Oxygen electrosorption on copper single crystal electrodes in sodium hydroxide solution

In a study of the initial stages of anodic oxidation of polycrystaUine copper electrodes in alkaline solutions [1 ], we measured potential sweep vol tammetry curves which show that formation of bulk Cu~O is preceded by electrosorption of oxygen species. The electrosorption occurs in two successive stages, each represented by a current peak, corresponding to a different submonolayer state with a different adsorption energy. We postulated that a priori heterogenei ty of the surface, e.g. exposure of various crystal planes, could be an explanation for the occurrence of multiple peaks. In order to test this hypothesis we have investigated the electrosorption of oxygen on carefully prepared copper single crystal surfaces. Clear evidence is found in our results, that the electrosorption of oxygen is a plane specific reaction. Each peak in the vol tammogram on polycrystaUine copper can be at t r ibuted to exposure of regions with specific adsorption sites as present in majority on different single crystal planes.