Soluble polybenzimidazoles incorporating Tröger’s base for high-temperature proton exchange membrane fuel cells

In this work, a novel dicarboxylic acid (TB–COOH) containing Tröger's base (TB) was synthesized, and newly TB-based polybenzimidazole (PBI) membranes were prepared as electrolytes for high-temperature proton exchange membrane (HT-PEM) fuel cells. The TB-based PBIs, upon treatment with triethylammonium salts, showed good processability. The as-prepared TB-based PBI membranes exhibit superior tensile strength above 126.6 MPa and high decomposition temperatures at 5% weight loss ranging from 374 °C to 411 °C. The residual weights of the TB-based PBI membranes remained at above 80% in Fenton's reagent at 80 °C for 48 h. Notably, with extra nitrogen atoms in the TB-based PBIs, their phosphoric acid uptakes show obvious improvement over the corresponding sulfonated polybenzimidazole (sPBI) without TB units, achieving the highest proton conductivity (93.2 mS cm−1) at 160 °C, 2.3 times that of 41.2 mS cm−1 from the sulfonated PBI (sPBI) membrane. The highest peak power density of the H2/air fuel cell reached 225.5 mW cm−2 under non-humidity conditions at 160 °C, much higher than the value of the sPBI membrane. Based on their excellent comprehensive performance, incorporating TB into chain backbones optimized the PBI electrolytes for HT-PEM applications.