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First Principles and Genetic Algorithm Studies of Lanthanide Metal Oxides for Optimal Fuel Cell Electrolyte DesignIsmail, Arif 07 September 2011 (has links)
As the demand for clean and renewable energy sources continues to grow, much
attention has been given to solid oxide fuel cells (SOFCs) due to their efficiency and low
operating temperature. However, the components of SOFCs must still be improved
before commercialization can be reached. Of particular interest is the solid electrolyte,
which conducts oxygen ions from the cathode to the anode. Samarium-doped ceria (SDC)
is the electrolyte of choice in most SOFCs today, due mostly to its high ionic
conductivity at low temperatures. However, the underlying principles that contribute to
high ionic conductivity in doped ceria remain unknown, and so it is difficult to improve
upon the design of SOFCs. This thesis focuses on identifying the atomistic interactions in
SDC which contribute to its favourable performance in the fuel cell.
Unfortunately, information as basic as the structure of SDC has not yet been
found due to the difficulty in experimentally characterizing and computationally
modelling the system. For instance, to evaluate 10.3% SDC, which is close to the 11.1%
concentration used in fuel cells, one must investigate 194 trillion configurations, due to
the numerous ways of arranging the Sm ions and oxygen vacancies in the simulation cell.
As an exhaustive search method is clearly unfeasible, we develop a genetic algorithm
(GA) to search the vast potential energy surface for the low-energy configurations, which will be most prevalent in the real material.
With the GA, we investigate the structure of SDC for the first time at the DFT+U
level of theory. Importantly, we find key differences in our results from prior calculations of this system which used less accurate methods, which demonstrate the importance of accurately modelling the system. Overall, our simulation results of the structure of SDCagree with experimental measurements. We identify the structural significance of defects in the doped ceria lattice which contribute to oxygen ion conductivity. Thus, the structure
of SDC found in this work provides a basis for developing better solid electrolytes, which
is of significant scientific and technological interest.
Following the structure search, we perform an investigation of the electronic properties of SDC, to understand more about the material. Notably, we compare our calculated density of states plot to XPS measurements of pure and reduced SDC. This allows us to parameterize the Hubbard (U) term for Sm, which had not yet been done. Importantly, the DFT+U treatment of the Sm ions also allowed us to observe in our
simulations the magnetization of SDC, which was found by experiment.
Finally, we also study the SDC surface, with an emphasis on its structural similarities to the bulk. Knowledge of the surface structure is important to be able to understand how fuel oxidation occurs in the fuel cell, as many reaction mechanisms occur on the surface of this porous material. The groundwork for such mechanistic studies is provided in this thesis.
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First Principles and Genetic Algorithm Studies of Lanthanide Metal Oxides for Optimal Fuel Cell Electrolyte DesignIsmail, Arif 07 September 2011 (has links)
As the demand for clean and renewable energy sources continues to grow, much
attention has been given to solid oxide fuel cells (SOFCs) due to their efficiency and low
operating temperature. However, the components of SOFCs must still be improved
before commercialization can be reached. Of particular interest is the solid electrolyte,
which conducts oxygen ions from the cathode to the anode. Samarium-doped ceria (SDC)
is the electrolyte of choice in most SOFCs today, due mostly to its high ionic
conductivity at low temperatures. However, the underlying principles that contribute to
high ionic conductivity in doped ceria remain unknown, and so it is difficult to improve
upon the design of SOFCs. This thesis focuses on identifying the atomistic interactions in
SDC which contribute to its favourable performance in the fuel cell.
Unfortunately, information as basic as the structure of SDC has not yet been
found due to the difficulty in experimentally characterizing and computationally
modelling the system. For instance, to evaluate 10.3% SDC, which is close to the 11.1%
concentration used in fuel cells, one must investigate 194 trillion configurations, due to
the numerous ways of arranging the Sm ions and oxygen vacancies in the simulation cell.
As an exhaustive search method is clearly unfeasible, we develop a genetic algorithm
(GA) to search the vast potential energy surface for the low-energy configurations, which will be most prevalent in the real material.
With the GA, we investigate the structure of SDC for the first time at the DFT+U
level of theory. Importantly, we find key differences in our results from prior calculations of this system which used less accurate methods, which demonstrate the importance of accurately modelling the system. Overall, our simulation results of the structure of SDCagree with experimental measurements. We identify the structural significance of defects in the doped ceria lattice which contribute to oxygen ion conductivity. Thus, the structure
of SDC found in this work provides a basis for developing better solid electrolytes, which
is of significant scientific and technological interest.
