Synthetic control over lattice strain in trimetallic AuCu-core Pt-shell nanoparticles

Core-shell nanoparticles can exhibit strongly enhanced performances in electro-, photo- and thermal catalysis. Lattice strain plays a key role in this and is induced by the mismatch between the crystal structure of the core and the shell met-al. However, investigating the impact of lattice strain has been challenging due to the lack of a material system in which lattice strain can be controlled systematically, hampering further progress in the field of core-shell catalysis. In this work, we achieve such a core-shell nanoparticle system through the colloidal synthesis of trimetallic Pt-shell Au1-xCux-core nanoparticles. Our seed-mediated growth methodology yields well-defined Au1-xCux-cores, tunable in composition from 0 at-% Cu to 77 at-% Cu, and monodisperse in size. Subsequent overgrowth results in uniform, epitaxially grown Pt-shells with a controlled thickness of ~3 atomic layers. By employing a multi-technique characterization strategy combining X-ray diffraction, electron diffraction and aberration corrected electron microscopy, we unravel the atomic structure of the trimetallic system on a single nanoparticle-, ensemble- and bulk scale level, and we unambiguously demonstrate the controlled variation of strain in the Pt-shell from -3.62 % compressive-, to +3.79 % tensile strain, while retaining full control over all other structural characteristics of the system.