La0.8Sr0.2FeO3 Research Articles

The effect of partial substitution of noble metal (Pd) at the B site of La0.6Sr0.4FeO3 as a supercapacitor electrode material.

Sol-gel combustion was used to produce the perovskite-type La0.6Sr0.4FeO3 (LSF) and La0.6Sr0.4Fe0.9Pd0.1O3 (LSFP) materials and assessed as supercapacitor electrodes. The synthesized materials' crystal structure, morphology, and electrochemical performance were thoroughly analyzed. The partial substitution of Pd in the B site of the LSF structure affected the electrochemical properties of this compound and improved its performance. In fact, the greatest effect of Pd substitution was on the content of oxygen vacancies, which are known as the active sites of the perovskite surface in the supercapacitor cell. The specific capacitance obtained for the sample containing Pd was about 80 F.g-1 at a current density of 1 A.g-1 in 1M KOH. In addition, this sample had a decreased intrinsic resistance to ion and electron diffusion. The remarkable structural and morphological features of LSFP contribute to its superior electrochemical performance. At a power density of 1000 W.kg-1 and a current density of 1 A.g-1, an LSFP symmetrical cell had an energy density of 44.45 W.h.kg-1.

Dual strategy of A-site ion substitution and self-assembled MoS2 wrapping to boost permittivity for reinforced microwave absorption performance

With the rapid development of electronic technology, how to effectively eliminate electromagnetic pollution has become a serious problem. Perovskite oxides have shown great potential in the field of electromagnetic wave absorption due to their unique structure and excellent physicochemical properties. Herein, by rationally manipulating the A-site ion substitution strategy, the theoretically directed doping of Sr ions into La ionic sites was utilized and the layered MoS2 was loaded by the hydrothermal process to modify its surface. Consequently, the introduced polarization phenomenon improved the dielectric performance of the perovskite oxides, achieving a collaborative dielectric/magnetic loss mechanism. Accordingly, the prepared La0.7Sr0.3FeO3(LSFO)/MoS2 as coating filler in the epoxy resin coating system can obtain the minimum reflection loss of –67.09 dB at 1.9 mm and the maximum effective absorption bandwidth of 7.28 GHz at 2.3 mm. More importantly, it also exhibits excellent absorption performance for multi-band electromagnetic waves, covering a wide range of specified frequency bands. It provides inspiration for exploring novel perovskite oxide-based electromagnetic wave absorbing coatings and broadens the choice of ideal candidate materials for designing highly efficient, multi-band absorbers to cope with sophisticated electromagnetic environments.

Methane conversion to syngas by chemical looping on La0.8Sr0.2FexCo1-xO3 (x = 0, 0.25, 0.50, 0.75) perovskites with CO2 co-feeding

Partial oxidation of methane (POM) by chemical looping with CO2 co-feeding on La0.8Sr0.2FeO3 (LSF) perovskite catalyst yielded a highly selective operation and enabled to extend the duration of reduction cycle. In this work, the conversion of methane to syngas was studied on La0.8Sr0.2Fe(x)Co(1-x)O3 (x = 0, 0.25, 0.5, 0.75) perovskites in chemical-looping mode, co-feeding CO2 and methane. The reaction was conducted at 850 °C, 15 min reduction (10% methane in N2, 0–3% CO2), and 10 min oxidation (10% O2 in N2) cycles. The perovskites activity decreased with increasing Co content, in the absence of CO2, due to intensified coke deposition on the catalyst. Addition of CO2 during the reduction step (1–3%) reduced coke accumulation. A run conducted on La0.8Sr0.2CoO3 (LSC) with continuous feeding of CO2 and periodical (on–off) methane feeding indicated that CO2 reacts with the accumulated coke in reverse-Boudouard reaction, increasing CO selectivity without affecting the methane conversion. XRD analysis of reduced Co-containing perovskites indicates a decreasing perovskite content. Metallic Co and La2O3 phases increased as the Co content in the fresh perovskite increased, increasing coke deposition. As the Co content increased, the process shifts from POM with oxygen replenishment (LSF) to cracking followed by reverse-Boudouard reaction (LSC).

