Preparation of sulfonated polyimide/polyvinyl alcohol composite membrane for vanadium redox flow battery applications

A novel series of sulfonated polyimide (SPI)/polyvinyl alcohol (PVA) composite membranes applied in vanadium redox flow battery (VRFB) is prepared and characterized in this work. With the hydrophilicity and good barrier of PVA, the composite membranes exhibit better hydrolysis stability and vanadium ion resistance than normal SPIs with five-membered rings. In VRFB single-cell tests, because of the highest proton selectivity, the SPI5/PVA5 composite membrane shows lower self-discharge rate, higher coulombic efficiency, and energy efficiency (EE) (79.5% vs 77.8% at 30 mA cm−2) than that of Nafion117. Besides, the composite membranes present stable performances up to 100 cycles without significant decline in EE.