Study of (La,Sr)(Ti,Ni)O3-δ materials for symmetrical Solid Oxide Cell electrode - Part B: Conditions of Ni exsolution

The stability of La_2xSr_1-2xTi_1-xNi_xO_3-δ (LSTN) and La_7x/4Sr_1-7x/4Ti_1-xNi_xO_3-δ (25LSTN) materials in high temperature reducing conditions has been studied with a special focus on the Ni exsolution process for SOFC anode / SOEC cathode application. In a general way, LSTN and 25LSTN compounds are stable after treatments at 800 °C in air and wet reducing atmosphere. The low chemical expansion makes them compatible with a use in an electrochemical Solid Oxide Cell. Those materials are therefore useful for an application as symmetric oxide cell electrode or only hydrogen electrode. In situ Nickel exsolution is evidenced at 800 °C in Ar/H₂(2%) but is limited by a slow kinetics and a higher temperature pre-reduction is preferred before a use as SOFC anode (SOEC cathode). Depending on the treatment, in situ reduction or pre-reduction (T>1000 °C), the compounds are not in the same thermodynamic equilibrium state.     

Bond ionicity,lattice energy,bond energy,and microwave dielectric properties of Ca1-xSrxWO4 ceramics

The Ca_1-xSr_xWO₄ (x?=?0, 0.02, 0.04, 0.06, 0.08, 0.10) ceramics were fabricated through solid-state reaction, and the relationships among microwave dielectric properties of Ca_1-xSr_xWO₄, bond ionicity, lattice energy and bond energy were systematically investigated for the first time. The patterns of X-ray diffractions of Ca_1-xSr_xWO₄ presented tetragonal scheelite structure and no second phase appeared throughout the entire compositions. Dielectric properties of Ca_1-xSr_xWO₄ were proved to be related to the microstructures: dielectric constant (ε_r) of Ca_1-xSr_xWO₄ was dependent on the bond ionicity; the quality factor (Q×f₀) of Ca_1-xSr_xWO₄ was affected by W-site lattice energy when intrinsic loss is dominant; the temperature coefficient of resonant frequency (|τ_f|) would increase if B-site bond energy decreased. Ca_1-xSr_xWO₄ ceramic showed excellent microwave dielectric properties, ε_r =?9.42, Q×f₀ =?79876?GHz and τ_f =??18.8?ppm/°C when x?=?0.08 and sintered at 1100?°C for 4?h.     

Investigation on thermoelectric properties of screen-printed La1-xSrxCrO3-In2O3 thermocouples for high temperature sensing

La_1-xSr_xCrO₃-In₂O₃ thick film thermocouples were fabricated by screen-printing method for high temperature sensing and the effects of Sr²⁺ content were investigated systematically. All La_1-xSr_xCrO₃ thick films showed well crystallization with orthorhombic unit cell. Their average particle sizes showed the tendency of first increase then decrease gradually with the increase of Sr²⁺ content, and the maximum of average particle size was 1.76?μm. At the same time, the conductivities were improved with the increase of Sr²⁺ content. The thermoelectric properties of La_1-xSr_xCrO₃ depended on the Sr²⁺ content and the average Seebeck coefficients had an exponential decay tendency with the increase of Sr²⁺ content. For La_1-xSr_xCrO₃ (x?=?0.1–0.4)-In₂O₃ thermocouples, excellent repeatability and stability were observed through multi-cycles and long-time usage testing at high temperature. The La_0.7Sr_0.3CrO₃-In₂O₃ thick film thermocouple with excellent thermal stability (drift rate: 0.81?°C/h) and reliability makes it become a promising candidate high sensitivity thermal sensor.     

