氧气气氛下Pt3Ni(111)表面结构变化的从头算原子热力学研究

采用从头算原子热力学方法系统研究了Ni-rich和Pt-rich条件下Pt₃Ni(111)在不同偏析、表面化学吸附氧覆盖度下560个可能结构的相对稳定性,构建了氧气气氛下Pt₃Ni(111)表面结构演化、直至满覆盖化学吸附氧的热力学相图.结果表明,随着氧的化学势的升高,在热力学上仅出现两类稳定的结构,主要包括没有化学吸附氧的干净Pt-skin表面,以及在很低氧的化学势下就形成的含有化学吸附氧的Ni-skin表面,而有化学吸附氧的PtNi表面合金化的中间结构则处于亚稳态.仔细分析发现,这些结构的形成主要由金属的偏析能、氧与两种金属成键强弱的差别、氧的化学势的高低三个因素共同决定.

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

The structural evolution of the Pt₃Ni(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.