Anion Exchange Polyelectrolytes with High Branching Ratio and Adjustable Free Volume for Anion Exchange Membrane Water Electrolysis

Abstract Rational design of polyelectrolytes that simultaneously meets the requirements for anion exchange membrane (AEM) and ionomer (AEI), especially the opposite gas permeation demands for anion exchange membrane water electrolysis (AEMWE) with similar chemical structure is challenging. To overcome the formation of insoluble gel at high branching ratio (BR), herein, a series of anion exchange polyelectrolytes of intrinsic microporosity with wide‐ranged fractional free volume and good solubility at high BR are fabricated through a stepwise nonstoichiometric superacid‐catalyzed polycondensation reaction. By precisely controlling the BR and free volume, a stable and porosity‐adjustable structure is generated, which not only addresses the conductivity–toughness trade‐off of AEM but also possesses high OH − conductivity for AEI. Most importantly, it fulfills the opposite gas permeation demands for AEM and AEI and decreases the overpotentials of ohmic polarization and mass transport by 76.2% and 44.2%, respectively. The membrane electrode assembly fabricated by the optimized AEM and AEI achieves 1.98 V (pure water) and 1.62 V (1 M KOH) at 1 A cm −2 with high stability. This work provides a strategy for rational design of polyelectrolytes that meets the requirements of AEM and AEI for high‐performance AEMWE.