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 s pectroscopy (UPS) are used to study the interface between a Ag(111) electro de and an alkaline electrolyte. Formation of a number of potential-dependen t adsorbates is observed above the point of zero charge (E-pze) of the Ag e lectrode. These are: OH groups (OHadsgamma-) and oxide-like species (O-ads( delta-)). Electrochemisorbed hydroxide species show by the appearance of Ra man bands at 540-560 cm(-1) and at 803-819 cm(-1), attributed to Ag-OH stre tching and AgO-H bending vibrations respectively. Strong isotope shift of t he Raman bands towards lower frequencies is observed in D2O solutions, prov ing their assignment. The O-ads(delta-) and OHadsgamma- species are charact erised 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 emer sed electrodes, showing the bands at 3.0 eV typical for the oxide-like adso rbates and 9.0 and 11.1 eV for hydroxo-groups. The OHadsgamma- and O-ads(de lta-) 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 cyc lic voltammetry, in situ SERS, ex situ XPS and UPS. (C) 2000 Elsevier Scien ce Ltd. All rights reserved.