Microstructure of surface-tailored platinum nanocrystals

Nanoscaled Pt-based materials are widely studied because of their applications as catalysts, in particular in fuel cells. The surface structure plays a key role in determining the reactivity of those systems. Fundamental interest to study the mechanisms of model reactions controlled by "size effects" in electrocatalysis has driven research toward the development of synthesis routes that allow a fine tuning of shape, mean size and size distribution of the produced nanoparticles. For instance it has been already shown that capping by polyacrylate allows cubes and tetrahedr, to be produced [1]. There is a limited number of ways to control the surface of the nanoparticles: among them, electrosorption is a powerful technique able to check the "extended" domains of (100) or (111) symmetry [4]. Here, 2-4 nm Pt nanostructures were produced by the water-in-oil [1,2] and by the polyol [5] methods. An efficient dispersion of the active metal on the support was obtained, but the electrochemical activity of these materials could be annihilated by the adsorption of the stabilizer, in some cases too strongly attached at the surface of the particles ( i.e. poly vinyl pyrrolidone). With the colloidal method and H2 as reducing agent of the Pt precursors, a remarkable enhancement of the ordered domains (100) and (111) is observed, correlated with grain morphology and defect density. The latter information was obtained both by HRTEM and by powder diffraction. In particular, the Whole Powder Pattern Modelling (WPPM) [2,3] was employed to extract a domain size distribution and information on lattice defects from the diffraction patterns. The results demonstrate that surface and size control can provide a viable route to tailor the activity and stability of platinum nanoparticle catalysts. [1] Solla-Gullon J., Vidal-Iglesias F.J., Herrero E., Feliu J.M., Aldaz A., Electrochem. Comm., 2006, 8, 189. [2] Scardi P., Leoni M., Acta Cryst. A, 2004, A58, 190. [3] Brimaud S., Coutanceau C., Garnier E., Léger J.M., Gérard F., Pronier S., Leoni M., J. Electroanal. Chem., 2007, 602, 226. [4] Solla-Gullon J., Vidal-Iglesias F.J., Rodriguez P., Herrero E., Feliu J.M., Clavilier J., Aldaz A., J. Phys. Chem.B, 2004, 108, 13573. [5] Niesz K., Koebel M.M., Somorjai G.A., Inorg. Chim. Acta, 2006, 359 2683