Electrochemical Characterization of Iodide Ions Adsorption Kinetics at Bi(111) Electrode from Three-Component Ionic Liquids Mixtures

Abstract

The electrochemical behavior of RTIL mixtures containing 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate and 1-ethyl-3-methylimidazolium iodide were characterized by using cyclic voltammetry and electrochemical impedance spectroscopy methods. The capacitance values of the system at potentials more positive than −0.6 V (vs. Ag|AgCl| mixture of RTIL) strongly depend on the chemical nature of the anions in the mixture. Also the strong adsorption of I − at Bi (111) By mixing two or more ionic liquids with different properties (viscosity, dielectric permeability, polarity) it is possible to maximize the advantage of RTIL as an electrolyte. [4][5][6][7][8] Our recent studies have shown that the addition of specifically adsorbed iodide ions strongly influences the electrochemical characteristics of RTILs systems increasing the specific capacitance and decreasing the series resistance values.9-12 For the further investigation of the specific adsorption of iodide ions from RTIL mixtures the 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMImOTF) was added to the 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF 4 ) + 1-ethyl-3-methylimidazolium iodide (EMImI) mixture. It is important that the imidazolium based ionic liquids with stable anions such as BF 4 − , PF 6 − and CF 3 SO 3 − exhibit air and moisture stability. These properties become important when electrochemical devices will be used outdoors. [13][14][15][16] The main aim of this work was to decrease the viscosity and reduce the price of the mixed electrolytes for possible practical use as an electrolyte for supercapacitors as well as different batteries. ExperimentalEMImBF 4 (Fluka Analytical, for electrochemistry, ≥99.0%, H 2 O < 200 ppm, electrochemical window from −2.2 to 3.5 V, melting point 15• C), EMImI (Merck KGaA, >99.5%, H 2 O < 300 ppm, melting point 79• C) and EMImOTF (Merc KGaA, >99.0%, melting point −12• C) were used for preparing the ionic liquid mixtures. For the three-component mixture, the equal volumes of EMImBF 4 and EMImOTF were mixed together and then 1 wt% of EMImI was added into the mixture under dark conditions. EMImI was dissolved by heating the mixture of ionic liquids up to 80• C (using Heidolph MR Hei-End magnetic stirrer with heating function) and cooled slowly down to 22• C inside a glove box (H 2 O ≤ 1.0 ppm). Before each measurement the mixture was saturated with Ar (99.9999%) for 2-3 h. All measurements were carried out in a threeelectrode electrochemical system using electrochemically polished * Electrochemical Society Active Member.z E-mail: enn.lust@ut.ee Bi(111) single crystal as a working electrode (WE) and Pt-net counter electrode. Newly prepared reference electrode (RE) Ag wire coated with AgCl deposited from HCl + H 2 O solution and thereafter very well tried has been used. The preparation of RE and electrochemical polishing of the WE and good long-term cycling stability has been described in published publications. 9,11,[17][18][19] RE was connected to th...

Electrochemical Investigation of 1-Ethyl-3-methylimidazolium Bromide and Tetrafluoroborate Mixture at Bi(111) Electrode Interface

“…7 the optimal Br − % is from 1 to 2% for EMImBr + EMImBF 4 systems, differently from I − system, where the blocking adsorption has been observed already for 2% EMImI system. 11,12 The C p value for 1% EMImI containing mixture is higher than that for 1% EMImBr containing mixture, indicating to the more active adsorption of I − than Br − ions at Bi(111). Likewise C p /C s vs. log f plots (Figs.…”

“…[11][12][13][14]26,36 Exploring new RTILs and their mixtures containing halide ions, we have tested the stability and kinetics of the Ag|AgHal reference electrodes. In the case of AgCl reference…”

“…complex models for the electrical double layer capacitance, that analyze the influence of the surface-active anion addition on the inner layer structure, dielectric permittivity, effective dipoles moment for dipole created at metal|RTIL interface, etc. 7,[11][12][13][14] To continue with the systematic research of halide ions, 1-ethyl-3-methylimidazolium bromide (EMImBr) was selected for the source of bromide ions. There are some theoretical and experimental studies of the thermal stability and decomposition mechanism of EMImBr.…”

“…22 Also, bromide salts with different cations such as dihydroxybenzene, 1-methyl-3-octadecylimidazolium, and 1-butyl-3-methyl-imidazolium have been tested for the supercapacitor application. [22][23][24] According to the detailed comparison of the adsorption data for halide ions measured in aqueous, organic and ionic liquids solutions, [10][11][12][13][14]25,26 it is clear that the mechanism of the specific adsorption of Br − from ionic liquid media needs to be further investigated at metal single crystal electrodes, as well as at carbon electrodes for the futher application of surface active RTIL mixtures in electrochemical muscles and nano-switches, electrodynamic actuators, energy storage and conversion systems, such as EDLCs, organic solar cells and secondary batteries.…”

Classical Density Functional Theory Insights for Supercapacitors

“…Formulating RTIL mixed electrolytes was recently proposed as an effective and convenient strategy to increase the capacitive performance of electrochemical capacitors [82]. However, little is known about how the properties of EDLCs containing RTIL mixtures would be affected by the electrolyte composition [83][84][85][86]. Here, we investigate the EDL structure and the capacitance of two RTILs, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF 4 , and their mixtures with onion-like carbon electrodes using experiment and the CDFT.…”