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

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

• Beth Savoy
• May 2007

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Outline

• Introduction
• Applications of ceria
• Ceria lattice
• Simulation technique
• Results
• Conclusions

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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

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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

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Lattice

• 4f15d16s2
• Fluorite structure
• CeOx 1.71ltxlt2

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LatticeHoles
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SimulationGULP energy minimization

• Born-model spherical, ionically charged
• Energy contributions (Ewald)

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SimulationPotential parameters
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SimulationMean-field approximation
Ce(1-x)ZrxO2
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ResultsLattice constant
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SimulationMott-Littleton point defect model
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Continuum (fixed lattice positions)
r1
Explicit relaxation
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SimulationVacancy formation
Release of oxygen gas
Ce4 at cation lattice point
Ce3 at cation lattice point
O2- at anion lattice point
Oxygen vacancy
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SimulationDecomposition of rxn
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ResultsDefect energies
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ResultsReduction energies
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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

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Future work

• Surface reduction energies
• Already reduced structures
• Oxygen migration activation energy

Balducci et. al.
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