricated an innovative class of Ru-based alloy nanoclusters. Impressively, carbon fiber cloth (CFC) supported RuNi nanoclusters could exhibit outstanding electrocatalytic performance toward the HER, in which the optimal composition RuNi/CFC could achieve a current density of 10 mA cm^-2 with an overpotential of merely 43.0 mV in 1 M KOH electrolyte, as well as a low Tafel slope of 30.4 mF dec^-1. In addition to the high HER activity in alkaline media, such Ru-based alloy nanoclusters are also demonstrated to be highly active and stable in acidic solution. Mechanistic studies reveal that the alloying effect facilitates water dissociation and optimizes hydrogen adsorption and desorption, thereby contributing to the outstanding HER performance. This work paves a new way for the rational fabrication of advanced electrocatalysts for boosting the HER.

A label-free electrochemical platform based on a thionine functionalized magnetic Fe-N-C electrocatalyst for the detection of microRNA-21

Taking a composite of a nanomaterial and a signal molecule as a substrate material can provide a label-free electrochemical platform. Besides, the nanomaterial with a high catalytic activity towards the signal molecule can improve the sensitivity of the platform. Herein, a thionine functionalized Fe-N-C nanocomposite was employed as the substrate. Firstly, the electrocatalytic activity of Fe-N-C towards the electroreduction of thionine was explored. Then, an immobilization-free and label-free electrochemical platform for the determination of microRNA-21 based on Fe-N-C-thionine/Fe₃O₄@AuNPs was constructed. A magnetic glassy carbon electrode (MGCE) was used to keep the magnetic Fe-N-C-thionine/Fe₃O₄@AuNPs modified onto the surface of the MGCE. Fe-N-C and Fe₃O₄ nanoparticles can co-catalyze the electroreduction of thionine and a strong electrochemical reduction signal of thionine could be realized in the differential pulse voltammetry (DPV) test. Also, a catalytic hairpin assembly (CHA) reaction was utilized to enhance the sensitivity of the developed electrochemical biosensor. Besides, the developed biosensor shows excellent specificity and reproducibility in the test of human serum samples, indicating its wide application prospects in the early-stage diagnosis of tumors.

A strategy for preparing high-efficiency and economical catalytic electrodes toward overall water splitting

Electrolyzing water technology to prepare high-purity hydrogen is currently an important field in energy development. However, the preparation of efficient, stable, and inexpensive hydrogen production technology from electrolyzed water is a major problem in hydrogen energy production. The key technology for hydrogen production from water electrolysis is to prepare highly efficient catalytic, stable and durable electrodes, which are used to reduce the overpotential of the hydrogen evolution reaction and the oxygen evolution reaction of electrolyzed water. The main strategies for preparing catalytic electrodes include: (i) choosing cheap, large specific surface area and stable base materials, (ii) modulating the intrinsic activity of the catalytic material through elemental doping and lattice changes, and (iii) adjusting the morphology and structure to increase the catalytic activity. Based on these findings, herein, we review the recent work in the field of hydrogen production by water electrolysis, introduce the preparation of catalytic electrodes based on nickel foam, carbon cloth and new flexible materials, and summarize the catalytic performance of metal oxides, phosphides, sulfides and nitrides in the hydrogen evolution and oxygen evolution reactions. Secondly, parameters such as the overpotential, Tafel slope, active site, turnover frequency, and stability are used as indicators to measure the performance of catalytic electrode materials. Finally, taking the material cost of the catalytic electrode as a reference, the successful preparations are comprehensively compared. The overall aim is to shed some light on the exploration of high-efficiency and economical electrodes in energy chemistry and also demonstrate that there is still room for discovering new combinations of electrodes including base materials, composition lattice changes and morphologies.

