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Previous issue date: 2013-07-31 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / Materials consisting of perovskite-type oxides (ABO3) have been developed in this
work for applications in fuel cell cathodes of solid oxide type (SOFC). These ceramic
materials are widely studied for this type of application because they have excellent electrical
properties, conductivity and electrocatalytic. The oxides LaMnO3, LaFeO3, LaFe0.2Mn0.8O3 e
La0.5Fe0.5MnO3 were synthesized by the method of microwave assisted combustion and after
sintering at 800?C in order to obtain the desired phases. The powders were characterized by
thermogravimetry (TG), X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning
electron microscopy (SEM) and voltammetric analysis (cyclic voltammetry and polarization
curves). The results obtained by XRF technique showed that the microwave synthesis method
was effective in obtaining doping oxides with values near stoichiometric. In general, powders
were obtained with particle size less than 0.5 μm, having a porous structure and uniform
particle size distribution. The particles showed spherical form, irregular and crowded of
varying sizes, according to the analysis of SEM. The behavior of the oxides opposite the
thermal stability was monitored by thermogravimetric curves (TG), which showed low weight
loss values for all samples, especially those of manganese had its structure. By means of Xray
diffraction of the samples sintered at 800?C was possible to observe the formation of
powders having high levels of crystallinity. Furthermore, undesirable phases such as La2O3
and MnOx were not identified in the diffractograms. These phases block the transport of
oxygen ions in the electrode/electrolyte interface, affecting the electrochemical activity of the
system. The voltammetric analysis of the electrocatalysts LF-800, LM-800, LF2M8-800 e
L5F5M-800 revealed that these materials are excellent electrical conductors, because it
increased the passage of electrical current of the working electrode significantly. Best
performance for the oxygen reduction reaction was observed with iron-rich structures,
considering that the materials obtained have characteristics suitable for use in fuel cell
cathodes of solid oxide type / Materiais constitu?dos de ?xidos do tipo perovskita (ABO3) t?m sido desenvolvidos no
presente trabalho para aplica??es em c?todos de c?lulas a combust?vel do tipo ?xidos s?lidos
(SOFC). Estes materiais cer?micos s?o amplamente estudados para esse tipo de aplica??o
porque apresentam ?timas propriedades el?tricas, condutoras e eletrocatal?ticas. Os ?xidos
LaMnO3, LaFeO3, LaFe0,2Mn0,8O3 e La0,5Fe0,5MnO3 foram sintetizados pelo m?todo de
combust?o assistida por microondas e logo ap?s sinterizados a 800?C a fim de obter as fases
desejadas. Os p?s obtidos foram caracterizados por termogravimetria (TG), difratometria de
raios-X (DRX), fluoresc?ncia de raios-X (FRX), microscopia eletr?nica de varredura (MEV)
e an?lise voltam?trica (voltametria c?clica e curvas de polariza??o). Os resultados obtidos
atrav?s da t?cnica de FRX evidenciam que a escolha do m?todo de s?ntese por microondas foi
eficaz na obten??o de ?xidos com valores de dopagens pr?ximos ao estequiom?trico. No
geral, foram obtidos p?s com tamanho de part?culas inferiores a 0,5 μm, apresentando
estrutura porosa e distribui??o de part?culas uniformes. As part?culas se apresentaram na
forma esf?rica, irregular e aglomerada de tamanhos variados, segundo a an?lise de MEV. O
comportamento dos ?xidos frente ? estabilidade t?rmica foi monitorado atrav?s das curvas
termogravim?tricas (TG), a qual mostrou baixos valores de perdas de massa para todas as
amostras, principalmente aquelas que apresentavam o mangan?s em sua estrutura. Por meio
da difratometria de raios-X das amostras sinterizadas a 800?C foi poss?vel observar a
forma??o de p?s com elevados valores de cristalinidade. Al?m disto, fases indesej?veis como
La2O3 e MnOx, n?o foram identificadas nos difratogramas. Estas fases bloqueiam o transporte
de ?ons oxig?nio na interface eletrodo/eletr?lito, comprometendo a atividade eletroqu?mica do
sistema. A an?lise voltam?trica dos eletrocatalisadores LF-800, LM-800, LF2M8-800 e
L5F5M-800 demonstrou que estes materiais s?o ?timos condutores, porque aumentaram a
passagem de corrente el?trica do eletrodo de trabalho de forma significativa. Melhor
desempenho para a rea??o de redu??o de oxig?nio foi observado com estruturas ricas em
ferro, considerando que os materiais obtidos possuem caracter?sticas apropriadas para
aplica??o em c?todos de c?lulas a combust?vel de ?xidos s?lidos
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/17744 |
| Date | 31 July 2013 |
| Creators | Costa, Rom?rio Cezar Pereira da |
| Contributors | CPF:01139059980, http://lattes.cnpq.br/2485073932883264, Silva, Ademir Oliveira da, CPF:16225422404, http://lattes.cnpq.br/3511004608337461, Melo, Dulce Maria de Ara?jo, CPF:06117988320, http://lattes.cnpq.br/3318871716111536, Oliveira, Jo?o Bosco Lucena de, CPF:19127537404, http://lattes.cnpq.br/1360004695124740, Castro, Suely Souza Leal de, CPF:05705753896, http://lattes.cnpq.br/9860381828526444, Huitle, Carlos Alberto Martinez |
| Publisher | Universidade Federal do Rio Grande do Norte, Programa de P?s-Gradua??o em Qu?mica, UFRN, BR, F?sico-Qu?mica; Qu?mica |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/masterThesis |
| Format | application/pdf |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/openAccess |
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