Eco-Friendly and Sustainable All-Green Synthesized NiCoS@CuO//AC Nanocomposite Electrode with Redox Mediator Electrolytes for High-Performance Energy Storage and Hydrogen Evolution Reaction Devices

An innovative NiCoS@CuO nanocomposite electrode material for hybrid supercapacitors (HSCs) is described. Environmentally friendly methods, such as neem leaf extract for CoS, Moringa oleifera leaf extract for NiS, and apple extract for CuO, are used in its synthesis and characterization. The electrochemical composite had a much higher specific capacity of 1353.44 C/g compared to the NiCoS electrode's 1021.24 C/g. Electrochemical performance was enhanced by the addition of a redox mediator (hydroquinone) to the electrolyte, which enhanced pseudocapacitive behavior and facilitated quicker electron exchange. After 5,000 cycles, the composite still had 88.2 percent of its original capacity, proving its remarkable cycling resilience. Further, the hybrid asymmetric supercapacitor (ASC) device achieved 282.3 C/g at 1.6 A/g, 41.53 Wh/kg energy density, and 1656.16 W/kg power density. The device was constructed using activated carbon (AC) serving as the negative electrode and NiCoS@CuO as the positive electrode. The NiCoS@CuO composite demonstrated encouraging results as an electrocatalyst for the hydrogen evolution process with a low overpotential of 35 mV and a Tafel slope of 38 mV/dec. These results show that NiCoS@CuO has great potential as a high-performance and efficient energy storage material for application in the production of renewable energy.