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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.

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

In view of the unfavorable panorama of actual energy supply practices, alternative sustainable energy sources and conversion approaches have acquired noteworthy significance in recent years. Among these, proton exchange membrane fuel cells (PEMFCs) are being considered as a pivotal building block in the transition towards a sustainable energy economy. The proton exchange membrane (PEM) is a vital component, as well as a performance-limiting factor, of the PEMFC. Consequently, the development of high performance PEM materials is of upmost importance for the advance of the PEMFC field. In this work, alternative PEM materials based on semi-interpenetrated networks from blends of poly(vinyledene fluoride) (PVDF) and sulfonated crosslinked acrylic polyelectrolytes (PE), as well as tri-phase PVDF/PE/zirconium-based composites, are studied. To alleviate the burden resulting from the vast number of possible combinations of the different precursors utilized in the preparation of the membranes, custom high throughput screening systems have been developed for their characterization. By coupling the data spaces obtained via these systems with the appropriate statistical and data analysis tools it was found that, despite not being directly involved in the proton transport process, the inert PVDF phase plays a major role on proton conductivity. Particularly, a univocal inverse correlation between the PVDF crystalline characteristics (i.e., crystallinity and crystallite size) and melt viscosity, and membrane proton conductivity was discovered. Membranes based on highly crystalline and viscous PVDF homopolymers exhibited reduced proton conductivity due to precluded segmental motion of the PE chains during crosslinking. In addition, a maximum effective amount of PE (55-60wt%) beneficial for proton conductivity was revealed. In the case of composite membranes, despite the fact that nanoparticle dispersion was thermodynamically limited, a general improvement in proton conductivity was evidenced at low to medium nanoparticle loadings (0.5 to 1wt%) in comparison to non-hybrid PVDF/PE references. This beneficial effect was particularly noticeable in membranes based on PVDF homopolymers (7% to 14.3% increment), where the nanoparticles induced a "healing" effect by providing proton-conducting paths between non-crosslinked PE channels separated by dense PVDF areas resulting from large PVDF crystallites. In general, the results presented herein are promising for the development of new cost-effective alternative PEMs.

Over the past three decades, the steady decrease in fossil energy resources, combined with a sustained increase in the demand for clean energy, has led the scientific community to develop new ways to produce energy. As is well known, one of the main challenges to overcome with fossil fuel-based energy sources is the reduction or even elimination of pollutant gases in the atmosphere. Although some advances have helped to slow the emission of greenhouse gases into the atmosphere (e.g., electric cars and more fuel-efficient gas-burning automobiles), most experts agree that it is not enough. Proton Exchange Membrane (PEM) fuel cells have been widely recognized as a potentially viable alternative for portable and stationary power generation, as well as for transportation. However, the widespread commercialization Proton Exchange Membrane Fuel Cells (PEMFCs) involves a thorough understanding of complex scientific and technological issues. This study investigated the various structure-property relationships and materials durability parameters associated with PEMFC development. First, the correlation between perfluorinated ionomer membranes and processing/performance issues in fuel cell systems was investigated. As confirmed by small-angle X-ray scattering data, impedance analysis, and dynamic mechanical analysis, solution processing with mixed organic-inorganic counterions was found to be effective in producing highly arranged perfluorinated sulfonic acid ionomer (PFSI) membranes with more favorable organization of the ionic domain. Moreover, thermal annealing was shown to enhance the proton mobility, thereby facilitating reorganization of the polymer backbone and the hydrophilic region for improved crystallinity and proton transport properties. This research also confirmed an increase in water uptake in the solution-processed membranes under investigation, which correlated to an increase in proton conductivity. Thus, annealing and solution-processing techniques were shown to be viable ways for controlling morphology and modulating the properties/performance of PFSI membranes. Second, this study investigated the role of the morphology on water and proton transport in perfluorinated ionomers. When annealed at high temperatures, a significant decrease in water uptake and an increase in crystallinity were observed, both of which are detrimental to fuel cell performance. Additionally, controlling the drying process was found to be crucial for optimizing the properties and performance of these membranes, since drying at temperatures close or above the α-relaxation temperature causes a major reorganization within the ionic domains. Third, although many investigations have looked at key PEMFC components, (e.g., the membrane, the catalyst, and the bipolar plates), there have been few studies of more "minor" components—namely, the performance and durability of seals, sealants, and adhesives, which are also exposed to harsh environmental conditions. When seals degrade or fail, reactant gases leak or are mixed, it can degrade the membrane electrode assembly (MEA), leading to a performance decrease in fuel cell stack performance. This portion of the research used degradation studies of certain proprietary elastomeric materials used as seals to investigate their overall stability and performance in fuel cell environments with applied mechanical stresses. Additionally, characterization of the mechanical and viscoelastic properties of these materials was conducted in order to predict the durability based on accelerated aging simulations as well. Continuous stress relaxation (CSR) characterization was performed on molded seals over a wide range of aging conditions using a customized CSR fixture. The effects of temperature, stress, and environmental conditions are reported in terms of changes in momentary and stress relaxations, chain scission and secondary crosslink formation. Aging studies provided insights on how anti-degradants or additives affect the performance and properties of sealing materials, as well as how a variety of environmental considerations might be improved to extend the lifetime of these elastomers. / Ph. D.

