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Fuel cells are devices for energy generation with very high theoretical efficiency. Many researches were been carried out in the last few decades in order to develop reliable fuel cells. Solid oxide fuel cells SOFC and polymeric exchange membrane fuel cells PEMFC are those with more potential for commercial use. Specially for SOFC cathodes, many perovskites have been proposed as potential materials for this application. Nevertheless, other components of SOFC, such as the electrolytes, anodes and interconnects, have also been targeted with potential perovskites. More recently, the use of perovskites in PEMFC has also been proposed and studied. As many perovskite compositions can be used in SOFC components, some of the most important are discussed in this chapter and some recent works in perovskites for PEMFC are also referred. As a whole, in this chapter, the reader will find the relationship between the properties of perovskites with their compositions and the main effects of dopant agents regarding the utilization of these materials in different components of SOFC and in electrodes of PEMFC.Keywords: SOFC, IT-SOFC, PEMFC, Nonstoichiometric compounds . IntroductionFuel cells are devices that convert the chemical energy of a fuel directly into electrical energy and heat. The most common fuel is H , but other hydrocarbon compounds such as methanol, methane, natural gas, ethanol or others can also be used. A single cell is composed of three main components anode, cathode and electrolyte. For the effective use of fuel cells, single cells must be interconnected to increase the power production, which requires the use of two more components interconnects, for the serial electrical connection, and sealants, for the hermetic sealing of the set. The electrodes are permeated by the gases, fuel in the anode and oxygen air in the cathode, and they catalyse electrochemical reactions through electron capitation or © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.conduction from or to the reactive sites the electrolyte, an electrical insulator, promotes ionic conductivity. Figure shows a general schematic drawing of a fuel cell operation. The residual water if pure H is used can be produced in the anode or in the cathode and it will depend of the nature of the electrolyte. If the electrolyte is a cationic conductor, the water will form in the cathode and, conversely, if it is an anionic conductor, the water will be formed in the anode. In general, a fuel cell works similarly to a battery however, its energy is not stored in its electrodes, so there is no need for recharging because there is a continuous supply of fuel in the anode and oxidants air in the cathode. The electrical work provided by the electrochemical reactions does not consume the cell's components, which keeps o...

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The development of solid oxide fuel cell has shown that the thin film concept for the electrode supported designs, based on the yttria-stabilized zirconia, is more promising than the research of new electrolyte materials. In this work, the spray pyrolysis process was investigated in order to obtain dense thin films of YSZ on porous ceramic substrates. High porosity LSM, a typical material of SOFC cathodes, was used as substrate. The precursor solution was obtained by zirconium and yttrium salts dissolved in a mixture of ethanol and propylene glycol, with volume ratio 1:1. The substrate was heated and maintained at a constant temperature (280°C, 340°C or 560°C). The as-obtained films were heat treated in a temperature of 700°C, aiming to obtain yttria-stabilized-zirconia films from the amorphous film. The morphology and microstructure of the films were characterized by scanning electron microscopy and X-ray diffraction.

For the combustion synthesis of strontium doped lanthanum manganite (LSM), different fuels can be used influencing the phase formation and also the powder morphology. Both are important features that can improve the material performance when used in a solid oxide fuel cell cathode. Urea and sucrose are fuels used to synthesize distinct LSM powders, thus the purpose of this work was to mix these fuels in order to obtain nanocrystalline LSM powders with a differentiated morphology, more convenient for the desired application. After calcination at 750°C for 3 hours the powder generated a pure phase LSM X-ray diffraction pattern and the micrographs taken in the transmission and scanning electron microscopes revealed a very peculiar morphology with specific surface area (BET) of 13 m²/g. Calcination led to a single phase and more crystalline material but showed no influence in the powder morphology.

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Previous studies showed the formation of new phases affecting the electrical properties of LSC thin films deposited on stainless steel substrates, which are commonly tested for ITSOFC and SOEC interconnects. A 4.3 μm thick La 0.6 Sr 0.4 CoO 3 coating was deposited on AISI430 steel by spray pyrolysis, followed by heat treatment (800°C/2h) and an oxidation in air (800°C/96h). The La 0.6 Sr 0.4 CoO 3 phase interacted with the metallic substrate and formed SrCrO 4 , causing degradation of the perovskite into La 0.9 Sr 0.1 CoO 3 . An EDS mapping showed Sr and Cr enrichment in the coating/substrate interface. TG analysis indicated a lower mass gain for the coated substrate. The total ASR at 800°C of the interconnect before and after oxidation was 3.23 Ω.cm 2 and 3.98 Ω.cm 2 , respectively. The Ea underwent very small variation, remaining around 0.24 eV (T≤300°C) and 0.65 eV (T≥400°C). The reaction of Cr from the substrate and Sr from LSC seems to have impaired the performance of the interconnect.

t is well known that nanostructured materials have relevant influences in properties behavior that can be achieved when compared with conventional materials. In this study is proposed an investigation of the electrical and microstructural properties of zinc oxide based varistors prepared with nanostructured zinc oxide powder obtained by a thermal evaporation process. Zinc oxide powder morphology was investigated by scanning and transmission electron microscopy (SEM and TEM, respectively) and the specific surface area evaluated by adsorption of N2. The varistors were prepared by the mixture of typical dopants with zinc oxide powders in a ball mill. The surface area of zinc oxide powder used was 17.4 m2/g with tetra-needle like morphology. After powder mixture process it was observed by TEM micrographs that most of the tetrapod shaped zinc oxide broke into needles well mixed with dopant particles. The compressed powders were sintering at 1050, 1150 and 1250°C for 1.5 h and densification over 94% were achieved in all tested temperatures. Preliminary electrical characterization reveals that nanostructured zinc oxide compositions have interesting varistor properties.