Poly(fluorenyl alkylene)-based anion exchange membranes for high-performance water electrolysis

Durable and high-performance anion exchange membranes (AEMs) are a pivotal issue for the industrial application of AEM water electrolysis (AEMWE). In this study, a series of poly(fluorenyl alkylene) copolymers with different contents of biphenyls and p-terphenyls are synthesized for the high-performance AEMWE. The resulting AEM with an appropriate content of p-terphenyl well facilitates the microphase separation to get a well-defined microstructure that effectively improves the ionic conductivity and reduces the swelling ratio. The AEM with 20 % p-terphenyl possesses an OH– conductivity of 155.7 mS cm−1, a water uptake of 128.7 %, and a swelling ratio of 33.8 % at 80 °C. Moreover, it also shows durable alkaline stability and retains 83.5 % of cationic groups after immersing in 5 M NaOH at 80 °C for 1440 h. The assembled AEMWE cell achieves an excellent current density of 4.9 A cm−2 at 2 V in 1 M KOH (80 °C) and 2200 h of long-term constant current (1 A cm−2) operation with a low voltage rising rate of 77 μV h−1. After this long-term operation, only 13.7 % of cationic groups are degraded in the AEM, showing excellent in-situ durability. Therefore, the developed AEMs should have great potential for applications in the AEMWE.