The anodic oxidation of silver in 1 M NaOH: electrochemistry, ex situ XPS and in situ X‐ray absorption spectroscopy

Abstract

AbstractWe have investigated the electrochemical formation of oxide layers on silver in 1 M NaOH (pH 13.8) using a combination of electrochemical techniques, X‐ray photoelectron spectroscopy (XPS) and surface sensitive grazing incidence X‐ray absorption spectroscopy (XAS). While the XPS experiments were performed after the removal of the samples from the electrolyte and transfer into an ultra‐high vacuum (UHV) system under inert conditions, the XAS experiments were performed in situ and under full potential control. The application of these techniques leads to a detailed, consistent picture of the anodic oxide layer formation process on silver. All the applied techniques proved that the anodic oxidation starts at potentials lower than the corresponding Nernst potential. Extended X‐ray absorption fine structure (EXAFS) investigations suggest that the underpotential Ag+ oxide layer of some few nanometres thickness has a rather disordered structure. Time resolved XPS and EXAFS experiments have shown that the growth of these disordered layers is diffusion controlled, i.e. the thickness increases with the square root of the oxidation time. For moderately higher potentials, i.e. slightly above the Nernst equilibrium potential, the thickness of the silver(I) oxide layer increases rapidly with potential and the structure is very similar to that of crystalline Ag2O. Copyright © 2006 John Wiley & Sons, Ltd.