LSCF Phase Research Articles

LaGaO3-based composite membrane with high oxygen permeability

This study presents the demonstration of the applicability of Sr and Mg co-doped LaGaO3 (LSGM), which is representative electrolyte material for solid oxide electrochemical cells due to its exceptional oxygen ionic conductivity, as oxygen transport membranes (OTMs). Herein, the oxygen flux of a LaGaO3-based composite membrane was systematically investigated by introducing Sr and Mg co-doped LaGaO3 as an ion-conductive material for composite membranes. To enhance the compatibility of the membrane and the surface exchange kinetics, perovskite LSCF phase containing La and Sr at the A-site was adopted as an electronic constituent in the membrane and active coating layer. Thus, the secondary phase between the two phases of the ionic and electronic conductors constituting the composite membrane was not observed. The highest oxygen flux (3.6 mL cm−2 min−1) was achieved in the LaGaO3-based membrane at 900 °C. The mechanism for enhancing the oxygen permeability via the active coating layer was confirmed by deriving the surface exchange kinetics under an operating atmosphere. These promising results indicate that LSGM represents a viable substitute for the oxygen-ion conductive materials utilized in dual-phase membranes.

Rietveld refinement and estimation of residual stress in GDC–LSCF oxygen transport membrane ceramic composites

The phase purity and crystal structure of dual-phase Ce.9Gd.1O2–δ–La.6Sr.4Co.2Fe.8O3–δ (GDC–LSCF) composites were refined using data obtained from X-ray diffraction (XRD) by employing the Rietveld method. Rietveld analysis indicated that the structures of GDC and LSCF phases are well crystallized as cubic Fm3̅m and rhombohedral R3̅c space groups, respectively. Scanning electron microscopy images showed smooth and dense structures, depicting a homogeneous crystalline structure of the samples. When the composites were cooled from their sintering temperature (1250 °C), compressive stresses were generated in the GDC and corresponding tensile stresses were generated in the LSCF due to differences in thermal expansion coefficients. The compressive residual stresses of the composites were investigated by high-angle XRD measurements using the well-known sin2ψ method. The average compressive residual stresses in GDC phase are estimated to be − 312 and − 290 MPa for 80 GDC–20 LSCF and 50 GDC–50 LSCF, respectively. The aim of this study is to provide a better understanding of the crystal structures and residual stresses in GDC–LSCF composites through XRD and the suitability of these composites for oxygen transport membranes.

Microstructural Control of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) Cathode by Validated Kinetic Monte Carlo Simulations

