LSCF Powder Research Articles

The Role of Oxygen Partial Pressure in Controlling the Phase Composition of La1−x Sr x Co y Fe1−y O3−δ Oxygen Transport Membranes Manufactured by Means of Plasma Spray-Physical Vapor Deposition

La0.58Sr0.4Co0.2Fe0.8O3−δ (LSCF) deposited on a metallic porous support by plasma spray-physical vapor deposition is a promising candidate for oxygen-permeation membranes. Ionic transport properties are regarded to depend on the fraction of perovskite phase present in the membrane. However, during processing, the LSCF powder decomposes into perovskite and secondary phases. In order to improve the ionic transport properties of the membranes, spraying was carried out at different oxygen partial pressures p(O2). It was found that coatings deposited at lower and higher oxygen partial pressures consist of 70% cubic/26% rhombohedral and 61% cubic/35% rhombohedral perovskite phases, respectively. During annealing, the formation of non-perovskite phases is driven by oxygen non-stoichiometry. The amount of oxygen added during spraying can be used to increase the perovskite phase fraction and suppress the formation of non-perovskite phases.

Electrochemical behavior of LSCF/GDC interface in symmetric cell: An application in solid oxide fuel cells

In present paper, La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF)/Ce0.9Gd0.1O1.95 (GDC)/LSCF structure has been studied to understand electrode/electrolyte interface. The nanocrystalline powder required for screen printing was obtained through solution combustion synthesis with glycine as a fuel. The LSCF powder synthesized at fuel to oxidant ratio of two is calcined at 900°C as TG–DTA reveals thermal stability only beyond 900°C. The X-ray diffraction pattern of calcined powder demonstrates rhombohedral perovskite structured LSCF with 27nm crystallite size. However, dynamic laser scattering shows 0.9μm sized agglomerates while TEM shows 74nm particles. For potential application in solid oxide fuel cells, the temperature programmed reduction and oxidation were done on the LSCF. The results exhibit strong reduction and oxidation behavior around 860 and 388°C, respectively. The cell with LSCF as an electrode shows minimum charge transfer resistance of 6.3Ωcm2 at 550°C.

Influence of sulfur impurities on the stability of La0.6Sr0.4Co0.2Fe0.8O3 cathode for solid oxide fuel cells

Abstract The initial degradation of a La0.6Sr0.4Fe0.8Co0.2O3 (LSCF) cathode for solid oxide fuel cells (SOFCs) was investigated. Degradation of the cathodic performance at 973 K was accelerated by decreasing the oxygen partial pressure from 20 to 10% due to the reduction of Fe3 + in LSCF. Sulfur contamination (1513 and 752 ppm) in the LSCF powder significantly increased the IR loss of the cathode within the initial few hours of SOFC operation. Impedance and conductivity measurements suggested that the increase in IR loss could be explained by the decrease in the electrical conductivity of LSCF due to the phase separation of Sr2 + from lattice or surface segregation of Sr, and the formation of SrSO4. Sintering of the LSCF powder electrode was enhanced at the Sr enriched part and the diffusion overpotential was significantly increased after degradation for 24 h. Therefore, sulfur impurities in the LSCF powder have a negative influence on the stability of cathode during the initial period of SOFC operation.

Characteristics of nano La0.6Sr0.4Co0.2Fe0.8O3−δ-infiltrated La0.8Sr0.2Ga0.8Mg0.2O3−δ scaffold cathode for enhanced oxygen reduction

The chemical compatibility and electrochemical properties of nanoLa0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF)-infiltrated La0.8Sr0.2Ga0.8Mg0.2O3−δ (LSGM) scaffold were manufactured and assessed for the application as a solid oxide fuel cell cathode with an LSGM electrolyte. When the LSCF and LSGM powder mixture was fired above 950 °C, the characteristic peaks of the two materials merged and an insulation peak (derived from LaSrGaO4) was observed. To prevent reactions between LSCF and LSGM, an infiltration technique was utilized with the LSGM as a scaffold. Using this infiltration technique, nano LSCF particles (approximately 100 nm) can be uniformly coated on the LSGM scaffold surface. Good nano particle adhesion was observed at the LSGM/LSCF interface, even at relatively low firing temperatures (850 °C). The cathode polarization resistance (Rp) of the nano LSCF infiltrated LSGM scaffold cathode was lower than that of a conventional LSCF cathode. The improvement in performance of the nano LSCF-infiltrated cathode was attributed to an increase in the number of triple phase boundaries (TPB) as a result of the nano LSCF coating. In addition, the oxygen reduction reaction (ORR) paths were extended from the TPBs to the LSCF surface because LSCF particles are considerably smaller than the LSCF oxygen ion penetration depth (3–4 μm) over the temperature range of 700 °C–800 °C.

