Battery-like supercapacitive behavior of urchin-shaped NiCo2O4 and comparison with NiCo2X4 (X = S, Se, Te)

Abstract

Bimetallic chalcogenides are promising as potential electrode materials for supercapacitors on account of their multiple oxidation states and better electroactivity. Anion effect on the electrochemical performance of urchin-shaped NiCo2X4, (X = O, S, Se, Te) is reported here. These materials crystallize in spinel cubic and monoclinic phases. Electron micrographs show that the materials possess a nanorod-like morphology that protrude from surfaces of microspheres. This gives it urchin-like appearance. Their structure enables ion permeability allowing for improved charge-discharge kinetics. The specific capacities obtained from 3-electrode electrochemical cell measurements are 137 mAh g−1 (492 C g−1), 108 mAh g−1 (390 C g−1), 76 mAh g−1 (272 C g−1) and 72 mAh g−1 (258 C g−1), respectively, for NiCo2O4, NiCo2S4, NiCo2Se4, and NiCo2Te4 at 2 A g−1. An asymmetric Swagelok device is fabricated for each chalcogenide material. Due to well-defined morphology and sufficient specific surface area, NiCo2O4 proved to be the best material delivering a maximum energy density of 34 Wh kg−1 and power density of 6 kW kg−1 followed by NiCo2Te4 delivering 22 Wh kg−1 and 11.25 kW kg−1. Higher electrical conductivity of the telluride-based materials makes them efficient supercapacitor electrodes. Selenium-based materials display better cyclic stability owing to the monoclinic phase.