Microstructural parameters such as Triple Phase Boundary (TPB) density, specific surface area, connectivity and tortuosity of different phases strongly affect the performance of solid oxide fuel cells (SOFCs). Degradation of SOFCs is partially attributed to the coarsening of electrode during operation. The Potts Kinetic Monte Carlo (KMC) model [1], proven as a robust tool to study all stages of the sintering process, is an ideal tool to analyze the microstructural evolution of electrodes due to sintering [2]. The KMC model considers following three sintering mechanisms: (i) curvature driven grain growth by short-range atomic diffusion across the grain boundaries; (ii) pore migration by long range surface diffusion of pores; and (iii) vacancies formation at grain boundaries and annihilation along grain boundaries to cause densification. Hence, in the KMC models, the microstructures are controlled by sintering temperatures (KBT) and frequencies (f), i.e., KBTgg , f gg for grain growth, KBTpm , f pm for pore migration, and KBTvf , f vf for vacancy formation and annihilation. As these sintering parameters are not material physical properties, we firstly calibrated these parameters in the KMC model by comparing the microstructural parameters measured from the simulated 3-dimensional (3D) microstructures and the FIB-SEM reconstructed 3D microstructures of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) cathode pellet samples with different densities. The sintering parameters were calibrated using an artificial neural network (ANN) consisting of input layer (sintering material parameters), hidden layers (information processing units) and output layer (microstructural parameters). Inputs/outputs functional relationships were learned from a limited number of KMC simulations based on ‘Design of Experiment (DoE)’ based parametric studies. The trained ANN predicted more input/output pairs to form a database containing ‘material parameter-microstructural parameters’ pairs. Input sintering parameters that result in microstructural parameters within a desired error intolerance of the experimental results are called calibrated parameters. In this study, we identified input parameters as K B T gg=1.16, f gg =0.68, K B T pm =1.48, f pm =0.20, K B T vf = 37.0, and f vf=0.52 for LSCF material. These calibrated parameters were validated successfully by predicting an extra experimental data, i.e. a further densified LSCF pellet sample. By using the validated KMC simulations, we comprehensively examined the effect of the powder morphology on the microstructural characteristics of a La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) cathode. A number of numerical samples consisting of packing of spheres or clumped spheres were created using a discrete element method (DEM), taking into account the morphology of powders such as particle size, particle size distribution (PSD), aspect ratio (AR), sphericity, and particle orientation. The packings were subject to quasi-static compression under tri-axial pressures until having a prescribed relative density. Then, these DEM-generated numerical structures with different particle morphology were submitted to the KMC simulations. Their effects on relative density, specific surface area, and connectivity and tortuosity factors of LSCF and pore phases were compared and analyzed. It is found in this study that using fine sized powder can improve the specific surface area and decrease the tortuosity factors of the LSCF phase. However, the decreased particle size at the same time enhances the sinterability of the LSCF, resulting in a decreased thermal stability of the LSCF cathode. The decreased particle size can also provide a decreased pore phase connectivity, which is disadvantageous for gas transport in the cathode. Secondly, a wider-PSD powder can improve the thermal stability by decreasing the sinterability of the powder. Another consequence of increasing width of PSD is that the pore phase tortuosity factor decreases, which benefits the gas transport in the cathode. The effect of the width of the PSD on the specific surface area and tortuosity factor of the LSCF phase is ignorable. Thirdly, powder with higher-AR particles has higher specific surface area and lower tortuosity factor for LSCF (better ionic and electronic conductivity). However, it also has a lower thermal stability and higher pore tortuosity factor. AR in the range of 1.0-2.0 seems has a very limited effect. Fourthly, powder with irregular shapes has better sinterability (poorer thermal stability). The tortuosity factors for LSCF and pores seems not significantly influenced in the study. Finally, in the case of elongated particles being used, alignment of particles in the green state will lead to lower sinterability of the packing, hence a better thermal stability of cathode. As a consequence of the particle alignment, anisotropic tortuosity factors for LSCF and pores have developed. In the alignment direction, the tortuosity factors appear smaller than the other orthogonal directions.

Investigation of La0.6Sr0.4Co0.2Fe0.8O3- δ Electrode Performance and Microstructural Evolutions Based on Three Dimensional Microstructure Reconstruction and Electrochemical Simulation

The influence of initial microstructure of gadolinium-doped-ceria (GDC) interlayer on La0.6Sr0.4Co0.2Fe0.8O3- d (LSCF) performance evolution was studied. The cell with the GDC interlayer fired at 1300 ˚C (GDC1300), in which SrZrO3 phase shows discontinuous formation between GDC interlayer and yttria-stabilized-zirconia (YSZ) electrolyte, showed gradual increase of polarization resistance during 100 hours operation. In contrast, when the GDC interlayer was fired at 1200 ˚C (GDC1200), continuous SrZrO3 layer was formed between interlayer electrolyte interface, and the cell showed large polarization resistance with recovery during operation. The Strontium oxide phase was formed inside the LSCF cathode phase after the operation of GDC1300 at 800 ˚C, whereas the GDC1300 operated at 700 ˚C and GDC1200 operated at either 700 ˚C or 800 ˚C showed no decomposition of LSCF phase. It is considered that the differences of performance and microstructural evolution are highly dependent on initial microstructures and operating temperatures.

Effect of powder morphology on the microstructural characteristics of La0.6Sr0.4Co0.2Fe0.8O3 cathode: A Kinetic Monte Carlo investigation

Microstructural parameters such as triple phase boundary (TPB) density, surface area density, connectivity and tortuosity of different phases strongly influence the performance of solid oxide fuel cells (SOFCs). In this study, the effect of the powder morphology on the microstructural parameters of a La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) cathode is comprehensively examined using Kinetic Monte Carlo (KMC) simulations. A number of numerical samples consisting of spheres or clumped spheres are created using a Discrete Element Method (DEM), taking into account the powder morphology such as particle size, particle size distribution, particle aspect ratio and sphericity, and particle orientation. The DEM-generated numerical structures with different particle morphologies are submitted to the KMC simulations. Their effects on relative density, densification rate, surface area density, tortuosity factor of LSCF phase and tortuosity factor and connectivity of the pore phase are compared and analyzed.

