Enhanced performance of high-temperature proton exchange membranes via polyfluorene cross-linked zwitterionic liquid

A satisfactory trade-off between physical/chemical stability and conductivity is crucial for high-temperature proton exchange membrane (HT-PEM) applications. Herein, a series of ether-free polyfluorenes cross-linked with zwitterionic liquids possessing both quaternary ammonium (QA+) and sulfonate ion (–SO3−) were prepared as crosslinked cHFTP–VIPSx via UV irradiation. Compared with non-crosslinked HFTP–TMA, crosslinked cHFTP–VIPSx exhibited enhanced conductivity, dimensional stability, oxidation stability, and phosphoric acid retention, which are attributed to the well-developed crosslinked structure and incorporated –SO3- groups. The as-fabricated H2/air single cell with a cross-linked cHFTP–VIPS30 achieved a higher peak power density (728 mW cm−2) than that of uncross-linked HFTP–TMA (287 mW cm−2) at 120 °C. Considering their enhanced performance, these cHFTP–VIPSx membranes cross-linked with zwitterionic liquid are promising HT-PEM materials for fuel cells.