Hydrothermal synthesis,sintering and characterization of nano La-manganite perovskite doped with Ca or Sr

Two lanthanum manganite perovskite-nanostructures, namely; La_xCa_(1-x)MnO₃ and La_xSr_(1-x)MnO₃ (x?=?0.1, 0.3, 0.5 and 1.0), were synthesized by hydrothermal method. To follow up the composition of formed phases, the synthesized powders were calcined at different temperatures. The obtained materials were investigated by X-ray diffraction (XRD) and transmission electron microscope (TEM). Moreover, the calcined powders were pressed at 100?MPa and sintered at variable temperatures; i.e. 1250, 1300, 1350 and 1450?°C. The phase composition and microstructural characteristics of sintered pervoskites were examined by XRD and scanning electron microscope (SEM). Furthermore, physical (bulk density and apparent porosity), electrical resistivity and magnetic properties were also determined. The results revealed that La_xCa_(1-x)MnO₃ and La_xSr_(1-x)MnO₃ nanostructures were successfully prepared by hydrothermal method. The physical properties of sintered pervoskites were strongly depended on dopant type and concentration. The maximum sintering temperature for La_xCa_(1-x)MnO₃ was 1400?°C while for La_xSr_(1-x)MnO₃ was 1450?°C, after which the materials have been fused. Materials doped with Ca or Sr exhibited lower resistivity. On the other side, the magnetic properties have been also improved after addition of Ca or Sr. This has been discussed based on the double exchange mechanism. La_xSr_1-xMnO₃ exhibited better magnetic properties than La_xCa_1-xMnO₃ and LaMnO₃. La_0.5Ca_0.5MnO₃ and La_0.5Sr_0.5MnO₃ exhibited the highest magnetization among the other pervoskites.     

Sol–gel synthesis of La0.6Sr0.4CoO3−x and Sm0.5Sr0.5CoO3−x cathode nanopowders for solid oxide fuel cells

Nano-powders of La_0.6Sr_0.4CoO_3?x (LSC) and Sm_0.5Sr_0.5CoO_3?x (SSC) compositions, which are being investigated as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) with La(Sr)Ga(Mg)O_3?x (LSGM) as the electrolyte, were synthesized by low-temperature sol–gel method using metal nitrates and citric acid. Thermal decomposition of the citrate gels was followed by simultaneous DSC/TGA methods. Development of phases in the gels, on heat treatments at various temperatures, was monitored by X-ray diffraction. Sol–gel powders calcined at 550–1000 °C consisted of a number of phases. Single perovskite phase La_0.6Sr_0.4CoO_3?x or Sm_0.5Sr_0.5CoO_3?x powders were obtained at 1200 °C and 1300 °C, respectively. Morphological analysis of the powders calcined at various temperatures was done by scanning electron microscopy. The average crystallite size of the powders was ～15 nm after 700 °C calcinations and slowly increased to 70–100 nm after heat treatments at 1300–1400 °C.     

Structure,mechanical properties and thermal stability of Ti1-xSixN coatings

Ti_1-xSi_xN coating is a promising candidate for wear resistant applications due to their super-hardness and high thermal stability. Here, we explored the structure, mechanical properties and thermal stability of Ti_1-xSi_xN (x?=?0, 0.13, 0.17 and 0.22) coatings deposited by cathodic arc evaporation. Monolithically grown Si-containing Ti_1-xSi_xN coatings, which are Si-solution in TiN for x?=?0.13 and 0.17, reveal a high hardness of 39.4?±?0.67 and 40.6?±?0.72?GPa, respectively. Then Ti_1-xSi_xN transforms into a nanocomposite structure consisting of cubic Ti(Si)N nanocrystallite enveloped by the amorphous SiN_x tissue phase for x?=?0.22, which exhibits a high hardness of 40.0?±?0.6?GPa. However, increasing of Si content leads to a significant increase in compressive stress from ?0.63?GPa for x?=?0 to ?3.78?GPa for x?=?0.13 to ?4.54?GPa for x?=?0.17 to ?5.51?GPa for x?=?0.22. The hardness of Ti_1-xSi_xN coatings can be maintained up to ~ 1000?°C due to the suppressed grain growth, and then decreases for further elevated annealing temperature, whereas the TiN coating exhibits a continuous drop in hardness towards its intrinsic value of ~ 21.3?GPa.     

