La gazéification est aujourd'hui l'une des stratégies les plus prometteuses pour valoriser les déchets en énergie. Cette technologie thermo-chimique permet une réduction de 95 % de la masse des intrants et génère des cendres inertes ainsi que du gaz de synthèse (syngaz). Le syngaz est un combustible gazeux composé principalement de monoxyde de carbone (CO), d'hydrogène (H2) et de dioxyde de carbone (CO2). Le syngaz peut être utilisé pour produire de la chaleur et de l'électricité. Il est également la pierre angulaire d'un grand nombre de produits à haute valeur ajoutée, allant de l'éthanol à l'ammoniac et l'hydrogène pur. Les applications en aval de la production de syngaz sont dictées par son pouvoir calorifique, lui-même dépendant de la teneur du gaz en H2. L’augmentation du contenu du syngaz en H2 est rendu possible par la conversion catalytique à la vapeur d’eau, largement répandu dans le cadre du reformage du méthane pour la production d'hydrogène. Au cours de cette réaction, le CO est converti en H2 et CO2 selon : CO + H2O → CO2 + H2. Ce processus est possible grâce à des catalyseurs métalliques mis en contact avec le CO et de la vapeur. La conversion catalytique à la vapeur d’eau a jusqu'ici été réservé pour de grandes installations industrielles car elle nécessite un capital et des charges d’exploitations très importantes. Par conséquent, les installations de plus petite échelle et traitant des intrants de faible qualité (biomasse, déchets, boues ...), n'ont pas accès à cette technologie. Ainsi, la seule utilisation de leur syngaz à faible pouvoir calorifique, est limitée à la génération de chaleur ou, tout au plus, d'électricité. Afin de permettre à ces installations une gamme d’application plus vaste de leurs syngaz, une alternative économique à base de catalyseur biologique est proposée par l’utilisation de bactéries hyperthermophiles hydrogénogènes. L'objectif de cette thèse est d'utiliser Carboxydothermus hydrogenoformans, une bactérie thermophile carboxydotrophe hydrogénogène comme catalyseur biologique pour la conversion du monoxyde de carbone en hydrogène. Pour cela, l’impact d'un phénomène de biominéralisation sur la production d’H2 a été étudié. Ensuite, la faisabilité et les limites de l’utilisation de la souche dans un bioréacteur ont été évaluées. Tout d'abord, la caractérisation de la phase inorganique prédominante lorsque C. hydrogenoformans est inoculé dans le milieu DSMZ, a révélé une biominéralisation de phosphate de calcium (CaP) cristallin en deux phases. L’analyse par diffraction des rayons X et spectrométrie infrarouge à transformée de Fourier de ce matériau biphasique indique une signature caractéristique de la Mg-whitlockite, alors que les images obtenues par microscopie électronique à transmission ont montré l'existence de nanotiges cristallines s’apparentant à de l’hydroxyapatite. Dans les deux cas, le mode de biominéralisation semble être biologiquement induit plutôt que contrôlé. L'impact du précipité de CaP endogène sur le transfert de masse du CO et la production d’H2 a ensuite été étudié. Les résultats ont été comparés aux valeurs obtenues dans un milieu où aucune précipitation n'est observée. Dans le milieu DSMZ, le KLa apparent (0.22 ± 0.005 min-1) et le rendement de production d’H2 (89.11 ± 6.69 %) étaient plus élevés que ceux obtenus avec le milieu modifié (0.19 ± 0.015 min-1 et 82.60 ± 3.62% respectivement). La présence du précipité n'a eu aucune incidence sur l'activité microbienne. En somme, le précipité de CaP offre une nouvelle stratégie pour améliorer les performances de transfert de masse du CO en utilisant les propriétés hydrophobes de gaz. En second lieu, la conversion du CO en H2 par la souche Carboxydothermus hydrogenoformans fut étudiée et optimisée dans un réacteur gazosiphon de 35 L. Parmi toutes les conditions opérationnelles, le paramètre majeur fut le ratio du débit de recirculation du gaz sur le débit d'alimentation en CO (QR:Qin). Ce ratio impacte à la fois l'activité biologique et le taux de transfert de masse gaz-liquide. En effet, au dessus d’un ratio de 40, les performances de conversion du CO en H2 sont limitées par l’activité biologique alors qu’en dessous, elles sont limitées par le transfert de masse. Cela se concrétise par une efficacité de conversion maximale de 90.4 ± 0.3 % et une activité spécifique de 2.7 ± 0.4 molCO·g–1VSS·d–1. Malgré des résultats prometteurs, les performances du bioréacteur ont été limitées par une faible densité cellulaire, typique de la croissance planctonique de C. hydrogenoformans. Cette limite est le facteur le plus contraignant pour des taux de charge de CO plus élevés. Ces performances ont été comparées à celles obtenues dans un réacteur à fibres creuses (BRFC) inoculé par la souche. En dépit d’une densité cellulaire et d’une activité volumétrique plus élevées, les performances du BRFC à tout le moins cinétiquement limitées quand elles n’étaient pas impactées par le transfert de masse, l'encrassement et le vieillissement de la membrane. Afin de parer à la dégénérescence de C. hydrogenoformans en cas de pénurie de CO, la croissance de la bactérie