Ce mémoire présente une synthèse des travaux dont l'objectif est de résoudre la problématique de la gestion de l'eau dans un système Pile à Combustible de type PEM en utilisant un humidificateur externe. Une analyse des différents organes de la ligne d'air du système, et plus spécifiquement de l'humidificateur membranaire, est réalisée afin d'en déterminer l'architecture la mieux adaptée aux conditions opératoires. Cette étude passe par la description et la compréhension des transferts de matière et de chaleur au sein de l'humidificateur, à travers des approches aussi bien numériques qu'expérimentales. Le volet numérique comporte un modèle fin de transferts couplés à travers une membrane en Nafion. Associé à une analyse thermodynamique du système d'humidification, il permet de définir deux paramètres caractérisant respectivement les échanges de matière et de chaleur aussi bien en fonction des conditions d'entrée des fluides qu'en fonction des caractéristiques géométriques de l'échangeur. Ces paramètres s'avèrent être des outils de dimensionnement intéressants. Le volet expérimental permet d'évaluer les interactions entre une pile à combustible, l'humidificateur membranaire et les autres organes de la ligne d'air. Outre l'analyse de la réponse de chaque composant à une variation du courant délivré par la pile, les investigations ont permis de vérifier que les conditions opératoires du système sont compatibles avec la technologie d'humidification choisie. / This report presents a synthesis of works carried out in order to solve the water management problematic in a PEM fuel cell system. An analysis of the different components of the system air line, and more specifically the membrane humidifier, is realized in order to determine the architecture allowing the optimal moisture content of air upstream the fuel cell whatever the operating conditions. This study involves the description and the understanding of coupled heat and mass transfers within the humidifier, through numerical and experimental approaches. The numerical section contains a model of coupled transfer through a Nafion membrane. Associated with a thermodynamic analysis of the humidifier, it allows to define two parameters characterizing respectively the mass exchanges and the heat transfers, according to the inlet conditions of the fluids or as well as to the exchanger geometry. These parameters turn out to be useful design tools. The experimental section allows to estimate the interactions between a fuel cell, the humidifier and the other air line components. Besides the analysis of components response to a current intensity variation, the investigations allowed to demonstrate that the operating conditions of the system is compatible with the chosen humidification technology.

For fuel cells to become commercially viable in a wider range of applications, the amount of catalyst must be reduced. One crucial area of the fuel cell assembly is the anode and cathode; these layers allow fuel and exhaust gases to diffuse, provide conduction paths for both protons and electrons, and house sites for electrocataytic reactions. Despite their multi-functionality and importance, these layers have received little attention in the way of engineering design. While Nafion and catalyst loading has been studied, the electrode layer is still considered a two-dimensional structure. By understanding the current electrode limitations, available materials, and interactions at the sites reaction sites, an intelligent, deliberate design of the anode and cathode layer can be undertaken. A three-dimensional, fibrous mat of continuous, networked proton-conducting fibers can decrease mass diffusion limitations while maintaining proton conductivity. Nafion can be formed into these types of fibers via the fabrication technique of electrospinning. By forcing a solution of Nafion, solvent, and carrier polymer through a small nozzle under high electric voltage, the polymer can be extruded into fibers with nanometer-scale diameters. The ability to control the fiber morphology lies with solution, environmental and equipment properties. In order to successfully fabricate Nafion nanofibers, we looked to both existing methodologies as well as mathematical models to try to predict behavior and fabricate our own nanofibers. Once fabricated, these mats are assembled in a membrane-electrode assembly and tested with both methanol and hydrogen as fuel, with performance compared against known data for conventional MEAs. We have been able to successfully electrospin Nafion® nanofibers continuously, creating fiber mats with fiber diameters near 400nm as verified by SEM. These mats were tested in a direct methanol fuel cell (DMFC) application as cathodes, and showed improved performance with a dilute methanol feed compared to conventional MEAs with equivalent Nafion and catalyst loading. An MEA fabricated with twin electrospun electrodes was compared against an equivalent conventional MEA, showing the same performance enhancement using a dilute methanol fuel.

