Hierarchical NiCo₂O₄@CuS composite electrode with enhanced surface area for high-performance hybrid supercapacitors

Hierarchical binder-free NiCo₂O₄@CuS composite electrodes have been successfully fabricated on a nickel foam surface using a facile hydrothermal method and directly used as a battery-type electrode material for supercapacitor applications. The surface morphological studies reveal that the composite electrode exhibited porous NiCo₂O₄ nanograss-like structures with CuS nanostructures. The surface area of the composite is significantly enhanced (91.38 m² g^-1) compared to NiCo₂O₄ (52.16 m² g^-1), with a predominant pore size of 3-6 nm. This synergistic combination enhanced the electrode's electrochemical properties. The NiCo₂O₄@CuS electrode delivered an impressive specific capacitance of 141.13 mA h g^-1 at 1 A g^-1, surpassing the performance of the bare NiCo₂O₄ electrode. The composite electrode also exhibited excellent rate capability and cycling stability, retaining 87.49% of its initial capacity at high current densities and 88.62% after 3000 cycles. A hybrid supercapacitor (HSC) device assembled using NiCo₂O₄@CuS and G-ink electrodes attained a peak energy density of 28.85 W h kg^-1 at a power density of 238.2 W kg^-1, outperforming many reported HSCs. Additionally, the HSC device demonstrated exceptional cycling stability, retaining 87.59% of its initial capacitance after 4000 cycles. The superior performance of the NiCo₂O₄@CuS composite electrode is attributed to the synergistic combination of NiCo₂O₄ and CuS, which promotes interfacial electron separation and facilitates rapid electron transfer.