The early stage of oxidation on Pd₆@Ag₃₂ and Ag₆@Pd₃₂ core-shell nanoalloys are calculated by the surface phase stability diagrams using a first-principles atomistic thermodynamics method in oxidizing atmospheres. Ag₃₈ nanoparticle with Δμ_O = − 0.95 eV is more stable than Pd₃₈ nanoparticle with Δμ_O = − 1.3 eV. Unexpectedly, Pd₆@Ag₃₂ core-shell nanoalloy with Δμ_O = − 0.9 eV exhibits better surface phase stability than Ag₃₈ nanoparticle but Pd-segregated Pd₆@Ag₃₂ nanoalloys have lower stability than Ag₃₈ nanoparticle. Meanwhile, Ag₆@Pd₃₂ core-shell nanoalloy with Δμ_O = − 1.5 eV displays lower surface phase stability than Pd₃₈ nanoparticle but Ag-segregated Ag₆@Pd₃₂ nanoalloys show better surface phase stability than Pd₃₈ nanoparticle. Surface-segregated Pd₆@Ag₃₂ and Ag₆@Pd₃₂ core-shell nanoalloys with more surface Ag atoms tend to possess the higher surface phase stability. More interestingly, the order of surface phase stability follows the same trend of atomic charges, that is, the more negative charges corresponding to the lower surface phase stability. In addition, oxidation of PdAg nanoalloys can greatly change electronic structure and atomic charges and have diverse influences on catalytic properties. Unlike bulk PdAg alloys, the oxygen-induced Pd surface segregation in Pd₆@Ag₃₂ core-shell nanoalloy takes place under high oxygen coverage rather than vacuum and medium oxygen coverage. The high oxygen coverage upto 24 oxygen atoms can segregate Pd to outer shell in Pd₆@Ag₃₂ core-shell nanoalloy and restrain the segregation of Ag onto Ag₆@Pd₃₂ core-shell nanoalloy. Our results can provide useful information for designing PdAg-based catalyst materials with appropriate surface phase stability towards fuel cells.

使用第一性原理原子热力学方法在氧化气氛中，通过表面相稳定性图，计算了Pd ₆ @Ag ₃₂和Ag ₆ @Pd ₃₂核-壳纳米合金的早期氧化。的Ag ₃₈纳米粒子与Δμ _ö  = - 0.95 eV的是除Pd更稳定₃₈的纳米颗粒与Δμ _ö = - 1.3 eV的。出乎意料的是，钯₆ @Ag ₃₂核-壳纳米合金与Δμ _ö  = - 0.9 eV的展品Ag相比更好的表面相稳定性₃₈的纳米颗粒，但钯偏析的Pd ₆ @Ag ₃₂纳米合金的稳定性低于Ag ₃₈纳米颗粒。同时，银₆ @Pd ₃₂与Δμ核-壳纳米合金_ö = -为1.5eV显示低于钯表面相稳定性₃₈纳米颗粒的Ag但偏析的Ag ₆ @Pd _32个纳米合金显示比钯更好的表面相稳定性₃₈纳米颗粒。表面分离的Pd ₆ @Ag ₃₂和Ag ₆ @Pd ₃₂具有更多表面Ag原子的核-壳纳米合金往往具有更高的表面相稳定性。更有趣的是，表面相稳定性的顺序遵循相同的原子电荷趋势，即负电荷越多，对应的表面相稳定性越低。此外，PdAg纳米合金的氧化可以极大地改变电子结构和原子电荷，并对催化性能产生多种影响。与块状PdAg合金不同，Pd ₆ @Ag ₃₂核壳纳米合金中氧诱导的Pd表面偏析发生在高氧覆盖率而不是真空和中氧覆盖率下。高达24个氧原子的高氧覆盖率可将Pd分离到Pd ₆ @Ag _32中的外壳上核-壳纳米合金，并抑制Ag在Ag ₆ @Pd ₃₂核-壳纳米合金上的偏析。我们的结果可为设计具有对燃料电池具有适当表面相稳定性的PdAg基催化剂材料提供有用的信息。