Adsorption of CO on PtBi2 and PtBi surfaces

Approximate molecular orbital calculations have been applied to explain the low CO poisoning effects observed at PtBi2 and PtBi electrodes. The bonding patterns for chemisorption of CO on the surfaces of Pt-Bi bulk alloys and pure Pt surfaces are quite similar. The major difference is not induced through much Pt-Bi bonding, but indirectly, by raising the Fermi level of the system, so that the C-O π* levels become practically filled upon interaction. This results in much lower adsorption energies than in the metallic Pt case, in accordance with experimental data. The calculations also imply C-O bond dissociation on the surface, a phenomenon not supported by experiment. CO adsorption at Pt-Pt bridge site (possible only on PtBi) is favored relative to atop chemisorption.