Facile Synthesis of Palladium-Based Nanocrystals with Different Crystal Phases and a Comparison of Their Catalytic Properties

A relatively unexplored aspect of noble-metal nanomaterials is polymorphism, or their ability to crystallize in different crystal phases. Here, a method is reported for the facile synthesis of Ru@Pd core-shell nanocrystals featuring polymorphism, with the core made of hexagonally close-packed (hcp)-Ru while the Pd shell takes either an hcp or face-centered cubic (fcc) phase. The polymorphism shows a dependence on the shell thickness, with shells thinner than approximate to 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@Pd-hcp nanocrystals outperform Ru@Pd-fcc in terms of both specific activity and peak potential. Density functional theory calculations are also performed to elucidate the origin of this performance enhancement.

Automated summary

This study reports a method for synthesizing Ru@Pd core-shell nanocrystals with polymorphism and reveals that the polymorphism depends on the thickness of the Pd shell. The injection rate serves as an experimental knob for controlling the phase, with Ru@Pd-hcp nanocrystals outperforming Ru@Pd-fcc in catalytic reactions. Density functional theory calculations are used to explain the enhancement in performance.