Effect of N doping on Cr-doped amorphous carbon /CrN /Ti multilayer coatings on 316L stainless steel bipolar plate for PEMFC: First principles calculation, structure and performance

To improve the corrosion resistance and interfacial contact resistance (ICR) 316L stainless steel bipolar plates used in proton exchange membrane fuel cells (PEMFCs), a series of three-layer amorphous carbon films were prepared by magnetron sputtering. The corrosion resistance and ICR of 316 L stainless steels are greatly improved by the Cr, N doped amorphous carbon and multilayer film structure. Ti and CrN were basement layer and transition layer, and amorphous carbon doping with Cr and N was the top layer. Nitrogen atoms, as the variable atoms, were added into the top layer, focusing on the relation between the N content and the film properties. First principles calculations were used to analyze the bond structure by Cr, N doping into amorphous carbon structure and to determine the reasons for the structural changes in the coating after doping the elements. The results revealed that the films are about 1.05 μm thick and without apparent defects. With increasing nitrogen flow rate, Cr–N bonds and C–N bonds appeared in the coating while promoting the graphitization of amorphous carbon. Compared with that of Cr-doped amorphous carbon coated steel, the corrosion current density of Cr, N co-doped amorphous carbon decreased to 8.1 × 10−9 A/cm2 in the +0.6 V (vs. SCE) potentiostatic polarization test, and as the ICR decreased to 1.3 mΩ cm2, the film exhibited outstanding corrosion resistance and conductivity properties. The Cr, N co-doped amorphous carbon/CrN/Ti composite film formed on 316L stainless steel might be appropriate used in PEMFCs.