Ordered mesoporous materials have attracted much attention recently for use in a wide range of applications. The oxidising materials, ceria (CeO₂) and CGO (Ce₀.₉Gd₀.₁O[subscript(2-δ)]) have both been synthesised with ordered mesopores, but a method for the simple fabrication of these materials in high yields with crystalline pore walls has not yet been reported in the literature. This thesis details the development of the vacuum impregnation method for the synthesis of ordered mesoporous materials with emphasis on ceria and CGO. Using the vacuum impregnation method both materials were successfully prepared. The materials exhibited the porous single crystal morphology in high yields, with unusual crystallographic features. Nitrogen physisorption, transmission electron microscopy (TEM), TEM tomography and temperature programmed studies were employed. Temperature programmed studies showed the materials to be catalytically active at lower temperatures than traditionally-prepared ceria. Photovoltaic studies showed that the materials exhibited efficient exciton quenching. The observation of nanowire extrusion during the synthetic procedure assisted in the postulation of a mechanism for product formation in the vacuum impregnation method. The vacuum impregnation method was subsequently shown to be applicable to the synthesis of other materials, with encouraging results presented for ordered mesoporous carbon and Zr₀.₈₄Y₀.₁₆O[subscript(2-δ)]. The syntheses of ordered mesoporous La₀.₈₅Sr₀.₁₅GaO[subscript(3-δ)] and La₀.₇₆Sr₀.₁₉CoO[subscript(3-δ)] were unsuccessful.

O uso e estudo de materiais híbridos para desenvolver novos materiais com qualidades superiores para aplicações em fotônica, sensores e áreas afins é um desafio para o químico. Neste contexto deve-se especular sobre as propriedades de associação de materiais orgânicos e inorgânicos para alcançar novas e melhores propriedades. Neste estudo, os óxidos metálicos (óxidos de cério em particular), uma classe especial entre nanopartículas inorgânicas, foram selecionados para explorar as suas aplicações com uma classe, também especial de compostos orgânicos, sendo no nosso estudo as Naftaleno Diimidas. Óxido de cério é um semicondutor, com uma “bandgap” larga, conhecido por sua capacidade catalítica e por sua simples manipulação para preparar filmes finos e nanopartículas. Derivados de Naftaleno Diimidas são conhecidos por sua superior atividade eletroquímica comparáveis aos dos Paraquat (metilviologênio), mas com amplitude maior de aplicações fotoquímicas. Foram sintetizadas Naftaleno Diimidas carregados positivamente e negativamente com propriedades surfactantes. Após a caracterização detalhada das Naftaleno Diimidas, incluindo auto-associação e interação com moléculas de surfactantes, a interação com nanopartículas de óxido de cério foram determinadas. As Naftaleno Diimidas interagiram de forma especial com nanopartículas de óxido de cério conferindo ausência de atividade hidrolítica e um comportamento fotocrômico singular. Propõe-se que o corante orgânico se adsorve nas ranhuras das nanopartículas e, além disso forma dímeros estáveis que têm importância para as novas fotoatividades observadas. / The use and study of hybrid materials is a challenge for the chemist to develop materials having new and superior qualities for applications in photonics, sensors and related areas. In this context one has to speculate on the properties of the organic and inorganic partners to achieve better and new properties. In this study the metal oxides (in particular Cerium Oxides), a special class among inorganic nanoparticles were selected to exploit their applications with an also special class of organic compounds the Naphthalene Diimides. Cerium Oxide is a wide bandgap semiconductor well known for its catalytic capabilities and for its simple manipulation to prepare thin films and nanoparticles. Naphthalene Diimides derivatives are known for their superior lectrochemical activities comparable to those of Paraquat (Methyl Viologen) but with larger amplitude of photochemical applications. Positively and negatively charged, surfactant like, Naphthalene Diimides, were synthesized. After detailed characterization of the Naphthalene Diimides including selfassociation and interaction with surfactant molecules, the interaction with Cerium Oxide nanoparticles was determined. Naphthalene Diimides interacted in a special manner with Cerium Oxide nanoparticles rendering hydrolytic inertness and novel photochromic behavior. The organic dye is proposed to adsorb in the crevices of the particles and furthermore forming stable dimers that accounts for the new photoactivities observed

