(176f) Computational Screening of Oxygen Vacancy Formation for Solar-Driven Isothermal CO2 and H2O Splitting with Metal Oxide Redox Materials

The isothermal splitting of CO₂ and H₂O with concentrated sunlight offers the prospect of an energy-efficient synthesis of renewable fuels since this approach circumvents large temperature swings between the reduction and oxidation steps as well as mechanical stress arising from rapid temperature changes. In analogy to the Sabatier principle in heterogeneous catalysis, this talk presents a volcano-like correlation of the thermodynamic redox equilibrium energetics of 29 solid bulk metal oxides that can be employed for the rational design of metal oxides redox materials. Since the underpinning thermochemical data is only available for a limited number of complex metal oxides, electronic structure calculations are employed to compute the formation of oxygen vacancies at the surfaces of TiO₂, Ti₂O₃, Cu₂O, ZnO, ZrO₂, YSZ, MoO₃, Ag₂O, CeO₂ and three perovskites. We find that the free energy of formation of the bulk metal oxides scales with the free energy of the oxygen vacancy formation at the surface which can be employed to estimate unknown free energies of formation for complex metal oxide solutions. The tendency of surface oxygen vacancies to migrate into the bulk is discussed based on density functional theory computations of sub-surface oxygen vacancies and the obtained trend is compared to the experimental oxygen self-diffusion constants.