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Iridium-based bimetallic alloy catalysts for the ethanol oxidation reaction for fuel cells modeled by density functional theoryCourtois, Julien 25 April 2013 (has links)
Current ethanol oxidation catalysts in direct ethanol fuel cells (typically platinum-based) suffer from low conversion and are susceptible to CO poisoning. Therefore we determined to find viable alternative catalysts for ethanol oxidation based on iridium using density functional theory to model bimetallic alloy (111) surfaces. Iridium was alloyed with another transition metals M in an overlayer (one layer of metal M on top of bulk iridium) or subsurface configuration (M is inserted under the first layer of iridium). Complete oxidation of ethanol is limited by the breaking of strong C-C bonds, so any catalyst must lower the barriers for C-C bond breaking. We modeled the reaction CH+CO →CHCO.Segregation energies were calculated and the subsurface configuration was the most stable configuration in the vast majority of alloy cases. CO adsorption was also studied and a lower CO adsorption energy was found in many alloy cases compared to pure Pt (, providing encouraging results about the possibility of reducing CO poisoning. Activation energies were lowered for the vast majority of the alloys used in an underlayer structure, reinforcing our interest in the underlayer structures or “subsurfaceâ€� alloys. Finally, we found, based on the CO adsorption energies, activation energies of the C-C breakage reaction, and metal cost, three important catalyst descriptors, a number of promising catalysts for the ethanol oxidation reaction. The most interesting alloys all adopted the underlayer structure Ir/M/Ir. With M = Ta, Hf, Nb, V, Zr, they demonstrated enhanced reactivity and high CO tolerance, having the advantage of reducing the cost of the catalyst, potentially substituting expensive platinum group metals by more affordable components.
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A Density Functional Theory of a Nickel-based Anode Catalyst for Application in a Direct Propane Fuel CellVafaeyan, Shadi 25 September 2012 (has links)
The maximum theoretical energy efficiency of fuel cells is much larger than those of the steam-power-turbine cycles that are currently used for generating electrical power. Similarly, direct hydrocarbon fuel cells, DHFCs, can theoretically be much more efficient than hydrogen fuel cells. Unfortunately the current densities (overall reaction rates) of DHFCs are substantially smaller than those of hydrogen fuel cells. The problem is that the exchange current density (catalytic reaction rate) is orders of magnitude smaller for DHFCs. Other work at the University of Ottawa has been directed toward the development of polymer electrolytes for DHFCs that operate above the boiling point of water, making corrosion rates much slower so that precious metal catalysts are not required. Propane (liquefied petroleum gas, LPG) was the hydrocarbon chosen for this research partly because infrastructure for its transportation and storage in rural areas already exists. In this work nickel based catalysts, an inexpensive replacement for the platinum based catalysts used in conventional fuel cells, were examined using density functional theory, DFT. The heats of propane adsorption for 3d metals, when plotted as a function of the number of 3d electrons in the metal atom, had the shape of a volcano plot, with the value for nickel being the peak value of the volcano plot. Also the C-H bond of the central carbon atom was longer for propane adsorbed on nickel than when adsorbed on any of the other metals, suggesting that the species adsorbed on nickel was less likely to desorb than those on other metals. The selectivity of the propyl radical reaction was examined. It was found that propyl radicals
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A Density Functional Theory of a Nickel-based Anode Catalyst for Application in a Direct Propane Fuel CellVafaeyan, Shadi 25 September 2012 (has links)
The maximum theoretical energy efficiency of fuel cells is much larger than those of the steam-power-turbine cycles that are currently used for generating electrical power. Similarly, direct hydrocarbon fuel cells, DHFCs, can theoretically be much more efficient than hydrogen fuel cells. Unfortunately the current densities (overall reaction rates) of DHFCs are substantially smaller than those of hydrogen fuel cells. The problem is that the exchange current density (catalytic reaction rate) is orders of magnitude smaller for DHFCs. Other work at the University of Ottawa has been directed toward the development of polymer electrolytes for DHFCs that operate above the boiling point of water, making corrosion rates much slower so that precious metal catalysts are not required. Propane (liquefied petroleum gas, LPG) was the hydrocarbon chosen for this research partly because infrastructure for its transportation and storage in rural areas already exists. In this work nickel based catalysts, an inexpensive replacement for the platinum based catalysts used in conventional fuel cells, were examined using density functional theory, DFT. The heats of propane adsorption for 3d metals, when plotted as a function of the number of 3d electrons in the metal atom, had the shape of a volcano plot, with the value for nickel being the peak value of the volcano plot. Also the C-H bond of the central carbon atom was longer for propane adsorbed on nickel than when adsorbed on any of the other metals, suggesting that the species adsorbed on nickel was less likely to desorb than those on other metals. The selectivity of the propyl radical reaction was examined. It was found that propyl radicals
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A Density Functional Theory of a Nickel-based Anode Catalyst for Application in a Direct Propane Fuel CellVafaeyan, Shadi January 2012 (has links)
The maximum theoretical energy efficiency of fuel cells is much larger than those of the steam-power-turbine cycles that are currently used for generating electrical power. Similarly, direct hydrocarbon fuel cells, DHFCs, can theoretically be much more efficient than hydrogen fuel cells. Unfortunately the current densities (overall reaction rates) of DHFCs are substantially smaller than those of hydrogen fuel cells. The problem is that the exchange current density (catalytic reaction rate) is orders of magnitude smaller for DHFCs. Other work at the University of Ottawa has been directed toward the development of polymer electrolytes for DHFCs that operate above the boiling point of water, making corrosion rates much slower so that precious metal catalysts are not required. Propane (liquefied petroleum gas, LPG) was the hydrocarbon chosen for this research partly because infrastructure for its transportation and storage in rural areas already exists. In this work nickel based catalysts, an inexpensive replacement for the platinum based catalysts used in conventional fuel cells, were examined using density functional theory, DFT. The heats of propane adsorption for 3d metals, when plotted as a function of the number of 3d electrons in the metal atom, had the shape of a volcano plot, with the value for nickel being the peak value of the volcano plot. Also the C-H bond of the central carbon atom was longer for propane adsorbed on nickel than when adsorbed on any of the other metals, suggesting that the species adsorbed on nickel was less likely to desorb than those on other metals. The selectivity of the propyl radical reaction was examined. It was found that propyl radicals
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Influ?ncia do m?todo de s?ntese e caracteriza??o de p?s comp?sitos de NiO- Ce1-xEuxO2-δ para anodos catal?ticos de c?lulas a combust?velMedeiros, Amanda Lucena de 06 February 2013 (has links)
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Previous issue date: 2013-02-06 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / Fuel cells are electrochemical devices that convert chemical energy into electricity.
