Enthalpic interactions in aqueous strong electrolytes upon addition of ionic liquids

Hard-Cation-Soft-Anion Ionic Liquids for PEDOT:PSS Treatment

A promising conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) experiences significant conductivity enhancement when treated with proper ionic liquids (ILs). Based on the hard-soft-acid-base principle, we propose a combination of a hydrophilic hard cation A⁺ (instead of the commonly used 1-ethyl-3-methyl imidazolium, EMIM⁺) and a hydrophobic soft anion X^- (such as tetracyanoborate, TCB^-) as the best ILs for this purpose. Such ILs would decouple hydrophilic-but-insulating PSS^- from conducting-but-hydrophobic PEDOT⁺ most efficiently by strong interactions with hydrophilic A⁺ and hydrophobic X^-, respectively. Such a favorable ion exchange between PEDOT⁺:PSS^- and A⁺:X^- ILs would allow the growth of conducting PEDOT⁺ domains decorated by X^-, not disturbed by PSS^- or A⁺. Using density functional theory calculations and molecular dynamics simulations, we demonstrate that a protic cation- (aliphatic N-alkyl pyrrolidinium, in particular) combined with the hydrophobic anion TCB^- indeed outperforms EMIM⁺ by promptly leaving hydrophobic TCB^- and strongly binding to hydrophilic PSS^-.

Water-assisted stability of carbene: cyclic voltammetric investigation of 1-ethyl-3-methylimidazolium ethylsulfate ionic liquid

In this work, we report electrochemical studies on imidazolium-based ionic liquids with an objective to explore the possibility of carbene formation in their dilute aqueous solutions. Conventionally, water plays a detrimental role during investigations involving ionic liquids, and this role has been investigated via electrochemical studies in aqueous ionic liquid solutions. There are varying opinions regarding the influence of water on the physicochemical behaviour of ionic liquids that require an in-depth understanding. To eludicate the role of water, we attempted to evaluate the electrochemical performance of ionic liquids in water as a solvent, and the influence of water on ionic liquids was explored through feasibility and stability studies on carbene formed in an aqueous imidazolium-based ionic liquid solution. The electrochemical investigation of an aqueous solution of 1-ethyl-3-methylimidazolium ethylsulfate ([EMIM][EtSO₄]) revealed a redox couple. Detailed investigations suggest that reduction of the imidazolium cation occurs at the C2 position, with subsequent formation of carbene. Furthermore, an anodic peak was found to be associated with the oxidation of carbene. The coulometric process associated with the anodic peaks indicated that the two-electron oxidation of carbene occurred. The stability of carbene in water was evaluated through the use of different protic and aprotic solvents. The hydrogen bond-forming ability of carbene with water seems to be responsible for its improved stability in water.