Insight of DFT and atomistic thermodynamics on the adsorption and insertion of halides onto the hydroxylated NiO(1 1 1) surface

Spin polarized, DFT + U periodic calculations have been used to study the interaction of halides (X) with a (1 x 1)-hydroxylated NiO(1 1 1) surface, a model of passivated nickel. The exchange of surface OH groups by the X ions and the insertion of the halides in the anionic sub-surface layer have been investigated. The substitution of OH by halides is favored by a smaller size of the halide ions and by a lower substitution proportion. An atomistic thermodynamic approach including solvent effects allows us to construct phase diagrams of the surface terminations as a function of the Cl and F concentrations in the aqueous solution. The higher proportion of OH substitution by F, and the lower insertion energy, as compared to Cl, may be related to stronger corrosion caused by F as compared to Cl.