Phase evolution and electrochemical performance of iron doped lanthanum strontium chromite in oxidizing and reducing atmosphere

Effect of oxygen partial pressure (PO2) on the processing and phase evolution in (La0.8Sr0.2)0.95Cr0.7Fe0.3O3 (LSCF) is investigated under high temperature electrochemical device fabrication conditions at 1400 °C and oxygen partial pressure (PO2) varying from 0.21 to 10−10 atm. Formation of Fe enriched phase is identified in the samples exposed to reducing atmosphere and the amount of the phase increases with decrease in PO2. LSCF dissociates and forms FeOx when exposed to Ar-3%H2-3%H2O at 1400 °C. LSCF decomposition and the formation of FeOx is in agreement with the thermodynamic simulation results obtained using ThermoCalc with the La-Sr-Cr-Fe-O thermodynamic database. Electrochemical impedance spectroscopy measurement on the symmetrical cell of configuration LSCF-YSZ/YSZ/LSCF-YSZ shows high polarization resistance in oxidizing atmosphere when compared to reducing atmosphere under operating conditions (T ∼ 950 °C and PO2 ∼ 0.21–10−16 atm). No degradation and microstructural changes are identified in the samples exposed to air for 80 h. Surface of LSCF phase is significantly modified in Ar-3%H2-3%H2O atmosphere after electrochemical testing for 80 h. Higher stability and electrochemical performance of LSCF is obtained in air when compared with Ar-3%H2-3%H2O. Unlike oxidizing atmosphere, post characterization TEM results show thin SrZrO3 layer formation at the LSCF/8YSZ interface in reducing atmosphere.

An investigation of oxygen reduction mechanism in nano-sized LSCF-SDC composite cathodes

The La0.6Sr0.4Co0.8Fe0.2O3−δ(LSCF)-Ce0.8Sm0.2O1.9(SDC) composite cathode for solid oxide fuel cells (SOFCs) based on SDC electrolyte, followed by being calcined at 1073 K, 1173 K, 1273 K, 1373 K and 1473 K, was prepared by infiltration of LSCF precursor solution into porous SDC scaffolds. The average LSCF particle size is about 50 nm, 0.1 μm, 0.15 μm, 0.2 μm and 1.2 μm respectively after being calcined at 1073 K, 1173 K, 1273 K, 1373 K and 1473 K for 4 h. The oxygen reduction reaction mechanism in the porous LSCF-SDC nano-sized composite cathode is studied through a comparison with that in the porous LSCF-SDC micro-size composite cathode. The oxygen reduction reaction mechanism in the LSCF-SDC composite cathodes is discussed in terms of frequency response, electrode resistance and reaction order at different oxygen partial pressures p(O2). Three elementary steps are considered to be involved in the cathode reaction: (ⅰ) Dissociation of molecular adsorbed oxygen into atom adsorbed oxygen on cathode surface; (ⅱ) Bulk diffusion of adsorbed of O2− in the bulk LSCF phase; (ⅲ) Oxygen ions transfer at the interface between the cathode and the electrolyte. For the cathodes sintered at 1073 K and 1173 K, the polar resistance in the medium frequency range was dominant and step (ⅱ) is the rate-determining step. The low frequency arc became obvious in the impedance spectra with increasing the calcination temperature of the LSCF precursors. The ratio of the polar resistance in the medium frequency range to the total cathode polar resistance decreases with increasing the calcination temperature, from 70.6% at 1073 K to 29.6% at 1473 K, but the ratio of the polar resistance in the low frequency range to the total cathode polar resistance increases with increasing the calcination temperature, from 4.9% at 1073 K to 58% at 1473 K, implying that the cathode process is limited by step (ⅲ) when the cathode calcination temperature is at 1473 K.

