Urea-based construction of hydrogen bonding networks for poly(biphenyl alkylene)s anion exchange membrane for fuel cells

In recent decades, the “trade-off” problem of anion exchange membranes (AEMs) has been a concern. Herein, a series of urea-based multication poly(biphenyl alkylene)s AEMs are prepared by obtaining an ether bond-free backbone through ultra-strong acid catalysis, grafting it with multication side chains, and then by accessing urea-based groups in different ratios. By accessing the urea group, noncovalent bonds are used to link the molecules to act as cross-links, giving them solubility that chemical cross-links do not have. The PBTA-DQA-35U membrane possessed the highest ionic conductivity of 62.43 mS/cm. Compared with the PBTA-DQA membrane (80°C, WU = 20.45%, SR = 17.67%), the PBTA-DQA-25U membrane showed an increase in water uptake but not much change in swelling (WU = 30.23%, SR = 19.36%), which was attributed to the fact that the hydrophilic urea groups provide cation transport sites while hydrogen bonding inhibits membrane swelling. The PBTA-DQA-35U ionic conductivity is retained above 75% after 960 h of alkali stability testing. The power density of the MEA device assembled using PBTA-DQA-35U membrane is 421.78 mW/cm².