"Metallic Bipolar Plate Technology for Automotive Fuel Cells"
Bipolar plates account for a large fraction of fuel cell cost. In this area, graphite-based materials have been used in previous technology demonstrations at Ford. However an alternative metallic bipolar plate technology shows promises to achieve cost and performance targets, and is amenable to high volume manufacturing processes. Metallic bipolar plate technology is also expected to significantly improve volumetric power density, which is a critical requirement for automotive applications. Ford has been experimenting with some metallic bipolar plate materials. One is nano-meter range gold (Au) coatings on stainless steel substrate materials, a.k.a. Au-nanoclad® supplied by Daido Steel (Japan). It was confirmed that the use of 10 nm thick coating helps to retain the noble properties of Au. Another one is so called Au-dot technology supplied by TreadStone Technologies, Inc. (Princeton, NJ). This metallic bipolar plate consists of a stainless steel substrate with corrosion resistant thin film coat. Thermally treated Au dots are deposited to create a highly electrically conductive path between surface of the plate and stainless steel substrate. Au dots cover only a small percentage of bipolar plate surface area. While Au is an expensive commodity, however the amounts of Au for both materials are very small and should not pose a large cost penalty. Ex-situ materials evaluation tests indicate excellent electrical and corrosion resistance properties for both materials and meet the USDOE target. And in-situ tests with short stacks with 300 cm2 active area were performed. Au nanoclad 20-cell stack was successfully operated through 2,500 hours of durability cycle test simulating real world operating conditions. Au-dot 10-cell stack was operated on a 1,000 hour successfully. Post analysis revealed no significant corrosion issue for both materials. Presently a Ford 20-cell stack development with improved Au-dot technology materials is undergoing for further durability cycle testings with TreadStone Technologies, Inc. (US Department of Energy Agreement # 09EE0000463).