Performance Of La0 Research Articles

Effect of low-loading of Ni on the activity of La0.9Sr0.1FeO3 perovskites for chemical looping dry reforming of methane

Methane dry reforming (MDR) is a very appealing process to bring back waste CO2 into the chemical production chain. Operating in chemical looping (CL) conditions allows to reduce deactivation by coke deposition and facilitates the use of concentrating solar energy to power this reaction. Perovskites have successfully applied as oxygen carriers for chemical looping, and those of the family La1−xSrxFeO3 having lower Sr content have showed high activity and cycling stability for MDR. To further enhance the performance of these oxygen carriers, in this work we evaluate the impact of dispersing Ni in low concentration (<1 mol %) on the performance of La0.9Sr0.1FeO3 for CL-MDR. Simple impregnation allows to distribute evenly the metal, which according to XPS is present as Ni2+ in the fresh material. CH4-TPR reveal that NiOx species are firstly reduced at around 650 ºC and they shift the onset of methane partial oxidation to lower temperatures with regards to the unmodified perovskite. However, during isothermal CL tests at 850 ºC, the presence of Ni does not modify much the syngas production during the methane reforming stage, although the H2/CO ratio increases with the presence of this metal. This indicates an increment in the contribution of methane cracking. In contrast, when feeding CO2, the generation of CO is greatly enhanced by the incorporation of Ni, particularly at a loading of 0.4 mol %, while higher metal concentration are slightly less effective. Higher CO generation is attributed to the promotion of reverse Boudouard reaction, which can remove the coke previously deposited in the methane reforming stage. Accordingly, the Ni/ La0.9Sr0.1FeO3 presents stable activity during several consecutive cycles.

Ca doping effect on the performance of La1−xCaxNiO3/CeO2-derived dual function materials for CO2 capture and hydrogenation to methane

CO2 valorization in form of synthetic natural gas is a convenient way to store large amounts of intermittent energy produced from renewable sources for long periods of time. Here reported research addresses the development of novel dual function materials (DFMs) for the utilization of CO2 from simulated post-combustion effluent by cyclic adsorption and in-situ methanation. These DFMs, obtained after the controlled reduction of 20% La1−xCaxNiO3/CeO2-type precursors (with x = 0–0.5), are widely characterized before and after catalytic tests. XRD diffractograms, H2-TPD experiments and STEM-EDS images denote that Ca-doping shows low influence on materials composition, slight detrimental effect on textural properties and no influence on Ni, La and Ce distribution. Meanwhile, the concentration of Ca-based species increases as long as La3+ substitution by Ca2+ increases, which leads to a progressively promotion of medium and, especially, strong basic sites concentration (CO2-TPD). As a result, the 20% La0.5Ca0.5NiO3/CeO2-derived DFM almost doubles (188.8 µmol g−1) the CH4 production of the 20% LaNiO3/CeO2-derived DFM (96.5 µmol g−1) at high temperatures. Indeed, this novel DFM enhances the methanation capacity of the conventional 15% Ni-15% CaO/Al2O3 DFM (143.0 µmol CH4 g−1), with higher stability during long-term experiments and adaptability under variable feed compositions, which further support the applicability of these novel DFMs. Thus, Ca doping emerges as an effective way of tailoring CO2 adsorption and in-situ hydrogenation to CH4 efficiency of 20% LaNiO3/CeO2-derived DFMs.

Impact of the Synthesis Method on Electrochemical Performance of La0.5Sr0.5MnO3 Perovskite Oxide as a Cathode Material in Alkaline Fuel Cells

Impact of the Synthesis Method on Electrochemical Performance of La0.5Sr0.5MnO3 Perovskite Oxide as a Cathode Material in Alkaline Fuel Cells

Microstructure and Performance of Ni-Free Nano La0.75Sr0.25Cr0.5Mn0.5O3 - Gd0.2Ce0.8Ox Composite Anode

