Facile Synthesis of Composition-Controlled Graphene-Supported PtPd Alloy Nanocatalysts and Their Applications in Methanol Electro-Oxidation and Lithium-Oxygen Batteries.

A new and simple approach is reported for the synthesis of uniformly dispersed PtPd alloy nanocatalysts supported on graphene nanoplatelets (GNPs) (PtPd-GNPs) through the introduction of bifunctional materials, which can modify the GNP surface and simultaneously reduce metal ions. With the use of poly(4-styrenesulfonic acid), poly(vinyl pyrrolidone), poly(diallyldimethylammonium chloride), and poly(vinyl alcohol) as bifunctional materials, PtPd-GNPs can be produced through a procedure that is far simpler than previously reported methods. The as-prepared nanocrystals on GNPs clearly exhibit uniform PtPd alloy structures of around 2 nm in size, which are strongly anchored and well distributed on the GNP sheets. The Pt/Pd atomic ratio and loading density of the nanocrystals on the GNPs are controlled easily by changing the metal precursor feed ratio and the mass ratio of GNP to the metal precursor, respectively. As a result of the synergism between Pt and Pd, the as-prepared PtPd-GNPs exhibit markedly enhanced electrocatalytic performance during methanol electro-oxidation compared with monometallic Pt-GNP or commercially available Pt/C. Furthermore, the PtPd-GNP nanocatalysts also show greatly enhanced catalytic activity toward the oxygen reduction/evolution reaction in a lithium-oxygen (Li-O2 ) process, resulting in greatly improved cycling stability of a Li-O2 battery.

Synthesis of chestnut-bur-like palladium nanostructures and their enhanced electrocatalytic activities for ethanol oxidation.

We report a facile method for the synthesis of Pd nanostructures with highly open structure and huge surface area by reducing Na2PdCl4 with ascorbic acid and using cetylpyridinium chloride (CPC) as a surfactant in an aqueous solution. The prepared Pd nanostructures had an average overall size of 70 nm and were composed of dozens of needle-like thin arms, originating from the same core, with an average thickness of 2.3 nm; the arms looked like chestnut-burs. Time evolution of Pd nanostructures implied that small Pd particles generated at the early stage of the reaction by fast reduction grew via the particle attachment growth mechanism. The morphology and size of the Pd nanostructures could be readily controlled by varying the concentration of CPC; depending on the amount of CPC, the reduction rates varied the morphology of the Pd nanostructures. Because of the huge surface area and possible catalytically active sites, the prepared chestnut-bur-like Pd nanostructures exhibited greater electrocatalytic activity toward ethanol electrooxidation compared to other Pd nanocatalysts, including cubic and octahedral Pd nanocrystals, and even commercial Pd/C.