Water-in-oil microemulsion synthesis of platinum-ruthenium nanoparticles, their characterization and electrocatalytic properties

Mixed platinum-ruthenium nanoparticles are prepared by water-in-oil reverse micro-emulsions of water/Triton X-100/propanol-2/cyclohexane. Nanoparticles formed in the microemulsions are characterized by transmission electron microscopy (TEM), electron diffraction (ED), X-ray diffractometry (XRD), energy-dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS). TEM results show a narrow distribution of Pt-Ru nanoparticles. A homogeneous alloy structure in the bimetallic nanoparticles is indicated by XRD analysis and ED analysis. The composition of the Pt-Ru nanoparticles can be easily controlled by the relative concentration of Pt and Ru in the initial precursor solution. The composition that was in the Pt-Ru nano-alloy is found to be the same as that in the original precursor solution. XPS analysis reveals the presence of Pt and Ru metal as well as some oxide of ruthenium. The effect of precursor concentration on microemulsion drop size was investigated by photo correlation spectroscopy (PCS) measurement. The size of Pt-Ru nanoparticles depends on the concentration of precursor in the aqueous phase. At low precursor concentration, the final particle size is about 2.5 nm and appears to be limited by nucleation. At high precursor concentration, the final particle size is about 4.5 nm and appears to be limited by the collisions and mixing with thousands of hydrazine droplets. The Pt-Ru nanoparticles supported on a carbon electrode possessed high dispersion and high catalytic activity for methanol oxidation at room temperature.