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

Andreas Nenning | Zendy; Alexander K. Opitz | Zendy; Christoph Rameshan | Zendy; Raffael Rameshan | Zendy; Raoul Blume | Zendy; Michael Hävecker | Zendy; Axel KnopGericke | Zendy; Günther Rupprechter | Zendy; Bernhard Klötzer | Zendy; Jürgen Fleig | Zendy

Open Access

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

Author(s) -

Andreas Nenning,

Alexander K. Opitz,

Christoph Rameshan,

Raffael Rameshan,

Raoul Blume,

Michael Hävecker,

Axel KnopGericke,

Günther Rupprechter,

Bernhard Klötzer,

Jürgen Fleig

Publication year - 2015

Publication title -

the journal of physical chemistry c

Language(s) - English

Resource type - Journals

SCImago Journal Rank - 1.401

H-Index - 289

eISSN - 1932-7455

pISSN - 1932-7447

DOI - 10.1021/acs.jpcc.5b08596

Subject(s) - polarization (electrochemistry) , ambient pressure , oxidizing agent , materials science , cathode , partial pressure , x ray photoelectron spectroscopy , oxide , reducing atmosphere , electrochemistry , perovskite (structure) , oxygen , dielectric spectroscopy , analytical chemistry (journal) , inorganic chemistry , chemistry , electrode , chemical engineering , thermodynamics , metallurgy , physics , organic chemistry , chromatography , engineering , crystallography

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 La 0.6 Sr 0.4 CoO 3-δ (LSC), La 0.6 Sr 0.4 FeO 3-δ (LSF), and SrTi 0.7 Fe 0.3 O 3-δ (STF) thin film model electrodes were investigated under well-defined electrochemical polarization as cathodes in oxidizing (O 2 ) and as anodes in reducing (H 2 /H 2 O) 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 Fe III in oxidizing atmosphere and as mixed Fe II/III in H 2 /H 2 O. Cathodic polarization in reducing atmosphere leads to the reversible formation of a catalytically active Fe 0 phase.

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