Phase-Dependent Electrochemical Performance of CoS (x = 1,9; y = 2,8) for Symmetric Supercapacitor Application.

Modulating the oxidation states of transition metal species is a practical approach to enhance redox activity and increase the number of active sites in electrode materials. Herein, we describe a simple one-step hydrothermal approach to prepare CoS with two different phases, cobalt pyrite (CoS) and cobalt pentlandite (CoS), to explain the influence of material microstructure and properties on electrochemical performance. The as-prepared CoS and CoS were investigated as symmetric supercapacitor (SC) devices for potential energy storage applications. CoS exhibited the highest specific gravimetric capacitance of 14.12 Fg at 0.2 mAcm with capacitance retention of 91.3% after 10,000 cycles, indicating robust cycling stability. In addition, the CoS SC device showed the highest energy (E) and power (P) density of 9.14 Whkg and 0.23 kWkg. These results highlight a simple approach of tailoring different phase syntheses of CoS structure toward high-performance electrode material for energy storage and conversion.