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Modeling Water Content Effects In Polymer Electrolyte Fuel Cells
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Book Synopsis Modeling Water Content Effects in Polymer Electrolyte Fuel Cells by :
Download or read book Modeling Water Content Effects in Polymer Electrolyte Fuel Cells written by and published by . This book was released on 1991 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: Water content and transport is the key factor in the one-dimensional, steady-state model of a complete polymer electrolyte fuel cell (PEFC) described here. Water diffusion coefficients, electroosmotic drag coefficients, water sorption isotherms, and membrane conductivities, all measured in our laboratory as functions of membrane water content, were used in the model. The model predicts a net-water-per-proton flux ratio of 0.2 H2O/H under typical operating conditions, which is much less than the measured electroosmotic drag coefficient for a fully hydrated membrane. It also predicts an increase in membrane resistance with increased current density and demonstrates the great advantage of thinner membranes in alleviating this resistance problem. Both of these predictions were verified experimentally under certain conditions. We also describe the sensitivity of the water concentration profile and associated observables to variations in the values of some of the transport parameters in anticipation of applying the model to fuel cells employing other membranes. 16 refs., 9 figs.
Book Synopsis Modeling and Diagnostics of Polymer Electrolyte Fuel Cells by : Ugur Pasaogullari
Download or read book Modeling and Diagnostics of Polymer Electrolyte Fuel Cells written by Ugur Pasaogullari and published by Springer Science & Business Media. This book was released on 2010-07-23 with total page 412 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume, presented by leading experts in the field, covers the latest advances in diagnostics and modeling of polymer electrolyte fuel cells, from understanding catalyst layer durability to start-up under freezing conditions.
Book Synopsis Modeling Water Management in Polymer-electrolyte Fuel Cells by : Adam Zev Weber
Download or read book Modeling Water Management in Polymer-electrolyte Fuel Cells written by Adam Zev Weber and published by . This book was released on 2004 with total page 880 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Polymer Electrolyte Fuel Cells by : Michael Eikerling
Download or read book Polymer Electrolyte Fuel Cells written by Michael Eikerling and published by CRC Press. This book was released on 2014-09-23 with total page 567 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book provides a systematic and profound account of scientific challenges in fuel cell research. The introductory chapters bring readers up to date on the urgency and implications of the global energy challenge, the prospects of electrochemical energy conversion technologies, and the thermodynamic and electrochemical principles underlying the op
Book Synopsis Fuel Cell Engines by : Matthew M. Mench
Download or read book Fuel Cell Engines written by Matthew M. Mench and published by John Wiley & Sons. This book was released on 2008-03-07 with total page 530 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fuel Cell Engines is an introduction to the fundamental principles of electrochemistry, thermodynamics, kinetics, material science and transport applied specifically to fuel cells. It covers scientific fundamentals and provides a basic understanding that enables proper technical decision-making.
Book Synopsis Modeling the Effects of Interfaces on Water Management and Performance of Polymer Electrolyte Fuel Cells by : Reyhan Taspinar
Download or read book Modeling the Effects of Interfaces on Water Management and Performance of Polymer Electrolyte Fuel Cells written by Reyhan Taspinar and published by . This book was released on 2016 with total page 194 pages. Available in PDF, EPUB and Kindle. Book excerpt: Polymer electrolyte fuel cells (PEFCs) are of great importance as a clean alternative to conventional heat engines. However, PEFCs need further improvements to be economically utilized in stationary and transport applications. To achieve the highest performance, a delicate water balance in PEFCs must be maintained. The polymer membrane must remain hydrated in order to maximize proton conductivity, while excess liquid water should be removed from the cathode to avoid any flooding issues. This water management issue is hypothesized to be affected by the interfaces of the components. Presently, little is known about the transport through the interfaces and its related effects on the water distribution and performance of the PEFCs. This Ph.D. work addresses this critical gap by exploring the effects of the interfaces on water management and performance of PEFCs through a computational modeling study. The overall objective of this dissertation study is to introduce a modeling framework which incorporates component interfaces in order to evaluate their effects on water transport and performance of PEFCs. To achieve this goal, a series of computational studies were established. First, a 2-D, steady state, multiphase PEFC model for the cathode side was developed. Then, the computational model was integrated with the key interfaces which dominates the overall water transport in PEFCs: (i) the microporous layer (MPL) catalyst layer (CL) interface which governs the mass and ohmic transport losses, (ii) morphologically modified MPL which provides pathways for water transport, and (iii) bipolar plate (BP) gas diffusion layer (GDL) interface where the contact resistance dominates. Using these models, an in-depth understanding of the roles of the interfaces in water transport and performance of PEFCs has been obtained. One of the most important findings is that the interfaces affect the water distribution inside the fuel cell components which leads to a significant drop in the cell performance.
