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Avdelningen Marina System på Kungliga Tekniska Högskolan har designat och konstruerat en autonom undervattensfarkost (AUV). I dagsläget drivs farkosten drivs av ett litiumpolymerbatteri. Ett bränslecellssystem bestående utav PEM-bränslecellsstackar (Polymerelektrolytbränslecell), metallhydrid och trycksatt syrgas har designats för att byta ut det befintliga litiumpolymerbatteriet. För att få ett säkert system är det utrustat med vätgassensor, trycksensor, voltmätare samt temperatursensor. Eftersom både syrgas och vätgas måste medföras i farkosten, jämfört med landgående fordon som kan utnyttja syret från omgivande atmosfär, har olika bränslelagringsmetoder undersökts. För att lagra syrgas har trycksatt gas valts, denna lagras i en tank gjord av kolfiber och ett har ett tryck på 300 bar. Vätgasen väljs att lagras i en FeTi-metallhydrid på grund av dess volymmässiga fördel. Metallhydrid är en volymeffektiv men viktineffektiv lagringsmetod, vilket gör att den är perfekt till en undervattensfarkost. Metallhydriden förvaras i en tank gjord av aluminium. Eftersom bränslecellerna producerar vatten har olika sätt att fånga upp detta undersökts. Regenerad cellulosa (disktrasa) har hög absorptionsförmåga och har därför valts för systemet. De bränslecellesstackar som införskaffades har testats med hjälp av programvaran Labview. De presterade något under vad tillverkaren hävdade, något som antas bero på effektbehov hos kontroller och fläktar. Olika driftbetingelser har undersökts för att kunna använda bränslecellsstackarnas fulla potential. Det slutgiltiga systemet får ej plats i farkosten. En teoretisk studie för när bränsleceller blir mer volymeffektiva än batterier visar att för ett helt optimerat system går gränsen vid 3 liter, vilket motsvarar att 822 normalliter vätgas måste tas med. I framtiden skulle en kemisk lagringsmetod av syrgas vara att föredra, exempelvis väteperoxid. Metallhydrid är ett bra sätt att lagra vätgas men tankmaterialet skulle kunna vara exempelvis rostfritt stål istället för aluminium så att tanken blir mer volymeffektiv på grund av den högre brottgränsen hos stålet. Ett syrgasflöde till bränslecellen istället för ut i farkostens atmosfär skulle kunna öka verkningsgraden och därmed räckvidden.

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Constitutive relationships are developed to describe the water transport characteristics of the gas diffusion layer (GDL) of proton exchange membrane fuel cells (PEMFCs). Additionally, experimental fixtures and procedures for the determination of the constitutive relationships are presented. The water transport relationships are incorporated into analytical models that assess the impact of the water transport relations and that make PEMFC performance predictions. The predicted performance is then compared to experimental results. The new constitutive relationships are significantly different than the currently popular relationships used in PEMFC modeling because they are derived from experiments on actual PEMFC gas diffusion layer materials. In prior work, properties of the GDL materials such as absolute permeability, liquid water relative permeability, porosity, and capillary behavior are often assumed or used as adjustment parameters in PEMFC models to simplify the model or to achieve good fits with polarization data. In this work, the constitutive relations are not assumed but are determined via newly developed experimental techniques. The experimental fixtures and procedures were used to characterize common GDL materials including carbon papers and carbon cloths, and to investigate common treatments applied to these materials such as the bulk application of a hydrophobic polymer within the porous structure. A one-dimensional model is developed to contrast results based on the new constitutive relations with results based on commonly used relationships from the PEMFC literature. The comparison reveals that water transport relationships can have a substantial impact on predicted GDL saturation, and consequently a significant impact on cell performance. The discrepancy in saturation between cases can be nearly an order of magnitude. A two-dimensional model is also presented that includes the impact of the compressed GDL region under the shoulder of a bipolar plate. Results show that the compression due to the bipolar plate shoulder causes a significant increase in liquid saturation, and a significant reduction in oxygen concentration and current density for the paper GDL. In contrast, compression under the shoulder has a minimal impact on the cloth GDL. Experimental inputs to the 2-D model include: absolute permeability, liquid water relative permeability, the slope of the capillary pressure function with saturation, total porosity, GDL thickness, high frequency resistance, and appropriate Tafel parameters. Computational polarization curve results are compared to experimental polarization behavior and good agreement is achieved. / Ph. D.

