Ce travail de thèse s'inscrit dans la continuité des travaux de recherche sur l'utilisation d'hétérocycles azotés pour l'élaboration de membranes échangeuses de protons pour piles à combustible de type PEMFC fonctionnant sous faible taux d'humidité relative (HR < 25 %) et à des températures allant jusqu'à 200 °C pour l'application automobile. Pour cela, trois nouveaux copolymères partiellement fluorés porteurs de trois groupements azole (imidazole, benzimidazole et 1H-1,2,4-triazole) ont été synthétisés et caractérisés. Ils ont ensuite été utilisés pour l'élaboration de membranes polymères (20 µm < épaisseurs < 100 µm) par mélange avec le s-PEEK. Ces membranes sont stables thermiquement jusqu'à 210 °C. Les trois séries de membranes ont été comparées et les meilleurs résultats de conductivité protonique ont été obtenus pour celles contenant le 1H-1,2,4-triazole (σ = 7,0 mS.cm-1, 140 °C, HR < 25 %). Les propriétés mécaniques de ces membranes ont été mesurées et ont montré des valeurs comparables à celles des principales membranes commerciales (de type Nafion®). Afin d'obtenir une meilleure structuration de ces membranes, une stratégie d'élaboration de pseudo réseaux semi-interpénétrés de s-PEEK dans un réseau polymère réticulé a été mise au point. Pour cela, de nouveaux terpolymères porteurs de groupements 1H-1,2,4-triazole et de groupements cyclocarbonate réticulables par la réaction cyclocarbonate / amine ont été synthétisés et caractérisés. Ces terpolymères ont été mélangés à du s-PEEK puis réticulés par une diamine pour former des pseudo réseaux semi-interpénétrés de faibles épaisseurs (20 µm < e < 60 µm) qui ont été caractérisés. Ces membranes à architecture pseudo réseaux semi-interpénétrés ont montré de meilleures propriétés mécaniques mais des valeurs de conductivité protonique légèrement inférieures à celles des membranes non réticulées. Enfin, les membranes réticulées ou non ont été dopées par l'acide phosphorique pour augmenter leurs valeurs de conductivité protonique. Des essais en mono-cellule de PAC de ces membranes dopées ont été effectués et ont montré de bonnes performances. Des estimations par extrapolations des résultats ont ensuite été effectuées à plus hautes températures (140 – 200 °C) et ont montré que les valeurs de conductivité protonique atteignent jusqu'à 210 et 250 mS.cm-1, à 180 et 200 °C, HR < 25 % (valeurs extrapolées). Ces valeurs extrapolées doivent être vérifiées par la réalisation de mesures de conductivité protonique à ces températures (140 – 200 °C). / This work concerns the syntheses and characterizations of new proton exchange polymer membranes containing N-heterocyclic compounds for PEMFC working under low relative humidity (HR < 25 %) and temperatures up to 200 °C for automotive applications. Three new partially fluorinated copolymers bearing different azole compounds (imidazole, benzimidazole or 1H-1,2,4-triazole) as pendant groups have been synthesized and characterized. Then, they have been used to synthesize blend polymer membranes with s-PEEK (20 µm < thickness < 100 µm) that showed thermal stabilities up to 210 °C. These new families of membranes have been compared and highest proton conductivity values have been observed for 1H-1,2,4-triazole containing membranes (σ = 7,0 mS.cm-1, 140 °C, HR < 25 %). Mechanical properties and oxidative stability of these membranes have been assessed and showed similar values than main commercially available membranes. To improve membranes structuration, pseudo semi-interpenetrating polymer networks have been synthesized. Thus, original cross-linkable terpolymers bearing 1H-1,2,4-triazole and cyclocabonate functions as pendant groups have been synthesized and blended with s-PEEK as linear polymer to synthesize new polymers membranes (20 µm < thickness < 60 µm). Cross-linking has been carried from the cyclocarbonate/diamine reaction to get pseudo semi-interpenetrated polymer networks. Finally, both pseudo semi-interpenetrated polymer networks and uncross-linked membranes were doped by immersion in phosphoric acid solution to increase proton conductivity of these materials. Single cell fuel cell tests have been carried out and showed good performances. High temperatures (140 – 180 °C) proton conductivity values of these doped membranes have been estimated from extrapolation curves and reached up to 210 and 250 mS.cm-1, at 180 and 200 °C, HR < 25 %, respectively (extrapolated values). Proton conductivity values should be assessed at these targeted temperatures (140 to 200 °C).