Book Synopsis PEM Fuel Cell Modeling and Simulation Using Matlab by : Colleen Spiegel
Download or read book PEM Fuel Cell Modeling and Simulation Using Matlab written by Colleen Spiegel and published by Elsevier. This book was released on 2011-08-29 with total page 454 pages. Available in PDF, EPUB and Kindle. Book excerpt: Although, the basic concept of a fuel cell is quite simple, creating new designs and optimizing their performance takes serious work and a mastery of several technical areas. PEM Fuel Cell Modeling and Simulation Using Matlab, provides design engineers and researchers with a valuable tool for understanding and overcoming barriers to designing and building the next generation of PEM Fuel Cells. With this book, engineers can test components and verify designs in the development phase, saving both time and money. Easy to read and understand, this book provides design and modelling tips for fuel cell components such as: modelling proton exchange structure, catalyst layers, gas diffusion, fuel distribution structures, fuel cell stacks and fuel cell plant. This book includes design advice and MATLAB and FEMLAB codes for Fuel Cell types such as: polymer electrolyte, direct methanol and solid oxide fuel cells. This book also includes types for one, two and three dimensional modeling and two-phase flow phenomena and microfluidics. *Modeling and design validation techniques *Covers most types of Fuel Cell including SOFC *MATLAB and FEMLAB modelling codes *Translates basic phenomena into mathematical equations
Book Synopsis Device and Materials Modeling in PEM Fuel Cells by : Stephen J. Paddison
Download or read book Device and Materials Modeling in PEM Fuel Cells written by Stephen J. Paddison and published by Springer Science & Business Media. This book was released on 2008-10-15 with total page 596 pages. Available in PDF, EPUB and Kindle. Book excerpt: Computational studies on fuel cell-related issues are increasingly common. These studies range from engineering level models of fuel cell systems and stacks to molecular level, electronic structure calculations on the behavior of membranes and catalysts, and everything in between. This volume explores this range. It is appropriate to ask what, if anything, does this work tell us that we cannot deduce intuitively? Does the emperor have any clothes? In answering this question resolutely in the affirmative, I will also take the liberty to comment a bit on what makes the effort worthwhile to both the perpetrator(s) of the computational study (hereafter I will use the blanket terms modeler and model for both engineering and chemical physics contexts) and to the rest of the world. The requirements of utility are different in the two spheres. As with any activity, there is a range of quality of work within the modeling community. So what constitutes a useful model? What are the best practices, serving both the needs of the promulgator and consumer? Some of the key com- nents are covered below. First, let me provide a word on my ‘credentials’ for such commentary. I have participated in, and sometimes initiated, a c- tinuous series of such efforts devoted to studies of PEMFC components and cells over the past 17 years. All that participation was from the experim- tal, qualitative side of the effort.
