This thesis focuses on the state-of-the-art spectroscopic approaches in studying polymer electrolytes for proton exchange membrane fuel cells. With the aim to optimize architectural and chemical design of hydrogen fuel cells, a variety of perfluorosulfonic acid (PFSA) membranes were explored to establish characteristics that ultimately improve PFSA electrolyte performance. The results of the detailed spectroscopic analyses helped to unveil a structure performance relationship. Solid-state nuclear magnetic resonance (ssNMR) spectroscopy was used to distinguish F and C environments, while scanning transmission X-ray microscopy coupled with X-ray absorption spectroscopy provided complementary chemical structural information with direct access to S and O environments. The combination of these two techniques provided advantages in identifying subtle chemical alterations in PFSAs. Furthermore, a novel ssNMR technique was developed with the purpose of probing local dynamics from the polymer perspective. This ¬¬19F dipolar recoupling ssNMR approach was validated and applied to PFSA membranes by monitoring the normalized double quantum build-up curves as a function of relative humidity (%RH) and temperature, and the polymer side chain showed higher local motion as response to temperature and %RH elevation compared to the backbone. The effective dipolar coupling constant was extracted to represent local dynamics and compared amongst tested PFSAs. A standardized metric, the dynamic order parameter, was also introduced and applied to the materials to quantitatively compare them within the same class. This new method provided an alternative way to extract site-specific local dynamics profile for materials with multiple resonances. Additionally, the combination of in situ fuel cell performance evaluation and ex situ ssNMR characterization created a connection between fundamental chemistry and bulk electrochemical measurements. As the first study to correlate these physicochemical properties to material performances, this work parameterized the structural impact at a molecular level and provided insight into improving polymer electrolyte materials. / Thesis / Doctor of Philosophy (PhD) / Proton exchange membrane fuel cells, which help to reduce the reliance on fossil fuels by locally producing only water and heat, have received a significant amount of research attention as an alternative power generator for vehicular and stand-alone energy applications. Perfluorosulfonic acid (PFSA) membranes, the most common commercial polymer electrolyte materials, have been investigated using modern analytical spectroscopies. Solid-state nuclear magnetic resonance (ssNMR) spectroscopy and synchrotron-based scanning transmission X-ray microscopy were used in elucidating material compositions with complementary information. Moreover, an advanced ssNMR method was developed and applied to a variety of PFSAs. Polymer backbones and side chains were separated spectroscopically, and were distinguished based on different local dynamics profiles extracted from the ssNMR experiments. Additionally, bulk material performance evaluations from electrochemical analyses were correlated to PFSA side chain local dynamics profiles. The integrated spectroscopic study illustrated in this thesis provided insight into understanding the structure-performance relationship of PFSA electrolytes.

A solid electrolyte is a crucial component of any solid state battery. Polymer gel electrolytes have received increasing attention in recent years due to their high ionic conductivity, flexibility, and improved safety. However, a general tradeoff usually exists between the mechanical properties and ionic conductivity in such materials. Molecular ionic composites (MICs) are a new type of rigid polymer gel electrolyte based on ionic liquids (ILs) and a double helical rigid-rod polyamide, poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) (PBDT). MICs have high ionic conductivity, high thermal and electrochemical stability, and widely tunable and high tensile modulus even at relatively low polymer content. MICs show great promise as solid electrolytes for solid state batteries. This dissertation describes the preparation and characterization of MIC electrolyte membranes. These transparent, flexible, and tough membranes are prepared through a convenient solvent casting process. A large variety of ILs, including both hydrophilic and hydrophobic examples, are suitable to prepare MIC electrolyte membranes by adjusting