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Item Open Access Porosity and permeability alterations in processes of biomineralization in porous media - microfluidic investigations and their interpretation(Stuttgart : Eigenverlag des Instituts für Wasser- und Umweltsystemmodellierung der Universität Stuttgart, 2022) Weinhardt, Felix; Class, Holger (apl. Prof. Dr.-Ing)Motivation: Biomineralization refers to microbially induced processes resulting in mineral formations. In addition to complex biomineral structures frequently formed by marine organisms, like corals or mussels, microbial activities may also indirectly induce mineralization. A famous example is the formation of stromatolites, which result from biofilm activities that locally alter the chemical and physical properties of the environment in favor of carbonate precipitation. Recently, biomineralization gained attention as an engineering application. Especially with the background of global warming and the objective to reduce CO2 emissions, biomineralization offers an innovative and sustainable alternative to the usage of conventional Portland cement, whose production currently contributes significantly to global CO2 emissions. The most widely used method of biomineralization in engineering applications, is ureolytic calcium carbonate precipitation, which relies on the hydrolysis of urea and the subsequent precipitation of calcium carbonate. The hydrolysis of urea at moderate temperatures is relatively slow and therefore needs to be catalyzed by the enzyme urease to be practical for applications. Urease can be extracted from plants, for example from ground jack beans, and the process is consequently referred to as enzyme-induced calcium carbonate precipitation (ECIP). Another method is microbially induced calcium carbonate precipitation (MICP), which uses ureolytic bacteria that produce the enzyme in situ. EICP and MICP applications allow for producing various construction materials, stabilizing soils, or creating hydraulic barriers in the subsurface. The latter can be used, for example, to remediate leakages at the top layer of gas storage reservoirs, or to contain contaminant plumes in aquifers. Especially when remediating leakages in the subsurface, the most crucial parameter to be controlled is its intrinsic permeability. A valuable tool for predicting and planning field applications is the use of numerical simulation at the scale of representative elementary volumes (REV). For that, the considered domain is subdivided into several REV’s, which do not resolve the pore space in detail, but represent it by averaged parameters, such as the porosity and permeability. The porosity describes the ratio of the pore space to the considered bulk volume, and the permeability quantifies the ease of fluid flow through a porous medium. A change in porosity generally also affects permeability. Therefore, for REV-scale simulations, constitutive relationships are utilized to describe permeability as a function of porosity. There are several porosity-permeability relationships in the literature, such as the Kozeny-Carman relationship, Verma-Pruess, or simple power-law relationships. These constitutive relationships can describe individual states but usually do not include the underlying processes. Different boundary conditions during biomineralization may influence the course of porosity-permeability relationships. However, these relationships have not yet been adequately addressed. Pore-scale simulations are, in principle, very well suited to investigate pore space changes and their effects on permeability systematically. However, these simulations also rely on simplifications and assumptions. Therefore, it is essential to conduct experimental studies to investigate the complex processes during calcium carbonate precipitation in detail at the pore scale. Recent studies have shown that microfluidic methods are particularly suitable for this purpose. However, previous microfluidic studies have not explicitly addressed the impact of biomineralization on hydraulic effects. Therefore, this work aims to identify relevant phenomena at the pore scale to conclude on the REV-scale parameters, porosity and permeability, and their relationship. Contributions: This work comprises three publications. First, a suitable microfluidic setup and workflow were developed in Weinhardt et al. [2021a] to study pore