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

Abstract

Polymer Electrolyte Membrane 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 diethylmethylammonium triflate ([dema][TfO]) PIL doped Nafion membrane at various PIL doping and temperature. 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 SO − 3 group of [TfO − ] anion or Nafion. The distribution of SO − 3 group (of [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 SO − 3 group of Nafion remain unaffected by PIL concentration. An increase in PIL doping level and temperature results in faster diffusion (higher ionic conductivity) which is in qualitative agreement with experiments. An atomic-level understanding of interfacial characteristic of quasi-solid Nafion membrane comprising with [dema][TfO] PIL is presented using classical MD simulations. Interactions of the ammonium cation with the SO − 3 group of [TfO − ] anion and Nafion membrane are similar. The intensity of hydrogen bond interactions between the ammonium cation with SO − 3 group decreases with an increase in Nafion:PIL ratios. This impact of increase in PIL doping is reflected in spatial density maps of SO − 3 distribution at the acidic site of the ammonium cation. The SO − 3 distribution over N-H bond vector becomes broad with increase in PIL concentration. The existence of weak hydrogen bonding between the alkyl tail length of the ammonium cation and [TfO − ] anion is seen from SDFs and the distribution of SO − 3 group around the alkyl tails increases Interfacial structure correlation of cation interactions with sulfonate groups (of anion or Nafion) in [dema][TfO] doped Nafion composite are competitive and equivalent.

Constructing Ionic Liquid-Filled Proton Transfer Channels within Nanocomposite Membrane by Using Functionalized Graphene Oxide

“…PEMFC operated under elevated temperatures (above 100 °C) and anhydrous conditions has been the focus of interest, due to the numerous advantages of high tolerance of catalyst to CO, simplified heat/water management, and improved electrode kinetics. − However, a fatal building block is the deficiency of water-independent high-performance proton exchange membrane (PEM). According to the transfer mechanism, protons can only be transported via short-distance (<0.275 nm) proton hopping from one hopping site to a neighboring one (i.e., Grotthuss mechanism) under water-free conditions. , Nevertheless, for most of the available proton conductive materials including perfluorosulfonic acid polymer, sulfonated aromatic, and heterocyclic, their relatively insufficient hopping sites and intrinsic “dead ends” restrict the anhydrous conduction ability. − It is demonstrated that the efficient approach for ultrafast anhydrous proton conduction is to create continuous water-independent conducting channels that meanwhile contain sufficient proton hopping sites.…”

Enhanced Performance of Polymer Electrolyte Membranes via Modification with Ionic Liquids for Fuel Cell Applications

“…The addition of ionic liquids causes changes in the original Nafion ® membrane structure and alkyl groups contained in the ionic liquid form hydrogen bonds with sulfonic acid groups in Nafion ® cation. The C-C-C=O and C=N bonds further reinforce internal structure of the membrane [22].…”

“…This can be explained by the strength of the bond between functional groups of polymer Nafion ® and the ionic liquid due to the presence of alkyl group as found in FT-IR analysis, which produced stronger structural bonds with polymer Nafion ® [22]. The chemical structure of ionic liquids is influenced by the degree of ionization protic.…”

Atomistic simulation study of the hydrated structure and transport dynamics of a novel multi acid side chain polyelectrolyte membrane

“…Recent classical MD studies of anion exchange membranes (AEM) have correctly captured the effects of different functional groups and the effects due to positions of these functional groups on conductivity [50] [51]. Nafion doped with protic-ionic liquid has also been simulated using classical MD in which the transport characteristics were found to be consistent with experiments [52]. A point to be noted in all the aforementioned examples is that classical MD is well suited to study different types of PEMs.…”