Ab initio study of element segregation and oxygen adsorption on PtPd and CoCr binary alloy surfaces

SURFACE SCIENCE

卷:602

Article

Dianat, Arezoo¹  Zimmermann, Janina²  Seriani, Nicola³  Bobeth, Manfred¹  Pompe, Wolfgang¹  Ciacchi, Lucio Colombi^2,4 

[1] Tech Univ Dresden, Inst Werkstoffwissensch, D-01069 Dresden, Germany

[2] Fraunhofer Inst Werkstoffmech, D-79108 Freiburg, Germany

[3] Univ Vienna, Inst Materialphys, A-1090 Vienna, Austria

[4] Univ Karlsruhe, Inst Zuverlassigkeit Bauteilen & Syst, D-76131 Karlsruhe, Germany

关键词: electronic structure calculations;    bimetallic surfaces;    alloying;    palladium;    platinum;    chromium;    cobalt;    chemisorption;   

DOI  :  10.1016/j.susc.2007.12.016

来源: Elsevier

【 摘 要 】

The segregation behavior of the bimetallic alloys PtPd and CoCr in the case, of bare surfaces and in the presence of an oxygen ad-layer has been studied by means of first-principles modeling based on density-functional theory (DFT). For both systems, change of the d-band filling due to charge transfer between the alloy components, resulting in a shift of the d-band center of surface atoms compared to the pure components, drives the surface segregation and governs the chemical reactivity of the bimetals. In contrast to previous findings but consistent with analogous PtNi alloy systems, enrichment of Pt atoms in the surface layer and of Pd atoms in the first subsurface layer has been found in Pt-rich PtPd alloy models, despite the lower surface energy of pure Pd compared to pure Pt. Similarly, Co surface and Cr subsurface segregation occurs in Co-rich CoCr alloys. However, in the presence of adsorbed oxygen, Pd and Cr occupy preferentially surface sites due to their lower electronegativity and thus stronger oxygen affinity compared to Pt and Co, respectively. In either cases, the calculated oxygen adsorption energies on the alloy surfaces are larger than on the pure components when the more noble components are present in the subsurface layers. (C) 2007 Elsevier B.V. All rights reserved.

【 授权许可】

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