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An investigation of ceria's oxygen storage capacity by computer simulation

An investigation of ceria's oxygen storage capacity by computer simulation. Beth Savoy May 2007. Outline. Introduction Applications of ceria Ceria lattice Simulation technique Results Conclusions. Introduction. Oxygen storage capacity High oxygen ion conductivity (500-800 ° C)

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An investigation of ceria's oxygen storage capacity by computer simulation

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  1. An investigation of ceria's oxygen storage capacity by computer simulation Beth Savoy May 2007

  2. Outline • Introduction • Applications of ceria • Ceria lattice • Simulation technique • Results • Conclusions

  3. Introduction • Oxygen storage capacity • High oxygen ion conductivity (500-800 °C) • What is studied? • Reduction energy • Defect cluster formation • Full range of mixed oxide Ce(1-x)ZrxO2

  4. Applications • Automotive catalyst • Store oxygen in lean conditions / release in rich conditions to remove pollutants • Electrolyte in solid oxide fuel cells (doped) • Oxygen ions move through ceria • Oxygen sensor • Self-cleaning oven

  5. Ce Ce Ce O O Ce Ce O O Ce Ce Lattice • 4f15d16s2 • Fluorite structure • CeOx 1.71<x<2

  6. LatticeHoles

  7. SimulationGULP energy minimization • Born-model – spherical, ionically charged • Energy contributions (Ewald)

  8. SimulationPotential parameters

  9. mass charge spring spring constant potential C6 term SimulationMean-field approximation • Ce(1-x)ZrxO2

  10. ResultsLattice constant

  11. SimulationMott-Littleton point defect model ∞ Continuum (fixed lattice positions) r1 Explicit relaxation

  12. SimulationVacancy formation Release of oxygen gas Ce4+ at cation lattice point Ce3+ at cation lattice point O2- at anion lattice point Oxygen vacancy

  13. SimulationDecomposition of rxn

  14. Balducci et. al (2000) Ewald c6 ResultsReduction energies

  15. Conclusions • Mean-field approximation good for Ce(1-x)ZrxO2 mixed oxide • Addition of ZrO2 above 50% lowers reduction energy • Association of defect clusters further lowers reduction energy • Ewald summation of short-range attractive terms important for convergence

  16. Future work • Surface reduction energies • Already reduced structures • Oxygen migration activation energy Balducci et. al.

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