A Low‐Cost,Self‐Standing NiCo2O4@CNT/CNT Multilayer Electrode for Flexible Asymmetric Solid‐State Supercapacitors

The demand for a new generation of flexible, portable, and high‐capacity power sources increases rapidly with the development of advanced wearable electronic devices. Here we report a simple process for large‐scale fabrication of self‐standing composite film electrodes composed of NiCo₂O₄@carbon nanotube (CNT) for supercapacitors. Among all composite electrodes prepared, the one fired in air displays the best electrochemical behavior, achieving a specific capacitance of 1,590 F g^?1 at 0.5 A g^?1 while maintaining excellent stability. The NiCo₂O₄@CNT/CNT film electrodes are fabricated via stacking NiCo₂O₄@CNT and CNT alternately through vacuum filtration. Lightweight, flexible, and self‐standing film electrodes (≈24.3 µm thick) exhibit high volumetric capacitance of 873 F cm^?3 (with an areal mass of 2.5 mg cm^?2) at 0.5 A g^?1. An all‐solid‐state asymmetric supercapacitor consists of a composite film electrode and a treated carbon cloth electrode has not only high energy density (≈27.6 Wh kg^?1) at 0.55 kW kg^?1 (including the weight of the two electrodes) but also excellent cycling stability (retaining ≈95% of the initial capacitance after 5000 cycles), demonstrating the potential for practical application in wearable devices.     

Identifying the Conversion Mechanism of NiCo2O4 during Sodiation–Desodiation Cycling by In Situ TEM

For alkali metal ion batteries, probing the ion storage mechanism (intercalation‐ or conversion‐type) and concomitant phase evolution during sodiation–desodiation cycling is critical to gain insights into understanding how the electrode functions and thus how it can be improved. Here, by using in situ transmission electron microscopy, the whole sodiation–desodiation process of spinel NiCo₂O₄ nanorods is tracked in real time. Upon the first sodiation, a two‐step conversion reaction mechanism has been revealed: NiCo₂O₄ is first converted into intermediate phases of CoO and NiO that are then further reduced to Co and Ni phases. Upon the first desodiation, Co and Ni cannot be recovered to original NiCo₂O₄ phase, and divalent metal oxides of CoO and NiO are identified as desodiated products for the first time. Such asymmetric conversion reactions account for the huge capacity loss during the first charging–discharging cycle of NiCo₂O₄‐based sodium‐ion batteries (SIBs). Impressively, a reversible and symmetric phase transformation between CoO/Co and NiO/Ni phases is established during subsequent sodiation–desodiation cycles. This work provides valuable insights into mechanistic understanding of phase evolution during sodiation–desodiation of NiCo₂O₄, with the hope of assistance in designing SIBs with improved performance.     

Hierarchical NiCo2S4 Nanowire Arrays Supported on Ni Foam: An Efficient and Durable Bifunctional Electrocatalyst for Oxygen and Hydrogen Evolution Reactions

A recent approach for solar‐to‐hydrogen generation has been water electrolysis using efficient, stable, and inexpensive bifunctional electrocatalysts within strong electrolytes. Herein, the direct growth of 1D NiCo₂S₄ nanowire (NW) arrays on a 3D Ni foam (NF) is described. This NiCo₂S₄ NW/NF array functions as an efficient bifunctional electrocatalyst for overall water splitting with excellent activity and stability. The 3D‐Ni foam facilitates the directional growth, exposing more active sites of the catalyst for electrochemical reactions at the electrode–electrolyte interface. The binder‐free, self‐made NiCo₂S₄ NW/NF electrode delivers a hydrogen production current density of 10 mA cm^–2 at an overpotential of 260 mV for the oxygen evolution reaction and at 210 mV (versus a reversible hydrogen electrode) for the hydrogen evolution reaction in 1 m KOH. This highly active and stable bifunctional electrocatalyst enables the preparation of an alkaline water electrolyzer that could deliver 10 mA cm^–2 under a cell voltage of 1.63 V. Because the nonprecious‐metal NiCo₂S₄ NW/NF foam‐based electrodes afford the vigorous and continuous evolution of both H₂ and O₂ at 1.68 V, generated using a solar panel, they appear to be promising water splitting devices for large‐scale solar‐to‐hydrogen generation.     

