Sulfurization of cobalt oxide to cobalt sulfide: A positrode for the high-performance supercapacitor

The conversion of transition metal oxide to sulfide has attracted researchers in the use of electrochemical energy devices due to their unique features, like highly oriented crystalline nanostructure, high electrochemical active sites, and tailored morphology. Herein, we demonstrate the preparation of binder-free cobalt sulfide (Co3S4) nanostructure by converting hydrothermally synthesized cobalt oxide (Co3O4) on nickel foam using the hydrothermal method. X-ray photoelectron and diffraction analysis confirms the chemical state and phase of Co3S4 after sulfurization process. The FE-SEM analysis reveals the synthesized nanostructures are rod-like morphology for both Co3O4 and Co3S4 grown on Ni foam. The electrochemical performance of the synthesized binder-free electrode was investigated using cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy analysis, which reveals the charge storage mechanism is like faradaic type intercalation and Co3S4/NF electrode reaches areal capacity of 543.7 μAh cm−2 at scan rate of 1 mV s−1 which is approximately 24-folds higher than the Co3O4/NF electrode (22.7 μAh cm−2). The self-discharge study was carried out to identify the factors behind the energy dissipation in the Co3S4/NF electrode. The experimental outcomes disclose insightful information on electrode material prepared via hydrothermal process, and it could accelerate the development of new high-energy density supercapacitor applications.