物理化学学报 >> 2010, Vol. 26 >> Issue (05): 1239-1248.doi: 10.3866/PKU.WHXB20100506

电化学 上一篇    下一篇

电极/离子液体界面电容

赵娣, 黄青, 金先波, 魏献军, 陈政   

  1. 武汉大学化学与分子科学学院, 武汉 430072; Department of Chemical and Environmental Engineering, Faculty of Engineering, The University of Nottingham, Nottingham NG7 2RD, UK
  • 收稿日期:2009-11-27 修回日期:2010-01-24 发布日期:2010-04-29
  • 通讯作者: 金先波, 陈政 E-mail:xbjin@whu.edu.cn; george.chen@nottingham.ac.uk

Capacitance at the Electrode/Ionic Liquid Interface

ZHAO Di, HUANG Qing, JIN Xian-Bo, WEI Xian-Jun, CHEN George Z.   

  1. 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
  • Received:2009-11-27 Revised:2010-01-24 Published:2010-04-29
  • Contact: JIN Xian-Bo, CHEN George Z. E-mail:xbjin@whu.edu.cn; george.chen@nottingham.ac.uk

摘要:

用电化学阻抗方法研究了铂片电极在BMIMPF6, BMIMBF4, BMIMClO4, BMIMTf2N, BMIMCl, BMIMBr, C3OHMIMBF4, C3OHMIMClO4和BMMIMPF6 (BMIM: 1-butyl-3-methylimidazolium; C3OHMIM: 1-(3-hydroxypropyl)-3-methylimidazolium; BMMIM: 1-butyl-2-methyl-3-methylimidazolium; Tf2N: bis(trifluoromethylsulfonyl)amide)等离子液体中的界面电容及结构.结果表明: 当阴、阳离子半径相差不大且不存在特性吸附时, 在零电荷电势附近, 电极/离子液体界面的电容-电势曲线将出现电容单峰或者双峰. 电极的零电荷电势对应于单峰的峰电势或者双峰之间的谷电势. 当电极电势远离零电荷电势时, 电极/离子液体界面成紧密层结构, 可由紧密层理论来描述. 如果存在离子的特性吸附, 相应的电容峰可能不再出现, 而表现为双层电容随电极电势对零电荷电势的偏离而单调增加. 还研究了添加小的Li+离子对电极/离子液体界面电容的影响. 通过向BMIMTf2N中加入LiTf2N, 发现Li+离子可以改变电极/离子液体界面的双层结构, 但无助于界面电容的提高, 甚至可能引起电容的降低. 最后探讨了不同条件下, 尤其考虑阴阳离子特性吸附时,电极/离子液体的界面结构.

关键词: 电化学电容, 离子液体, 电极/电解液界面, 界面离子排列, 电化学阻抗谱

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 words: Electrochemical capacitance, Ionic liquid, Electrode/electrolyte interface, Interfacial ion collocation, Electrochemical impedance spectroscopy

MSC2000: 

  • O646