Neste trabalho foi estudado o condutor protônico HPb2Nb3O10. nH2O , por Ressonância Magnética Nuclear pulsada do próton \'ANTPOT.1H\'. Tanto o estudo da forma de linha como a relaxação spin-rede, em função da temperatura, refletem a mobilidade das espécies protônicas neste material. O início dos movimentos iônicos e moleculares produzem um forte estreitamento da largura de linha acima de 130 K. Os dados da taxa de relaxação spin-rede (1/T1) mostra um máximo entre 253 K e 273 K que depende da hidratação (n). As energias de ativação obtidas dos resultados de relaxação e largura de linha variam entre 0,14eV e 0,4eV, dependendo da hidratação. Os resultados de condutividade e RMN são consistente com um mecanismo de condução do tipo Grotthus, que consiste numa sucessão de movimentos reorientacionais e saltos de prótons. O coeficiente de difusão protônica foi estimado dos parâmetros obtidos de RMN sendo da ordem de 10-8 cm2/s. Este valor leva a uma condutividade da ordem de 10-3 S/ cm. / The protonic conductor HPb2Nb3O10. nH2O , was studied by pulsed Nuclear Magnetic Resonance (NMR) of \'ANTPOT.1H\'. The temperature dependence of the spin-lattice relaxation rate (1/\'T IND.1\') and line width, reflect the mobility of the protonic species present in this material. The onset of ionic and molecular motions produces a strong narrowing of the line at temperatures above 130 K. The spin-lattice relaxation data, obtained above 200 K, shows a maximum in 1/\'T IND.1\', peaking in the range 253 K to 273 K, depending on the value of n. Activation energies of protonic motions, measured from line width and relaxation data, are n dependent and lies in the range of 0,14 eV to 0,4 eV. Results of NMR and conductivity are consistent with the Grotthus conduction mechanism, consisting of a succession of molecular re-orientations and proton jumps. The protonic diffusion coefficient was estimated from the parameters obtained from NMR relaxation and found to be of the order of 10-8 cm2/s, leading to a conductivity of about 10-3 S/ cm.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第16396号 / 工博第3477号 / 新制||工||1525(附属図書館) / 29027 / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 田中 功, 教授 乾 晴行, 准教授 宇田 哲也 / 学位規則第4条第1項該当

Philosophiae Doctor - PhD / The need for simplified polymer electrolyte membrane fuel cell (PEMFCs) systems, which do not require extensive fuel processing, has led to increased study in the field of high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) applications. Although these HT-PEMFCs can operate with less complex systems, they are not without their own challenges; challenges which are introduced due to their higher operation temperature. This study aims to address two of the main challenges associated with HT-PEMFCs; the need for alternative catalyst layer (CL) ionomers and the prevention of excess phosphoric acid (PA) leaching into the CL. The first part of the study involves the evaluation of suitable proton conducting materials for use in the CL of high temperature membrane electrode assemblies (HT-MEAs), with the final part of the study focusing on development of a novel MEA architecture comprising an acid controlling region. The feasibility of the materials in HT-MEAs was evaluated by comparison to standard MEA configurations.

