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Intrinsic Electrochemical and Strain Effects in Nanoparticles Mikhail Mamatkulov, and Jean-Sébastien Filhol J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/jp3099494 • Publication Date (Web): 12 Dec 2012 Downloaded from http://pubs.acs.org on December 15, 2012
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The Journal of Physical Chemistry
Intrinsic Electrochemical and Strain Effects in Nanoparticles
Mikhail Mamatkulov2, Jean-Sébastien Filhol1* 1
Institut Charles Gerhardt Montpellier
UMR 5253 CNRS-UM2-ENSCM-UM1 C.T.M.M., Université Montpellier 2 - Bât. 15 - CC-15001 Place Eugène Bataillon 34 095 Montpellier Cédex 5 – France 2
Boreskov Institute of Catalysis, Russian Academy of Sciences, 630090 Novosibirsk, Russia
Abstract We have performed a density functional theory investigation of the {111} facet of a 201 Pt atoms nanoparticle (NP), in order to explain its particular reactivity compared to a corresponding (111) surface. Then, notable differences in physical properties and reactivity between {111} facets and (111) surfaces can be correlated with: i) strain effect due to the contraction of surface Pt-Pt distance; ii) electrochemical effects due to spontaneous negative charging of the {111} facet leading to a very strong local electric field (20.106 V.cm-1). The latter effect only occurs in systems of nanometric size like nanoparticles because of the combination of the nanoparticle high capacitance and of different local work-function in facets and edges. The nanoparticle {111} facet with an adsorbed CO molecule exhibits an electronic structure, adsorption energy and C-O stretch frequency extremely close to that of a strained and charged (111) surface. This study suggests that metallic NPs behave like intrinsic electrochemical systems with a potential tuned by their size and shape explaining part of their specific reactivity. Reciprocally, large NP facets reactivity could be investigated by simple charged strained surfaces that would give inexpensive models. Finally, this intrinsic electrochemical effect could be used to better understand charge transfer effects on catalysis, electro-catalysis and help to design new kinds of tunable catalysts. Keywords: Density Functional Theory, reactivity, Stark effect, CO frequency, electric field, capacitance, electronic properties.
I Introduction *
Corresponding author:
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The Journal of Physical Chemistry
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Transition metals are widely used as catalysts. Since the active sites are usually located on the surface, metals tend to be dispersed in working catalysts as nano-sized particles (NPs), to maximize their area/volume ratio. But, catalytic properties do not directly scale with the particle size: small (