space changes and the associated hydraulic effects reliably. This paper illustrated the benefits and insights of combining optical microscopy and micro X-ray computed tomography (micro XRCT) with hydraulic measurements in microfluidic chips. The elaborated workflow allowed for quantitative analysis of the evolution of calcium carbonate precipitates in terms of their size, shape, and spatial distribution. At the same time, their influence on differential pressure could be observed as a measure of flow resistance. Consequently, porosity and permeability changes could be determined. Along with this paper, we published two data sets [Weinhardt et al., 2021b, Vahid Dastjerdi et al., 2021] and set the basis for two other publications. In the second publication [von Wolff et al., 2021], the simulation results of a pore-scale numerical model, developed by Lars von Wolff, were compared to the experimental data of the first paper [Weinhardt et al., 2021b]. We observed a good agreement between the experimental data and the model results. The numerical studies complemented the experimental observations in allowing for accurate analysis of crystal growth as a function of local velocity profiles. In particular, we observed that crystal aggregates tend to grow toward the upstream side, where the supply of reaction products is higher than on the downstream side. Crystal growth during biomineralization under continuous inflow is thus strongly dependent on the locally varying velocities in a porous medium. In the third publication [Weinhardt et al., 2022a], we conducted further microfluidic experiments based on the experimental setup and workflow of the first contribution and published another data set [Weinhardt et al., 2022b]. We used microfluidic cells with a different, more realistic pore structure and investigated the influence of different injection strategies. We found that the development of preferential flow paths during EICP application may depend on the given boundary conditions. Constant inflow rates can lead to the development of preferential flow paths and keep them open. Gradually reduced inflow rates can mitigate this effect. In addition, we concluded that the coexistence of multiple calcium carbonate polymorphs and their transformations could influence the temporal evolution of porosity-permeability relationships.Item Open Access A model-based framework for the assessment of energy-efficiency and CO2-mitigation measures in multi-cylinder paper drying(Stuttgart : Universität Stuttgart, Institut für Energiewirtschaft und Rationelle Energieanwendung, 2022) Godin, Hélène; Radgen, Peter (Prof. Dr.-Ing.)Thesis on the effect of energy-efficiency and CO2-mitigation measures in multi-cylinder paper drying.Item Open Access Steam-oxygen fluidized bed gasification of sewage sludge(2023) Schmid, Max; Scheffknecht, Günter (Univ.-Prof. Dr. techn.)Sewage sludge is a residue that is generated unavoidably by the population. On a first sight, sewage sludge may be a hazardous waste that requires safe disposal. By looking closer, it is recognized as secondary resource. The mineral fraction contains valuable elements such as phosphorous, which can be retrieved as secondary raw material. This thesis focuses on the organic fraction, which is a renewable fuel and carbon source and can be used to substitute fossil carbon in fuels and chemicals. The first step in converting sewage sludge to renewable goods is syngas production via gasification. The experimental work of this thesis demonstrated the feasibility of synthesis gas production from sewage sludge by steam-oxygen fluidized bed gasification. It was shown that the process works reliably in the investigated 20 kW scale and that the syngas contains high H2 and CO concentrations and is thus suitable for synthesis of fuels and chemicals. The impurities NH3, H2S, COS and tar species, including heterocyclic species such as pyridine, were measured in considerable concentrations in the syngas. Small amounts of limestone bed additive enabled cracking of heavy tars and partial capture of H2S and COS. It was further found that the cold gas efficiency increases with rising gasification temperature due to improved tar and char conversion at higher temperatures. The typical operation temperature 850 °C requires an oxygen ratio of 0.33, obtaining a cold gas efficiency of 63 %. Moreover, the H2/CO-ratio could be controlled efficiently