Influence of oxygen adsorption on the chemical stability and conductivity of transition metal ceramic coatings: First-principle calculations

Considering their excellent chemical stability and conductivity, transition metal carbide and transition metal nitride coatings are adopted to protect metallic bipolar plates in this study. However, the inevitable adsorption of oxygen on these coatings in the cathodic environment of proton exchange membrane fuel cell (PEMFC) influences their chemical stabilities and conductivities. To asses this influence, first-principle calculations are conducted using CrN, TiC and TiN as examples. We show that in the case of CrN, CrOx ionic bonds are formed on CrN (111), and TiOx formed on TiC (111) and TiN (111) for the case of TiC and TiN, respectively. In addition, the overlapping in the electron density difference distribution of CrO is more significant than that of TiO (TiN) and TiO (TiC). This suggests that CrN has a better chemical stability than TiN or TiC, and therefore, is more suitable for the protective coating of metallic bipolar plates, especially in the cathodic environment of PEMFC.