NATALIA KONDO MONTEIRO

NATALIA KONDO MONTEIRO

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Low temperature synthesis and properties of gadolinium-doped cerium oxide nanoparticles
2017 - MACHADO, M.F.S.; MORAES, L.P.R.; MONTEIRO, N.K.; ESPOSITO, V.; FLORIO, D.Z. de; MARANI, D.; FONSECA, F.C.
Gadolinium-doped cerium oxide (GDC) is an attractive ceramic material for solid oxide fuel cells (SOFCs) both as the electrolyte and in composite electrodes operating at low and intermediate temperatures. GDC exhibits high oxygen ion conductivity at a wide range of temperatures and displays a high resistance to carbon deposition when hydrocarbons are used as fuels. However, an inconvenience of ceria-based oxides is the high sintering temperature needed to obtain a fully dense ceramic body. In this study, a green chemistry route for the synthesis of 10 mol% GDC nanoparticles is proposed. The aqueous precipitation method starts from the nitrates of both cerium and gadolinium and uses excess hexamethylenetetramine (HMT) to produce crystalline GDC at 80 ºC. Such a low temperature synthesis provides control over particle size and sinterability of the material at low temperatures.
Synthesis of Ru-doped double perovskite anode for SOFC
2017 - MONTEIRO, N.K.; CANDIDO, G.A.S.; FONSECA, F.C.
Pr0.5Ba0.5MnO3 was studied as the precursor phase of the double perovskite PrBaMn2O5+δ (PBMO) anode material for solid oxide fuel cells (SOFC). The general properties were studied in both the pristine compound and Ru-doped samples Pr0.5Ba0.5Mn1-xRuxO3 (PBMRu). Ru substitution at the B-site is expected to enhance the catalytic properties of the ceramic towards ethanol or methane fuels. The studied compounds were synthesized by the polymeric precursor method and characterized by thermogravimetric analyses, X-rays diffraction (XRD), and electrical transport properties. The experimental data show PBMO phase formation occurring at ~800°C and single phase compounds at ~1100°C up to ~10 at.% of Ru substituted. Similar ionic radius of Ru3+ and Mn3+ results in little effect on both the crystalline structure and electrical conductivity as compared to the pristine compound.
Optimization of spin-coated electrodes for electrolyte-supported solid oxide fuel cells
2017 - NOBREGA, SHAYENNE D. da; MONTEIRO, NATALIA K.; TABUTI, FRANCISCO; FLORIO, DANIEL Z. de; FONSECA, FABIO C.
Electrodes for electrolyte-supported solid oxide fuel cells (SOFC’s) were fabricated by spin coating. Strontium- doped lanthanum manganite (LSM) cathode and nickel yttria-stabilized zirconia cermet anodes were synthesized and processed for enhanced deposition conditions. The influence of electrode microstructural parameters was investigated by a systematic experimental procedure aiming at optimized electrochemical performance of single cells. Polarization curves showed a strong dependence on both electrode thickness and sintering temperature. By a systematic control of such parameters, the performance of single cells was significantly enhanced due to decreasing of polarization resistance from 26 Ω cm² to 0.6 Ω cm² at 800°C. The results showed that spin-coated electrodes can be optimized for fast and cost effective fabrication of SOFCs.
Synthesis and characterization of a doubleperovskite anode for solid oxide fuel cells
2016 - MONTEIRO, NATALIA K.; SILVA, GABRIEL A.C. da; FONSECA, FABIO C.
Solid oxide fuel cells are one of the most efficient devices for the direct conversion of the chemical energy of a fuel into electricity. Nonetheless, standard solid oxide fuel cells (SOFC) with Ni/yttria-stabilized zirconia cermet anode have a serious decrease of their lifetime when fed with carbon-containing fuels due to coke formation. Ceramics with perovskite structure have been pointed out as good candidates to anodes. In this study, the Pr0.5Ba0.5MnO3 was used as the precursor phase of the double perovskite PrBaMn2O5+δ (PBMO), present at reducing conditions. The transport and catalytic properties were studied in the pristine compound and in Ru-doped samples Pr0.5Ba0.5Mn1-xRuxO3 (Ru-PBMO). Ru substitution at the B-site is expected to enhance the catalytic properties of the ceramic toward ethanol for SOFC’s running on such fuel. Simultaneous thermogravimetric and differential thermal analysis (TG/DTA) were used to monitor the thermal evolution of polymeric resins up to 1400 °C. Ceramic powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses. The electrical properties of sintered samples were evaluated by dc 4-probe technique, in the 25 - 800 °C temperature range. The TG/DTA and XRD data show mass loss stabilization and crystalline phase formation occurring at ~800°C. The evolution of the XRD pattern upon calcining temperature indicated the formation of single phase of Ru-PBMO samples at ~1100°C. The initial results suggest that PBMO and PBMO-Ru compounds are promising SOFC anodes for carbon containing fuels.