Magnetocaloric effect in La1-xSrxCoO3 undergoing a second-order phase transition

We have prepared rhombohedral La_1-xSr_xCoO_3-δ (x?=?0.2–0.5) compounds with a mass density ρ?≈?5.5?g/cm³. Their magnetocaloric (MC) effect is studied via the magnetic-entropy change (ΔS_m) and relative cooling power (RCP), which are calculated from initial magnetization data recorded at different temperatures. Results reveal that the ΔS_m magnitude is maximum (ΔS_max) around the ferromagnetic-paramagnetic phase transition and dependent on both the applied-field (H) magnitude and Sr content (x). For H =?50?kOe, |ΔS_max| can be tuned in the range of 1.6–2.7?J/kg?K, corresponding to RCP values of 89–141?J/kg. Among the studied La_1-xSr_xCoO_3-δ samples, the samples with x?=?0.3–0.5 have the largest |ΔS_max| values. If combining these samples as MC blocks in refrigeration application, the working temperature range of a cooling device could range from 204 to ~280?K, with |ΔS_max| stable at ~2.6?J/kg?K and RCP ≈?198?J/kg. We have also assessed the phase-transition type and magnetic order and found La_1-xSr_xCoO_3-δ undergoing a second-order phase transition. Magnetic order tends to change from the long-range type to the short-range one when x varies from 0.2 to 0.5. This is in good agreement with the results obtained from the analysis of critical behavior.     

Toward oxygen fully stoichiometric La1-xSrxCoO3 (0.5≤x≤0.9) perovskites: Itinerant magnetic mechanism more than double exchange one's

We report a two steps synthesis of strontium rich cobaltates La_1-xSr_xCoO_3-δ (0.5 ≤ x ≤ 0.9) compounds. Following the standard solid state procedure, an oxygen intercalation process has been carried out. All the compounds show a perovskite related type structure. Samples have been characterized from chemical and structural point of view. The cubic “a” cell parameter saturates with the oxygen deficiency parameters δ that is controlled by the thermodynamic parameters (p_O2; T). The magnetic properties studies were carried out before and after oxygen intercalation process and a continuous transfer from a localized character to an itinerant one's when oxygen is up taken is supported. A complete magnetic phase diagram with respect to temperature is proposed. One further evidence for attaining of Co^+3.58 against Co^+3.70 in La_0.3Sr_0.7CoO_3-δ with the help of electrochemical oxidation that definitively both metal like behavior and higher than 280 K paramagnetic to ferromagnetic temperature phase transition unambiguously signed an oxygen stoichiometry close to 3 in La_1-xSr_xCoO₃ perovskites serie.     

Enhanced photocatalytic activity of La1-xSrxCoO3/Ag3PO4 induced by the synergistic effect of doping and heterojunction

This study sought to design and synthesize a series of perovskite-based La_1-xSr_xCoO₃/Ag₃PO₄ (with x = 0–1) heterojunction photocatalysts with different Strontium (Sr) doping contents by a simple sol-gel method and properties of the material were comprehensively characterized. Moreover, tetracycline (TC) was chosen as the target pollutant to assess the effect of Sr doping on the catalytic performance of LaCoO₃/Ag₃PO₄. Our results demonstrated that the partial replacement of La³⁺ with Sr²⁺ coupled with shifting Co³⁺ to the mixed-valence state of Co³⁺-Co⁴⁺ led to the formation of substantially more oxygen vacancies in the crystal lattice of La_1-xSr_xCoO₃/Ag₃PO₄. Therefore, the doped catalyst La_1-xSr_xCoO₃/Ag₃PO₄ exhibited enhanced photocatalytic performance. When x = 0.9, the obtained La_0·1Sr_0·9CoO₃/Ag₃PO₄ exhibit an optimal performance for TC degradation. Kinetic analyses demonstrated that the degradation rate constant of TC in La_0·1Sr_0·9CoO₃/Ag₃PO₄ system was 0.0098 min^?1, which is 1.78 times that of LaCoO₃/Ag₃PO₄, and 2.45 times that of SrCoO₃/Ag₃PO₄. Additionally, free radical sequestration experiments indicated that OH^?, h⁺, and O₂^?? all participated in the degradation of TC in the following order: h⁺>O₂^??>OH^?. Finally, analyses of photocatalytic mechanisms suggested that the enhanced photocatalytic activity of La_0·1Sr_0·9CoO₃/Ag₃PO₄ was due to its strong electron transfer properties and the formation of substantially more surface oxygen vacancies in Sr-doped La_0·1Sr_0·9CoO₃.     

