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Thermal treatment is a general and efficient way to synthesize intermetallic catalysts and may involve complicated physical processes. So far, the mechanisms leading to the size and composition heterogeneity, as well as the phase segregation behavior in Pt-Co nanoparticles (NPs) are still not well understood. Via in-situ environmental transmission electron microscopy, the formation dynamics and segregation behaviors of Pt-Co alloyed NPs during the thermal treatment were investigated. It is found that Pt-Co NPs on zeolitic imidazolate frameworks-67-derived nanocarbon (NC) are formed consecutively through both particle migration coalescence and the Ostwald ripening process. The existence of Pt NPs is found to affect the movement of Co NPs during their migration. With the help of theoretical calculations, the correlations between the composition and migration of the Pt and Co during the ripening process were uncovered. These complex alloying processes are revealed as key factors leading to the heterogeneity of the synthesized Pt-Co alloyed NPs. Under oxidation environment, the Pt-Co NPs become surface faceted gradually, which can be attributed to the oxygen facilitated relatively higher segregation rate of Co from the (111) surface. This work advances the fundamental understanding of design, synthesis, and durability of the Pt-based nanocatalysts.
We acknowledge the support from the National Natural Science Foundation of China (Nos. 52072345, U21A20328, 22103047, and 12174348), the China Postdoctoral Science Foundation (No. 2021T140621), the Natural Science Foundation of Henan Province (No. 222300420077), and Henan Center for Outstanding Overseas Scientists (No. GZS201903). D. S. acknowledges the support from Strategic Priority Research Program (B) (No. XDB33030200) of Chinese Academy of Sciences. The electron microscopy work was performed at the Center for Functional Nanomaterials, which is a US DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DE-SC0012704.