Synergetic Effect of NiO_x Decoration and Oxygen Plasma Treatment on Electrochemical Capacitor Performance of Vertical Graphene Nanosheets

Vertical graphene nanosheets (VGNs) are emerging supercapacitor (SC) electrode materials due to their well-defined three-dimensional structure and remarkable properties. Although VGNs garnered a lot of attention as potential supercapacitor electrode materials, further enhancement of their electrochemical capacitance performance is of high demand. Herein, we report the enhanced electrochemical capacitance of NiOx/VGN hybrid electrodes. The as-grown VGN exhibited a capacitance value of 0.15 mF cm–2, which was found to increase up to 9 mF cm–2 with NiOx decoration. A further enhancement of capacitance to 16.8 mF cm–2 was observed on oxygen plasma treatment. The spin-polarized ab initio density functional theory (DFT) calculations confirmed charge transfer between the NiOx clusters and VGNs. The charge transfer and in turn the charge redistribution around the NiOx cluster were further enhanced with the oxygen plasma treatment. The enhancement of the capacitance value was correlated with the increase in the Ni2+/Ni3+ ratio, surface charge density, and consequently the pseudocapacitance.