INDUCED ADSORPTION OF SULFATE BISULFATE ANIONS BY SUBMONOLAYER AMOUNTS OF COPPER ON DELIBERATELY STEPPED PT SURFACES/

The presence of submonolayer amounts of underpotentially deposited cop per induces the adsorption of sulfate/bisulfate on Pt stepped surfaces . The surfaces studied include the (111) and (110) surfaces and the st epped surfaces of(10,10,9), (554), (332), (221) and (331), which corre spond to (111) terrace widths of 19, 9, 5, 3 and 2 atoms, respectively , with monatomic (110) steps. The amount of induced sulfate/bisulfate adsorption increased with decreasing terrace width (increasing step-si te density) up to the Pt(221) surface, which has a three-atom wide ter race. In contrast, for the (331) surface, with a two-atom wide terrace , the amount of induced adsorption decreased, suggesting that a three- atom terrace is the minimum width to accommodate the copper adatom and co-adsorbed anion. This type of induced adsorption was not observed f or the (111) surface which indicates that the step sites are responsib le for the observed behaviour.