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 metal. 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 AuCu-core nanoparticles. Our seed-mediated growth methodology yields well-defined AuCu-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.