This dissertation presents chemical sensors that are based on an emerging optical fiber sensing technology for the determination of the presence and concentration of hydrogen peroxide (H2O2) at low concentrations. The motivation to determine hydrogen peroxide lies on the fact that this chemical species is generated as a by-product of the operation of hydrogen-based polymer electrolyte membrane fuel cells (PEMFCs), and the presence and formation of this peroxide has been associated with the chemical degradation that results in low durability of PEMFCs. Currently, there are no techniques that allow the hydrogen peroxide to be determined in situ in PEMFCs in a reliable manner, since the only report of this type of measurement was performed using electrochemical techniques, which can be affected by the environmental conditions and that can alter the proper operation of the PEMFCs. The sensors presented in this dissertation are designed to detect the presence and quantify hydrogen peroxide in solution at the conditions at which PEMFCs operate. Since they are made using fused silica optical fibers and are based on a spectroscopic technique to perform the detection of H2O2 , they are not affected by the electromagnetic fields or the harsh chemical environment inside PEMFCs. In addition, they are able to still detect the presence of H2O2 at the operating temperatures. The construction of the sensing film on the tip of an optical fiber and its small size (125 µm diameter), make the sensors here developed an ideal solution for being deployed in situ in PEMFCs, ensuring that they would be minimally invasive and that the operation of the fuel cell would not be compromised by the presence of the sensor. The sensors developed in this dissertation not only present design characteristics that are applicable to PEMFCs, they are also suitable for applications in other fields such as environmental, defense, and biological processes. / Graduate / 0548 / 0756 / 0791 / jfbotero@gmail.com

This dissertation presents chemical sensors that are based on an emerging optical fiber sensing technology for the determination of the presence and concentration of hydrogen peroxide (H2O2) at low concentrations. The motivation to determine hydrogen peroxide lies on the fact that this chemical species is generated as a by-product of the operation of hydrogen-based polymer electrolyte membrane fuel cells (PEMFCs), and the presence and formation of this peroxide has been associated with the chemical degradation that results in low durability of PEMFCs. Currently, there are no techniques that allow the hydrogen peroxide to be determined in situ in PEMFCs in a reliable manner, since the only report of this type of measurement was performed using electrochemical techniques, which can be affected by the environmental conditions and that can alter the proper operation of the PEMFCs. The sensors presented in this dissertation are designed to detect the presence and quantify hydrogen peroxide in solution at the conditions at which PEMFCs operate. Since they are made using fused silica optical fibers and are based on a spectroscopic technique to perform the detection of H2O2 , they are not affected by the electromagnetic fields or the harsh chemical environment inside PEMFCs. In addition, they are able to still detect the presence of H2O2 at the operating temperatures. The construction of the sensing film on the tip of an optical fiber and its small size (125 µm diameter), make the sensors here developed an ideal solution for being deployed in situ in PEMFCs, ensuring that they would be minimally invasive and that the operation of the fuel cell would not be compromised by the presence of the sensor. The sensors developed in this dissertation not only present design characteristics that are applicable to PEMFCs, they are also suitable for applications in other fields such as environmental, defense, and biological processes. / Graduate / 0548 / 0756 / 0791 / jfbotero@gmail.com

In this work, a broad range of analytical methods was applied to the study of the following three materials systems: yttria-stabilised zirconia (YSZ), samarium-doped ceria (SDC) and SDC-supported metal catalysts. YSZ and SDC were studied in the light of their application as solid electrolytes in Solid Oxide Fuel Cells. The SDC-supported metal catalysts were evaluated for application in the reforming of methanol. The conductive properties of YSZ pellets derived from powders of different Y contents and particle size ranges were investigated using Impedance Spectroscopy (IS). Comparative studies of the crystallography (by X-ray Powder Diffraction (XRD)), morphology (by Scanning and Transmission Electron Microscopy (SEM, TEM)), chemical composition (by Energy Dispersive X-ray Spectroscopy (EDX) and Inductively Coupled Plasma Mass Spectroscopy (ICP-MS)) and sintering behaviour (dilatometry) were employed in the overall assessment of the conductivity results collected. Detailed studies of three SDC compositions were performed on nanopowders prepared by a low temperature method developed in the Baker group. Modifications led to a simple and reliable method for producing high quality materials with crystallites of ~10 nm diameter. The products were confirmed by XRD and TEM to be single-phase materials. Thermogravimetric analysis, dilatometry, specific surface area determination, elemental analysis and IS were carried out on these SDC powders. The relationships between particle size, chemical composition, sintering conditions and conductivity were studied in detail allowing optimum sintering conditions to be identified and ionic migration and defect association enthalpies to be calculated. Finally, the interesting results obtained for the SDC nanopowders were a driving force for the preparation of SDC-supported metal catalysts. These were prepared by three different methods and characterised in terms of crystallographic phase, specific surface area and bulk and surface chemical composition. Isothermal catalytic tests showed that all catalysts had some activity for the reforming of methanol and that some compositions showed both very high conversions and high selectivities to hydrogen. These catalysts are of interest for further study and possibly for commercial application.

