Perovskite redox materials for renewable hydrogen generation : exploration and synthesis of perovskite-type oxides for Chemical Looping applications

The transition towards sustainable energy systems necessitates the development of efficient methods for green hydrogen production. This master's thesis investigates the potential of perovskite-type oxides (ABO3-δ) as oxygen carriers for Chemical Looping systems, specifically for hydrogen generation via the Steam-Iron Process (SIP). Unlike traditional iron oxides, perovskites offer a flexible structure that allows for the tuning of redox properties and thermal stability through ionic substitution. The master thesis focuses on the synthesis and characterization of a series of perovskites based on calcium (Ca), lanthanum (La), iron (Fe), and manganese (Mn). A reproducible synthesis methodology was established to prepare 13 samples with different compositions and stoichiometries between them. The structural integrity and phase purity of the synthesized materials were evaluated using X-ray Diffraction (XRD), while the oxygen exchange capacity and redox kinetics were analysed via Thermogravimetric Analysis (TGA) under isothermal reduction and oxidation cycles with CO and CO2, respectively, at 800 °C. XRD results confirmed that manganate-based perovskites, such as CaMnO3 and LaMnO3, achieved high structural fidelity, whereas pure ferrites exhibited incomplete stabilization and the presence of secondary phases. TGA revealed that iron- containing structures demonstrate a higher capacity for oxygen release (vacancy formation) but lower thermal stability. Conversely, calcium substitution at the A-site enhanced thermal stability but was found to reduce reaction kinetics in certain compositions. The primary conclusion of this study identifies Sample 4 (LaFeO3) and Sample 13 (Ca0.5La0.5FeO3-δ) as the most promising candidates. These specific compositions demonstrated a synergistic effect between iron, lanthanum and calcium, outperforming other compounds due to its exceptional CO2 splitting performance (high Oxygen Exchange Capacity) and rapid oxidation kinetics, validating its suitability for continuous hydrogen production in fluidized bed systems.