Induced adsorption of sulfate/bisulfate anions by submonolayer amounts of copper on deliberately stepped Pt surfaces

The presence of submonolayer amounts of underpotentially deposited copper induces the adsorption of sulfate/bisulfate on Pt stepped surfaces. The surfaces studied include the (111) and (110) surfaces and the stepped surfaces of(10,10,9), (554), (332), (221) and (331), which correspond 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-site density) up to the Pt(221) surface, which has a three-atom wide terrace. 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 for the (111) surface which indicates that the step sites are responsible for the observed behaviour.