Electrochemical Characteristics of the Copper(II)-Copper(I) Redox Couple in Dimethyl Sulfoxide Solutions

Abstract

A study of the electrochemical characteristics of the copper(II)/copper(I) redox couple has been made in chloride and bromide media in dimethyl sulfoxide (Me₂SO) and their aqueous analogues. The formal potentials of the Cu^II/Cu^I couple in the Me₂SO media are approximately 0.15 V less positive than in their aqueous counterparts probably due to a combination of solvation and complexation effects. Diffusion coefficients for both Cu^I and Cu^II are 5-10 times lower in Me₂SO than in H₂O as a result of the higher viscosity of Me₂SO solutions. Heterogeneous electron-transfer rate constants for the Cu^II/Cu^I system on platinum are also an order of magnitude smaller than in aqueous solution. In general the electrochemical characteristics of the Cu^II/Cu^I system parallel those reported elsewhere for the Fe^III/Fe^II couple. However, a detailed investigation of the Cu^II/Cu^I system by cyclic voltammetry indicates that the overall electrode process is complex, probably involving a quasi-reversible electron-transfer step coupled to a rate-determining loss of Cl ^- from Cu^II.