Influence of particle size and shape on electrical and mechanical properties of graphite reinforced conductive polymer composites for the bipolar plate of PEM fuel cells

Abstract

Graphite reinforced conductive polymer composites (CPCs) with high filler loadings were fabricated by compression molding technique. Various sizes and shapes of graphite particles were mixed with phenol resin to impart the electrical conductivity in composites. Fabricated CPCs showed good electrical conductivity (>100 S/cm) and flexural strength (>40 MPa) for the bipolar plate of polymer electrolyte membrane (PEM) fuel cells. The electrical conductivity of CPCs was affected by the formation of conductive networks among graphite particles. CPCs made of sphere-type particles (SG-CPCs) had the same physical density regardless of particle size; and they also showed the same bulk electrical conductivity. This means that there is a close correlation between the electrical conductivity and the densification level, or density, of graphite/phenol compounds. The particle shape was also a principal factor in influencing electrical conductivity. In this study, the electrical conductivity of CPCs made of flake-type graphite particles (FG-CPCs) was higher than that of SG-CPCs due to the difference of the densification characteristic. The flexural strength of SG-CPCs tended to increase with decreasing graphite particle size because the interfacial coherence between graphite particle and phenol resin increased as graphite particle size decreased. This influence of interfacial coherence was also founded in the variation of particle shape. FG-CPCs have higher flexural strength than SG-CPCs because a flake-type particle has larger specific area than a sphere-type particle.