Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / by Catherine E. Teague. / M.S.

It has become a case of great desire and, in some instances, a requirement to have systems in engineering be energy efficient, in addition to being effectively powerful. It is rare that there is a single technique that has the range to make this possible in a wide collection of areas in the field. The work done in this thesis exhibits how Pulse Width Modulation (PWM) bridges LEDs, plug in vehicles, fuel cells and batteries, all seemingly different sub categories of electrical engineering. It stems from an undergraduate directed independent study supervised by Dr. Zilouchian that encircled LEDs and electric vehicles and how they contribute to a smart electric grid. This thesis covers the design and development of a prototype board that test how PWM saves energy, prolongs lifespan and provides a host of customizable features in manufactured LED lights that are used in the marine industry. Additionally, the concept of charging batteries that provide power to electric vehicles was explored. It is stressed that consumers who are interested in electric vehicles are concerned about refueling and recharge times. It is natural that a competing product, such as the electric vehicle in a world dominated by internal combustion engines, will perform on par if not better than existing choices. Tests are conducted to investigate the methods of fast battery charging and the challenges this technique creates. Attention is also given to the development of a pulsed Proton Exchange Membrane (PEM) fuel cell, specifically to prove whether pulse modulation is more efficient in a hydrogen producing fuel cell as opposed to direct-driven voltage and current alternatives. / by Wayne W. Watt. / Thesis (M.S.C.S.)--Florida Atlantic University, 2011. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 200?. Mode of access: World Wide Web.

Orientador: José Luz Silveira. / Coorientador: Celso Eduardo Tuna / Banca: José Alexandre Matelli / Banca: Lúcia Bollini Braga Maciel / Resumo: A busca por fontes alternativas de geração de energia, menos agressivas ao meio ambiente e a base de combustíveis renováveis tem despertado grande interesse na comunidade científica. A utilização de células a combustível têm então ganhado espaço. A célula a combustível de óxido sólido SOFC destaca-se principalmente para fins estacionários, pois apresenta uma alta eficiência elétrica, por possibilitar o aproveitamento do calor liberado durante seu funcionamento e também pela capacidade de utilizar uma vasta gama de combustíveis. A produção do biogás através de resíduos para a geração de energia está consolidada em muitos países do mundo e inúmeros são os ganhos ecológicos da utilização deste. Nesta dissertação foi analisada a associação de célula a combustível de óxido sólido com um reformador a vapor de biogás. Através da reforma um gás de síntese (rico em hidrogênio) é obtido e encaminhado para a célula a combustível; uma câmara de combustão permite queimar o hidrogênio que não reagiu na célula e um recuperador de ar recicla parte do ar que não foi consumido na célula. Trocadores de calor também são utilizados para reaproveitar a energia contida nos gases de exaustão no processo e para a produção simultânea de água quente. A fim de avaliar a atratividade deste sistema foram realizadas análises de desempenho segundo as Leis da Termodinâmica, seguida de estudo econômico, baseada nas correntes de energia do sistema de cogeração. Em etapa final foi realizada a quantificação das emissões de poluentes do sistema, buscando a determinação do dióxido de carbono equivalente, do indicador de poluição e da eficiência ecológica do processo. Conclui-se que o sistema de cogeração proposto é uma opção interessante para geração de energia, apresentando bom desempenho energético e ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The search for alternative sources of power generation, less harmful to the environment using renewable fuels has aroused great interest in the scientific community. The use of fuel cells has gained ground then. The Solid Oxide Fuel Cell (SOFC) stands out especially for stationary purposes; it presents a high electrical efficiency by enabling use of the heat