pH ‐dependent self‐crosslinking of high‐performance anion exchange membrane for fuel cells

Anion exchange membrane fuel cells are currently limited by the lack of durable, high‐performance anion exchange membranes (AEMs). Herein, we develop a pH‐dependent self‐crosslinking strategy to fabricate large‐area AEMs without external crosslinking agents that leverages the protonation of a precursor polymer under acidic conditions (pH <7) to maintain solubility, while an alkaline environment (pH >7) induces deprotonation and triggers a Menshutkin reaction for self‐crosslinking. The resulting self‐crosslinked network in the AEMs (OH − form) effectively restricts polymer chain mobility and enhances interchain entanglement, leading to low water uptake (28.6%), minimal swelling (10.2%), high mechanical strength (70.2 MPa), and good alkaline stability over 5000 h (only 3.1% conductivity loss). Furthermore, the membrane demonstrates high hydroxide conductivity and reduced H 2 permeability, enabling high‐performance fuel cells operation with a peak power density of 2.10 W cm −2 and extended durability under harsh conditions (0.6 A cm −2 , 80°C).