Oxide Growth and Place-Exchange on Au(111) in Alkaline Electrolyte.

Understanding the oxidation processes of noble metals is essential for the elaborate design of functional and stable materials for electrochemical applications, where electrocatalysis is currently central due to the need for efficient direct energy conversion devices. Single crystalline gold (Au(111)) is an important noble metal standard, as it has high relevance as an electrocatalyst material and is best suited for the study of fundamental surface and interface processes due to its high nobility and the model applicability of the processes at its electrified solid/liquid interface. Under electrochemical conditions, Au(111) oxidation proceeds via a place-exchange mechanism, in which surface Au atoms exchange positions with adsorbed oxygen species. While this process is well studied in acidic media, where it results in the nucleation and growth of adatom and vacancy islands alongside partial dissolution, its behavior in alkaline media remains less explored. Here, we investigate the oxidation of Au(111) in 0.1 M NaOH, providing new insights into the oxidation process and associated surface restructuring mechanisms. Using electrochemical scanning tunneling microscopy, we directly observe the growth of a surface oxide layer across the Au(111) terraces, which reveals the slow, kinetically limited dynamics of the place-exchange process. Once this place-exchange process has occurred, the pristine surface structure is not restored upon electrochemical reduction within experimental time scales, as vacancy islands form and persist. These findings are crucial for developing strategies to mitigate catalyst degradation and enhance the stability of Au-based materials in electrochemical applications.