**4. Conclusions**

TiNb and TiNbN films with low Ti content were coated on 316L SS by magnetron sputtering with a view to application for bipolar plates in PEMFC. The electrochemical testing indicates that TiNb coating has the best corrosion resistance in cathode simulation electrolyte solutions. At 0.19 V vs MSE, the stable corrosion current density of TiNb/316L SS is lower than 1 <sup>μ</sup>A·cm<sup>−</sup>2. The ICR measurements show that the contact conductivity of TiNb/316L SS is higher than that of substrate. Compared with 316L SS and the TiNb coating, TiNbN film shows moderate corrosion resistance but the lowest ICR. According to XRD analysis, the main component of TiNbN is a solid solution of cubic NbN and TiN. The morphologies of TiNb and TiNbN characterized by SEM reveal that both coatings provide smooth surfaces. It can be concluded that the TiNb/316L SS is a kind of promising bipolar plate material with high corrosion resistance. Nevertheless, the conductivity of TiNb/316L SS still needs to be improved. In the future, multilayer coatings consisting of TiNb and TiNbN with optimized atomic ratios will be studied with aim to improve material's corrosion resistance and conductivity further.

**Author Contributions:** Conceptualization, K.S.; methodology, K.S. and X.-F.X.; resources, X.L., Y.Z. and W.-W.L.; writing—original draft preparation, K.S.; writing—review and editing, X.-F.X., J.O.J., S.-B.W. and L.Y.; project administration, X.-F.X., J.O.J. and Q.-F.L.

**Funding:** This research was funded by National Key R&D Program of China (2016YFE0102700), Major Science and Technology Projects of Shanxi Province (20181101006) and Innovation Fund Denmark by the project Wind2H (5185-00025B).

**Conflicts of Interest:** The authors declare no conflict of interest.
