Nature of Solvent/Nonsolvent Strategy in Achieving Superior Polybenzimidazole Membrane for Vanadium Redox Flow Battery

The tightly connected structure of polybenzimidazole (PBI) membrane can be relaxed by solvent/nonsolvent solution to achieve a high proton conductivity for vanadium redox flow battery (VRFB). However, the nature behind the solvent/nonsolvent strategy is not unraveled. This work proposes a guideline to analyze the effect of PBI membrane relaxing formulas based on the interactions between different components in membranes. The supreme-efficient PBI membrane derived by the DMSO/formamide formula according to the guideline displays a marvelous performance for VRFB, with the proton conductivity boosted by 4300 % (from 1.93 to 83.33 mS cm⁻¹), and VRFB assembled with this membrane achieves an outstanding energy efficiency of 82.5 % under 200 mA cm⁻². Moreover, this work profoundly unravels the structure, property and performance relationship of PBI membrane, which is of great value for the development of membranes.