In recent years an emphasis has been placed on the development of alternative and clean energy sources to reduce the global use of fossil fuels. One of these alternatives entails the use of H2 as an energy carrier, which can be obtained amongst others using thermochemical processes, for example the hybrid sulphur process (HyS). The HyS process is based on the thermal decomposition of sulphuric acid into water, sulphur dioxide and oxygen. The subsequent chemical conversion of the sulphur dioxide saturated water back to sulphuric acid and hydrogen is achieved in an electrolyser using a platinum coated proton exchange membrane. This depolarised electrolysis requires a theoretical voltage of only 0.158 V compared to water electrolysis requiring approximately 1.23 V. One of the steps in the development of this technology at the North-West University, entailed the establishment of the platinum coating technology which entailed two steps; firstly using newly obtained equipment to manufacture the membrane electro catalyst assemblies (MEA’s) and gas diffusion electrodes (GDE’s) and secondly to test these MEA’s and GDE’s using sulphur dioxide depolarized electrolysis by comparing the manufactured MEA’s and GDE’s to commercially available MEA’s and GDE’s. Different MEA’s and GDE’s were manufactured using both a screen printing (for the microporous layer deposition) and a spraying technique. The catalyst loadings were varied as well as the type and thickness of the proton exchange membranes used. The proton exchange membranes that were included in this study were Nafion 117®, sPSU-PBIOO and SfS-PBIOO membranes whereas the gas diffusion layer consisted of carbon paper with varying thicknesses (EC-TP01-030 – 0.11 mm and EC-TP01-060 – 0.19mm). MEA and GDE were prepared by first preparing an ink that was used both for MEA and GDE spraying. The MEA’s were prepared by spraying various catalyst coatings onto the proton exchange membranes containing 0.3, 0.6 and 0.9 mg/cm2 platinum respectively. The GDE’s were first coated by a micro porous carbon layer using the screen printing technique in order to attain a suitable surface for catalyst deposition. Using the spraying technique GDE’s containing 0.3, 0.6, 0.9 mg/cm2 platinum were prepared. After SEM analysis, the MEA’s and GDE’s performance was measured using SO2 depolarized electrolysis. From the electrolysis experiments, the voltage vs. current density generated during operation, the hydrogen production, the sulphuric acid generation and the hydrogen production efficiency was obtained. From the results it became clear that while the catalyst loading had little effect on performance there were a number of factors that did have a significant influence. These included the type of proton exchange membrane, the membrane thickness and whether the catalyst coating was applied to the proton exchange membrane (MEA) or to the gas diffusion layer (GDE). During SO2 depolarized electrolysis VI curves were generated which gave an indication of the performance of the GDE’s and MEA’s. The best preforming GDE was GDE-3 (0.46V @ 320 mA/cm2), which included a GDE EC-TP01-060, while the best preforming MEA’s were NAF-4 (0.69V @ 320mA/cm2) consisting of a Nafion117 based MEA and PBI-1 (0.43V @ 320mA/cm2) made from a sPSU-PBIOO blended membrane. During hydrogen production it became clear that the GDE’s produced the most hydrogen (best was GDE-02 a in house manufactured GDE yielding 67.3 mL/min @ 0.8V), followed by the Nafion® MEA’s (best was NAF-4 a commercial MEA yielding 57.61 mL/min @ 0.74V) and the PBI based MEA’s. , (best was PBI-2 with 67.11 mL/min @ 0.88V). Due to the small amounts of acid produced and the SO2 crossover, a significant error margin was observed when measuring the amount of sulphuric acid produced. Nonetheless, a direct correlation could still be seen between the acid and the hydrogen production as had been expected from literature. The highest sulphuric acid concentrations produced using the tested GDE’s and MEA’s from this study were the in-house manufactured GDE-01 (3.572mol/L @ 0.8V), the commercial NAF-4 (4.456mol/L @ 0.64V) and the in-house manufactured PBI-2 (3.344mol/L @ 0.8V). The overall efficiency of the GDE’s were similar, ranging from less than 10% at low voltages (± 0.6V) increasing to approximately 60% at ± 0.8V. For the MEA’s larger variation was observed with NAF-4 reaching efficiencies of nearly 80% at 0.7V. In terms of consistency of performance it was shown that the Nafion MEA’s preformed most consistently followed by the GDE’s and lastly the PBI based MEA’s which for the PBI based membranes can probably be ascribed to the significant difference in thickness of the thin PBI vs. the Nafion based membranes. In summary the study has shown the results between the commercially obtained and the in-house manufactured GDE’s and MEA’s were comparable confirming the suitability of the coating techniques evaluated in this study. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

In recent years an emphasis has been placed on the development of alternative and clean energy sources to reduce the global use of fossil fuels. One of these alternatives entails the use of H2 as an energy carrier, which can be obtained amongst others using thermochemical processes, for example the hybrid sulphur process (HyS). The HyS process is based on the thermal decomposition of sulphuric acid into water, sulphur dioxide and oxygen. The subsequent chemical conversion of the sulphur dioxide saturated water back to sulphuric acid and hydrogen is achieved in an electrolyser using a platinum coated proton exchange membrane. This depolarised electrolysis requires a theoretical voltage of only 0.158 V compared to water electrolysis requiring approximately 1.23 V. One of the steps in the development of this technology at the North-West University, entailed the establishment of the platinum coating technology which entailed two steps; firstly using newly obtained equipment to manufacture the membrane electro catalyst assemblies (MEA’s) and gas diffusion electrodes (GDE’s) and secondly to test these MEA’s and GDE’s using sulphur dioxide depolarized electrolysis by comparing the manufactured MEA’s and GDE’s to commercially available MEA’s and GDE’s. Different MEA’s and GDE’s were manufactured using both a screen printing (for the microporous layer deposition) and a spraying technique. The catalyst loadings were varied as well as the type and thickness of the proton exchange membranes used. The proton exchange membranes that were included in this study were Nafion 117®, sPSU-PBIOO and SfS-PBIOO membranes whereas the gas diffusion layer consisted of carbon paper with varying thicknesses (EC-TP01-030 – 0.11 mm and EC-TP01-060 – 0.19mm). MEA and GDE were prepared by first preparing an ink that was used both for MEA and GDE spraying. The MEA’s were prepared by spraying various catalyst coatings onto the proton exchange membranes containing 0.3, 0.6 and 0.9 mg/cm2 platinum respectively. The GDE’s were first coated by a micro porous carbon layer using the screen printing technique in order to attain a suitable surface for catalyst deposition. Using the spraying technique GDE’s containing 0.3, 0.6, 0.9 mg/cm2 platinum were prepared. After SEM analysis, the MEA’s and GDE’s performance was measured using SO2 depolarized electrolysis. From the electrolysis experiments, the voltage vs. current density generated during operation, the hydrogen production, the sulphuric acid generation and the hydrogen production efficiency was obtained. From the results it became clear that while the catalyst loading had little effect on performance there were a number of factors that did have a significant influence. These included the type of proton exchange membrane, the membrane thickness and whether the catalyst coating was applied to the proton exchange membrane (MEA) or to the gas diffusion layer (GDE). During SO2 depolarized electrolysis VI curves were generated which gave an indication of the performance of the GDE’s and MEA’s. The best preforming GDE was GDE-3 (0.46V @ 320 mA/cm2), which included a GDE EC-TP01-060, while the best preforming MEA’s were NAF-4 (0.69V @ 320mA/cm2) consisting of a Nafion117 based MEA and PBI-1 (0.43V @ 320mA/cm2) made from a sPSU-PBIOO blended membrane. During hydrogen