Neste trabalho foi estudado o condutor protônico HPb2Nb3O10. nH2O , por Ressonância Magnética Nuclear pulsada do próton \'ANTPOT.1H\'. Tanto o estudo da forma de linha como a relaxação spin-rede, em função da temperatura, refletem a mobilidade das espécies protônicas neste material. O início dos movimentos iônicos e moleculares produzem um forte estreitamento da largura de linha acima de 130 K. Os dados da taxa de relaxação spin-rede (1/T1) mostra um máximo entre 253 K e 273 K que depende da hidratação (n). As energias de ativação obtidas dos resultados de relaxação e largura de linha variam entre 0,14eV e 0,4eV, dependendo da hidratação. Os resultados de condutividade e RMN são consistente com um mecanismo de condução do tipo Grotthus, que consiste numa sucessão de movimentos reorientacionais e saltos de prótons. O coeficiente de difusão protônica foi estimado dos parâmetros obtidos de RMN sendo da ordem de 10-8 cm2/s. Este valor leva a uma condutividade da ordem de 10-3 S/ cm. / The protonic conductor HPb2Nb3O10. nH2O , was studied by pulsed Nuclear Magnetic Resonance (NMR) of \'ANTPOT.1H\'. The temperature dependence of the spin-lattice relaxation rate (1/\'T IND.1\') and line width, reflect the mobility of the protonic species present in this material. The onset of ionic and molecular motions produces a strong narrowing of the line at temperatures above 130 K. The spin-lattice relaxation data, obtained above 200 K, shows a maximum in 1/\'T IND.1\', peaking in the range 253 K to 273 K, depending on the value of n. Activation energies of protonic motions, measured from line width and relaxation data, are n dependent and lies in the range of 0,14 eV to 0,4 eV. Results of NMR and conductivity are consistent with the Grotthus conduction mechanism, consisting of a succession of molecular re-orientations and proton jumps. The protonic diffusion coefficient was estimated from the parameters obtained from NMR relaxation and found to be of the order of 10-8 cm2/s, leading to a conductivity of about 10-3 S/ cm.

There are many interesting applications of proton conducting oxides, such as electrolytes in fuel cells, hydrogen sensors and catalytic membranes for hydrogenation or dehydrogenation of organic compounds. Previous work explored doping BaTiO3 with the Rare Earth Element (REE) Sc to introduce oxygen vacancies in the structure, making it a Proton Conductor (PC). PC oxides are often perovskite materials, ABX3, wherethe A- or B-site are doped in such a way that less oxygen can be contained, creating oxygen vacancies. When these materials are then hydrated so that water molecules occupy the vacancies, hydrogen is essentially added to the system in the form of protons. This study expanded on those results, exploring possible dopants that are non-REEs, theoretically improving availability and cost. Fe and Al were chosen as B-site dopants and Sr was included as an alternative to Ba as the A-site cation, compensating for the smaller size of the Fe- and Al atoms compared to Ti. Solid state synthesis was used to manufacture the different compounds and then X-Ray Diffraction (XRD), ThermoGravimetric Analysis (TGA) and Differential Thermal Analysis (DTA) were used inorder to investigate their properties. The main focus was to explore ift he materials could be synthesised using this method, their structures and how they reacted to hydration. All Al doped samples could not be made phase pure with the synthesis parameters used. BaTi0.5Fe0.5Oy was stabilised by the inclusion of Ti, as it did not decompose during hydration, unlike pure BaFeOx. Significant hydration was achieved in a wet nitrogen atmosphere at 185°C, but its structure type was hexagonal, which is known to be unfavourable for proton conduction. SrTi0.5Fe0.5Oy had a cubic structure which is a beneficial structural trait for proton conduction, but negligible hydration was observed by TGA. A small increase in cell volume indicates that it might still have taken up some water, but the methods used for hydration were not optimal for this material. The oxygen content of the materials was not determined in this project and methods such as Mössbauer spectroscopy and iodometric titration should be included in any related future studies.

