Surface Studies of Cu x Co3 − x O 4 Electrodes for the Electrocatalysis of Oxygen Evolution

The surface properties of the spinel oxide , used as an electrocatalyst for oxygen evolution, were investigated. The oxide was obtained by thermal decomposition of the nitrate precursors, in air, on a nickel substrate. X‐ray photoelectron spectroscopy (XPS) analyses have shown that , and cations are present at the surface of a freshly prepared electrode, octahedral and species being predominant when the oxide is prepared at 300°C. Quantitative analysis has evidenced depletion of the cations at the surface, following a strong anodic treatment in KOH solution, suggesting a preferential dissolution of these species. The resistivity value of 0.047 Ω cm, measured at 25°C on a homogeneous nonporous film, is indicative of semiconductor material. The charge carrier density is . Capacitance measurements reveal a p‐type behavior at the surface with a flatband potential of 0.45 V vs. NHE (normal hydrogen electrode), suggesting that the oxygen evolution takes place on a metallized surface. The coverage of the oxide surface by the adsorbed species is significant at high pH values, but the bond strength is relatively weak. The surface redox transition observed at the electrode prior to the oxygen evolution is ascribed to the oxidation of species to .