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The electrochemical performance of hybrid capacitors is seriously affected by the slow charging and discharging of the bulk phase. Here, Co-doped amorphous NiMoS4 modified with reduced graphene oxide (rGO) was prepared by a simple one-step hydrothermal method, and the obtained Co-doped NiMoS4/rGO nanocomposite (Ni1−xCoxMoS4/rGO) exhibits a high specific surface area, realizing the redox reaction from the bulk to the surface. Owing to the doping of Co with abundant redox active sites and the support of rGO sheets with high conductivity and a stable structure, the Ni1−xCoxMoS4/rGO anode assembled with an oxidized needle coke (NCO) cathode shows an excellent energy density of 28.9 W h kg−1 at a power density of 968.3 W kg−1. In addition, the hybrid supercapacitor displays a superior cycling performance with a capacity retention of 92.4% after 10 000 cycles. The construction of the Co-doped NiMoS4/rGO nanocomposite provides an effective strategy to boost the activity and stability of amorphous NiMoS4 for high-performance hybrid supercapacitors. [ABSTRACT FROM AUTHOR]

Constructing a 3D hierarchical structure of electrode materials is a fast-developing technology to meet the increasing demand of high-rate electrochemical capacitors. Here, hierarchical CoNi2S4 nanofibers with pompom-like morphology are successfully synthesized via a two-step anion exchange reaction. The obtained CoNi2S4 nanofibers interweave densely with each other from inner core to external surface, constructing a stable 3D nanostructure. The pompom-like CoNi2S4 nanofibers have a high specific surface area of 169.7 m2 g−1 and a uniform nanopore size distribution in the range of 1–10 nm. Benefiting from these structural features, the pompom-like CoNi2S4 nanofibers provide more effective charge transport during electrochemical reactions compared with other 3D hierarchical structured CoNi2S4, such as flower-like nanosheets and urchin-like nanoneedles prepared by conventional methods. When evaluated as electrode materials in electrochemical tests, CoNi2S4 nanofibers with pompom-like hierarchical structure deliver a high specific capacitance of 2078.9 F g−1 at 0.5 A g−1 and an excellent rate capability of 844.4 F g−1 at 50 A g−1. The assembled CoNi2S4 nanofibers//activated carbon asymmetric electrochemical capacitor exhibits a good energy density of 48.2 W h kg−1 at a power density of 850 W kg−1, and a good cycling stability with 92.6% of its capacitance retained after 1000 cycles, suggesting that the pompom-like CoNi2S4 nanofibers can be applied as promising electrode materials for high-rate electrochemical capacitors. [ABSTRACT FROM AUTHOR]

Nickel phosphate (Ni3(PO4)2) is a promising electrode material for electrochemical capacitors, but the low intrinsic electrical conductivity and poor rate capability of Ni3(PO4)2 are the main challenges. To tackle these problems, amorphous mesoporous Ni3(PO4)2 with a pore diameter of 2–10 nm is grown on reduced graphene oxide (rGO), and a Ni3(PO4)2/rGO composite is obtained via a facile hydrothermal-calcination method in this work. The Ni3(PO4)2/rGO composite calcined at 300 °C (Ni3(PO4)2/rGO-300) possesses a uniform particle size and a high specific surface area of 198.72 m2 g−1. Benefiting from the structural characteristics, the synergistic effect of components and the high specific surface area, the Ni3(PO4)2/rGO-300 composite exhibits an extremely high specific capacitance of 1726 F g−1 at 0.5 A g−1 and an excellent rate capability of 850 F g−1 at 25 A g−1. In addition, the assembled Ni3(PO4)2/rGO-300//activated carbon asymmetric electrochemical capacitor delivers a good energy density of 57.42 W h kg−1 at a power density of 160 W kg−1. Compared with Ni3(PO4)2/rGO composites calcined at other temperatures and other nickel–phosphorus compounds reported in the literature, the Ni3(PO4)2/rGO-300 composite containing amorphous mesoporous Ni3(PO4)2 exhibits superior electrochemical performance, representing a new kind of electrode material for electrochemical capacitors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Amorphous/crystalline H-NiMoS 4 /NiS 2 hollow sphere was successfully constructed. • A high specific capacitance and good cycling performance was obtained. • The capacity retention of HSC was 83.7% after 20,000 cycles. • The HSC displayed a high energy density of 38.6 Wh kg−1 at 958.6 W kg−1. Phase engineering offers a promising strategy to tailor the physiochemical properties to further improve their electrochemical performance toward energy storage. However, it remains a challenge to fabricate well-defined amorphous/crystalline hetero-phase metal sulfides with high-density heterointerfaces. Herein, the synthesis of hetero-phase combination of amorphous NiMoS 4 and crystalline NiS 2 that possesses hollow nanosphere structure decorated by nanosheets (named as H-NiMoS 4 /NiS 2) is reported. Benefiting from the construction of the hollow nanosphere coated by nanosheets, amorphous/crystalline hetero-phase junction, and strong Ni-S hybridization, H-NiMoS 4 /NiS 2 electrode exhibits high specific capacity, outstanding rate capability and excellent cycling stability. Moreover, an all-solid-state supercapacitor was assembled with H-NiMoS 4 /NiS 2 as cathode and needle coke oxide (NCO) as anode, which can achieve remarkably high energy density of 38.6 Wh kg−1 at a power density of 958.6 W kg−1 and outstanding capacity retention of 83.7% after 20,000 cycling. The preparation of novel H-NiMoS 4 /NiS 2 nanomaterial with a hetero-phase of amorphous and crystalline provides a new solution for improving the structural stability and capacitor storage performance as electrodes for supercapacitors. [ABSTRACT FROM AUTHOR]

[Display omitted] 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 NiMoO 4 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 NiMoO 4 -Ag/rGO composite. Benefiting from the synergetic contributions of structural and componential properties, NiMoO 4 -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 NiMoO 4 -Ag/rGO electrode shows an enhanced cycling stability due to the two-dimensional towards two-dimensional (2D-2D) interface coupling between rGO and NiMoO 4 nanosheets, and the stable 3D hydrangea-like micro-architecture. Moreover, NiMoO 4 -Ag/rGO with 5–15 nm pore structure and enhanced conductivity exhibits improved charge transfer and ions diffusion. Besides, NiMoO 4 -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 NiMoO 4 -Ag/rGO composite can provide an effective strategy to solve the poor electrochemical stability and slow electron/ion transfer of NiMoO 4 material as supercapacitors electrode. [ABSTRACT FROM AUTHOR]