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

Authors：Wang, Tao; Zhao, Yu; Ma, Ruoxi; Li, Lijuan; Ling, Qianjun; Li, Xueliang^*; Ding, Yunsheng; Wei, Haibing^*

Source：Synthetic Metals, 2023, 296: 117385.

DOI：10.1016/j.synthmet.2023.117385

• Anion exchange membranes
• Poly(quaterphenylene alkylene)s
• Backbone rigidity
• High conductivity
• Dimensional stability

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 degrees C of 75 wt% and 14 %, respectively. Meanwhile, the immiscibility of hydrophilic double-cation side chain and the hydrophobic poly(arylene alky-lene) 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 degrees 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 degrees 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.