D. Tech. (Department of Mechanical Engineering, Faculty of Engineering and Technology), Vaal University of Technology. / On account of their lightweight, low-cost, corrosion resistance, and good formability, conductive polymer composites (CPCs) are promising for the production bipolar plate (BP) for polymer electrolyte membrane fuel cell (PEMFC). However, a high conductive filler loading is needed to impart the required level of electrical conductivity to the insulating polymer matrix and as a consequence, the toughness of the plate deteriorates considerably. By using immiscible blend of polymers that have complementary hardness and ductility as matrix, with conducting multi-fillers of different morphologies, it is possible to optimize the matrix strength characteristics and favour the formation of conducting network to produce CPC meeting BP performance standards. Of course, a lot will depend on the formulation of the most favourable composition and production variables. In this regard, polypropylene-epoxy and polyethylene-epoxy blends, filled with zero- and two-dimensional carbon forms – graphite, carbon black (CB), and graphene (Gr) – were investigated over an extensive range of compositions and compression moulding pressures, in this study. Several compounding runs (using melt mixing), at different stages, followed by compression molding, were done. The goal is to obtain combination of composite formulation and processing conditions that will produce the most promising combination of properties for BP application. In the first stage of the investigations, by using thermogravimetric analysis, two-stage decomposition behavior of PP-epoxy and PE-epoxy blends was revealed, which confirms the immiscibility of PP and PE with epoxy resin. Scanning electron microscope (SEM) micrographs of the PP-epoxy and PE-epoxy blends revealed a co-continuous structure, which can be attributed to the close-to-symmetric composition of the blend and compatibilizers added. Preferential localization of synthetic graphite (SG), CB, and Gr in the polymer blends was also revealed by the SEM micrographs. This confirms the fact that CPCs based on PP-epoxy and PE-epoxy blends can be explored further. PP-epoxy and PE-epoxy blends filled with only SG, 30 – 80 wt %, were produced and characterized for their electrical conductivity and flexural properties. In-plane electrical conductivity ranged from 12.09 to 68.03 Scm-1 for PP-epoxy/SG and 11.68 to 72.96 Scm-1 for PE-epoxy/SG composites produced. These are higher than values reported for several single matrix polymer composites at similar filler loadings. With reference to the United States Department of Energy performance targets for BPs, PE-epoxy/SG composites performed better in terms of electrical conductivity, while PP-epoxy/SG composites exhibited better flexural properties. Thereafter, using SG and CB double filler, PE-epoxy/SG/CB composites performed better than PP-epoxy/SG/CB composites in terms of electrical conductivity, while PP-epoxy/SG/CB composites exhibited superior flexural properties than the PE-epoxy/SG/CB composites at similar filler loadings. However, with respect to the DOE targets, composites based on PP-epoxy blend exhibited a more promising combination of electrical conductivity and flexural properties than PE-epoxy blend matrix. PP-epoxy filled with SG/CB was studied further, by using graphene (Gr) as second minor filler. In-plane and through plane electrical conductivities as well as thermal conductivity and thermal diffusivity of the PP-epoxy/SG/CB/Gr composites increased as total filler content was increased from 65 to 85 wt%. It implies that more conductive networks between filler particles were formed. Also, flexural strength, flexural modulus, and impact strength decreased as the total filler content increased from 65 to 85 wt%. The reduced flexural properties could be due to increased agglomeration of CB and Gr, and poor filler wetting at higher filler loadings and low matrix material, which leads to the formation of microvoids and a reduction of the load bearing capacity of composites. With respect to the DOE targets, PP-EP/SG/CB/Gr composite with 80 wt% (i.e., PP/EP/73G/6.2CB/0.8Gr) filler has the best combination of properties. Further improvement in properties of the PP-EP/SG/CB/Gr composite with 80 wt% filler was achieved by molding at higher pressures. As molding pressure was increased from 4.35 to 13.05 MPa, in-plane electrical conductivity increased from 116.31 to 144.99 Scm-1, while flexural strength increased from 29.62 to 42.57 MPa, satisfying the performance requirement targets for bipolar plates.

