Enhanced Corrosion Resistance of SS304 Stainless Steel and Titanium Coated with Alternate Layers of TiN and ZrN in a Simulated O2-rich Environment of a Unitized Regenerative Fuel Cell

Abstract

In this study, alternative layers of titanium nitride/zirconium nitride (TiN/ZrN) were coated on the surface of SS304 stainless steel and titanium (Ti) to enhance their corrosion resistance in a simulated oxygen (O2)-rich environment of a unitized regenerative fuel cell (URFC). The cathodic arc evaporation physical vapor deposition (CAE-PVD) technique was used to coat the multilayers. The effect of the 02 on the electrochemical behavior of the TiN/ZrN-coated SS304 and Ti in the O2-rich environment with acid and fluoride (F-) ions was investigated. The results showed that the TiN/ZrN coating with a nano-composite structure improved the corrosion resistance about 243 and six times, respectively, as compared with uncoated Ti and SS304 in the O2-rich environment with F- ions and acid. This coating also increases the corrosion potential of Ti from 0.097 to 0.302 V and that of SS304 from -0.085 to 0.080 V. These coatings outperformed CrN and TiN coatings on SS316L or Ti surfaces in an 02-rich environment. The improved results are due to the dense columnar microstructure of the nano-composite TiN/ZrN layer, which provides strong chemical protection from the hydrogen (H+) and F- ions, even in the presence of O2, thereby preventing any direct corrosive attack on the substrate. The presence of O2 in the solution containing the F- ions and acid slightly increased the corrosion rate of the TiN/ZrN layer as compared to that of hydrogen gas.