L'objectif de cette thèse a consisté à étudier des procédés de fabrication de couches de diffusion de gaz (GDL) en silicium poreux appliqués à l'intégration de micropiles à combustible de type PEMFC sur plaquette de silicium. Deux types de couches ont été étudiés : sur surface plane (2D) et sur surface texturée (3D). Les couches de diffusion de gaz ont été réalisées par l'anodisation de silicium de type N fortement résistif. Une localisation des motifs poreux a été obtenue par ouverture d'un masque en polysilicium sur oxyde thermique de silicium. Seules les GDL 2D entièrement macroporeuses assuraient un débit d'hydrogène compatible avec les objectifs de fabrication d'une micropile prototype. Le prototype a permis de valider la compabilité de la couche de diffusion de gaz avec les étapes d'empilement des couches actives constitutive de la micropile. Son fonctionnement nous a permis d'atteindre une densité de puissance de 250 mW/cm². / This thesis work deals with porous silicon gas diffusion layer (GDL) fabrication process. The aim was to integrate this GDL into proton exchange membrane micro fuel cells (PEMFC). Consequently, the GDL must be localized in specific wafer areas. We have also developed 2D and 3D structures. To produce a GDL, we have anodized low doped N type silicon subrates. thus, we have fabricated macroporous GDL and double layer structures made up of a mesaporous layer on a macroporous one. Patterning of the GDL has been obtained through a hard mask (polysilicon on top of a silicon oxide layer) or using a localized doping. We have concluded this work by achieving micro fuel cell prototypes with macroporous silicon gas diffusion layers. After validation of micro PEMFC active layer mechanical stacking, we have measured a maximum power density of about 250 mW/cm².

Transport phenomena in high porosity open-cell fibrous structures have been the focus of many recent industrial and academic investigations. Unique features of these structures such as relatively low cost, ultra-low density, high surface area to volume ratio, and the ability to mix the passing fluid make them excellent candidates for a variety of thermofluid applications including fuel cells, compact heat exchangers and cooling of microelectronics. This thesis contributes to improved understanding of thermal transport phenomena in fuel cell gas diffusion layers (GDLs) and metal foams and describes new experimental techniques and analytic models to characterize and predict effective transport properties. Heat transfer through the GDL is a key process in the design and operation of a proton exchange membrane (PEM) fuel cell. The analysis of this process requires determination of the effective thermal conductivity as well as the thermal contact resistance (TCR) associated with the interface between the GDL and adjacent surfaces/ layers. The effective thermal conductivity significantly differs in through-plane and in-plane directions due to anisotropy of the GDL micro-structure. Also, the high porosity of GDLs makes the contribution of TCR against the heat flow through the medium more pronounced. A test bed was designed and built to measure the thermal contact resistance and effective thermal conductivity in both through-plane and in-plane directions under vacuum and ambient conditions. The developed experimental program allows the separation of effective thermal conductivity and thermal contact resistance. For GDLs, measurements are performed under a wide range of compressive loads using Toray carbon paper samples. To study the effect of cyclic compression, which may happen during the operation of a fuel cell stack, measurements are performed on the thermal and structural properties of GDL at different loading-unloading cycles. The static compression measurements are complemented by a compact analytical model that achieves good agreement with experimental data. The outcomes of the cyclic compression measurements show a significant hysteresis in the loading and unloading cycle data for total thermal resistance, TCR, effective thermal conductivity, thickness, and porosity. It is found that after 5 loading/unloading cycles, the geometrical, mechanical, and thermal parameters reach a“steady-state”condition and remain unchanged. A key finding of this study is that the TCR is the dominant component of the GDL total thermal resistance with a significant hysteresis resulting in up to a 34 % difference between the loading and unloading cycle data. Neglecting this phenomenon may result in significant errors in evaluating heat transfer rates and temperature distributions. In-plane thermal experiments were performed using Toray carbon paper samples with different polytetrafluoroethylene (PTFE) content at the mean temperature of 65−70◦C. The measurements are complemented by a compact analytical model that achieves good agreement with experimental data. Results show that the in-plane effective thermal conductivity remains approximately constant, k ≈ 17.5W/mK, over a wide range of PTFE content, and it is approximately 12 times higher than