Fe–Ni–Cr alloy as bipolar plate of PEMFC by multi-steps surface modification

•Heat treatment is optimized for multi-step treatments.•FeO is formed on surface by heat treatment in O2 and 250 °C.•FeO is deleted by electrochemical treatment.•Cr2O3/Cr7C3/C coatings are formed by multi-steps treatment.•Performances are promising for Fe–Ni–Cr alloy.

Fe–Ni–Cr alloy is a potential material as the bipolar plate for proton exchange membrane fuel cell (PEMFC). However, its interfacial contact resistance is too high and the corrosion resistance is too low to survive in the hostile environment. An approach of preparing the composite coating layers in O2 is reported in this manuscript. The plate is first treated in acid solution, and then is heat treated in O2 at 250 °C for 2 h, at last is treated by electrochemical method. The ICR for the treated plate is only 9.4 mΩ cm2 at the compaction force of 240 N cm−2, and corrosion current density is 4.62 × 10−8 A cm−2. Microstructures for differential treatments have been analyzed by FE-SEM, XPS and AES. The results indicate that high carbon concentration within surface area has been aroused by chemical treatment, and then FeO/Cr7C3 layer has been in-situ formed by heat treatment. Thereafter electro-chemical treatment has the function of clearing the FeO away and forming dense Cr2O3/Cr7C3/C layer, which improves the performance of bipolar plate effectively.