Types and preparation methods of surface coatings on metal bipolar plates

The working environment of the hydrogen fuel cell is acidic, so the bipolar plate as the supporting skeleton needs to have good corrosion resistance. It is necessary to prevent the bipolar plate from being passivated under oxygen-rich conditions and causing an increase in contact resistance, and to prevent the service environment Corrosion of medium metals.

Usually, in order to solve the corrosion problem of battery components, the surface of metal bipolar plates is coated with corrosion-resistant coatings. The types include: metal and alloy coatings, metal compound coatings, metal carbide coatings, metal nitride coatings, and non-metallic coatings. Layers, etc., some coatings can not only improve the anti-corrosion performance of the surface, but also ensure the conductivity and other properties of the surface.

The surface of stainless steel or Ti alloy battery bipolar plates is usually electroplated with a Ni-W-P or Ni-Cu-P alloy layer, or a dense Ni-Cu layer. Its thermal stability, conductivity and corrosion resistance are better than TiN plating. . When using the electroplating process, pre-plating or impact plating treatment is required to obtain an anti-corrosion coating that is firmly combined with the stainless steel and titanium alloy substrate.

The surface of the 316L stainless steel bipolar plate can be coated with TiN, CrN, and TiCrN coatings through magnetron sputtering to improve its corrosion resistance while maintaining low surface contact resistance and good conductivity.

It is also a good method to electroplat dark nickel or electroless nickel-phosphorus alloy plating on the anode side surface of the metal bipolar plate. It is necessary to choose a low-stress electroless nickel plating process and a high-phosphorus content electroless nickel plating process. The resulting nickel plating layer has a bonding strength, Corrosion resistance and electrical conductivity are both good.

The nickel plating process parameters can also be adjusted to produce a certain degree of hydrophobicity on the surface of the nickel plating layer. In this way, the battery will not be easily wetted by the electrolyte solution during operation, thereby avoiding the loss of the electrolyte solution in the battery.

The flexible "wet seal" design of metal bipolar plates may cause carbon corrosion of stainless steel bipolar plates. Therefore, it is very necessary to perform "aluminizing" protection treatment on the frame of such stainless steel bipolar plates. .

For titanium alloy metal bipolar plates, plasma nitriding and other technologies can be used for surface modification to improve their corrosion resistance. And the necessary polishing treatment is carried out before and after nitriding. The purpose is to improve the corrosion resistance of the nitrided layer by making the surface smooth and bright.