title: Ce K edge XAS of ceria-based redox materials under realistic conditions for the two-step solar thermochemical dissociation of water and/or CO2.
abstract: X-ray absorption spectroscopy was used to characterise ceria-based materials under realistic conditions present in a reactor for solar thermochemical two-step water and carbon dioxide splitting. A setup suitable for in situ measurements in transmission mode at the cerium K edge from room temperature up to 1773 K is presented. Time-resolved X-ray absorption near-edge structure (XANES) data, collected for a 10 mol% hafnium-doped ceria sample (Ce0.9Hf0.1O2-δ) during reduction at 1773 K in a flow of inert gas and during re-oxidation by CO2 at 1073 K, enables the quantitative determination of the non-stoichiometry δ of the fluorite-type structure. XANES analysis suggests the formation of the hexagonal Ce2O3 phase upon reduction in 2% hydrogen/helium at 1773 K. We discuss the experimental limitations and possibilities of high-temperature in situ XAS at edges of lower energy as well as the importance of the technique for understanding and improving the properties of ceria-based oxygen storage materials for thermochemical solar energy conversion.
authors.affiliation: Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
authors.forename: Matthäus
authors.initials: M
authors.lastname: Rothensteiner
authors.forename: Simone
authors.initials: S
authors.lastname: Sala
authors.forename: Alexander
authors.initials: A
authors.lastname: Bonk
authors.forename: Ulrich
authors.initials: U
authors.lastname: Vogt
authors.forename: Hermann
authors.initials: H
authors.lastname: Emerich
authors.forename: Jeroen A
authors.initials: JA
authors.lastname: van Bokhoven