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Abstract: This paper analyses the electrocatalytic performance of a 60%NiO/Ce0.9Zr0.1O2 anode under reducing atmospheres, using a symmetric cell configuration, [anode/electrolyte/anode], with Samaria doped Ceria (SDC) as electrolyte. This anode exhibited excellent performance in H2 atmosphere in comparison with conventional anode materials. A dual chamber solid oxide fuel cell with 60%NiO/Ce0.9Zr0.1O2 anode, SDC electrolyte, and Pt cathode was constructed and tested under H2 atmospheres at intermediate temperatures. Good values of power densities were obtained, indicating the good performance of 60%NiO/Ce0.9Zr0.1O2 in the operating conditions. [Copyright &y& Elsevier]

Abstract: The solid solution Ce0.8Sm0.2O2−δ (20CSO) was synthesized by freeze-drying precursor procedure. Well-crystallized powders with nanometric grain sizes were obtained after calcining the precursor at 375°C for 4h. The effect of SiO2-addition and sintering temperature on the properties of the bulk and grain boundary processes were studied. For this purpose, 20CSO–SiO2 samples were prepared by the addition of 0.05 or 0.5mol% SiO2 to Ce0.8Sm0.2O2−δ , in the form of tetraethyl orthosilicate (TEOS). Also, 2mol% Co was added to some of the precalcined compositions with and without silica-addition. Cobalt free samples were sintered at 1400, 1500 and 1600°C and cobalt-added samples were sintered 1150°C, for 10h to obtain dense pellets. The electrical behaviour of the bulk was revealed to be nearly independent on sintering temperature and/or on the addition of impurities of SiO2 and Co to the grain boundaries. This was explained by the low solubility of impurities in the grain fluorite structure. However, the grain boundary resistance showed important differences as function of sintering temperature and with the presence of impurities. The analysis of grain boundary properties suggests that segregated impurities affect the microstructure and also segregation of Sm at the space charge layer, thus changing both the specific grain boundary conductivity and microstructural parameters. [Copyright &y& Elsevier]

Abstract: Polycrystalline powders of BaCe0.9Ln0.1O3−δ (Ln=La, Nd, Sm, Gd, Yb, Tb and Y) have been prepared using a freeze-drying precursor route at 1000°C. In order to decrease the densification temperature, different sintering aids (e.g. Co, Zn, Ni, Fe and Cu) were added by mixing the polycrystalline powders with a nitrate solution containing these metals. This allows obtaining dense ceramics at temperatures as low as 1000°C, when compared to samples without sintering aids at 1400°C. The effect of aid content and sintering temperature on the microstructure and electrical conductivity were investigated by scanning electron microscopy and impedance spectroscopy. The addition of small amounts of transition metals does not produce observable structural changes by conventional X-ray powder diffraction. However, the bulk and total conductivities decrease when compared to samples without transition metals. Zn seems to be the most effective sintering element for BaCe0.9Ln0.1O3−δ electrolytes because it does not cause significant changes in the ionic and electronic conductivities. [Copyright &y& Elsevier]

Abstract: The performance of La2NiO4 cathode material and Ce1–x Sm x O2–δ (x =0.1, 0.2, 0.3, 0.4) electrolyte system was analyzed. Ceria-based materials were prepared by the freeze-drying precursor route whereas La2NiO4 was prepared by the nitrate–citrate procedure. Electrolyte pellets were obtained after sintering the powders at 1600°C for 10h. Also dense ceria-based electrolytes samples were obtained by calcining the powders at 1150°C after the addition of 2mol%-Co. Interface polarization measurements were performed by impedance spectroscopy in air at open circuit voltage, using symmetrical cells prepared after the deposition of porous La2NiO4-electrodes on the Ce1–x Sm x O2–δ system. X-ray diffraction (XRD) of cathode materials after using in symmetrical cells confirmed no significant reaction between La2NiO4 and ceria-based electrolytes. The efficiency of the cathode material is highly dependent on the composition of the electrolyte, and low-content Sm-doped ceria samples revealed an important decrease in the performance of the system. Differences in electrochemical behaviour were attributed principally to the oxide ion transference between cathode and electrolyte, and were correlated to the conductivity of the electrolyte. In this way cobalt-doped electrolytes with a Sm-content ≤30% perform better than free-cobalt samples due to the increase in grain boundary conductivity. Finally, composites of the ceria-based materials and La2NiO4 to use as cathode were prepared and an important increase of the interface performance was observed compared to La2NiO4 pure cathode. Predictions of maximun power density were obtained by the mixed transport properties of the electrolytes and by the interface polarization results. The use of composite materials could allow to increase the performance of the cell from 170mWcm−2 for pure La2NiO4 cathode, to 370mWcm−2 for La2NiO4–Ce0.8Sm0.2O2–δ cathode, both working with Ce0.8Sm0.2O2–δ electrolyte 300μm in thickness and Ni–Ce0.8Sm0.2O2–δ as anode at 800°C. [Copyright &y& Elsevier]

Abstract: Nanocrystalline powders of CGO materials with different contents of Gd were prepared by a freeze-drying method and used to prepare dense ceramic samples. This method allowed one to obtain good quality samples to re-examine the reducibility of CGO materials. These materials were characterized by a combination of coulometric titration, impedance spectroscopy and ion blocking measurements to evaluate changes in point defect chemistry and mixed conducting properties. We have examined the onset of n-type conductivity as a function of temperature and oxygen partial pressure, and this information was used to re-examine the mixed transport properties in reducing conditions imposed by fuels, and also the OCV obtained with CGO solid electrolyte cells under air/CGO/fuel gradients. The polaron mobility was also evaluated and was found to depend slightly on temperature and to decrease with increasing oxygen deficiency. This confirmed that the electronic conductivity is mainly dependent on reducibility. [Copyright &y& Elsevier]