Desenvolvimento de eletrocatalisador de PdCu/C para uso em ânodos de célula a combustível de hidrazina

Trabalho de conclusão de curso (graduação)—Universidade de Brasília, [Instituto de Química], 2017.O estudo de celulas a combustivel surgiu com a necessidade de novos recursos de energia e de tecnologias tendo em vista a atual escassez dos recursos energeticos. Uma celula a combustivel e basicamente um dispositivo de conversao de energia quimica em energia eletrica de forma direta, tendo uma vasta aplicacao. As celulas que utilizam PEMFC – Próton Exchange Membrane Fuel Cell, sao as que apresentam maior densidade de potencia e tambem fazem parte da classe das celulas que tem uma baixa faixa de temperatura para sua operacao. Uma celula a combustivel geralmente utiliza como combustivel o hidrogenio. A hidrazina e um liquido combustivel que ja vem sendo estudado em celulas a combustivel de baixas temperaturas como alternativa ao uso do hidrogenio, possuindo varios pontos positivos a seu favor: i) em sua eletro-oxidacao nao ha producao de CO2, e ii) nao ter producao de espécies que envenenam os eletro-catalisadores atraves de uma forte adsorcao superficial. Devido a baixa faixa de temperatura de operacao, e necessario o uso de eletrocatalisadores, podendo ser formados por Au, Pt, Pd Ag e tendo como base o Cu. Foram sintetizados catalisadores com tres tipos diferentes de proporcao metalica Pd/Cu, sendo todos com uma porcentagem de metal de 20% e 80% carbono. Depois de prontos, foram feitas as caracterizacoes por DRX e avaliacao da composicao. A seguinte etapa foi executada mediante a montagem de um esquema de celula a combustivel. Apos a montagem foi testado o desempenho da celula com ajuda de um potenciostato/galvanostato disponivel na Central Analitica do Instituto de Quimica, e um sistema experimental desenvolvido no Laboratorio de Desenvolvimento de Processos Quimicos. O objetivo geral do presente trabalho e executar o projeto de uma celula combustivel e testar seu desempenho com os catalisadores de paladio (Pd), em variadas proporcoes da liga metalica com cobre (Cu) sintetizados para o estudo. Em virtude disso tendo como resultados mais significativos, temos em destaque a sintese dos eletrocatalisadores, sua caracterização fisico-quimica, e a demonstracao da proporcao Pd/Cu mais adequada para o Maximo desempenho da celula.The study of fuel cells came up with a need for new energy sources and technologies in view of the current scarcity of energy resources. A fuel cell is basically a device of conversion of chemical energy into electricity directly, having a wide application. Fuel cells that use PEMFC - Proton Exchange Membrane Fuel Cell, have a higher power density and are also part of the class of cells that have a low temperature range for their operation. A fuel cell usually uses hydrogen as fuel. Hydrazine is a liquid fuel that is under study in cells with low temperature as an alternative to the utilization of hydrogen, having several positive points to its advantage: i) in its electro-oxidation, there is no CO2 production, and ii) no production of species that poison the electro-catalysts through a strong surface adsorption. Due to the low operating temperature range, it is necessary to use electrocatalysts. These catalysts can be formed by Au, Pt, Pd Ag all based on Cu. Catalysts with three different proportions of the Pd/Cu metal were synthesized, all with a metallic percentage of 20% and 80% of carbon. Once prepared, some characterizations were made by XRD and EDX. The next step was the setup of a fuel cell scheme. The cell performance was tested with aid of a potentiostat/galvanostat available at the Analytical Center of the Institute of Chemistry (CAIQ-UnB), and an experimental system developed at the Laboratory of Chemical Process Development. The general goal of the present project is to perform the design of a fuel cell and test its performance with the palladium (Pd) catalysts, in various proportions with copper (Cu). Due to this, the most significant results are the synthesis of the electrocatalysts, their physico-chemical characterization and the analysis of the most adequate Pd/Cu ratio in order to maximize the electrochemical performance

