Impact of humid atmospheres on oxygen exchange properties, surface-near elemental composition, and surface morphology of La0.6Sr0.4CoO3−δ

Bucher, Edith; Sitte, Werner; Klauser, Frederik; Bertel, E.

doi:10.1016/j.ssi.2011.12.005

Cited by 96 publications

(100 citation statements)

References 22 publications

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“…6a the elemental depth profiles of the non-degraded LSC sample are depicted, confirming a homogenous composition within the first 200 nm of the sample. Abrupt changes in the topmost layer are an artifact originating from carbon or hydrate/hydroxyl species adsorbed at the surface [18]. Indeed, significant amounts of carbon have been detected by XPS before the first sputtering step but are omitted from the profiles in Figs.…”

Section: X-ray Photoelectron Spectroscopymentioning

confidence: 99%

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Long-term stability of the IT-SOFC cathode materials La0.6Sr0.4CoO3−δ and La2NiO4+δ against combined chromium and silicon poisoning

et al. 2015

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Long-term degradation effects of combined Cr-and Si-poisoning on the promising IT-SOFC cathode materials La 0.6 Sr 0.4 CoO 3-δ and La 2 NiO 4+δ were investigated at 700°C in dry and humid atmospheres for subsequent periods of 1000 hours using dcconductivity relaxation measurements. Degradation-induced changes in chemical composition and morphology of the contaminated sample surfaces were studied by atomic force microscopy, X-ray photoelectron spectroscopy and scanning electron microscopy with energy and wavelength dispersive X-ray analysis. Upon exposure to humid, Cr-and Si-containing gas flows both materials exhibit a strong decrease of the chemical surface exchange coefficient of oxygen by a factor 110 and 40 for La 0.6 Sr 0.4 CoO 3-δ and La 2 NiO 4+δ , respectively, which can be attributed to the formation of Cr-containing crystallites on the degraded sample surfaces. Post-test analyses confirm large amounts of Cr accompanied by a Sr-enrichment within the first 600 nm of the surface of La 0.6 Sr 0.4 CoO 3-δ , indicating the decomposition of the perovskite phase by SrCrO 4 -formation. For La 2 NiO 4+δ the penetration depth of chromium is significantly less and Cr-traces up to a depth of up to 140 nm were determined by depth profiling. For both compounds silicon was found to spread in small patches across the entire sample surface as determined by elemental mapping analysis.

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Section: X-ray Photoelectron Spectroscopymentioning

confidence: 99%

“…On this latter point Sr appears to play an important role, since it is used as a substituent in many cathode materials and has often been observed in reaction phases like Sr-silicates [11,17,18] and SrCrO 4 [2,19]. Judging from thermodynamic stabilities calcium and barium are expected to have a similar tendency to chromate formation [20].…”

Section: Introductionmentioning

confidence: 99%

Long-term stability of the IT-SOFC cathode materials La0.6Sr0.4CoO3−δ and La2NiO4+δ against combined chromium and silicon poisoning

et al. 2015

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“…Still, most of the Sr segregation observations have been made on thin film samples, where it is straightforward to measure surface composition using techniques such as X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and secondary ion mass spectrometry (SIMS). [12][13][14][15] Recently Rupp et al 16 reported a novel technique utilizing chemical etching with on-line inductively coupled plasma optical emission spectrometry (ICP-OES) detection to successfully quantify Sr-rich surface phases on dense La 0.6 Sr 0.4 CoO 3-δ (LSC) thin films. There is only one report of a measurement of a practical porous LSCF electrode that showed Sr segregation, measured via XPS, along with electrochemical performance degradation.…”

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confidence: 99%

Mechanisms of Performance Degradation of (La,Sr)(Co,Fe)O_3-δSolid Oxide Fuel Cell Cathodes

Wang

Yakal-Kremski

Yeh

et al. 2016

J. Electrochem. Soc.

129

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Symmetric cells with porous La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) electrodes on Gd 0.1 Ce 0.9 O 1.95 (GDC) electrolytes were aged at 800 • C for 800 hours in ambient air. Electrochemical impedance spectroscopy (EIS) measurements performed periodically at 700 • C showed a continuous increase of the polarization resistance from 0.15 to 0.34 · cm 2 . Three-dimensional (3D) tomographic analysis using focused ion beam-scanning electron microscopy (FIB-SEM) showed negligible changes due to the ageing, suggesting that the observed resistance increase was not caused by electrode morphological evolution. However, an increased amount, by a factor of 3, of a water-soluble Sr rich surface phase on the aged LSCF electrode was detected by an etching procedure coupled with inductively coupled plasma-optical emission spectrometry (ICP-OES). The electrochemical analysis in combination with the microstructural parameters determined by FIB-SEM was used to examine the effect of Sr segregation on the rate of oxygen surface exchange, based on the Adler-Lane-Steele (ALS) model. 1-6However, a number of MIEC materials including LSCF exhibit Sr surface segregation, which has been proposed to hinder the oxygen surface exchange process. [7][8][9][10][11] This is believed to be an important issue for the stability of advanced SOFCs utilizing MIEC cathodes. Still, most of the Sr segregation observations have been made on thin film samples, where it is straightforward to measure surface composition using techniques such as X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and secondary ion mass spectrometry (SIMS).12-15 Recently Rupp et al. 16 reported a novel technique utilizing chemical etching with on-line inductively coupled plasma optical emission spectrometry (ICP-OES) detection to successfully quantify Sr-rich surface phases on dense La 0.6 Sr 0.4 CoO 3-δ (LSC) thin films. There is only one report of a measurement of a practical porous LSCF electrode that showed Sr segregation, measured via XPS, along with electrochemical performance degradation. 11The distinction between thin film and bulk electrode samples is potentially important. Thin films are often characterized by columnar growth with very high grain boundary densities, they may exhibit significant stress, and the thermal history is usually very different from that of porous electrodes (preparation mostly below 800• C). Although the measured properties of well-prepared polycrystalline thin-film electrodes normally agree reasonably well with values from bulk materials, 17 in some cases such as epitaxial thin film electrodes, properties may deviate significantly.18 Also, SOFC stacks with LSCF cathodes have been shown to provide reasonably stable long-term performance, 19 an observation that appears to be at odds with the Sr segregation and related degradation observed for thin-film LSCF.In this work, we investigated the degradation mechanisms, especially Sr surface segregation, of porous LSCF cathodes. LSCF symmetric-electrode cells with Gd 0.1 Ce 0.9 ...

