Methylated polybenzimidazole and its application as a blend component in covalently cross-linked anion-exchange membranes for DMFC

In the present work, the development and the characterization of new anion exchange membranes (AEMs) based on a methylated polybenzimidazole (mPBIOO) and their application in direct methanol fuel cell (DMFC) are described. For the preparation of methylated PBIOO (mPBIOO), a gentle methylation method was developed by using dimethyl carbonate (DMC) and 1,4-diazabicyclo[2.2.2]octane (DABCO). The synthesis of covalent cross-linked AEMs was achieved using the mPBIOO, sulfinated polysulfone (PPSU-SO2Li), DABCO and diiodobutane (DIB). The AEMs had IECs of more than 2.0 meq g−1, which indicates a high concentration of anion-exchange groups. Depending on the cross-linking degree, the methanol gravimetric uptake reached a maximum of 43% (by mass) and all AEMs showed an excellent ex situ alkaline stability. After 10 d in aqueous KOH (1 M) at 90 °C the IECs, ionic conductivities, and mechanical stabilities did not show a significant decrease. DMFC measurements show a performance improvement of a factor of three when the membranes were solvent (dimethylacetamide) extracted before integration into the fuel cell. With the usage of non-Pt catalysts, a maximum power density of 120 mW cm−2 was achieved.