the solvents used in the casting process. The prepared membranes show a biphasic internal structure consisting of a PBDT-rich “bundle” phase and an IL-rich “puddle” (interconnected fluid) phase. Similar to the bulk MIC ingots prepared previously through an interfacial ion exchange process, the MIC membranes also have high ionic conductivity and tensile modulus at low polymer content. A MIC membrane composed of 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Pyr₁₄TFSI), LiTFSI, and PBDT in a mass ratio of 8:1:1 is tested as a solid electrolyte for lithium metal batteries. This electrolyte membrane shows high ionic conductivity and high rigidity. The shear storage modulus of this MIC electrolyte membrane only decreases by 35% when heated to 200 °C from room temperature, suggesting great mechanical stability at high temperatures. The electrolyte membrane is successfully used as solid electrolyte for a Li/LiFePO₄ battery working over a large temperature range from 23 to 150 °C, and the discharge capacity retention of the cell is as high as 99% after 50 cycles at 150 °C. By replacing the IL in the MIC with a charge-neutral liquid, single-ion-conducting polymer gel electrolyte composed of PBDT and polyethylene glycol (PEG) oligomer are obtained. Similar to the MICs, these single-ion-conducting materials also have high Young’s modulus and biphasic internal structures. This study reveals that the counter ion (Li⁺ or Na⁺) of the PBDT has a major effect on both the ionic conductivity and modulus of the materials. Due to the stronger intermolecular interactions, LiPBDT-PEG demonstrates lower ionic conductivity but higher Young’s modulus. This dissertation also evaluates the viability of rigid PBDT as a polymer binder for electrodes. Aqueous solution-processed LiFePO₄ electrodes with only 3 wt% PBDT demonstrate stable cycling over 1000 cycles without obvious capacity decay, and the rate capacity of these aqueous solution-processed electrodes are comparable to the electrodes prepared with conventional poly(vinylidene difluoride) (PVDF) as the binder, suggesting PBDT can serve as a potential electrode binder for commercial applications. / A solid electrolyte is a crucial component of any solid state battery. Polymer gel electrolytes have received increasing attention in recent years due to their high ionic conductivity, flexibility, and improved safety. However, a general tradeoff usually exists between the mechanical properties and ionic conductivity in such materials. Molecular ionic composites (MICs) are a new type of rigid polymer gel electrolyte based on ionic liquids (ILs) and a double helical rigid-rod polyamide, poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) (PBDT). MICs have high ionic conductivity, high thermal and electrochemical stability, and widely tunable and high tensile modulus even at relatively low polymer content. MICs show great promise as solid electrolytes for solid state batteries. This dissertation describes the preparation and characterization of MIC electrolyte membranes. These transparent, flexible, and tough membranes are prepared through a convenient solvent casting process. A large variety of ILs, including both hydrophilic and hydrophobic examples, are suitable to prepare MIC electrolyte membranes by adjusting the solvents used in the casting process. The prepared membranes show a biphasic internal structure consisting of a PBDT-rich "bundle" phase and an IL-rich "puddle" (interconnected fluid) phase. Similar to the bulk MIC ingots prepared previously through an interfacial ion exchange process, the MIC membranes also have high ionic conductivity and tensile modulus at low polymer content. A MIC membrane composed of 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Pyr14TFSI), LiTFSI, and PBDT in a mass ratio of 8:1:1 is tested as a solid electrolyte for lithium metal batteries. This electrolyte membrane shows high ionic conductivity and high rigidity. The shear storage modulus of this MIC electrolyte membrane only decreases by 35% when heated to 200 °C from room temperature, suggesting great mechanical stability at high temperatures. The electrolyte membrane is successfully used as solid electrolyte for a Li/LiFePO4 battery working over a large temperature range from 23 to 150 °C, and the discharge capacity retention of the cell is as high as 99% after 50 cycles at 150 °C. By replacing the IL in the MIC with a charge-neutral liquid, single-ion-conducting polymer gel electrolyte composed of PBDT and polyethylene glycol (PEG) oligomer are obtained. Similar to the MICs, these single-ion-conducting materials also have high Young's modulus and biphasic internal structures. This study reveals that the counter ion (Li+ or Na+) of the PBDT has a major effect on both the ionic conductivity and modulus of the materials. Due to the stronger intermolecular interactions, LiPBDT-PEG demonstrates lower ionic conductivity but higher Young's modulus. This dissertation also evaluates the viability of rigid PBDT as a polymer binder for electrodes. Aqueous solution-processed LiFePO4 electrodes with only 3 wt% PBDT demonstrate stable cycling over 1000 cycles without obvious capacity decay, and the rate capacity of these aqueous solution-processed electrodes are comparable to the electrodes prepared with conventional poly(vinylidene difluoride) (PVDF) as the binder, suggesting PBDT can serve as a potential electrode binder for commercial applications. / Doctor of Philosophy / Solid state batteries are widely considered as the pathway to next-generation high performance batteries. In a solid state lithium battery, the liquid organic carbonate electrolyte is replaced with a solid electrolyte. Polymer gel electrolytes are a type of potential solid electrolyte that have been widely studied in recent decades. This dissertation describes the application of a rigid polymer in preparing polymer gel electrolytes. This highly charged and rigid polymer is a water-soluble polyamide known as PBDT with a double helical structure akin to DNA. Through a modified solvent casting process, a new type of polymer gel electrolyte, known as molecular ionic composite (MIC), is prepared using PBDT and various ionic liquids. Extra salt (which can contain lithium) can also be incorporated into the MIC membrane. This type of new polymer gel electrolyte is rigid with high tensile modulus even at high temperatures and low polymer (PBDT) content. MIC membranes are used as solid electrolytes for lithium metal batteries working over a wide temperature range from 23 to 150 °C. A rigid polymer gel electrolyte can also be obtained by replacing the ionic liquids in MICs with polyethylene glycol. Besides the application in preparing solid electrolytes, PBDT is also evaluated as a polymer binder for aqueous processed electrodes. Preliminary study reveals that PBDT holds great potential for a range of commercial energy storage applications.

Hydrogen fuel cells, and notably the polymer electrolyte fuel cell (PEFC), present an important opportunity to reduce greenhouse gas emissions within a range of sectors of society, particularly for transportation and portable products. Despite several decades of research and development, there exist three main hurdles to full commercialisation; namely infrastructure, costs, and durability. This thesis considers the latter of these. The lifetime target for an automotive fuel cell power plant is to survive 5000 hours of usage before significant performance loss; current demonstration projects have only accomplished half of this target, often due to PEFC stack component degradation. Health management techniques have been identified as an opportunity to overcome the durability limitations. By monitoring the PEFC for faulty operation, it is hoped that control actions can be made to restore or maintain performance, and achieve the desired lifetime durability. This thesis presents fault detection and diagnosis approaches with the goal of isolating a range of component degradation modes from within the PEFC construction. Fault detection is achieved through residual analysis against an electrochemical model of healthy stack condition. An expert knowledge-based diagnostic approach is developed for fault isolation. This analysis is enabled through fuzzy logic calculations, which allows for computational reasoning against linguistic terminology and expert understanding of degradation phenomena. An experimental test bench has been utilised to test the health management processes, and demonstrate functionality. Through different steady-state and dynamic loading conditions, including a simulation of automotive application, diagnosis results can be observed for PEFC degradation cases. This research contributes to the areas of reliability analysis and health management of PEFC fuel cells. Established PEFC models have been updated to represent more accurately an application PEFC. The fuzzy logic knowledge-based diagnostic is the greatest novel contribution, with no examples of this application in the literature.

