Excellent anti-corrosion and conductivity of NbN coated on Ti bipolar plate by controlling N2 flow rates

The metal bipolar plates which play a crucial role in proton exchange membrane fuel cells (PEMFCs) are applied extensively due to their excellent property. However, the degraded corrosion resistance by corrosive ion and the increased interfacial contact resistance by passivation layer under acidic operating environment will affect the efficiency of PEMFCs. Metal nitride can solve that problem in some extent, however, the effect of nitrogen flow rates on the metal nitride formation during coating deposition is unclear. To solve these, NbN coatings with different N2 flow rates were applied to the bare Ti substrate via magnetron sputtering and thereafter studied. Compared with bare Ti substrate, outstanding anticorrosion performance is exhibited for the coated sample, whose corrosion current decreased three orders of magnitude (∼10−8 A/cm2) in simulated PEMFC cathode environment and the interfacial contact resistance decreased to tenth of that bare Ti substrate (∼5 mΩ cm2).