Ultrathin Mesoporous NiCo2O4 Nanosheets Supported on Ni Foam as Advanced Electrodes for Supercapacitors

A facile two‐step method is developed for large‐scale growth of ultrathin mesoporous nickel cobaltite (NiCo₂O₄) nanosheets on conductive nickel foam with robust adhesion as a high‐performance electrode for electrochemical capacitors. The synthesis involves the co‐electrodeposition of a bimetallic (Ni, Co) hydroxide precursor on a Ni foam support and subsequent thermal transformation to spinel mesoporous NiCo₂O₄. The as‐prepared ultrathin NiCo₂O₄ nanosheets with the thickness of a few nanometers possess many interparticle mesopores with a size range from 2 to 5 nm. The nickel foam supported ultrathin mesoporous NiCo₂O₄ nanosheets promise fast electron and ion transport, large electroactive surface area, and excellent structural stability. As a result, superior pseudocapacitive performance is achieved with an ultrahigh specific capacitance of 1450 F g^?1, even at a very high current density of 20 A g^?1, and excellent cycling performance at high rates, suggesting its promising application as an efficient electrode for electrochemical capacitors.     

Molecular Design of Mesoporous NiCo2O4 and NiCo2S4 with Sub‐Micrometer‐Polyhedron Architectures for Efficient Pseudocapacitive Energy Storage

Spinel‐type NiCo₂O₄ (NCO) and NiCo₂S₄ (NCS) polyhedron architectures with sizes of 500–600 nm and rich mesopores with diameters of 1–2 nm are prepared facilely by the molecular design of Ni and Co into polyhedron‐shaped zeolitic imidazolate frameworks as solid precursors. Both as‐prepared NCO and NCS nanostructures exhibit excellent pseudocapacitance and stability as electrodes in supercapacitors. In particular, the exchange of O^2? in the lattice of NCO with S^2? obviously improves the electrochemical performance. NCS shows a highly attractive capacitance of 1296 F g^?1 at a current density of 1 A g^?1, ultrahigh rate capability with 93.2% capacitance retention at 10 A g^?1, and excellent cycling stability with a capacitance retention of 94.5% after cycling at 1 A g^?1 for 6000 times. The asymmetric supercapacitor with an NCS negative electrode and an active carbon positive electrode delivers a very attractive energy density of 44.8 Wh kg^?1 at power density 794.5 W kg^?1, and a favorable energy density of 37.7 Wh kg^?1 is still achieved at a high power density of 7981.1 W kg^?1. The specific mesoporous polyhedron architecture contributes significantly to the outstanding electrochemical performances of both NCO and NCS for capacitive energy storage.     

Ultrathin‐Nanosheet‐Induced Synthesis of 3D Transition Metal Oxides Networks for Lithium Ion Battery Anodes

A general ultrathin‐nanosheet‐induced strategy for producing a 3D mesoporous network of Co₃O₄ is reported. The fabrication process introduces a 3D N‐doped carbon network to adsorb metal cobalt ions via dipping process. Then, this carbon matrix serves as the sacrificed template, whose N‐doping effect and ultrathin nanosheet features play critical roles for controlling the formation of Co₃O₄ networks. The obtained material exhibits a 3D interconnected architecture with large specific surface area and abundant mesopores, which is constructed by nanoparticles. Merited by the optimized structure in three length scales of nanoparticles–mesopores–networks, this Co₃O₄ nanostructure possesses superior performance as a LIB anode: high capacity (1033 mAh g^?1 at 0.1 A g^?1) and long‐life stability (700 cycles at 5 A g^?1). Moreover, this strategy is verified to be effective for producing other transition metal oxides, including Fe₂O₃, ZnO, Mn₃O₄, NiCo₂O₄, and CoFe₂O₄.     

A Targeted Functional Design for Highly Efficient and Stable Cathodes for Rechargeable Li‐Ion Batteries

Despite the great success of Li‐ion batteries (LIBs) up to now, higher demand has been raised with the emergence of the new generation electrics, such as portable devices and electrical vehicles. Even with the improvement on anodes, the cathodes with high capacity and long‐lastingness still remain a challenge. New 3D NiCo₂O₄@V₂O₅ core–shell arrays (CSAs) on carbon cloth as cathodes in LIBs have been reported in this work. The nanodesigned materials realize the theoretical specific capacity of V₂O₅ with high power rate based on the total mass of the framework and amount of active materials. The electrodes achieve superb cycling stability, among the most stable cathodes for LIBs ever reported. From both in situ transmission electron microscopy and quantum level calculations, the 3D NiCo₂O₄ nanosheet frameworks provide high electron conductivity and the skeleton of the robust CSAs without participating in the lithiation/delithiation; the thickness of the layered V₂O₅ plays a key role for Li diffusivity and the capacity contribution of electrodes. The structures herein point to new design concepts for high‐performance nanoarchitectures for LIB cathodes.     

