With the development of hydrogen fuel cell technology continuing to advance, rapid characterization of membranes is increasingly important for design purposes. Pressurized blister testing has been suggested as an accelerated characterization alternative to traditional relative humidity (RH) cycling tests, and is the focus of this project. Prior efforts to determine the stress state present in the pressurized membrane blister test, however, have required constitutive properties of the membrane (Young's modulus and Poisson's ratio), along with Hencky's classic model for circular membrane stresses. Herein we describe an analysis method and computer vision imaging technique that are capable of determining the stress state in a pressurized circular membrane based solely on simple equilibrium equations and geometric considerations. This analysis method is applied to an image of the blister during testing, and the only additional required data is the pressure at the time the image was taken. By pressurizing circular blisters, an equi-biaxial, mechanical stress state is induced, simulating membrane stresses experienced during fuel cell operation as humidity levels fluctuate. The analysis leverages membrane theory and the axisymmetric geometry to determine the stress state from a profile image of the inflated blister. As a check for the method, an elastomer with known constitutive properties was analyzed using both the previous Hencky's solution method, as well as the new computer vision imaging method. The comparison of stress calculation results show that the two methods agree within 5 percent. A primary mechanism of membrane failure through mechanical stressors is the growth of local defects (usually chemically induced) due to the cyclic equi-biaxial stress state. In order to better understand and characterize the effect of disparate initial defects on CCM, two primary methods to defect membranes were introduced. The first was a compression against sandpaper method meant to simulate GDL compression, and the second was a targeted method using a hypodermic needle to initiate a defect at a central location on the membrane prior to pressurization. Observing the pressure decay in these defected blisters as compared to undefected tests showed that, while undefected samples did not experience pressure decay until failure, defected samples began showing signs of leaking through pressurization cycle profiles and steady state pressures achieved. Pressure data showed that samples tended to lose pressure more quickly with increasing initial defect severity. Undefected samples exhibited no pressure loss until the moment of failure, which was often catastrophic and instantaneous. Sandpaper defected samples exhibited a slow decay in cycle steady state pressure throughout tests, with no increase in cycle pressurization time. Needle samples showed a slow decay in cycle steady state pressure as well as an increase in time for the cycles to reach steady state. The needle defects were the most locally severe and thus the pressure decay indicators were most significant out of all the samples tested. The blister test method rapidly cycles mechanical stresses in a CCM, and elucidates signs of leaking that correlate to flaw development in recorded pressure data. With further development, it might serve as a robust method to quickly test flaw growth rate and development in CCM samples. / Master of Science / Fuel cells are a technology used to supply energy to many sources. In fuel cells, the membrane can limit the lifetime of the entire cell, as the membrane separates the reactant gases allowing the generation of power. If that membrane develops holes or cracks, the fuel cell won't be able to generate as much power, and cell replacement is costly in time and money. Thus, it is important to develop robust membranes to avoid loss in efficiency as much as possible. The research here focuses on rapidly testing how long these membranes last, so that membrane performance can be appropriately ranked, leading to faster technological improvements. We developed two main methods for use in combination with existing blister pressurization equipment; an image-based method that can determine the forces in the membrane, and a novel method to defect membranes before testing. The first method uses a code-based approach to process the image of the blister profile and return stresses. The second method defects the blister before testing so the growth of the defect can be observed over time. Leaking characteristics in the blister were identified in several tests, and the severity of the defects was determined from this information. Thus, the development of the defects can be monitored through these leak characteristics.

Proton exchange membrane fuel cells (PEMFC) are attractive energy sources for power trains in vehicles because of their low operating temperature that enables fast start-up and high power densities. Cost reduction and durability are the key issues to be solved before PEMFCs can be successfully commercialized. The major portion of fuel cell cost is associated with the catalyst layer which is typically comprised of carbon-supported Pt and ionomer. The degradation of the catalyst layer is one of the major failure modes that can cause voltage degradation and limit the service life of the fuel cell stack during operation. To develop a highly durable and better performing catalyst layer, topics such as the causes for the degradation, modes of failure, different mechanisms and effect of degradation on fuel cell performance must be studied thoroughly. Key degradation modes of catalyst layer are carbon corrosion and Pt dissolution. These two modes change the electrode structure in the membrane electrode assembly (MEA) and result in catalyst layer thinning, CO2 evolution, Pt deposition in the membrane and Pt agglomeration. Alteration of the electrode morphology can lead to voltage degradation. Accelerated stress tests (ASTs) which simulate the conditions and environments to which fuel cells are subject, but which can be completed in a timely manner, are commonly used to investigate the degradation of the various components. One of the current challenges in employing these ASTs is to relate the performance loss under a given set of conditions to the various