Alkali metal halide-coated perovskite redox catalysts for anaerobic oxidative dehydrogenation of n-butane.

Oxidative dehydrogenation (ODH) of n-butane has the potential to efficiently produce butadiene without equilibrium limitation or coke formation. Despite extensive research efforts, single-pass butadiene yields are limited to <23% in conventional catalytic ODH with gaseous O2. This article reports molten LiBr as an effective promoter to modify a redox-active perovskite oxide, i.e., La0.8Sr0.2FeO3 (LSF), for chemical looping–oxidative dehydrogenation of n-butane (CL-ODHB). Under the working state, the redox catalyst is composed of a molten LiBr layer covering the solid LSF substrate. Characterizations and ab initio molecular dynamics (AIMD) simulations indicate that peroxide species formed on LSF react with molten LiBr to form active atomic Br, which act as reaction intermediates for C─H bond activation. Meanwhile, molten LiBr layer inhibits unselective CO2 formation, leading to 42.5% butadiene yield. The redox catalyst design strategy can be extended to CL-ODH of other light alkanes such as iso-butane conversion to iso-butylene, providing a generalized approach for olefin production.

Characteristics and gas sensor applications of ZnO-Perovskite heterostructure

In this study, zinc oxide (ZnO) nanofibers were prepared using the electrospinning method, and the effects of different spinning voltages and annealing temperatures on the fiber structure were tested. La0.8Sr0.2FeO3 (LSFO) perovskite film was prepared by a sol-gel method. Then we dip LSFO on ZnO nanofiber and grow it on the interdigital gold electrode substrate for gas sensors. The results show that the ZnO/LSFO heterostructure gas sensor has a good sensing response to H2S gas and exhibits good gas selectivity. The best gas response is 52.17% under 4 ppm H2S and work temperature 200°C, which has good recovery and reproducibility.

Controlled template removal from nanocast La0.8Sr0.2FeO3 for enhanced CO2 conversion by reverse water gas shift chemical looping

This study addresses an enhanced CO2 conversion of mesoporous La0.8Sr0.2FeO3 (LSF) perovskite synthesized using a nanocasting method in reverse water gas shift chemical looping (RWGS-CL) process. The effects of controlled template removal from the nanocast LSF on its textural property and resulting redox reactivity were thoroughly investigated. LSF was first impregnated on SBA-15 (a mesoporous silica template), which was removed by NaOH etching to monitor the residual Si content. Specific surface area, total pore volume, and metal dispersion of the nanocast LSF were dramatically enhanced as the residual Si content decreased, but Si contents of < 5 wt% caused the mesoporous structure to collapse. Temperature-programmed experiments revealed that both the reactivity and capacity of reducible oxygen were maximized by optimizing residual Si content at 10 wt%. XPS analyses showed that the atomic ratio of surface oxygen to lattice oxygen, a key indicator of CO productivity, was also maximized at a Si content of 10 wt%. The mesoporous LSF with this Si content achieved the highest average CO yield of 2.80 mmol/g for RWGS-CL at 600 °C, which was 5.9 fold-higher than that achieved by bulk LSF.

Exsolution Synthesis of Nanocomposite Perovskites with Tunable Electrical and Magnetic Properties

AbstractNanostructured functional oxides play an important role in enabling clean energy technologies and novel memory and processor devices. Using thin‐film La0.6Sr0.4FeO3 (LSF) as a model system, the novel utility of exsolution in fabricating self‐assembled metal oxide nanocomposites with tunable functionalities is shown. Exsolution triggers the formation of metallic iron (Fe0) nanoparticles, Ruddlesden–Popper domains, and nm‐scale percolated Fe‐deficient channels in LSF. Combining multimodal characterization with numerical modeling, the chemical, magnetic, and electrical properties of the exsolution‐synthesized nanocomposite at different stages of Fe0 exsolution as well as during redox cycling are assessed. After exsolution, the electronic conductivity of the nanocomposite LSF increased by more than two orders of magnitude. Based on numerical analysis representing all the constituents, it is expected that this increase in conductivity originates mainly from the Fe‐deficient percolating channels formed during exsolution. Moreover, the exsolved nanocomposite is redox‐active even at moderate temperatures. Such redox capabilities can enable dynamic control of the nanocomposite functionality by tailoring the oxygen non‐stoichiometry. This concept is demonstrated with a continuous modulation of magnetization between 0 and 110 emu cm−3. These findings point out that exsolution may serve as a platform for scalable fabrication of complex metal oxide nanocomposites for electrochemical and electronic applications.