released during operation and also by the capacity to use a wide range of fuels. The production of biogas through waste to power generation is established in many countries of the world and there are many ecological gains in this use. This dissertation analyzed the association between a solid oxide fuel cell with a biogas steam reformer. By reforming a synthesis gas (hydrogen-rich) is obtained and sent to the fuel cell; a combustion chamber allows to burn hydrogen unreacted in the cell and an air recuperator recycles part of the air that has not been consumed in the cell. Heat exchangers are also used for recovering the energy contained in the exhaust gases in the process and the simultaneous production of hot water. In order to evaluate the attractiveness of this system performance analyzes were conducted according to the Laws of Thermodynamics, then a economic study was performed based on energy currents of the cogeneration system. In the final step, the quantification of system pollutant emissions is made, seeking the determination of carbon dioxide equivalent, pollution indicator and ecological efficiency. It is concluded that the proposed cogeneration system is an interesting option for energy production, with good energy and exergetic performance. Regarding economic aspects, the payback period was considered high, since it is a residential system; this scenario should change, the trend that the compact SOFC reach a lower value with the spread of its use, by increasing the production volume of these. ... (Complete abstract click electronic access below) / Mestre

Made available in DSpace on 2015-04-22T22:02:02Z (GMT). No. of bitstreams: 1 DISSERTACAO-CLEUTON DE SOUZA SILVA.pdf: 1557616 bytes, checksum: c0477dc397214e5783a5d2ca234ee08a (MD5) Previous issue date: 2009-01-14 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This work presents a theoretical study and modeling of the metal-porphyrins monomers and the search of the porphyrin-metal complexes that can act as a potential catalyst to make the cleavage of the O2 bond for use in fuel cell. All calculations were made by the Gaussian package on the Windows OS, using the DFT, by the B3LYP functional, and the 6-31G and LANL2DZ basis set. The studied porphyrin-metal complexes were those formed by the porphyrin ring and the Si, Ni, Ge, Co, Fe, Mo and Sn metals in the different oxidation states. The obtained theoretical model was satisfactory for the description of role played by the metal-porphyrins complexes in the catalysis of the O2 molecule. In the obtained model, the porphyrin-metal- complexes showed the capability of aggregate the O2 molecules and weaken the strength of this chemical bond facilitating the final reduction process in the catalyst. In general, although not acting as a catalyst in the oxygen reduction reaction (o.r.r.), can be observed the importance of the porphyrin ring to a possible use in PEM fuel cell, that is, facilitating the catalysis process in the latter step of the reaction process. / Este trabalho apresenta uma modelagem teórica de monômeros de metaloporfirinas e a busca de metais para o núcleo porfirínico que apresentem o melhor potencial como catalisadores para a quebra da ligação O-O para aplicação em células a combustível. Os cálculos foram realizados em plataforma de Windows, através do pacote GaussianTM 2003, utilizando abordagem da Teoria do Funcional de Densidade (DFT) e o uso do funcional b3lyp com bases de 3-21G, 6-31G e lanl2dz. As porfirinas estudas foram Si+4-porfirina, Si+2-porfirina, Ni+2-porfirina, Ge+2-porfirina, Co+2-porfirina, Co+3-porfirina, Fe+2-porfirina, Mo+6-porfirina e Sn+2-porfirina. O modelo químico-quântico adotado mostrou-se satisfatório para descrição da atuação das metaloporfirinas na catálise do O2, mostrando que as metaloporfirinas podem auxiliar no processo eletroquímico, uma vez que os resultados mostram que todas podem ser capazes de agregar as moléculas de O2, enfraquecendo a ligação O-O para posterior redução num catalisador. No geral, embora não atuando como catalisador da r.r.o., pôde-se observar a importância do macrociclo porfirínico para uma possível atuação em células a combustível do tipo PEM, ou seja, facilitando a catálise numa etapa posterior do processo reacional.

