Composition optimization of arc ion plated CrNx films on 316L stainless steel as bipolar plates for polymer electrolyte membrane fuel cells

Thin films of CrNx with different nitrogen contents are deposited on 316L stainless steel (SS316L) as bipolar plates for polymer electrolyte membrane fuel cells (PEMFCs) by arc ion plating (AIP) through adjusting nitrogen gas flow rate. The optimal N2 flow rate and resultant N content in CrNx films are determined by evaluating the interfacial contact resistance (ICR) between carbon papers and the coated samples, and the corrosion resistance in the simulated PEMFC conditions. After coating CrNx films, the performance of SS316L bipolar plates is obviously improved, and has a close relationship with N content in the CrNx films. Compared with the bare SS316L, the CrNx coated SS316L exhibits a reduced ICR by one order of magnitude and the corrosion resistance increases by two orders of magnitude. The results show that CrN0.86 film coated SS316L bipolar plates present best performance, i.e. the ICR of CrN0.86 film coated sample reduces to 8.8 mΩ cm2 under 1.0 MPa compaction pressure, and the corrosion current density almost reaches 10−7 A cm−2. The analysis indicates that the enhanced performance of the coated SS316L bipolar plates is related to the high film density determined by AIP, and the variation of phase structure and film composition.

► As a successive study of Cr/CrN/Cr multilayer (J. Power Sources 196 (2011) 3249), composition optimization of CrNx films, which will serve as the outmost layer of Cr/CrN multilayer in our future work, was performed.
► The enhanced performance of the samples coated with CrN0.85 film, which holds the optimal composition point, was discussed from a material and physical point of view.
► Compared with bare SS316L plates, the coated samples exhibit ICR (one order of magnitude lower) and better anticorrosion performance.