Design Principles of Perovskites for Thermochemical Oxygen Separation

Separation and concentration of O2 from gas mixtures is central to several sustainable energy technologies, such as solar‐driven synthesis of liquid hydrocarbon fuels from CO2, H2O, and concentrated sunlight. We introduce a rationale for designing metal oxide redox materials for oxygen separation through “thermochemical pumping” of O2 against a pO2 gradient with low‐grade process heat. Electronic structure calculations show that the activity of O vacancies in metal oxides pinpoints the ideal oxygen exchange capacity of perovskites. Thermogravimetric analysis and high‐temperature X‐ray diffraction for SrCoO3−δ, BaCoO3−δ and BaMnO3−δ perovskites and Ag2O and Cu2O references confirm the predicted performance of SrCoO3−δ, which surpasses the performance of state‐of‐the‐art Cu2O at these conditions with an oxygen exchange capacity of 44 mmol O 2 mol SrCoO 3−δ−1 exchanged at 12.1 μmol O 2 min−1 g−1 at 600–900 K. The redox trends are understood due to lattice expansion and electronic charge transfer. Heat and pump thermochemically: Gas‐phase O2 separation often limits the solar‐to‐fuel energy conversion efficiency of solar‐driven thermochemical H2O and CO2 splitting. A method is proposed by which O2 is separated from gas mixtures through “pumping” O2 against a partial pressure gradient using metal oxide redox materials and low‐temperature solar‐thermal process heat. Design principles for perovskite reactants are developed and demonstrated.