Sulfonated poly (ether ether ketone) asymmetrical pore-filling PTFE composite membrane with highly selective for vanadium flow batteries

The preparation and development of low-cost and highly ion-selective membranes, are necessary to facilitate the practical application of vanadium redox flow batteries (VRFB). In this study, a polytetrafluoroethylene (PTFE) asymmetric-filled proton exchange membrane was designed and prepared through casting and filling sulfonated poly (ether ether ketone) (SPEEK) attached to the PTFE membrane surface or infiltrated into the membrane matrix, which can synergistically promote proton transport and inhibit vanadium ion permeability. The test results showed that the asymmetrically cast composite membrane (U–S/P/S) had the highest ion selectivity (3.27 × 10 3  S min cm −3 ) and the lowest VO 2+ permeability (1.09 × 10 −8  cm −2  min). In addition, the U–S/P/S composite membrane has excellent VRFB performance with a stable energy efficiency of more than 70 % and ultra-long self-discharge time (141 h) at current density of 80 mA cm −2 , Meanwhile, the maximum power density of U–S/P/S is 871.93 mW cm −2 at 250 mA cm −2 . It is worth mentioning that the U–S/P/S membrane has a more stable battery performance when the U–S surface is oriented toward the negative side of the battery, and the U–S/P/S membrane exhibits more excellent VRFB performance than N212. And highly ion-selective proton exchange membranes with PTFE as the support show great promise for VRFB applications.