(748g) Materials Design for Thermochemical Oxygen Separation Via Perovskite-Based Redox Cycling

The separation and concentration of O₂ from gas mixtures is of great importance for various sustainable energy technologies, such as solar fuel production via thermochemical splitting of CO₂ and H₂O into CO and H₂, the feedstock for the synthesis of hydrocarbon fuels and chemicals. A rationale is introduced to design perovskites for oxygen separation via “thermochemical pumping” of O₂ against a pO₂ gradient with low-grade process heat. We show that the ideal oxygen exchange capacity of perovskites can be determined from the activity of oxygen vacancies quantified with electronic structure computations. The predicted material properties are validated by thermogravimetric analysis and high-temperature X-ray diffraction for SrCoO_3-δ, BaCoO_3-δ and BaMnO_3-δ perovskites and Ag₂O and Cu₂O metal oxide references. These measurements confirm that the performance of SrCoO_3-δ - having an oxygen exchange capacity of 44 mmol O₂ mol^-1 SrCoO_3-δ and an oxygen exchange rate of 12.1 µmol O₂ min^-1 g^-1 at 600-900 K - surpasses the performance of state-of-the-art Cu₂O at the same conditions. We show how the presented redox trends can be understood due to lattice expansion and the magnitude of electronic charge transfer.