O condutor protônico zirconato de bário dopado com ítrio (BaZr1-xYxO3-δ, BZYx) é um material promissor para a aplicação como eletrólito sólido em células a combustível operacional em temperaturas intermediárias (400 a 700 oC). No entanto, sua natureza refratária (ponto de fusão ~ 2600 oC) faz com que para sua densificação, necessária para sua aplicação como eletrólito, sejam necessários altas temperaturas e longos tempos de tratamento térmico (1600 a 1800 °C por 24 a 48 h). Tais condições extremas causam um desvio da estequiometria de bário que afeta a química de defeitos do material e, consequentemente a diminuição da condutividade protônica do BZYx. Portanto, o processamento desse eletrólito sólido em menores temperaturas, preservando sua estequiometria, formando uma microestrutura densa e com baixa resistividade inter-granular são os principais objetivos e desafios da comunidade científica. Visando aumentar a sinterabilidade das partículas, o BZY foi preparado pelo método dos peróxidos oxidantes (OPM). O procedimento experimental original do OPM foi modificado e otimizado para viabilizar a formação do BZYx, com x = 10 a 50 mol% de Y3+. Dentre as modificações, a síntese foi feita com e sem o controle da atmosfera, em câmara de luvas sob atmosfera de nitrogênio e ao ar, respectivamente. As propriedades estruturais, morfológicas, térmicas, termodinâmicas e elétricas das composições de BZYx foram investigadas. As amostras produzidas foram calcinadas em diversas temperaturas e investigadas quanto à sua sinterabilidade e densificação. Os pós de BZYx, com x = 10 a 50 mol% de Y3+, produzidos com controle da atmosfera foram investigados quanto às suas propriedades termodinâmicas. Os valores de entalpia de formação a partir dos óxidos (ΔHf,ox) foram calculados com os dados obtidos por calorimetria de dissolução a alta temperatura. As amostras de BZY10 e BZY20 produzidas com controle da atmosfera atingiram condutividade elétrica total de 1,6 x 10-3 e 1,3 x 10-3 S/cm a 530 oC, respectivamente. A alta resistividade inter-granular contribui para a alta resistividade total das amostras. A análise por espectroscopia Raman e os valores de ΔHf,ox obtidos sugerem que para valores de Y3+ > 20 mol% ocorrem interações defeito-defeito na estrutura cristalina, causando à diminuição de sítios efetivos para a hidratação e a diminuição da mobilidade dos prótons na estrutura e, consequentemente, a diminuição da condutividade protônica total. / The proton conductor oxide yttrium doped barium zirconate (BaZr1-xYxO3-δ, BZYx) is a promising solid electrolyte for solid oxide fuel cells (SOFC) operating at intermediate temperatures (400 to 700 oC). However, the BZY refractory nature (MP ~ 2600 oC) inhibits the achievement of the densification needed for application in SOFCs (relative density ≥ 95% T.D.), requiring long dwell times and high temperatures (T ≥ 1600 oC, t ≥ 24 h). Those extreme conditions cause barium stoichiometry deviation, which affects the defect chemistry and the depletion of proton conductivity. Therefore, BZY processing in less aggressive conditions, preserving cation stoichiometry, leading to dense microstructures with low intergranular resistivity are the great challenges of the scientific community nowadays. Aiming to increase particles sinterability, BZYx (x = 10 to 50 mol% of Y3+), solid solutions where synthesized by the Oxidant Peroxide Method (OPM). The original OPM experimental procedure was modified to allow the BZY formation with different dopant content. One of the modifications was to carry out the synthesis under laboratory and nitrogen atmospheres. The study of structural, thermal, morphological, thermochemical and electrical properties of all samples was performed. The samples where calcined at different temperatures and the particles sinterability and densification were also investigated. The thermochemical properties of BZYx solid solutions were investigated by high temperature oxide melt solution calorimetry, for evaluation of the formation enthalpies (ΔHf,ox). The total electrical conductivity of the BZY10 and BZY20 sintered samples synthesized under nitrogen was 1.6 x 10-3 and 1.3 x 10-3 S/cm at 530 oC, respectively. The blocking of charge carriers at interfaces contributes to the low total electrical conductivity. Raman spectroscopy analysis and the evaluated ΔHf,ox values obtained suggest that from 20 mol% Y3+, defect interaction might happen, leading to vacancy clustering. This effect might cause the depletion of mobile oxygen vacancies, affecting the mobility of protons, with a decrease in proton conductivity.

