Trade-Off between Degradation Efficiency and Recyclability: Zeolite-Enhanced Ni3-xCoxS4 Catalyst for Photocatalytic Degradation of Methylene Blue.

We herein report successful syntheses of both nickel cobalt sulfide (NCS) and its composite with zeolite (NCS@Z) using a solvothermal method. Techniques such as EDX analysis, SEM, and molar ratio determination were used for product characterization. The incorporation of NCS significantly changed the surface roughness and active sites of the zeolite, improving the efficiency of methylene blue degradation and its reusability, especially under UV irradiation. In comparing the pseudo-first order rates, the highest degradation efficiency of methylene blue was achieved with NCS-2@Z, having a degradation extent of 91.07% under UV irradiation. This environmentally friendly approach offers a promising solution for the remediation of methylene blue contamination in various industries.

CoS2/carbon network flexible film with Co-N bond/π-π interaction enables superior mechanical properties and high-rate sodium ion storage.

Flexible electrodes based on conversion-type materials have potential applications in low-cost and high-performance flexible sodium-ion batteries (FSIBs), owing to their high theoretical capacity and appropriate sodiation potential. However, they suffer from flexible electrodes with poor mechanical properties and sluggish reaction kinetics. In this study, freestanding CoS2 nanoparticles coupled with graphene oxides and carbon nanotubes (CoS2/GO/CNTs) flexible films with robust and interconnected architectures were successfully synthesized. CoS2/GO/CNTs flexible film displays high electronic conductivity and superior mechanical properties (average tensile strength of 21.27 MPa and average toughness of 393.18 KJ m-3) owing to the defect bridge for electron transfer and the formation of the π-π interactions between CNTs and GO. In addition, the close contact between the CoS2 nanoparticles and carbon networks enabled by the Co-N chemical bond prevents the self-aggregation of the CoS2 nanoparticles. As a result, the CoS2/GO/CNTs flexible film delivered superior rate capability (213.5 mAh g-1 at 6 A g-1, better than most reported flexible anode) and long-term cycling stability. Moreover, the conversion reaction that occurred in the CoS2/GO/CNTs flexible film exhibited pseudocapacitive behavior. This study provides meaningful insights into the development of flexible electrodes with superior mechanical properties and electrochemical performance for energy storage.

Rod-like Ni-CoS2@NC@C: Structural design, heteroatom doping and carbon confinement engineering to synergistically boost sodium storage performance.

Currently, conversion-type transition metal sulfides have been extensively favored as the anodes for sodium-ion batteries due to their excellent redox reversibility and high theoretical capacity; however, they generally suffer from large volume expansion and structural instability during repeatedly Na+ de/intercalation. Herein, spatially dual-confined Ni-doped CoS2@NC@C microrods (Ni-CoS2@NC@C) are developed via structural design, heteroatom doping and carbon confinement to boost sodium storage performance of the material. The morphology of one-dimensional-structured microrods effectively enlarges the electrode/electrolyte contact area, while the confinement of dual-carbon layers greatly alleviates the volume change-induced stress, pulverization, agglomeration of the material during charging and discharging. Moreover, the introduction of Ni improves the electrical conductivity of the material by modulating the electronic structure and enlarges the interlayer distance to accelerate Na+ diffusion. Accordingly, the as-prepared Ni-CoS2@NC@C exhibits superb electrochemical properties, delivering the satisfactory cycling performance of 526.6 mA h g-1 after 250 cycles at 1 A g-1, excellent rate performance of 410.9 mA h g-1 at 5 A g-1 and superior long cycling life of 502.5 mA h g-1 after 1,500 cycles at 5 A g-1. This study provides an innovative idea to improve sodium storage performance of conversion-type transition metal sulfides through the comprehensive strategy of structural design, heteroatom doping and carbon confinement.

Spin Effect to Promote Reaction Kinetics and Overall Performance of Lithium-Sulfur Batteries under External Magnetic Field.

Lithium-sulfur batteries (LSBs) are still limited by the shuttle of lithium polysulfides (LiPS) and the slow Li-S reaction. Herein, we demonstrate that when using cobalt sulfide as a catalytic additive, an external magnetic field generated by a permanent magnet can significantly improve the LiPS adsorption ability and the Li-S reaction kinetics. More specifically, the results show both experimentally and theoretically how an electron spin polarization of Co ions reduces electron repulsion and enhances the degree of orbital hybridization, thus resulting in LSBs with unprecedented performance and stability. Under an external magnetic field, LSBs with 0.0084 % per cycle decay rate at 2 C during 8150 cycles are produced. Overall, this work not only demonstrates an effective strategy to promote LiPS adsorption and electrochemical conversion in LSBs at no additional energy cost but also enriches the application of the spin effect in the electrocatalysis fields.

Manipulating the electrocatalytic activity of sulfur cathode via distinct cobalt sulfides as sulfur host materials in lithium-sulfur batteries.

For the better development of lithium-sulfur (Li-S) batteries, it is necessary to fabricate sulfur hosts with cheap, rapid sulfur reaction dynamic and inhibiting the shuttling effect of lithium polysulfides (LiPSs). Herein, four hollow cubic materials with two kinds of nitrogen-doped carbon derived from Prussian blue analogues (PBA) precursor, Co9S8/MnS/NC@NC-400, CoS2/MnS/NC@NC-500, CoS1.097/MnS/NC@NC-600 and CoS1.097/MnS/NC@NC-700, are reported when the vulcanization temperatures are regulated at 400 °C, 500 °C, 600 °C and 700 °C, respectively. Among them, Co9S8/MnS/NC@NC-400, CoS2/MnS/NC@NC-500 and CoS1.097/MnS/NC@NC-600 have the similar hollow cubic structure, which can physically confine the LiPSs's shuttle, however, the Co vacancies of CoS1.097 in the CoS1.097/MnS/NC@NC-600 can promote the rearrangement of surface electrons, which is beneficial to the diffusion of Li+/e-, improving the electrochemical reaction kinetics. As for the CoS1.097/MnS/NC@NC-700 with the same substance but almost collapsed structure, the CoS1.097/MnS/NC@NC-600 can accommodate the volume expansion of sulfur conversion. In the four sulfur-host materials, the CoS1.097/MnS/NC@NC-600 not only displays the outstanding adsorption ability on LiPSs, but also presents the best electrocatalytic activity in the Li2S potentiostatic deposition experiments and active sulfur reduction/oxidation conversion reactions, greatly promoting the electrochemical performances of Li-S batteries. The S@CoS1.097/MnS/NC@NC-600 cathode can deliver 1010.2 mA h g-1 at 0.5 C and maintain 651.1 mA h g-1 after 200 cycles. In addition, the in-situ X-ray diffraction (in-situ XRD) test reveals that the sulfur conversion mechanism is the processes of the α-S8 â†’ Li2S â†’ ß-S8 (first cycle), then ß-S8 â†” Li2S during the subsequent cycles. Based on the fundamental understanding of the design and preparation of CoxSy/MnS/NC@NC hosts with the desired adsorption and catalysis functions, the work can provide new insights and reveal the defect-engineering to develop the advanced Li-S batteries.

Designing a carbon nanofiber-encapsulated iron carbide anode and nickel-cobalt sulfide-decorated carbon nanofiber cathode for high-performance supercapacitors.

To meet the crucial demand for high-performance supercapacitors, much effort has been devoted to exploring electrode materials with nanostructures and electroactive chemical compositions. Herein, iron carbide nanoparticles are encapsulated into carbon nanofibers (Fe3C@CNF-650) through electrospinning and annealing methods. Nickel-cobalt sulfide nanoparticles are hydrothermally grown on electrospun carbon nanofibers (CNF@NiCoS-650). The Faradaic electrochemical reactions of transition metal compounds improve the specific capacitance of the developed electrode. Meanwhile, the electrically conductive framework of carbon nanofibers facilitates Faradic charge transport. In detail, the Fe3C@CNF-650 anode and CNF@NiCoS-650 cathode achieve specific capacitances of 1551 and 205 F g-1, respectively, at a current density of 1 A g-1. A hybrid supercapacitor that is fabricated from the Fe3C@CNF-650 anode and CNF@NiCoS-650 cathode delivers an energy density of 43.2 Wh kg-1 at a power density of 800 W kg-1. The designed nanostructures are promising for practical supercapacitor applications.

Degradation of sulfamethoxazole using PMS activated by cobalt sulfides encapsulated in nitrogen and sulfur co-doped graphene.

