Perovskite Monolithic Structures for Solar-Powered Thermochemical Redox Cycles

Abstract

The utilization of solar heat offers great potential in the context of energy supply. Solar heat can play an essential role overcoming challenges of the industrial transfer away from fossil energy sources. Concentrated solar heat is versatile and can be used to produce electricity, supply thermal energy in industrial processes or to drive chemical reactions. Thermochemical redox cycles, powered by concentrated solar heat, have shown promising results in a variety of processes within the past years. They can be utilized in the context of water and carbondioxide splitting for syngas production, energy storage, oxygen pumping and air separation. Perovskites in the form of ABO3 mixed metal oxides are a versatile material class for such thermochemical redox cycles. The large number of possible compositions, available through the formation of solid solutions with various Aand B-site cations, allow fine tuning of thermodynamic characteristics of the material in order to fit the requirements of a desired process. Furthermore, perovskites can be reduced and oxidized non-stoichiometrically, meaning they do not undergo severe changes in their crystal structure upon reduction and oxidation. Especially in applications where threedimensional structures are utilized, structural stability is of utter importance. In this context, perovskites can be beneficial in comparison to competing redox systems, such as Mn 2O3/Mn3O4 and Fe2O3/Fe3O4, due to their favorable thermodynamic, kinetic and thermomechanic characteristics. The presented work focuses on so-called down-stream processes, such as thermal and thermochemical energy storage and thermochemical oxygen pumping. These processes are performed away from a solar receiver and require temperatures up to 1100 °C. This work covers the complete chain of development from screening of suitable perovskite compositions in small-scale test-setups and analysis techniques, over the production of stable, open porous, monolithic structures of identified compositions, the characterization of such structures and the demonstration of their utilization in a lab-scale reactor. The results showed that open porous structures made from CaMnO3 and its A-site Srsubstituted variants offer great potential for thermochemical energy storage and thermochemical oxygen pumping. In this context, Ca0.9Sr0.1MnO3-δ was shown to be a particularly promising material composition for the utilization of monolithic open porous strucures.