Regensburg 2004 – wissenschaftliches Programm

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O: Oberflächenphysik

O 46: Grenzfläche fest-flüssig

O 46.5: Vortrag

Freitag, 12. März 2004, 12:15–12:30, H45

Structural and electronic effects in the electrochemical properties of UHV prepared bimetallic Pt/Ru(0001) electrodes — •H.E. Hoster, E. Filonenko, and R.J. Behm — Abteilung Oberflächenchemie und Katalyse, Universität Ulm, 89069 Ulm

Combining UHV-STM with cyclic voltammetry in an electrochemical prechamber, we have investigated the adsorption of H and OH in HClO4 solution on two different, well-defined types of bimetallic Pt/Ru(0001) surfaces. On pure Ru(0001) the removal of OHad in the cathodic scan, together with the simultaneous adsorption of Hupd, and its counterpart in the reverse scan direction exhibit a significant hysteresis. In the presence of vapor deposited Pt monolayer islands, these processes proceed much more rapidly in a couple of sharp peaks around 100 mV RHE, with no apparent hysteresis. We explain the enhanced H adsorption by a kinetic promotion effect, including facile hydrogen adsorption on the Pt islands and subsequent spill-over to the Ru areas, where the adsorbed hydrogen can react with OHad. In the anodic scan, the Pt sites in turn allow for a faster oxidation of H adsorbed at Ru. On atomically smooth PtxRuy/Ru(0001) surface alloys, which are formed by subsequent annealing of the Pt covered substrate to higher temperatures, adsorption of OH and H are again modified significantly. Comparing results for different Pt surface contents, where the concentration and ensemble size distribution of the Pt surface atoms are determined by atomically resolved STM images with chemical contrast, allows conclusions on the effect of specific adsorption ensembles and adsorption sites.

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