Regensburg 2013 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 45: Metal Substrates II

O 45.1: Vortrag

Mittwoch, 13. März 2013, 10:30–10:45, H42

Coadsorption of deuterium and CO on submonolayer Pt films on Ru(0001) model surfaces — Heinrich Hartmann, •Joachim Bansmann, Thomas Diemant, and R. Jürgen Behm — Institute of Surface Chemistry and Catalysis, Ulm University, D-89069 Ulm

Pt surfaces modified by Ru are of high interest for applications in low temperature Polymer Electrolyte (PE) fuel cells. Here, we report on a combined TPD/IRAS study of coadsorbed hydrogen (deuterium) and CO and their interaction with model surfaces, e.g., submonolayer Pt films on Ru(0001) with varying Pt coverages. The experimental results show that a closed CO layer completely blocks the adsorption of D₂. On a surface partly covered by CO, D₂ adsorption is still possible, however a considerable decrease of the D_ad adsorption energy is observed. In the reverse case, pre-adsorbed D_ad also reduces the amount of subsequently adsorbed CO, although CO adsorption is possible even on a closed D_ad layer. This phenomenon leads to very high total coverages (exceeding 1 ML) and an additional destabilization of the coadsorbed species. Pre-adsorbed D_ad has the strongest influence on the CO adsorption on Pt films with low Pt coverage (< 0.3 ML Pt). This trend can be explained by the considerably weaker D_ad binding energy on Pt islands compared to the Ru surface) which leads to a decreasing initial D_ad coverage and facilitates the displacement of D_ad by post-adsorbed CO. For the same reason the influence of pre-adsorbed CO on D₂ adsorption considerably increases with increasing Pt coverage, since D_ad is displaced to the less favorable Pt sites.