In situ STM study of the initial stages of electrochemical oxide formation at the Ag(111)/0.1 M NaOH(aq) interface

The atomic structure of surface layers and the local changes of surface morphology during the initial stages of anodic oxidation of Ag(111) in an aqueous 0.1 M NaOH solution have been investigated by in situ scanning tunneling microscopy (STM) under different polarization conditions. The surface oxide formation starts at underpotentials, i.e. at electrode potentials E below the Nernst-potential E-3DAg2O (vs. SHE) = 0.4 V for the formation of the three-dimensional (3D) bulk Ag2O phase. An ordered overlayer showing distinct Moire pattern is observed in the potential range -0.1 V < E (vs. SHE) < 0.1 V. The appearance of the Moire structure is assigned to the strong OH adsorption, which induces a stretching of the 2D lattice of the OH-terminated topmost Ag(111) monolayer. In situ STM imaging at higher potentials (0.1 V < E (vs. SHE) < 0.3 V) shows the occurrence of a Ag dissolution process followed by an underpotential oxide formation in agreement with previous electrochemical measurements and in situ X-ray absorption studies. (C) 2003 Elsevier B.V. All rights reserved.