Aryl-Tethered Pendant Sterically Shielded Imidazoliums for Durable Anion Exchange Membranes

Conventional quaternary-ammonium-based anion-exchange membranes (AEMs) with insufficient alkaline stability limit the durability of AEM water electrolyzers (AEMWEs). Here we report novel poly(arylimidazolium) membranes (QAI-x) that overcome this barrier through an aryl-tethered pendant sterically shielded imidazolium cation. This architecture sterically protects the imidazolium cation while avoiding the introduction of a benzylic cation-polymer linkage. Combined with ether-free polyaromatic backbones, the QAI-x membranes simultaneously achieve enhanced chemical stability and dimensional stability, with no measurable loss in hydroxide conductivity after 4000 h in 1 M KOH at 80°C, resistance to Fenton oxidation, and limited dimensional swelling despite relatively high water uptake. In AEMWEs, QAI-x membranes support voltage decay rates as low as 9 µV h^-1 over 5400 h in 1 M KOH and 16 µV h^-1 over 2000 h in 5 M KOH at 80°C and 2.5 V, substantially outperforming commercial benchmarks. Cell operation is further demonstrated for more than 1000 h at 3 A cm^-2 under a dry-cathode configuration. These results highlight aryl-tethered steric shielding as a promising molecular-design strategy for durable AEMs.