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Reactive stability of promising scalable doped ceria materials for thermochemical two-step CO2 dissociation


Jacot, Roger; Naik, J Madhusudhan; Moré, René; Michalsky, Ronald; Steinfeld, Aldo; Patzke, Greta R (2018). Reactive stability of promising scalable doped ceria materials for thermochemical two-step CO2 dissociation. Journal of Materials Chemistry A, 6(14):5807-5816.

Abstract

Metal-doped ceria (Ce1−xMxO2−δ) is an attractive redox-active material for thermo/electrochemical synthesis of renewable fuels due to its high mixed ionic/electronic conductivity and variable valence (Ce4+/Ce3+) and oxygen nonstoichiometry (δ) at high temperatures. Previously, we have investigated all 26 potentially tetravalent dopants for efficient thermochemical splitting of CO2. Here, we fine-tune the dopant activity (x = 0.10 Zr4+, 0.10 Hf4+, 0.07 Ta5+, and 0.05 Nb5+) of all thermally stable ceria materials with an oxygen exchange capacity (OEC) surpassing that of pristine ceria (CeO2−δ), and we employ thermogravimetric analysis to evaluate long-term stability of their OEC over 50 consecutive redox cycles. Each cycle swings between 40 min ceria oxidation with approximately 500 mbar CO2 at 1000 °C and 90 min ceria reduction in about 0.01 mbar O2 at 1500 °C. Along with analyses of phase purity and stability (PXRD), of composition and dopant concentration (EDX and ICP-MS), and of sintering via SEM, the cycling results show long-term stable OEC and kinetics of the oxygen exchange for Zr-, Hf-, and Nb-doped ceria, despite their distinctly sintered particle surfaces. This attractive performance is rationalized by characterizing oxidation states and oxygen vacancies and by excluding surface carbonation through Raman and FT-IR spectroscopy. Furthermore, we find that introducing stable oxygen vacancies in Ce0.95Hf0.05O2−δ by doping with additional 5% lower-valent Li+, Mg2+, Ca2+, Y3+, and Er3+ does not significantly accelerate the oxygen exchange kinetics. From this first comprehensive long-term stability study of systematically optimized ceria, we propose ceria co-doped with permutations of Hf4+, Zr4+, and Nb5+, yielding an optimal average dopant radius of 0.8 Å, as the benchmark redox material for thermochemical production of solar fuels.

Abstract

Metal-doped ceria (Ce1−xMxO2−δ) is an attractive redox-active material for thermo/electrochemical synthesis of renewable fuels due to its high mixed ionic/electronic conductivity and variable valence (Ce4+/Ce3+) and oxygen nonstoichiometry (δ) at high temperatures. Previously, we have investigated all 26 potentially tetravalent dopants for efficient thermochemical splitting of CO2. Here, we fine-tune the dopant activity (x = 0.10 Zr4+, 0.10 Hf4+, 0.07 Ta5+, and 0.05 Nb5+) of all thermally stable ceria materials with an oxygen exchange capacity (OEC) surpassing that of pristine ceria (CeO2−δ), and we employ thermogravimetric analysis to evaluate long-term stability of their OEC over 50 consecutive redox cycles. Each cycle swings between 40 min ceria oxidation with approximately 500 mbar CO2 at 1000 °C and 90 min ceria reduction in about 0.01 mbar O2 at 1500 °C. Along with analyses of phase purity and stability (PXRD), of composition and dopant concentration (EDX and ICP-MS), and of sintering via SEM, the cycling results show long-term stable OEC and kinetics of the oxygen exchange for Zr-, Hf-, and Nb-doped ceria, despite their distinctly sintered particle surfaces. This attractive performance is rationalized by characterizing oxidation states and oxygen vacancies and by excluding surface carbonation through Raman and FT-IR spectroscopy. Furthermore, we find that introducing stable oxygen vacancies in Ce0.95Hf0.05O2−δ by doping with additional 5% lower-valent Li+, Mg2+, Ca2+, Y3+, and Er3+ does not significantly accelerate the oxygen exchange kinetics. From this first comprehensive long-term stability study of systematically optimized ceria, we propose ceria co-doped with permutations of Hf4+, Zr4+, and Nb5+, yielding an optimal average dopant radius of 0.8 Å, as the benchmark redox material for thermochemical production of solar fuels.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
08 Research Priority Programs > Solar Light to Chemical Energy Conversion
Dewey Decimal Classification:540 Chemistry
Scopus Subject Areas:Physical Sciences > General Chemistry
Physical Sciences > Renewable Energy, Sustainability and the Environment
Physical Sciences > General Materials Science
Language:English
Date:1 January 2018
Deposited On:07 Mar 2019 07:38
Last Modified:29 Jul 2020 10:06
Publisher:Royal Society of Chemistry
ISSN:2050-7488
OA Status:Closed
Publisher DOI:https://doi.org/10.1039/c7ta10966k
Project Information:
  • : FunderH2020
  • : Grant ID654408
  • : Project TitleSUN-to-LIQUID - SUNlight-to-LIQUID: Integrated solar-thermochemical synthesis of liquid hydrocarbon fuels
  • : FunderSNSF
  • : Grant ID200021_162435
  • : Project TitleDesign of perovskite and doped-ceria redox materials for high performance solar thermochemical splitting of H2O and CO2

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