Titanium oxynitride (TiON) coatings by reactive magnetron sputtering were studied to functionalize metallic bipolar plates of PEMFC (Polymer Electrolyte Membrane Fuel Cell). Stoichiometric TiN is a ceramic often used as a coating for its conductivity, hardness, and golden color. Under PEMFC’s environment (acidic and 80°C), it displays a low interfacial contact resistance (ICR), however, its chemical stability, notably at high potential, is not enough to avoid oxidation and increase of ICR. Here, oxynitride titanium coatings are studied to offer enhanced stability under high-potential PEMFC conditions while a low ICR is maintained.

Ex-situ potentiodynamic tests, Electrochemical Impedance Spectrometry (EIS), and ICR measurements have been carried out to identify the optimum content of oxygen that enables maintaining a low ICR for the application while improving corrosion properties compared to TiN. The microstructure and chemical composition of the coating have been investigated.

It was found adding oxygen to TiN improves the chemical stability of the material, in particular at high potential. This is coming from the higher stability of ionocovalent bonds than the metallic bonds in the mixture. A composition was found which maximizes chemical stability while maintaining low ICR. Oxygen also modifies the microstructure which is more refined with larger columns and less active surface.