Download or read book Experimental Characterization of Water Sorption and Transport Properties of Polymer Electrolyte Membranes for Fuel Cells written by Libeth Maldonado Sánchez and published by . This book was released on 2012 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The overall aim of this PhD thesis was to characterize the properties of commercial Nafion N115 and Nafion NRE212 membranes in term of water sorption, transport, and mechanical properties over a wide range of experimental conditions. Because of the high dispersion of the data in the literature, our primary objective was to gather a comprehensive set of experimental measurements and to compare them with published results. Simple and reproducible protocols allowed us to measure the membrane properties over a wide range of experimental conditions and to study the influence of certain parameters on their evolution. For example, the samples were heat-treated at different temperatures and the effect of thermal history on water sorption, transport and mechanical properties was investigated. Nafion membranes were also exposed to moderate temperature (60°C - 80°C) and constant relative humidity (RH = 0.3 to 0.95) for long periods of time, which is known to cause a so-called ?hygrothermal aging? resulting in a decrease in their sorption capacity and proton conductivity. Such effects were observed but they appeared to be reversible and without noticeable consequences in term of fuel cell performance. Our experimental results can be used in studies involving water transport, water management and durability of fuel cells, especially for numerical simulation or modelling. More fundamentally, they can help understanding the thermodynamics of sorption and transport phenomena in PFSA membranes.

Download or read book Experimental Characterization of Water Transport in Polymer Electrolyte Membrane Fuel Cells written by Dusan Spernjak and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Water management is among the key factors in maximizing the performance and durability of a polymer electrolyte membrane (PEM) fuel cell, since the cell operation is strongly influenced by water transport and distribution. Reactant starvation caused by flooding on either side of the cell may lead to substantial reduction in performance, and in the case of anode flooding, permanent damage to the catalyst layer. However, correlating the water dynamics to cell performance has been a challenge, mainly due to limited ability of current experimental tools to obtain spatially resolved information about the water content. In the present work, liquid water formation, transport and removal were studied in situ at the catalyst layer, gas diffusion layer (GDL), and the flow field channels. Two factors that greatly influence water management, the gas diffusion layer and the flow field configuration, were investigated in operating fuel cells. The results show that the limiting current and maximum power can be more than doubled through efficient liquid water removal: by changing the GDL or by altering the flow field configuration. The level of cathode flow field flooding was visualized in situ and recognized as a criterion for evaluating the water removal capacity of the GDL materials. When compared at same current (i.e. water production rate), higher amount of liquid water in the cathode channel indicated that the water has been efficiently removed from the catalyst layer. Visualization of the anode channel was used to investigate the influence of the microporous layer (MPL) on water transport. No liquid water was observed in the anode flow field unless cathode GDLs had an MPL. MPL on the cathode side creates a pressure barrier for water produced at the catalyst layer. Water is pushed across the membrane to the anode side, resulting in the anode flow field flooding. Throughout this work, water dynamics on both cathode and anode sides were investigated. A novel experimental approach for water metrology in PEM fuel cells is presented, where neutron and optical images were obtained simultaneously in situ. Liquid water dynamics in the flow field (channels and manifolds) were recorded on a digital camera through the optical window, while the integrated water content across the cell thickness was measured by neutron imaging. The concurrent images provide complementary data that allow one to separate the water distribution in the flow field from the remainder of the cell thickness, which has been a great challenge in water management studies. It was shown that such an approach enables improved interpretation of the water metrology data obtained independently from neutron and optical imaging. Utility of the combined technique was demonstrated through case studies typical of fuel cell operation. Water content and dynamics were characterized and compared in an operating cell by simultaneous neutron and optical imaging for three basic flow field configurations in bipolar plates of PEM fuel cells: parallel, serpentine, and interdigitated. The transient water content within the cell measured using neutron imaging is correlated with optical data as well as with temporal variations in the cell output and pressure differentials across the flow fields. The flow field layout had a major impact on cell performance and its dynamic response as it resulted in substantially different water content and distribution. Among the three configurations explored, serpentine flow field showed stable output across the current range and resulted in the highest limiting current, which came at the expense of the largest pressure differential across the flow field. Flooding in the anode channels occurred in all flow fields, however it was in the parallel and interdigitated flow field that it caused substantial reduction in cell performance at high currents. The collective contribution of this work should prove useful in (i) improving the understanding of water transport in PEM fuel cells, (ii) advancing experimental techniques for water management studies, and (iii) validating and developing fuel cell models with multiphase flow.

