Visualization of Electrooxidation on Palladium Single Crystal Surfaces via In Situ Raman Spectroscopy

The electrooxidation of catalyst surfaces is across various electrocatalytic reactions, directly impacting their activity, stability and selectivity. Precisely characterizing the electrooxidation on well-defined surfaces is essential to understanding electrocatalytic reactions comprehensively. Herein, we employed in situ Raman spectroscopy to monitor the electrooxidation process of palladium single crystal. Our findings reveal that the Pd surface's initial electrooxidation process involves forming *OH intermediate and ClO₄⁻ ions facilitate the deprotonation process, leading to the formation of PdO_x. Subsequently, under deep electrooxidation potential range, the oxygen atoms within PdO_x contribute to creating surface-bound peroxide species, ultimately resulting in oxygen generation. The adsorption strength of *OH and the coverage of ClO₄⁻ can be adjusted by the controllable electronic effect, resulting in different oxidation rates. This study offers valuable insights into elucidating the electrooxidation mechanisms underlying a range of electrocatalytic reactions, thereby contributing to the rational design of catalysts.