REACTIVE DEPOSITION OF COBALT ELECTRODES .2. ROLE OF BUBBLING OXYGEN

The role of bubbling oxygen in the deposition of cobalt in cobalt chloride solutions has been investigated using a rotating ring-disk electrode. In the presence of bubbling oxygen, oxygen reduction takes place prior to the deposition of cobalt, and the potential shifts more than 100 mV to the cathodic side for the cobalt deposition as compared to the deposition of cobalt in the absence of oxygen. In the presence of Cl− ions, oxygen is mainly reduced through the formation of OH− and HO2− ions as intermediate products. The rate of the O2 reduction is controlled by the oxygen partial pressure in the bubbling gases. During reactive deposition of cobalt, the HO2− ions are decomposed by Co(OH)2 which is oxidized to form various cobalt oxides. Cobalt is mainly deposited through further reduction of cobalt oxides such as CoOOH and codeposition of Co2+ ions with cobalt oxides/hydroxides as intermediates. This process is responsible for the formation of the high surface area and highly porous cobalt structure. © 1990, The Electrochemical Society, Inc. All rights reserved.