The mechanism of oxygen evolution at superactivated gold electrodes in aqueous alkaline solution

Abstract

The cathodic superactivation of gold using a repetitive potential cycling procedure is reported, and its significance for the oxygen evolution reaction is discussed. The superactivated surfaces exhibit a transient oxygen evolution response subsequent to monolayer oxidation and prior to extensive visible oxygen evolution. The kinetics of this oxygen evolution process are studied using a variety of transient and steady-state electrochemical techniques. The Tafel slope is shown to decrease with increased activation of the gold surface from ca. 120 to ca. 48 mV dec−1, and the charge transfer kinetics are enhanced by over three orders of magnitude for the superactivated electrodes. A mechanistic scheme involving the formation of monomeric Au(III) hydroxyl complexes of the form Au(OH)6 3− is proposed. The latter are of a transient nature and may be regarded as intermediates in the early stages of hydrous s-oxide growth. These labile species may catalyse oxygen evolution by enhancing the formation of peroxy species that subsequently decompose with loss of oxygen gas from the surface oxide. This novel mechanistic route is in excellent agreement with recent literature studies and has the potential to unite a number of strands in the current understanding of the oxygen evolution reaction at gold surfaces.