Doped Lanthanum Cobaltite Research Articles

Phase equilibria and defect chemistry of the La-Sr-Co-O system

Strontium doped lanthanum cobaltite (LSC, La1−xSrxCoO3−δ) is a promising oxygen electrode material for intermediate temperature solid oxide cells (SOCs) and oxygen membranes. Its application in service is however impeded by its thermodynamic instability. The present work is aiming to identify the phase stability of LSC by thermodynamic modeling of the La-Sr-Co-O system using the CALculation of PHAse Diagrams (CALPHAD) method coupled with experiments. The calculated results based on the developed database are validated using experimental data both from literature and the present work. General agreement is achieved between model predictions and experimental results. Other properties of the LSC perovskite, such as oxygen non-stoichiometry and cation distribution, are also calculated and predicted based on the developed La-Sr-Co-O database. These calculations can provide important guidance in designing LSC-based materials for various applications and the established thermodynamic functions can serve as input for further thermodynamic calculations on altered and even more complex perovskites.

Spin state crossover and colossal magnetoresistance in barium-doped cobaltites

Investigation of the crystal structure, magnetic and transport properties of both the stoichiometric and anion-deficient Ba2+-doped lanthanum cobaltites was performed. Anomalous temperature behavior of the structural parameters as well as the magnetic, electrical and magnetotransport characteristics was found due to concurrence of magnetic interactions. It was shown that the anion deficiency stabilized insulating antiferromagnetism and destroyed conductive ferromagnetism. We argue that the ferromagnetism developed on the basis of Co3+/Co4+ ions with one eg electron (i.e., possessing the intermediate-spin (IS) state), while the presence of two eg electrons (corresponding to the high-spin (HS) state) favored the antiferromagnetic order. The covalent component of the chemical bond stabilized an electronic configuration close to the IS state. The colossal magnetoresistance arose at a concentration or temperature boundary (where ferromagnetic and antiferromagnetic phases or clusters coexist) as a result of the field-induced spin transition from mixed HS/low-spin state (predominantly antiferromagnetic and insulating) to IS (predominantly ferromagnetic and highly conductive) state.

New insights on the co-electrolysis of CO2 and H2O through a solid oxide electrolyser operating at intermediate temperatures

A solid oxide electrolyser cell based on a Ni-yttria-stabilized zirconia (Ni-YSZ) supporting cathode, a double layer YSZ and Gadolinia-doped Ceria (GDC) electrolyte and a strontium doped lanthanum cobaltite anode (LSC) was investigated for the co-electrolysis of H2O and CO2 in the range of temperatures between 525 °C and 700 °C. The flow rate of the inlet stream was selected in order to reproduce practical operating conditions conventionally adopted for solid oxide electrolysis stacks. The flow of CO2 and H2O, was 2 times of that required by the faradaic reaction at high current densities in order to achieve an utilization close to 50%. A steady-state galvanostatic operating mode was selected in combination with the analysis of the effluents by gas-chromatography. Electrochemical studies also included electrochemical impedance spectroscopy (EIS) and polarization curves. The results showed an increase of CO content versus H2 in the formed syngas promoted by the increase of temperature. A small occurrence of methane was observed at 525 °C. The post operation analysis of the spent cell excluded the presence of carbon but it showed a fracture occurring in the cell at the interface cathode-electrolyte possibly as consequence of the re-oxidation of the cathode at the high operating temperatures. Such evidence suggests that an improvement of cell microstructure for high temperature solid oxide electrolysis is required.

