Highly Conductive, Strong, Thin and Lightweight Graphite-Phenolic Resin Composite for Bipolar Plates in Proton Exchange Membrane Fuel Cells

Composite materials for bipolar plates in proton exchange membrane fuel cells were fabricated from synthetic graphite (SG), natural graphite (NG), or expanded graphite (EG) and phenolic resin and compared. EG turned out to be the best candidate, exhibiting 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 thickness of ~0.9 mm, and in-plane conductivity of 182 S/cm. A sandwich structure of buckypaper-composite-buckypaper was created to explore the effects of buckypaper. Multi-walled carbon nanotubes (MWCNTs) were incorporated into EG-resin composite to seek potential benefits through nanostructuring. A modified approach of measuring through-plane conductivity capable of separating bulk resistance from contact resistance was proposed. Corrosion resistance of EG-based composites was also assessed. The EG composite offering low thickness and density with competitive properties demonstrates great potential for weight and volume reduction of fuel cell stacks.