The correlation between microstructure and performance of La0.75Sr0.25Cr0.5Mn0.5O3 - Gd0.2Ce0.8Ox (LSCM-GDC) solid oxide fuel cell (SOFC) anode is investigated. The fuel electrode is fabricated with the nano-composite powder prepared through colloidal-processing-based approach. The well dispersed nano-powder results in the limited particle coarsening during sintering and fine electrode microstructure. The influences of sintering temperature and electrode thickness on polarization resistance are investigated. The lowered sintering temperature results in particle size below 100 nm, which improves electrochemical performance. On the other hand, porosity over 57% inhibits percolation of the solid phases, in particular the LSCM. The performance of thinner composite electrode is superior, which is in good agreement with the deteriorated LSCM and GDC percolations. The electrochemical performance of the optimized electrode is competitive to the conventional Ni-YSZ, Ni-GDC, and LSCM-GDC anodes fabricated with submicron powders.

A Dual Reactor for Isothermal Thermochemical Cycles of H2O/CO2 Co-Splitting Using La0.3Sr0.7Co0.7Fe0.3O3 as an Oxygen Carrier

Catalytic performance of La0.3Sr0.7Co0.7Fe0.3O3 (LSCF3773 or LSCF) catalyst for syngas production via two step thermochemical cycles of H2O and CO2 co-splitting was investigated. Oxygen storage capacity (OSC) was found to depend on reduction temperature, rather than the oxidation temperature. The highest oxygen vacancy (Δδ) was achieved when the reduction and oxidation temperature were both fixed at 900 °C with the feed ratio (H2O to CO2) of 3 to 1, with an increasing amount of CO2 in the feed mixture. CO productivity reached its plateau at high ratios of H2O to CO2 (1:1, 1:2, and 1:2.5), while the total productivities were reduced with the same ratios. This indicated the existence of a CO2 blockage, which was the result of either high Ea of CO2 dissociation or high Ea of CO desorption, resulting in the loss in active species. From the results, it can be concluded that H2O and CO2 splitting reactions were competitive reactions. Ea of H2O and CO2 splitting was estimated at 31.01 kJ/mol and 48.05 kJ/mol, respectively, which agreed with the results obtained from the experimentation of the effect of the oxidation temperature. A dual-reactors system was applied to provide a continuous product stream, where the operation mode was switched between the reduction and oxidation step. The isothermal thermochemical cycles process, where the reduction and oxidation were performed at the same temperature, was also carried out in order to increase the overall efficiency of the process. The optimal time for the reduction and oxidation step was found to be 30 min for each step, giving total productivity of the syngas mixture at 28,000 μmol/g, approximately.

Isothermal redox cycling of A‐ and B‐site substituted manganite‐based perovskites for CO2 conversion

AbstractConversion of CO2 into fuels and valuable chemicals can simultaneously address two major global issues: climate change and the increasing energy demand. Most of the previous studies regarding the thermochemical splitting of CO2 into CO have been carried out at elevated temperatures of up to 1400°C. In this study, under isothermal reaction conditions, manganite‐based perovskites are used to convert CO2 to CO in a thermogravimetric analyzer (TGA). In addition, the use of CH4 as a reducing agent has lowered the reaction temperatures (≤900°C). This study primarily focuses on the influence of A‐ and B‐site substitution on the redox performances of the manganite‐based perovskites. Based on the redox performances of four samples (CaMnO3, La0.5Ca0.5MnO3, La0.5Sr0.5MnO3, and Y0.5Sr0.5MnO3) with different A‐site compositions, La0.5Sr0.5MnO3 displays the best stability. Similarly, in the La1‐xSrxMnO3 perovskite family (x = 0.5, 0.25, and 0.10), the performance of La0.5Sr0.5MnO3 outshines the other two compositions. It is observed that as the Sr content increases, the activation energy for reduction decreases. Substituting Mn with Al and Fe in the B‐site of the La1‐xSrxMnO3 perovskite, did not enhance the performance. The perovskite materials investigated have shown decrease in activity after the first cycle, possibly due to sintering and powder densification. However, after the first cycle, the perovskites illustrated good stability for 10 redox cycles. In this paper, size variance and metal‐oxygen bond strength provide the best explanation for the trends observed during the reduction of the perovskites.

