Formation of oxides on copper in alkaline solution and their photoelectrochemical properties

The anodic formation of Cu(I) and Cu(II) oxides on polycrystalline copper in a deaerated alkaline solution is studied using the technique of the synchronous recording of transients of the photocurrent and polarization current. The oxide formation in a currentless mode is analyzed via the synchronous recording of photopotential and corrosion potential. It is found that copper is susceptible to corrosion oxidation due to traces of dissolved oxygen with the formation of a Cu(I) oxide. The preliminary formation of the underlayer of anodic Cu(I) oxide on copper hinders its further corrosion oxidation. It is confirmed that copper oxides Cu₂O and CuO, which appear on copper in both anodic and corrosion modes of formation, are p-type semiconductors. The initial stage of anodic oxidation of copper is characterized by the formation of an intermediate compound of Cu(I), possibly CuOH, which exhibits n-type conductivity. A film of Cu(I) oxide is thin and has a band gap of 2.2 eV for indirect optical transitions. Anodic polarization in the range of potentials of CuO formation leads to the formation of a thicker oxide film, which is a mixture of Cu(I) and Cu(II) oxides.