Electrochemical studies of lithium tetrasulphide in solution in liquid ammonia

Abstract

Solutions of lithium tetrasulphide in liquid ammonia have been studied with cyclic voltammetric and electrochemical impedance techniques. It has been shown previously from spectroscopic techniques that the S 4 2− polysulphide is partly disproportionated in liquid ammonia. This disproportionation produces the S 3 − radical, in equilibrium with its dimer S 6 2−, together with at least one species more reduced than S 4 2−. Comparison of the experimental data with a theoretical analysis of cyclic voltammetry shows that both electroactive species of a redox couple are present in solution at the equilibrium state. Analysis of the experimental data and numerical simulations shows that we are dealing with a one-electron, moderately fast charge transfer reaction between S 3 − and S 3 2−. It is observed from both experimental techniques that the redox mechanism is influenced by homogeneous chemical reactions (CE mechanism). The chemical reactions coupled with the reduced species, S 3 2−, or with the oxidized species S 3 − are discussed. The concentration of both electroactive species is estimated and is shown to be much lower than the concentration of the solution.