Sulfonated polyimide/AlOOH composite membranes with decreased vanadium permeability and increased stability for vanadium redox flow battery

A series of sulfonated polyimide (SPI)/boehmite (AlOOH) (5.0, 10.0, 15.0, 20.0 wt.%) composite membranes are fabricated by blending for vanadium redox flow battery (VRFB) application. SEM images illustrate the compatibility between SPI and AlOOH. Both EDS and XRD results verify the existence of AlOOH in the SPI/AlOOH composite membrane, and FT-IR spectrums show the interaction between SPI and AlOOH. The SPI/AlOOH membranes have improved stability in 0.1 mol L−1 VO2 + + 3.0 mol L−1 H2SO4 solutions at 40 °C than pure SPI membrane. The SPI/AlOOH-10 % membrane possesses the highest proton selectivity among all SPI/AlOOH membranes. The VRFB with the SPI/AlOOH-10 % membrane presents a higher coulombic efficiency (94.30–97.60 %) and energy efficiency (83.10–64.78 %) at the current density ranged from 20 to 80 mA cm−2 than that with Nafion 117 membrane. The open circuit voltage tests show that the SPI/AlOOH-10 % membrane has longer self-discharge time (117 h) compared with Nafion 117 (72 h). Furthermore, the cycling charge-discharge tests indicate that the SPI/AlOOH-10 % membrane has good operation stability in VRFB system. Therefore, the low-cost SPI/AlOOH membrane with excellent battery performance exhibits a great potential for application in VRFB.