Elaboração e caracterização de filmes finos para catodo de pilhas a combustível de óxido sólido.

Abstract

This study aimed to improve the prepare conditions of porous films of the solid oxide fuel cell cathode (SOFC), to study cathodic half cells and to study aunit cell elaborate wich a thick electrolyte (1.6 mm).In the first stage was realized a rheological study to optimize thesuspension used to deposit composite cathode films. Nine suspension were prepared (S1 to S9) with different volumetric powder fractions (F) of(La0,8Mn0,2)0.95MnO3 (LSM) / Ytria stabilized zirconia (YSZ) 50/50 in weight and different amounts of dispersant (ethylcellulose). The results showed a better performance of the suspensions S5 (F = 0095 and 4% of dispersant) and S7 (F = 0.14 and 2% of dispersant). The images obtained by scanning electronic microscopy (SEM) and optical microscopy confirmed the rheological study conclusions.The suspension S7 was used to elaborate the Célula 1 (pure LSM) and Célula 2 (functional layer addition). The two half-cells were studied byimpedance spectroscopy and power measures. The Célula 2 showed better results, even with little damage during the operation. There wasnt any improvement in performance when it used the La0,59Sr0,4CoO3 (LSC) (better ionic conductor than LSM) as the current collector layer (Célula 5) due to incompatibility with the YSZ. The results also showed that cathode prepared with LSM by citrate route (Célula 2) has better electrical performance than that made with LSM Pechini (Célula 3), despite the higher specific surface area and higher catalytic activityof the last one (catalytic tests), due to lack of composite cathode homogeneity and the LSM grain densification during Celula 3 sintering.Finally, it was studied a thick electrolyte unit cell (Célula 4) prepared withpreviously optimized cathode and anode made by LaMPaC other members. It obtained an unsatisfactory electric performance that can be justified by the electrolyte thickness (1.6 mm) and because the other components are not yet optimized.