An efficient reduction route for the production of Pd-Pt nanoparticles anchored on graphene nanosheets for use as durable oxygen reduction electrocatalysts

Pt and Pd-Pt nanoparticles were anchored on reduced graphene oxide (RGO) with the aid of poly(diallyldimethylammonium chloride) (PDDA), where Pt and Pd ions were first attached to PDDA-functionalized graphene oxide sheets and the encased metal ions and graphene oxide were then reduced simultaneously by ethylene glycol. As supported by transmission electron microscopy, metal nanoparticles, of small particle size even at a high metal loading, were chemically attached to PDDA-RGO. X-ray diffraction indicates that the as-prepared Pd-Pt nanoparticles have a single-phase fcc structure and are principally alloys of Pd and Pt. Among the RGO-supported Pt and Pd-Pt catalysts, Pt nanoparticles anchored on PDDA-RGO exhibit the highest activity for the oxygen reduction reaction (ORR), and the ORR activity of the Pd-Pt alloy electrocatalysts increases with Pt content. All the catalysts demonstrate an enhanced ORR durability when PDDA is present; strongly suggesting that PDDA plays a crucial role in the dispersion and stabilization of the metal nanoparticles on RGO. The ORR activities of the Pd-Pt catalysts remain enhanced even after accelerated durability testing. The formation of a Pt-rich shell, as confirmed by X-ray photoelectron spectroscopy and CO stripping voltammetry, may account for the increased activity. (C) 2011 Elsevier Ltd. All rights reserved.