Mass-Transport-Engineered CCM Architecture Employing MPL-Free Carbon Paper and Graphene-Coated Ni Foam Channels for...

High-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) enable simplified water and thermal management and high-current-density operation under dry H₂/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.