Multiwalled Carbon Nanotube-Filled Polymer Composites for Direct Injection Molding of Bipolar Plates

Abstract

Fuel cell bipolar plates are commonly fabricated from graphite, however the associated machining costs are a major limitation to fuel cell commercialization. A promising alternative approach to bipolar plate manufacturing is injection molding of polymer composites. Injection molding is well-suited for mass production and polymeric materials can significantly reduce the weight of the bipolar plate. In this study, polymer composites based on nylon were injection molded with different weight percentages of conductive filler. Initially, carbon fiber was added to nylon 6,6 at weight percentages ranging from 10 to 50%. Results show that the percolation threshold for carbon fiber in nylon occurs around 25 wt%. Multiwalled carbon nanotubes (MWCNTs) were then added to the direct injection-molded nylon/carbon fiber composites to investigate the synergistic effects of multiple conductive fillers. By introducing carbon nanotubes into the polymer matrix, the nanotubes act as a bridge between the carbon fibers. SEM images show that the MWCNTs fill the void between fibers due to their smaller size and their ease of dispersion. This bridging creates more conductive pathways within the polymer matrix, increasing the electrical conductivity of the composite. Samples with MWCNTs reached conductivities of 64 S/cm, nearing the United States Department of Energy technical target for bipolar plate conductivity (>100 S/cm).