Theoretical Study of Oxygen Vacancy Formation at LSC/GDC Interface

Introduction Doped lanthanum cobaltite and its derivatives are used as cathode materials in solid oxide fuel cell (SOFC). For a high catalytic activity, the improvement of properties governing the cathode performance is important. It is generally regarded that one of the important factors is the electronic structure of cathode material. Recently, the influence of the lattice strain on the kinetics of the oxygen reduction reaction (ORR) was reported [1]. In addition, the heterostructured oxide interface ((La,Sr)2CoO4±δ/La1-xSrxCoO3-δ (LSC)) and thin-film heterostructure interface (La0.6Sr0.4Co0.2Fe0.8O3-δ/gadolinium-doped CeO2 (GDC)) enhanced the surface oxygen exchange kinetics and ORR activity [2,3]. These results indicate the possibility that the structural change near interface changes the electronic structure of cathode materials. Detailed understandings of electronic structure of doped lanthanum cobaltite near the interface is important to design the high catalytic cathode materials. In this study, we analyzed the stability of oxygen vacancy in LSC of LSC/GDC interface by using the density functional theory (DFT) calculation. Computational Details We used LaO-terminated (001) surface of cubic LaCoO3 crystal structure. Half of La atoms were substituted by Sr atoms in LaO layers in LSC slab model (La6Sr6Co8O28). As a surface of CeO2, we used (111) surface model (Ce14O28) from the surface stability. GDC surface model was prepared based on the previous DFT calculation [4]. The interface of LSC and GDC was modeled from CoO2-terminated LSC(001) and GDC(110) surfaces. The initial spin configuration of Co3+ ion was set as intermediate spin state. GGA-PAW potentials were applied with cutoff energy of 600 eV and 1×1×1 k-points. We employed GGA+U to improve the description of Co 3d and Ce 4f electrons. All DFT calculations were performed by using VASP. Results and Discussion We first analyzed the charge distribution near LSC/GDC interface. In case of LSC/CeO2 interface, the electron transferred from CeO2 to LSC. We clearly observed the larger electron transfer from GDC to LSC. These results indicate that the LSC region near CeO2 or GDC interface shows the negatively charged structure. We analyzed the oxygen vacancy formation energy in LSC. The oxygen vacancy formation energy from surface at LSC/GDC interface was more stable than that of LSC model. Although the oxygen vacancy formation energy from 2ndlayer in LSC model was stable, unstable oxygen vacancy formation energy was obtained in the LSC/GDC interface model. One of the reasons of oxygen vacancy formation energy difference between LSC and LSC/GDC interface is an effect of electron transfer from GDC to LSC. The atomic position change at interface is also influenced the oxygen vacancy formation energy. To see the relation between oxygen vacancy formation energy and distance from interface, we prepared larger LSC/GDC interface models. Details are discussed in the presentation. Acknowledgement This work was supported by CREST, Japan Science and Technology Agency. All calculations were performed on the HA8000 computer systems in Research Institute for Information Technology, Kyushu University. The activities of Advanced Automotive Research Collaborative Laboratory in Hiroshima University are supported by Mazda Corporation. The activities of INAMORI Frontier Research Center in Kyushu University are supported by Kyocera Corporation.

First-Principles Study on Oxygen Reduction Reaction over La1-xSrxCoO3-δ

Understanding the electrode kinetics in solid oxide fuel cells is important to realize the highly efficient system. Doped lanthanum cobaltite and its derivatives are used as cathode materials in solid oxide fuel cell. As results of considerable number of studies, it is generally accepted that the dissociative adsorption of oxygen at the cathode surface is one of the rate-determining steps. Toward the rational design of cathode materials, we discuss how the electronic structure affects the surface kinetics of doped cobaltite in this study. We focus on La0.5Sr0.5CoO3-δ (LSC) as cathode material and discuss the properties (001) surface with LaO termination based on density functional theory method. We investigated the oxygen adsorption energy and vacancy formation energy by changing the spin states of Co in LSC. The calculated properties are discussed in the context of the kinetic process of oxygen reduction at LSC surface together with future perspectives.

Preparation and characterization of cerium doped LaCoO3 perovskite

Cerium doped lanthanum cobaltite perovskites La1–x Ce x CoO3 with x = 0, 0.2, 0.4 were prepared by the sol-gel method (calcined for 5 h at 750°C) and characterized by X-ray diffraction, X-ray absorption, energy dispersive X-ray spectroscopy and Brunauer–Emmett–Teller surface area analysis. The results showed that the cerium doping promoted the structural transformation of LaCoO3 from rhombohedral into cubic structure. High specific surface area and small crystallite size were achieved at x = 0.2. The X-ray absorption results confirmed the formation of compound La1–x Ce x CoO3.

(Invited) Surface Composition and Oxygen Exchange Properties of Alkaline Earth-Free Perovskites; LaCo0.6Ni0.4O3

It is well known that alkaline earth additives in conventional perovskite-based solid oxide electrode materials tend to segregate rapidly to the outer surfaces, which is associated with degradation in device performance. It may be possible to avoid these problems by developing materials which do not contain alkaline earth dopants; however, without the oxygen vacancies introduced by alkaline earth doping, the oxygen transport and electro-catalytic properties may suffer. Here, we investigate oxygen transport in the nickel doped lanthanum cobaltite system, and find that the relatively low oxygen diffusivity is dominated by grain boundary transport. Despite this, at higher temperatures, the surface exchange coefficient is comparable to state-of-the-art Sr doped cobaltites. The surface composition of the annealed samples measured by Low Energy Ion Scattering spectroscopy does not appear different from the as-polished samples, suggesting that the surface composition is indeed more stable for this alkaline earth free material.

