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Extreme high temperature redox kinetics in ceria: exploration of the transition from gas-phase to material-kinetic limitations

Ji, Ho-Il and Davenport, Timothy C. and Gopal, Chirranjeevi Balaji and Haile, Sossina M. (2016) Extreme high temperature redox kinetics in ceria: exploration of the transition from gas-phase to material-kinetic limitations. Physical Chemistry Chemical Physics, 18 (31). pp. 21554-21561. ISSN 1463-9076. http://resolver.caltech.edu/CaltechAUTHORS:20160725-124108237

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Abstract

The redox kinetics of undoped ceria (CeO_(2−δ)) are investigated by the electrical conductivity relaxation method in the oxygen partial pressure range of −4.3 ≤ log(pO_2/atm) ≤ −2.0 at 1400 °C. It is demonstrated that extremely large gas flow rates, relative to the mass of the oxide, are required in order to overcome gas phase limitations and access the material kinetic properties. Using these high flow rate conditions, the surface reaction rate constant k_(chem) is found to obey the correlation log(k_(chem)/cm s^(−1)) = (0.84 ± 0.02) × log(pO_2/atm) − (0.99 ± 0.05) and increases with oxygen partial pressure. This increase contrasts the known behavior of the dominant defect species, oxygen vacancies and free electrons, which decrease in concentration with increasing oxygen partial pressure. For the sample geometries employed, diffusion was too fast to be detected. At low gas flow rates, the relaxation process becomes limited by the capacity of the sweep gas to supply/remove oxygen to/from the oxide. An analytical expression is derived for the relaxation in the gas-phase limited regime, and the result reveals an exponential decay profile, identical in form to that known for a surface reaction limited process. Thus, measurements under varied gas flow rates are required to differentiate between surface reaction limited and gas flow limited behavior.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1039/c6cp01935hDOIArticle
http://pubs.rsc.org/en/Content/ArticleLanding/2016/CP/C6CP01935HPublisherArticle
ORCID:
AuthorORCID
Ji, Ho-Il0000-0002-6194-991X
Haile, Sossina M.0000-0002-5293-6252
Additional Information:© 2016 the Owner Societies. Received 23rd March 2016, Accepted 7th July 2016, First published online 18 Jul 2016. This material is based upon work supported by the U.S. Department of Energy, through ARPA-e Contract DE-AR0000182. Support for T. C. D. was provided by an EERE Postdoctoral Research Award.
Funders:
Funding AgencyGrant Number
ARPA-EDE-AR0000182
Record Number:CaltechAUTHORS:20160725-124108237
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20160725-124108237
Official Citation:Extreme high temperature redox kinetics in ceria: exploration of the transition from gas-phase to material-kinetic limitations Ho-Il Ji, Timothy C. Davenport, Chirranjeevi Balaji Gopal and Sossina M. Haile Phys. Chem. Chem. Phys., 2016,18, 21554-21561 DOI: 10.1039/C6CP01935H
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:69199
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:25 Jul 2016 22:03
Last Modified:08 Nov 2017 21:26

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