On Capacitive Processes at the Interface between 1-Ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate and Au(111)

Abstract

Electrochemical impedance spectroscopy was used for characterizing the interface between the ultrapure room-temperature ionic liquid, 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)-trifluorophosphate, [EMIm]FAP, and a Au(111) working electrode (WE). Plots of the potentialdependent spectroscopic data in the complex capacitance plane (CCP) reveal the existence of three distinct processes taking place on different time scales. At all WE potentials ranging from -0.5 to þ1.0 V versus a Pt pseudo-reference electrode, a highfrequency semicircle was detected in the CCP, which was attributed to the formation of an electrochemical double layer (EDL). At intermediate frequencies, a second capacitive process was observed, which is most likely related to electrode de-/reconstruction in the cathodic regime and to a strong interaction between the Au(111) surface and FAPanions in the anodic regime. When the WE potential becomes either more negative than -0.4 V or more positive than þ0.8 V, a third ultraslow process was detected, which seems to become Faradaic in the low-frequency limit. To extract differential capacitance values for EDL formation and for the second capacitive process, the complex capacitance data were fitted to an empirical Cole-Cole type equation. We find a significant hysteresis in the potential dependence of the differential double-layer capacitance (C EDL ). The capacitance relaxation strength of the second process is particular high at electrode potentials around þ0.4 V and at potentials more negative than -0.4 V.

The Differential Capacitance of Ionic Liquid / Metal Electrode Interfaces – A Critical Comparison of Experimental Results with Theoretical Predictions

“…The same index n indicates that the respective cathodic and anodic current density peaks are based on the same redox process. A discussion of the origin of these current density peaks is beyond the scope of the present [25,26,30].…”

“…Thus, it is important to carry out studies on the interface between well-defined electrodes and very pure ionic liquids and to establish suitable methods for the extraction of capacitance data from broadband EIS spectra. Potential-dependent differential capacitance data were extracted from broadband impedance spectra in the following way [25,26]: (i) conversion of complex impedance data into complex capacitance data; (ii) fit of the complex capacitance data with an empirical Cole-Cole equation. The obtained capacitance curves are critically compared with theoretical predictions of mean-field models [17,19,20].…”

The interface between Au(100) and 1-butyl-3-methyl-imidazolium-bis(trifluoromethylsulfonyl)imide

“…For the present system, Au(100) | BMITf 2 N, both circuits were applicable. Alternatively, the equivalent circuit of Figure 2.a was found to be appropriate for Au(100) | BMIPF 6 and Au(100) | BMITf 2 N; the circuit of Figure 2.b was definitely inappropriate for Au(100)|BMIPF 6 , but appropriate for Au(100)|BMITf 2 N, Au(111)|BMIPF 6 [16], Au(100)|guanidinium-based ILs [20], and also for the Au(111)| [EMI][FAP] 4 system [38]. The connection of the models and systems, just as the physical meaning of the W-and/or CPE-elements still remains an open issue.…”

Computer simulations of ionic liquids at electrochemical interfaces

“…71 While Mo simulations, [72][73][74] modified MSA theory, 75 and DF have revealed that the DC can have both negative a temperature dependence for the restricted primitiv negative temperature dependence is expected for t and temperature of our simulations. that the use of single-frequency measurements could lead to misleading results [98][99][100] . Although some of the experimental problems do not arise in computer simulations, where, for example, it is much easier to study a perfect monocrystalline surface than a polycrystalline one, they also have their drawbacks.…”