Pulse reverse electrodeposited nickel cobalt sulfide nanosheets on Ni foam as battery-type electrode for battery supercapacitor hybrids

Nickel cobalt sulfide (NiaCobS) is one of promising active materials for battery supercapacitor hybrids (BSH), owing to the bimetallic nature and high electronegativity of sulfide. Electrodeposition technique is well applied to grow nanomaterials on conductive substrate since it is simple and the uniform deposition is easy to obtain. Other than normal parameters like applied potentials, currents, durations, and electrolyte compositions, the pulse reverse electrodeposition (PRE) technique is another promising way to fabricate nanomaterials on conductive substrates with repeated cathodic/anodic depositions. In this study, the PRE technique is firstly proposed to fabricate NiaCobS nanosheets on Ni foam as the battery-type electrode for BSH. The vertical grown NiaCobS nanosheet array is successfully fabricated with sizes and densities varied by applying different PRE cycles. The optimized NiaCobS electrode shows a specific capacitance (CF) of 1.75 F/cm(2) at 5 mV/s, due to the suitable size and density of the nanosheet array to provide numerous active sites for generating redox reactions. This optimized electrode also presents excellent high-rate capacity with the CF retention of 65% at eight-fold scan rate and current density enhancements. At power density of 6 mW/cm(2) the maximum energy density of 1.25 mu Wh/cm(2) as well as the C-F retention of 88% and Coulombic efficiency higher than 90% in 6500 times charge/discharge process are also achieved for the BSH composed of the optimized NiaCobS electrode and the activated carbon electrode.