Surface structure and relaxation at the Pt 3Sn(1 1 1)/electrolyte interface

Abstract

In situ surface X-ray scattering (SXS) measurements have been performed to determine the surface structure of Pt 3Sn(1 1 1) in sulfuric acid electrolyte. Potentiodynamic measurements indicate that the ultra high vacuum (UHV) prepared p(2 × 2) 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 ∼2% 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 ∼0.6%, whereas the Sn atoms are expanded by ∼6% of the layer spacing. The potential-induced buckling of the surface layer is also observed in CO-saturated electrolyte and is a precursor to Sn dissolution which occurs at ∼1.0 V, causing irreversible roughening of the surface.