Solar Redox Cycling of Ceria Structures Based on Fiber Boards, Foams, and Biomimetic Cork-Derived Ecoceramics for Two-Step Thermochemical H2O and CO2 Splitting
Résumé
Solar thermochemical conversion of H 2 O and captured CO 2 is considered for the production of high-value solar fuels and CO 2 valorization, using non-stoichiometric oxygen-exchange redox materials. This work aims to compare the thermochemical cycle performance of different ceria structures, including biomimetic cork-templated ceria (CTCe), ceria foam (CeF) and ceria bulk fiber (CeFB), to study the effect of the morphology on fuel production from two-step H 2 O and CO 2 splitting via solar redox cycling. The considered materials underwent thermochemical cycles in a directly-irradiated solar reactor under various operating conditions. Typically, a thermal reduction at 1400 °C under Ar at atmospheric pressure, using concentrated solar energy, was carried out followed by an oxidation step with H 2 O or CO 2 between 800°C-1050°C. The comparison of the fuel production rate and yield from the reactive materials highlighted the importance of the material thermal stability during cycling. CTCe and CeF showed a good O 2 and fuel production stability over repeated cycles, while CeFB exhibited a decrease of the production because of sintering and thermal gradient due to its low thermal conductivity. Biomimetic CTCe showed a higher fuel production rate compared to the other investigated materials, explained by the favorable microstructure of the cork-based ceramic. The morphology obtained from the cork structure led to the improvement of the redox activity, demonstrating the relevance of studying this material for thermochemical H 2 O and CO 2 splitting cycles. In addition, the impact of the operating conditions was investigated. A decrease of the starting oxidation temperature, an increase of the CO 2 molar fraction (lower CO:CO 2 ratio) or a high total gas flow rate favoring gas product dilution had beneficial impact on the CO (or H 2) production rate.
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