the through-plane conductivity. Using the test bed designed for the through-plane thermal conductivity measurement, the effective thermal conductivity and thermal contact resistance of ERG Duocel aluminum foam samples were measured under varying compressive loads for a variety of porosities and pore densities. Also, an experimental program associated with an image analysis technique is developed to find the size and distribution of contact spots at different compressive loads. Results show that the porosity and the effective thermal conductivity remain unchanged with the variation of pressure in the range of 0 to 2 MPa; but TCR decreases significantly with pressure due to an increase in contact area. Moreover, the ratio of contact area to cross-sectional area is 0-0.013, depending upon the compressive force, porosity, and pore density. This study clarifies the impact of compression on the thermal and structural properties of GDLs and metal foams and provides new insights on the importance of TCR which is a critical interfacial transport phenomenon. / Graduate

A new type of fuel cell architecture, the fuel cell ribbon, is presented. The fuel cell ribbon architecture relies on the gas diffusion layer (GDL) to conduct electrical current in-plane to adjacent cells or collector terminals. The potential advantages of the fuel cell ribbon architecture with respect to conventional fuel cell stacks include reduced manufacturing costs, reduced weight, reduced volume, and reduced component cost. The critical component of fuel cell ribbon assemblies, the gas diffusion media, is investigated herein. Analytical models which focus on the electrical loses within the gas diffusion media of the novel architecture are developed. The materials and treatments necessary to fabricate novel gas diffusion media for fuel cell ribbon assemblies are presented. Experimental results for the novel gas diffusion media of are also presented. One dimensional and two dimensional analytical models were developed for the fuel cell ribbon. The models presented in this work focus on the losses associated with the transport of the electrons in fuel cell ribbon assemblies, rather than the complex system of equations that governs the rate of electron production. The 1-D model indicated that the GDL used in ribbon cells must exhibit an in-plane resistance which is approximately an order of magnitude lower than the resistance of gas diffusion media typically used in conventional fuel cells. A 2-D model was developed with which a parametric study of GDL properties and ribbon cell dimensions was performed. The parametric study indicated that ribbon cells of useful size can be constructed using novel diffusion media that offer reduced resistivity, and that the ribbon cells can produce as much as 80-85% of the power density produced in a conventional fuel cell. Novel gas diffusion media for fuel cell ribbons that have the necessary characteristics suggested by the analytical study were developed.. Properties and performance for a commercially available gas diffusion media, ELAT, were measured as a reference for the novel media developed. The increased thickness PAN (ITPN) series diffusion media was constructed of PAN based fibers exhibiting similar resistive properties to the fibers used in ELAT. The ITPN series of materials were woven in a manner which made them approximately twice the thickness of ELAT, effectively reducing their in-plane resistance to half the resistance exhibited by ELAT. The coarsely woven pitch (CWPT) series of materials were constructed in a manner which yielded a similar number of fibers in the plane of the material to ELAT and a similar material thickness to ELAT, but the fibers used were mesophase pitch based fibers which exhibit a resistivity of approximately one-tenth the resistivity of the fibers used to make the ELAT and ITPN materials. The reduction in fiber resistivity led to the CWPT material having an in-plane resistance an order of magnitude lower than ELAT. The widely used ELAT material exhibited an in-plane resistance of 0.39 Ω/sq., a through-plane area specific resistance of 0.007 Ω-cm2, and a Darcy permeability coefficient of 8.1 Darcys. The novel diffusion materials exhibited in-plane resistances in the range of 0.18-0.036 Ω/sq., through-plane area specific resistances in the range of 0.017-0.013 Ω-cm2, and Darcy permeability coefficients in the range of 30-150 Darcys. Experiments were performed to validate the analytical model and to prove the feasibility of fuel cell ribbon concept. When the novel gas diffusers were adhered to a catalyzed membrane and tested in a ribbon test assembly utilizing serpentine flow channels and in-plane current collection, a range of performance was achieved between 0.28-0.4 A/cm2 at a cell output potential of 0.5 V. In contrast, when ELAT was adhered to a catalyzed membrane and tested in the fixture requiring in-plane conduction, a current density of 0.21 A/cm2 was achieved at 0.5 V. Additionally, the 2-D finite element model was used to predict the performance of a ribbon cell based on the cells performance when a conventional method of through-plane conduction was utilized. The agreement between the experimental data and the model predictions was very good for the ELAT and ITPN materials, whereas the predictions for the CWPT materials showed more significant deviation which was likely due to mass transport and contact resistance effects. / Master of Science

