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Tuning the catalytic activity of Ag(110)-supported Fe phthalocyanine in the oxygen reduction reaction

A careful choice of the surface coverage of iron phthalocyanine (FePc) on Ag (110) around the single monolayer allows us to drive with high precision both the long-range supramolecular arrangement and the local adsorption geometry of FePc molecules on the given surface. We show that this opens up the possibility of sharply switching the catalytic activity of FePc in the oxygen reduction reaction and contextual surface oxidation in a reproducible way. A comprehensive and detailed picture built on diverse experimental evidence from scanning tunnelling microscopy, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy, coupled with density functional theory calculations, sheds new light on the nature of the catalytically active molecule–surface coordination and on the boundary conditions for its occurrence. The results are of relevance for the improvement of the catalytic efficiency of metallo-macrocycles as viable substitutes for platinum in the cathodic compartment of low-temperature fuel cells.
F. Sedona, et al. http://www.nature.com/nmat/journal/v11/n11/pdf/nmat3453.pdf

A combination of different techniques such as Scanning Tunneling Microscope, synchrotron radiation X-ray photoelectron and absorption spectroscopy combined with density functional theory (DFT) calculations shows that the molecular local chemisorption site and the long-range supramolecular arrangement of Metallo-Phthalocyanine molecules in the monolayer coverage range on a metal surface can be controlled by fine tuning of the overlayer coverage. This in turn opens the possibility of reliably mastering adsorption-site-selective properties such as the molecular catalytic activity, as will be shown here with respect to the FePc-catalysed oxygen reduction reaction, which can be reproducibly switched on or quenched by controlling the Fe-Phthalocyanine local adsorption site in the single-ML range. Our claims are substantiated by characterizing the molecular coordination in the catalytically active phase in the presence of oxygen and by checking that the Fe-Phthalocyanine molecules remain intact throughout the catalytic cycle. Finally, we show that the catalyst pushes the Ag support oxidation to levels unattainable in ultra high vacuum by dosing oxygen on clean silver single-crystal surfaces, and that reduced oxygen thus formed can be fully removed by providing hydrogen ions to the interface. The supramolecular assembly and faster electron transfer rates in the shape complementary heterojunction lead to a larger active volume and enhanced exciton dissociation rate. This work provides fundamental mechanistic insights on the improved efficiency of organic photovoltaic devices that incorporate these concave/convex D/A materials.

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Tuning the catalytic activity of Ag(110) supported Fe phthalocyanine in the oxygen reduction reaction, F. Sedona,    M. Di Marino, D. Forrer, A. Vittadini, M. Casarin, A. Cossaro, L. Floreano, A. Verdini and M. Sambi
Last Updated on Friday, 19 December 2014 17:40