Hydrophilic/hydrophobic-bi-comb-shaped amphoteric membrane for vanadium redox flow battery

A novel hydrophilic/hydrophobic bi-comb-shaped amphoteric membrane was for the first time designed by the one-pot reactions of PBI with bromohexane and 1,3-propanesultone. The sulfonic acid chain promotes the formation of amphoteric ion clusters, while the alkyl side chain enhances the packing of hydrophobic segments. This unique structure design optimizes the segregated microphase morphology of the membrane, which is proved by TEM. Compared to the membrane without alkyl side chain, the bi-comb-shaped membrane shows a lowered area resistance (0.58 vs. 0.96 Ω cm2) as well as a reduced swelling ratio (11.7% vs. 14.3%). As a result, the cell with the bi-comb-shaped membrane exhibits improved voltage efficiency, thus achieving increased energy efficiency. In addition, the membrane of this structure occupies excellent cycle stability. The cell efficiencies maintain almost stable for 250 cycles, and the chemical structure has no change after immersing in the electrolyte solution for 28 days.