La synthèse contrôlée de nanoparticules constitue toujours un enjeu majeur en science des matériaux (pour des applications telles que la catalyse par exemple) et la voie «fluides supercritiques» permet de répondre en partie à ce challenge. Dans ce contexte, ce travail de thèse a été consacré à l’élaboration de nanostructures d’oxyde de cérium aux caractéristiques contrôlées (tailles, morphologies, propriétés de surface,…) par synthèse solvothermale supercritique. A partir de l’étude de l’influence des paramètres opératoires du procédé sur les caractéristiques physico-chimiques des nanomatériaux obtenus, des mécanismes de formation et de fonctionnalisation de surface ont été proposés. D’un point de vue applicatif, ces poudres ont été caractérisées qualitativement et quantitativement vis-à-vis de la capture réversible du CO2. / The controlled synthesis of nanoparticles remains of key importance in materials science (for applications such as catalysis for instance) and “supercritical fluids” processes allow partially addressing this challenge. In this context, this PhD work has been dedicated to the synthesis of cerium oxide nanostructures with controlled characteristics (size, morphology, surface property,…) by supercritical solvothermal approaches. Through the study of the influence of process operating parameters on physicochemical characteristics of the synthesized materials, formation and surface modification mechanisms have been proposed. From an applicative point of view, powders have been submitted to qualitative and quantitative characterization towards CO2 capture.

Submitted by LUIZIANA APARECIDA GONZAGA null (lugonzaga@outlook.com) on 2017-10-17T01:17:58Z No. of bitstreams: 1 Dissertação de Mestrado - Luiziana Gonzaga.pdf: 3098359 bytes, checksum: d7f683fd9ec29fe64f0d8885301dc5ca (MD5) / Approved for entry into archive by Monique Sasaki (sayumi_sasaki@hotmail.com) on 2017-10-18T18:59:58Z (GMT) No. of bitstreams: 1 gonzaga_la_me_rcla.pdf: 3098359 bytes, checksum: d7f683fd9ec29fe64f0d8885301dc5ca (MD5) / Made available in DSpace on 2017-10-18T18:59:58Z (GMT). No. of bitstreams: 1 gonzaga_la_me_rcla.pdf: 3098359 bytes, checksum: d7f683fd9ec29fe64f0d8885301dc5ca (MD5) Previous issue date: 2017-07-25 / Nos últimos anos, o estudo de materiais cerâmicos vem evoluindo muito rapidamente, principalmente os estudos relacionados com cerâmicas avançadas. As diversas aplicações envolvendo esses materiais, tais como pigmentos cerâmicos com partículas nanométricas, justificam cada vez mais a necessidade de uma melhor compreensão da influência da adição de dopantes nas propriedades finais dos materiais. No presente trabalho propõe-se analisar e estudar as propriedades estruturais e morfológicas de pigmentos cerâmicos a base de óxido de cério (CeO2) e dopados com diferentes porcentagens molares de lantânio (5 e 10%) e praseodímio (1%). Um dos principais objetivos foi obter pigmentos cerâmicos com tamanho de partícula nanométrico de baixa toxicidade. O processo químico adotado para a obtenção dos pós foi o método dos precursores poliméricos. As nanopartículas foram estruturalmente caracterizadas por difração de raios X (DRX), espectroscopia Raman e espectroscopia de absorção de raios X (XAS). A forma e o tamanho das nanopartículas foram observados por intermédio da microscopia eletrônica de varredura (MEV). A caracterização óptica foi realizada utlizando-se dos resultados de reflectância difusa para obtenção das coordenadas colorimétricas. Os padrões de DRX e espectros Raman indicam a formação de soluções sólidas cristalinas monofásicas com estrutura cúbica do tipo fluorita, pertencentes ao grupo espacial Fm3m. O tamanho dos grãos foi da ordem de 20 a 30 nanômetros, como estimado por MEV. Por reflectância difusa e coordenadas colorimétricas foi determinado que as amostras de CeO2 e CL (óxido de cério dopado com lantânio) possuem coloração amarela enquanto as amostras CLP (óxido de cério dopado com lantânio e praseodímio) e CP (óxido de cério dopado com praseodímio) possuem