Fuel cells have long been seen as an alternative to combustion powered and diesel powered engines and turbines. Production of energy via a fuel cell conversion method can generate up to 60% efficiency in comparison to 30% using a combustion powered engine, with low co-production of harmful side-products. The polymer electrolyte membrane (PEM) adapted for the fuel cell application is one of the main components that determines the overall efficiency. This research project was focused towards novel PEMs, such as sulfonated poly(etheretherketone) or SPEEK, which are cost-efficient and robust with high proton conductivities under hydrated conditions. The degree of sulfonation (DS) of a particular SPEEK polymer determines the proton conducting ability, as well as the long term durability. For SPEEK with high DS, the proton conduction is facile, but the mechanical stability of the polymer decreases almost proportionally. While low DS SPEEK does not have sufficient sulfonic acid density for fast proton conduction in the membrane, the membrane keeps its mechanical integrity under fully saturated conditions. The main purpose of this work was to address both issues encountered with SPEEK sulfonated to low and high DS. The addition of both solid acids and synthetic cross-links were studied to address the main downfalls of the respective SPEEK polymers. Optimization of these techniques led to increased understanding of PEMs and notably better electrochemical performance of these fuel cell materials. Oxo-acids such as tungsten (VI) oxide (WO3) and phosphotungstic acid (PTA) have been identified as candidate materials for creating SPEEK composite membranes. The chemistry of these oxo-acids is well known, with their use as highly acidic catalyst iv centers adopted for countless homogeneous and heterogeneous, organic and inorganic reactions. Uniform dispersion of WO3 hydrate in SPEEK solution was done by a sol-gel process in which the filler particles were grown in an ionomer solution, cast and allowed to dry. PTA composites were made by adding the solid acid directly to a solution of the ionomer and casting. The latter casting was allowed to dry and Cs+ - exchanged to stabilize the PTA from dissolution and leaching from the membrane. The chemical and physical properties of these membranes were characterized and evaluated using mainly conductometric and X-ray photoelectron spectroscopic methods. Composite SPEEK/ PTA membranes showed a 50% decrease in PEM resistance under hydrogen fuel cell testing conditions, while SPEEK/ WO3 composites demonstrated a ten-fold increase in the membrane's in-plane proton conductivity. The chemical and physical properties of these composites changed with respect to their synthesis and fabrication procedures. This study will expound upon their relations.

<p> Today' s commercial proton exchange membranes for fuel cell applications use a liquid electrolyte such as water to facilitate the conduction process. The vapour pressure of water limits the operating temperature of a fuel cell, resulting in a decrease in efficiency as the electrolyte evaporates. Anhydrous electrolytes such as acidified polybenzimidazole or poly(vinyl-4-imidazole) are able to transport ions without using water as an electrolyte. </p> <p> The mechanism of ion transport involves the structural diffusion of the ions through the solid-state lattice. Compounds modeling the basic modes of the ionic conductivity are used in the solid-state nuclear magnetic resonance (NMR) investigation. The hydrogen-bonding structures of model compounds are established using diffraction paired with 1H solid-state double quantum NMR. The structural studies of the compounds reveal a continuous network of hydrogen bonded molecules. The structural motif is based on strong N-H••O and 0-H••O hydrogen bonds between the ions of the material. The dynamics of the hydrogen bonds observed in the 1H NMR and the multinuclear studies using the CODEX (Centerband Only Detection of EXchange) pulse sequence define the mechanism of ionic conductivity in these model compounds. </p> <p> These solid-state NMR techniques are then applied to a novel electrolyte material consisting of a solid electrolyte inside the pores of a host polymer material. This new material is able to transport protons at high temperatures without the use of an aqueous electrolyte. The properties and mechanism of ion transport is investigated using solid­ state NMR and impedance spectroscopy. </p> / Thesis / Doctor of Philosophy (PhD)

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The major challenge of the research was to characterize and develop concepts for establishing structure/property relationships between the functionality of the polymer backbone, the states of water and the membrane transport properties. Most of the hydrocarbon based random copolymers reported in the literature show reduced proton conductivity at low water content. This was attributed to the formation of an isolated morphology. Over the last few years our group has synthesized thermally stable multiblock copolymers with varying chemical structures and compositions. Block copolymers consist of two or more incompatible polymers (i.e. blocks) that are chemically conjoined in the same chain. The transport properties of the multiblock copolymers showed a strong dependence on the morphology in contrast to the random copolymers. Irrespective of the nature of the backbone, the transport properties scaled with the block lengths of the copolymers. An increase in block length for a given series of block copolymer was associated with improved proton conduction, particularly under partially hydrated conditions compared to the random copolymers. The structure-property relationship of the proton conductivity and self-diffusion coefficient of water was obtained as a function of the volume fraction of water for all the random and block copolymers. At a given volume fraction, the block copolymers displayed both higher self-diffusion coefficients of water and proton conductivities relative to the random copolymers. This improvement in transport properties indicates the presence of desired and favorable morphology for the blocks. For DMFC applications, the block copolymers also showed low methanol permeability and high selectivity. The states of water in the copolymers were characterized using DSC and NMR relaxation techniques. At similar ionic contents, the free water concentration increased with increasing block lengths. The distribution of the states of water in the copolymers correlates to transport properties. This knowledge, coupled with the state of water experiments, transport measurements, and chemical structure of the copolymers provided a fundamental picture of how the chemical nature of a phase separated copolymer influences its transport properties. The experimental procedure involved impedance spectroscopy, DSC, TGA, FTIR, DMA, pulse gradient stimulated echo (PGSE) NMR, NMR relaxation experiments and various electrochemical fuel cell performance experiments. / Ph. D.