Theoretical Study on Oxygen Dissociation Reaction on LaSrCoO3

Introduction Doped lanthanum cobaltite and its derivatives are used as cathode materials in solid oxide fuel cell (SOFC). For a high catalytic activity, the improvement of properties governing the cathode performance is important. It is generally regarded that one of the important factors is electronic structure of cathode material. It is known that the Co ion in doped lanthanum cobaltite shows three spin states, such as low spin (LS), intermediate spin (IS), and high spin (HS). Hong et al. pointed out that the change of electronic structure due to the difference of spin states affect the formation energy of oxygen vacancy in LaCoO3 bulk system. Although it is expected that the high catalytic materials for oxygen adsorption and dissociation on oxide surface are proposed by the controlling the electronic structure of doped lanthanum cobaltite, the effect of electronic structure due to the difference of spin states of Co ion is unclear for the surface reactions on doped lanthanum cobaltite. In this study, we analyzed the stability of oxygen vacancy and surface reaction of oxygen under the different spin states of Co ion in Sr doped LaCoO3by using density functional theory (DFT) calculation. Computational Details We used LaSrO-terminated (001) surface of cubic LaSrCoO3 crystal structure. Half of La atoms were substituted by Sr atoms in LaO layers to analyze the effect of segregation of Sr in La6Sr6Co8O28 slab model. GGA-PBE with PAW potentials were applied with cutoff energy of 600 eV and 2x2x1 k-points. The initial spin configuration was constrained, such as LS, IS, and HS states, to obtain the different electronic structures. All DFT calculations were performed by using VASP. Results and Discussion We first analyzed the oxygen vacancy formation energy on the surface of La6Sr6Co8O28. The vacancy formation energies of one oxygen on surface under the LS, IS, and HS states were 0.92, 1.03, and 0.95 eV, respectively. The vacancy formation energies of two oxygen on surface under the LS, IS, and HS states were 3.27, 2.36, and 1.90 eV, respectively. The oxygen vacancy formation became unstable when the number of oxygen vacancy increases in all spin states. The oxygen vacancy formation energy for HS was the smallest compared with LS and IS states for two oxygen vacancy systems. We found that the difference of spin state of Co ion affects the oxygen vacancy formation energy on surface of LaSrCoO3. In addition, we analyzed the stability of oxygen vacancy under the different Sr configurations to understand the effect Sr segregation. Details are discussed in the presentation. Acknowledgement The activities of INAMORI Frontier Research Center are supported by KYOCERA Corporation. All calculations are performed on the HA8000 computer systems in Research Institute for Information Technology, Kyushu University. Reference [1] W. T. Hong, M. Gadre, Y. -L. Lee, M. D. Biegalski, H. M. Christen, D. Morgan, and Y. Shao-Horn, J. Phys. Chem. Lett., 4, 2493 (2013).

Theoretical Study on Oxygen Dissociation Reaction on LaSrCoO3

Doped lanthanum cobaltite and its derivatives are used as cathode materials in solid oxide fuel cell. It is expected that the high catalytic materials for oxygen adsorption and dissociation on oxide surface are found by the controlling the electronic structure of doped lanthanum cobaltite. In this study, we analyzed the stability of oxygen vacancy and surface reaction of oxygen under different spin states of Co ion in Sr doped LaCoO3 by using density functional theory. We clearly found that the difference of oxygen vacancy position and spin state of Co ion affects the reactivity of oxygen on surface.

(Invited) Theoretical Approach for Understanding Oxygen Reduction at the Cathode Surface of Solid Oxide Fuel Cell

