Corrosion behavior of a ZrCN coated Ti alloy with potential application as a bipolar plate for proton exchange membrane fuel cell

Abstract

To improve the corrosion resistance, surface electrical conductivity and wettability of Ti–6Al–4V used in polymer electrolyte membrane fuel cell (PEMFC), a ZrCN nanocrystalline coating was deposited on Ti–6Al–4V substrate using double cathode glow discharge technique. The new coating exhibited a nanocomposite structure, consisting of amorphous C, CNx and nanocrystalline ZrCN. The effect of the HF concentrations on the corrosion behavior of the coating was investigated by potentiodynamic, potentiostatic polarizations and electrochemical impedance spectroscopy (EIS) in a simulated the operating conditions of a PEMFC. With increasing HF concentrations, the corrosion potential (Ecorr) decreased and the corrosion current density (icorr) of the ZrCN coating increased, indicating that corrosion resistance decreased with the increase of HF concentrations. However, at any given concentration of HF, the corrosion resistance of the ZrCN coating was significantly higher than that of uncoated Ti–6Al–4V. The results of EIS measurements showed that with increasing the concentration of HF, the resistance of the passive film (Rb) formed on the ZrCN coating decreased slightly, being of the order of magnitude of ∼107 Ω cm2, which was an improvement by four orders of magnitude compared to uncoated Ti-6A1-4V. At a compaction force of 140 N cm−2, no perceptible difference in the interfacial contact resistance (ICR) of ZrCN-coated Ti-6A1-4V was observed before and after potentiostatic polarization for 120 min, and its ICR values were reduced by one order of magnitude in comparison to that of uncoated Ti-6A1-4V. Moreover, ZrCN-coated Ti-6A1-4V exhibited a much low surface wettability than uncoated Ti–6Al–4V alloy, which was beneficial for both water management and improving corrosion resistance.