Improved electrochemical performance of Bi doped La0.8Sr0.2FeO3-δ nanofiber cathode for IT-SOFCs via electrospinning

In this study, perovskite La_0.8-xBi_xSr_0.2FeO_3-δ (LBSF, x = 0.0–0.5) nanofibers with great crystallinity were prepared by electrospinning method and used as cathodes for intermediate temperature solid oxide fuel cells (IT-SOFCs). The symmetric cells of nanofiber-based LBSF electrode on Sm_0.2Ce_0.8O_1.9 (SDC) electrolyte show excellent electrochemical performance. The La_0.4Bi_0.4Sr_0.2FeO_3-δ (LBSF4) cathode has the best performance with a polarization resistance (R_P) of 0.126 Ω cm² at 650 °C. The anode-supported single cell with LBSF4 as the cathode film and Ni-SDC as the anode has a maximum power density of 448 mW cm^-2 at 650 °C using wet H₂ as the fuel. In addition, the LBSF4 cathode with fibrous structure exhibits outstanding electrochemical behavior. The catalytic activity of the cathode was improved due to the incorporation of the Bi element, indicating that LBSF4 is promising as a cathode material in the field of IT-SOFCs.     

Characterization of Sr1–xDyxCoO3–δ (x = 0.1, 0.2, 0.3) Cathode Materials for IT‐SOFCs

The cobaltate perovskites Sr_1–xDy_xCoO_3–δ (SDCO, x = 0.1, 0.2, 0.3) materials were synthesized and evaluated as cathode for La_0.8Sr_0.2Ga_0.8Mg_0.2O_3–δ solid electrolyte supported intermediate‐temperature‐solid oxide fuel cells (IT‐SOFCs). The crystal structure of Sr_0.9Dy_0.1CoO_3–δ was defined in the cubic Pm–3m space group (No. 221), Sr_0.8Dy_0.2CoO_3–δ and Sr_0.7Dy_0.3CoO_3–δ had a tetragonal I4/mmm structure. The electrical conductivities were all higher than 100 S cm^–1 in the temperature of 170–800 °C. The polarization resistance (R_p) and its activation energy (E_a) increased with increasing x. SEM analysis confirmed the porous microstructure of the SDCO cathodes and good LSGM|LDC|SDCO adherence. Sr_0.9Dy_0.1CoO_3–δ exhibited the best cathode characteristics with a maximum test‐cell power density of 841 mW cm^–2, being a high potential candidate of cathode material for IT‐SOFCs.     

Effect of Mn-doping on the structure and electrical properties of (Pb0.325Sr0.675)TiO3 ceramics

