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Article

Adsorption and Dissociation of O₂ on Pt−Co and Pt−Fe Alloys

Ye Xu,^† Andrei V. Ruban,^‡ and Manos Mavrikakis*^†

Contribution from the Department of Chemical and Biological Engineering, University of Wisconsin

Madison, Madison, Wisconsin 53706, and Center for Atomic-scale Materials Physics, Department of Physics, Technical University of Denmark, DK-2800 Lyngby, Denmark

J. Am. Chem. Soc., 2004, 126 (14), pp 4717–4725

DOI: 10.1021/ja031701+

Publication Date (Web): March 20, 2004

†

University of WisconsinMadison.

‡

Technical University of Denmark.

To whom correspondence should be addressed.

manos@engr.wisc.edu

Abstract

Self-consistent periodic density functional theory calculations (GGA-PW91) have been performed to study the adsorption of O and O₂ and the dissociation of O₂ on the (111) facets of ordered Pt₃Co and Pt₃Fe alloys and on monolayer Pt skins covering these two alloys. Results are compared with those obtained on two Pt(111) surfaces, one at the equilibrium lattice constant and the other laterally compressed by 2% to match the strain in the Pt alloys. The absolute magnitudes of the binding energies of O and O₂ follow the same order in the two alloy systems: Pt skin < compressed Pt(111) < Pt(111) < Pt₃Co(111) or Pt₃Fe(111). The reduced activity of the compressed Pt(111) and Pt skins for oxygen can be rationalized as being due to the shifting of the d-band center increasingly away from the Fermi level. We propose that an alleviation of poisoning by O and enhanced rates for reactions involving O may be some of the reasons why Pt skins are more active for the oxygen reduction reaction in low-temperature fuel cells. Finally, a linear correlation between the transition-state and final-state energies of O₂ dissociation on monometallic and bimetallic surfaces is revealed, pointing to a simple way to screen for improved cathode catalysts.

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