Fabrication and Characterization of a Tubular Solid Oxide Fuel Cell with Impregnated Perovskite Electrodes

The tubular cells were produced by a simple and inexpensive method, suitable for mass production. A porous YSZ backbone was co-cast with a thin layer of YSZ electrolyte over it. After rolling in tubular shape and co-sintering, the porous backbone was impregnated with functional perovskite materials, the nickel doped lanthanum calcium titanate LCNT (La0.43Ca0.37Ni0.06Ti0.94O3- γ) for the fuel side and the lanthanum strontium ferrite LSF (La0.8Sr0.2FeO3) for the air electrode. The LCNT perovskite was proposed as the alternative fuel electrode due to its mixed ionic and electronic conductivity (MIEC) properties and catalytical activity supplemented by exsolved Ni nanoparticles. The electrochemical poling at high potential, so-called 'switching', can increase the activity of LCNT due to facilitated reduction and exsolution. After switching at 2.1 V for 2 min, the tubular cell performance in fuel cell mode increased threefold. The impedance analysis indicated a reduction of ohmic and polarisation resistance on the whole frequency range and facilitated electrode kinetics under applied voltage.

Synthesis and processing of SOFC components for the fabrication and characterization of anode supported cells

In this article, it is intended to evaluate the performances of previously synthesized different nanometric compounds as SOFC components under real conditions. For this purpose, anodic supports SOFCs have been manufactured in different configurations.The compounds NiO-(Y2O3)0.08(ZrO2)0.92 (NiO–YSZ), (Y2O3)0.08(ZrO2)0.92 (YSZ), Sm0.2Ce0.8O1.9 (SDC), La0.6Sr0.4FeO3 (LSF) and LaNi0.6Fe0.4O3 (LNF) were used as anode support, electrolyte, barrier, cathode and contact layer, respectively. To obtain the cells, the anode supports were produced by uniaxial pressing and the remaining layers were added using the airbrush technique, assembling them by different sintering processes. The cells developed have been electrochemically tested in a temperature range between 750 and 865°C. Additionally, degradation tests have been carried out under constant current. Moreover, to characterize the microstructure of the cells, a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectroscopy (EDX) analyzer has been used.The results obtained show that the incorporation of cathode and contact layers increases the power densities and decreases the total resistances of the cells with respect to the cell without cathode, especially with the addition of the LNF contact layer. Despite the improvement obtained, more tests have to be carried out in order to optimize the performance of SOFC devices in degradation tests.

Sources of performance degradation in thin film La0.6Sr0.4FeO3 air electrodes

Origins of long-term oxygen reduction activity degradation at 700 °C in polymeric precursor-derived La0.6Sr0.4FeO3 (LSF) thin film cathodes were investigated. Electrochemical impedance spectroscopy measurements revealed that the LSF thin films pre-calcined at 900 °C (LSF-900) exhibited much faster electrochemical activity loss than did LSF pre-calcined at 700 °C (LSF-700). As similar losses in surface area were determined upon scanning electron microscopy image analyses of samples, microstructure evolution was excluded as a possible reason for the difference in degradation rates. Upon X-ray diffraction analyses and comparison of results with literature, it was suggested that small amounts of Ruddlesden-Popper type (La, Sr)2FeO4 (214) phases were present throughout the 100 hour exposure of both LSF-700 and LSF-900 to 700 °C, thus not affecting the long-term performance degradation rates. X-ray photoelectron spectroscopy analyses revealed that the ratio of surface-bound Sr to the lattice-bound one increased significantly in LSF-900, suggesting electrochemically inactive SrO/Sr(OH)2/SrCO3 rich layer formation and thus contributing to fast activity loss. Overall, it was established that microstructural evolution was not the sole source of degradation in LSF-based cathodes. Since LSF thin films deposited by a solution precursor onto YSZ electrolytes constitute a model structure, the results obtained in the present study can also provide useful information on the degradation of LSF-YSZ composite cathodes prepared by LSF infiltration into YSZ scaffolds.

