ELECTROCHEMICAL STUDIES OF LITHIUM TETRASULFIDE IN SOLUTION IN LIQUID-AMMONIA

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 S42- polysulphide is partly disproportionated in liquid ammonia. This disproportionation produces the S3- radical, in equilibrium with its dimer S62-, together with at least one species more reduced than S42-. 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 S3- and S32-. 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, S32-, or with the oxidized species S3- are discussed. The concentration of both electroactive species is estimated and is shown to be much lower than the concentration of the solution. © 1990.