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The extent of surface oxidation of a smooth platinum electrode and the electrode capacitance were measured for various conditions of anodization. The electrolytic formation of the surface platinum oxide is shown to be a highly irreversible reaction. A mechanism which involves a hydroxyl radical intermediate of the oxygen evolution reaction is proposed for the surface oxide formation reaction. This mechanism is supported by the shapes of the anodic and cathodic charging curves on platinum and the interrelationships of the electrode potential, the electrode capacitance, and the extent of surface oxidation. From these same interrelationships it was also concluded that the steady‐state evolution of oxygen occurs on a surface which has at least one atom of oxygen per surface platinum atom and that the rate‐determining step in the oxygen evolution reaction is the electrolytic discharge of oxygen‐containing radicals which are adsorbed on the electrode surface. The surface oxide is reduced at potentials several hundred millivolts cathodic to the potential required to form the oxide. The reduction of the surface oxide is shown to be a first order reaction. The rate of the reduction increases with increasingly cathodic electrode potential.
Laitinen et al. (Fri,) studied this question.