by altering the steam to carbon ratio, as steam promotes the water gas shift reaction in the gasifier to achieve the desired stoichiometry for synthesis, however, resulting in higher energy demand for steam provision. The experimental results can be utilized for process design, e.g., for a TRL 7-demonstrator. Furthermore, a gasifier model was developed and an integrated process chain was simulated to assess the conversion of sewage sludge to synthetic natural gas (SNG) with and without inclusion of power-to-gas through electrolysis. The total efficiency of the conversion including own consumption for the case without electrolysis was 51 % with a carbon utilization of 33 %. These values could be enhanced by inclusion of power-to-gas. It was predicted that the produced SNG has a CH4-concentration of between 0.81 m3 m 3 and 0.84 m3 m 3 and nitrogen concentrations of up to 0.16 m3 m 3 originating from fuel-bound nitrogen. The simulations on process integration showed that up to 20% of the sewage sludge feed can be dried by heat integration. This implies that also external heat sources have to be used for drying. Overall, the steam-oxygen gasification proved to be an efficient and technically feasible process for sewage sludge treatment and can be considered as an alternative to fluidized bed incineration for future mono-treatment plants.Item Open Access Improvement of quench front modelling for thermohydraulic system codes(Stuttgart : Universität Stuttgart, Institut für Kernenergetik und Energiesysteme, 2020) D'Alessandro, Christophe; Starflinger, Jörg (Prof. Dr.-Ing.)The accident of Fukushima in Japan in March 2011 highlighted the need of further research on severe accidents and on the prediction capabilities of current integral system codes. The present work deals with simulation of quenching of hot particles bed, which may form in the core from the melting and fragmentation of core components during a severe accident. The coolability of hot debris bed, still generating decay heat and threatening to re-melt, is a key-issue in terms of severe accident management. Codes that are supposed to be used as decision-making tools have to be able to calculate accident sequences quickly and accurately enough. For this reason, the computation domain is typically coarsely discretized, yielding large mesh cells (mesh size > 20 cm). The capabilities of COCOMO-3D regarding simulations of quenching of hot debris bed is first assessed against experiments such as DEBRIS and PEARL, or by simulating the quenching of a reactor-scale debris bed, on which larger mesh cells can be generated like for integral codes. The latter simulation with large cells yields strong computation instabilities, due to the fact that two-phase cells, represented as a homogeneous water-steam mixture, are no longer representative of the real topology. Therefore, a new method is developed in order to track and reconstruct the quench front in an unstructured meshing evolving with time. Additionally, the mass, momentum and energy conservation equations for water and steam have to be locally adapted in order to take into account the moving quench front. Moreover, the present work proposes a method to reproduce the geometry of the debris bed domain, since a coarse meshing cannot reproduce pre-defined bed geometries properly, i.e. without smearing of the boundaries. The new modelling is verified against base cases that are analytically solvable. Finally, the capability of simulating with coarse meshing (and large cells), quickly and without any instabilities, was assessed by repeating the reactor-scale simulations.Item Open Access Development of a moving bed reactor for thermochemical heat storage with Ca(OH)2(2024) Cosquillo Mejia, Aldo Miguel; Thess, André (Prof. Dr. rer. nat. habil.)The use of the reaction system Ca(OH)2/CaO offers several advantages as a heat storage system. For instance, as a thermochemical reaction it has a high energy density and offers the possibility to store the chemical potential energy for long periods of time without energy losses. This is of particular interest when seasonal storage applications are sought. Furthermore, its low cost, proven cyclability and generally worldwide availability as natural resource makes it economically and sustainably attractive. Nevertheless, the inherent properties of the base powder material e.g. low thermal conductivity and tendency to