Electrically-Conductive Polymer Composites for Injection-Molded Bipolar Plates

Abstract

Bipolar plates are one of the primary components of polymer electrolyte membrane fuel cells. These plates deliver reactants to electrodes, remove reaction byproducts, transfer heat, provide mechanical stability, and conduct electrical current. While graphite is the most commonly used material for fabrication of bipolar plates, the machining costs associated with graphite are a major drawback to mass production. In addition, graphite-based plates make the greatest contribution to the weight of the fuel cell stack. For this reason, we are exploring electrically-conductive polymer composites as an alternative to the traditional metal alloys commonly used for fuel cell bipolar plates. Polymer composites can reduce both the weight and cost of the bipolar plate, while still providing sufficient electrical properties. The main objective of this research is to injection mold polymer composites that will meet United States Department of Energy technical targets for bipolar plate electrical conductivity (> 100 S/cm). In this study, conductive fillers (carbon fiber and carbon nanotubes) were added to nylon at various weight percentages, ranging from 0 to 50%, in order to determine the optimal filler-to-polymer ratio. Sample compositions were then compared by measuring electrical conductivity using a four-point probe method. Conductivities greater than 150 S/cm were achieved, exceeding the US DOE technical target.