This master’s thesis deals with supercapacitors and polymer gel electrolytes. The practical part deals with the preparation of samples of polymer gel electrolyte with addition of alkali salts by measuring their electrical conductivity and evaluation potential windows.

Předkládaná práce se zabývá výzkumem nových materiálů a metod přípravy gelových polymerních elektrolytů (GPE) na bázi methakrylátů, které lze zejména vzhledem k jejich mechanickým vlastnostem s výhodou využít při konstrukci elektrochromních (EC) prvků.

Hydrogen has the potential to become an important energy carrier in the future with many areas of applications, as a clean fuel for transportation, heating, power generation in places where electricity use is not fit, etc. Already today hydrogen plays a key role in numerous industries such as petroleum refineries and chemical industries. There are different production methods for hydrogen. Today, natural gas reforming is the most commonly used. With the growing importance of green production paths, hydrogen production by electrolysis is expected to grow. Two main electrolyzer technologies are used today; alkaline and polymer electrolyte membrane electrolyzer. High-temperature electrolyzers are also interesting techniques, where solid oxide is under development and molten carbonate electrolyzers is researched. In this thesis, a comparative life cycle analysis was performed on the alkaline and molten carbonate electrolyzer. Due to inaccurate inventory data for the molten carbonate electrolyzer, those results are excluded from the published thesis. The environmental performance of the alkaline electrolyzer technology was compared to that of the solid oxide and the polymer electrolyte membrane electrolyzers. The system boundaries were set as cradle to gate. Thereby, the life cycle steps included in the study are raw material extraction, electrolyzer manufacturing, hydrogen production, and transports in between these steps. The functional unit was chosen as 100 kg produced hydrogen gas. The results show that the polymer electrolyte membrane electrolyzer has the lowest environmental impact out of the compared technologies. It is also determined that the lifetime and the current density of the electrolyzers have significant impact on their environmental performance. Moreover, it is established that electricity for hydrogen production has the highest environmental impact out of the electrolyzers life cycle steps. Therefore, it is important to make sure that the electricity used for hydrogen production derives from renewable sources. / Vätgas har potential att spela en viktig roll som energibärare i framtiden med många användningsområden, såsom ett rent bränsle för transporter, uppvärmning, kraftförsörjning där elproduktion inte är lämpligt, med mera. Redan idag är vätgas ett viktigt inslag i flera industrier, där ibland raffinaderier och kemiska industrier. Det finns flera metoder för att producera vätgas, där reformering av naturgas är den största produktionsmetoden idag. I framtiden spås vätgasproduktion med elektrolys bli allt viktigare, då hållbara produktionsprocesser prioriteras allt mer. Idag används främst två elektrolysörtekniker, alkalisk och polymerelektrolyt. Utöver dessa är högtemperaturelektrolysörer också intressanta tekniker, där fastoxidelektrolysören är under utveckling och smältkarbonatelektrolysören är på forskningsstadium. I det här examensarbetet har en jämförande livscykelanalys utförts på alkalisk- och smältkarbonatelektrolysören. På grund av felaktiga indata för smältkarbonatelektrolysören har dessa resultat uteslutits från den publika rapporten. Miljöpåverkan från den alkaliska elektrolysören har sedan jämförts med miljöpåverkan från fastoxid- och polymerelektrolytelektrolysörerna. Systemgränserna sattes till vagga till grind. De livscykelsteg som inkluderats i studien är därmed råmaterialutvinning, elektrolysörtillverkning, vätgasproduktion och transporter mellan dessa steg. Den funktionella enheten valdes till 100 kg producerad vätgas.  Resultaten visar att polymerelektrolytteknologin har den lägsta miljöpåverkan utav de tekniker som jämförts. Resultaten påvisar också att livstiden och strömtätheten för de olika teknikerna har signifikant påverkan på teknikernas miljöpåverkan. Dessutom fastslås att elektriciteten för vätgasproduktion har högst miljöpåverkan utav de studerade livscykelstegen. Därför är det viktigt att elektriciteten som används för vätgasproduktionen kommer ifrån förnybara källor.

