Sulfonated polysulfones BisAS and BPS were fabricated into dense polymer films, and their water and ion transport properties were systematically characterized. Fundamental NaCl and water transport properties were correlated with polymer chemistry, and water and NaCl permeability were found to increase with degree of sulfonation due to the increasing polymer water content. The BisAS backbone structure was found to result in greater water uptake, increasing water and salt permeability, though the polysulfones show evidence of sensitivity to the thermal casting process as well. Additionally, water and ion permeability and sorption values were determined for select polymers when exposed to a feed consisting of mixtures of monovalent and divalent cation salts. The divalent cations were found to sorb into the polymer much more favorably than the monovalent sodium, similarly to charged materials found in the literature. The sodium permeability of sulfonated polysulfones was found to increase in the presence of divalent cations by ratios of 2 to 5 times more than when exposed to an equivalent increase in feed charge concentration of monovalent cations. It has been hypothesized the more strongly charged divalent cations are neutralizing the sulfonate charges and suppressing Donnan exclusionary effects that reduce salt transport in charged polymers. / text

The proton exchange membrane fuel cell (PEMFC) is a potential electrochemicalpower device for vehicles, auxiliary power units and small-scale power plants. In themembrane electrode assembly (MEA), which is the core of the PEMFC single cell,oxygen in air and hydrogen electrochemically react on separate sides of a membraneand electrical energy is generated. The main challenges of the technology are associatedwith cost and lifetime. To meet these demands, firstly, the component expensesought to be reduced. Secondly, enabling system operation at elevated temperatures,i.e. up to 120 °C, would decrease the complexity of the system and subsequentlyresult in decreased system cost. These aspects and the demand for sufficientlifetime are the strong motives for development of new materials in the field.In this thesis, MEAs based on alternative materials are investigatedwith focus on hydrocarbon proton-conducting polymers, i.e. ionomers, and newcatalyst supports. The materials are evaluated by electrochemical methods, such ascyclic voltammetry, polarisation and impedance measurements; morphological studiesare also undertaken. The choice of ionomers, used in the porous electrodes andmembrane, is crucial in the development of high-performing stable MEAs for dynamicoperating conditions. The MEAs are optimised in terms of electrode compositionand preparation, as these parameters influence the electrode structure andthus the MEA performance. The successfully developed MEAs, based on the hydrocarbonionomer sulfonated polysulfone (sPSU), show promising fuel cell performancein a wide temperature range. Yet, these membranes induce mass-transportlimitations in the electrodes, resulting in deteriorated MEA performance. Further,the structure of the hydrated membranes is examined by nuclear magnetic resonancecryoporometry, revealing a relation between water domain size distributionand mechanical stability of the sPSU membranes. The sPSU electrodes possessproperties similar to those of the Nafion electrode, resulting in high fuel cell performancewhen combined with a high-performing membrane. Also, new catalystsupports are investigated; composite electrodes, in which deposition of platinum(Pt) onto titanium dioxide reduces the direct contact between Pt and carbon, showpromising performance and ex-situ stability. Use of graphitised carbon as catalystsupport improves the electrode stability as revealed by a fuel cell degradation study.The thesis reveals the importance of a precise MEA developmentstrategy, involving a broad methodology for investigating new materials both as integratedMEAs and as separate components. As the MEA components and processesinteract, a holistic approach is required to enable successful design of newMEAs and ultimately development of high-performing low-cost PEMFC systems. / QC 20100922

This thesis reports on the synthesis and characterisation of various types of oxidised multiwalled carbon nanotubes (O-MWCNTs) modified polymeric membranes. These OMWCNT modified polymeric membranes were then assessed in terms of their remediation potential, in particular for the removal of estrogenic hormones, dissolved proteins and salts from brackish water sources. The fabricated O-MWCNT-based polyethersulfone (PES) membranes were applied as (i) adsorptive membranes, (ii) molecular-sieving membranes and (iii) as membrane substrates for thin-film composite nanofiltration (NF) membrane preparation. The research work commences with the preparation of MWCNTs via a facile catalytic chemical vapour deposition method and their chemical oxidation with strong acids in order to introduce hydrophilic carboxylic (–COOH) and hydroxyl (–OH) surface functional group moieties on the MWCNT outer walls. Intrinsically, MWCNTs are chemically inert and tend to form agglomerated nanoclusters (due to van der Waals interaction forces), which induce further difficulties in their homogenous dispersion in polar solvents (such as N-methyl-2- pyrrolidone and dimethylacetamide) employed to dissolve the polymers in the study. The introduction of these oxygen-containing moieties was therefore necessary to aid the dispersion of MWCNTs in organic solvents and for their enhanced interaction with PES and sulfonated polysulfone (SPSf). The PES/O-MWCNT ultrafiltration (UF) membranes were produced via a non-solvent induced phase separation (NIPS) method and employed in the adsorptive removal of natural hormone estrone (E1). The PES/O-MWCNT UF membranes thus prepared were characterised using SEM, AFM, zeta potential measurements and MWCO experiments. It was found that the adsorption of E1 initially increased with an increase in O-MWCNT content followed by a constant decline on further increments. Moreover, the inclusion of OMWCNTs (0.5 wt.