Incorporation of metal-organic framework in polymer membrane enhances vanadium flow battery performance

The metal-organic framework (MOF) is utilized as functional additive in non-perfluorinated polymer membrane for vanadium flow battery (VFB) application for the first time. The UiO-66 series can be easily modified to form suitable pore size distribution and are robust toward aqueous and acidic conditions. Owing to the different stokes radius of protons and vanadium ions, the additive micoporous UiO-66 series increase membranes’ proton selectivity effectively. Outstandingly, the VFBs with MOF-loaded polymer membranes exhibit higher coulombic efficiency and energy efficiency than those using neat polymer membrane and the perfluorinated Nafion 115 membrane at the same conditions. Moreover, the blend membranes present ultra-long self-discharge time up to 200 h and stable performance for 100 charge-discharge cycles without significant decline in energy efficiency. The MOF-loaded polymer membranes are promising for VFB applications due to the high efficiency, excellent stability, low cost and easy designation and functionality.