COLL 610 |
| Direct Methanol Fuel Cells (DMFCs) are a leading candidate for portable power applications where low temperatures and high fuel energy density are required. Among the open questions which remain in our understanding of the catalysts used in DMFCs are the electronic states and local chemistry of the metal atoms in the nanoparticle catalysts. Specially modified fuel cells and the high brilliance of third generation synchrotron undulator beams now permit direct structural investigation of these sytems during normal operation. The technique of X-ray Absorption Spectroscopy (XAS) is particularly suited to these nanostructured materials as it is sensitive to both electronic structure and atom-specific local structural parameters. XAS experiments conducted at the Materials Research Collaborative Access Team beamline, in conjunction with x-ray fluorescence and powder diffraction studies, have provided us with a structural model of the industry standard Pt/Ru (1:1 composition) catalyst. The ~3nm nanoparticles are a not-quite-random face centered cubic alloy with composition approximately 2:1 Pt:Ru. About 50% of the Ru in the catalyst is outside the nanoparticles in a presumably amorphous phase. The potential dependent data indicate that the Pt in always metallic while the Ru has a constant small quantity of short (1.86Å) bonds to oxygen. A further elucidation of the role of the amorphous Ru phase as well as information on the chemistry taking place on the surface of the nanoparticles will be possible using this technique. |
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Physical and Computational Characterization of Nanostructured Electrocatalysts
2:00 PM-4:20 PM, Thursday, 14 September 2006 Sir Francis Drake -- Empire Room, Oral
Division of Colloid & Surface Chemistry |