Niobium-based thin films on 304 stainless steel for proton exchange membrane fuel cell bipolar plates

The durability and efficiency of proton exchange membrane fuel cells (PEM-FCs) are limited by corrosion of metallic bipolar plates, requiring protective coatings with high electrical conductivity. In this study, niobium (Nb) films were directly deposited on SS304 substrates by DC sputtering for 30–90 min to obtain coatings with different structural properties. The deposited Nb films were uniform, dense, and crack-free. Corrosion performance under simulated PEM-FC conditions revealed that the Nb90 coating provided the best protection, showing the lowest corrosion current density (0.098 μA cm−2) and the highest impedance value (111054 Ω cm−2) in both anode and cathode environments. Nb coatings also significantly reduced interfacial contact resistance (ICR). Under a compaction force of 150 N cm−2, the Nb90 coating achieved a low ICR of 5 mΩ cm2. Scratch testing indicated that Nb60 and Nb90 coatings exhibited stable deformation behavior without sudden failure, confirming improved scratch resistance and adhesion compared with Nb30. Accelerated start–stop cycling between 0.6 and 1.2 V for 1000 cycles demonstrated excellent durability of the optimized Nb90 coating, with stable impedance behavior and defect-free surface morphology under simulated PEMFC conditions. These findings highlight the strong potential of Nb coatings for durable PEM-FC bipolar plate applications.