Síntese química de materiais a base de zirconato de cálcio para células a combustível de óxido sólido (SOFC)

Abstract

The fuel cells allow electrical energy production from an environmentally clean electrochemical reaction. Among several tipes the solid oxide fuel cell (SOFC) operates at high temperatures, allowing the conversion of a hydrogen-based fuel into electricity, in which water is generated as a by-product. The main element from the SOFC is a unitary cell formed by the union of three components being them the anode, the cathode and the electrolyte. In this thesis, composite ceramic materials CaZrO 3 -La 0;6 Sr0;4MnO3 , CaZrO3-NiO and CaZrO 3 were synthesized by combustion, for application as cathode, anode and electrolyte, respectively. The ceramic material CaZrO 3 is a ionic and protonic conductor and high temperature resistant. The combustion synthesis method was chosen due to its capability to generate materials with different porosities and densities obtained by the very characteristics of the combustion reaction. In order to obtain a suitable pellet, it is necessary to sinter layers with appropriate mechanical, thermal and textural characteristics and with adjustment of the thermal expansion coefficients, requiring an excellent joint between them. The composite ceramic materials formed were characterized by Scanning Electron Microscopy (SEM), Dilatometry, Thermogravimetry, X-Ray Diffraction (XRD) and Impedance Spectroscopy (EIS). Its characterization had the objective of obtaining the main components for the formation of a SOFC cell through the combustion method. The results demonstrated that the materials synthesized by the combustion method have the potential to be used in a SOFC cell. The CaZrO3 was used in the three monocelle components for better compatibility in terms of thermal expansion between the joints. At 800°C it was confirmed that CaZrO 3 was formed on the electrolyte, anode and cathode. The mass loss and the retraction were close, and the cathode and the anode presented a considerable porosity, as analyzed by SEM. In the EIS the analyzes showed a low activation energy and the materials were compatible, a fact that is essential for the construction of a suitable SOFC cell. The mobile species in each phase of the three components showed oxygen vacancies, electrons conduction in the NiO composite and electronic holes in the cathode.