Les recherches réalisées au cours de ce doctorat portent sur l’étude et l’optimisation de mélanges de polymères, utilisés en tant qu’électrolytes solides polymères (SPEs) dans les batteries lithium et lithium-ion. Les composants de la batterie doivent pouvoir être mis en forme par un procédé sans solvant (extrusion), afin de réduire les impacts du solvant sur les propriétés de la batterie et d’optimiser la production (diminution de la toxicité et du temps de production). Pour répondre à ces objectifs, une étude a d’abord été menée sur des mélanges de polymères, sélectionnés d’après leurs propriétés individuelles, en se concentrant notamment sur les interactions entre le sel de lithium et chaque polymère. Un classement des interactions a été développé et a permis de montrer que le principal facteur les favorisant est le nombre donneur des groupements fonctionnels polaires présents sur les chaînes polymères. Enfin, les effets de ces interactions sur les phénomènes de transport ionique dans les mélanges ont été investigués. Par la suite, l’étude s’est focalisée sur les couples de polymères ayant des propriétés prometteuses et complémentaires, tels que le poly(oxyde d’éthylène) (POE) ou le polycaprolactone (PCL), qui ont des conductivités ioniques élevées, et un copolymère butadiène-acrylonitrile hydrogéné (HNBR), qui possède des propriétés mécaniques intéressantes mais une conductivité ionique limitée. Il a été conclu que ces mélanges présentent des propriétés encourageantes, comparées aux SPEs composés d’un unique polymère, telles que des conductivités ioniques élevées sur une large plage de températures, ainsi que de meilleures propriétés de stabilités mécanique et thermique. La dernière partie de ces travaux s’est portée sur l’optimisation des propriétés de ces mélanges, par une méthode innovante de réticulation sélective d’une des phases. Pour conclure ce doctorat, l’objectif final a été de réaliser un prototype performant de batterie lithium tout solide, entièrement obtenu par extrusion, et dont l’électrolyte et le liant au sein des électrodes composites sont composés des électrolytes polymères optimisés. Les résultats prometteurs obtenus ont permis la soumission d’un brevet, en association avec le partenaire industriel (TotalEnergies). / The research carried out during this PhD is focused on the study and optimization of polymer blends, used as solid polymer electrolytes (SPEs) in lithium and lithium-ion batteries. All components of the battery must be shaped by a solvent-free process (extrusion), in order to limit impacts of the solvent on the battery properties and improve the production process (reduce toxicity and production time). To achieve these objectives, a study was first conducted on a set of polymer blends, selected on the basis of their individual properties, with particular emphasis on the interactions between the lithium salt and each polymer. A ranking of the lithium salt solvating ability of these polymers was developed and revealed that the main factor affecting these interactions is the donor number of polar functional groups on the polymer backbones. The effects of these interactions on the ionic transport phenomena in blend electrolytes have been examined. Subsequent work focused on polymer couples with the most promising and complementary properties, such as poly(ethylene oxide) (PEO) or polycaprolactone (PCL), which exhibit high ionic conductivities, and a hydrogenated nitrile butadiene rubber (HNBR) with interesting mechanical properties but a lower ionic conductivity. It was concluded that these blends show encouraging properties, compared to single-polymer SPEs, such as higher ionic conductivities over a wide temperature range, as well as improved mechanical and thermal stability properties. The final research project was the optimization of these blend electrolytes using an innovative method of selective cross-linking of one of the polymer phases. The main aim of this thesis was to develop an efficient prototype of an all-solid-state lithium battery, entirely obtained by extrusion, in which both the electrolyte and the binder of the composite electrodes are composed of optimized polymer electrolytes. The promising results obtained have led to the filing of a patent, in association with the industrial partner (TotalEnergies).

