Electrode-Electrolyte Interfaces Investigated with X-Ray Standing Waves: Cu(111)/Pb, Tl

Abstract

We report on the results of the in-situ structural characterization of underpotential deposited Tl and Pb on Cu(ll1) electrodes with x-ray standing waves. These measurements show that submonolayer amounts of Tl and Pb are adsorbed at a distance normal to the Cu(111) surface, which is consistent with a threefold coordinated adsorption site for both, Tl and Pb. On oxidized Cu(111) surfaces, the adsorbate relaxes inward by ab out 0.3 A in both cases. This can be under- stood by oxygen incorporation into the Cu(ll1) surface for which a model is proposed. Oxidation and reduction of the Cu electrodes can be controlled by the electrode potential and were monitored by cyclic voltammetry. The x-ray standing wave technique is explained briefly in particular with respect to its application towards the characterization of electrode-electrolyte interfaces.