PNNL

Abstract

This report describes a novel strategy of chromium-assisted shape control in the synthesis of platinum nanocubes with high monodispersity. The use of a certain concentration ratio of platinum vs. chromium precursors (typically 1:1) has been demonstrated to enable an effective adsorption of Cr species on the nanocrystal in selective blocking of the adsorption of capping molecules on the different surfaces for the nanocube formation. The cubic shape was evidenced by both high-resolution TEM and x-ray diffraction characterizations, whereas the composition was analyzed by both bulk and surfacesensitive techniques (DCP-AES, EDS and XPS). The results indicated that practically there was no Cr in the nanocubes or only a trace of Cr on the nanocrystal surfaces, demonstrating a high effectiveness in producing Pt nanocubes. A combination of effective oxidative leaving of the adsorbed Cr species and the weaker adsorption of capping molecules on Pt(111) constitutes the kinetic driving force for a faster growth rate of Pt(111) than Pt(100) faces. The understanding of the synergistic correlation between surface metal adsorption and ligand encapsulation in creating a difference in the kinetic growth on different nanocrystal facets has important implication to the design of advanced catalysts.