Formic acid self-poisoning on bismuth-modified stepped electrodes

The poison formation reaction from formic acid has been studied on five different platinum stepped surfaces modified by irreversibly adsorbed bismuth. These surfaces combine (111) symmetry terraces of different widths and monoatomic steps having (110) and (100) symmetry. Their Miller indices are: Pt(775) and Pt(553), for the (110) steps, and Pt(15,13,13), Pt(544) and Pt(755) for the (100) steps. On these surfaces, bismuth deposits preferentially on the steps, and the deposition on the terrace takes place only once the step sites have been completely covered. Bismuth-modified Pt(111) vicinal surfaces show different behavior for the poison formation reaction from formic acid depending on the step symmetry and terrace width. Surfaces with wide terraces in each zone (Pt(775) and Pt(15,13,13)) exhibit behavior that can be compared to the Pt(111) electrode, i.e, poison formation is strongly inhibited once the bismuth is adsorbed on the terrace sites. On the other hand, for Pt(553) and Pt(755) surfaces, the effect of bismuth is not dependent on the adsorption site, i.e. similar inhibition of poisoning is observed when bismuth is deposited on the step or on the terrace sites. An intermediate case is observed for Pt(544) surfaces. These differences can be rationalized taking into account the different energies and the topography of the surfaces. (C) 2001 Elsevier Science B.V. All rights reserved.