Battery-like supercapacitive behavior of urchin-shaped NiCo 2 O 4 and comparison with NiCo 2 X 4 (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 NiCo 2 X 4, (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 NiCo 2 O 4 , NiCo 2 S 4 , NiCo 2 Se 4 , and NiCo 2 Te 4 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, NiCo 2 O 4 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 NiCo 2 Te 4 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.