Advanced porous PBI membranes with tunable performance induced by the polymer-solvent interaction for flow battery application

The polymer-solvent interaction was utilized to construct porous polybenzimidazole (PBI) membranes with tunable morphology for vanadium flow battery (VFB) application. Solvent treatment was employed to investigate the polymer-solvent interaction experimentally, further to study the membrane formation mechanism. By varying the form and strength of the polymer-solvent interaction, the membrane morphology could be easily controlled and an optimized performance could also be achieved. As a result, a columbic efficiency of 99.29% and an energy efficiency of 81.93% at 200 mA cm(-2) were realized by using an optimized membrane, which is the highest value ever reported for porous membranes at a so high current density by far. The Flory-Huggins interaction parameter was then utilized to quantify the strength of the polymer-solvent interaction. Based on the experimental investigation and quantitative calculation, the relationship between the polymer-solvent interaction and membrane performance was clearly clarified, and the membrane formation mechanism became more unequivocal as well. This paper thereby supplies an efficient concept to fabricate porous membranes with well controlled morphology and performance.