Στην εργασία αυτή εφαρμόσθηκε η τεχνική της ηλεκτρονικής δέσμης(e-beam) για την απόθεση του οξειδίου του ζιρκονίου σταθεροποιημένου με οξείδιο του υττρίου (ZrO2 8%mol Y2O3 : 8YSZ) - υλικό το οποίο αποτελεί τη δημοφιλέστερη επιλογή για χρήση ως ηλεκτρολύτη σε κελιά καυσίμου στερεού ηλεκτρολύτη (Solid Oxide Fuel Cells: SOFCs). Με τη φυσική αυτή τεχνική αποτέθηκε πληθώρα υμενίων σε διάφορα υποστρώματα, αλλά κυρίως σε δισκία NiO-YSZ, που είναι το ηλεκτρόδιο ανόδου σε SOFCs. Αυτού του τύπου τα κελιά καυσίμου παρουσιάζουν μεγάλη πυκνότητα ισχύος και λειτουργούν σε θερμοκρασίες οι οποίες κυμαίνονται από 800-1000οC. Η λειτουργία σε υψηλές θερμοκρασίες εισάγει προβλήματα που σχετίζονται με τη διαθεσιμότητα των υλικών και την αντοχή τους κάτω από αντίστοιχες συνθήκες για μεγάλο χρονικό διάστημα. Προκειμένου να μειωθεί η θερμοκρασία λειτουργίας χωρίς αυτό να έχει επίπτωση στην απόδοση του κελιού επιδιώχθηκε η κατασκευή υμενίων ηλεκτρολυτών μικρού πάχους (~1μm). Τα υμένια αυτά, μετά την κατασκευή τους υπέστησαν θερμική κατεργασία (ανόπτηση) σε διάφορες θερμοκρασίες και εξετάστηκαν οι φυσικές τους ιδιότητες με διάφορες τεχνικές, με σκοπό να προσδιοριστούν οι παράμετροι εκείνες οι οποίες επηρεάζουν την ανάπτυξη των φιλμ, το δομή και τη μορφολογία τους. Στοιχειομετρικά τα υμένια δε διαφέρουν αισθητά από το υλικό από το οποίο προέρχονται. Από τις ποσοτικές μετρήσεις βλέπουμε ότι σε σχέση με το αρχικό υλικό ο κατά βάρος λόγος Y2O3/ZrO2 στο υμένιο δε μεταβάλλεται. Ο χαρακτηρισμός της δομής των μικτών οξειδίων πραγματοποιήθηκε με μεθόδους περίθλασης ακτίνων Χ. Από τα αποτελέσματα προέκυψε ότι η αρχικά μικροκρυσταλλική δομή της σκόνης, με αύξηση της θερμοκρασίας πύρωσης και μεγέθυνσης των κόκκων, μετατρέπεται σε μακροκρυσταλλική με την κυβική δομή του πλέγματος φθορίτη. Η μορφολογία των αποτιθέμενων υμενίων μελετήθηκε με ηλεκτρονικό μικροσκόπιο σάρωσης. Βρέθηκε ότι υμένια που κατασκευάστηκαν με υψηλούς ρυθμούς εξάχνωσης έχουν μικρότερο πορώδες, παρουσιάζουν μεγαλύτερη συνοχή και εμφανίζουν λιγότερα ή και καθόλου ρήγματα μετά από θερμική επεξεργασία. Έγινε προσπάθεια λειαίνοντας την επιφάνεια υποστρωμάτων να μειωθεί το πορώδες τους ώστε να γίνει δυνατή η απόθεση ακόμη λεπτότερων υμενίων. Έτσι, κατασκευάστηκαν υμένια με πάχος από 600-1500nm, τα οποία παρουσιάζουν όλες εκείνες τις επιθυμητές ιδιότητες και αποτελούν ενδιαφέρουσα πρόταση για εφαρμογή σε κελιά καυσίμου στερεού ηλεκτρολύτη. / In this project we have applied the technique of e-beam evaporation for the deposition of zirconium oxide stabilized with yttrium oxide (ZrO2 8%mol Y2O3: 8YSZ) - a material which constitutes the most popular choice for use as electrolyte in solid oxide fuel cells. With this physical technique we have deposited many films on various substrates and especially on NiO-YSZ pellets, which constitute the anode in SOFCs. This type of fuel cells presents high energy density when working at temperatures in the 800-1000oC range. However, the operation in high temperatures introduces problems that are related with availability of materials and their performance under extreme conditions for a long period of time. In order to reduce the cell’s working temperature without affecting its efficiency we have deposited thin films with thickness in the ~1μm range. After preparation the films have been thermically treated (annealed) in various temperatures and their physical properties have been investigated with various techniques, in order to determine the parameters that affect the films' growth, structure and morphology. In terms of composition the films do not differ much from the evaporating material. From quantitative measurements we see that the Y2O3-ZrO2 weight ratio in both the evaporating material and the film is identical. The characterization of the structure of mixed oxides was realized with methods of X ray diffraction. From the corresponding spectra we see that YSZ's microcrystalline structure, with increase of temperature [annealing] and subsequent enlargement of grains, is initially changed to macrocrystalline, with the cubic flourite structure. The morphology of the deposited films was studied with a Scanning Electron Microscope. Thus, it was found that films that were manufactured at high deposition rates have smaller porosity and present better cohesion and thermal behavior. Polishing techniques have been used to further decrease the substrate's porosity, in order to be able to deposit thinner functional films. Thus, we were able to manufacture films with thickness from 600-1500nm, that exhibited desirable properties and constitute an interesting alternative for use in SOFCs.