Fuel cells are known for their high efficiency and have the potential to become a major technology for producing clean energy, especially when the fuel, e.g. hydrogen, is produced from renewable energy sources such as wind or solar. Currently, the two main obstacles to wide-spread commercialization are their high cost and the short operational lifetime of certain components. Polymer electrolyte membrane (PEM) fuel cells have been a focus of attention in recent years, due to their use of hydrogen as a fuel, their comparatively low operating temperature and flexibility for use in both stationary and portable (automotive) applications. Perfluorosulfonic acid membranes are the leading ionomers for use in PEM hydrogen fuel cells. They combine essential qualities, such as high mechanical and thermal stability, with high proton conductivity. However, they are expensive and currently show insufficient chemical stability towards radicals formed during fuel cell operation, resulting in degradation that leads to premature failure. The incorporation of durability improving additives into perfluorosulfonic acid membranes is discussed in this work. iv Cerium oxide (ceria) is a well-known radical scavenger that has been used in the biological and medical field. It is able to quench radicals by facilely switching between its Ce(III) and Ce(IV) oxidation states. In this work, cerium oxide nanoparticles were added to perfluorosulfonic acid membranes and subjected to ex-situ and in-situ accelerated durability tests. The two ceria formulations, an in-house synthesized and commercially available material, were found to consist of crystalline particles of 2 – 5 nm and 20 – 150 nm size, respectively, that did not change size or shape when incorporated into the membranes. At higher temperature and relative humidity in gas flowing conditions, ceria in membranes is found to be reduced to its ionic form by virtue of the acidic environment. In ex-situ Fenton testing, the inclusion of ceria into membranes reduced the emission of fluoride, a strong indicator of degradation, by an order of magnitude with both liquid and gaseous hydrogen peroxide. In open-circuit voltage (OCV) hold fuel cell testing, ceria improved durability, as measured by several parameters such as OCV decay rate, fluoride emission and cell performance, over several hundred hours and influenced the formation of the platinum band typically found after durability testing.

<p dir="ltr">Catalyzing a green hydrogen economy can accelerate progress towards achieving the goal of a sustainable energy map with net-zero carbon emissions by rapid strides. An environmentally benign electrochemical energy conversion system is the Polymer Electrolyte Fuel Cell (PEFC) which uses hydrogen as a fuel to produce electricity and is notably used in a variety of markets such as industries, commercial setups, and across the transportation sector, and is gaining prominence for use in heavy-duty vehicles such as buses and trucks. Despite its potential, the commercialization of PEFCs needs to address several challenges which are manifested in the form of mass transport limitations and deleterious mechanisms at the interfacial scale under severe operating conditions. Achieving a robust electrochemical performance in this context is predicated on desired interactions at the triple-phase boundary of the electrochemical engine of the PEFC – the porous cathode catalyst layer (CCL) where the principal oxygen reduction reaction (ORR) takes place. The liquid water produced as a byproduct of the ORR helps minimize membrane dehydration; however, excess water renders the reaction sites inactive causing reactant starvation. In addition, the oxidation of the carbonaceous support in the electrode and loss of valuable electrochemically active surface area (ECSA) pose major barriers that need to be overcome to ameliorate the life expectancy of the PEFC.</p><p dir="ltr">In this thesis, the multimodal physicochemical interactions occurring inside the catalyst layer are investigated through a synergistic blend of visualization and computational techniques. The spatiotemporal dynamics of capillary force-driven liquid transport that ensues concentration polarization thereby affecting the desired response will be probed in detail. The drop in efficacy of the ORR due to competing catalyst aging mechanisms and the impact of degradation stressors on chemical potential-induced instability will be examined. The reaction-transport-mechanics interplay in core-shell nanoparticles, a robust class of electrocatalysts that promises better mass activity compared to the single metal counterparts is further highlighted. Finally, the influence of electrode microstructural attributes on the electrochemical performance of the reverse mode of fuel cell operation, i.e., Proton Exchange Membrane Water Electrolyzers (PEMWEs) is investigated through a mesoscale lens.</p>

The need for energy efficient, clean and quiet, energy conversion devices for mobile and stationary applications has presented proton exchange membrane (PEM) fuel cells as a potential energy source. The use of PEM fuel cells for automotive and other transient applications, where there are rapid changes in load, presents a need for better understanding of transient behavior. In particular at low humidity operations; one of the factors critical to the performance and durability of fuel cell systems is water transport in various fuel cell layers, including water absorption in membrane. An essential aspect to optimization of transient behavior of fuel cells is a fundamental understanding of response of fuel cell system to dynamic changes in load and operating parameters. This forms the first objective of the dissertation. An insight in to the time scales associated with various transport phenomena will be discussed in detail. In the second component on the study, the effects of membrane properties on the dynamic behavior of the fuel cells are analyzed with focus on membrane dry-out for low humidity operations. The mechanical behavior of the membrane is directly related to the changes in humidity levels in membrane and is explored as a part third objective of the dissertation. Numerical studies addressing this objective will be presented. Finally, porous media undergoing physical deposition (or erosion) are common in many applications, including electrochemical systems such as fuel cells (for example, electrodes, catalyst layer s, etc.) and batteries. The transport properties of these porous media are a function of the deposition and the change in the porous structures with time. A dynamic fractal model is introduced to describe such structures undergoing deposition and, in turn, to evaluate the changes in their physical properties as a function of the deposition. / Ph. D.

