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Acta Phys. -Chim. Sin.  2010, Vol. 26 Issue (05): 1239-1248    DOI: 10.3866/PKU.WHXB20100506
ELECTROCHEMISTRY     
Capacitance at the Electrode/Ionic Liquid Interface
ZHAO Di, HUANG Qing, JIN Xian-Bo, WEI Xian-Jun, CHEN George Z.
College of Chemistry and Molecular Science, Wuhan University, Wuhan 430072, P. R. China; Department of Chemical and Environmental Engineering, Faculty of Engineering, The University of Nottingham, Nottingham NG7 2RD, UK
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Abstract  

The interfacial structure and capacitance of a Pt foil electrode were investigated by electrochemical impedance spectroscopy in various ionic liquids including BMIMPF6, BMIMBF4, BMIMClO4, BMIMTf2N, BMIMCl, BMIMBr, C3OHMIMBF4, C3OHMIMClO4 and BMMIMPF6 (BMIM: 1-butyl-3-methylimidazolium, C3OHMIM: 1-(3-hydroxypropyl)-3-methylimidazolium, BMMIM: 1-butyl-2-methyl-3-methylimidazolium, Tf2N: bis(trifluoromethylsulfonyl)amide). The results indicate that when the anion and cation of the ionic liquid are of comparable size and do not adsorb specifically on the electrode, the“capacitance-potential”curve near the potential of zero charge exhibits either one peak or two peaks. The potential of zero charge corresponds to either the peak potential or the valley potential on the capacitance-potential curve with one peak or two peaks, respectively. When the potential is positive or negative to the potential of zero charge, the structure of the“electrode/ionic liquid”interface could be explained by the compact layer theories. In the presence of specific ion adsorption, the capacitance peak disappears and while the electrode potential shifts against the potential of zero charge, the interfacial capacitance rapidly increases. The effects of small Li+ ions on the electrode/ionic liquid interfacial structure and capacitance were also studied. When LiTf2N was added to BMIMTf2N, the small Li + ion changed the ionic composition and hence the structure of the electrode/ionic liquid interface, and also decreased the interfacial capacitance. Based on these findings, the arrangement and conformation of the anions and cations of the ionic liquid at the electrode/ionic liquid interface are elaborated under different conditions with particular attention to the specific adsorption of both the cation and the anion.



Key wordsElectrochemical capacitance      Ionic liquid      Electrode/electrolyte interface      Interfacial ion collocation      Electrochemical impedance spectroscopy     
Received: 27 November 2009      Published: 22 March 2010
MSC2000:  O646  
Corresponding Authors: JIN Xian-Bo, CHEN George Z.     E-mail: xbjin@whu.edu.cn; george.chen@nottingham.ac.uk
Cite this article:

ZHAO Di, HUANG Qing, JIN Xian-Bo, WEI Xian-Jun, CHEN George Z.. Capacitance at the Electrode/Ionic Liquid Interface. Acta Phys. -Chim. Sin., 2010, 26(05): 1239-1248.

URL:

http://www.whxb.pku.edu.cn/10.3866/PKU.WHXB20100506     OR     http://www.whxb.pku.edu.cn/Y2010/V26/I05/1239

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