OXYGEN EVOLUTION ON POTASSIUM TANTALATE ANODES

The electrochemical evolution of oxygen from semiconducting potassium tantalate anodes is interpreted in terms of electron tunneling from surface oxide ions to empty levels in the conduction band as the rate-determining step. The surface ions are replenished by reaction with water molecules. The total density of states is shown to be about one monolayer, but the currents at surface fields up to ca 5.0 × 106 V/cm depend only on a small fraction of these states distributed exponentially in energy above the valence band edge. © 1968.