Electrochemical study of gold electrodes with anodic oxide films—I. Formation and reduction behaviour of anodic oxides on gold

Abstract

Up to three types of oxide are formed during anodic polarization of gold. The first formed oxides (oxides I and II, surface oxides, inner oxides) can be selectively electrochemically reduced and reformed in the presence of the last formed oxide (oxide III, bulk oxide, outer oxide). It is shown that a second type of oxide (oxide II) is not formed before oxide I reaches a thickness of two monolayers, ie 1.5 mC cm −2 oxide charge. This critical limit is independent of pH, electrolyte, ionic strength, buffer, buffer capacity or surface roughness. A severe influence of insufficient buffer capacity in potentiodynamic surface oxide formation and reduction is experimentally shown, discussed and explained. It is suggested that the onset of oxide II formation can be used for surface roughness determinations.