Coking resistant Ni–La0.8Sr0.2FeO3 composite anode improves the stability of syngas-fueled SOFC

An improved SOFC anode with excellent stability against carbon deposition with syngas as fuel is reported. The anode material is Ni–La0.8Sr0.2FeO3 (LSF) composite synthesized by anhydrous impregnation. After reduction in wet H2 (3% H2O), the material partially decomposes to SrLaFeO4 and exsolved Fe. The exsolved Fe forms Ni–Fe alloy with impregnated Ni. The particle size of Ni–Fe alloy is about 20–50 nm. The Ni–Fe alloy nanoparticles disperse on the surface of the La0.8Sr0.2FeO3 and SrLaFeO4 oxides. The increase of Ni content promotes the exsolution of Fe and increases the reaction sites of Ni–Fe alloy. With the increase of the Ni content, the electrical conductivity and catalytic activity are enhanced, which improves the electrochemical performance of the single cell. The cell with 10 mol.% Ni impregnated Ni-LSF as anode achieves a maximum power density of 550 mW cm−2 at 700 °C fueled with syngas. The strong interaction of the nano-sized Ni–Fe alloy with the LaxSryFeOz (La0.8Sr0.2FeO3 or SrLaFeO4) oxide substrate efficiently suppresses carbon deposition with high graphitization degree. Besides, the SrLaFeO4 phase which can accommodate interstitial oxygen facilitates the removal of the deposited carbon.

Controlling antiferromagnetic domains in patterned La0.7Sr0.3FeO3 thin films

Transition metal oxide thin films and heterostructures are promising platforms to achieve full control of the antiferromagnetic (AFM) domain structure in patterned features as needed for AFM spintronic devices. In this work, soft x-ray photoemission electron microscopy was utilized to image AFM domains in micromagnets patterned into La0.7Sr0.3FeO3 (LSFO) thin films and La0.7Sr0.3MnO3 (LSMO)/LSFO superlattices. A delicate balance exists between magnetocrystalline anisotropy, shape anisotropy, and exchange interactions such that the AFM domain structure can be controlled using parameters such as LSFO and LSMO layer thickness, micromagnet shape, and temperature. In LSFO thin films, shape anisotropy gains importance only in micromagnets where at least one extended edge is aligned parallel to an AFM easy axis. In contrast, in the limit of ultrathin LSFO layers in the LSMO/LSFO superlattice, shape anisotropy effects dominate such that the AFM spin axes at micromagnet edges can be aligned along any in-plane crystallographic direction.

The role of CuO modified La0·7Sr0·3FeO3 perovskite on intermediate-temperature partial oxidation of methane via chemical looping scheme

Synthesis gas production via chemical-looping partial oxidation (CLPO) of methane reduces operating cost and likely avoids carbon dioxide emissions. Previous studies exhibit La0·7Sr0·3FeO3 (LSF) a good high-temperature oxygen carrier, but not being applicable in intermediate-temperature CLPO processes. This work proposes a CuO modified LSF (xCuO/LSF, x = 2,5,10,15) for enhancing the reactivity of oxygen carriers at relatively low temperatures. Characterization methods, including N2 physisorption, ICP-OES, H2-TPR, XRD and XPS, are implemented to determine properties of xCuO/LSF. Fixed-bed experiments determine the best candidate under 750 °C is 10CuO/LSF. The methane conversion rate of 10CuO/LSF is more than 3 times compared to that of unmodified LSF and the concentration of syngas increases by 375% with the H2/CO molar ratio of about 2.5. The regenerability of 10CuO/LSF proves to be good. This study provides a promising and simple way to lower the operating temperature of the CLPO process, likely leading a considerable energy saving.