%) in the PES membrane matrix resulted in an increase in the maximum adsorption capacity for E1 compared to pristine PES membrane, i.e., 31.25 mg/g adsorption capacity was achieved for PES/O-MWCNT compared to 23.81 mg/g for bare PES UF membrane. Based on the correlation coefficients, the Freundlich isotherm provided a better fit for the adsorption data and the adsorption kinetics followed the pseudo-second order kinetic model. Interestingly, after five regeneration cycles, the PES/O-MWCNT membranes were found to maintain similar adsorption efficiencies. The PES/O-MWCNT membranes thus prepared, present a viable approach for the removal of natural hormones and other endocrine disruptors present in water systems compared to the use of common adsorbents such as activated carbon, which end up generating large amounts of chemical sludge that require disposal in the environment. The third part of the study focused on the controlled formation of macrovoid-free polyethersulfone/sulfonated polysulfone (PES/SPSf) UF membranes with high water permeabilities, mechanical strength and antifouling properties, in the presence of O-MWCNTs. To date, the majority of polymeric nanocomposite membranes modified with O-MWCNTs as nanofillers, generally have finger-like structures and macrovoids in the membrane sublayer. While the presence of finger-like structures is favoured for the reduction in mass flow resistance, their presence induces mechanically weak points in the membrane and reduces the nanocomposite membranes’ mechanical strength properties and long-term performance stability. As such macrovoid-free PES/SPSf/O-MWCNT membranes were fabricated via the NIPS techniques, using H2O and polyethylene glycol (PEG 20 kDa) as non-solvent additives. The SEM cross-sectional images showed that a fully sponge-like morphology of the PES/SPSf membrane can be achieved in the presence of different loadings of O-MWCNTs. This was attributable to the formation of stronger hydrogen bonds between the SPSf polymer and non-solvent additives i.e., H2O, PEG 20kDa and OMWCNTs. The combination of the macrovoid-free morphology and homogenous distribution of high mechanical strength O-MWCNTs in the membrane matrix provided excellent mechanical strength enhancements for PES/SPSf/O-MWCNT membranes. Additionally, pure water flux initially increased from 598 L/m2 .h to 713 L/m2 .h followed by a decline to 578 L/m2 .h upon further increments in O-MWCNT contents, due to agglomeration of O-MWCNTs at higher loadings. The fabricated PES/SPSf/O-MWCNT membranes also displayed superior antifouling properties (FRR > 90%) and antibacterial properties (99% bacterial killing ratio) against E. coli bacteria. The fabricated support fabricfree PES/SPSf/O-MWCNT UF membranes with macrovoid-free sublayer morphologies displayed attractive features for use as UF membranes in the pre-treatment stages of water treatment and as support substrates for the preparation of TFC membranes. In general, sponge-like and macrovoid-free membrane structures are regarded as unfit for use as support membranes for TFC membrane preparation since they increase the membrane’s resistance to water flow, thereby reducing the overall TFC membrane permeability. This assumption has largely been based on sponge-like and macrovoid-free membranes structures achieved through the use of extremely high polymer concentrations, particularly using polysulfone (PSf) polymer. Hence, the sponge-like structures formed are very dense and less porous. Nevertheless, the macrovoid-free PES/SPSf/O-MWCNT membranes produced in this study, consisted of open cellular network microstructures within the membrane sublayer, which could be visualised at higher SEM magnifications. This part of the work therefore investigated the role of hydrophilic, macrovoid-free PES/SPSf and PES/SPSf/O-MWCNT as support membranes on the performance of TFC NF membranes. The TFC NF membranes were prepared via an efficient interfacial polymerization reaction between piperazine (PIP) and trimesoyl chloride (TMC). The deposition of the polyamide thin-film layer was confirmed by ATR-FTIR, SEM, AFM, contact angle and zeta potential measurements. Membrane performance results showed that TFC NF membranes fabricated on PES/SPSf/O-MWCNT support membranes displayed a 35% improvement in pure water flux with comparable salt rejections from those prepared on bare PES/SPSf support membranes. Salt rejection followed the order of Na2SO4 > MgSO4 > NaCl, which is typical for negatively charged NF membranes. It was established that the presence of hydrophilic O-MWCNTs in the support membrane allowed for the formation of a thin polyamide layer on the top surface of the support membrane, which gave rise to enhanced water permeability of the TFC NF membrane and the possibility of polyamide rejection layer within the support membrane pore channels. To further improve the performance of the TFC NF membranes, in particular, the monovalent/bivalent salt selectivity, a mixture of PIP and 2,4-diaminobenzene sulfonic acid (2,4-DABSA) at different weight ratios was prepared in the aqueous solution and reacted with TMC in the organic phase solution. It was found that the addition of low monomer weight ratio of 2,4-DABSA in the amine mixture, lead to the generation of a sulfonated TFC NF membrane with superior membrane performance in terms of pure water permeability (30.2 L/m2 .h), monovalent/bivalent salt selectivity (𝛼NaCl/Na2SO4 = 