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O: Fachverband Oberflächenphysik

O 39: Metal substrates: Solid-liquid interfaces

O 39.4: Vortrag

Mittwoch, 25. März 2009, 15:45–16:00, SCH A315

Optimizing a bimetallic surface - electrochemical oxygen reduction at Pt_xRu_1-x/Ru(0001) surface alloys — •Otavio Alves, Harry E. Hoster, and R. Jürgen Behm — Institute of Surface Chemistry and Catalysis, Ulm University, 89069 Ulm, Germany

We report on the activity of Pt_xRu_1-x/Ru(0001) surface alloys [1] prepared in ultrahigh vacuum (UHV) towards the electrochemical oxygen reduction reaction (ORR). The potential-dependent reaction currents are measured in a wall-jet type flow cell sited in an electrochemical pre-chamber attached to the main UHV system. The kinetically controlled currents depend on the Pt:Ru ratio and exhibit an optimum close to a Pt content of 100%. The high activity of the Pt_xRu_1-x/Ru(0001) surface alloys can be rationalized by the versatility of mixed adsorption sites whose reactivity is between that of Ru(0001) on the one hand, which binds reactive intermediates too strongly, and Pt monolayer islands (Pt_xML/Ru(0001), x = 0...1) on the other hand, whose lower activities are attributed to the sluggish O₂ dissociation as predicted from strain and vertical ligand effects [2,3]. We discuss in how far the high optimum Pt content can be rationalized in an atomic-scale picture of the reaction process.

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