Double-layer ePTFE-reinforced membrane for high-performance vanadium redox flow batteries

A double-layer ePTFE-reinforced PFSA membrane (PEM-DR) was developed via solution casting to enhance the mechanical durability and vanadium ion barrier capability of membranes for vanadium redox flow batteries (VRFBs). Compared with the single-layer reinforced membrane (PEM-SR), PEM-DR exhibits markedly improved mechanical strength, reduced swelling, and enhanced dimensional stability. PEM-SR exhibits insufficient comprehensive performance and obvious cross-sectional structural defects after long-term cycling, while the dual-layer structure of PEM-DR enables uniform stress distribution during cyclic volume variation and effectively mitigates long-term cycling-induced delamination. Quantified EE outputs of 90.23 %, 84.99 % and 83.39 % are acquired for PEM-DR at 50, 100 and 150 mA cm−2 respectively; the longest cycle life is exhibited by PEM-DR, which is three times longer than those of 50 μm Nafion commercial membrane, and twice as long as that of PEM-SR. The double-layer ePTFE reinforcement effectively suppresses vanadium ion crossover and mitigates membrane deformation under cyclic mechanical stress and acidic oxidative conditions. PEM-DR delivers superior electrochemical stability, minimal capacity decay, and excellent long-term cycling performance in VRFBs. These results demonstrate that the double-layer reinforcement architecture significantly enhances membrane durability while maintaining high battery performance, providing a promising strategy for the development of advanced PEMs for durable VRFB operation.