The Effect of Ionic Liquid Covalent Bonding to Sol‐Gel Processed Film on Ion Accumulation and Transfer

Abstract

Accumulation of electroactive anions into a silicate film with covalently bonded room temperature ionic liquid film deposited on an indium tin oxide electrode was studied and compared with an electrode modified with an unconfined room temperature ionic liquid. A thin film containing imidazolium cationic groups was obtained by sol-gel processing of the ionic liquid precursor 1-methyl-3-(3-trimethoxysilylpropyl)imidazolium bis(trifluoromethylsulfonyl)imide together with tetramethylorthosilicate on the electrode surface. Profilometry shows that the obtained film is not smooth and its approximate thickness is above 1 mm. It is to some extent permeable for a neutral redox probe -1,1'-ferrocene dimethanol. However, it acts as a sponge for electroactive ions like Fe(CN) 6 3À , Fe(CN) 6 4À and IrCl 6 3À . This effect can be traced by cyclic voltammetry down to a concentration equal to 10 À7 mol dm À3 . Some accumulation of the redox active ions also occurs at the electrode modified with the ionic liquid precursor, but the voltammetric signal is significantly smaller compare with the bare electrode. The electrochemical oxidation of the redox liquid tbutyloferrocene deposited on silicate confined ionic liquid film is followed by the expulsion of the electrogenerated cation into an aqueous solution. On the other hand, the voltammetry obtained with the electrode modified with tbutyloferrocene solution in the ionic liquid precursor exhibits anion sensitive voltammetry. This is explained by anion insertion into the unconfined ionic liquid deposit following t-butylferricinium cation formation.

A review on electrodes modified with ionic liquids

“…4). Despite to earlier reported use of IL in extraction process [59], this application of IL- modified electrodes was not much later developed, perhaps because exhaustive accumulation of redox active anions takes minutes or tens of minutes [9,46,54,57,58]. This is due to slow electrochemical probe transport in viscous IL film [58,60], hindered ion transfer and hydrophobic nature of deposit.…”

“…Simple redox voltammetry was observed for electrodes modified with liquid deposit of redox probe solution in IL [47,48,[54][55][56]. The specific mechanism of electrode reaction was identified as ion transfer across IL/aqueous solution interface coupled to the electrochemical redox process (Fig.…”

“…In other study, gold electrode was premodified by self-assembled 2-aminoethanethiol to achieve good wetting by IL [47] or paraffin-impregnated graphite was used [56]. Typically, microliter amount of IL was deposited at working electrode and other electrodes remained in aqueous phase [9,33,48,[51][52][53][54]. The system where small volume of IL covers working, counter and reference electrodes was reported [57,58].…”

“…Some attention was paid to electrochemical behavior of electrodes modified with insoluble redox probe deposit next covered by IL deposit [61,62] or modified with redox probe solution in IL [47,48,[54][55][56]61]. The first approach was used to minimize the volume of ionic liquid.…”

“…For some studies, unmodified electrode substrates like basal plane pyrolytic graphite (bppg) [9,33,51], glassy carbon [52,53], gold [48] or ITO [54] were applied. Also, edge plane pyrolytic graphite [55] with well-developed surface was used.…”