| Abstract
| - The amount of poison formed and oxidatively desorbed upon the dissociative adsorption of formic acidon bismuth-modified Pt[n(111) × 100 and 110] electrodes has been investigated and found to decreaselinearly with bismuth coverage on the step sites. For Pt(544) and Pt(554) (i.e., nine atom wide (111)terraces with (100) and (110) steps, respectively), the amount of charge to oxidatively desorb the poisondecreases from 80 and 220 μC/cm2, respectively, to similar values of 25 and 30 μC/cm2, respectively, whenthe step sites are completely blocked with bismuth and the (111) terraces are bare. As the step site densityof the platinum surface is increased, the amount of charge corresponding to the adsorbed poison, whenthe step sites are completely blocked with bismuth, decreases on the surfaces with (100) steps but remainsconstant or slightly increases on the surfaces with (110) steps. As bismuth is deposited on the (111) terraces,the amount of poison formed on both electrodes is greatly diminished, so that when bismuth coveragesof ca. 0.09 are attained on the (111) terraces, little poison is formed. While both the (100) and (110) steppedsurfaces exhibit this rapid diminution in poison formation with bismuth coverage on the (111) terraces,the (100) stepped surfaces reach the minimum at a faster rate, suggesting that the (110) steps influencethe surface by making it more reactive to the poison formation reaction, even when they are blocked withbismuth. For formic acid oxidation, the (110) stepped Pt surfaces are less active than the (100) steppedsurfaces when bismuth is only adsorbed on the step sites but become more active when bismuth is adsorbedon both the steps and partially on the (111) terraces.
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