O alto custo da produção de hidrogênio puro para ser usado como combustível para uma reação de oxidação de hidrogênio (ROH) em células a combustível faz com que seja atrativo o uso de hidrogênio gerado através da reforma de combustíveis fóssil. Entretanto, o hidrogênio gerado por reforma de outros combustíveis possui contaminantes como CO, que por se adsorver fortemente sobre a superfície do eletrodo de platina, prejudica em muito o processo de oxidação do hidrogênio. Assim o estudo de novos catalisadores mais resistentes a essa contaminação e de outros mecanismos que contribuam para um melhor desempenha de uma célula a combustível do tipo PEMFC, se faz necessário. Esse presente trabalho tem como objetivo o estudo dos catalisadores PtMo/C - 80:20, PtMoO2/C, PtMoO3/C, que foram sintetizados, e PtMoPtRu/C, PtMoPt3Fe/C e PtMoPt3FePtRu/C que foram obtidos através da mistura do PtMo/C - 80:20 sintetizado com os PtRu/C e PtFe/C que são comerciais, através da realização de curvas de polarização no estado estacionário, voltametrias cíclicas e degradação eletroquímica acelerada. Também foi avaliada a eficiência da membrana de Aquivion&reg;, com relação ao cruzamento de subprodutos da degradação dos eletrodos, através de curvas de polarização no estado estacionário, voltametrias cíclicas e variação de temperatura de operação da célula PEMFC. O método usado para a síntese dos eletrocatalisadores se mostrou eficiente na obtenção dos catalisadores, obtendo-se os catalisadores com proporção bem próxima da desejada. Os resultados mostraram uma grande estabilidade química dos catalisadores mistos sendo o PtMoPt3FePtRu/C o mais estável e o PtMoPtRu/C o catalisador mais ativo para uma ROH. Os experimentos com a membrana de Aquivion&reg; mostraram que essa é capaz de diminuir o cruzamento de subprodutos da degradação dos eletrodos. / The high cost of pure hydrogen production to be used as fuel for a hydrogen oxidation reaction (HOR) in fuel cells makes it attractive to use hydrogen generated by reforming of fossil fuels. However, the hydrogen generated by reforming other fuels has contaminants such as CO, which adsorb strongly on the surface of the platinum electrode, affect much the hydrogen oxidation process. Thus the study of new catalysts more resistant to such contamination and other mechanisms that contribute to a better performs of a fuel cell of the PEMFC type, it is necessary. This present study aims to study of catalysts PtMo/C - 80:20 PtMoO2/C, PtMoO3/C, which were synthesized and PtMoPtRu/C, PtMoPt3Fe/C and PtMoPt3FePtRu/C which were obtained by mixing the PtMo/C - 80:20 synthesized with PtRu/C and PtFe/C which are commercial, by performing polarization curves at steady state, cyclic voltammetry and electrochemical degradation accelerated. It also evaluated the efficiency of Aquivion&reg; membrane with respect to the cross-products of degradation of the electrodes by means of polarization curves at steady state, cyclic voltammetry and operating temperature range of the cell PEMFC. The method used for the synthesis of electrocatalysts proved efficient in obtaining the catalysts, the catalysts obtaining very near to the desired proportion. The results showed a great chemical stability of the mixed catalyst being PtMoPt3FePtRu/C more stable and PtMoPtRu/C as catalyst more active for HOR. Experiments with Aquivion&reg; membrane have shown that this can reduce the cross-products of degradation of the electrodes.

