Synergistic poly(imidobiphenyl-spirofluorene) framework in amino-polybenzimidazole for high-temperature proton exchange membranes with enhanced conductivity and acid retention

The addition of SBF is conducive to enhancing PA retention. • The proton conductivity of AmPBI-SBF-40 at 180 °C could reach 203.3 mS cm −1 . • The PA retention of AmPBI-SBF-20 at 160 °C/0% RH was 84% after 240 h. • The peak power density of the AmPBI-SBF-40 was 1018.6 mW cm −2 at 180 °C. In this study, a poly(imidobiphenyl-spirofluorene) (SBF) framework was incorporated into the molecular chains of amino-functionalized polybenzimidazole (AmPBI) through rational molecular structure design, resulting in the successful preparation of a series of novel high-temperature proton exchange membranes. The imidazole functional group forms strong hydrogen bonds with phosphoric acid (PA), while the microporous framework constructed by spirofluorene units creates continuous additional proton transport pathways. The synergistic effect of these dual advantages significantly enhances PA uptake capacity and high-temperature proton conduction efficiency of the resulting membranes. In addition, the unique pore structure of the phthalimide units effectively traps free PA molecules within the membrane matrix, thereby inhibiting PA leaching and markedly improving PA retention capability. Electrochemical test results show that the AmPBI-SBF-40 membrane exhibits a proton conductivity as high as 203.3 mS cm −1 at 180 °C. Under the same temperature conditions, its single-cell peak power density reaches 1018.6 mW cm −2 . After undergoing a 240-h long-term acid leaching test under extreme high-temperature conditions of 160 °C/0% RH, the PA retention rate of the AmPBI-SBF-20 membrane remained at 84%. These results confirm that this series of modified composite membranes exhibits excellent high-temperature proton conductivity, single-cell output performance, and long-term chemical stability. Download: Download high-res image (145KB) Download: Download full-size image