In this study cobalt sulfides (Co9S8) coated on the nitrogen and sulfur co-doped graphene (Co9S8@S-N-RG) was firstly prepared and used for degradation of antibiotic sulfamethoxazole (SMX). The results showed that SMX could be completely degraded by Co9S8@S-N-RG-activated peroxymonosulfate (PMS) within 20 min with its mineralization efficiency of 38.7%. The SMX degradation rate followed pseudo first-order kinetics with kinetic constant of 0.377 min-1 that was higher than that induced by Co9S8, N-RG, S-N-RG and Co9S8@S-RG, indicating Co9S8@S-N-RG had superior catalytic activity. Co9S8@S-N-RG can activate PMS to produce sulfate radicals and hydroxyl radicals, while sulfate radicals played major role. Co9S8 participated in PMS activation in which Co2+ was involved in sulfate radicals formation, while sulfur species facilitated the conversion of Co3+ to Co2+. In addition, carbon defects, CO, pyridinic N and pyrrolic N also contributed to PMS activation.The superior catalytic activity was attributed to the synergistic effect of Co9S8 and S-N-RG. This study could provide an efficient and stable PMS activator, and insight into the PMS activation mechanism by Co9S8@S-N-RG.

Comparative study on supercapacitive and oxygen evolution reaction applications of hollow nanostructured cobalt sulfides.

Due to the diversity of sulfur valence in cobalt-based sulfides, it is difficult to control the crystal phase and composition of the products during synthesis. Herein, a one-pot hydrothermal method is reported to self-assemble the cobalt sulfides (CoS2, Co9S8and Co3S4) with hollow nanostructures. The whole preparation process is simple and mild, avoiding high temperature calcination. The performances of the three kinds of cobalt sulfide in superior supercapacitors and electrocatalytic oxygen evolution performance applications follow the order of CoS2 > Co9S8 > Co3S4. Further analysis demonstrates that the performance difference in these cobalt sulfides may be attributed to three factors: the presence ofS22-,the coordination environment of Co and the presence of continuous network of Co-Co bonds. The distinctive electrochemical performance of CoS2and Co9S8may help us to better understand the excellent electrochemical activity of metal polysulfides and metal sulfides after doping or alloying. Therefore, this work may provide a reference in understanding and designing the electrode materials for highly efficient applications in the fields of energy storage and conversion.

Sulfur vacancies enriched Nickel-Cobalt sulfides hollow spheres with high performance for All-Solid-State hybrid supercapacitor.

To pursue excellent performance of supercapacitor, an electrode material with designed morphology and tailored intrinsic properties is indeed desired. Herein, nickel-cobalt sulfides hollow spheres decorated with rich sulfur vacancies r-NiCo2S4 HSs) are prepared via an anion exchange of Ni-Co coordination polymer spheres, combined with wet chemical reduction. The r-NiCo2S4 HSs sample delivers excellent performance as an electrode: it possesses a high specific capacity (763.5C g-1 at 1 A/g), favorable cyclability (91.40% after 5000 cycles at 10 A/g) and rate capacity (522.68C g-1 at 15 A/g). Additionally, an all-solid-state hybrid supercapacitor device, assembled with r-NiCo2S4 HSs as the positive electrode and N/S co-doped activated carbon nanosheets as the negative electrode, presents an excellent energy density of 50.76 Wh kg-1 under 800 W kg-1 and feasible stability. Thus, combining hollow structure with sulfur vacancies could not only increase more active sites and ensure sufficient redox reactions, but also enhance electronic conductivity, facilitate ions / electrons transport and shorten diffusion path, which could be regarded as a promising approach to develop electrode materials with outstanding performance.

In situ synthesis of nitrogen site activated cobalt sulfide@N, S dual-doped carbon composite for a high-performance asymmetric supercapacitor.

Cobalt sulfides with high theoretical capacity are considered as potential electrodes for supercapacitors (SCs). However, the insufficient reactive sites and low electrical conductivity of bulky cobalt sulfides restrict their applications. Here, we proposed an efficient approach for in situ formation of nitrogen site activated cobalt sulfide@N, S dual-doped carbon composite (CS@NSC) by vulcanizing the cobalt-glutamine complex (CG) precursor in a tube furnace. The effects of the molecular structure and calcination temperature of CG precursors on the morphology, structure and electrochemical performance of CS@NSC were studied. The designed CS@NSC-2 exhibited a specific capacity of 593 C g-1 at the current density of 1 A g-1 and good cyclic stability with 88.7% retention after 2000 cycles. Moreover, an asymmetric supercapacitor (ASC) was fabricated by CS@NSC-2 (positive electrode) and activated carbon (AC) (negative electrode), which delivered ultra-high energy density of 67.8 Wh kg-1 at a power density of 400 W kg-1 and possessed 83.1% capacitance retention after 5000 cycles. The eco-friendly method was also suitable for synthesizing nickel sulfide. This work may provide an innovative horizon for the in situ formation of active sites in electrode materials.

