Efficiency and Oxidation Performance of Densely Flexible Side-Chain Piperidinium-Functionalized Anion Exchange Membranes for Vanadium Redox Flow Batteries

In order to improve the performance of vanadium redox flow batteries (VRFBs), a series of anion exchange membranes (PAES-8mPip-x) containing multiple flexible side-chain piperidinium structures were selected for use as ionic membranes for VRFBs. The relationship between their battery performance and chemical structure was systematically investigated, and their oxidation stability and degradation mechanism in strong oxidizing solution were studied in detail. These membranes exhibited high SO42– conductivity as well as low area specific resistance due to the incorporation of densely flexible side-chain piperidinium. Their SO42– conductivity and area-specific resistance are in the range of 9.6–18.1 mS cm–1 and 0.19–0.34 Ω cm2 at 20 °C, respectively. The single battery assembled with the representative PAES-8mPip-0.25 displayed high efficiencies, and its coulombic efficiency, voltage efficiency, and energy efficiency were 94.78, 90.15, and 85.44% at a current density of 60 mA cm–2, respectively, which were higher than those of Nafion 212 (94.19, 89.08, and 83.90%) at the same testing condition. What is more, it was found that these AEMs had good stability in strong oxidizing solution. Although their polymer backbone was degraded to a certain extent in 1.5 mol L–1 VO2+/3 mol L–1 H2SO4 at 40 °C, the flexible piperidinium in side chains did not undergo significant chemical degradation. Related research results provide a scientific basis for the design of high-performance anion membrane materials for VRFBs.