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

Authors: 
Ezbiri, M., ETH Zurich
Allen, K. M., Sandia National Laboratories
Michalsky, R., ETH Zurich
Gálvez, M. E., Sorbonne Universités, UPMC, Univ. Paris 6
Steinfeld, A., ETH Zurich

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 SrCoO3-δ, BaCoO3-δ and BaMnO3-δ perovskites and Ag2O and Cu2O metal oxide references. These measurements confirm that the performance of SrCoO3-δ - having an oxygen exchange capacity of 44 mmol O2 mol-1 SrCoO3-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.