EFFECTS OF SUBSURFACE OXYGEN ON ELECTRODEPOSITION OF CADMIUM ON COPPER

In aqueous media, the electrochemistry of Cu is complicated by surface layers of native oxides. It is difficult to experimentally control th e growth of these oxide films. These oxides also penetrate into subsur face regions and interfere with other surface reactions. Here, we comb ine potential step experiments with numerical calculations to study su ch an interface in a neutral electrolyte of NaClO4. Both in situ and e x situ sources of surface oxidation are investigated. Electrodepositio n of Cd2+ is studied in the presence of surface oxides on Cu. The depo sition of Cd2+ and catalytic reduction of O-2 affect each other. This complicates direct coulometric measurement of the Cd-coverage. An alte rnative method is demonstrated to determine the coverage isotherm of e lectrodeposition under these conditions. A phenomenological framework is developed to characterize the electrochemical features of the unavo idable surface oxides of Cu. (C) 1998 Elsevier Science Ltd. All rights reserved.