Thickness and Chemistry of Electrochemically Formed Oxide Films on Au(111) Probed with Ambient Pressure X-ray Photoelectron Spectroscopy

High Resolution Image Download MS PowerPoint Slide The increasing demand for advances in efficient electrochemical (EC) energy conversion requires a fundamental understanding of the EC interface, which is challenging to study in situ. High-resolution ambient-pressure X-ray photoelectron spectroscopy, in combination with an EC cell, has been used in a dip-and-pull approach to study the EC oxidation of a Au(111) model electrode during oxidation and water electrolysis conditions. The behavior of Au(111) in 0.05 M H 2 SO 4 was studied in a controlled gaseous environment of ∼13 mbar of water vapor after fully withdrawing the sample from the electrolyte at increasing anodic potential steps. Above 1.5 V RHE, a thin 2D Au(OH) 3 film of ≈ 5 Å is observed and exhibits a stable thickness until the onset of the oxygen evolution reaction (OER, ≈ 1.8 V RHE ). From the onset of OER, a thicker bulk-like 3D Au(OH) 3 /Au 2 O 3 mixture rapidly grows to a thickness of ≈ 21 Å at 2.02 V RHE . The initial 2D film exhibits self-limited kinetics, typically described by the Cabrera–Mott model and the point-defect model. The subsequent rapid growth of thicker bulk-like 3D islands suggests a disruption of the passive state coupled with the onset of OER. These results highlight surface passivation, which inhibits further oxidation due to surface oxidation, and provide quantitative and detailed insights into changes in the surface chemical composition of Au(111) under anodic polarization.