Phase-Controlled Synthesis of Ru Nanocrystals via Template-Directed Growth: Surface Energy versus Bulk Energy.

Abstract

Despite the successful control of crystal phase using template-directed growth, much remains unknown about the underlying mechanisms. Here, we demonstrate that the crystal phase taken by the deposited metal depends on the lateral size of face-centered cubic (<i>fcc)-</i>Pd nanoplate templates with 12 nm plates giving <i>fcc</i>-Ru while 18-26 nm plates result in hexagonal closed-packed (<i>hcp</i>)-Ru. Although Ru overlayers with a metastable <i>fcc</i>- (high in bulk energy) or stable <i>hcp</i>-phase (low in bulk energy) can be epitaxially deposited on the basal planes, the lattice mismatch will lead to jagged <i>hcp</i>- (high in surface energy) and smooth <i>fcc</i>-facets (low in surface energy), respectively, on the side faces. As the proportion of basal and side faces on the nanoplates varies with lateral size, the crystal phase will change depending on the relative contributions from the surface and bulk energies. The Pd@<i>fcc-</i>Ru outperforms the Pd@<i>hcp-</i>Ru nanoplates toward ethylene glycol and glycerol oxidation reactions.