coloração que varia do magenta-alaranjado ao vermelho-amarronzado. Tonalidades mais intensas foram obtidas nos pigmentos dopados com praseodímio submetidos a tratamento térmico a 800 ºC. / In the last few years, the study of ceramic materials has increased very fast, mainly studies related to advanced ceramics. The several applications of these materials as ceramic pigments in nanometric scale justify more and more the need for a better understanding of the influence of the dopant addition on the final properties of the materials. In this present work, it was studied structural and morphological properties of ceramic pigments based on cerium oxide (CeO2) and doped with differents molar percentages of lanthanum (5 and 10%) and praseodymium (1%). The goal of this work was to obtain nanosized ceramic pigments with a low-toxicity. The chemical route adopted to obtain materials was the polymeric precursor method. The nanoparticles were structurally characterized by X-Ray Diffraction (XRD), Raman Spectroscopy, Scanning Electron Microscopy (SEM) and X-Ray absorption spectroscopy (XAS). Optical characterization was carried out using the results of diffuse reflectance to obtain the colorimetric coordinates. The XRD patterns and Raman spectra indicate the formation of crystalline solid solutions with single phase and cubic structure (fluorite), all belongs to the space group Fm3m. The obtained grain size was in nanoscale range, 20 to 30 nm, according to MEV. By diffuse reflectance tecnique and colorimetric coordinates were verified that the CeO2 and CL (cerium oxide doped with lanthanum) samples possess yellow coloration and the CLP (cerium oxide doped with lanthanum and praseodymium) and CP (cerium oxide doped with praseodymium) samples present coloration that varies from magenta-orange to red-brown. More intense shades were obtained in pigments doped with praseodymium at 800 ºC temperature.

abstract: As world energy demands increase, research into more efficient energy production methods has become imperative. Heterogeneous catalysis and nanoscience are used to promote chemical transformations important for energy production. These concepts are important in solid oxide fuel cells (SOFCs) which have attracted attention because of their potential to provide an efficient and environmentally favorable power generation system. The SOFC is also fuel-flexible with the ability to run directly on many fuels other than hydrogen. Internal fuel reforming directly in the anode of the SOFC would greatly reduce the cost and complexity of the device. Methane is the simplest hydrocarbon and a main component in natural gas, making it useful when testing catalysts on the laboratory scale. Nickel (Ni) and gadolinium (Gd) doped ceria (CeO2) catalysts for potential use in the SOFC anode were synthesized with a spray drying method and tested for catalytic performance using partial oxidation of methane and steam reforming. The relationships between catalytic performance and structure were then investigated using X-ray diffraction, transmission electron microscopy, and environmental transmission electron microscopy. The possibility of solid solutions, segregated phases, and surface layers of Ni were explored. Results for a 10 at.% Ni in CeO2 catalyst reveal a poor catalytic behavior while a 20 at.% Ni in CeO2 catalyst is shown to have superior activity. The inclusion of both 10 at.% Gd and 10 at.% Ni in CeO2 enhances the catalytic performance. Analysis of the presence of Ni in all 3 samples reveals Ni heterogeneity and little evidence for extensive solid solution doping. Ni is found in small domains throughout CeO2 particles. In the 20 at.% Ni sample a segregated, catalytically active NiO phase is observed. Overall, it is found that significant interaction between Ni and CeO2 occurs that could affect the synthesis and functionality of the SOFC anode. / Dissertation/Thesis / M.S. Materials Science and Engineering 2012