Book Synopsis The Chemistry of Membranes Used in Fuel Cells by : Shulamith Schlick
Download or read book The Chemistry of Membranes Used in Fuel Cells written by Shulamith Schlick and published by John Wiley & Sons. This book was released on 2018-02-13 with total page 300 pages. Available in PDF, EPUB and Kindle. Book excerpt: Examines the important topic of fuel cell science by way of combining membrane design, chemical degradation mechanisms, and stabilization strategies This book describes the mechanism of membrane degradation and stabilization, as well as the search for stable membranes that can be used in alkaline fuel cells. Arranged in ten chapters, the book presents detailed studies that can help readers understand the attack and degradation mechanisms of polymer membranes and mitigation strategies. Coverage starts from fundamentals and moves to different fuel cell membrane types and methods to profile and analyze them. The Chemistry of Membranes Used in Fuel Cells: Degradation and Stabilization features chapters on: Fuel Cell Fundamentals: The Evolution of Fuel Cells and their Components; Degradation Mechanism of Perfluorinated Membranes; Ranking the Stability of Perfluorinated Membranes Used in Fuel Cells to Attack by Hydroxyl Radicals; Stabilization Mechanism of Perfluorinated Membranes by Ce(III) and Mn(II); Hydrocarbon Proton Exchange Membranes; Stabilization of Perfluorinated Membranes Using Nanoparticle Additives; Degradation Mechanism in Aquivion Perfluorinated Membranes and Stabilization Strategies; Anion Exchange Membrane Fuel Cells: Synthesis and Stability; In-depth Profiling of Degradation Processes in Nafion Due to Pt Dissolution and Migration into the Membrane; and Quantum Mechanical Calculations of the Degradation Mechanism in Perfluorinated Membranes. Brings together aspects of membrane design, chemical degradation mechanisms and stabilization strategies Emphasizes chemistry of fuel cells, which is underemphasized in other books Includes discussion of fuel cell performance and behavior, analytical profiling methods, and quantum mechanical calculations The Chemistry of Membranes Used in Fuel Cells is an ideal book for polymer scientists, chemists, chemical engineers, electrochemists, material scientists, energy and electrical engineers, and physicists. It is also important for grad students studying advanced polymers and applications.
Book Synopsis Polymer Electrolyte Fuel Cell Degradation by : Matthew M. Mench
Download or read book Polymer Electrolyte Fuel Cell Degradation written by Matthew M. Mench and published by Academic Press. This book was released on 2012 with total page 474 pages. Available in PDF, EPUB and Kindle. Book excerpt: For full market implementation of PEM fuel cells to become a reality, two main limiting technical issues must be overcome- cost and durability. This cutting-edge volume directly addresses the state-of-the-art advances in durability within every fuel cell stack component. [...] chapters on durability in the individual fuel cell components -- membranes, electrodes, diffusion media, and bipolar plates -- highlight specific degradation modes and mitigation strategies. The book also includes chapters which synthesize the component-related failure modes to examine experimental diagnostics, computational modeling, and laboratory protocol"--Back cover.
Book Synopsis Water Content Estimation and Control of PEM Fuel Cell Stack and the Individual Cell in Vehicle by : Po Hong
Download or read book Water Content Estimation and Control of PEM Fuel Cell Stack and the Individual Cell in Vehicle written by Po Hong and published by Springer Nature. This book was released on 2022-01-17 with total page 159 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book focuses on water content estimation and control of the PEM fuel cell stack and the individual cell in vehicle. Firstly, the mathematical connection between polarization curve and equivalent circuit model proves importance of MEA and its feasibility to study water content. Optimizing structure of MEA realizes the internal water content recirculation of a fuel cell and improves its performance under middle or lower current density. The influence of water content on performance of MEA is quantified, and variation of equivalent circuit model is an excellent indicator of water content. Secondly, the comprehensive online AC impedance measurement method is put forward, including current excitation method, weak voltage and current signal processing method, and method for analyzing measurement error, and experiment validates measurement accuracy. The high-frequency impedance and statistical characteristic are proposed as indicator of water content. Finally, the dynamic model of the air supply system of a fuel cell engine is established and the closed-loop control of the air supply system and the water content estimation are decoupled. The experiment on a fuel cell system validates the proposed method for searching optimized operating conditions and the water management strategy.
