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Free keywords:
Ag(111); Sub-monolayer oxidation; Alkaline electrolyte; Surface enhanced Raman spectroscopy (SERS); X-ray photoelectron spectroscopy (XPS); ultraviolet photoelectron spectroscopy (UPS)
Abstract:
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 (Epzc) of the Ag electrode. These are: OH groups (OHadsγ−) and oxide-like species (Oadsδ−). 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 Oadsδ− and OHadsγ− species are characterised by the O 1s 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 OHadsγ− and Oadsδ− species are negatively charged, as evidenced by the adsorption of Na+ on the Ag electrode positive to the Epzc. A mechanism of the Ag(111) sub-monolayer oxidation is suggested on the basis of combined evidence from cyclic voltammetry, in situ SERS, ex situ XPS and UPS.
