Regensburg 2013 – scientific programme

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O: Fachverband Oberflächenphysik

O 76: Focussed Session: Solid-liquid Interfaces II

O 76.1: Topical Talk

Thursday, March 14, 2013, 16:00–16:30, H31

The origin of the high oxygen reduction activity on PtX (X= Sc, Y, La, Sm, Gd and ..) alloys and their activation mechanism. — •Ib Chorkendorff — Technical University of Denmark, Kgs. Lyngby, Denmark

There is a strong demand for improving the anode material of the Proton Exchange Membrane Fuel Cell, either by increasing the activity and thereby being able to reduce the loading or by replacing Pt entirely. Recently we have found a new class of alloys, which are very active towards the Oxygen Reduction Reaction (ORR). The first catalyst were predicted in a DFT screening study which pointed for activity and stability towards Pt3Sc and Pt3Y and the latter proved particular active by a factor 7-8 times as active as polycrystalline Pt. We have since expanded the number of catalyst to also include Zr, Hf, and La, but the most active and stable catalysts seems to be Pt5Ga. By comparison to our recent studies of PtCu catalyst it is possible to identify the surface composition more accurately. The Pt and Y, La, and Gd catalysts are among the most active and stable forming a rather thick skin consisting of several monolayers of Pt. This skin is found to be under compression (although the bulk alloy is expanded compared to pure Pt) leading to the necessary lower binding energy of oxygen explaining the enhanced ORR activity. The skin formation has been investigated by a broad range of surface science methods and the progress concerning the combination of ORR activity and structural investigation of polycrystalline, single crystal, and mass selected nanoparticles will be discussed.