Este trabalho apresenta resultados de estudos e caracterizações de Conjuntos Eletrodo/Membrana (MEAs) de Células a Combustível a Membrana Polimérica (PEMFC). Algumas condições de operação de células e diferentes processos de produção de MEA foram investigados. A técnica de Espectroscopia de Impedância Eletroquímica (EIE) (em situ - 0 a 16 A) foi usada \"on-line\" como uma ferramenta de diagnóstico, relativa ao desempenho de célula. As medidas de EIE foram feitas através do Sistema de EIE para células a combustível FC350 (GAMRY), junto a um PC4 Potentiostato/Galvanostato e conectado à carga dinâmica (TDI) para experimentos de EIE \"on-line\" (100 mHz - 10 kHz, dU = 5 mV). MEAs com 25 cm2 de área ativa, usando eletrocatalisadores PtM/C 20 % (M = Ru, Sn ou Ni) fabricados usando o Método de Redução por Álcool (MRA). A tinta catalítica foi diretamente aplicada no Tecido de Carbono (GDL) e este prensado na membrana de Nafion® (105). MEAs usando eletrocatalisadores Pt/C e PtRu/C 20 % da E-TEK foram fabricados para comparação. Todos os cátodos foram confeccionados com Pt/C 20% da E-TEK. Foram fixadas as concentrações de metal nobre em 0,4 mg Pt.cm-2 no anodo e 0,6 mg Pt.cm-2 no catodo (E-TEK). Diagramas de Nyquist dos MEAs com Pt/C e PtRu/C da E-TEK ou PtM/C MRA apresentaram as mesmas resistências de ôhmicas para os MEAs. Este fato pode ser explicado por supressão de aglomerados durante o processo de preparação do MEA ou pela homogeneidade do eletrocatalisador ancorado ao carbono. Também pôde ser observado, a baixas densidades atuais que há uma diferença de desempenho significante entre o eletrocatalisadores da ETEK e os preparados pelo MRA. Os resultados das curvas de polarização confirmaram que PtM/C MRA apresentara um aumento de atividade para as células alimentadas com metanol e etanol. A técnica de EIE se mostrou eficiente para a avaliação do método de preparação dos MEAs e do desempenho da célula, os resultados de EIE mostraram uma coerência na escolha do modelo do circuito elétrico para os MEAs utilizando hidrogênio, metanol e etanol. Esta coerência indica que outras resistências não consideradas no modelo não são relevantes na resistência total dos MEAs. / This work reports results of studies and characterization on Membrane Electrode Assemblies (MEAs) for Proton Exchange Membrane Fuel Cell (PEMFC). Some cell operation conditions and different processes of MEA production were investigated. The Electrochemical Impedance Spectroscopy Technique (EIS) (in situ - 0 to 16 A) was used \"on-line\" as a tool for diagnosis, concerning the cell performance. The EIS measurements were carried out with a FC350 Fuel Cell EIS System (GAMRY), coupled to a PC4 Potentiostat/Galvanostat and connected to the electronic load (TDI) for \"on-line\" EIS experiments (100 mHz - 10 kHz, dU = 5 mV). MEAs with 25 cm2 surface area, using PtM/C 20% (M = Ru, Sn or Ni) electrocatalysts were manufactured using the Alcohol Reduction Process (ARP). The catalytic ink was applied directly into the Carbon Cloth (GDL) and pressed in the NafionR membrane (105). MEAs using Pt/C and PtRu/C 20% from E-TEK electrocatalysts were manufactured by comparison. All the cathodes were sprayed with Pt/C 20% from E-TEK. The noble metal concentrations used were set to 0.4 mg Pt.cm-2 at the anode and 0.6 mg Pt.cm-2 at the cathode (E-TEK). Nyquist diagrams of the MEAs with Pt/C and PtRu/C from E-TEK or PtM/C (M = Ru, Sn or Ni) ARP showed essentially the same ohmic resistances for the MEAs. This fact can be explained by suppression of agglomerates during the MEA preparation process or by the homogeneity of the anchored electrocatalysts at the carbon surface. It could also be observed, at low current densities, that there was a significant performance difference between the electrocatalysts from E-TEK and those prepared with the Alcohol Reduction Process. The polarization curves results confirmed that the PtM/C (M = Ru, Sn or Ni) ARP showed an activity increase for the methanol and ethanol fed cells. The technique of EIE was shown efficient for the evaluation of the method preparation of MEAs and the acting of the cell, the results of EIE showed coherence in the choice of the model the electric circuit for MEAs using hydrogen, methanol and ethanol. This coherence indicates that other resistances no considered in the model are not relevant in the total resistance of MEAs.