Download or read book Catalyst Layers in Polymer Electrolyte Membrane Fuel Cells written by Jian Zhao and published by . This book was released on 2019 with total page 171 pages. Available in PDF, EPUB and Kindle. Book excerpt: The structure of the catalyst layers (CLs) has a decisive impact on the performance, durability, and cost of polymer electrolyte membrane (PEM) fuel cells - these are the main technical challenges to the commercialization of PEM fuel cells. The porous CL conventionally consists of carbon-based platinum (Pt/C) and ionomer (Nafion polymer). An ideal CL should maintain the desired structure with sufficient gas diffusion and water removal channels (pores), proton transport media (ionomer), electron travel pathways (catalyst particles), and optimal three-phase boundaries (TPBs) where electrochemical reaction occurs (reaction sites). Practically, the CL is formed during the fabrication process which determines the physical structures, often represented by porosity, mean pore size, pore size distribution (PSD) and specific surface area. The physical structures, in turn, determine the effective transport properties such as effective mass diffusion coefficient and permeability for the reactant in the CLs. However, there is still no clear understanding of what is the optimal structure for the CLs. To investigate the structure of CLs, three aspects are studied in the present thesis work: (i) the effect of fabrication process on the resulting structure, (ii) the effect of the CL structure on its macro-properties, and (iii) the effect of the structure and macro-properties on the mass transport phenomena and the associated cell performance. Many factors including fabrication techniques and CL compositions have a significant impact on the structure formation of CLs. However, how these factors affect the structure is still unclear. Additionally, there lacks experimental characterization of the structure such as porosity, PSD, specific surface area, mean pore size, and surface fractal dimension, as well as mass transport properties such as effective diffusion coefficient and gas permeability for the CLs in literature. With the experimentally determined structural and mass transport parameters of the CLs and the associated electrodes, the mass transport phenomena in PEM fuel cells can be quantitatively analyzed. In the present thesis work, the CL pore structure is experimentally characterized by the method of standard porosimetry (MSP), which is established based on the phenomenon of capillary equilibrium in the wetted porous materials. By the means of MSP, a comprehensive characterization of the structure in terms of porosity, PSD, specific surface area, mean pore size, and surface fractal dimension is obtained. In addition, the effective diffusion coefficient of the CL is studied by the modified Loschmidt Cell, built based on the Fick's law of diffusion. The parameters including effective diffusion coefficient, diffusion resistivity, and its relation with the porosity and mean pore size is investigated. Further, the permeability is measured based on Darcy's law via a custom-engineered apparatus developed in my thesis work. The effect of Pt loading, temperature, flow rate, and gas species is explored in this thesis study. With the experimentally determined pore structure characterization and mass transport properties, a numerical study is performed for the better understanding of the mass transport mechanisms in the porous electrodes. The cell performance conducted in our lab is also reported in the present thesis for a better understanding of the ex-situ experiment and a comparison with the numerical modeling. The experimental and numerical studies presented in the present thesis work is of great significance to (i) understand the structure of the CLs, (ii) to understand the relation between the structure and the mass transport properties such as the effective diffusion coefficient and permeability, and (iii) to understand the effect of the structural parameters and mass transport properties on the mass transport phenomena and hence the cell performance in the PEM fuel cells.

Download or read book Synthesis and Characterization of Polymer Electrolyte Membranes with Controlled Ion Transport Properties written by Kui Xu and published by . This book was released on 2011 with total page 159 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Characterization of Transport Properties of Gas Diffusion Layers for Polymer Electrolyte Fuel Cells written by Michael James Bluemle and published by . This book was released on 2004 with total page 192 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Electrochemical Polymer Electrolyte Membranes written by Jianhua Fang and published by CRC Press. This book was released on 2015-04-17 with total page 639 pages. Available in PDF, EPUB and Kindle. Book excerpt: Electrochemical Polymer Electrolyte Membranes covers PEMs from fundamentals to applications, describing their structure, properties, characterization, synthesis, and use in electrochemical energy storage and solar energy conversion technologies. Featuring chapters authored by leading experts from academia and industry, this authoritative text: Disc

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.

