Surface segregation in bimetallic Pt3M (M = Fe, Co, Ni) alloys with adsorbed oxygen

Surface segregation of Pt3M (M = Fe, Co, and Ni) alloys under oxygen environment has been examined using periodic density functional theory. The segregation trend at a (1 1 1) surface is found to be substantially modified by the adsorbed oxygen. Our calculations indicate that under 1/4 monolayer O coverage both the Pt-segregated and M-segregated surfaces are less stable than the non-segregated one. Further analysis reveals that segregation energy under adsorption environments can be expressed as the sum of the segregation energy under vacuum conditions and the adsorption energy difference of the segregated and non-segregated alloy systems. Therefore, the surface segregation trend under adsorption conditions is directly correlated to the surface-adsorbate binding strength.