Τα κελιά καυσίμου είναι ηλεκτροχημικές διατάξεις που μετατρέπουν με συνεχή τρόπο τη χημική ενέργεια ενός καυσίμου και ενός οξειδωτικού σε ηλεκτρική με ταυτόχρονη παραγωγή νερού. Μια πολύ σημαντική κατηγορία κελιών είναι είναι τα κελιά καυσίμου πολυμερικής μεβράνης.Λειτουργία σε θερμοκρασίες πάνω από 100ºC έχει διάφορα πλεονεκτήματα.Ένας ιδανικός πολυμερικός ηλεκτρολύτης θα πρέπει να είναι ανθεκτικός, να έχει καλές μηχανικές ιδιότητες, υψηλή θερμική και οξειδωτική σταθερότητα και υψηλή ιοντική αγωγιμότητα, η οποία εξαρτάται από την ικανότητά του να εμποτίζεται με κάποιο μέσο όπως ένα ισχυρό οξύ, π.χ. το φωσφορικό οξύ. Το πρώτο μέρος της παρούσας διατριβής αφορά τη σύνθεση αρωματικών πολυαιθέρων που φέρουν πολικές ομάδες πυριδίνης στη κύρια αλυσίδα, μαζί με πλευρικές σουλφονομάδες με στόχο τη δημιουργία μιας μεμβράνης που θα είναι ικανή να απορροφά φωσφορικό οξύ αλλά και νερό.Το οξύ θα διασφαλίσει υψηλές τιμές ιοντικής αγωγιμότητας ενώ η παρουσία νερού θα αυξήσει την ιοντική αγωγιμότητα.Επιπλέον παρασκευάστηκαν σύνθετες μεμβράνες, με την εισαγωγή ανόργανων εγκλεισμάτων(τροποποιημένος με όξινες σουλφονικές ομάδες μοντμοριλλονίτης (SO3-MMT) στην υδρόφοβη πολυμερική μήτρα του TPS®. Στο δεύτερο μέρος της παρούσας διατριβής αναπτύχθηκαν θερμικά διασυνδεδεμένοι πολυμερικοί ηλεκτρολύτες. Συντέθηκαν 3 νέα μονομερή και συμπολυμερή με πλευρικές ομάδες στυρολίου στη κύρια αλυσίδα.Η θερμική κατεργασία των συμπολυμερών σε υψηλή θερμοκρασία οδήγησε σε διασύνδεση της δομής χωρίς τη χρήση θερμικών εκκινητών. Ακολούθησε πλήρης χαρακτηρισμός των ιδιοτήτων όλων των νέων δομών. Τέλος, έλαβε χώρα εφαρμογή και μελέτη της απόδοσης σε μοναδιαία κυψελίδα καυσίμου. / Fuel cells are devices that convert the chemical energy of a fuel and an oxidant to electrical with simultaneous production of water. Polymer Exchange Membrane Fuel Cell (PEMFC) represents an important class of fuel cells.Operating above 150ºC has many advantages. The ideal polymer electrolyte should exhibit long term durability, good mechanical properties, high thermal/chemical and oxidative stability and high ionic conductivity which depends on the ability to be doped with a strong acid. In the first part of this thesis aromatic copolymers bearing in the main chain basic pyridine groups combined with side chain acidic sulfonate groups were synthesized, making them capable of absorbing phosphoric acid and water. The phosphoric acid will ensure high proton conductivities while presence of water will further improve the performance of the cell. Furthermore composite membranes were prepared by adding inorganic fillers( functionalized montmorrilonite with sulfonic groups, SO3-MMT)in TPS® polymer matrix. In the second part of this thesis thermal cross- linked polymer electrolytes were developed for their use in high temperature PEMFC.Three new monomers and a series of copolymers in high temperature led to crosslinking without using thermal initiators.These properties of all the new structures were fully characterized with conventional techniques. thermal cross-linked copolymers were .chosen for the membrane electrode assembly (MEA) preparation for a preliminary study of the performance of the cell in high temperatures.

