Low-temperature fuel cells are limited by the oxygen reduction reaction, and their widespread implementation in automotive vehicles is hindered by the cost of platinum, currently the best-known catalyst for reducing oxygen in terms of both activity and stability. One solution is to decrease the amount of platinum required, for example by alloying, but without detrimentally affecting its properties. The alloy PtxY is known to be active and stable, but its synthesis in nanoparticulate form has proved challenging, which limits its further study. Herein we demonstrate the synthesis, characterization and catalyst testing of model PtxY nanoparticles prepared through the gas-aggregation technique. The catalysts reported here are highly active, with a mass activity of up to 3.05 A mgPt(-1) at 0.9 V versus a reversible hydrogen electrode. Using a variety of characterization techniques, we show that the enhanced activity of PtxY over elemental platinum results exclusively from a compressive strain exerted on the platinum surface atoms by the alloy core.

Eine Frage der Größe: Der Einfluss der Partikelgröße auf die Aktivität größenselektierter Platin‐Cluster in der Sauerstoffreduktionsreaktion (ORR) wurde untersucht. Die Aktivität der Pt‐Nanopartikel sank mit kleiner werdender Größe der Nanopartikel, entsprechend einer Abnahme des Anteils an Terrassen auf der Oberfläche der Pt‐Nanopartikel (jk=kinetische Stromdichte, siehe Bild).

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We have prepared an yttrium modified Pt(111) single crystal under ultra-high vacuum conditions, simulating a bulk alloy. A Pt overlayer is formed upon annealing the crystal above 800 K. The annealed structure binds CO weaker than Pt(111), with a pronounced peak at 295 K in the temperature programmed desorption of CO. When depositing a large amount of yttrium at 1173 K, a (1.88 × 1.88)R30° structure relative to Pt(111) was observed by low energy electron diffraction. Such an electron diffraction pattern could correspond to a (2 × 2)R30° structure under 6% compressive strain. This structure is in agreement with the structure of the vacancies in a Pt Kagomé layer in Pt5Y rotated 30° with respect to the bulk of the Pt(111). The Pt overlayer is relatively stable in air; however, after performing oxygen reduction activity measurements in an electrochemical cell, a thick Pt overlayer was measured by the angle resolved X-ray photoelectron spectroscopy depth profile. The activity of the annealed Y/Pt(111) for the oxygen reduction reaction was similar to that of polycrystalline Pt3Y.

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ABSTRACT:Conditions for an attractive and productive protocol for the position-selective intramolecular C-H amination of aliphatic groups (Hofmann-Löffler reaction) are reported employing sulfonimides as nitrogen sources. N-Iodosuccinimide is the only required promoter for this transformation, which is conveniently initiated by visible light. The overall transformation provides pyrrolidines under mild and selective conditions as demonstrated for 17 different substrates.The intramolecular C-H amination of aliphatic groups has recently attracted significant interest from the synthetic community. Major work has focused on the identification of suitable transition metal catalysts to provide the aforementioned transformation. 1 Directed evolution of metalloproteins has recently emerged as a complimentary approach. 2 An alternative consists of the use of small organocatalysts 3 as non-metallic promoters, which, due to their capability to avoid metal contamination, is of major importance to fields such as biological and medicinal synthesis.From a historical perspective, the halide-mediated C-N bond formation at non-activated hydrocarbons was discovered over a century ago and is well established as the Hofmann-Löffler reaction. 4 The general conditions call for preformation of a halogenated amine, which upon irradiation in the presence of strong acid promotes C-H halogenation, which is usually followed by basemediated pyrrolidine formation. A useful modification providing significantly milder reaction conditions was introduced by Suarez, 5 who reported that Hofmann-Löffler-type cyclization reactions can be conducted in the presence of a mixture of molecular iodine and a hypervalent iodine reagent of the general structure ArI(O 2 CR) 2 . 6 This protocol was employed by Fan, who demonstrated its compatibility with sulfonamides as nitrogen sources. 7 We have recently demonstrated that this reaction can be conducted with catalytic amounts of iodine and the use of a single equivalent of hypervalent iodine(III) as the terminal oxidant. 8 This accomplishment has demonstrated that iodine catalysis is indeed feasible within the borders of the Hofmann-Löffler reaction, provided that the iodine concentration is maintained at a sufficient level to perpetuate the two intertwined catalytic cycles. However, the permanent requirement of using a hypervalent iodine reagent as a terminal oxidant 9 has triggered interest in whether the reaction could also be conducted with just a single amount of halide reagent as a stoichiometric promoter. Such a reaction would serve as an important addition to the existing protocols for Hofmann-Löffler reactions.

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Image transmission using incoherent optical fiber bundles (IOFBs) requires prior calibration to obtain the spatial in-out fiber correspondence necessary to reconstruct the image captured by the pseudo-sensor. This information is recorded in a Look-Up Table called the Reconstruction Table (RT), used later for reordering the fiber positions and reconstructing the original image. This paper presents a very fast method based on image-scanning using spaces encoded by a weighted binary code to obtain the in-out correspondence. The results demonstrate that this technique yields a remarkable reduction in processing time and the image reconstruction quality is very good compared to previous techniques based on spot or line scanning, for example.