Pb_0.325Sr_0.675Ti_1-xMn_xO₃ ceramics (x?=?0, 0.001, 0.005, 0.01, and 0.05) were successfully prepared by traditional solid-state reaction method. It was found that the lattice constant calculated through Rietveld refinement initially increased and then decreased with increasing Mn content, which was attributed to the variation in valence state of Mn and Ti ions. The microstructure gradually varied from the coexistence of large grains and fine grains for x?=?0 to the uniform grain for x?=?0.05 by increasing the doping Mn ions. With increasing Mn content from x?=?0 to x?=?0.05, the Curie temperature (Tc) dramatically decreased from 25?°C to ??40?°C and dielectric maximum decreased from 27,100 to 13,200. Pb_0.325Sr_0.675Ti_1-xMn_xO₃ ceramics with x?=?0.001 showed the lowest dielectric loss of 0.006 with a relatively high dielectric peak value of ~ 21,000. The grain boundaries resistance obtained from the complex impedance decreased with the increase of Mn content. The decrease in resistance was ascribed to oxygen vacancies and electronics produced by the change of ionic valence state. X-ray photoemission spectroscopy revealed that Ti ions were Ti⁴⁺ and the valences of Mn ions were deduced to be mainly in the form of Mn²⁺ and/or Mn³⁺ for ceramics with low content of Mn, while the Ti ions were in the form of Ti³⁺ and Ti⁴⁺ and Mn ions were diverse valence states with the coexistence of Mn²⁺, Mn³⁺, and Mn⁴⁺ for ceramics with x?=?0.01 and 0.05.     

Mechanical and thermal expansion studies on Ca0.5Sr0.5Zr4-xTixP6O24 ceramics

Ca_0.5Sr_0.5Zr_4-xTi_xP₆O₂₄ (x?=?0?0.2) ceramics belonging to the NZP family were prepared and dense ceramics with no microcracks were obtained. All of the ceramic samples were still composed of the typical NZP structure with a small amount of Ti⁴⁺ substitution for Zr⁴⁺. The mechanical and thermal expansion properties of the ceramics were characterized and the result showed that the flexural strength monotonically increased to 66.5?MPa. The thermal expansion coefficient varied from 1.8 to 3.4?×?10^?6/°C with Ti⁴⁺ content increasing. Thus, it was clear that the substitution of Ti⁴⁺ for Zr⁴⁺ had obvious effects on the sinterability, mechanical and thermal expansion properties of Ca_0.5Sr_0.5Zr_4-xTi_xP₆O₂₄ ceramics, which were discussed in detail.     

Study of structure and conductivity of Li3/8Sr7/16-3x/2LaxZr1/4Nb3/4O3 solid electrolytes

Li_3/8Sr_7/16-3x/2La_xZr_1/4Nb_3/4O₃ (x = 0, 0.05, 0.10, 0.15, 0.20) were synthesized using the conventional solid-state reaction method. In order to increase the vacancy concentration, La³⁺ was doped on the Sr²⁺ site. Crystal structures of doped samples were characterized by X-ray diffraction. Except, perovskite-type Li_3/8Sr_7/16-3x/2La_xZr_1/4Nb_3/4O₃ (x = 0, 0.05, 0.10, 0.15) samples were fabricated by heat treatment at 1250 °C, 1275 °C, 1275 °C and 1275 °C, respectively, for 15 h. Lattice sizes decreased with the increase of doping amounts because of the smaller ion radius of La³⁺ compared to that of Sr²⁺. Ionic conductivities of the samples were measured by AC impedance spectroscopy. The results showed that the ionic conductivity increases at first and then decreases with raising doping amounts and sintering temperatures. So the optimized composition Li_3/8Sr_7/16-3x/2La_xZr_1/4Nb_3/4O₃ (x = 0.05) sintered at 1275 °C was selected with the highest total conductivity of 3.33 × 10^?5 S cm^?1at 30 °C and an activation energy of 0.27 eV. Additionally, potentiostatic polarization test was used to evaluate the electronic conductivity. The optimal composition Li_3/8Sr_7/16-3x/2La_xZr_1/4Nb_3/4O₃ (x = 0.05) as a possible Li-ion conducting solid electrolyte has an electronic conductivity of only 8.39 × 10^?9 S cm^?1.     

