Thermochemical Activity of Single- and Dual-Phase Oxide Compounds Based on Ceria, Ferrites, and Perovskites for Two-Step Synthetic Fuel Production.

This study focuses on the generation of solar thermochemical fuel (hydrogen, syngas) from CO 2 and H 2 O molecules via two-step thermochemical cycles involving intermediate oxygen-carrier redox materials. Different classes of redox-active compounds based on ferrite, fluorite, and perovskite oxide structures are investigated, including their synthesis and characterization associated with experimental performance assessment in two-step redox cycles. Their redox activity is investigated by focusing on their ability to perform the splitting of CO 2 during thermochemical cycles while quantifying fuel yields, production rates, and performance stability. The shaping of materials as reticulated foam structures is then evaluated to highlight the effect of morphology on reactivity. A series of single-phase materials including spinel ferrite, fluorite, and perovskite formulations are first investigated and compared to state-of-the-art materials. NiFe 2 O 4 foam exhibits a CO 2 -splitting activity similar to its powder analog after reduction at 1400 °C, surpassing the performance of ceria but with much slower oxidation kinetics. On the other hand, although identified as high-performing materials in other studies, Ce 0.9 Fe 0.1 O 2 , Ca 0.5 Ce 0.5 MnO 3 , Ce 0.2 Sr 1.8 MnO 4 , and Sm 0.6 Ca 0.4 Mn 0.8 Al 0.2 O 3 are not found to be attractive candidates in this work (compared with La 0.5 Sr 0.5 Mn 0.9 Mg 0.1 O 3 ). In the second part, characterizations and performance evaluation of dual-phase materials (ceria/ferrite and ceria/perovskite composites) are performed and compared to single-phase materials to assess a potential synergistic effect on fuel production. The ceria/ferrite composite does not provide any enhanced redox activity. In contrast, ceria/perovskite dual-phase compounds in the form of powders and foams are found to enhance the CO 2 -splitting performance compared to ceria.