Highly conductive and dimensionally stable anion exchange membranes enabled by rigid poly(arylene alkylene) backbones

Dimensionally and chemically stable anion exchange membranes with excellent ion conductivity are highly desired in electrochemical energy conversion technologies. Herein, we present a design using rigid arylene units, i.e., p-tetraphenylene and p-terphenylene, to suppress the water sorption of quaternized poly(arylene alkylene) membranes with high ion contents. Of note, side chain double-quaternary ammonium (QA) functionalized poly(q-tetraphenylene-co-p-terphenylene alkylene) membrane P(4PA-co-3PA)-D100 with the IEC value as high as 2.93 mmol g−1 showed very limited water uptake and swelling at 80 °C of 75 wt% and 14 %, respectively. Meanwhile, the immiscibility of hydrophilic double-cation side chain and the hydrophobic poly(arylene alkylene) backbone drives the formation of phase-separated morphology. As a result, P(4PA-co-3PA)-D100 showed an exceptional conductivity of 227.8 mS cm−1 at 80 °C with activation energy of 10.5 kJ mol−1. Despite the rigid poly(arylene alkylene) backbone with highly chemical durability and oxidative stability, the tandem tethered double cation in the side chain showed a 11 % QA moiety loss after a 1000-h treatment in 2 M NaOH at 80 °C. Moreover, a good peak power density of 550 mW cm−2 at the current density of 1.06 A cm−2 was achieved for P(4PA-co-3PA)-D100 with the gases flow of 200 mL min−1. This work demonstrates that, in addition to the approach of cross-linking, the highly conductive AEMs with excellent dimensional stability can be achieved by improving the rigidity of polymer backbones.