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 Advanced Materials for Membrane Preparation written by Maria Giovanna Buonomenna and published by Bentham Science Publishers. This book was released on 2012 with total page 303 pages. Available in PDF, EPUB and Kindle. Book excerpt: The need to reduce pollution and the waste of energy and resources imposes a wider diffusion of environmentally friendly membrane systems. The expanding domain of membrane operations demands tailored materials with unprecedented performances and resistanc

Download or read book Computational Materials Chemistry and Biochemistry From Bold Initiatives to the Last Mile written by Sadasivan Shankar and published by Springer Nature. This book was released on 2021-01-25 with total page 1344 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a broad and nuanced overview of the achievements and legacy of Professor William (“Bill”) Goddard in the field of computational materials and molecular science. Leading researchers from around the globe discuss Goddard’s work and its lasting impacts, which can be seen in today’s cutting-edge chemistry, materials science, and biology techniques. Each section of the book closes with an outline of the prospects for future developments. In the course of a career spanning more than 50 years, Goddard’s seminal work has led to dramatic advances in a diverse range of science and engineering fields. Presenting scientific essays and reflections by students, postdoctoral associates, collaborators and colleagues, the book describes the contributions of one of the world’s greatest materials and molecular scientists in the context of theory, experimentation, and applications, and examines his legacy in each area, from conceptualization (the first mile) to developments and extensions aimed at applications, and lastly to de novo design (the last mile). Goddard’s passion for science, his insights, and his ability to actively engage with his collaborators in bold initiatives is a model for us all. As he enters his second half-century of scientific research and education, this book inspires future generations of students and researchers to employ and extend these powerful techniques and insights to tackle today’s critical problems in biology, chemistry, and materials. Examples highlighted in the book include new materials for photocatalysts to convert water and CO2 into fuels, novel catalysts for the highly selective and active catalysis of alkanes to valuable organics, simulating the chemistry in film growth to develop two-dimensional functional films, and predicting ligand–protein binding and activation to enable the design of targeted drugs with minimal side effects.

Download or read book Polymer Membranes for Fuel Cells written by Javaid Zaidi and published by Springer Science & Business Media. This book was released on 2010-07-15 with total page 439 pages. Available in PDF, EPUB and Kindle. Book excerpt: From the late-1960’s, perfluorosulfonic acid (PFSAs) ionomers have dominated the PEM fuel cell industry as the membrane material of choice. The “gold standard’ amongst the many variations that exist today has been, and to a great extent still is, DuPont’s Nafion® family of materials. However, there is significant concern in the industry that these materials will not meet the cost, performance, and durability requirementsnecessary to drive commercialization in key market segments – es- cially automotive. Indeed, Honda has already put fuel cell vehicles in the hands of real end users that have home-grown fuel cell stack technology incorporating hydrocarbon-based ionomers. “Polymer Membranes in Fuel Cells” takes an in-depth look at the new chem- tries and membrane technologies that have been developed over the years to address the concerns associated with the materials currently in use. Unlike the PFSAs, which were originally developed for the chlor-alkali industry, the more recent hydrocarbon and composite materials have been developed to meet the specific requirements of PEM Fuel Cells. Having said this, most of the work has been based on derivatives of known polymers, such as poly(ether-ether ketones), to ensure that the critical requirement of low cost is met. More aggressive operational requi- ments have also spurred the development on new materials; for example, the need for operation at higher temperature under low relative humidity has spawned the creation of a plethora of new polymers with potential application in PEM Fuel Cells.

