It is desirable to increase the operation temperature of proton exchange membrane fuel cells above 100oC due to fast electrode kinetics, high tolerance to fuel impurities and simple thermal and water management. In this study / the objective is to develop a high temperature proton exchange membrane fuel cell. Phosphoric acid doped polybenzimidazole membrane was chosen as the electrolyte material. Polybenzimidazole was synthesized with different molecular weights (18700-118500) by changing the synthesis conditions such as reaction time (18-24h) and temperature (185-200oC). The formation of polybenzimidazole was confirmed by FTIR, H-NMR and elemental analysis. The synthesized polymers were used to prepare homogeneous membranes which have good mechanical strength and high thermal stability. Phosphoric acid doped membranes were used to prepare membrane electrode assemblies. Dry hydrogen and oxygen gases were fed to the anode and cathode sides of the cell respectively, at a flow rate of 0.1 slpm for fuel cell tests. It was achieved to operate the single cell up to 160oC. The observed maximum power output was increased considerably from 0.015 W/cm2 to 0.061 W/cm2 at 150oC when the binder of the catalyst was changed from polybenzimidazole to polybenzimidazole and polyvinylidene fluoride mixture. The power outputs of 0.032 W/cm2 and 0.063 W/cm2 were obtained when the fuel cell operating temperatures changed as 125oC and 160oC respectively. The single cell test presents 0.035 W/cm2 and 0.070 W/cm2 with membrane thicknesses of 100 &micro / m and 70 &micro / m respectively. So it can be concluded that thinner membranes give better performances at higher temperatures.

Membrane electrode assembly (MEA) is the foundation of the single cell as well as the core of the fuel cell when generating electricity. Its work efficiency is the key factor for single cell performance. This study aims to understand the variation between the conventional method and the decal method during the MEA process. By observing the microstructure morphology of electrode and the performance of single cell, as well as analyzing internal resistance and its stabilization, the advantages and disadvantages of MEA in the two methods is analyzed. The decal condition is 135¢XC, 15 kg/cm , 2.5 min at a high temperature (50¢XC 3M methanol), in air-breathing under atmosphere system. The maximum power density is approximately 22.5 mW/cm which is very close to the result of conventional method. The decal method is better than the conventional method particularly in regards to the high current density performance. It shows that there is an efficient influence of the decal method on the methanol mass transfer and it also improves its polarization and enlarges the current. If the single cell is operated in the high temperature, the fuel mass transfer can be advanced in the decal method and its performance can be raised. However, in the manufacturing process, more time has to be spent when producing the MEA. This experiment can be used as a reference on the single cell operation environment and manufacturing time for future studies.

A distinctive field in the coatings industry is the coating of porous media, with broad applications in paper, apparel, textile, electronics, bioengineering, filtration and energy sector. A primary industrial scale process that can be used to coat porous media in a fast and flexible manner is slot die extrusion. A major concern when coating porous media with a wetting fluid is fluid penetration into the substrate. Although some level of penetration is desirable to obtain specific material properties, inadequate or excessive fluid penetration can negatively affect the strength, functionality or performance of the resulting material. In spite of its apparent industrial importance, limited modeling and experimental work has been conducted to study fluid penetration into porous media during fabrication. The effects of processing parameters on the penetration depth, the effects of penetration on material quality, and the method to predict and control the penetration depth are not well understood. This dissertation is composed of two parts. Part I is an applied study for coating onto porous media. This part focuses on the first objective of this dissertation which is to elucidate clearly the feasibility, advantages and disadvantages of the direct coating method as a potential fabrication route for membrane electrode assembly (MEA). MEA samples are fabricated using both traditional and the direct coating methods. Then, the quality and performance of the MEA samples are examined. Experimental results in Part I demonstrate that it is feasible to fabricate MEAs using the direct coating method. However, Nafion® solution penetrates into the catalyst layer during the coating process and causes lower performance of fuel cells, which is the motivation for Part II of this thesis. The objective of Part II is to fundamentally understand the fluid penetration process and predict the penetration depth when directly coating porous media, using a comprehensive approach. A series of computational and analytical models are developed to predict the penetration depth for both Newtonian and non-Newtonian fluids with or without capillary pressure. Finally the accuracy of developed models are validated through experiments. The relative error between the predicted and experimentally measured penetration depth is generally lower than 20%.

