Effect of nitrides on the corrosion behaviour of 316L SS bipolar plates for Proton Exchange Membrane Fuel Cell (PEMFC)

• All the developed coatings exhibit single-phase structure despite bi-layer coating.
• Higher surface roughness and hence higher contact angle value of TiN/TiAlN coating favoursfavours PEMFC wetting operation condition.
• Higher Rct and lower Qdl values for TiN coating ensures higher corrosion resistance.
• Conductivity and Surface resistance values of TiN and TiAlN coatings meet DOE requirements.

Currently stainless steel is the material on which extensive research interest is being focused for the purpose of using it as bipolar plates (Bp) for Proton Exchange Membrane Fuel Cell (PEMFC) because of its suitable physical and mechanical properties. In the present study TiN, TiAlN mono-layer and TiN/TiAlN bi-layer coatings were developed on 316L stainless steel (SS) by physical vapourvapour deposition (PVD) technique. The X-ray diffraction (XRD) patterns and Raman spectrum confirmed TiN cubic structure was formed for all the coatings. An increased surface roughness determined by atomic force microscopy (AFM) and high contact angle value with water for TiN/TiAlN qualify the Bp for the wet operating conditions in PEMFC. The electrochemical corrosion behaviour of the uncoated and coated specimens have been studied by Electrochemical impedance spectroscopy (EIS) as well as Potentiodynamic and Potentiostatic polarization studies in 0.5 M H2SO4 with 2 ppm of fluoride ions at 80 °C purged with air to simulate the PEMFC environment. The corrosion protection performance is in the order of TiAlN < 316L SS < TiN/TiAlN < TiN and the corrosion current (icorr) density obtained for TiN and TiN/TiAlN are less than 1 μA/cm2. Surface resistance measurements showed that TiN has 0.8 m Ω cm2 and exhibits more conductivity after the polarization studies.