Increasing global demand and dependence on fossil fuels, coupled with environmental concerns arising from their use, have sparked interest in alternative energy sources. Hydrogen-powered fuel cells are a promising solution, offering a clean, scalable method for energy production. The most prominent low-temperature fuel cell devices today operate under an acidic environment, using a semi-permeable proton exchange membrane (PEM) to separate the two electrodes. However, their caustic operating conditions present unique stability and activity issues for the metal catalysts and ultimately necessitates the use of platinum-group materials, severely limiting commercial viability. A potential solution is to operate the fuel cell device under an alkaline environment using an anion exchange membrane (AEM), transporting hydroxide ions in lieu of protons. The basic environment opens the door for cheaper catalysts based on nickel and molybdenum, eliminating the cost barrier associated with PEM fuel cells. Unfortunately, typical AEMs exhibit poorer ionic conductivity and stability compared to traditional acidic membranes (e.g. Nafion), offsetting any potential cost advantage they may afford. This dissertation discusses design rationales towards enhancing the macroscopic properties of AEMs. Specifically, I present two experimental design motifs for improving the device viability of AEMs. In the first case, I present a semi-interpenetrating network design where a linear AEM ionomer is stabilized by a crosslinked poly(styrene-co-divinylbenzene) matrix. The crosslinked network acts as a reinforcing scaffold, dramatically increasing dimensional stability while maintaining excellent anion conductivity. Prototypical single-stack fuel cells with enhanced performance and stability have been fabricated from these materials, validating the design choices. In the second approach, I demonstrate the ability to increase hydroxide conductivity by tuning the nanostructure of the polymer electrolyte. Specifically, I show that tethering hydrophilic poly(ethylene glycol) grafts onto a benzyltrimethylammonium polysulfone benchmark AEM results in phase-separated, water-rich domains on the order of 5 to 10 nm. These domains serve as an ion transport pathway, facilitating the diffusion of hydroxide anions and consequently enhancing the efficiency of hydroxide conduction. Finally, in order to better understand the phase behavior and structure-property relationships of typical AEM materials, we have developed coarse-grained simulations and fundamental polymer theory to elucidate the thermodynamic behavior of random copolymers. We find that both the stochastic distribution of monomers along the polymer backbone as well as the overall stiffness of the polymer chain heavily influences its phase behavior (i.e., morphology and critical point). The ultimate objective is to provide not only a theoretical basis for understanding and explaining structure-property relationships in existing AEM materials, but to provide a set of general design guidelines moving forward.

The development of fuel cells is indispensable to enable the hydrogen society. Anion exchange membrane fuel cells (AEMFCs) have triggered great interest over the past few years. In this dissertation, electrocatalysis in alkaline media and polymer electrolytes for AEMFCs have been explored from fundamental aspects to practical applications. For the oxygen reduction reaction (ORR) in alkaline media, electrochemically dealloyed Pd-M (M = Ni, Mn) nanoparticle catalysts were developed to enhance electrocatalytic activity. The electrochemical dealloying process was demonstrated to be effective in selectively leaching out the less noble metal and metal oxides on the surface. The higher atomic concentration of electrochemically active Pd exposed on the surface of the nanoparticles was found to be the reason for the enhanced ORR activity in alkaline media. These findings provide insights for the rational design of the composition and structure of electrocatalysts with enhanced electrocatalytic activity, based on post-synthesis modification methods. From a fundamental perspective, to explain and predict the electrocatalytic activity of heterogenous reactions, the energy of intermediates is usually used as an activity descriptor. However, this was recently called into questions. We developed a novel method, based on fast scan rate cyclic voltammetry, to directly measure the kinetics of the electro-adsorption processes. The Had adsorption reaction, the elementary step of the hydrogen evolution reaction (HER), on Pt(111) in acid was found to be >100x faster than in alkaline media, although the Had binding energy was the same. Together, with cation effects and isotope effects found in alkaline media, we demonstrated that the slow kinetics of the HER at high pH are not due to an unfavorable Had binding energy but to the high barrier of interfacial water reorganization. Polymer electrolytes in AEMFCs, namely anion exchange membranes and ionomers, play important roles in the transport of anions and water molecules. In situ characterization of these materials in their electrochemical environment is critical for understanding the anion transport mechanism and improving the design of them. The anion exchange and water dynamics in a perspective phosphonium-based AEM during the methanol oxidation process were studied with the electrochemical quartz crystal microbalance (EQCM). The results provide insights of the anion exchange process in the membranes during the reaction and emphasize the importance of characterizing the membranes in a hydrated electrochemical environment. The influence of ion exchange capacity (IEC) on the solubility, the ionomer viscoelasticity in water and the transport of charged and uncharged species, of a promising polyethylene piperidinium methyl (PEPM) ionomer were also investigated. The design of ionomers and membranes, with suitable IEC for their different functions in AEMFCs from the aspect of solubility, mechanical properties and mass transport, can be guided via this work.

