Nils Fredebeul-Beverungen, Maximilian Steinhorst, Maurizio Giorgio, Otmar Zimmer, Volker Weihnacht, Teja Roch, Fraunhofer Institute for Material and Beam Technology IWS, Dresden, Germany
This presentation explores the potential of two methods for coating metallic bipolar plates. Regarding the use of arc evaporation technologies, solutions from Fraunhofer IWS are presented. The focus is on carbon, chromi-um, and titanium coatings, as well as coating systems applied to 100 µm thick stainless-steel sheets made of chromium-nickel steel (316L). The analysis covers both their electrical properties, particularly the interfacial contact resistance (ICR) against the carbon gas diffusion layer, and their electrochemical stability in H₂SO₄. Additionally, double-layer systems consisting of a carbon layer with a metallic interlayer are examined as both pre- and post-coatings.
The results demonstrate that both metallic coatings and carbon coating systems can be produced with contact resistances below the Department of Energy's required ICR of 10 mΩ cm². It was found that sputtered metallic coatings exhibit lower contact resistances compared to those deposited by arc evaporation. In contrast, carbon coatings deposited by arc evaporation achieved the lowest ICR, even compared to sputtered carbon coatings. Regarding the electrochemical properties, both potentiodynamic and potentiostatic studies revealed that carbon coating systems with a titanium metallic interlayer demonstrate good results. For the investigations of formed bipolar half plates, an exemplary bipolar plate geometry with a relevant flow field design was selected and embossed into the surface using hydroforming.