Au(111)-supported Platinum Nanoparticles: Ripening and Activity
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Au(111)-supported Platinum Nanoparticles: Ripening and Activity Sarah Wieghold1, Lea Nienhaus2, Armin Siebel3, Maximilian Krause1, Patricia Wand1, Martin Gruebele2,4, Ueli Heiz1 and Friedrich Esch1 1
Chair of Physical Chemistry, 3Chair of Electrochemistry, Department of Chemistry and Catalysis Research Center, Technische Universität München, Lichtenbergstraße 4, D-85747 Garching, Germany 2 Beckman Institute for Advanced Science and Technology and Department of Chemistry, 4 Department of Physics, University of Illinois, Urbana, IL 61801, U.S.A. ABSTRACT The recent spotlight on supported nanoparticles (NPs) has attracted attention in the field of catalysis and fuel cell technology. Supported NPs can be used as model catalysts to gain a fundamental understanding of the catalytic properties at the interface. Here, especially the wetchemical preparation of platinum NPs in alkaline ethylene glycol is a powerful approach to synthesize stable particles with a narrow size distribution in the nanometer regime. We combine high resolution imaging by scanning tunneling microscopy with electrochemical characterization by cyclic voltammetry to gain insights into the underlying degradation mechanism of supported platinum NPs, paving the way toward a rational design of supported catalysts with controlled activity and stability. INTRODUCTION Nanomaterials, including nanoparticles (NPs), are widely employed in the field of catalysis, e.g. in hydrogenation1, organic cross-coupling reactions2, as well for hydrogen oxidation and evolution.3, 4 Their great potential is related to a high material efficiency and properties that can be tuned by size, shape and interaction with support and solvents. For catalytic applications, a stable and active catalyst material is required that exposes a high specific surface area, even upon ongoing reaction. However, strong solvent interactions lead to particle ripening, especially if the particles are not stabilized at all or only by weakly bonded agents. Thus, ligand-functionalized particles show great promise in combining enhanced stability with retention of the particles’ accessibility to reactants and specific activity. For a sustainable use, nanocatalysts are commonly supported on a surface. However, strong interactions between the support and the nanomaterial result in unfavorable effects such as degradation and activity loss, while interactions between the nanocatalyst and solvent can also result in the detachment and dissolution of single atoms of the NPs. These stability issues are investigated in this contribution. As a model system, we synthesized platinum NPs via the polyol approach that can be tuned to obtain particles in the nanometer regime.5, 6 Here, the particles are stabilized by a weakly adsorbed ethylene glycol (EG) sub-layer with a narrow size-distribution.7 The NPs were supported on a bare Au surface enabling detailed investigations of support and coverage effects.5, 8 In a second part, the stability and the electrochemical activity of the NPs has been investigated by either modify
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