Reduction of Oxide Layers on Au(111): The Interplay between Reduction Rate, Dissolution, and Restructuring

Abstract

Dissolution and redeposition processes determine the stability of electrode materials. In this work, we address these processes in situ during oxidation and subsequent reduction of Au(111) electrodes in an acidic electrolyte (0.1 M H2SO4). We used complementary techniques, namely, electrochemical scanning tunneling microscopy (EC-STM) and on-line inductively coupled plasma mass spectrometry (ICP–MS). We observed that the reduction rate distinctively influences dissolution and the resulting morphology of the surface. Slow reduction leads to formation of monoatomic holes with a diameter of 1–9 nm on the surface. Dissolved Au species formed during reduction are detected in the bulk electrolyte. During fast reduction, however, the formed holes are much smaller and additional two-dimensional Au islands are formed. Almost no dissolved Au was detected in the electrolyte during reduction. We assign the observed differences to competing processes, namely, diffusion of the dissolved Au species into the solution and direct renucleation of dissolved Au.