Engineering Pt/Ionomer Interface via Strengthening Hydrogen-Bond Network for High-Performance Low-Pt Fuel Cells

A critical challenge in proton-exchange membrane fuel cells (PEMFCs) is the severely limited catalyst utilization at conventional Pt/perfluorosulfonic acid (PFSA) ionomer interfaces, primarily due to Pt poisoning and impeded mass transport from strong PFSA adsorption. However, existing strategies to mitigate poisoning often struggle to balance adequate proton conductivity with efficient oxygen permeability. In this study, we report hydroxyl‑functionalized covalent organic framework (COF‑366‑OH) as a multifunctional additive that engineers the Pt/ionomer interface and synergistically enhances active-site availability, proton accessibility, and oxygen flux. The periodically aligned hydroxyl groups in COF‑366‑OH establish a strengthened hydrogen‑bond network with sulfonate groups of PFSA ionomers, which mitigates Pt poisoning and homogenizes ionomer distribution. Coupled with its ordered mesopores, this design enables efficient oxygen diffusion. Consequently, COF‑366‑OH‑modified electrode exhibits a 19% increase in dry-proton accessibility and a 33% reduction in oxygen‑transfer resistance. At an ultralow Pt loading of 0.05 mg_Pt cm^-2, the membrane electrode assembly incorporating the COF‑366‑OH‑modified Pt/C cathode achieves peak power densities of 1.67 W cm^-2 (H₂‑O₂) and 0.83 W cm^-2 (H₂‑air), representing improvements of 57.5% and 31.7% over the conventional Pt/C cathode, respectively. This work demonstrates a hydrogen‑bond-driven interface engineering strategy that simultaneously addresses Pt poisoning and mass‑transport limitations, providing a promising direction for low‑Pt PEMFCs.