Structural study of Pt-Fe nanoparticles: New insights into pt bimetallic nanoparticle formation with oxidized Fe species

Abstract

A combination of physicochemical methods allowed us to assess a structure of comparatively monodisperse 3-4 nm Pt-FexOy nanoparticles (NPs) synthesized by thermal decomposition of platinum acetylacetonate in the presence of iron oxide NPs as an iron source. Unlike traditional PtFe alloys composed of zerovalent Pt and Fe species with the surface enriched by Pt atoms, the NPs discussed in this work contain Pt(0) and oxidized Fe species (most probably Fe3+ or Fe2+) as is proven by X-ray photoelectron spectroscopy (XPS). Angular dependence XPS measurements demonstrated the absence of the core-shell structure, although a minor enrichment of the NP surface with Fe species was observed. High-resolution transmission electron microscopy and X-ray powder diffraction (XRD) reveal that these Pt-FexOy NPs are not alloys, but consist of different domains; i.e., they have a "cluster-in-cluster" morphology. A comparison of the XPS and XRD data allowed us to conclude that the NPs also include amorphous iron oxide. These results allow better understanding of the mechanism of such NP formation and possible predictions of their catalytic performance.