Anion adsorption on Pd-Pt(111) electrodes in sulphuric acid solution

Anion adsorption at palladium-covered Pt(lll) electrodes has been studied i n sulphuric acid solutions using cyclic voltammetry, charge displacement an d in situ FTIR experiments. The infrared spectra obtained for partially cov ered Pt(lll) substrates show distinct bands for adsorbed (bi)sulphate on pl atinum and palladium surface atoms with frequencies similar to those observ ed for the bare and fully covered Pt(lll) electrode surfaces, respectively. This observation is in agreement with the epitaxial growth of palladium on Pt(lll). Increasing the palladium coverage in the (sub)monolayer range is shown to shift;(bi)sulphate adsorption towards less positive potentials, wh ereas the total amount of adsorbed anions on the ensemble of palladium and platinum domains is approximately constant. Combination of CO displacement and voltammetric curves allows the determination of the potential of zero t otal charge (pztc) as a function of the palladium coverage. The pztc shifts from 0.33 to 0.235 V when the palladium coverage on the Pt(lll) is increas ed up to a monolayer. The oxidation of the CO adlayer resulting from the ch arge displacement experiments has also been studied. The oxidation of adsor bed CO on palladium-covered Pt(lll) electrodes takes place at higher potent ials than on Pt(lll). The pztc values have been used to calculate the contr ibution from anion adsorption to the charge obtained from the integration o f the CO stripping voltammograms. Coverage values calculated for the CO adl ayers generated during the CO displacement experiments at the palladium-cov ered Pt(lll) electrodes diminish as the palladium coverage increases. (C) 2 001 Elsevier Science B.V. All rights reserved.