Development of Lightweight, Thermally Conductive Bipolar Plates for Improved Thermal Management in Fuel Cells (King, Keith)
Fundamental and applied research needs to be done to improve the potential for fuel cells to be used in stationary and transportation applications. The goal of this project is to develop lightweight composite materials to be used for bipolar plates within a fuel cell. Bipolar plates require high thermal and electrical conductivity. Dr. King, Beth Johnson (M.S. graduate student working on this project), and several undergraduate students (Michael Via, Charles Ciarkowski, and Daniel Woldring) have extruded and molded into test specimens polypropylene (Dow H7012-35RN, a semi-crystalline thermoplastic homopolymer) based composites containing different carbon fillers (Akzo Nobel’s Ketjenblack EC-600 JD carbon black, Asbury Carbon’s Thermocarb TC-300 synthetic graphite particles, and Hyperion Catalysis International’s FIBRIL carbon nanotubes). Composites containing varying amounts of a single filler along with combinations of different fillers were fabricated and tested. Results to-date indicate that the compression molded composite containing 2.5 wt% carbon black, 65 wt% synthetic graphite, and 6 wt% carbon nanotubes in polypropylene have an electrical conductivity of 91 S/cm and a thermal conductivity values of 6.6 W/m.K (through-plane) and 24 W/m.K (in-plane). These values are near the DOE conductivity targets of 100 S/cm and > 20 W/m.K. In addition, an order has been placed for a new Nanoflash thermal conductivity device, using funds from this project. Delivery is expected in December 2008/January 2009.
Also, the electrical conductivity of this system was modeled using three electrical conductivity models (Mamunya, Addivite, and Global Effective Media). All of the models performed relatively well for each composite system. However, the Mamunya and Additive equations were better for synthetic graphite composites. The Global Effective Media equation was better for carbon nanotube composites.