Preparation and performances of 3D hierarchical core-shell structural NiCo2S4@NiMoO4·xH2O nanoneedles for electrochemical energy storage

Constructing CoNC coordination in Co9S8 embedded N,S-codoped carbon nanotube as an advanced electrode for supercapacitor and Na-ion battery

Yolk-shell-structured transition metal sulfides (TMSs)/carbon nanocomposites are highly desirable in advanced energy storage system, such as sodium-ion batteries (SIBs) and supercapacitors (SCs). Nevertheless, practical applications are still prevented by the loose attachment of TMSs with carbon caused by conversion stress, the aggregation of TMSs nanoparticles and the sluggish ion transport caused by high crystallinity of carbon. Here, the disperse hollow Co9S8 nanoparticles encapsulated into N,S-codoped carbon nanotubes (CNTs) with poor crystallinity through CoNC bond was synthesized (CS-NSCNT) to overcome the above obstacles. The designed CS-NSCNT can provide the short diffusion path and prevent the huge volume expansion of conversion reaction. Moreover, the established CoNC bond endows the strong interaction and regulates the electronic structure thus promote the stability and rate performance effectively. The CS-NSCNT SCs's electrode delivers a high specific capacitance of 1150 F g-1 at 1 A g-1, with a high cycling life stability and rate performance. For SIBs, the CS-NSCNT cathode demonstrates an initial reversible capacity of 475 mAh g-1 at 0.1 A g-1 and an excellent rate performance with a capacity retention of 53 % at 10 A g-1. This work may satisfy the long-stability, high-capacitance/capacity, high-power/energy density application requirements of future applications.

Hydrangea-like NiMoO4-Ag/rGO as Battery-type electrode for hybrid supercapacitors with superior stability

It is a great challenge to design electrode materials with good stability and high specific capacitance for supercapacitors. Herein, a three-dimensional (3D) hydrangea-like NiMoO₄ micro-architecture with Ag nanoparticles anchored on the surface has been designed by adding EDTA-2Na, which was assembled with reduced graphene oxide (rGO) and named as NiMoO₄-Ag/rGO composite. Benefiting from the synergetic contributions of structural and componential properties, NiMoO₄-Ag/rGO composite exhibits a high specific capacitance of 566.4 C g^-1 at 1 A g^-1, and great cycling performance with 90.5% capacitance retention after 1000 cycles at 10 A g^-1. The NiMoO₄-Ag/rGO electrode shows an enhanced cycling stability due to the two-dimensional towards two-dimensional (2D-2D) interface coupling between rGO and NiMoO₄ nanosheets, and the stable 3D hydrangea-like micro-architecture. Moreover, NiMoO₄-Ag/rGO with 5-15 nm pore structure and enhanced conductivity exhibits improved charge transfer and ions diffusion. Besides, NiMoO₄-Ag/rGO//AC capacitor displays an outstanding energy density of 40.98 Wh kg^-1 at 800 kW kg^-1, and an excellent cycling performance with 73.3% capacitance retention at 10 A g^-1 after 8000 cycles. The synthesis of NiMoO₄-Ag/rGO composite can provide an effective strategy to solve the poor electrochemical stability and slow electron/ion transfer of NiMoO₄ material as supercapacitors electrode.

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.

High-performance supercapacitor based on highly active P-doped one-dimension/two-dimension hierarchical NiCo2O4/NiMoO4 for efficient energy storage

Multi-dimensional metal oxides have become a promising alternative electrode material for supercapacitors due to their inherent large surface area. Herein, P-doped NiCo₂O₄/NiMoO₄ multi-dimensional nanostructures are synthesized on carbon clothes (CC) with a continuous multistep strategy. Especially, P has the best synergistic effect with transition metals, such as optimal deprotonation energy and OH^- adsorption energy, which can further enhance electrochemical reaction activity. For the above reasons, the P-NiCo₂O₄/NiMoO₄@CC electrode exhibits an ultra-high specific capacitance of 2334.0 F g^-1 at 1 A g^-1. After 1500 cycles at a current density of 10 A g^-1, its specific capacity still maintains 93.7%. Besides, a P-NiCo₂O₄/NiMoO₄@CC//activated carbon device (hybrid supercapacitor or device) was also prepared with a maximum energy density of 45.1 Wh kg^-1 at a power density of 800 W kg^-1. In particular, the capacity retention rate is still 89.97% after 8000 cycles due to its excellent structural stability. Our work demonstrates the vast potential of multi-dimensional metal oxides in energy storage.

Modish Designation of Hollow-Tubular rGO-NiMoO4@Ni-Co-S Hybrid Core-shell Electrodes with Multichannel Superconductive Pathways for High-Performance Asymmetric Supercapacitors

The scrupulous designation of hollow and porous electroactive materials incorporating prolific redox-active polyphase transition-metal oxide decorated with polyphase transition-metal sulfide onto rGO (reduced graphene oxide)-supported conductive substrate has never been an easy task due to the very good coordination affair of sulfur toward transition metals. Herein, cost-effective hydrothermal growth followed by a metal-organic framework (MOF)-mediated sulfidation approach is employed to achieve burl-like Ni-Co-S nanomaterial-integrated hollow and porous NiMoO₄ nanotubes onto rGO-coated Ni foam (rGO-NiMoO₄@Ni-Co-S) as the electrode material for supercapacitors. The open framework of the rGO-Co-MOF template after the etching and sulfidation process not only enables the creation of a tubular structure of NiMoO₄ nanorods but also provides convenient ion-electron pathways to promote rapid faradic reactions for the hybrid composite electrode. Owing to the unique hollow and tubular structure, the as-fabricated rGO-NiMoO₄@Ni-Co-S electrode exhibits a high specific capacity of 318 mA h g^-1 at 1 A g^-1 and remarkable cyclic performance of 88.87% after 10,000 consecutive charge-discharge cycles in an aqueous 2 M KOH electrolyte on a three-electrode configuration. Moreover, the assembled rGO-NiMoO₄@Ni-Co-S//rGO-MDC (MOF-derived carbon) asymmetric supercapacitor device exhibits a satisfactory energy density of 57.24 W h kg^-1 at a power density of 801.8 W kg^-1 with an admirable life span of 90.89% after 10,000 repeated cycles.

Sponge-like NiCo2S4 nanosheets supported on nickel foam as high-performance electrode materials for asymmetric supercapacitors

Herein, binder-free sponge-like NiCo₂S₄ nanosheets supported on Ni foam with ultra-high mass loading were synthesized via a facile one-step hydrothermal route.