Titanium Nitride Polyaniline Bilayer Coating for Metallic Bipolar Plates used in Polymer Electrolyte Fuel Cells

Abstract

Two materials, polyaniline (PANI) and titanium nitride (TiN), used for bipolar plate (BPP) coatings have each shown promise in improving the corrosion resistance and contact resistance, respectively, of metallic bipolar plates. Polyaniline was shown to provide a barrier for the bipolar plate and to effectively lower the corrosion currents observed in ex situ corrosion tests. However, the interfacial contact resistance (ICR) between polyaniline coatings and gas diffusion layer (GDL) is high and results in high electrical losses. On the other hand, TiN is reported to achieve good conductivity and in some cases improved corrosion resistance. The two materials have also been investigated together in a composite coating and showed promising results, but the contact resistance of the coating was still too high for use in a commercial fuel cell. In this study, the application of an additional layer of TiN over the TiN-polyaniline composite coating (a bilayer coating) is investigated. Composite bilayered PANI TiN coatings were deposited upon SS316L substrates. The optimized coating achieved U.S. Department of Energy (DoE) targets with potentiostatic corrosion currents of ∼0.024 μA cm−2 and ICR values of 11.2 mΩ cm2. PANI polymerization was confirmed, using Fourier-transform infrared (FTIR) spectroscopy and TiN loadings were investigated with energy dispersive X-ray (EDX) spectroscopy.