L’objectif de ce travail de thèse porte sur l’étude et la compréhension des phénomènes de la dégradation de la couche de diffusion des gaz. Ce composant de la PEMFC n’a pas été beaucoup discuté dans la littérature d’où le manque d’informations sur ses mécanismes de vieillissement. La dégradation physico-chimique en ex-situ de la GDL est tout d’abord étudiée par immersion et par voie électrochimique à fort potentiel. Plusieurs techniques d’analyses spectroscopiques, microscopiques et électrochimiques ont été utilisées dans le but de comprendre l’origine de cette dégradation. Les résultats de ces techniques montrent que les propriétés physico-chimiques de la GDL dépendent fortement des conditions opératoires des AST réalisés. La structure de la GDL a été gravement dégradée par voie électrochimique en particulier à 1,2 et 1,4 V vs. ECS. Cependant, l’immersion dans l’acide ou dans l’eau n’a pas réellement montré de changement au niveau de la morphologie et la structure par rapport à son état initial. Par contre, les résultats trouvés indiquent qu’indépendamment des conditions opératoires utilisées et contrairement à ce qui a été mentionné dans certaines publications, le PTFE des couches macro et microporeuse est relativement stable à la dégradation par comparaison aux composés carbonés. De plus, l’impact du vieillissement de la GDL sur la réponse de la pile étudiée par chronopotentiométrie, courbes tension vs. courant et spectroscopie d’impédance montrent une dégradation de la performance électrique de la pile à fortes densités de courant en particulier dans le cas des GDL dégradées à 1,2 et 1,4 V vs. ECS. Enfin, pour comparer les résultats des AST ex-situ à ceux d’un vieillissement in-situ, un cyclage dynamique de conduite, FCDLC, qui consiste en une variation du courant et de la tension de la pile sur un cycle de 1200 secondes, a été conduit pendant 1000 heures. Les résultats de ce cyclage montrent une dégradation de la surface active et une augmentation de la densité de courant de fuite. En contrepartie, ce FCDLC n’a pas beaucoup d’impact sur le vieillissement de la GDL par comparaison aux résultats trouvés des AST ex-situ / The aim of this work is to understand the mechanism of gas diffusion layer degradation. Comparing to other PEMFC components, these layer has not been much discussed in the literature. First, in order to study ageing phenomena, ex-situ physico-chemical degradation of the GDL is carried out using acid and water immersion or electrochemical degradation at high potential. Several spectroscopic, microscopic and electrochemical techniques have been used to identify GDL degradation properties. The results of these experiments show that physicochemical properties of GDL depend strongly on the operating conditions of the ASTs produced. The structure of the GDL aged at 1.2 and 1.4 V vs. ECS has been severely changed. However, immersed GDL in acid or water did not actually show any change in morphology and structure compared to its initial state. On the other hand, the results obtained indicate that, independently of the operating conditions, and contrary to what has been mentioned in certain publications, the PTFE of the macro and microporous layers is relatively stable during AST compared to the carbon compounds. Moreover, the impact of aging of the GDL on the fuel cell response determined by chronopotentiometry, polarization curves and impedance spectroscopy show a degradation of the electrical performance of the cell, at high current density, in particular in the case aged GDL at 1.2 and 1.4 V vs. ECS. Finally, to compare ex-situ ASTs and in-situ aging impact, dynamic driving cycling, FCDLC, which consists of a variation of the current and the voltage of the fuel cell over a cycle of 1200 seconds, was conducted for 1000 hours. The result of the electrochemical characterization during cycling show that the active surface is degraded and the leakage current density is increased. However, this FCDLC does not affect the GDL properties compared to the results obtained with the ex-situ degradation experiments

