Effect of oxygen substitution and phase on nickel selenide nanostructures for supercapacitor applications

Abstract

Electrochemical supercapacitors are the eminent technology for the progress of energy storage devices. The current manuscript deals with the formation of oxygen substituted nickel selenide nanostructures and their use as active electrode material for supercapacitor, expecting an enhanced performance owing to their sheet-like geometry, high specific surface area and porous assembly. In this context, Ni(OH)<inf>2</inf> (nickel hydroxide) nanostructures were synthesized employing one-pot hydrothermal method and the ion-exchange reaction of Ni(OH)<inf>2</inf> nanostructures with selenium resulted in cubic-NiSe<inf>2</inf> (nickel selenide) nanostructures. Further, annealing NiSe<inf>2</inf> nanostructures at intermediate pressure (10-3 Torr) has realized the partial oxygen substitution in place of selenium, resulting in NiSe/NiO nanostructures along with phase change from cubic-NiSe<inf>2</inf> to hexagonal-NiSe. Supercapacitor electrodes fabricated using NiSe/NiO nanostructures delivered the specific capacitance of 83.5 F g-1 at the scan rate of 2 mV s-1, which is surprisingly more than a double as compared with pristine NiSe<inf>2</inf> electrodes (37.4 F g-1). Annealing at intermediate pressure and high temperature significantly enhanced the specific capacitances of the nanostructured electrodes and also accompanied with the good capacitance retention of 94% for 5000 CV cycles. © 2018 IOP Publishing Ltd.