Sinterização Convencional e por micro-ondas da perovskita BaCe0,2Zr0,7Y0,1O3-δ para utilização em células a combustível de óxido sólido.

Abstract

Fuel cells consist of two electrodes separated by an electrolyte and produce energy from renewable sources. Among the types of fuel cells are Solid Oxide Fuel Cells (SOFC), which operate with a dense solid ceramic electrolyte and whose operating temperature is the highest compared to other types. A promising route to reduce the operating temperature of this type of fuel cell is the use of ceramics with proton conduction, such as perovskites based on barium cerate and barium zirconate, which, however, require long times and high temperatures of sintering. To improve the sinterability of these ceramics, resources that can be used are the addition of oxides that act as sintering aids and other unconventional sintering methods, such as those using microwave radiation. In this work, the conventional (between 1200°C and 1500°C/4h) and microwave (between 1300°C and 1500°C/0.5h) sintering of BaCe0.2Zr0.7Y0.1O3-δ perovskite was studied (BCZY) to act as a SOFC electrolyte with proton conductivity. The synthesis method used was the solid state reaction, and ZnO and NiO oxides were used as sintering additives, in the percentages of 2 and 4% mol for each oxide. After synthesis, in all studied compositions, three more phases were identified in the X-ray diffractograms, in addition to the BCZY phase. After conventional and microwave sintering, peaks exclusively referring to the BCZY phase were verified. The addition of oxides, used as sintering additives, proved to be efficient, as the relative densities reached values above 95%, even at the lowest temperatures of conventional sintering. In microwave sintering, additives also had an effect on sinterability and, compared to the conventional method, a reduction of 3.5 hours in the firing level was obtained. In the microstructural analysis, performed by scanning electron microscopy with EDS mapping, second phases were identified in the compositions with the use of additives and a greater homogeneity in the distribution of elements for microwave sintering. In the dense samples, impedance spectroscopy measurements were performed, where the highest values of total conductivity were found for the composition with 2%mol ZnO and 2%mol NiO, sintered at 1300°C/4h conventionally. In microwave sintering, the highest conductivity value, comparable to the conventional one, was observed for a burning condition of 1400°C/0.5h, in the composition with 2%mol ZnO.