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 A Study of Polymer Electrolyte Membranes and Associated Interfacial Systems Via Molecular Dynamics Simulations written by Junwu Liu and published by . This book was released on 2009 with total page 222 pages. Available in PDF, EPUB and Kindle. Book excerpt: The development of novel polymer electrolyte membrane (PEM) materials which operate at high temperature (i.e.> 100°C) and low humidity conditions and efficiently transport protons has been a major focus for PEM fuel cell technology. The motivation behind a high temperature PEM fuel cell is based on the fact that, at high temperature, the catalysts used in the fuel cell are more active and less susceptible to poisoning due to impurities in the feed stream. The challenge lies in the fact that as the temperature is increased, the membrane loses water and its ability to transport protons. The successful design and synthesis of high-performance PEMs would benefit from a fundamental, molecular-scale understanding of how polymer chemistry, hydration levels, and morphology affect proton mobility within the membrane. Additionally, substantially less work has concentrated on the molecular-level details of proton transport at the multi-phase interfaces among the PEM, vapor, water, electrodes, and catalyst surface. The electrochemical processes occurred at such interfaces dictate the performance of the PEM fuel cells. Understanding the structural and dynamic properties at these interfaces is, therefore, crucial for the optimization of current energy devices. All such information cannot come from experimental investigations alone, but requires knowledge of multiscale simulations which are successful in bridging distinct time and length scales, providing insights into the morphology and structure through analysis of the molecular processes. The first objective of this work is to use molecular dynamic (MD) simulations to investigate the nanophase-segregated structure in the PEM as a function of polymer chemistry and hydration levels. The variables probed to define polymer chemistry include (1) side chain length, (2) equivalent weight, and (3) molecular weight. We examine the structure in attempts to establish a relationship between the polymer chemical composition and the hydrated morphology and transport properties. The second objective is to use MD simulations to generate the structure of the interfaces involving the PEM within the Membrane-Electrode Assemblies (MEAs). These interfaces include (1) the PEM/vapor interface, (2) the PEM/vapor/catalyst interface, and (3) the PEM/vapor/carbon electrode interface. We examine these interfaces in order to establish an understanding of the structure of these interfaces as a function of water content.

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 Mass and Charge Transport in Hydrated Polymeric Membranes written by Marshall T. McDonnell and published by . This book was released on 2016 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt: Mass and charge transport through hydrated polymer membranes has significant importance for many areas of engineering and industry. Multi-scale modeling and simulation techniques were used to study transport in relation to two specific membrane applications: (1) food packaging and (2) additives for polymer electrolytes. Chitosan/chitin films were studied due to their use as a sustainable, biodegradable food packaging film. The effects of hydration on the solvation, diffusivity, solubility, and permeability of oxygen molecules in these films were studied via molecular dynamics and confined random walk simulations. With increasing hydration, the membrane was observed to have a more homogeneous water distribution with the polymer chains being fully solvated. Insight from this work will help guide molecular modeling of chitosan/chitin membranes and experimental synthesis of these membranes, specifically highlighting efforts to chemically tailor chitosan membranes to favor discrete as opposed to continuous aqueous domains to help reduce oxygen permeability. Additives for proton exchange membranes (PEMs) were studied to aid in the developing next-generation membrane materials for fuel cell applications. We calculate and present predictions of our analytical model that describes the fundamental relationship between the nanoscale structure of PEMs and their proton conductivity using a set of structural descriptors, accounting for nanopore size, functionalization and connectivity in order to predict proton conductivities in PEMs. The model reproduces experimentally determined conductivities in two current PEM materials. To extend the model based on structural descriptors of PEMs, we studied polyethylene glycol (PEG), a polymer used in electrochemistry applications due to it hydrophilicity and pH-dependent behavior in aqueous environments. We conducted ab initio molecular dynamics simulations of an excess proton in bulk water and aqueous triethylene glycol (TEG) solution and reactive molecular dynamics simulations of an excess proton in bulk water, aqueous TEG solution, and aqueous PEG solution. We determined differences in protonic defect structures, kinetics, thermodynamics, and hydrogen-bond networks associated with structural diffusion between systems. Driving forces for polymeric membrane design goals include economics, efficiency, energy consumption and sustainable production. Insight from this work hopes to aid in determining key design parameters and reduce time-to-discovery for developing next-generation polymeric membranes.

Download or read book Nanostructured Polymer Membranes Volume 2 written by Visakh P. M. and published by John Wiley & Sons. This book was released on 2016-08-26 with total page 556 pages. Available in PDF, EPUB and Kindle. Book excerpt: The 2nd volume on applications with discuss the various aspects of state-of-the-art, new challenges and opportunities for gas and vapor separation of polymer membranes, membranes for wastewater treatment, polymer electrolyte membranes and methanol fuel cells, polymer membranes for water desalination, optical, electrochemical and anion/polyanion sensors, polymeric pervaporation membranes, organic-organic separation, biopolymer electrolytes for energy devices, carbon nanoparticles for pervaporation polymeric membranes, and mixed matrix membranes for nanofiltration application.