In situ sinterable cathode with nanocrystalline La 0.6Sr 0.4Co 0.2Fe 0.8O 3− δ for solid oxide fuel cells

A nanocrystalline powder with a lanthanum based iron- and cobalt-containing perovskite, La 0.6Sr 0.4Co 0.2Fe 0.8O 3−δ (LSCF), is investigated for solid oxide fuel cell (SOFC) applications at a relatively low operating temperature (600–800 °C). A LSCF powder with a high surface area of 88 m 2 g −1, which is synthesized via a complex method with using inorganic nano dispersants, is printed onto an anode supported cell as a cathode electrode. A LSCF cathode without a sintering process (in situ sintered cathode) is characterized and compared with that of a sintering process at 780 °C (ex situ sintered cathode). The in situ sintered SOFC shows 0.51 A cm −2 at 0.9 V and 730 °C, which is comparable with that of the ex situ sintered SOFC. The conventional process for SOFCs, the ex situ sintered SOFC, including a heat treatment process after printing the cathodes, is time consuming and costly. The in situ sinterable nanocrystalline LSCF cathode may be effective for making the process simple and cost effective.

Fabrication of Porous LSCF-SDC Carbonates Composite Cathode for Solid Oxide Fuel Cell (SOFC) Applications

Composite cathodes made of perovskite La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) and SDC carbonates (SDC-(Li/Na)2CO3) were investigated in relation to their structure, morphology, thermal expansion coefficient and porosity. As a first step, the LSCF powder was prepared by sol-gel technique. This was followed by the preparation of the LSCF-SDC carbonates composite cathode by mixing the LSCF with SDC-(Li/Na)2CO3 electrolyte via solid state reaction in various compositions, i.e. 30, 40 and 50 wt.%, namely 70LSCF-30SDC7030, 60LSCF-40SDC7030 and 50LSCF-50SDC7030, respectively. The powder mixtures were then calcined at 680oC. The resultant powder was fine with surface area of about 3.39-7.42 m2/g and particle size of 0.56-0.66µm. The powder consists of two distinct phases, i.e. LSCF and SDC-(Li/Na)2CO3 as confirmed with x-ray diffraction. The microstructures were observed under scanning electron microscopy (SEM). Increasing the amount of the SDC-(Li/Na)2CO3 electrolyte in the composite cathode was found to bring the thermal expansion of the cathode closer to that of the electrolyte. The cathode pellets were later compacted at different pressures (27, 32 and 37 MPa) and sintered at 600oC. The optimum porosity (20.99-24.98%) was achieved for samples with SDC-(Li/Na)2CO3 content of 30-50% sintered at 600oC and cold pressed at 37 MPa.

Characterization of LaNi xCo yFe 1 − x − yO 3 as a cathode material for solid oxide fuel cells

We prepared LaNi x Co y Fe 1 − x − y O 3 with 0.2 ≤ x ≤ 0.6 and 0.1 ≤ y ≤ 0.4 (LNCF) powder and investigated its characteristics as a cathode material for solid oxide fuel cells. To investigate the crystal structure of LNCF, we analyzed LNCF powder using X-ray diffraction. The crystal structure of LNCF belongs to a rhombohedral system. High total conductivity above 100 S cm − 1 at 1073 K was obtained for LNCF. When x in this system is 0.6, the total conductivity at 1073 K is more than 500 S cm − 1 . This conductivity is greater than that of La 0.6Sr 0.4Co 0.2Fe 0.8O 3 (LSCF) between 323 and 1323 K. The average coefficient of thermal expansion of LNCF is smaller than that of LSCF. To investigate the chemical stability against Cr 2O 3, we heated LNCF-Cr 2O 3, LSCF-Cr 2O 3 and La 0.6Sr 0.4CoO 3 (LSC)-Cr 2O 3 powder mixtures at 1073 K for 0–1000 h. We found that LNCF powder was less reactive with Cr 2O 3 than LSCF and LSC powder.