No description available.

No description available.

Polymer electrolyte membrane (PEM) fuel cell (FC) stacks require elastomeric gaskets for each cell to keep the reactant gases within their respective regions[1]. If any gasket degrades or fails, the reactant gases can leak or mix with each other directly during operation or standby, affecting the overall operation and performance of the FC. The elastomeric gaskets used as FC seals are exposed to a range of environmental conditions, and concurrently, subjected to mechanical compression between the bipolar plates forming the cell. The combination of mechanical stress and environmental exposure may result in degradation of the seal material[2] over a period of time. In order to address the durability and make reliability predictions, the long-term stability of the gaskets in FC assemblies is critical. The aim of this study is to investigate the performance of elastomeric seals in a simulated FC environment in the presence of mechanical stresses. The overall scope of the study includes mechanical and viscoelastic properties characterization, and lifetime durability predictions based on an accelerated characterization approach. With the help of finite element analysis software, ABAQUS, a fixture was designed to perform strain-based accelerated characterization of seal material in air, deionized (DI) water, 50v/50v ethylene glycol/water solution, and 0.1M sulfuric acid solution. Dogbone samples were strained to different levels in the custom fixture and submerged in liquid solutions at 90°C and in air at 90°C and 120°C. It was observed that mechanical properties such as tensile strength, strain to break, 100% modulus, crosslink density, and tensile set degrade due to aging and the extent of change (increase or decrease) depends significantly on the strain level on the specimen. Trouser tear tests were conducted on reinforced specimens in air and deionized water (DI) to evaluate the tear resistance of an elastomeric seal material intended for proton exchange membrane fuel cells. Plots relating the crack growth rate with tearing energy were obtained at various temperatures and provided significant insight into the rate and temperature dependence of the tearing strength of the seal material. Stick-slip crack propagation was observed at all temperatures and loading rates, although the behavior was suppressed significantly at low loading rates and high temperatures. Crack growth rate versus tearing energy data at different temperatures was shifted to construct a master curve and an estimate on the threshold value of tear energy was obtained which may be helpful in designing components where material tear is of concern. Strain energy release rate (SERR) value, calculated using the J-integral approach for a pre-existing crack in ABAQUS, was used to estimate the crack growth rate in a given seal cross-section to predict lifetime. In order to assess the viscoelastic behavior and to investigate the long term stress relaxation behavior of the seal material, compression stress relaxation (CSR) tests were performed on molded seals, called as SMORS, over a range of environmental conditions using a custom-designed fixture. The effect of temperature and environment was evident on material property changes and presented in terms of momentary properties and stress relaxation behavior. Various mechanisms involved in material degradation, chain scission and crosslinking, were suggested and insights were gained into how cure state and level of antidegradants in a material dictate the material behavior during the first phase of environmental exposure leading to change in material properties. Ring samples made of silicone were also tested using the fixture to obtain insight additional into material degradation due to aging. Results presented from testing on SMORS showed a lot more variation in data as compared to neat silicone rings due to the complexity involved in making SMORS. For understanding the deformation behavior of an elastomeric seal and its sealing performance, finite element characterization of seal cross-section was carried out on O-ring and SMORS cross-section. The effect of a seal's layout on distribution and magnitude of contact stresses and contact width was investigated for the O-ring and the information obtained thereby helped to analyze a complex assembly such as SMORS, where several interfaces and boundary conditions are involved. Stress/strain profiles were generated to visualize their concentration and distribution in the seal cross-section. Frictionless and rough interfacial conditions between seal material and platens were assumed and it was found that its effect on contact width and peak contact pressure was insignificant. Results obtained from FEA on SMORS were validated through comparison with contact mechanics approach and experimental data and it was found that Lindley's equation correlates well with experimental data whereas ABAQUS overestimates the load values at a given compression. Lindley's approach may be used to develop contact pressure profiles that may help estimate peak contact pressure at a given time so leaking can be avoided. / Ph. D.

