Effects of Mo content on microstructure and corrosion resistance of arc ion plated Ti–Mo–N films on 316L stainless steel as bipolar plates for polymer exchange membrane fuel cells

• Ti–Mo–N films were fabricated using arc ion plating combining magnetron sputtering.
• TiN film with a (111) preferred orientation shows the best corrosion resistance.
• Mo content exerts strong influence on preferred orientation of the Ti–Mo–N films.

Bipolar plates are one of the most important components in PEMFC stack and have multiple functions, such as separators and current collectors, distributing reactions uniformly, and etc. Stainless steel is ideal candidate for bipolar plates owing to good thermal and electrical conductivity, good mechanical properties etc. However, stainless steel plate still cannot resist the corrosion of working condition. In this work, ternary Ti–Mo–N film was fabricated on 316L stainless steel (SS316L) as a surface modification layer to enhance the corrosion resistance. Effects of Mo content on the microstructure and corrosion resistance of Ti–Mo–N films are systematically investigated by altering sputtering current of the Mo target. XRD results reveal that the preferred orientation changes from [111] to [220] direction as Mo content in the film increases. The synthesized Ti–Mo–N films form a substitutional solid solution of (Ti, Mo)N where larger Mo atoms replace Ti in TiN crystal lattice. The TiN-coated SS316L sample shows the best corrosion resistance. While Mo content in the Ti–Mo–N films increases, the corrosion resistance gradually degrades. Compared with the uncoated samples, all the Ti–Mo–N film coated samples show enhanced corrosion resistance in simulated PEMFC working condition.