Role of surface defects in the electrocatalytic behaviour of copper in base

There is increasing evidence, for example, from recently published surface enhanced Raman spectroscopy data, that copper, silver and gold electrode surfaces in base, may exist in an oxidized state at unusually low potentials. In the present work, which was carried out using electrochemical techniques, up to six oxide reduction peaks were recorded for copper in base in the region below 0.6 V vs RHE. One of these peaks, at about -0.6 V vs RHE, was particularly prominent; this occured at a potential 1.0 V more negative than the standard potential for the Cu/Cu2O electrode reaction in aqueous media. Such behaviour is rationalized in terms of the involvement of nonequilibrium (and hence unstable) active states of the metal surface; these states may be regarded as adatoms or minute clusters (the lowering of the redox potential being due to the unusually low lattice stabilization energy of these active metal atoms). Copper and its oxides, especially Cu2O, are of major interest from a catalytic, electrocatalytic, photocatalytic and microelectronics fabrication viewpoint and the involvement of the active states of the metal, as a key ingredient in several of these areas, is outlined.