Hydrogen fuel cells, and notably the polymer electrolyte fuel cell (PEFC), present an important opportunity to reduce greenhouse gas emissions within a range of sectors of society, particularly for transportation and portable products. Despite several decades of research and development, there exist three main hurdles to full commercialisation; namely infrastructure, costs, and durability. This thesis considers the latter of these. The lifetime target for an automotive fuel cell power plant is to survive 5000 hours of usage before significant performance loss; current demonstration projects have only accomplished half of this target, often due to PEFC stack component degradation. Health management techniques have been identified as an opportunity to overcome the durability limitations. By monitoring the PEFC for faulty operation, it is hoped that control actions can be made to restore or maintain performance, and achieve the desired lifetime durability. This thesis presents fault detection and diagnosis approaches with the goal of isolating a range of component degradation modes from within the PEFC construction. Fault detection is achieved through residual analysis against an electrochemical model of healthy stack condition. An expert knowledge-based diagnostic approach is developed for fault isolation. This analysis is enabled through fuzzy logic calculations, which allows for computational reasoning against linguistic terminology and expert understanding of degradation phenomena. An experimental test bench has been utilised to test the health management processes, and demonstrate functionality. Through different steady-state and dynamic loading conditions, including a simulation of automotive application, diagnosis results can be observed for PEFC degradation cases. This research contributes to the areas of reliability analysis and health management of PEFC fuel cells. Established PEFC models have been updated to represent more accurately an application PEFC. The fuzzy logic knowledge-based diagnostic is the greatest novel contribution, with no examples of this application in the literature.

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.

