In Honor of Nobel Laureate Prof. M Stanley Whittingham
| EXPLORING THE REDOX PROPERTIES IN THE CeO2-UO2 SYSTEM Lee Shelly1; Shmulik Hayun1; Brian Rosen2; Danielle Schweke3; Albert Danon4; 1BEN-GURION UNIVERSITY OF THE NEGEV, Beer-Sheva, Israel; 2DEPARTMENT OF MATERIALS SCIENCE AND ENGINEERING, TEL AVIV UNIVERSITY,, Tel Aviv, Israel; 3NUCLEAR RESEARCH CENTRE - NEGEV, Beer-Sheva, Israel; 4NUCLEAR RESEARCH CENTRE - NEGEV, Beer-Sheva, Israel; PAPER: 53/Geochemistry/Regular (Oral) OS SCHEDULED: 15:15/Wed. 29 Nov. 2023/Coral Reef ABSTRACT: The Ce-U-O system has gained much attention due to its relevance to the nuclear industry and its unique properties (the Ce and U cations form a complete solid solution in the fluorite structure and can withstand different possible oxidation states). Mixed fluorite oxide powders of Ce1-xUxO2±δ; compositions were also found to be particularly active for H2 production through thermochemical water splitting. In the present work, we explore the reduction-oxidation properties of the mixed oxides with x=0.1, 0.25, and 0.5. We report a particularly high oxygen Storage capacity (OSC) for x≥0.25 and show that the oxygen extracted from those mixed oxides is of a different origin than that extracted from CeO2. While in ceria, oxygen is extracted from the tetrahedral sites, leading to the formation of oxygen vacancies, the extracted oxygen in Ce1-xUxO2±δ (x≥0.25) is essentially excess oxygen in the fluorite lattice (which penetrates the oxide in ambient or oxidative conditions spontaneously). This property, which is clearly related to the change of valency of the U cations, allows for a higher OSC and lower activation energy for oxygen extraction from the mixed oxides compared to ceria. The mixed oxide powders are shown to be structurally stable, retaining their fluorite structure following reduction under Ar-5%H2 until 1000°C or oxidation in air until 1000°C. The presented results provide new insights into the Ce-U-O system, which may be exploited for future technical applications, for thermochemical water splitting or as a solid electrolyte. References: 1. D. Schweke, Y. Mordehovitz, M. Halabi, L. Shelly, S. Hayun, Defect Chemistry of Oxides for Energy Applications, Adv. Mater. 30 (2018). https://doi.org/10.1002/adma.201706300 2. L. Shelly, D. Schweke, S. Zalkind, N. Shamir, S. Barzilai, T. Gouder, S. Hayun, Effect of U Content on the Activation of H2O on Ce<sub>1-x</sub>U<sub>x</sub>O<sub>2+δ</sub> Surfaces, Chem. Mater. 30 (2018) 8650–8660. https://doi.org/10.1021/acs.chemmater.8b03894. 3. Guo, X., Wu, D., Ushakov, S.V. et al. Energetics of hydration on uranium oxide and peroxide surfaces. Journal of Materials Research 34, 3319–3325 (2019). https://doi.org/10.1557/jmr.2019.192 |
