An investigation into TiN-coated 316L stainless steel as a bipolar plate material for PEM fuel cells

In order to reduce the cost, weight and volume of the bipolar plates, considerable attention is being paid to developing metallic bipolar plates to replace the non-porous graphite bipolar plates that are in current use. However, metals are prone to corrosion in the proton exchange membrane (PEM) fuel cell environments, which decreases the ionic conductivity of the membrane and lowers the overall performance of the fuel cells. In this study, TiN was coated on SS316L using a physical vapor deposition (PVD) technology (plasma enhanced reactive evaporation) to increase the corrosion resistance of the base SS316L. X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical methods were used to characterize the TiN-coated SS316L. XRD showed that the TiN coating had a face-centered-cubic (fcc) structure. Potentiodynamic tests and electrochemical impedance tests showed that the corrosion resistance of SS316L was significantly increased in 0.5 M H2SO4 at 70 degrees C by coating with TiN. In order to investigate the suitability of these coated materials as cathodes and anodes in a PEMFC, potentiostatic tests were conducted under both simulated cathode and anode conditions. The simulated anode environment was -0.1 V versus SCE purged with H-2 and the simulated cathode environment was 0.6 V versus SCE purged with O-2. In the simulated anode conditions, the corrosion current of TiN-coated SS316L is -4 x 10(-5) A cm(-2), which is lower than that of the uncoated SS316L (about -1 x 10(-6) A cm(-2)). In the simulated cathode conditions, the corrosion current of TiN-coated SS316L is increased to 2.5 x 10(-5) A cm(-2), which is higher than that of the uncoated SS316L (about 5 x 10(-6) A cm(-2)). This is because pitting corrosion had taken place on the TiN-coated specimen. (c) 2007 Elsevier B.V. All rights reserved.