La pila de combustible de baja temperatura es una tecnología limpia y ecológica que permite la conversión directa de la energía química de un combustible, como hidrógeno o alcohol, en electricidad. Son varias las aplicaciones de esta tecnología y se están aplicando en sectores como automoción, industria naval, aeronaves no tripuladas, electrónica de consumo, etc. Para el uso masivo de esta tecnología son necesarias mejoras en el diseño del electrolito, monocelda y stack; lo que constituye el objetivo principal de este proyecto. Las membranas electrolito deben cumplir condiciones muy específicas, como buena estabilidad mecánica y química. Las que actualmente se encuentran en el mercado presentan inconvenientes como crossover y elevado coste. Para superar estas desventajas, en este trabajo se ha desarrollado y aplicado una metodología que permite establecer un procedimiento para diseñar membranas con propiedades específicas optimizadas. Así, uno de los objetivos del presente estudio es correlacionar las propiedades dieléctricas, la dinámica molecular y la conductividad con la composición de la membrana para predecir su comportamiento. Por esta razón, se han preparado y caracterizado membranas compuestas de alcohol polivinílico con masas moleculares distintas, entrecruzadas con ácido sulfosuccínico, a las que se les ha añadido distintas proporciones de óxido de grafeno. Una vez analizada su estructura química final por medio de espectroscopía infrarroja, su morfología superficial mediante microscopía electrónica de transmisión y sus propiedades y estabilidad térmica por calorimetría diferencial de barrido y análisis termogravimétrico, se estudió y modelizó su comportamiento eléctrico. Para ello, se determinaron las corrientes de polarización/despolarización y los espectros de relajaciones dieléctricas con el fin de obtener la capacidad de transferencia iónica, la movilidad molecular, la conductividad eléctrica y protónica y establecer el mecanismo que gobierna la movilidad de los protones a través del electrolito. Las monoceldas que se prepararon con las membranas compuestas se ensayaron con hidrógeno/oxígeno. Asimismo, estas membranas se evaluaron con metanol/oxígeno en la ETSIAE de la UPM, en el marco de los proyectos del Ministerio de Economía y Competitividad DOME-POL(ENE2011-28735-C02-01) y POLYCELL(ENE2014-53734-C2-1-R). De este modo, se fijó la concentración óptima de metanol, se obtuvieron las curvas características de voltaje y los valores de máxima potencia para cada electrolito. Al mismo tiempo, se ensayó una membrana comercial de Nafion117, que se tomó como referencia. Las curvas de voltaje-intensidad se modelizaron aplicando un modelo 0D, teniendo en cuenta los mecanismos dominantes de pérdidas de voltaje y aplicando la simplificación de Tafel. Los parámetros más significativos se relacionaron con la estructura y propie-dades del electrolito. Basándose en los resultados obtenidos para el electrolito y la monocelda, se ha diseñado un sistema de stack con las prestaciones necesarias para alimentar un motor brussless, que sustituye a un motor de combustión interna en una maqueta de camión teledirigido. Para ello, se diseñó una celda unitaria con el programa Solidworks. Los patrones de flujo de la placa bipolar, se evaluaron mediante las pérdidas de carga que se obtuvieron por simulaciones. También se llevó a cabo la selección de materiales más adecuados para la construcción de la celda, que se elaboró en placas de grafito laminado. Además, se determinó su potencia máxima para el sistema metanol/oxígeno. Con estos resultados se calculó el tamaño y número de celdas del stack y se seleccionaron los elementos auxiliares a partir de los cauda-les de fluido necesarios. Con todo ello, se ha contribuido a optimizar el diseño de los electrolitos, monoceldas y stacks para pilas de combustible de intercambio protónico con el fin de impulsa / The low temperature fuel cell is a clean and ecological technology that allows the direct conversion of the chemical energy of a fuel, such as hydrogen or alcohol, into electricity. There are several applications of this technology and they are being applied in sectors such as automotives, naval industry, unmanned aircrafts, consumer electronics, etc. For the massive use of this technology, improvements are needed in the design of the electrolyte, cell and stack; what constitutes the main objective