O uso e estudo de materiais híbridos para desenvolver novos materiais com qualidades superiores para aplicações em fotônica, sensores e áreas afins é um desafio para o químico. Neste contexto deve-se especular sobre as propriedades de associação de materiais orgânicos e inorgânicos para alcançar novas e melhores propriedades. Neste estudo, os óxidos metálicos (óxidos de cério em particular), uma classe especial entre nanopartículas inorgânicas, foram selecionados para explorar as suas aplicações com uma classe, também especial de compostos orgânicos, sendo no nosso estudo as Naftaleno Diimidas. Óxido de cério é um semicondutor, com uma “bandgap” larga, conhecido por sua capacidade catalítica e por sua simples manipulação para preparar filmes finos e nanopartículas. Derivados de Naftaleno Diimidas são conhecidos por sua superior atividade eletroquímica comparáveis aos dos Paraquat (metilviologênio), mas com amplitude maior de aplicações fotoquímicas. Foram sintetizadas Naftaleno Diimidas carregados positivamente e negativamente com propriedades surfactantes. Após a caracterização detalhada das Naftaleno Diimidas, incluindo auto-associação e interação com moléculas de surfactantes, a interação com nanopartículas de óxido de cério foram determinadas. As Naftaleno Diimidas interagiram de forma especial com nanopartículas de óxido de cério conferindo ausência de atividade hidrolítica e um comportamento fotocrômico singular. Propõe-se que o corante orgânico se adsorve nas ranhuras das nanopartículas e, além disso forma dímeros estáveis que têm importância para as novas fotoatividades observadas. / The use and study of hybrid materials is a challenge for the chemist to develop materials having new and superior qualities for applications in photonics, sensors and related areas. In this context one has to speculate on the properties of the organic and inorganic partners to achieve better and new properties. In this study the metal oxides (in particular Cerium Oxides), a special class among inorganic nanoparticles were selected to exploit their applications with an also special class of organic compounds the Naphthalene Diimides. Cerium Oxide is a wide bandgap semiconductor well known for its catalytic capabilities and for its simple manipulation to prepare thin films and nanoparticles. Naphthalene Diimides derivatives are known for their superior lectrochemical activities comparable to those of Paraquat (Methyl Viologen) but with larger amplitude of photochemical applications. Positively and negatively charged, surfactant like, Naphthalene Diimides, were synthesized. After detailed characterization of the Naphthalene Diimides including selfassociation and interaction with surfactant molecules, the interaction with Cerium Oxide nanoparticles was determined. Naphthalene Diimides interacted in a special manner with Cerium Oxide nanoparticles rendering hydrolytic inertness and novel photochromic behavior. The organic dye is proposed to adsorb in the crevices of the particles and furthermore forming stable dimers that accounts for the new photoactivities observed

Ceria based materials have attracted a great deal of interest particularly in area of UV shielding, oxide ion conductivity, solid state electrolyte for fuel cells, automotive exhaust catalysis, water gas shift (WGS) reaction catalysis and also in thermo-chemical water splitting cycles to generate hydrogen. Therefore great deal of efforts was devoted to synthesize nanocrystalline ceria and related materials with different shape and sizes. For example, hierarchically mesostructured doped CeO2 showed potential photvoltic response for solar cell applications. Substitution of lower valent metal ions (Ca2+, Gd3+, Tb3+, Sm3+) in CeO2 enhances oxide ion conductivity for solid oxide fuel cell applications. Eventhough ZrO2 is a nonreducible oxide, CeO2-ZrO2 solid solution has attracted a lot of attention in exhaust catalysis because it exhibited high oxygen storage capacity (OSC). Noble metal ion (M = Pt4+/2+, Au3+, Rh3+, Pd2+ and Ag+) substituted CeO2 (Ce1-xMxO2-δ and Ti1-xMxO2-δ, x = 0.01-0.03) prepared by solution combustion method have shown much higher three-way catalytic property compared same amount of noble metal impregnated to CeO2. Ionically substituted Pt and Au in CeO2 also showed high WGS activity. CeO2-MOx (M= Mn, Fe, Cu, Ni) mixed oxides have shown high activity for hydrogen generation by thermal splitting of water. In chapter 1, we have discussed recent developments on various synthesis strategies of ceria based materials for specific catalytic application. In this thesis, we have explored new route to synthesize Ce1-xMxO2-δ and Ti1-xMxO2-δ (M = transition metal, noble metal) nanocrystallites. Specifically we have addressed the effect of reducible metal ion substitution on the OSC of CeO2 for auto exhaust treatment, hydrogen generation and electro-chemical applications. Controlled synthesis of CeO2 and Ce1-xMxO2-δ (M = Zr, Ti, Y, Pr and Fe) nanocrystallites by hydrothermal method is presented in Chapter 2. The method is based on complexation of metal ion by diethylenetriamine (DETA) or melamine and the simultaneous hydrolysis of metal ion complexes in hydrothermal condition. Size of the crystallites can be controlled by varying the time and temperature of the reaction. 