Sandwich‐Like Free‐Standing Covalent Organic Framework Anion Exchange Membranes for Water Electrolysis

Covalent organic frameworks (COFs) offer well‐defined pores for efficient ion transport but suffer from poor mechanical stability. Herein, a sandwich‐like free‐standing COF‐based anion exchange membrane (COF‐AEM) is prepared, combining a COF core with in situ‐grown functional polymer layers. This strategy not only overcomes the polymer/COF incompatibility but also retains the intrinsic nanopores of the COF framework, enabling ion transport with a conductivity of 110 mS cm −1 at 80 °C under a remarkably low ion exchange capacity (IEC) (1.53 mmol g −1 ). Furthermore, the rigid and hydrophobic COF core effectively mitigates the membrane swelling ratio (SR) (5.2% @ 80 °C), while its combination with the flexible hydrophilic polymer skin enhances the robustness of the COF‐AEM simultaneously, achieving a tensile strength of 21.4 MPa. Demonstrated in alkaline water electrolysis, this represents the first free‐standing COF‐AEM for such applications. Our design expands COF‐AEM structural diversity, offering a promising approach for advanced ion‐conductive materials.