Regensburg 2007 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 67: Symposium: The Solid-Liquid Interface: A Challenge for Theoreticians II
O 67.3: Vortrag
Freitag, 30. März 2007, 11:15–11:30, H38
Structural stability and OH adsorption properties of Au/Pt(111) surfaces — •Yoshihiro Gohda and Axel Groß — Institute of Theor. Chemistry, Ulm Univ., 89069 Ulm/Germany
Platinum-based bimetallic electrodes are of current interest for electrochemical and electrocatalytic applications to fuel cells for example. The structural stability of such electrodes is one of the most important prerequisites. Furthermore, OH groups adsorbed on the electrode surface are produced in the initial stage of the oxygen reduction at the cathode. The OH adsorption could also be of importance during the consumption of water in the electro-oxidation of methanol at the anode. A fundamental understanding of OH adsorption properties should thus be helpful for a better description of such reactions on the atomic scale.
Here we report first-principles calculations on the structural stability of Au/Pt(111) surfaces and the OH adsorption on them. We have found that 1-monolayer (ML) thick surface alloys on Pt(111) are energetically preferred compared to the decomposition into the clean Pt(111) surface and Au droplets. They are also more stable than 2-ML thick alloys with the same Au concentration, too, because Au atoms that are larger than Pt atoms prefer to be located in the uppermost layer where they reduce the surface stress which is in general tensile. This bimetallic surface system favors separating into two phases at 0 K: the clean Pt(111) surface and the Au/Pt(111) overlayer. In contrast, stable surface alloy formation due to entropy effects is seen for the Au0.5Pt0.5 composition at 800 K. Calculations for the OH adsorption will also be reported.