Η Υδρογόνωση του Διοξειδίου του Άνθρακα έχει προσελκύσει διεθνώς το ενδιαφέρον της επιστημονικής κοινότητας τόσο ως πιθανή πηγή ανανεώσιμων καυσίμων όσο και ως μέσο μείωσης των εκπομπών του CO2. Στην παρούσα μελέτη χρησιμοποιείται το φαινόμενο της Ηλεκτροχημικής Ενίσχυσης (Η/Ε) της κατάλυσης (EPOC) ή μη- Φαρανταϊκή Ηλεκτροχημική Τροποποίηση της καταλυτικής ενεργότητας (φαινόμενο NEMCA) για την ενίσχυση του ρυθμού και της εκλεκτικότητας της υδρογόνωσης του CO2 σε καταλύτη ρουθηνίου (Ru) υποστηριζόμενου σε πρωτονιακό αγωγό ΒZY. Αρχικά γίνεται μια Εισαγωγή για το Διοξείδιο του Άνθρακα στην οποία και εξηγείται η αναγκαιότητα της περεταίρω μελέτης της αντίδρασης υδρογόνωσης του CO2. Στο Κεφάλαιο 1 γίνεται μια εκτεταμένη αναφορά στους στερεούς ηλεκτρολύτες, με ιδιαίτερη έμφαση στους στερεούς ηλεκτρολύτες πρωτονιακής αγωγιμότητας. Στη συνέχεια στο δεύτερο Κεφάλαιο περιγράφεται το φαινόμενο της Ηλεκτροχημικής Ενίσχυσης της κατάλυσης, γίνεται μια αναφορά των μελετών Η/Ε που έχουν προηγηθεί και παρατίθενται οι κανόνες που διέπουν το συγκεκριμένο φαινόμενο. Στο τρίτο Κεφάλαιο γίνεται βιβλιογραφική ανασκόπηση της συγκεκριμένης αντίδρασης τόσο καταλυτικά όσο και ηλεκτροκαταλυτικά. Στο Κεφάλαιο 4 ακολουθεί η περιγραφή της πειραματικής διάταξης καθώς και ο χαρακτηρισμός του καταλύτη αλλά και τα πειράματα χαρακτηρισμού του ηλεκτρολύτη. Έπειτα, στο Κεφάλαιο 5 παρουσιάζονται τα πειραματικά αποτελέσματα (θερμοκρασιακά, κινητικά, δυναμικής απόκρισης κτλ.), καθώς και μια ποιοτική ανάλυση των παραπάνω αποτελεσμάτων. Και τέλος παρατίθενται τα συνολικά συμπεράσματα της συγκεκριμένης μελέτης. / The Hydrogenation of Carbon Dioxide has attracted international interest in the scientific community as a potential source of renewable fuels and as a means of reducing CO2 emissions. In this study the phenomenon of Electrochemical Promotion of Catalysis (EPOC) or non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA) is used in order to enhance the rate and selectivity of this reaction on a Ruthenium (Ru) catalyst deposited on a proton conductor (BZY). The electrochemical promotion of the hydrogenation of CO2 on polycrystalline Ru deposited on a BZY (BaZr0.85Y0.15O3 + 1wt% NiO), a proton conductor in wet atmospheres, was investigated at temperatures 250 to 450oC and atmospheric pressure. Methane and CO were the only detectable products. It was found that the selectivity to CH4 is very significantly enhanced by proton removal from the catalyst via electrochemically controlled spillover of atomic H from the catalyst surface to the proton-conducting support. The apparent Faradaic efficiency of the process takes values up to 500 and depends strongly on the porous Ru catalyst film thickness. The results strongly suggest that the observed strong promotional effect is due to the formation and surface migration of a promoting formate anion generated via potential controlled disproportionation of formic acid adsorbed at the catalyst-proton conducting support interface. This is the first successful electrochemical promotion study of a hydrogenation reaction at temperatures as low as 250oC. There is an up to fourfold enhancement in catalytic rate of CH4 formation with concomitant 50% suppression of the CO formation rate which proceeds in a parallel route.

