Corrosion, Contact Resistance, and Surface Characteristics of Stamped and Hydroformed Metallic Bipolar Plates for PEMFC

In a quest for achieving sustainable mobility, improved fuel efficiency, enhanced driving performance and drastically reduced the tail-pile emissions necessitate the replacement of conventional energy conversion systems with environmentally-friendly technologies as well as lightweighting in transportation vehicles. Fuel cell technology is believed to be a promising avenue to achieve such a long desired sustainable transportation goal. However, for its widespread commercial success, there are some issues that need to be addressed. This study aims to investigate two of these underlying issues: corrosion and contact resistance in bipolar plates, which arise during the use fuel cell stacks, and are direct effects of production, material, surface, and coating conditions. Repeatability and robustness of manufacturing method (stamping, and hydroforming), corrosion and contact resistance of stainless steel bipolar plates (BPP), and tribological issues of forming dies in which bipolar plates are formed were investigated in this study. First, the effects of manufacturing conditions on formed bipolar plate quality and process repeatability were investigated. Second, corrosion and contact resistance tests for manufactured bipolar plates as well as blank stainless steel sheets were performed. Based on the corrosion test results, a faster stamping speed is found to be preferable for higher corrosion resistance and shorter production time. On the contrary, higher pressure rates in hydroforming are found to lower the corrosion resistance. Thus, a compromise between corrosion performance and production rate is needed in hydroforming for mass production purposes. According to the preliminary contact resistance tests, hydroformed bipolar plates showed better interfacial electrical conductivity than stamped plates. Also, the test results confirmed that surface coating is necessary to improve corrosion and contact properties to meet the DOE goals. Finally, relatively larger surface topography changes were observed on the manufactured bipolar plates compared to the forming die surfaces after several hundreds of BPP production.