Corrosion-resistant and electrically conductive (TiVCrNbMo)N high-entropy nitride coatings for PEM fuel cell bipolar plates

To develop an electrically conductive, yet corrosion resistant, coating for metallic bipolar plates used in proton exchange membrane fuel cells (PEMFCs) environments, a series of novel (TiVCrNbMo)N high-entropy nitride (HEN) coatings were deposited in a mixed N₂/Ar atmosphere using a double-cathode glow discharge system. The influence of varying N₂/Ar flow ratios on the electrochemical corrosion behavior and interfacial contact resistance (ICR) of the coatings was systematically investigated to inform the development of high-performance protective coatings for metallic bipolar plates. All the HEN coatings exhibited a single-phase face-centered cubic (FCC) solid solution with equiaxed nanoscale grains. Corrosion resistance in a simulated acidic PEMFC environment was evaluated using a range of electrochemical analytical approaches. The results indicated that the i_corr values and the current density at a potential of +0.6 V_SCE for the HEN coatings prepared at N₂:Ar flow ratios of 1:10 and 1:5 coating are of the order of 10⁻⁸ Acm⁻² and 10⁻⁷ A cm⁻², respectively, both of which are three orders of magnitude less than that for the uncoated CP-Ti. Regardless of whether measurements were taken before or after potentiostatic polarization, the ICR values of the as-deposited HEN coatings decreased with increasing N₂/Ar flow ratio under a compaction force of 140 N cm⁻². In particular, for the HEN coating prepared at a N₂:Ar flow ratio of 1:5, the ICR values are 16.2 and 20.4 mΩ·cm² before and after potentiostatic testing, respectively, which approach the US DOE 2025 target for surface resistance of metallic BPs. Furthermore, first-principles calculations were used to assess the impact of surface passive films on the coatings'electrical conductivity.