Made available in DSpace on 2014-10-09T12:42:20Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:59:42Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:42:20Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:59:42Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Sistemas de PEMFC são capazes de gerar energia elétrica com alta eficiência e baixa ou nenhuma emissão de poluentes, porém questões de custo e durabilidade impedem sua ampla comercialização. Nesse trabalho foi desenvolvido um MEA com eletrocatalisadores à base de paládio. Foram sintetizados e caracterizados eletrocatalisadores Pd/C, Pt/C e Ligas PdPt/C com diferentes razões entre metais e carbono. Foi realizado um estudo da razão entre ionômero de Nafion e eletrocatalisador para formação de triplas fases reacionais de máximos desempenhos, criado um modelo matemático para transpor esse ajuste para eletrocatalisadores com diferentes razões entre metal e suporte, considerando os aspectos volumétricos da camada catalisadora, e então realizado um estudo da espessura da camada catalisadora. Para as caracterizações foram utilizadas as técnicas de Difração de Raios-X, Microscopias Eletrônicas de Transmissão e de Varredura, Energia Dispersiva de Raios-X, Picnometria a Gás, Porosimetria por Intrusão de Mercúrio, Adsorção de Gás, segundo as equações de BET e BJH, Análise Termo Gravimétrica e feitas as determinações de diâmetros de partículas, de áreas de superfície específica e de parâmetros de rede. Todos os eletrocatalisadores foram usados no preparo de MEAs que foram avaliados em célula unitária de 5 cm2 entre 25 e 100 °C a 1 atm; e a melhor composição foi avaliada também a 3 atm. No estudo dos metais para as reações, visando reduzir a platina aplicada aos eletrodos, sem perdas de desempenho, foram selecionados Pd/C para ânodos e PdPt/C 1:1 para cátodos. A estrutura de MEA desenvolvida utilizou 0,25 mgPt.cm-2 e resultou em densidades de potência de até 550 mW.cm-2 e potências de até 2,2 kWe por grama de platina. A estimativa realizada mostrou que houve uma redução de até 64,5 % nos custos em relação à estrutura de MEA previamente conhecida. Em função da temperatura e pressão de operação foram obtidos valores a partir de R$ 3.540,73 para o preparo de MEAs para cada quilowatt instalado. Com base em estudos recentes, concluiu-se que o custo do MEA desenvolvido é compatível às aplicações estacionárias de PEMFC. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP / FAPESP: 10/10028-1

Submitted by Pedro Silva Filho (pfsilva@ipen.br) on 2017-11-22T16:42:40Z No. of bitstreams: 0 / Made available in DSpace on 2017-11-22T16:42:40Z (GMT). No. of bitstreams: 0 / Neste trabalho foi estudado o efeito da adição de íons haletos (Cl-, Br- e I-) sobre a morfologia das nanopartículas de Pt na produção de catalisadores de Pt/C e PtSnO2/C. Foi desenvolvida uma metodologia de síntese simples capaz de produzir nanopartículas de Pt predominantemente cúbicas com orientação preferencial Pt(100), diretamente suportadas em carbono sem o uso de agentes estabilizantes. Brometo de potássio foi utilizado como agente direcionador de superfície para obtenção do material preferencialmente orientado. O controle de adição do precursor de Pt e de KBr foi crucial para obter nanocubos de Pt de 8 nm bem dispersos sobre o suporte. Na preparação dos catalisadores de PtSnO2/C, o processo de adição do SnCl2 também foi decisivo na obtenção das nanopartículas de Pt com tamanho e morfologia de interesse. Nanocubos de Pt coexistindo com SnO2 disperso foram exclusivamente obtidos ao adicionar o SnCl2 na etapa final da síntese, quando as nanopartículas cúbicas de Pt já estavam formadas. Enriquecidos de domínios Pt(100), os materiais em forma cúbica de Pt/C e PtSnO2/C se mostraram menos afetados pelo acúmulo dos intermediários indesejados provenientes da reação de eletro-oxidação de etanol e foram mais tolerantes ao envenenamento por monóxido de carbono. Resultados similares foram observados para a oxidação de CO e metanol, utilizados como apoio para compreensão da eletro-oxidação de etanol. O efeito morfológico destes materiais no desempenho elétrico em célula a combustível de etanol direto foi avaliado. Pt/C e PtSnO2/C contendo nanopartículas de Pt com orientação preferencial Pt(100) forneceram maiores valores de densidade de potência e de seletividade para CO2 comparados aos catalisadores de Pt/C e PtSnO2/C com nanopartículas de Pt sem orientação preferencial. / Tese (Doutorado em Tecnologia Nuclear) / IPEN/T / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