La2-xSrxCoO4±λ(x=0～1.0)催化剂的结构及催化性能

采用聚乙二醇凝胶法制备了Co系类钙钛矿La_2-xSr_xCoO_4±λ(x=0～1.0)复合氧化物,研究了系数x对催化剂的结构和催化性能的影响,考察了它们对 CO和C₃H₈的氧化反应活性,并运用XRD、IR、BET、TPD和化学分析等方法对催化剂进行了表征.结果表明：该类复合氧化物具有K₂NiF₄结构,它们的结构和催化性能随系数x不同而变化,其中以LaSrCoO_4-λ催化活性最好,这是由LaSrCoO_4-λ的晶格氧更易移动、Co³⁺离子含量更高,氧空位和反应时化学吸附氧更多所致.     

Effects of La doping on electrical conductivity,thermal expansion and electrochemical performance in LaxSr1–xCo0.9Sb0.1O3–δ cathodes for IT–SOFCs

Perovskite oxides La_xSr_1–xCo_0.9Sb_0.1O_3–δ (LSCSbx, x=0.0–0.8) are investigated as IT–SOFC cathodes supported with La_0.9Sr_0.1Ga_0.8Mg_0.2O_3–δ (LSGM) electrolyte. All LSCSbx oxides have a tetragonal distorted perovskite structure with s.g. P4/mmm, while a La₂Co₂O₅ impurity phase was observed within La doping levels at x=0.6–0.8. The LSCSb0.4 has a good chemical compatibility with LSGM electrolyte for temperatures up to 1050 °C. XPS examinations indicate the existence of Co³⁺/Co⁴⁺ mixed valence states in LSCSbx. The conductivity increases with La doping and the LSCSbx with x=0.4 exhibits the highest electrical conductivity (e.g., 673–1637 S cm⁻¹ at 300–850 °C). The thermal expansion coefficient (TEC) decreases from 25.89×10^–6 K^–1 for x=0.0 to 18.5×10^–6 K^–1 for x=0.6 at 30–900 °C. Among the LSCSbx compositions, the LSCSb0.2 exhibits the lowest polarization resistance (R_p), which is merely 0.069 Ω cm² at 700 °C. The maximum power density of the cell with LSCSb0.2 cathode on 300 µm thick LSGM electrolyte attains 564 mW cm^–2 at 850 °C, which is higher than that of SrCo_0.9Sb_0.1O_3–δ (SCSb) cathode. All of the results indicate that LSCSb0.2 is a promising material for application in IT–SOFCs cathodes.     

Enhanced sinterability and conductivity of cobalt doped lanthanum niobate as electrolyte for proton-conducting solid oxide fuel cell

La_0.95Ca_0.05Nb_1-xCo_xO₄ (x?=?0, 0.01, 0.02, 0.03, 0.05) compounds have been synthesized by a conventional solid state reaction method at 1150?°C. Co and Ca have been simultaneously introduced into LaNbO₄ solid solution for the first time, taking the place of La and Nb sites, respectively. Dense ceramic pellets of La_0.95Ca_0.05Nb_1-xCo_xO₄ have been prepared by sintering at 1300?°C with the utilization of cobalt as the sintering aid. The conductivity measurement has been carried out for all the samples in wet air. The results demonstrate that conductivity of La_0.95Ca_0.05Nb_1-xCo_xO₄ compounds are higher than that of LaNbO₄ attributed to additional oxygen vacancies generated by Co and Ca co-doping. The strategy of doping cobalt as a sintering aid proposed in this work could be served as a valid way to enhance the sinterability and electrical conductivity of LaNbO₄ based proton conducting oxides.     