La pile à combustible convertit l’énergie chimique des réactants en énergie électrique continue, en chaleur et en eau. Elle est généralement utilisée autour d’un point de fonctionnement (ou zone) correspondant à un maximum de puissance électrique. Le courant continu produit par la réaction d’oxydo-réduction est proportionnel à la surface active de la pile et la tension, qui est d’environ 0,6 V au point de nominal de fonctionnement, peut être augmentée par la mise en série de plusieurs cellules (constituant un stack). En raison de son faible niveau de tension continue, son utilisation dans des systèmes électriques nécessitent de l’associer à des convertisseurs de puissance. Les travaux effectués dans le cadre de cette thèse s’intéressent au potentiel d’une source électrique continue basse tension et plus exactement à l’utilisation de la pile à combustible en fonctionnement source de courant commandée (par le débit d’un des réactants). L’expertise du laboratoire GREEN dans le domaine des supraconducteurs, nous a conduits naturellement vers une application innovante à savoir substituer les alimentations de puissance dédiées aux dispositifs supraconducteurs par une pile à combustible. Un premier essai prometteur mené sur une bobine supraconductrice de 4 mH a mis en évidence tout le potentiel d’une telle application et nous a encouragés à étendre l’étude à des bobines supraconductrices fortement inductives, des plusieurs henrys. En effet, les énergies mises en jeu sont alors plus importantes et exigent de dimensionner avec soin le banc d’essai, aussi bien du point de vue de la protection de la pile que des conditions opératoires. Pour ce faire, une modélisation et une expérimentation d’un ensemble pile à combustible/bobine supraconductrice ont également été réalisées. En parallèle du travail mené sur la partie alimentation de la bobine supraconductrice, nous avons travaillé sur le dimensionnement d’un dispositif supraconducteur innovant, communément appelé aimant vectoriel, à trois axes. Ce système peut servir comme charge pour une pile à combustible mais aussi, et surtout, comme outils de caractérisation d’échantillons supraconducteurs. Cet aimant vectoriel permet d’orienter dans les 3 directions de l’espace un champ magnétique de plusieurs teslas, uniforme à plus de 95 % dans une sphère de 100 mm de diamètre. Ce dimensionnement, nous a permis de concevoir et réaliser la structure supportant le bobinage du fil et de choisir un certain fil supraconducteur. Le système complet devant coûter moins de 50 k€, cryostat inclus, nous nous sommes orientés vers du fil supraconducteur à basse température critique, refroidi à l’hélium liquide / The fuel cell (FC) converts the chemical energy of the reactants into direct electrical energy, heat and water. The FC is generally used around an operating point (or area) corresponding to a maximum of electric power. The direct current produced by the redox reaction is proportional to the active surface of the single cell and its voltage, which is approximately 0.6 V at the nominal operating point, can be increase by connecting several cells in series (constituting a stack). Due to its low DC voltage amplitude, its use in electrical systems requires the use of power converters. In this work, we have been interested taking benefit of such DC low voltage power source and more precisely the use of the FC as a current source controllable by the one of the reactant flow rates. The expertise of GREEN laboratory in the field of superconductors has naturally led us to an innovative application, namely to substitute the power supplies dedicated to the superconducting devices by a FC. A first promising test conducted on a 4 mH superconducting coil highlighted the full potential of such an application and encouraged us to extend the study to highly inductive superconducting coils where the energies involved are more important. This requires to carefully design the test bench with a protection system for the FC as well as operating conditions. To this end, a FC model supplying a superconducting coil has been developed and tested experimentally. At the same time, we have focused on the supply part of the superconducting coil by designing an innovative superconducting device, commonly called a three-axis vector magnet. This system can be used as a load for a fuel cell, but also, and above all, as a tool for the characterization of superconducting samples. This vector magnet allows to orient a magnetic field of several tesla in the three space directions, with a uniformity of more than 95 % in a 100 mm sphere of diameter. This design allowed us to realize the windings supporting structure and to choose a superconducting wire. The complete system has to cost less than 50 k€, including the cryostat, we have finally choose a superconducting wire with low critical temperature, cooled by liquid helium

