Influence of Ti content on the corrosion properties and contact resistance of CrTiN coating in simulated proton exchange membrane fuel cells

Abstract

CrTiN coatings with different Ti content are deposited on stainless steel 316L (SS316L) substrate as bipolar plates for proton exchange membrane fuel cells (PEMFCs) by close field unbalanced magnetron sputter ion planting (CFUBMSIP). The effect of Ti incorporation on the surface morphology, phase structure, electrochemical properties, interfacial contact resistance (ICR) and contact angle with water are investigated. Scanning electron microscope (SEM) results indicate that Ti doped coatings are compact and dense. X-ray diffraction (XRD) and nanoindentation hardness results show that Ti incorporated coatings have grain refinement and solid solution phase. From electrochemical test results, CrTiN-4A coating has the highest corrosion potential of 0.1825 V in the anodic PEMFCs environment. It also has the most stable and lowest current density both in simulated anodic and cathodic environments after potentiostatic polarization. Furthermore, electrochemical impedance spectroscopy (EIS) studies reveal that the corrosion resistance of CrTiN-4A coating is higher than other coatings and bare SS316L. ICR results show that CrTiN-4A coating has the lowest ICR of 4.57 mΩ cm2 at a compaction of 1.4 MPa before potentiometric polarization. In addition, the contact angles of CrTiN-4A coating before and after potentiostatic polarization are 109.0° and 99.5°, respectively.