Controlled alloying of Pt-Rh nanoparticles by the polyol approach

We report on a facile synthesis strategy for the reaction matrix platinum(II)-acetylacetonate − rhodium(III)-acetylacetonate − polyvinylpyrrolidone − 1,4-butanediol and show that phase pure Pt-Rh alloyed nanoparticles can be achieved with compositional control based on simultaneous decomposition of Pt- and Rh-metal precursors. By combining data from powder X-ray diffraction, (high-resolution) transmission electron microscopy [(HR)TEM], energy dispersive X-ray spectroscopy (EDS) and kinetic experiments, we describe key parameters for compositional control. Powder X-ray diffraction suggests a crystallite size of around 4 nm, less than the size of polycrystalline particles, of around 7 nm in average and with different morphologies, as imaged by TEM. High-Angle Annular Dark Field Scanning TEM and EDS show some compositional fluctuations between and within in the received Pt-Rh nanoparticles. Based on insight to the reaction kinetics of the individual Pt and Rh metal precursors, recipes are fine-tuned to provide bimetallic nanoparticles with controlled average composition, including achieving the identical Pt/Rh molar ratio for the resulting nanoparticles as defined by the precursor mixture prior to the simultaneous reduction step. The adopted approach adds value beyond the Pt-Rh system and shows that control of precursor reactivity is essential to provide exact metal compositions of bimetallic nanoparticles for use in fundamental studies and applications.