A highly proton-conductive and vanadium-rejected long-side-chain sulfonated polybenzimidazole membrane for redox flow battery

A long-side-chain sulfonated polybenzimidazole (PBI-PS) membrane was successfully prepared by the reaction of PBI with 1, 3-propanesultone for improving the efficiencies of vanadium redox flow battery. The interaction between sulfonic acid and imidazole groups provides the PBI-PS membrane with excellent swelling resistance, leading to a swelling ratio of only 13% for the membrane with IEC of as high as 3.18 mmol g(-1). This results in an ultra-low vanadium permeability (6.5 x 10(-9) cm(2) s(-1)). The introduction of sulfonic acid-terminated flexible side chain in the membrane also constructs good microphase separation structure, leading to a low area resistance of 0.51 Omega cm(2), which is close to Nafion 212 (0.41 Omega cm(2)). This membrane exhibits excellent cell performance. The voltage and energy efficiencies are up to 90.73% and 89.13% at 80 mA cm(-2), respectively. Furthermore, the efficiencies remain constant values for 200 cycles, and no changes in chemical structure and cell efficiencies are observed after 720 h immersion in electrolyte solution.