ROTATING-RING-DISK STUDY OF THE INFLUENCE OF PH ON THE CU(II)/CU(I)/CU(O) ELECTRODE-REACTIONS AT GOLD IN AQUEOUS 0.5 M SULFATE-SOLUTION

Depending on pH and copper(II) concentration up to three reduction and four oxidation waves may be observed by cyclic voltammetry at a rotating polycrystalline gold ring-disk electrode in sulphate solution. These are related to the reduction of copper(II) (oxidation of deposited copper metal), to underpotential deposition (dissolution), the deposition (dissolution) of a copper layer adjacent to the underpotential layer and of bulk copper. Analysis of the dependence of the ring currents on electrode rotation rate and copper(II) concentration shows the importance of the dismutation of copper(I). The observed pH effects can be explained by the presence of different hydrated copper(II) species, hydrolysis of copper(I) and the formation of Cu2O on the disk electrode surface.