Several groups are studying and researching major factors which influence high temperature proton exchange membrane fuel cells. These factors include material type, temperature, and fuel cell lifespan. Only a few groups research the optimization of the size of the fuel channels within the fuel cell. For channel optimization, a model was created to find the optimum flow channel and rib widths. The approach used was to code the losses due to activation, concentration, and ohmic polarizations to yield the fuel cell voltage and power expected from the fuel cell itself. The model utilizes the specified cell parameters including the material properties, fuel cell temperature, and channel size. This method gives an initial view of how a fuel cell will perform given specific parameters. It is not limited to one fuel cell size, allowing future research efforts to utilize this model to optimize flow channels in a variety of fuel cells.

Polymer electrolyte membrane (PEM) fuel cells have increasingly become promising green energy sources for automobile and stationary cogeneration applications but its success in commercialization depends on performance optimization and manufacturing cost. The activation losses, expensive platinum catalyst, and water flooding phenomenon are the key factors currently hindering commercialization of PEM fuel cells. These factors are associated with the cathode catalyst layer (CCL), which is about ten micrometers thick. Given the small scale of this layer, it is extremely difficult to study transport phenomena inside the catalyst layer experimentally, either intrusively or non-intrusively. Therefore, mathematical and numerical models become the only means to provide insight on the physical phenomena occurring inside the CCL and to optimize the CCL designs before building a prototype for engineering application. In this thesis research, a comprehensive two-phase mathematical model for the CCL has been derived from the fundamental conservation equations using a volume-averaging method. The model also considers several water transport and physical processes that are involved in the CCL. The processes are: (a) electro-osmotic transport from the membrane to the CCL, (b) back-diffusion of water from the CCL to the membrane, (c) condensation and evaporation of water, and (d) removal of liquid water to the gas flow channel through the gas diffusion layer (GDL). A simple analytical model for the activation overpotential in the CCL has also been developed and an optimization study has been carried out using the analytical activation overpotential formulation. Further, the mathematical model has been simplified for the CCL and an analytical approach has been provided for the liquid water transport in the catalyst layer. The volume-averaged mathematical model of the CCL is finally implemented numerically along with an investigation how the physical structure of a catalyst layer affects fuel cell performance. Since the numerical model requires various effective transport properties, a set of mathematical expressions has been developed for estimating the effective transport properties in the CCL and GDL of a PEM fuel cell. The two-dimensional (2D) numerical model has been compared with the analytical model to validate the numerical results. Subsequently, using this validated model, 2D numerical studies have been carried out to investigate the effect of various physical and wetting properties of CCL and GDL on the performance of a PEM fuel cell. It has been observed that the wetting properties of a CCL control the flooding behavior, and hydrophilic characteristics of the CCL play a significant role on the cell performance. To investigate the effect of concentration variation in the flow channel, a three-dimensional numerical simulation is also presented.

Polymer electrolyte membrane (PEM) fuel cells are promising alternative green power source for mobile, portable and stationary applications. However, their cost, durability, and performance are impacted by their sensitivity to impurities in fuel stream. Carbon monoxide (CO), an impurity commonly present in the hydrogen gas produced from hydrocarbon fuels, is known to have a significant degrading effect on PEM fuel cell performance because CO has a strong affinity to the platinum-based catalyst. At present, most studies in literature are limited to either experimental or simplified-dimensional analysis/modeling. In this thesis research, a three-dimensional (3D) multiphase PEM fuel cell model with the CO poisoning and O2 bleeding is developed based on the conservation laws for mass, momentum, energy, and species, and implemented in the commercial software Fluent (6.3.26) through the user-defined functions. Numerical simulations are conducted to simulate a single PEM fuel cell including flow channels, gas diffusion layers, catalyst layers, and PEM. The simulation results are compared with experimental data favorably. The result shows that the reaction rate of hydrogen in the anode catalyst layer is higher near the membrane layer, decreasing towards the gas diffusion layer (GDL) interface, and the reaction rate in general is higher in the inlet region and decreases towards the exit region of the flow channel. It means that the outlet of anode catalyst layer next to the flow channel and GDL has suffered the most significant poisoning effect. The result helps optimize the design of anode catalyst layer by embedding more platinum on the most poisoned area to increase available surface for hydrogen adsorption; similarly, reducing platinum loading on the less poisoned area. The fuel cell performance can be almost fully recovered when switching the anode fuel mixture to pure hydrogen, though it takes a long period of time. The reaction rate of hydrogen decreases significantly along the flow channel when impurity mixture is provided; while there is little change along the channel for pure hydrogen fuel. Adding oxygen into the anode fuel mixture can mitigate CO poisoning, but there is a time delay when the oxygen is introduced into the anode stream and when the performance starts to recover. It is observed that at the beginning of oxygen introduced in the anode stream the recovery rate in the region adjacent to the channel outlet is faster than the rate in the region close to the inlet. This difference in the recovery rate gradually becomes smaller over time. In addition, the influence of CO poisoning and oxygen bleeding on multi-phase water is investigated. The influence on dissolved water is only clearly seen in the anode catalyst layer next to the land area. Finally, response to sudden load changes is simulated by changing cell voltage. It is found that the overshoot and undershoot are more significant at high current densities.

