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. 2019 Sep 17;24(18):3382.
doi: 10.3390/molecules24183382.

Electrical and Electrochemical Behavior of Carbon Paste Electrodes Modified with Ionic Liquids Based in N-Octylpyridinium Bis(Trifluoromethylsulfonyl)Imide. A Theoretical and Experimental Study

Carla Báez  1   2 , Freddy Navarro  3 , Francesca Fuenzalida  4 , María J Aguirre  5 , M Carmen Arévalo  6 , María Afonso  7 , Camilo García  8 , Galo Ramírez  9 , J Antonio Palenzuela  10
Affiliations

Electrical and Electrochemical Behavior of Carbon Paste Electrodes Modified with Ionic Liquids Based in N-Octylpyridinium Bis(Trifluoromethylsulfonyl)Imide. A Theoretical and Experimental Study

Carla Báez et al. Molecules. .

Abstract

In this work, we studied carbon paste electrodes (CPEs) with two kinds of binders: mineral oil or ionic liquids (IL) derived from N-substituted octyl pyridinium bis(trifluoromethylsulfonyl)imide with the substituents H-, CH3-, CN- and CF3-. The work aims to study this series of IL and determine a possible effect of the substituent of the cation in the behavior of the IL as a binder of graphite for obtaining IL-CPEs. The electrochemical response and the electrical behavior were measured by cyclic voltammetry and electrochemical impedance spectroscopy, respectively. Surprisingly, the substituent does not affect the cyclic voltammetry response because in all the cases, high resistance and high capacitive currents were obtained. The best response in terms of conductivity is obtained by CPE. In the case of impedance measurements, the substituent does not cause differences, and in all the cases, the IL-CPEs show nearly the same responses. CPE shows lower capacitance and higher resistance for diffusion compared to the IL-CPEs due to his lower porosity. The high resistance showed by the IL-CPEs by cyclic voltammetry can be attributed to poorly intermolecular forces among graphite, water, electrolyte, and ILs as demonstrated by theoretical calculations.

Keywords: N-octyl pyridinium bis(trifluoromethylsulfonyl)imide; intramolecular forces of ionic liquid; ionic-liquid carbon paste electrodes.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Schematic representation of the ionic liquids (ILs) where R is H-, CH3-, CN-, or CF3-. Proton-label is shown.
Figure 2
Figure 2
Voltammetric response of carbon paste electrodes (CPE) and modified electrodes. Experiments realized in an Ar-bubbled solution of Britton–Robinson buffer (BR) at pH 3. Scan rate: 100 mVs−1.
Figure 3
Figure 3
Nyquist plot for CPE and ILs modified electrodes. Frequency range: 100,000–0.01 Hz. Sinusoidal potential pulse = 5 mV. All measurements at open circuit potentials. Britton–Robinson buffer pH = 3.00.
Scheme 1
Scheme 1
The equivalent circuit proposed. Rs = resistance of solution, CPedl = constant phase element, W = Warburg impedance.
Figure 4
Figure 4
(A,B) Bode plot for CPE and ILs modified electrodes. Frequency range: 100,000–0.01 Hz. Sinusoidal potential pulse = 5 mV. All measurements at open circuit potentials. Britton–Robinson buffer pH = 3.00.
Figure 5
Figure 5
The four spatial arrangements studied. (A) The structure where cation with the alkyl chain is perpendicular to the aromatic ring and the anion outside of the cavity. (B) The same structure from A, but the anion is inside the cavity. (C) The cation is almost lineal, and the anion is outside of the cavity. (D) The cation is the same structure that C, but the anion is inside of the cavity. Only the unsubstituted pyridinium derivatives are shown for clarity.
Figure 6
Figure 6
Non-covalent bond critical points (BCP) and critical bond paths for the ionic liquid in the four arrangements studied. (A) The structure where cation with the alkyl chain is perpendicular to the aromatic ring and the anion outside of the cavity. (B) The same structure from A, but the anion is inside the cavity. (C) The cation is almost lineal, and the anion is outside of the cavity. (D) The cation is the same structure that C, but the anion is inside of the cavity. Only the unsubstituted pyridinium derivatives are shown for clarity.
Figure 7
Figure 7
Non-covalent critical bond points and critical bond paths for the four ionic liquids studied in the B-type arrangements. (A) Unmodified IL; (B) CH3- modified IL; (C) CN- modified IL; (D) CF3- modified IL.
Figure 8
Figure 8
Reduced Density Gradient (RDG) plot of the ionic liquid in arrangement B. (A) Unmodified IL; (B) CF3- modified IL.
Figure 9
Figure 9
Scatter plot of the RDG analysis of the four arrangements of the unsubstituted (R = H) ionic liquids. (A) The structure where cation with the alkyl chain is perpendicular to the aromatic ring and the anion outside of the cavity. (B) The same structure from A, but the anion is inside the cavity. (C) The cation is almost lineal, and the anion is outside of the cavity. (D) The cation is the same structure that C, but the anion is inside of the cavity
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