Electrodeposition of silver on stepped platinum electrode surfaces with (1 0 0)-oriented terraces: Generation of confined reaction sites

Ag monolayers and sub-monolayers were deposited onto Pt(s)[n(1 0 0) × (1 1 1)] electrodes both in the over potential deposition (OPD) region under diffusion limited conditions and in the under potential deposition (UPD) region. Diffusion limited deposition from Ag+ concentrations in the micromolar range was monitored by the suppression of the hydrogen adsorption peaks; selective suppression of the peaks for hydrogen adsorption at (1 0 0) terraces sites as opposed to that at (1 1 1) step sites demonstrates that Ag is preferentially deposited at terrace sites. Underpotential deposition gives rise to three peaks: Two large peaks correspond to Ag deposition in the first and the second layer. An additional small peak increases linearly with step density and is due to Ag deposition at the (1 1 1) step sites. Its peak potential, which is lower than that of Ag deposition at terraces, again demonstrates the lower stability of Ag at step sites as compared to terrace sites. By controlling the upper potential limit for the oxidative removal of deposited Ag, Ag at steps can be selectively removed and reaction sites consisting of one dimensional rows of Pt atoms can be generated. At these, formic acid is oxidised at a high rate, whereas methanol cannot be oxidised at all. Poison formation (adsorption of CO) is inhibited completely for both fuels.