Influence of Bi1.5Y0.5O3 Active Layer on the Performance of Nanostructured La0.8Sr0.2MnO3 Cathode

The efficiency of solid oxide fuel cell cathodes can be improved by microstructural optimization and using active layers, such as doped bismuth oxides. In this work, Bi1.5Y0.5O3 (BYO) films are prepared by spray-pyrolysis deposition at reduced temperatures on a Zr0.84Y0.16O1.92 (YSZ) electrolyte. The influence of the BYO film on the performance of an La0.8Sr0.2MnO3 (LSM) cathode prepared by traditional screen-printing and spray-pyrolysis is investigated. A complete structural, morphological, and electrochemical characterization is carried out by X-ray diffraction, electron microscopy, and impedance spectroscopy. The incorporation of BYO films decreases the Area Specific Resistance (ASR) of screen-printed cathodes from 6.4 to 2.2 Ω cm2 at 650 °C. However, further improvements are observed for the nanostructured electrodes prepared by spray-pyrolysis with ASRs of 0.55 and 1.15 Ω cm2 at 650 °C for cathodes with and without an active layer, respectively. These results demonstrate that microstructural control using optimized fabrication methods is desirable to obtain high-efficiency electrodes for solid oxide fuel cell (SOFC) applications.

Oxygen diffusion and electrochemical performance of La0.6−xSr0.4BaxCo1−yFeyO3−δ

La0.6−xSr0.4BaxCo1−yFeyO3−δ (x = 0, 0.2, y = 0.1, 0.2, 0.3, 0.4) were prepared by the glycine–nitrate process. The electrochemical property and oxygen diffusion behavior of La0.6−xSr0.4BaxCo1−yFeyO3−δ were investigated. The electrochemical impedance spectroscopy analysis suggests that doping with an appropriate amount of iron and barium improves the catalytic performance. La0.4Sr0.4Ba0.2Co0.9Fe0.1O3−δ calcined at 950 °C exhibits the minimum polarization resistance of 0.0349 Ω cm2 at 750 °C. The doping of Fe improves the sintering performance. The crystalline size of La0.6−xSr0.4BaxCo1−yFeyO3−δ becomes smaller with the doping amount of Ba, which increase the number of active sites. The doping of Ba decreases the oxygen vacancy formation energy and increases the oxygen vacancy concentration, which accelerates the oxygen diffusion. Further, the single cell performance for La0.4Sr0.4Ba0.2Co0.9Fe0.1O3−δ as cathode shows the maximum power density of 539.49 W cm−2 at 750 °C.

Further improvement in performances of La0.6Sr0.4Co0.2Fe0.8O3−δ - doped ceria composite oxygen electrodes with infiltrated doped ceria nanoparticles for reversible solid oxide cells

We have developed high-performance oxygen electrodes for reversible solid oxide cells. La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) - (CeO2)0.8(SmO1.5)0.2 (SDC) composite scaffolds were infiltrated with SDC nanoparticles. The electrode with 30 vol% load of SDC nanoparticles exhibited very low overpotentials, η ≤ 0.010 V for anodic and |η| ≤ 0.030 V for cathodic reactions at 0.7 A cm−2 and 800 °C, which was ascribed to a noticeable increase in the exchange current densities. The electrodes have shown very stable performance under anodic oxygen evolution operation at −0.5 A cm−2 and 750 °C for 400 h. Such electrodes developed are extremely promising oxygen electrodes for R-SOC ever reported.