Electrocatalysis of gold-based nanoparticles and nanoclusters

Gold (Au)-based nanomaterials, including nanoparticles (NPs) and nanoclusters (NCs), have shown great potential in many electrocatalytic reactions due to their excellent catalytic ability and selectivity. In recent years, Au-based nanostructured materials have been considered as one of the most promising non-platinum (Pt) electrocatalysts. The controlled synthesis of Au-based NPs and NCs and the delicate microstructure adjustment play a vital role in regulating their catalytic activity toward various reactions. This review focuses on the latest progress in the synthesis of efficient Au-based NP and NC electrocatalysts, highlighting the relationship between Au nanostructures and their catalytic activity. This review first discusses the parameters of Au-based nanomaterials that determine their electrocatalytic performance, including composition, particle size and architecture. Subsequently, the latest electrocatalytic applications of Au-based NPs and NCs in various reactions are provided. Finally, some challenges and opportunities are highlighted, which will guide the rational design of Au-based NPs and NCs as promising electrocatalysts.

Two-dimension on two-dimension growth: hierarchical Ni0.2Mo0.8N/Fe-doped Ni3N nanosheet array for overall water splitting

Developing advanced electrocatalysts with low cost for electrocatalytic water splitting are highly desirable. Herein, we report the design of two-dimension on two-dimension growth of hierarchical Ni0.2Mo0.8N nanosheets on Fe-doped Ni3N nanosheets supported on Ni foam (Ni0.2Mo0.8N/Fe-Ni3N/NF) via hydrothermal reaction and nitridation treatment. In the hierarchical structures, small Ni0.2Mo0.8N nanosheets were uniformly anchored on Fe-Ni3N nanosheets. Due to enhanced electron transfer between Ni0.2Mo0.8N and Fe-Ni3N, Ni0.2Mo0.8N/Fe-Ni3N/NF exhibits superior electrocatalytic activity for the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). After stability tests for 50 h, Ni0.2Mo0.8N/Fe-Ni3N/NF exhibits negligible degradation of the current density for the OER (91% remain) and HER (95% remain), suggesting excellent stability. Owing to the outstanding performance, Ni0.2Mo0.8N/Fe-Ni3N/NF display a cell voltage of 1.54 V (10 mA cm-2) for electrocatalytic overall water splitting.

Heteroatom-Doping of Non-Noble Metal-Based Catalysts for Electrocatalytic Hydrogen Evolution: An Electronic Structure Tuning Strategy

Electrocatalytic water splitting for hydrogen production is an appealing way to reduce carbon emissions and generate renewable fuels. This promising process, however, is limited by its sluggish reaction kinetics and high-cost catalysts. Construction of low-cost and high-performance non-noble metal-based catalysts have been one of the most effective approaches to address these grand challenges. Notably, the electronic structure tuning strategy, which could subtly tailor the electronic states, band structures, and adsorption ability of the catalysts, has become a pivotal way to further enhance the electrochemical water splitting reactions based on non-noble metal-based catalysts. Particularly, heteroatom-doping plays an effective role in regulating the electronic structure and optimizing the intrinsic activity of the catalysts. Nevertheless, the reaction kinetics, and in particular, the functional mechanisms of the hetero-dopants in catalysts yet remains ambiguous. Herein, the recent progress is comprehensively reviewed in heteroatom doped non-noble metal-based electrocatalysts for hydrogen evolution reaction, particularly focus on the electronic tuning effect of hetero-dopants in the catalysts and the corresponding synthetic pathway, catalytic performance, and activity origin. This review also attempts to establish an intrinsic correlation between the localized electronic structures and the catalytic properties, so as to provide a good reference for developing advanced low-cost catalysts.

Thermal Puffing Promoting the Synthesis of N-Doped Hierarchical Porous Carbon-CoO x Composites for Alkaline Water Reduction

N-doped porous carbon-based catalysts hold great promise for hydrogen evolution reaction (HER) due to their plentiful cavity construction, high specific surface area, and flexible metal assemblies. Nevertheless, the cumbersome synthetic process and the use of highly corrosive chemicals greatly increase the production costs and pollutions. Herein, we report a facile and eco-friendly thermal puffing strategy, which imitates the popcorn forming process, for the fabrication of N-doped hierarchical porous carbon-CoO x catalysts. The results indicate that the well-developed porosity and high specific surface area (696 m2 g-1) of CoO x -NC-1.0 are achieved during the thermal expansion. Impressively, the as-prepared CoO x -NC-1.0 with ultralow Co loading (0.67 wt %) presents admirable HER performance to drive 10 mA cm-2 at an overpotential of 189 mV in the alkaline electrolyte. Especially, the activity of CoO x -NC-1.0 can be maintained for a continuous ∼70 h test. Such an excellent property of CoO x -NC not only derives from the hierarchical porous structure but is also due to the higher ratio of graphitic-N and pyridinic-N, which promotes the better electrical conductivity and formation of more active Co0 for HER, respectively. Moreover, this strategy is applicable to the fabrication of other transition metal-based hierarchical porous composites, which opens new possibilities for exploring promising candidates to substituted commercial Pt/C.

