Pd-Pt Bimetallic Nanodendrites with High Activity for Oxygen Reduction

Controlling the morphology of Pt nanostructures can provide a great opportunity to improve their catalytic properties and increase their activity on a mass basis. We synthesized Pd-Pt bimetallic nanodendrites consisting of a dense array of Pt branches on a Pd core by reducing K2PtCl4 with L-ascorbic acid in the presence of uniform Pd nanocrystal seeds in an aqueous solution. The Pt branches supported on faceted Pd nanocrystals exhibited relatively large surface areas and particularly active facets toward the oxygen reduction reaction (ORR), the rate-determining step in a proton-exchange membrane fuel cell. The Pd-Pt nanodendrites were two and a half times more active on the basis of equivalent Pt mass for the ORR than the state-of-the-art Pt/C catalyst and five times more active than the first-generation supportless Pt-black catalyst. Platinum (Pt) is the most effective catalystto facilitate both hydrogen oxidation andoxygen reduction in a proton-exchange membrane (PEM) fuel cell (1–4), but several critical issues still need to be addressed before such cells can be commercialized for automo-tive applications: For example, the oxygen re-duction reaction (ORR) is kinetically limited a