sur pyruvate en tant que seule source de carbone a été également caractérisée. Fait intéressant, en présence simultanée de pyruvate et de CO, C. hydrogenoformans n’a amorcé la consommation de pyruvate qu’une fois le CO épuisé. Cela a été attribué à un mécanisme d'inhibition du métabolisme du pyruvate par le CO, faisant ainsi du pyruvate le candidat idéal pour un système in situ de secours. / Gasification is today one of the most promising strategies to recover energy from waste. This thermo-chemical technology allows a 95% weight reduction of the input and generates inorganic inert ashes as well as a synthesis gas (syngas). Syngas is a gaseous fuel mainly composed of carbon monoxide (CO), hydrogen (H2) and carbon dioxide (CO2). Syngas can be burned to produce heat and electricity. It is also the building block of many high added- value products ranging from ethanol to ammonia and pure hydrogen. Downstream applications of syngas production will depend on its heating value, which is determined by its content in H2. Upgrading the H2 content in syngas is performed by the water-gas shift (WGS) reaction, widely utilized during methane reforming for hydrogen production. During the WGS reaction CO is converted to H2 and CO2 according to: CO + H2O → CO2 + H2. This process is achieved using a metallic catalyst in a heterogeneous gas-phase reaction with CO and steam. The WGS reaction has so far been reserved for large-scale gasification plants and requires high capital and operational expenditures. Hence, smaller scale plants that process low-grade materials (biomass, waste, sludge...), would not have access to such technology. The only possible outcome with the synthesis gas (syngas) produced and which generally has a poor heating value, is to generate heat or at best, electricity. In order to offer small plants access to the WGS reaction and to a higher range of products from their syngas, an alternative to the expensive and energy-intensive established catalyst-based WGS is here considered, such as extreme-thermophilic microbial processes carried out by hydrogenogens. The goal of this thesis was to use Carboxydothermus hydrogenoformans, a thermophilic carboxydotrophic hydrogenogenic bacterium as a biological catalyst for the WGS reaction. This was done by characterizing the impact of a growth-associated biomineralization phenomenon on H2 production and assessing the feasibility and limitations of using the strain in a bioreactor. First, characterization of the predominant inorganic phase when Carboxydothermus hydrogenoformans was inoculated in the DSMZ medium revealed the biomineralization of two crystalline CaP phases. The X-ray diffractometry peaks and Fourier transform infrared spectroscopy spectrum of this biphasic material consistently showed features characteristic of Mg-whitlockite, whereas transmission electron microscopy analysis showed the existence of hydroxyapatite-like nanorods crystals. In both cases, the mode of biomineralization appears to be biologically induced rather than biologically controlled. The impact of the endogenous CaP precipitate on CO mass transfer and H2 production was thus assessed and compared to a medium where no precipitation was observed. In the DSMZ medium, the apparent KLa (0.22 ±0.005 min-1) and H2 production yield (89.11 ±6.69%) were higher than the ones obtained in the modified medium (0.19 ±0.015 min-1 and 82.60 ±3.62% respectively). The presence of the precipitate had no impact on C. hydrogenoformans CO uptake. Overall, the CaP precipitate offers a novel strategy for gas-liquid mass transfer enhancement using CO hydrophobic properties. Second, the conversion of CO into H2 by C. hydrogenoformans was investigated and optimized in a 35 L gas-lift reactor. Upon all operational conditions, the ratio of gas recirculation over CO feed flow rates (QR:Qin) was the major parameter that impacted both biological activity and volumetric gas-liquid mass transfer. The CO conversion performance of the gas lift reactor was kinetically limited over a QR:Qin ratio of 40, and mass transfer limited below that ratio, resulting in a maximum conversion efficiency of 90.4±0.3% and a biological activity of 2.7±0.4 molCO· g–1VSS· day–1. Despite very promising results, CO conversion performance was limited by a low cell density, typical of C. hydrogenoformans planktonic growth. This limitation was found to be the most restrictive factor for higher CO loading rates. Results were compared to the performance of the strain inoculated in a hollow fiber membrane bioreactor where performance, despite the higher cell density and volumetric activity, was biokinetically limited, when not limited by gas–liquid mass transfer, membrane fouling and aging. To avoid any C. hydrogenoformans decay during potential CO shortages, growth of the bacterium on pyruvate as a sole carbon source was characterized. Interestingly, when grown simultaneously on pyruvate and CO, pyruvate consumption was initiated upon CO depletion. This was attributed to the inhibition of pyruvate oxidation by CO, making pyruvate the ideal candidate for an in-situ back-up system.