Degradation of (La,Sr)(Co,Fe)O3-Δ SOFC Cathodes at the Nanometre Scale and below

For developing solid oxide fuel cells operating at intermediate temperatures (ITSOFCs), metallic materials have become a preferential choice for the interconnect due to their low cost and excellent physical and chemical properties. However the presence of chromium in all commonly used metallic alloys has been found to cause poisoning of the cathode leading to rapid electrochemical performance degradation of the cathodes including one of the most promising (La,Sr)(Co,Fe)O3-δ (LSCF) perovskite oxides [1-3]. Despite the extensive research on the chromium deposition and poisoning processes, careful microstructural studies, especially at the nanoscale, are rare, which can provide valuable information for the fundamental understanding of the Cr poisoning mechanisms required for developing Cr tolerant cathode materials. In this paper, we examine the Cr poisoning mechanisms in (La0.6Sr0.4)0.95(Co0.2Fe0.8)O3-δ (LSCF6428) materials by correlating the bulk electrochemical properties of the cell with their structural and chemical change at multi-scales down to the nanometer level. Cells with LSCF cathodes were prepared, and the effect of Cr poisoning on the electrochemical behavior of the cell was assessed by impedance spectroscopy. The change in nano/microstructure and chemistry due to poisoning were studied in parallel by a combination of advanced ion and electron microscopy techniques including focus ion beam (FIB) tomography, high resolution (scanning) transmission electron microscopy ((s)TEM) and analytical STEM. The systematic combination of bulk and high-resolution analysis on the same cells allows, for the first time, to directly correlate Cr induced performance degradation with subtle and localized structural/chemical changes of the cathode down to the atomic scale. Up to two orders of magnitude reduction in conductivity, oxygen surface exchange rate and diffusivity were observed in Cr poisoned LSCF6428 samples. These effects are associated with the formation of nanometer size SrCrO4; grain boundary segregation of Cr; enhanced B-site element exsolution (both Fe and Co); and reduction in the Fe valence, the latter two being related to Cr substitution in the LSCF phase. The finding that significant degradation of the cathode happens before obvious microscale change points to new critical SOFC degradation mechanisms effective at the nanometer scale and below, which provide new insight for the development of future poisoning resistant electrode materials not only for SOFCs but also for other devices such as solid oxide electrolysis cells.

Degradation factors in (La,Sr)(Co,Fe)O3-δ cathode/Sm2O3–CeO2 interlayer/Y2O3–ZrO2 electrolyte system during operation of solid oxide fuel cells

In this study, the miscrostructural change of the LSCF/SDC/YSZ system upon discharge was analyzed quantitatively by the focused ion beam–scanning electron microscopy as well as the transmission electron microscopy. It is widely recognized that the formation of highly-resistive SrZrO3 phase degrades the cell performance in this system. In fact, the ohmic loss and cathodic overpotential increased in response to the six-fold increase in the volume of SrZrO3 phase after 400 h of discharge at 1000 °C. However, the microstructural change proceeded in the whole part of this system, indicating that various degradation factors need to be considered; e.g., 1) the agglomeration of SDC and LSCF phases, 2) the reduction in triple phase boundary length, and 3) the formation of ceria-zirconia solid solution.

Flash Sintering of (La, Sr)(Co, Fe)O3–Gd‐Doped CeO2 Composite

Sintering of composites constituted by two nonstoichiometric phases (La0.6Sr0.4)(Co0.2Fe0.8)O3 (LSCF) and Gd0.1Ce0.9O2 (GDC) under constant electric field in constant heating rate experiment is studied in this work. The requirements of field and temperature for composite systematically increase with GDC amounts this indicating the importance of material conductivity. Sintering/grain growth rate is higher in the composite compared to pure LSCF phase. Flash‐sintering phenomenon in the composite is explained on the basis of three factors: (1) large and continuous increase in conductivity of LSCF acts as source of defects, (2) maintenance of sufficient local temperature because of GDC during continuous conductivity increase facilitates the cationic diffusion, and (3) reduction reactions of LSCF, during polaron hopping conduction, and of GDC phase at higher temperature activate the sintering process.

Electrocatalytic performance enhancement of La0.6Sr0.4Co0.2Fe0.8O3-δ–Y2O3 stabilized ZrO2 cathodes prepared by an impregnation technique

The electrocatalytic performance of the oxygen-reduction reaction of La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF)–Y2O3 stabilized ZrO2 (YSZ) cathodes prepared by an impregnation technique has been investigated as cathodes for intermediate temperature solid oxide fuel cells. The electrocatalytic activity of LSCF-YSZ cathodes increases with the introduction of LSCF phases to the YSZ scaffold. The introduction of surfactants into LSCF-precursor solutions during preparation has a great effect on the microstructure and electrochemical performance of LSCF-YSZ composite cathodes. N-ethyl-perfluoyooctylsulfonamide (DF10) is a type of commonly used nonionic flusurfactant which affects the LSCF particles' morphology on the YSZ scaffold. Using N-ethyl-perfluoyooctylsulfonamide (DF10) + acetylacetone during the preparation of LSCF-YSZ composite cathodes decreases the electrode polarization resistance (Re) of cathodes from 0.45 to 0.18 Ω cm2. We obtained a notable improvement in the electrochemical performance of LSCF-YSZ-composite cathodes with uniform and continuous LSCF particle distribution on the surface of YSZ scaffold.

