Correlation of thermal properties and electrical conductivity of La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>Cu<Subscript>0.2</Subscript>Fe<Subscript>0.8</Subscript>O<Subscript>3−δ</Subscript> material for solid oxide fuel cells

A copper-doped ferrite with the chemical composition La_0.7Sr_0.3Cu_0.2Fe_0.8O_3−δ (LaSrCuFe) was prepared using the classical ceramics method starting from the oxides. The linear thermal expansion coefficient in air was measured in the temperature range between 550 and 1,250 K to be between 10 × 10⁻⁶ and 15 × 10⁻⁶ K⁻¹. The electrical conductivity in air was found to be higher than 100 S cm⁻¹ for temperatures lower than 1,100 K. A change of oxygen stoichiometry was found above 650 K in an atmosphere of 20 vol% oxygen with argon. This change can be correlated with the electrical conductivity.     

Electrochemical behavior of Ln0.6Sr0.4Co0.2Fe0.8O3−δ (Ln=Ce, Gd, Sm, Dy) materials used as cathode of IT-SOFC

The perovskite-type compounds Ln_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (Ln=Ce, Sm, Gd, Dy) used as the cathodes of intermediate temperature solid oxide fuel cell (IT-SOFC) were studied. The cells consisted of anode supported Sm-doped-ceria electrolyte bi-layer and cathode with 0.65 cm² effective area. Open-circuit voltage (OCV), V–I and P–I curves of the cells were measured over a temperature range from 400 to 800 °C, using H₂–3%H₂O as fuel and air as oxidant. Polarization potential of electrodes were measured with asymmetry three-electrode method during cell discharging. The results indicated that, Dy-SCF material cathode behaved with high catalytic activity for oxygen dissociation at low temperatures. For each cell with a particular cathode, there was a transition temperature, at which OCV of the cell reached the highest value. When temperature was higher than the transition temperature, OCV of the cell increases with decreasing temperature, whereas as temperature was lower than that, OCV decreased with lowering temperature.     

Ca-doped PrBa1-xCaxCoCuO5+δ (x = 0–0.2) as cathode materials for solid oxide fuel cells

Ca-doped perovskite oxides PrBa_1-xCa_xCoCuO_5+δ (PBCCCO, x = 0–0.2) were prepared and investigated as SOFC cathode materials. PBCCCO samples are single perovskite structure with P4/mmm space group. Pr, Cu and Co ions in PBCCCO samples exist in the form of Pr³⁺/Pr⁴⁺, Cu²⁺/Cu⁺ and Co³⁺/Co⁴⁺ multi-valence states. The average TECs of PBCCCO samples were reduced from 17.4 × 10^?6 K^?1 (x = 0) to 16.7 × 10^?6 (x = 0.1) and 16.1 × 10^?6 K^?1 (x = 0.2) whin RT-900°С. The electrical conductivity and electrochemical catalytic activity of PBCCCO perovskites was enhanced obviously by Ca doping. The ASR values decreased by 60.1% (@650 °C), 68.9% (@700 °C), 71.0% (@750 °C) and 72.8% (@800 °C) respectively when Ca doping content increased from x = 0 to 0.2. These results suggest PBCCCO sample with Ca doing content x = 0.2 can be a promising cathode for IT-SOFC.     

钙钛矿型固体电解质材料的研究进展

钙钛矿型材料是近些年来人们发现的离子导电率较高的固体电解质材料。本文将钙钛矿型固体电解质材料分为氧离子导电型和氢离子导电型两种类型,分别介绍了它们的导电机理及近期研究进展。     

Self-assembled La0.6Sr0.4FeO3-δ-La1.2Sr0.8NiO4+δ composite cathode for protonic ceramic fuel cells

The oxygen reduction reaction at the cathode is an essential process for protonic ceramic fuel cells. Composite cathode materials are commonly used towards the multiple requirements including high surface oxygen activity as well as sufficient electronic and ionic conductivities. In this study, a cobalt-free composite cathode composed of a perovskite La_0.6Sr_0.4FeO_3-δ phase and a Ruddlesden-Popper La_1.2Sr_0.8NiO_4+δ phase is synthesized with a self-assembly technology. The cathode process is mainly controlled by (I) the reduction of adsorbed oxygen atom to O⁻ on the surface and (II) the migration of O⁻ from the surface into the lattice. The former benefits from the high electrical conductivity of La_0.6Sr_0.4FeO_3-δ, and the latter is accelerated by La_1.2Sr_0.8NiO_4+δ attributed to its superior oxygen activity. The one-pot synthesized composite cathode shows an enhanced synergistic effect due to the uniform distribution of the two phases at the nanoscale. The cathode shows the lowest polarization resistances of 0.055 and 0.095 Ω cm² at 700 °C in oxygen and air, respectively. The results show that self-assembled La_0.6Sr_0.4FeO_3-δ-La_1.2Sr_0.8NiO_4+δ nanocomposite is a promising cathode material for protonic ceramic fuel cells.     

