THE PARTICIPATION OF INTERFACIAL HYDROUS OXIDE SPECIES IN SOME ANODIC REACTIONS AT COPPER ELECTRODES IN BASE

The anodic behavior of copper is surprisingly complex as this element can exhibit 4 (0, +1, +2, +3) oxidation states and most of its oxides can exist in two distinct forms, anhydrous and hydrated. Hydrous oxides in general have been widely ignored, but an appreciation of their properties is essential for a complete understanding of the behavior of metals. In the present case attention was focused on the behavior of copper in base at low potentials where a minor Cu adatom/ Cu(I) hydrous oxide transition seemed to occur. Evidence for the latter included the observation that an oxide reduction peak occurred under certain conditions at ca. 0.05V (RHE); this is significantly lower than the usual value for Cu2O, Cu(OH)2, or CuO reduction. Furthermore, the same value was observed for the onset (anodic sweep)/termination (cathodic sweep) potential for other reactions on copper in base, e.g., formaldehyde oxidation or copper dissolution in the presence of CN− ions. As in the case of previous work with other metals, the response for low-coverage hydrous oxide formation on copper in base is not obvious on the anodic sweep in cyclic voltammetry experiments; however, prior data from ac work provide evidence for the type of effect postulated here. The behavior of copper, as may be expected, bears a distinct similarity to that of silver and gold; similar proposals were made recently for the latter metals. The catalytic activity of copper in base at higher potentials is attributed to mediation of interfacial processes by other redox transitions in this system. © 1990, The Electrochemical Society, Inc. All rights reserved.