Sulfonating and polyhedral oligomeric silsesquioxane crosslinking in one step to build multiple proton pathways for proton exchange membrane fuel cells over a wide temperature range

Developing proton exchange membrane fuel cells (PEMFCs) operating over a wide temperature range can avoid additional internal/external heating or cooling devices for the PEMFCs operating. Polybenzimidazole (PBI) doped with phosphoric acid (PA) exhibits significant potential in high-temperature proton exchange membrane fuel cells (HT-PEMFCs). Nevertheless, the traditional PA-PBI membranes are limited to operating within 140∼180 °C. In this work, a sulfonated polyhedral oligomeric silsesquioxane crosslinked polybenzimidazole membrane enriched pyridine and diazafluorene (CSPBI-X) is prepared where the sulfonation and crosslinking are accomplished by one-step heating. The theoretical calculations confirm that PA molecules have strong interactions with sulfonic acid groups and nitrogen-containing groups, enabling the membrane to achieve proton conductivity in a wide temperature range (80–180 °C). Moreover, the cross-linked sulfonated membranes have excellent PA retention ratio as high as 83.8% under 80 °C and 40% relative humidity for 120 h. Remarkably, with the acid doping level of 7.6, the proton conductivity of the CSPBI-20 membrane reaches 0.0491 S cm −1 and 0.145 S cm −1 at 80 °C and 180 °C in dry state, respectively. The highest power density of the CSPBI-20 at 80, 100, 120, 140, 160, and 180 °C is 257.3, 362.9, 485.3, 604.6, 755.3, and 956.1 mW cm −2 , respectively.