agglomerate present a major challenge when designing reactors. A cost-efficient solution is the detachment of the power and capacity i.e. the use of moving bed reactors. Nevertheless, due to the unfavourable characteristics of the material, it has to be subject of modifications to ensure efficient heat and mass transport. In this thesis, three reactors were developed and set into operation for the thermal cycling of modified Ca(OH)2 and demonstration of the moving bed concept. The first design corresponds to a reaction chamber designed for the rapid cycling and real-time tracking of the reacting material under technical scale. In addition, further material analysis (e.g. TGA, XRD and dynamometry) contributed to an extensive assessment of the granules. Two different samples were cycled 20 times in this setup: granules coated with Al2O3 nanostructured particles and Ca(OH)2/CaCO3 composites. The operation of the reactor was demonstrated as well as the full conversion of the granules. The positive effect on the particle stabilisation given by the Al2O3 coating and the CaCO3 share in the composites was confirmed and at the same time no evidence of agglomeration was found. The second design is an indirectly heated reactor with a tube bundle heat exchanger. After 6 thermochemical cycles conducted with two different samples, CaO granules encapsulated in a ceramic shell and Ca(OH)2 granules coated with Al2O3 nanostructured particles, it was proven that both modifications contribute to the particle stabilisation. Although the encapsulated granules proved the moving bed concept of the reactor, the energy density was significantly lower and their conversion incomplete. In contrast, the coated granules displayed a complete conversion with energy density higher than the powder storage material. However, the natural change in dimensions of the reactive material, as a result of the thermal cycling, could not be prevented and therefore the movement of the bed was hindered. After combining the experimental results of the indirect moving bed reactor and the determined characteristics of the storage granules, a novel directly heated reactor concept was developed. The lab scale reactor was designed taking into consideration two main concerns: to supply enough thermal energy to drive the conversion of the granules while avoiding the fluidisation of the bed. The latter condition seeks to minimise the mechanical impact on the particle stability of the granules. Due to the higher energy density, the Ca(OH)2 granules coated with Al2O3 were selected for a 10-fold thermochemical cycle in this reactor. Besides the full conversion of the storage granules, the movement of the material in this novel reactor configuration was demonstrated for the first time. Furthermore, it was discovered that the interaction between Ca(OH)2 and Al2O3 produces a layer that confers the enhanced stability of the granules. Therefore, the results of this work can be used as the starting point for the upscale of the reactor design towards a pilot facility that works with Ca(OH)2 modified following the particle stabilisation approach.Item Open Access Entwicklung und Analyse einer selbstkühlenden und substratunabhängigen Beschichtung für technische Textilien unter Nutzung der energiefreien Strahlungskühlung(2024) Zimmermann, Lea; Gresser, Götz T. (Prof. Dr.-Ing.)Aufgrund des Klimawandels, des Bevölkerungswachstums und des städtischen Wärmeinseleffekts (UHI) ist der Bedarf an Kühlenergie insbesondere in städtischen Gebieten gestiegen und wird voraussichtlich auch in Zukunft weiter zunehmen. Bisherige konventionelle Kühlsysteme für Gebäude wie Klimaanlagen basieren auf thermodynamischen Kreisläufen, die einen großen Teil des Strombedarfs ausmachen und gleichzeitig Abwärme und Kohlendioxid (CO2) an die Umwelt abgeben. Technologien wie die Strahlungskühlung bieten eine nachhaltige und energiefreie Lösung, indem sie die Wellenlängenbereiche der Atmosphäre, die für elektromagnetische Strahlung transparent sind, das so genannte atmosphärische Fenster (8-13 µm), nutzen, um Wärmestrahlung in den kälteren (3 K) Weltraum abzugeben. Durch die Entwicklung von Beschichtungen, die selektiv Wärme durch die Atmosphäre abstrahlen und weniger Sonnenwärme absorbieren, ist eine Abkühlung unter die Umgebungstemperatur auch tagsüber möglich. Während sich bisherige Veröffentlichungen im Bereich der textilen Gebäudekühlung auf