Estudo da estrutura e propriedades elétricas da perovskita BaCe0,2Zr0,7X0,1O3-δ (X=Y, Er e Dy) para eletrólitos de células a combustível.

Abstract

In view of the demand for clean and efficient energy sources, solid oxide fuel cells (SOFC) emerge as an alternative able to produce electrical energy with high efficiency and without the emission of greenhouse gases using hydrogen as fuel. The high operation temperature is the main technological and economical obstacle to the extensive application of these type of fuel cell. The use of proton conducting electrolytes is the best alternative to reduce the operation temperature of SOFC, however the obtainment electrolytes combining stability and high conductivity is necessary for that. Barium zirconate can combine these characteristics when doped with certain metals, such as yttrium, but its high refractoriness hinders the capacity to obtain dense microstructures. This work evaluates the possibility of obtaining BaCe0,2Zr0,7X0,1O3-δ (X = Y, Dy, or Er) compositions from oxide precursors through solid state reaction, and the effect of sintering temperature and time in the densification and grain growth. The viability of using zinc oxide as a sintering agent was evaluated as well. The synthesis route applied, with two calcination steps, was not sufficient to promote the development of the final composition although, through structural analysis by Rietveld refinement of the sintered product, it was possible to verify that the desired compositions were achieved. The effect sintering time and temperature is small when compared with the effect obtained by the addition of zinc oxide. Dysprosium provided the highest conductivities values, while the high grain boundary resistivity on the yttrium containing composition caused it to produce a considerably lower conductivity than the other compositions. Thus, dysprosium shows the greatest potential as dopant for these zirconates