Caracterização dos eletrocatalisadores LaMnO3, LaFeO3,LaFe0,2Mn0,8O3 E La0,5Fe0,5MnO3 preparados por autocombustão assistida por microondas para cátodos de células a combustível do tipo SOFC

摘要

Materials consisting of perovskite-type oxides (ABO3) have been developed in thiswork for applications in fuel cell cathodes of solid oxide type (SOFC). These ceramicmaterials are widely studied for this type of application because they have excellent electricalproperties, conductivity and electrocatalytic. The oxides LaMnO3, LaFeO3, LaFe0.2Mn0.8O3 eLa0.5Fe0.5MnO3 were synthesized by the method of microwave assisted combustion and aftersintering at 800°C in order to obtain the desired phases. The powders were characterized bythermogravimetry (TG), X-ray diffraction (XRD), X-ray fluorescence (XRF), scanningelectron microscopy (SEM) and voltammetric analysis (cyclic voltammetry and polarizationcurves). The results obtained by XRF technique showed that the microwave synthesis methodwas effective in obtaining doping oxides with values near stoichiometric. In general, powderswere obtained with particle size less than 0.5 μm, having a porous structure and uniformparticle size distribution. The particles showed spherical form, irregular and crowded ofvarying sizes, according to the analysis of SEM. The behavior of the oxides opposite thethermal stability was monitored by thermogravimetric curves (TG), which showed low weightloss values for all samples, especially those of manganese had its structure. By means of Xraydiffraction of the samples sintered at 800°C was possible to observe the formation ofpowders having high levels of crystallinity. Furthermore, undesirable phases such as La2O3and MnOx were not identified in the diffractograms. These phases block the transport ofoxygen ions in the electrode/electrolyte interface, affecting the electrochemical activity of thesystem. The voltammetric analysis of the electrocatalysts LF-800, LM-800, LF2M8-800 eL5F5M-800 revealed that these materials are excellent electrical conductors, because itincreased the passage of electrical current of the working electrode significantly. Bestperformance for the oxygen reduction reaction was observed with iron-rich structures,considering that the materials obtained have characteristics suitable for use in fuel cellcathodes of solid oxide type