Abstract:

The mesoscopic structure of Nafion-[Bmim][TfO] ionic liquid (IL) composite membrane was studied using dissipative particle dynamics (DPD) simulations. The effects of temperature and IL concentration on the mesoscopic structure were investigated. Microphase-separation phenomena were observed. Analyses of the pore size distributions under different conditions indicated that with the increasing IL concentration in composite membrane, the aggregated state was transformed from dispersed IL clusters to coherent IL channels. A chamber structure was formed when the IL concentration was very high. The structure of ionic liquid channels became more complex with increasing temperature and the chamber was transformed into new branches of channels, indicating that the IL channels became more coherent at elevated temperatures. The interfacial distribution probabilities and radial distribution functions indicated that the alkyl chains of ionic liquids were embedded in the Nafion backbone, and changes in the distribution of sulfonic acid groups in the side chains directly affected the distribution of imidazole groups and anions at the microphase interface. In this work, the mesoscopic structures of Nafion-IL composite membrane at the molecular level were explored and valuable insights for developing new high-temperature proton-conducting polyelectrolyte materials were obtained.

Key words: Fuel cell, Polyelectrolyte, Ionic liquid, Dissipative particle dynamics, Mesoscopic structure, Microphase separation