Density functional theory within the GGA + U framework has been used to study surface slabs of Co3O4. The thermodynamic stability of the surfaces was assessed in terms of the surface free energy as a function of oxygen potential. At any given condition of temperature and oxygen partial pressure, the various (1 1 0) and (1 1 1) terminations are always less stable than the most stable (1 0 0) terminations. Under oxygen-rich conditions, a Co3O4 (1 0 0) surface exposing Co in octahedral positions is thermodynamically preferred, while under oxygen-lean conditions, a Co3O4 (1 0 0) surface exposing Co atoms in tetrahedral and octahedral positions is preferred. (C) 2010 Elsevier B.V. All rights reserved.