Fatty Acid Content, Oxidation Markers and Mercury in Fish Oil Supplements Commercialized in Brasília, Brazil

Fish oil supplements are good sources of eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids, which are important in the prevention and treatment of hypertriglyceridemia. The purpose of this study was to examine the content of EPA and DHA, oxidation markers and mercury of fish oil supplements marketed in Brasilia, Brazil. Fatty acid contents were determined by gas chromatography using internal (C23:0) and external methyl ester standards. For this analysis, samples were prepared by alkali-catalyzed methylation with boron trifluoride (14% in methanol). Mercury was determined by direct vapor detection method. Oxidation markers were evaluated by measuring peroxide value (PV), anisidine value (AV) and by calculating TOTOX. The adequacy of EPA and DHA ranged from 75.9 to 105.1% and from 88.9 to 137.4%, respectively, compared to the information in the label. Mercury concentration was above limit of quantification levels, between 11 and 15 mg/kg in 14.4% of the products. Twenty percent of the products exceeded recommended levels of PV and TOTOX. Despite the high percentage of adequacy of the parameters analyzed, about 2/3 of the products showed some inadequacies according to the law. These data deserve concern due to the potential side effects of oxidized and contaminated fish oils to their proclaimed health benefits. This survey shows the relevance of constant monitoring of fish oil quality, considering current legislation and scientific advance. DOI: http://dx.doi.org/10.17807/orbital.v11i3.1390<br /

Promoting Effect of Cu on Pd Applied to the Hydrazine Electro-Oxidation and Direct Hydrazine Fuel Cells

Use of liquid fuels in fuel cells is advantageous due to the easier and safer handling, transportation, and storage. Among the different options, hydrazine is of interest since the formation of highly poisoning carbonaceous species is avoided, in addition to its high energy density. In the search for more active direct hydrazine fuel cells (DHFC), this study analyzes the influence of Cu as an auxiliary metal on Pd. Three different PdxCu/C (x = 3, 1, and 0.33) catalysts were prepared by chemical reduction with NaBH4. The materials were physiochemically characterized by X-ray diffraction, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Electrochemical analysis in a three-electrode glass cell and a single-cell DHFC was also carried out to study the impact on the electroactivity. Cu exerts a beneficial effect by reducing the adsorption energies of the adsorbed species and donating oxidized species for the completion of the hydrazine electro-oxidation, optimally balanced in the Pd1Cu/C (maximum power density of 180 mW cm&minus;2). As a counterpoint, Cu slightly promotes the non-faradaic decomposition of hydrazine, seen by a larger H2 signal in mass spectroscopy in the anode exhaust at high current densities, which results in a slight loss in faradaic efficiency

Promoting Effect of Cu on Pd Applied to the Hydrazine Electro-Oxidation and Direct Hydrazine Fuel Cells

Use of liquid fuels in fuel cells is advantageous due to the easier and safer handling, transportation, and storage. Among the different options, hydrazine is of interest since the formation of highly poisoning carbonaceous species is avoided, in addition to its high energy density. In the search for more active direct hydrazine fuel cells (DHFC), this study analyzes the influence of Cu as an auxiliary metal on Pd. Three different PdxCu/C (x = 3, 1, and 0.33) catalysts were prepared by chemical reduction with NaBH4. The materials were physiochemically characterized by X-ray diffraction, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Electrochemical analysis in a three-electrode glass cell and a single-cell DHFC was also carried out to study the impact on the electroactivity. Cu exerts a beneficial effect by reducing the adsorption energies of the adsorbed species and donating oxidized species for the completion of the hydrazine electro-oxidation, optimally balanced in the Pd1Cu/C (maximum power density of 180 mW cm−2). As a counterpoint, Cu slightly promotes the non-faradaic decomposition of hydrazine, seen by a larger H2 signal in mass spectroscopy in the anode exhaust at high current densities, which results in a slight loss in faradaic efficiency