Istoriografijoje XVIII a. vadinamas moterų amžiumi ne tik dėl to, kad pačios moterys pradėjo aktyviau reikštis įvairiose gyvenimo sferose, bet ir dėl to, kad amžininkai pradėjo diskusijas apie moterų vietą ir tikslus „vyriškame“ pasaulyje. Šios Apšvietos epochos diskusijos, prasidėjusios Prancūzijoje, pasiekė ir Abiejų Tautų Respubliką (ATR) ir, žinoma, Lietuvos Didžiąją Kunigaikštystę. Moterų aktyvumas priklausė ne tik nuo Apšvietos epochoje atsiradusių diskusijų dėl moterų padėties visuomenėje, bet ir nuo naujų kultūrinių bei geopolitinių aplinkybių. Darbo tikslas – remiantis šaltiniais ir istoriografija, išskirti ir išanalizuoti būdingiausias moterims veiklas XVIII a. Lietuvos Didžiojoje Kunigaikštystėje. Šiam tikslui išsikeliame šiuos uždavinius: 1) remiantis istoriografija ir šaltiniais, apibrėžti moterų veiklų sąlygas šeimoje ir visuomenėje; 2) išskirti būdingiausias moterims veiklas XVIII a.; 3) remiantis istoriografija ir šaltiniais, atskirai išanalizuoti tų veiklų priežastis, tikslus ir aplinkybes; 4) remiantis moterų sukurtais šaltiniais, išanalizuoti jų pasirinktos veiklos priežastis ir aplinkybes. Didelis dėmesys pradėtas skirti moterų ugdymui bei išsilavinimui. Čia labiausiai pasižymėjo vienuolės, kurių žinioje dažnai buvo mergaičių auklėjimas. Viena populiariausių moterų veiklų yra literatūrinė. Šaltiniuose aptikta informacija leidžia teigti, kad atsiminimų, dienoraščių, eilių rašymas buvo plačiai paplitęs tarp moterų. Atsiminimus, dienoraščius ir t. t. moterys... [toliau žr. visą tekstą] / The XVIIIth century deservedly is calling as the women’s century, not only because contemporaries started discussions about women place and aims in the masculine world, and yet women started to play up in different playgrounds by themselves. Such discussions of Age of Enlightenment have been started in France, and reached Polish-Lithuanian Commonwealth (PLC) and The Grand Duchy of Lithuania as well. The women activity depended not only on those discussions about women state in society, and yet of new cultural and geopolitical circumstances. The aim of this researching is to identity and analyse the most typical women’s activities at XVIIIth century in The Grand Duchy of Lithuania on ground of historiography and origins. There are four tasks to fulfil this aim: 1) to identity and analyse the circumstances of women’s activities in the family and society on ground of historiography and origins; 2) to identity the most typical women’s activities at XVIIIth century; 3) to analyze the reasons, aims and circumstances of particular activities on ground of historiography and origins; 4) to analyze women’s activities reasons and circumstances on ground of origins created by women. Though women’s legal status was deferent than men, but their status quo depended on women’s temper. Often woman’s status in the public life depended on her status in her own family. Also there showed up new meaning of women role in society, on ground of first partition (1772). Woman had been ranked as... [to full text]

The thesis explores the possible use of parametric object definitions during capacity analysis to support Open Building design processes.The study proposes that design criteria regarding possible size, position and relation of design elements can be formulated and modeled parametrically. Then developed parametric data can be used as library objects during the exploration of dwelling unit layout alternatives. Parametric models, holding explicit design information can be shared, modified and re-used in different design cases. The process and criteria used in the study are based on S.A.R. (Stichting Architecten Research) methods described in the study, "Variations - The Systematic Design of Supports" focused particularly on residential building types. Parallel to the S.A.R methods, the study focuses on the spatial capacity analysis between a floor plate and a number of alternative dwelling unit layout arrangements. Other capacity analyses such as structural, daylight or thermal performances can be formulated and studied in a similar way, but are not included in this study.GDL (Geometric Description Language), a programming medium for ArchiCAD software, is used for the production of parametric models. The Keyenburg housing project designed by Dutch architect Frans Van Der Werf is taken as a base-building model to demonstrate the development and the use of parametric models.Keywords: Open Building, capacity analysis, parametric objects, design constraints, GDL (Geometric Description Language) / Department of Architecture

In this work, a steady-state, one-dimensional model was developed for the cathode side of the PEM fuel cell. The model results compared well with available literature results. The effects of operating temperature, cathode gas pressure, cathode gas porosity, and membrane thickness were studied. Carbon materials used for the gas diffusion layer (GDL) were characterized. The materials were: untreated and Teflon-treated carbon paper and untreated and Teflon-treated carbon cloth. Physisorption data were analyzed using the BET and the BJH methods to determine surface area and pore size distribution. Capillary flow porometry measurements provided the bubble point, mean flow, and smallest pore diameters and pore size distribution. Gas permeability measurements were performed. Mercury/non-mercury intrusion porosimetry measurements were performed to obtain pore size distribution and cumulative pore volume. The microstructure structure of the materials was examined using Scanning Electron Microscopy. The elemental composition of the samples was measured using Energy Dispersive X-ray Spectroscopy.