Nano-structured cathodes based on La 0.6Sr 0.4Co 0.2Fe 0.8O 3− δ for solid oxide fuel cells

Lanthanum-based iron- and cobalt-containing perovskite is a promising cathode material because of its electrocatalytic activity at a relatively low operating temperature in solid oxide fuel cells (SOFCs), i.e., 700–800 °C. To enhance the electrocatalytic reduction of oxidants on La 0.6Sr 0.4Co 0.2Fe 0.8O 3− δ (LSCF), nanocrystalline LSCF materials are successfully fabricated using a complexing method with chelants and inorganic nano dispersants. When inorganic dispersants are added to the synthesis process, the surface area of the LSCF powder increases from 18 to 88 m 2 g −1, which results in higher electrocatalytic activity of the cathode. The performance of a unit cell of a SOFC with nanocrystalline LSCF powders synthesized with nano dispersants is increased by 60%, from 0.7 to 1.2 W cm −2.

Effect of calcination temperature on electrochemical properties of cathodes for solid oxide fuel cells

This article is concerned with the electrochemical properties of La 0.6Sr 0.4Co 0.2Fe 0.8O 3 − δ (LSCF) as a cathode with respect to its calcination temperature in solid oxide fuel cells (SOFCs). To determine these properties, LSCF powder was synthesized using a modified glycine nitrate process (GNP), followed by calcinations from 1073 K to 1373 K. Its X-ray diffraction (XRD) patterns gradually sharpened as the calcination temperature increased. Also, the specific surface area of the powder decreased due to particle sintering as the calcination temperature increased. Scanning electronic microscopy (SEM) images from calcined LSCF powder at various temperatures show that the particle shapes are quite similar. However, the particle size slightly increased with increasing calcination temperature. The electrode with LSCF powder calcined at 1273 K showed a lower area specific resistance (ASR) value of 0.68 Ω cm 2 at 973 K than the electrode using commercial LSCF powder. Furthermore, the effect of the sieving process of the cathode powder after wet ball milling on its electrochemical properties was investigated in detail. From particle size analysis, it was observed that the sieved powder, after wet ball milling, shows a bi-modal particle size distribution, whereas the unsieved powder had a single mode distribution. The LSCF electrode with unsieved powder showed a 5 times smaller ASR value than that with the sieved powder.

Synthesis Characteristics of LSCF Powder and Its Electrochemical Studies for IT-SOFC Unit Cell Using Pechini Process

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Electrophoretic Codeposition of La0.6Sr0.4Co0.8Fe0.2O3−δ and Carbon Nanotubes for Developing Composite Cathodes for Intermediate Temperature Solid Oxide Fuel Cells

Carbon nanotubes (CNTs)/La0.6Sr0.4Co0.8Fe0.2O3−δ (LSCF) composite films have been fabricated by electrophoretic codeposition on Ce0.9Gd0.1O1.95 (CGO) substrates. CNTs are used as a sacrificial phase to produce ordered porous LSCF cathodes for intermediate temperature solid oxide fuel cells. The synthesis of LSCF powder by a modified sol–gel route is presented. The possible mechanism of formation of CNT/LSCF composite nanoparticles in suspension is discussed. Moreover the optimal suspension composition and the conditions for achieving successful electrophoretic deposition (EPD) of CNTs/LSCF composite nanoparticles were evaluated. Experimental results showed that the CNTs were homogeneously distributed and mixed with LSCF nanoparticles forming a mesh‐like structure, which resulted in a highly porous LSCF film when the CNTs were burned out during heat treatment in air at 800°C for 2 h. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X‐ray diffraction (XRD) techniques were employed to characterize the microstructure of the precursors and of the composite films.

