Pt intermetallic line compounds, such as with Pb and Bi, have been observed to improve dramatically the anode carbon monoxide (CO) tolerance of fuel cells for oxidation of small organic molecules. We have used density functional theory to study the CO and H adsorption on different surfaces of these line compounds. Among different surface orientations of PtPb and PtBi, we find (100)B and (110) have much lower cleavage energies and CO adsorption energies than (100)A and (001) and also much lower CO adsorption energies than Pt(111). Thus, (100)B and (110) are the surfaces most relevant to experimental observations, and the increased CO tolerance is not attributable to the (001) surface of the line compounds as assumed experimentally, because it binds CO the strongest, even more strongly than Pt(111). We also find that CO is not likely to dissociate on these materials. Finally, we correlate d-band center and CO adsorption energy for these non close-packed systems by developing a more universal form of the original d-band center model that includes effects of symmetry of adsorption site and local relaxation. We find that the increased CO tolerance arises from a downward shift of Pt d-band center because of alloying, which also accounts for the difference between PtPb and PtBi.
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