Navegando por Autor "Souza, Graziele L."

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Citrate–hydrothermal synthesis, structure and electrochemical performance of La0.6Sr0.4Co0.2Fe0.8O3−δ cathodes for IT-SOFCs
(Elsevier, 2013) Garcia, Laurênia Martins Pereira; Macedo, Daniel Araújo de; Souza, Graziele L.; Motta, Fabiana Villela da; Paskocimas, Carlos Alberto; Nascimento, Rubens Maribondo do
La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) powders were synthesized by a combination of citrate and hydrothermal methods. The thermal decomposition behavior of the as-prepared powder was carried out by simultaneous thermogravimetry–differential thermal analysis. The calcined powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and particle size distribution (PSD). Screen-printed LSCF/CGO/LSCF symmetrical cells were sintered between 1150 and 1200 °C and studied by impedance spectroscopy in order to assess the cathode kinetics for the oxygen reduction reaction. Rietveld refinement of XRD data showed the formation of a single perovskite LSCF phase with crystallite size of 53 nm at 900 °C. The best area specific resistance (ASR) value, measured in static air, was found to be 0.34 Ω cm2 at 750 °C, demonstrating that the novel citrate–hydrothermal method is an effective way to prepare cathode materials for SOFC. Cathode performance can be further enhanced by additional surface modification through impregnation with Pr-containing solution, reaching 0.17 Ω cm2 at 750 °C. Furthermore, the activation energy of the PrOx-impregnated cathode is 83.4 kJ/mol, i.e., much lower than 123.8 kJ/mol, the best value determined for PrOx-free cathodes
Effect of a zirconia interlayer on the morphological properties of LaSrMnO3- 4YSZ composite films obtained by spin coating
(Journal of Ceramic Processing Research, 2011-12-31) Macedo, Daniel Araújo de; Souza, Graziele L.; Cesário, Moises Rômolos; Cela, Beatriz; Martinelli, Antonio Eduardo; Paskocimas, Carlos Alberto; Nascimento, Rubens Maribondo do
In this study, a chemical route was adopted to obtain strontium-doped lanthanum manganite (LaSrMnO3 or LSM) powders in order to prepare LaSrMnO3-4YSZ (4 mol% Y2O3) composite films by the suspension spin coating method onto 4YSZ and 8YSZ/8YSZ-NiO substrates with or without the application of a zirconia interlayer in the film/substrate interface. The multilayers were sintered at 1150 o C for 6 h and the effect of the interlayer on the morphological properties of the films has been investigated by scanning electron microscopy. The results show that in the less roughn substrates the application of the interlayer (~500 nm) not only improved the adhesion in the film/substrate interface, but also avoided new coating failures. All the films were porous, crack-free and with a thickness below 30 μm, desirable features for application as SOFC cathodes
A versatile route for the preparation of Ni–CGO cermets from nanocomposite powders
(Elsevier, 2013-05) Macedo, Daniel Araújo de; Souza, Graziele L.; Cela, Beatriz; Paskocimas, Carlos Alberto; Martinelli, Antonio Eduardo; Figueiredo, Filipe Miguel Henriques Lebre Ramos; Marques, Fernando M. B.; Nascimento, Rubens Maribondo do
A comparative microstructural study between Ni–Ce0.9Gd0.1O1.95 (Ni–CGO) anodes obtained from NiO–CGO nanocomposite powders prepared by in situ one-step synthesis and by mechanical mixture (two-step synthesis) of NiO and CGO powders is reported. The open porosity and microstructure of sintered and reduced pellets were investigated as a function of the citric acid content used as pore forming agent. Nanosized crystallites for the one-step and two-step routes were around 18 nm and 24 nm against 16 nm and 37 nm, for CGO and NiO, respectively. Overall results show that both routes provided suitable microstructures either for anode-support, or for functional anodes for solid oxide fuel cells (SOFCs), with more versatile characteristics in the case of the one-step route. The electrical characterization of selected NiO–CGO samples, carried out between 90 and 260 °C by impedance spectroscopy, confirms electrical percolation of both phases in the composites. However, based on combined microstructural and impedance data, it seems clear that the one-step processing route is the best approach to make SOFC anodes with improved performance

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Navegando por Autor "Souza, Graziele L."