Made available in DSpace on 2015-04-22T22:02:06Z (GMT). No. of bitstreams: 1 DISSERTACAO VERA LUCIA.pdf: 1075794 bytes, checksum: 33b5d3d47e6787d71b4d7ed96ae837be (MD5) Previous issue date: 2010-04-23 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The direct methanol fuel cells are powers alternatives of energy to do support mainly the batteries. The scientific society come in last decades realizing experiments to overcome the technical barriers that block her commercialization. The effect of methanol crossover, from the anode to the cathode through the membrane, is a very serious problem that that severely reduces the cell voltage, current density, fuel utilization and hence the cell performance. The aim this work is better understand the effect of methanol crossover in this type of technology e try to minimize his negative effects improving the efficiency of fuel cell. To this were prepared electrocatalyts of Pt with an second metal so much in anode as us in cathode using three differents methods: alcohol reduction (MRA), ethylene glycol (MRE) and formic acid (MAF) as reducing agents. The electrodes were prepared following technical of the literature, membrane and electrode assemblies were prepared by pressing an anode and a cathode (Pt onto each side of a Nafion 117 membrane at a pressure of 500 kg cm−2 at 125 ◦C for 180 s. The physical characterization of the electrocatalysts was gone by energy dispersive analysis by X-rays and powder X-ray diffractometer pattern. The effect of methanol crossover was investigate through of electrochemical tests realized in unit cell with PtMo/C and PtRu/C, anode, PtCo/C and PtNi/C, cathode, electrocatalysts. The results showed that alcohol reduction method is better to prepared PtMo/C electrocatalyst, however, its catalytic activity is very lower for methanol oxidation that PtRu/C providing high rate of methanol crossover and reduces cell performance. The results found to the PtCo/C e PtNi/C electrocalysts prepared in this laboratory are approximate the commercials and showed efficient to oxygen reduction reaction and tolerant for methanol oxidation. Thus, we can to affirm that the minimize of effect of methanol crossover lead the increase in cell. / As células a combustível de metanol direto são fontes alternativas de energia para dar suporte principalmente às baterias. A sociedade científica vem nas últimas décadas realizando experimentos para superação das barreiras técnicas que impedem sua comercialização. O efeito crossover de metanol, do anodo para o cátodo através da membrana, é um problema muito sério que reduz severamente o potencial da célula, a densidade de corrente, a utilização de combustível e, portanto o desempenho da célula. O objetivo deste trabalho é compreender melhor o efeito crossover de metanol neste tipo de tecnologia e tentar minimizar os efeitos negativos melhorando a eficiência da célula a combustível. Para isso foram preparados eletrocatalisadores de Pt com a impregnação de um segundo metal tanto para o ânodo como para o cátodo usando três diferentes métodos: redução por álcool (MRA), etilenoglicol (MRE) e ácido fórmico (MAF) como agentes redutores. A fabricação dos eletrodos seguiu a técnica de pintura e o eletrólito empregado foi a membrana de Nafion 117. Para a caracterização física dos eletrocatalisadores modificados, amostras foram submetidos às técnicas de energia dispersiva de raio-x e difração de raios-X. O grau de crossover de metanol através da membrana foi investigado durante os testes eletroquímicos dos eletrodos modificados de PtMo/C, ânodo, e PtCo/C e PtNi/C, cátodo, por meio de curvas de polarização realizados na célula unitária. Os resultados mostraram que o método de redução por álcool é o melhor para impregnação da platina, porém a liga formada por este metal possui atividade catalítica ineficiente para oxidação do metanol o que conduz a elevado efeito crossover de metanol e consequentemente desempenho eletroquímico reduzido. Os eletrodos de PtCo/C e PtNi/C modificados tiveram resultados aproximados aos comerciais e mostram-se eficientes para redução do oxigênio e tolerantes a oxidação de metanol. Assim, podemos afirmar que minimizando os efeitos do crossover de metanol sob o desempenho eletroquímico podemos obter células de metanol direto eficientes e capazes de dar suporte às baterias .

