Enhanced corrosion resistance and electrical conductivity of Nb/NbN multilayer coatings prepared by the combination methods of magnetron sputtering and pulse laser deposition

High anti-corrosion and good electrical conductivity are the basic requirements for metal bipolar plates (BPs) in proton exchange membrane water electrolysis (PEMWE). In this work, Nb/NbN multilayer coatings are deposited on Ti BPs by the combination methods of magnetron sputtering and pulse laser deposition. It is demonstrated that the growth of columnar grains in the Nb/NbN multilayer coatings can be cut off by the multilayer interface, and the surface roughness is significantly reduced from 0.099 μm of single-layer Nb coating down to 0.045 μm of Nb/NbN/Nb/NbN multilayer coatings. As a result, the corrosion current density is remarkably reduced from 3.1 × 10⁻⁵ A cm⁻² down to 4.5 × 10⁻⁸ A cm⁻². Moreover, the interfacial contact resistance is substantially lowered from 50.7 mΩ cm² down to 8.8 mΩ cm² @ 1.5 MPa, owing to the compact structure and Nb transition layer. Accordingly, Nb/NbN multilayer coatings have the potential applications in PEMWE.