Scalable Synthesis of Palladium Icosahedra in Plug Reactors for the Production of Oxygen Reduction Reaction Catalysts

We have synthesized Pd icosahedra with uniform, controllable sizes in plug reactors separated by air. The oxygen contained in the air segments not only contributed to the generation of a reductant from diethylene glycol in situ, but also oxidized elemental Pd back to the ionic form by oxidative etching and thus slowed down the reduction kinetics. Compared to droplet reactors involving silicone oil or fluorocarbon, the use of air as a carrier phase could reduce the production cost by avoiding additional procedures for the separation of products from the oil. The average diameters of the Pd icosahedra could be readily controlled in the range of 12-20 nm. The Pd icosahedra were further employed as seeds for the production of Pd@Pt_2-3L core-shell icosahedra, which could serve as a catalyst toward the oxygen reduction reaction with greatly enhanced activity. We believe that the plug reactors could be extended to other types of noble-metal nanocrystals for their scale-up production.