Oxygen reduction reactions in the SOFC cathode of Ag/CeO2

Jeng-Han Wang, Mei Lin Liu, M. C. Lin

Research output: Contribution to journalArticle

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Abstract

The interactions between oxygen molecules and a silver surface or a CeO2(111) supported atomic layer of silver are predicted using first-principles calculations based on spin polarized DFT with PAW method. The juncture between the CeO2(111), the atomic layer of silver, and O2 represents a triple-phase boundary (TPB) whereas the interface between silver surfaces and O2 corresponds to a 2-phase boundary (2PB) in a solid oxide fuel cell (SOFC). Results suggest that the O2 dissociation process on a monolayer of silver supported by CeO2(111) surfaces (or TPB) with oxygen vacancies has lower reaction barrier than on silver surfaces (or 2PB), and the dissociated oxygen ions can quickly bond with subsurface Ce atom via a barrierless and highly exothermic reaction. The oxygen vacancies at TPB are found to be responsible for the lower energy barrier and high exothermicity because of the strong interaction between subsurface Ce and adspecies, implying that oxygen molecules prefer being reduced at TPB than on silver surfaces (2PB). The results suggest that, for a silver-based cathode in a SOFC, the adsorption and dissociation of oxygen occur rapidly and the most stable surface oxygen species would be the dissociated oxygen ion with - 0.78|e| Bader charges; the rate of oxygen reduction is most likely limited by subsequent processes such as diffusion or incorporation of the oxygen ions into the electrolyte.

Original languageEnglish
Pages (from-to)939-947
Number of pages9
JournalSolid State Ionics
Volume177
Issue number9-10
DOIs
Publication statusPublished - 2006 Mar 31

Fingerprint

cell cathodes
solid oxide fuel cells
Solid oxide fuel cells (SOFC)
Silver
Phase boundaries
Cathodes
silver
Oxygen
oxygen
oxygen ions
Oxygen vacancies
Ions
dissociation
Molecules
Exothermic reactions
exothermic reactions
Energy barriers
Discrete Fourier transforms
Electrolytes
molecules

Keywords

  • Ceria (CeO)
  • First-principles calculations
  • Silver surface
  • Solid state oxide fuel cell (SOFC)
  • Triple phase boundary (TPB)

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics

Cite this

Oxygen reduction reactions in the SOFC cathode of Ag/CeO2. / Wang, Jeng-Han; Liu, Mei Lin; Lin, M. C.

In: Solid State Ionics, Vol. 177, No. 9-10, 31.03.2006, p. 939-947.

Research output: Contribution to journalArticle

Wang, Jeng-Han ; Liu, Mei Lin ; Lin, M. C. / Oxygen reduction reactions in the SOFC cathode of Ag/CeO2. In: Solid State Ionics. 2006 ; Vol. 177, No. 9-10. pp. 939-947.
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AB - The interactions between oxygen molecules and a silver surface or a CeO2(111) supported atomic layer of silver are predicted using first-principles calculations based on spin polarized DFT with PAW method. The juncture between the CeO2(111), the atomic layer of silver, and O2 represents a triple-phase boundary (TPB) whereas the interface between silver surfaces and O2 corresponds to a 2-phase boundary (2PB) in a solid oxide fuel cell (SOFC). Results suggest that the O2 dissociation process on a monolayer of silver supported by CeO2(111) surfaces (or TPB) with oxygen vacancies has lower reaction barrier than on silver surfaces (or 2PB), and the dissociated oxygen ions can quickly bond with subsurface Ce atom via a barrierless and highly exothermic reaction. The oxygen vacancies at TPB are found to be responsible for the lower energy barrier and high exothermicity because of the strong interaction between subsurface Ce and adspecies, implying that oxygen molecules prefer being reduced at TPB than on silver surfaces (2PB). The results suggest that, for a silver-based cathode in a SOFC, the adsorption and dissociation of oxygen occur rapidly and the most stable surface oxygen species would be the dissociated oxygen ion with - 0.78|e| Bader charges; the rate of oxygen reduction is most likely limited by subsequent processes such as diffusion or incorporation of the oxygen ions into the electrolyte.

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