of this project. The electrolyte membranes must meet very specific conditions, such as good mechanical and chemical stability. Those currently on the market have drawbacks such as crossover and high cost. To overcome these disadvantages, in this work has been developed and applied a methodology that allows to establish a procedure to design membranes with specific optimized properties. Thus, one of the objectives of the present study is to correlate dielectric properties, molecular dynamics and conductivity with the composition of the membrane to predict its behavior. For this reason, membranes composed of polyvinyl alcohol with different molecular masses, cross-linked with sulfosuccinic acid, with different proportions of graphene oxide have been prepared and characterized . Once analyzed its final chemical structure by means of infrared spectroscopy, its surface morphology by transmission electron microscopy and its properties and thermal stability by differential scanning calorimetry and thermogravimetric analysis, its electrical behavior was studied and modeled. For this reason, the polarization / depolarization currents and the dielectric relaxation spectra were determined in order to obtain the capacity of ionic transfer, the molecular mobility, the electrical and protonic conductivity and to establish the mechanism that governs the mobility of the protons through the electrolyte. The monocells were equipped with the composite membranes and tested with hydrogen/oxygen. Also, these membranes were evaluated in another methanol / oxygen test bench of the ETSIAE of the UPM, within the framework of the projects of the Ministry of Economy and Competitiveness DOMEPOL (ENE2011-28735-C02-01) and POLYCELL (ENE2014 -53734-C2-1-R). In this way, the optimum concentration of methanol was fixed, the voltage characteristic curves and the maximum power values for each electrolyte were obtained. At the same time, a commercial membrane of Nafion117 was tested, which was taken as a reference. The voltage-intensity curves were modeled applying a 0D model, taking into account the dominant mechanisms of voltage losses and applying the simplification of Tafel. The most significant parameters were related to the structure and properties of the electrolyte. Based on the results obtained for the electrolyte and the single cell, a stack system has been designed with the necessary features to power a bruss-less motor, which replaces an internal combustion engine in a remote-controlled truck model. To do this, a unit cell was designed with the Solidworks program. The flow patterns of the bipolar plate were evaluated by the load losses that were obtained by simulations. The selection of the most suitable materials for the construction of the cell was also carried out, which was elaborated in laminated graphite plates. In addition, its maximum power for the methanol / oxygen system was determined. With these results, the size and number of cells in the stack were calculated and the auxiliary elements were selected from the necessary fluid flow rates. With all this, it has helped to optimize the design of electrolytes, cells and stacks for proton exchange fuel cells in order to boost this technology in a generalized way. / La pila de combustible de baixa temperatura és una tecnologia neta i ecològica que permet la conversió directa de l'energia química d'un combustible, com hidrogen o alcohol, en electricitat. Són diverses les aplicacions d'aquesta tecnologia i s'estan aplicant en sectors com automoció, indústria naval, aeronaus no tripulades, electrònica de consum, etc. Per a l'ús massiu d'aquesta tecnologia són necessàries millores en el disseny de l'electròlit, monocelda i stack; el que constitueix l'objectiu principal d'aquest projecte. Les membranes electròlit han de complir condicions molt específiques, com una bona estabilitat mecànica i química. Les que actualment es troben al mercat presenten inconvenients com crossover i elevat cost. Per superar aquestes desventaxes, en aquest treball s'ha desenvolupat i aplicat una metodologia que permet establir un procediment per dissenyar membranes amb propietats específiques optimitzades. Així, un dels objectius d'aquest estudi és correlacionar les propietats dielèctriques, la dinàmica molecular i la conductivitat amb la composició de la membrana per a predir el seu compor-tament. Per aquesta raó, s'han preparat