In situ CO oxidation on well characterized Pt 3 Sn(hkl) surfaces: A selective review V. Stamenkovic ´ * , M. Arenz, B.B. Blizanac, K.J.J. Mayrhofer, P.N. Ross, N.M. Markovic ´ Materials Sciences Division, Lawrence Berkeley National Laboratory, University of California, 1 Cyclotron Road, MS 2R 100, Berkeley, CA 94720, United States Received 22 September 2004; accepted for publication 14 December 2004 Available online 5 January 2005 Abstract Bimetallic single crystals Pt 3 Sn(110)andPt 3 Sn(111) have been characterized for in situ CO oxidation. Surface com- position and structure were established in ultra high vacuum (UHV) by Auger electron spectroscopy, low energy ion scattering spectroscopy (LEISS) and low energy electron diffraction (LEED). LEED patterns of Pt 3 Sn(hkl) are consis- tent with the surface composition, determined by LEISS, of 25 or 50 at.% Sn. Following UHV characterization crys- tals were transferred into the electrochemical environment where surface electrochemistry of adsorbed CO was studied in situ by infrared spectroscopy. Changes in band morphology and vibrational properties: splitting of the band and increase in the frequency mode, were found on Pt 3 Sn(hkl) and correlated to Pt(hkl) surfaces. Continuous oxidative removal of adsorbed CO starts as low as E < 0.1 V, which is an important property for CO-tolerant catalysts. In addi- tion to electronic effects, other factors, such as surface structure and intermolecular repulsion between adsorbed species are responsible for high catalytic activity of Pt 3 Sn(hkl) alloys. Ó 2005 Elsevier B.V. All rights reserved. Keywords: CO oxidation; PtSn alloy; Surface composition/structure; In situ FTIR spectroscopy; Metal–electrolyte interfaces 1. Introduction The opportunity to study in situ electro- oxidation of carbon monoxide [1–8] under fuel cell reaction conditions has brought significant progress in understanding of interfacial electro- chemistry on metallic surfaces. In combina- tion with conventional electrochemical methods these techniques have been used to find con- nections between the microscopic surface struc- tures and the macroscopic kinetic rates of the reactions. 0039-6028/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.susc.2004.12.018 * Corresponding author. Tel.: +1 5104864793; fax: +1 5104865530. E-mail address: vrstamenkovic@lbl.gov (V. Stamenkovic ´). Surface Science 576 (2005) 145–157 www.elsevier.com/locate/susc