Download or read book Modeling of Water Sorption and Swelling in Polymer Electrolyte Membranes written by Motahareh Safiollah and published by . This book was released on 2015 with total page 71 pages. Available in PDF, EPUB and Kindle. Book excerpt: The polymer electrolyte membrane (PEM) fulfills vital functions as separator, proton conductor, and electronic insulator in a polymer electrolyte fuel cell (PEFC). The well-studied and practically used solid polymer electrolyte membranes are perfluorosulfonic acid (PFSA) polymer membranes such as Nafion. These membranes offer high proton conductivity, high mechanical strength and good chemical stability. The efficiency of the chemical-to-electrical energy conversion in a PEFC critically depends on the ability of the PEM to transport protons from the anode to the cathode. Proton conductivity of the PEM is a key parameter to achieve high power density and performance. The main variable to characterize the state of a PEM and determine its transport properties is its water content. In particular, the proton conductivity is highly sensitive to the level of hydration. Membranes experience continuous stresses and consequently continuous loss of performance throughout their operational life. Chemical degradation alters the chemical structure of the PEM, which affects the water distribution in it. A consistent description of water sorption and swelling under conditions relevant for the PEFC operation lies at the heart of understanding transport properties, performance and degradation phenomena. This work expands on a previously developed poroelectroelastic model of water sorption in PEMs [Soft Matter 7, 5976 (2011)]. The theory relates the charge density at the pore walls to a microscopic swelling parameter. Extended to the water sorption equilibrium in a pore ensemble, the model reconciles microscopic swelling in a single pore with macroscopic swelling of the membrane. This work provides a generalized treatment of elastic effects in PEMs. Different deformation modes of polymeric pore walls are used to derive stress-strain relationships that determine the law of swelling. Moreover, this work enhances the diagnostic capabilities of the model; it provides the statistical pore size distribution as well as a statistical distribution of microscopic fluid and elastic pressures inside the PEM. Thereafter, the model is applied to different sets of water sorption data for PEMs that had undergone either hygrothermal aging or chemical degradation. The model-based analysis provides mechanistic explanations of structural changes and their impact on microscopic distributions of charge density and elastic properties in PEMs.

Download or read book PEM Fuel Cells written by Yun Wang and published by Momentum Press. This book was released on 2013-04-06 with total page 450 pages. Available in PDF, EPUB and Kindle. Book excerpt: Polymer Electrolyte Membrane (PEM) fuel cells convert chemical energy in hydrogen into electrical energy with water as the only by-product. Thus, PEM fuel cells hold great promise to reduce both pollutant emissions and dependency on fossil fuels, especially for transportation—passenger cars, utility vehicles, and buses—and small-scale stationary and portable power generators. But one of the greatest challenges to realizing the high efficiency and zero emissions potential of PEM fuel cells technology is heat and water management. This book provides an introduction to the essential concepts for effective thermal and water management in PEM fuel cells and an assessment on the current status of fundamental research in this field. The book offers you: • An overview of current energy and environmental challenges and their imperatives for the development of renewable energy resources, including discussion of the role of PEM fuel cells in addressing these issues; • Reviews of basic principles pertaining to PEM fuel cells, including thermodynamics, electrochemical reaction kinetics, flow, heat and mass transfer; and • Descriptions and discussions of water transport and management within a PEM fuel cell, including vapor- and liquid-phase water removal from the electrodes, the effects of two-phase flow, and solid water or ice dynamics and removal, particularly the specialized case of starting a PEM fuel cell at sub-freezing temperatures (cold start) and the various processes related to ice formation.

Download or read book Membranes for Low Temperature Fuel Cells written by Surbhi Sharma and published by Walter de Gruyter GmbH & Co KG. This book was released on 2019-06-04 with total page 172 pages. Available in PDF, EPUB and Kindle. Book excerpt: Membranes for Low Temperature Fuel Cells provides a comprehensive review of novel and state-of-the-art polymer electrolyte membrane fuel cells (PEMFC) membranes. The author highlights requirements and considerations for a membrane as an integral part of PEMFC and its interactions with other components. It is an indispensible resource for anyone interested in new PEMFC membrane materials and concerned with the development, optimisation and testing of such membranes. Various composite membranes (polymer and non-polymer) are discussed along with analyses of the latest fi ller materials like graphene, ionic liquids, polymeric ionic liquids, nanostructured metal oxides and membrane concepts unfolding in the field of PEMFC. This book provides the latest academic and technical developments in PEMFC membranes with thorough insights into various preparation, characterisation, and testing methods utilised. Factors affecting proton conduction, water adsorption, and transportation behaviour of membranes are also deliberated upon. Provides the latest academic and technical developments in PEMFC membranes. Reviews recent literature on ex situ studies and in situ single-cell and stack tests investigating the durability (chemical, thermomechanical) and degradation of membranes. Surbhi Sharma, MSc, PhD Working on graphene oxide and fuel cells since 2007, she has published about 50 research articles/book chapters and holds a patent. She has also been awarded various research grants.