Download or read book Polymer Membranes written by T. deV. Naylor and published by iSmithers Rapra Publishing. This book was released on 1996 with total page 146 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report describes the constitution and application of polymeric membranes in separation processes. The separation processes covered are reverse osmosis and nanofiltration, ultrafiltration, gas separation, pervaporation and ion exchange. An additional indexed section containing several hundred abstracts from the Rapra Polymer Library database provides useful references for further reading.

Download or read book Poly cyclohexadiene Based Polymer Electrolyte Membranes for Fuel Cell Applications written by and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The goal of this research project was to create and develop fuel cell membranes having high proton conductivity at high temperatures and high chemical and mechanical durability. Poly(1,3-cyclohexadiene) (PCHD) is of interest as an alternative polymer electrolyte membrane (PEM) material due to its ring-like structure which is expected to impart superior mechanical and thermal properties, and due to the fact that PCHD can readily be incorporated into a range of homopolymer and copolymer structures. PCHD can be aromatized, sulfonated, or fluorinated, allowing for tuning of key performance structure and properties. These factors include good proton transport, hydrophilicity, permeability (including fuel gas impermeability), good mechanical properties, morphology, thermal stability, crystallinity, and cost. The basic building block, 1,3-cyclohexadiene, is a hydrocarbon monomer that could be inexpensively produced on a commercial scale (pricing typical of other hydrocarbon monomers). Optimal material properties will result in novel low cost PEM membranes engineered for high conductivity at elevated temperatures and low relative humidities, as well as good performance and durability. The primary objectives of this project were: (1) To design, synthesize and characterize new non-Nafion PEM materials that conduct protons at low (25-50%) RH and at temperatures ranging from room temperature to 120 C; and (2) To achieve these objectives, a range of homopolymer and copolymer materials incorporating poly(cyclohexadiene) (PCHD) will be synthesized, derivatized, and characterized. These two objectives have been achieved. Sulfonated and crosslinked PCHD homopolymer membranes exhibit proton conductivities similar to Nafion in the mid-RH range, are superior to Nafion at higher RH, but are poorer than Nafion at RH

Download or read book Polymer and Small Molecule Designs for Anion Conducting Membranes written by Sedef P. Ertem and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Fuel cells are one of the oldest sustainable energy generation devices, converting chemical energy into electrical energy via reverse-electrolysis reactions. With the rapid development of polymer science, solid polymer electrolyte (SPE) membranes replaced the conventional liquid ion transport media, rendering low-temperature fuel cells more accessible for applications in portable electronics and transportation. However, SPE fuel cells are still far from commercialization due to high operation cost, and insufficient lifetime and performance limitations. Anion exchange membrane fuel cells (AEMFCs) are inexpensive alternatives to current proton exchange membrane fuel cell (PEMFC) technology, which relies on utilizing expensive noble-metal catalysts and perfluorinated SPE materials. Unlike PEMFCs, there is not an ideal AEM material that provides efficient ion transport, while being mechanically robust and chemically stable under strong alkaline conditions. The objectives of this dissertation are to investigate macromolecular design parameters to obtain robust membranes with efficient ion conductivities, and molecular design parameters to obtain alkaline stable ammonium cations as an alternative to the benchmark benzyltrimethylammonium (BTMA) cation. Macromolecular design parameters were explored by systematic variations of polymer architecture from random, to graft, to symmetric pentablock copolymer structures. Solvent processable random copolymers of polyisoprene-ran-poly(vinyl- benzyltrimethylammonium chloride) were synthesized via polymerization of commercially available monomers. Robust membranes were obtained by thermal or photocross-linking of unsaturated isoprene units. Depending on the copolymer composition, choice of cross-linking method, and the hydrophobicity of the cross-linker, microphase-separated morphologies were obtained forming a connected network of ion clusters. Connectivity improved ion conductivity by two to three orders of magnitude even at low hydration numbers. Connected ionic networks with larger domain sizes were obtained when polymer chains with fixed cations were grafted onto a hydrophobic backbone. Systematic change of graft length and graft density showed a strong correlation with domain connectivity. At a fixed graft density, increasing graft length improved domain connectivity and ion conductivity at the expense of excessive water uptake and dimensional instability. At a fixed graft length, increased graft density improved domain connectivity due to decreased domain size and distance, without compromising membrane dimensional stability. Compared to analogous random copolymers two to three times higher ion conductivities were obtained at relatively low hydration, reaching chloride ion conductivities as high as 50 mS/cm at 60 oC and 95 % relative humidity. A symmetric ABCBA pentablock was functionalized to obtain a midblock quaternary ammonium functionalized polymer that are analogous to midblock sulfonated Nexar® pentablock copolymers which have been commercialized by Kraton Polymers. X-ray scattering and transmission electron microscopy revealed formation of a microphase-separated inverse morphology where the minor ionic component formed the connected phase. Membranes had elastomeric properties and superior water management to graft copolymers while providing two to three times higher ion conductivity at an equivalent ion concentration. This work represents the first example of a midblock quaternized pentablock copolymer and the investigation of the structure-morphology-property relationships. Lastly, improved alkaline stability of hexyltrimethylammonium (HTMA) cations were investigated on a molecular level, by systematic structural design. Phenyl, phenyl ether, and benzyl ether attached HTMA small molecule cations were synthesized. These three spacer-modified cations were found to be six to ten times more stable than the conventional BTMA cation. The linker chemistry did not influence the overall alkaline stability, enabling easy access to stable ammonium cations. Analogous styrenic monomers, and their homopolymers were synthesized. High stability of the homopolymer cations was confirmed in comparison to poly(BTMA). This study provided a deeper understanding of ammonium degradation mechanisms under strong alkaline conditions, and proposed monomer designs for easy incorporation of stable ammonium cations onto polymers.

