Ln0.6Sr0.4 FeO3-δ(Ln=La、Nd、Ce)阴极材料的制备与表征

以甘氨酸-硝酸盐水溶液为前驱体合成了Sr掺杂的稀土铁酸盐Ln0.6Sr0.4FeO3-δ(Ln=La、Nd、Ce)粉体.对制备过程的化学键变化、样品的热稳定性、物相形成过程及导电性进行了表征.结果表明,甘氨酸-硝酸盐合成法成相温度低于1000℃.坯体烧结较粉状样品更有利于钙钛矿物相的形成,La0.6Sr0.4FeO3-δ及Nd0.6Sr0.4FeO3-δ坯体1000℃煅烧2h即可形成近乎单一的钙钛矿相(ABO3);Ce0.6 Sr0.4 FeO3-δ是CeO2立方萤石相和产物钙钛矿相共存,两相难分主次.合成样品低温下的导电行为符合小极化子导电机制;1200℃烧结的La0.6Sr0.4FeO3-δ样品在测试全温度范围内(450～800℃)电导率超过100S/cm,Nd0.6Sr0.4FeO3-δ在中温区(600～800℃)电导率＞60S/cm;Ce0.6Sr0.4FeO3-δ样品的电导率不理想.     

Characterization of layered perovskite oxides NdBa1−xSrxCo2O5+δ (x = 0 and 0.5) as cathode materials for IT-SOFC

The crystal structure, thermal expansion, and electrochemical properties of the layered perovskite series NdBa_1−xSr_xCo₂O_5+δ (x = 0 and 0.5) were investigated to study the effects of substituting Sr for Ba on a layered perovskite oxide.     

Porous Cu/YSZ anodes processed by aqueous tape casting for IT-SOFC

Porous copper/yttria-stabilized zirconia (Cu/YSZ) thin tapes were produced to be used as anodes in intermediate temperature solid oxide fuel cells (IT-SOFC). The use of copper in these cermets promises a better chemical resistance and a lower operating temperature for SOFC. Graphite and cassava starch were used as pore forming agents, which led to porosity values between 30 and 40%. Tapes were obtained by aqueous tape casting with controlled thickness (300–2000 μm). Before casting, CuO/YSZ aqueous suspensions were formulated based on rheological characterization. Sintering was carried out at 1150 °C during 1 h. Cu/YSZ tapes were obtained after redox reaction, performed at 400, 600 and 800 °C.     

Electro-morphological,structural, thermal and ionic conduction properties of Gd/Pr co-doped ceria electrolytes exhibiting mixed Pr3+/Pr4+ cations

Gd_0.2-xPr_xCe_0.8O_1.90, (x?=?0, 0.02, 0.04, 0.06, 0.08, 0.10) has been synthesized by means of a simple co-precipitation route based on ammonium carbonate as the precipitating agent. The as-synthesized precursors are cerium-gadolinium-praseodymium amorphous hydroxycarbonates, which are nanometric in size with highly homogeneous morphology, leading to reactive doped and co-doped nanocrystalline (≈13?nm) ceria after a mild thermal treatment (2?h at 600?°C). The obtained results highlight the very positive effect of Pr on the powders’ sintering behaviour, which favour a better densification of the final pellets, thus improving both their microstructure (with relative densities of 97–99% after sintering at 1250?°C for 3?h) and electrochemical properties (up to 1.25·10–1?S?cm^?1 at 800?°C for sample 6Pr) compared to the state-of-art ceria-based electrolytes. Through a comprehensive characterization, a relation was formed between the Pr content and the microstructural features of the sintered pellets and their electrical behaviour. The amount of Pr doping was investigated over a wide range and 6?mol% has been established to be optimal (possessing the lowest electronic conductivity contribution). Definitely, these results indicate that Gd_0.2-xPr_xCe_0.8O_1.90 has an excellent set of characteristics, both microstructural and electrical, and a convenient fabrication process, thus making it perfectly suitable for IT-SOFC practical applications.     

Synthesis and characterization of 10%Gd doped ceria (GDC) deposited on NiO-GDC anode-grade-ceramic substrate as half cell for IT-SOFC

In the present research work spray pyrolysis technique (SPT) is employed to synthesize GDC (10%Gd doped ceria) thin films on anode-grade-ceramic substrate (porous NiO-GDC). The film/substrate structure was characterized for their micro-structural and electrical properties along with their interfacial-quality. By optimization of preparative parameters of SPT and modification of surface of anode-grade ceramic substrate, we were able to prepare the GDC films having thickness of the order of 13 μm on NiO-GDC substrate. Further to improve the interfacial quality and densification of film, annealing of structure at 1000 °C for 8 h was carried out which leads to fully dense (>96%) GDC films, forming a gas-tight interface with substrate. Impedance measurements revealed that grain interior conductivity for GDC/NiO-GDC half-cell was of the order of 0.1S/cm at 500 °C which is the desired conductivity for successful operation of IT-SOFC. The activation energy for grain interior and grain-boundary conduction estimated for GDC/NiO-GDC was 1.07 eV and 0.93 eV, respectively.     

