Preparation of novel structure polybenzimidazole with thiophene ring for high performance proton conducting membrane in vanadium flow battery

Polybenzimidazole (PBI) has been extensively exploited as a good proton conducting membrane (PCM) material for energy storage. However, low proton conductivity of PBI severely restricts its practical applications. In order to obtain high proton conductivity membranes, new structure polybenzimidazole (TM-OPBI) with thiophene ring as side chain is synthesized. Additionally, the TM-OPBI membranes with different thiophene content are thoroughly investigated for their physicochemical properties and single cell performance. The results indicate that the protonated thiophene ring exhibits the dual role of accelerating proton transport as well as repelling vanadium ions permeation, therefore, the proton conductivity and vanadium resistance enhance simultaneously as the increasing of thiophene ring content. Namely, the trade-off effect for the PCM is solved. When the content of the thiophene monomer is 12%, the TM-OPBI-12 membrane displays almost the same area resistance and much better vanadium resistance than Nafion 115 membrane. Even more, the cell assembled with TM-OPBI-12 membrane shows higher coulombic efficiencies (CEs), larger discharge capacity, longer self-discharge time than cell with Nafion 115 membrane. This work highlights a novel PBI material that has the special group to be used as excellent performance for vanadium flow battery.