The gas diffusion layer (GDL) is one of the key components in a polymer electrolyte membrane (PEM) fuel cell. It performs several functions including the transport of reactant gases and product water to and from the catalyst layer, conduction of both electrons and heat produced in the catalyst layer, as well as mechanical support for the membrane. The overarching goal of this work is to thoroughly examine the GDL structure and properties for use in PEM fuel cells, and more specifically, to determine how to characterize the GDL experimentally ex-situ, to understand its performance in-situ, and to relate theory to performance through controlled experimentation. Thus, the impact of readily measured effective water vapor diffusivity on the performance of the GDL is investigated and shown to correlate to the wet limiting current density, as a surrogate of the oxygen diffusivity to which it is more directly related. The influence of microporous layer (MPL) design and construction on the fuel cell performance is studied and recommendations are made for optimal MPL designs for different operating conditions. A method for modifying the PTFE (Teflon) distribution within the GDL is proposed and the impact of distribution of PTFE in the GDL on fuel cell performance is studied. A method for characterizing the surface roughness of the GDL is developed and the impact of surface roughness on various ex-situ GDL properties is investigated. Finally, a detailed analysis of the physical structure and permeability of the GDL is provided and a theoretical model is proposed to predict both dry and wet gas flow within a GDL based on mercury intrusion porosimetry and porometry data. It is hoped that this work will contribute to an improved understanding of the functioning and structure of the GDL and hence advance PEM fuel cell technology.

Aufgrund des weltweit steigenden Energiebedarfs, dessen Deckung derzeit größtenteils auf fossilen Brennstoffen basiert, ist es nötig geworden, die Entwicklung alternativer Möglichkeiten zur Erzeugung von Elektroenergie als Primärenergie voranzutreiben. Eine dieser alternativen Möglichkeiten ist die Brennstoffezellentechnologie, welche sowohl in stationären als auch mobilen Anwendungen zum Einsatz kommen kann. Ihrer weitreichenden Verbreitung stehen bislang die aufgrund des großen Fertigungsaufwandes hohen Herstellungskosten der benötigten Komponenten im Wege. Hierzu zählen die Gasdiffusionslagen des weit verbreiteten Typs der wasserstoffbetriebenen Polymerelektrolytbrennstoffzelle. Es treten zwischen den einzelnen Fertigungsschritten im Herstellungsprozess dieser Gasdiffusionslagen Wechselwirkungen auf, die zu unerwünschten Materialveränderungen führen. Die Ursachen dieser Wechselwirkungen sind nicht vollends verstanden. Eine Vertiefung des Verständnisses der Herstellungsprozesse soll die Grundlage für eine Optimierung der Prozessführung bilden. Es sollen eine Kostenreduktion sowie eine Leistungssteigerung der Gasdiffusionslagen ermöglicht werden.:1 Einleitung 1 2 Stand der Technik 5 2.1 Brennstoffzellen 5 2.2 Gasdiffusionslagen 11 3 Problemstellung und Zielsetzung 17 4 Analyse und Klassifizierung von GDL-Fehlern 20 4.1 Fehlerklassifizierung 22 4.2 Fehleridentifizierung 26 4.3 Auswahl zu analysierender Fehlerbilder 27 4.4 Charakteristika der ausgewählten Fehlerbilder 42 4.4.1 Bahndeformationen 42 4.4.2 Umlaufende Verdickungen von Wickeln in Umfangsrichtung 44 4.4.3 Längs- und Queraufrauhungen sowie Rauhspuren 45 5 Theoretische Grundlagen 49 5.1 Physikalische und mechanische Grundlagen 49 5.1.1 Zug-, Biege- und Druckspannungen in Warenbahnen 49 5.1.2 Elastizitäts- und Kompressionsmoduli 