Achieving ultrahigh corrosion resistance and conductive zirconium oxynitride coating on metal bipolar plates by plasma enhanced atomic layer deposition

Susceptibility to corrosion of metal bipolar plates limits their application in polymer electrolyte membrane fuel cells (PEMFCs) and hence, the development of a conductive coating with high corrosion resistance is essential. Zirconium nitride (ZrN) exhibits high corrosion resistance but the interfacial contact resistance (ICR) after the long-term test is not satisfied owing to the surface oxidation and the corrosion products. To further improve the corrosion resistance and retain a considerable electrical conductivity, herein, we present a novel zirconium oxynitride (Zr2N2O) coating on 304 stainless steel by incorporating a controlled amount of oxygen into ZrN with plasma enhanced atomic layer deposition. The corrosion current density of the Zr2N2O coated specimen is found to be over one order of magnitude lower than that of the ZrN coated substrate. More importantly, after the long-term test, the ICR of Zr2N2O coated specimen is much smaller than that of ZrN coated specimen owing to the improved oxidation resistance and decreased corrosion rate, suggesting incorporating a controlled amount of oxygen into conductive coating is a feasible strategy to achieve an ultrahigh corrosion resistance while retaining a considerable electrical conductivity.