Towards designing La 1−x Sr x Co y Fe 1−y O 3−d with enhanced phase stability: Role of the defect structure

Abstract Generally, La 1 − x Sr x Co y Fe 1 − y O 3 − δ -phases (LSCF) as mixed ionic electronic conductors (MIEC) are applied as electrode material in solid oxide fuel cells and as oxygen separation membranes in zero CO 2 emission power plants. LSCF phases are synthesized using magnetron sputtering from a compound target. The chemical composition could be controlled via synthesis temperature variations as the sticking coefficient is a function of temperature. With decreased synthesis temperature a significant change in chemical composition is observed resulting in an increased A-site deficiency. This leads to an extension of the cubic stability range to temperatures as low as 450 °C. Thus, structural transition from the low-temperature rhombohedral modification to the high-temperature cubic structure, accompanied by considerable volume change, will be suppressed. This significantly lowers mechanical stresses on the MIEC-material during application and is expected to increase the lifetime of the cells and membranes. The experimental results are consistent with ab initio density functional theory calculations performed on A-site deficient as well as fully stoichiometric LSCF phases. A-site deficient cubic phases are more stable than the stoichiometric phases. No significant difference in Young's modulus is obtained.

Citrate–hydrothermal synthesis, structure and electrochemical performance of La0.6Sr0.4Co0.2Fe0.8O3−δ cathodes for IT-SOFCs

Abstract La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3− δ (LSCF) powders were synthesized by a combination of citrate and hydrothermal methods. The thermal decomposition behavior of the as-prepared powder was carried out by simultaneous thermogravimetry–differential thermal analysis. The calcined powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and particle size distribution (PSD). Screen-printed LSCF/CGO/LSCF symmetrical cells were sintered between 1150 and 1200 °C and studied by impedance spectroscopy in order to assess the cathode kinetics for the oxygen reduction reaction. Rietveld refinement of XRD data showed the formation of a single perovskite LSCF phase with crystallite size of 53 nm at 900 °C. The best area specific resistance (ASR) value, measured in static air, was found to be 0.34 Ω cm 2 at 750 °C, demonstrating that the novel citrate–hydrothermal method is an effective way to prepare cathode materials for SOFC. Cathode performance can be further enhanced by additional surface modification through impregnation with Pr-containing solution, reaching 0.17 Ω cm 2 at 750 °C. Furthermore, the activation energy of the PrO x -impregnated cathode is 83.4 kJ/mol, i.e., much lower than 123.8 kJ/mol, the best value determined for PrO x -free cathodes.

Structural and electrical properties of La0.7Sr0.3Co0.5Fe0.5O3 powders synthesized by solid state reaction

Abstract This work investigates the effect of synthesis parameters (calcination temperature, milling conditions and sintering temperature) on the structural, morphological and electrical properties of La 0.7 Sr 0.3 Co 0.5 Fe 0.5 O 3 (LSCF) powders prepared by the solid state reaction. The thermogravimetric profile showed that the minimum temperature needed for the carbonate decomposition and formation of perovskite phase is 800 °C. SEM analysis revealed the loose and porous structure of the powder materials. The XRD patterns demonstrate that milling parameters such as grinding balls:sample ratio, rotational speed, and milling time influence the structural properties. The results revealed that powders synthesized with grinding balls:sample ratio of 8:1, 500 rpm and 4 h of milling present pure LSCF phase. Porosity of the pellets decreased with increasing sintering temperature from 950 to 1100 °C. Electrical conductivity was measured at 400–1000 °C and correlated with sintering temperature.

Preparation of Nanocomposite GDC/LSCF Cathode Material for IT-SOFC by Induction Plasma Spraying

Homogeneous mixtures of Ce0.8Gd0.2O1.9 (GDC) and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) nanopowders were successfully synthesized using induction plasma by axial injection of a solution. The resulting nanocomposite powders consisted of two kinds of nanopowders with different mass ratio of GDC/LSCF, such as 3/7 and 6/4. The morphological features, crystallinity, and the phases of the synthesized powders were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), local energy-dispersive x-ray spectroscopy (EDS) analysis, and x-ray diffraction (XRD). The nanopowders are almost globular in shape with a diameter smaller than 100 nm and their BET specific areas are around 20 m2 g−1. The GDC and LSCF phases are well distributed in the nanopowders. In addition, suspensions, made with the as-synthesized composite nanopowders and ethanol, were used to deposit cathode coatings using suspension plasma spray (SPS). Micro-nanostructures of the coatings are discussed. The coatings are homogeneous and porous (51% porosity) with cauliflower structures.

