Corrosion resistance and conductivity of Nb/NbN/Mo-containing NbN multilayer coatings for PEM water electrolysis

The inadequate corrosion resistance and conductivity of metal bipolar plates are major obstacles to the commercialization of proton exchange membrane water electrolysis (PEMWE). In this work, Nb/NbN/Mo-containing NbN multilayer coatings of a Nb interlayer, a NbN intermediate layer, and a Mo-containing NbN top layer are deposited on a titanium substrate from bottom to top by magnetron sputtering to enhance its corrosion resistance and conductivity. The microstructure, electrochemical corrosion behavior, and conductivity of the coating are systematically investigated. The results indicate that molybdenum addition substantially enhances both corrosion resistance and conductivity of coatings. Among all coatings, Mo-NbN-60W coating exhibits the best corrosion resistance and interfacial conductivity due to the doping of Mo reducing the lattice constant and grain size of the coating, inhibiting the growth of columnar crystals. Under simulated PEMWE anode conditions, the Mo-NbN-60W coating exhibits a corrosion current density of 0.98 μA/cm², which is reduced by nearly 27 times compared to Ti substrate. The interfacial contact resistance of the Mo-NbN-60W coating is 5.62 mΩ·cm² at 1.4 MPa, approximately one-fifth that of the Ti substrate, and meets the performance requirements of the Department of Energy 2025 targets (ICR<10 mΩ·cm2). This work demonstrates that the Mo-containing NbN multilayer coating has the potential to become a highly corrosion-resistant and conductive bipolar plates material for PEMWE.