El objetivo general de la tesis doctoral ha sido el desarrollo de electrodos selectivos de tecnología avanzada para su uso en celdas de combustible de hidrógeno/oxígeno de alta eficiencia que operan a baja temperatura. A tal fin, se prepararon electrocatalizadores de nanopartículas de Pt con orientación cristalográfica preferencial (111), los cuales exhiben la mayor actividad catalítica para la reacción de electrorreducción de oxígeno, cuya cinética lenta es una de las principales limitaciones en el proceso de conversión de energía. La obtención de las nanopartículas sobre sustratos carbonosos se realizó mediante la aplicación de una técnica de electrólisis pulsante. Se diseñaron y construyeron electrodos porosos de difusión de gas catalizados con los que se construyeron ensambles electrodo-membrana de intercambio de protones (PEM)-electrodo. Se diseñó y construyó un prototipo de celda de combustible unitaria de hidrógeno/oxígeno de tecnología PEM y se evaluó su comportamiento en operación y estabilidad a tiempos largos. Se determinó que la incorporación en el cátodo de los electrocatalizadores de Pt altamente facetados tipo (111), desarrollados en el transcurso de la tesis, mejoran el comportamiento en operación de la celda de combustible de hidrógeno/oxígeno de tecnología PEM. Finalmente, se elaboró un protocolo de testeo para celdas de combustible de hidrógeno/oxígeno PEM.

L'économie actuelle repose sur l'utilisation d'énergies fossiles dont les réserves sont limitées. En plus, l'utilisation de ces ressources a un impact négatif sur l'environnement dû à l'émission des gaz polluants et du CO2. Il est donc nécessaire de remplacer les ressources fossiles par les énergies renouvelables. Les énergies renouvelables peuvent être facilement converties en électricité pour une utilisation directe, mais l'électricité ne peut pas être stockée en grande quantité. Dans ce contexte, l'hydrogène pourrait servir de vecteur énergétique. Il est possible de produire de l'hydrogène par électrolyse de l'eau. L'hydrogène sera ensuite utilisé via une pile à combustible pour fournir de l'électricité et de la chaleur. Ce procédé ne produit que de l'eau qui va être re-consommé ensuite par l'électrolyse.Ce travail de thèse est axé sur la production d'hydrogène par électrolyse de l'eau en milieu acide par la technologie PEM (proton exchange membrane). L'objectif est de remplacer le platine, catalyseur de la réduction à la cathode par des complexes de cobalt de type cobalt-oxime.Le premier chapitre traite différents aspects de l'électrolyse de l'eau et différents catalyseurs étudiés dans la littérature.Le second chapitre décrit différentes techniques expérimentales utilisées pour caractériser les complexes étudiés.Le chapitre trois décrit la synthèse et l'activité catalytique des complexes de cobalt-oxime en solution dans l'acétonitrile vis-à-vis de la réduction des protons en hydrogène.Le chapitre quatre présente les premiers travaux obtenus en utilisant les complexes de cobalt-oxime à la place du platine dans les électrolyseurs PEM.

La production d'hydrogène et de dioxygène par électrolyse PEM (PEM " Proton Exchange Membrane ") de l'eau s'effectue grâce à la présence de métaux nobles dans les couches catalytiques: à la cathode, le platine supporté sur du carbone est généralement utilisé (les chargements en métaux nobles sont faibles de l'ordre de 0,5 mg/cm²) ; à l'anode, la production d'oxygène s'effectue à des potentiels élevés (> 1,6 V vs. ESH). Les oxydes de métaux nobles sont utilisés seuls dans la couche active anodique et servent à la fois de catalyseurs et de conducteurs électroniques. Comme ils sont parmi les métaux les plus denses, pour obtenir une continuité électrique de la couche anodique, les chargements doivent être très élevés, de l'ordre de 2-3 mg/cm².Cette thèse propose ainsi de développer de nouveaux matériaux supports stables électrochimiquement et bons conducteurs électroniques pour séparer les fonctions de catalyse et de conduction électronique. Pour cela, des assemblages membrane électrodes intégrant des particules de titane comme support de catalyseur anodique ont été préparés dans notre laboratoire. Testés en mono-cellule de 25 cm², leurs principales caractéristiques ont été déterminées par voltampérométrie cyclique, spectroscopie d'impédance et grâce à des courbes de polarisations à différentes températures. La comparaison des résultats obtenus entre ces anodes " innovantes " et celles à base de catalyseur seul a permis de mettre en évidence la présence d'un chargement anodique seuil de 0,5 mg/cm² en dessous duquel la présence d'un support de catalyseur est nécessaire pour assurer la percolation électrique. Grâce à l'utilisation de ce support de catalyseur bon marché, les chargements anodiques ont pu être réduits jusqu'à des valeurs aussi faibles que 0,1 mg/cm² IrO2, soit une réduction de dix fois au minimum par rapport aux taux généralement employés dans la littérature, tout en maintenant des performances identiques.

