Morphology-Tailored NiS ₂ @gCN Composite for Enhanced Hybrid Supercapacitor Performance

Supercapacitors are emerging as key technologies to meet the growing demand for efficient energy storage. Nickel-based sulfides exhibit excellent potential in supercapacitor applications due to their unique physicochemical properties. In this study, a controllable and efficient strategy was developed to synthesize nickel disulfide (NiS2) hollow microspheres via a hydrothermal process. These were subsequently embedded in a graphitic carbon nitride (gCN) conductive matrix (NiS2@gCN) through mechanical grinding. Comprehensive structural, morphological, and spectroscopic analyses confirmed the synergistic interactions between NiS2 and gCN. Electrochemical evaluations using galvanostatic charge–discharge, cyclic voltammetry, and electrochemical impedance spectroscopy demonstrated battery-type hybrid supercapacitor behavior. The NiS2@gCN electrode delivered a high specific capacity of 514 C/g, outperforming those of pristine NiS2 (370 C/g) and gCN (162 C/g). Furthermore, the NiS2@gCN system achieved an energy density of 118 Wh/kg and a power density of 1307 W/kg with excellent cycling stability. These results highlight the NiS2@gCN composite as a promising electrode material for high-performance battery-type hybrid supercapacitors.