In response to growing concerns regarding global warming and climate change, reduction of CO2 emissions becomes a priority for many countries, especially the developed ones such as the UK. Residential applications are considered among the most important areas for substantial reduction of CO2 emissions because they represent a major part of the total consumed energy in those countries. For instance, in the UK, residential applications are currently accountable for about 150 Mt CO2 emissions, which represents approximately 25% of the whole CO2 emissions [1-2]. In order to achieve a significant CO2 reduction, many strategies must be adopted in the policy of these countries. One of these strategies is to introduce micro combined heat and power (μCHP) systems into residential energy systems, since they offer several advantages over traditional systems. A significant amount of research has been carried out in this field; however, in terms of integrating such systems into residential energy systems, significant work is yet to be conducted. This is because of the complexity of these systems and their interdependency on many uncertain variables, energy demand of a house is a case in point. In order to achieve such integration, this research focuses on the optimisation and operation of μCHP systems in residential energy systems as essential steps towards integration of these systems, so it deals with the optimisation and operation of a μCHP system within a building taking into account that the system is grid-connected in order to export or import electricity in certain cases. A comprehensive review that summarises key points that outline the trend of previous research in this field has been carried out. The reviewed areas include: technologies used as residential μCHP units, modelling of the μCHP systems, sizing of μCHP systems and operation strategies used for such systems. To further this, a generic model for sizing of μCHP system’s components to meet different residential application has been developed by the author. Two different online operation strategies of residential μCHP systems, namely: an online linear programming optimiser (LPO) and a real time fuzzy logic operation strategy (FLOS) have been developed. The performance of the novel online operation strategies, in terms of their ability to reduce operation costs, has been evaluated. Both the LPO and the FLOS were found to have their advantages when compared with the traditional operation strategies of μCHP systems in terms of operation costs and CO2 emissions. This research should therefore be useful in informing design and operation decisions during developing and implementing μCHP technologies in residential applications, especially single dwellings.

D. Tech. (Department of Mechanical Engineering, Faculty of Engineering and Technology), Vaal University of Technology. / On account of their lightweight, low-cost, corrosion resistance, and good formability, conductive polymer composites (CPCs) are promising for the production bipolar plate (BP) for polymer electrolyte membrane fuel cell (PEMFC). However, a high conductive filler loading is needed to impart the required level of electrical conductivity to the insulating polymer matrix and as a consequence, the toughness of the plate deteriorates considerably. By using immiscible blend of polymers that have complementary hardness and ductility as matrix, with conducting multi-fillers of different morphologies, it is possible to optimize the matrix strength characteristics and favour the formation of conducting network to produce CPC meeting BP performance standards. Of course, a lot will depend on the formulation of the most favourable composition and production variables. In this regard, polypropylene-epoxy and polyethylene-epoxy blends, filled with zero- and two-dimensional carbon forms – graphite, carbon black (CB), and graphene (Gr) – were investigated over an extensive range of compositions and compression moulding pressures, in this study. Several compounding runs (using melt mixing), at different stages, followed by compression molding, were done. The goal is to obtain combination of composite formulation and processing conditions that will produce the most promising combination of properties for BP application. In the first stage of the investigations, by using thermogravimetric analysis, two-stage decomposition behavior of PP-epoxy and PE-epoxy blends was revealed, which confirms the immiscibility of PP and PE with epoxy resin. Scanning electron microscope (SEM) micrographs of the PP-epoxy and PE-epoxy blends revealed a co-continuous structure, which can be attributed to the close-to-symmetric composition of the blend and compatibilizers added. Preferential localization of synthetic graphite (SG), CB, and Gr in the polymer blends was also revealed by the SEM micrographs. This confirms the fact that CPCs based on PP-epoxy and PE-epoxy blends can be explored further. PP-epoxy and PE-epoxy blends filled with only SG, 30 – 80 wt %, were produced and characterized for their electrical conductivity and flexural properties. In-plane electrical conductivity ranged from 12.09 to 68.03 Scm-1 for PP-epoxy/SG and 11.68 to 72.96 Scm-1 for PE-epoxy/SG composites produced. These are higher than values reported for several single matrix polymer composites at similar filler loadings. With reference to the United States Department of Energy performance targets for BPs, PE-epoxy/SG composites performed better in terms of electrical conductivity, while PP-epoxy/SG composites exhibited better flexural properties. Thereafter, using SG and CB double filler, PE-epoxy/SG/CB composites performed better than PP-epoxy/SG/CB composites in terms of electrical conductivity, while PP-epoxy/SG/CB composites exhibited superior flexural properties than the PE-epoxy/SG/CB composites at similar filler loadings. However, with respect to the DOE targets, composites based on PP-epoxy blend exhibited a more promising combination of electrical conductivity and flexural properties than PE-epoxy blend matrix. PP-epoxy filled with SG/CB was studied further, by using graphene (Gr) as second minor filler. In-plane and through plane electrical conductivities as well as thermal conductivity and thermal diffusivity of the PP-epoxy/SG/CB/Gr composites increased as total filler content was increased from 65 to 85 wt%. It implies that more conductive networks between filler particles were formed. Also, flexural strength, flexural modulus, and impact strength decreased as the total filler content increased from 65 to 85 wt%. The reduced flexural properties could be due to increased agglomeration of CB and Gr, and poor filler wetting at higher filler loadings and low matrix material, which leads to the formation of microvoids and a reduction of the load bearing capacity of composites. With respect to the DOE targets, PP-EP/SG/CB/Gr composite with 80 wt% (i.e., PP/EP/73G/6.2CB/0.8Gr) filler has the best combination of properties. Further improvement in properties of the PP-EP/SG/CB/Gr composite with 80 wt% filler was achieved by molding at higher pressures. As molding pressure was increased from 4.35 to 13.05 MPa, in-plane electrical conductivity increased from 116.31 to 144.99 Scm-1, while flexural strength increased from 29.62 to 42.57 MPa, satisfying the performance requirement targets for bipolar plates.