15% Fe3+ ion substituted CeO2 (Ce0.85Fe0.15O2-δ) nanocrystallites have shown higher oxygen storage capacity than Ce0.5Zr0.5O2 at lower temperature. A brief description of material characterization techniques such as powder X-ray diffraction (XRD) and Rietveld refinement of structure, high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) is presented. The home-built hydrogen uptake measurement system for OSC study and temperature programmed catalytic reaction system with a quadrupole mass spectrometer and an on-line gas-chromatograph for gas analysis is also described in this chapter. In chapter 3, hydrothermal synthesis of Ce1-xCrxO2+δ (0≤x≤1/3) nanocrystallites is presented. Up to 33% Cr ion substitution in CeO2 could be achieved only by the complexation of Ce(NH4)2(NO3)6 and CrO3 with DETA and simultaneous hydrolysis of the complexes in hydrothermal condition at 200 oC. Powder XRD, XPS and TEM studies confirm that the compound crystallizes in cubic fluorite structure where Ce exist in +4 oxidation state and Cr exist in 4+ and +6 (mixed valance) oxidation states in the ratio of 2: 1. Composition x = 0.33 (Ce2/3Cr1/3O2+δ) showed higher OSC (0.33 mol of [O]) than the maximum OSC observed for CeO2-ZrO2 solid solutions. Formation and higher OSC of Ce2/3Cr1/3O2+δ is attributed to interaction of Ce4+/3+ and Cr3+/4+/6+ redox couples in fluorite structure. The material shows oxygen evolution at ~400 oC in air and hence it is a true oxygen storage material. Oxygen evolution property of Ce0.67Cr0.33O2.11 and subsequent generation of hydrogen by thermal splitting of water is presented in chapter 4. Among the ceria based oxides, Ce0.67Cr0.33O2.11 being the only compound like UO2+δ to have excess oxygen possessing fluorite structure, it releases a large proportion of its lattice oxygen (0.167 M [O]/mole of compound) by heating the material under N2 flow at relatively low temperature (465 oC) directly and almost stoichiometric amount of H2 (0.152 M/Mol of compound) is generated at much lower temperature (65 oC) by thermosplitting of water. The reversible nature of oxygen release and intake of this material is attributed to its fluorite structure and internal coupling between the Ce4+/Ce3+ and Cr4+/6+/Cr3+ redox couples. In chapter 5, we present the hydrothermal synthesis and three-way catalytic activity of Ce1-xRuxO2-δ (0≤x≤0.1) nanocrystallites. Powder XRD, Rietveld refinement, TEM and XPS reveals that the compounds crystallized in fluorite structure where Ru exist in +4 state and Ce in mixed valent (+3, +4) state. Substitution of Ru4+ ion in CeO2 activated the lattice oxygen and Ce0.9Ru0.1O2-δ can reversibly releases 0.42[O]/mol of compound, which is higher than maximum OSC of 0.22 [O]/mol of compound observed for Ce0.50Zr0.50O2. Utilization of higher OSC of Ce1-xRuxO2-δ (x = 0.05 and 0.10) is also shown by low temperature CO oxidation with these catalysts, both in presence/absence of feed oxygen. Ru4+ ion act as active centre for reducing molecules (CO, hydrocarbon ‘HC’) and oxide ion vacancy acts as an active centre for O2 and NOx in this compound. Ce1-xRuxO2-δ not only act as a high oxygen storage material but it also shows high activity towards CO, hydrocarbon ‘HC’ oxidation and NO reduction by CO at low temperature with high N2 selectivity for 3-way catalysis. Study of water gas shift reaction over Ce0.95Ru0.05O2-δ catalyst is presented in chapter 6. The catalyst showed very high WGS activity in terms of high conversion rate (20.5 μmol.g-1.s-1 at 275 oC) and low activation energy (~50.6 kcal/mol). The reason for this seems to be high adsorption propensity of CO on Ru4+ ion and easy extraction of oxygen from lattice to form CO2. This step creates oxide ion vacancy in the catalyst lattice and H2O can adsorb on lattice sites oxygen vacancy and