El constante desarrollo industrial y tecnológico ha establecido un escenario dónde, la demanda energética, en especial la eléctrica, se incrementa rápidamente. En este sentido la creciente explotación de los combustibles fósiles, ha logrado en las últimas décadas una fuerte reducción de sus yacimientos y el incremento de la contaminación ambiental. Tomando conciencia de estos problemas surgió la necesidad de diversificar las fuentes primarias de energía, introduciendo fuentes alternativas sustentables y no contaminantes. Entre éstas, las de origen renovable presentan algunas características que las hacen atractivas: complementariedad, libre disponibilidad y capacidad de generación inagotable. En este contexto, como una alternativa a los tradicionales vectores energéticos basados en combustibles fósiles, aparece la posibilidad de emplear un nuevo vector: el hidrógeno, un recurso no contaminante y eficiente. Además, empleado conjuntamente con Pilas de Combustible, puede producir electricidad y calor, con agua pura como único residuo. En base a lo expuesto, en esta tesis se aborda el desarrollo de un Sistema Híbrido de Generación de Energía Eléctrica versátil, basado en una Pila de Combustible PEM y Supercapacitores. De las tecnologías desarrolladas, las Pilas de Combustible tipo PEM, han demostrado un excelente desempeño como fuentes de energía en diversas aplicaciones, gracias a su reducido tamaño, robustez y baja temperatura de operación. Los Supercapacitores, presentan una alta densidad de potencia y frente a otras tecnologías tradicionales actuales son mas compactos, robustos y poseen mayor vida útil. De esta manera, esta combinación permite obtener un sistema de generación de alta densidad energética (gracias al funcionamiento continuo de las primeras) y muy buen desempeño dinámico. El sistema desarrollado tiene por objetivo ser utilizado como fuente de alimentación flexible en múltiples aplicaciones o bien, como una potente herramienta para el desarrollo de avanzadas estrategias de gestión de energía, en ámbito de laboratorio.

Proton exchange membrane (PEM) fuel cells are competitive with other emerging technologies that are being considered for automotive transportation. Commercialization of PEM fuel cells would decrease emissions of criteria pollutants and greenhouse gases and reduce US dependence on foreign oil. However, many challenges exist that prevent this technology from being realized, including power requirements, durability, on-board fuel storage, fuel distribution, and cost. This dissertation focuses on fuel-cell durability, or more specifically catalyst stability. New techniques to comprehensively observe and pin-point degradation mechanisms are needed to identify stable catalysts. In this text, an in operando method to measure changes in catalyst particle size at the cathode of a PEM fuel cell is demonstrated. The pair distribution function analysis of X-ray diffraction patterns, generated from an operating fuel cell exposed to accelerated degradation conditions, was used to observe the growth of catalyst particles. The stability of Pt/C and PtCo/C electrodes, with different initial particle sizes, was monitored over 3000 potential cycles. The increase in particle size was fit to a linear trend as a function of cycle number for symmetric linear sweeps of potential. The most stable electrocatalyst was found to be alloyed PtCo with a larger initial particle size. A better understanding of oxide growth kinetics and its role in platinum dissolution is needed to develop a comprehensive fuel-cell performance model. There is an ongoing debate present in the current literature regarding which oxide species are involved in the oxide growth mechanism. This dissertation discusses the results of in operando X-ray absorption spectroscopy studies, where it was found that PtO2 is present at longer hold times. A new method to quantify EXAFS data is presented, and the extent of oxidation is directly compared to electrochemical data. This comparison indicated that PtO2 was formed at the expense of an initial oxide species, and these steps were included in a proposed mechanism for platinum oxidation. Simulations of platinum oxidation in literature have yet to fully replicate an experimental cyclic voltammogram. A modified Butler-Volmer rate equation is presented in this thesis. The effect of including an extra parameter, χ, in the rate equations was explored. It was found that while the χ-parameter allowed the cathodic peak width to be decoupled from the Tafel slope for the platinum-oxide reduction, its inclusion could not address all observed experimental characteristics. Exploration of this concept concluded that current is not a function of only potential and coverage. To that end, a heterogeneous oxide layer was introduced. In this model, place-exchanged PtO2 structures of varying energy states are formed through a single transition state. This treatment allowed, for the first time, the simulation of the correct current-potential behavior under varying scan rates and upper potential limits. Particle size plays a critical role in catalysts stability. The properties of nanoparticles can differ significantly from bulk values, yet few tools exist to measure these values at the nanoscale. Surface stress and surface energy are diagnostic criterion that can be used to differentiate nano from bulk properties. The pair distribution function technique was used to measure lattice strain and particle size of platinum nanoparticles supported on carbon. The effect of adsorbates on surface stress was examined and compared to previous literature studies. Furthermore, a methodology for measuring the surface energy of supported platinum nanoparticles has been developed. While the results of this work are significant, many more challenges need to be addressed before fuel-cell vehicles are marketed. Recommendations for future work in the field of catalyst durability are addressed.

