Sulfonated polyimide (SPI) and ZrO 2 are blended to prepare a series of novel SPI/ZrO 2 composite membranes for vanadium redox flow battery (VRFB) application. Results of atomic force microscopy and X-ray diffraction reveal that ZrO 2 is successfully composited with SPI. All SPI/ZrO 2 membranes possess high proton conductivity (2. ). SPI/ZrO 2 -15% membrane is determined as the optimum one on account of its higher proton selectivity and improved chemical stability. The VRFB with SPI/ZrO 2 -15% membrane presents higher coulombic efficiency and energy efficiency than that with Nafion 117 membrane at the current density, which ranged from 20 to 80 mA cm
À2. Cycling tests indicate that the SPI/ZrO 2 -15% membrane has good operation stability in the VRFB system.
A series of fluorine‐containing branched sulfonated polyimide (Fb‐SPI) membranes with different degrees of branching (0–12 %) were synthesized through polycondensation. The chemical structure of Fb‐SPI‐10 membrane was confirmed using ATR‐FTIR and 1H NMR spectroscopy. The physico‐chemical properties of Fb‐SPI membranes were systematically investigated and compared to linear SPI (l‐SPI) and Nafion 117 membranes. The vanadium‐ion permeabilities of Fb‐SPI membranes (2.45–0.99×10−7 cm2 min−1) are much lower than that of Nafion 117 (17.1×10−7 cm2 min−1) membranes. Besides, the chemical stability of Fb‐SPI membranes is superior to that of l‐SPI membranes. During 500‐time continuous cyclic charge‐discharge measurements, the VRFB assembled with a Fb‐SPI‐10 membrane shows higher coulombic efficiency (98.4–99.7 %), higher or close energy efficiency (69.0–79.7 %) from 40 to 80 mA cm−2, and higher or close capacity retention (52.8–100 %) from 40 to 70 mA cm−2 compared with a device using a Nafion 117 membrane. All of these results demonstrate that the as‐selected Fb‐SPI‐10 membrane has promising potential for VRFB applications.
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