High entropy alloy nitrides with integrated nanowire/nanosheet architecture for efficient alkaline hydrogen evolution reactions

We report the in situ synthesis of FeCoNiCuMnN high entropy alloy nitrides with unique integrated nanowire/nanosheet architecture on carbon cloth by hydrothermal reaction and subsequent calcination.

Porous silicon film overcoating biomass char-supported catalysts for improved activity and stability in biomass pyrolysis tar decomposition

A C-SiO2 core–shell structure catalyst was prepared via a two-step pyrolysis method, and the support effect and reaction mechanism were discussed for this novel system.

Promoting Electrocatalytic Activity and Stability via Er0.4Bi1.6O3-δ In Situ Decorated La0.8Sr0.2MnO3-δ Oxygen Electrode in Reversible Solid Oxide Cell

Weak electrocatalytic activity of the La_0.8Sr_0.2MnO_3-δ (LSM) oxygen electrode at medium and low temperatures leads to decreasing performance both in the solid oxide fuel cell (SOFC) mode and the solid oxide electrolysis cell (SOEC) mode. Herein, we design an Er_0.4Bi_1.6O_3-δ (ESB) functionalized La_0.8Sr_0.2MnO_3-δ (labeled as LSM/ESB) oxygen electrode via a one-step co-synthesis modified Pechini method. The unique LSM/ESB with polarization resistance of only 0.029 Ω·cm² at 750 °C enables a highly enhanced rate of oxygen reduction and evolution reaction. The single cell with the LSM/ESB electrode achieves a maximum power density of 1.747 W cm^-2 at 750 °C, 2.6 times higher than that of the mechanically mixed LSM-ESB electrode (0.667 W cm^-2). In the SOEC mode, it also shows the improved performance of the LSM/ESB electrode. Furthermore, the cell exhibits admirable durability of 90 h in the fuel cell mode and excellent reversibility. The better performance can be concluded as a better surface-active state and a tighter connection between the LSM and ESB particles of LSM/ESB via a co-synthesis process. This work proposes a novel strategy to advance the application of the one-step modified Pechini technology for an efficient and stable oxygen electrode.

Common-Ion Effect Triggered Highly Sustained Seawater Electrolysis with Additional NaCl Production

Developing efficient seawater-electrolysis system for mass production of hydrogen is highly desirable due to the abundance of seawater. However, continuous electrolysis with seawater feeding boosts the concentration of sodium chloride in the electrolyzer, leading to severe electrode corrosion and chlorine evolution. Herein, the common-ion effect was utilized into the electrolyzer to depress the solubility of NaCl. Specifically, utilization of 6 M NaOH halved the solubility of NaCl in the electrolyte, affording efficient, durable, and sustained seawater electrolysis in NaCl-saturated electrolytes with triple production of H₂, O₂, and crystalline NaCl. Ternary NiCoFe phosphide was employed as a bifunctional anode and cathode in simulative and Ca/Mg-free seawater-electrolysis systems, which could stably work under 500 mA/cm² for over 100 h. We attribute the high stability to the increased Na⁺ concentration, which reduces the concentration of dissolved Cl⁻ in the electrolyte according to the common-ion effect, resulting in crystallization of NaCl, eliminated anode corrosion, and chlorine oxidation during continuous supplementation of Ca/Mg-free seawater to the electrolysis system.

