Ionic liquids electropolymerization

Fig. 4 Resonant frequency changes with time due to repetitive FIA melamine injections, for the MIP-QCM chemosensor. Melamine concentration is indicated with number at each curve. Inset shows FIA calibration plots for (1) melamine and its interfering compounds, such as (2) ammeline, (3) cyanuric acid, and (4) cyromazine. Volume of the injected sample solution was 100 pL. The flow rate of the 1 mM FIC1 carrier solution was 35 pL min-1. The MIP film was prepared by electropolymerization of 0.3 mM bis(2,2 -bithienyl)-benzo-[18-crown-6]methane functional monomer and 0.3 mM 3,3 -bis[2,2 -bis(2,2 -bithiophene-5-yl)]thianaphthene cross-linking monomer, in the presence of 0.1 mM melamine, in the trihexyl(tetradecyl)phosphonium tris(pentafluor-oethy 1)-trifluorophosphate ionic liquid ACN (1 1 v/v) solution, which was 0.9 mM in trifluoroacetic acid (pH = 3.0). The melamine template was extracted from the MIP film with 0.01 M NaOH before the determinations (adapted from [134])...

As vehicles for the electropolymerization of benzene to form the conducting polymer poly (p-phenylene).47 Ionic liquids are said to be good alternatives to liquid sulfur dioxide. 

Comparison of the chronoamperograms recorded during EDOT electropolymerization in the two different ionic liquids and two conventional acetonitrile-based electrolytes allows some conclusions to be drawn about the mechanism of polymer deposition of PEDOT from these different media (Figure 7.12) [80], The current transients suggest that the process is initially much slower in the solution... 

Endres et al. [82] have demonstrated the suitability of an air- and water-stable ionic liquid for the electropolymerization of benzene. This synthesis is normally restricted to media such as concentrated sulfuric acid, liquid SO2 or liquid HF as the solution must be completely anhydrous. The ionic liquid used, l-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate, can be dried to below 3 ppm water, and this ionic liquid is also exceptionally stable, particularly in the anodic regime. Using this ionic liquid, poly(para-phenylene) was successfully deposited onto platinum as a coherent, electroactive film. Electrochemical quartz crystal microbalance techniques were also used to study the deposition and redox behavior of the polymer from this ionic liquid (Section 7.4.1) [83]. 

Li et al. [93] have used l-ethylimidazolium trifluoroacetate, which is a Bronsted acidic ionic liquid, as a medium for the electropolymerization of aniline. They report that in this ionic liquid the oxidation potential of aniline is lower (0.58 V compared to 0.83 V in 0.5 M H2SO4) and that the growth rate of the polymer is increased. Further, the resultant films are smooth, strongly adhered to the Pt working electrode and are very electrochemically stable. Similar results have been reported by Liu et al. [92], who found that this was the best ionic liquid for the polymerization of aniline, compared to the unsatisfactory results observed in other protic ionic liquids 1-butylimidazolium tetrafluoroborate, 1-butylimidazolium nitrate and 1-butylimidazolium p-toluenesulfonate, as well as the l-butyl-3-methylimidazolium hydrogen sulfate and l-butyl-3-methyimidazolium dihydrogen phosphate. 

Ahmad S (2009) Electropolymerization of poly(methyl pyrrole)/carbon nanotubes composites derived from ionic liquid. Polym Eng Sd 49 916-921... 

Improved electropolymerization was also found by Forster and coworkers using ionic liquids as the electrolyte. Electropolymerization of Ru(aphen)32+ (aphen = 5-amino-1,10-phenanthroline) 11 in this medium gave thicker films with improved conductivity. The films showed electrochemiluminescence (ECL) in the presence of tripropylamine [37]. 

Higher coloration efficiency, larger charge capacity, enhanced cycling stability and faster color-bleach rates were observed for nanofibrUlar PANI films, obtained by electropolymerization from an aqueous medium in the presence of an ionic liquid (1-ethyl, 3-methylimidazolium bromide), as compared to that shown by nonfibrillar PANI films fabricated from PEG solution [279]. 

Other electrolytes have been tested. Saccharin sodium hydrate was recently proposed by Bazzaoui et al. [91], as well as saccharin added to oxalic acid as supporting electrolyte [92]. In this latter case an improvement with respect to the oxalic acid electrolyte was attributed to a reinforcement of the barrier effect of the passive layer. Less usual ways have been explored with ionic liquids as media for electropolymerization. Formation of highly conducting PPy on iron in l-butyl-3-methylimidazolium hexafluorophosphate was reported [93] however, it does not seem promising because such solvents are expensive and also because adhesion to the metal is poor. 

