Enhanced mechanical and electrical properties of carbon composite bipolar plates in PEMFCs via wet mixing and CNT optimization

This study presents a systematic investigation into optimizing resin-based carbon composite bipolar plates for proton exchange membrane fuel cells (PEMFCs). It focuses on the interplay among carbon nanotube (CNT) loading, graphite particle size, and dispersion methods. CNTs (0–10 wt%) were added as nanoscale conductive reinforcements. Their dispersion was achieved via dry and solvent-assisted wet mixing processes. Graphite fillers with different particle sizes (small and large) were used to examine effects on conductive network formation and interfacial contact with the matrix and CNTs. The composites were characterized by bulk density, Vickers hardness, three-point flexural strength, in-plane electrical conductivity, and interfacial contact resistance (ICR). Scanning electron microscopy showed that wet mixing significantly improved CNT dispersion and interfacial adhesion. This promoted continuous conductive pathways and enhanced structural integrity. An optimal CNT content of 7 wt% was identified. Higher contents led to performance decline due to CNT agglomeration and microstructural heterogeneity. Composites with large graphite particles had superior electrical conductivity and lower ICR. This was attributed to enhanced particle–particle contact area and efficient CNT bridging across interstitial spaces. The optimized formulation (W-LG-CNT7) achieved a power density of 0.86 W/cm2 and an open-circuit voltage of 0.97 V in a single-cell PEMFC. It retained 91.8% flexural strength after 1000 h phosphoric acid immersion, indicating strong chemical durability. These results highlight the importance of nanoscale and microscale design in developing durable, high-performance PEMFC bipolar plates.