Tailoring Carbon Additives Synergy in Co‐Continuous <scp>PVDF</scp> / <scp>PET</scp> Nanocomposites for Enhanced <scp>PEM</scp> Fuel Cell Bipolar Plates

ABSTRACT The advancement of proton exchange membrane fuel cells (PEMFCs) requires the development of bipolar plates (BPPs) that are lightweight, mechanically and thermally performant, and possess adequate electrical conductivity. This study investigates co‐continuous nanocomposites based on a blend of polyvinylidene fluoride (PVDF) and polyethylene terephthalate (PET), reinforced with hybrid electrically conductive fillers. A total filler loading of 60 wt.% was employed, comprising combinations of graphite (GR), carbon black (CB), carbon fiber (CF), and multi‐walled carbon nanotubes (MWCNTs). Morphological analysis revealed that, beyond the co‐continuous structure of the PVDF/PET matrix and the preferential localization of the conductive fillers within the PET phase, the strategic combination of micro‐ and nanoscale fillers promoted the formation of continuous conductive networks. Thermogravimetric analysis indicated excellent thermal stability, with a maximum decomposition temperature of 438°C for graphite‐rich formulations, accompanied by an ash content of ~80%. Electrical resistivity was markedly reduced through hybrid filler incorporation, with the best‐performing formulation (2.5/7.5/3.0 wt.% CF/CB/MWCNTs) achieving 0.087 Ω·cm (through‐plane) and 0.042 Ω·cm (in‐plane). Mechanical characterization showed that CB enhanced flexural strength, CF increased stiffness, and MWCNTs improved overall mechanical integrity, underscoring the synergistic effect of the filler system. Water uptake remained low across all samples, with a minimum of 0.023% observed for 1 wt.% MWCNTs after 168 h, and only 0.068% at 3 wt.%. Polarization curve analysis demonstrated that the inclusion of 2.5 wt.% CF and 7.5 wt.% CB significantly enhanced the electrochemical performance of PEMFCs, validating the potential of these hybrid‐filled PVDF/PET nanocomposites for next‐generation BPP applications.