Abstract
Nickel–cobalt sulfide is a promising material for supercapacitor positive electrodes due to its high theoretical capacitance. Herein, the electrochemical properties of nickel–cobalt sulfide nanostructures synthesized via a two‐stage hydrothermal method are investigated and the synthesis conditions to achieve high mass loading while maintaining high specific capacitance are determined. The nanostructural morphology and effective mass loading of the electrodes (≈10 mg cm−2) enable the achievement of a high specific capacitance value of 8.1 F cm−2 at a current density of 5 mA cm−2. A hybrid capacitor is made using optimized nickel–cobalt sulfide electrodes as the positive electrode and activated carbon as the negative electrode. The device exhibits a maximum operation potential window of 1.75 V and an energy density of 51.2 Wh kg−1 at a power density of 262.5 W kg−1. Electrochemical measurements demonstrate that the device maintains a capacitance retention rate of 95% after 10 000 charge–discharge cycles within a working voltage of 1.8 V. High electrochemical performances compared with others devices‐based water electrolytes make it promising for the energy storage device.