REACTIVE DEPOSITION OF COBALT ELECTRODES .3. ROLE OF ANIONS

In the presence of bubbling oxygen, the most important effect of anions in the solutions is on the pathways of oxygen reduction during reactive deposition of cobalt. In the presence of Cl− ions, oxygen reduction proceeds mainly through a two-electron process to form HO2 and OH− ions as intermediate products. On the other hand, oxygen is also reduced by a two-electron pathway, but with the formation of H2O2 ions as the main product in the presence of SO4− ions. However, in acetate solutions, a likely mechanism of oxygen reduction is a four-electron pathway with the formation of water. During reactive deposition of cobalt, oxygen reduction takes place prior to the deposition of cobalt and the potential shifts to the cathodic side as compared to the deposition of cobalt in the absence of oxygen. Cobalt deposition processes and the porous structure of cobalt electrodes are therefore directly affected by the pathways of oxygen reduction. © 1990, The Electrochemical Society, Inc. All rights reserved.