Stefan Saager, Ludwig Decker, Thomas Modes, Jörg Neidhardt, Lars Klose, Frank-Holm Rögner, Bert Scheffel, Burkhard Zimmermann, Olaf Zywitzki, Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, Dresden, Germany
To successfully ramp up the hydrogen economy, highly productive and cost-effective conversion technologies are required. For profitable manufacturing of bipolar plates for electrolyzers and fuel cells, the transition of state-of-the-art technologies to roll-to-roll processes is a promising approach. To this end, plasma-activated electron beam physical vapor deposition (EB-PVD) using spotless arc-activated deposition (SAD) was tested in an in-line process for the highly productive and efficient coating of thin metal foils as well as highly filled graphite compound foils as feedstock materials for bipolar plates. Bipolar plates have to perform with long-term stability in a chemically aggressive environment and therefore require protective coatings such as titanium. At the same time, sufficient electrical conductivity must be ensured, for example by an additional carbon coating. Using plasma-activated EB-PVD, for example, dense coatings with high corrosion resistance can be applied to metal strip before it is stamped into bipolar plates. Coating the material prior to the embossing process is considered as a decisive step for upscaling production in the roll-to-roll process. One challenge for that purpose is a high formability of the coating, which requires a dense and nanocrystalline microstructure. However, in addition to the microstructural effects, temperature restrictions of the substrate must be taken into account, especially when temperature-sensitive or very thin substrates are to be processed.
In this talk, the advantages of continuous PVD technology for bipolar plate production will be demonstrated. Pieces of 250 mm wide and 100 µm thick metallic foils as well as on 150 mm wide highly filled graphite compound foils were plasma pre-treated in a first process step. Afterwards, titanium coatings with a thickness range of 100 nm were prepared at process speeds of 10 m/min by EB-PVD with and without SAD. FE-SEM analyses reveal that nanocrystalline and more dense layers were deposited by SAD process. Furthermore, after applying additional 180° bending test on Ti-coated steel samples, cracks occurred in coatings prepared without SAD, whereas Ti layers deposited by SAD show a very ductile behavior without formation of cracks during bending. Furthermore, the suitability of the coating for electrolyzer and fuel cell application have been evaluated.