Strontium-doped Lanthanum Manganate Research Articles

Preparation and Particle Size Study of Cobalt Substituted Strontium Doped Lanthanum Manganate Films by Sol-gel and Heat Treatment Method

In order to study the effect of B-position element substitution on strontium doped lanthanum manganate microstructure and resistivity temperature property, the cobalt substituted strontium doped lanthanum manganate ceramic powders with La0.6Sr0.4CoxMn1-xO3 as the main component was prepared by sol gel method combined with heat treatment process at first, then the cobalt substituted strontium doped lanthanum manganate films was prepared by silk-screen printing on the Alumina ceramic substrate. The results showed that when the x value sequentially varied from 0 to 0.2,0.4,0.6,0.8, the particle size property of films would be changed by the change of the crystal structure, which was produced by the B-position cobalt substitution. It could be seen from the results that the average radius of the five powders were concentrated in the range of 16.4-19.6nm.

Electrochemical gas–electricity cogeneration through direct carbon solid oxide fuel cells

Solid oxide fuel cells (SOFCs), with yttrium stabilized zirconia (YSZ) as electrolyte, composite of strontium-doped lanthanum manganate (LSM) and YSZ as cathode, and cermet of silver and gadolinium-doped ceria (GDC) as anode, are prepared and tested with 5wt% Fe-loaded activated carbon as fuel and ambient air as oxidant. It is found that electricity and CO gas can be cogenerated in the direct carbon SOFCs through the electrochemical oxidation of CO and the Boudouard reaction. The gas–electricity cogeneration performances are investigated by taking the operating time of the DC-SOFCs as a measure of rate decrease of the Boudouard reaction. Three single cells and a two-cell-stack are tested and characterized in terms of electrical power output, CO production rate, electrical conversion efficiency, and overall conversion efficiency. It turns out that a rapid rate of the Boudouard reaction is necessary for getting high electrical power and CO production. Taking the emitted CO as part of the power output, an overall efficiency of 76.5% for the single cell, and of 72.5% for the stack, is obtained.

Preparation of nano-crystalline strontium-doped lanthanum manganate (LSM) powder and porous film by aerosol flame deposition

To improve the performance of the cathode, many groups have studied the relationship between the cathode microstructure and the electrochemical performance. In this study, a porous La0.8Sr0.2MnO3±δ (LSM) cathode film with primary particles of under 10nm diameters was prepared by aerosol flame deposition (AFD). The AFD technique was applied to synthesize the spherical particles and dense LSM thin film. The cathode performance was improved, and the polarization resistance was decreased by extending the active triple phase boundary. The electrochemical characteristics were investigated in the temperature range of 600–900°C and oxygen partial pressure range of 0.1–1.0atm. For oxygen reduction reaction on the LSM cathode, it was turned out that both oxygen atom diffusion and oxygen ion transfer from the three phase boundary to the yttria-stabilized zirconia electrolyte lattice were the rate-determining steps with comparable contributions. The polarization resistance of the prepared LSM film decreased from 206 to 1.7Ωcm2 with increasing temperature from about 600 to 900°C and the activation energy was 1.48eV.

Aerosol Jet Printing and Microstructure of SOFC Electrolyte and Cathode Layers

We report the cathode layer optimization efforts undertaken to improve the cell performance of a previously reported (10) aerosol jet printed SOFC with strontium doped lanthanum manganate (LSM) based cathode. The cathode current collection layer, LSM with different thicknesses, solids loading in printing ink, and sintering temperature was examined. These parameters were observed to have a significant impact on the cell performance, changing the maximum power density of cells from 200 - 460 mW/cm2 at 850 ºC, depending on the processing conditions. Low voltage scanning electron microscopy was used to clearly distinguish the different phases of the composite LSM/YSZ layer. This method was used as a diagnostic tool to qualitatively assess the feasibility of "on the fly mixing" of the individually aerosolized inks. Cells with printed gadolinia doped ceria (GDC)-lanthanum strontium cobalt ferrite (LSCF) cathodes showed a performance, about twice that of cells with LSM cathodes.

Progress Toward Inkjet Deposition of Segmented-in-Series Solid-Oxide Fuel Cell Architectures

This paper presents our progress in applying inkjet-printing technology in fabrication of solid-oxide fuel cells (SOFCs) in the segmented-in-series architecture. Cell materials include a nickel anode, yttria-stabilized zirconia electrolyte, strontium-doped lanthanum manganate cathode, and lanthanum-doped strontium titanate interconnect. Inks are formulated from commercially sourced powders, and printed onto porous, chemically inert, partially stabilized zirconia supports. Accurate registration of SOFC materials is observed at a feature size of approximately 100 μm. After high-temperature sintering, good adhesion between SOFC materials and the support is also evident.

