Screening of Perovskite Materials Utilizing DFT Calculated Oxygen Vacancy Formation Energies As Descriptors for Carbon Dioxide Conversion

CO₂ conversion to useful hydrocarbon fuels has been the prime interest in recent times due to increased global demands for fuel and also to reduce the atmospheric CO₂ for a better climate. Amongst the different CO₂ conversion routes, the thermochemical route of CO₂ conversion to CO has garnered a lot of attention. The thermochemical process works in two simple steps, the first being the creation of oxygen vacancy active sites on mixed metal oxides or perovskite oxides. In the second step, the CO₂ is reduced to CO over these reduced material, thereby regenerating the original materials. Perovskite oxides of the structure ABO₃ have been successfully used for this purpose owing to their high stability in both stoichiometric and oxygen deficient forms. Screening over a vast range of perovskite is hence, necessary to search for better materials. Since, oxygen vacancy formation is a key parameter of the process, oxygen vacancy formation energy has been proposed as an appropriate descriptor for the CO₂ conversion reaction in these cycles. Density functional theory (DFT) calculated energies are being used for this purpose. DFT+U energies are also calculated to account for the Hubbard effect. All the energies have been calculating using the Vienna ab-initio Simulation Package (VASP-5.2.8). Since the perovskites are known to exhibit great stability at mixed metal configurations, we have screened over ABO₃, A1_0.5A2_0.5BO₃ and AB1_0.5B2_0.5O_3. The A, A1, and A2 sites are occupied by one of the following metals La, Sr, Ba, or Ca. The B, B1, and B2 sites are occupied by one of these metals Cr, Mn, Fe, Co, Ni, Cu, Al or Ga. Based on these energies we would like to propose new A1_0.5A2_0.5B1_0.5B2_0.5O₃ type of materials.