Surface structure and relaxation at the Pt3Sn(111)/electrolyte interface

In situ surface X-ray scattering (SXS) measurements have been performed to determine the surface structure of Pt3Sn(1 1 1) in sulfuric acid electrolyte. Potentiodynamic measurements indicate that the ultra high vacuum (UHV) prepared p(2x2) alloy surface structure is stable upon transfer to electrolyte and remains stable during subsequent cycling of the applied potential. A detailed structural study by crystal truncation rod (CTR) analysis shows that the surface layer of Pt and Sn atoms undergoes an expansion of similar to2% of the (1 1 1) layer spacing at low potential (0.05 V vs. reversible hydrogen electrode) in CO-free electrolyte. At 0.55 V the expansion of the Pt atoms is reduced to similar to0.6%, whereas the Sri atoms are expanded by similar to6% of the layer spacing, The potential-induced buckling of the surface layer is also observed in CO-saturated electrolyte and is a precursor to Sri dissolution which occurs at similar to1.0 V, causing irreversible roughening of the surface. (C) 2003 Elsevier B.V. All rights reserved.