(539f) Self-Standing Covalent Organic Framework Membranes for Flow Batteryself-Standing Covalent Organic Framework Membranes for Flow Battery

Covalent organic frameworks (COFs), which are chemically constructed by predesigned building blocks, have flourished as a new type of crystalline porous material. Attributed to their uniform aperture, large porosity, and robust scaffoldings, COFs display great potential to be assembled into proton permselective membranes for overcoming the ubiquitous tradeoff between selectivity and proton permeability and providing excellent cycling stability. Up to now, owing to the enormous difficulty to prepare self-standing COF membranes, COFs applied in flow battery are mostly combined with amorphous polymers which play a predominant role, greatly hindering the full use of ordered pore channels.

Here, for the first time, free-standing COF membranes constructed through the controlled crystallization method were utilized in aqueous organic flow battery. Moreover, sulfonated poly (ether ether ketone) (SPEEK) was further introduced into COF membranes to manipulate the membrane structure. The more ordered pore channels from enhanced crystallization and higher continuity of hopping sites from additional acid groups between COF grains synergistically assist in creating proton transfer highway, thus contributing to the excellent battery performance (energy efficiency of 81% at 40 mA cm^-2) (Figure 1). Our work provides a new orientation to design COF membranes with fully-used ordered channels for proton permselective application.