Planar-conjugated hyperbranched poly(aryl piperidinium) anion exchange membranes for sustainable energy devices

Anion exchange membranes (AEMs) are pivotal for advancing fuel cells and water electrolysis. However, their widespread adoption is hindered by the sluggish ion transport and inadequate durability. Herein, by tuning the number of conjugated aromatic rings and the branching sites within the monomers, a series of hyperbranched poly(aryl piperidinium) AEMs with coplanar polycyclic aromatic units are prepared to address the poor mechanical properties of rigid conjugated AEMs. The results indicate that the introduction of planar-conjugated triphenylene (TY) units in the polymer backbone facilitates ordered interchain aggregation driven by π-π stacking interaction to form well-defined ion-conductive channels while suppressing excessive swelling and enhancing the membrane stability. The hyperbranched AEM containing the TY units (QTPTY) possesses excellent mechanical properties with 55.9 MPa of stress and 60.3% of strain. Additionally, the QTPTY membrane achieves an exceptional OH− conductivity of 146.4 mS cm−1 at 80 °C, with 94.7% conductivity retention and mechanical properties reduction below 2% after 1600 h in 2 M NaOH. In an H2/O2 fuel cell, QTPTY delivers a peak power density of 1.43 W cm−2, surpassing linear and the other two π-conjugated hyperbranched analogs. In water electrolysis, the AEM exhibits a current density of 2.30 A cm−2 at 1.80 V, exceeding the 2026 targets of the U.S. Department of Energy. This work demonstrates that planar-conjugated hyperbranched architectures have a significant potential in designing robust, high-performance AEMs for sustainable energy technologies.