High-performance pyridine-containing fluorinated poly(aryl ether) membranes for vanadium flow batteries

Vanadium flow battery (VFB) is increasingly attractive for large-scale energy storage. However, developing high-power-density VFB remains challenging due to the lack of high-performance membranes. Here, we report a novel pyridine-containing fluorinated poly(aryl ether)(PyPEF) membrane for VFB. PyPEF membranes are pre-swelled with H3PO4 (85 wt%) and then exchanged with H2SO4 (3 mol L−1) to obtain the resulting H2SO4-doped PyPEF membranes. The basic pyridine groups are protonated to form positively charged groups and pre-swelled by H3PO4 to build highly connected ionic transport channels, which provide high selectivity and enhanced conductivity for the membrane. Moreover, the rigid, strongly hydrophobic perfluorophenyl-containing PyPEF backbone has high swelling resistance. As a result, the H2SO4-doped PyPEF membranes exhibit low swelling, high selectivity, high conductivity, and robust mechanical strength. The VFB with PyPEF-90 membrane delivered excellent battery performance, 91.7% energy efficiency at 80 mA cm−2, and 80.3% energy efficiency at 260 mA cm−2. In addition, the VFB with PyPEF-90 membrane maintained stable performance after continuously running for 1200 cycles at a much high current density of 220 and 200 mA cm−2, showing excellent stability.