Nickel-Iron Nitride-Nickel Sulfide Composites for Oxygen Evolution Electrocatalysis

Advance applications like water splitting system and rechargeable metal-air battery are highly dependent on efficient electrocatalyst for the oxygen evolution reaction (OER). Heterostructured materials, with a high active surface area and electron effect, accomplish enhanced catalytic performance. Here, a nitride-sulfide composite (FeNi₃N-Ni₃S₂) has been prepared by a simple hydrothermal process coupled with nitridation. The prepared composite electrocatalyst FeNi₃N-Ni₃S₂ possesses lower electron densities compared to those of FeNi₃N and Ni₃S₂, lessening the activation energy (E_a) toward the OER. Consequently, the prepared FeNi₃N-Ni₃S₂ exhibits excellent OER performance with a low overpotential (230 mV) and a small Tafel slope (38 mV dec^-1). Highly stable FeNi₃N-Ni₃S₂ composite delivers lower charging voltage and extended lifetime in rechargeable Zn-air battery, compared with IrO₂.

Holey Cobalt-Iron Nitride Nanosheet Arrays as High-Performance Bifunctional Electrocatalysts for Overall Water Splitting

Designing efficient metal nitride electrocatalysts with advantageous nanostructures toward overall water splitting is of great significance for energy conversion. In this work, holey cobalt-iron nitride nanosheet arrays grown on Ni foam substrate (CoFeN_x HNAs/NF) are prepared via a facile hydrothermal and subsequent thermal nitridation method. This unique HNA architecture can not only expose abundant active sites but also facilitate the charge/mass transfer. Resulting from these merits, the CoFeN_x HNAs/NF exhibits high catalytic performance with overpotentials of 200 and 260 mV at 10 mA cm^-2 for the hydrogen evolution reaction (HER) and 50 mA cm^-2 for the oxygen evolution reaction (OER), respectively. Furthermore, when using CoFeN_x-500 HNAs/NF as both anode and cathode, the alkaline electrolyzer could afford a current density of 10 mA cm^-2 at 1.592 V, higher than many other metal nitride-based electrocatalysts. This work signifies a simple approach to prepare holey metal nitride nanosheet arrays, which can be applied in various fields of energy conversion and storage.

Self-Supported FeP-CoMoP Hierarchical Nanostructures for Efficient Hydrogen Evolution

Fabricating highly efficient electrocatalysts for electrochemical hydrogen generation is a top priority to relief the global energy crisis and environmental contamination. Herein, a rational synthetic strategy is developed for constructing well-defined FeP-CoMoP hierarchical nanostructures (HNSs). In general terms, the self-supported Co nanorods (NRs) are grown on conductive carbon cloth and directly serve as a self-sacrificing template. After solvothermal treatment, Co NRs are converted into well-ordered Co-Mo nanotubes (NTs). Subsequently, the small-sized Fe oxyhydroxide nanorods arrays are hydrothermally grown on the surface of Co-Mo NTs to form Fe-Co-Mo HNSs, which are then converted into FeP-CoMoP HNSs through a facile phosphorization treatment. FeP-CoMoP HNSs display high activity for hydrogen evolution reaction (HER) with an ultralow cathodic overpotential of 33 mV at 10 mA cm^-2 and a Tafel slope of 51 mV dec^-1 . Moreover, FeP-CoMoP HNSs also possess an excellent electrochemical durability in alkaline media. First-principles density functional theory (DFT) calculations demonstrate that the remarkable HER activitiy of FeP-CoMoP HNSs originates from the synergistic effect between FeP and CoMoP.

A size tunable bimetallic nickel-zinc nitride as a multi-functional co-catalyst on nitrogen doped titania boosts solar energy conversion

To enable high-efficiency solar energy conversion, rational design and preparation of low cost and stable semiconductor photocatalysts with associated co-catalysts are desirable. However preparation of efficient catalytic systems remains a challenge. Here, N-doped TiO2/ternary nickel-zinc nitride (N-TiO2-Ni3ZnN) nanocomposites have been shown to be a multi-functional catalyst for photocatalytic reactions. The particle size of Ni3ZnN can be readily tuned using N-TiO2 nanospheres as the active support. Due to its high conductivity and Pt-like properties, Ni3ZnN promotes charge separation and transfer, as well as reaction kinetics. The material shows co-catalytic performance relevant for multiple reactions, demonstrating its multifunctionality. Density functional theory (DFT) based calculations confirm the intrinsic metallic properties of Ni3ZnN. N-TiO2-Ni3ZnN exhibits evidently improved photocatalytic performances as compared to N-TiO2 under visible light irradiation.

