Potential use of deep eutectic solvents (DESs) to enhance anhydrous proton conductivity of Nafion 115® membrane for fuel cell applications

Abstract

In this research, the potential use of deep eutectic solvents (DESs) as electrolyte within the Nafion 115® membrane was evaluated. The DESs were synthesized by sodium iodide (NaI) as hydrogen bond acceptor (HBA) and ethylene glycol (EG) as hydrogen bond donor (HBD) with different molar ratios. The measured thermal properties of the synthesized DESs revealed proper thermal stability for application at moderate temperatures. Besides, the DESs provided suitable proton conductivities which were highly dependent on the HBD/HBA molar ratio. The effects of DES utilization on the mechanical properties, crystallinity, and proton conductivity of Nafion 115® membrane were also evaluated. The results showed that a specific interaction can be arisen between DES and Nafion. The paramount Nafion/DES (NDES) membrane showed high proton conductivity of 153 mS/cm at 100 °Cat anhydrous conditions which was significantly higher than those previously reported for Nafion/ionic liquid (NIL) membranes. For a better evaluation, the proton conductivity data were compared to an upper bound which follows the relationship: T=Kσn. The boosted fuel cell performance of the Nafion/DES (NDES) composite membrane at anhydrous condition suggests that the synthesized DESs can be considered as promising alternatives for water and conventional ionic liquids for fuel cell applications.