High-strength, ultra-thin anion exchange membranes with a branched structure toward alkaline membrane fuel cells

The preparation of self-supporting anion exchange membranes with enhanced mechanical strength and ultrathin thickness is still a challenge to improve the performance of fuel cells. In this work, we developed 9-dodecylidene-9H-fluorene (DDF) as a branched monomer to construct branched structures based on poly(arylene piperidinium)s. After introducing a 2.5% molar ratio of DDF, quaternized poly(piperidinium-triphenyl-dodecylidenefluorene) (PPTDF-QA) possesses low water swelling (below 25% at 80 °C) and high mechanical strength (over 70 MPa). The obvious phase-separation behavior of the branched membranes induced by the long alkyl chain improves hydroxide conductivity which reaches 168 mS cm−1 at 80 °C. Meanwhile, the thickness of branched PPTDF-QA can be optimized to 8 μm. The present work reveals that a facile branched monomer can promote the formation of a microphase-separated morphology of the membrane to fabricate high-performance anion exchange membranes.