Carbazole-Enabled Topology Engineering of Poly(terphenyl piperidinium) Membranes for Durable and Efficient Anion Exchange Membrane Water Electrolysis

Abstract The development of high-performance anion exchange membranes (AEMs) for alkaline water electrolysis requires simultaneous optimization of hydroxide conductivity, mechanical robustness, and long-term alkaline stability, which remains a significant challenge. Here, we report a carbazole-based molecular branching strategy to regulate the hierarchical structure of quaternized poly(terphenyl piperidinium) (QPTP) membranes and establish the relationship between branching architecture and membrane performance. Four structurally distinct carbazole-based branching units, including 4,4′-bis(9-carbazolyl)–1,1-biphenyl, 1,3-bis(9-carbazolyl)benzene (mCP), 1,3,5-tris(9-carbazolyl)benzene, and 9-(biphenyl-4-yl)-9H-carbazole, are incorporated into the QPTP backbone to systematically investigate their chemical structure effects on physicochemical properties of AEMs. The nitrogen rich carbazole moieties simultaneously enhance hydroxide transport while reinforcing mechanical integrity. Among the investigated membranes, the asymmetric mCP-branched QPTP-mCP-6% membrane exhibits an optimized balance of properties, delivering a high hydroxide conductivity of 130.3 mS cm–1 at 80 °C, a tensile strength of 35.8 MPa, and excellent alkaline durability with nearly 100% conductivity retention after 2100 h immersion in 1 M KOH at 80 °C. When integrated into an AEM water electrolyzer equipped with nonprecious metal catalysts, the QPTP-mCP-6% membrane achieves a current density of 2.05 A cm–2 at 1.8 V and 80 °C in 1 M KOH, while maintaining stable operation for 400 h at 1000 mA cm–2. This work provides fundamental insights into molecular branching regulation and demonstrates carbazole-enabled topology engineering as an effective strategy for developing durable, high-efficiency AEMs for alkaline water electrolysis.