Benzylmethyl-containing poly(arylene ether nitrile) as anion exchange membranes for alkaline fuel cells

A series of novel quaternized benzylmethyl-containing poly(arylene ether nitrile)s (QPENs) were synthesized via condensation polymerization, bromination and quaternization. N,N,N′,N′-tetramethyl-1,6-diaminohexane dissolved in isopropanol was used as the quaternization reagent for the preparation of target anion exchange membranes (AEMs). 1H NMR spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and gel permeation chromatography (GPC) were used to characterize the as-synthesized copolymers. The ratio of hydrophilic to hydrophobic segment on the polymer backbone was varied to study the structure–property of the AEMs. With strong nitrile dipole interchain interactions and a self-crosslinked structure, the resulting AEMs possess a self-anti-swelling property resulting in a low water uptake and swelling ratio. The AEMs show high ionic conductivity (under hydrated conditions) above the magnitude of 10−2Scm−1. The membranes with distinct phase separation morphology have a higher ionic exchange capacity (IEC). The methanol permeability of the AEMs in the range 3.18–9.69×10−8cm2s−1 at 30°C and 8.92–25.57×10−8cm2s−1 at 60°C is lower than that of Nafion®117. The AEMs show an excellent alkaline stability in a 2M NaOH solution at 60°C for 1080h. A single cell with the QPEN membrane shows an open circuit voltage of 0.84V. A maximum power density of 79.1mWcm−2 at a current density of 207mAcm−2 can be achieved at 60°C. In summary the AEMs are good candidates for evaluation in fuel cells. [Display omitted] •The nitrile dipole interchain interactions induced a self-crosslinked structure.•Benzylmethyl-containing poly(arylene ether nitrile) was synthesized.•AEMs show high ionic conductivity above the magnitude of 10−2Scm−1.•The AEMs show excellent alkaline stability in a 2M NaOH solution at 60°C.