Influence of Electrode Material on Oxygen Overvoltage: A Theoretical Analysis

Variations of overvoltage for oxygen evolution from one metal to another primarily result from variations in the energy of the bond M–OH. The overvoltage decreases approximately in a linear manner with increasing bond energy. This relationship is verified experimentally for Ag, Au, Cd, Co, Cu, Fe, Ni, Pb, Pd, and Pt, for electrolysis in one N potassium hydroxide at one amp cm—2; the experimental data are those reported by Hickling and Hill. Bond energies for M–OH are calculated by three different thermodynamic cycles involving, respectively, the standard heat contents of the hydroxide, the oxide, and spectroscopic data for molecules MO. Variations of the energy of the bond M–OH, as the electrode is oxidized to a higher valence, also account for sudden breaks in plots of overvoltage against logarithm of current density. Finally, there is essentially no correlation between the oxygen overvoltage for different metals and the corresponding work functions.