Book Synopsis Liquid Water Dynamics in a Model Polymer Electrolyte Fuel Cell Flow Channel by : Christopher David Lee Miller
Download or read book Liquid Water Dynamics in a Model Polymer Electrolyte Fuel Cell Flow Channel written by Christopher David Lee Miller and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Water management in a polymer electrolyte fuel cell is a critical issue in ensuring high cell performance. The water production, due to both electro-osmotic drag and the chemical reaction, in the cathode side of the fuel cell leads to liquid water formation in the gas diffusion layer and the reactant flow channel. If this water is allowed to accumulate in the fuel cell, the transport of reactants to the membrane assembly will be inhibited and cell performance will suffer. In order to maximize the potential performance of a fuel cell, understanding of the liquid water dynamics is required, and a two-phase flow numerical model has been for this purpose. If an accurate numerical model can be created the development cycle for new flow channel designs can be accelerated. The methodology adopted for the numerical simulation of dynamic two-phase flow is the volume of fluid (VOF) method. The major drawback of current VOF models is in the implementation of the three phase contact line. Current models use a constant static contact angle, which does not take into account real dynamics. This results in non-physical phenomena such as spherical and suspended droplets, instead of the experimentally observed attached semi-spherical droplets with the trailing edge of the droplet forming a tail. To remedy this shortcoming, the implementation of a dynamic contact angle relation is required. The relations used in the current work follows the Hoffman formulation where the dynamic contact angle is obtained as?D. A function of the capillary number, based on the contact line velocity, and of the equilibrium contact angle. The function was implemented within the commercial CFD framework of Fluent using user defined functions. The dynamic contact angle models were able to better predict the droplet dynamics, providing elongated droplet profiles. The dynamic contact angle model was also able to provide more realistic pressure profiles down the channel length. Parametric studies show the dramatic effects that air speed and static contact angle have upon the droplet dynamics. It was also observed that water injection velocity had a relatively small effect on the model. The dynamic contact angle model was found to be consistent with experimental work conducted in our laboratory in which the spinning motion of the fluid within the water droplet was observed [7]. The improved physical representation achieved with the new model results in more reliable simulations and provides a good foundation for the numerical modeling of fuel cell flow channels.
Book Synopsis Modeling and High-Resolution-Imaging Studies of Water-Content Profiles in a Polymer-Electrolyte-Fuel-Cell Membrane-Electrode Assembly by :
Download or read book Modeling and High-Resolution-Imaging Studies of Water-Content Profiles in a Polymer-Electrolyte-Fuel-Cell Membrane-Electrode Assembly written by and published by . This book was released on 2008 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: Water-content profiles across the membrane electrode assembly of a polymer-electrolyte fuel cell were measured using high-resolution neutron imaging and compared to mathematical-modeling predictions. It was found that the membrane held considerably more water than the other membrane-electrode constituents (catalyst layers, microporous layers, and macroporous gas-diffusion layers) at low temperatures, 40 and 60 C. The water content in the membrane and the assembly decreased drastically at 80 C where vapor transport and a heat-pipe effect began to dominate the water removal from the membrane-electrode assembly. In the regimes where vapor transport was significant, the through-plane water-content profile skewed towards the cathode. Similar trends were observed as the relative humidity of the inlet gases was lowered. This combined experimental and modeling approach has been beneficial in rationalizing the results of each and given insight into future directions for new experimental work and refinements to currently available models.
Book Synopsis Modeling Water Management in Polymer-Electrolyte Fuel Cells by :
Download or read book Modeling Water Management in Polymer-Electrolyte Fuel Cells written by and published by . This book was released on 2007 with total page 205 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fuel cells may become the energy-delivery devices of the 21st century with realization of a carbon-neutral energy economy. Although there are many types of fuel cells, polymerelectrolyte fuel cells (PEFCs) are receiving the most attention for automotive and small stationary applications. In a PEFC, hydrogen and oxygen are combined electrochemically to produce water, electricity, and waste heat. During the operation of a PEFC, many interrelated and complex phenomena occur. These processes include mass and heat transfer, electrochemical reactions, and ionic and electronic transport. Most of these processes occur in the through-plane direction in what we term the PEFC sandwich as shown in Figure 1. This sandwich comprises multiple layers including diffusion media that can be composite structures containing a macroporous gas-diffusion layer (GDL) and microporous layer (MPL), catalyst layers (CLs), flow fields or bipolar plates, and a membrane. During operation fuel is fed into the anode flow field, moves through the diffusion medium, and reacts electrochemically at the anode CL to form hydrogen ions and electrons. The oxidant, usually oxygen in air, is fed into the cathode flow field, moves through the diffusion medium, and is electrochemically reduced at the cathode CL by combination with the generated protons and electrons. The water, either liquid or vapor, produced by the reduction of oxygen at the cathode exits the PEFC through either the cathode or anode flow field. The electrons generated at the anode pass through an external circuit and may be used to perform work before they are consumed at the cathode. The performance of a PEFC is most often reported in the form of a polarization curve, as shown in Figure 2. Roughly speaking, the polarization curve can be broken down into various regions. First, it should be noted that the equilibrium potential differs from the open-circuit voltage due mainly to hydrogen crossover through the membrane (i.e., a mixed potential on the cathode) and the resulting effects of the kinetic reactions. Next, at low currents, the behavior of a PEFC is dominated by kinetic losses. These losses mainly stem from the high overpotential of the oxygen-reduction reaction (ORR). As the current is increased, ohmic losses become a factor in lowering the overall cell potential. These ohmic losses are mainly from ionic losses in the electrodes and separator. At high currents, mass-transport limitations become increasingly important. These losses are due to reactants not being able to reach the electrocatalytic sites. Key among the issues facing PEFCs today is water management. Due to their low operating temperature (
Book Synopsis Modeling and Control of PEM Fuel Cells by : Maria Laura Sarmiento Carnevali
Download or read book Modeling and Control of PEM Fuel Cells written by Maria Laura Sarmiento Carnevali and published by . This book was released on 2019 with total page 183 pages. Available in PDF, EPUB and Kindle. Book excerpt: In recent years, the PEM fuel cell technology has been incorporated to the R&D plans of many key companies in the automotive, stationary power and portable electronics sectors. However, despite current developments, the technology is not mature enough to be significantly introduced into the energy market. Performance, durability and cost are the key challenges. The performance and durability of PEM fue! cells significantly depend on variations in the concentrations of hydrogen and oxygen in the gas channels, water activity in the catalyst layers and other backing layers, water content in the polymer electrolyte membrane, as well as temperature, among other variables. Such variables exhibit intemal spatial dependence in the direction of the fuel and air streams of the anode and cathode. Highly non-uniform spatial distributions in PEM fuel cells result in local over-heating, cell flooding, accelerated ageing, and lower power output than expected. Despite the importance of spatial variations of certain variables in PEM fuel cells, not many works available in the literature target the control of spatial profiles. Most control-oriented designs use lumped-parameter models because of their simplicity and convenience for controller performance. In contrast, this Doctoral Thesis targets the distributed parameter modelling and control of PEM fuel cells. In the modelling part, the research addresses the detailed development of a non-linear distributed parameter model of a single PEM fuel cell, which incorporates the effects of spatial variations of variables that are relevant to its proper performance. The model is first used to analyse important cell intemal spatial profiles, and it is later simplified in arder to decrease its computational complexity and make it suitable for control purposes. In this task, two different model order reduction techniques are applied and compared. The purpose of the control part is to tackle water management and supply of reactants, which are two major PEM fuel cell operation challenges with important degradation consequences. In this part of the Thesis, two decentralised control strategies based on distributed parameter model predictive controllers are designed, implemented and analysed via simulation environment State observers are also designed to estímate intemal unmeasurable spatial profiles necessary for the control action. The aim of the first strategy is to monitor and control observed water activity spatial profiles on both sides of the membrana to appropriate levels. These target values are carefully chosen to combine proper membrane, catalyst layer and gas diffusion layer humídification, whilst the rate of accumulation of excess liquid water is reduced. The key objective of this approach is to decrease the frequency of water removal actions that cause disruption in the power supplied by the cell, increased parasitic losses or degradation of cell efficiency. The second strategy is a variation of the previous water activity control strategy, which includes the control of spatial distribution of gases in the fuel and air channels. This integrated solution aims to avoid starvation of reactants by controlling corresponding concentration spatial profiles. This approach is intended to prevent PEM fuel cell degradation due to corrosion mechanisms, and thennal stress caused by the consequences of reactant starvation.
