Tuning poly(isatin biphenyl) anion exchange membranes by copolymerization and branching

Abstract

The cardo structure and long side chain of poly(isatin biphenyl) are conducive to the motion and aggregation of cations over mainchain type membranes, therefore it is used as the pristine membrane. It is well known that random copolymerization and branching can effectively modify the configuration and properties of polymers. Herein, we use random copolymerization and branching to improve the behaviors of poly(isatin biphenyl) anion exchange membranes (AEMs). High-curvature random copolymers (QPIDBP-n) and high free volume branched polymers (b-QPIBP-x) are synthesized via polycondensation. The random copolymerization results in the formation of a twisted chain structure, while the introduction of branching agent leads to the formation of orderly stacking of chains. Both of these approaches have been demonstrated to boost the microphase-separated morphology of the pristine polymer. A series of QPIDBP-n and b-QPIBP-x are tested and an optimal ratio is explored. QPIDBP-40 and b-QPIBP-5 exhibit high overall performance. Among the as-prepared membranes, b-QPIBP-5 exhibits the highest conductivity (80 °C, 160.7 mS cm−1) with a swelling ratio of 20.7 %. The residual conductivity of b-QPIBP-5 is 93.1 % after the 1200 h alkali stability test. The cell assembled by b-QPIBP-5 achieves a peak power density of 680 mW cm−2. Moreover, the b-QPIBP-5 based cell holds 88.6 % voltage after the in-situ stability test for 50 h.