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.     

Effect of sintering temperature on structural and electrical properties of gadolinium doped ceria (Ce<Subscript>0·9</Subscript>Gd<Subscript>0·1</Subscript>O<Subscript>1·95</Subscript>)

Gadolinium doped ceria oxide is one of the promising materials as an electrolyte for IT-SOFCs. Ce_0·9Gd_0·1O_1·95 (GDC10) powder was prepared by solid state reaction and sintered at 1473 K, 1573 K, 1673 K and 1773 K. All samples were studied using X-ray diffraction, scanning electron micrograph and d.c. conductivity measurement. The crystallinity and surface morphology of the samples improved with sintering temperature. Further, the electrical conductivity measurement indicated that the conduction mechanism is mainly ionic. The conductivity of samples sintered at 1673 K and 1773 K at 800°C are of the order of 0·1 S-cm⁻¹. The activation energies decreased from 1·25–0·82 eV with increase in sintering temperature.     

Effects of cerium doping on the performance of LSCF cathodes for intermediate temperature solid oxide fuel cells

In this paper, effects of Ce substitution of La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) on the crystal structure have been investigated by XRD Rietveld refinement and results show that Ce doping at La-sites leads to lattice expansion without changing centrosymmetric cubic space group of LSCF. The electrochemical results suggest that the electrocatalytic activity of LSCF cathodes is enhanced by Ce doping. The values of oxygen surface exchange coefficient of LSCF, LCSCF03, LCSCF06, measured by electrical conductivity relaxation (ECR) method, are 5.6 × 10^?4 cm s^?1, 1.0 × 10^?3 cm s^?1, 3 × 10^?3 cm s^?1 at 750 °C respectively, implying that oxygen surface exchange coefficients are increased by Ce doping compared with that of LSCF. The enhancement of electrochemical performance of LSCF cathodes can be ascribed to the increase of the concentration of oxygen vacancies obtained from the thermogravimetric results, which results in faster kinetics of oxygen transport by Ce doping.     

Investigation of Sm0.5Sr0.5CoO3−δ/Co3O4 composite cathode for intermediate-temperature solid oxide fuel cells

The electrochemical properties of an Sm_0.5Sr_0.5CoO_3−δ/Co₃O₄ (SSC/Co₃O₄) composite cathode were investigated as a function of the cathode-firing temperature, SSC/Co₃O₄ composition, oxygen partial pressure and CO₂ treatment. The results showed that the composite cathodes had an optimal microstructure at a firing temperature of about 1100 °C, while the optimum Co₃O₄ content in the composite cathode was about 40 wt.%. A single cell with this optimized C₄₀-1100 cathode exhibited a very low polarization resistance of 0.058 Ω cm², and yielded a maximum power density of 1092 mW cm⁻² with humidified hydrogen fuel and air oxidant at 600 °C. The maximum power density reached 1452 mW cm⁻² when pure oxygen was used as the oxidant for a cell with a C₃₀-1100 cathode operating at 600 °C due to the enhanced open-circuit voltage and accelerated oxygen surface-exchange rate. X-ray diffraction and thermogravimetric analyses, as well as the electrochemical properties of a CO₂-treated cathode, also implied promising applications of such highly efficient SSC/Co₃O₄ composite cathodes in single-chamber fuel cells with direct hydrocarbon fuels operating at temperatures below 500 °C.     

Synthesis and performance of Sr1.5LaxMnO4 as cathode materials for intermediate temperature solid oxide fuel cell

A-site non-stoichiometric materials Sr_1.5La_xMnO₄ (x = 0.35, 0.40, 0.45) are prepared via solid state reaction. The structure of these materials is determined to be tetragonal. Both the lattice volume and the thermal expansion coefficient reduce with the decrease of lanthanum content. On the contrary, the conductivity increases and the maximum value of 13.9 S cm⁻¹ is found for Sr_1.5La_0.35MnO₄ at 750 °C in air. AC impedance spectroscopy and DC polarization measurements are used to study the electrode performance. The optimum composition of Sr_1.5La_0.35MnO₄ results in 0.25 Ω cm² area specific resistance (ASR) at 750 °C in air. The oxygen partial pressure measurement indicates that the charge transfer process is the rate-limiting step of the electrode reactions.