Doped lanthanum cobaltite and its derivatives are used as cathode materials in solid oxide fuel cell (SOFC), thus the cathodic reaction mechanism has been extensively investigated. As results, it is generally accepted that the dissociative adsorption of oxygen at the cathode surface is one of rate-determining steps. Therefore, it is important to understand factors governing the surface kinetics. Preceding experimental and theoretical studies have pointed out the correlation between electronic structure of doped lanthanum cobaltites and oxygen dissociation properties on surface, formation energy of oxygen vacancy, and oxygen diffusivity [1-6]. In our preceding study [7], we focused on the change of spin states in LaCoO3 to have a basis for analyzing catalytic properties of the material at the operation temperature. Further analyses in collaboration with experimental observation have clarified the electronic properties of LaCoO3 at the operation temperature on the basis of density functional theory calculations taking into account the statistical thermodynamics [8]. As an extension of our preceding studies, we will discuss how the electronic structure affects the surface kinetics in this study. We adopted the La0.5Sr0.5O3-δ as cathode material and prepared the (001) surface model with the LaO termination. The model consists of five layers with the total 48 atoms. For the electronic structure calculations, we used Vienna Ab initio Simulation Package (VASP) based on the density functional theory. U parameter is adopted as correction for electronic correlation calculation. We investigated the oxygen adsorption energy, vacancy formation energy and oxygen dissociation energy by changing the spin states of Co in La0.5Sr0.5O3-δ. We observed dependency of the calculated energies and the spin states. Based on the calculated properties, we will discuss the kinetic process of oxygen reduction at La0.5Sr0.5O3-δ surface together with the perspectives of future analysis.

Interfaces and Durability for Different LSCF/CGO/YSZ Systems for IT-SOFC

The challenging issues for the development of solid oxide fuel cells (SOFCs) include lowering the operating temperature down to 700 °C (IT-SOFC) in order to increase their lifetime and reduce the overall cost. Consequently, the overpotentials generated at the cathodic interface and the decrease in ionic conductivity of the electrolyte resulted in a loss of performances. Today, doped-lanthanum cobaltites (LSCF) [1–2] are known to be promising cathodes because of high mixed ionic and electronic conductivities. However, the major problem is the chemical reactivity between LSCF and the typical yttria-stabilized zirconia (YSZ) electrolyte. The reactivity between LSCF and YSZ starts above 1000 °C, inducing the formation of insulating phases in ionic conductivity (SrZrO3 and La2Zr2O7 )[3]. This reactivity is due to the diffusion of Sr and La, which results in the destabilization of LSCF structure at higher temperature. In order to improve the electrical performances of the cell by limiting the diffusion of cations, a buffer layer, based on gadolinia-doped ceria (CGO) [4-5], is usually deposited between the LSCF cathode and the YSZ electrolyte. A dense CGO interlayer has been reported to improve electrical performances of the cell and to favour Sr2+ [5] retention but no effect of the CGO thickness has been reported in the literature on its efficiency to improve the durability of the cell. LSCF/CGO/YSZ half-cells were consisted in a dense Ce0.9Gd0.1O2- δ buffer layer, with different thicknesses (0.11, 0.45, 1.11 to 2 mm), prepared by DC magnetron sputtering on a homemade YSZ substrate. Porous La0.6Sr0.4Co0.2Fe0.8O3- δ cathode layer, 4 mm thick, was fabricated using electrostatic spray deposition [2]. The microstructure, thickness, crystalline state and composition of films have been characterized respectively by FEG-SEM, X-ray diffraction and microanalyses. An aging investigation of all LSCF/CGO/YSZ half cells was performed for 550 h in air at 700°C, using electrochemical impedance spectroscopy (EIS). Spectra of LSCF cathode were recorded at OCV using a Solartron (SI 1280B) potentiostat/galvanostat frequency response analyzer with frequencies ranging between 0.01 Hz and 20 kHz. For the electrolyte CGO/YSZ system, impedance measurements were carried out using a HP 4192 measuring unit within the frequency range from 5 Hz to 13 MHz. EIS measurements have shown that the initial electrolyte series (RS) (Fig.1a) is strongly decreased from 80 to 40 Ω.cm since a 0.11mm thick CGO layer is added due to the enhancement of the ionic current collecting between YSZ and LSCF. After 550 h, a low RS variation is observed and becomes weaker with CGO layer due to a better contact. The relative Rpol variation after 550 h, is strongly reduced to reach a minimal value of 57% when the CGO layer is only 0.11 mm thick with comparison to 677% on the LSCF/YSZ system without CGO layer. The electrode response resulted from a major contribution at high frequency (HF) (Fig. 2a) and a minor one at low frequency (LF) corresponding to cathode-electrolyte interface and oxygen-cathode exchange, respectively. These EIS data are consistent with X-ray microanalysis where Sr2+ migration was only detected at LSCF/YSZ interface. The lowest Rpol and the lowest relative Rpol variation,has been observedfor an optimized CGO thickness of only 0.11 mm, after 550 h at 700°C in air. Durability tests under current densities by EIS of these systems will also be discussed References [1]L. W. Tai et al, Solid State Ionics (1995) 76: 259-271 [2] Marinha et al., J. Solid State Chemis-try. 182 (2009) 1742 [3] Kostogloudis et al., Solid State Ionics. 135 (2000) 529. [4] Mai et al., Solid State Ionics. 177 (2006) 2103. [5] Jordan et al , Solid State Ionics. 179 (2008) 919. Figure 1