A robust Mn@FeNi-S/graphene oxide nanocomposite as a high-efficiency catalyst for the non-enzymatic electrochemical detection of hydrogen peroxide

Exploring high-efficiency, stable, and cost-effective electrocatalysts for electrochemical activities is greatly desirable and challenging. Herein, a newly designed hybrid catalyst with manganese-doped FeNi-S encapsulated into graphene oxide (Mn@FeNi-S/GO) with unprecedented electrocatalytic activity was developed by simple one-step heat treatment followed by sonication. X-ray powder diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), and N₂ sorption isotherm demonstrated the successful formation of Mn@FeNi-S/GO. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) further confirmed the kinetic-favourable adsorption of hydrogen peroxide (H₂O₂) onto the surface sites of Mn@FeNi-S/GO. Additionally, the synergetic effects between Mn@FeNi-S and GO are regarded as significant contributors to an efficient electron transfer path, and they promote the capture of H₂O₂ in hybrid catalysts. Under an optimal condition, a biosensor-based Mn@FeNi-S/GO electrode exhibits a high sensitivity of 8.929 μA μM^-1 cm^-2 and a detection limit of 8.84 nM with a wide detection range for H₂O₂ and excellent selectivity; also, it is capable of online monitoring H₂O₂ derived from apple juice and human blood serum.

Strong electronic coupled FeNi3/Fe2(MoO4)3 nanohybrids for enhancing the electrocatalytic activity for the oxygen evolution reaction

Strong electronically coupled FeNi₃/Fe₂(MoO₄)₃ hybrid nanomaterials were successfully fabricated to enhance the electrocatalytic activity for the oxygen evolution reaction.

Engineering ultrasmall metal nanoclusters for photocatalytic and electrocatalytic applications

In view of many of the fundamental properties of ultrasmall noble metal nanoclusters progressively being uncovered, it has become increasingly clear that this class of materials has enormous potential for photocatalytic and electrocatalytic applications due to their unique electronic and optical properties. In this Minireview, we highlight the key electronic and optical properties of metal nanoclusters which are essential to photocatalysis and electrocatalysis. We further use these properties as the basis for our discussion to map out directions or principles for the rational design of high performance photocatalysts and electrocatalysts, highlighting several successful attempts along this direction.

Nickel-Based Transition Metal Nitride Electrocatalysts for the Oxygen Evolution Reaction

Electrocatalysis is an efficient and promising means of energy conversion, with minimal environmental footprint. To enhance reaction rates, catalysts are required to minimize overpotential. Alternatives to noble metal electrocatalysts are essential to address these needs on a large scale. In this context, transition metal nitride (TMN) nanoparticles have attracted much attention owing to their high catalytic activity, distinctive electronic structures, and enhanced surface morphologies. Nickel-based materials are an ideal choice for electrocatalysts given nickel's abundance and low cost in comparison to noble metals. In this Minireview, advancements made specifically in Ni-based binary and ternary TMNs as electrocatalysts for the oxygen evolution reaction (OER) are critically evaluated. When used as OER electrocatalysts, Ni-based nanomaterials with 3 D architectures on a suitable support (e.g., a foam support) speed up electron transfer as a result of well-oriented crystal structures and also assist intermediate diffusion, during reaction, of evolved gases. 2 D Ni-based nitride sheet materials synthesized without supports usually perform better than 3 D supported electrocatalysts. The focus of this Minireview is a systematic description of OER activity for state-of-the-art Ni-based nitrides as nanostructured electrocatalysts.

