A novel fluorinated acid-base sulfonated polyimide membrane with sulfoalkyl side-chain for vanadium redox flow battery

A novel fluorinated acid-base sulfonated polyimide membrane (s-f-SPI) with trifluoromethyl (-CF3), sidechain-type-SO3H and benzimidazole groups was synthesized by a 2-step method for vanadium redox flow battery applications. A series of physico-chemical properties of s-f-SPI membrane were researched systematacially. The acid-base pairs between the side-chain-type-SO3H and protonated imidazole groups provided more channels for proton-transport, enhancing the proton conductivity (0.51 x10(-1) S cm(-1) at similar to 25 degrees C), and Donnan effect of the imidazole groups impeded the penetration of vanadium-ion (3.95 x10(-7) cm(2) min(-1)). In VRFB tests, s-f-SPI membrane exhibited a coulombic efficiency (CE) of 98.1% and an energy efficiency (EE) of 81.2% at a current density of 100 mA cm(-2), higher than those of Nafion 212 (CE: 94.1%, EE: 76.5%). Furthermore, the VRFB with s-f-SPI membrane showed a stable performance in the 500 cycles charging-discharging test at 100 mA cm(-2), and the morphology and structure remained unchanged after the cycle test. These results demonstrate that the s-f-SPI membrane has great potential for VRFB applications. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

A novel fluorinated acid-base sulfonated polyimide membrane was synthesized for vanadium redox flow battery applications, exhibiting improved proton conductivity and resistance to vanadium ion penetration. The membrane showed higher coulombic and energy efficiency compared to Nafion 212 in VRFB tests, and maintained stable performance in 500 cycle charging-discharging test. These results demonstrate the great potential of the s-f-SPI membrane for VRFB applications.