Pr0.6Sr0.4CoO3−δ electrocatalyst for solid oxide fuel cell cathode introduced via infiltration

Effects of infiltrated Pr_0.6Sr_0.4CoO_3−δ (PSCo) electrocatalyst on SOFC cathode performance have been studied. Nano-sized particulate catalysts, deposited on surfaces of a composite cathode of Sm₂O₃ doped CeO₂ (SDC) and La_1−xSr_xCo_1−yFe_yO_3−δ (LSCF), are assumed to effectively widen active sites, or triple phase boundaries, for the oxygen reduction reaction. Area specific resistance of commercially available cells has been decreased by 36–40% with the addition of 23 wt% PSCo electrocatalyst on cathode. Analysis of the impedance spectra demonstrates that PSCo electrocatalyst plays a significant role in dissociation of oxygen molecules and adsorption of oxygen atoms into the cathode. A total of 200 h operation of the cells demonstrated that catalytic activity of PSCo has not been significantly degraded. Simultaneous operations of multiple cells using a parallel-cell testing system have made it possible to compare the performance of several cells with high reliability.     

Electrochemical performance of silver-modified Ba0.5Sr0.5Co0.8Fe0.2O3−δ cathodes prepared via electroless deposition

Silver-modified Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) cathodes for intermediate-temperature solid-oxide fuel cells (IT-SOFCs) were prepared by an electroless deposition process using N₂H₄ as the reducing agent at room temperature. This fabrication technique together with tailored electrode porosity, modified the BSCF electrodes with silver content that varied from 0.3 to 30 wt.% without damaging the electrode microstructure. Both the Ag loading and firing temperatures were found to have a significant impact on the electrode performance, which could facilitate or block the electrochemical processes of the BSCF-based cathodes, processes that include charge-transfer, oxygen adsorption and oxygen electrochemical reduction. At an optimal Ag loading of 3.0 wt.% and firing temperature of 850 °C, an area specific resistance of only 0.042 Ω cm² at 600 °C was achieved for a modified BSCF cathode.     

Upconversion Luminescence in Yb/Ln (Ln = Er,Tm) Doped Oxyhalide Glasses Containing CsPbBr3 Perovskite Nanocrystals

Yb/Ln (Ln=Er, Tm) doped TeO₂-based glasses containing CsPbBr₃ perovskite quantum dots were successfully prepared via in-situ glass crystallization. The nanocomposites yield typical green downshifting luminescence attributing to CsPbBr₃ exciton recombination under UV excitation, and produce Er³⁺ green, Er³⁺ red and Tm³⁺ blue upconversion emissions under 980 nm laser excitation. Impressively, specific Ln³⁺ emissions will be quenched with the precipitation of CsPbBr₃ in glass, enabling to finely tune upconversion emitting color. Spectroscopic characterizations evidence that the luminescence quenching is originated from non-radiative reabsorption effect induced by the precipitation of CsPbBr₃ rather than energy transfers from Ln³⁺ to CsPbBr₃. Finally, these nanocomposites are demonstrated to exhibit superior water resistance due to the effective protecting role of dense structural glass, particularly, about 95% downshifting luminescence of CsPbBr₃ and upconversion luminescence of Er³⁺ related to pristine ones are retained after immersing the products in water up to 30 days.     

Tuning the dielectric,ferroelectric and electromechanical properties of Ba0.83Ca0.10Sr0.07TiO3–MnFe2O4 multiferroic composites

We report the successful synthesis of Ba_0.83Ca_0.10Sr_0.07TiO₃–MnFe₂O₄ multiferroic composites showing significant improvement in electromechanical and magnetoelectric properties. All the composite samples have formed a diphasic perovskite-ferrite composite without the presence of any impurity or intermediate phase. The bare as well as composite samples have shown classical dielectric behavior even at higher ferrite substituted samples. The electrical characteristics of composite samples have shown slight deterioration, which is mainly attributed to non-ferroelectric MnFe₂O₄. However, the composites still exhibit high enough piezoelectric behavior and the modification in the electromechanical response of composites is mainly caused by a change in applied stress with MnFe₂O₄ addition. The M-H loops of composites have demonstrated a ferrimagnetic behavior with a substantial increase in saturation magnetization on increasing the ferrite concentration. Further, the composites have shown better coupling between the ferroelectric and ferrimagnetic phases, which has resulted in an improved magnetoelectric characteristic. The role of oxygen vacancies on ferroelectric and magnetic properties of prepared composites has been systematically studied.     