The proton exchange membrane fuel cell generates electricity from hydrogen and oxygen (from air) through electrocatalytic reactions in an electrochemical cell. The Pt/C catalyst, commonly used in PEM fuel cells, is very sensitive to impurities that can interact with the active catalyst sites and limit fuel cell performance. Unfortunately, most hydrogen is currently produced from fossil sources, and inevitably contains impurities. The subject of this thesis is the effect of hydrogen impurities on the operation of a PEM fuel cell using a Pt/C anode. The impurities studied are carbon monoxide (CO), carbon dioxide (CO2), and selected hydrocarbons. Particular focus is given to the interaction between the impurities studied and the anode catalyst. The main method used in the study involved performing cyclic voltammetry and mass spectrometry, simultaneously. Other electrochemical techniques are also employed. The results show that all the impurities studied adsorb to some extent on the Pt/C catalyst surface, and require potentials comparable to that of CO oxidation, i.e., about 0.6V, or higher to be removed by oxidation to CO2. For complete oxidation of propene, and toluene, potentials of above 0.8, and 1.0V, respectively, are required. The unsaturated hydrocarbons can be desorbed to some extent by reduction, but oxidation is required for complete removal. Adsorption of ethene, propene, and CO2 is dependent on the presence of adsorbed or gaseous hydrogen. Hydrogen inhibits ethene and propene adsorption, but facilitates CO2 adsorption. Adsorption of methane and propane is very limited and high concentrations of methane cause dilution effects only. The adlayer formed on the Pt/C anode catalyst in the presence of CO2, or moderate amounts of hydrocarbons, is found to be insffuciently complete to notably interfere with the hydrogen oxidation reaction. Higher concentrations of toluene do, however, limit the reaction. / Polymerelektrolytbränslecellen genererar elektricitet fran vätgas och syrgas (fran luft) genom elektrokatalytiska reaktioner i en elektrokemisk cell. Den platina-baserade katalysator som oftast används i dessa bränsleceller är känslig mot föroreningar, då dessa kan interagera med katalysatorns aktiva yta, och därmed begränsna bränslecellens prestanda. Tyvärr produceras dagens vätgas huvudsakligen fran fossila källor och innehåller därför oundvikligen föroreningar. Denna avhandling behandlar hur olika vätgasföroreningar påverkar katalysatorns aktivitet och bränslecellens drift. De föroreningar som studeras är kolmonoxid (CO) och koldioxid (CO2), samt ett antal mindre kolväten. Störst fokus ligger på hur dessa föroreningar interagerar med anodens Pt/C katalysator. Den metod som huvudsakligen används är cyklisk voltammetri kombinerat med masspektrometri, men flera elektrokemiska metoder har använts. Resultaten visar att alla undersökta föroreningar adsorberar på Pt/C katalysatorns yta i större eller mindre utstreckning. For att avlägsna det adsoberade skiktet genom oxidation till CO2 krävs potentialer jämförbara med CO oxidation, dvs ca 0,6V, eller högre. Fullständig oxidation av propen eller toluen kräver potentialer högre än 0,8V respektive 1,0V. De omättade kolvätena kan delvis avlägsnas genom reduktion, men fullständig avlägsning kräver oxidation. Närvaron av väte, i gasform eller adsorberat pa katalysatorn, hämmar adsorptionen av eten och propen, men främjar CO2 adsorption. Metan och propan adsorberar i mycket begränsad utstreckning på Pt/C katalysatorns yta. De prestandaförluster som uppstår av höga koncentrationer av metan förklaras av utspädning av vätgasen. Det adsorberade skiktet som bildas när Pt/C katalysatorn exponeras för CO2 eller måttliga koncentrationer av studerade kolväten, är inte tillräckligt heltäckande for att märkbart påverka vätgasreduktionen. Däremot kan höga koncentrationer av toluen begränsa reaktionen. / <p>QC 20161010</p>

