Corrosion resistance and conductivity of NbN-coated 316L stainless steel bipolar plates for proton exchange membrane fuel cells

NbN coatings were deposited by multi-arc ion plating at different nitrogen partial pressure (PN) to improve the corrosion resistance and conductivity of metallic bipolar plates. With increasing PN, the phase composition of the coating transformed from a mixture of β-Nb2N and δ’-NbN to δ-NbN, which was accompanied by grain refinement. The coating deposited at a relatively high PN (3.5 Pa) exhibited the lowest ICR and corrosion current density of 12.75 mΩ·cm2 and 2.619 × 10−6 A/cm2, respectively. The influence of the phase composition, microstructure, and surface morphology on the anti-corrosion behavior and conductivity of the coating were analyzed in detail.