Durability of high performance Ni–yttria stabilized zirconia supported solid oxide electrolysis cells at high current density

We report the durability of a solid oxide electrolysis cell (SOEC) with a record low initial area specific resistance (ASR) and a record low degradation rate. The cell consists of a Ni–yttria stabilized zirconia (YSZ) cermet as support and active fuel electrode, a YSZ electrolyte, a gadolinia doped ceria (CGO) inter-diffusion barrier, and a strontium doped lanthanum cobaltite (LSC)–CGO composite oxygen electrode. The cell was tested at 800 °C and −1 A cm−2 converting 31% of a 0.1:0.45:0.45 mixture of H2:H2O:CO2 for approximately 2700 h, demonstrating an initial ASR of 200 mΩ cm2 and a steady degradation rate of ≤12 mV (or 0.9%) per 1000 h. Electrochemical impedance spectroscopy (EIS) was used to study in situ changes in the electrochemical response of the cell and the retrieved data was treated to deconvolute resistive contributions from the physiochemical processes occurring within the cell. The results showed rapid initial fuel electrode degradation during the first 350 h followed by partial reactivation. The serial resistance was found to increase with time but in an exponentially decaying behavior. A discussion is made based on the detailed electrochemical results together with post-mortem microstructural analysis.

Effect of Carbon Dioxide on the Cathodic Performance of Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are ideally suited for environmentally benign conversion of chemical energy in hydrocarbons to electricity. While medium scale SOFC power systems in the hundreds of kWe have been demonstrated, larger scale application of such systems have been hobbled by still too high cost. In order to bring down the cost of these systems, manufacturing costs have to be decreased while the power densities have to be improved. Achieving these twin goals will require the reduction of operating temperatures of the cells. On a single cell level, the largest source of performance loss at lower operating temperatures occurs in the cathode. Thus many different groups are presently investigating a slew of new cathode materials. While the performance of the new cathode materials are impressive under controlled operating conditions, it is presently not clear whether they will stand up to the rigorous and punishing operating environments of actual fuel cell stacks. In particular the interfacial and bulk stability of the new generation of cathode materials such as strontium doped lanthanum cobaltites, strontium doped lanthanum cobaltites , and lanthanum nickelates when exposed to anodic gases such as carbon dioxide and water vapor is presently unknown. Exposure to at least trace amounts of anodic gases during the lifetime of the stack is a likely occurrence and could arise from back diffusion, pinholes in the electrolyte and/or interconnection, or compromised seals. Thus, it is important to have a clear understanding of the thermodynamic and kinetic stability of both the interfaces and the bulk of the cathode material under exposure to the aforementioned anodic gases. In this paper, we present results from a study that combines electrochemical and x-ray measurements of the impact of carbon dioxide exposure on strontium doped lanthanum cobalt iron oxide (LSCF), as a function of strontium dopant concentration, gas composition, and temperature. These are combined with computational studies of the stability of the LSCF cathode to carbon dioxide exposure. The longer term goal of this study is to identify cathode compositions which have long term stability to exposure to trace anode side gases.

Effect of calcium doping on LaCoO3 prepared by Pechini method

Abstract Calcium doped lanthanum cobaltite (La1 − xCaxCoO3) (x = 0, 0.2, 0.4, 0.6, 0.8) with different concentrations has been prepared by modified Pechini type polymerizable method. The X-ray diffraction pattern of the calcium doped samples shows the formation of perovskite material in cubic structure. Scanning electron and transmission electron microscopic analysis shows the porous nature of the prepared material. The appearance of peak at 347.5 eV for calcium confirms its presence in the doped samples. Conductance spectra analysis reveals the frequency independent behavior of the samples and the conductivity is related with the particle size. The sample doped with 0.6% of calcium is found to show high conductivity. The temperature dependent conductivity indicates Arrhenius type behavior.