Στα πλαίσια της αναζήτησης νέων µεθόδων παραγωγής ενέργειας υψηλής απόδοσης και φιλικής προς το περιβάλλον, ένα µεγάλο µέρος των ερευνητικών δραστηριοτήτων σε διεθνή κλίµακα έχει στραφεί στην ανάπτυξη της τεχνολογίας των κελίων καυσίµου στερεού ηλεκτρολύτη, SOFC’s (Solid Oxide Fuel Cell’s). Λόγω της φιλικότητάς τους προς το περιβάλλον τα SOFC’s µπορεί να εισαχθούν για χρήση και σε αστικές περιοχές, όπου παράλληλα µε την παραγόµενη ηλεκτρική ενέργεια, είναι δυνατόν να αξιοποιηθεί και η εκλυόµενη θερµική ενέργεια για θέρµανση χώρων, αυξάνοντας συνολικά την αποτελεσµατικότητά τους. Ένα από τα µειονεκτήµατα που εµφανίζονται κατά την µακρόχρονη λειτουργία ενός «State of the art» κελίου καυσίµου αποτελούµενο από Ni/YSZ-κεραµοµεταλλικό (άνοδος) – YSZ (ηλεκτρολύτη) – LaMnO3 περοβσκίτης (κάθοδος) – LaCrO3 περοβσκίτης (συνδέτης) είναι η υποβάθµιση της απόδοσής του, η οποία µεταξύ άλλων οφείλεται και στην αστάθεια της µικροδοµής του κεραµοµεταλλικού ηλεκτροδίου της ανόδου, λόγω συσσωµάτωσης της µεταλλικής φάσης. Στόχος της εργασίας ήταν η βελτίωση της ευστάθειας της µικροδοµής, καθώς και η διερεύνηση της δυνατότητας ελάττωσης του ποσοστού συµµετοχής της µεταλλικής φάσης στο κεραµοµεταλλικό υλικό του ηλεκτροδίου της ανόδου, χωρίς σηµαντική απώλεια σε ηλεκτρική αγωγιµότητα. Για τον σκοπό αυτό παρασκευάσθηκαν, χαρακτηρίσθηκαν και ελέγχθηκαν οι ιδιότητες µικτών κεραµικών οξειδίων επιλεγµένων συνθέσεων του τριµερούς συστήµατος ZrO2-Y2O3-TiO2 (η Cr2O3) καθώς και τα αντίστοιχα κεραµοµεταλλικά Ni/ZrO2-Y2O3-TiO2 µε προσθήκη 30,40 και 45 vol% Ni. Aπό τα αποτελέσµατα προέκυψε ότι σε θερµοκρασία πύρωσης 1400ºC σχηµατίζονται µικτά οξείδια µε την κυβική δοµή του πλέγµατος φθορίτη και συντελεστή θερµικής διαστολής αντίστοιχο του ηλεκτρολύτη (YSZ). Η ηλεκτρική τους αγωγιµότητα σε ατµόσφαιρα Ar+4%H2 είναι µικτού τύπου (ιοντική + ηλεκτρονιακή), όµως λόγω της χαµηλής απόλυτης τιµής στην θερµοκρασιακή περιοχή λειτουργίας του κελίου καυσίµου (900-1000ºC) δεν προσφέρονται για χρήση αυτούσια, ως κεραµικές άνοδοι. ΠΕΡΙΛΗΨΗ-ABSTRACT 6 Από πειράµατα διαβροχής στο σύστηµα Ni σε επαφή µε τα µικτά οξείδια προέκυψε ότι η παρουσία TiO2 βελτιώνει την συνάφεια και ως εκ τούτου την ισχύ του δεσµού στην διεπιφάνεια µετάλλου/κεραµικού. Η βελτίωση των διεπιφανειακών ιδιοτήτων έχει σαν αποτέλεσµα των ελάττωση του συντελεστού διαστολής των κεραµεταλλικών και την καλλίτερη µηχανική προσαρµογή τους στον ηλεκτρολύτη (YSZ).Επίσης, λόγω της µείωσης του ρυθµού συσσωµάτωσης των σωµατιδίων της µεταλλικής φάσης, οι τιµές της ηλεκτρικής αγωγιµότητας των κεραµοµεταλλικών παραµένουν σε υψηλά επίπεδα και µετά από µακροχρόνια παραµονή σε συνθήκες λειτουργίας (1000ºC, 1000h). Πρώτες ηλεκτροχηµικές µετρήσεις σε κελία καυσίµου µε κεραµοµεταλλική άνοδο, αποτελούµενη από επιλεγµένη σύνθεση µικτού οξείδίου του τριµερούς συστήµατος ως κεραµικής συνιστώσας, έδωσαν ενθαρρυντικά αποτελέσµατα αφήνοντας σηµαντικά περιθώρια για επίτευξη ικανοποιητικών επιδόσεων, µε βελτίωση του τρόπου κατασκευής. / Within the research framework for the development of alternative, friendly to the environment methods for the production of energy, significant effort is focusing on the SOFC’s (Solid Oxide Fuel Cell’s) technology. Due to their low pollutant emissions fuel cells can be applied inside civil areas were the electrical power can be used together with the thermal energy generated by the cell, increasing the total performance of the device. The “state of the art” fuel cell structure is the anode electrode (Ni/YSZ cermet), the electrolyte (YSZ), the cathode electrode (LaMnO3 perowskite) and the interconnector (LaCrO3 perowskite). One of the disadvantages of fuel cells is the performance degradation due to the instability of the YSZ/Ni anode electrode microstructure caused by metal phase sintering. This work aims to the improvement of microstructure stability as well as the possibility of reducing the amount of the metallic phase to the anode cermet without affecting its electrical properties. New ceramic materials of the ternary system ZrO2-Y2O3-TiO2 (or Cr2O3) were produced and characterized as well as their corresponding cermets Ni/ZrO2-Y2O3-TiO2 by the addition of 30,40 and 45 vol% Ni. After calcination at 1400ºC mixed oxides are formed having cubic fluorite crystal structure and similar thermal expansion properties to the YSZ ceramic oxide. The electrical conductivity in reducing atmosphere Ar+4%H2 is of electronic and ionic type but due to the low values in the working temperature range of a fuel cell (900-1000ºC) they cannot be used independently as anode materials. Wetting experiments of the system Ni in contact to those mixed oxides showed that TiO2 presence enhances the adherence and the bond strength at the metal ceramic interface. Improvement of the interfacial properties results to the decrease of cermets thermal expansion improving in this way the mechanical adjustment of the anode to the electrolyte. Also due to the decrease of the sintering tendency of the metallic phase particles, the electrical conductivity values remain at high values after long term annealing at high temperature (1000ºC, 1000h). Early electrochemical tests performed to fuel cells having a selected anode material showed encouraging results leaving space for improvement especially to the construction methods used in order to achieve satisfactory performance.

