Perovskites Used in Fuel Cells

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

Deposition of nanostructured LSM perovskite thin film on dense YSZ substrate by airbrushed solution combustion (ASC) for application in SOFC cathodes

[EN] To make SOFC high efficiency energy generation devices, thin ceramic films are proposed as their main components. The rate of the oxygen reduction reaction is relevant for the overall performance of the SOFC, hence a lot of attention is given to the cathodes and their interfaces. The airbrushed solution combustion (ASC) method was used to fabricate an LSM thin film on a dense YSZ substrate. A single phase LSM perovskite was obtained with very thin and interconnected porosity, and a small average grain size (55 nm). The nanostructured LSM thin film electrode showed a low total activation energy (1.27 eV) at high temperatures, but a high area specific resistance at 850°C (55 Ω.cm²). The activation energy for the dissociative adsorption and diffusion of oxygen was significantly low (1.27eV), while the charge transfer and oxygen ion migration activation energy at the LSM/YSZ interface (1.28 eV) was closer to those usually reported.The authors would like to thank Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNpQ) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) in Brazil and Instituto de Cerámica y Vidrio (ICV) and Consejo Superior de Investigaciones Científicas (CSIC) in Spain.Peer reviewe

Propriedades elétricas e microestruturais de varistores à base de SnO2 sinterizados por microondas

An investigation was made of the microstructural and electrical properties of SnO2-based varistors microwave sintered at 1200 ºC, applying a heating rate of 120 ºC/min and treatment times of 10, 20, 30, 40, 50 and 60 min. The system used in this study was (98.95-X) %SnO2.1.0%CoO.0.05%Cr2O3.X%Ta2O5, where X corresponds to 0.05 and 0.065 mol%. Sintering was carried out in a domestic microwave oven (2.45 GHz) fitted for lab use. Silicon carbide was placed in a refractory vessel to form a heating chamber surrounding the sample holder. The pellets were examined by scanning electron microscopy, X-ray diffractometry, direct current measurements and impedance spectroscopy. The parameters of density, medium grain size, coefficient of nonlinearity, breakdown electrical field, leakage current, and height and width of the potential barrier were analyzed.Foi feito um estudo das propriedades microestruturais e elétricas de varistores à base de SnO2, sinterizados por microondas a 1200 ºC, com uma taxa de aquecimento de 120 ºC/min e tempos de tratamento de 10, 20, 30, 40, 50 e 60 min. O sistema utilizado neste estudo foi de (98,95-X) %SnO2.1,0%CoO.0,05%Cr2O3.X%Ta2O5, onde X corresponde a 0,05 e 0,065 mol%. A sinterização foi feita em um forno de microondas doméstico (2,45 GHz), equipado para uso em laboratório. Carbeto de silício foi colocado em um recipiente refratário para formar uma câmara de aquecimento em torno do suporte da amostra. As amostras foram analisadas por microscopia eletrônica de varredura, difração de raios X, medições de corrente dc e espectroscopia de impedância. Os seguintes parâmetros foram analisados: densidade, tamanho médio de grão, coeficiente de não-linearidade, campo de rigidez dielétrica, corrente de fuga, e altura e largura da barreira de potencial

Eletrodo, eletrólito, célula a combustível óxido sólido e processo de produção de energia

Universidade Federal do Rio Grande do SulEngenhariaDepositad

Mixed electrical conduction of calcium aluminates synthesized by polymeric precursors

A study of the electrical transport properties of calcium aluminate (CA) with coexisting C3A and C12A7 phases was carried out. In this work, powders resulting from synthesis based on the polymer precursor method. The resulting product was characterized by means of XRD, Raman, and UV-visible analysis to obtain the optical BG and by EIS. From the XRD and Raman analyses, the presence and coexistence of the two self-modified phases were confirmed. In this biphasic composition, celite phase was estimated to be the major phase. An optical BG of 5.69 eV at room temperature was calculated, and under the condition of a reducing atmosphere in the temperature range of 750-950 ºC, an activation energy for conduction of 2.98 eV was determined by EIS measurements. Further, in this biphasic sample, the electronic conduction transport might be governed by the mayenite minor phase due to its large defect nature and concentration compared to celite. In oxidizing conditions, the activation energy for electrical conduction was 1.42 eV, which is somewhat higher than that observed by other authors in mayenite single phase; this result was explained by taking into account the coexistence of biphasic material and an actual chemical defect scenario in SMCM is discussed

Processo de produção de polímeros em fibras

Universidade Federal do Rio Grande do SulEngenhariaDepositad

In situ drug release measuring in α-TCP cement by electrochemical impedance spectroscopy

The use of drug delivery systems is a good technique to leave the right quantity of medicine in the patient’s body in a suitable dose, because the drug application is delivered directly to the affected region. The current techniques such as HPLC and UV–Vis for the drug delivery calculation has some disadvantages, as the accuracy and the loss of the sample after characterization. With the aim of reducing the amount of material used during the characterization and have a nondestructive test with instantaneous results, the present paper shows the possibility of using electrochemical impedance spectroscopy (EIS) to have a drug delivery measurement during the release phenomena for a calcium phosphate cement (CFC) delivery system with gentamicin sulfate (GS) and lidocaine hydrochloride (LH), at a ratio of 1% and 2%, respectively. The equivalent circuit and the chemical mechanism involved during the measurements have been proposed as a tool to determine the drug delivery profile. The method has been compared with the UV–Vis technique. XRD was realized to verify conditions, before and after release. It was possible to verify the potential for using EIS as an instant technique to quantify drug delivery

Processo de obtenção de filme cerâmico sobre substrato por combustão de solução aspergida (CSA)

Universidade Federal do Rio Grande do SulEngenhariaDepositad

Processo de obtenção de ligante "binder" baseado em poli (isopreno) utilizado na moldagem de pós por injeção (MPI) e uso

Universidade Federal do Rio Grande do SulEngenhariaDepositad