We have employed x-ray absorption spectroscopy, including surface EXAFS (extended x-ray absorption fine structure) and x-ray standing waves (XSW) in the in-situ structural study of electrochemical interfaces. The SEXAFS technique was used to study the structure of half a monolayer of copper underpotentially deposited on a Pt(111) electrode. From analysis of the data a Cu-Cu distance of 2.85 Å and a coordination number of six were determined, strongly suggesting that the deposit is largely composed of clustered sites. The electrosorption isotherm of iodide on a Pt(111) electrode surface was measured in situ using x-ray absorption spectroscopy, and it exhibited two plateaus which we ascribe to changes in packing density and surface structure. Using x-ray standing waves, we have studied the potential dependence of the adsorption of iodide onto a Pt/C LSM and have interpreted the results in terms of distributional changes in the vicinity of the electrode surface.
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