<p>This thesis evaluates the use of Fourier Transform Infrared Spectroscopy (FTIR) as an approach to the increasingly difficult air sampling challenges within the field of occupational and environmental hygiene. The application of FTIR is exemplified by the assessment of emissions from and exposures in the sawmill and pellet industries. </p><p>Open path FTIR was applied in the sawsheds and the terpene levels were monitored for several days. Traditional adsorbent sampling was used to evaluate the FTIR measurements. The volatile emissions from wood pellets were investigated in warehouses and in domestic storage rooms. </p><p>The installation of open path FTIR in the harsh sawmill environment proved useful, however, attention must be paid to vibrations, beam blockage and limited sensitivity. Adsorbent sampling showed good agreement with open path FTIR. The uncontrolled airflows in sawsheds caused significant underestimation of emission rates. By the use of FTIR and a tracer gas a more accurate estimate was obtained. The total emission from processing of Scots pine was estimated to 660 g/m³ of roundwood under bark, and can amount to 700 tons annually from a large sawmill.</p><p>Hexanal (111±32 mg/m³) and CO (56±4mg/m³) were recorded in pellet warehouses. Storage of wood pellets constitutes a potential occupational and domestic health hazard. Experiments from kiln drying of lumber show that the emissions of hexanal and carbon monoxide are not limited to wood pellets but are caused by general degradation processes of wood, facilitated by drying at elevated temperature. This is the first published report where low-temperature emission of carbon monoxide from wood materials is described. </p><p>The FTIR method is a significant advancement in measurement technology. The retrieved data offers unparalleled information. It offers robust, convenient and efficient monitoring of gases over extended periods. FTIR spectroscopy should be considered a standard technique within the field of occupational and environmental hygiene.</p>

<p>The HIV protease is an essential enzyme for HIV replication and constitutes an important target in the treatment of HIV/AIDS. Efficient combination therapies using inhibitors of the reverse transcriptase and protease enzymes have led many to reevaluate HIV infections from a terminal condition to a chronic-but-manageable disease in the developed world. Unfortunately, the emergence of drug resistant viral strains and severe treatment-related adverse effects limit the benefits of current anti-HIV/AIDS drugs for many patients. Furthermore, less than one in ten patients infected with HIV in low- and middle-income countries have access to proper treatment. These important shortcomings highlight the need for new, cost effective anti-HIV/AIDS drugs with unique properties.</p><p>Microwave heating has recently emerged as a productivity-enhancing tool for the medicinal chemist. Reaction times can often be reduced from hours to minutes or seconds and chemistry previously considered impractical or unattainable can now be accessed.</p><p>In this thesis, the search for unique HIV-1 protease inhibitors and the development and application of new microwave-promoted synthetic methods useful in small-scale medicinal chemistry applications are presented. Protocols for rapid amino- and hydrazidocarbonylations were developed. Mo(CO)₆ was used as a solid source of carbon monoxide, enabling a safe, efficient and simple way to exploit carbonylation chemistry without the direct use of toxic carbon monoxide gas. The aminocarbonylation methodology was applied in the synthesis of two series of new HIV-1 protease inhibitors. A biological evaluation suggested that <i>ortho</i>-substitution of P1 and/or P1’ benzyl side chains might provide a new approach to HIV-1 protease inhibitors with novel properties. To assess the scope and limitations of the <i>ortho</i>-substitution concept, a new series of compounds exhibiting fair potency was prepared by various microwave-heated, palladium-catalyzed coupling reactions. Finally, computer modeling was applied to rationalize the binding-modes and structure-activity relationships of these HIV-1 protease inhibitors.</p>

