Chemistry

More Precious Than Platinum?

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Science  17 Jun 2011:
Vol. 332, Issue 6036, pp. 1360-1361
DOI: 10.1126/science.332.6036.1360-d

Solid oxide fuel cells (SOFCs) complete their electric circuit by transporting reduced oxygen ions through a solid electrolyte from cathode to anode. When ceramic oxides are used as the reduction catalyst, the SOFC needs to operate above 700°C. Platinum catalysts can operate at lower temperature, but they are very expensive and easily poisoned by small concentrations of carbon monoxide (CO) or hydrogen sulfide (H2S) in the fuel source. Holme and Prinz used density functional theory calculations to design a non-noble metal catalyst with a d-band center near that of platinum, so that only weak metal-oxygen bonds would form. The authors started by looking at alloys of copper and zinc, and found that the best composition was Cu5Zn8. When Ag substituted for Cu at the adsorption site, the absorption energy was very close to the ideal value. Particles and dense layers were then fabricated, and the best results were obtained for AgxCu5-xZn8 with an overcoating of Ag. This alloy showed promising performance (though still below that of Pt) and, importantly, had better resistance to H2S and CO poisoning.

J. Phys. Chem. C 115, 10.1021/jp2022538 (2011).

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