La technologie de piles à combustible PEM (Proton Exchange Membrane) voit encore sa commercialisation limitée du fait de son coût élevé. L'un des éléments les plus coûteux est le catalyseur, constitué de platine, métal noble, représentant 25 % du coût global. L'étude mise en place dans le cadre de cette thèse s'oriente vers l'amélioration de l'utilisation de cet élément. La voie de nanostructuration s'avère d'un intérêt majeur afin de maintenir des tailles de structure proposant des propriétés électrocatalytiques intéressantes. De plus, l'élaboration électrochimique de catalyseurs présente l'avantage majeur de remplir l'une des conditions nécessaires en pile à combustible : le contact électronique. La réunion des deux précédents points nous a permis de mettre en place un procédé d'élaboration électrochimique de nanostructures, ensuite charactérisées par méthodes électrochimiques et physiques afin d'évaluer et de comprendre leurs propriétés catalytiques.

<p>The purpose of this paper is to identify the current status of fuel cell technology and to establish whether said technology is mature enough to be implemented into the Swedish Armed Forces. The question to be answered in this paper is as follows: Can hydrogen gas and fuel cells be used as an alternative source of energy within the Swedish Armed Forces?</p><p>This paper is based on theoretical studies and reports from prior research done on fuel cells. By studying these facts a predictive answer has been obtained. The answer I have come to, is that the maturity of fuel cell technology is currently inadequate for the Swedish Armed Forces to implement, especially considering its harsh working conditions.</p>

In its present form, polymer electrolyte membrane fuel cell (PEMFC) technology requires some method of humidification to ensure that high performance and long life of the fuel cell membrane is maintained. External humidification utilizing ‘gas to gas’ membrane based planar humidifiers is one method of humidifying fuel cell reactant gases. This type of humidification offers the benefit of recycling heat and moisture from the fuel cell exhaust, and returning it to the reactants entering the fuel cell. In designing a planar membrane based fuel cell humidifier the two important areas to be considered are: - humidifier channel and plate design; and - humidifier membrane selection. In this work a humidifier design procedure was developed based on prototype humidifier testing. This design procedure involves selection of design parameters based on a dimensionless parameter which describes the ratio of gas residence time, and water diffusion time from the membrane surface. Humidifiers of different flow channel geometries were created with a rapid prototyping technique. These humidifier units were tested at different operating conditions in an attempt to validate the design equations involving a design parameter which is the ratio between the residence times of gas in the humidifier over the diffusion time of water from the surface of the membrane into the channel. This parameter offers a good starting point for humidifier design, the target value of this parameter was found to be between 2.0 and 4.0, with a desired value of 3.0. A fuel cell stack humidifier design procedure and suggestions are presented based this parameter. The design also considers designing a humidifier on limited volume constraints in which the humidifier would have to fit into the fuel cell system. A membrane selection procedure was developed based on design criteria requirements developed during this work for the fuel cell humidifier. This criterion includes high water permeation, low air permeation, good mechanical strength, robust handling, and long lifetime under various operating conditions. . Specific values for membrane selection included a water flux of greater than 14 kg m-2 h-1 in a water permeation test, less than 3 cm3 min-1 cm-2 kPa-1 air permeation when the membrane was dry, and a lifetime of at least 1500 hours of operation without performance degradation. Sixty membranes from various sources were screened for candidacy for use in the humidifier application. Membranes which passed the initial screenings were tested for durability at high and moderate temperature conditions. These membranes were operated until failure, at which time analysis was completed to determine the failure modes of the membrane. Mitigation strategies were proposed when applicable. Recommendations were made for membrane materials for the proposed operating requirements. Suggested membranes materials included those based on UHMWPE and inorganic additives, as well as homogenous membranes based on Nylon 6,6, PEEK, and PFSA.

