The Chemical Evolution of the La0.6Sr0.4CoO3−Δ Surface Under SOFC Operating Conditions and Its Implications for Electrochemical Oxygen Exchange Activity

Alexander Karl Opitz, Christoph Rameshan, Markus Kubicek, Ghislain M. Rupp, Andreas Nenning, Thomas Götsch, Raoul Blume, Michael Hävecker, Axel Knop-Gericke, Günther Rupprechter, Bernhard Klötzer, Jürgen Fleig

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Abstract

Owing to its extraordinary high activity for catalysing the oxygen exchange reaction, strontium doped LaCoO3 (LSC) is one of the most promising materials for solid oxide fuel cell (SOFC) cathodes. However, under SOFC operating conditions this material suffers from performance degradation. This loss of electrochemical activity has been extensively studied in the past and an accumulation of strontium at the LSC surface has been shown to be responsible for most of the degradation effects. The present study sheds further light onto LSC surface changes also occurring under SOFC operating conditions. In-situ near ambient pressure X-ray photoelectron spectroscopy measurements were conducted at temperatures between 400 and 790 °C. Simultaneously, electrochemical impedance measurements were performed to characterise the catalytic activity of the LSC electrode surface for O2 reduction. This combination allowed a correlation of the loss in electro-catalytic activity with the appearance of an additional La-containing Sr-oxide species at the LSC surface. This additional Sr-oxide species preferentially covers electrochemically active Co sites at the surface, and thus very effectively decreases the oxygen exchange performance of LSC. Formation of precipitates, in contrast, was found to play a less important role for the electrochemical degradation of LSC.
Original languageEnglish
Pages (from-to)2129-2141
Number of pages13
JournalTopics in catalysis
Volume61.2018
Issue number20
Early online date20 Oct 2018
DOIs
Publication statusPublished - 1 Dec 2018
Externally publishedYes

Bibliographical note

Publisher Copyright: © 2018, The Author(s).

Keywords

  • Impedance spectroscopy
  • NAP-XPS
  • Oxygen reduction
  • Perovskite-type electrode
  • SOFC cathode
  • Strontium segregation

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