Download or read book Perfluorinated Polymer Electrolyte Membranes for Fuel Cells written by Tatsuhiro Okada and published by Nova Science Pub Incorporated. This book was released on 2008 with total page 116 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this book the authors focus on the ion and water transport characteristics in Nafion and other perfluorinated ionomer membranes that are recently attracting attention in various fields such as water electrolysis, mineral recovery, electrochemical devises and energy conversion. Methodology of measurements and data analysis is first presented that enables basic characterisation of transport parameters in the perfluorinated ionomer membranes. Cation exchange isotherm data are collected in binary cation systems, with the aim to see the behaviours of cationic species that exist with H+ in the membrane. Water transference coefficients, ionic transference numbers, ionic mobilities and other membrane transport parameters are measured in single and mixed counter cation systems using electrochemical methods. Diffusion coefficients of water and cations are also measured by pulsed-field-gradient spin-echo NMR (PGSE-NMR) at various temperatures in different kinds of perfluorinated ionomer membranes. The results are discussed in two perspectives. One is to predict the hydration state in perfluorosulfonated ionomer membranes in relation to the possible degradation of performances in fuel cells under contaminated conditions with foreign cations. An analytical formulation of membrane transport equations with proper boundary conditions is proposed, and using various parameters of membrane transport, a simple diagnosis of water dehydration problem is carried out. This analysis leads one to an effective control of fuel cell operation conditions, especially from viewpoint of proper water management. The others are to elucidate the ion and water transport mechanisms in the membrane in relation to polymer structures (e.g., different ion exchange capacity), and to propose a new design concept of polymer electrolyte membranes for fuel cell applications. Additionally for this purpose methanol and other alcohols are penetrated into the membrane, and alcohol permeability, membrane swelling, ionic conductivity and diffusion coefficients of water and CH3 are measured systematically for various kinds of membranes to cope with the problem of methanol crossover in direct methanol fuel cells (DMFCs).It is found that in order to realise a high ionic conductivity in the membrane, one should aim at a polymer structure through molecular design that takes into account the relative size of ions with a hydration shell against the size and atmosphere of ionic channels. For DMFC, a partially cross-linked polymer chain with high degree of hydrophilic ion transport paths based on phase-separated structures is recommended. Various possibilities of such polymer electrolytes are discussed.

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

Download or read book Water Transport Properties of Fuel Cell Ionomers written by and published by . This book was released on 1991 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt: We will report transport parameters measured for several available perfluorosulfonate membranes. The water sorption characteristics, diffusion coefficient of water, electroosmotic drag, and conductivity will be compared for these materials. The intrinsic properties of the membranes will be the basis of our comparison. An objective look at transport parameters should enable us to compare membranes without the skewing effects of extensive features such as membrane thickness. 8 refs., 4 figs., 2 tabs.

Download or read book Structures and Transport Properties of Hydrated Water soluble Dendrimer grafted Polymer Membranes for Application to Polymer Electrolyte Membrane Fuel Cells written by Seung Soon Jang and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fuel Cells and Hydrogen written by Viktor Hacker and published by Elsevier. This book was released on 2018-07-20 with total page 298 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fuel Cells and Hydrogen: From Fundamentals to Applied Research provides an overview of the basic principles of fuel cell and hydrogen technology, which subsequently allows the reader to delve more deeply into applied research. In addition to covering the basic principles of fuel cells and hydrogen technologies, the book examines the principles and methods to develop and test fuel cells, the evaluation of the performance and lifetime of fuel cells and the concepts of hydrogen production. Fuel Cells and Hydrogen: From Fundamentals to Applied Research acts as an invaluable reference book for fuel cell developers and students, researchers in industry entering the area of fuel cells and lecturers teaching fuel cells and hydrogen technology. Includes laboratory methods for fuel cell characterization and manufacture Outlines approaches in modelling components, cells and stacks Covers practical and theoretical methods for hydrogen production and storage

Download or read book Experimental Characterization of the Compressive Behaviour of Gas Diffusion Layers in Polymer Electrolyte Membrane Fuel Cells written by Sogol Roohparvarzadeh and published by . This book was released on 2014 with total page 76 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Understanding the Effects of Compression and Constraints on Water Uptake of Fuel Cell Membranes written by and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Accurate characterization of polymer-electrolyte fuel cells (PEFCs) requires understanding the impact of mechanical and electrochemical loads on cell components. An essential aspect of this relationship is the effect of compression on the polymer membrane?s water-uptake behavior and transport properties. However, there is limited information on the impact of physical constraints on membrane properties. In this paper, we investigate both theoretically and experimentally how the water uptake of Nafion membrane changes under external compression loads. The swelling of a compressed membrane is modeled by modifying the swelling pressure in the polymer backbone which relies on the changes in the microscopic volume of the polymer. The model successfully predicts the water content of the compressed membrane measured through in-situ swelling-compression tests and neutron imaging. The results show that external mechanical loads could reduce the water content and conductivity of the membrane, especially at lower temperatures, higher humidities, and in liquid water. The modeling framework and experimental data provide valuable insight for the swelling and conductivity of constrained and compressed membranes, which are of interest in electrochemical devices such as batteries and fuel cells.