Influence of Electrolyte Scaffold Microstructure and Loading of MIEC Material on the Electrochemical Performance of RSOC Fuel Electrode

AbstractPerovskite‐based mixed ionic electronic conductive (MIEC) oxides have been synthesized and studied as promising redox‐stable solid oxide cell (SOC) electrode materials. In order to enhance performance of MIEC electrode materials, influence of porous electrolyte structure as well as the loading of the electroactive material on the performance of La0.8Sr0.2Cr0.49Mn0.49Ni0.02O3‐δ – (Sc2O3)0.1(CeO2)0.01(ZrO2)0.89 (LSCMN‐ScCeSZ) and Sr2Fe1.5Mo0.5O6‐δ (Sc2O3)0.1(CeO2)0.01(ZrO2)0.89 (SFM‐ScCeSZ) MIEC electrodes have been studied. The results indicated that pre‐calcination and milling process of ScCeSZ electrolyte powder increased the average pore sizes and the overall porosity of scaffolds by about 10 vol.%. However, due to the use of pre‐calcined electrolyte powder with increased particle sizes, specific area of electrolyte scaffolds and catalytic activity decreased at lower MIEC loadings. Porous scaffold with highest open porosity of 81% was used to study the influence of different MIEC materials at high loadings on the performance of composite electrodes. Results indicated that optimal loading depends on the properties of MIEC material and it was found to be 30 and 50 wt.% for SFM and LSCMN, respectively. The highest current density values 1.11 and 0.78 A cm−2 were measured for electrolysis mode at 850 °C, at potential 1.5 V and 30% of absolute humidity for SFM and LSCMN composite electrodes, respectively.

Interfacial reaction between YSZ electrolyte and La0.7Sr0.3VO3 perovskite anode for application

The synthesis and performance of La0.7Sr0.3VO3/YSZ composites are investigated as alternative anodes for the direct utilization of methane (i.e., biogas) in solid oxide fuel cells. In this study, the structural stability between Sr-doped lanthanum vanadate and yttria-stabilized zirconia was investigated by using the powder mixture annealed at various periods of time and temperatures. The chemical reaction between these two materials in the temperature ranging from 1100 to 1400 °C was examined by X-ray diffraction (XRD) and electron probe microanalysis (EPMA) analyses. According to the examination of La0.7Sr0.3VO3/YSZ powder mixture after heat treatment at 1100–1400 °C, no second phase was detected when the La0.7Sr0.3VO3/YSZ powder mixture was heated at 1100 °C. The reaction products of perovskite SrZrO3 were formed when the specimens were heated treatment at over 1200 °C. Owing to the further diffusion of Sr cations from La0.7Sr0.3VO3 toward the reaction layer/YSZ interface via the reaction layer, the reaction layer was extended into the YSZ. The interfacial reaction behavior between electrode and electrolyte pellets of the reaction couple was examined by EPMA. No reaction products were observed as La0.7Sr0.3VO3/YSZ composite co-fired at 1100 °C. The reaction products of perovskite SrZrO3 were formed when the specimens were heat treated at over 1200 °C. The bonding energy between La-O (188 kcal/mol) is stronger than Sr-O (83.6 kcal/mol). Thus, Sr ions tend to migrate and react with YSZ much faster than La ions. Furthermore, when the Sr concentration increases to 70%, excess of SrZrO3 formation leads to the phase decomposition of perovskite La0.3Sr0.7VO3.

Performance of La0.5Sr0.5Fe0.9Mo0.1O3 − δ–Sm0.2Ce0.8O2 − δ composite cathode for CeO2- and LaGaO3-based solid oxide fuel cells

The La0.5Sr0.5Fe0.9Mo0.1O3 − δ–x wt.% SDC (LSFMo-xSDC, x = 0, 20, and 30) samples were evaluated as potential cathodes for solid oxide fuel cells (SOFCs) based on both La0.9Sr0.1Ga0.8Mg0.2O3 − δ (LSGM) and Sm0.2Ce0.8O2 − δ (SDC) electrolytes. The LSFMo cathode is chemically compatible with the LSGM and SDC electrolytes with temperature up to 1000 °C. Through the comparison of the polarization resistances (Rp) of the LSFMo cathode on LSGM and SDC electrolytes, only a small difference of ~ 13–15% in the Rp was obtained. To further improve the electrochemical performance of the LSFMo cathode, 20 and 30 wt.% SDC were introduced into the LSFMo cathode. The LSGM/SDC-supported single cell with LSFMo-20SDC composite cathode was found to show the optimal performance and excellent power cycle and long-time stability. In addition, the electrical conductivity and thermal expansion coefficient (TEC) for the LSFMo-20SDC cathode were also detected and evaluated. Our results show that the LSFMo-20SDC is a very promising candidate for use in the cathode of SOFC.

