Bilayer CrN/Cr coating-modified 316L stainless steel bipolar plates for high temperature polymer electrolyte fuel cells

Abstract

In this work, a bilayer CrN/Cr coating was deposited on the surface of a 0.1 mm-thick SS316L specimen with a size of 60 × 60 mm2 by means of a reactive magnetron sputtering method. Using a specially-designed electrochemical cell for simulating the HT-PEFC environment, various electrochemical tests, including potentiodynamic polarization, potentiostatic polarization and EIS, were performed in order to evaluate the anti-corrosion properties and stability of the bilayer CrN/Cr coating in simulated HT-PEFC environments. Additionally, ex-situ characterizations using XRD, SEM + EDX and ICR were carried out to investigate the crystal structure and composition of CrN/Cr coating, surface morphologies and the interfacial contact resistance of samples before and after corrosion tests. The results show that the bilayer CrN/Cr coating could provide a more than 99.9% protective effect on the substrate (SS316L) in the simulated HT-PEFC environment at RT and 130 °C, and reduce the corrosion rates of BPPs more than 600 times in both the simulated cathodic and anodic environments of a HT-PEFC. Furthermore, an ICR value of CrN/Cr SS316L (5.5 mΩ cm2) is around one order of magnitude lower than that of the bare SS316L substrate (47 mΩ cm2) in a typical pressing force for assembling fuel cells (140 N cm−2).