Open Scaffolded Triple‐Phase Interface for Alleviating Pt Poisoning and Boosting Mass Transport in PEMFCs

ABSTRACT The conventional triple‐phase interface (TPI) in proton exchange membrane fuel cells (PEMFCs) relies on dense ionomer encapsulation to conduct protons, but this inevitably poisons platinum (Pt) catalysts and blocks oxygen transport. Here, we replace this closed architecture with an open, scaffolded TPI constructed by introducing sulfonated covalent organic framework (SCOF) nanosheets as a rigid, porous scaffold within the Pt‐ionomer matrix. Unlike the conventional ionomer film that intimately coats Pt, the SCOF scaffold acts as a physical spacer that suppresses direct ionomer adsorption, while its ordered nanochannels serve as dedicated proton highways and its intrinsic porosity facilitates oxygen diffusion. This open architecture decouples the competing requirements of proton conduction and catalyst accessibility, concurrently mitigating Pt poisoning and enhancing mass transport. Accordingly, the engineered cathode exhibits substantially reduced sulfonate‐group coverage and improved proton conduction, alongside a significantly decreased pressure‐independent oxygen transport resistance. At an ultralow Pt loading of 0.05 mg Pt cm −2 , the system delivers a peak power density of 0.86 W cm −2 under H 2 /air, representing a 24% improvement over the conventional counterpart. This work establishes an open‐scaffold design paradigm that fundamentally breaks away from the traditional ionomer‐encapsulated TPI, offering a generalizable route to high‐performance, low‐Pt‐loading PEMFCs.