SFG experiment and ab initio study of the chemisorption of CN on low-index platinum surfaces |
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Authors: | M Tadjeddine J-P Flament A Tadjeddine |
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Institution: | a D.C.M.R. UMR CNRS 7651, École Polytechnique, 91128 Palaiseau Cedex, France b Laboratoire de Physique des Lasers, Atomes et Molécules (UMR CNRS 8523), Centre d’Étude et de Recherche Lasers et Applications (CERLA, FR CNRS 7416), Université de Lille-1, Bât. P5, 59655 Villeneuve d’Ascq Cedex, France c LURE-CNRS, Bât. 209D, Université Paris-Sud, 91405 Orsay Cedex, France |
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Abstract: | A dual analysis is proposed in order to have a better understanding of the adsorption of the cyanide ions on a platinum electrode. The SFG (Sum Frequency Generation) spectroscopy allows the in situ vibrational study and the SFG spectra of the CN− species adsorbed on single crystal Pt electrode allow a systematic study of the low-index platinum surfaces. This experimental work is supported by ab initio calculations using density functional theory and cluster models. For each surface orientation and each geometry, a cluster model of 20-30 Pt atoms has been built in order to interpret the chemisorption of the CN− ions through four kinds of adsorption geometry: on-top or bridge site, bonding via C or N atoms. Geometries have been optimized and adsorption energies, electronic properties and vibrational frequencies have been computed. From the electronic properties, we can propose an analysis of the bonding mechanism for each studied kind of adsorption.The SFG spectra of the CN−/Pt(1 1 1) system present an unique resonance owing to the top C adsorption. It is mainly the same for the CN−/Pt(1 0 0) system. It is also the case for the SFG spectra of the CN−/Pt(1 1 0) system recorded at negative electrochemical voltage; at more positive voltage, a second resonance appears at a lower frequency, owing to the top N adsorption.Experimental and theoretical values of the C-N stretching frequencies are in excellent agreement. |
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Keywords: | Cyanide Chemisorption Sum frequency generation experiment Difference frequency generation experiment Electrochemistry Density functional calculations Metallic surfaces Platinum |
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