The oxygen evolution reaction on cobalt Part I. Reaction order experiments and impedance measurements

Abstract

It was found that the oxygen evolution reaction on cobalt in concentrated KOH solutions can be described differently for low and high overpotentials. In the overpotential range from 150 to 280 mV, the reaction has a Tafel slope of approximately 40 mV and a reaction order with respect to the KOH activity at constant overpotential of 0.6; in the overpotential range from 300 to 400 mV, the reaction has a slope of 60–80 mV and a reaction order of 0.3–0.4. The effective capacitance showed a slight maximum at the potential where it is proposed that the character of the rate-determining step changes. By incorporating the water activity (which changes for changing hydroxyl ion activities) in the calculations, an extra diagnostic criterion was obtained. From our results we propose a modified Krasil'shchikov reaction mechanism for the low overpotential region.