Tailoring of material properties in pervskites for solar thermochemical applications

Kurzfassung

In light of the negative impact of CO2 emissions on the climate, the industry needs to transition to a fossil-free one. Due to the fluctuating nature of renewable energies, such as wind and solar, energy storage gains in importance. Thermochemical energy storage serves as an excellent long-term and seasonal storage. Here, one important and already well-established chemical commodity is ammonia. To produce fossil-free ammonia, green nitrogen is required. Green nitrogen can be produced sustainably using solar thermochemical cycles. The selected redox material is crucial for efficiency and operating conditions, such as temperatures. Perovskites have emerged as a suitable material class for this purpose. Perovskites have the advantage that they can be composed of many different elements. Thus, understanding the impact of partial elemental substitution in perovskites is essential to tailor the material properties. The impact of partial substitution on the crystal structure is analyzed by X-ray diffraction (XRD) applying the Rietveld refinement, high-temperature XRD, and complemented with the analysis of molecular vibrations by Raman spectroscopy. Thermodynamical changes are analyzed by thermogravimetric analysis (TGA) applying the van’t Hoff approach. The results reveal that the changes in the crystal structure impact the thermodynamic properties. The reduction and oxidation kinetics are as well analyzed by TGA. This work shows that oxidation kinetics can be affected by both element substitution and microstructural changes. Finally, the impact of the material composition on the energetic requirements for an air separation process is analyzed by thermodynamic-based energy calculations. Small-scale packed-bed reactor experiments validate them. All in all, this work highlights the effects of partial element substitution and microstructure on the perovskite properties in terms of efficiency and operating conditions. Understanding these effects enables tailoring of material properties for solar thermochemical applications to get the right feature.