High-performance and durable anion-exchange membrane water electrolysers with high-molecular-weight polycarbazole-based anion-conducting polymer

Anion-exchange membrane water electrolysis is a promising technology for economical green hydrogen production; however, the corresponding industrial applications are limited by the lack of reliable polymer electrolytes. To address this problem, we developed chain-extender-derived high-molecular-weight hexyltrimethylammonium-tethered polycarbazoles (HQPC-TMA-x's) with compelling membrane characteristics, including high ionic conductivity, mechanical robustness, and high alkaline stability. Owing to its polycarbazole backbone, HQPC-TMA-x alleviated the problems due to ionomer adsorption on the electrode. In the single-cell configuration, the best-performing polymer (HQPC-TMA-2.4) achieved an unprecedented current density of 14.6 A cm⁻² at 2.0 V with a Ni-Fe alloy anode and low-cost cell hardware, additionally showing superior pure-water-electrolysis and direct-seawater-electrolysis performances. HQPC-TMA-2.4 exhibited in situ durability at a high current density of 1.0 A cm⁻² for 1000 h with low irreversible degradation rates of 52 and 6 μV h⁻¹ for platinum group metal (PGM) and PGM-free cells, respectively, demonstrating the reliability of this polymer in practical settings.