Polarization Characteristics and Chemistry in Reversible Tubular Solid-Oxide Cells Operating on Mixtures of H2, CO, H2O , and CO2

This paper reports the results of combined experimental and modeling studies of reversible solid-oxide cells. The tubular cells are fabricated using a Ni–YSZ (yttria-stabilized zirconia) fuel-electrode support, a dense YSZ electrolyte membrane, and a strontium-doped lanthanum manganate–YSZ composite air electrode. Experiments are designed to systematically vary gas-phase species partial pressures and operating temperatures. The fuels are mixtures of , CO, , , and Ar. Performance is measured under anodic (fuel cell) and cathodic (electrolysis) polarization. The models consider reactive porous-media transport within the composite electrodes, thermal chemistry on Ni and YSZ surfaces, and charge-transfer chemistry. All chemistry is modeled with elementary reversible reactions. Close coupling between experimental measurements and model-based interpretation provides a basis for establishing reaction pathways and rates. In addition to advancing fundamental understanding, the resulting detailed reaction mechanisms are valuable for incorporation into predictive models that can be used for design and optimization of fuel-cell and electrolysis systems.

Two-Dimensional Modeling of Self-Propagating High-Temperature Synthesis of Strontium-Doped Lanthanum Manganate

A two-dimensional finite element model is developed to study the reaction kinetics and heat transfer during the self-propagating high-temperature synthesis of La0.6Sr0.4MnO3, a cathode and interconnect material used in solid oxide fuel cells. The activation energy of La0.6Sr0.4MnO3 formation was calculated from experimental temperature history. The calculated spatial-temporal temperature profile, heat generation rate, reaction conversion, and flow pattern of surrounding gas during the reaction are reported in this work. Hot spots are found at the corner near the ignition point shortly after the ignition. The model provided a simple and reliable way to design a large-scale production of La0.6Sr0.4MnO3.

Inkjet Printing of Anode Supported SOFC: Comparison of Slurry Pasted Cathode and Printed Cathode

Solid oxide fuel cells (SOFCs) were fabricated by depositing NiO/yttria-stabilized zirconia (YSZ) anode interlayer, YSZ electrolyte layer, and strontium-doped lanthanum manganate (LSM)-YSZ and LSM cathode layers on a NiO―YSZ support using an inkjet printing method with potential for high reproducibility and design flexibility. The cells exhibited a stable open-circuit voltage of 1.1 V and a maximum power density of 430―460 mW/cm 2 at 850°C for hydrogen. For comparison, cells similar in all respects except for utilizing conventional hand-pasted slurry for the cathode layers, were tested and shown to have similar electrochemical performance. Altering the rheological property of the ink and/or the printing process parameter altered the microstructure of printed layers.

Performances and Degradation Phenomena of Solid Oxide Anode Supported Cells With LSM and LSCF Cathodes: An Experimental Assessment

The performance of solid oxide fuel cells is affected by various polarization losses, usually grouped in Ohmic, activation, and concentration polarizations. Under typical operating conditions, these polarization losses are largely dependent on cell materials, electrode microstructures, and cell geometry: as an example, the performance of a tubular cell is strongly limited by the Ohmic polarization due to the long current path of electrons, while in a planar cell each of these losses has a comparable effect. It is therefore of interest, in the case of planar geometry, to investigate the main performance limiting factors. In this paper, a performance evaluation of planar circular-shaped seal-less SOFC cells was performed. Two different designs of planar cells are considered. Both have a porous NiO-YSZ (yttria stabilized zirconia) anode as mechanical support, a NiO-YSZ anode active layer, and an YSZ electrolyte, and they only differ in the cathode design: (1) strontium doped lanthanum manganate (LSM)-YSZ cathode functional layer and LSM cathode current collector layer; (2) yttria doped ceria blocking layer and lanthanum strontium cobalt ferrite oxide (LSCF) functional layer. The characterization was performed by taking V-I measurements over a range of temperatures between 650°C and 840°C with hydrogen as fuel and air as oxidant. The experimental data analysis consisted in the analysis of some typical performance indicators (maximum power density (MPD); current density at 0.7V). The dependence of the cell performance on the various polarization contributions was rationalized on the basis of an analytical model—through a parameter estimation of the experimental data—devoted to the determination of the main polarization losses. Based on the results of the investigation, it is concluded that LSCF cathodes are really effective in decreasing the cathode activation polarization, allowing the reduction in operating temperature.

Experimental investigations of the microscopic features and polarization limiting factors of planar SOFCs with LSM and LSCF cathodes

