Tailoring MicrophaseSeparation through Backbone SubstituentModulation in Poly(biphenyl alkylene) Anion Exchange Membranes

Anion exchange membrane (AEM) water electrolysis serves as an attractive approach for cost-effective hydrogen generation. However, achieving AEMs with both high ionic conductivity and robust alkaline stability remains challenging. Herein, a series of ether-free quaternized poly(biphenyl alkylene) (PBPN-R) AEMs bearing pendant quaternary ammonium groups with varied backbone substituents are designed and prepared. Among these, the PBPN-CF3Ph membrane, which has a 4-(trifluoromethyl)phenyl backbone substituent, exhibits well-defined microphase separation, resulting in the highest OH– conductivity (141 mS cm–1) and the lowest swelling ratio (18.5%) at 80 °C. Moreover, the PBPN-CF3Ph membrane preserves 88.6% of its original conductivity following a 1440 h aging in 1 M KOH at 80 °C. When implemented in a water electrolyzer, PBPN-CF3Ph delivered a current density of 5.0 A cm–2 at 2.0 V and demonstrated stable operation over 1670 h. This work highlights backbone substituent modulation as an effective strategy for advanced AEMs.