A relatively unexplored aspect of noble-metal nanomaterials is polymorphism, or their ability to crystallize in different crystal phases. Such a change in crystal structure can result in a corresponding change in properties. Palladium is usually found in the fcc phase, but recently, it has been been engineered to take on the metastable hcp phase as well. Here we report a method for the facile synthesis of Ru@Pd core-shell nanocrystals featuring polymorphism, with the core made of hcp-Ru while the Pd shell takes either an hcp or fcc phase. The polymorphism shows a dependence on the shell thickness, with shells thinner than ca. 1.4 nm taking the hcp phase whereas the thicker ones revert to fcc. The injection rate provides an experimental knob for controlling the phase, with one-shot and drop-wise injection of the Pd precursor corresponding to fcc-Pd and hcp-Pd shells, respectively. When these nanocrystals are tested as catalysts toward formic acid oxidation, the Ru@Pdhcp nanocrystals outperform Ru@Pdfcc in terms of both specific activity and peak potential. Density functional theory calculations are also performed to elucidate the origin of this performance enhancement.

Facile synthesis of palladium-based nanocrystals with different crystal phases

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.