Alkaline Anion Exchange Membranes for Fuel Cells Build the fuel cells of the future with this cutting-edge material Alkaline anion exchange membranes (AAEMs) are cutting-edge polyelectrolyte materials with growing renewable energy applications including fuel cells, batteries, hydrogen electrolyzers and electrodialysis technologies. Their use in relatively new alkaline exchange membrane fuel cells (AEMFCs) is designed to produce cost-effective clean energy (electricity) produced by a chemical reaction. Rigorous studies are being conducted to meet the requirements of AAEMs precisely tailored for high anion conductivity and durability for future high energy efficient devices. Hence, over the past few years the academic and industrial scientific communities have explored various polymeric, composite and inorganic materials and studied their properties as a potential AAEM. The accumulated literature in this area of investigation is vast and in order to provide the community with the tools needed to strive forward, there is a clear need to condense this information in a single volume. Alkaline Anion Exchange Membranes for Fuel Cells meets this need with a comprehensive overview of the properties of these membranes and their applications. The book considers recent developments, common challenges, and the long-term prospects for this field of research and engineering. It constitutes a one-stop resource for the development and production of AAEM fuel cells and related electrochemical applications. Alkaline Anion Exchange Membranes for Fuel Cells readers will find: Discussion of electrochemical applications like redox flow batteries, water electrolysis, and many more Detailed treatment of specially tailored cationic groups such as quaternary ammonium and guanidinium Expert advice on efficient fabrication and electrode assembly Alkaline Anion Exchange Membranes for Fuel Cells is ideal for electrochemists, materials scientists, polymer chemists, electrical engineers, and anyone working in power technology or related fields.

This issue of ECS Transactions reports on research, development, and engineering of polymer electrolyte fuel cells (PEFCs), as well as low-temperature direct-fuel cells using either anion or cation exchange membranes. It discusses diagnostic techniques and systems design for both acid and alkaline fuel cells, catalysts and membranes for acid fuel cells, and catalysts and membranes for alkaline fuel cells.

Anion exchange membranes (AEMs) are polymer-based electrolyte solids that conduct anions (OH-, HCO3-, Cl-, et al.), with positively charged groups bound covalently to the polymer backbones. There has been a strong and growing worldwide interest in the use of anion exchange membranes for electrochemical energy conversion and storage systems. Anion exchange membrane fuel cells (AEMFCs) have been regarded as promising energy conversion devices for stationary and mobile applications due to their potential low cost. To realize high-performance AEMFCs, new polymeric membranes are needed that are highly conductive and chemically stable. Herein, cross-linked, multication side chain, and fluorene side chain AEMs based on poly(2,6-dimethyl-1,4-phenylene oxide)s (PPO) were synthesized. PPO was chosen as an AEM substrate because of its ease of functionalization at large scale and relatively good stability and membrane properties. To produce anion conductive and durable polymer electrolytes for alkaline fuel cell applications, a series of cross-linked quaternary ammonium functionalized poly(2,6-dimethyl-1,4-phenylene oxide)s with mass-based ion exchange capacities (IEC) ranging from 1.80 to 2.55 mmol/g were synthesized via thiol-ene click chemistry. From small angle X-ray scattering (SAXS), it was found that the cross-linked membranes developed micro-phase separation between the polar PPO backbone and the hydrophobic alkyl side chains. The ion conductivity, dimensional stability, and alkaline durability of the cross-linked membranes were evaluated. The hydroxide ion conductivity of the cross-linked samples reached 60 mS/cm in liquid water at room temperature. The chemical stabilities of the membranes were evaluated under severe, accelerated aging conditions and degradation was quantified by measuring ion conductivity changes during aging. The cross-linked membranes retained their relatively high ion conductivity and good mechanical properties both in 1 M and 4 M NaOH at 80 °C after 500 h. Attenuated total reflection (ATR) spectra were used to study the degradation pathways of the membranes, and it was discovered that [beta]-hydrogen (Hofmann) elimination was likely to be the major pathway for degradation in these membranes. Side-chain containing AEMs with one, two or three cations per side chain were designed and synthesized, enabling a study of how the degree of polymer backbone functionalization and arrangement of cations on the side chain impact AEM properties. A systematic study of anion exchange membranes (AEMs) with multiple cations per side chain site was conducted to demonstrate how this motif can boost both the conductivity and stability of poly(2,6-dimethyl-1,4-phenylene oxide)-based AEMs. The highest conductivity, up to 99 mS/cm at room temperature, was observed for a triple-cation side chain AEM with 5 or 6 methylene groups between cations. This conductivity was considerably higher than AEM samples based on benzyltrimethyl ammonium or benzyldimethylhexyl ammonium groups with only one cation per side chain site. In addition to high conductivity, the multication side chain AEMs showed good alkaline and dimensional stabilities. High retention of ion exchange capacity (IEC) (93% retention) and ionic conductivity (90% retention) were observed for the triple-cation side chain AEMs during degradation testing in 1 M NaOH at 80 °C for 500 h. Based on the high-performance triple-cation side chain AEM, a Pt-catalyzed fuel cell with a peak power density of 364 mW/cm2 was achieved at 60 °C under 100% related humidity. Anion-conductive copolymers, poly(2,6-dimethyl-1,4-phenylene oxide)s containing fluorene side chains with pendant alkyltrimethylammonium groups, were synthesized via Suzuki-Miyaura coupling of aryl bromides with fluorene-boronic acids. The quaternized copolymers produced ductile, transparent membranes which were soluble in dimethyl formamide, dimethyl sulfoxide and methanol at room temperature. The fluorene side chain-containing membranes showed considerably higher hydroxide ion conductivities, up to 176 mS/cm at 80 °C, compared to that of typical anion exchange membranes based on the benzyltrimethyl ammonium moiety. The results of titration and hydroxide ion conductivity measurements demonstrated excellent chemical stability of the fluorene side chain-containing anion exchange membranes (AEMs), even after 1000 h immersion in 1 M NaOH at 80 °C. The results of this study suggest a scalable route for the preparation of AEMs for practical alkaline fuel cell applications. A unique approach was employed to toughen AEMs by crosslinking the AEMs using commercial Jeffamine additives. Compared to the BTMA40 membrane, the 10% Jeffamine cross-linked membrane demonstrated significantly higher elongation at break. To be specific, the hydrated BTMA40 membrane showed a 51.7% elongation at break, while the 10% Jeffamine cross-linked membrane had a 166.8 % elongation at break. Clearly, the introducing of hydrophilic cross-linked network greatly enhanced the toughness of the AEMs. Overall, this thesis details a number of strategies for the large-scale production of PPO-based anion exchange membranes. These strategies will be useful in going forward in the design and deployment of hydroxide, bromide, bicarbonate, and chloride-conducting membranes for water purification and electrochemical technology.

