Modeling Electrical Conductivity of Injection-Molded Polymer Composite Bipolar Plates

Bipolar plates can be responsible for up to 40% of the total stack cost and 80% of the weight of a polymer electrolyte membrane fuel cell. To reduce these cost and weight limitations, this work explores modeling and injection molding of polymer composites. A fiber contact model was developed to predict electrical conductivity based upon direction in the material, fiber length and diameter, fiber resistivity, fiber volume fraction, and fiber angle of alignment. Fiber alignment was measured experimentally by imaging cross sections of injection-molded nylon/nickel-coated carbon fiber (NiCF) composites. Composites were molded with NiCF loadings ranging from 5 to 40 wt%. Up to 15 wt%, modeling predictions show good correlation with experimental conductivity measurements. Samples with at least 15 wt% NiCF exceeded the United States Department of Energy technical target for bipolar plate conductivity (>100 S/cm), reaching 250 S/cm.