Comparative Study of Proton Conducting Ionic Liquid Doped Nafion Membranes Elaborated by Swelling and Casting Methods: Processing Conditions, Morphology, and Functional Properties

Abstract

Trifluoromethanesulfonate of triethylammmonium (TFTEA) doped Nafion-TEA membranes have been evaluated to understand the impact of different elaboration methods, i.e., swelling and casting, on their nanoscale morphology using SANS and resulting functional properties such as electrochemical, thermomechanical, and transport properties. The effect of transformation of acidic side chains of Nafion into ammonium side chains (Nafion-TEA) was first compared for the Nafion-TEA membrane elaborated by casting with the one elaborated by modification of extruded commercial Nafion117 membrane. Concerning TFTEA doped membranes, their nanostructuration is very similar whatever the processing mode despite some key differences. The casting based membranes exhibit higher and/or more heterogeneous swelling of ionic domains of Nafion-TEA by TFTEA and lower impact of TFTEA on the long-range crystalline order in Nafion-TEA. Casting based membranes present better thermomechanical properties compared to swelling based membranes above 150 °C and sustain a storage modulus of 1 MPa in the temperature range of 150−180 °C. With increasing TFTEA content as well as temperature, both types of membranes show an increase in the ionic conductivity of a similar order but no significant changes in hydrogen and oxygen-permeability coefficients. Both kinds of doped membranes exhibit similar sorption behavior (e.g., an increase in water uptake with increasing TFTEA content), though the results from GAB modeling suggest that morphology developed by casting is more favorable for the sorption of water molecules in middle range activity. Current density of 0.85 A/cm 2 at 0.6 V was obtained with a membrane containing 20% TFTEA.

New polymer electrolyte membrane for medium-temperature fuel cell applications based on cross-linked polyimide Matrimid and hydrophobic protic ionic liquid

“…Thus, the obtained data clearly indicate that the proton transport in PI/BAIM-TFSI membranes is realized mainly by vehicle mechanism. The content of 50% of ionic liquid in dielectric PI matrix is probably insufficient to realize the hopping mechanism of proton transport, which was found to dominate in commercial PBI and Nafion membranes impregnated with commonly used PILs TEA-TF or [dema][TfO] [49,50]. It can be explained by the fact that both PBI or Nafion polymer matrix and PIL participate in the proton transport, whereas in PI/BAIM-TFSI membranes, the polymer matrix does not contain proton-conducting sites.…”

Ammonium-based protic ionic liquid doped Nafion membranes as anhydrous fuel cell electrolytes

“…The similarities seen in scattering intensity peak profiles for both N-S TfO and N-S Nafion atomic pairs suggest that interactions of the ammonium cation with SO − 3 group (of [TfO − ] anion or Nafion) are quite competitive and equivalent. These similarities in peak height 16,19,21 The effect of temperature is insignificant on scattering intensity profiles as seen in Figure S5 of Supporting Information.…”

Synthesis and Properties of Poly(imides) and Poly(imides)/Ionic Liquid Composites Bearing a Benzimidazole Moiety

“…In previous studies, commercial Nafion® membranes have been doped with ionic liquids, giving them adequate values of ionic conductivity [25,26]. On another hand, composite membranes based on poly(imides)/ionic liquids and PBI/ionic liquids were synthesized, and an increase of the proton conductivity values of such materials was observed [27,28,29].…”