MONTE-CARLO SIMULATION OF CO ADLAYERS ELECTROOXIDATION ON PT(111)

Numerical simulations of the electrooxidation of CO adsorbed on Pt(111 ) surfaces are presented. For adlayers prepared by CO dosage, the nume rical results confirm previous proposals, based upon current experimen tal information, concerning the CO distribution on the Pt surface. Spe cifically, whereas at low coverages (below 1/3) CO forms open and easi ly 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 dist ributions at low and high coverages. We also present new experiments o n the electrooxidation of CO adsorbed on Pt(111) upon the dissociative adsorption of formic acid. In this case our results indicate that a s ingle oxidation peak remains up to coverages below 2/3. This striking new result is also reproduced in our simulations by laking the same ki netic 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. (C) 19 98 Elsevier Science B.V. All rights reserved.