Defect-rich honeycomb-like nickel cobalt sulfides on graphene through rapid microwave-induced synthesis for ultrahigh rate supercapacitors.

Nickel cobalt sulfides (NCS) are regarded as potential energy storage materials due to the versatile valent states and rich electrochemical activity, but their sluggish synthesis process and inferior rate performance hinder them from large-scale application. Herein, microwave-induced strategy has been employed for efficient synthesis of honeycomb-like NCS/graphene composites, which are explored as ultrahigh rate battery-type electrodes for supercapacitors. Due to the internal heat mechanism, the synthesis time of NCS by microwave could be shortened from hours to minutes. Density functional theory was simulated to uncover the interfacial effect between NCS and graphene, and the resulted Schottky barrier is in favor of enhancing redox activity and capacity. Ultimately, the obtained defect-rich nickel cobalt sulfides/graphene with thermal treatment (NCS/G-H) could exhibit a high specific capacitance of 1186 F g-1 at 1 A g-1 and sustain 89.8% capacity even after the increase of current density over 20 times, which is much superior to bare NCS and NCS/graphene. Furthermore, the assembled NCS/G-H hybrid supercapacitor delivers supreme energy density of 46.4 Wh kg-1, and retains outstanding long-term stability of 89.2% after 10 k cycles. These results indicate that the synthesized NCS/G-H by time-saving microwave-induced liquid process could be served as high rate materials for supercapacitors.

Phase Engineering of Iron-Cobalt Sulfides for Zn-Air and Na-Ion Batteries.

Rechargeable batteries are promising platforms for sustainable development of energy conversion and storage technologies. Highly efficient multifunctional electrodes based on bimetallic sulfides for rechargeable batteries are extremely desirable but still challenging to tailor with controllable phase and structure. Here, we report a colloidal strategy to fabricate FeCo-based bimetallic sulfides on reduced graphene oxide (rGO), which are expected to display highly efficient oxygen electrocatalysis and sodium storage performances. Specifically, as-screened FeCo8S8 nanosheets (NSs) on rGO originating from suitable tailoring of the Co9S8 matrix with Fe at the atomic level exhibited a very low potential difference (0.77 V) at 10 mA cm-2 and negligible voltage loss after 200 cycles as an air electrode for Zn-air batteries. For Na-ion batteries, FeCo8S8 NS/rGO demonstrated a superior high-rate capability (188 mAh g-1 at 20 A g-1) with long-term cycling stability. The bifunctional electrocatalytic property and sodium storage performance are attributed to not only the synergistic effect of Fe/Co but also the optimized catalytic activity and ion transport ability by the in situ rGO hybrid. This work demonstrates the potential applications of FeCo-based bimetallic sulfides as efficient electrode materials for both rechargeable Zn-air and Na-ion batteries.

Dual-Functional Multichannel Carbon Framework Embedded with CoS2 Nanoparticles: Promoting the Phase Transformation for High-Loading Li-S Batteries.

Lithium-sulfur batteries have been considered as one of the most promising energy storage devices due to their high theoretical capacity and low cost. They go through complicated multistep electrochemical reactions from solid (sulfur)-liquid (soluble polysulfide) to liquid (soluble polysulfide)-solid (Li2S) during the discharge process. Actually, during this process, the transition from liquid phase (Li2S4) to solid phase (Li2S) at 2.1 V plateau is a difficult step with sluggish kinetics, thus leading to low sulfur utilization and discharge capacity. To promote the transition processes and enhance the sulfur utilization, CoS2@multichannel carbon nanofiber composites (CoS2@MCNFs) serving as sulfur host were successfully synthesized. Herein, CoS2 catalysts are proven to be beneficial not only for enhancing the phase-transition kinetics but also for adsorbing soluble polysulfide. Besides, unlike other carbon materials, MCNFs have plenty of hollow channels and thus enhance sulfur loading and conductivity. Accordingly, the discharge capacity increases 32% more than that of electrode without CoS2. And a very low capacity fade rate of 0.03% per cycle (over 450 cycles) is obtained at a 0.5C rate. This work has opened up new ideas for enhancing sulfur utilization for high sulfur-loading electrode.

