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

Abstract

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 CoxSy with two different phases, cobalt pyrite (CoS2) and cobalt pentlandite (Co9S8), to explain the influence of material microstructure and properties on electrochemical performance. The as-prepared CoS2 and Co9S8 were investigated as symmetric supercapacitor (SC) devices for potential energy storage applications. Co9S8 exhibited the highest specific gravimetric capacitance of 14.12 Fg(-1) at 0.2 mAcm(-2) with capacitance retention of 91.3% after 10,000 cycles, indicating robust cycling stability. In addition, the Co9S8 SC device showed the highest energy (E) and power (P) density of 9.14 Whkg(-1) and 0.23 kWkg(-1). These results highlight a simple approach of tailoring different phase syntheses of CoxSy structure toward high-performance electrode material for energy storage and conversion.