Mono and Diatomic Reactive Oxygen Species Produced upon O2 Interaction with the (111) Facet of Cobalt Spinel at Various Conditions - Molecular DFT and Atomistic Thermodynamic Investigations

Periodic spin unrestricted DFT + U calculations joined with atomistic thermodynamics were used to study the location, structure, and stability along with the electronic and magnetic properties of various surface oxygen species and oxygen vacancies, produced under different thermodynamic conditions on the (111) surface of the cobalt spinel nano-octahedra. The density of state alignment diagrams between dioxygen and cobalt centers were used to rationalize speciation of the surface oxygen varieties into diatomic superoxo (μ-CoO3c–O2–CoT3c, η2-O2–CoO3c) or intrafacial peroxo ([O–Osurf.]2–) and monoatomic metal–oxo (CoT3c–O, CoO3c–O) entities. It was shown that the surface cobalt cations work in tandem constituting dual CoO3c–CoT3c sites for O2 adsorption, where the CoO3c dxz(β) and dyz(β) states act as spin-polarized electron donor centers, producing the most stable bridging μ-CoO3c–O2–CoT3c adducts (ΔEa = −1.86 eV). The single site mono- and bidentate binding modes η1-O2–CoO3c (ΔEa = −1.66 eV) and η2-O2–CoO3...