Ether-Free Poly(p-terphenyl-co-acetylpyridine) Membranes with Different Thicknesses for Vanadium Redox Flow Batteries

The preparation of thin polymer membranes with excellent ion selectivity, good chemical stability, and high battery performance is a research hotspot for vanadium redox flow batteries (VRFBs). Herein, aryl-ether free poly(p-terphenyl-co-acetylpyridine) (termed as PTAP) was synthesized through a facile one-pot Friedel–Crafts polyhydroxyalkylation reaction. Due to the presence of a large amount of pyridine groups, the PTAP membrane exhibits good sulfonic acid absorption capability and low area resistance. Meanwhile the PTAP membrane displays ultralow vanadium ion permeability and excellent chemical stability simultaneously. The effect of thickness of PTAP membranes on the properties has been investigated systematically. As benchmarks, polybenzimidazole (PBI) membranes with different thicknesses of 54 and 118 μm, Nafion 115 and Nafion 212 have been studied accordingly. Consequently, the thin PTAP-55μm membrane exhibits the lowest vanadium ion permeability (4.6 × 10–8 cm2 min–1) among all the membranes. Meanwhile, it also achieves a low area resistance of 0.45 Ω cm2, high tensile strength of 34.9 MPa, and good chemical stability toward VO2+ ions. The VRFB based on PTAP-55μm shows a high energy efficiency of 85.6% at 80 mA cm–2 and maintains high Coulombic efficiency (∼99.4%) and stable energy efficiency (∼81.5%) during the long-term operation at 100 mA cm–2.