Solid Oxide Fuel Cells are fuel cells that operate at high temperatures usually in the range of 600oC to 1000oC and employ solid ceramics as the electrolyte. In Solid Oxide Fuel Cells oxygen ions (O2- ) are the ionic charge carriers. Solid Oxide Fuel Cells are known for their higher electrical efficiency of about 50-60% [1] compared to other types of fuel cells and are considered very suitable in stationary power generation applications. It is very important to study the effects of different parameters on the performance of Solid Oxide Fuel Cells and for this purpose the experimental or numerical simulation method can be adopted as the research method of choice. Numerical simulation involves constructing a mathematical model of the Solid Oxide Fuel Cell and use of specifically designed software programs that allows the user to manipulate the model to evaluate the system performance under various configurations and in real time. A model is only usable when it is validated with experimental results. Once it is validated, numerical simulation can give accurate, consistent and efficient results. Modeling allows testing and development of new materials, fuels, geometries, operating conditions without disrupting the existing system configuration. In addition, it is possible to measure internal variables which are experimentally difficult or impossible to measure and study the effects of different operating parameters on power generated, efficiency, current density, maximum temperatures reached, stresses caused by temperature gradients and effects of thermal expansion for electrolytes, electrodes and interconnects. iv Since Solid Oxide Fuel Cell simulation involves a large number of parameters and complicated equations, mostly Partial Differential Equations, the situation calls for a sophisticated simulation technique and hence a Finite Element Method (FEM) multiphysics approach will be employed. This can provide three-dimensional localized information inside the fuel cell. For this thesis, COMSOL Multiphysics® version 4.2a will be used for simulation purposes because it has a Batteries & Fuel Cells module, the ability to incorporate custom Partial Differential Equations and the ability to integrate with and utilize the capabilities of other tools like MATLAB ® , Pro/Engineer® , SolidWorks® . Fuel Cells can be modeled at the system or stack or cell or the electrode level. This thesis will study Solid Oxide Fuel Cell modeling at the cell level. Once the model can be validated against experimental data for the cell level, then modeling at higher levels can be accomplished in the future. Here the research focus is on Solid Oxide Fuel Cells that use hydrogen as the fuel. The study focuses on solid oxide fuel cells that use 3-layered, 4-layered and 6-layered electrolytes using pure YSZ or pure SCSZ or a combination of layers of YSZ and SCSZ. A major part of this research will be to compare SOFC performance of the different configurations of these electrolytes. The cathode and anode material used are (La0.6Sr0.4)0.95-0.99Co0.2Fe0.8O3 and Ni-YSZ respectively

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