A Self‐Standing High‐Performance Hydrogen Evolution Electrode with Nanostructured NiCo2O4/CuS Heterostructures

An efficient self‐standing 3D hydrogen evolution cathode has been developed by coating nickel cobaltite (NiCo₂O₄)/CuS nanowire heterostructures on a carbon fiber paper (CFP). The obtained CFP/NiCo₂O₄/CuS electrode shows exceptional hydrogen evolution reaction (HER) performance and excellent durability in acidic conditions. Remarkably, as an integrated 3D hydrogen‐evolving cathode operating in acidic electrolytes, CFP/NiCo₂O₄/CuS maintains its activity more than 50 h and exhibits an onset overpotential of 31.1 mV, an exchange current density of 0.246 mA cm^?2, and a Tafel slope of 41 mV dec^?1. Compared to other non‐Pt electrocatalysts reported to date, CFP/NiCo₂O₄/CuS exhibits the highest HER activity and can be used in HER to produce H₂ with nearly quantitative faradaic yield in acidic aqueous media with stable activity. Furthermore, by using CFP/NiCo₂O₄/CuS as a self‐standing electrode in a water electrolyzer, a current density of 18 mA cm^?2 can be achieved at a voltage of 1.5 V which can be driven by a single‐cell battery. This strategy provides an effective, durable, and non‐Pt electrode for water splitting and hydrogen generation.     

Engineering an Earth‐Abundant Element‐Based Bifunctional Electrocatalyst for Highly Efficient and Durable Overall Water Splitting

The simultaneous and efficient evolution of hydrogen and oxygen with earth‐abundant, highly active, and robust bifunctional electrocatalysts is a significant concern in water splitting. Herein, non‐noble metal‐based Ni–Co–S bifunctional catalysts with tunable stoichiometry and morphology are realized. The engineering of electronic structure and subsequent morphological design synergistically contributes to significantly elevated electrocatalytic performance. Stable overpotentials (η₁₀) of 243 mV (vs reversible hydrogen electrode) for oxygen evolution reaction (OER) and 80 mV for hydrogen evolution reaction (HER), as well as Tafel slopes of 54.9 mV dec^?1 for OER and 58.5 mV dec^?1 for HER, are demonstrated. In addition, density functional theory calculations are performed to determine the optimal electronic structure via the electron density differences to verify the enhanced OER activity is related to the Co top site on the (110) surface. Moreover, the tandem bifunctional NiCo₂S₄ exhibit a required voltage of 1.58 V (J = 10 mA cm^?2) for simultaneous OER and HER, and no obvious performance decay is observed after 72 h. When integrated with a GaAs solar cell, the resulting photoassisted water splitting electrolyzer shows a certified solar‐to‐hydrogen efficiency of up to 18.01%, further demonstrating the feasibility of engineering protocols and the promising potential of bifunctional NiCo₂S₄ for large‐scale overall water splitting.     

A Dendritic Nickel Cobalt Sulfide Nanostructure for Alkaline Battery Electrodes

A uniform dendritic NiCo₂S₄@NiCo₂S₄ hierarchical nanostructure of width ≈100 nm is successfully designed and synthesized. From kinetic analysis of the electrochemical reactions, those electrodes function in rechargeable alkaline batteries (RABs). The dendritic structure exhibited by the electrodes has a high discharge‐specific capacity of 4.43 mAh cm^?2 at a high current density of 240 mA cm^?2 with a good rate capability of 70.1% after increasing the current densities from 40 to 240 mA cm^?2. At low scan rate of 0.5 mV s^?1 in cyclic voltammetry test, the semidiffusion controlled electrochemical reaction contributes ≈92% of the total capacity, this value decreases to ≈43% at a high scan rate of 20 mV s^?1. These results enable a detailed analysis of the reaction mechanism for RABs and suggest design concepts for new electrode materials.     