GÜMÜŞ AKIM TOPLAYICI MÜREKKEPLERİNDE FRİT BULUNMASININ KATI OKSİT YAKIT HÜCRESİ KATOTLARININ ELEKTROKİMYASAL PERFORMANSINA ETKİSİ

Silver (Ag) inks are often used as precursors to form current collector layers on the intermediate-temperature solid oxide fuel cell (SOFC) cathodes. It has been common practice to add glassy phase (frit) particles into the Ag inks to achieve good adhesion between the current collector and the cathode layers upon firing. However, insufficient attention has been given to the effects of frit content on the microstructure and the current collecting properties of Ag layers. This study presents the effect of frit addition on the measured electrochemical performance of La0.6Sr0.4FeO3 (LSF) thin film cathodes. Microstructural analyses reveal that frit addition significantly densifies the Ag current collector layer. The glassy phase replacing Ag reduces the contact area between the Ag particles and the LSF thin film cathode, resulting in increased ohmic resistances. The glassy phase also seals the electrocatalytic surface of the LSF thin film, thus enhancing the cathode polarization resistances. Electrochemical impedance spectroscopy measurements on symmetrical half-cells reveal that ohmic resistances matching the resistivity of the yttria stabilized zirconia electrolyte (YSZ) and acceptable cathode polarization resistances (e.g., 0.5 Ωcm2 at 700℃ in air) can be obtained when frit-free Ag current collector inks are used.

Surface modification of SOFC cathodes by Co, Ni, and Pd oxides

The effect of adding transition-metal catalysts to the surfaces of Solid-Oxide-Fuel-Cell (SOFC) cathodes was examined. Monolayer amounts of Pd, Ni, and Co were deposited by atomic layer deposition (ALD) to cathodes prepared by impregnation of La0.8Sr0.2FeO3 (LSF), La0.8Sr0.2CoO3 (LSCo), and La0.6Sr0.4 Co0.2Fe0.8O3 (LSCF) into YSZ scaffolds. Incorporating the catalysts by ALD allowed modification of the surface composition without changing the cathode surface area or structure. X-ray Photoelectron Spectroscopy and High Sensitivity-Low Energy Ion Scattering were used to confirm ALD growth rates that were measured gravimetrically. Electrochemical impedance spectroscopy indicated that the addition of Pd had a small negative effect on all of the cathodes. Ni and Co exhibited only a small effect on LSCo and LSCF cathodes but both decreased the cathode impedance for LSF. It is suggested that an essential feature in cathode promotion by Co and Ni is that these cations are incorporated into the perovskite surface and thereby increase the concentration of oxygen vacancies, while Pd only blocked adsorption sites.

Improving Oxygen Electrodes by Infiltration and Surface Decoration

For improving competitiveness of SOEC/SOFC-technology it is desirable to reduce the temperature of operation down towards 500 °C – 600 °C. This requires improvement of the oxygen electrode such that this does not limit performance. Here, we report results on modifying various back-bone type oxygen electrodes via infiltration of materials targeting a surface decoration with Pr-oxide or Pr,Ni,Cu-oxides. Different composite back-bone electrodes (based on micron-sized particles) were investigated; La0.6Sr0.4Co0.2Fe0.8O3/Ce0.9Gd0.1O2, (LSCF/CGO), La0.6Sr0.4FeO3 (LSF), and LaNi0.6Fe0.4O3/Ce0.9Gd0.1O2 (LNF/CGO). Marked performance improvements could be achieved with the infiltration, including a reduction by a factor of 3 of the polarization resistance at 600 °C for both LSF and the LSCF/CGO based state of the art electrodes. In a LNF/CGO composite backbone, infiltration with Pr-nitrate led to marked electrode performance improvement; reaching 0.14 Ωcm2 at 550 °C and 0.4 Ωcm2 at 500 °C, sufficiently fast not to limit overall cell performance (at 550 °C).

