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Monodisperse 8 nm Pt nanocubes are synthesized by reducing Pt(acac)2 in the presence of oleic acid, oleylamine, and a trace amount of Fe(CO)5. Self-assembly of these nanocubes results in a (100) textured array. The nanocubes show an enhanced catalysis toward oxygen reduction, and their specific activity is over twice as high as that from the commercial Pt nanoparticles.

We report the design and synthesis of multimetallic Au/Pt-bimetallic nanoparticles as a highly durable electrocatalyst for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells. This system was first studied on well-defined Pt and FePt thin films deposited on a Au(111) surface, which has guided the development of novel synthetic routes toward shape-controlled Au nanoparticles coated with a Pt-bimetallic alloy. It has been demonstrated that these multimetallic Au/FePt(3) nanoparticles possess both the high catalytic activity of Pt-bimetallic alloys and the superior durability of the tailored morphology and composition profile, with mass-activity enhancement of more than 1 order of magnitude over Pt catalysts. The reported synergy between well-defined surfaces and nanoparticle synthesis offers a persuasive approach toward advanced functional nanomaterials.

Katalytische Pflastersteine: Monodisperse Platinnanopartikel mit definierter Größe (3–7 nm) und Form (Polyeder, angeschnittener Würfel oder Würfel) wurden hergestellt. Die würfelförmigen Nanopartikel sind ein viel aktiverer Katalysator in der elektrochemischen Sauerstoffreduktion: Die Stromdichte J ist für 7 nm große Würfel viermal so hoch wie für die anderen Formen (siehe Bild) und spricht für ein großes Potenzial beim Einsatz in Brennstoffzellen.

A remaining challenge for deployment of proton-exchange membrane fuel cells is the limited durability of Pt-nanoscale materials that operate at high voltages during the cathodic oxygen reduction reaction. In this work, atomic-scale insight into well-defined single crystalline, thin-film, and nanoscale surfaces exposed Pt dissolution trends that governed the design and synthesis of durable materials. A newly defined metric, intrinsic dissolution, is essential to understanding the correlation between the measured Pt loss, surface structure, size and ratio of Pt-nanoparticles in carbon support. It was found that utilization of Au underlayer promotes ordering of Pt surface atoms towards (111)structure, while Au on the surface selectively protects low-coordinated Pt sites. This mitigation strategy was applied towards 3 nm Pt 3 Au/C nanoparticles, resulting in elimination of Pt dissolution in liquid electrolyte, including 30-fold durability improvement vs. 3 nm Pt/C over extended potential range up to 1.2 V.

Rational synthesis of Pt-Au(n) nanoparticles (NPs) has been achieved by overgrowing Au on Pt with n, the number of Pt-Au heterojunctions in each particle, controlled from 1 to 4, and the corresponding NPs in pear-, peanut-, or clover-like morphology. Monte Carlo simulation reveals that the morphology control can be correlated to a thermodynamic equilibrium of the Au coherence energy, the overall particle surface energy, and the heterogeneous Pt-Au interfacial energy in the composite system, which is manipulated by the seeding particle size and solvent polarity. The developed synthetic strategy together with the provided fundamental understanding of heterogeneous nucleation and heterostructure growth could have great potential toward the rational synthesis of composite nanomaterials with morphology control for advanced catalytic and other functional applications.

We have studied the effect of additional elements of Sn, Pb, Sb, and Bi on the ordering of L10–CoPt films. All of these additives are demonstrated to be very effective to promote the ordering and developing of a very large coercivity of the samples annealed at 400 °C. It is worth noting that this annealing temperature for ordering is 200 °C lower than that of pure CoPt. The crystallographic and chemical analyses have revealed that these additives easily diffuse and segregate onto the film surfaces by postannealing because of their very low surface free energy and extremely low solubility in Co. Therefore, it seems reasonable to conclude that the ordering in the CoPt film is significantly promoted at much lower temperature by the aid of a lot of defects produced by the additives excreted by postannealing.

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