Oxygen Evolution at Platinum Electrodes in Alkaline Solutions: I . Dependence on Solution pH and Oxide Film Thickness

The oxygen evolution reaction (OER) at platinum electrodes in alkaline solutions of various p H's is reexamined. The existence of two linear regions is confirmed, each having a different dependence on Pt oxide film thickness and the OH − concentration. At low current densities (c.d.) , and, at high c.d., it is 120 mV/decade. While the rate of the OER is independent of the oxide film thickness at the electrodes at low c.d., it is strongly dependent on the film thickness at high c.d., as shown by the large decrease of the rates at a given potential with increasing film thickness. At low c.d., the reaction order with respect to OH − is two, while, at high c.d., the order is . The fractional reaction order at high c.d., is unusual and cannot be accounted for by any standard mechanism proposed in the literature for the OER. These results show that the mechanism of the OER at platinum in alkaline solutions is complex and still not thoroughly understood.