Carbon fiber/phenolic composite bipolar plate reinforced with nano-size carbon black

Abstract

Polymer electrolyte membrane fuel cell or proton exchange membrane fuel cell (PEMFC) 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. New bipolar plates have been developed using continuous carbon fiber/epoxy composite to reduce both the manufacturing cost and volume rather than using graphite, followed by graphite coating on the surface of bipolar plate to reduce the contact resistance of the carbon composite bipolar plate as low as graphite bipolar plate. However, the carbon fiber/epoxy bipolar plates with graphite coating may not be adequate in mass production. In this study, the bipolar plate has been fabricated using carbon fabric/phenolic composite for the mass production because the phenolic resin is cured much faster than epoxy resin. Since the phenolic resin is generally brittle after cure, it is mixed with nano-size carbon black to increase its ductility. The surface of carbon fabric/phenolic composite bipolar plates has been treated with flame to reduce the contact resistance between the bipolar plates and GDLs. To optimize the flame treatment process, both the electrical conductivity in the through-thickness direction and flexural strength of the composites have been measured with respect to the flame temperature and treatment time of the flame surface treatment. The experimental results show that the contact resistance of the carbon fabric/phenolic composites decreases as the flame treatment temperature and time are increased because the degree of carbonization of the phenolic resin is proportional to the temperature and time of the flame surface treatment, while the flexural strength of bipolar plates decreases because the carbonization of phenolic resin increases its britteness. Therefore, an optimum flame surface treatment temperature and time of the caron fabric/phenolic composite bipolar plates are investigated for the high electrical conductivities and mechanical properties.