Density functional theory study of SO ₂ -adsorbed Ni(1 1 1) and hydroxylated NiO(1 1 1) surface

Spin polarized, DFT + U periodic calculation is used as an effective way to model the adsorption process of SO ₂ on hydroxylated NiO(1 1 1) surface. The adsorption of atomic O and O ₂ on the clean Ni(1 1 1) surface is calculated to investigate the forming process of passive film. The molecular and dissociated adsorptions of H ₂ O on NiO(1 1 1) surface are evaluated to construct defect-free hydroxylated NiO(1 1 1) surface. The adsorption of SO ₂ and atomic O on clean Ni(1 1 1) surface is also investigated to compare with the adsorption capacity between passive film and substrate. With respect to the single adsorption process of SO ₂ on defect-free hydroxylated NiO(1 1 1) surface, the effects of O vacancy of surface and atomic O closed to the surface are investigated. The calculation results show that there is no chemical adsorption of SO ₂ on the defect-free hydroxylated NiO(1 1 1) surface with or without atomic O. Either single SO ₂ or SO ₂ with atomic O prefer adsorbing on the hydroxylated NiO(1 1 1) surface with O vacancies. The adsorption behavior is strengthened with the increase of percentage of surface O vacancy. The existence of atomic O leads to the production of SO ₃ on the hydroxylated NiO(1 1 1) surface and strengthens the adsorption capacity of SO ₂ . Furthermore, the results also reveal the relationship between the charge transfer and the adsorption energy of SO ₂ and atomic O on the hydroxylated NiO(1 1 1) surface and clean Ni(1 1 1) surface. We inferred that broken passive film susceptibility to corrosion compare with substrate when surface O vacancies aggregate and its concentration large enough.