Recently, due to the unique properties and structures such as large geometric surface area, electrical conductivity and light weight, 3D structured carbon materials have been attracting extensive attention from scientists. Moreover, the materials, which can provide well-defined pathways for reactants to easily access active sites, are extremely useful for energy conversion as well as environmental and catalysis applications. To date, many precursors have been used for fabrication of 3D structured carbon materials including pitch, carbon nanotubes, graphene, and polymer foams. This thesis, as shown in the thesis title, focus on two main aspects: the study of the characteristics of melamine based carbon foam synthesized at different conditions and their applications. In paper I, it was revealed that through a simple, one-step pyrolysis process, flexible carbon foam synthesized from melamine foam (BasotectÒ, BASF) was obtained. Additionally, through a pyrolysis-activation process, activated carbon foam which possesses hydrophilic nature and high surface area was successfully synthesized. The characteristics of carbon foam such as the hydrophobic/hydrophilic nature, electrical conductivity, mechanical properties and surface chemistry were studied. It was shown that carbon foam could be successfully used as an absorbent in environmental applications e.g. removing of spill oil from water (paper I) or as support for heterogeneous catalysts, which in turn was used not only in gas phase reactions (paper I and IV) but also in an aqueous phase reaction (paper II). Importantly, when combined with a SpinChem® rotating bed reactor (SRBR) (paper II), the monolithic carbon foam/SRBR system brought more advantages than using the foam alone. Additionally, the work in paper III showed the potential of carbon foam in an energy conversion application as anode electrode substrate in alkaline water electrolysis. In summary, the versatility of the carbon foam has been proven through abovementioned lab scale studies and due to the simple, scalable and cost effective pyrolysis and activation processes used for the production, it has potential to be used in large-scale applications.

La mise au point récente d’une nouvelle technique permettant l’enrichissement de l’eau en oxygène par électrolyse relance l’intérêt de recherches sur les bénéfices potentiels de cette modalité d’oxygénation. Dans ce contexte, nos objectifs étaient de caractériser les effets de cette eau enrichie en oxygène sur la respiration mitochondriale, l’oxygénation tissulaire périphérique lors d’un état de stabilité hémodynamique, et sur la performance et la production de stress oxydant lors d’un exercice physique. Les résultats mettent en évidence un effet de l’administration de l’eau enrichie en oxygène par électrolyse au niveau cellulaire et tissulaire.Le mécanisme, expliquant à la fois une meilleure affinité de la mitochondrie pour l’oxygène et les effets sur l’oxygénation périphérique, pourrait être dû à un effet qualitatif sur la diffusion de l’oxygène au niveau tissulaire. / The recent development of a new technique for enriching water in oxygen by electrolysis relaunch the research interest on the potential benefits of this modality of oxygenation. In this context, our objective was to characterize the effects of 02-water on mitochondrial respiration, peripheral tissue oxygenation during a state of hemodynamic stability, and on the performance and the production of oxidative stress in a sub-maximal exercise. The results show an effect of the administration of water enriched in oxygen by electrolysis at the cellular and tissue level. The mechanism explaining both a better affinity of mitochondria for oxygen and the effects on peripheral oxygenation could be due to aqualitative effect on the diffusion of oxygen at the tissue level.