production it became clear that the GDE’s produced the most hydrogen (best was GDE-02 a in house manufactured GDE yielding 67.3 mL/min @ 0.8V), followed by the Nafion® MEA’s (best was NAF-4 a commercial MEA yielding 57.61 mL/min @ 0.74V) and the PBI based MEA’s. , (best was PBI-2 with 67.11 mL/min @ 0.88V). Due to the small amounts of acid produced and the SO2 crossover, a significant error margin was observed when measuring the amount of sulphuric acid produced. Nonetheless, a direct correlation could still be seen between the acid and the hydrogen production as had been expected from literature. The highest sulphuric acid concentrations produced using the tested GDE’s and MEA’s from this study were the in-house manufactured GDE-01 (3.572mol/L @ 0.8V), the commercial NAF-4 (4.456mol/L @ 0.64V) and the in-house manufactured PBI-2 (3.344mol/L @ 0.8V). The overall efficiency of the GDE’s were similar, ranging from less than 10% at low voltages (± 0.6V) increasing to approximately 60% at ± 0.8V. For the MEA’s larger variation was observed with NAF-4 reaching efficiencies of nearly 80% at 0.7V. In terms of consistency of performance it was shown that the Nafion MEA’s preformed most consistently followed by the GDE’s and lastly the PBI based MEA’s which for the PBI based membranes can probably be ascribed to the significant difference in thickness of the thin PBI vs. the Nafion based membranes. In summary the study has shown the results between the commercially obtained and the in-house manufactured GDE’s and MEA’s were comparable confirming the suitability of the coating techniques evaluated in this study. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

Water management is a serious issue that affects the performance and durability of PEM fuel cells. It is known, from previous experimental investigations, that surface wettability has influence on water behaviour and fuel cell performance. This finding has lead researchers to develop numerical tools for further investigation of the liquid water behaviour in gas channels. The Volume-of-Fluid (VOF) method has been used in a wide range of studies for its advantage of showing the multi-phase interface in a Computational Fluid Dynamics (CFD) simulation to understand liquid water behaviour in gas channels. In this thesis, numerical study has been carried out to examine the behaviour of liquid water in gas channels. The dynamic movement of the liquid water in the channel and the associated pressure drop, water saturation and water coverage of the GDL have been investigated. Firstly, flow diffusion into the GDL was examined to determine its effect on liquid droplet behaviour in a small section of a gas channel. Furthermore, the effects of the percentage of flow diffusion, GDL wettability, pore size, and water inlet velocity were investigated. Fluid diffusion into GDL found to have insignificant impact on liquid water behaviour so further investigations has been carried with a solid GDL surface. Secondly, gas channel geometry effect on liquid water behaviour was studied. Square, semicircle, triangle, trapezoid with a long base and trapezoid with a short base were compared to find suitable cross section geometry to carry wall wettability investigations. Among the examined geometries, the square cross section showed reasonable results for both scenarios of geometry design, fixed Reynolds number and fixed GDL interface. The effect of wall wettability was assessed by comparing nine different wall/GDL wettability combinations for straight and bend channels. Wall wettability found to have an impact on liquid water behaviour but not as much as GDL wettability. It affects liquid water saturation in the channel by a great deal by accumulating water in the channel edges affecting water behaviour. This was also proven in the last test case of a long channel where water accumulation was investigated by running the calculation until the percentage of water saturation is stabilized. It is also concluded that changing wall wettability from hydrophobic to hydrophilic doubles the percentage of channel occupied by liquid water and increases the time to reach steady state.

