Navegando por Autor "Figueiredo, Filipe Miguel Henriques Lebre Ramos"
Agora exibindo 1 - 3 de 3
- Resultados por página
- Opções de Ordenação
Artigo Ni–CGO cermet anodes from nanocomposite powders: Microstructural and electrochemical assessment(Elsevier, 2014-09) Macedo, Daniel Araújo de; Figueiredo, Filipe Miguel Henriques Lebre Ramos; Paskocimas, Carlos Alberto; Martinelli, Antonio Eduardo; Nascimento, Rubens Maribondo do; Marques, Fernando M.B.In this study, composite powders synthesized by a novel one-step sol–gel method were used to obtain Ni–CGO anodes, while anodes of the same composition prepared from commercial powders were used as reference. The anodes performance was studied by impedance spectroscopy and dc polarization in the temperature range of 650–750 °C in flowing humidified 10% H2+90% N2 gas mixtures, using a three-electrode configuration cell, with clear advantage for the novel one-step route. One-step anodes fired at 1450 °C showed an area specific resistance of 0.15 Ω cm2 under open circuit conditions and an anodic overpotential of 91 mV at 750 °C for a current density of 322 mA/cm2, which are amongst the best results mentioned in the literature. The enhanced electrochemical performance of one-step anodes is mainly attributed to unique microstructural features, namely small grain size (submicrometer scale even after firing at 1450 °C) and homogeneous phase distribution, which is expected to extend the triple-phase boundary lengthArtigo One-step synthesis of composite electrolytes of Eu-doped ceria and alkali metal carbonates(Elsevier, 2013-12-13) Nascimento, Rubens Maribondo do; Rajesh, Surendran; Macedo, Daniel Araújo de; Souza, Graziele Lopes de; Figueiredo, Filipe Miguel Henriques Lebre Ramos; Marques, Fernando M. B.Europium-doped ceria (EDC, Ce0.9Eu0.1O2 d)/alkaline carbonate (LNC, (Li,Na)2CO3) composite ceramics prepared through a one-step citrate-based route were analyzed by powder X-ray diffraction, infrared and laser Raman spectroscopies as well as scanning and transmission electron microscopy. The electrochemical behavior of the electrolyte material was studied by impedance spectroscopy in air, CO2 and N2 þ H2 (90/10 vol%, respectively) gas mixtures, in the temperature range 300e600 C. The sub micrometric and even nanosized ceramic particles appeared as merged inside the mixed carbonates, with modest grain to grain necking. The EDC/LNC composite electrolytes showed a conductivity of 0.27 S cm 1 at 600 C in air, amongst the best ever reported, exceeding the usual requirements for fuel cell applicationsArtigo 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 doA 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