Coating a layer of conductive and corrosion-resistant coating on the surface of titanium can effectively avoid the formation of oxide film on the surface of the titanium bipolar plate and meet the performance requirements of the plate. besides corrosion resistance and excellent electrical conductivity, the coating also needs good bonding strength with the matrix. at the same time, because the temperature of PEMFC will change at room temperature and around 80 C, it is necessary that the coating and matrix material have similar thermal expansion coefficients to avoid delamination and cracks in the process of temperature change, thus losing the protection of the material.
Commonly used coatings are classified into two categories: metal-based coatings (noble metals, metal-carbon/nitride) and carbon-based coatings (graphite, conductive polymers, amorphous carbon, etc.).
Performance parameters of different coated titanium bipolar plates
As an important part of the hydrogen fuel cell, the bipolar plate plays a decisive role in the performance, cost, and durability of the cell. cost and durability are two important issues restricting the commercialization of hydrogen fuel cells. The cost of bipolar plates depends to a certain extent on the material of plates, flow field processing, and the preparation process of plate coating.
Graphite and carbon matrix composites can no longer meet the performance requirements of the hydrogen fuel cell. Metal materials have become the mainstream materials for bipolar plates of the hydrogen fuel cell.in addition, high power has always been the goal of hydrogen fuel cells. titanium and titanium alloys in metal materials have low density and high specific strength. They have excellent corrosion resistance in hydrogen fuel cells and can significantly reduce the weight and volume of bipolar plates, which significantly improves the mass and volume specific power of the battery. moreover, corrosion products produced by titanium and titanium alloys during long-term service operation are less toxic to proton exchange mode and catalysts, which is conducive to improving the stability and durability of battery operation.
Metal carbon/nitride and amorphous carbon coatings prepared on the surface of titanium bipolar plates have superior comprehensive properties and have high research and application value. However, these coatings are prone to pinhole defects. Therefore, the main objectives of current research are to improve the compactness of coatings, the bonding strength of film matrix, and the surface conductivity of coatings. In addition, the coating should be hydrophobic to facilitate the discharge of reaction-generated water.
To meet these comprehensive properties, higher requirements are put forward for the structural design and the composition of the coating. composite and nano-structure of coating can improve the compactness, corrosion resistance, and conductivity of coating to a certain extent and enhance the service stability and reliability of titanium plate, which is the main development direction in the future.
