Pt-Cu nanoctahedra were successfully synthesized through a simultaneous reduction of platinum(II) acetylacetonate and copper(I)/(II) chloride in the presence of tungsten hexacarbonyl, oleylamine and oleic acid at high temperature. Comparative studies of electrocatalysis on Pt nanocubes, the {111}terminated Pt-Cu nanoctahedra and {100}-bounded Pt-Cu nanocubes with similar composition and size indicate that the activity of Pt-Cu nanocrystals towards formic acid oxidation is shape-dependent, and is higher than that of Pt nanocubes.

We report a Kirkwood-Alder transition in a system of nonspherical Pt(3)Cu(2) nanoctahedra coated with oleic acid and oleylamine ligands. Using both transmission electron microscopy tomography with 3D reconstruction analysis and synchrotron-based in-situ grazing-incidence small-angle X-ray scattering (GISAXS) techniques, we specifically determined that these nanoctahedra can assemble into an open structure in which the nanoctahedra are arranged tip-to-tip to form a bcc superlattice with a low packing efficiency. Using in-situ and real-time GISAXS, we further observed a "nanoctahedron crystallization" as a soft Kirkwood-Alder transition, that is, the soft nanoactahedra crystallize at a critical concentration and possess continuous crystalline states during a period of solvent evaporation. Finally, we found a reversible change of the superlattice constant during the solvent annealing and evaporation/drying processes.

We explore the possibility of preparation of Pt3M (M = Fe, Ni and Co) nanocubes using carbon monoxide as an alternative protocol under different experimental conditions. The results suggest that the sole carbon monoxide flow at ambient pressure can enable the formation of binary Pt-M nanocrystals, but it is inadequate to facilitate the formation of Pt3M nanocubes in the given system under specified conditions.

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