High-Energy All-Solid-State Symmetric Supercapacitor Based on Ni₃S₂ Mesoporous Nanosheet-Decorated Three-Dimensional Reduced Graphene Oxide

The hybrid approach offers opportunities to simultaneously exploit the features of capacitive (especially carbon) and faradaic (redox electroactive) materials to increase energy density and power density of supercapacitors. To achieve an optimized overall electrochemical performance, we have synthesized a hybrid supercapacitor electrode consisting of vertically aligned Ni 3 S 2 mesoporous nanosheets on three-dimensional reduced graphene oxide (Ni 3 S 2 /3DrGO) supported by Ni foam with a controllable composition and morphological structure, which thus improve the electrical conductivity as well as provide more chemical reaction sites and shorten the migration path for electrons and ions. By taking advantage of the rational structural features and excellent electrical conductance ability, the Ni 3 S 2 /3DrGO hybrid nanostructure shows greatly improved electrochemical capacitive performance, including high specific capacitance of 1886 F g –1 (1621 F g –1 ) at current density of 1.0 A g –1 (20.0 A g –1 ) and excellent rate capability and cycling stability. Remarkably, an all-solid-state symmetric supercapacitor fabricated by using our pseudocapacitive hybrid nanostructures delivers a high energy density (58.9 Wh kg –1 ), high power density (3.7 kW kg –1 at 45.8 Wh kg –1 ), and excellent cycling stability (92% capacitance retention after 30 000 charge–discharge cycles at a constant current density of 10 A g –1 ). These electrochemical performances are superior to those of the previously reported symmetric supercapacitors, suggesting that these hybrid nanostructures have a huge potential for high-performance energy conversion and storage devices.