The replacement or loading-reduction of precious metal catalysts with low-cost, earth-abundant materials is an important step for the development of next-generation industrial chemical processes. By decreasing the potential cost of an electrolyzer device or enabling new pathways of upgrading biomass-derived oxygenates (BDOs), the nitrides and oxides of earth-abundant transition metals may be strategically utilized for the modular use of renewable power or the transition of conventional chemical feedstocks to renewable sources. This thesis uses a combination of electrochemical and surface science techniques to study the catalytic properties of nitrogen- and oxygen-modified earth-abundant materials for the electrolysis of water, and the surface reactions of three BDOs: ethanol, glycerol, and tetrahydrofurfuryl alcohol (THFA). The development of stable, active, and low-cost electrocatalysts with reduced platinum group metal (PGM) loading for the hydrogen evolution reaction (HER) is an important step towards the grid-level implementation of electrolyzers. In this thesis, the electrochemical stability of tungsten nitride (WN) and niobium nitride (NbN) was characterized over broad pH-potential regimes, from which pseudo-Pourbaix diagrams were developed. In addition, unmodified and platinum-modified WN and NbN thin films were assessed for HER, where monolayer (ML) Pt-modification led to Pt-like HER activity in acid electrolyte. The selective bond scission of oxygen-rich and functionally complex biomass-derived oxygenates offers a unique opportunity to convert renewable biomass, as opposed to fossil fuels, into important industrial feedstocks. The fundamental surface reactions of three BDOs, either lignin-derived or biofuel-derived, was studied in this thesis. Ethanol reforming was studied on unmodified and Pt-modified Mo2N thin film surfaces for the production of synthesis gas, or syngas, a CO and H₂ gas feedstock for Fischer-Tropsch synthesis. Mo₂N, and the Mo₂C carbide analogue, have exhibited strong oxophilicity for the reaction of simple and complex alcohols that results in unselective C-O bond scission. Pt-modification was used to selectively conserve the C-O bond for CO production, and cleave the C-H and C-C bonds for H2 generation. Pt-modification shifted the reaction pathway from undesired decomposition on Mo₂N to reforming, while inhibiting undesired pathways such as ethylene or methane production. The hydrodeoxygenation (HDO) of glycerol, the primary manufacturing byproduct of biodiesel, to propylene was studied on WOx-modified Pt(111) surfaces. Two WOx active sites were observed for the deoxygenation of glycerol: Brønsted acid WOx sites for dehydration and oxygen vacancy sites for hydrodeoxygenation (HDO). While the undesired dehydration of glycerol to acrolein was most active on surfaces with thick WOx coverages, propylene production via the HDO pathway was more facile at intermediate coverages. Lastly, the ring-opening of THFA, a promising biomass-derived platform oxygenate, was studied on WOx/Pt(111) surfaces. The desired ring-opened product, 1,5-PeD, was also used as a probe molecule to study binding and desorption on WOx/Pt(111) surfaces. This work indicates that WOx-modification weakens the interaction between the ring-opened intermediate and the surface, to an extent that facilitates the hydrogenation of the 1,5-PeD-like intermediate and the desorption of gas-phase 1,5-PeD.

Cette thèse porte sur l’étude et le développement d’électrocatalyseurs à base d’iridium pour la réaction de dégagement de dioxygène (OER) dans les électrolyseurs à membrane échangeuse de protons. En raison de la dégradation marquée des électrocatalyseurs en conditions OER, nous nous sommes particulièrement intéressés à la recherche d’un compromis optimal entre activité catalytique et stabilité. Différents électrocatalyseurs (supportés sur noir de carbone, supportés sur oxydes métalliques dopés et non-supportés) ont été synthétisés et caractérisés par des méthodes électrochimiques et physico-chimiques, notamment par spectroscopie photoélectronique X, microscopie électronique en transmission à localisation identique et spectrométrie de masse à plasma à couplage inductif. Les électrocatalyseurs supportés sont les moins stables en conditions OER, notamment du fait de l’agglomération, la coalescence, la dissolution et le détachement des nanoparticules d’oxyde d’iridium. Ces deux derniers mécanismes de dégradation sont exacerbés par la corrosion des supports carbonés et la dissolution des éléments composant les supports oxydes métalliques dopés. Les électrocatalyseurs non-supportés offrent ainsi le meilleur compromis entre activité et stabilité. Les degrés d’oxydation Ir(III) et Ir(V) ont été identifiés comme les plus actifs pour l’OER en électrolyte acide tandis que l’oxyde Ir(IV) est le plus stable, l’espèce la moins stable étant l’iridium métallique Ir(0). La dégradation des couches catalytiques en cellule d’électrolyse PEM ne semble impacter que très peu les performances globales d’électrolyse par rapport à la dégradation des collecteurs de courant. / This thesis focuses on the study and the development of iridium-based electrocatalysts for the oxygen evolution reaction (OER) in proton exchange membrane water electrolyzers. This work investigates in particular electrocatalyst degradation phenomena and aims at reaching an optimal OER activity-stability ratio. Various electrocatalysts (supported on high-surface area carbon, supported on doped-metal oxides and unsupported) have been synthetized and characterized by electrochemical and physico-chemical methods such as X-ray photoelectron spectroscopy, identical-location transmission electron microscopy and inductively coupled plasma mass spectrometry. Supported electrocatalysts feature stability limitations in OER conditions as revealed by agglomeration, coalescence, dissolution, and detachment of iridium oxide nanoparticles, these last two degradation mechanisms being amplified by corrosion of the carbon supports and dissolution of the elements composing the doped metal oxide supports. Unsupported electrocatalysts currently represent the best compromise between OER activity and stability. Ir(III) and Ir(V) oxides were shown to be the most active towards the OER while Ir(IV) oxide is the most stable, the least stable species being metallic iridium Ir(0). In real PEM water electrolyzers, the global electrolysis performance seems to be less impacted by the degradation of catalytic layers than the degradation of current collectors.

