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Stainless steels have received wide attention as a substitute material for bipolar plates in high temperature proton exchange membrane fuel cell (HT-PEMFC). In the present work, the CrN, CrAlN and multilayer CrN/CrAlN coatings were deposited on 316L SS to increase the corrosion resistance and decrease the interfacial contact resistance. The deposited coatings exhibited face centered cubic phase structure and it was verified from the X-ray diffraction pattern. X-ray photo electron spectroscopy results showed the formation of both CrN and CrAlN layers on 316L SS. CrN/CrAlN coating is more helpful in water management due to low surface roughness and high contact angle in the HT-PEMFC environment. The corrosion resistance behavior of all the samples were studied in 85% H3PO4 solution at 140 °C purged with H2 (HT-PEMFC anode) and O2 (HT-PEMFC cathode) gases. The results showed that all the coatings considerably improved the performance of 316L SS and superior corrosion resistance was observed for CrN/CrAlN multilayer coating, whose protective efficiency was 98.12% and 96.14% in the two simulated HT-PEMFC environments. The results of electrochemical impedance spectroscopic studies demonstrated higher impedance for CrN/CrAlN coating. Surface morphological studies performed after corrosion studies revealed that protection ability of CrN/CrAlN coating still remained acceptable. A very low interfacial contact resistance value of 6 mΩ cm2 at 140 N/cm2 was observed for CrN/CrAlN coating. Moreover, after corrosion studies, the interfacial contact resistance value of CrN/CrAlN coated 316L was much lower than that of CrN and CrAlN coatings due to the increased oxidation resistance. The maximum power density of about 0.93 W/cm2 at 2 A/cm2 and output voltage of 0.96 V was observed for CrN/CrAlN coating.

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.

In the present work, polydopamine was coated on titania nanotubes (TNTA) by self-polymerization process. Prior to polydopamine coating, TNTA was sintered at 500 °C for 3 h to obtain the anatase/rutile phase. The physicochemical characterization of PDA-TNTA was done by field emission scanning electron microscopy (FE-SEM), attenuated total reflectance fourier transform infrared spectroscopy (ATR-FTIR), UV-Visible spectroscopy and wettability analysis. Polydopamine forms a sheath on the TNTA and diminished the corrosion rate. The high surface-to-volume ratio of PDA-TNTA provided a platform to improve apatite formation, cell adhesion and proliferation. The tailoring of TNTA surface with polydopamine could provide a promising implant material in bone tissue engineering.