Interfacial Interactions in Aprotic Ionic Liquid Based Protonic Membrane and Its Correlation with High Temperature Conductivity and Thermal Properties

Abstract

Novel supported liquid membranes (SLMs) have been developed by impregnating Nafion and Hyflon membranes with ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMI-BTSI). These supported liquid membranes were characterized in terms of their ionic liquid uptake behavior, leaching of ionic liquid by water, thermal stability, mechanical properties, glass transition temperature, ion exchange capacity, and proton conductivity. In general, modified membranes are more flexible than unmodified samples due to the plasticization effects of the ionic liquid. However, these supported liquid membranes exhibit a significant increase in their operational stability and proton conductivity over unmodified membranes. We also demonstrate that proton conductivity of these supported liquid membranes allows conduction of protons in anhydrous conditions with conductivity increasing with temperature. Conductivity of up to 3.58 mS cm(-1) has been achieved at 160 degrees C in dry conditions, making these materials promising for various electrochemical applications.

Ion transport in sulfonated polymers

“…Extensive research by various groups has established that the use of ionic salts, that is, ILs, composed of heterocyclic diazoles and counter-ions, can substantially improve the transport properties of sulfonated PEMs since the degree of ion dissociation, local concentration of ions, and T g of the membranes can be manipulated. [81][82][83][84] Such manipulations should also cause a large alteration in the thermodynamic properties of the PEMs, leading to an increasing number of fundamental studies on the thermodynamics of ILs-containing sulfonated PEMs. 46 For IL-incorporated sulfonated PEMs, the key factors governing the anhydrous transport properties should be the type of ILs (cations and anions) and the amounts of ILs within the PEMs.…”

Enhanced proton transport in nanostructured polymer electrolyte/ionic liquid membranes under water-free conditions

“…The reported conductivities range from 10 − 4 to 10 − 3 S cm − 1 (refs 21-23). When Nafion, a current state-of-the-art PEM, is impregnated with different ILs, the reported anhydrous conductivity lies in the range of 0.001 − 0.1 S cm − 1 at 100 − 200 °C [24][25][26] . Note that the conductivities of Nafion/IL systems are significantly dependent on variables such as the sample preparation temperature and casting solvent [27][28][29] .…”

“…Based on the efforts to reduce the costs of membranes, the morphologies and proton conductivities of hydrocarbon-based PEM/IL composite systems with sulphonated poly(aryl ether ketone) (SPAEK) and poly(ethyl ether ketone) (SPEEK) have recently been investigated 26,29 . An ionic conductivity of ~1×10 − 2 S cm − 1 is obtained at 180 °C when large amounts of ILs are incorporated.…”

Incorporation of Hyperbranched Supramolecules into Nafion Ionic Domains via Impregnation and In-Situ Photopolymerization

“…One notable approach is the in-situ impregnation (or doping) by means of incorporating functional small molecules such as ionic liquids within the Nafion ionic domains/clusters [6][7][8][9]. Infusion of ionic liquids into Nafion has afforded considerable improvement in ionic conduction.…”

“…Infusion of ionic liquids into Nafion has afforded considerable improvement in ionic conduction. In addition, the occurrence of specific interaction has been identified, i.e., hydrogen and/or ionic bonding between these small molecules and the sulfonate groups of Nafion has helped retaining these functional small molecules during use [8,9].…”