Ultra-thin, mechanically durable reinforced sulfonated poly(fluorenyl biphenyl) indole proton exchange membrane for fuel cell

Mechanically durable and highly proton-conductive proton exchange membrane (PEM) is a crucial component for PEM fuel cell (PEMFC). Herein, we report a facile method to fabricate poly(tetrafluoroethylene) (PTFE)-reinforced composite membrane based on sulfonated poly(fluorenyl biphenyl) indole ionomer (PTFE-SPFBI). The resultant reinforced membrane exhibits an ultra-thin and dense structure, leading to a reduced swelling ratio, exceptional mechanical durability (with over 200 % elongation at break), and high chemical stability, primarily attributed to the presence of PTFE support. The ultra-thin nature of the PTFE-SPFBI membrane, coupled with its superior proton conductivity, significantly contributes to its performance in fuel cells, achieving a maximum power density of 778 mW cm−2. Notably, this reinforced membrane exhibits remarkable endurance in open-circuit voltage (OCV) test, demonstrating its ability to sustain operation for more than 500 h at 90 °C and 30 % relative humidity. Overall, our work introduces a straightforward and promising approach for the fabrication of high-performance pore-filling PEMs using hydrocarbon ionomers, emphasizing enhanced durability and proton conductivity.