regenerate the lattice by releasing H2. Even in presence of externally fed CO2 and H2, complete conversion of CO to CO2 was observed with 100 % H2 selectivity with Ce0.95Ru0.05O2-δcatalyst in the temperature range of 305-385 oC and no trace of methane formation was observed in this temperature range. Catalyst does not deactivate in long duration on/off WGS reaction cycle because sintering of noble metal or active sites is avoided in this catalyst as Ru4+ ion is substituted in CeO2 lattice. Due to highly acidic nature of Ru4+ ion, surface carbonated formation is prohibited. In chapter 7, synthesis of Ce1-xFexO2-δ (0≤x≤0.45) and Ce0.65Fe0.33Pd0.02O2-δnanocrystallites is presented by sonochemical method. Powder XRD, XPS and TEM studies confirm that the compounds of ~4 nm sizes is crystallized in fluorite structure where Fe is in +3, Ce is in +4 and Pd is in +2 oxidation state. Due to substitution of smaller Fe3+ ion in CeO2, lattice oxygen is activated and Ce0.67Fe0.33O1.835 reversibly releases 0.31[O] up to 600 oC which is higher or comparable to the maximum OSC observed for CeO2-ZrO2 based solid solutions. Due to internal interaction of Pd2+/0(0.89 V), Fe3+/2+ (0.77 V) with Ce4+/3+ (1.61 V) redox couples, Pd ion accelerates the electron transfer from Fe2+ to Ce4+ in Ce0.65Fe0.33Pd0.02O1.815, making it a high oxygen storage material as well as highly active catalyst for CO oxidation and WGS reaction. Activation energy for CO oxidation with O2 over Ce0.65Fe0.33Pd0.02O1.815 is found as low as 38 kJ/mol. CO conversion to CO2 is 100% H2 specific in WGS reaction with these catalysts. Conversion rate was found as high 27.2 μmol.g-1.s-1 and activation energy was found 46.4 kJ/mol for Ce0.65Fe0.33Pd0.02O1.815. Only 1-3% Pt, Pd ion can be substituted in CeO2 is by the solution combustion method. We show that even up to 10% of Pt and Pd ion can be substituted in CeO2 by sonication method. In chapter 8, we present the sonochemical synthesis redox property and methanol electro-oxidation activity of hierarchical Ce1-xMxO2-δ (M = Pt and Pd, 0≤x≤0.1) nanocrystallites. Powder XRD, TEM, SEM and XPS study confirms that hierarchical structure compound crystallize in fluorite structure. Pt exists in +4 state and Ce in mixed valent (+3, +4) state in Ce1-xPtxO2-δ and Pd exist in +2 state and Ce in mixed valent (+3, +4) state in Ce1-xPdxO2-δ. Substitution of Pt and Pd ion in CeO2 activated the lattice oxygen. Hydrogen absorption study show higher H/Pt ratio ~8.1 and H/Pd ratio ~4.2 in respective oxides. Reversible nature of higher oxygen storage capacity or higher H/P, H/Pd ratio is due to interaction of redox couples of Pt4+/2+(0.91V), Pt2+/0(1.18V), Pd2+/0(0.92V) and Ce4+/3+(1.61V). Due to participation of lattice oxygen, Ce0.95Pt0.05O1.95 and Ce0.95Pd0.05O1.90 have shown higher electro-oxidation of methanol compared to same moles of Pt in 5%Pt/C. In chapter 9, we present sonochemical synthesis of Ti1-xPtxO2 (0≤x≤0.1) nanocrystallites: a new high capacity anode material for rechargeable Li ion battery. Continuing our interest in synthesis of nanomaterials, we thought if we can extend the same sonochemical method to synthesize metal ion doped TiO2. Doping of TiO2 with a suitable metal ion where dopant redox potential couples with that of titanium (Ti4+) and act as catalyst for additional reduction of Ti4+ to Ti2+ (Ti4+ →Ti3+→Ti2+) is envisaged here to enhance lithium storage even higher than one Li/TiO2. 10 atom % Pt ion substituted TiO2, Ti0.9Pt0.1O2 nanocrystallites of ~4 nm size was synthesized by sonochemical method using diethylenetriamine (DETA) as complexing agent. Powder XRD, Rietveld refinement, TEM and XPS studies reveal that Ti0.9Pt0.1O2 nanocrystallites crystallize in anatase structure and both Ti and Pt are in 4+ oxidation state. Due to Pt4+ ion substitution in TiO2, reducibility of TiO2 was enhanced and Ti4+ was reduced up to Ti2+ state via coupling of Pt states (Pt4+/Pt2+/Pt0) with Ti states (Ti4+/Ti3+/Ti2+). Galvanostatic cycling of Ti0.9Pt0.1O2 against lithium showed very high capacity of 430 mAhg-1 or exchange of ~1.5Li/Ti0.9Pt0.1O2 which is much higher than the highest capacity of 305 mAhg-1 or insertion of ~0.9Li/TiO2 achieved for TiO2(B) nanowires. In chapter 10, we present the conclusions and critical review on the study of transition metal and noble metal ion substituted CeO2 and TiO2.

