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.

A matter of size: The particle size effect on the activity of the oxygen reduction reaction of size‐selected platinum clusters was studied. The ORR activity decreased with decreasing Pt nanoparticle size, corresponding to a decrease in the fraction of terraces on the surfaces of the Pt nanoparticles (jk=kinetic current density, see picture).

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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