Evaluation of the corrosion behavior of a TiN-coated 316L SS bipolar plate using dynamic electrochemical impedance spectroscopy

Abstract

In the present investigation, the corrosion behavior of TiN-coated 316L SS was evaluated for use in a proton-exchange membrane fuel cell using dynamic electrochemical impedance spectroscopy (DEIS). The TiN coating was developed on 316L SS using the cathodic arc deposition (CAD) technique, with the developed coating confirmed by Raman spectrum. SEM cross-section studies revealed a dense microstructure with a 4 μm thickness of the coating. AFM results showed a high surface roughness for the TiN coating, which enhances the high water contact angle appropriate for the PEMFC operating environment. DEIS studies were carried out at an open circuit potential to 0.6 V with 0.03 V step potential in a solution containing 0.5 M H₂SO₄ and 2 ppm HF. The variation in impedance behavior in the passive film on the substrate and coating as a function of the potential exhibited distinctive charge-transfer resistance, double-layer capacitance, and coating resistance. An unusual low impedance behavior of the TiN coating was observed at 0.32 to 0.48 V. The corrosion current density, surface resistance, and conductivity for the TiN-coating parameters fulfilled the Department of Energy's (DOE's) 2020 targets. The lower interfacial contact resistance (ICR) value of the TiN coating satisfied the DOE's 2017 target for bipolar plates (BPs) and approached close to the DOE's 2020 targets.