Submitted by Rosivalda Pereira (mrs.pereira@ufma.br) on 2017-06-02T18:25:24Z No. of bitstreams: 1 UlissesRego.pdf: 1474234 bytes, checksum: a8cb075e16a2eff24833d0907c52e571 (MD5) / Made available in DSpace on 2017-06-02T18:25:24Z (GMT). No. of bitstreams: 1 UlissesRego.pdf: 1474234 bytes, checksum: a8cb075e16a2eff24833d0907c52e571 (MD5) Previous issue date: 2011-01-25 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPQ) / This work consisted in the preparation and study of catalytic activity for reduction of molecular oxygen (ROM) based on head-treated coordination compounds with nitrogenated ligands, impregnated on carbon nanosupports (nanotube - NTC, and nanoparticles - Vulcan). The following ions complexes [Fe(bipy)3]2+ and [Fe(TPTZ)2]2+ (2,2 '-bipyridine and 2 ,4,6-tris (2-pyridyl) -1,3,5-triazine) were synthesized and characterized in solution (electron spectroscopy in the region UV-vis, cyclic voltammetry). The following materials were prepared C1: Fe(10%)-Bipy/NTC; C2: Fe(5%) -Bipy/NTC; C3: Fe(5%)-Bipy/Vulcan and C4: Fe(5%)-TPTZ/Vulcan. The comparison between C1 and C2, and between C2 and C3 materials, showed, respectively, the effect of metal loading and the nature of the carbon support on their catalytic efficiency. The comparison among all and C4 (already reported in the literature) allowed the verification of experimental methodology employed. The effect of temperature on the electrocatalytic performance was observed for C1. The following pyrolysis temperatures were used: 600-1000 oC. The results showed that metal loading and the nature of the support influence the catalytic ability of the materials. The best pyrolysis temperature observed to generate active sites in C1 for the ROM was at 800 oC. All materials were treated at this temperature, and the efficiency order observed was: C4 (Fe (5%) -TPTZ/Vulcan) >> C1 (Fe(10%)-Bipy/NTC) > C2 (Fe(5%)-Bipy/NTC) > C3 (Fe (5%) -Bipy/Vulcan). For not heat treated materials, the activity order observed was: C3 (Fe(5%)-Bipy/Vulcan) C4 (Fe (5%)-TPTZ/Vulcan) > C1 (Fe (10%)-bipy/NTC) > C2 (Fe (5%) -Bipy/NTC). C2 and C3 catalysts showed a tendency to reduce the molecular oxygen according to 2e- mechanism, while C1 and C4 materials by 4e- mechanism. For some reason, the TPTZ ligand favored the generation of catalytic sites more efficient than Bipy in these materials. / Este trabalho consistiu na preparação e estudos de atividade de catalisadores para redução do oxigênio molecular (ROM) à base de compostos de coordenação com ligantes nitrogenados, impregnados em nanosuportes de carbono e tratados termicamente (nanotubos – NTC; e nanopartículas – Vulcan). Os íons complexos sintetizados e caracterizados em solução por espectrofotometria eletrônica na região Uv-vis, voltametria cíclica, foram: [Fe(Bipy)3]2+ e [Fe(TPTZ)2]2+ (2,2’-bipiridina e 2,4,6-tris(2-piridil)-1,3,5-triazina). Os seguintes materiais foram preparados C1: Fe(10%)-Bipy/NTC; C2: Fe(5%)-Bipy/NTC; C3: Fe(5%)-Bipy/Vulcan e C4: Fe(5%)-TPTZ/Vulcan. A comparação entre os materiais C1 e C2, e entre C2 e C3 permitiu verificar, respectivamente, o efeito da carga do metal e da natureza do suporte de carbono na eficiência catalítica dos materiais. A comparação de todos com o C4 (já relatado na literatura) permitiu a verificação da metodologia experimental empregada. O efeito da temperatura na eficiência eletrocatalítica foi verificado para o C1, empregando-se as temperaturas de pirólise de 600 – 1000 oC. Os resultados mostraram que o suporte e a concentração do metal influenciam na capacidade catalítica dos materiais. A melhor temperatura de pirólise do C1 para a geração de sítios ativos para a ROM foi 800 oC. Os demais materiais foram tratados a esta temperatura, e a ordem de eficiência observada foi: C4 (Fe(5%)-TPTZ/Vulcan) >> C1 (Fe(10%)-Bipy/NTC) > C2 (Fe(5%)-Bipy/NTC) > C3 (Fe(5%)-Bipy/Vulcan). Para os materiais não tratados termicamente, a ordem de atividade observada foi: C3 (Fe(5%)-Bipy/Vulcan) C4 (Fe(5%)-TPTZ/Vulcan) > C1 (Fe(10%)- Bipy/NTC) > C2 (Fe(5%)-Bipy/NTC). Os catalisadores C2 e C3 apresentaram uma tendência em reduzir o oxigênio via um mecanismo de 2e-, enquanto os materiais C1 e C4 por mecanismo de 4e-. O ligante TPTZ, de algum modo, favoreceu mais a geração de sítios catalíticos eficientes nestes materiais que a Bipy.

