Enhancing the corrosion resistance of ferritic stainless steel bipolar plates by forming an outer Cr2O3-rich passive film in simulated PEMFC cathodic environments

In this study, a high Cr ferritic stainless steel was prepared by optimizing the alloy composition. It exhibited excellent corrosion resistance by forming an outer Cr 2 O 3 -rich layer passive film in the simulated PEMFC cathodic environment. The steel possessed a higher self-corrosion potential (−0.146 V MSE ) and lower self-corrosion current density (7.31×10 −7 A/cm 2 ) compared to AISI 316L, with a potentiostatic polarization current density at 0.23 V MSE of <0.46 μA/cm 2 . The steel underwent only minor pitting corrosion following potentiodynamic and potentiostatic polarization. Notably, the formation of a compact Cr 2 O 3 -rich outer layer was due to more Cr in the matrix promoting the diffusion of Cr into the passive film and the formation of Cr 2 O 3 , preventing the oxidation of internal Fe and Mo. Reducing the pitting corrosion of the steel due to the lower donor concentration and flat band potential inhibited aggressive F − attacks on the passive films. In addition, the minimal Mo 6+ content in the passive film implied that Mo possibly contributed less to the corrosion resistance of the steel, offering inspiration for optimizing Mo addition in high Cr ferritic stainless steels.