Covalent organic framework composite membrane for long lifespan alkaline zinc-based flow battery

Membranes capable of efficient ion transport are highly demanded for separation and energy conversion and storage, such as flow batteries and fuel cells. Beyond the primary benefits of high ion selectivity and conductivity, the ideal membrane must also exhibit robust chemical and physical stability for industrial applications. Herein, we develop a composite membrane (COFs-M) incorporating designed olefin-linked ultramicroporous COF nanosheets (pore size 0.6 nm) with selective ion transport ability and outstanding chemical stability under highly alkaline conditions (6 M NaOH). The COFs-M membrane demonstrates exceptional hydroxide ion transport efficiency, achieving an area resistance of 0.82 Ω cm 2 and facilitating the operation of an alkaline zinc-based flow battery at a remarkable current density of 320 mA cm −2 , achieving a voltage efficiency of 81.56 %. Additionally, the membrane allows the battery to maintain long-cycle stability over 350 cycles with a dendrite-free zinc morphology at a current density of 200 mA cm −2 .