Boosting Transport Kinetics of Cobalt Sulfides Yolk-Shell Spheres by Anion Doping for Advanced Lithium and Sodium Storage.

Cobalt sulfides have been popularly used in energy storage because of their high theoretical capacity and abundant redox reactions. However, poor reaction kinetics, rapid capacity decay, and severe polarization owing to volume changes during electrochemical reaction are still huge challenges for cobalt sulfides in practical applications. Herein, cobalt sulfide yolk-shell spheres were synthesized by phosphorus doping (P-CoS) to stabilize the structure of cobalt sulfides and improve their electronic/ion conductivity. Kinetic tests and density functional theory calculations confirm that the introduction of phosphorus into cobalt sulfides greatly reduces the diffusion barrier of Li+ in the intrinsic structure, thereby improving the reaction kinetics of electrode materials during the Li+ insertion/extraction process. In consequence, the P-CoS electrode delivers a high lithium storage capacity (781 mAh g-1 after 100 cycles at 0.2 A g-1 ), excellent rate capability (489 mAh g-1 at 10 A g-1 ), and outstanding cycling stability (no significant capacity decay over 4000 cycles at 5 A g-1 ). Especially for sodium-ion battery application, the P-CoS electrode expresses a striking capacity of approximately 260 mAh g-1 at 2 A g-1 after 900 cycles.

Enhancing the electrochemical performance of nickel cobalt sulfides hollow nanospheres by structural modulation for asymmetric supercapacitors.

The development of nickel cobalt sulfides electrodes with excellent electrochemical performance is important for supercapacitor applications. In this study, we constructed well-defined hierarchical nanosheet-built NiCo2S4/Co9S8 hollow nanospheres based on morphology and structural engineering. A combination of structural and compositional advantages endowed NiCo2S4/Co9S8 hollow nanospheres with enhanced electrochemical performance with favorable capacitance of 1008 F g-1 at 1 A g-1, exceeding that of single-component NiS (616 F g-1 at 1 A g-1) and Co3S4 (430 F g-1 at 1 A g-1). Furthermore, an assembled asymmetric supercapacitor (ASC) comprising NiCo2S4/Co9S8 hollow nanospheres and activated carbon achieved a high energy density up to 36.7 Wh kg-1 at 800 W kg-1, suggesting that it could be a promising electroactive material for energy storage devices.

In Situ Formation of Co9S8 Nanoclusters in Sulfur-Doped Carbon Foam as a Sustainable and High-Rate Sodium-Ion Anode.

Transition-metal sulfides hold great promise as anode materials for sodium-ion batteries due to the high theoretical capacity and excellent redox reversibility based on multielectron conversion reactions. In this work, an elaborate composite, cobalt sulfide nanoclusters embedded in honeycomb-like sulfur-doped carbon foam (Co9S8@S-CF), is prepared via a facile sulfur-assisting calcination strategy, which tactfully induces the co-occurrence of in situ pore-forming, sulfidation, sulfur doping, and carbonization. Notably, sulfur-doped carbon foam (S-CF) possesses abundant voids, which are subject to construction of three-dimensional ionic/electronic pathways, leading to high sodium-ion accessibility and ultrafast sodium-ion/electron transportation toward Co9S8 nanoclusters. When worked as an anode in sodium-ion batteries, it delivers a remarkable capacity of 373 mA h g-1 over 1000 cycles at 0.25 C, achieving superior capacity retention of 80%. Furthermore, this anode could achieve unprecedented rate capability with a reversible capacity of 180 mA h g-1 at 50 C (20 A g-1), which significantly precedes those reported previously.

Interfacial engineering of cobalt sulfide/graphene hybrids for highly efficient ammonia electrosynthesis.