High-Performance Symmetric Supercapacitor Constructed Using Carbon Cloth Boosted by Engineering Oxygen-Containing Functional Groups

Carbon materials display appealing physical, chemical, and mechanical properties and have been extensively studied as supercapacitor electrodes. The surface engineering further allows us to tune their capability of adsorption/desorption and catalysis. Therefore, a facile and inexpensive chemical-acid-etching approach has been developed to activate the carbon cloth as an electrode for supercapacitor. The capacitance of the acid-etched carbon cloth electrode can approach 5310 mF cm^-2 at a current density of 5 mA cm^-2 with remarkable recycling stability. The all-solid-state symmetric supercapacitor delivered a high energy density of 4.27 mWh cm^-3 at a power density of 1.32 W cm^-3. Furthermore, this symmetric supercapacitor exhibited outstanding mechanical flexibility, and the capacity remained nearly unchanged after 1000 bending cycles.

Robust NiCoP/CoP Heterostructures for Highly Efficient Hydrogen Evolution Electrocatalysis in Alkaline Solution

Electrocatalytic hydrogen evolution reaction, the cornerstone of the emerging hydrogen economy, can be essentially facilitated by robustly heterostructural electrocatalysts. Herein, we report a highly active and stably heterostructural electrocatalyst consisting of NiCoP nanowires decorated with CoP nanoparticles on a nickel foam (NiCoP-CoP/NF) for effective hydrogen evolution. The CoP nanoparticles are strongly interfaced with NiCoP nanowires producing abundant electrocatalytically active sites. Combined with the integrated catalyst design, NiCoP-CoP/NF affords a remarkable hydrogen evolution performance in terms of high activity, enhanced kinetics, and outstanding durability in an alkaline electrolyte, superior to most of the Co (or Ni)-phosphide-based catalysts reported previously. Density functional theory calculations demonstrate that there is an interfacial effect between NiCoP and CoP, which allows a preferable hydrogen adsorption and thus contributes to the significantly enhanced performance. Furthermore, an electrolyzer employing NiCoP-CoP/NF as the cathode and RuO₂/NF as the anode (NiCoP-CoP/NF||RuO₂/NF) exhibits excellent water-splitting activity and outstanding durability, which is comparable to that of the benchmark Pt-C/NF||RuO₂/NF electrolyzer.

Synthesis of Ni4.5Fe4.5S8/Ni3S2 film on Ni3Fe alloy foam as an excellent electrocatalyst for the oxygen evolution reaction

Directly synthesizing bicomponent electrocatalysts in the nanostructured form from bulk alloy foam has many potential advantages: robust stability, synergistic effects and fast electron transfer. Here, Ni4.5Fe4.5S8/Ni3S2 film with micrometer thickness on bulk substrate was synthesized by a simple one-step hydrothermally assisted sulfurization of Ni3Fe alloy foam for the oxygen evolution reaction (OER) in basic media. Benefiting from the synergetic effect of the bicomponent, reduced interfacial resistance between electrocatalyst and metal substrate, and more exposed catalytic sites on the microstructured film, the as-prepared electrocatalyst (Ni4.5Fe4.5S8/Ni3S2‖Ni3Fe) behaves as a highly efficient and robust oxygen evolution electrode with felicitous current density in alkaline electrolytes (1 M KOH). It requires an overpotential of only 264 mV to drive 100 mA cm-2 with its catalytic activity being maintained for at least 20 h in 1 M KOH. In the near future, this kind of synthesis strategy can be easily extended to investigate many electrocatalysts derived from 3D alloyed foam with various ratios of the different components, opening new avenue for understanding the relationship between material properties and electrochemical performance.

Promotion of Overall Water Splitting Activity Over a Wide pH Range by Interfacial Electrical Effects of Metallic NiCo-nitrides Nanoparticle/NiCo2O4 Nanoflake/graphite Fibers

Many efforts have been made to develop bifunctional electrocatalysts to facilitate overall water splitting. Here, a fibrous bifunctional 3D electrocatalyst is reported for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) with high performance. The remarkable electrochemical performance is attributed of the catalysts to a number of factors: the metallic character of the three components (i.e., Ni3N, CoN, and NiCo2O4); the electronic structure, nanoflake-nanosphere network with abundant electroactive sites, and the electric field effect at the interfaces between different components. The oxide-nitride/graphite fibers have the lowest overpotential requirements of 71 and 183 mV at 10 mA cm-2 for HER and OER in alkaline medium, respectively. These values are comparable to those of commercial Pt/C (20 wt%) and RuO2. The electrodes also show a response to HER and OER in both neutral and acid media. Furthermore, the 3D structure can be highlighted by all-round electrodes for overall water splitting. The calculations on the changes in electrons transfer and the Femi level from oxides to oxides/nitrides reveal that the observed superb electrocatalytic performance can be attributed to the presence of Ni3N and CoN derived from the in situ nitridation of NiCo2O4.

