Effect of Al content on the corrosion resistance and conductivity of metal nitride coating in the cathode environment of PEMFCs

Abstract

In this paper, TiN coatings doped with various Al contents are settled on stainless steel 316L (SS316L) as bipolar plates of proton exchange membrane fuel cells (PEMFCs) through closed field unbalanced magnetron sputter ion planting. The influence of Al doping on the phase structure, surface morphology, corrosion resistance, passive film, interfacial contact resistance (ICR) and contact angle are studied. According to results of X-ray diffraction (XRD), the TiAlN coated samples have grain refinement. From the results of scanning electron microscope (SEM), TiAlN coatings are dense and uniform. Based on the potentiodynamic polarization test results, TiAlN-2A coating exhibits the highest corrosion potential of 0.17 VSCE and the lowest corrosion current density of 1.42×10−7 A cm−2 in the simulated PEMFCs cathode environment, which completely meets the DOE 2020 technical targets (<1×10−6 A cm−2), as well as the best stability and the lowest current density in the cathode potentiostatic polarization test. In addition, the electrochemical impedance spectroscopy (EIS) test reveals that TiAlN-2A coating has the highest corrosion resistance than bare SS316L and the rest coatings. Capacitance analysis shows that TiAlN-2A coated sample has lower electron donor concentration, which indicates better corrosion resistance. According to ICR results, at compaction of 1.4 MPa, the ICR value of TiAlN-2A coating is 12.6 mΩ cm2, which is close to satisfy the DOE 2020 technical targets (≤10 mΩ cm2). In addition, the corrosion and conductivity mechanism is also investigated.