Estudo da microestrutura e da condutividade elétrica de perovisquita BaCe0,2Zr0,7M0,1O3-d (M = Y, Gd)

Abstract

Fuel cells are electrochemical devices that generate electrical energy from redox reactions and have emerged as an alternative in the current search for renewable sources. Solid Oxide Fuel Cells (SOFC) with proton conductor electrolytes are studied for operating at reduced temperatures (when compared to ionic conductors) and by forming water as a by-product of the reaction at the cathode which reduces the fuel dilution that occurs in ionic conductors, where water is formed at the anode, increasing the efficiency of the device. Perovskite structure materials based on barium cerate and barium zirconate, their combinations and the addition of rare earth dopants, have been extensively investigated in order to optimize the proton conductivity and chemical resistance of the compound in oxidizing and reducing atmospheres. In the present work, the compositions BaZr0,7Ce0,2Y0,1O3-d (BCZY) and BaZr0,7Ce0,2Gd0,1O3-d (BCZG), obtained from mixtures of oxides and by the Pechini route have been studied in order to analyze the differences provided by different processes. In addition, the use of zinc oxide is evaluated as a sintering aid, promoting greater density and a larger average grain size. Another objective was to verify the performance of dopants, yttrium or gadolinium. By XRD analysis, it was found that by the Pechini route the formation of compounds occurs after calcination, however, for BCZG there is a formation in a cerium-rich phase after sintering. By mixtures of oxides, after calcination, it was found two or three phases, however, after sintering, they are only the characteristic indicators of the perovskite structure. The compounds selected by the route by Pechini, even with the addition of ZnO, and by the mixture of oxides with one calcination step, present a porosity above 20%. The compositions resulting from the route with two calcinations showed higher values densification (above 90%), in which there was a greater influence of zinc oxide for the compound BCZY, which showed an increase in grain size, as observed by SEM. With these dense samples, impedance spectroscopy measurements were performed, which showed a higher conductivity for the BCZY composition with the use of the sintering additive in a humid atmosphere.