The effect of surface vacancies on the interactions of Cl with a α-Fe2O3 (0001) surface and the role of Cl in depassivation.

• Interactions of Cl with the α-Fe 2 O 3 (0001) surface are studied. • The Cl adsorption is stronger on the lower charged Fe sites. • The subsurface Cl is less stable than adsorbed Cl. • Cl lowers the surface Fe vacancy formation energy. • Fe vacancy is more stable in the bulk while O vacancy is more stable on the surface. This study provides molecular insights into the initial stages of Cl-induced depassivation of iron passive film by studying the interactions of Cl with pristine and vacancy surfaces of α-Fe 2 O 3 (0001). Subsurface Cl is found to be less stable than adsorbed Cl which contradicts the ion exchange model that postulates Cl ingress into the passive film. Comparison of vacancy formation energy shows that Cl can enhance the surface Fe vacancy formation, which is consistent with the point defect model. Additionally, the energy difference of vacancies in different oxide layers supports the diffusion direction proposed by the point defect model. [ABSTRACT FROM AUTHOR]