Low temperature synthesis of gadolinium-doped cerium oxide nanoparticles
2016 - MORAES, LETICIA P.R. de; MONTEIRO, NATALIA K.; MACHADO, MARINA F. de; ESPOSITO, VINCENZO; FLORIO, DANIEL Z. de; MARANI, DEBORA; FONSECA, FABIO C.
In this study, a green chemistry route for the synthesis of gadolinium-doped ceria (GDC) nanoparticles is reported. The aqueous based reflux method uses nitrates of both ceria and gadolinium and hexamethylenetetramine as starting materials to produce GDC at 80 ºC. As-produced powders were found to be crystalline fluoritetype structure GDC before any heat treatment, with crystallite size ≤ 10 nm, as inferred by X-rays diffraction analyses. Energy dispersive X-ray spectroscopy data revealed that GDC powders, with gadolinium concentration in the 0 - 20 mol% range, have composition close to the nominal values, within the experimental error. Thermogravimetric analyses (TG) evidenced that main mass loss (~7%) occurs at < 400 °C. Sintering behavior was studied by dilatometry of cylindrical pellets pressed using both as-produced and calcined (400 °C for 1 hour in air) powders. The retraction profile of the as-produced samples resembles the TG data, showing plateaus that correspond to the observed mass loss events. On the other hand, sintering of calcined samples exhibited onset of shrinkage at T ~ 600 °C and a continuous retraction up to 1400°C (~17% total retraction). The experimental results indicate that the synthesis method results in GDC with good properties for application in electrochemical devices, such as fuel cells and solardriven thermochemical reactors.
Síntese e caracterização de manganita-cromita de lantânio dopada com rutênio para anodos de células a combustível de óxidos sólidos
2011 - MONTEIRO, NATALIA K.
Diversos anodos para célula a combustível de óxido sólido (SOFC) têm sido estudados devido aos problemas de deterioração dos anodos tradicionalmente usados, os compósitos à base de zircônia estabilizada/Ni (YSZ/Ni). Estudos prévios evidenciaram que a perovskita La0,75Sr0,25Cr0,50Mn0,50O3 (LSCM) possui desempenho similar em SOFCs usando hidrogênio e metano como combustível, tornando essa cerâmica um possível substituto dos compósitos à base de níquel. No presente estudo, foram sintetizados compostos La0,75Sr0,25Cr0,50-xMn0,50- yRux,yO3 (LSCM-Ru) pelo método dos precursores poliméricos. Análises termogravimétrica e térmica diferencial (TG/ATD) simultâneas e difração de raios X (DRX) foram utilizadas para monitorar a evolução térmica das resinas precursoras e a formação de fase dos compostos. As propriedades elétricas de amostras sinterizadas foram estudadas pela técnica de 4 pontas de prova dc na faixa de temperatura entre 25 °C e 800 °C. Os resultados experimentais indicaram a formação de fase única dos compostos LSCM-Ru calcinados a ~1200 °C. Os parâmetros de rede, calculados a partir dos dados de DRX, revelaram que a substituição parcial dos íons Cr ou Mn pelo Ru não altera significativamente a estrutura cristalina do LSCM até x,y ~ 0,10; uma característica consistente com os raios iônicos similares dos cátions Cr, Mn e Ru com número de coordenação seis. Medidas de resistividade elétrica ao ar mostraram que o mecanismo de transporte não é alterado e que o efeito da substituição de Ru nas propriedades elétricas do composto depende do íon substituído (Cr ou Mn) de maneira consistente com suas substituições parciais. Os testes de SOFCs unitárias revelaram que células com os anodos constituídos por uma camada coletora de corrente do anodo cerâmico LSCM-Ru e uma camada funcional de YSZ/Ni têm desempenho superior a células contendo apenas o anodo cerâmico. As células contendo os anodos cerâmicos LSCM-Ru foram testadas em hidrogênio e etanol, entre 800 °C e 950 °C, e mostraram desempenho em etanol superior ao em hidrogênio; uma característica que foi associada às propriedades de transporte eletrônico dos compostos LSCM-Ru em atmosfera redutora. Os resultados sugerem que os compostos LSCM com substituição parcial de Ru são anodos promissores para SOFC operando com etanol.
A direct ethanol anode for solid oxide fuel cell based on a chromite-manganite with catalytic ruthenium nanoparticles
2012 - MONTEIRO, N.K.; NORONHA, F.B.; COSTA, L.O.O. da; LINARDI, M.; FONSECA, F.C.
Ceramic oxide anode with precipitated catalytic nanoparticles for ethanol fueled SOFC
2011 - MONTEIRO, N.K.; NOBREGA, S.D.; FONSECA, F.C.