Electrical Transport Properties of Large,Individual NiCo2O4 Nanoplates

Understanding the electrical transport properties of individual semiconductor nanostructures is crucial to advancing their practical applications in high‐performance nanodevices. Large‐sized individual nanostructures with smooth surfaces are preferred because they can be easily made into nanodevices using conventional photolithography procedures rather than having to rely on costly and complex electron‐beam lithography techniques. In this study, micrometer‐sized NiCo₂O₄ nanoplates are successfully prepared from their corresponding hydroxide precursor using a quasi‐topotactic transformation. The Co/Ni atomic arrangement shows no changes during the transformation from the rhombohedral LDH precursor (space group R$ \bar 3 $ m) to the cubic NiCo₂O₄ spinel (space group Fd $ \bar 3 $ m), and the nanoplate retains its initial morphology during the conversion process. In particular, electrical transport within an individual NiCo₂O₄ nanoplate is further investigated. The mechanisms of electrical conduction in the low‐temperature range (T < 100 K) can be explained in terms of the Mott's variable‐range hopping model. At high temperatures (T > 100 K), both the variable‐range hopping and nearest‐neighbor hopping mechanisms contribute to the electrical transport properties of the NiCo₂O₄ nanoplate. These initial results will be useful to understanding the fundamental characteristics of these nanoplates and to designing functional nanodevices from NiCo₂O₄ nanostructures.     

Mesoporous NiCo2O4 Nanowire Arrays Grown on Carbon Textiles as Binder‐Free Flexible Electrodes for Energy Storage

Binary metal oxides has been regarded as a promising class of electrode materials for high‐performance energy storage devices since it offers higher electrochemical activity and higher capacity than mono‐metal oxide. Besides, rational design of electrode architectures is an effective solution to further enhance electrochemical performance of energy storage devices. Here, the advanced electrode architectures consisting of carbon textiles uniformally covered by mesoporous NiCo₂O₄ nanowire arrays (NWAs) are successfully fabricated by a simple surfactant‐assisted hydrothermal method combined with a short post annealing treatment, which can be directly applied as self‐supported electrodes for energy storage devices, such as Li‐ion batteries, supercapacitors. The as‐prepared mesoporous NiCo₂O₄ nanowires consist of numerous highly crystalline nanoparticles, leaving a large number of mesopores to alleviate the volume change during the charge/discharge process. Electrode architectures presented here promise fast electron transport by direct connection to the growth substrate and facile ion diffusion path provided by both the abundant mesoporous structure in nanowires and large open spaces between neighboring nanowires, which ensures every nanowire participates in the ultrafast electrochemical reaction. Benefiting from the intrinsic materials and architectures features, the unique binder‐free NiCo₂O₄/carbon textiles exhibit high specific capacity/capacitance, excellent rate capability, and cycling stability.     

Fast and Reversible Li Ion Insertion in Carbon‐Encapsulated Li3VO4 as Anode for Lithium‐Ion Battery

Carbon‐encapsulated Li₃VO₄ is synthesized by a facile environmentally benign solid‐state method with organic metallic precursor VO(C₅H₇O₂)₂ being chosen as both V and carbon sources yielding a core–shell nanostructure with lithium introduced in the subsequent annealing process. The Li₃VO₄ encapsulated with carbon presents exceeding rate capability (a reversible capability of 450, 340, 169, and 106 mAh g^?1 at 0.1 C, 10 C, 50 C, and 80 C, respectively) and long cyclic performance (80% capacity retention after 2000 cycles at 10 C) as an anode in lithium‐ion batteries. The superior performance is derived from the structural features of the carbon‐encapsulated Li₃VO₄ composite with oxygen vacancies in Li₃VO₄, which increase surface energy and could possibly serve as a nucleation center, thus facilitating phase transitions. The in situ generated carbon shell not only facilitates electron transport, but also suppresses Li₃VO₄ particle growth during the calcination process. The encouraging results demonstrate the significant potential of carbon encapsulated Li₃VO₄ for high power batteries. In addition, the simple generic synthesis method is applicable to the fabrication of a variety of electrode materials for batteries and supercapacitors with unique core–shell structure with mesoporous carbon shell.     

Bowtie‐Shaped NiCo2O4 Catalysts for Low‐Temperature Methane Combustion

Bowtie‐shaped NiCo₂O₄ nanostructures are prepared using a hydrothermal method. Variation of the synthesis parameters, including reaction time, additives, and calcination temperature, allows an understanding of the origin of the bowtie‐shaped structure to be developed. Methane oxidation experiments performed using temperature‐programed oxidation (TPO) show that the new materials, which do not contain precious metals, have excellent activity for low‐temperature methane combustion, with 100% conversion at ≈410 °C (gas hourly space velocity (GHSV): 90 000 mL (STP) g^?1 h^?1). The structure–activity relationships of the bowtie‐shaped nanostructures are explored.     

