Fuel Cell - DOT™
Superior and low cost coating for metallic bipolar plates
The global hydrogen economy is expanding at a fast pace. To support this expansion, the demand for fuel cells and electrolyzers is expanding as well. In order to gain acceptance, fuel cell and electrolyzer stacks need to meet some tough requirements. They need to show stable, reliable performance at high demand levels over time. In addition to these performance and durability requirements, they need to achieve acceptable price performance levels. In a number of applications, the Polymer Electrolyte Membrane (PEM) stacks are moving from graphite towards the use of titanium and stainless steel bipolar plates.
The fundamentals
The DOT™ technology is a duplex treatment. A coating is needed to protect the stainless steel bipolar plate from leaching metals in to the cell and poisoning the functionality of the membrane, leading to reduced performance of the stack over time. The initial layer is based on titanium deposited by the well-proven sputter PVD technology.
The second step is based on thermal spraying ‘DOTs’ of a noble metal, like gold or platinum. Because of the thermal spray temperature, the exposed titanium will form a corrosion resistant titanium oxide, and the noble metal DOTs fuse to the metallic surface, thereby providing excellent adhesion and conductivity. Alternatively DOTs can be applied to Titanium substrates directly for especially Electrolyzer applications. A solid gold coating is seen as the reference as it offers the necessary corrosion resistance in parallel with low, steady electrical resistance. As the DOTs are in direct contact with the membrane, they are the highly conductive pathways for the cell’s electrical current. The electrical resistance is set by the total surface area coverage by the DOTs, but 2 to 6% surface area coverage with gold DOTs gives comparable results as solid gold coating with 100% coverage. The reduced use of noble metals makes the DOT™ technology an affordable solution while maintaining high technical performance levels.
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