Effect of potential on corrosion behavior and contact resistance of electrochemically nitrided 446 stainless steel in simulated cathode environment of proton exchange membrane fuel cell

The surface of 446 stainless steel was nitrided through an electrochemical treatment. The corrosion behavior and surface conductivity were investigated in a simulated cathode environment (i.e., 5 × 10⁻⁴ mol L⁻¹ H₂SO₄ + 0.1 ppm HF solution at 80 ℃) for proton exchange membrane fuel cell at different anodic polarization potentials. X-ray photoelectron spectroscopy analysis indicates that the nitriding treatment mainly produces Cr-nitrides in the surface layer of specimen. Under the free corrosion condition, the nitrided specimen displays spontaneous passivation and a much higher corrosion resistance than the untreated specimen. The electrochemical nitridation results in almost no change in the anodic polarization features but a lower anodic dissolution rate and contact resistance for 446 stainless steel. The stable passive current density and interface contact resistance values are about 150 nA cm⁻² and 7 mΩ cm², respectively, after the potentiostatic polarization at the typical potential 0.6 V_SCE. The dissolution of nitrides occurs at the anodic potentials, especially in the oxygen evolution region, but the remained nitrides are favorable for surface conductivity.