Synergistic Effect of Nickel and Cobalt in Nanowire Array for High Energy Storage with Rapid Charge Transfer in Asymmetric Supercapacitor

Abstract We introduce a unique asymmetric supercapacitor design that combines a vertically aligned Ni−Co alloy‐type nanowire ( NiCoNW ) array electrode with a graphene flakes ( GFs ) electrode. The sandwiching of these two electrodes enables the device to operate at a high working potential window of 2.0 V. The improved response of the device is attributed to the asymmetric design and a high charge transfer in the NiCoNWs compared with pure metals. The optimized presence of Co in the alloy increases the rate of hydroxide formation in an alkaline solution during the gas evolution reaction. The use of GFs to modify the graphite electrode ( GFs@Graphite ) provided a more stable response at high current densities. We obtain extremely stable cyclic voltammetry (CV) plots even at very high scan rates (500 V/s) and galvanostatic charge–discharge curves with longer charge–discharge times. The highest capacitance achieved for the assembled device ( Asy‐NiCoNWs/GFs@Graphite ) is 339 F/cm 3 (volumetric) at a current density of 5.0 A/cm 3 . In addition, a remarkable cycling retention of ∼100 % is observed after 10000 continuous potential cycles.