Hierarchical NiS@CoS with Controllable Core-Shell Structure by Two-Step Strategy for Supercapacitor Electrodes

Constructing hierarchical core-shell configuration from well-known metal sulfides is one way to further tune and utilize unique species. Herein, a novel core-shell structure is developed based on CoS deposited on NiS nanosheets, which involves hydrothermal and electrodeposition method. The micromorphology of the composite electrode can be optimized by adjusting the cycles of electrodeposition. Taking advantages of the highly conductive, open framework of the core-shell nanolayer, the 5-NiS@CoS electrode shows a specific capacitance of 1210 F g(-1) at a current density of 1 A g(-1) (retaining 82% from 1 to 10 A g(-1), while NiS substrate is only 39%). The specific capacitance retention rate is 80.94% at 10 A g(-1) after 2000 cycles (NiS substrate is 59.6%). Moreover, NiS@CoS//AC asymmetric supercapacitor device delivers an energy density of 24.1 Wh kg(-1) at a power density of 752.15 W kg(-1) and remarkable stability (over 80% retention after 5000 cycles). This work may prompt the exploration of the synthesis of inexpensive compounds incorporating highly reactive components for supercapacitors.