The geometric structure of 38-atom AgPd and AgCu nanoalloys is obtained by the genetic algorithm and density functional theory for all compositions and their surface phase stability diagrams are established to provide a clear image for the initial oxidation process. Ag surface segregation is confirmed for both AgPd and AgCu nanoalloys in vacuum. Pure Pd and Cu nanoparticles have lower surface phase stability than bulk metals to be oxidized and the alloying can improve the oxidation resistance. Segregated AgCu nanoalloys have higher phase stability than mixed AgCu in vacuum and have lower surface phase stability than mixed AgCu nanoalloys in an oxygen atmosphere. Unexpectedly, segregated AgPd nanoalloys have both higher phase stability in vacuum and higher surface phase stability in an oxygen atmosphere than that of mixed AgPd nanoalloys. The higher surface phase stability of segregated AgPd nanoalloy could be attributed to the slight elevation of Pd Milliken charge and negative shift of d-band center. Compared with the selective oxidation in conventional alloy oxidation models where the selective oxidation is related to alloy composition, the nanoalloy oxidation is proposed to correlate with surface segregation in AgPd and AgCu nanoalloys in this work, which promotes the development of the conventional alloy oxidation models in that the surface segregation is a precursor to the surface oxidation of nanoalloy and plays a critical role in the selective oxidation of nanoalloy.

通过遗传算法和密度泛函理论获得了所有组成的38原子AgPd和AgCu纳米合金的几何结构，并建立了它们的表面相稳定性图，为初始氧化过程提供了清晰的图像。在真空中，AgPd和AgCu纳米合金的Ag表面偏析得到确认。纯Pd和Cu纳米粒子的表面相稳定性低于要氧化的大块金属，合金化可以提高抗氧化性。分离的AgCu纳米合金在真空中比混合的AgCu纳米合金具有更高的相稳定性，并且在氧气气氛中比混合的AgCu纳米合金具有更低的表面相稳定性。出乎意料的是，与混合的AgPd纳米合金相比，偏析的AgPd纳米合金在真空中具有更高的相稳定性，在氧气气氛中具有更高的表面相稳定性。偏析的AgPd纳米合金的较高表面相稳定性可归因于Pd Milliken电荷的轻微升高和d谱带中心的负移。与选择合金与合金成分有关的常规合金氧化模型中的选择氧化相比，本研究提出了纳米合金氧化与AgPd和AgCu纳米合金中的表面偏析相关，从而促进了常规合金氧化模型的发展。表面偏析是纳米合金表面氧化的先兆，并且在纳米合金的选择性氧化中起着关键作用。