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.