Dimitry Zemlyanov

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

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 ( E pzc ) of the Ag electrode. These are: OH groups (OH ads γ − ) and oxide-like species (O ads δ − ). 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 D 2 O solutions, proving their assignment. The O ads δ − and OH ads γ − 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 OH ads γ − and O ads δ − 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(111) sub-monolayer oxidation is suggested on the basis of combined evidence from cyclic voltammetry, in situ SERS, ex situ XPS and UPS.

Effect of oxygen on NO adsorption on the Ag(111) surface: evidence for a NO3,ads species

The formation of a AgNO3 layer revealed by O 1s and N 1s spectra was observed after exposure of the Ag(1 1 1) surface to a NO/O2 mixture at 330 K and pressures in the mbar range; at lower pressure no N-containing complexes form. The AgNO3 layer decomposes in vacuum at 450 K resulting in the formation of a highly stable Oγ species. The Oγ species changes the reactivity of the silver surface to NO adsorption. The NO3,ads species is found on the surface after an exposure of Oγ/Ag(1 1 1) to NO.