Download or read book Advances in Fuel Cells written by and published by Elsevier. This book was released on 2007-04-23 with total page 499 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fuel cells have been recognized to be destined to form the cornerstone of energy technologies in the twenty-first century. The rapid advances in fuel cell system development have left current information available only in scattered journals and Internet sites. Advances in Fuel Cells fills the information gap between regularly scheduled journals and university level textbooks by providing in-depth coverage over a broad scope. The present volume provides informative chapters on thermodynamic performance of fuel cells, macroscopic modeling of polymer-electrolyte membranes, the prospects for phosphonated polymers as proton-exchange fuel cell membranes, polymer electrolyte membranes for direct methanol fuel cells, materials for state of the art PEM fuel cells, and their suitability for operation above 100°C, analytical modelling of direct methanol fuel cells, and methanol reforming processes. Includes contributions by leading experts working in both academic and industrial R&D Disseminates the latest research discoveries A valuable resource for senior undergraduates and graduate students, it provides in-depth coverage over a broad scope
Book Synopsis Advanced Models for Predicting Performance of Polymer Electrolyte Membrane Fuel Cells by : Sai K. Kamarajugadda
Download or read book Advanced Models for Predicting Performance of Polymer Electrolyte Membrane Fuel Cells written by Sai K. Kamarajugadda and published by . This book was released on 2012 with total page 184 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: The primary objective of this study is to develop a multi-scale computational fluid dynamics (CFD) model to predict the performance of a polymer electrolyte membrane fuel cell (PEMFC). In particular, two critical factors affecting PEMFC performance, namely water and current transport through the polymer electrolyte membrane, and the effect of the cathode catalyst layer structure and composition are examined in detail. The implementation of phenomenological membrane models within CFD codes requires coupling of the conservation equation for the so-called water content within the membrane to the conservation equations for species mass outside the membrane. The first part of this dissertation investigates the accuracy and efficiency of various strategies for implementing phenomenological membrane models within the framework of a CFD code for prediction of the overall PEMFC performance. First, three popular phenomenological membrane models are investigated, and the accuracy of each model is assessed by comparing predicted results against experimental data. Results indicate that the Springer model and the Nguyen and White model over-predict the drying of the membrane, while the Fuller and Newman model provides the best match with experimental data. Following these studies, three strategies for implementation of the membrane model are investigated: (1) two-dimensional (2D) transport of water and current in membrane, (2) one-dimensional (1D) transport and (3) 1D transport with approximate transport properties. Fuller and Newman's membrane model is used for these studies. The results obtained using the three approaches are found to be within 4% of each other, while there is no significant difference in the computational time required by the three strategies, indicating that an analytical 1D transport model for the membrane that uses approximate properties is adequate for describing transport through it. In the second part of the dissertation, the effect of the cathode catalyst layer's structure and composition on the overall performance of a PEMFC is investigated. The starting point of this investigation is the well-known flooded agglomerate model, which is generalized to address the effects of ionomer (Nafion) loading, catalyst (platinum) loading, platinum/carbon ratio, cathode layer thickness, and agglomerate size and shape. Initially, spherical agglomerates are considered. This allows for an analytical solution of the governing equations. Following this, the model is generalized in order to account for arbitrary agglomerate shapes. The generalized flooded agglomerate model is first validated against previously published results, and then used to study the effect of the agglomerate shape (single sphere vs. intersecting spheres) and size on the oxidation reduction reaction (ORR) rate at the agglomerate scale. Results from the agglomerate scale studies indicate that the current per unit volume generated by the agglomerates is proportional to the surface-area-to-volume ratio of the agglomerates. It shows that, for a given agglomerate volume, the ORR is more efficient for non-spherical agglomerates than for spherical agglomerates. The generalized flooded agglomerate model provides the current generated per unit volume at the agglomerate scale, which is much smaller than a typical control volume used in CFD calculations of the overall PEMFC, i.e., it is a sub-grid scale model. This sub-grid scale agglomerate model is then embedded within a 2D CFD code for the prediction of the overall performance of the fuel cell. In order to do so, lookup tables are first generated and logarithmic interpolation is used. The integrated model is used to explore a wide range of the compositional and structural parameter space, mentioned earlier. In each case, the model is able to correctly predict the trends observed by past experimental studies. It is found that the performance trends are often different at intermediate versus high current densities - the former being governed by agglomerate-scale (or local) losses, while the latter is governed by catalyst layer thickness-scale (or global) losses. The presence of an optimal performance with varying Nafion content in the cathode is more due to the local agglomerate-scale mass transport and conductivity losses in the polymer coating around the agglomerates than due to the amount of Nafion within the agglomerate. It is also found that platinum mass loading needs to be at a moderate level in order to optimize fuel cell performance, even if cost is to be disregarded. For agglomerates of small size, the shape of the agglomerate is found to have a smaller effect on overall PEMFC performance than for agglomerates of larger size. The results from this dissertation provide, for the first time, a quantitative confirmation of the assumption of 1D transport of water and current within the membrane. Second, the generalized flooded agglomerate model developed as part of this dissertation presents a new framework for incorporating cathode structure and composition into full-scale CFD models for predicting PEMFC performance.