Electrocatalytic N2 reduction reaction (NRR) into ammonia (NH3), especially if driven by renewable energy, represents a potentially clean and sustainable strategy for replacing traditional Haber-Bosch process and dealing with climate change effect. However, electrocatalytic NRR process under ambient conditions often suffers from low Faradaic efficiency and high overpotential. Developing newly regulative methods for highly efficient NRR electrocatalysts is of great significance for NH3 synthesis. Here, we propose an interfacial engineering strategy for designing a class of strongly coupled hybrid materials as highly active electrocatalysts for catalytic N2 fixation. X-ray absorption near-edge spectroscopy (XANES) spectra confirm the successful construction of strong bridging bonds (Co-N/S-C) at the interface between CoS x nanoparticles and NS-G (nitrogen- and sulfur-doped reduced graphene). These bridging bonds can accelerate the reaction kinetics by acting as an electron transport channel, enabling electrocatalytic NRR at a low overpotential. As expected, CoS2/NS-G hybrids show superior NRR activity with a high NH3 Faradaic efficiency of 25.9% at -0.05 V versus reversible hydrogen electrode (RHE). Moreover, this strategy is general and can be extended to a series of other strongly coupled metal sulfide hybrids. This work provides an approach to design advanced materials for ammonia production.

In Situ Electrodeposition of Cobalt Sulfide Nanosheet Arrays on Carbon Cloth as a Highly Efficient Bifunctional Electrocatalyst for Oxygen Evolution and Reduction Reactions.

As one of the advanced cobalt-based materials, cobalt sulfides with novel architecture have attracted huge interest due to the low cost, easy availability, and promising bifunctional activity for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), which is essential for next-generation energy storage devices. Herein, we demonstrated a facile and clean electrochemical technique to directly synthesize CoS nanosheets with high purity onto the surface of carbon cloth, and a quick thermal treatment was performed to further improve the catalytic performance (CoS-A). This novel electrochemical technique avoids the use of the binder, surfactant, and other organic additives, which may cause poor electric conductivity as well as undesirable surface wettability, exhibiting great potential of the large-scale applications. The obtained CoS-A exhibits a superior electrocatalytic performance for the OER and ORR, with a high ORR current density (-1.51 mA cm-2 at 0.2 V), considerable OER current density (148 mA cm-2 at 1.9 V), and excellent durability in continuous measurement for over 12 h. The approach offers a powerful yet simple method to control the phase, composition, and morphology of a highly active CoS catalyst, which provides a new idea for the design of high-performance catalysts.

Sb Nanoparticles Anchored on Nitrogen-Doped Amorphous Carbon-Coated Ultrathin CoSx Nanosheets for Excellent Performance in Lithium-Ion Batteries.

Compared to single-component materials, hybrid materials with various components display superior electrochemical performance. In this work, two-dimensional CoSx@NC@Sb nanosheets assembled by ultrathin CoSx nanosheets (∼4 nm) and a thin layer of N-doped amorphous carbon (NC) combined with colloidlike Sb nanoparticles are designed and synthesized via a solvothermal route accompanied by a carbonization and Sb deposition procedure. If applied in lithium-ion batteries (LIBs), the hybrids exhibit a specific capacity of 960 mA h g-1 at the 100th cycle at 0.1 A g-1. Moreover, the reversible capacity still maintains at 494 mA h g-1 after 500 cycles at a high rate of 10 A g-1. All enhanced electrochemical properties of the hybrids are attributed to the synergistic effect of the two components and their unique structural features, which can effectively increase the electrical conductivity, shorten the pathway of Li+ diffusion, accommodate the volume variation, and inhibit the aggregation and pulverization of the electrode. We believe that the current work can provide a new strategy for designing and fabricating high-performance anode materials for LIBs.

Hierarchical NiCo2 S4 Nanotube@NiCo2 S4 Nanosheet Arrays on Ni Foam for High-Performance Supercapacitors.

Hierarchical NiCo2 S4 nanotube@NiCo2 S4 nanosheet arrays on Ni foam have been successfully synthesized. Owing to the unique hierarchical structure, enhanced capacitive performance can be attained. A specific capacitance up to 4.38 F cm(-2) is attained at 5 mA cm(-2) , which is much higher than the specific capacitance values of NiCo2 O4 nanosheet arrays, NiCo2 S4 nanosheet arrays and NiCo2 S4 nanotube arrays on Ni foam. The hierarchical NiCo2 S4 nanostructure shows superior cycling stability; after 5000 cycles, the specific capacitance still maintains 3.5 F cm(-2) . In addition, through the morphology and crystal structure measurement after cycling stability test, it is found that the NiCo2 S4 electroactive materials are gradually corroded; however, the NiCo2 S4 phase can still be well-maintained. Our results show that hierarchical NiCo2 S4 nanostructures are suitable electroactive materials for high performance supercapacitors.