Human’s energy demand is growing and there is a necessity to solve questions of sustainable energetics, such as security of energy supply, energy efficiency and environment protection. Possible way of the solution of these problems is new and more efficient technologies and new energy sources. Fuel cells are one of the developing and environmentally clean technologies. This master’s report is dealing with cogeneration technologies and only fuel cells are analyzed thoroughly. Most usable type of fuel cells for decentralized power and heat generation is identified and its operating principles and properties are analyzed. Advantages and disadvantages of solid oxide fuel cells are given. Power of the fuel cell is chosen in the particular case, when energy demand of building complex of the hospital is analyzed. The fuel cell is integrated into the energy supply system with other equipment. There are made several alternatives to estimate the operation of the system technologically and economically. The simple pay back period and the net present value are used to estimate economical benefit of the system, when prices of energetic sources and fuel cells are varied. Finally, academic knowledge and calculation results are summarized and conclusions of the final report are given.

High temperature proton conducting perovskite oxides are very attractive materials for applications in electrochemical devices, such as solid oxide fuel cells (SOFCs) and hydrogen permeation membranes. A better understanding of the hydrogen oxidation mechanism over the metal/proton conductor interface, is critical for rational design to further enhance the performances of the applications. However, kinetic studies focused on the metal/proton system are limited, compared with the intensively studied metal/oxygen ion conductor system, e.g., Ni/YSZ (yttrium stabilized zirconia, Zr₁-ₓYₓO₂-δ). This work presents an elementary kinetic model developed to assess reaction pathway of hydrogen oxidation/reduction on metal/proton conductor interface. Individual rate expressions and overall hydrogen partial pressure dependencies of current density and polarization resistance were derived in different rate limiting cases. The model is testified by tailored experiments on Pt/BaZr₀.₁Ce₀.₇Y₀.₁Yb₀.₁O₃-δ (BZCYYb) interface using pattern electrodes. Comparison of electrochemical testing and the theoretical predictions indicates the dissociation of hydrogen is the rate-limiting step (RLS), instead of charge transfer, displaying behavior different from metal/oxygen ion conductor interfaces. The kinetic model presented in this thesis is validated by high quantitative agreement with experiments under various conditions. The discovery not only contributes to the fundamental understanding of the hydrogen oxidation kinetics over metal/proton conductors, but provides insights for rational design of hydrogen oxidation catalysts in a variety of electrochemical systems.

