Continuous-flow synthesis of Pd@Pt core-shell nanoparticles

A flow manufacturing process was investigated for the synthesis of Pd@Pt core-shell nanoparticles (NPs) with high productivity and exact structural control. Pd@Pt core-shell NPs were successfully synthesized in a flow reactor using polyvinylpyrrolidone (PVP) as a capping agent. However, the oxygen reduction reaction (ORR) activity of the Pd@Pt/PVP/C catalyst was found to be significantly lower than that of commercial Pt/C as the remaining PVP inhibited ORR. In order to improve ORR activity, it is necessary to support the highly dispersed Pd@Pt NPs on activated carbon without the use of PVP. Cyclic voltammetry, transmission electron microscopy, and X-ray absorption fine structure analyses showed that Pd@Pt NPs could be uniformly dispersed on activated carbon by adding bis(2-methoxyethyl) ether (diglyme) as a capping agent. The particle size and core-shell structure of the Pd@Pt NPs did not differ significantly between the NPs synthesized with PVP or diglyme, indicating that advanced structural control was possible without PVP. Furthermore, the mass activity per Pt weight of the Pd@Pt/C catalyst using diglyme was found to be 1.8-fold higher than that of Pt/C. We thus succeeded in synthesizing Pd@Pt core-shell NPs with precisely controlled structure and high ORR activity by flow process.