Preparation and performance of nanometric Ti/TiN multi-layer physical vapor deposited coating on 316L stainless steel as bipolar plate for proton exchange membrane fuel cells

The current research mainly focuses on surface properties, corrosion resistance and interfacial contact resistance (ICR) of nanometric titanium/titanium nitride (Ti/TiN) multi-layer coating deposited on 316L stainless steel via physical vapor deposition (PVD) technique for using in proton exchange membrane fuel cell (PEMFC) bipolar plate (BPP) application. The phase and microstructure of the coated BPPs is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and contact angle examinations. The performance of the BPPs is investigated by electrochemical corrosion tests including electrochemical impedance spectroscopy (EIS), potentiodynamic and potentiostatic polarization tests at two conditions including at ambient temperature and in the simulated PEMFC cathode environment. Electrochemical test results reveal that the Ti/TiN coating increases the polarization resistance of 316L stainless steel by 26 orders of magnitude at ambient temperature and by 1000 orders of magnitude in the simulated PEMFC cathode environment. The corresponding ICR of the BPPs is measured ex-situ in a PEMFC set-up. It is observed that the coated BPP has ICR value of 11 and 18 mΩ cm2 before and after potentiostatic polarization, respectively. Hence, the Ti/TiN coating studied in this work has promising properties as BPP material and is potentially suitable alternative to replace the graphite BPP in PEMFC.