Optimization of nickel cobalt sulphide nanostructures for supercapacitors application

In this study, nickel cobalt sulphide nanostructures have been synthesized by the hydrothermal synthesis technique at different reaction times of 8 h, 12 h, and 14 h and are named as NCS-I, NCS-II, and NCS-III, respectively. All the nanostructures have been characterized structurally, morphologically, optically and electrochemically, and the best electrochemical behaviour has been exhibited by the NCS-II nanostructure. The crystallite size for the NCS-II sample comes out to be 45.21 nm from X-ray Diffraction, and the specific surface area and pore diameter are calculated to be 35.8 m²/g and 2–16 nm, respectively. The flower-like morphology is exhibited by the NCS-II nanocomposite. As synthesized NCS-I, NCS-II, and NCS-III nanostructures exhibit 2.80 eV, 3.15 eV, and 2.84 eV band gaps, respectively. The supercapacitive behaviour of nickel cobalt sulphide nanocomposites has been studied by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy measurements using FTO Glass and nickel foam as the substrates for electrodes. It has been observed that better electrochemical behaviour is exhibited by NCS structures deposited on Nickel foam substrate due to better conductivity, less electrical resistance, and porous three-dimensional structure of nickel foam. The highest value of energy density has been obtained for the NCS-II nanostructure on Nickel foam (41.1 Wh kg⁻¹ at current densities of 2.6 A g⁻¹) owing to its flower-like morphology. The NCS-II nanocomposite on Nickel foam has retained 74% capacitance after 4000 cycles with a coulombic efficiency of 87.21%, making it an appropriate candidate for flexible supercapacitors.