Surface Science 416 (1998) 371–383 Monte Carlo simulation of CO adlayers electrooxidation on Pt(111) J.M. Orts a,*, E. Louis b, L.M. Sander b,1, J.M. Feliu a, A. Aldaz a, J. Clavilier c a Departamento de Quı ´mica Fı ´sica, Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain b Departamento de Fı ´sica Aplicada, Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain c Laboratoire de Physico-Chimie de Surfaces (URA 425), Universite ´ Pierre et Marie Curie, Ecole National Superieure de Chimie, Paris, France Received 5 February 1998; accepted for publication 25 June 1998 Abstract Numerical simulations of the electrooxidation of CO adsorbed on Pt(111) surfaces are presented. For adlayers prepared by CO dosage, the numerical results confirm previous proposals, based upon current experimental information, concerning the CO distribution on the Pt surface. Specifically, whereas at low coverages (below 1/3) CO forms open and easily oxidizable structures, at high coverages compact domains hinder the oxidation process. The two peaks observed in the voltametric profiles are thus a consequence of topological differences between the CO distributions at low and high coverages. We also present new experiments on the electrooxidation of CO adsorbed on Pt(111) upon the dissociative adsorption of formic acid. In this case our results indicate that a single oxidation peak remains up to coverages below 2/3. This striking new result is also reproduced in our simulations by taking the same kinetic parameters as in the previous case, and assuming that the CO are distributed on a honeycomb lattice, an assumption consistent with the characteristics of the dissociative adsorption of formic acid. © 1998 Elsevier Science B.V. All rights reserved. Keywords: Carbon monoxide; Computer simulations; Metal–electrolyte interfaces; Models of surface chemical reactions; Platinum; Single crystal surfaces 1. Introduction important development of the electrochemistry of well-defined single crystal metal surfaces. A number of experimental techniques have been The electrochemistry of well-defined surfaces has applied to the study of the electrode surface, undergone a significant improvement as a result especially interesting are those applicable under in of the development of relatively simple techniques situ conditions. In particular, scanning tunneling for the preparation and handling of single crystal microscopy (STM ) [3], surface X-ray scattering electrode surfaces [1,2], ensuring conditions of (SXRS) [4], and Fourier transform infrared high cleanliness and a rather low density of defects spectroscopy (FTIRS ) [5], have provided valuable (steps, vacancies, etc.). This has resulted in the information about surface structure and composi- tion of the substrates as well as of adsorbate * Corresponding author. monolayers. On the other hand, classical electro- 1 Permanent address: Department of Physics, The University of Michigan, Ann Arbor, MI 48109-1120, USA. chemical techniques, such as voltammetry [6], 0039-6028/98/$ – see front matter © 1998 Elsevier Science B.V. All rights reserved. PII: S0039-6028(98)00526-3