On the mechanism of Ag(111) sub-monolayer oxidation:: a combined electrochemical, in situ SERS and ex situ XPS study

In the present work in situ surface enhanced Raman spectroscopy (SERS), ex situ X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) are used to study the interface between a Ag(111) electrode and an alkaline electrolyte. Formation of a number of potential-dependent adsorbates is observed above the point of zero charge (E-pze) of the Ag electrode. These are: OH groups (OHadsgamma-) and oxide-like species (O-ads(delta-)). Electrochemisorbed hydroxide species show by the appearance of Raman bands at 540-560 cm(-1) and at 803-819 cm(-1), attributed to Ag-OH stretching and AgO-H bending vibrations respectively. Strong isotope shift of the Raman bands towards lower frequencies is observed in D2O solutions, proving their assignment. The O-ads(delta-) and OHadsgamma- species are characterised by the O Is peaks at ca. 529.5 and 531.6, respectively. Formation of the above-mentioned species is verified also by the UP spectra of the emersed electrodes, showing the bands at 3.0 eV typical for the oxide-like adsorbates and 9.0 and 11.1 eV for hydroxo-groups. The OHadsgamma- and O-ads(delta-) species are negatively charged, as evidenced by the adsorption of Na+ on the Ag electrode positive to the E-pzc. A mechanism of the Ag(lll) sub-monolayer oxidation is suggested on the basis of combined evidence from cyclic voltammetry, in situ SERS, ex situ XPS and UPS. (C) 2000 Elsevier Science Ltd. All rights reserved.