Navegando por Autor "Loureiro, Francisco J. A."
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Artigo Cathodic polarisation of composite LSCF-SDC IT-SOFC electrode synthesised by one-step microwave self-assisted combustion(Elsevier, 2019-05) Nascimento, Rubens Maribondo do; Loureiro, Francisco J. A.; Macedo, Daniel Araújo de; Cesário, Moises Rômolos; Grilo, João Paulo de Freitas; Yaremchenko, Aleksey A.; Fagg, Duncan PaulNano-sized composite La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF)-Ce0.8Sm0.2O1.9 (SDC) powder was synthesised by one-step microwave self-assisted combustion synthesis and characterized by X-ray diffraction and transmission electron microscopy. Electrochemical performance of composite LSCF-SDC cathode in contact with Ce0.8Gd0.2O1.9 (GDC) solid electrolyte under steady state polarisation was studied employing electrochemical impedance spectroscopy in 3-electrode cell configuration. The evolution of elementary steps of oxygen reduction reaction was analysed under cathodic polarisation in potentiostatic mode (up to −0.8 V) in the temperature range 650–750 °C. The composite LSCF-SDC cathode prepared by one-step microwave combustion route demonstrated a lower overall polarisation resistance when compared to literature reports of similar cathodes produced by other synthesis routesArtigo Proteic sol–gel synthesis of Gd-doped ceria: a comprehensive structural, chemical, microstructural and electrical analysis(Springer, 2020-09-21) Paskocimas, Carlos Alberto; Araújo, Allan Jedson Menezes de; Grilo, João Paulo de Freitas; Loureiro, Francisco J. A.; Holz, Laura I. V.; Macedo, Daniel Araújo de; Fagg, Duncan PaulGd-doped ceria (Ce1-xGdxO2-d; x = 0, 0.1 and 0.2) is one of the best ceramic electrolytes for application in solid oxide electrochemical devices. This work reports an innovative and environmentally friendly route known as ‘‘proteic sol–gel synthesis’’ using gelatin for their preparation. Materials are characterized via hermogravimetric analysis, X-ray diffractometry, scanning electron microscopy, Raman and X-ray photoelectron spectroscopies, and electrochemical impedance spectroscopy. The proposed method allows to produce pure phase nanosized powders at 400 C that exhibit excellent sinterability at 1350 C. Significant differences are found in the bulk at lower temperatures, with estimated defect association enthalpies of 0.45 and 0.56 eV for the compositions containing 10 and 20 mol% Gd, respectively, leading to an increased bulk conductivity in the first case. In contrast, identical grain boundary Schottky barrier height values of around 0.2 V are a possible result of the relatively low sintering temperature, decreasing the extent of the acceptor dopant segregation to the grain boundaries due to insufficient cation mobility. This leads to similar specific grain boundary characteristics in both doped compositions. Overall, this work provides a rational understanding of a novel route for the synthesis of CGO ceramics with competitive performance and decreased sintering temperature