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

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 variedmore » gas flow rates are required to differentiate between surface reaction limited and gas flow limited behavior.« less

Authors:
 [1];  [2];  [3];  [4]
  1. Northwestern Univ., Evanston, IL (United States). Materials Science and Engineering; California Inst. of Technology (CalTech), Pasadena, CA (United States). Materials Science
  2. Northwestern Univ., Evanston, IL (United States). Materials Science and Engineering
  3. California Inst. of Technology (CalTech), Pasadena, CA (United States). Materials Science
  4. Northwestern Univ., Evanston, IL (United States). Materials Science and Engineering and Applied Physics; California Inst. of Technology (CalTech), Pasadena, CA (United States). Materials Science and Chemistry and Chemical Engineering
Publication Date:
Research Org.:
Univ. of Minnesota, Minneapolis, MN (United States)
Sponsoring Org.:
USDOE Advanced Research Projects Agency - Energy (ARPA-E); USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
1437253
Grant/Contract Number:  
AR0000182
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physical Chemistry Chemical Physics. PCCP (Print)
Additional Journal Information:
Journal Name: Physical Chemistry Chemical Physics. PCCP (Print); Journal Volume: 18; Journal Issue: 31; Journal ID: ISSN 1463-9076
Publisher:
Royal Society of Chemistry
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE

Citation Formats

Ji, Ho-Il, Davenport, Timothy C., Gopal, Chirranjeevi Balaji, and Haile, Sossina M. Extreme high temperature redox kinetics in ceria: exploration of the transition from gas-phase to material-kinetic limitations. United States: N. p., 2016. Web. doi:10.1039/c6cp01935h.
Ji, Ho-Il, Davenport, Timothy C., Gopal, Chirranjeevi Balaji, & Haile, Sossina M. Extreme high temperature redox kinetics in ceria: exploration of the transition from gas-phase to material-kinetic limitations. United States. doi:10.1039/c6cp01935h.
Ji, Ho-Il, Davenport, Timothy C., Gopal, Chirranjeevi Balaji, and Haile, Sossina M. Mon . "Extreme high temperature redox kinetics in ceria: exploration of the transition from gas-phase to material-kinetic limitations". United States. doi:10.1039/c6cp01935h. https://www.osti.gov/servlets/purl/1437253.
@article{osti_1437253,
title = {Extreme high temperature redox kinetics in ceria: exploration of the transition from gas-phase to material-kinetic limitations},
author = {Ji, Ho-Il and Davenport, Timothy C. and Gopal, Chirranjeevi Balaji and Haile, Sossina M.},
abstractNote = {The redox kinetics of undoped ceria (CeO2-δ) are investigated by the electrical conductivity relaxation method in the oxygen partial pressure range of -4.3 ≤ log(pO2/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 kchem is found to obey the correlation log(kchem/cm s-1) = (0.84 ± 0.02) × log(pO2/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.},
doi = {10.1039/c6cp01935h},
journal = {Physical Chemistry Chemical Physics. PCCP (Print)},
number = 31,
volume = 18,
place = {United States},
year = {Mon Jul 18 00:00:00 EDT 2016},
month = {Mon Jul 18 00:00:00 EDT 2016}
}

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Works referenced in this record:

A thermodynamic study of nonstoichiometric cerium dioxide
journal, November 1975

  • Panlener, R. J.; Blumenthal, R. N.; Garnier, J. E.
  • Journal of Physics and Chemistry of Solids, Vol. 36, Issue 11, p. 1213-1222
  • DOI: 10.1016/0022-3697(75)90192-4