UC Irvine

Platinum-based metallic NPs hold considerable interest due to their applications especially in catalysis. The catalytic performance depends on their morphology, structure, and composition. The response under thermal stimuli remains complex and is not fully elucidated. TEM is an indispensable method for characterizing materials from the atomic level to nanoscale. In situ TEM has enabled unprecedented capabilities for observing the real-time evolution of materials during dynamic processes. This study investigates the thermally induced structural and chemical evolutions of Pt-based NPs with different structures and elemental compositions using in situ TEM. In situ TEM generates massive datasets, necessitating effective tools for data analysis. Image segmentation using machine learning was developed to analyze STEM images and quantify NPs behavior at elevated temperatures.The first NP system investigated is Pt-Ni NPs. We synthesized NPs with two distinct structures. In situ TEM reveals morphological evolution from truncated octahedron to spherical-like isotropic shapes, followed by pancake-like ellipsoid shapes. In situ STEM with EDS mapping shows that solid-solution compositional configuration is retained over a large temperature range, while core-shell NPs undergo irreversible solid-solution transitions through chemical homogenization at elevated temperatures. The study extends to quinary PdCuPtNiCo NPs with core-shell and HEA structures. STEM and EDS mapping examine the crystal structure and mixing patterns. In situ experiments reveal that chemical evolutions during heating are controlled by mass transfer with nearby NPs. Without mass transfer, NPs maintain their solid solution structure; however, mass transfer with background atom clusters or neighboring NPs leads to the formation of Janus structures after heating. Overall, this work provides new scientific knowledge about structural and chemical evolutions of metallic NPs model systems during heat treatment. The obtained knowledge can be used as design principles to extend to other multimetallic systems to improve materials’ performance in real applications.