Stable Anion Exchange Membrane Bearing Quinuclidinium for High‐performance Water Electrolysis

Abstract Anion exchange membranes (AEMs) are core components in anion exchange membrane water electrolyzers (AEM‐WEs). However, the stability of functional quaternary ammonium cations, especially under high temperatures and harsh alkaline conditions, seriously affects their performance and durability. Herein, we synthesized a 1‐methyl‐3,3‐diphenylquinuclidinium molecular building unit. Density functional theory (DFT) calculations and accelerated aging analysis indicated that the quinine ring structure was exceedingly stable, and the S N 2 degradation mechanism dominated. Through acid‐catalyzed Friedel–Crafts polymerization, a series of branched poly(aryl‐quinuclidinium) (PAQ‐x) AEMs with controllable molecular weight and adjustable ion exchange capacity (IEC) were prepared. The stable quinine structure in PAQ‐x was verified and retained in the ex situ alkaline stability. Furthermore, the branched polymer structure reduces the swelling rate and water uptake to achieve a tradeoff between dimensional stability and ionic conductivity, significantly improving the membrane's overall performance. Importantly, PAQ‐5 was used in non‐noble metal‐based AEM‐WE, achieving a high current density of 8 A cm −2 at 2 V and excellent stability over 2446 h in a gradient constant current test. Based on the excellent alkaline stability of this diaryl‐quinuclidinium group, it can be further considered as a multifunctional building unit to create multi‐topological polymers for energy conversion devices used in alkaline environments.