Enhanced thermally and electrically conductive modified carbon paper based on MPCFs and PAN-CFs hybrid skeleton decorated with GNPs for fuel cells

As the primary gas diffusion layer (GDL) substrate in proton exchange membrane fuel cells (PEMFCs), carbon paper must provide mechanical support, efficient thermal and electrical conduction, and effective mass transport. However, conventional carbon paper often exhibits limited mechanical strength and inadequate electrical and thermal conductivities, which restricts overall cell performance, ultimately making modification essential. Herein, we fabricated a modified carbon paper consisting of an interwoven skeleton of mesophase pitch-based carbon fibers (MPCFs) and polyacrylonitrile-based carbon fibers (PAN-CFs), with graphite nanoplates (GNPs) anchored onto the fiber surfaces. The hybrid carbon felt was prepared by rapid filtration, in which MPCFs bridged adjacent PAN-CFs or penetrated vertically into interlayer voids, establishing additional pathways that enhanced both electrical and thermal conduction. GNPs were subsequently introduced through impregnation with a GNP dispersion, adhering to both fiber types and forming nanoscale protrusions. These protrusions increased fiber surface roughness, strengthened the fiber/resin carbon interface, and improved the mechanical properties of the carbon paper. Moreover, GNPs filled interstitial voids within the skeleton, forming finer branched networks that further augmented electrical and thermal conductivity. When loaded with 24 g/m² of MPCFs and impregnated with a 2 wt% GNP dispersion, the modified carbon paper exhibited a flexural strength of 22.91 MPa and a tensile strength of 25.99 MPa, representing increases of 67 % and 89 %, respectively, over the unmodified material. The in-plane and through-plane thermal conductivities reached 37.09 W/(m·K) and 8.83 W/(m·K), respectively, while the in-plane electrical resistivity was reduced to 3.74 mΩ cm. These values signify a notable improvement compared to the unmodified carbon paper, which exhibited an in-plane thermal conductivity of 12.20 W/(m·K), through-plane thermal conductivity of 0.04 W/(m·K), and in-plane electrical resistivity of 8.80 mΩ cm. In fuel cell tests, the modified carbon paper achieved a peak power density of 1.33 W/cm², outperforming the unmodified reference by 125 %. This work demonstrates a synergistic modification strategy using MPCFs and GNPs to simultaneously enhance the mechanical, thermal, and electrical properties of carbon paper. The proposed approach offers a promising pathway toward developing high-performance GDLs for advanced PEMFC applications.