Magister Scientiae - MSc / Fuel cells convert chemical energy from a fuel into electricity through chemical reaction with oxygen. This possesses some challenges like slow oxygen reduction reaction (ORR), overpotential, and methanol fuel cross over in a direct methanol fuel cell (DMFC). These challenges cause inefficiency and use of higher amounts of the expensive platinum catalyst.Several binary catalysts with better ORR activity have been reported. In this study we investigate the best catalyst with better ORR and MOR performances and lower over-potentials for PEMFC and DMFC applications by comparing the in-house catalysts (10%Pt/C, 20%Pt/C,30%Pt15%Ru/C, 40%Pt20%Ru/C, 30%PtCo/C, 20%Pt20%Cu/C and 20%PtSn/C) with the commercial platinum based catalysts (10%Pt/C, 20%Pt/C, 20%Pt10%Ru/C, 20%PtCo/C,20%PtCu/C and 20%PtSn/C) using the cyclic voltammetry and the rotating disk electrode to determine their oxygen reduction reaction and methanol tolerance. HRTEM and XRD techniques were used to determine their particle size, arrangement and the atomic composition. It was observed that the 20%Pt/C in-house catalyst gave the best ORR activity and higher methanol oxidation current peaks compared to others catalysts followed by 20%Pt10%Ru/C commercial catalyst. The 20%PtCo/C commercial, 30%PtCo/C in-house and 20%PtSn/C in-house catalysts were found to be the most methanol tolerant catalysts making them the best catalysts for ORR in DMFC. It was observed that the ORR activity of 20%PtCo/C commercial and 30%PtCo/C inhouse catalysts were enhanced when heat treated at 350 0C. From XRD and HRTEM studies, the particle sizes were between 2.72nm to 5.02nm with little agglomeration but after the heat treatment, the particles were nicely dispersed on the carbon support.

>Magister Scientiae - MSc / The purpose of this study was to develop a high performance-lower cost catalyst to be applied in Direct Methanol Fuel Cells (DMFC). The study also aimed to prepare plurimetallic supported platinum (Pt), platinum-ruthenium (PtRu), platinum-ruthenium-vanadium (PtRuV) and platinum ruthenium-vanadium-iron (PtRuVFe) upon multi-walled carbon nanotube (MWCNT) as well as upon multiwalled carbon nanotube-titanium oxide (MWCNT/TiO2) supports. Platinum is very active but prone to poisoning by carbon monoxide (CO), which may be present in the fuel used in fuel cells. The focus on the use of methanol was because of its better reaction kinetics, and better performance in direct methanol fuel cells (DMFC) better than proton exchange membrane fuel cell (PEMFC). When Pt is alloyed with another platinum group metals (PGM) the alloying decreases the over-potential for reactions critical in the fuel cells. Proton exchange membrane fuel cell (PEMFC) performance may be improved at low metal loading, when supported pluri-metallic catalysts are applied since the trimetallic catalysts may promote high catalyst utilisation. In practice, DMFC require electrodes with a Pt loading to achieve acceptance fuel cell (FC) power performance. The aim of this study was therefore the reduction of the catalyst loading through further improvement of mass activity of Pt based catalysts by partial substitution of the noble metal/metals, and the use of a carbon support that will provide high surface area, good electrical conductivity and high stability. MWCNT supported pluri-metallic (PtRuVFe,) and bimetallic (PtRu) nanoparticles possessed characteristic of increased surface area, improved electron transfer rate, enhance electro-catalytic activity and promoted stability.

