Electrochemical reduction of oxygen on gold surfaces: A density functional theory study of intermediates and reaction paths

Electron density functional theory simulations are used to model the electrochemical reduction of oxygen on gold surfaces. Adsorption energies and geometry specifications of various intermediates are reported for gas phase adsorption. The elementary reactions of the electrochemical reduction of oxygen are discussed, including the effects of the electrode potential. A general reaction pathway diagram is presented. It is found that the relative stability of the intermediates, although able to provide insight into the elementary steps, cannot fully describe the observed experimental data of structural selectivity of An(100) and Au(111) electrodes in alkaline solution. To comprehend the complexity of the system, it is suggested that one has to consider in detail the activation energies of the elementary steps including the role of water. By ab initio molecular dynamics simulations including water, it is also shown that water plays an important role in the process of reduction of oxygen via proton exchange, resulting in an intermediate hydroperoxyl OOH and hydroxyl OH on the surface, making OOH one of the most important intermediates in the oxygen reduction reaction.