A novel multilayer membrane electrode assembly (MEA) for polymer electrolyte membrane fuel cells (PEMFCs) is fabricated in this work, within a single spray-coating device. For the first time, direct membrane deposition is used to fabricate a PEMFC by spraying the short-side-chain ionomer Aquivion directly onto the gas diffusion electrodes. The fully sprayed MEA, with an Aquivion membrane 10 μm in thickness, achieved a high power density of 1.6 W/cm2 for H2/air operation at 300 kPaabs. This is one of the highest reported values for thin composite membranes operated in H2/air atmosphere. By the means of confocal laser scanning microscopy, individual carbon fibers from the gas diffusion layer are identified to penetrate through the micro porous layer (MPL), likely causing a low electrical cell resistance in the range of 150 Ω cm2 through the thin sprayed membranes. By spraying a 200 nm graphene oxide/cerium oxide (GO/CeO2) interlayer between two layers of Aquivion ionomer, the impact of the electrical short is eliminated and the hydrogen crossover current density is reduced to about 1 mA/cm2. The peak power density of the interlayer-containing MEA drops only by 10% compared to a pure Aquivion membrane of similar thickness.

The presented thesis focuses on studying the interaction between rhodium and cerium oxide and its impact on the reactivity. We investigated two different systems, Rh/CeOx and Rh-CeOx, by means of the photoelectron spectroscopy and the temperature programmed reactions. Rh/CeOx stands for rhodium nanoparticles supported by cerium oxide thin film. We show that there is an electronic metal-substrate interaction between rhodium and cerium oxide. The type of the interaction depends on a degree of cerium oxide reduction and it has a tremendous impact on the reactivity of the system. On the other hand, Rh-CeOx represents cerium oxide thin films doped by rhodium. We characterized the properties of the films with various concentration of rhodium. We show that the morphology, chemical composition and reactivity of the samples strongly depend on the concentration of the rhodium dopant. Powered by TCPDF (www.tcpdf.org)

Present doctoral thesis is focused on electron microscopy and spectroscopy investigation of novel metal-oxide anode catalyst for fuel cell application. Catalyst based on Pt- doped cerium oxide in form of thin layers prepared by simultaneous magnetron sputtering deposition on intermediate carbonaceous films grown on silicon substrate has been studied. The influence of catalyst support composition (a-C and CNx films), deposition time of CeOx layer and other deposition parameters, as deposition rate, composition of working atmosphere and Pt concentration on the morphology of Pt-CeOx layers has been investigated mainly by Transmission Electron Microscopy (TEM). The obtained results have shown that by suitable preparation conditions combination we are able to tune final morphology and composition of catalyst. Composition of carbonaceous films and Pt-CeOx layers was examined by complementary spectroscopy techniques - Energy Dispersive X-ray Spectroscopy (EDX), Electron Energy Loss Spectroscopy (EELS) and X-ray Photoelectron Spectroscopy (XPS). Such prepared porous structures of Pt-CeOx are of promising as anode catalytic material for real fuel cell application. Keywords: cerium oxide, platinum, fuel cell, magnetron sputtering, Transmission Electron Microscopy