Two diazonium perfluoroalkyl arylsulfonimide (PFSI) zwitterionic monomers, 4-diazonium perfluoro(3-oxapent-4-ene)benzenesulfonimide (I) and 4-(trifluoromethyl)-2-diazonium perfluoro(3-oxapent-4-ene)benzenesulfonimide (II) have been synthesized from perfluoro(3-oxapent-4-ene) sulfonyl fluoride (POPF) for proton exchange membrane fuel cells. PFSI polymers are proposed as new electrolytes due to their better thermal stability, inertness to electrochemical conditions, and lower susceptibility to oxidative degradation and dehydration. For a better integration between the electrode and the electrolyte, the PFSI polymers are expected to be grafted onto the carbon electrode via the diazonium moiety. All the reaction intermediates and the final product were characterized with 1H NMR, 19F NMR and IR spectroscopies.

3-Diazonium- 4-(trifluorovinyloxy) - perfluorobutanesulfonyl benzenesulfonimide zwitterionic monomer (see figure 1) is proposed to be polymerized and further act as a new electrolyte for Polymer exchange membrane fuel cells (PEMFCs). One reason is that, the aromatic trifluorovinyl aryl ether (TFVE) group can easily be homopolymerized to aromatic perfluorocyclobutane (PFCB) polymer. Furthermore, the diazonium moiety in the monomer is expected to covalently attach the electrolyte to the carbon electrodes support. The perfluoroalkyl(aryl) sulfonimide (PFSI) pendant provides good chemical and mechanical stability as well as better proton conductivity. Several multi-step synthetic schemes are designed to obtain such monomer from perfluoroalkyl(aryl) sulfonimide (PFSI). Among them, the purified coupling product 4-OCF2CF2Br-3-NO2-PhSO2(M) SO2C4F9 from the first approach was successfully completed. The next stages of the work will involve dehalogenation, reduction, and diazotization to achieve the targeting monomer. All the intermediates were characterized by 1H and 19F NMR and FT-IR spectroscopy.

The subject of this thesis relates to the design of new polymer electrolytes for battery and fuel cell applications. Classical Molecular Dynamics (MD) modelling studies are reported of the nano-structure and the local structure and dynamics for two types of polymer electrolyte host: poly(ethylene oxide) (PEO) for lithium batteries and perfluorosulfonic acid (PFSA) for polymer-based fuel cells. Both polymers have been modified by side-chain substitution, and the effect of this on charge-carrier transport has been investigated. The PEO system contains a 89-343 EO-unit backbone with 3-15 EO-unit side-chains, separated by 5-50 EO backbone units, for LiPF6 salt concentrations corresponding to Li:EO ratios of 1:10 and 1:30; the PFSA systems correspond to commercial Nafion®, Hyflon® (Dow®) and Aciplex® fuel-cell membranes, where the major differences again lie in the side-chain lengths. The PEO mobility is clearly enhanced by the introduction of side-chains, but is decreased on insertion of Li salts; mobilities differ by a factor of 2-3. At the higher Li concentration, many short side-chains (3-5 EO-units) give the highest ion mobility, while the mobility was greatest for side-chain lengths of 7-9 EO units at the lower concentration. A picture emerges of optimal Li+-ion mobility correlating with an optimal number of Li+ ions in the vicinity of mobile polymer segments, yet not involved in significant cross-linkages within the polymer host. Mobility in the PFSA-systems is promoted by higher water content. The influence of different side-chain lengths on local structure was minor, with Hyflon® displaying a somewhat lower degree of phase separation than Nafion®. Furthermore, the velocities of the water molecules and hydronium ions increase steadily from the polymer backbone/water interface towards the centre of the proton-conducting water channels. Because of its shorter side-chain length, the number of hydronium ions in the water channels is ~50% higher in Hyflon® than in Nafion® beyond the sulphonate end-groups; their hydronium-ion velocities are also ~10% higher. MD simulation has thus been shown to be a valuable tool to achieve better understanding of how to promote charge-carrier transport in polymer electrolyte hosts. Side-chains are shown to play a fundamental rôle in promoting local dynamics and influencing the nano-structure of these materials.