This thesis evaluates the use of Fourier Transform Infrared Spectroscopy (FTIR) as an approach to the increasingly difficult air sampling challenges within the field of occupational and environmental hygiene. The application of FTIR is exemplified by the assessment of emissions from and exposures in the sawmill and pellet industries. Open path FTIR was applied in the sawsheds and the terpene levels were monitored for several days. Traditional adsorbent sampling was used to evaluate the FTIR measurements. The volatile emissions from wood pellets were investigated in warehouses and in domestic storage rooms. The installation of open path FTIR in the harsh sawmill environment proved useful, however, attention must be paid to vibrations, beam blockage and limited sensitivity. Adsorbent sampling showed good agreement with open path FTIR. The uncontrolled airflows in sawsheds caused significant underestimation of emission rates. By the use of FTIR and a tracer gas a more accurate estimate was obtained. The total emission from processing of Scots pine was estimated to 660 g/m3 of roundwood under bark, and can amount to 700 tons annually from a large sawmill. Hexanal (111±32 mg/m3) and CO (56±4mg/m3) were recorded in pellet warehouses. Storage of wood pellets constitutes a potential occupational and domestic health hazard. Experiments from kiln drying of lumber show that the emissions of hexanal and carbon monoxide are not limited to wood pellets but are caused by general degradation processes of wood, facilitated by drying at elevated temperature. This is the first published report where low-temperature emission of carbon monoxide from wood materials is described. The FTIR method is a significant advancement in measurement technology. The retrieved data offers unparalleled information. It offers robust, convenient and efficient monitoring of gases over extended periods. FTIR spectroscopy should be considered a standard technique within the field of occupational and environmental hygiene.

The HIV protease is an essential enzyme for HIV replication and constitutes an important target in the treatment of HIV/AIDS. Efficient combination therapies using inhibitors of the reverse transcriptase and protease enzymes have led many to reevaluate HIV infections from a terminal condition to a chronic-but-manageable disease in the developed world. Unfortunately, the emergence of drug resistant viral strains and severe treatment-related adverse effects limit the benefits of current anti-HIV/AIDS drugs for many patients. Furthermore, less than one in ten patients infected with HIV in low- and middle-income countries have access to proper treatment. These important shortcomings highlight the need for new, cost effective anti-HIV/AIDS drugs with unique properties. Microwave heating has recently emerged as a productivity-enhancing tool for the medicinal chemist. Reaction times can often be reduced from hours to minutes or seconds and chemistry previously considered impractical or unattainable can now be accessed. In this thesis, the search for unique HIV-1 protease inhibitors and the development and application of new microwave-promoted synthetic methods useful in small-scale medicinal chemistry applications are presented. Protocols for rapid amino- and hydrazidocarbonylations were developed. Mo(CO)6 was used as a solid source of carbon monoxide, enabling a safe, efficient and simple way to exploit carbonylation chemistry without the direct use of toxic carbon monoxide gas. The aminocarbonylation methodology was applied in the synthesis of two series of new HIV-1 protease inhibitors. A biological evaluation suggested that ortho-substitution of P1 and/or P1’ benzyl side chains might provide a new approach to HIV-1 protease inhibitors with novel properties. To assess the scope and limitations of the ortho-substitution concept, a new series of compounds exhibiting fair potency was prepared by various microwave-heated, palladium-catalyzed coupling reactions. Finally, computer modeling was applied to rationalize the binding-modes and structure-activity relationships of these HIV-1 protease inhibitors.

