Structure and dynamics of the interface between a Ag single crystal electrode and an aqueous electrolyte

Abstract

The aim of this work is to elucidate the initial steps of the electrochemical oxidation of Ag(111) in alkaline electrolytes. We use electrochemical as well as ex situ (XPS) and in situ (SHG) spectroscopic techniques to reconstruct the Ag(111)/electrolyte interface as a complex dynamic entity. Moving in the direction from negative to positive potentials we first observe specific adsorption of hydroxide ions, which starts at ca. −1.1 V vs. Ag/Ag₂O in 0.1 M NaOH. SHG data prove that hydroxide retains its negative charge. At −0.3 V oxidation of the surface sets in with the formation of negatively charged adsorbed oxygen species and Ag⁺ ions, which give rise to peaks at 528.2 ± 0.2 eV and at 367.7 eV in the O 1s and the Ag 3d_5/2 XP spectra, respectively. Around −0.1 V the adlayer is transformed into an ordered surface oxide phase which grows via a nucleation and growth mechanism. Above the reversible Ag/Ag₂O potential the 2D Ag(I) oxide transforms into a 3D Ag(I) oxide. The electrochemical oxidation is compared with the previously studied gas-phase process, demonstrating both remarkable similarities as well as some differences.