An atomistic thermodynamics study of the structural evolution of the Pt3Ni(111) surface in an oxygen environment

Abstract

The structural evolution of the Pt 3 Ni(111) surface under oxidizing conditions was studied by ab initio atomistic thermodynamics. The thermodynamic phase diagram from Ni-rich to Pt-rich conditions with oxygen coverages up to one monolayer was constructed from their 560 possible surface structures. With an increase in the oxygen chemical potential, there were only two types of thermodynamically stable structures, which were a clean Pt-skin surface and a Ni-skin surface with chemisorbed oxygen, regardless of the underlying Pt-rich or Ni-rich conditions. Bimetallic surfaces with chemisorbed oxygen were only metastable. The detail analysis revealed that the structural evolution is determined by the factors of segregation cost, difference between oxygen-metal (Pt and Ni) bonding strength, and oxygen chemical potential. With a gradual increase of oxygen chemical potential, the clean Pt-skin surfaces of Pt 3 Ni(111) transit to the oxygen-chemisorbed Ni-skin surfaces without stable oxygen-chemisorbed PtNi surface alloys formed.