A reação de redução de oxigênio (RRO) foi estudada em eletrocatalisadores com estruturas do tipo core-shell formadas por monocamadas de Pt depositadas sobre nanopartículas a base de Au e Pd, e estruturas hollow formadas de Pt. As nanopartículas core-shell foram sintetizadas por deposição em regime de subtensão utilizando-se substratos de Au e Pd. As estruturas hollow foram preparadas a partir de nanopartículas core-shell de Pt sobre Ni ou Co, seguido por ciclagem eletroquímica em eletrólito ácido. Os eletrocatalisadores foram caracterizados utilizando-se as técnicas de Energia Dispersiva, Difração e Espectroscopia de Absorção de Raios X e Microscopia Eletrônica de Transmissão. Os testes eletroquímicos foram feitos voltametria cíclica e curvas de polarização em eletrodo rotatório. Os catalisadores do tipo core-shell mostraram uma alta atividade para a RRO, o que foi associado a mudanças nas propriedades eletrônicas e geométricas da Pt, causadas pela presença dos átomos de Au e Pd, que conduzem a uma menor força de adsorção Pt-O. Neste caso, temos um melhor balanço de reatividade para as tendências opostas de quebra e formação de ligações nos intermediários reacionais adsorvidos na superficie do eletrocatalisador. As nanopartículas de Pt hollow apresentaram maior atividade que o electrocalisador de Pt/C. Isto foi atribuído aos fenômenos de contração da rede cristalina e abaixamento do centro de banda d da Pt devido à ligação da Pt com Ni ou Co remanescente na partícula. Estas estruturas mostraram que é possível o desenvolvimento de eletrocalisadores com baixa carga de platina, mas com atividade superior ao do material no estado-da-arte de Pt/C, através de modificações na estrutura e composição da nanopartícula. / The oxygen reduction reaction (ORR) was studied on eletrocatalysts with core-shell structures formed by Pt monolayers deposited on Au and Pd, and by hollow strutures of Pt. The core-shell nanoparticles were synthesized by the Under Potention Deposition technique, using Au and Pd as substrates. The hollow structures were prepared starting foram core-shell nanoparticles of Pt deposited on Ni or Co, followed by electrochemical cycling in acid media. The eletrocatalysts were characterized using techniques of X Ray Diffration, Energy Dispersive X Ray Spectroscopy, X Ray Absorpion Spectroscopy, and Transmission Electron Microscopy. The electrochemical tests were cyclic voltammetry, and polarization curves with rotating disk electrode. The core-shell electrocatalysts howed high activity for the ORR, this increase being associated with changes in the geometric and electronic properties of Pt, caused by the presence of Au and Pd atoms, leading to a lower adsorpion strength of Pt-O. This effect conducts to a better balance of reactivity for the two opposing tendencies of breaking and bond formation in the reaction intermediates adsorbed on the catalyst surface. The Pt hollow nanoparticles showed higher activity in relation to that of Pt/C, which was attributed to the effects of contraction of the Pt lattice and the Pt electronic strutucture modification, which results ind down-shift of the Pt d-band center, leading to a lower Pt-O adsorption strength. This work has demonstrated that it is possible to design electrocatalyst structures with low Pt loading, but with higher electrocatalytic activity compared to that of the state-of-the-art Pt/C material, using changes in the nanoparticle structure and composition.

O envelhecimento dos eletrocatalisadores utilizados em cátodos de células a combustível de eletrólito polimérico (PEMFCs) é um dos principais fatores que restringem sua aplicação como conversores de energia em larga escala. Esse trabalho visa contribuir para o aprimoramento da estabilidade de nanopartículas de platina (NPs de Pt) por meio da modificação do suporte catalítico aos quais encontram-se impregnadas. Desse modo, foram realizadas sínteses de suportes catalíticos baseados em óxidos de molibdênio (MoO3 e MoO2) ancorados em carbono Vulcan® XC72-R, sendo os materiais produzidos caracterizados física, estrutural e eletroquimicamente antes e após a impregnação de NPs de Pt. Para investigar a estabilidade dos eletrocatalisadores, foi realizado um teste de degradação eletroquímico acelerado, o qual consistiu em aplicar os ciclos de potenciais entre 0,6 e 1,0 V vs. ERH por