In Situ TEM for Structural and Chemical Evolutions of Bimetallic Pt–Ni Nanoparticles at Elevated Temperatures: Implications for Heterogeneous Catalysis

Platinum-based bimetallic nanoparticles (NPs) are of great interest for their applications in catalysis. The catalytic properties of these NPs are significantly dependent on their morphology, structure, and composition, whose response to thermal input remains challenging to be fully understood. This study investigates the thermally induced structural and chemical evolutions of single-crystalline Pt–Ni NPs using in situ transmission electron microscopy. The observed morphological evolution includes the facet development from a truncated octahedron to a spherical-like isotropic shape, followed by the formation of a pancake-like ellipsoid shape at high temperatures due to surface atom migration and interfacial wetting enabled by the particle–substrate interaction. Comparative investigations by in situ scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy mapping elucidate that the solid-solution compositional configuration can be retained over a large temperature range, while core–shell NPs undergo irreversible solid-solution transitions through chemical homogenization at elevated temperatures. These findings elucidate the effect of thermal input on the structural evolution and compositional redistribution of Pt–Ni bimetallic NPs, offering valuable insights into the design of heterogeneous catalysts.