i caracteritzat membranes compostes d'alcohol polivinílic amb masses moleculars diferents, entrecreuades amb àcid sulfosuccínic, a les quals se'ls ha afegit diferents proporcions d'òxid de grafè. Un cop analitzada la seva estructura química final per mitjà d'espectroscòpia infraroja, la seva morfologia superficial mitjançant microscòpia electrònica de transmissió i les seves propietats i estabilitat tèrmica per calorimetria diferencial d'escombrat i anàlisi termogravimètrica, es va estudiar i modelitzar el seu comportament elèctric. Per això, es van determinar les corrents de polarització / despolarització i els espectres de relaxacions dielèctriques per tal d'obtenir la capacitat de transferència iònica, la mobilitat molecular, la conductivitat elèctrica i protònica i establir el mecanisme que governa la mobilitat de els protons a través de l'electròlit. Les monoceldas es van equipar amb les membranes compostes i es van assajar amb hidrogen / oxigen. Així mateix, aquestes membranes es van avaluar en un altre banc d'assaig amb metanol / oxigen de la ETSIAE de la UPM, en el marc dels projectes del ministeri d'Economia i Competitivitat DOMEPOL (ENE2011-28735-C02-01) i POLYCELL (ENE2014 -53.734-C2-1-R). D'aquesta manera, es va fixar la concentració òptima de metanol, es van obtenir les corbes característiques de voltatge i els valors de màxima potència per a cada electròlit. Alhora, es va assajar una membrana comercial de Nafion117, que es va prendre com a referència. Les corbes de voltatge-intensitat es modelaren aplicant un model 0D, tenint en compte els mecanismes dominants de pèrdues de voltatge i aplicant la simplificació de Tafel. Els paràmetres més significatives es van relacionar amb l'estructura i propietats de l'electròlit. Basant-se en els resultats obtinguts per l'electròlit i la monocelda, s'ha dissenyat un sistema de stack amb les prestacions necessàries per alimentar un motor Bruss-less, que substitueix un motor de combustió interna en una maqueta de camió teledirígit. Per a això, es va dissenyar una cel·la unitària amb el programa Solidworks. Els patrons de flux de la placa bipolar, es van avaluar mitjançant les pèrdues de càrrega que es van obtenir per simulacions. També es va dur a terme la selecció de materials més adequats per a la construcció de la cel·la, que es va elaborar en plaques de grafit laminat. A més, es va determinar la seva potència màxima per al sistema metanol / oxigen. Amb aquests resultats es va calcular la mida i nombre de cel·les de l'stack i es van seleccionar els elements auxiliars a partir dels cabals de fluid necessaris. Amb tot això, s'ha contribuït a optimitzar el disseny dels electròlits, monoceldas i stacks per a piles de combustible d'intercanvi protònic p / González Guisasola, CF. (2018). Modelización del electrolito, monocelda y stack en pilas de combustible poliméricas [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/102522

The Polymer Electrolyte Membrane (PEM) fuel cell has a great potential in leading the future energy generation due to its advantages of zero emissions, higher power density and efficiency. For a PEM fuel cell, the Membrane-Electrode Assembly (MEA) is the key component which consists of a membrane, two catalyst layers and two gas diffusion layers (GDL). The success of optimum PEM fuel cell power output relies on the mass transport to the electrode especially on the cathode side. The carbon based GDL is one of the most important components in the fuel cell since it has one of the basic roles of providing path ways for reactant gases transport to the catalyst layer as well as excess water removal. A detailed understanding and visualization of the GDL from micro-scale level is limited by traditional numerical tool such as CFD and experimental methods due to the complex geometry of the porous GDL structural. In order to take the actual geometry information of the porous GDL into consideration, the x-ray tomography technique is employed which is able to reconstructed the actual structure of the carbon paper or carbon cloth GDLs to three-dimensional digital binary image which can be read directly by the LB model to carry out the simulation. This research work contributes to develop the combined methodology of x-ray tomography based the three-dimensional single phase Lattice Boltzmann (LB) simulation. This newly developed methodology demonstrates its capacity of simulating