Stability of composite anion exchange membranes with various functional groups and their performance for energy conversion

In this study, we report the relative stabilities of anion exchange membranes (AEMs) comprised of different functional groups. The base membrane was synthesized from vinylbenzyl chloride (VBC) that was cross-linked by divinylbenzene (DVB) using a porous polyethylene (PE) substrate, and subsequently quaternized by functional groups including ammonium, diammonium, and phosphonium types. Every synthetic process was confirmed by FTIR spectra, and hydroxide ion conductivity, ion-exchange capacity, and water uptake. For the various functional groups, the membrane stabilities were examined under alkaline and accelerated oxidative conditions. The membranes were found to be reasonably stable under alkaline conditions, whereas the oxidative stability was significantly dependent on the structures of the functional groups. Moreover, an alkaline fuel cell test was performed at 60 °C for selected membranes. Membranes quaternized with trimethylamine (PE-TMA) and triethylamine (PE-TEA) showed the highest power density, while PE-TEA exhibited a higher oxidative stability. Also, the PE-TEA composite membrane was successfully tested for a non-aqueous vanadium redox flow battery.