Cobalt ferrite, CoFe2O4 (CFO), nanocrystals are efficient and competitive anode materials in the field of electrochemical water splitting. Using density functional theory with on-site Hubbard U corrections (DFT+U), we have investigated the structural, electronic, and magnetic properties of CFO (001)/(100) surfaces, as well as their reactivities toward water adsorption. Special attention has been focused on the formation of oxygen vacancies (VO), due to their key role in the oxidation activity of metal oxides, often based on the Mars–van Krevelen mechanism. Our results show that vacancy formation is easiest at oxygen sites that are not bound to tetrahedrally coordinated Fe. Water adsorbs mainly in molecular form on the Co/Fe metal cations, whereas it dissociates at defects. In comparison to other spinels, CFO is similar to NiFe2O4, exhibiting relatively low energy cost of VO formation and a strong affinity of the vacancies toward water. These findings suggest that CFO may be a more promising oxidation catalyst than NiCo2O4 and Co3O4.

Dioxygen activation pathways on the (001) surfaces of cobalt ferrite, CoFe2O4, were investigated computationally using density functional theory and the hybrid Perdew‐Burke‐Ernzerhof exchange‐correlation functional (PBE0) within the periodic electrostatic embedded cluster model. We considered two terminations: the A‐layer exposing Fe2+ and Co2+ metal sites in tetrahedral and octahedral positions, respectively, and the B‐layer exposing octahedrally coordinated Co3+. On the A‐layer, molecular oxygen is chemisorbed as a superoxide on the Fe monocenter or bridging a Fe−Co cation pair, whereas on the B‐layer it is adsorbed at the most stable anionic vacancy. Activation is promoted by transfer of electrons provided by the d metal centers onto the adsorbed oxygen. The subsequent dissociation of dioxygen into monoatomic species and surface reoxidation have been identified as the most critical steps that may limit the rate of the oxidation processes. Of the reactive metal‐O species, [FeIII−O]2+ is thermodynamically most stable, while the oxygen of the Co−O species may easily migrate across the A‐layer with barriers smaller than the associative desorption.

Iron and cobalt-based oxides crystallizing in the spinel structure are efficient and affordable catalysts for the oxidation of organics, yet, the detailed understanding of their surface structure and reactivity is...