Analysis of Heating Processes for the Production of Bipolar Plates in PEM Fuel Cells

Sammanfattning: Polymer electrolyte membrane fuel cells (PEMFCs) are a promising alternative to combustion engines and batteries in vehicles. PEMFCs are more efficient than combustion engines, and cars powered by PEMFCs tend to have longer ranges than battery powered cars and has a short fuelling time. To gain significant market shares, the costs of PEMFCs need to be reduced. This work aims to achieve this by improving the production process of bipolar plates, which significantly contribute to the total cost of fuel cells. In conventional production methods bipolar plates are formed by stamping at room temperature which limits the degree of deformation that can be achieved before exceeding the structural integrity of the material. It is expected that stamping at elevated temperatures will increase the forming limit of the material and therefore the flexibility in forming the channel geometry of bipolar plates. This has the potential to simplify the manufacturing process and improve the resulting performance of fuel cells.  The goal of this thesis is to establish to what degree the forming at elevated temperatures facilitates higher degrees of deformation. Different heating methods are benchmarked and analysed numerically in order to identify the most suitable one for stamping experiments at elevated temperatures. Out of six investigated heating concepts, direct resistive heating is identified as the most suitable one. The suitability of the concept is supported by numerical simulations. The direct resistive heating system is designed and integrated into the existing experimental setup.  Four flow channel geometries with channel widths of 1 mm, 0.8 mm, 0.6 mm, and 0.56 mm are investigated in stamping experiments using the identified heating method. Samples are formed at 150 °C, 300 °C, 600 °C, and 900 °C. Hexagonal Boron Nitride is used as a lubricant. The stamping experiments performed at elevated temperatures indicate that the formability of the bipolar plates improves as compared to the cold-formed reference experiments. The best results are obtained at 900 °C where the average channel depth, which can be formed before cracks are observed in the samples, could be improved by 27% compared to channels formed at room temperature.