An investigation on the microstructural and electrical properties of La0.85DxSr0.15–xGa0.8Mg0.2O2.825 (D = Ba and Ca) electrolytes in solid oxide fuel cells

La_0.85D_xSr_0.15–xGa_0.8Mg_0.2O_2.825 (D = Ba and Ca, x?=?0, 0.01, 0.03, 0.05, and 0.07) electrolytes were synthesized using a solid-state reaction method, calcined at 1400?°C for 5?h, and sintered at 1400?°C for 5?h. The microstructures, electrical properties, and cell performances of the electrolytes and fuel cells were analyzed by X-ray diffraction, scanning electron microscopy, impedance analysis, and electrochemical analysis. La_0.85Ba_xSr_0.15–xGa_0.8Mg_0.2O_2.825 (LBSGM) and La_0.85Ca_xSr_0.15–xGa_0.8Mg_0.2O_2.825 (LCSGM) exhibit a dense structure and a cubic perovskite phase. Further, they contain small amounts of a secondary phase. The lattice constants of LBSGM and LCSGM are 0.3913–0.3914?nm and 0.3906–0.3909?nm, respectively. The average grain size of the sample increases with increasing Ba²⁺ or Ca²⁺ content. The conductivity of LCSGM (0.197–0.174?S/cm) is usually higher than that of LBSGM (0.181–0.162?S/cm) at 800?°C. The cells with La_0.85Sr_0.15Ga_0.8Mg_0.2O_2.825 and La_0.85Ca_0.03Sr_0.12Ga_0.8Mg_0.2O_2.825 electrolytes exhibit high open-circuit voltages and maximum power densities of 0.96?V and 542?mW/cm² and 0.94?V and 567?mW/cm², respectively, at 800?°C.     

Conductivity and electrochemical performance of (Ba0.5Sr0.5)0.8La0.2CoO3−δ cathode for intermediate-temperature solid oxide fuel cell

This study reports the successful preparation of a single-phase cubic (Ba_0.5Sr_0.5)_0.8La_0.2CoO_3?δ perovskite by the citrate–EDTA complexing method. Its crystal structure, thermogravimetry, coefficient of thermal expansion, electric conductivity, and electrochemical performance were investigated to determine its suitability as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Its coefficient of thermal expansion shows abnormal expansion at 300 °C, which is associated with the loss of lattice oxygen. The maximum conductivity of a (Ba_0.5Sr_0.5)_0.8La_0.2CoO_3?δ electrode is 689 S/cm at 300 °C. Above 300 °C, the electronic conductivity of (Ba_0.5Sr_0.5)_0.8La_0.2CoO_3?δ decreases due to the formation of oxygen vacancies. The charge-transfer resistance and gas phase diffusion resistance of a (Ba_0.5Sr_0.5)_0.8La_0.2CoO_3?δ–Ce_0.8Sm_0.2O_1.9 composite cathode are 0.045 Ω cm² and 0.28 Ω cm², respectively, at 750 °C.     

Chemical Bulk Diffusion Coefficient of a La0.5Sr0.5CoO3−δ Cathode for Intermediate‐Temperature Solid Oxide Fuel Cells

In the first part of this study, the characteristics of a La_0.5Sr_0.5CoO_3?δ cathode are described, including its chemical bulk diffusion coefficient (D_chem), and electrical conductivity relaxation experiments are performed to obtain experimental D_chem measurements of this cathode. The second part of this study describes two methods to improve the single‐cell performance of solid oxide fuel cells. One method uses a composite cathode, i.e., a mix of 30 wt% electrolyte and 70 wt% cathode; the other method uses an electrolyte‐infiltrated cathode, i.e., an active ionic‐conductive electrolyte with nano‐sized particles is deposited onto a porous cathode surface using the infiltration method. In this work, 0.2M Ce_0.8Sm_0.2O_1.9 (SDC)‐infiltrated La_0.5Sr_0.5CoO_3?δ exhibits a maximum peak power density of 1221 mW/cm² at an operating temperature of 700°C with a thick‐film SDC electrolyte (30 μm), a NiO + SDC anode (1 mm) and a La_0.5Sr_0.5CoO_3?δ cathode (10 μm). The enhancement in electrochemical performances using the electrolyte‐infiltrated cathode is attributed to the creation of electrolyte/cathode phase boundaries, which considerably increases the number of electrochemical sites available for the oxygen reduction reaction.