Effect of electrolyte cations on electrochemical performance of pseudocapacitive CuS electrode

Abstract

In the emerging field of electrochemical energy storage devices (EESDs), lithium (Li) ion-based EESDs are currently dominant. However, due to the high cost and lack of Li resources, researchers and industries look forward to replace Li with low-cost, safe, and highly abundant elements. Nowadays, immense research work on sodium (Na+), magnesium (Mg2+), and potassium (K+) ion–based EESDs are going on to replace Li-based EESDs. For any EESDs, the selection of a good electrolyte is a crucial task. The interaction of any ions with the electrode materials depends on the ionic radii, hydrated sphere size, conductivity, viscosity, and other parameters of selected electrolyte ions. In this manuscript, we explored the electrochemical behaviour of cationic species of various electrolytes (such as Na2SO4, MgSO4, K2SO4, and Li2SO4) with pseudocapacitive copper sulphide (CuS) electrodes. CuS is synthesized by a simple wet chemical route and characterized by various analytical techniques. Cyclic voltammetry and charge–discharge studies reveal that cations of each electrolyte are uniformly participating in the reduction and oxidation process. The rising trade of capacitance is observed with cations Li+\u2009<\u2009K+\u2009<\u2009Mg2+\u2009<\u2009Na+. Pseuodocapacitive contribution profile of CuS with each electrolyte confirming that the charge storage mechanism of cations is mainly controlled by both diffusion and capacitive process. The electrochemical impedance spectroscopy profile of the examined electrolytes reveals that the Na+ ions show a low charge transfer resistance (2.497 Ω) as compared to others, which conclude that the Na+ ion–based electrolyte is an appropriate choice for the EESDs.