Dual-sided symmetric crystalline orientation of covalent organic framework membranes for unidirectional anhydrous proton conduction

Two-dimensional covalent organic frameworks (2D COFs) have sparkled wide-ranging research to explore proton-conducting materials. However, the powder-pressed pellets or continuous membranes of 2D COFs are composed of randomly arranged crystallites, which are undesirable for proton transport via a shortcut pathway. We report a controlled strategy for preparing a conformably oriented free-standing COF membrane to address the critical challenge. A monofunctional aldehyde precursor is used as a modulator to enhance reversible association and optimize growth orientation in an interfacial polymerization system. The preferred face-on alignment is achieved throughout the membrane from its flat side to the nanoflake-standing side and, in turn, generates the unidirectional pore channels for accommodating 1,2,4-triazole as proton carriers. The composite merges distinctive features including orientation, crystallinity, porosity, and mechanical strength into one system, exhibiting ultrafast and stable anhydrous proton conduction at high operating temperatures with low activation energy. Our findings offer an innovative strategy for the oriented crystallization of free-standing COF membranes for energy conversion applications.