High-Performance Proton Exchange Membranes Based on Block Polybenzimidazole and Organic–Inorganic Fillers with a Low Acid Doping Level

Herein, composite proton exchange membranes based on block polybenzimidazole (bPBI) and a phosphotungstic acid-ionic liquid (PWA-IL) organic–inorganic filler have been prepared. The bPBI was prepared by block copolymerization of poly[2,2′-(p-phenylene)-5,5′-benzimidazole] and poly(4,4′-diphenylether-5,5′-bibenzimidazole) oligomers. bPBI combined the advantages of both rigid and flexible segments. The block structure of the segmented block copolymer helped build proton transmission channels and made the transmission of protons easier. The PWA-IL was evenly distributed in the membranes. The PWA-IL has good electrochemical properties and can also form hydrogen bonds with phosphoric acid (PA), which is beneficial to proton conduction. The membranes had excellent mechanical properties (11 MPa) owing to the low acid doping level (ADL). Moreover, the membranes exhibit 0.05 S cm–1 proton conductivity at 170 °C at a low ADL and exhibit over 60% PA retention.