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 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. Particularly stainless steel for fuel cells has the right mix of formability, mechanical properties and affordability. The tough electrochemical conditions require improved corrosion resistance of the stainless steel, while maintaining a high electrical conductivity. IHI Ionbond has several coatings in its portfolio to perform that task. Two well tested and established coatings are described below.
Fuel Cell DOT™ Technology
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. 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.
The DOTs technology is also applied on titanium bipolar plates. In this case only the thermal spray process is applied, no need for an initial titanium coating by PVD.
Fuel Cell Carbon Technology
The carbon coating is needed to enable electrical conductivity and to protect the stainless steel bipolar plates from leaching metals into the cell and poisoning the functionality of the membrane, leading to reduced performance of the stack over time. The carbon coating is deposited by the well-proven sputter PVD technology.
Good performance in terms of adhesion, conductivity and corrosion resistance are obtained by implementing plasma surface cleaning and a special metal-based adhesion layer in the total coating solution. The carbon coating process is optimized to enable good durability during normal automotive operating conditions, and to withstand high voltage peaks that may occur during cold start events.