Recent efforts toward the commercialization of hydrogen fuel cells, a sustainable energy technology, have led to interest in the effects of industrial processing parameters on the morphology and properties of fuel cell ionomers. The ionomer functions as a solid electrolyte membrane on the order of microns thick and as a thin film on the order of tens of nanometers in the catalyst layer. Industrial manufacture of the membrane and catalyst layer is typically a roll-to-roll process that involves casting a colloidal dispersion of the fuel cell ionomer in predominantly mixed alcohol/water solvent systems onto a backing film or substrate, followed by evaporation of the solvent and annealing of the ionomer at elevated temperatures. The current benchmark fuel cell ionomers are a class of polymers with pendant perfluorinated side chains terminating in sulfonic acid groups, called perflurosulfonic acid ionomers (PFSAs). The purpose of this dissertation is to investigate the effects of industrial processing parameters such as dispersion solvent composition, solvent evaporation temperature, and annealing temperature on fuel cell-relevant properties of PFSA solid electrolyte membranes and model thin films. Particular focus is given to newer-generation PFSAs and the effect of their different chemical structures on the morphology and properties of dispersions, membranes, and thin films. Dipole-dipole interactions between colloidal aggregates modulated by solvent composition were found to significantly influence the viscosity of PFSA dispersions. A framework of PFSA-solvent interactions is developed to predict the onset of dipole-dipole interactions as a function of PFSA chemical structure and solvent composition. Increased steric hindrance of shorter PFSA side chain chemical structures is found to inhibit morphological development, resulting in membranes with poorer wet and dry mechanical properties. A shorter side-chain PFSA is suggested to require higher processing temperatures to achieve performance equivalent to a PFSA with slightly longer side chain. The morphology and properties of model PFSA thin films are demonstrated to decay to quasi-equilibrium values upon physical aging at both low and high relative humidity (RH). Thin film swelling curves are demonstrated to be superposable by implementing an aging time-RH shift factor, allowing for prediction of quasi-equilibration times under given fuel cell operating conditions. / Doctor of Philosophy / Interest in environmentally friendly, sustainable energy sources has led to significant industrial, academic, and governmental efforts to commercialize hydrogen fuel cells. Hydrogen gas is split into protons and electrons in the anode catalyst layer. The electrons flow through an external circuit to produce electricity, while the protons are transported from the catalyst layer through a solid electrolyte membrane to the anode to react with oxygen to form water. A key component of hydrogen fuel cells is an ion-containing polymer called an ionomer that is required for the transport of (1) protons in the solid electrolyte membrane and (2) protons and reactant gases in the catalyst layer. The solid electrolyte membrane and catalyst layer can be industrially produced by a continuous process that involves dispersing the ionomer in a mixed alcohol/water solvent and coating it onto a backing film, followed by evaporation of the solvent and annealing of the ionomer. The present work is an investigation of the effect of industrially-relevant processing parameters on the morphology and properties of a class of ionomers called perfluorosulfonic acid ionomers (PFSAs), which phase separate into hydrophilic domains that serve as transport pathways and hydrophobic domains that impart thermomechanical stability. Practical aspects of the processing and function of PFSAs, including viscosity of the PFSA dispersion, minimum processing temperature to achieve solvent stability, and physical aging of the PFSA during fuel cell operation are shown to be fundamentally related to the PFSA chemical structure and morphology.

