Mass‐Transport–Engineered CCM Architecture Employing MPL‐Free Carbon Paper and Graphene‐Coated Ni Foam Channels for High‐Temperature PEM Fuel Cells

ABSTRACT High‐temperature polymer electrolyte membrane fuel cells (HT‐PEMFCs) enable simplified water and thermal management and high‐current‐density operation under dry H ₂ /air conditions, but their performance is limited by phosphoric‐acid (PA) loss, oxygen‐transport resistance, and poor interfacial contact in catalyst‐coated‐substrate (CCS) designs. Although ion‐pair membranes with protonated phosphonic‐acid ionomers have enabled catalyst‐coated‐membrane (CCM) fabrication with PA‐doped membranes, PA flooding and severe oxygen‐transport resistance associated with microporous‐layer (MPL) gas diffusion layers (GDLs) and graphite channels remain major bottlenecks. Here, we present a mass‐transport‐engineered CCM architecture that exploits structural freedoms inaccessible in CCS‐based HT‐PEMFCs. By decoupling catalyst deposition from the porous substrate, CCM processing enables the use of an MPL‐free carbon paper, eliminating nanoporous Knudsen diffusion resistance and shortening oxygen diffusion pathways. To mitigate the increased PA migration induced by the MPL‐free carbon paper, a rib‐free graphene‐coated Ni foam (G‐foam) flow field is introduced. The 3D open‐cell G‐foam enhances convective oxygen delivery, while its hydrophobic multilayer‐graphene surface mitigates PA leaching and reduces interfacial contact resistance. The resulting CCM–MPL‐free carbon paper–G‐foam architecture exhibits reduced oxygen‐transport resistance, enhanced catalyst utilization, and lower proton‐transport resistance. Peak power densities of 0.865 W cm ^{− 2} are achieved with stable 200‐h operation and negligible PA accumulation.