The paper deals with the microscopic and polarization evaluation of planar circular-shaped seal-less SOFC cells from InDEC ® with an outline of performance limiting factors at reduced temperature. The cells consist of porous NiO–YSZ anode as mechanical support, NiO–YSZ anode active layer, yttria-stabilized zirconia (YSZ) electrolyte, and only differ for the cathode design. A first design (ASC1) with strontium doped lanthanum manganate LSM–YSZ cathode functional layer (CFL) and LSM cathode current collector layer (CCCL); the second design (ASC2) with yttria doped ceria (YDC) barrier layer and lanthanum strontium cobalt ferrite oxide (LSCF) cathode. The microscopic analysis was performed using SEM methods. The electrical characterization was performed by taking current–voltage measurements over a range of temperatures between 650 and 840 °C with hydrogen as fuel, and air as oxidant. The analysis of performance showed that at 740 °C the voltage of 700 mV is reached at around a double value of current density in the case of ASC2. Further, the dependence of performance on the various polarization contributions was rationalized on the basis of an analytical model. Through a parameter estimation on the experimental data, it was possible to determine some polarization parameters for the two cells such as the effective exchange current densities, ohmic resistance and anodic limiting current density. It is shown that the performance limitation at low temperature is due to activation polarization for ASC1 and ohmic polarization for ASC2. Based on the results of the investigation, it is concluded that LSCF cathodes are really effective for decreasing the cathode activation polarization, allowing the reduction of operating temperature.

Nanocomposite Ag–LSM solid oxide fuel cell electrodes

Advances in infiltration technology have enabled the creation of innovative electrode architectures that are key to highly effective SOFC anodes and cathodes. In this work, an Ag-infiltrated electrode has been created using a pre-sintered porous scandia-stabilized zirconia (SSZ) electrode backbone. The well-sintered SSZ provides a highly connected ion-conducting pathway throughout the electrode, while the nanometer thickness of the Ag particle layer minimizes the oxygen transport resistance that otherwise limits reaction rates in typical Ag composite electrodes. The new Ag composite electrode had minimal activation polarization by 750 °C. The infiltration technology has allowed for incorporation of additional nanoscale electrocatalysts. Here, an Ag–LSM (strontium-doped lanthanum manganate) composite was produced, that takes advantage of each component catalyst and demonstrates a further enhanced effectiveness of the cathode Ag metal catalyst, producing relatively stable cell power densities of 316 mW cm −2 at 0.7 V (and 467 mW cm −2 peak power at ∼0.4 V) for over 500 h.

Dependence of polarization in anode-supported solid oxide fuel cells on various cell parameters

The performance of solid oxide fuel cells (SOFCs) is affected by various polarization losses, namely, ohmic polarization, activation polarization and concentration polarization. Under given operating conditions, these polarization losses are largely dependent on cell materials, electrode microstructures, and cell geometric parameters. Solid oxide fuel cells (SOFC) with yttria-stabilized zirconia (YSZ) electrolyte, Ni–YSZ anode support, Ni–YSZ anode interlayer, strontium doped lanthanum manganate (LSM)–YSZ cathode interlayer, and LSM current collector, were fabricated. The effect of various parameters on cell performance was evaluated. The parameters investigated were: (1) YSZ electrolyte thickness, (2) cathode interlayer thickness, (3) anode support thickness, and (4) anode support porosity. Cells were tested over a range of temperatures between 600 and 800 °C with hydrogen as fuel, and air as oxidant. Ohmic contribution was determined using the current interruption technique. The effect of these cell parameters on ohmic polarization and on cell performance was experimentally measured. Dependence of cell performance on various parameters was rationalized on the basis of a simple analytical model. Based on the results of the cell parameter study, a cell with optimized parameters was fabricated and tested. The corresponding maximum power density at 800 °C was ∼1.8 W cm −2.

Functionally Graded Cathodes for Honeycomb Solid Oxide Fuel Cells

Functionally graded cathodes were fabricated by slurry coating process for honeycomb solid oxide fuel cells with yttria-stabilized zirconia (YSZ) electrolytes. The cathodes are composed of strontium-doped lanthanum manganate (LSM), gadolinia-doped ceria, and La 0 . 6 Sr 0 . 4 Co 0 . 2 Fe 0 . 8 O 3 (LSCF). The LSM content was gradually decreased, while the LSCF content was gradually increased with the increasing distance away from the electolyte-electrode interface. Scanning electron microscopy investigation and electrochemical impedance spectroscopy measurements revealed that the electrochemical performance of the graded cathodes depends sensitively on the microstructures that were primarily determined by firing temperatures. The cathodes graded in composition show interfacial resistances about 10 times lower than traditional LSM-YSZ cathodes that have similar microstructures and thickness. The graded cathode fired at low temperature has an interfacial resistance as low as 0.47 Ω cm 2 at 750°C, which is very encouraging for developing honeycomb fuel cells operated below 800°C.

Fabrication and performance of advanced multi-layer SOFC cathodes

Multilayered cathodes for solid oxide fuel cells are presented. The cathodes are composed of strontium doped lanthanum manganate and yttria stabilised zirconia, the ratio of which is increased with increasing distance from a supporting zirconia electrolyte. Some cathodes additionally carry a number of layers with a graded transition from manganite to cobaltite to add an electronically highly efficient current collector. The cathodes were prepared by spray painting and low temperature sintering. Electrochemical measurements revealed a performance up to 0.2 Ω cm 2 at 750°C for the first generation of these cathodes. The electrochemical performance was found to be influenced further by the microstructure at the interface close to the solid electrolyte and the quality of electrical contact thorough the sintered electrode.