Ternary Oxide Nanocrystals: Universal Laser‐Hydrothermal Synthesis,Optoelectronic and Electrochemical Applications

Ternary oxide nanocrystals (TONs) have received growing attention for their great potential applications in optoelectronics and electrochemistry despite the current scarcity of universal, facile, and green synthesis methods. Here, we introduce a universal laser‐hydrothermal approach for various TONs and demonstrate their potential for high‐performance photodetectors (PDs) and pseudocapacitors. The obtained clean surface is derived by laser ablation in liquid (LAL) and subsequent hydrothermal growth. The LAL‐generated precursors contain many kinds of highly reactive species, including H⁺, OH^?, metal ions, and clusters, which facilitate the fast and facile formation of various TONs in the subsequent hydrothermal process. The universality of the method is systematically proven by the synthesis of a series of TONs, including Zn₂GeO₄, NiCo₂O₄, Zn₂SnO₄, ZnFe₂O₄, ZnMnO₃, and Fe₂GeO₄. Significantly, the absence of chemical additives, such as surfactants, guarantees highly clean surfaces, which further benefits the electron transport through the nanocrystals, and thus in the resultant devices. This is also exemplified by a Zn₂GeO₄‐nanorod‐based, deep‐ultraviolet PD and NiCo₂O₄ nanocrystal supercapacitors.     

Scale‐Up Biomass Pathway to Cobalt Single‐Site Catalysts Anchored on N‐Doped Porous Carbon Nanobelt with Ultrahigh Surface Area

Porous Co? N? C catalysts with ultrahigh surface area are highly required for catalytic reactions. Here, a scale‐up method to synthesize gram‐quantities of isolated Co single‐site catalysts anchored on N‐doped porous carbon nanobelt (Co‐ISA/CNB) by pyrolysis of biomass‐derived chitosan is reported. The usage of ZnCl₂ and CoCl₂ salts as effective activation–graphitization agents can introduce a porous belt‐like nanostructure with ultrahigh specific surface area (2513 m² g^?1) and high graphitization degree. Spherical aberration correction electron microscopy and X‐ray absorption fine structure analysis reveal that Co species are present as isolated single sites and stabilized by nitrogen in CoN₄ structure. All these characters make Co‐ISA/CNB an efficient catalyst for selective oxidation of aromatic alkanes at room temperature. For oxidation of ethylbenzene, the Co‐ISA/CNB catalysts yield a conversion up to 98% with 99% selectivity, while Co nanoparticles are inert. Density functional theory calculations reveal that the generated Co?O centers on isolated Co single sites are responsible for the excellent catalytic efficiency.     

Controllable Urchin‐Like NiCo2S4 Microsphere Synergized with Sulfur‐Doped Graphene as Bifunctional Catalyst for Superior Rechargeable Zn–Air Battery

Rechargeable zinc–air batteries (ZnABs) are attracting great interest due to their high theoretical specific energy, safety, and economic viability. However, their performance and large‐scale practical applications are largely limited by poor durability and high overpotential on the air‐cathode due to the slow kinetics of the oxygen reduction and evolution reactions (ORR/OER). Therefore, it is highly desired to exploit an ideal bifunctional catalyst to endow the obtained ZnABs with excellent ORR/OER catalytic performances. Herein, a new nonprecious‐metal bifunctional catalyst of urchin‐like NiCo₂S₄ microsphere synergized with sulfur‐doped graphene nanosheets (S‐GNS/NiCo₂S₄) is controllably designed and synthesized by simply tailoring the structure and electronic arrangement, which endow the as‐prepared catalyst with excellent electroactivity and long‐term durability toward ORR and OER. Importantly, ZnABs constructed by this outstanding catalyst exhibit high power density, small charge/discharge voltage gap, and excellent cycle stability, notably outperforming the more costly commercial Pt/C + Ir/C mixture catalyst. These excellent electrocatalytic performances together with the simplicity of the synthetic method, make the urchin‐like NiCo₂S₄ microsphere/S‐GNS hybrid nanostructure exhibit great promise as a superior air‐cathode catalyst for high‐performance rechargeable ZnABs.     

