Phase-Dependent Electrochemical Performance of CoxSy (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 Co_xS_y 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 Co_xS_y structure toward high-performance electrode material for energy storage and conversion.