This thesis concerns biogas-operated fuel cells. Fuel cell technology may contribute to more efficient energy use, reduce emissions and also perhaps revolutionize current energy systems. The technology is, however, still immature and has not yet been implemented as dominant in any application or niche market. Research and development is currently being carried out to investigate whether fuel cells can live up to their full potential and to further advance the technology. The research of thesis contributes by exploring the potential of using fuel cells as energy converters of biogas to electricity. The work includes results from four different experimental test facilities and concerns experiments performed at cell, stack and fuel cell system levels. The studies on cell and stack level have focused on the influence of CO, CO2 and air bleed on the current distribution during transient operation. The dynamic response has been evaluated on a single cell, a segmented cell and at stack level. Two fuel cell systems, a 4 kW PEFC system and a 5 kW SOFC system have been operated on upgraded biogas. A significant outcome is that the possibility of operating both PEFCs and SOFCs on biogas has been established. No interruptions or rapid performance loss could be associated with the upgraded biogas during operation. From the studies at cell and stack level, it is clear that CO causes significant changes in the current distribution in a PEFC; air bleed may recover the uneven current distribution and also the drop in cell voltage due to CO and CO2 poisoning. The recovery of cell performance during air bleed occurs evenly over the electrode surface even when the O2 partial pressure is far too low to fully recover the CO poisoning. The O2 supplied to the anode reacts on the anode catalyst and no O2 was measured at the cell outlet for air bleed levels up to 5 %. Reformed biogas and other gases with high CO2 content are thus, from dilution and CO-poisoning perspectives, suitable for PEFC systems. The present work has enhanced our understanding of biogas-operated fuel cells and will serve as basis for future studies. / QC20100708

The catalytic oxidation activity of platinum particles in automobile catalysts is thought to originate from the presence of highly reactive superficial oxide phases which form under oxygen-rich reaction conditions. The thermodynamic stability of platinum oxide surfaces and thin films was studied, as well as their reactivities towards oxidation of carbon compounds by means of first-principles atomistic thermodynamics calculations and molecular dynamics simulations based on density functional theory. On the Pt(111) surface the most stable superficial oxide phase is found to be a thin layer of alpha-PtO2, which appears not to be reactive towards either methane dissociation or carbon monoxide oxidation. A PtO-like structure is most stable on the Pt(100) surface at oxygen coverages of one monolayer, while the formation of a coherent and stress-free Pt3O4 film is favoured at higher coverages. Bulk Pt3O4 is found to be thermodynamically stable in a region around 900 K at atmospheric pressure. The computed net driving force for the dissociation of methane on the Pt3O4(100) surface is much larger than on all other metallic and oxide surfaces investigated. Moreover, the enthalpy barrier for the adsorption of CO molecules on oxygen atoms of this surface is as low as 0.34 eV, and desorption of CO2 is observed to occur without any appreciable energy barrier in molecular dynamics simulations. These results, combined, indicate a high catalytic oxidation activity of Pt3O4 phases that can be relevant in the contexts of Pt-based automobile catalysts and gas sensors.

Graphene has been shown to be very powerful as a transducer in many biosensor applications due to its high sensitivity. This enables smaller surfaces and therefore less material consumption when producing sensors and concequently cheaper and more portable sensors compared to the commercially available sensors today. The electrical properties of graphene are very sensitive to gas exposure why presence of molecules or small changes in concentration could easily be detected when using graphene as a sensing layer. Graphene is sensitive towards many molecules and in order to detect and possibly identify gas molecules the surface needs to be functionalized. The intention of this project was to use nanoparticles (NPs) to further increase sensitivity and specificity towards selected molecules and also enable biofunctionalization of the NPs, and by that tune the electrical properties of the graphene. This study proposes the use of Fe3O4 and TiO2 NPs to enable sensitive detection of volatile gases and possibly further functionalization of the NPs using biomolecules as a detecting agent in a liquid-phasebiosensor application. The interaction between graphene and NPs have been investigated using several surface charactarization methods and electrical measurements for detection of gaseous molecules and also molecules in a liquid solution. The characterizing methods used are XPS, AFM with surface-potential mapping and Raman spectroscopy with reflectance mapping in order to investigate the NPs interaction with the graphene surface. Sensors where manufactured for gas-phase detection of CO, formaldehyde, benzene and NH3 specifically and display differences in sensitivity and behavior of the Fe3O4 and TiO2 NPs respectively. For liquid measurements the difference in behavior in two buffers was investigated using an in-house flow-cell setup. The surface charecterizing measurements indicated that just a small difference could be found between the two NPs, however a significant change in sensor response could be detected as a function of coverage. The liquid and gas-phase measurements rendered information on differences in sensitivity between the NPs and between analytes where TiO2 showed a higher level of sensitivity towards most of the gases investigated. Both Fe3O4 and TiO2 NP coated graphene showed capability to detect formaldehyde and benzene down to 50 ppb and 5 ppb respectively. The sensitive gas detection could help protecting individuals being exposed to a hazardous level of volatile gases if concentrations increase rapidly or at a long term exposure with lower concentrations, improving saftey and health where these gases are present.

