Synthesis And Characteriation Of Imidazolium-based Ion Exchange Membranes

The development of ion-exchange membrane was significant for thecommercialization of the ion-exchange membrane fuel cells. The proton conductivity ofthe perfluorinated sulfonic acid membrane represented by Nafion membrane would reducerapidly due to the severe water evaporation under the enhanced temperature. Quaternaryammonium cation-based anion exchange membrane is the widely used anion exchangemembrane, while the alkaline stability of the cation under high PH and high temperature ispoor. In this manuscript, we prepared high temperature proton exchange membrane byreplacing water with phosphoric acid as the proton carrier. In addition, alkaline stablenovel anion-exchange membranes were also designed and synthesized.The main work is as follows:(1) Phosphoric acid-doped anhydrous high temperature proton exchange membraneswere synthesized. The properties of the yield membranes in terms of proton conductivity,phosphoric acid uptake, chemical stability, and mechanical properties were characterized.The resultant membranes showed good mechanical properties, high chemical stability, andhigh proton conductivity at160oC under anhydrous conditions (up to the order of10-2Scm-1).(2) Novel anion exchange membranes (AEMs) containing imidazolium cation andpoly(arylene ether sulfone) side chains were prepared. The produced membranes havegood mechanical properties, high conductivity up to1.6×10-2S cm-1at room temperature.They can be soluble in DMSO and DMF, while insoluble in water and methanol. Inaddition, they were stable in1M KOH at60oC for20days.(3) A serials of imidazolium cations with different substituents were synthesized. Theeffects of substituent positions and substituents at C2position on the alkaline stability ofthem were characterized by1H NMR. The results indicated that C2-substitution groupsaffected the alkaline stability of the imidazolium cations drastically.1,2-dibutyl-3-methylimidazolium cation ([C2-BBMIm]+) exhibited the highest alkaline stability at the elevated temperatures. Its corresponding anion exchange membrane alsoshowed enchanced alkaline stability, and high conductivity.