Fiber Reinforced Compound Foil Bipolar Plates for Compact Fuel Cells

Hydrogen fuel cells are seen as one approach to fossil fuel substitution, e.g., in the automotive industry. Fuel cells consist of multiple bipolar plates, which, due to their complex requirements, are made of either expensivcoated metals or polymers filled with graphite, so-called graphite polymer compounds. The advantage of the compound bipolar plates is that they do not require an expensive coating, which is crucial for the lifetime of metallic bipolar plates. However, the injection molding process and the inferior mechanical properties of the compound foils yield in a high wall thickness, which increases the volume and decreases the power density of the fuel cell. In this project, in cooperation with the Hydrogen And Fuel Cell Center (ZBT), the wall thickness is intended to be decreased by incorporating a foil extrusion process instead of injection molding and by reinforcing the foils with carbon fibers.

An essential research topic is the method how the fiber reinforcement is realized for 0.4 mm thick compound foils. First, the impregnability of fibers by graphite polymer compounds is limited. Second, the fiber reinforcement, while fulfilling an important mechanical function, may impair other essential functions such as electric conductivity or the contact conditions of bipolar plates in a stack. Therefore, a comprehensive material characterization is needed and properties need to be optimized.

Furthermore, the materials are characterized for their mechanical properties for a FE simulation to be performed. This simulation is essential for the design of the necessary fiber reinforcement so that the bipolar plate can withstand the external and media pressures during the assembly and fuel cell lifetime, as well as the elevated operating temperatures. This method allows the determination of the influence of fiber reinforcement, foil thickness, channel structures, material properties etc.

The project “Fiber reinforced compound foil bipolar plates for compact fuel cells” is funded by the Federal Ministry of Economics and Climate Action on the basis of a decision by the German Bundestag (funding reference 22342 N).