Οι κυψέλες καυσίμου είναι ηλεκτροχημικές διατάξεις οι οποίες επιτρέπουν την απευθείας μετατροπή της ελεύθερης χημικής ενέργειας ενός καυσίμου σε ηλεκτρική. Οι κυψέλες καυσίμου πολυμερικής μεμβράνης (ΡΕΜ) αποτελούν μία υποσχόμενη τεχνολογία που βρίσκεται κοντά στο στάδιο της εμπορευματοποίησης. Το κυριότερο καύσιμο που χρησιμοποιείται στις κυψέλες καυσίμου είναι το υδρογόνο, το οποίο παράγεται συνήθως από αναμόρφωση υδρογονανθράκων ή αλκοολών. Το μονοξείδιο του άνθρακα που παράγεται επίσης κατά την διαδικασία της αναμόρφωσης αποτελεί ένα σημαντικό άλυτο πρόβλημα στις κυψέλες ΡΕΜ, καθώς η ρόφησή του στην άνοδο της κυψέλης προκαλεί την υποβάθμιση της λειτουργίας της. Το φαινόμενο της ηλεκτροχημικής ενίσχυσης συνίσταται στην μη-φαρανταϊκή τροποποίηση της ενεργότητας ενός καταλύτη που βρίσκεται σε επαφή με έναν στερεό ηλεκτρολύτη, ως αποτέλεσμα της μετακίνησης προωθητικών ειδών από τον ηλεκτρολύτη προς την καταλυτική διεπιφάνεια μετάλλου/αερίου, που προκαλείται από την επιβολή ρεύματος ή δυναμικού μεταξύ του καταλύτη και ενός ηλεκτροδίου αναφοράς. Στην παρούσα διατριβή μελετήθηκε η ηλεκτροχημική ενίσχυση της οξείδωσης μίγματος αναμόρφωσης μεθανόλης από ανόδους πλατίνας και χρυσού μίας κυψέλης ΡΕΜ. Αποδείχθηκε πως η ηλεκτροχημική ενίσχυση επηρεάζεται σημαντικά από το διαχεόμενο διαμέσου της πολυμερικής μεμβράνης οξυγόνο, όπως επίσης και από τις συνθήκες λειτουργίας της κυψέλης καυσίμου. Επίσης μελετήθηκε η ηλεκτρική απόδοση ανόδων πλατίνας και χρυσού παρουσία CO. Προσδιορίστηκαν οι τιμές της ενθαλπίας ρόφησης του CO στα ηλεκτρόδια πλατίνας και χρυσού, καθώς και οι τιμές της ενέργειας ενεργοποίησης της απομάκρυνσης του CO από το κάθε ηλεκτρόδιο. Επίσης μελετήθηκε η επίδραση της θερμοκρασίας στο φαινόμενο της πολλαπλότητας μονίμων καταστάσεων κατά την λειτουργία κυψελών ΡΕΜ. Παρατηρήθηκε εξασθένηση του φαινομένου με την αύξηση της θερμοκρασίας, σε συμφωνία με τις προβλέψεις του μοντέλου γ. / Fuel cells are electrochemical devices which convert chemical energy of a fuel directly to electricity. Polymer electrolyte membrane (PEM) fuel cells are close to commercialization. The most common fuel used is hydrogen, which is usually produced via hydrocarbons or alcohol reforming. However, during this process, carbon monoxide is formed as well, adsorbs strongly on the anode of the cell and thus impairs significantly its performance. The electrochemical promotion effect is a phenomenon where application of constant current or potential between a catalyst supported on a solid electrolyte and a reference electrode, leads to non-Faradaic changes in catalytic activity. In this thesis, it was studied the electrochemical promotion of oxidation of a methanol reformate mixture on platinum and gold anodes of a PEM fuel cell. It was found that electrochemical promotion is influenced by oxygen crossover through the polymer membrane and also by the cell operating conditions. Moreover, the electrical efficiency of platinum and gold anodes in presence of CO was studied and the values of the heat of CO adsorption on each anode and the activation energies of CO removal were estimated. Finally, the effect of temperature on the phenomenon of steady-state multiplicities was studied. It was found that increasing the temperature, the phenomenon of multiplicities is suppressed in agreement with the gama model.