La0.5Sr0.5Fe0.9Mo0.1O3-δ-CeO2 anode catalyst for Co-Producing electricity and ethylene from ethane in proton-conducting solid oxide fuel cells

A La_0.5Sr_0.5Fe_0.9Mo_0.1O_3-δ-CeO₂ (LSFM-CeO₂) composite was prepared by impregnating CeO₂ into porous La_0.5Sr_0.5Fe_0.9Mo_0.1O_3-δ perovskite and was used as an anode material for proton-conducting solid oxide fuel cells (SOFCs). The maximum power densities of the BaZr_0.1Ce_0.7Y_0.2O_3-δ (BZCY) electrolyte-supported single cell with LSFM-CeO₂ as the anode reached 291 mW cm^?2 and 190 mW cm^?2 in hydrogen and ethane fuel at 750 °C, respectively, which are significantly higher than those of a single cell with only LSFM as the anode. Additionally, the ethylene selectivity and ethylene yield from ethane for the fuel cell at 750 °C were as high as 93.4% and 37.1%, respectively. The single cell also showed negligible degradation in performance and no carbon deposition during continuous operation for 22 h under an ethane fuel atmosphere. The improved electrochemical performance due to the impregnation of CeO₂ can be a result of enhanced electronic and ionic conductivity, abundant active sites, and a broad three-phase interface in the resultant composite anode. The LSFM-CeO₂ composite is believed to be a promising anode material for proton-conducting SOFCs for co-producing electricity and high-value chemicals from hydrocarbon fuels.     

Effect of impregnation of La0.85Sr0.15MnO3/yttria stabilized zirconia solid oxide fuel cell cathodes with La0.85Sr0.15MnO3 or Al2O3 nano-particles

Strontium substituted lanthanum manganite and yttria stabilized zirconia solid oxide fuel cell composite electrodes were impregnated with nano-particles of strontium substituted lanthanum manganite or alumina. A clear positive effect was observed on low performing electrodes and on good performing electrodes if the temperature was kept low after the impregnation with strontium substituted lanthanum manganite. On good performing electrodes the effect disappeared on heating. Alumina nano-particles had a detrimental effect on the activity of the strontium substituted lanthanum manganite based electrodes.     

Image analysis of the porous yttria-stabilized zirconia (YSZ) structure for a lanthanum ferrite-impregnated solid oxide fuel cell (SOFC) electrode

Image analysis and quantification were performed on porous scaffolds for building SOFC cathodes using the two types of YSZ powders. The two powders (U1 and U2) showed different particle size distribution and sinterability at 1300?°C. AC impedance on symmetrical cells was used to evaluate the performance of the electrode impregnated with 35-wt.% La_0.8Sr_0.2FeO₃. For example, at 700?°C, the electrode from U2 powder shows a polarization resistance (R_p) of 0.21?Ω?cm², and series resistance (R_s) of 8.5?Ω?cm² for an YSZ electrolyte of 2-mm thickness, lower than the electrode from U1 powder (0.25?Ω?cm² for R_p and 10?Ω?cm² for R_s) does. The quantitative study on image of the sintered scaffold indicates that U2 powder is better at producing architecture of high porosity or long triple phase boundary (TPB), which is attributed as the reason for the higher performance of the LSF-impregnated electrode.     

掺杂对钡铁氧体吸波性能影响研究

本实验采溶胶-凝胶法制备钡铁氧体前驱体,煅烧前驱体。用X射线衍射仪（XRD）、微波分光仪对煅烧后产物的物相、微波吸收性能进行研究。结果表明用溶胶-凝胶法制备了钡铁氧体前驱体,二价金属阳离子微过量制备了较纯的铁氧体;铁氧体的烧成温度为800℃,掺杂后烧成温度为900℃。在11GHz,钡铁氧体和掺杂锶的钡铁氧体的反射损耗分别为-12．0dB和-15．9dB。