Chiu, Ka Lok = 多孔生物遺態氧化銅/氧化鈰/氧化鋁之複合物料的製作及其定性分析 / 趙家樂. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references. / Abstract also in Chinese. / Chiu, Ka Lok = Duo kong sheng wu yi tai yang hua tong/yang hua shi/yang hua lu zhi fu he wu liao de zhi zuo ji qi ding xing fen xi / Zhao Jiale. / Abstract --- p.i / 摘要 --- p.iii / Acknowledgment --- p.v / Table of contents --- p.vi / List of table captions --- p.x / List of figure captions --- p.xi / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Carbon monoxide (CO) --- p.1 / Chapter 1.2 --- Production of hydrogen from methanol for fuel cell --- p.2 / Chapter 1.3 --- Catalysts for CO oxidation and methanol reforming --- p.5 / Chapter 1.4 --- Copper-based catalysts --- p.6 / Chapter 1.5 --- Mechanisms in the catalytic processes --- p.7 / Chapter 1.6 --- Synthesis of Cu-based catalysts --- p.10 / Chapter 1.7 --- Potential applications of the biomorphic CuO/CeO2/Al2O3 catalyst --- p.11 / Chapter 1.8 --- Objectives and the thesis layout --- p.12 / Chapter 1.9 --- References --- p.13 / Chapter Chapter 2 --- Methods and Instrumentation --- p.16 / Chapter 2.1 --- Sample preparations --- p.16 / Chapter 2.1.1 --- Syntheses of the biomorphic samples --- p.16 / Chapter 2.1.2 --- Syntheses of the control samples (R1 and R2) --- p.17 / Chapter 2.2 --- Characterization --- p.18 / Chapter 2.2.1 --- Scanning electron microscope (SEM) --- p.18 / Chapter 2.2.2 --- Transmission electron microscopy (TEM) --- p.19 / Chapter 2.2.3 --- X-ray powder diffractometry (XRD) --- p.20 / Chapter 2.2.4 --- Fourier transform infrared (FTIR) spectroscopy --- p.21 / Chapter 2.2.5 --- Raman scattering (RS) spectroscopy --- p.22 / Chapter 2.2.6 --- Differential thermal analysis (DTA) --- p.22 / Chapter 2.2.7 --- Thermogravimetric analysis (TGA) --- p.23 / Chapter 2.2.8 --- Gas sorption surface analysis (GSSA) --- p.24 / Chapter 2.3 --- Catalytic activity --- p.25 / Chapter 2.3.1 --- CO oxidation --- p.25 / Chapter 2.3.2 --- Partial oxidation of methanol (POMe) --- p.27 / Chapter 2.3.3 --- Steam reforming of methanol (SRMe) --- p.28 / Chapter 2.4 --- References --- p.29 / Chapter Chapter 3 --- "Results, discussions and characterization" --- p.31 / Chapter 3.1 --- Biomorphic samples --- p.31 / Chapter 3.1.1 --- Macrostructures --- p.31 / Chapter 3.1.2 --- SEM and TEM results --- p.32 / Chapter 3.1.3 --- XRD analysis and chemical compositions --- p.35 / Chapter 3.1.4 --- RS results --- p.41 / Chapter 3.1.5 --- FTIR results --- p.44 / Chapter 3.1.6 --- Thermal property --- p.46 / Chapter 3.1.7 --- Porosity analysis --- p.48 / Chapter 3.2 --- Control sample R1 --- p.52 / Chapter 3.2.1 --- Microstructures --- p.52 / Chapter 3.2.2 --- Surface area and porosity --- p.55 / Chapter 3.2.3 --- Thermal property --- p.56 / Chapter 3.2.4 --- "XRD, FTIR and RS results" --- p.58 / Chapter 3.3 --- Control sample R2 --- p.60 / Chapter 3.3.1 --- Microstructures --- p.60 / Chapter 3.3.2 --- Surface area and porosity --- p.61 / Chapter 3.3.3 --- "XRD, FTIR and RS results" --- p.62 / Chapter 3.3.4 --- Thermal property --- p.63 / Chapter 3.4 --- Formation mechanisms of the biomorphic samples --- p.64 / Chapter 3.5 --- Impacts of the Cu/Ce/Al ratios on the CuO dispersion --- p.66 / Chapter 3.6 --- Cotton biotemplate --- p.66 / Chapter 3.7 --- Formation mechanisms of R1 and R2 --- p.67 / Chapter 3.8 --- References --- p.69 / Chapter Chapter 4 --- Evaluations of Catalytic Activities --- p.71 / Chapter 4.1 --- CO oxidation --- p.71 / Chapter 4.2 --- POMe --- p.79 / Chapter 4.3 --- SRMe --- p.91 / Chapter 4.4 --- Physical properties of the biomorphic samples before and after the reactions --- p.97 / Chapter 4.5 --- Structure of the sample and its catalytic performance --- p.102 / Chapter 4.6 --- CuO dispersion and the catalytic performance --- p.103 / Chapter 4.7 --- Al2O3 and CeO2 and the catalytic performance --- p.105 / Chapter 4.8 --- Catalytic performance of the biomorphic samples and R2 --- p.108 / Chapter 4.9 --- References --- p.109 / Chapter Chapter 5 --- Conclusions and suggestions for further studies --- p.110 / Chapter 5.1 --- Conclusions --- p.110 / Chapter 5.2 --- Future works --- p.112 / Chapter 5.3 --- References --- p.114

Neste trabalho foram analisados diferentes parâmetros geométricos para canais de fluxo em células a combustível tipo PEMFC e sua influência no desempenho do sistema, utilizando a fluidodinâmica computacional. Na análise dos modelos matemáticos, verificou-se que o modelo de aglomerado inundado descreve com maior fidelidade o comportamento de células a combustível, enquanto as equações de Butler-Volmer não consideram as perdas por transporte de massa. Foram avaliadas as seções transversais retangular, trapezoidal e em degrau. O modelo com canais de seção retangular apresentou desempenho elétrico ligeiramente superior, porém os canais com seção trapezoidal propiciam um melhor gerenciamento de água. Em todos os aspectos estudados, os canais com seção em degrau se comportaram de forma análoga aos canais com seção trapezoidal, porém sua construção é menos complexa. Também foram analisadas as configurações serpentina e interdigitada em células de 5 cm², e sua influência na uniformidade da densidade de corrente. Não foram observadas diferenças significativas quanto à eficiência elétrica entre células com as duas configurações. A configuração interdigitada propiciou distribuição mais uniforme de geração de corrente, pois os reagentes são fornecidos em alta concentração por uma maior área da célula. Assim, esta configuração é preferível para aumento de escala. / In this work, different geometric parameters for PEMFC flow channels and their influence in cell performance were analyzed using computational fluid dynamics. At first, two mathematical models, the flooded agglomerate model and the Butler-Volmer equations, were compared. It was verified that the equations do not consider mass-transfer losses, while the agglomerate model describes the system more accurately. In a second analysis, rectangular, trapezoidal and step-shaped cross-sections were evaluated. The model with rectangular channels showed a slightly higher electrical performance; however, trapezoidal channels provided better water management. Cells with step-shaped cross-sections were found to be superior to those with trapezoidal channels, due to lower constructive complexity, even though their performance was similar to that of trapezoidal cross-sections in every aspect. Further studies analyzed serpentine and interdigitated channel patterns in 5 cm² cells and their influence in current density uniformity. Again, electrical performance was very similar for both patterns. However, the interdigitated pattern provided more spatial uniformity in current generation, because concentrated reactants are supplied to a wider area of the cell. Thus, this pattern is preferable for fuel cell scaling-up.