Effects of PdO modification on the performance of La0.6Sr0.4Co0.2Fe0.8O3−δ cathodes for solid oxide fuel cells: A first principle study

Effects of palladium (Pd) impregnation on the performance of La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) cathodes are investigated with density functional theory plus U (DFT + U) and experimental methods. In-situ high temperature X-ray diffractometer results show that the impregnated Pd species exist at states of palladium oxide (PdO) at 700 °C. The measured electrochemical impedance spectroscopy at 700 °C indicates PdO modification promotes the catalytic activity of LSCF cathodes. The modification structure of PdO on LSCF surfaces and effects of PdO modification on the performance of LSCF cathodes are investigated with DFT + U methods. The results show that B-8 with PdO molecule modification by a parallel posture on LSCF surface is the most stable structure. O2 prefers to be adsorbed on AO-terminated surfaces rather than that on BO2-terminated ones. The oxygen surface adsorption activity of LSCF surface is improved by PdO modification. The calculated partial densities of states (PDOS) and Fermi level of O2 adsorption on LSCF surfaces imply that the charge transfer is easier with PdO modification than that without PdO modification because PdO acts as a metal-like modification. The PdO modification on LSCF surface leads to a better oxygen surface adsorption activity of LSCF cathodes.

Synthesis and performance of La0.5Sr0.5CoO3 cathode for solid oxide fuel cells

Synthesis and performance of La0.5Sr0.5CoO3 cathode for solid oxide fuel cells

Selectivity enhancement for higher alcohol product in Fischer-Tropsch synthesis over nickel-substituted La0.9Sr0.1CoO3 perovskite catalysts

The performance of La0.9Sr0.1Co1−xNixO3 perovskite catalysts with different Ni substitution levels was evaluated in the Fischer-Tropsch (F-T) synthesis for higher alcohol production. It was found that Ni substitution improved the catalyst’s reducibility and had a positive effect on higher alcohol synthesis (HAS) from syngas. Only a limited amount of Ni ions can enter into the perovskite structure and then form Co-Ni alloy after reduction. Catalyst characterisation and activity test results indicate that the synergistic effects of the two metal species in the Co-Ni are responsible for the catalytic activity improvement. For high Ni-substituted perovskite catalysts (x≥0.5), the extra-lattice Ni segregates on the catalyst surface and promotes CO methanation during the F-T reaction. A significant deviation of methanol selectivity from the Anderson-Schulz-Flory (ASF) linear distribution was detected for catalysts containing both Ni and Co, suggesting that the alcohol formation mechanism is altered with nickel substitution in La0.9Sr0.1Co1−xNixO3 perovskite catalysts. The La0.9Sr0.1Co0.9Ni0.1O3 perovskite catalyst exhibited the highest selectivity towards higher alcohols. The effect of reaction temperature on the catalytic activity is also discussed.

Performance of La0.6Sr0.4Co1−yFeyO3 (y=0.2, 0.5 and 0.8) nanostructured cathodes for intermediate-temperature solid-oxide fuel cells: Influence of microstructure and composition

We investigated the electrochemical properties of Co–Fe perovskites, which can be used as cathodes for intermediate-temperature solid-oxide fuel cells (IT-SOFCs). We studied the electrochemical properties of nanostructured mixed ionic-electronic conductors for IT-SOFC cathodes with compositions of La0.6Sr0.4Co1−yFeyO3 (y=0.2, 0.5 and 0.8). We analyzed the performance of two types of nanostructures: nanorods and nanotubes. Our results show that the electrochemical performance is highly influenced by the form of nanostructure, whereas the effect of composition is less significant.