The purpose of this paper is to identify the current status of fuel cell technology and to establish whether said technology is mature enough to be implemented into the Swedish Armed Forces. The question to be answered in this paper is as follows: Can hydrogen gas and fuel cells be used as an alternative source of energy within the Swedish Armed Forces? This paper is based on theoretical studies and reports from prior research done on fuel cells. By studying these facts a predictive answer has been obtained. The answer I have come to, is that the maturity of fuel cell technology is currently inadequate for the Swedish Armed Forces to implement, especially considering its harsh working conditions.

In its present form, polymer electrolyte membrane fuel cell (PEMFC) technology requires some method of humidification to ensure that high performance and long life of the fuel cell membrane is maintained. External humidification utilizing ‘gas to gas’ membrane based planar humidifiers is one method of humidifying fuel cell reactant gases. This type of humidification offers the benefit of recycling heat and moisture from the fuel cell exhaust, and returning it to the reactants entering the fuel cell. In designing a planar membrane based fuel cell humidifier the two important areas to be considered are: - humidifier channel and plate design; and - humidifier membrane selection. In this work a humidifier design procedure was developed based on prototype humidifier testing. This design procedure involves selection of design parameters based on a dimensionless parameter which describes the ratio of gas residence time, and water diffusion time from the membrane surface. Humidifiers of different flow channel geometries were created with a rapid prototyping technique. These humidifier units were tested at different operating conditions in an attempt to validate the design equations involving a design parameter which is the ratio between the residence times of gas in the humidifier over the diffusion time of water from the surface of the membrane into the channel. This parameter offers a good starting point for humidifier design, the target value of this parameter was found to be between 2.0 and 4.0, with a desired value of 3.0. A fuel cell stack humidifier design procedure and suggestions are presented based this parameter. The design also considers designing a humidifier on limited volume constraints in which the humidifier would have to fit into the fuel cell system. A membrane selection procedure was developed based on design criteria requirements developed during this work for the fuel cell humidifier. This criterion includes high water permeation, low air permeation, good mechanical strength, robust handling, and long lifetime under various operating conditions. . Specific values for membrane selection included a water flux of greater than 14 kg m-2 h-1 in a water permeation test, less than 3 cm3 min-1 cm-2 kPa-1 air permeation when the membrane was dry, and a lifetime of at least 1500 hours of operation without performance degradation. Sixty membranes from various sources were screened for candidacy for use in the humidifier application. Membranes which passed the initial screenings were tested for durability at high and moderate temperature conditions. These membranes were operated until failure, at which time analysis was completed to determine the failure modes of the membrane. Mitigation strategies were proposed when applicable. Recommendations were made for membrane materials for the proposed operating requirements. Suggested membranes materials included those based on UHMWPE and inorganic additives, as well as homogenous membranes based on Nylon 6,6, PEEK, and PFSA.

The durability and performance of commercially available polymer electrolyte membrane fuel cell (PEMFC) technology depends heavily on adequate humidification of the membrane electrode assembly (MEA). Early generation automotive fuel cell stacks will likely rely on an external humidification process based on gas-to-gas membrane planar humidifiers to humidify the inlet cathode stream. The membrane-based humidifier systems allow the reactants to receive recycled heat and moisture from the cathode outlet stream. The objective of this thesis is to develop a flexible, computer-based simulation tool that can be used to aid in the design of these planar humidifier systems. The simulation is based on fundamental mass transfer concepts and experimental membrane behaviour based on literature results. It was determined that the mass transfer resistance through the membrane is several orders of magnitude higher than the resistance contributed by the gas diffusion media (GDM) and thus the mass transfer resistance through the GDM are not considered. An important point to note is that the Schroeder’s Paradox observed in perfluorosulfonic acid (PFSA) membranes implies that membranes in contact with liquid water will exhibit higher mass transfer than membranes in contact with saturated water vapour despite the fact that the water activity in both situations are unity. Initial simulations for which no liquid water was present resulted in a humidifier water transfer rate less than half the rate observed experimentally. Thus it was hypothesized that condensed liquid water was present on the wet-side of the humidifier membrane and as such this work assumes a fraction of the membrane surface is covered by liquid water while the rest of the membrane is exposed to gaseous water concentrations comparable to the bulk channel stream above the GDM. For typical operating conditions the outlet wet-side stream retains 92% of the inlet water content and as such it was hypothesized that constant fractional liquid water coverage across the membrane could be assumed. Later simulations confirmed the validity of this hypothesis. Six models of water coverage estimation were derived using least squares and factorial design methods. The models were compared however no single method was determined to be superior for all situations as the methods exhibit similar sums of squared error.

