Márcia Caldeira Brant

Montagem e caracterização elétrica de pilhas a combustível de óxido sólido (PaCOS)

This paper is focused on a review of the design features and the electrochemistry characterization of anode-supported planar SOFC. Studies and results of metallic alloy interconnectors and recovery for protection against corrosion and for contact layer are showed. Moreover a discussion of examples of measurements of impedance spectrometry, according to the literature and our experimental results are made. For the anode supported fuel cells the power density varies from 0.1 to 0.5 Wcm2, according to results in the literature (showed in this paper). For electrolyte supported fuel cell the power density can be 10 Wcm-2 for high temperatures. An English-Portuguese glossary of most used terms in SOFC stack is given for greater clarity and to introduce new terms to the reader.

Modelagem tridimensional de pilhas a combustível de óxido sólido

The computational modeling contribute for design, dimensioning and also for performance evaluation of Solid Oxide Fuel Cells. Nevertheless, the modeling is complex due to of large quantity of physics phenomena involved. In addition of physics phenomena, the present dimensions raise difficulties to validate the results. In this work, the interconnect channels adjacent to an anode have modeled aiming evaluate the flowing in this system. The validation of procedures and considerations has done by indirect mode. The flowing at interconnect has been evaluate through the Navier-Stokes equations and at anode it has been used the Darcys Law. The technique of finite volume has used to solving of equations. It has been used typical values of permeability, while viscosity and density have been numerically determined, considering a mixture of hydrogen and water. It has been considered steady state and isotropy in relation of all physical properties determined at different temperatures. It have been analyzed the influences at the flowing by ratio between the porosity of anode and viscosity of mixture H2O and H2O; density and temperature. A study of how the mesh affects the results also has been done. It has been possible the see that, when the mixtures of hydrogen/water enters at porous media, the flowing suffer a reduction of velocity in relation of medium value applied at entering. The pressure, in this situation, does not show significant reduction.

Propriedades reológicas e microestruturais de eletrólito de ZrO2/Y2O3

To reduce the operating temperature of solid oxide fuel cells, structures with thin films electrolytes, deposited by spray coating on porous anode were developed. The slurries used for the fabrication of the films were prepared using appropriates suspensions with ytria-stabilized zirconia (YSZ) powers, solvents, dispersants, binders and plasticizers appropriates. In this work the study of the influence of the binders in the stability of the suspensions and the microstructures properties of the YSZ films were done. Three slurries were made with different composition of binders (0.5; 1.0 and 2.0 % in weight). All of them showed pseudo-plastics and thixotropics flow behavior, according to viscosities measurements and shear rate. The films were sintered to 1500 oC /6 hours. The images of scanning electron micrographs (SEM) were treated by Quantikov program to determine the porosity of the film and average grain size of YSZ. The films showed adequate porosity for being used as SOFC electrolyte (between 0.2 and 0.4%) and average grain size between 2.0 and 6.0 µ m. The spray coating is a suitable technique to fabricate the YSZ electrolytes for SOFC.

Estudo da contiguidade das fases do cermet Ni/ZEI

The electrochemical activity of the metallic-ceramic composite (Cermet) Ni/Zr0,85Y0,15O0,93 (Ni/YSZ) used as anode in stacks of solid oxide fuel cell (SOFC) is controlled by the intrinsic conductivity of its phases, by the available paths for the electric conduction and the diffusion of the fuel gas. These properties are highly influenced by microstructural parameters such as space distribution of the phases, forms and average size of the particles that constitute the Cermet. In this work, some microstructural parameters of anode phases: Ni, YSZ and pores are determined in tablets of the Cermet Ni/YSZ through the treatment of images acquired with optic microscopy. Relating these parameters with the Quantitative Stereological Theory it was possible to calculate the proximity of the phases. The anodes were prepared from mixtures of NiO powder and YSZ powder at mass ratios of NiO/YSZ: 33/67, 56/44, 75/25 and 82/18 and uniaxial pressed into cylindrical pellets. After sintering, the tablets were reduced to Ni/YSZ in hydrogen atmosphere at 900oC for 2 hours. The transversal surface of each sample was treated and observed with optical microscopy. The images were analyzed with the software Quantikov to determine the microstructural parameters: intercept linear medium and volumetric fraction of the phases. Using these parameters, the contiguity of each phase present in the Cermet was calculated. To prove the validity of the technique, the values of the microstructural parameters based on the composition of the powders were compared to the values based on the image treatment.

NiO/YSZ Composites for SOFC: Synthesis and Characterization

Solid oxide fuel cell (SOFC) works at high temperature and is normally used in stationary devices which are of wide interest in the world market. The most currently SOFC developers utilize yttria-stabilized zirconia (YSZ) as electrolyte, strontium-doped lanthanum manganite (LSM) as cathode and a Ni/YSZ cermet obtained from NiO/YSZ in situ reduction as anode. The electrode performance is directly influenced by powder grain sizes, homogeneity, purity, and amount of Ni. Although physical mixture is a simpler procedure it hardly gives homogeneous materials as suitable to SOFC applications. Alternative chemical methods are sol-gel, impregnation and those derived from Pechini route. The present work compares thermal stability and hydrogen reducibility of NiO/YSZ composites prepared by impregnation (I), Pechini (P) and physical mixture (PM) procedures.Copyright