Controlled Oxygen Incorporation in TiN Coatings via Heat Treatment for Applications in PEMFC Metallic Bipolar Plates

Abstract

Improving the corrosion resistance while maintaining good electrical conductivity is of vital importance for the application of stainless steel in bipolar plates of polymer electrolyte membrane fuel cells (PEMFCs). Transition nitride coatings on steel surfaces, such as TiN, is considered as a possible solution. However, most coatings still fail to exhibit good corrosion resistance and high electrical conductivity simultaneously, especially after corrosion testing. This study prepares TiN on 316L stainless steel (SS) and conducts heat treatment on the TiN deposited samples at different temperatures. The corrosion behaviours of the prepared samples are investigated under the simulated working environments of fuel cell. Our results demonstrate that heat treatment at appropriate temperatures is an effective approach to improve the corrosion resistance of TiN coatings while maintaining a considerable electrical conductivity. The interfacial contact resistance (ICR) test results indicate that high temperature (450 °C) heat treatment has detrimental effect on the electrical conductivity of samples due to the formation of a thick oxide dominated layer, while samples heat treated at 300 °C only form graded layers with suitable oxide amount which endows the coated specimens with a very low ICR value both before and after corrosion tests. This suggests that the heat treatment of TiN coatings under suitable conditions is a feasible strategy to simultaneously achieve an enhanced corrosion resistance and a good electrical conductivity of the TiN coated samples for bipolar plates in PEMFCs.