Surface Structure of Co3O4 (111) under Reactive Gas-Phase Environments

In this work, we thoroughly examined the structure of the Co3O4 (111) surface under oxidative and reductive conditions, i.e. in equilibrium with realistic pressures of O-2/H2O and H-2/H2O, using density functional theory with self-interaction and dispersion corrections. We found that this surface is, in fact, hydroxylated under most reaction conditions and that subjecting the surface to H-2 increases surface Co2+ concentration. Large structural distortions facilitate the reduction and stabilization of the Co-rich termination. At 423 K, hydroxylation readily occurs on both the O-rich and Co-rich surfaces even at water pressures as low as 10(-15) bar, and nondissociated water molecules appear on the O-rich surface when the water pressure is above similar to 10(-11) bar. Our approach showed good agreement with hybrid functional calculations and vibrational spectroscopy experiments. Under most catalytic conditions, where water is present as a reactant, product, or impurity, we predict that the Co3O4 (111) surface will be hydroxylated. Hydroxyl groups and structural distortions undoubtedly play large roles in shaping the surfaces catalytic properties and interaction with supported structures. The results of the study show the necessity of the inclusion of hydroxylation and surface Co concentration in computational studies of Co3O4 and provide surface structures under various conditions to aid in future studies on the structure and catalytic reactivity of Co3O4 (111) used as a support or as an active phase.