Changes in Bimetallic Catalysts

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Science  02 Jan 2004:
Vol. 303, Issue 5654, pp. 17
DOI: 10.1126/science.303.5654.17b

One of the problems that can plague fuel cells is poisoning by CO adsorption; one solution is to alloy platinum (Pt) with other metals, such as ruthenium or tin (Sn), that can more readily react with water, binding a hydroxyl group while liberating a proton and an electron. This hydroxyl group can then react with CO molecules on Pt atoms, liberating CO2 and another proton and electron. In order to understand these processes better, several groups have been studying model single-crystal catalysts as summarized by Koper. In particular, Gallagher et al. have examined changes in a Pt3Sn(111) surface immersed in a sulfuric acid electrolyte with in situ surface x-ray scattering, which can resolve small changes in structure. At low applied potentials (0.05 V), the entire surface layer undergoes a expansion of about 2%, but at 0.55 V, the Pt atoms in the outermost layer contract inward to an expansion of only 0.6%, whereas the Sn atoms expand outward by 6%. This buckling of the surface is also observed under CO saturation at 0.55 V and appears to be a precursor to Sn desorption that occurs at 1.0 V. The ability to observe such changes bodes well for more detailed studies of these reactions. — PDS

Surf. Sci. 10.1016/j.susc.2003.10.045 (2003); Surf. Sci. 544, L729 (2003).

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