Active screen plasma surface co-alloying treatments of 316 stainless steel with nitrogen and silver for fuel cell bipolar plates

• Radically reduced interfacial contact resistance of 316 by surface N/Ag co-alloying
• A duplex surface layer structure produced by one-step plasma surface treatment

Due to their good mechanical and corrosion properties, relatively low cost and ease of manufacture, 316 austenitic stainless steel has been researched as a promising candidate material for bipolar plates in proton exchange membrane fuel cells. However, its interfacial contact resistance (ICR) is about 16 times higher than that of the Department of Energy target (10 mΩ cm2), which leads to undesirable fuel cell performance. In this work, active screen plasma (ASP) surface co-alloying treatments with both nitrogen and silver were developed to modify the surface of 316 stainless steel to reduce its ICR required for high-performance bipolar plates. The treated surfaces were fully studied by means of scanning electron microscopy, X-ray diffraction, glow discharge optical emission spectroscopy and energy dispersive spectroscopy. The experimental results demonstrated that a duplex surface layer structure consisting of an Ag-rich surface deposition layer supported by an S-phase case was generated by the ASP surface co-alloying treatment. The ASP co-alloying treated surfaces showed increased corrosion potential and reduced corrosion current density, and significantly improved surface electrical conductivity. This could be attributed to the introduction of metallic Ag particles by this novel surface plasma treatment.