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 Polymer Membranes for Fuel Cells written by Javaid Zaidi and published by Springer. This book was released on 2010-11-16 with total page 550 pages. Available in PDF, EPUB and Kindle. Book excerpt: From the late-1960’s, perfluorosulfonic acid (PFSAs) ionomers have dominated the PEM fuel cell industry as the membrane material of choice. The “gold standard’ amongst the many variations that exist today has been, and to a great extent still is, DuPont’s Nafion® family of materials. However, there is significant concern in the industry that these materials will not meet the cost, performance, and durability requirementsnecessary to drive commercialization in key market segments – es- cially automotive. Indeed, Honda has already put fuel cell vehicles in the hands of real end users that have home-grown fuel cell stack technology incorporating hydrocarbon-based ionomers. “Polymer Membranes in Fuel Cells” takes an in-depth look at the new chem- tries and membrane technologies that have been developed over the years to address the concerns associated with the materials currently in use. Unlike the PFSAs, which were originally developed for the chlor-alkali industry, the more recent hydrocarbon and composite materials have been developed to meet the specific requirements of PEM Fuel Cells. Having said this, most of the work has been based on derivatives of known polymers, such as poly(ether-ether ketones), to ensure that the critical requirement of low cost is met. More aggressive operational requi- ments have also spurred the development on new materials; for example, the need for operation at higher temperature under low relative humidity has spawned the creation of a plethora of new polymers with potential application in PEM Fuel Cells.

