Performance and structure of Ti-doped amorphous carbon/CrN/Ti multilayer coating deposited on 316L stainless steel for use as bipolar plate in proton exchange membrane fuel cell

In order to improve the corrosion resistance and conductivity of stainless steel bipolar plates, three-layer Ti-doped amorphous carbon/CrN/Ti films were deposited on 316L stainless steel used for bipolar plates in PEMFCs. Titanium as the doped element added into amorphous carbon. Magnetron sputtering technology was used to deposit the films and control the titanium doped content by different titanium target currents. The structure transformation law of Ti content in amorphous carbon coating was studied. The application principle of corrosion resistance and conductivity of bipolar plates during the transformation of the coating structure from amorphous carbon to carbide was analyzed. With increasing Ti-doped content, the sp2/sp3 ratio increased, and the amorphous carbon film gradually transformed to titanium carbide matrix film. Characterization of the electrochemical corrosion confirmed that the anti-corrosion property of the films was closely related to the Ti-C phase and sp2/sp3 ratio. Ti-doped amorphous carbon/CrN/Ti film, which is built at 1A Ti target current, has the best corrosion current density. The interfacial contact resistance (ICR) first decreased and then increased with increasing Ti content. When excessive doping of titanium atoms makes the coating become a TiC matrix, the corrosion resistance and ICR property of the coating worsen. The film's state of chemical bonds after electrochemical corrosion was tested by XPS to study the ICR increase mechanism. The Ti-doped amorphous carbon/CrN/Ti multilayer film can be used as a modified coating of 316L stainless steel bipolar plates for PEMFCs.