Hydrogen gas (H2), that is not produced from fossil oil or natural gas, is expected to become a cornerstone in the energy transition strategy in Europe. The recent years, technological and economic advances in the electrolyzer area, along with political and corporate support, have put H2 at the forefront of many countries’ climate change agenda. Consequently, green H2 is poised to play a large role in the coming energy transition to combat climate change. The possible advantages of integrating H2 production with a combined heat and power plant, or CHP, is investigated in this study. More precisely, the water electrolysis is carried out based on the purified flue gas condensate water and excess heat is recovered as district heating. A comparison of today’s three most common electrolyzer technologies was made, where Proton Exchange Membrane, or PEM, technology was chosen for this project, mainly for its high purity of H2 gas, robust construction, and the ability to run it as a fuel cell. Based on a mass and energy balance, a model including the integration of a PEM with a generic CHP plant was developed. The model was made modifiable, making it possible to change governing parameters, to be able to investigate different possible scenarios. Production flows, losses and other relevant data was calculated from the model. Operational data for the PEM electrolyzer were collected from several manufacturers where a mean value of the data was used as a base-case for the calculations. Based on literature and consulting experts, several assumptions were made, for example the selling price of H2 and the price for electricity. From the base-case were two cases made: a linear and non-linear case. The linear case uses the same input data each year for 20 years, while the non-linear case uses a changing input data each year for 20 years. Calculations were based on an electrolyzer size of 1,4 MW, where auxiliary equipment consumed additional 0,04 MW, resulting in a total energy consumption of 1,44 MW. An operational temperature of 80°C was assumed along with an operational pressure of 5 and 30 bar for the anode and cathode respectively. This resulted in an H2 production flow of 26 kg/h, a process water requirement of 0,2 m3/h, and a possible heat recovery amount of 0,34 MWh with a relevant temperature for the use in district heating. The study shows that the condensate-water at E.ON could provide for ~4000 hours of operation in the wintertime. To enable full operation all year around, a purchase of tap water would be necessary. The economical calculations resulted in an H2 production cost of 53 SEK/kg for the linear case and 58 SEK/kg for the non-linear case. The linear case showed a positive internal rate of return, or IRR, of 1,7%, while the non-linear case resulted in IRR < -25%. A sensitive analysis was made to examine governing parameters. The results of the sensitivity analysis showed that the largest driving variables, that significantly affect the IRR, are the price for electricity and the selling price for H2. The largest OPEX cost was found to be the price of electricity. The results showed that it is feasible to produce H2 at E.ON Örebro in a resource efficient way under certain circumstances, correlated to the electricity and H2 market. With a low electricity price and a selling price of ~50 SEK/kg for H2, good profitability is expected.  It is also clear that future work should focus the areas of O2 usage, infrastructure, and market investigation for a more definitive conclusion.

Den globala ekonomin är idag starkt kopplad till utsläpp av växthusgaser samtidigt som det finns en stark enighet bland världens ledande länder att kraftigt minska de globala utsläppen i enlighet med Parisavtalet. Vätgas som produceras från förnyelsebara energikällor anses utgöra en nyckelroll för ett antal olika applikationsområden de kommande decennierna, där bland transportsektorn. Trots att framställningsprocessen bygger på väl utvecklad teknik finns det än idag väldigt få storskaliga produktionsanläggningar av grön vätgas, men teknikutvecklingen inom området är skyndsam. Rederi AB Gotland är idag Sveriges äldsta rederi och således en av de största aktörerna inom Gotlands transportsektorn. Företaget ser idag över möjligheten för att driftsätta Sveriges första storskaliga vätgasdrivna gods- och passagerarfartyg, GotlandHorizon, vilket är en viktig del i företagets miljöarbete. Huvudsakligen avser företaget attvätgasen produceras lokalt på Gotland, vilket föranleder till en rad olika tekniska utmaningarrelaterade till elproduktion, vätgasframställning och distributionssystem. Med bakgrund av detta har en förstudie tillsammans med Uppsala universitet och projektet “Vätgasbaserad färjetrafik” genomförts för att påvisa och kartlägga viktiga aspekter kring ett framtida produktionssystem av grön vätgas samt kartlägga vilka tekniska lösningar som inom tidsramen för projektet är tekniskt genomförbara. Resultatet av förstudien ska kunna användas som grund för utformning av framtida beräkningsmodeller. Av förstudien framgår det att vattenelektrolys i kombination med en utbyggnation av vindkraft teoretiskt kan möta både det efterfrågade elbehovet för elektricitet