curto período de tempo. Os resultados mostraram que os métodos de síntese utilizados foram satisfatórios, levando a formação dos catalisadores com as proporções bem próximas das requeridas. O catalisador Pt/MoO3-C apresentou a maior atividade específica frente a reação de redução de oxigênio (RRO), atribuída a efeitos sinérgicos metal/suporte. Quando investigada a estabilidade dos materiais frente ao teste de degradação eletroquímico acelerado, observou-se que, a princípio, nenhum dos óxidos de molibdênio diminui a extensão da degradação da platina. Analisando-se as atividades específicas frente à RRO para cada catalisador antes e após o envelhecimento eletroquímico, foi observado que Pt/MoO2-C apresentou-se como o material mais estável dentre os demais. / The aging of Pt based electrocatalysts used in the polymer electrolyte fuel cell (PEMFC) cathodes is one of the main issues that restrict its wide application as energy converters. This work aims to contribute to the improvement of the stability of platinum nanoparticles (Pt NPs) by modification of the catalyst support at which they are impregnated. Thus, syntheses of catalyst supports based on molybdenum oxide (MoO3 and MoO2) anchored on Vulcan® XC72-R carbon were carried out and the produced materials were characterized physically, structurally and electrochemically prior and after impregnation of the Pt NPs. To investigate their stability, an electrochemical accelerated degradation test was performed, which consisted of applying a large number of short duration potential cycling steps between 0.6 and 1.0 V vs. RHE. The results showed that the synthetic methods used here were satisfactory, leading to the formation of catalysts with compositions near to those expected. The Pt/MoO3-C catalyst showed the highest specific activity toward the oxygen reduction reaction (ORR), and this was attributed to metal/support synergistic effects. When the stability against electrochemical accelerated degradation test of the materials was investigated, it was observed that, in principle, none of the molybdenum oxides really decreases the extent of platinum degradation. However, comparing the specific activities towards the ORR for each catalyst, before and after electrochemical aging, it is concluded that Pt/MoO2-C is the most stable material among all others.

Polymer electrolytes are widely used as ion transport media in vital applications such as energy storage devices and electrochemical displays. To further develop these materials, it is important to understand their ionic conductivity mechanisms. It has long been thought that ionic conduction in a polymer electrolyte occurs in the amorphous phase, while the crystalline phase is insulating. However, this picture has recently been challenged by the discovery of the crystalline system LiXF6∙PEO6 (X=P, As or Sb) which exhibits higher conductivity than its amorphous counterpart. Their structures comprise interlocking hemi-helical PEO-chain pairs containing Li+ ions and separating them from the XF6- anions. The first Molecular Dynamics (MD) simulation study of the LiPF6∙PEO6 system is presented in this thesis. Although its conductivity is too low for most applications at ambient temperature, it can be enhanced by iso- and aliovalent anion doping. It is shown that the diffraction-determined structure is well reproduced on simulating the system using an infinite PEO-chain model. The Li-Oet coordination number here becomes 6 instead of 5; minor changes also occur in the polymer backbone configuration. The crystallographic asymmetric unit and diffraction profiles are also reproduced. On simulating a shorter-chain system (n=22), more resembling the real material, the structure retains its double hemi-helices, but the polymer adopts a more relaxed conformation, facilitating the formation of Li+-PF6- pairs. Infinite-chain simulation shows the ionic conduction to be dominated by anion motion, in contrast to earlier NMR results. The effects of doping are also reproduced. Shortening the polymer chain-length has the effect of raising the transport number for lithium, thereby bring it into better agreement with experiment. It can be concluded that it is critical to take polymer chain-length and chain-termination into account when modelling ionic conductivity mechanisms in crystalline polymer electrolytes.