life-limiting factors and material changes. In this study, various degradation modes of the cathode catalyst layer are isolated to study their relative impact on performance loss ‗Fingerprints‘ of identifiable performance losses due to carbon corrosion are developed for MEAs with 0.4 mg cm−2 cathode platinum loadings. The fingerprint is used to determine the extent of performance loss due to carbon corrosion and Pt dissolution in cases where both mechanisms operate. This method of deconvoluting the contributions to performance loss is validated by comparison to the measured performance losses when the catalyst layer is subjected to an AST in which Pt dissolution is predominant. The limitations of this method iv are discussed in detail. The developed fingerprint suggests that carbon loss leading to CO2 evolution during carbon corrosion ASTs contributes to performance loss of the cell. A mechanistic model for carbon corrosion of the cathode catalyst layer based on one appearing in the literature is developed and validated by comparison of the predicted carbon losses to those measured during various carbon corrosion ASTs. Practical use of the model is verified by comparing the predicted and experimentally observed performance losses. Analysis of the model reveals that the reversible adsorption of water and subsequent oxidation of the carbon site onto which water is adsorbed is the main cause of the current decay during ASTs. Operation of PEM fuel cells at higher cell temperatures and lower relative humidities accelerates Pt dissolution in the catalyst layer during ASTs. In this study, the effects of temperature and relative humidity on MEA degradation are investigated by applying a newly developed AST protocol in which Pt dissolution is predominant and involves the application of a potentiostatic square-wave pulse with a repeating pattern of 3s at 0.6 V followed by 3s at 1.0 V. This protocol is applied at three different temperatures (40°C, 60°C and 80°C) to the same MEA. A diagnostic signature is developed to estimate kinetic losses by making use of the effective platinum surface area (EPSA) obtained from cyclic voltammograms. The analysis indicates that performance degradation occurs mainly due to the loss of Pt in electrical contact with the support and becomes particularly large at 80°C. This Pt dissolution AST protocol is also investigated at three different relative humidities (100%, 50% and 0%). Electrochemical impedance spectroscopy measurements of the MEAs show an increase in both the polarization and ohmic resistances during the course of the AST. Analysis by cyclic voltammetry shows a slight increase in EPSA when the humidity increases from 50% to 100%. The proton resistivity of the ionomer measured by carrying out impedance measurements on MEAs with H2 being fed on the anode side and N2 on the cathode side is found to increase by the time it reaches its end-of-life state when operated under 0 % RH conditions.

Ett konsortium bestående av Scania, JOAB, Powercell, KTH och Renova samarbetade för att designa och konstruera en bränslecellsdriven sopbil inom ett FFI-finansierade projekt. Sopbilen har sedan dess varit i drift i Göteborg från 2020 till 2023, med en vätgasinfrastruktur bestående av en tankstation vid tidpunkten för detta arbete. Under den tiden har bränslecellen genomgått kör- och stillastående tester. Verkliga kördata på sopbilens system och bränslecell registrerades. Databaserna var osynkroniserade i tid och därför krävdes datasynkronisering. Detta examensarbete inleddes med huvudsyftet att utveckla ett accelererat åldringstest för bränslecellen baserat på denna applikation. Ett ytterligare syfte var att utvärdera bränslecellens åldrande. På grund av de tillgängliga variablerna baserades bränslecellens åldrande på försämring av elektrisk effekt vid konstanta temperaturer och strömmar. En testcykel (eller effekt-cykel) baserad på testkörningen av sopbilen utvecklades istället. Genom att använda den etablerade metoden "k-means clustering" på bränslecellens effekt-cykler skapades en testcykel som var representativ för sopbils-körning från 2020 till 2023. Testcykeln validerades baserat på ett statistiskt kriterium, verifiering och ytterligare arbete krävs dock. Efter 141,80 timmars bränslecellsdrift kunde ingen åldring identifieras. Mer data från sopbilen behövs och faktumet att ytterligare en vätgastankstation kommer att installeras under 2023 i Göteborg innebär att sopbilens körmönster kan förändras. Resultaten från denna avhandling lägger dock grunden för framtida forskning och erbjuder ett tillvägagångssätt för att studera den bränslecellsdrivna sopbilen. / A consortium consisting of Scania, JOAB, Powercell Sweden AB, KTH, and Renova collaborated to design and engineer a fuel cell-powered refuse truck within a FFI-funded project. The refuse truck has been operational in Gothenburg since 2020, with a hydrogen gas infrastructure of one refuelling station at the time of this work. From 2020 to 2023, the fuel cell has gone through driving and standing still tests. Real drive data on the truck's system and fuel cell was recorded. The databases were unsynchronised in time, hence data synchronisation was required.  This thesis began with the main aim of developing an accelerated stress test for the fuel cell based on this application. Additionally, the aim was to evaluate the ageing of the fuel cell. Due to the available variables, fuel cell ageing was based on deterioration of fuel cell powers at constant temperatures and currents.  A test cycle (or power cycle) based on refuse truck test driving was developed instead. By utilising the established “k-means clustering” method on fuel cell power cycles, a test cycle representative of the truck operation from 2020 to 2023 was made. The test cycle was validated based on a statistical criterion, although verification and further work are required. After 141.80 hours of fuel cell power requests no ageing could be identified. More data from refuse truck operation is needed, also considering that an additional hydrogen refuelling station will be put in place in 2023 in Gothenburg, hence the drive pattern might vary. In this context, however, the results from this thesis lay the foundation for future research and offer an approach to study the fuel cell truck.