Fluorene-containing poly(arylene ether sulfone)s as anion exchange membranes for alkaline fuel cells

A series of novel quaternized fluorene-containing poly(arylene ether sulfone)s (APESs) were synthesized. Bromination rather than chloromethylation was used for the conversion of –CH3 to reactive –CH2Br. N,N,N׳,N׳-tetramethyl-1,6-diaminohexane (TMHDA) dissolved in isopropanol (IPA) was used as a quaternization reagent for the preparation of target anion exchange membranes (AEMs). Fourier transform infrared spectroscopy (FT-IR), 1H NMR spectroscopy and gel permeation chromatography (GPC) were used to characterize the as-synthesized copolymers. The ratio of hydrophilic to hydrophobic monomers was varied to study the structure property of the AEMs. The obtained AEMs were characterized by scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Water uptake (WU), swelling ratio, ionic exchange capacity (IEC), ionic conductivity, methanol permeability and alkaline stability were also studied. These AEMs have good properties as polymer electrolyte materials with high ionic conductivity (under hydrated conditions) in the range 2.89–8.85×10−2 S cm−1 and 5.60–15.64×10−2 S cm−1 at 30 and 80 °C, respectively. The methanol permeability of the AEMs in the range 5.99–14.51×10−8 cm s−1 is lower than that of Nafion® 117 (1.82×10−6 cm s−1). The AEMs show excellent alkaline stability in 1 M KOH solution at 60 °C for a long time. Single cell testing using APES-0.8 showed an open circuit voltage of 0.89 V. A maximum power density of 146 mW cm−2 at a current density of 423 mA cm−2 can be achieved at 60 °C. In summary the AEMs are good candidates for evaluation in fuel cell applications.