One-pot synthesis of core–shell-like Pt3Co nanoparticle electrocatalyst with Pt-enriched surface for oxygen reduction reaction in fuel cells

2–3 nm sized Pt3Co nanoparticles (NPs) with Pt-enriched shells on a carbon support were prepared by a one-step ultrasound polyol process on Pt(acac)2 (acac = acetylacetonate) and Co(acac)2. The ultrasound facilitates the conversion of Co(acac)2 and retards the conversion of Pt(acac)2 into NPs, which can be explained with the different vapour pressures of the metal precursors. The Pt-enriched shell structure of the NPs by this method, as opposed to the alloy-like elemental distribution of the NPs synthesized in similar conditions but without ultrasound, was evidenced by transmission electron microscopy, magnetism data, extended X-ray absorption fine structure analyses, and chemical replacement tests of Co with Ru3+. Electrochemical oxygen reduction reaction data of these NPs showed improved performance from the commercial Pt/C with the NPs with Pt-enriched shells showing the highest activity.