Download or read book Water Hydrogen Bonding in Proton Exchange and Neutral Polymer Membranes written by Sarah Smedley and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Understanding the dynamics of water sorbed into polymer films is critical to reveal structure-property relationships in membranes for energy and water treatment applications, where membranes must interact with water to facilitate or inhibit the transport of ions. The chemical structure of the polymer has drastic effects on the transport properties of the membrane due to the morphological structure of the polymer and how water is interacting with the functional groups on the polymer backbone. Therefore studying the dynamics of water adsorbed into a membrane will give insight into how water-polymer interactions influence transport properties of the film. With a better understanding of how to design materials to have specific properties, we can accelerate development of smarter materials for both energy and water treatment applications to increase efficiency and create high-flux materials and processes. The goal of this dissertation is to investigate the water-polymer interactions in proton exchange and uncharged membranes and make correlations to their charge densities and transport properties. A linear Fourier Transform Infrared (FTIR) spectroscopic method for measuring the hydrogen bonding distribution of water sorbed in proton exchange membranes is described in this thesis. The information on the distribution of the microenvironments of water in an ionic polymer is critical to understanding the effects of different acidic groups on the proton conductivity of proton exchange membranes at low relative humidity. The OD stretch of dilute HOD in H2O is a single, well-defined vibrational band. When HOD in dilute H2O is sorbed into a proton exchange membrane, the OD stretch peak shifts based on the microenvironment that water encounters within the nanophase separated structure of the material. This peak shift is a signature of different hydrogen bonding populations within the membrane, which can be deconvoluted rigorously for dilute HOD in H2O compared to only qualitative observations that can be made with pure D2O or H2O. The theory and experimental practice of determining the hydrogen bonding distribution of water in a range of proton exchange membranes bearing aromatic sulfonate and perfluorosulfonate groups using this OD stretch technique is discussed. The OD stretch of dilute HOD in H2O absorbed in a series of sulfonated syndiotactic poly(styrene) and sulfonated poly(sulfone) membranes was studied using FTIR spectroscopy to measure how the character of the sulfonate headgroup and the backbone polarity influenced the water-membrane interactions. Using a three-state model, the OD stretch yielded information about the populations of absorbed water participating in hydrogen bonds with polymer-tethered sulfonate groups, water in an intermediate state, or water hydrogen bonding with other water molecules. The perflouroalkyl sulfonate moiety, which behaves as a superacid, consistently displayed the largest fraction of headgroup-associated water due to its strong acidic character. Measurements of the OD stretch gave insight to the strength of the hydrogen bonds formed between water and the sulfonate groups. Water associated with the superacid displayed an OD stretch peak position that was blueshifted by 39 cm-1 compared to the aryl sulfonate associated water with an OD stretching frequency that was centered at 2547 cm-1. The polarity of the polymer backbone also affected the OD stretch peak position. As hydration increased, the OD peak stretching frequency in poly(styrene)-based membranes displayed a redshift from 2566 cm-1 to 2553 cm-1, whereas there was no OD peak maxima shift in poly(sulfone)-based membranes due to the greater amount of intermediate water in the more polar poly(sulfone) backbone system.To further understand how the acidity of the sulfonate can be altered and how the acidity affects the hydrogen bonding network of water in a polymer membrane, various polymers with small chemical differences in the perfluorosulfonate sidechain were studied. In addition to the vibrational spectroscopy measurements using HOD as a probe, the partial charges of the sulfonate groups were calculating using DMol3 DFT calculations. The calculations and the experimentally determined peak position of the OD stretch both correlated to give a ranking of acidity for the various sidechains. It was found that having a thioether linkage instead of an ether linkage (typical linkage for perflurosulfonates) increased the acidity of the sulfonate group due to the capability of sulfur to expand its octet and more readily accept additional electron density. Through DFT geometry optimization, it was discovered that the thioether linkage prefers a kinked configuration while the ether linkage gives a more linear sidechain structure. This structural configuration correlated to experimental findings allowing more water to interact with the sulfonate group containing the ether linkage than the thioether linkage due to the sulfonate group being more easily accessible, even though the thioether sidechain is more acidic.Three sulfonated poly(arylene sulfone) based polymers were studied using FTIR and DFT calculations to better understand how the acidity of the sulfonate groups were affected by the placement on the backbone. By increasing the number of sulfone groups, which have electron withdrawing properties, flanking the sulfonated aromatic ring, the acidity was increased. The charge density of a sulfonate group flanked by two sulfone groups was -1.626 (in units of fundamental charge), while the charge density of a sulfonate group flanked by one sulfone group increased to -1.703. Additionally, if the subsequent ring was unsulfonated, the charge density further increased to 1.737, indicating that some stability is gained by both available rings being sulfonated. The differences in charge density are reflected in the water uptake and conductivity measurements, where the samples with the lowest charge density had the highest water uptake and conductivity. The deconvoluted OD peak revealed that the sample with two sulfone groups flanking the sulfonated aromatic ring contains the highest amount of bulk-like water, which led to the increased conductivity. The polyamide active layer of commercially available reverse osmosis membranes was studied at various relative humilities to better understand how the structure of the active layer changes when hydrated. The fingerprint region was used to analyze changes in the vibrational signature of specific functional groups and to understand how different chemical moieties interact with water. Using the difference spectrum, the water-polymer interactions could be quantified and correlated to transport properties of the membrane. Increasing the amount of free carboxylic acid groups on the backbone will lead to an active layer that is less crosslinked and contains a greater number of larger pores, which results in a higher flux. Active layers that contained a smaller concentration of free carboxylic acids were more highly crosslinked and had a higher amount of smaller pores, resulting in a lower flux. In summary, by studying the water hydrogen bonding network in various proton exchange membranes and neutral polyamide membranes, a new understanding of structure-property relationships has been developed. This will lead to a greater understanding of transport properties and conductivity in various polymer membranes. Expanding this fundamental knowledge will lead to the development of smarter materials for energy and reverse osmosis applications, and the ideas developed here can be extended to new types of materials used for various needs.

