Mass Transfer of Protons during Electrodeposition of Cobalt in Chloride Electrolytes

Abstract

In acid cobalt chloride electrolytes, the electrodeposition of cobalt and the evolution of hydrogen take place simultaneously. On a rotating platinum disk 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 1 order of magnitude lower compared to what was expected from literature values. This was attributed to water drag when transporting cobalt ions toward the electrode. The variations in the calculated diffusion coefficients were explained by the change in the transfer number when the proton concentration was changed and in the potential gradient when the potential was varied. © 2010 The Electrochemical Society.