the flow characteristics and transport phenomena in the porous media by dealing with collision of the particles at pore-scale. The results reveal the heterogeneous nature of the GDL structures which influence the transportation of the reactants in terms of physical parameters of the GDLs such as porosity, permeability and tortuosity. The compression effects on the carbon cloth GDLs have been investigated. The results show that the c applied compression pressure on the GDLs will have negative effects on average pore size, porosity as well as through-plane permeability. A compression pressure range is suggested by the results which gives optimum in-plane permeability to through-plane permeability. The compression effects on one-dimensional water and oxygen partial pressures in the main flow direction have been studied at low, medium and high current densities. It s been observed that the water and oxygen pressure drop across the GDL increase with increasing the compression pressure. Key Words: PEM fuel cell, GDL, LB simulation, SPSC, SPMC, x-ray tomography, carbon paper, carbon cloth, porosity, permeability, degree of anisotropy, tortuosity, flow transport.

<p>In this thesis, direct hydrogen Proton Exchange Membrane (PEM) fuel cell systems in vehicles are investigated through modelling, field tests and public acceptance surveys.</p><p>A computer model of a 50 kW PEM fuel cell system was developed. The fuel cell system efficiency is approximately 50% between 10 and 45% of the rated power. The fuel cell auxiliary system,<i> e.g.</i> compressor and pumps, was shown to clearly affect the overall fuel cell system electrical efficiency. Two hydrogen on-board storage options, compressed and cryogenic hydrogen, were modelled for the above-mentioned system. Results show that the release of compressed gaseous hydrogen needs approximately 1 kW of heat, which can be managed internally with heat from the fuel cell stack. In the case of cryogenic hydrogen, the estimated heat demand of 13 kW requires an extra heat source. </p><p>A phase change based (PCM) thermal management solution to keep a 50 kW PEM fuel cell stack warm during dormancy in a cold climate (-20 °C) was investigated through simulation and experiments. It was shown that a combination of PCM (salt hydrate or paraffin wax) and vacuum insulation materials was able to keep a fuel cell stack from freezing for about three days. This is a simple and potentially inexpensive solution, although development on issues such as weight, volume and encapsulation materials is needed </p><p>Two different vehicle platforms, fuel cell vehicles and fuel cell hybrid vehicles, were used to study the fuel consumption and the air, water and heat management of the fuel cell system under varying operating conditions, <i>e.g.</i> duty cycles and ambient conditions. For a compact vehicle, with a 50 kW fuel cell system, the fuel consumption was significantly reduced, ~ 50 %, compared to a gasoline-fuelled vehicle of similar size. A bus with 200 kW fuel cell system was studied and compared to a diesel bus of comparable size. The fuel consumption of the fuel cell bus displayed a reduction of 33-37 %. The performance of a fuel cell hybrid vehicle,<i> i.e.</i> a 50 kW fuel cell system and a 12 Ah power-assist battery pack in series configuration, was studied. The simulation results show that the vehicle fuel consumption increases with 10-19 % when the altitude increases from 0 to 3000 m. As expected, the air compressor with its load-following strategy was found to be the main parasitic power (~ 40 % of the fuel cell system net power output at the altitude of 3000 m). Ambient air temperature and relative humidity affect mostly the fuel cell system heat management but also its water balance. In designing the system, factors such as control strategy, duty cycles and ambient conditions need to taken into account.