Sulfonated polyimide/phosphotungstic acid composite membrane for vanadium redox flow battery applications

A novel sulfonated polyimide (SPI) membrane embedded with the phosphotungstic acid (SPI/PWA membrane) for vanadium redox flow battery (VRB) has been prepared with low capacity loss, low cost, and high energy efficiency (EE); the proportion of PWA in the composite membrane is 15%. The mechanical strength, vanadium ions permeability, and performance of the membrane in the VRB single cell were characterized. Results showed that the SPI/PWA membrane possessed low permeability of vanadium ions, accompanied by higher mechanical strength than the Nafion117 membrane. The VRB single cell with SPI/PWA composite membrane showed 7.6% higher coulombic efficiency, 4.6% higher EE, but lower capacity loss in comparison with the one with Nafion117 membrane at the current density 40 mA cm？2. The good cell performance, low capacity loss, and high vanadium ions barrier properties of the blend membrane is of significant interest for VRB applications