Differential Capacitance of the Electrical Double Layer in Imidazolium-Based Ionic Liquids: Influence of Potential, Cation Size, and Temperature
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- 作者：Vera Lockett ; Rossen Sedev ; John Ralston ; Mike Horne ; Theo Rodopoulos
- 刊名：Journal of Physical Chemistry C
- 出版年：2008
- 出版时间：May 15, 2008
- 年：2008
- 卷：112
- 期：19
- 页码：7486 - 7495
- 全文大小：166K
- 年卷期：v.112,no.19(May 15, 2008)
- ISSN：1932-7455
文摘
The interfaces formed at glassy carbon electrodes in three low-temperature ionic liquids (1-methyl-3-ethylimidazolium chloride, emimCl; 1-methyl-3-butylimidazolium chloride, bmimCl; and 1-methyl-3-hexylimidazolium chloride, hmimCl) were investigated by cyclic voltammetry and impedance spectroscopy.The potential dependence of the differential double layer capacitance was measured at several temperaturesbetween 80 and 140 
C, and the temperature response was found to be broadly similar to that obtained withhigh-temperature molten salts. The differential capacitance/potential curves have a minimum and two sidebranches. The minimum corresponds to the point of zero charge. The differential capacitance increases in theorder hmimCl < bmimCl < emimCl because the double layer is thinner when imidazolium (Rmim) cationswith shorter alkyl chain lengths are used. The impedance spectra and capacitance curves indicate that cationsare adsorbed at the open-circuit potential and that their surface excess concentration increases with negativepolarization. Adsorption of the cation becomes stronger as the length of the alkyl chain decreases. Adsorptionof chloride anions occurs at positive potentials and is weakest with bmimCl. The increase in the differentialcapacitance with temperature is most probably due to ion association within the double layer, which diminishesas temperature increases. The electrochemical window narrows as the temperature increases but is almostunaffected by the length of the alkyl chain of the Rmim cation.
C, and the temperature response was found to be broadly similar to that obtained withhigh-temperature molten salts. The differential capacitance/potential curves have a minimum and two sidebranches. The minimum corresponds to the point of zero charge. The differential capacitance increases in theorder hmimCl < bmimCl < emimCl because the double layer is thinner when imidazolium (Rmim) cationswith shorter alkyl chain lengths are used. The impedance spectra and capacitance curves indicate that cationsare adsorbed at the open-circuit potential and that their surface excess concentration increases with negativepolarization. Adsorption of the cation becomes stronger as the length of the alkyl chain decreases. Adsorptionof chloride anions occurs at positive potentials and is weakest with bmimCl. The increase in the differentialcapacitance with temperature is most probably due to ion association within the double layer, which diminishesas temperature increases. The electrochemical window narrows as the temperature increases but is almostunaffected by the length of the alkyl chain of the Rmim cation.