Following the structure search, we perform an investigation of the electronic properties of SDC, to understand more about the material. Notably, we compare our calculated density of states plot to XPS measurements of pure and reduced SDC. This allows us to parameterize the Hubbard (U) term for Sm, which had not yet been done. Importantly, the DFT+U treatment of the Sm ions also allowed us to observe in our
simulations the magnetization of SDC, which was found by experiment.
Finally, we also study the SDC surface, with an emphasis on its structural similarities to the bulk. Knowledge of the surface structure is important to be able to understand how fuel oxidation occurs in the fuel cell, as many reaction mechanisms occur on the surface of this porous material. The groundwork for such mechanistic studies is provided in this thesis.
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Preparacao de eletrolitos solidos ceramicos de zirconia estabilizada com calciaCAPRONI, ERICA 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:48:18Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:08Z (GMT). No. of bitstreams: 1
09307.pdf: 3599752 bytes, checksum: c720dc7c7bbb65919b1861882ea4796e (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP / FAPESP:01/08029-0
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Eletrolitos sólidos cerâmicos a base de óxido de zircônio para a detecção de oxigênioCAPRONI, ERICA 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:52:58Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:59:04Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP / FAPESP:03/07331-0
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Projeto, montagem e caracterizacao de um sensor de fluor com eletrolito solido ceramico de PbFsub2PORTELLA, KLEBER F. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:42:42Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:12Z (GMT). No. of bitstreams: 1
05232.pdf: 6473842 bytes, checksum: 88d593005dc2c79ae422916e7fcaf0d9 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Obtencao e caracterizacao de eletrolitos solidos de ceria-gadoliniaROCHA, RENATA A. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:46:00Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:05:08Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP / FAPESP:99/12494-9
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Preparacao e condutividade eletrica de eletrolitos solidos de toria-itriaCOSENTINO, IVANA C. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:41:05Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:15Z (GMT). No. of bitstreams: 1
04687.pdf: 7600406 bytes, checksum: 7fc9c77439b889fea7b339da3aea0adb (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Preparacao de eletrolitos solidos ceramicos de zirconia estabilizada com calciaCAPRONI, ERICA 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:48:18Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:08Z (GMT). No. of bitstreams: 1
09307.pdf: 3599752 bytes, checksum: c720dc7c7bbb65919b1861882ea4796e (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP / FAPESP:01/08029-0
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Eletrolitos sólidos cerâmicos a base de óxido de zircônio para a detecção de oxigênioCAPRONI, ERICA 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:52:58Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:59:04Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Tendo como vantagem a elevada resistência ao choque térmico da zircônia:magnésia e a alta condutividade iônica da zircônia:ítria, compósitos dessas cerâmicas foram preparados por meio da mistura, em diferentes concentrações, de eletrólitos sólidos de ZrO2: 8,6 mol% MgO e de ZrO2: 3 mol% Y2O3, compactação e sinterização. A caracterização microestrutural foi feita por meio de difração de raios X e microscopia eletrônica de varredura. A análise do comportamento térmico foi feita por dilatometria. As propriedades elétricas foram estudadas por meio de espectroscopia de impedância. Foi feita uma montagem experimental para monitorar a resposta elétrica gerada em função do teor de oxigênio a altas temperaturas. Os principais resultados mostram que os compósitos cerâmicos são parcialmente estabilizados nas fases monoclínica, cúbica e tetragonal, e apresentam comportamento térmico similar ao apresentado por eletrólitos sólidos de zircônia:magnésia de dispositivos sensores de oxigênio. Além disso, os resultados de análise de espectroscopia de impedância mostram que a adição da zircônia:ítria melhora o comportamento elétrico da zircônia:magnésia, e que resposta elétrica gerada é dependente do teor de oxigênio a 1000 °C, mostrando ser possível construir sensores de oxigênio utilizando compósitos cerâmicos. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP / FAPESP:03/07331-0
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Projeto, montagem e caracterizacao de um sensor de fluor com eletrolito solido ceramico de PbFsub2PORTELLA, KLEBER F. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:42:42Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:12Z (GMT). No. of bitstreams: 1
05232.pdf: 6473842 bytes, checksum: 88d593005dc2c79ae422916e7fcaf0d9 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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