Tailoring COFs with Water and Oxygen Pathways for Efficient Catalyst Interfaces in PEMFCs.

Proton exchange membrane fuel cells (PEMFCs) have gained significant attention due to their high efficiency and clean emissions. However, reducing platinum (Pt) loadings in PEMFCs remains challenging due to the high mass transport resistance near the catalyst surfaces. This study investigates phosphorylated covalent organic frameworks (P-rCOFs) as ionomers in PEMFCs, aiming to optimize the three-phase interface at the catalyst surface. Through the protonation of tertiary amine sites and precise structural engineering of side chains within the COF framework, well-defined transport channels are created to enhance water and oxygen mass transfer. The results demonstrate that P-rCOF-C4 significantly improves the catalytic performance of commercial Pt/C catalysts, with a half-wave potential 37 mV higher than Nafion. Furthermore, a PEMFC incorporating P-rCOF-C4 as an ionomer binder achieves a peak power density of 2.40 W cm-2 at 0.1 mg cm-2 catalyst loading, a 1.5 fold increase over Nafion. This work underscores the potential of P-rCOFs in optimizing the three-phase interface, offering a promising pathway for more efficient and cost-effective PEMFCs.