Optimal method for preparing sulfonated polyaryletherketones with high ion exchange capacity by acid-catalyzed crosslinking for proton exchange membrane fuel cells

Sulfonated polyaryletherketones (SPAEK) bearing four sulfonic acid groups on the phenyl side groups were synthesized. The benzophenone moiety of polymer backbone was further reduced to benzydrol group with sodium borohydride. The membranes were crosslinked by acid-catalyzed Friedel-Crafts reaction without sacrifice of sulfonic acid groups and ion exchange capacity (IEC) values. Crosslinked membranes with the same IEC value but different water uptake could be prepared. The optimal crosslinking condition was investigated to achieve lower water uptake, better chemical stability (Fenton's test), and higher proton conductivity. In addition, the hydrophilic ionic channels from originally course and disordered could be modified to be narrow and continuous by this crosslinking method. The crosslinked membranes, CS4PH-40-PEKOH (IEC = 2.4 meq./g), reduced water uptake from 200 to 88% and the weight loss was reduced from 11 to 5% during the Fenton test compared to uncrosslinked one (S4PH-40-PEK). The membrane showed comparable proton conductivity (0.01-0.19 S/cm) to Nafion 212 at 80 degrees C from low to high relative humidity (RH). Single H-2/O-2 fuel cell based on the crosslinked SPAEK with catalyst loading of 0.25 mg/cm(2) (Pd/C) exhibited a peak power density of 220.3 mW/cm(2), which was close to that of Nafion 212 (214.0 mW/cm(2)) at 80 degrees C under 53% RH. These membranes provide a good option as proton exchange membrane with high ion exchange capacity for fuel cells.

Automated summary

Crosslinked SPAEK membranes with reduced water uptake and improved chemical stability and proton conductivity were prepared by optimizing crosslinking conditions. These membranes showed comparable proton conductivity to Nafion 212 and exhibited high power density in H-2/O-2 fuel cell tests, making them a promising option for proton exchange membranes in fuel cells.