52 5.1.3 Elastizität und Plastizität 53 5.1.4 Umformmechanismen im GDL-Basisvliesstoff und Versagensarten von Fasern 54 5.2 Statistik 55 5.2.1 Korrelationsanalyse 55 5.2.2 Regressionsanalyse 56 5.2.3 Zweistichproben-t-Tests und Konfidenzintervalle 56 5.2.4 Stichprobenumfang 57 5.3 Qualitätsregelkreise 58 6 Eingesetzte Untersuchungsmethoden 60 6.1 Mechanische Eigenschaften 64 6.1.1 Höchstzugkraft und Höchstzugkraftdehnung 64 6.1.2 Elastizitätsmodul und Kompressibilität 66 6.1.3 Elastische und plastische Deformation bei Zugbelastungen 67 6.1.4 Flächenmasse 70 6.1.5 Biegesteifigkeit 72 6.1.6 Dickenmessung 74 6.2 Thermische Eigenschaften 75 6.2.1 Wärmeleitfähigkeit 75 6.3 Bildgebende Verfahren 78 6.3.1 Schliffbildmikroskopie 78 6.3.2 Rasterelektronenmikroskopie 78 6.3.3 µ-Computertomographie 79 7 Herstellungsverfahren der untersuchten Gasdiffusionslagen im Überblick 81 8 Basisvliesstoffherstellung 84 8.1 Prozess der Vliesbildung und Verfestigung 84 8.2 Charakterisierung des GDL-Basisvliesstoffes 90 8.3 Fehlerbilder des GDL-Basisvliesstoffes 103 9 Dickenkalibrierung 113 9.1 Prozess der Dickenkalibrierung des GDL-Basisvliesstoffes 113 9.2 Charakterisierung des dickenkalibrierten GDL-Basisvliesstoffes 120 9.3 Fehlerbilder des dickenkalibrierten GDL-Basisvliesstoffes 130 9.3.1 Prozessbeobachtung 130 9.3.2 Hypothesenbildung und Verifikation 135 9.3.3 Maßnahmen zur Fehlervermeidung 146 10 Carbonisierung 156 10.1 Prozess der Carbonisierung 156 10.2 Charakterisierung carbonisierten GDL-Substrates 157 10.3 Fehlerbilder im Carbonisierprozess 163 11 Data Mining für die GDL-Herstellung 167 11.1 Datenerhebung 167 11.2 Auszuwertende Parameter 172 11.3 Ergebnisse der Parameteranalysen 173 12 Qualitätsregelkreise zum GDL-Produktionsprozess 178 12.1 Wulstbildung und Längsaufrauhung 178 12.2 Queraufrauhung 181 13 Zusammenfassung und Ausblick 184 14 Literaturverzeichnis 186 15 Abbildungsverzeichnis 192 16 Abkürzungsverzeichnis 201 17 Formelverzeichnis 203 18 Anlagenverzeichnis 204 / Due to worldwide increasing energy consumption, which is mainly covered by fossile fuels nowadays, it has become a necessity to further develop alternative possibilities to create electricity as primary energy. One alternative technology to accomplish this is fuel cell technology which can be used in stationary as well as in mobile applications. One aspect hindering its widespread use is the high manufacturing cost of the needed components due to the complicated production processes. Among these are gad diffusion layers of the commonly used hydrogen-driven polymer electrolyte fuel cells. There are interactions occurring between the several production steps leading to unwanted changes in material properties. The causes of these interactions are not completely understood. A deeper understanding of these shall be the basis for optimizations in process design and therefore cost reductions and improvements in performance of gas diffusion layers can be achieved.:1 Einleitung 1 2 Stand der Technik 5 2.1 Brennstoffzellen 5 2.2 Gasdiffusionslagen 11 3 Problemstellung und Zielsetzung 17 4 Analyse und Klassifizierung von GDL-Fehlern 20 4.1 Fehlerklassifizierung 22 4.2 Fehleridentifizierung 26 4.3 Auswahl zu analysierender Fehlerbilder 27 4.4 Charakteristika der ausgewählten Fehlerbilder 42 4.4.1 Bahndeformationen 42 4.4.2 Umlaufende Verdickungen von Wickeln in Umfangsrichtung 44 4.4.3 Längs- und Queraufrauhungen sowie Rauhspuren 45 5 Theoretische Grundlagen 49 5.1 Physikalische und mechanische Grundlagen 49 5.1.1 Zug-, Biege- und Druckspannungen in Warenbahnen 49 5.1.2 Elastizitäts- und Kompressionsmoduli 52 5.1.3 Elastizität und Plastizität 53 