Το Η2 είναι το ελαφρύτερο και πλέον άφθονο στοιχείο στη φύση. Βρίσκεται παντού στη γη, στο νερό, στα ορυκτά καύσιμα και σε όλα τα έμβια όντα. Αν το Η2 αξιοποιηθεί κατάλληλα και χρησιμοποιηθεί για τροφοδοσία των κελιών καυσίμου, θα ελαχιστοποιηθεί η εξάρτηση του σύγχρονου πολιτισμού από τα ορυκτά καύσιμα, με συνεπακόλουθο τη μείωση των εκπομπών βλαβερών αερίων στην ατμόσφαιρα. Η χαμηλή θερμοκρασία λειτουργίας των κελιών καυσίμου πολυμερούς ηλεκτρολύτη (PEMFCs) προσφέρει πολλά πλεονεκτήματα και σε συνδυασμό με την υψηλή πυκνότητα ισχύος που αποδίδουν, τα καθιστά κύριους υποψήφιους για εφαρμογή στην αυτοκίνηση. Ωστόσο, η χαμηλή θερμοκρασία εγείρει και σημαντικά προβλήματα, όπως η χρήση ευγενών μετάλλων για την επιτάχυνση των αντιδράσεων και η ευαισθησία σε φαινόμενα δηλητηρίασης. Το κυριότερο δηλητήριο είναι το CO, βασικό παραπροϊόν των διεργασιών παραγωγής H2 από τους υδρογονάνθρακες, οι οποίοι προς το παρόν αποτελούν την κύρια πηγή του. Στην παρούσα διδακτορική διατριβή εξετάστηκαν τα φαινόμενα δηλητηρίασης από το CO της ανόδου του PEMFC. Καθώς το CO δεσμεύεται ισχυρότερα στην επιφάνεια του Pt από το καύσιμο Η2, η παρουσία του στην τροφοδοσία ακόμα και σε ίχνη απενεργοποιεί δραματικά τη λειτουργία της ανόδου. Έτσι, μελετήθηκαν διμεταλλικά και τριμεταλλικά καταλυτικά συστήματα, βασισμένα στο Pt, για την πιθανή αντιμετώπιση του προβλήματος, διαμέσου εξασθένισης του δεσμού Pt-CO ή ενίσχυσης της ηλεκτροχημικής οξείδωσής του από το Η2Ο, που είναι άφθονο στο περιβάλλον ενός PEMFC. Στο κεφάλαιο 1 περιγράφονται οι βιβλιογραφικές πληροφορίες για την τεχνολογία του Η2, όπως μέθοδοι παραγωγής του, καθαρισμού του και αποθήκευσης/μεταφοράς του. Στο κεφάλαιο 2 αναφέρονται οι βασικές αρχές λειτουργίας των κελιών καυσίμου, όσον αφορά στη θερμοδυναμική και στην κινητική, στα είδη τους και στις πιθανές εφαρμογές τους. Στο κεφάλαιο 3 γίνεται εκτενής περιγραφή των δομικών στοιχείων που απαρτίζουν ένα PEMFC, και βιβλιογραφική ανασκόπηση των καταλυτικών συστημάτων που έχουν μελετηθεί για τις βασικές αντιδράσεις. Στο κεφάλαιο 4 περιγράφονται συνοπτικά οι μέθοδοι χαρακτηρισμού και ανάλυσης καθώς και οι πειραματικές διατάξεις που χρησιμοποιήθηκαν. Στο κεφάλαιο 5 εξετάστηκε η επίδραση του υποστρώματος TiO2 στα χαρακτηριστικά του Pt, όσον αφορά την αλληλεπίδρασή του με το CO, σε διάταξη μονής κυψέλης καυσίμου. Παρουσιάστηκε αυξημένη ενεργότητα για την ηλεκτροοοξείδωση του CO και ασθενέστερη αλληλεπίδρασή του με την επιφάνεια του Pt, συντελώντας σε ενεργοποιημένη ρόφηση. Στο κεφάλαιο 6 με φασματοσκοπία υπερύθρου μελετήθηκαν τα χαρακτηριστικά της ρόφησης/εκρόφησης του CO σε μια σειρά καταλυτών Pt-Mo σε υπόστρωμα TiO2. Παρουσία των οξειδίων του Mo η θερμοκρασία εκρόφησης του CO ήταν σημαντικά μειωμένη σε σχέση με μονομεταλλικό Pt, υποδεικνύοντας ασθενέστερο δεσμό του CO με την καταλυτική επιφάνεια. Ωστόσο, παρουσία H2 ο δεσμός ισχυροποιείται, με αποτέλεσμα η εκρόφηση να πραγματοποιείται σε υψηλότερη θερμοκρασία. Αυτό εξηγήθηκε με βάση την ανταγωνιστική αντίδραση του H2 με τις οξειδικές ομάδες, τόσο του υποστρώματος TiO2, όσο και των οξειδίων του Mo. Στο κεφάλαιο 7 εξετάστηκε η οξείδωση του CO σε καταλύτη Pt4Mo/C, δεδομένου του αποσταθεροποιητικού ρόλου του Mo στα χαρακτηριστικά της αλληλεπίδρασης με το CO. Έτσι, αναγνωρίστηκε η ικανότητα των οξειδίων του Mo να διασπούν το Η2Ο σε δυναμικά που συμπίπτουν με τη λειτουργία της ανόδου ενός PEMFC, ενώ παρουσίασαν ενεργότητα για την οξείδωση του CO σε συνθήκες ανοιχτού κυκλώματος διαμέσου της αντίδρασης μετατόπισης με ατμό σε χαμηλή θερμοκρασία μέχρι και 60οC. Ωστόσο, η παραπάνω ιδιότητες δεν ήταν κατανεμημένες ομοιόμορφα στην καταλυτική επιφάνεια, παρά μόνο στη διεπιφάνεια Pt/MoOx, ενώ οι θέσεις μονομεταλλικού Pt παρουσίασαν έντονα φαινόμενα δηλητηρίασης. Επιπλέον, το Mo παρουσιάστηκε ευαίσθητο σε φαινόμενα διάλυσης στο όξινο υδατικό περιβάλλον του PEMFC για δυναμικά μεγαλύτερα από 0.2 V. Στο κεφάλαιο 8 μελετήθηκε η αλληλεπίδραση του CO με τριμεταλλικό καταλύτη Pt-Ru-Co σε σύγκριση με εμπορικό PtRu/C. Ο τριμεταλλικός καταλύτης παρουσιάστηκε ενεργότερος, με χαμηλότερη φαινόμενη ενέργεια ενεργοποίησης για την οξείδωση ροφημένου CO, εμφανίζοντας ισχυρότερη εξάρτηση από το εφαρμοζόμενο δυναμικό. / Hydrogen is the lighter and more abundant element in nature. It is everywhere in earth, water, fossil fuels and in all the living creatures. If H2 can be properly extracted and utilized as a fuel in fuel cells, the dependence of the