High performance engineering materials, poly(arylene ether)s, having very good mechanical properties, excellent oxidative and hydrolytic stability are promising candidates for alternative materials used in the field of Proton Exchange Membrane Fuel Cells (PEMFCs) and Reverse Osmosis (RO) applications. In particular, wholly aromatic sulfonated poly(arylene ether sulfone)s are of considerable interest in the field of PEMFCs and RO, due to their affordability, high Tg, and the ease of sulfonation. Proton exchange membrane fuels cells (PEMFCs) are one of the primary alternate source of energy. A Proton exchange membrane (PEM) is one of the key component in a PEMFC and it needs to have good proton conductivity under partially humidified conditions. One of the strategies to increase proton conductivity under partially RH conditions is to synthesize hydrophobic-hydrophilic multiblock copolymers with high Ion exchange capacity (IEC) values to ensure sufficient ion channel size. In this thesis two multiblock systems were synthesized incorporating trisulfonated hydrophilic oligomers and were characterized in the first two chapters of the thesis. The first multiblock system incorporated a non-fluorinated biphenol-based hydrophobic block. The second study was focused on synthesizing a fluorinated benzonitrile-based hydrophobic block. A fluorinated monomer was incorporated with the aim to improve phase separation which might lead to increased performance under partially humidified conditions. The third study featured synthesis and characterization of a novel hydroquinone-based random copolymer system precursor, which after post-sulfonation, shall form mono-sulfonated polysulfone materials with potential applications in reverse osmosis. The ratio of the amount of hydroquinone incorporated in the copolymer were varied during the synthesis of the precursor to facilitate control over the post-sulfonation process. The simple and low cost process of post-sulfonating the random copolymer enables the precursor to be a promising material to be used in the reverse osmosis application. / Master of Science

The need for sustainable energy use has motivated the exploration of renewable alternative fuels and fuel conversion technology on a global scale. Fuel cells, which convert chemical energy directly into electrical energy with high efficiency and low emissions, provide a promising strategy for achieving energy sustainability. The current progress in fuel cell commercialization is mainly in portable and stationary applications, but fuel cell technology for transportation applications, which make up a substantial portion of the global energy market, have seen little commercial success. Proton exchange membrane fuel cells (PEMFCs) have high potential for addressing the future energy needs of the transportation energy sector. However, one of the prevailing limitations of the PEMFC is the availability of high-performance, cost-effective electrolyte materials. These materials may be realized in the near future by developing multi-functional polymer blends targeted at specific performance capabilities. Due to the near-infinite possibilities of polymer combinations and processing techniques high-throughput polymer characterization techniques are necessary to effectively and systematically screen for optimal materials and relevant structure-property relationships. In this work, a high-throughput mass transport assay (HT-MTA) has been developed to characterize water flux and permeability at multiple sample locations in parallel. The functionality of HT-MTA was evaluated using standard Nafion® films and a model semi-interpenetrated polymer network with commercial polyvinylidine fluoride as the host matrix for a proprietary polyelectrolyte supplied by Arkema, Inc. To further demonstrate the utility of HT-MTA, the instrument was incorporated into the lab's current high-throughput characterization toolset and used to investigate the mechanisms and effects of rapid free radical degradation of Nafion® membranes based on various concentrations of hydrogen peroxide and iron(II) sulfate in solution. The results have been used suggest the effects of these regent components on preferential degradation pathways and will prove to be useful in later simulating the membrane performance during in-situ fuel cell lifetime which is both time-intensive and costly. The high-throughput toolset was also used to develop a novel optimized blend consisting of polyetherimide (PEI), a low-cost high performance resin, and sulfonated PEI (S-PEI) made using a relatively mild post sulfonation reaction with trimethylsilyl chlorosulfonate. The effects of blend composition and thermal annealing on film performance were evaluated and the polymer system was shown to have optimal performance properties that should prove to be useful in other high-performance applications where mechanical strength is critical. In general, this work shows promising results for efficiently developing advanced polymer materials using high-throughput screening techniques.

