Evolution of Intermediates on Metal Oxide Photoanodes in a Full pH Range
Xing Ji, Yinqing Ou, Lu Huang, Li‐Yong Gan, Yunhuai Zhang, Peng Xiao
Abstract
Understanding the function of intermediates generated at the photoanode/electrolyte interface is crucial for unraveling the reaction mechanisms and enhancing the efficiency of oxygen evolution reaction (OER). Previous studies have recognized one type of intermediate M═O on Fe 2 O 3 in near-neutral electrolytes and verified it as the active species. Herein, we investigate the intermediates on metal oxides, including TiO 2, Fe 2 O 3, and WO 3, using operando infrared spectroscopy and in situ light–dark electrochemical scans in a full pH range. We identified the low valence M–OH species at the metal oxide/electrolyte interface in pH = 11∼13, as well as the high valence M═O species in pH = 1∼11. Density functional theory calculations point to a strong influence of the protonation or hydroxylation on the stability of the intermediates, resulting in the evolution of intermediates under different pH. We demonstrate the double role of M–OH intermediates which trigger recombination in near-neutral electrolytes and serve as an active center under high alkaline conditions, thus mediating the OER performance and making the reaction transition from single-site to multisite mechanisms as the pH increases. Our work provides a significant reference for understanding the relationship between the OER catalytic mechanism and the performance of photoanodes based on the clarification of the intermediates.