Due to the development of new materials, fuel cells are emerging as generating
clean energy generator. Among the types of fuel cells, categorized according to the
electrode type, the solid oxide fuel cells (SOFC) stand out due to be the only device
entirely made of solid particles. Beyond that, their operation temperature is relatively
high (between 500 and 1000 ?C), allowing them to operate with high efficiency.
Another aspect that promotes the use of SOFC over other cells is their ability to
operate with different fuels. The CeO2 based materials doped with rare earth (TR+3)
may be used as alternatives to traditional NiO-YSZ anodes as they have higher ionic
conductivity and smaller ohmic losses compared to YSZ, and can operate at lower
temperatures (500-800?C). In the composition of the anode, the concentration of NiO,
acting as a catalyst in YSZ provides high electrical conductivity and high
electrochemical activity of reactions, providing internal reform in the cell. In this work
compounds of NiO - Ce1-xEuxO2-δ (x = 0.1, 0.2 and 0.3) were synthesized from
polymeric precursor, Pechini, method of combustion and also by microwave-assisted
hydrothermal method. The materials were characterized by the techniques of TG,
TPR, XRD and FEG-SEM. The refinement of data obtained by X-ray diffraction
showed that all powders of NiO - Cex-1EuxO2-δ crystallized in a cubic phase with
fluorite structure, and also the presence of Ni. Through the characterizations can be
proved that all routes of preparation used were effective for producing ceramics with
characteristics suitable for application as SOFC anodes, but the microwave-assisted
hydrothermal method showed a significant reduction in the average grain size and
improved control of the compositions of the phases / C?lulas a combust?vel s?o dispositivos eletroqu?micos que convertem a energia
qu?mica em el?trica. Em virtude do desenvolvimento de novos materiais, as c?lulas a
combust?vel v?m se destacando como promissores na gera??o de energia de forma
limpa. Dentre os tipos de c?lulas a combust?vel, classificadas de acordo com o tipo
de eletr?lito, destacam-se as de ?xido s?lido (SOFC), por serem as ?nicas
inteiramente constitu?das por s?lidos. Al?m disso, pela sua temperatura de opera??o
ser relativamente elevada (entre 500 e 1000 ?C), estas c?lulas operam com alta
efici?ncia. Outro aspecto que favorece o emprego de SOFC ? a sua habilidade de
operar com diferentes combust?veis, como fontes de hidrog?nio.Os materiais a base
de CeO2 dopados com terras raras (TR+3) podem ser utilizados como alternativas
aos tradicionais anodos de NiO-YSZ. Al?m de maior condutividade i?nica maior e
menores perdas ?hmicas, elas podem operar a temperaturas mais baixas (500-
800?C). Na composi??o do anodo, a concentra??o de NiO, atuando como catalisador
confere alta condutividade el?trica e alta atividade eletroqu?mica das rea??es,
proporcionando a reforma interna do combust?vel na c?lula. Neste trabalho
compostos de NiO - Ce1-xEuxO2-δ (x = 0,1; 0,2 e 0,3), foram sintetizados a partir do
m?todo dos precursores polim?ricos, Pechini, do m?todo de combust?o e, tamb?m,
pelo m?todo hidrotermal assistido por micro-ondas. Os materiais obtidos foram
caracterizados atrav?s das t?cnicas de TG, DRX, TPR e MEV-FEG. O refinamento
dos dados obtidos pela difra??o de raios X indicou que todos os p?s de NiO - Ce1-
xEuxO2-δ cristalizaram-se em uma fase c?bica com estrutura fluorita, e tamb?m a
presen?a de NiO. Todas as rotas de prepara??o utilizadas mostraram-se eficientes
para a produ??o de p?s com caracter?sticas adequadas para aplica??o como anodos
de SOFC, por?m o m?todo hidrotermal assistido por micro-ondas apresentou
significativa redu??o do tamanho m?dio de gr?os e melhor controle das
composi??es das fases
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