Asymmetric cycling of vanadium redox flow batteries with a poly(arylene piperidinium)-based anion exchange membrane

The potential application of a 50 μm thick anion exchange membrane prepared based on poly(terphenyl piperidinium-co-trifluoroacetophenone) (PTPT) is investigated for vanadium redox flow batteries (VRFBs). The PTPT exhibits a considerably lower vanadium permeation than Nafion 212. Therefore, the self-discharge duration of the VRFB based on PTPT is much longer than the VRFB based on Nafion 212. Besides, PTPT shows oxidative stability almost as good as Nafion 212 during immersion in an ex-situ immersion test for more than 400 h. Comparing the VRFB performance when symmetric and asymmetric electrolyte volumes are used yields interesting results. The results show that asymmetric cycling is more effective and efficient for the VRFB assembled with PTPT than Nafion 212 as the capacity fade of 0.03% cycle⁻¹, and the highest coulombic efficiency of 98.8% is attained. Furthermore, the color change of the membrane during cycling can be reversed using a straightforward post-treatment method.