Highly Conductive and Strong Graphite-Phenolic Resin Composite for Bipolar Plate Applications

Composite materials for bipolar plate applications in proton exchange membrane fuel cells were fabricated from synthetic graphite (SG), natural graphite (NG), or expanded graphite (EG) and novolac phenolic resin using compression molding. In comparing the resultant samples, the EG composite exhibited the best properties with a density of ∼1.55 g/cm3, flexural strength of 109 MPa, and modulus of 24 GPa even with a high graphite loading of 80 wt % and a low plate thickness of ∼0.9 mm, as well as in-plane conductivity of 182 S/cm. The EG content was further varied to find the optimal composition. The effects of using carbon nanotube sheets (buckypapers) or multiwalled carbon nanotubes as reinforcements to the EG-resin composite were investigated. A modified approach of measuring through-plane electrical conductivity capable of separated analysis of bulk resistance and interfacial contact resistance was attempted. The corrosion resistance, thermal conductivity, and gas permeability of EG-based composites were also assessed.