och således Gotland Horizons vätgasbehov. Det uppskattade elbehovet för framställning av vätgas genom vattenelektrolys motsvarar dock Gotlands idag totala energikonsumtion, vilket såldes utgör en storutmaning. En annan viktig faktor för processen är en tillförlitlig processvattenförsörjning. Gotland har de senaste åren haft en problematisk grundvattensituation samt att dricksvattenproduktionen på Gotland är begränsad. I studien har de viktiga aspekterna kring utformningen av produktionssystemets analyserats. De ekonomiska aspekterna har också redovisats för att ligga till grund för en optimeringsmodell för vidare analys och optimering av produktionssystemet. Av de beräkningsmodeller som genomförts påvisas att både havsbaserad- samt landbaserad vindkraft kan tillgodose behovet av elproduktion för vattenelektrolys, det är snarare en fråga om hur systemet ska optimeras samt vilka synergieffekter som respektive system kan medförasom bestämmer systemets utformning. Solenergi har ansetts vara tekniskt möjligt men till bakgrund av att efterfrågan på elektricitet året runt är hög anses anläggningen bli orealistiskt stor. Också aspekter gällande produktionssystemet utformning, centraliserat eller decentraliserats, har diskuterats. Till bakgrund av de stora ekonomiska storskalsfördelarna som uppskattas för elektrolysörer inom de kommande åren anses ett centraliserat produktionssystem vara det mest tänkbara utifrån ett ekonomiskt perspektiv. Det har också konstaterats att havsbaserade vätgaspipelines kan bli aktuellt vid havsbaserad vätgasproduktion, det för att minimera kapitalkostnaderna för distributionen av energivektor, vilket skulle kunna minska produktionskostnaderna för vätgas från havsbaserad vindkraft. / The global economy today is strongly linked to greenhouse gas emissions while there is a strong consensus among the world's leading countries to significantly reduce global emissions in accordance with the Paris Agreement. Hydrogen produced from renewable energy sources is considered to play a key role within a several different application areas in the coming decades, including the transport sector. Even though the production process is based on welldeveloped technology, there are still very few large-scale production facilities of green hydrogen, but technological development in the field is rapid. Rederi AB Gotland is today Sweden's oldest shipping company and thus one of the largest players in Gotland's transport sector. The company is currently reviewing the possibility of commissioning Sweden's first large-scale hydrogen-powered freight and passenger vessel, Gotland Horizon, which is an important part of the company's environmental work. Mainly, the company intends that the hydrogen is produced locally on Gotland, which leads to a variety of technical challenges related to electricity production, hydrogen production and distribution systems. With this background, a feasibility study together with Uppsala University and the project "Hydrogen-based ferry traffic" has been carried out to demonstrate and map important aspects of a future production system of green hydrogen and to map which technical solutions within the time frame of the project are technically feasible. The results of the feasibility study can be used as a basis for designing future calculation models. The feasibility study shows that water electrolysis in combination with an expansion of wind power can theoretically meet both the demanded electricity demand for electricity and thus Gotland Horizon's hydrogen needs. However, the estimated electricity demand to produce hydrogen through water electrolysis corresponds to Gotland's current total energy consumption, which was sold poses a major challenge. Another important factor for the process is a reliable process water supply. In recent years, Gotland has had a problematic groundwater situation and the drinking water production on Gotland is limited. In the study, the important aspects of the design of the production system have been analyzed. The economic aspects have also been accounted for to form the basis for an optimization model for further analysis and optimization of the production system. From the calculation models carried out, it is shown that both offshore and onshore wind power can meet the need for electricity production for water electrolysis, it is rather a question of how the system should be optimized and what synergies each system can bring that determine the design of the system. Solar energy has been considered technically possible, but given that the demand for electricity all year round is high, the plant is considered to be unrealistically large. Aspects of the design of the production system, centralised or decentralised, have also been discussed. Considering the large economic economies of scale appreciated for electrolysers in the coming years, a centralized production system is considered the most conceivable from an economic perspective. It has also been recognized that offshore hydrogen pipelines may be relevant in offshore hydrogen production, in order to minimize the capital costs of energy vector distribution, which could reduce the production costs of hydrogen from offshore wind.