Download or read book Water and Salt Transport Structure property Relationships in Polymer Membranes for Desalination and Power Generation Applications written by Geoffrey Matthew Geise and published by . This book was released on 2012 with total page 768 pages. Available in PDF, EPUB and Kindle. Book excerpt: Providing sustainable supplies of water and energy is a critical global challenge. Polymer membranes dominate desalination and could be crucial to power generation applications, which include reverse osmosis (RO), nanofiltration (NF), forward osmosis (FO), pressure-retarded osmosis (PRO), electrodialysis (ED), membrane capacitive deionization (CDI), and reverse electrodialysis (RED). Improved membranes with tailored water and salt transport properties are required to extend and optimize these technologies. Water and salt transport structure/property relationships provide the fundamental framework for optimizing polymer materials for membrane applications. The water and salt transport and free volume properties of a series of sulfonated styrenic pentablock copolymers were characterized. The polymers' water uptake and water permeability increase with degree of sulfonation, and the block molecular weights could be used to tune water uptake, permeability, and selectivity properties. The presence of fixed charge groups, i.e., sulfonate groups, on the polymer backbone influence the material's salt transport properties. Specifically, the salt permeability increases strongly with increasing salt concentration, and this increase is a result of increases in both salt sorption and diffusivity with salt concentration. The data for the sulfonated polymers, including a sulfonated polysulfone random copolymer, are compared to those for an uncharged polymer to determine the influence of polymer charge on salt transport properties. The sulfonated styrenic pentablock copolymer permeability data are compared to literature data using the water permeability and water/salt selectivity tradeoff relationship. Fundamental transport property comparisons can be made using this relationship. The effect of osmotic de-swelling on the polymers and the transport properties of composite membranes made from sulfonated styrenic pentablock copolymers are also discussed. The sulfonated styrenic pentablock copolymers were exposed to multi-valent ions to determine their effect on the polymer's salt transport properties. Magnesium chloride permeability depends less on upstream salt concentration than sodium chloride permeability, presumably due to stronger association between the sulfonate groups and magnesium compared to sodium ions. Triethylaluminum was used to neutralize the polymer's sulfonic acid functionality and presumably cross-link the polymer. The mechanical, transport, and free volume properties of these aluminum neutralized polymers were studied.

Download or read book Organic Inorganic Composite Polymer Electrolyte Membranes written by Dr Inamuddin and published by Springer. This book was released on 2018-07-28 with total page 460 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume explores the latest developments in the area of polymer electrolyte membranes (PEMs) used for high-temperature fuel cells. Featuring contributions from an international array of researchers, it presents a unified viewpoint on the operating principles of fuel cells, various methodologies used for the fabrication of PEMs, and issues related to the chemical and mechanical stabilities of the membranes. Special attention is given to the fabrication of electrospun nanocomposite membranes. The editors have consciously placed an emphasis on developments in the area of fast-growing and promising PEM materials obtained via hygroscopic inorganic fillers, solid proton conductors, heterocyclic solvents, ionic liquids, anhydrous H3PO4 blends, and heteropolyacids. This book is intended for fuel cell researchers and students who are interested in a deeper understanding of the organic–inorganic membranes used in fuel cells, membrane fabrication methodologies, properties and clean energy applications.