Inhibition of polymeric densification at platinum/ionomer interface via enlarging tetrafluoroethylene spacing in perfluorinated sulfonic-acid ionomer

Polymer electrolyte fuel cells hold great potential for powering heavy-duty vehicles (HDVs) run by clean hydrogen, but a major challenge lies in the ionomer poisoning of scarce platinum (Pt) catalysts, which hinders the Pt utilization and cell efficiency. Here, we report a simple yet effective approach to mitigate polymeric densification at the Pt/ionomer interface, via enlarging tetrafluoroethylene (TFE) spacing between neighboring side chains. Ionomers with weaker confinement to Pt, arising from strengthened hydrophobic interactions, suppress the specific adsorption and lead to less-densified ionomer morphology. Despite having a lower ion-exchange capacity, they exhibited high accessibilities (over 80%) and a significant reduction of 22–8% in sulfonate coverage, hence resulting in two-fold improvements in activity and local transport towards the oxygen reduction reaction. This strategy offers a key solution to unlock the full potential of Pt, offering seamless integration into current manufacturing processes, thus accelerating the sustainability and scalability of fuel cell technology.