The electropolymerization of thiophene-derivatives was conducted in a glove box using a two-electrode setup equipped with a Cu-mesh as counter electrode. The electrolyte used was the ionic liquid [BMIM][TFSI], which was deoxygenated by bubbling with nitrogen for 40 min and dried overnight with molecular sieves prior to use, containing 0.2M of either 2,2 -bithiophene or 3-methylthiophene [40]. Electrosynthesis was conducted under potentiostatic conditions at 3.2-3.4 V and 3.6-3.7 V for bi- and methylthiophene, respectively. Thereafter, the films were successively rinsed in [EMIM][BF4] and DI water, dried, and freed from their templated by dissolution in pure diethyl ether or a 2 1 mixture of diethyl ether and hexane. 

Electrochemical functionalization of single-walled carbon nanotubes (SWNTs] with PANl has also been done in ionic liquids [197], SWNTs are covalently functionalized during the electropolymerization of aniline in ionic liquids. This methodology provides a novel way by which large amount of SWNTs (15 mg/ml] can be modified by aniline electro chemically. 

Figure 3.3 Changes in the in situ FTIR-ATR spectra obtained in the wavenumber range 1600-700 cm" during electropolymerization of O.IM EDOT in the ionic liquid [BMIM][Bp4]. Potential cycling was performed between -0.95 and +1.3 V using a 50 mV/s scan rate. IR spectra were recorded at the end of each scan at about -0.95 V. Reprinted from Ref. [55], Copyright [2004], with permission from Elsevier.

Sekiguchi,K.,Atobe,M.,andFuchigami,T. (2002).Electropolymerization of pyrrole in l-ethyl-3-methylimidazolium trifluoromethanesul-fonate room temperature ionic liquid. Electrochem. Commun., 4, pp. 881-885. 

Deepa, M., and Ahmad, S. (2008). Potypyrrole films electropolymerized from ionic liquids and in a traditional liquid electrol3d e A comparison of morphology and electro-optical properties. European Polymer Journal, 44, pp. 3288-3299. 

As discussed in Section 7.4.3, graphene can also be produced by the electrochemical exfoliation of graphite using ILs or other solvent combinations as electrolyte. Saxena et al. reported on electropolymerization of FOOT using both electrochemically exfoliated graphene (fluoro alkyl phosphate-based ionic liquid functionalized graphene [ILFG]] and rGO as electrolytes [99],... 

Siju, C., Raja, L., Shivaprakash, N., and Sindhu, S. (2015). Gray to transmissive eiectrochromic switching based on electropolymerized REDOT-ionic liquid functionalized graphene films, J. Solid State Electrochem, pp. 1-10. 

A non-enzymatic H2O2 sensor based on Prussian Blue (PB], also known as an artificial peroxidase, was accomplished by step-by-step electrodeposition of polyaniline on a glassy carbon electrode (GCE] modified with MWCNTs followed by potentiostatic deposition of PB [42]. By using PB instead of peroxidase, the linear calibration range could be improved and interference due to oxygen prevented. A non-enzymatic H2O2 sensor based on PANI-SWCNT electropolymerized in the ionic liquid (IL]... 

Pringle J. M., Fors5d h M., Wallace G. G., and MacFarlane D. R, Solution-surface electropolymerization a route to morphologically novel poly(pyrrole) using an ionic liquid. Macromolecules, 2006, 39, 7193-7195. 

Finally, nanocomposites incorporating electrogenerated PPy have known a growing interest in the last decade, especially those based on carbon nanotubes (CNT). Indeed CNT-PPy hybrids exhibit very high capacitance that makes them promising materials for supercapacitors. Several methods can be envisaged for the obtention of CNT-PPy hybrids electropolymerization on a CNT-array-modified electrode, coelectrodeposition from mixtures of surfactant stabilized aqueous CNT dispersion with the monomer or from mixtures in an ionic liquid layer on the electrode, and alternatively direct electrodeposition of PPy on CNT in a cavity microelectrode. ... 

Electropolymerized films of Co(III) tetrakis(4-hydroxyphenyl)porphyrin, doped with ionic liquid (CoPbr-IL/G) functionalized graphene gave O2 electroreduction [90]. l-Butyl-3-melhylimidazolium tetrafluoroborate was used as IL. It is noteworthy that the performance of CoPor-IL/G resulted better than that of cobalt porphyrin alone, in terms of potential required and amount of undesired H2O2. 

Kaplan A, Soifer L, Eliyahu D, Korin E, Bettelheim A. Electrocatalytic activity towards oxygen reduction of electropolymerized cobalt porphyrin doped with ionic-liquid-functionalized graphene. J Electrochem Soc 2015 162 H481-5. 

Electrooxidative polymerization of pyrrole, thiophene, and aniline was achieved in various imidazolium ionic liquids [26-28]. l-Butyl-3-methylimidazolium tetrafluoroborate and hexafluorophosphate ([BMIM])[BF4] and [BMIM] [PFe]) for electropolymerization and notably 7i-conjugated polymers thus obtained are highly stable, and they can undergo electrochemical doping and dedoping in the ionic liquids up to million cycles. In addition, the polymers have cycleswitching speeds as fast as 100 m. 

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