Phosphonated ionomer modulates electrochemical interfaces in high temperature polymer electrolyte membrane fuel cells

Liquid phosphoric acid (PA), as the proton carrier for high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs), presents challenges such as catalyst poisoning, high gas transport resistance and electrolyte loss. These issues significantly impede the performance and durability of HT-PEMFCs, thereby limiting their potential for further application. In this study, poly(2,3,5,6-tetrafluorostylene-4phosphonic acid) (PWN) with intrinsic proton conduction ability was employed as catalyst layer binder to reveal the impacts of the ionomer's molecular structure on mass transport within the catalyst layer. Our findings demonstrated that increasing the phosphorylation degree of PWN could enhance both pore formation at the catalyst layer and electrode acidophilic capability while improving proton conduction ability and reducing cells' internal resistance. However, adverse effects included increased local oxygen transport resistance and decreased catalyst utilization resulting from electrode acidophilic capability. This research offers valuable insights for the relationships between micro-scale molecule structure, mesoscale electrode architecture, and membrane electrode assembly design in HT-PEMFCs. (c) 2025 Published by Elsevier B.V. and Science Press on behalf of Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences.