Plasma-activated EB-PVD for High-Throughput Continuous Coating of Bipolar Plates

For highly productive and cost-effective 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 for the so called "pre-coating". To this end, protective coatings such as Ti thin films have been deposited by plasma-activated electron beam physical vapor deposition (EB-PVD) using spotless arc-activated deposition (SAD) in an in-line process applied on thin metal foils as well as on carbon-filled polymers as feedstock materials for bipolar plates. Using plasma-activated EB-PVD, dense coatings with high corrosion resistance can be applied to metal strip before embossing 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 is to achieve high formability of the coating, which requires a dense and nanocrystalline microstructure. However, in addition to microstructural effects, substrate temperature limits must also be considered, especially when processing temperature-sensitive or very thin substrates.
For this purpose, pieces of 250 mm wide and 100 μm thick metal foils as well as on 150 mm wide highly filled graphite compound foils of polymer plate were plasma pre-treated. Subsequently, 100-200 nm thick Ti layers were deposited by EB-PVD with and without SAD at a process speed of 10 m/min. FE-SEM and XRD analyses show that nanocrystalline and denser layers were deposited by SAD process. During deformation by 180° bending test on Ti-coated steel samples, cracks appeared in the films prepared without SAD, whereas the SAD-deposited Ti films showed very ductile behavior without crack formation during bending.