Dresden. Fuel cell vehicles fueled with hydrogen are still rare and expensive. According to the Fraunhofer Institute for Materials and Beam Technology IWS in Dresden, this is primarily due to the gold-coated bipolar plates (BiP) in fuel cells - “a core component” whose production is complex and expensive. According to their own statements, the IWS, the Daimler Group and the Finnish steel company Outokumpu Nirosta have now developed “an inexpensive alternative”. The technology enables “continuous production” of bipolar plates. Instead of gold, these would be coated very thinly with carbon. “This concept is suitable for mass production and can greatly reduce manufacturing costs,” say the researchers.
PEM fuel cells, which consist of stacks of many individual cells, each with a proton exchange membrane (PEM) in the middle, are widely used. There are electrodes on the right and left of this membrane 
Catalysts, a gas diffusion layer (GDL) and the bipolar plates arranged on the very outside on both sides. “Hydrogen and oxygen flow into the cell through these plates. “They each consist of two stainless steel half-sheets onto which special structures for gas flow and heat dissipation are embossed in a forming process and which are then welded together,” explain the scientists. Because steel surfaces conduct electricity only moderately well, bipolar plates are often coated with gold to prevent rust. The precious metal ensures that the current can flow well and that the contact resistance between the gas diffusion layer and the bipolar plate remains low.
However, the high price of gold is problematic. On the other hand, “the stainless steel sheets for the plates are first formed and welded together in order to then coat them in batches,” says Teja Roch from IWS: “This is a very complex and lengthy process.”
The scientists are convinced that the new process now presented could halve the coating costs in mass production. Instead of gold, they coat the steel sheets, which are around 50 to 100 micrometers (thousandths of a millimeter) thick, with a graphite-like layer that is only a few nanometers (millionths of a millimeter) thick. Even in the pre-production stage, this carbon layer achieved “a similarly low contact resistance as gold”. If the process were refined, the layer would “conduct electricity at least as well as the precious metal.”
The coating using physical vapor deposition (PVD) only takes seconds. In the future, stack producers will also be able to “coate entire rolls of sheet metal on a continuous production line before forming.” The Fraunhofer layer is so durable that it can withstand the forming and welding processes.
The development was funded by the Federal Ministry of Economics as part of the “miniBIP II” joint project.
deep link
https://www.iws.fraunhofer.de/de/presseundmedien/presseinformationen/2020/presseinformation_2020-09.html
https://www.iws.fraunhofer.de/content/dam/iws/de/documents/publikationen/infoblaetter/i-160-01_bipolarplatte_de.pdf
Photos
(above) The bipolar plate from Daimler (above) is provided with a carbon layer (below), which reduces the contact resistance and at the same time increases the corrosion resistance / © Fraunhofer IWS
(below) The steel sheets, which are approximately 50 to 100 micrometers thick, are coated with a graphite-like layer that is only a few nanometers thick / © Fraunhofer IWS
