Redefinition of the Active Species and the Mechanism of the Oxygen Evolution Reaction on Gold Oxide

Accurately identifying the active species of catalytic materials and understanding how they catalyze the oxygen evolution reaction (OER) are critical for the development of energy storage technologies. In this contribution, we identify two pH-dependent active oxides by mapping the reduction behavior of gold oxide and by in situ surface-enhanced Raman spectroscopy. It was found that alpha-oxide is preferentially formed in an acidic solution, whereas beta-oxide, Au(OH)(3), is preferably formed in an alkaline solution. In line with the presence of two different surface structures on gold, there are two OER mechanisms: one mechanism wherein water splitting occurs via proton-coupled electron-transfer steps mediated by alpha-oxide and the other mechanism wherein electron transfer and proton transfer are decoupled and mediated by a deprotonated form of Au(OH)(3). This identification of pH-dependent oxides offers a different perspective in our understanding of the OER mechanism on metal oxides in a full pH scale range.