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 mu m, Nafion 115 and Nafion 212 have been studied accordingly. Consequently, the thin PTAP-55 mu m membrane exhibits the lowest vanadium ion permeability (4.6 x 10(-8) cm(2) min(-1)) among all the membranes. Meanwhile, it also achieves a low area resistance of 0.45 Omega cm(2), high tensile strength of 34.9 MPa, and good chemical stability toward VO2+ ions. The VRFB based on PTAP-55 mu m shows a high energy efficiency of 85.6% at 80 mA cm(-2) and maintains high Coulombic efficiency (similar to 99.4%) and stable energy efficiency (similar to 81.5%) during the long-term operation at 100 mA cm(-2).

Automated summary

In this study, aryl-ether free poly(p-terphenyl-co-acetylpyridine) (PTAP) was synthesized through a one-pot Friedel-Crafts polyhydroxyalkylation reaction. The resulting PTAP membrane exhibited good sulfonic acid absorption capability, low area resistance, ultralow vanadium ion permeability, and excellent chemical stability. The VRFB based on PTAP-55 μm membrane showed high energy efficiency and stable operation.