Cycling performance and efficiency of sulfonated poly(sulfone) membranes in vanadium redox flow batteries

As an alternative to Nafion (R) ion exchange membrane, an inexpensive commercially-available Radel (R) polymer was sulfonated, fabricated into a thin membrane, and evaluated for its performance in a vanadium redox flow battery (VRFB). The sulfonated Radel (S-Radel) membrane showed almost an order of magnitude lower permeability of VO(2+) ions (2.07 x 10(-7) cm(2)/min), compared to Nafion 117 (1.29 x 10(-6) cm(2)/min), resulting in better coulombic efficiency (-98% vs. 95% at 50 mA/cm(2)) and lower capacity loss per cycle. Even though the S-Radel membrane had a slightly higher membrane resistance, the energy efficiency of the VRFB with the S-Radel membrane was comparable to that of Nafion because of its better coulombic efficiency resulting from the lower vanadium ion crossover. The S-Radel membrane exhibited good performance up to 40 cycles, but a decline in performance at later cycles was observed, likely as a result of membrane degradation. Published by Elsevier BM.