Vätgas kan framställas från förnybara energikällor genom vattenelektrolys med anjonbytande membran (AEMWE). AEMWE har vissa fördelar jämfört med traditionell alkalisk vattenelektrolys och elektrolysmed protonledande membran. Till exempel finns det möjlighet att använda alkalisk elektrolyt (även rent vatten) och billiga platinagruppsmetallfria katalysatorer tillsammans med ett anjonbytesmembran. Den största utmaningen med tekniken är att uppnå utmärkt och stabil prestanda för membran och elektroder. AemionTM anjonbytande membran (AEMs) av olika tjocklek, vattenupptag och kapacitet undersöktes i ett AEMWE system med 5 cm2 elektrodarea. Elektrokemisk prestanda hos dessa kommersiella AEM studerades med hjälp av porösa nickel elektroder. Bland de undersökta membranen visade AF2-HWP8-75-X stabil prestanda med en högfrekvent resistans (HFR) på 90 mΩ•cm2 och kunde nå en strömtäthet på 0,8 A/cm2 vid 2,38 V med 1 M KOH vid 60 ˚C.  AEMWE med AF2-HWP8-75-X och olika elektrodkombinationer undersöktes under samma driftsförhållanden. En elektrodkombination med Raney-Ni och NiFeO som katod respektive anod visade bäst prestanda under utvärderingen och gav en strömtäthet på 1,06 och 3,08 A/cm2 vid 2,00 respektive 2,32 V. KOH-lösningens temperatur och koncentration sänktes till 45 ˚C respektive 0,1 M för att undersöka effekten av driftsparametrar på flödescellens prestanda. Flödescellen uppvisade god stabilitet under de nya driftsförhållandena, men dess prestanda minskade avsevärt. Den nådde en strömtäthet på 0,8 A/cm2 vid 2,25 V. / Hydrogen can be produced from renewable energy sources using a novel anion exchange membrane water electrolysis (AEMWE) system. AEMWE has some benefits over the currently used state-of-the-art alkaline and proton exchange membrane water electrolysis systems. For instance, there is a possibility of using alkaline electrolytes (even pure water) and low-cost platinum-group-metal free catalysts together with an ion exchange membrane. However, the main challenge is that the AEMWE system should show excellent and stable performance, depending on the stability of the membrane and the electrodes. AemionTM anion exchange membranes (AEMs) of different thickness and water uptake capacity were investigated using a 5 cm2 AEMWE system. The electrochemical behaviour of these commercial AEMs was studied using nickel (Ni) felt electrodes. Among the investigated AEMs, the AF2-HWP8-75-X showed stable performance with a high frequency resistance (HFR) of 90 mΩ•cm2 and was able to reach a current density of 0.8 A/cm2 at 2.38 V using 1 M KOH at 60 ˚C.  AEMWE systems based on AF2-HWP8-75-X and different electrode combinations were examined under the same operating conditions. An electrode combination with Raney-Ni and NiFeO as cathode and anode, respectively, showed the best performance during the degradation test and provided a current density of 1.06 and 3.08 A/cm2 at 2.00 and 2.32 V, respectively. The operating temperature and concentration of the KOH solution were reduced to 45 ˚C and 0.1 M, respectively, to study the effect of operating parameters on the flow cell performance. The flow cell showed good stability under the new operating conditions, but its performance was reduced significantly. It reached a current density of 0.8 A/cm2 at 2.25 V.

This study has focused on solid oxide electrolyser cells for high temperature steam electrolysis. Solid oxide electrolysis is the reverse operation of solid oxide fuel cells (SOFC), so many of the same component materials may be used. However, other electrode materials are of interest to improve performance and efficiency. In this work anode materials were investigated for use in solid oxide electrolysers. Perovskite materials of the form L₁₋ｘSrｘMO₃ , where M is Mn, Co, or Fe. LSM is a well understood electrode material for the SOFC. Under electrolysis operation LSM performed well and no interface reactions were observed between the anode and YSZ electrolyte. LSM has a relatively low conductivity and the electrode reaction is limited to the triple phase boundary regions. Mixed ionic-electronic conductors of LSCo and LSF were investigated, with these materials the anode reaction is not limited to triple phase boundaries. The LSCo anode had adherence problems in the electrolysis cells due to the thermal expansion coefficient mismatch with the YSZ electrolyte. The LSCo reacted with the YSZ at the anode/electrolyte interface forming insulating zirconate phases. Due to these issues the LSCo anode cells performed the poorest of the three. The performance of electrolysis cells with LSF anode exceeded both LSM and LSCo, particularly under steam operation, although an interface reaction between the LSF anode and YSZ electrolyte was observed. In addition to the anode material studies this work included the development of solid oxide electrolyser tubes from tape cast precursor materials. Tape casting is a cheap processing method, which allows for co-firing of all ceramic components. The design development resulted in a solid design, which can be fabricated reliably, and balances strength with performance. The design used LSM anode, YSZ electrolyte, and Ni-YSZ cathode materials but could easily be adapted for the use of other component materials. Proper sintering rates, cathode tape formulation, tube length, tape thickness, and electrolyte thickness were factors explored in this work to improve the electrolyser tubes.