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.

Including chemical, synthetic, and cross-disciplinary approaches; this book includes the necessary techniques and technologies to help readers better understand polymers for polymer electrolyte membrane (PEM) fuel cells. The methods in the book are essential to researchers and scientists in the field and will lead to further development in polymer and fuel cell technologies. • Provides complete, essential, and comprehensive overview of polymer applications for PEM fuel cells • Emphasizes state-of-the-art developments and methods, like PEMs for novel fuel cells and polymers for fuel cell catalysts • Includes detailed chapters on major topics, like PEM for direct liquid fuel cells and fluoropolymers and non-fluorinated polymers for PEM • Has relevance to a range of industries – like polymer engineering, materials, and green technology – involved with fuel cell technologies and R&D

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.

This book consists of the nine sections: i) the first three sections are related to polymeric electrolyte composites; ii) the next two sections relate to gas diffusion layers (GDLs); iii) the next two sections relate to membrane¬–electrode assembly (MEA); iv) and the final two sections deal with the numerical simulation of flow fields for polymer electrolyte fuel cells (PEFCs). All sections describe recent results of the study of the main components of PEFC stacks. The studies provide the underlying material, electrochemical, and/or mechanical aspects that enhance the mass transport of gas, ions (liquid), and electrons for a better performance of PEFCs and the electrochemical reactions at the triple-phase boundary in electrodes. Each study offers the fundamentals, a comprehensive background, and cutting-edge technology on the aforementioned materials and mass transport phenomena.

The Encyclopedia of Electrochemical Power Sources, Second Edition, is a comprehensive seven-volume set that serves as a vital interdisciplinary reference for those working with batteries, fuel cells, electrolyzers, supercapacitors, and photo-electrochemical cells. With an increased focus on the environmental and economic impacts of electrochemical power sources, this work not only consolidates extensive coverage of the field but also serves as a gateway to the latest literature for professionals and students alike. The field of electrochemical power sources has experienced significant growth and development since the first edition was published in 2009. This is reflected in the exponential growth of the battery market, the improvement of many conventional systems, and the introduction of new systems and technologies. This completely revised second edition captures these advancements, providing updates on all scientific, technical, and economic developments over the past decade. Thematically arranged, this edition delves into crucial areas such as batteries, fuel cells, electrolyzers, supercapacitors, and photo-electrochemical cells. It explores challenges and advancements in electrode and electrolyte materials, structural design, optimization, application of novel materials, and performance analysis. This comprehensive resource, with its focus on the future of electrochemical power sources, is an essential tool for navigating this rapidly evolving field. - Covers the main types of power sources, including their operating principles, systems, materials, and applications - Serves as a primary source of information for electrochemists, materials scientists, energy technologists, and engineers - Incorporates 365 articles, with timely coverage of environmental and sustainability aspects - Arranged thematically to facilitate easy navigation of topics and easy exploration of the field across its key branches - Follows a consistent structure and features elements such as key objective boxes, summaries, figures, references, and cross-references etc., to help students, faculty, and professionals alike