global economy on fossil fuels will be minimized, resulting in significant attenuation of the greenhouse gases emissions in the atmosphere. The low operation temperature of the polymer electrolyte membrane fuel cells (PEMFCs) offers a lot of advantages. In combination with the high power density yielded by the PEMFCs renders them as the main candidates for application in automotive industry. However, the low temperature raises significant problems, such as the use of noble metals for the acceleration of the basic reactions and the susceptibility in poisoning phenomena. The basic poison is carbon monoxide (CO), one of the main side-products of H2 production from fossil fuels, which for the moment is the main source of H2. In this thesis, the poisoning phenomena of the PEMFCs anode electrocatalysts from CO were investigated. Since CO is bounded on the surface of Pt stronger than the H2 fuel, its presence in the fuel feed in ppm levels deactivates the anode electrocatalyst. In order to eliminate this problem, bimetallic and ternary catalytic systems, based on Pt, were studied with the aim to reduce the Pt-CO bond strength or to promote the electrocatalytic oxidation of CO by water, which is abundant in the PEMFC environment. In chapter 1 is reported the literature information about H2 technology, such as H2 production and cleaning methods and the transport and storage infrastructure. In chapter 2, the basic thermodynamic and kinetic rules of fuel cells operation are referred together with the types of fuel cells and the possible applications. In chapter 3 the structural characteristics of the PEMFCs are outlined and the basic catalytic systems that have been studied for the fuel cell reactions are reviewed. The catalysts’ characterization methods, as well as the experimental procedures utilized in this thesis, are briefly described in chapter 4. In chapter 5 the effect of TiO2 support on the CO chemisorption’s and oxidative properties of Pt was investigated in a single PEMFC configuration. The activity of the CO electrooxidation reaction was enhanced and the Pt-CO bond was destabilized comparing to a commercial Pt/C catalyst. In chapter 6 the CO adsorption/desorption properties were studied by Infrared Spectroscopy, on a series of Pt-Mo catalysts supported on anatase TiO2. The presence of Mo oxides on the catalyst surface reduces significantly the CO desorption temperature in comparison to monometallic TiO2 supported Pt, suggesting the weak CO bonding on the catalytic surface. However, in the presence of H2, the Pt-CO bond strengthens, resulting in higher CO desorption temperature for all the catalysts tested. This was explained on the basis of competitive reaction of H2 with the oxidic surface species, originating from the TiO2 support and the surface Mo oxides. The CO electrooxidation activity of a Pt4Mo/C catalyst is described in chapter 7, considering the destabilizing effect of Mo on the Pt-CO bond. The surface Mo oxide species were able to dissociate H2O at potential values that coincide with the potential window of the PEMFC anode operation. This catalyst oxidized CO under open circuit conditions through the water gas shift reaction and at temperature as low as 60oC. However, the catalytic activity was not homogeneously distributed on the entire catalyst surface, but it was located at the Pt/MoOx interface, with the monometallic Pt sites to be strongly susceptible to CO poisoning. Furthermore, Mo was sensitive to dissolution phenomena in the hydrous acidic environment of the PEMFC for potentials higher than 0.2 V vs. rhe. Finally, in chapter 8 is described the interaction of CO with a ternary Pt-Ru-Co catalyst surface, in comparison to a commercial PtRu/C catalyst. The ternary catalyst was more active for the adsorbed CO electrooxidation, with a lower apparent activation energy than the bimetallic commercial one. The ternary catalyst exhibited zero reaction order with respect to CO partial pressure, while the PtRu/C showed negative reaction order due to competitive adsorption of CO and oxidic species for the same catalytic sites. The kinetic rate constant of the CO electrooxidation reaction for the ternary catalyst showed stronger dependence on the applied potential.

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.

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.

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