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). 1 H 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 −2   S   cm −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 −8   cm 2   s −1 at 30   °C and 8.92–25.57×10 −8   cm 2   s −1 at 60   °C is lower than that of Nafion ® 117. The AEMs show an excellent alkaline stability in a 2   M NaOH solution at 60   °C for 1080   h. A single cell with the QPEN membrane shows an open circuit voltage of 0.84   V. A maximum power density of 79.1   mW   cm −2 at a current density of 207   mA   cm −2 can be achieved at 60   °C. In summary the AEMs are good candidates for evaluation in fuel cells.