spezifische Faserstrukturen und textile Trägermaterialien sowie komplexe Mehrschichtaufbauten konzentrierten, was den Einsatz für hochskalierte Außenanwendungen einschränkt, zielt diese Arbeit auf die Entwicklung einer neuartigen, substratunabhängigen Beschichtung mit spektral selektiven Strahlungseigenschaften hin. Durch die detaillierte Abstimmung von Beschichtungsparametern wie der Partikelkonzentration, verteilung und -größe in Kombination mit niedrig emittierenden und solarreflektierenden Partikeln sowie einem stark im mittleren Infrarot emittierenden Matrixmaterial, wird eine substratunabhängige Kühlung unter die Umgebungstemperatur erreicht, gezeigt am Beispiel von drei für den Membran- und Zeltbau typischen Gewebetypen. Darüber hinaus ist die Beschichtung so konzipiert, dass sie einfach auf verschiedene textile Materialien appliziert werden kann und gleichzeitig eine geringe Dicke aufweist, um hohe Flexibilität und Skalierbarkeit zu gewährleisten. Um die Funktionsweise des entwickelten Beschichtungssystems weiter zu validieren, wurden Tests im Freien mit einem konzipierten Messaufbau durchgeführt, um Temperaturunterschiede und Kühlleistungen unter realen Wetterbedingungen zu messen. Die Ergebnisse zeigen, dass die Temperatur der Beschichtung (zwischen 7-19 Uhr) an einem heißen Sommertag um durchschnittlich 2 °C unter der Umgebungstemperatur liegt. Darüber hinaus wird ein thermisches Modell an textile Materialien angepasst und validiert, um die Kühlleistung für verschiedene Wetterszenarien zu simulieren und zu berechnen. Damit leistet diese Arbeit einen Beitrag zur Weiterentwicklung nachhaltiger textilbasierter Kühltechnologien und bietet eine vielversprechende Lösung für den wachsenden Bedarf an energieeffizienter Kühlung in städtischen Umgebungen.Item Open Access Modelling the energy yield of bifacial photovoltaic plants and their integration into European power supply systems(Stuttgart : Universität Stuttgart, Institut für Energiewirtschaft und Rationelle Energieanwendung, 2022) Chudinzow, Dimitrij; Hufendiek, Kai (Prof. Dr.-Ing.)Bifacial photovoltaic systems (B-PV) offer the advantage over conventional, monofacial photovoltaic systems (C-PV) that the irradiation hitting the back can also be converted into electricity. Thanks to this property, B-PV offer the possibility of significantly increasing the energy yield and reducing the cost of electricity. Furthermore, vertically installed bifacial PV systems (VBPV) facing east and west can achieve a generation profile complementary to C-PV, which can help to increase the economic efficiency of market-oriented PV systems and reduce integration costs in national power supply systems. Despite these promising features, B-PV has long played a minor role in research, development and application, leaving knowledge gaps in the areas of “energy yield simulation”, “field design” and “integration into power supply systems”. The present thesis contributes to closing these knowledge gaps. In the first step, the state of the art in energy yield modelling of B-PV as of 2016 was analysed. It was found that the adequate modelling of cast ground shadows, the irradiation absorbed from the front and the back, as well as the yield-reducing effects of the module rows on each other, represents a knowledge gap. Using a newly developed energy yield model, methods were developed to address this knowledge gap. This was essentially achieved by combining three-dimensional modelling of the PV system and methods from the field of irradiation exchange. This approach made it possible to quantify and classify the influence of important irradiation and installation parameters on the energy yield. In addition, a breakdown of the total absorbed irradiation into eight components became possible, which allows a site-dependent identification of the most important irradiation contributions. As a result, it was shown, among other things, that the presence of ground shadows can reduce the backside contribution to electricity generation by almost 30 % and the total annual electricity generation by up to 4 %. This illustrates the importance of thorough modelling of ground-reflected irradiance for a sound energy yield prediction. While decades of experience in field design of C-PV have led to reliable design guidelines on how to achieve minimum cost of electricity, this level of knowledge is not yet available to the same extent for