Thesis. (M. Tech. (Dept. Electronic Engineering, Faculty of Engineering and Technology))--Vaal University of Technology, 2011. / There are a number of ways to produce hydrogen using solar energy as the primary source. Water electrolysis, which uses solar electrical energy, is the rapidly available process. Hydrogen can be produced by using solar electric energy from photovoltaic (PV) modules for the electrolysis of water without emitting carbon dioxide or requiring fossil fuels. Solar hydrogen energy systems are considered one of the cleanest hydrogen production technologies, where the hydrogen is obtained from sunlight by directly connecting the photovoltaic modules to the hydrogen generator. This dissertation presents a designed solar photovoltaic electrolyser hydrogen production and storage system for various applications such as in the power generation and telecommunications industries. Various experiments were performed on the designed system to ensure its reliability and conformity with theoretical findings. The purity of the generated hydrogen was determined. The relationship between the amount of solar irradiance reaching the surface of the PV panel, the PV panel surface temperature, the PV panel tilt angle and the maximum power point voltage and current of the PV panel array were also considered. The effect of dust on the panel voltage and current outputs was also determined. Finally, the factors to consider when designing a solar photovoltaic electrolyser hydrogen system (based on this study) were enumerated.

Οι κυψέλες καυσίμου είναι ηλεκτροχημικές διατάξεις οι οποίες επιτρέπουν την απευθείας μετατροπή της ελεύθερης χημικής ενέργειας ενός καυσίμου σε ηλεκτρική. Η λειτουργία τους βασίζεται σε μία αντίδραση οξείδωσης ενός καυσίμου, η οποία λαμβάνει χώρα στην άνοδο, και σε μία αντίδραση αναγωγής ενός οξειδωτικού μέσου, η οποία λαμβάνει χώρα στην κάθοδο. Οι κυψέλες καυσίμου πολυμερικής μεμβράνης (ΡΕΜ) χρησιμοποιούν ηλεκτρολύτη αγωγιμότητας Η+, το θερμοκρασιακό εύρος λειτουργίας τους είναι 30-100oC και αποτελούν μία υποσχόμενη τεχνολογία, που βρίσκεται πολύ κοντά στο στάδιο της εμπορευματοποίησης. Το κυριότερο καύσιμο που χρησιμοποιείται στις κυψέλες καυσίμου είναι το Η2, το οποίο παράγεται συνήθως από διεργασίες αναμόρφωσης υδρογονανθράκων ή αλκοολών. Το μονοξείδιο του άνθρακα που παράγεται επίσης κατά την διαδικασία της αναμόρφωσης, αποτελεί ένα σημαντικό άλυτο πρόβλημα στις κυψέλες καυσίμου τύπου ΡΕΜ, καθώς η ρόφησή του στην άνοδο της κυψέλης, παρεμποδίζει τη ρόφηση του Η2. Στην παρούσα εργασία μελετάται η ηλεκτρόλυση του νερού με χρήση μεμβρανών πρωτονιακής αγωγιμότητας καθώς και η μελέτη της βελτίωσης της απόδοσης κελιών καυσίμου τύπου ΡΕΜ μέσω τριοδικής λειτουργίας υπό συνθήκες δηλητηριασμού με CO. Στο πρώτο κεφάλαιο της εργασίας γίνεται μια εισαγωγή στην τεχνολογία των κυψελών καυσίμου, την αρχή λειτουργίας τους και τις θερμοδυναμικές αρχές που την διέπουν. Στην συνέχεια περιγράφονται εκτενώς τα χαρακτηριστικά των κυψελών καυσίμου πολυμερικής μεμβράνης, τα state-of-the-art υλικά που χρησιμοποιούνται και το πρόβλημα της διαχείρισης του νερού. Το δεύτερο κεφάλαιο αποτελεί επίσης εισαγωγικό κεφάλαιο και αναφέρεται στη σημασία του υδρογόνου. Το υδρογόνο δεν αποτελεί μόνο ένα καύσιμο, είναι ένα καύσιμο το οποίο δύναται να αλλάξει άμεσα την σημερινή δομή της οικονομίας που βασίζεται στα ορυκτά καύσιμα (fossil fuels). Στο κεφάλαιο αυτό, αρχικά γίνεται μια ιστορική αναδρομή και στη συνέχεια αναλύονται οι μέθοδοι παραγωγής του και ο ρόλος του ως καύσιμο. Το τρίτο κεφάλαιο αφορά την ηλεκτρόλυση του νερού η οποία γίνεται με χρήση διατάξεων που χρησιμοποιούν ως ηλεκτρολύτη μια πολυμερική μεμβράνη πρωτονιακής αγωγιμότητας. Αρχικά, γίνεται μια θεωρητική εισαγωγή στη διαδικασία ηλεκτρόλυσης του νερού και στη συνέχεια μια αναφορά στις διατάξεις οι οποίες χρησιμοποιούνται για ηλεκτρόλυση. Ακολουθεί