5.1.4 Umformmechanismen im GDL-Basisvliesstoff und Versagensarten von Fasern 54 5.2 Statistik 55 5.2.1 Korrelationsanalyse 55 5.2.2 Regressionsanalyse 56 5.2.3 Zweistichproben-t-Tests und Konfidenzintervalle 56 5.2.4 Stichprobenumfang 57 5.3 Qualitätsregelkreise 58 6 Eingesetzte Untersuchungsmethoden 60 6.1 Mechanische Eigenschaften 64 6.1.1 Höchstzugkraft und Höchstzugkraftdehnung 64 6.1.2 Elastizitätsmodul und Kompressibilität 66 6.1.3 Elastische und plastische Deformation bei Zugbelastungen 67 6.1.4 Flächenmasse 70 6.1.5 Biegesteifigkeit 72 6.1.6 Dickenmessung 74 6.2 Thermische Eigenschaften 75 6.2.1 Wärmeleitfähigkeit 75 6.3 Bildgebende Verfahren 78 6.3.1 Schliffbildmikroskopie 78 6.3.2 Rasterelektronenmikroskopie 78 6.3.3 µ-Computertomographie 79 7 Herstellungsverfahren der untersuchten Gasdiffusionslagen im Überblick 81 8 Basisvliesstoffherstellung 84 8.1 Prozess der Vliesbildung und Verfestigung 84 8.2 Charakterisierung des GDL-Basisvliesstoffes 90 8.3 Fehlerbilder des GDL-Basisvliesstoffes 103 9 Dickenkalibrierung 113 9.1 Prozess der Dickenkalibrierung des GDL-Basisvliesstoffes 113 9.2 Charakterisierung des dickenkalibrierten GDL-Basisvliesstoffes 120 9.3 Fehlerbilder des dickenkalibrierten GDL-Basisvliesstoffes 130 9.3.1 Prozessbeobachtung 130 9.3.2 Hypothesenbildung und Verifikation 135 9.3.3 Maßnahmen zur Fehlervermeidung 146 10 Carbonisierung 156 10.1 Prozess der Carbonisierung 156 10.2 Charakterisierung carbonisierten GDL-Substrates 157 10.3 Fehlerbilder im Carbonisierprozess 163 11 Data Mining für die GDL-Herstellung 167 11.1 Datenerhebung 167 11.2 Auszuwertende Parameter 172 11.3 Ergebnisse der Parameteranalysen 173 12 Qualitätsregelkreise zum GDL-Produktionsprozess 178 12.1 Wulstbildung und Längsaufrauhung 178 12.2 Queraufrauhung 181 13 Zusammenfassung und Ausblick 184 14 Literaturverzeichnis 186 15 Abbildungsverzeichnis 192 16 Abkürzungsverzeichnis 201 17 Formelverzeichnis 203 18 Anlagenverzeichnis 204

The excessive presence of liquid water in a gas diffusion layer (GDL) hinders the access of reactant gases to the active sites of the catalyst layer leading to decreased performance of a polymer electrolyte membrane fuel cell (PEMFC). Therefore, GDLs are usually treated with a hydrophobic agent to render their fibres more hydrophobic in order to facilitate gas transport and water removal. Numerous studies have been conducted to investigate water transport in PEMFCs in recent years; however, the behaviour of liquid water in a GDL at a pore-level is poorly understood. Macroscopic models fail to incorporate the influence of the structural morphology of GDLs on liquid water transport behaviour. Experimental methods are not conducive towards a good understanding at a microscopic level because of the diminutive size of the GDLs porous structure. Alternatively, the Lattice Boltzmann (LB) method has gathered interest as it is found to be particularly useful in fluid flow simulations in porous media due to its capability to incorporate the complex boundaries of actual GDL structures. To date, most studies on fluid transport in GDLs integrated artificial structures generated by stochastic simulation techniques to the LB models. The stochastic-based model, however, does not represent closely the microscopic features of the actual GDL as manufactured. In addition, comparison of liquid water transport behaviour in different GDL structures using the LB method is rare since only a single GDL material has been utilised in most of those studies. This thesis aims to develop our understanding of liquid water transport behaviour in GDLs with morphologically different structures under varying