B-PV. To contribute closing this knowledge gap, the second step was to use the newly developed model to investigate for eight European sites how different installation parameters affect the energy yield and cost of electricity of non-tracking and single-axis tracking B-PV. From this, general recommendations for the field design were derived, depending on latitude and irradiation conditions. The results showed, among other things, that with increasing latitude of the investigated site, an increase in the row spacing leads to an ever higher energy yield gain. If the energy yield is to be achieved by brightening the soil (e.g. with bright gravel), which is associated with additional costs, a reduction in the electricity generation costs is possible with a suitable overall configuration of the PV field. This illustrates that the complex interactions of radiation absorption must always be investigated holistically in order to find the cost optimum. A validation of the simulation model showed that the angle-dependent absorption of irradiation on the front side is well represented by the simulation model. Only at a tilt angle of 90° do larger deviations occur. The angle-dependent electricity generation (front + rear side) is also well captured by the model, with larger deviations occurring at a tilt angle of 0° (module is parallel to the ground). At cloudy weather, the model tends to overestimate the electricity generation by approx. 5 %, at sunnier weather the electricity generation is underpredicted by 10 %-15 %. The highest underprediction of generated electricity was observed at a tilt angle of 0° with a 20 % deviation. National power supply systems with high shares of installed C-PV capacity face the challenge of nearly simultaneous power generation from these systems because they are generally oriented towards the equator. This results in a generation peak at midday, while in the mornings and afternoons electricity generation is usually significantly lower. On the one hand, this simultaneity leads to decreasing electricity prices on the stock exchange, which endangers the profitability of PV systems. On the other hand, the total costs of power supply systems increase due to the need to maintain power plant reserves and electricity storage. VBPV enables feed-in profiles that have a peak in the morning and a peak in the afternoon. Consequently, in the third step, it was investigated which energetic and economic advantages could result from the use of VBPV compared to C-PV. The economic analyses from a business perspective were carried out for twelve locations in four European countries, while the cost-reducing effects in a power supply system were investigated with the help of a cost-minimising electricity market model using Germany as an example. It could be shown that above a latitude of 50°, VBPV always has a higher annual electricity generation than C-PV. An analysis of historical electricity prices in Germany showed that although C-PV always had a higher net present value, the difference to VBPV constantly decreased with decreasing electricity prices, which indicates an increasing competitiveness of VBPV. At the system level, VBPV was found to play an essential role in a cost-minimal electricity system with a high share of renewables and a high CO2-reduction. In the most ambitious of the climate scenarios investigated, VBPV would account for about 70 % of the total installed PV capacity and enable an annual system cost reduction of about 0.6 %.Item Open Access Leaching of fly ash particulate matter in MEA solutions and its relevance to the CO2 capture process with flue gas of coal-fired power plants(2020) Schallert, Bernd; Scheffknecht, Günter (Prof. Dr.)This study underlines the relevance of leaching of fly ash particulate matter to carbon capture plants and strives for a better understanding of the solubility of various elements and heavy metals, especially Fe, in MEA solutions and of relevant leaching parameters.Item Open Access Long-term exposure of European population subgroups to PM2.5 and NO2(Stuttgart : Universität Stuttgart, Institut für Energiewirtschaft und Rationelle Energieanwendung, 2020) Li, Naixin; Friedrich, Rainer (Prof. Dr.