This thesis studies the performance of solid polymer lithium batteries from room temperature to elevated temperatures using mainly electrochemical techniques, with emphasis on the bulk properties of the polymer electrolyte and the electrode-electrolyte interfaces. Its contributions include: 1) Demonstrated the relationship between polymer segmental motion and ionic conductivity indeed has a Vogel-Tammann-Fulcher (VTF) dependence, and improved the conductivity of the graft copolymer electrolyte (GCE) by almost an order of magnitude by changing the ion-conducting block from poly(oxyethylene) methacrylate (POEM) to a block with a lower glass transition temperature \((T_g)\) poly(oxyethylene) acrylate (POEA). 2) Identified the rate-limiting step in the battery occurs at the cathode-electrolyte interface using both full cell and symmetric cell electrochemical impedance spectroscopy (EIS), improved the battery rate capability by using the GCE as both the electrolyte and the cathode binder to reduce the resistance at the cathode-electrolyte interface, and used TEM and SEM to visualize the polymer-particle interface (full cells with \(LiFePO_4\) as the cathode active material and lithium metal as the anode were assembled and tested). 3) Applied the solid polymer battery to oil and gas drilling application, performed high temperature (up to 210°C) cycling (both isothermal and thermal cycling), and demonstrated for the first time, current exchange between a solid polymer electrolyte and a liquid lithium metal. Both the cell open-circuit-voltage (OCV) and the overall GCE mass remained stable up to 200°C, suggesting that the GCE is electrochemically and gravimetrically stable at high temperatures. Used full cell EIS to study the behavior of the various battery parameters as a function of cycling and temperature. 4) Identified the thermal instability of the cell was due to the reactivity of lithium metal and its passivation film at high temperatures, and used Li/GCE/Li symmetric cell EIS to study the thermal stability of the anode-electrolyte interface, which was responsible for the fast capacity fade observed at high temperatures. 5) Proposed a new electrolyte material and a new battery design called polymer ionic liquid (PIL) battery that can dramatically improve the safety, energy density, and rate capability of rechargeable lithium batteries. / Engineering and Applied Sciences

A procedure is presented to analyze select geometric and effective properties of the porous transport layer (PTL) of the polymer electrolyte membrane fuel cell (PEMFC) in com- pressed and uncompressed states using micro-computed X-ray tomography (Micro CT). A method of compression using a novel device design was employed to mimic the non-homogeneous compression conditions found in functioning fuel cells. The process also features open source image processing and CFD analysis through the use of software packages Fiji and OpenFOAM (proprietary software is also used such as Matlab). Tomographic images of a PTL sample in different compressive states are first analyzed by measuring local porosity values in the through-plane and both in- plane directions. The objective of this study was to develop a method for imaging the PTL structure to show directionality within its properties using relatively inexpensive and non-destructional means. Three different PTL types were tested, one without any additives, one with Polytetrafluoroethylene (PTFE) and one with PTFE and a microporous layer (MPL). Non-homogeneous porosity was shown to exist with the highest and least variable porosity values obtained from the in-plane direction that was in-line with the direction of fibres. Porosity values compared well with values obtained from the literature. The profile of the PTL with MPL added was unattainable using this procedure as the resolution of the Micro CT was too low to resolve its pore space. The next stage involved the effective properties analysis which included effective electronic conductivity and effective diffusivity. It was found that the through-plane values for the effective electronic conductivity study were higher than expected. The ratio between through-plane and in-plane was found to be much higher than expected from literature. Lack of sufficient resolution of fibre contacts has been shown to play a role in this discrepancy. These contact problems were shown not too affect measurements of diffusivity in the pore phase. The in-plane direction parallel to the direction of fibres was found to have the highest values of effective transport properties. Effective diffusivity ratios of between 0.1 and 0.37 were found to be reasonable with the limited experimental evidence found in literature. The it was found that the Bruggeman relation for calculating diffusivity and percolation theory by Tomadakis and Sotirchos over predicted the values for diffusion within the PTL and it is suggested that these theories are not suitable for predicting diffusivity for this material. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2012-02-02 15:46:29.395

Polymer electrolyte membrane fuel cells (PEMFCs) have been looked as potential alternative energy conversion devices to conventional energy conversion systems such as combustion engines. Proton conducting membranes (PEMs) are one critical component of PEMFCs. The development of novel electrolyte membranes with dense structure, good mechanical flexibility, and high proton conductivity, but with little or no dependence on humidity at temperatures above 100¡ãC remains an important challenge to the realization of practical PEM fuel cells. In this thesis, to solve the technical difficulties existing in current high temperature PEM systems based on phosphoric acid and imidazole, a new type of proton conducting species 1H-1,2,3-triazole has been explored, and proved to have high proton conductivity and also enough electrochemical stability for fuel cell applications. In further experiments, effective methods have been developed to synthesize triazole derivatives and polymers. The properties of the synthesized polymers have studied and reported in this thesis. Preliminary computational simulations have also been performed to study the proton conducting mechanism to provide intrinsic information of the proton conducting process in 1H-1,2,3-triazole. In the final part, research works on other proton conducting species including H3PO4 and other heterocycles have been reported.