Fabrication and Performance of La0.6Sr0.4Co0.2Fe0.8O3−δ Infiltrated-Yttria-Stabilized Zirconia Cathode on Anode-Supported Solid Oxide Fuel Cell

The three layers with porous yttria-stabilized zirconia (YSZ) backbone/dense YSZ/porous NiO–YSZ were fabricated by tape-casting process, respectively, then laminated together and co-fired at 1300 °C for 5 h. The cathode material La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) was loaded by infiltrating the precursor of metal ions into porous YSZ backbone. As a result, LSCF nanoparticles with the size of 60–100 nm were uniformly distributed on YSZ backbone. The power density was 1.046 W cm−2 and the polarization resistance was 0.17 Ω cm2 at 800 °C in humidified H2 (3 vol.% H2O). But the stability was not good enough, especially in early operating stage, e.g., 20 h. After that, it showed good stability for the following 70 h operating under a constant voltage of 0.7 V at 750 °C. This is due to the growth and agglomeration of LSCF nanoparticles at early steps, which reduced the three phase boundaries (TPBs).

The performance of La0.6Sr1.4MnO4 layered perovskite electrode material for intermediate temperature symmetrical solid oxide fuel cells

A layered perovskite electrode material, La0.6Sr1.4MnO4+δ (LSMO4), has been studied for intermediate temperature symmetrical solid oxide fuel cells (IT-SSOFCs) on La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) electrolyte. The chemical compatibility tests indicate that no reaction occurred between LSMO4 oxide and LSGM electrolyte at temperature up to 1000 °C both in air and 5% H2. The lower conductivity in 5% H2 and higher conduction activation energy than those in air would be caused by poorer overlap of both σ and π bonds. DFT + U calculations also show that oxygen vacancies which formed in reducing atmosphere may block the 3D hopping path for electrons or holes through Mn–O–Mn chains. For LSMO4 electrode, SEM results indicate that the electrode formed good contact with the electrolyte after being sintered at 900 °C for 2 h. At 800 °C, the polarization resistance of the LSMO4 cathode is about 0.87 Ω cm2 in air, while the polarization resistance of the LSMO4 anode is about 2.07 Ω cm2 in 5% H2. LSMO4 exhibits better electrochemical activity for oxygen reduction than that for hydrogen oxidation. A cell with LSGM electrolyte, LSMO4–LSGM mixture as anode and cathode simultaneously displays a maximum power density of 59 mW cm−2 at 800 °C.

The impact of sulfur contamination on the performance of La0.6Sr0.4Co0.2Fe0.8O3−δ oxygen transport membranes

An oxygen transport membrane made from La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 − δ (LSCF6428) has been tested for air separation by oxygen permeation at 900 °C with the introduction of sulfur in the form of hydrogen sulfide. 200 ppm of hydrogen sulfide was fed either in the sweep-side (argon-side) or the air-side. The membrane was exposed to hydrogen sulfide for 100 h. Results show that the presence of hydrogen sulfide negatively influenced the oxygen permeation due to the formation of strontium sulfate blocking the oxygen permeation pathway. When the hydrogen sulfide was removed from the system, the oxygen permeation was partially restored in the case of argon-side contamination, while being fully restored in the case of air-side contamination. • Sulfur was introduced to an LSCF6428 membrane in the form of hydrogen sulfide. • Hydrogen sulfide was fed either in the argon-side or the air-side. • Oxygen permeation sharply decreased during hydrogen sulfide introduction. • Segregation of strontium to the air-side increased strontium sulfate formation. • In case of argon-side contamination, the oxygen permeation could not be restored. • In case of air-side contamination, the oxygen permeation was fully restored.

Compatibility and Performance of La0.675Sr0.325Sc0.99Al0.01O3 Perovskite-type Oxide as an Electrolyte Material for SOFCs

Compatibility and Performance of La0.675Sr0.325Sc0.99Al0.01O3 Perovskite-type Oxide as an Electrolyte Material for SOFCs