Identification of hydroperoxy species as reaction intermediates in the electrochemical evolution of oxygen on gold.

Efficient electrochemical splitting of H2O to O2 and H2 fuels has become an important goal in the quest for a renewable source of energy. A major source of the inefficiency of this process is the significant overpotential associated with the anodic oxygen evolution reaction (OER). Understanding the mechanism of the OER could help in identifying the elementary processes contributing to OER overpotential and their relationship to the anode composition and morphology. While the OER has been investigated both experimentally and theoretically for over 50 years, its mechanism and the identity of the chemical intermediates involved remain uncertain. Two principal pathways have been postulated for the OER on metal surfaces, such as gold (Au). The first involves a direct recombination of oxygen atoms to give O2, as shown in Equations (1)–(4): Mþ H2O ! M OHþ Hþ þ e ðIn acidsÞ ð1Þ M OH ! M Oþ Hþ þ e ðM 1⁄4 metal site, e 1⁄4 electronÞ ð2Þ M OHþM OH ! M Oþ H2OþM ð3Þ M OþM O ! O2 þ 2M ð4Þ