One of the main challenges to transform highly useful Direct Methanol Fuel Cells (DMFC) into a commercially viable technology has been to develop a low cost polymer electrolyte membrane (PEM) with high proton conductivity, high stability and low methanol crossover under operating conditions desirably including high temperatures. Nafion, the widely used PEM, fails to meet all of these criteria simultaneously. Recently developed acid-base polymer blend membranes constitute a promising class of PEMs alternative to Nafion on above criteria. Even though some of these membranes produce better performance than Nafion, they still present numerous opportunities for maximizing high temperature proton conductivity and dimensional stability with concomitant minimization of methanol crossover. Our contribution embarks on the fundamental study of one such novel class of blend membranes viz., sulfonated poly (ether ether ketone) (SPEEK)(95 % by weight) blended with polysulfone tethered with base (5 % by weight) such as 2-aminobenzimidazole (ABIm), 5-amino-benzotriazole (BTraz) and 1H-perimidine (PImd), developed by Manthiram group at The University of Texas at Austin. In this work, we report extensive all-atom classical as well as ab-initio molecular dynamics (MD) simulations of such water-methanol solvated blend membranes (as well as pure SPEEK and Nafion) the first time. Our approach consists of three steps: (1) Predict dynamical properties such as diffusivities of water, methanol and proton in such membranes (2) Validate against experiments (3) Develop understanding on the interplay between basic chemistry, structure and properties, the knowledge that can potentially be used to develop better candidate membranes. In particular, we elucidate the impact of simple, fundamental physiochemical features of the polymeric membranes such as hydrophilicity, hydrophobicity, structure or the size of the base on the structural manifestations on the bigger scale such as nanophase segregation, hydrogen bonding or pore sizes, which ultimately affect the permeant transport through such systems. / text

No description available.

