Structure of the NiFe2O4(001) surface in contact with gaseous O2 and water vapor

Nickel ferrite, NiFe2O4, is a material with interesting physical properties and useful technological applications. We have used Density-functional theory with on-site Coulomb repulsion U term to study the structure, electronic properties, and energetics of the NiFe2O4(001) surface and its interaction with water both in the absence and in the presence of surface oxygen vacancies. In a humid environment, water adsorbs dissociatively on the surface oxygen vacancies leading to the formation of surface hydroxyls. At high temperature, water desorbs leaving a surface containing oxygen vacancies. These defects could represent useful reactive sites for various catalytic reactions.