Dual-phase CoS2/Co3S4 nanostructures for enhanced electrochemical charge storage in symmetric supercapacitors

Abstract

The rational design of nanostructured heterophase materials has emerged as an effective strategy for enhancing charge storage and transport in electrochemical energy-storage systems. Herein, a dual-phase CoS2/Co3S4 nanostructured heterostructure was synthesized via a hydrothermal route and investigated as an electrode material for supercapacitors. Structural characterization confirmed the formation of crystalline CoS2 and Co3S4 phases, while electron microscopy revealed hierarchical micro–nanostructures composed of interconnected nanoparticles that provide abundant electrochemically active interfaces. The electrochemical charge storage behavior was systematically evaluated using cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy in both three- and two-electrode configurations. Detailed kinetic analysis using b-value determination and Dunn’s model demonstrated the combined contribution of surface-controlled and diffusion-governed charge-storage processes. The electrode delivered a specific capacitance of 716.8 F g−1 at 0.5 A g−1 in a three-electrode system. In a two electrode configuration, the symmetric supercapacitor delivered a capacitance of 303.3 F g−1 with an energy density of 2.42 Wh kg−1 at a power density of 60 W kg−1. The device also demonstrated appreciable electrochemical stability with capacitance retention of 90% and 88% after 2000 charge–discharge cycles in three- and two-electrode systems, respectively. The enhanced performance is attributed to heterophase-induced charge-transfer pathways and improved ion accessibility arising from the hierarchical nanostructure. This study highlights the role of intrinsic phase-engineered cobalt sulfide nanostructures in governing electrochemical functionality and provides insights for the development of advanced nanomaterials for next-generation energy-storage technologies.