25.0) at low operating pressures (3 bar) and salt concentrations in the range of brackish waters. This was attributable to the combined presence of sulfonic acid groups on the membrane surface and the formation of the thin polyamide layer. Moreover, sulfonated TFC NF membranes exhibited good antifouling properties against bovine serum albumin (BSA), with FRR of 96.4% after three cycles of fouling and cleaning, with a fairly stable membrane performance over a 10-day period of pure water flux and Na2SO4 rejection testing. Indeed, the use of a macrovoid-free PES/SPSf/O-MWCNT support membrane did not only provide the mechanical strength for the deposition of TFC NF membrane, but also their open, cellular network microstructure, combined with high hydrophilicity and large surface pore sizes were beneficial in the reduction of polyamide layer thickness, and subsequently in the enhancement of TFC NF membrane performance. The study provided insightful information on lesser known aspects of O-MWCNT incorporated polymeric membranes, with regards to membrane structural configurations in relation to the membrane structure-performance relationships. It has been deduced that (i) the right combination of membrane surface characteristics and adsorbate solution chemistry is necessary for an open UF membrane to display reasonable removal efficiencies for low molecular-weight solutes, (ii) the combination of macrovoid-free membrane morphology with good dispersion of O-MWCNTs in the polymer matrix is necessary to realise significant enhancements in the mechanical properties of sulfonated membrane and (iii) formation of a thin sulfonated polyamide layer on top of the hydrophilic PES/SPSf/O-MWCNT support membrane is necessary to achieve high salt selectivity, and allow for the sulfonated TFC NF membrane to be operated at low pressures. / College of Engineering, Science and Technology

Les piles à combustible sont une technologie en pleine expansion dans le domaine du transport automobile.Les membranes polymères les plus utilisées actuellement dans ces systèmes sont celles à base de Nafion.Leur principal point faible se trouve dans leurs performances limitées au-delà de 80°C, où la membranedevient défaillante et l'eau ne peut plus assurer la conduction protonique. Le projet EUBECELL se proposede résoudre ce problème en mettant au point un système de pile à combustible fonctionnant à l'éthanol et àplus de 120°C. Cette thèse s'inscrit dans ce projet et se concentre sur l'élaboration de nouvelles membranespolymères conductrices de protons. Deux voies sont envisagées : l'amélioration des propriétés du Nafion àhaute température et le remplacement du Nafion par un polymère haute performance auquel on donne uneconductivité.L'amélioration du Nafion se fait par l'ajout de conducteurs liquides ioniques protiques (CLIPs), produitsayant donc une conductivité protonique venant s'ajouter à celle du Nafion. Un premier CLIP est synthétisé,caractérisé puis ajouté au Nafion et les performances des membranes obtenues mesurées. Les résultatsencourageants obtenus incitent à synthétiser d'autres CLIPs à partir de la même amine et en variant le contreion.D'autres mélanges Nafion-CLIPs sont ainsi synthétisés et caractérisés.Les polymères hautes performances étudiés ici pour remplacer le Nafion sont dans un premier temps despolysulfones sulfonées. Les polysulfones étant des polymères qui résistent aux températures élevées et lasulfonation leur donnant une conductivité. Pour conserver de meilleures propriétés après sulfonation, nousprocédons à une extrusion du film polymère suivi d'une sulfonation. Nous mettons donc au point unprotocole de sulfonation hétérogène. Les membranes obtenues sont ensuite caractérisées et leursperformances mesurées. Dans un deuxième temps nous travaillons sur des membranes macroporeuses, àforte tenue mécanique, que nous remplissons avec les CLIPs utilisés auparavant. Les membranes sont alorsaussi caractérisées et leurs performances mesurées. / Fuel cells are an ever-expanding technology in the field of automotive transport. The polymer membranesthat are currently the most widely used are Nafion-based membranes. Their weakest point is their drastic lossof performances beyond the threshold of 80°C, where the membranes fails and water cannot ensure protonconduction anymore. The EUBECELLproject sets to achieve making a fuel cell system functioning above120°C and using ethanol as a fuel. This thesis is part of the project and focus on elaborating new protonconductingpolymer membranes. Two main ways are explored: improving the performances of Nafion athigh temperature and replacing Nafion with conductivity-added high-performance polymers.Improving Nafion's performances is achieved by adding proton conducting ionic liquids (PCILs), productsthat have a proton conductivity that adds to Nafion's own. A first PCIL is synthesized, characterized and thenadded to Nafion, the resulting membranes' performances then measured. The encouraging results that weobtain makes us synthesize more PCILs, from the same amine than the first, varying the counter-ion. OtherNafion-PCIL mixes are made and then characterized.The high-performance polymer investigated for replacing Nafion are, first, sulfonated polysulfones.Polysulfones are high-temperature resistant polymers and sulfonation gives them conductivity. To keep betterproperties after the sulfonation, we proceed to extrude the films before sulfonating them. We elaborate anheterogeneous sulfonation protocol for them. The resulting membranes are then characterized and theirperformances measured. Second, we work on macroporous membranes, with high mechanical strength,which we fill with the PCILs that we previously used. The membranes are then also characterized and theirperformances measured.