Thesis (Ph.D.(Chemistry)) -- University of Limpopo, 2020 / The interest on the use of proton exchange membrane (PEM) fuel cells for vehicle application has increase due to its efficiency, high power density and rapid start up. The on-board reforming process is used to generate hydrogen; however, this process simultaneously produces 1% CO which poisons Pt-based anode catalyst. Previous studies have shown that supported Pd-based catalysts have very good stability on preferential oxidation (PROX) of CO, but these catalysts suffer from lower selectivity. Metal oxides such as Co3O4 and CeO2 are known to have high oxygen vacancy which promotes CO oxidation. Furthermore, the pre-treatment of the catalysts by hydrazine as well as the addition of MnOx species have been shown to improve the surface properties of metal/metal oxides catalysts. The study envisages that the modification of PROX catalysts will improve the CO conversion and its selectivity while maintaining higher stability. In this work, as-prepared (Co3O4) and hydrazine treated cobalt (Co3O4(H)) based catalysts were prepared by precipitation method and investigated at temperature range of 40-220 oC for preferential oxidation (PROX) of CO in excess hydrogen. The FTIR and XPS data of hydrazine treated Co3O4 does not show peak ratio differences, indicating that usual amounts of Co3+ and Co2+ were formed. An improved surface reducibility with smaller crystallite size was noted on Co3O4(H) catalyst, which indicate some surface transformation. Interestingly, the in-situ treatment of standalone Co3O4(H) decreased the maximum CO conversion temperature (T100%) from 160 oC (over Co3O4) to 100 oC. The Co3O4(H) catalyst showed good stability, with approximately 85% CO conversion at 100 oC for 21 h, as compared to fast deactivation of the Co3O4 catalyst. However, the Co3O4(H) catalyst was unstable in both CO2 and the moisture environment. Based on the spent hydrazine treated (CoO(H)) cobalt catalyst, the high PROX is associated with the formation of Co3+ species as confirmed by XRD, XPS, and TPR data. The Pd species was incorporated on different Co3O4 by improved wet impregnation method and this has improved the surface area of the overall catalysts. However, the presence of Pd species on Co3O4(H) catalyst decreased the CO conversion due to formation of moisture. Although, the Pd on Co3O4(H) had lower activity, the catalyst showed better stability under both moisture and CO2 conditions at 100 oC for 21 h. vi The 2wt.% metal oxides (MnO2, CeO2, Cr3O4, TiO2, MgO) on cobalt, and Pd on CeO2- Co3O4 and MnO2-Co3O4 were prepared by co-precipitation method and the structural composition was confirmed by XRD, FTIR, XPS and TPR data. Although, 2wt.%MnO2 on Co3O4(H) showed higher activity at 80 oC, both MnO2 and CeO2 improved the activity of Co3O4(H) at 100 oC. The higher activity of MnO2 is attributed to the higher surface area of the composite catalyst, in relation to ceria composite catalyst. Although the MnO2 species transformed the structure of Co3O4 by lowering the oxidation state to Co2+, the spent catalyst showed transformation from Co2+ to Co3+ during PROX, as confirmed by TPR data. Studies on the effects of CeO2 loading on Co3O4 catalysts, showed an optimum activity over 2wt.%CeO2-Co3O4 as compared to other ceria loadings (i.e., 3, 5, 8, 10, 15, 30wt.%CeO2). However, upon addition of 0.5wt.%Pd species on 2wt.%CeO2- Co3O4(H) composite, the activity of the catalyst decreased slightly at 100 oC, which could be due to a decreased surface area. Although its activity is lower, the catalyst has shown good stability in dry, moisture and CO2 conditions at 100 oC for 21 h. In addition, studies were also undertaken on the effect of MnO2 concentration on Co3O4 catalysts. The data shows that 7wt.%MnO2 species improved the activity of Co3O4 catalyst at 60 oC, however, the catalyst could not improve the activities at higher temperatures. This low activity is associated with a decrease in surface area as concentration increases. The presence of 0.5wt.%Pd species on 7wt.%MnO2-Co3O4 increased the activity at 60 and 80 oC, which could be due to reduction of Co3+ to Co2+ in the presence of Pd, as confirmed by XPS data. The catalyst has shown good stability in dry, moisture, and CO2 conditions at 100 oC for 21 h. The hydrazine treated cobalt-based catalysts in the presence of palladium and manganese oxide is the promising catalysts for proton exchange membrane fuel cells technology. / National Research Foundation (NRF) , Faculty of Science and Agriculture University of Limpopo and School of Physical and Mineral Sciences