wettability conditions based on the LB method and the X-ray computed tomography (XCT) technique. GDLs with paper and felt structures were reconstructed into 3D digital volumetric models via the XCT process. The digital models were then incorporated into a LB solver to model water saturation distribution through the GDL domains. The GDL wettability was also altered so that the effect on liquid water behaviour in the GDL could be examined. This project is divided into three main sections. In the sensitivity analysis, the effect of image resolution on gas permeability through the X-ray reconstructed GDL was carried out using a single-phase LB model. It was found that the resolution variation could significantly affect the resulting gas permeability in both principal and off-principal directions, as well as computational time. An optimum resolution, however, exists at 2.72 μm/pixel, which consumed 400 times less computational time with less than 8% difference in the resulting permeability compared to the base resolution. This study also served as a guideline for selecting a resolution for generating the XCT images of the GDLs which were utilised in the following studies. In the structure analysis, the structures of the paper and felt GDLs were generated using the XCT and the key properties of each GDL, including thickness, porosity, permeability and tortuosity, were characterised. The thickness and the through-plane porosity distributions of each GDL were examined based on the tomography images. The resulting local through-plane porosity distributions were then used to calculate through-plane permeability and tortuosity distributions using an analytical model available in the literature. This study revealed the heterogeneity of the GDLs and how the heterogeneous nature of the GDL structures affects others properties of the GDLs. In this study, the absolute through-plane permeability and tortuosity of the X-ray-reconstructed GDL samples were also characterised using the single-phase LB model. The results from the two models were then compared and validated against data in the literature. In the water transport analysis, the two-phase LB model was employed to examine the effects of GDL structures on the behaviour of liquid water in the GDLs, including invasion patterns, saturation distribution and breakthrough behaviour under varying GDL wettability conditions. It was found that wettability was responsible for invasion patterns and water saturation levels whilst the GDL structure was mostly responsible for breakthrough occurrence and saturation distribution. It was observed that water travelled with stable displacement saturating all pores in hydrophilic GDLs, while it travelled with capillary fingering causing decreased saturation in hydrophobic GDLs, about 50% in the highly hydrophobic cases. The GDL structure was found to play a key role in breakthrough behaviour in the hydrophilic GDL as it was seen that the through-plane fibres in the felt structure and the through-plane binders in the paper structure encouraged water removal from the GDL in the thickness direction. Conversely, the GDL structure was found to have negligible influence on breakthrough in the hydrophobic GDL. Each GDL structure, however, contributed to a distinct difference in water distribution in the GDL with hydrophobic wettability. The work presented in this thesis contributes to the understanding of liquid water transport behaviour in the GDLs under the combined effects of the GDL structures and wettability conditions, which is essential for the development of effective PEMFC water management and the design of future GDL materials.