Synthesis and Study of LSCF Perovskites for IT SOFC Cathode Application

Iron- and cobalt-containing perovskites LaxSr1 xCoyFe1-yO3{plus minus}δ, (х = 0.8; 0.6 and у = 0.8; 0.2) were synthesized via solid state reaction method. Some samples were synthesized using two different iron oxides (Fe2O3 and Fe3O4). Phase composition of synthesized powders was studied by XRD. It was revealed that formation of the perovskite structure occurs at temperatures higher 900 {degree sign}C. Mixing LSCF powder with gadolinia doped ceria (GDC) in proportion 50:50 mas. % composite materials were prepared. Conductivity measurements were carried out with circle-shaped samples. The highest conductivity at the target temperature of 600 {degree sign}C was observed on composite La0,6Sr0,4Co0,8Fe0,2O3-δ-GDC samples. Study of a fracture surface of compacted samples has shown that adding of GDC enhances the both conductivity and sinterability of powders changing the fracture mechanism of cathode material from intergranular to the cleavage one.

Chemical compatibility and electrochemical property of intermediate-temperature SOFC cathodes under Cr poisoning condition

We have investigated the relationship between the chemical compatibility and electrochemical properties of La 0.6Sr 0.4Fe 0.8Co 0.2O 3 (LSCF), LaNi 0.6Fe 0.4O 3 (LNF), and La 0.8Sr 0.2MnO 3 (LSM) as a cathode against the Cr poisoning condition. Powder mixtures of LSCF–Cr 2O 3, LSM–Cr 2O 3, and LNF–Cr 2O 3 were heated at 1073 K and analyzed by X-ray powder diffraction with the Rietveld refinement. It was found that LNF powder was less reactive with Cr 2O 3 than LSCF and LSM powder from the viewpoint of the consumption of Cr 2O 3 in the mixtures. From electrochemical measurement, it was found that the cathodic overvoltage was almost unchanged for cells with LNF cathode, either in the presence or absence of a Cr-containing alloy. On the other hand, the cells with LSCF and LSM cathode in the presence of the alloy exhibited a steep increase in the overvoltage curve. These results show that LNF cathode is more stable against Cr poisoning than the other two cathodes. Therefore, we expect LNF to be a long-life cathode with high stability against Cr poisoning in solid oxide fuel cell because of the low reactivity of LNF with Cr 2O 3.

Catalytic perovskite hollow fibre membrane reactors for methane oxidative coupling

Using the prepared La 0.6Sr 0.4Co 0.2Fe 0.8O 3 (LSCF) hollow fibre membranes via the phase inversion and sintering technique, the catalytic perovskite hollow fibre membrane reactors (HFMRs) without or with additional OCM catalyst inside the fibre lumen were designed and tested for the methane oxidative coupling reaction. LSCF powder possesses almost zero C 2 selectivity, but the blank LSCF hollow fibre membrane reactor shows a higher C 2 selectivity up to 71.9%. Application of additional SrTi 0.9Li 0.1O 3 catalyst in the fibre lumen is able to increase methane conversion and oxygen permeation rate remarkably but decrease the C 2 selectivity. There is an optimum temperature to obtain the maximum C 2 selectivity for either the packed or the blank membrane reactor. The membrane reactor exhibits appreciable advantages over the traditional packed bed reactor. A maximum C 2 yield close to 21% can be achieved in the packed hollow fibre membrane reactor.

Low temperature processing of interlayer-free La 0.6Sr 0.4Co 0.2Fe 0.8O 3− δ cathodes for intermediate temperature solid oxide fuel cells

Nanocrystalline La 0.6Sr 0.4Co 0.2Fe 0.8O 3− δ (LSCF) powder with a specific surface area of 22.9 m 2 g −1 and an average particle size of 175 nm was prepared by a nitrate-glycine solution combustion method and subsequent ball-milling. The LSCF precalcined at 800 °C (LSCF-800) shows very good low-temperature sintering activity, and can well adhere to electrolyte after sintering at 700 °C and above. The single cell Ni–YSZ/YSZ/LSCF-800 with the cathode sintered at 750 °C demonstrates the lowest polarization resistance and good electrical generation performance, but poor cathode microstructure stability. The sintering activity of LSCF cathode can be tailored through the control of the precalcination temperature of the precursor powder. Precalcining of LSCF powder at 900 °C (LSCF-900) increases the optimum sintering temperature of the cathode to 850 °C and improves the microstructure stability. The cell Ni–YSZ/YSZ/LSCF-900 with this cathode demonstrates excellent generation performances with the maximum power density greater than 1.0 W cm −2 and the power density of above 0.80 W cm −2 at 0.7 V under operation at 700 °C. Low temperature processing of the interlayer-free LSCF cathode with good microstructure is beneficial to simplifying the cell structure and improving fuel cell performance.

