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

Abstract

Polymer electrolyte membranes doped with Protic Ionic Liquids (PILs) can serve as promising materials for anhydrous proton conduction. In the present study, molecular dynamics simulations are performed to characterize the structure and dynamics of a diethylmethylammonium triflate ([dema][TfO]) PIL doped Nafion membrane at various PIL doping and temperatures. The polymer membrane PIL interface structure shows that the hydrogen bonding interactions predominantly exist between the acidic site (N–H) of the ammonium cation and SO₃⁻ group of the [TfO⁻] anion or Nafion. The distribution of the SO₃⁻ group (of the [TfO⁻] anion or Nafion) around the ammonium cation increases with PIL concentration. The existence of weak hydrogen bonding interactions between the alkyl hydrogen atoms of the [dema⁺] and the SO₃⁻ group of Nafion remains unaffected by the PIL concentration. An increase in the PIL doping level and temperature results in faster diffusion (higher ionic conductivity) which is in qualitative agreement with experiments.