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  Ambient Pressure XPS Study of Mixed Conducting Perovskite-type SOFC Cathode and Anode Materials under Well-Defined Electrochemical Polarization

Nenning, A., Opitz, A. K., Rameshan, C., Rameshan, R., Blume, R., Hävecker, M., et al. (2016). Ambient Pressure XPS Study of Mixed Conducting Perovskite-type SOFC Cathode and Anode Materials under Well-Defined Electrochemical Polarization. The Journal of Physical Chemistry C, 120(3), 1461-1471. doi:10.1021/acs.jpcc.5b08596.

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 Creators:
Nenning, Andreas1, Author
Opitz, Alexander K.1, Author
Rameshan, Christoph1, Author
Rameshan, Raffael2, Author           
Blume, Raoul2, Author           
Hävecker, Michael2, Author           
Knop-Gericke, Axel2, Author           
Rupprechter, Günther1, Author
Klötzer, Bernhard3, Author
Fleig, Jürgen1, Author
Affiliations:
1Department of Chemistry, TU Vienna, Getreidemarkt 9, 1060 Vienna, Austria, ou_persistent22              
2Inorganic Chemistry, Fritz Haber Institute, Max Planck Society, ou_24023              
3Department of Physical Chemistry, University of Innsbruck, Innrain 80-82, 6020 Innsbruck, Austria, ou_persistent22              

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 Abstract: The oxygen exchange activity of mixed conducting oxide surfaces has been widely investigated, but a detailed understanding of the corresponding reaction mechanisms and the rate-limiting steps is largely still missing. Combined in situ investigation of electrochemically polarized model electrode surfaces under realistic temperature and pressure conditions by near-ambient pressure (NAP) XPS and impedance spectroscopy enables very surface-sensitive chemical analysis and may detect species that are involved in the rate-limiting step. In the present study, acceptor-doped perovskite-type La0.6Sr0.4CoO3-δ (LSC), La0.6Sr0.4FeO3-δ (LSF), and SrTi0.7Fe0.3O3-δ (STF) thin film model electrodes were investigated under well-defined electrochemical polarization as cathodes in oxidizing (O2) and as anodes in reducing (H2/H2O) atmospheres. In oxidizing atmosphere all materials exhibit additional surface species of strontium and oxygen. The polaron-type electronic conduction mechanism of LSF and STF and the metal-like mechanism of LSC are reflected by distinct differences in the valence band spectra. Switching between oxidizing and reducing atmosphere as well as electrochemical polarization cause reversible shifts in the measured binding energy. This can be correlated to a Fermi level shift due to variations in the chemical potential of oxygen. Changes of oxidation states were detected on Fe, which appears as FeIII in oxidizing atmosphere and as mixed FeII/III in H2/H2O. Cathodic polarization in reducing atmosphere leads to the reversible formation of a catalytically active Fe0 phase.

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 Dates: 2015-09-032015-122015-12-172016-01-28
 Publication Status: Published in print
 Pages: 11
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1021/acs.jpcc.5b08596
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Title: The Journal of Physical Chemistry C
  Abbreviation : J. Phys. Chem. C
Source Genre: Journal
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Publ. Info: Washington DC : American Chemical Society
Pages: 11 Volume / Issue: 120 (3) Sequence Number: - Start / End Page: 1461 - 1471 Identifier: ISSN: 1932-7447
CoNE: https://pure.mpg.de/cone/journals/resource/954926947766