In Situ Surface Extended X-ray Absorption Fine Structure Spectroscopy of a Lead Monolayer at a Silver(111) Electrode/ Electrolyte Interface

Abstract

With use of fluorescence detection and grazing incidence excitation, the X-ray absorption spectrum was obtained, at the PbL111edge, of a monoatomic adlayer of lead on a silver( 111) electrode immersed in solution. The adlayer was produced by underpotential deposition from aqueous lead acetate/sodium acetate electrolyte. The edge position and the near-edge structure confirm that the lead is fully reduced to the zerovalent state. The extended X-ray absorption fine structure (EXAFS) contains no detectable contribution from lead-silver scattering, either because the lead layer is incommensurate with the underlying silver lattice or because there is large thermal motion of the lead atoms. Instead, the fine structure is due to scattering from a single type of light atom, most likely oxygen. This oxygen must arise from adsorbed water molecules or acetate ions. The lead-oxygen distance changes with the electrode potential from 2.33 ± 0.02 A at -0.53 V to 2.38 ± 0.02 A at -1 V (vs. Ag/AgCl, 3 M KC1). © 1987, American Chemical Society. All rights reserved.