Στην παρούσα διατριβή αναπτύχθηκε ένα μοντέλο βασιζόμενο σε πρώτες αρχές με σκοπό την περιγραφή και την πρόβλεψη της πρωτονιακής αγωγιμότητας των πλήρως ενυδατωμένων μεμβρανών Nafion (το κυριότερο υλικό που χρησιμοποιείται ως ηλεκτρολύτης στις κυψέλες καυσίμου τύπου PEM) και των ιδιαίτερων χαρακτηριστικών αυτής, όπως τη γραμμική εξάρτηση από το πάχος της μεμβράνης, το δυναμικό του κελιού και τη μερική πίεση του υδρογόνου. Το μοντέλο εστιάζει στη μετανάστευση των πρωτονίων που είναι συνδεδεμένα στις σουλφονομάδες και χρησιμοποιεί την κατανομή φορτίου Poisson-Boltzmann γύρω από κάθε πρωτόνιο, σε συνδυασμό με την εξίσωση Gamow, που δίνει την πιθανότητα να συμβεί το φαινόμενο σήραγγος σε παραβολικό φράγμα δυναμικού. Προτείνεται ότι το μήκος που διανύεται κατά την πραγματοποίηση του φαινομένου σήραγγος ισούται με το μήκος κύματος του πρωτονίου και ότι κάθε πρωτόνιο περιβάλλεται από το νέφος Debye-Hückel. Το μοντέλο, που δεν εμπεριέχει προσαρμόσιμες παραμέτρους, λύνεται αναλυτικά και οι προβλέψεις του είναι σε ημιποσοτική συμφωνία με το πείραμα. Στις προβλέψεις αυτές συμπεριλαμβάνεται η τάξη μεγέθους της αγωγιμότητας, η γραμμική εξάρτηση της αγωγιμότητας με το πάχος της μεμβράνης, η εκθετική εξάρτηση από το δυναμικό και η ισχυρή εξάρτηση με τη μερική πίεση του υδρογόνου. Μελετήθηκε η κινητική, οι ταλαντώσεις και η ηλεκτροχημική ενίσχυση της οξείδωσης του CO σε καταλυτικό υμένιο Pt εναποτεθειμένο σε YSZ, χρησιμοποιώντας ως βάση την απόλυτη κλίμακα του ηλεκτροδίου του οξυγόνου. Βρέθηκε ότι η ηλεκτροχημική ενίσχυση είναι μικρή (ρ<3, Λ~300) όταν οι τιμές του δυναμικού του καταλύτη, UWR, είναι ανάμεσα σε 0.2 και 0.4 V και πολύ σημαντική (ρ~9, Λ~1500) όταν το UWR υπερβαίνει την τιμή 0.4 V. Η απότομη αλλαγή που παρατηρείται κατά την μετάβαση στην έντονη ηλεκτροχημική ενίσχυση συνοδεύεται και από απότομη αλλαγή στην κινητική της αντίδρασης και στο δυναμικό του καταλύτη. Μέσω της σύγκρισης των πειραματικών αποτελεσμάτων του κεφαλαίου και ανεξάρτητων μετρήσεων του έργου εξόδου μεταβάλλοντας το δυναμικό του καταλύτη για το ίδιο σύστημα, βρέθηκε ότι η μετάβαση οφείλεται στην έντονη μετανάστευση προωθητικών ειδών, Ο2-, από τη YSZ στην επιφάνεια του καταλύτη και την συνεπαγόμενη δημιουργία μιας πυκνής αποτελεσματικής διπλοστιβάδας στη διεπιφάνεια του καταλύτη με τα αέρια αντιδρώντα. Τέλος εξετάστηκε μια τροποποιημένη κυψέλη καυσίμου τύπου PEM η οποία λειτουργεί σε συνθήκες δηλητηρίασης από CO κατά την τριοδική λειτουργία. Στο τριοδικό κελί καυσίμου τύπου PEM εκτός της ανόδου και της καθόδου εισάγεται ένα τρίτο ηλεκτρόδιο το οποίο δημιουργεί ένα επιπλέον βοηθητικό κύκλωμα το οποίο λειτουργεί με ηλεκτρολυτικά ρεύματα και επιτρέπει τη λειτουργία της κυψέλης σε δυναμικά μεταξύ της ανόδου και της καθόδου ανέφικτα κατά τη συμβατική λειτουργία. Βρέθηκε ότι είναι δυνατό να ενισχυθεί η συνολική θερμοδυναμική ενεργειακή απόδοση όταν χρησιμοποιείται ως καύσιμο μίγμα αναμόρφωσης μεθανόλης που αντιστοιχεί σε συνθήκες έντονης δηλητηρίασης από CO. / In the present work a first principles model was developed to describe and predict the protonic conductivity of fully hydrated Nafion membranes and its peculiar non-linear dependence on membrane thickness, potential and PH2. The model focuses on the surface migration of protons between adjacent sulfonate groups and utilizes the Poisson-Boltzmann charge distribution around each proton combined with the basic Gamow equation of quantum mechanics for proton tunneling, for parabolic potential barrier. It was shown that the proton tunneling distance equals the proton wavelength and that each proton surrounded by its Debye-Hückel cloud behaves as a leaking nanobattery. The model, which contains no adjustable parameters, is solved analytically and its predictions are in semiquantitative agreement with experiment, including the magnitude of the conductivity, its linear increase with membrane thickness, its exponential increase with potential and its strong dependence on partial pressure of hydrogen. Moreover it was investigated the kinetics, rate oscillations and electrochemical promotion of CO oxidation on Pt deposited on YSZ using a standard oxygen reference electrode. It was found that electropromotion is small (ρ<3) when the catalyst potential UWR, is between 0.2 and 0.4V and very pronounced (ρ~9, Λ~1500) when UWR exceeds 0.4V. This sharp transition in the electropromotion behavior is accompanied by an abrupt change in reaction kinetics and in catalyst potential. It was shown via comparison with independent catalyst potential–catalyst work function measurements that the transition corresponds to the onset of extensive O2- spillover from YSZ onto the catalyst surface, and concomitant establishment of an effective double layer at the catalyst-gas interface, which is the cause of the highly active electropromoted state Furthermore it was studied a modified PEM fuel cell running in CO poisoning conditions by the triode operation. In addition to the anode and cathode, the triode PEM fuel cell introduces a third electrode together with an auxiliary circuit which is run in the electrolytic mode and permits fuel cell operation under previously inaccessible anode-cathode potential differences. It was found that it is possible to enhance the overall thermodynamic efficiency when it is used a methanol reformate mixture as a fuel, which corresponds to intense CO poisoning conditions.