το πειραματικό μέρος, όπου περιγράφονται η παρασκευή της συστοιχίας ανόδου/ηλεκτρολύτη/καθόδου (ΜΕΑ), της πειραματικής διάταξης, της προετοιμασίας των καταλυτών καθώς και η παρουσίαση των πειραματικών αποτελεσμάτων. Κατά την ηλεκτρόλυση του νερού σε κελί καυσίμου τύπου PEM, παρατηρήθηκε 100% εκλεκτικότητα σε οξυγόνο, χρησιμοποιώντας ηλεκτρόδια IrO2 εναποτεθημένα με τη μέθοδο του sputtering σε υπόστρωμα Ti/C. Βρέθηκε ότι το ποσοστό του Nafion επηρεάζει τόσο το ρυθμό παραγωγής οξυγόνου όσο και την εκλεκτικότητα και προστατεύει τις θέσεις C-IrO2 για παραγωγή CO2 και οδηγεί σε 100% εκλεκτικότητα προς οξυγόνο. Στο τέταρτο κεφάλαιο μελετάται η τριοδική λειτουργία των κυψελών καυσίμου υπό συνθήκες δηλητηριασμού της ανόδου με CO. Ένα από τα σημαντικότερα προβλήματα της χρήσης των κελιών καυσίμου είναι ο δηλητηριασμός του ανοδικού ηλεκτροδίου πλατίνας από CO. Αυτό συμβαίνει διότι κατά την αναμόρφωση των ασθενών υδρογονανθράκων ή υγρών αλκοολών σε υδρογόνο, ταυτόχρονα παράγονται σημαντικά επίπεδα μονοξειδίου του άνθρακα τα οποία δηλητηριάζουν την άνοδο και οδηγούν σε υποβάθμιση της απόδοσης του κελιού. Ο σκοπός της μελέτης αυτής είναι να ερευνηθεί μια εναλλακτική προσέγγιση για την ενίσχυση της απόδοσης των PEMFCs υπό συνθήκες δηλητηριασμού με CO, χρησιμοποιώντας την πρόσφατη περιγραφή του σχεδιασμού και της λειτουργίας των τριοδικών κελιών καυσίμου. Αρχικά στο τέταρτο κεφάλαιο, γίνεται περιγραφή της αρχής λειτουργίας της τριοδικής διάταξης, της προετοιμασίας των ηλεκτροδίων καθώς και της παρασκευής της ΜΕΑ. Επίσης περιγράφεται η ακριβής γεωμετρία της διάταξης του τριοδικού PEMFC με τα ηλεκτρικά κυκλώματα και η ακριβής γεωμετρία της συστοιχίας των τριοδικών PEMFCs. Στη συνέχεια περιγράφεται αναλυτικά η πειραματική διαδικασία που ακολουθήθηκε για τη λήψη των πειραματικών δεδομένων και ακολουθούν τα πειραματικά αποτελέσματα. Πρώτα παρουσιάζονται τα πειραματικά αποτελέσματα για τη συμβατική λειτουργία με τροφοδοσία Η2. Ακολουθούν τα αποτελέσματα για τη συμβατική λειτουργία του κελιού υπό δηλητηριασμό με CO και τέλος, παρουσιάζονται τα πειραματικά αποτελέσματα της τριοδικής λειτουργίας. Αναφέρεται επίσης αναλυτικά η εξέταση του μηχανισμού της τριοδικής λειτουργίας και το πώς θα μπορούσε να υπάρξει πρακτική εφαρμογή συστοιχιών, οι οποίες θα αποτελούνται από μια τριοδική κυψέλη. Η τριοδική λειτουργία των κελιών καυσίμου τύπου PEM υπό συνθήκες δηλητηριασμού της ανόδου με CO, οδηγεί σε σημαντική αύξηση της ισχύος του κελιού και συγκεκριμένα η τιμή της είναι τρείς φορές μεγαλύτερη από εκείνη που παράγεται κατά τη συμβατική λειτουργία της κυψέλης καυσίμου. Η αύξηση της παραγόμενης ισχύος, είναι μεγαλύτερη κατά ένα παράγοντα της τάξης του 1.32 από την ισχύ που καταναλώνεται στο βοηθητικό κύκλωμα, και οφείλεται σε σημαντική μείωση της ανοδικής υπέρτασης, η οποία με τη σειρά της είναι αποτέλεσμα του εφοδιασμού της ανόδου με πρωτόνια μέσω του βοηθητικού κυκλώματος. Αυτός ο εφοδιασμός με πρωτόνια, αυξάνει το ηλεκτροχημικό δυναμικό των πρωτονίων και το χημικό δυναμικό του υδρογόνου στην άνοδο, με αποτέλεσμα να μειώνεται η κάλυψη της ανόδου με CO και έτσι να ενισχύεται ο ρυθμός της ηλεκτροχημικής του οξείδωσης. Τέλος, στο κεφάλαιο 5 παρουσιάζονται τα τελικά συμπεράσματα που έχουν προκύψει από την παρούσα μελέτη, καθώς και προτάσεις για μελλοντική εργασία. / Fuel cells are electrochemical devices that can convert the chemical energy of a reaction directly into electrical energy. Their operation is based on the oxidation of a fuel, taking part at the anode, and the reduction of an oxidant, taking part at the cathode. Polymer Electrolyte Membrane (PEM) fuel cells use as the electrolyte a polymer membrane with H+ conductivity. PEMs work at a temperature range 30-100oC and this technology is promising and close to commercialization. The most common fuel used is hydrogen. However, H2 is not directly available, and has to be extracted