<p>The aim of my work is to model a segment of a unit cell of a fuel cell stack using numerical methods which is classified as computational fluid dynamics and implementing the work in a commercial computational fluid dynamics package, FLUENT. The focus of my work is to study the thermal distribution within this segment. The results of the work aid in a better understanding of the fuel cell operation in this temperature range. At the time of my investigation experimental results were unavailable for validation and therefore my results are compared to previously published results published. The outcome of the results corresponds to this, where the current flux density increases with the increasing of operating temperature and fixed operating voltage and the temperature variation across the fuel cell at varying operating voltages. It is in the anticipation of determining actual and or unique material input parameters that this work is done and at which point this studies results would contribute to the understanding high temperature PEM fuel cell thermal behaviour, significantly.</p>

The proton exchange membrane fuel cell (PEMFC) is a potential electrochemicalpower device for vehicles, auxiliary power units and small-scale power plants. In themembrane electrode assembly (MEA), which is the core of the PEMFC single cell,oxygen in air and hydrogen electrochemically react on separate sides of a membraneand electrical energy is generated. The main challenges of the technology are associatedwith cost and lifetime. To meet these demands, firstly, the component expensesought to be reduced. Secondly, enabling system operation at elevated temperatures,i.e. up to 120 °C, would decrease the complexity of the system and subsequentlyresult in decreased system cost. These aspects and the demand for sufficientlifetime are the strong motives for development of new materials in the field.In this thesis, MEAs based on alternative materials are investigatedwith focus on hydrocarbon proton-conducting polymers, i.e. ionomers, and newcatalyst supports. The materials are evaluated by electrochemical methods, such ascyclic voltammetry, polarisation and impedance measurements; morphological studiesare also undertaken. The choice of ionomers, used in the porous electrodes andmembrane, is crucial in the development of high-performing stable MEAs for dynamicoperating conditions. The MEAs are optimised in terms of electrode compositionand preparation, as these parameters influence the electrode structure andthus the MEA performance. The successfully developed MEAs, based on the hydrocarbonionomer sulfonated polysulfone (sPSU), show promising fuel cell performancein a wide temperature range. Yet, these membranes induce mass-transportlimitations in the electrodes, resulting in deteriorated MEA performance. Further,the structure of the hydrated membranes is examined by nuclear magnetic resonancecryoporometry, revealing a relation between water domain size distributionand mechanical stability of the sPSU membranes. The sPSU electrodes possessproperties similar to those of the Nafion electrode, resulting in high fuel cell performancewhen combined with a high-performing membrane. Also, new catalystsupports are investigated; composite electrodes, in which deposition of platinum(Pt) onto titanium dioxide reduces the direct contact between Pt and carbon, showpromising performance and ex-situ stability. Use of graphitised carbon as catalystsupport improves the electrode stability as revealed by a fuel cell degradation study.The thesis reveals the importance of a precise MEA developmentstrategy, involving a broad methodology for investigating new materials both as integratedMEAs and as separate components. As the MEA components and processesinteract, a holistic approach is required to enable successful design of newMEAs and ultimately development of high-performing low-cost PEMFC systems. / QC 20100922

In this thesis, direct hydrogen Proton Exchange Membrane (PEM) fuel cell systems in vehicles are investigated through modelling, field tests and public acceptance surveys. 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, e.g. 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. 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 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, e.g. 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.e. 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. 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. 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. / QC 20101020