Defect Structure and Defect-Induced Expansion of MIEC Oxides - Doped Lanthanum Cobaltites

Perovskites based upon substituted LaCoO3-δ are the state-of-the-art materials for a variety of different devices for moderate high temperature applications such as solid oxide fuel cells (SOFCs) and mixed ionic and electronic conducting (MIEC) membranes. The unique feature of the oxides is their ability to undergo both thermal expansion and that induced by the defects of oxygen nonstoichiometry in the oxide lattice. The latter is chemical or defect-induced expansion. This property is extremely sensitive to the defect structure of the oxide material. Therefore reliable data on the defect structure of oxides materials is of key importance to understanding the origin of their chemically induced lattice strain. On the other hand, precisely measured with ppm-resolution chemical expansion of crystal cell of the oxide allows to better understand its local electronic and defect structure.

Defect Structure and Defect-Induced Expansion of MIEC Oxides - Doped Lanthanum Cobaltites

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Defect Structure and Defect-Induced Expansion of MIEC Oxides: Doped Lanthanum Cobaltites

Perovskites based upon substituted LaCoO3−δ are the state-of-the-art materials for a variety of different devices for moderate high temperature applications such as solid oxide fuel cells (SOFCs) and mixed ionic and electronic conducting (MIEC) membranes. The unique feature of the oxides is their ability to undergo both thermal expansion and that induced by the defects of oxygen nonstoichiometry in the oxide lattice. The latter is chemical or defect-induced expansion. This property is extremely sensitive to the defect structure of the oxide material. Therefore reliable data on the defect structure of oxide materials is of key importance to understanding the origin of their chemically induced lattice strain. On the other hand, chemical expansion of oxide crystal cell precisely measured with ppm-resolution allows better understanding its local electronic and defect structure.

Impedance Modeling of Solid Oxide Fuel Cell Cathodes

A 1-dimensional impedance model for a solid oxide fuel cell cathode is formulated and applied to a cathode consisting of 50/50 wt% strontium doped lanthanum cobaltite and gadolinia doped ceria. A total of 42 impedance spectra were recorded in the temperature range: 555-852°C and in the oxygen partial pressure range 0.028-1.00 atm. The recorded impedance spectra were successfully analyzed using the developed impedance model in the investigated temperature and oxygen partial pressure range. It is also demonstrated that the model can be used to predict how impedance spectra evolve with different physical parameters such as the cathode thickness.

Mechanical behavior and electrical conductivity of La 1− xCa xCoO 3 ( x = 0, 0.2, 0.4, 0.55) perovskites

This paper compares the important mechanical properties and the electrical conductivities from room temperature to 800 °C of four LaCoO 3 based cobaltite compositions with 0, 20, 40 and 55% Ca 2+ ions substituted on the A site of the perovskite structure respectively. Ca 2+ doped lanthanum cobaltite materials are strong candidates for use as cathodes in lower temperature solid oxide fuel cells operating at or below 800 °C. Among these four cobaltite compositions, two (LaCoO 3 and La 0.8Ca 0.2CoO 3) were found to be phase pure materials, whereas the remaining two compositions (La 0.6Ca 0.4CoO 3 and La 0.45Ca 0.55CoO 3) contained precipitation of secondary phases such as CaO and Co 3O 4. The mechanical properties of the four compositions, in terms of Young's modulus, four-point bending strength and fracture toughness measurements, were measured at both room temperature and 800 °C. At room temperature, doping with Ca 2+ was found to substantially increase the mechanical properties of the cobaltites, whereas at 800 °C the pure LaCoO 3 composition exhibited higher modulus and strength values than La 0.8Ca 0.2CoO 3. All of the four compositions exhibited ferroelastic behavior, as shown by the hysteresis loops generated during uniaxial load–unload compression tests. Electrical conductivity measurements showed the La 0.8Ca 0.2CoO 3 composition to have the highest conductivity among the four compositions.

Sulfur as Pollutant Species on the Cathode Side of a SOFC System

In order to link electrochemical performance degradation of the cathode in a large solid oxide fuel cell (SOFC) to the presence of pollutant species, a spatially-resolved study of contaminants was performed. Distribution maps of pollutants over the cell allowed to identify their sources. Besides chromium and silicon, sulfur was found as a major pollutant species. Its preferential reaction with strontium doped lanthanum cobaltite (LSC), forming strontium sulfate SrSO4, compared to strontium doped lanthanum manganite (LSM) is revealed here. When sulfur poisoning arises in combination with chromium, a sulfur-containing strontium chromate compound is formed.