O condutor protônico zirconato de bário dopado com ítrio (BaZr1-xYxO3-δ, BZYx) é um material promissor para a aplicação como eletrólito sólido em células a combustível operacional em temperaturas intermediárias (400 a 700 oC). No entanto, sua natureza refratária (ponto de fusão ~ 2600 oC) faz com que para sua densificação, necessária para sua aplicação como eletrólito, sejam necessários altas temperaturas e longos tempos de tratamento térmico (1600 a 1800 °C por 24 a 48 h). Tais condições extremas causam um desvio da estequiometria de bário que afeta a química de defeitos do material e, consequentemente a diminuição da condutividade protônica do BZYx. Portanto, o processamento desse eletrólito sólido em menores temperaturas, preservando sua estequiometria, formando uma microestrutura densa e com baixa resistividade inter-granular são os principais objetivos e desafios da comunidade científica. Visando aumentar a sinterabilidade das partículas, o BZY foi preparado pelo método dos peróxidos oxidantes (OPM). O procedimento experimental original do OPM foi modificado e otimizado para viabilizar a formação do BZYx, com x = 10 a 50 mol% de Y3+. Dentre as modificações, a síntese foi feita com e sem o controle da atmosfera, em câmara de luvas sob atmosfera de nitrogênio e ao ar, respectivamente. As propriedades estruturais, morfológicas, térmicas, termodinâmicas e elétricas das composições de BZYx foram investigadas. As amostras produzidas foram calcinadas em diversas temperaturas e investigadas quanto à sua sinterabilidade e densificação. Os pós de BZYx, com x = 10 a 50 mol% de Y3+, produzidos com controle da atmosfera foram investigados quanto às suas propriedades termodinâmicas. Os valores de entalpia de formação a partir dos óxidos (ΔHf,ox) foram calculados com os dados obtidos por calorimetria de dissolução a alta temperatura. As amostras de BZY10 e BZY20 produzidas com controle da atmosfera atingiram condutividade elétrica total de 1,6 x 10-3 e 1,3 x 10-3 S/cm a 530 oC, respectivamente. A alta resistividade inter-granular contribui para a alta resistividade total das amostras. A análise por espectroscopia Raman e os valores de ΔHf,ox obtidos sugerem que para valores de Y3+ > 20 mol% ocorrem interações defeito-defeito na estrutura cristalina, causando à diminuição de sítios efetivos para a hidratação e a diminuição da mobilidade dos prótons na estrutura e, consequentemente, a diminuição da condutividade protônica total. / The proton conductor oxide yttrium doped barium zirconate (BaZr1-xYxO3-δ, BZYx) is a promising solid electrolyte for solid oxide fuel cells (SOFC) operating at intermediate temperatures (400 to 700 oC). However, the BZY refractory nature (MP ~ 2600 oC) inhibits the achievement of the densification needed for application in SOFCs (relative density ≥ 95% T.D.), requiring long dwell times and high temperatures (T ≥ 1600 oC, t ≥ 24 h). Those extreme conditions cause barium stoichiometry deviation, which affects the defect chemistry and the depletion of proton conductivity. Therefore, BZY processing in less aggressive conditions, preserving cation stoichiometry, leading to dense microstructures with low intergranular resistivity are the great challenges of the scientific community nowadays. Aiming to increase particles sinterability, BZYx (x = 10 to 50 mol% of Y3+), solid solutions where synthesized by the Oxidant Peroxide Method (OPM). The original OPM experimental procedure was modified to allow the BZY formation with different dopant content. One of the modifications was to carry out the synthesis under laboratory and nitrogen atmospheres. The study of structural, thermal, morphological, thermochemical and electrical properties of all samples was performed. The samples where calcined at different temperatures and the particles sinterability and densification were also investigated. The thermochemical properties of BZYx solid solutions were investigated by high temperature oxide melt solution calorimetry, for evaluation of the formation enthalpies (ΔHf,ox). The total electrical conductivity of the BZY10 and BZY20 sintered samples synthesized under nitrogen was 1.6 x 10-3 and 1.3 x 10-3 S/cm at 530 oC, respectively. The blocking of charge carriers at interfaces contributes to the low total electrical conductivity. Raman spectroscopy analysis and the evaluated ΔHf,ox values obtained suggest that from 20 mol% Y3+, defect interaction might happen, leading to vacancy clustering. This effect might cause the depletion of mobile oxygen vacancies, affecting the mobility of protons, with a decrease in proton conductivity.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第14574号 / 工博第3042号 / 新制||工||1453(附属図書館) / 26926 / UT51-2009-D286 / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 粟倉 泰弘, 教授 杉村 博之, 教授 田中 功 / 学位規則第4条第1項該当

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第16852号 / 工博第3573号 / 新制||工||1540(附属図書館) / 29527 / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 田中 功, 教授 乾 晴行, 准教授 宇田 哲也 / 学位規則第4条第1項該当