Surface analytical investigations of the electrochemical double layer on silver electrodes in alkaline media

The electrochemical double layer on Ag in aqueous solutions was examined ex situ with X-ray photoelectron spectroscopy (XPS) and UV-photoelectron spectroscopy (UPS). The specimens were removed from the electrolyte with hydrophobic surfaces and under potential control. The potential dependent surface concentrations of the adsorbed anions, cations and the surface excess charge, as well as the amount of adsorbed water were determined. The results obtained for the double layer on Ag in 1 M NaClO4+0.1 Ecl NaOH were compared with an acidic perchlorate solution and pure 1 M NaOH. We found evidence for a specific adsorption of hydroxide ions in the basic electrolyte; i.e, the OH--surface concentration has to be considered for a proper determination of the cationic excess charge and the potential of zero charge. The observed systematic XPS binding energy shifts of the adsorbate species with respect to the metal core levels and the measured work function changes suggest that the electrochemical adsorbates are not in electronic equilibrium with the metal. (C) 1998 Elsevier Science Ltd. All rights reserved.