Molecular Design of Non-Fluorinated Aryl-Extended Carbazole-Based Polymeric Membranes for Anion Exchange and Bipolar Membrane Water Electrolysis

The development of durable anion-exchange membranes (AEMs) that combine rapid hydroxide transport with restrained hydration and dimensional stability remains a central challenge for alkaline electrochemical technologies. Here, we synthesize a series of ether-free, arylexpanded carbazole-based AEMs bearing systematically varied N-alkyl substituents: N-ethyl (HCz-Et), N-butyl (HCz-Bu), and N-hexyl (HCz-Hex). This systematic modification allows us to investigate how N-alkyl substitution within a common aromatic framework affects the physical, chemical, and mechanical properties of the resulting AEMs. Within this aryl-expanded series, increasing the N-alkyl chain length progressively suppressed water uptake and dimensional expansion while maintaining high hydroxide conductivity at elevated temperature. Specifically, HCz-Hex exhibited a water uptake of 18.7% and swelling ratio of 4.2%, with an OH − conductivity of 178mS cm −1 at 80 ◦C, indicating that this architecture can sustain efficient ion transport with limited membrane swelling. Furthermore, HCz-Hex retained ≈ 91% of its initial ion-exchange capacity (IEC) after 1000 h in 1M KOH at 80 ◦C. This balance of hydration control, conductivity, and alkaline stability translates directly to device performance: HCz-Hex reaches ≈ 2.05V at 2.0A cm −2 in pure-water-fed AEM electrolysis at 70 ◦C and 6A cm −2 at ≈ 2.19V in 1M KOH at 55 ◦C, while sustaining operation at 1.0A cm −2 for ≈ 1000 h. Beyond AEM electrolysis, coupling HCz-Hex with the non-fluorinated cation-exchange polymer SPEEK produces a fully non-fluorinated, Nafion-free bipolar membrane (BPM), enabling BPM water electrolysis at ≈ 2.03V at 1.0A cm −2 with a reported water-dissociation overpotential of approximately 80mV. This study provides a basis for designing non-fluorinated AEMs with tailored membrane properties for high-performance AEM and BPM electrolysis.