Preparation and investigation of electrical and electrochemical properties of lanthanum-based cathode for solid oxide fuel cell

In this paper, electrical and electrochemical properties of La 0.6Sr 0.4Co 0.2Fe 0.8O 3− δ (LSCF) cathode have been studied. The sample is prepared by solid-state reaction method. The results of the X-ray diffraction have been analyzed by FullProf software and it has been found that LSCF phase has been formed. Resistance of the sample versus temperature in air atmosphere has been measured and the results show that, it decreases by increasing temperature. Activation energy for electrical conductivity has been calculated by fitting the Arrhenius plot with experimental data. Also, resistance of sample has been measured at the different temperature ranges and in the presence of Oxygen/Argon atmosphere. Using electrical relaxation technique and some approximations, ionic diffusion coefficient and activation energy for ionic conductivity have been calculated.

La 0.8 Sr 0.2 Co 0.8 Fe 0.2 O 3 Nanoparticles Formed in Micropores of La0.8Sr0.2MnO3–Yttria Stabilized Zirconia Cathodes

La 0.8 Sr 0.2 Co 0.8 Fe 0.2 O 3 (LSCF) nanoparticles are formed in micropores of La0.8Sr0.2MnO2(LSM)-yttria stabilized zirconia (YSZ) cathodes by reaction-infiltration method. Bismuth nitrate is added in the precursor nitrate solution for LSCF as the reaction promoter. The LSCF phase is observed at 600°C by the addition of bismuth nitrate, and about 100nm particle size LSCF(Bi) is homogenously distributed on the LSM-YSZ surface. The electrode impedance of LSM-YSZ/YSZ/LSM-YSZ cells is examined and has found that the electrode polarization resistance is extremely reduced by the LSCF(Bi) infiltration in LSM-YSZ. The performance of the anode support fuel cell of Ni-YSZ/YSZ/LSM-YSZ is examined at 700°C. The LSCF(Bi) infiltrated LSM-YSZ cathode significantly enhanced the cell performance with a 97%H2-3%H2 fuel at 700°C. The maximum power density of 0.35W∕cm2 is attended.

Solid oxide fuel cell cathodes by infiltration of La 0.6Sr 0.4Co 0.2Fe 0.8O 3 − δ into Gd-Doped Ceria

This paper describes the structure and electrochemical properties of solid oxide fuel cell cathodes prepared by infiltration of La 0.6Sr 0.4Co 0.2Fe 0.8O 3 − δ (LSCF) into porous Gd-Doped Ceria (GDC). The GDC scaffolds were prepared by partial sintering of GDC compacts on dense GDC electrolytes. LSCF was introduced into these structures by multiple infiltrations of aqueous nitrate solutions followed by firing. The cathode polarization resistance, measured using electrochemical impedance spectroscopy on symmetrical cells, showed a pronounced minimum as a function of GDC firing temperature at 1100–1200 °C, where the microstructure was well-necked but porous with ~ 300-nm-sized particles. Increasing the infiltrated LSCF loading decreased the polarization resistance up to the highest loading tested, 12.5 vol.%. Decreasing the LSCF firing temperature decreased the polarization resistance due to a decrease in the LSCF feature size from ~ 1 μm at 1200 °C to ~ 50 nm at 800 °C. Thus, the infiltration method allowed separate control over the microstructures of the GDC and LSCF phases. The lowest polarization resistance measured at 600 °C was 0.24 Ω cm 2.

Nano-structured (La, Sr)(Co, Fe)O 3 + YSZ composite cathodes for intermediate temperature solid oxide fuel cells

A nano-structured La 0.8Sr 0.2Co 0.5Fe 0.5O 3 + Y 2O 3 doped ZrO 2 (LSCF + YSZ) composite cathode was prepared by impregnation of a LSCF-containing solution into porous YSZ structure presintered on the YSZ electrolyte. The result shows that the LSCF phase was formed at 700 °C, forming a nano-structured, effective and functional LSCF + YSZ composite cathode that not only produces high triple phase boundaries for the O 2 reduction reaction, but also provides a structurally stable interface between the LSCF and YSZ. The electrode polarization resistance for the O 2 reduction reaction is from 0.539 to 0.047 Ω cm 2 between 600 and 750 °C, indicating the promising potential the LSCF + YSZ as a high performance cathode for intermediate temperature solid oxide fuel cells.