Preparation of Thin and Dense Lanthanum Cobaltite Coating on Porous Tubular Alumina Supports by Electrophoretic Deposition

The electrophoretic deposition (EPD) process is one of several ceramic powder assembling technologies using a simultaneous colloidal process and electrochemical driving force. For the further development of the EPD technique, the possibility and the usefulness of preparing a thin and dense ceramic coating on non-electronically conductive porous tubular ceramics using the EPD technique was investigated. La 0.8 Sr 0.2 Co 0.8 Sr 0.2 O 3-δ (LSCF) was used as the deposition material and a porous alumina tube was used as the deposition substrate. Methanol (MeOH) was suitable as a dispersing medium for the LSCF powder. LSCF particles were positively charged in MeOH. For the fabrication of a uniform EPD layer, the cathode was placed in a porous alumina tube. The insides of the porous alumina tubes were filled with MeOH and the cathode did not make contact with the EPD bath. A 39μm (200 g/m 2 ) thick uniform LSCF powder coating was obtained by EPD at 100 V for 10 min. After sintering at 1500°C for 5 h, a 20 μm dense membrane was obtained.

Mixed conducting ceramic hollow‐fiber membranes for air separation

AbstractMixed conducting ceramic hollow‐fiber membranes, which possess an asymmetric structure, were prepared by a combined phase inversion and sintering technique where precursors of the hollow fibers were first spun using a polymer solution containing suspended LSCF powders and were then sintered at elevated temperature. By controlling the weight ratio of the LSCF powder to the polymer binder, sintering temperature, and time, the LSCF hollow fibers with gastight properties have been prepared and evaluated using an apparatus developed during the course of this study. Using the gastight LSCF hollow fibers, a membrane module was assembled for air separation. The performances of the module for air separation have been studied under various operating modes and at different temperatures and feed flow rates both experimentally and theoretically. The results reveal that the surface exchange reaction at the downstream side is much more important than that at the upstream side, especially for lower operating temperatures. The porous inner surface of the prepared LSCF hollow‐fiber membranes substantially favors the oxygen permeation when air is fed in the shell side of the membrane module. At high operating temperatures, oxygen permeation can be enhanced by the countercurrent flow operation. Vacuum operation favors the oxygen permeation kinetically in the LSCF hollow‐fiber membrane modules. © 2005 American Institute of Chemical Engineers AIChE J, 2005

Perovskite-type ceramic membrane: synthesis, oxygen permeation and membrane reactor performance for oxidative coupling of methane

La 1− x Sr x Co 1− y Fe y O 3− δ perovskite-type oxides are typical of mixed-conducting ceramic membrane materials with very high oxygen semipermeability. In this study, several different synthesis methods were compared for the preparation of La 0.8Sr 0.2Co 0.6Fe 0.4O 3− δ (LSCF) powders. The coprecipitation method was found most suitable for preparation of the LSCF powder in terms of processibility into dense ceramic membranes. The oxygen permeation flux through 1.85 mm LSCF membrane exposed to O 2/N 2 mixture and helium is about 1×10 −7 mol/cm 2 s at 950°C. The oxygen permeation flux increases sharply around 825°C due to an order–disorder transition of the oxygen vacancies in the membrane. Oxidative coupling of methane (OCM) was performed in the LSCF membrane reactor with one membrane surface exposed to O 2/N 2 mixture stream and other to CH 4/He mixture stream. At temperatures higher than 850°C, high C 2 selectivity (70–90%) and yield (10–18%) were achieved with a feed ratio (He/CH 4) of 40–90. The C 2 selectivity dropped dramatically to less than 40% as the He/CH 4 ratio decreased to 20. The surface catalytic properties for OCM of LSCF membranes strongly depend on the oxygen activity of the membrane surface exposed to methane stream.