Fuel cells are electrochemical energy devices that convert the chemical energy in a fuel into electrical energy. Although they are more efficient, clean, and reliable than fossil fuel combustion systems, they have not been widely adopted because of manufacturing challenges and high production cost. The most expensive component of a fuel cell is the membrane electrode assembly (MEA), which consists of an ionomer membrane coated with catalyst material. Best performing MEAs are currently fabricated by depositing and drying liquid catalyst ink on the membrane, however, this process is limited to individual preparation by hand due to the membrane’s rapid water absorption that leads to shape deformation and coating defects. This work models the swelling and drying phenomena of the membrane and coating during manufacturing, and then applies the results to develop and control a continuous coating line for the production of defect free fuel cell MEAs. A continuous coating line can reduce the costs and time needed to fabricate the MEA, incentivizing the commercialization and widespread adoption of fuel cells. Membrane swelling is a three-dimensional, transient, coupled mass transfer, heat transfer, and solid mechanics problem. Existing models describe the membrane’s behavior in operating conditions, but none predict the behavior during manufacturing. This work develops a novel physics-based model that describes the behavior of the membrane and coating in a continuous manufacturing scenario and incorporates effects that are missing from existing models. A model that can predict wrinkles, the most commonly observed defect during manufacturing, is presented. Simulation results from the above models are used to design and develop an improved continuous MEA coating process that includes pre-swelling and two-stage drying of the coated membrane. A prototype pilot-scale coating line to implement and test the improved coating process is designed and constructed. Finally, a Linear-Quadratic-Gaussian type controller is developed using the physics-based model of the manufacturing process to optimally control the temperature and humidity of the drying zones, and its effectiveness when implemented on the coating line is discussed. / text

Made available in DSpace on 2014-10-09T12:41:22Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:21Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:41:22Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:21Z (GMT). No. of bitstreams: 0 / Custo e durabilidade ainda são os maiores impeditivos para a entrada das células a combustível no mercado de dispositivos usados para produção de eletricidade. Assim, o objetivo deste trabalho foi avaliar a durabilidade dos conjuntos eletrodo-membrana-eletrodo (MEAs) produzidos no IPEN pelo método de impressão à tela para uso em células a combustível do tipo PEM. Para tanto, foi necessário desenvolver um protocolo adequado de teste de durabilidade de longa duração, visando obter estimativas da taxa de queda do potencial elétrico da célula a combustível ao longo do tempo e, assim, fazer inferência a respeito do tempo de vida deste dispositivo. Os MEAs testados durante este estudo foram preparados pelo método de impressão à tela com catalisador de Pt/C comercial e membrana Nafion® 115. O aprimoramento do protocolo de teste de durabilidade de longa duração se deu pela escolha dos procedimentos a serem executados e pelo ajuste de alguns parâmetros de operação da célula a combustível, tais como temperatura da célula, fluxo de H2 e fluxo de O2. Para a análise dos dados obtidos com os testes, foram aplicados métodos estatísticos de ajuste de modelos e curvas de polarização. Além disso, amostras da camada catalítica de um dos MEAs utilizados nos testes de durabilidade de longa duração foram analisadas por meio de microscopia eletrônica de transmissão (MET) para serem comparadas com amostras da camada catalítica de um MEA de controle. Para se avaliar o desempenho global da célula a combustível do tipo PEM em operações de longa duração, um dos grandes desafios foi fazer a separação entre as componentes de perda de desempenho que são reversíveis das irreversíveis. As estimativas obtidas para a taxa de queda do potencial elétrico da célula a combustível ao longo do tempo variaram num intervalo de 108,19 a 318,15 μV.h-1. Estes resultados podem ser considerados satisfatórios quando comparados com valores apresentados na literatura. Finalmente, as imagens obtidas por MET mostraram uma tendência de aumento no tamanho médio das partículas Pt em decorrência do tempo de operação dos MEAs, mas que não implicou numa queda significativa do desempenho das células a combustível do tipo PEM testadas. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Mechanical fatigue testing has shown that MEAs (membrane electrode assemblies) fail at lower stresses than PEMs (proton exchange membranes) at comparable times under load. The failure of MEAs at lower stresses is influenced by the presence of mud cracks in the catalyst layers acting as stress concentrators. Fatigue testing of MEAs has shown that smaller-scale cracking occurs in the membrane within these mud cracks, leading to leaking during mechanical fatigue testing and the failure of the membrane. In addition, this testing of MEAs has further established that the cyclic pressurization pattern, which affects the viscoelastic behavior of the membranes, has a significant effect on the relative lifetime of the MEA. To investigate this behavior, pressure-loaded blister tests were performed at 90 °C to determine the biaxial fatigue strength of Gore-Primea® Series 57 MEAs. In these volume-controlled tests, the leak rate was measured as a function of fatigue cycles. Failure was defined as occurring when the leak rate exceeded a specified threshold. Post-mortem characterization FESEM (field emission scanning electron microscopy) was conducted to provide visual documentation of leaking failure sites. To elucidate the viscoelastic behavior of the MEA based on these results, testing was conducted using a DMA to determine the stress relaxation behavior of the membrane. This data was then used in a FEA program (ABAQUS) to determine its effect on the mechanical behavior of the MEAs. A linear damage accumulation model used the ABAQUS results to predict lifetimes of the membrane in the MEAs. The models showed that under volume-controlled loading, the stress decays with time and the stress dropped towards the edges of the blisters. The lifetimes of the MEAs varied depending on the cycling pattern applied. This is important for understanding failure mechanisms of MEAs under fatigue loading, and will help the fuel cell industry in designing membranes that better withstand imposed hygrothermal stresses experienced during typical operating conditions. / Master of Science

Made available in DSpace on 2014-10-09T12:55:01Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:05:59Z (GMT). No. of bitstreams: 0 / O processo de Impressão à Tela foi desenvolvido neste trabalho para ser aplicável à deposição de camadas catalíticas em eletrólitos utilizados em PEMFC. Inicialmente foram construídos conjuntos eletrodos-membrana (MEAs) de 25 cm2 de área ativa e comparados com outros produzidos pelo método de Aspersão. Os dois métodos produziram MEAs que apresentaram densidades de corrente acima de 600 mA.cm-2 a 600 mV. Foi conduzido um estudo para o aumento de escala do MEA para 144 cm2 de área ativa. Para este fim, foi projetada uma célula para abrigar os MEAs destas dimensões. Neste projeto, o perfil dos canais de distribuição de gás foi desenvolvido através da ferramenta de fluido dinâmica computacional Comsol Multiphysics, sendo que, para o projeto das placas componentes da célula foi utilizado o AutoCAD. Os MEAs de 144 cm2 confeccionados por Aspersão e por Impressão à Tela foram confrontados com MEAs comerciais de iguais dimensões. Estes apresentaram melhor desempenho a 600 mV, entretanto são mais custosos que a solução desenvolvida neste estudo. O novo método apresentou-se adequado para a confecção de MEAs de baixo custo de diferentes geometrias e para a produção de lotes a serem utilizados em pequenos módulos de potência. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Ces travaux de thèse s'inscrivent dans le contexte des efforts de recherches menés pour proposer des matériaux susceptibles de lever les verrous technologiques au développement des piles à combustible à membrane. L'un de ces enjeux est l'augmentation de la température de fonctionnement (150 - 250 °C) afin d'améliorer les cinétiques réactionnelles permettant une diminution de la quantité de catalyseur ainsi qu'une simplification de la gestion de l'eau, une réduction du système de refroidissement et une meilleure résistance à l'empoisonnement au monoxyde de carbone du platine. La motivation de cette étude a été de substituer au carbone un matériau support de catalyseur avec une plus grande résistance électrochimique.Notre choix s'est porté sur le carbure de tungstène qui, en plus d'une conductivité électronique élevée, présente une activité catalytique pour l'oxydation de l'hydrogène et la réduction de l'oxygène en milieu acide. La mise au point d'une méthode de synthèse innovante par voie hydrothermale a permis l'élaboration de microsphères de carbure de tungstène (MCT) de surface spécifique élevée (68 m2.g-1 avec 4 % de carbone résiduel) et d'architecture inusuelle. Des nanoparticules de platine de taille contrôlée ont été préparées par méthode polyol afin d'être déposées en surface des MCT. Après caractérisations électrochimiques ex-situ couplées à des analyses de surface (XPS) de ces catalyseurs Pt/WC, la mise en forme d'électrodes par enduction et transfert sur la membrane a permis la réalisation d'assemblages membrane - électrode et leurs caractérisations en pile à combustible. Des membranes polybenzimidazole dopé acide phosphorique (PBI-H3PO4) ont été utilisées pour remplacer les membranes Nafion afin d'augmenter la température de fonctionnement. / The objective of this work was to develop alternative suitable materials to increase operating temperature of a Proton Exchange Membrane Fuel Cell. The increase of the operating temperature (150 - 250 °C) is attractive for cost reduction and reliability in terms of reaction kinetics, catalyst tolerance, heat rejection and water management. Our work was focused on tungsten carbide which has an high electrical conductivity and exhibits a significant catalytic activity for hydrogen oxidation and oxygen reduction in acidic environment. We have reported a novel approach to produce tungsten carbide microspheres (TCM) with an high surface area (68 m2.g-1 including only 4 % of residual carbon) and an unusual architecture. Platinum nanoparticles were prepared by polyol method and were then deposited on TCM. Physical, chemical as well as electrochemical characterisations of WC supported platinum nanoparticles Pt/WC are described and discussed in comparison with a platinum electrocatalyst on a commercial carbon support (Vulcan XC-72R). Membrane Electrode Assembly was then prepared by coating - decal process, and characterised by single cell test and compared to conventional Pt/C assembly. Phosphoric acid doped polybenzimidazole PBI(H3PO4) was used as electrolyte to replace Nafion membrane in order to carry out fuel cell testing at higher temperature.

The demand for higher efficiency and cleaner power sources increases daily. The Direct Methanol Fuel Cells (DMFC) is one of those power sources that produces reliable electrical energy at high efficiencies and very low pollution levels. Remote telecommunication sites need power sources that can deliver reliable power. This dissertation informs the reader about the working principles of the DMFC and the materials it consists of. A good amount of theoretical background is also given on the DMFC, especially on the Membrane Electrode Assembly (MEA). Different membranes as well as their properties are discussed. Results from other researchers on DMFCs are also captured. A DMFC stack including a test rig, was built. The DMFC stack consisted of five single DMFC cells. Each cell contained an MEA, Gas Diffusion Layers (GDLS), highly corrosive resistant metal support grids, bipolar flow field plates and end plates. The DMFC stack was operated and tested in a test rig. The test rig held the air blower which supplied the cathode with the required oxidant (air), and the methanol solution tank plus its liquid pump. The liquid pump circulated the methanol solution through the anode side of the stack. It was observed that the DMFC is very susceptible to corrosion, especially if the methanol solution becomes conductive owing to solubility of C02 in it. Methanol itself is a corrosive substance. However the results obtained from the experiments clearly indicate that the DMFC can be implemented as an electrical power source for telecommunications.