On the link between bulk and surface properties of mixed ion electron conducting materials Ln0.5Sr0.5Co0.8Fe0.2O3−δ(Ln = La, Pr, Nd)

Tamimi, Mazin A.; Tomkiewicz, Alex C.; Huq, Ashfia; McIntosh, Steven

doi:10.1039/c4ta04760e

Cited by 16 publications

(18 citation statements)

References 56 publications

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“…Third, it has been shown that the processes represented by k and D * are intimately linked, raising questions as to how readily they can be separately measured. 35,36 …”

Section: Discussionmentioning

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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“…Third, it has been shown that the processes represented by k and D * are intimately linked, raising questions as to how readily they can be separately measured. 35,36 …”

Section: Discussionmentioning

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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“…To this end several groups have been applying the state-of-the-art technique of Low Energy Ion Scattering (LEIS) spectroscopy to study the surface composition of solid oxide electrode materials after exposure to conditions representative of those they will encounter under operation (1,(23)(24)(25)(26). For example, figure 2 shows LEIS analysis of LSCF samples annealed for 8 hours at different temperatures.…”

Section: Surface Segregationmentioning

confidence: 99%

Surface Composition and Oxygen Transport Properties of LSCF: From Bulk Ceramics to Devices

et al. 2015

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Although the oxygen surface exchange reactions are of utmost importance for Solid Oxide Fuel Cells and Solid Oxide Electrolyser operation and performance, these reactions are rather poorly understood. One part of the puzzle is understanding the composition of the surfaces and interfaces participating in the reactions. Ion beam techniques constitute powerful probes of the surface composition, as well as the oxygen transport properties. Here, we use the well-known mixed conducting perovskite LSCF to illustrate how ion beam techniques such as secondary ion mass spectrometry (SIMS) and low energy ion scattering (LEIS) can be used to study fundamental materials properties such as oxygen tracer diffusion and strontium segregation, as well as segregation and impurity migration processes in model electrode structures.

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“…Like SIMS, LEIS is often performed ex situ, where it can be applied to study electrode materials after treatment in high temperatures and gas atmospheres typical of operation conditions [70,97,98,99,100]. While one expects qualitative similarities in the ex situ results on polycrystalline, dense ceramics or thin films and the surface chemistry of real, porous ceramic electrodes in operando, some differences owing to the microstructure and environment changes (e.g., surface-to-volume ratio, surface curvature, grain boundary density, impurity gas concentration, impact of adjacent cell layers, etc.)…”

Section: Role Of Surface Chemistrymentioning

confidence: 99%

Roles of Bulk and Surface Chemistry in the Oxygen Exchange Kinetics and Related Properties of Mixed Conducting Perovskite Oxide Electrodes

Perry

Ishihara

2016

Materials

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Mixed conducting perovskite oxides and related structures serving as electrodes for electrochemical oxygen incorporation and evolution in solid oxide fuel and electrolysis cells, respectively, play a significant role in determining the cell efficiency and lifetime. Desired improvements in catalytic activity for rapid surface oxygen exchange, fast bulk transport (electronic and ionic), and thermo-chemo-mechanical stability of oxygen electrodes will require increased understanding of the impact of both bulk and surface chemistry on these properties. This review highlights selected work at the International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University, set in the context of work in the broader community, aiming to characterize and understand relationships between bulk and surface composition and oxygen electrode performance. Insights into aspects of bulk point defect chemistry, electronic structure, crystal structure, and cation choice that impact carrier concentrations and mobilities, surface exchange kinetics, and chemical expansion coefficients are emerging. At the same time, an understanding of the relationship between bulk and surface chemistry is being developed that may assist design of electrodes with more robust surface chemistries, e.g., impurity tolerance or limited surface segregation. Ion scattering techniques (e.g., secondary ion mass spectrometry, SIMS, or low energy ion scattering spectroscopy, LEIS) with high surface sensitivity and increasing lateral resolution are proving useful for measuring surface exchange kinetics, diffusivity, and corresponding outer monolayer chemistry of electrodes exposed to typical operating conditions. Beyond consideration of chemical composition, the use of strain and/or a high density of active interfaces also show promise for enhancing performance.

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On the link between bulk and surface properties of mixed ion electron conducting materials Ln_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ(Ln = La, Pr, Nd)

Cited by 16 publications

References 56 publications

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

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

Surface Composition and Oxygen Transport Properties of LSCF: From Bulk Ceramics to Devices

Roles of Bulk and Surface Chemistry in the Oxygen Exchange Kinetics and Related Properties of Mixed Conducting Perovskite Oxide Electrodes

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On the link between bulk and surface properties of mixed ion electron conducting materials Ln0.5Sr0.5Co0.8Fe0.2O3−δ(Ln = La, Pr, Nd)

Cited by 16 publications

References 56 publications

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

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

Surface Composition and Oxygen Transport Properties of LSCF: From Bulk Ceramics to Devices

Roles of Bulk and Surface Chemistry in the Oxygen Exchange Kinetics and Related Properties of Mixed Conducting Perovskite Oxide Electrodes

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Product

Resources

About

On the link between bulk and surface properties of mixed ion electron conducting materials Ln_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ(Ln = La, Pr, Nd)

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

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