Effects of coating thickness on corrosion and contact resistance behavior of TiN coated AISI 316L as bipolar plates for PEMFC

In the polymer electrolyte membrane fuel cells (PEMFCs), low corrosion resistance and high interfacial contact resistance (ICR) are two controversial issues in usage of AISI 316L stainless steel as a metallic bipolar plate. For solving these problems, investigation and development of different coatings and/or surface treatments are inevitable. Corrosion behavior and ICR of AISI 316L specimens coated with 1, 2, and 3 µm thick TiN were investigated. Potentiodynamic (PD), potentiostatic (PS) and electrochemical impedance spectroscopy (EIS) tests were conducted at 80 °C in pH3 H2SO4+2 ppm HF solution purged with either O2 or H2 under both simulated cathodic and anodic conditions. The PS corrosion test results revealed that the current densities of the specimens were below 1 µA cm−2. In the simulated cathodic condition, an increase of coating thickness from 1 to 3 µm led to a relatively large decrease of the current density from 0.76 to 0.43 µA cm−2. Furthermore, the ICR values of the coated specimens after the PS test were lower than that of the uncoated specimen before the PS. In general, the TiN coating decreases the ICR, and has enough corrosion resistance in simulated PEMFC conditions. However, none of the coatings achieved the DOE ICR targets.