Effect of Different N2 Partial Pressures on the Corrosion Properties and Conductivity of NbNx Coated Titanium Bipolar Plates for PEMFCs

Metal nitride coatings have been considered as a promising approach to improve the performance of metal bipolar plates for proton exchange membrane fuel cells (PEMFCs). In this study, NbNx coatings with three different ratios of N2/Ar (1:2, 1:1 and 3:1) were prepared on TC4 alloy substrates using the double glow plasma alloying technology. The NbNx coatings are homogeneous and dense, and the phase of the coating transforms from hexagonal β-Nb2N to δ′-NbN phase as the nitrogen content increases. All coatings demonstrate high protective efficiency, with the coating (N2/Ar ratio of 3:1) displaying the lowest current density of 8.92×10−6 A/cm2 at a working voltage of 0.6 V. The EIS results also show that this coating has the best corrosion resistance. Notably, it also presents the lowest interfacial contact resistance of 7.29 mΩ·cm2 at 1.5 MPa and good hydrophobicity. More importantly, this study provides a new idea and method for corrosion-resistant coatings of metal bipolar plates for PEMFC applications.