Proton exchange membrane fuel cell (PEMFC) has been considered as one of the most promising energy conversion devices for the future in automotive applications. One of the major technical challenges for the commercialization of PEMFC is the effective start-up from subzero temperatures, often referred to as “cold start”. The major problem of PEMFC cold start is that the product water freezes when the temperature inside the PEMFC is lower than the freezing point. If the catalyst layer (CL) is fully occupied by ice before the cell temperature rises above the freezing point, the electrochemical reaction may stop due to the blockage of the reaction sites. However, only a few of the previous PEMFC studies paid attention to cold start. Hence, understanding the ice formation mechanisms and optimizing the design and operational strategies for PEMFC cold start are critically important. In this research, an experimental setup for the cold start testing with simultaneous measurement of current and temperature distributions is designed and built; a one-dimensional (1D) analytical model for quick estimate of purging durations before the cold start processes is formulated; and a comprehensive three-dimensional (3D) PEMFC cold start model is developed. The unique feature of the cold start experiment is the inclusion of the simultaneous measurement of current and temperature distributions. Since most of the previous numerical models are limited to either 1D or two-dimensional (2D) or 3D but only considering a section of the entire cell due to computational requirement, the measured distribution data are critically important to better understand the PEMFC cold start characteristics. With a full set of conservation equations, the 3D model comprehensively accounts for the various transport phenomena during the cold start processes. The unique feature of this model is the inclusion of: (i) the water freezing in the membrane electrolyte and its effects on the membrane conductivity; (ii) the non-equilibrium mass transfer between the water in the ionomer and the water (vapour, liquid and ice) in the pore region of the CL; and (iii) both the water freezing and melting in the CL and gas diffusion layer (GDL). This model therefore provides the fundamental framework for the future top-down multi-dimensional multiphase modelling of PEMFC. The experimental and numerical results elaborate the ice formation mechanisms and other important transport phenomena during the PEMFC cold start processes. The effects of the various cell designs, operating conditions and external heating methods on the cold start performance are studied. Independent tests are carried out to identify and optimize the important design and operational parameters.

Proton Exchange Membrane (PEM) fuel cell stack requires gaskets and seals in each cell to keep the hydrogen and air/oxygen within their respective regions. The stability of the gaskets is critical to the operating life as well as the electrochemical performance of the fuel cell. Chemical degradation of five elastomeric gasket materials in a simulated and an aggressive accelerated fuel cell solution at PEM operating temperature for up to 63 weeks was investigated in this work. The five materials are Copolymeric Resin (CR), Liquid Silicone Rubber (LSR), Fluorosilicone Rubber (FSR), Ethylene Propylene Diene Monomer Rubber (EPDM), and Fluoroelastomer Copolymer (FKM). In order to assess the durability of the materials, observation of chemical degradation level, dynamic mechanical analysis, and micro-indentation test were adopted in this study. This experimental result showed that the influence of the chemical reaction could affect the material surface condition. Also, the chemical reaction could affect material¡¦s mechanical properties had been changed over the soaking time. By considering the level of chemical degradation and mechanical properties, the experimental results showed that EPDM is recommended as the best choice of sealing material for using in a PEMFC.