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 ß-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.

Experimental and Computational Evidence of Highly Active Fe Impurity Sites on the Surface of Oxidized Au for the Electrocatalytic Oxidation of Water in Basic Media

“…that removal of Fe impurities from alkaline electrolyte results in a decrease in OER activity over Au . Subsequent work by Doyle and Lyons has proposed that “superactive” sites are formed on the surface of an Au electrode during low‐potential cycling in unpurified NaOH . The authors ascribed the increased activity to the formation of highly active hydrous monomeric Au III surfaquo species.…”

Electro-oxidation of a cobalt based steel in LiOH: a non-noble metal based electro-catalyst suitable for durable water-splitting in an acidic milieu

“…These are reasonable efficiencies for the OER upon a non-noble metal based electrocatalyst in highly corrosive media. Anodized AISI 304 steel exhibited in 0.1 M KOH at 10 mA cm −2 75.5% charge-to-oxygen conversion 28 after 4000 s. Noble metal containing catalysts, 44,45 especially IrO 2 -RuO 2 , 21,46,47 are known for their high OER efficiency in the acidic regime. We have chosen commercially available IrO 2 -RuO 2 sputtered on titanium as the reference sample (sample IrO 2 -RuO 2 ) for OER activity and stability at pH 1.…”

Steel-based electrocatalysts for efficient and durable oxygen evolution in acidic media

“…Figure 7c) at pH 1 and leads to a Tafel slope of 149.6 mV dec -1(Figure 7c). Noble metal containing catalysts58,59 , especially IrO 2 -RuO 2 30, 60 are known for its high OER efficiency in acidic regime.Commercially available IrO 2 -RuO 2 (sample Ir-RuO 2 ) outperforms sample Ni42Li205, as can be taken from the Tafel lines of Ir-RuO 2 which were found to be shifted to lower overpotentials by ~ 100 mV at pH 1, by ~ 180 mV at pH 0 respectively(Figure 7c, d). Recently, an overpotential in-between 0.27 and 0.32 V for OER upon IrO 2 at 10 mA cm -2 in 1 M H 2 SO 4 30 and ~ 420 mV in 0.1 M HClO 4 60 was determined and agrees quite well with our values derived from Tafel lines recorded for sample Ir-RuO 2 in 0.5 M H 2 SO 4 (…”