A study on the electrical resistance of carbon/phenolic composite bipolar plates for PEMFC

Abstract

The polymer electrolyte membrane fuel cell (PEMFC) or proton exchange membrane fuel cell is composed of bipolar plates, end plates, membrane electrode assemblies (MEAs) and gas diffusion layers (GDLs). Among the constituents of PEMFCs, the bipolar plates are major components, which make up a large portion of the stack volume and cost. In this study, the bipolar plate has been developed using carbon fabric/phenolic composite and flame surface treatment for mass production. Plain weave carbon fiber is used to increase the manufacturing productivity and to decrease the bulk electric resistance. A graphite coating and dummy method is developed to measure the bulk resistance in through thickness direction of the bipolar plate. The experimental results show that the bulk resistance of the plain weave carbon composite bipolar plate is about 50% less than that of a carbon composite bipolar plate made of unidirectional carbon fiber epoxy composites with the same thickness. Phenolic resin is used because it cures much faster and is cheaper than other resins. Because the phenolic resin becomes brittle after being fully cured, it is mixed with carbon black to increase its ductility. The surface of the carbon fabric/phenolic composite bipolar plates has been treated with flame to reduce the interfacial contact resistance. The experimental results show that the contact resistance of the carbon fabric/phenolic composites bipolar plate decreases as the flame-treatment temperature and time are increased due to the degree of carbonization of the phenolic resin, while the flexural strength decreases. Therefore, the optimum flame surface treatment temperature and processing time for the carbon fabric/phenolic composite bipolar plates are investigated to optimize the electrical conductivities and mechanical properties.