This thesis presents experimental and simulated data gathered specifically to assess air-cooled proton exchange membrane (PEM) fuel cells as a heat and electrical power source for residential combined heat and power (CHP). The experiments and simulations focused on the air-cooled Ballard Nexa fuel cell. The experimental characterization provided data to assess the CHP potential of the Nexa and validate the model used for the simulations. The model was designed to be applicable to any air-cooled PEM fuel cell. Based on hourly load data, four Nexa fuel cells would be required to meet the peak electrical load of a typical coastal British Columbia residence. For a year of operation with the four fuel cells meeting 100% of the electrical load, simultaneous heat generation would meet approximately 96% of the space heating requirements and overall fuel cell efficiency would be 70%. However, the temperature of the coolant expelled from the Nexa varies with load and is typically too low to provide for occupant comfort based on typical ventilation system requirements. For a year of operation, the coolant mean temperature rise is only 8.3 +/- 3.4 K above ambient temperature. To improve performance as a CHP heat engine, the Nexa and other air-cooled PEM fuel cells need to expel coolant at temperatures above 325 K. To determine if PEM fuel cells are capable of achieving this coolant temperature, a model was developed that simulates cooling system heat transfer. The model is specifically designed to determine coolant and stack temperature based on cooling system and stack design (i.e. geometry). Simulations using the model suggest that coolant mass flow through the Nexa can be reduced so that the desired coolant temperatures can be achieved without the Nexa stack exceeding 345 K during normal operation. Several observations are made from the presented research: 1) PEM fuel cell coolant air can be maintained at 325 K for residential space heating while maintaining the stack at a temperature below the 353 K Nafion design limits chosen for the simulations; 2) The pressure drop through PEM cooling systems needs to be considered for all stack and cooling system design geometries because blower power to overcome the pressure drop can become very large for designs specifically chosen to minimize stack temperature or for stacks with long cooling channels; 3) For the air-cooled Nexa fuel cell stack, heat transfer occurring within the fuel cell cooling channels is better approximated using a constant heat flux mean Nusselt correlation than a constant channel temperature Nusselt correlation. This is particularly true at higher output currents where stack temperature differences can exceed 8 K.

Fibre-optic sensing techniques for application in polymer electrolyte fuel cells (PEMFC) are presented in this thesis. Temperature, relative humidity (RH) and air-water two-phase flow sensors are developed and demonstrated based on optical fibre Bragg gratings (FBG). Bragg gratings offer the following characteristics that warrant their development for application in PEMFCs: small size, environmental compatibility and the possibility of multiplexed multi-parameter sensing. Contributions of this work are in novel sensor development and implementation strategies. Important installation design considerations include the sensor proximity to the catalyst layer, sensor strain relief and minimal bending of the fibre. With these considerations, the dynamic and steady-state performance of FBG temperature sensors distributed throughout the flow-field of a single cell PEMFC was validated with a co-located micro-thermocouple. In the development of FBGs for in situ measurement of relative humidity, a polyimide-coated FBG based RH sensor is presented with significantly improved response time and sensitivity over previously reported designs. The RH inside a PEMFC under transient operating conditions is monitored. Step increases in current induce significantly larger increases in RH near the outlet than near the inlet of the cell, and associated transients within the fuel cell are found on a time scale approaching the sensor response time. Finally, to complete the suite of FBG sensors for water management in PEMFCs, an evanescent field based FBG sensor embedded in a microchannel for the measurement of two-phase flow dynamics is presented. Using high speed video for validation, it is established that the novel sensor enables the measurement of droplet average velocity and size in flow regimes representative of an operating fuel cell. / Graduate