High Proton Conductivity Membrane Based on Sulfonated Polybenzimidazole by Doping Ethylenediaminetetraacetic Acid-Modified MOF-808 for Vanadium Flow Battery

The composite membrane (sPBI–MGE-x) is prepared by introducing MOF-808-grafted ethylenediaminetetraacetic acid (EDTA) into the sulfonated polybenzimidazole (sPBI) with a sulfonation degree of 50. MOF-808, one of Zr-based metal organic frameworks, has tunable pore size, plenty of pathways for proton transport, and superior acid stability. After MOF-808 is grafted by EDTA, the obtained MOF-808-EDTA (MGE) has the amino and carboxyl groups, which can provide additional proton transport channels and the acid–base pair effect between amino and sulfonic acid groups can further strengthen the interaction between MGE and sPBI. Therefore, compared with the pristine sPBI membrane (12.5 mS cm–1), the sPBI–MGE-2 composite membrane exhibits high proton conductivity (30.8 mS cm–1) and remarkable energy efficiency (83.81%) largely at 60 mA cm–2.