Rational design of forest-like nickel sulfide hierarchical architectures with ultrahigh areal capacity as a binder-free cathode material for hybrid supercapacitors

Evolution of a simple, efficient and reproducible strategy for the rational design of hierarchically structured metal chalcogenide-based supercapacitors has attracted considerable research interest in recent years. Herein, a facile wet-chemistry approach is employed to design three-dimensional forest-like porous nickel sulfide nanotrees on nickel foam (NiS NTs/Ni foam) for use as a cathode material in hybrid supercapacitors. The growth time plays a crucial role in controlling the surface morphology, and the optimal growth conditions (3 h at 85 °C) led to the growth of forest-like NiS NTs/Ni foam with reliable adherence. The forest-like NiS NTs/Ni foam shows maximum areal and specific capacities of 752.71 μA h cm^-2 and 342.1 mA h g^-1 at a current density of 4 mA cm^-2, with an excellent cycling stability of 89.4%. This result is primarily due to the availability of more surface-active sites in the well-defined hierarchical architecture, which allow the rapid diffusion of electrolyte ions and minimize the electron transport limitation. Utilizing the hierarchical NiS NTs/Ni foam as a cathode and activated carbon-based anode, we further fabricated a hybrid supercapacitor, which demonstrates a wide potential window of 1.6 V with high areal energy and power densities of 0.472 mW h cm^-2 and 21.5 mW cm^-2, respectively. The fabricated hybrid supercapacitor is successfully utilized to drive various electronic gadgets for real-life applications. The electrochemical performance of a hierarchically structured NiS-based binder-free electrode with our facile approach paves a new pathway for the development of novel metal chalcogenides for high-performance hybrid supercapacitors.