</p><p>An evaluation of the performance and maintenance of three fuel cell buses in operation in Stockholm in the demonstration project Clean Urban Transport for Europe (CUTE) was performed. The availability of the buses was high, over 85 % during the summer months and even higher availability during the fall of 2004. Cold climate-caused failures, totalling 9 % of all fuel cell propulsion system failures, did not involve the fuel cell stacks but the auxiliary system. The fuel consumption was however rather high at 7.5 L diesel equivalents/10km (per July 2004). This is thought to be, to some extent, due to the robust but not energy-optimized powertrain of the buses. Hybridization in future design may have beneficial effects on the fuel consumption. </p><p>Surveys towards hydrogen and fuel cell technology of more than 500 fuel cell bus passengers on route 66 and 23 fuel cell bus drivers in Stockholm were performed. The passengers were in general positive towards fuel cell buses and felt safe with the technology. Newspapers and bus stops were the main sources of information on the fuel cell bus project, but more information was wanted. Safety, punctuality and frequency were rated as the most important factors in the choice of public transportation means. The environment was also rated as an important factor. More than half of the bus passengers were nevertheless unwilling to pay a higher fee for introducing more fuel cell buses in Stockholm’s public transportation. The drivers were positive to the fuel cell bus project, stating that the fuel cell buses were better than diesel buses with respect to pollutant emissions from the exhausts, smell and general passenger comfort. Also, driving experience, acceleration and general comfort for the driver were reported to be better than or similar to those of a conventional bus.</p>

Cette thèse porte sur la modélisation des piles à combustible à membrane d'échange de protons (PEMFC), en vue de leur surveillance et de leur diagnostic par spectroscopie d'impédance. La première partie du document présente le principe de fonctionnement de ces piles, ainsi que l'état de l'art de la modélisation et des méthodes de surveillance et diagnostic. Le modèle physique multi échelle particulièrement détaillé publié en 2005 par A.A. Franco sert de point de départ. Il est simplifié de façon à aboutir à un système d'équations aux dérivées partielles en une unique dimension spatiale. L'objectif principal de la seconde partie est l'analyse harmonique du fonctionnement de la pile. En s'inspirant de travaux classiques sur l'analyse géométrique de réseaux de réactions électrochimiques, un modèle réduit compatible avec la thermodynamique est obtenu. Cette classe de systèmes dynamiques permet de déterminer, pour un tel réseau, une formule analytique de l'impédance de l'anode et de la cathode d'une pile PEMFC. Un modèle complet de la pile est obtenu en connectant ces éléments à des éléments représentant la membrane, les couches diffuses et les couches de diffusion des gaz. Les modèles précédents supposent la pile représentée par une cellule unique et homogène. Afin de permettre d'en décrire les hétérogénéités spatiales, nous proposons finalement un résultat de modélisation réduite d'un réseau de cellules représentées par leur impédance. Ce modèle approxime l'impédance globale du réseau par une "cellule moyenne", connectée à deux cellules "série" et "parallèle" représentatives d'écart par rapport à la moyenne. / This PhD thesis focuses on reduced modeling of PEM fuel cell for supervision and diagnosis by impedance spectroscopy. The first part of the document presents the principle of the PEM fuel cell, as well as the state of the art of modeling and of the methods for supervision and diagnosis. The multiscale dynamic model published in 2005 by A.A. Franco is particularly detailed and serves as a starting point. It is simplified, in order to obtain a system of partial differential equations in a single spatial dimension. The second part is devoted to harmonic analysis of the PEM Fuel cell. Inspired by classical work on the geometric analysis of electrochemical reactions networks, a model compatible with thermodynamics is obtained. This class of dynamic systems allows establishing, for such a network, an analytical formula of the impedance of the anode and the cathode of the PEM fuel cell. A complete model of the cell is obtained by connecting these elements to the membrane, diffuse layers and gas diffusion layer. The previous models assumed the PEM Fuel cell represented by a single, homogeneous, cell. In order to describe the possible spatial heterogeneities, we finally propose a result of reduced modeling for the impedance of a cell network. This model approximates the overall impedance of the network by a "mean cell", connected to two cells, put in "serial" and "parallel", and representative of the deviations from the average.