Corrosion-resistant characteristics of nitrided Ni-free stainless steel for bipolar plate of polymer electrolyte fuel cell

In this study, the effect of a high temperature nitriding treatment on the characteristics of the Ni-free stainless steel (SUS445) used as the metallic bipolar plate of a polymer electrolyte fuel cell (PEFC) was investigated. The phase structure, composition, electrical conductivity and electrochemical corrosion resistance of the stainless steel after the nitriding treatment (SUS445-N) were analyzed. The supersaturated nitrogen phase γN, nitrides CrN and Cr2N in the nitride layer with a good electrical conductivity were observed and confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The corrosion resistance of the nitrided SUS445-N stainless steel was significantly improved due to the formation of the chromium-containing nitrides. The conducted fuel cell durability test revealed that when using the nitrided SUS445-N stainless steel as the bipolar plate, the fuel cell voltage performance was almost the same as that using the graphite carbon as the bipolar plate for 2500 h.