-Ing.)Numerous epidemiological studies have demonstrated the damaging influence of air pollutants on human health. However, the environmental health studies up to now use urban background concentrations in the ambient air to estimate the health risks, while the inhalation of toxic substances, i.e. the concentration of pollutants, where the exposed person breathes, is the relevant indicator for estimating the health impacts. The main objective of this thesis is to assess the long-term exposure to fine particles and nitrogen dioxide for different European subgroups that are characterised by certain features including age, gender, region and socio-economic status. The exposure simulation is realised by developing a probabilistic model that incorporates an air quality model for estimating the ambient pollutant concentration, a mass-balance model for assessing the concentration of indoor micro-environments and a life course trajectory model for predicting retrospectively the transition between socio-economic states. The results of the exposure modelling are subsequently incorporated with exposure response functions (ERFs), aggregation factors and monetary values to assess health impacts and damage costs.Item Open Access CO and H2S in H2: contamination, recovery and mitigation strategies in PEMFCs with ultra-low Pt loaded anode electrodes(2024) Prass, Sebastian; Friedrich, K. Andreas (Prof. Dr. rer. nat.)Einige der größten Hürden für die Kommerzialisierung von Fahrzeugen mit Brennstoffzellenantrieb (engl. Proton Exchange Membrane Fuel Cell, PEMFC) sind die Kosten und Lebensdauer der Systeme, sowie die fehlende Infrastruktur, die den Wasserstoff (H2) bereitstellt. Zur Verringerung der PEMFC-Kosten ist eine Reduktion des Gehalts an Katalysatoren der Platin (Pt)-Gruppe nötig, was jedoch durch Vergiftungsmechanismen erschwert wird, deren Wirkung bei niedrigeren Pt-Beladungen pro aktiver Fläche ([µgPt/cm²]) zunimmt. Verunreinigungen im H2, die durch kostenintensive Reinigungsverfahren herausgefiltert werden, beeinträchtigen die PEMFC-Leistung und Lebensdauer. Sind Kontaminations- und Erholungsmechanismen bekannt, können Betriebsweisen angepasst und der Katalysatorgehalt einerseits verringert, sowie die Herstellung und Aufreinigung des H2 andererseits kosteneffizienter gestaltet werden. Diese Dissertation untersucht daher die Auswirkung einer Verringerung der Platinbeladung der Anodenelektrode auf die Toleranz gegenüber Kohlenmonoxid (CO) und Schwefelwasserstoff (H2S) im H2 anhand von Einzelzellen unter Verwendung klassischer elektrochemischer Charakterisierungsverfahren. Zunächst ist die Charakterisierung niedrig beladener Elektroden per Zyklovoltammetrie (engl. Cyclic Voltammetry, CV) durch Artefakte erschwert, die normalerweise bei höheren Beladungen (>100 µgPt/cm²) nicht auftreten. Bei niedrigen Beladungen (<50 µgPt/cm²) kann es zu einer spontanen Oxidation von angesammeltem Permeat-Wasserstoff während des kathodischen CV-Vorschubs kommen, was den Pt-Oxid-Reduktionsstrom überlappt und die Bestimmung der aktiven Fläche (engl. Electrochemically Active Surface Area, ECSA) beeinträchtigt. Werden PEMFCs mit gering beladenen Anodenelektroden (<25 µgPt/cm²) und H2 betrieben, der CO in Konzentrationen enthält, die gemäß H2-Qualitätsstandard ISO 14687 zulässig sind, kommt es zu inakzeptablen Spannungsabfällen von bis zu 40%. Dies deutet darauf hin, dass die CO-Toleranz des Katalysators verbessert, oder der ISO-Grenzwert für CO verringert werden sollte. Ist H2S in Konzentrationen gemäß ISO 14687 im H2 enthalten, kommt es während chronoamperometrischer Tests zu Spannungseinbrüchen, die bei niedrig beladenen Elektroden Schwefeldosisabhängig früher auftreten. Andererseits können sich PEMFCs durch Stopp/Start (engl. Shut-Down/Start-Up, SD/SU)-Prozeduren von Schwefelvergiftungen erholen. Gemeinsam mit den erst nach Dutzenden Stunden auftretenden Spannungseinbrüchen wirft diese Erholung durch SD/SUs die Frage auf, ob der ISO-Grenzwert für Schwefelspezies einer Anpassung bedarf. Eine Beschichtung des Pt-Katalysators in der Anodenelektrode mit einer Siliziumoxidschicht (SiO2-Pt/C) verbessert die Leistung und Toleranz der PEMFC beim Betrieb mit reinem und H2S-kontaminiertem H2, verschlechtert jedoch deren CO-Toleranz. Während die Verbesserung der Leistung und H2S-Toleranz auf Einflüsse des SiO2 auf Wassermanagement und Mobilität oxidierter Schwefelspezies zurückzuführen ist, steht die Verschlechterung der CO-Toleranz im Zusammenhang mit erschwerter Bildung und Mobilität der OH-Gruppen, die für die CO-Oxidation notwendig und in erhöhten Potentialen für CO-Oxidation sichtbar sind.