T he development of conductive polymer composites (CPCs) is a promising and growing field of research. CPCs are highly resistant to corrosion and have low densities, two properties that might result in the materials replacing metals in several applications. For example, the composites are increasingly being used in the preparation of monopolar and bipolar plates for use in fuel cells, which pro- duce electricity using oxygen and hydrogen, with water as the only by-product. Bipolar plates are so-called because they have gas-flow channels on both sides (whereas monopolar plates have gas- flow channels on one side and cooling channels on the other). The gas-flow channels guide the gases (hydrogen and oxygen) through the cell, and the cooling channels cool the cell from the heat produced during its operation. The bipolar plate is one of the most important components of the cell, because it provides the connection between the indi- vidual cells, supplies the anode with hydrogen and the cathode with oxygen, and separates the two gases from each other. 1,2 CPCs are typically made of a polymer (either thermoplas- tic or thermoset) and an electrically conductive additive (for example, graphite, carbon black, carbon nanotubes, or graphene). How the CPCs are processed highly affects their conductivity, because processing directly affects the dis- persion of the conductive fillers in the polymer matrices. The type and polarity of the matrix material also affects the conductivity of the CPC: the more polar the matrix, the bet- ter the connection between the matrix and filler. Given this complex relationship, in choosing the ideal polymer and filler it is difficult to fulfill the requirements of good electri- cal conductivity, robust mechanical properties, and easy processability for fuel cell development. 3 Here we examine the effect of different conductive fillers and polymers on the resultant CPCs for use in fuel cells. Materials: PP, PBT, and Conductive Fillers The two polymers we used—polypropylene (PP) and poly(butylene terephthalate) (PBT)—have the same flowability (45 g/10 min), but PBT is approximately twice as polar as PP. Additionally, we used crystalline natural graphite (in the 42 | PLASTICS ENGINEERING | FEBRUARY 2014 | www.4spe.org | www.plasticsengineering.org Developing Bipolar Plates for Fuel Cells Conductive polymer composites, prepared by injection and compression molding, make interesting candidates for these components By Anett Király and Ferenc Ronkay Department of Polymer Engineering, Budapest University of Technology and Economics, Budapest, Hungary Figure 1: Electrical conductivity as a function of the filler content for composites containing carbon black (CB) or graphite (G) (1,E–x = 10 -x ; PBT= poly(butylene terephthalate); PP = polypropylene; “vol%” = percent by volume)