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“…The transport of Si-species via the gas phase and Sipoisoning of the samples can be assumed to be negligible since only dry test gases (estimated humidity ≤ 3 ppm; see above) were used. According to previous studies 10,16,18,19,37 and thermodynamic data [38][39][40] Si-transport in the form of Si(OH) 4 (g) occurs in oxidizing atmospheres only in the presence of significant amounts of…”

Section: Methodsmentioning

confidence: 84%

Impact of SO₂on the Oxygen Exchange Kinetics of the Promising SOFC/SOEC Air Electrode Material La_0.8Ca_0.2FeO_3-δ

Berger

Bucher

Gspan

et al. 2017

J. Electrochem. Soc.

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The mass and charge transport properties of La 0.8 Ca 0.2 FeO 3-δ (LCF82) were determined at 600-800 • C and pO 2 = 0.1 bar. The electronic conductivity is in the range of 112 S cm −1 at 700 • C. The chemical surface exchange coefficient (k chem ) and the chemical diffusion coefficient of oxygen (D chem ) were measured. LCF82 shows exceptionally fast oxygen exchange kinetics in pure O 2 -Ar at 700 • C. Long-term measurements at 700 • C in pure O 2 -Ar showed an excellent stability of the kinetic parameters during 1000 h. However, when 2 ppm of sulfur dioxide were added, k chem decreased by a factor of 40 within the first 24 h. After further 1000 h, the total decrease in k chem amounted to two orders of magnitude. Post-test analyses of LCF82 were performed by SEM-EDXS, XPS, and STEM. Ca-enrichment and La-/Fe-depletion of the LCF82 surface occurred during the first 1000 h without SO 2 . At the surface of the sample exposed to 2 ppm SO 2 for additional 1000 h, CaSO 4 crystals with diameters of 1-2 μm and an underlying layer of Fe 2 O 3 (thickness approx. 300-450 nm) were found. Remarkably, LCF82 shows faster oxygen exchange kinetics than La 0.6 Sr 0.4 CoO 3-δ even in the degraded state. Therefore, LCF82 is suggested as a promising material for SOFC and SOEC air electrodes.

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Impact of humid atmospheres on oxygen exchange properties, surface-near elemental composition, and surface morphology of La0.6Sr0.4CoO3−δ

Cited by 96 publications

References 22 publications

Long-term stability of the IT-SOFC cathode materials La0.6Sr0.4CoO3−δ and La2NiO4+δ against combined chromium and silicon poisoning

Long-term stability of the IT-SOFC cathode materials La0.6Sr0.4CoO3−δ and La2NiO4+δ against combined chromium and silicon poisoning

Mechanisms of Performance Degradation of (La,Sr)(Co,Fe)O_3-δSolid Oxide Fuel Cell Cathodes

Impact of SO₂on the Oxygen Exchange Kinetics of the Promising SOFC/SOEC Air Electrode Material La_0.8Ca_0.2FeO_3-δ

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Impact of humid atmospheres on oxygen exchange properties, surface-near elemental composition, and surface morphology of La0.6Sr0.4CoO3−δ

Cited by 96 publications

References 22 publications

Long-term stability of the IT-SOFC cathode materials La0.6Sr0.4CoO3−δ and La2NiO4+δ against combined chromium and silicon poisoning

Long-term stability of the IT-SOFC cathode materials La0.6Sr0.4CoO3−δ and La2NiO4+δ against combined chromium and silicon poisoning

Mechanisms of Performance Degradation of (La,Sr)(Co,Fe)O3-δSolid Oxide Fuel Cell Cathodes

Impact of SO2on the Oxygen Exchange Kinetics of the Promising SOFC/SOEC Air Electrode Material La0.8Ca0.2FeO3-δ

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Product

Resources

About

Mechanisms of Performance Degradation of (La,Sr)(Co,Fe)O_3-δSolid Oxide Fuel Cell Cathodes

Impact of SO₂on the Oxygen Exchange Kinetics of the Promising SOFC/SOEC Air Electrode Material La_0.8Ca_0.2FeO_3-δ