Proton Transport during Electrodeposition of Cobalt in Chloride Electrolytes

In acid cobalt chloride electrolytes the electrodeposition of cobalt and evolution of hydrogen take place simultaneously. On a rotating platinum disc electrode the current efficiency for cobalt deposition was calculated based on the anodic charge needed for stripping of the cobalt deposits divided by the total cathodic charge. The results showed a decrease in current efficiency with increasing rotation rate. From the partial current density for hydrogen evolution the diffusion coefficient for protons was calculated. The derived diffusion coefficients varied with overpotential and pH, but were always one order of magnitude lower compared to what was expected from literature values. This was attributed to water drag when transporting cobalt ions towards the electrode. The variations in the calculated diffusion coefficients were explained by change in the transfer number when the proton concentration was changed.