Corrosion Resistance, Adhesion Strength, and Electrical Conductivity of 316L Bipolar Plates Treated with Combined Plasma Nitriding and TiN Coating

Abstract

To enhance the corrosion resistance, adhesion strength, and electrical conductivity of bipolar plates for proton exchange membrane fuel cells (PEMFCs), a duplex surface treatment comprising plasma nitriding (PN) followed by arc ion plating of a TiN coating was applied to 316L stainless steel. The duplex coating exhibited a bilayer structure with a TiN top layer (~1.3 μm) and a nitrided diffusion layer (~9.2 μm). Compared with a single TiN coating, it showed superior corrosion resistance in both cathode and anode environments, with corrosion current densities of 0.069 and 0.422 μA·cm−2, respectively, and maintained stable performance over 10,000 s of potentiostatic polarization. Its interfacial contact resistance at 140 N·cm−2 was 7.84 mΩ·cm2, below the Department of Energy (DOE) 2025 target of 10 mΩ·cm2. The water contact angle also increased, benefiting water management. The nitrided interlayer substantially enhanced the adhesion strength of the TiN coating. These findings confirm that the sequential combination of plasma nitriding and TiN coating is an effective strategy for improving the corrosion resistance, electrical conductivity, and adhesion of stainless steel bipolar plates for PEMFC applications.