Made available in DSpace on 2014-12-17T14:07:01Z (GMT). No. of bitstreams: 1 SamaraMV_DISSERT.pdf: 3021267 bytes, checksum: 443b2ba79e877562b95c18cd66a9716c (MD5) Previous issue date: 2012-03-22 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / Cells the solid oxide fuel are systems capable to directly convert energy of a chemical reaction into electric energy in clean, quiet way and if its components in the solid state differentiate of excessively the techniques for having all. Its more common geometric configurations are: the tubular one and to glide. Geometry to glide beyond the usual components (anode, cathode and electrolyte) needs interconnect and sealant. E the search for materials adjusted for these components is currently the biggest challenge found for the production of the cells. The sealants need to present chemical stability in high temperatures, to provoke electric isolation, to have coefficient of compatible thermal expansion with the excessively component ones. For presenting these characteristics the glass-ceramics materials are recommended for the application. In this work the study of the partial substitution of the ZrO2 for the Al2O3 in system LZS became it aiming at the formation of system LZAS, this with the addition of natural spodumene with 10, 20 and 30% in mass. The compositions had been casting to a temperature of 1500?C and later quickly cooled with the objective to continue amorphous. Each composition was worn out for attainment of a dust with average diameter of approximately 3?m and characterized by the techniques of DRX, FRX, MEV, dilatometric analysis and particle size analysis. Later the samples had been conformed and treated thermally with temperatures in the interval between 700-1000 ?C, with platform of 10 minutes and 1 hour. The analyses for the treated samples had been: dilatometric analysis, DRX, FRX, electrical conductivity and tack. The results point with respect to the viability of the use of system LZAS for use as sealant a time that had presented good results as isolating electric, they had adhered to a material with similar ? of the components of a SOFC and had presented steady crystalline phases / Pilhas a combust?vel de ?xido s?lido (PaCOS) s?o sistemas capazes de converter energia de uma rea??o qu?mica diretamente em energia el?trica de maneira limpa, silenciosa e se diferenciam das demais t?cnicas por ter todos os seus componentes no estado s?lido. Suas configura??es geom?tricas mais comuns s?o: a tubular e a planar. A geometria planar al?m dos componentes usuais (anodo, catodo e eletr?lito) necessita de interconectores e selantes. E a busca por materiais adequados para esses componentes ? atualmente o maior desafio encontrado para a produ??o das pilhas. Os selantes precisam apresentar estabilidade qu?mica em altas temperaturas, provocar isolamento el?trico e ter coeficiente de dilata??o t?rmica compat?vel com os demais componentes. Por apresentarem essas caracter?sticas os materiais vitrocer?micos s?o os mais recomendados para a aplica??o. Neste trabalho fez-se o estudo da substitui??o parcial da Zr02 pela Al2O3 no sistema LZS visando a forma??o do sistema LZAS, isso com a adi??o 10, 20 e 30% em massa de espodum?nio natural. As composi??es foram fundidas a uma temperatura de 1500?C e depois resfriadas rapidamente com o objetivo de continuarem amorfas. Cada composi??o foi mo?da para obten??o de um p? com di?metro m?dio de aproximadamente 3?m e caracterizada pelas t?cnicas de DRX, FRX, MEV, dilatometria e granulometria. Posteriormente as amostras foram preparadas por compacta??o e tratadas termicamente com temperaturas no intervalo entre 700-1000 ?C, com patamar de 10min e 1h. As an?lises para as amostras tratadas foram: dilatometria, DRX, FRX, condutividade el?trica e ader?ncia. Os resultados apontam para a viabilidade do sistema LZAS para uso como selante uma vez que apresentaram bons resultados como isolante el?trico, aderiram a um material com coeficiente de dilata??o t?rmica (?) semelhante a dos componentes de uma PaCOS e apresentaram fases cristalinas est?veis / 2020-01-01

Made available in DSpace on 2014-12-17T14:07:09Z (GMT). No. of bitstreams: 1 AmandaLM_DISSERT.pdf: 3676559 bytes, checksum: 256cb3ce22bbf3b5f114a2ff3021de96 (MD5) 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

Made available in DSpace on 2014-10-09T12:53:18Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:59:02Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

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Made available in DSpace on 2014-10-09T12:26:10Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:18Z (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:04/00364-3