This research addresses the manufacturing problems of the fuel cell in an applied industrial approach with the aim of investigating the technology of manufacturing of Proton Exchange Membrane (PEM) fuel cells, and using this technology in reducing the cost of manufacturing through simplifying the design and using less exotic materials. The first chapter of this thesis briefly discusses possible energy alternatives to fossil fuels, arriving at the importance of hydrogen energy and fuel cells. The chapter is concluded with the main aims of this study. A review of the relevant literature is presented in chapter 2 aiming to learn from the experience of previous researchers, and to avoid the duplication in the current work. Understanding the proper working principles and the mechanisms causing performance losses in fuel cells is very important in order to devise techniques for reducing these losses and their cost. This is covered in the third chapter of this thesis which discusses the theoretical background of the fuel cell science. The design of the fuel cell module is detailed in chapter 4, supported with detailed engineering drawings and a full description of the design methodology. So as to operate the fuel cell; the reactant gases had to be prepared and the performance and operating conditions of the fuel cell tested, this required a test facility and gas conditioning unit which has been designed and built for this research. The details of this unit are presented in chapter 5. In addition to the experimental testing of the fuel cell under various geometric arrangements, a three dimensional 3D fully coupled numerical model was used to model the performances of the fuel cell. A full analysis of the experimental and computational results is presented in chapter 6. Finally, the conclusions of this work and recommendations for further investigations are presented in chapter 7 of this thesis. In this work, an understanding of voltage loss mechanism in the fuel cell based on thermodynamic irreversibility is introduced for the first time and a comprehensive formula for efficiency based on the actual operating temperature is presented. Furthermore, a novel design of a 100W (PEMFC) module which is apt to reduce the cost of manufacturing and improve water and thermal management of the fuel cell is presented. The work also included the design and manufacturing of a test facility and gas conditioning unit for PEM fuel cells which will be useful in performing further experiments on fuel cells in future research work. Taking into consideration that fuel cell technology is not properly revealed in the open literature, where most of the work on fuel cells does not offer sufficient information on the design details and calculations, this thesis is expected to be useful in the manifestation of fuel cell technology. It is also hoped that the work achieved in this study is useful for the advancement of fuel cell science and technology.

Proton exchange membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC) are attractive power sources as they offer high conversion efficiencies with low or no pollution. However, the most commonly used platinum electrocatalyst is expensive and the world supply of Pt is limited. In addition, the slow oxygen reduction and methanol oxidation kinetics as well as the poisoning of the Pt catalyst at the cathode resulting from methanol permeation from the anode through the Nafion membrane to the cathode lead to significant performance loss. Also, the electrocatalyst utilization in the electrodes also needs to be improved to reduce the overall cost of the electrocatalysts and improve the fuel cell performance. This dissertation explores nanostructured Pt alloys with lower cost and higher catalytic activity than Pt for oxygen reduction in PEMFC to understand the effect of synthesis and structure on the catalytic activity, methanol tolerant Pt/TiOx nanocomposites for oxygen reduction in DMFC, nanostructured Pt-Ru alloys for methanol oxidation in DMFC, and improvement in the utilization of Pt by optimizing the membrane-electrode assembly (MEA) fabrication. From a systematic investigation of a series of Pt-M alloys (M = Fe, Co, Ni, and Cu), the catalytic activity of Pt-M alloys is correlated with the extent of atomic ordering. More ordered Pt alloys exhibit higher catalytic activity than disordered Pt alloys. The higher activity of the ordered Pt alloys is found to relate to various factors including the Pt-Pt distance, Pt: 5d orbital vacancy, {100} planar density and surface atomic configuration. The catalytic activity of the Pt alloys is also influenced by the synthesis method. Low temperature solution methods usually result in smaller particle size and higher surface area, while high temperature routes result in larger particle size and lower surface area but with a greater extent of alloying. Pt/TiOx/C nanocomposites exhibit higher performance than Pt for oxygen reduction in DMFC. The nanocomposites show higher electrchochemical surface area, lower charge transfer resistance, and higher methanol tolerance than Pt. Pt-Ru alloy synthesized by a reverse microemulsion method exhibits higher catalytic surface area than the commercial Pt-Ru. The higher catalytic activity is attributed to a better control of the particle size, crystallinity, and microstructure. Membrane-electrode assemblies (MEAs) fabricated by a modified thin film method exhibit much higher electrocatalyst utilization efficiency and performance than the conventional MEAs in PEMFC. Power densities of 715 and 610 mW/cm2 are obtained at a Pt loading of, respectively, 0.1 and 0.05 mg/cm2 and 90 oC. The higher electrocatalyst utilization is attributed to the thin catalyst layer and a better continuity of the membrane/catalysts layer interface compared to that in the conventional MEAs. / text