Redox equilibria in the In(III)-In(I)-In system in aqueous KBr solutions II. A rotating ring-disc electrode study

Abstract

The open-circuit behaviour of thick indium films formed onto gold by the electroreduction of In(III) has been investigated in acidified aqueous KBr solutions using the rotating ring-disc electrode technique. The spontaneous dissolution of indium metal immersed in the solution containing its own ions of higher valency yields In(I) ions. Information about the equilibrium and mechanism of the process studied was drawn from measurements of the limiting ring current and disc potential as a function of the electrode rotation rate. It was proved that the overall reaction 2In+In(III)⇄3In(I) occurs as a coupling of two electrochemical steps: In⇄In(I)+e−, and In(III)+2e−⇄In(I). The cathodic half-reaction is the rate-determining step, whereas the anodic half-reaction is reversible.