Boosting Ionomer Oxygen Transport via Pore Confinement in Carbon Supports for Low-Pt Fuel Cells

Low-Pt proton exchange membrane fuel cells (PEMFCs) are promising for hydrogen energy implementation, yet oxygen transport through ionomer-covered catalyst surfaces becomes increasingly limiting due to the resistance associated with dense ionomer films. Herein, we demonstrate a pore-confinement strategy to manipulate the spatial locality of Pt nanoparticles within porous carbon supports, enabling simultaneous regulation of ionomer distribution and molecular organization. Pt nanoparticles were selectively positioned on the external surfaces (Ptext/PC) or within the internal nanopores (Ptint/PC) of otherwise comparable supports, while maintaining similar Pt loading, particle size, and pore characteristics. Under H2-air condition, Ptint/PC delivered a peak power density ∼1.3 times higher than that of Ptext/PC, but a similar current density in the high-voltage region. Electrochemical analyses reveal that the performance enhancement originates from improved oxygen transport rather than catalytic activity. Wide-angle X-ray scattering and molecular dynamics simulations reveal that the Pt nanoparticles confined within mesopores disrupt the dense packing of ionomer backbones, thereby boosting oxygen permeability at the catalyst–ionomer interface. By establishing a direct relationship between Pt locality, ionomer distribution, backbone organization, and oxygen transport, this work identifies catalyst locality as an effective parameter for engineering interfacial mass transport and provides a new design principle for low-Pt PEMFCs.