from other sources, usually via hydrocarbon or alcohol reforming. During this procedure carbon monoxide is formed as well. When a reformate mixture is fed to the anode of a PEM, CO adsorbs strongly on the anode, leaving few remaining sites for the adsorption of H2, and thus causing severe degradation in PEMs performance. The aim of this thesis was to study τhe role of Nafion content in sputtered IrO2 based anodes for low temperature PEM water electrolysis and also it was examined the enhanced performance of CO poisoned proton exchange membrane fuel cells via triode operation. The first chapter refers to the technology of fuel cells, their operating principles and the thermodynamic aspects. It is focused on the PEM fuel cells, the state-of-the-art materials used and the problem of water management. The second chapter gives an introduction about hydrogen which is a very prominent fuel and can straightly change the economy that is based on fossil fuels. Firstly, in this chapter is presenting, a throwback of hydrogen and a short presentation of methods of hydrogen production. Chapter 3 refers to PEM water electrolysis. It is presenting a theoretical introduction about electrolysis process and a description of the sets up that are used for electrolysis. The procedure for preparing a membrane electrode assembly and the experimental setup are also described. Stable water electrolysis was achieved in a PEM, with 100% selectivity to oxygen, using IrO2 electrodes sputter-deposited on a Ti/C support interfaced with the Nafion electrolyte. It was found that the amount of Nafion content on the electrode can affect both the rate of the oxygen evolution and the oxygen selectivity. It also appears that Nafion ionomer addition protects the C-IrO2 active sites for carbon oxidation leading to 100% selectivity to oxygen. In chapter 4 is studied the effect of triode operation on the performance of CO poisoned PEM fuel cells One of the main problems associated with the practical utilization of PEMFC units is that of CO poisoning of the Pt-based anode. This is because hydrogen-rich reformates of light hydrocarbons or liquid alcohols inevitably contain significant levels of carbon monoxide that poisons the anode and degrades fuel cell performance. The objective of this work is to investigate an alternative approach for enhancing the PEMFC performance under CO poisoning conditions by using the recently described triode fuel cell design and operation. Firstly, in chapter 4 it is described, the operating principle of the triode set up, the preparation of the electrodes and the MEA preparation. Also it is described the exact geometry of the triode set up and the schematic of a possible design of a triode PEMFC stack. It is delineated the procedure that was followed in order to obtain all the experimental data. First are presented the experimental results obtained in the conventional fuel cell operation mode without and with CO added to the anode feed gas and then proceed with the detailed presentation of the triode operation results. Ιt is also mentioned the investigation of the triode operation mechanism and the design of a triode PEMFC stuck. Triode operation of CO poisoned PEM fuel cells leads to very significant, threefold, increase in power output of the fuel cell circuit. This increase in power output is up to a factor of 1.32 larger than the power sacrificed in the auxiliary circuit and is mainly due to a significant decrease in anodic overpotential caused by the supply of protons to the anode via the auxiliary electrode. This proton supply increases the electrochemical potential of protons and chemical potential of hydrogen at the anode, thus decreasing the coverage of CO and enhancing its electrooxidation rate. Finally, the general conclusions of this study and proposals for future studies are given in chapter 5.