Cobalt‐Doping in Molybdenum‐Carbide Nanowires Toward Efficient Electrocatalytic Hydrogen Evolution

Efficient hydrogen evolution reaction (HER) over noble‐metal‐free electrocatalysts provides one of the most promising pathways to face the energy crisis. Herein, facile cobalt‐doping based on Co‐modified MoO_x–amine precursors is developed to optimize the electrochemical HER over Mo₂C nanowires. The effective Co‐doping into Mo₂C crystal structure increases the electron density around Fermi level, resulting in the reduced strength of Mo–H for facilitated HER kinetics. As expected, the Co‐Mo₂C nanowires with an optimal Co/Mo ratio of 0.020 display a low overpotential (η₁₀ = 140 and 118 mV for reaching a current density of –10 mA cm^?2; η₁₀₀ = 200 and 195 mV for reaching a current density of –100 mA cm^?2), a small Tafel slope (39 and 44 mV dec^?1), and a low onset overpotential (40 and 25 mV) in 0.5 m H₂SO₄ and 1.0 m KOH, respectively. This work highlights a feasible strategy to explore efficient electrocatalysts via engineering on composition and nanostructure.     

Electron Transfer-Induced Metal Spin-Crossover at NiCo2S4/ReS2 2D–2D Interfaces for Promoting pH-universal Hydrogen Evolution Reaction

The development of an efficient pH-universal hydrogen evolution reaction (HER) electrocatalyst is essential for practical hydrogen production. Here, an efficient and stable pH-universal HER electrocatalyst composed of the strongly coupled 2D NiCo₂S₄ and 2D ReS₂ nanosheets (NiCo₂S₄/ReS₂) is demonstrated. The NiCo₂S₄/ReS₂ 2D–2D nanocomposite is directly grown on the surface of the carbon cloth substrate, which exhibits excellent HER performance with overpotentials of 85 and 126 mV at a current density of 10 mA cm⁻² and Tafel slopes of 78.3 and 67.8 mV dec⁻¹ under both alkaline and acidic conditions, respectively. Theoretical and experimental characterizations reveal that the chemical coupling between NiCo₂S₄ and ReS₂ layers induces electron transfer from Ni and Co to interfacial Re-neighbored S atoms, enabling beneficial H atom adsorption and desorption for both acidic and alkaline HER. Simultaneously, an electron transfer-induced spin-crossover generates high-spin interfacial Ni and Co atoms that promote water dissociation kinetics at the NiCo₂S₄/ReS₂ interface, which is the origin of the superior alkaline HER activity. NiCo₂S₄/ReS₂ also shows decent catalytic activity and long-term durability for oxygen evolution reaction, and finally bifunctionality for overall water splitting. This study suggests a rational strategy to enhance water dissociation kinetics by inducing spin-crossover via electron transfer.     

Dual Active Sites Engineering on Sea Urchin-Like CoNiS Hollow Nanosphere for Stabilizing Oxygen Electrocatalysis via a Template-Free Vulcanization Strategy

Manipulating electronic structure and defects is crucial to achieve on-demand functionalities of bimetallic sulfide catalysts for oxygen reduction/evolution reactions (ORR/OER). Here, via a vulcanization strategy, defects-abundant NiCo₂S₄ needles obtained from sea urchin-like NiCo₂O₄ are anchored on surface of hollow carbon-sphere (NiCo₂S₄/HCS). NiCo₂S₄ nanoneedles (≈7.5 nm) are radially grown on shell of HCS with a cavity (254.5 m² g⁻¹), and their surface becomes rougher after vulcanization due to anion exchange reaction. As-marked NiCo₂S₄/HCS-3 exhibits better ORR activity (half-wave potential of 0.89 V) and methanol tolerance than Pt/C (0.86 V). NiCo₂S₄/HCS-3 shows a lower OER overpotential (310 mV) than RuO₂ and retains 90.9% of initial activity after 9 h. Notably, zinc–air battery with NiCo₂S₄/HCS-3 reveals highly-stable charging/discharging voltages of 2.11/1.16 V with a negligible fading for 200 h. NiCo₂S₄ grown on outer/inner surfaces of HCS expands spatial distribution of active sites to enhance reactants-electrode contact and charge transfer. Theoretical calculation shows that Co-site with an electronic state near Fermi energy level is chiefly-responsible for ORR, while Ni-site mainly affords high OER activity. Bader charge analyses reveal that S doping increases the charge density and redox active sites in NiCo₂S₄. It sheds light on the understanding of electrocatalytic mechanisms on bimetallic sulfides for electronic device.