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.