Novel sulfonated polyimide/polyvinyl alcohol blend membranes for vanadium redox flow battery applications

The synthesis and characterization of novel sulfonated polyimide (SPI)/polyvinyl alcohol (PVA) blend membranes for use in vanadium redox flow battery (VRB) are presented in this work. The SPIs with angled structure were synthesized using 4,4-oxydiphthalic anhydride (ODPA), sodium 2-aminosulphanilate (SAS) and 4,4'-diamino-3,3'-dimethyldiphenylmethane (DMMDA). The degree of sulfonation (DS) was regulated through variation of the molar ratio of SAS to DMMDA. The PVA/SPI blend membranes were prepared and applied in VRBs. Many basic properties of the membranes were characterized, particularly the water and oxidative stability. The blend membranes exhibit excellent water and oxidative stability. The proton conductivity, vanadium ion permeability and proton selectivity increase with DS due to the highly-dispersed phase-separated microstructure. In VRB single cell tests, the VRBs with blend membranes show lower charge capacity loss, higher coulombic efficiency (CE) and higher energy efficiency (EE) than with Nafion 117 membrane. Furthermore, the blend membranes present stable performances up to 100 cycles without significant decline in EE. All experimental results indicate that the blend membranes show promising prospects for application in VRBs.