Thermally nitrided Cu–5.3Cr alloy for application as metallic separators in PEMFCs

Cr-nitride which offers good electrical conductivity and corrosion resistance was formed on the surface of Cu–5.3 (wt.%)Cr alloy and its characteristic properties including electrochemical behavior and electrical conductivity were evaluated. The sample was annealed for 12 h in a temperature range of 600–1000 °C in a nitrogen atmosphere. Nitridation of Cr in Cu–5.3Cr alloy occurred at about 600 °C and followed Cr → Cr2N → CrN phase transformation sequence. A continuous Cr-nitride was formed at 1000 °C, but not below 900 °C. Corrosion behavior of the continuously nitrided sample was investigated in simulated PEMFC environments. Corrosion resistance of the nitrided sample was improved in an anode environment, but not in a cathode environment. This was attributed to the dissolution of Cu through pin-hole defects on the surface of the nitrided sample just in the cathode environment. Interfacial contact resistance of the nitrided Cu–5.3Cr alloy was satisfied the target value. Furthermore, there was no recession of electrical conductivity after polarization.