Scalable fabrication of sulfonated COF composite membranes with superior mechanical stability and proton conductivity enabled by a dual-function intercalant

Sulfonated covalent organic framework (COF) enabled rapid proton conduction via densely and orderly arranged sulfonic acid groups, yet weak interlamellar interactions between COF nanosheets hindered the fabrication of defect-free, large-area membranes. Herein, we employed one-dimensional sulfonated cellulose nanocrystals (SCNC) as dual-function intercalant to achieve the large-scale fabrication of high-performance sulfonated COF nanosheets-based composite membranes. This dual-function intercalant not only combined a rigid framework with proton conduction functionality, but also bridged the COF nanosheets (TpBd-(SO 3 H) 2 ) through hydrogen bonds and π–π interactions, and endowed TpBd-(SO 3 H) 2 /SCNC-0.3 composite membrane with an outstanding mechanical strength of ∼67 MPa and excellent proton conductivity of ∼439 mS cm −1 (90 °C, 95% RH). Moreover, composite membranes up to ∼400 cm 2 were easily produced by the solution casting technique, with properties that matched those of their smaller counterparts. The successful production of several other sulfonated COF nanosheets-based composite membranes demonstrated the general applicability of this approach. This study provided a new mindset for the large-scale preparation of sulfonated COF-based composite membranes, and marked an important step toward their broader implementation.