Phase transition of doped LaFeO3 anode in reducing atmosphere and their power generation property in intermediate temperature solid oxide fuel cell

In general, transition metal-doped La0.6Sr0.4FeO3 (LSF) has been used as a cathode material for intermediate temperature solid oxide fuel cells (IT-SOFCs) because of its high mixed electronic−ionic conductivity and catalytic properties. Recently, some research groups have been investigating the doped LSF as an anode material. In this study, we evaluated the influence of dopant in LSF on anodic properties of LSF in SOFCs. Whereas Mn-doped LSF showed typical perovskite oxide structure even after reduction in hydrogen at high temperature, the LSF and Co-doped LSF exhibited phase transition partially to LaSrFeO4 and exsolution of metal particles after reduction. The phase transition and metal exsolution occurred at temperature higher than 1008 K in a reducing atmosphere. Despite the partial phase transition, the cell using Co-doped LSF anode exhibited fairly high power density of 1.33 W/cm2 at 1173 K with the lowest polarization resistance. These results may originate from the high oxygen-ion conductivity of LaSrFeO4–La(Sr)Fe(Co)O3 and the high hydrogen oxidation property of the Co–Fe particles on ceramic anode surface.

SOFC cathodic layers using wet powder spraying technique with self synthesized nanopowders

Abstracts In this work, a wet powder spraying method has been investigated as a facile low cost route to deposit electrode layer on SOFC electrolyte support. A particular focus has been examining the interfacial stability of the deposited layers, and determining the influence of the thickness of the different layers, as well as the ball milling regime used to produce the electrode inks. The developed system consist of an yttria stabilized zirconia electrolyte support, a La0.6Sr0.4FeO3 (LSF) cathode, a Sm0.2Ce0.8O1.9 (SDC) barrier layer between the electrolyte and the cathode, and LaNi0.6Fe0.4O3 (LNF) as a contact layer, for a future integration with the SOFC interconnector. The electrolyte supports (300 μm thickness and 9 mm diameter) supports were prepared by uniaxial pressing, while the deposition of thin barrier layers, cathode and contact layer were carried out by manual spray coating.

Compositional optimization of ceramic composite electrodes without metal catalysts for steam and CO2 electrolysis

Several cathode materials for solid oxide fuel cells with mixed electronic and ionic conductivity were applied to the feed-side electrode for steam and CO2 electrolysis; the feed-side electrode was exposed to a reducing atmosphere and carbon dioxide, and the feasibility of using a ceramic composite electrode without any metal catalysts was investigated. Ceramic composite electrodes composed of La0.8Sr0.2FeO3 (LSF), or La0.8Sr0.2MnO3 (LSM) were fabricated using the infiltration method. LSF showed good chemical stability but low electrical conductivity in co-electrolysis mode. LSM showed a good electrical conductivity, but its chemical stability was poor in co-electrolysis mode. Good chemical stability, high electrical conductivity, and good electrode performance could be obtained from a solid solution of LSF and LSM (La0.8Sr0.2Mn0.5Fe0.5O3, LSMF). The electrode performance of LSMF was almost twice as good as that of La0.8Sr0.2Cr0.5Mn0.5O3 (LSCM).

Enhanced performance of La0.8Sr0.2MnO3 cathode for solid oxide fuel cells by co-infiltration of metal and ceramic precursors

The electrochemical performance of a La0.8Sr0.2MnO3 (LSM) cathode electrode of solid oxide fuel cells (SOFCs) was promoted by the infiltration of metallic (Ag) and ceramic (La0.8Sr0.2FeO3 (LSF), CeO2) nano-catalysts. Electrochemical and microstructural techniques were used to investigate the effects of the addition of the infiltrated materials. The SEM observations showed that a well-dispersed arrangement of catalyst nano-particles is formed on the micron-sized LSM backbone. Electrochemical impedance spectroscopy (EIS) along with the analysis of distribution of relaxation time (DRT) and polarization measurement were conducted using a three electrode configuration setup. The EIS results revealed that the effect of the Ag nano-catalyst in lowering the polarization resistance is more sensible at lower temperatures, whereas LSF has more impact on the reduction of polarization resistance at higher temperatures. The best performance enhancement was achieved by the co-infiltration of Ag-ceria into the LSM electrode. The co-infiltration of Ag and ceria reduced the polarization resistance of the electrode to 2.5% of that for the pure LSM electrode. Furthermore, the infiltration of Ag solution reduced the electrode overpotential by about 114% at 700 °C.