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

Author(s)

Arezoo Dianat, Janina Zimmermann, Nicola Seriani, Manfred Bobeth, Wolfgang Pompe, Lucio Colombi Ciacchi

Abstract

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.

Organisation(s)

Computational Materials Physics

External organisation(s)

Technische Universität Dresden, Fraunhofer-Institut für Werkstoffmechanik IWM, Karlsruher Institut für Technologie

Journal

Surface Science

Volume

602

Pages

876–884

No. of pages

ISSN

0039-6028

DOI

https://doi.org/10.1016/j.susc.2007.12.016

Publication date

2008

Peer reviewed

Yes

Austrian Fields of Science 2012

103018 Materials physics

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