• • 50SOPBI-act membrane achieved record ionic conductivity of 135 mS cm−1 at room temperature and 358 mS cm−1 at 80 °C in 1 M KOH, outperforming all existing AEMWE and ISMWE systems, enabling efficient low-alkali electrolysis.
• • The SPBI membranes were synthesized via copolymerization of sulfonated and non-sulfonated monomers, allowing tunable sulfonation degrees to balance conductivity and alkali stability without crosslinking, facilitating scale-up.
• • Deprotonated benzimidazole rings increase electron density on ether carbon atoms, enhancing the stability of aromatic ethers in alkaline environments, addressing the degradation issue common in AEMWE.
• • The 50SOPBI-act membrane exhibited acceptable swelling behavior and excellent conductivity across a wide range of alkaline concentrations, demonstrating its potential for practical water electrolysis at low alkali concentrations.