Facile synthesis of hierarchical porous NixCo1-xSeO3 networks with controllable composition as a new and efficient water oxidation catalyst

Electrocatalysts are of significant importance for hydrogen production via water splitting. To replace noble metal based electrocatalysts, exploring new counterparts is critical for their large-scale and widespread deployment. In this paper, we report the synthesis of nickel-cobalt selenite (Ni0.5Co0.5SeO3) networks on nickel foam with promising electrocatalytic performance through a facile electrodeposition method. The networked structure built with interconnected nanosheets along with the three-dimensional backbone of nickel foam is able to provide a large surface area for the reaction to take place and simultaneously offer connected channels for charge carriers to pass through, consequently realizing the enhancement of oxygen evolution reaction (OER) electrocatalytic activity. Importantly, the hierarchical channel structure affords vast spaces to buffer the volume change during repeated redox reactions and offers feasible channels for gas release, leading to good electrochemical stability. The best sample with an optimized composition shows superior catalytic activity with a high current density of 243.6 mA cm-2 at an overpotential of 500 mV and excellent stability.

Efficient Hydrogen Evolution Activity and Overall Water Splitting of Metallic Co4N Nanowires through Tunable d-Orbitals with Ultrafast Incorporation of FeOOH

Cobalt nitride electrocatalysts have been investigated and proven to show excellent oxygen evolution reaction activity owing to their excellent metallic properties, but their hydrogen evolution reaction (HER) properties are rarely reported because of their unsatisfactory molecular energy level, especially the d-orbital. Herein, taking Co₄N as a case study, we tune the d-orbital of metallic Co₄N nanowires via rapid formation of iron oxyhydroxide (FeOOH). Experimental analyses show that FeOOH@Co₄N/SSM exhibits excellent HER catalytic activity with considerable low onset overpotential (22 mV), small Tafel slope (34 mV dec^-1), and excellent stability at current densities ranging from 20 to 100 mA cm^-2. Additionally, theoretical assessments display that the hybridization of Co₄N with FeOOH is beneficiary for optimizing and promoting the free energy of H adsorption due to the tuning of d-orbital. An overall water-splitting device assembled based on bifunctional FeOOH@Co₄N/SSM delivers an onset potential of 1.48 V with excellent stability up to 4 days. This shows a new strategy for designing a high-performance water-splitting device based on cobalt-based electrocatalysts.

Morphology and electronic structure modulation induced by fluorine doping in nickel-based heterostructures for robust bifunctional electrocatalysis

Fabrication of advanced electrocatalysts with high activity and durability is urgently needed to achieve energy conversion and pollution treatment at the same time. Herein, we highlight a fluorine-doped nickel-based heterostructure, in which fluorine doping displays a dual effect in Ni(OH)2 nanosheets/Ni3S2 heteronanorods. On the one hand, fluorine doping can facilitate the formation of Ni(OH)2 nanosheets/Ni3S2 heteronanorods through one-step in situ growth on nickel foams. The unique heterostructure enables good exposure of abundant active sites and highly active heterointerfaces. On the other hand, the uniform incorporation of fluorine can effectively modulate the electron density at the Fermi level of Ni3S2, contributing to the improved electrical conductivity and charge transfer efficiency, further improving the electrocatalytic activity in the oxygen evolution reaction (OER) and urea oxidation reaction (UOR). The optimal heterostructure presents a low overpotential of 360 mV to reach the OER current density of 100 mA cm-2. Finally, this heterostructure also displays a superior UOR anodic peak current of about 322.9 mA cm-2, almost the highest value at the anodic peak compared to the literature.