Reactive Deposition of Cobalt Electrodes: VII . Mechanistic Study in the Presence of Dissolved Oxygen—Calculation of Kinetic Parameters

The effect of the colloid layer on the mechanism and kinetics of cobalt deposition in the presence of dissolved oxygen has been quantitatively investigated. In the presence of oxygen, the reduction of Co2+ ions is a single two‐electron process, and the deposition of cobalt is through a three‐dimensional progressive nucleation and crystal growth mechanism under the diffusion/interfacial electron transfer control, as in the case of absence of oxygen. However, in the presence of oxygen, the kinetics of cobalt deposition are greatly influenced by the dynamic states, i.e., the forming and breaking processes of the colloid layer at the electrode surface, and are related to the reduction of Co2 ions in the presence and absence of a colloid layer. The porous structure of the cobalt electrode formed in the presence of oxygen is directly dependent on the characteristics of localized nucleation and limited crystal growth processes. In the presence of the colloid layer at the electrode surface, the exchange current density and Tafel slope for the reduction of Co2+ions were found to be and 95 mV/decade, respectively. When the inhibiting effect of the colloid layer is eliminated, of and Tafel slope of 30 mV/decade were obtained, which are very close to the values found in the absence of oxygen reported in literature. The electron transfer rate and diffusion coefficient of Co2+ ions are both decreased due to the existence of the colloid layer in the vicinity of the electrode surface.