This thesis comprises six chapters. Chapter 1 introduces the background to the project. In this chapter, issues of energy problems, the advantages of H2 and materials and methods for storage are introduced and then the subject is focused on porous metal-organic frameworks (MOFs), a new class of porous materials which are good candidates as on-board storage materials combining with the fuel cell technology. Three topics are discussed about porous materials, (i) metal nodes as secondary building units (SBUs) to prepare porous MOFs, (ii) the strategy in design and synthesis for hydrogen storage in MOFs, (iii) review of gas storage by H2, CH4 and CO2 in MOFs. Chapters 2 to 6 are the results and discussions from my work. They are separated based on different metal cation system. Chapter 2 describes materials prepared from Mg(II) cations and bi- or tricarboxylate ligands. H2L1, H2L2 were purchased from commercial suppliers and three carboxylate ligands were synthesized. All have been employed in the preparation of MOFs to give five Mg(II) framework materials: {Mg3(L1)3(DMA)4}∞ 1, [Mg3(L2)3(DMF)4]∞ 2, [Mg3(L3)3(DMF)4]∞ 3, {[Mg3(L4)2(DMA)4]•(DMA)4}∞ 4, {[Mg3(L5)2(DMA)4]•(DMA)4}∞ 5. The structures of these compounds obtained from single crystal X-ray diffraction and porosity in network are discussed. H2 adsorption measurement is carried out on {[Mg3(L5)2(DMA)4]•(DMA)4}∞ 5, which gives a uptake of 2.06 wt% at 20 bar at 77 K. Chapter 3 describes materials prepared from Ni(II) cations and tetracarboxylate ligands. {[Ni2(L6)(H2O)4]•(DMF)3(EtOH)(H2O)5}∞ 6, {[Ni2(L7)(H2O)5]•(DMF)2(EtOH)2(H2O)6}∞ 7, {[Ni2(L8)(H2O)5]•(DMF)3(EtOH)2(H2O)7}∞ 8 are afforded. Analyses of structure, thermal stability and porosity of the compounds are discussed. Chapter 4 describes MOF materials prepared from Cu(II) cation and tri- or tetracarboxylate ligands. {[Cu2(L12)(H2O)2]•(DMF)3(C2H5OH)3(H2O)5}∞ 13, {[Cu2(L13)(H2O)2]•(DMF)3(C2H5OH)4(H2O)7}∞ 14, {[Cu3(L14)2(H2O)3]•(DMF)2(C4H8O2)4(H2O)5}∞ 15, {[Cu3(L14)2(H2O)3]•(DMF)1.5(DMSO)3(H2O)6}∞ 16, {[Cu2(L15)(H2O)2]•(DMF)(C4H8O2)2(H2O)5}∞ 17, {[Cu2(L16)(H2O)2]•(DMF)(C4H8O2)1.5(H2O)4}∞ 18, {[Cu2(L17)(H2O)2]•(DMF)0.5(C4H8O2)(H2O)3}∞ 19 are affored. Analyses of structure, thermal stability and porosity of the compounds are discussed. Gas adsorption measurements (N2, Ar, H2, CH4 and CO2) are carried out on porous materials. Chapter 5 describes a new (4,8)-connected polyhedral framework with mixed pores was synthesised based on Cu(II) cation and a tetrabranched octacarboxylate ligand {[Cu4L18(H2O)4]•10DMF•C4H8O2•8H2O}∞ 20. Analyses of structure, thermal stability and porosity of the compounds are discussed. Gas adsorption measurements (N2, Ar, H2, CH4 and CO2) are carried out this compound, which gives a hydrogen uptake of 2.5 wt% at 1 bar and 6 wt% at 20 bar at 77 K. Chapter 6 summarizes the crystal structure and gas adsorption of the MOF materials obtained in each chapter.

In order to mitigate the effects of climate change and reduce dependence on fossil fuels, carbon-neutral methods of electricity generation are required. Solid oxide fuel cells (SOFCs) have the potential to operate at high efficiencies, while liquid hydrocarbon fuels require little or no new infrastructure and can be manufactured sustainably. Using hydrocarbons in SOFCs introduces the problem of carbon deposition, which can be reduced or eliminated by judicious choice of the SOFC materials, the operating conditions or the fuel itself. The aim of this project was to investigate the relationships between fuel composition and SOFC performance, and thus to formulate fuels which would perform well independent of catalyst or operating conditions. Three principal hypotheses were studied. Any SOFC fuel has to be oxidised, and for hydrocarbons both carbon-oxygen and hydrogen-oxygen bonds have to be formed. Oxygenated fuels contain these bonds already (for example, alcohols and carboxylic acids), and so may react more easily. Higher hydrocarbons are known to deposit carbon readily, which may be due to a tendency to decompose through the breaking of a C-C bond. Removing C-C bonds from a molecule (for example, ethers and amides) may reduce this tendency. Fuels are typically diluted with water, which improves reforming but reduces the energy density. If an oxidising agent could also act as a fuel, then overall efficiency would improve. Various fuels, with carbon content ranging from one to four atoms per molecule, were used in microtubular SOFCs. To investigate the effect of oxygenation level, alcohols and and carboxylic acids were compared. The equivalent ethers, esters and amides were also tested to eliminate carbon-carbon bonding. Some fuels were then mixed with methanoic acid to improve energy density. Exhaust gases were analysed with mass spectrometry, electrical performance with a datalogging potentiostat and carbon deposition rates with temperature-programmed oxidation. It was found that oxygenating a fuel improves reforming and reduces the rate of carbon deposition through a favourable route to CO/CO2. Eliminating carbon-carbon bonds from a molecule also reduces carbon deposition. The principal advantage of blending with methanoic acid was the ability to formulate a single phase fuel with molecules previously immiscible with water.

No description available.

Fuel processing is one of the essential parts for development of intermediate solid oxide fuel cells (IT-SOFC). Natural gas (methane) is considered as the most abundant and cost effective fuel for the production of hydrogen for IT-SOFC. The primary aim of this thesis is to use a novel precursor material—layered double hydroxide (LDH) – for developing a new type of cost effective, highly active and long lasting catalyst which can reform natural gas in IT-SOFC anode environment. Small amount of noble metals Pd, Rh and Pt are used as promoters to enhance the catalyst’s performance as while maintaining the cost relatively low. The research objectives are achieved by a series of studies including catalysts synthesis, characterisation and the catalytic activities. The thesis initially gives a comprehensive review on fuel cell and SOFC technology, steam methane reforming and reforming catalyst to provide better understanding of the research. Experimental studies include the effects of the synthetic conditions of the LDH precursors and thermal treatments on the physical, chemical behaviours and catalytic activities of the catalysts and promotional effects by noble metals. The LDH derived catalysts compositions, promoter quantities and operating conditions are optimised for the best performance in the IT-SOFC anode environment. A new method for the development of precursor sol for easy coating of the anode is developed and studied. The sol preparation is achieved by acid attack. The sol developed is found to produce better coating and has very high catalytic properties after activation. The catalysts developed were tested for their stability and self-activation ability to ensure its use in the commercial cells. The findings of the present study indicate that the catalysts developed show excellent catalytic performance and these catalysts have very high potential for further commercialisation in IT-SOFC.

Increasing carbon emissions and insecurities in oil supply have led to heightened interest in hydrogen powered fuel cells. Preferably, the cell runs on hydrogen gas, though due to the sensitivity of the catalytic components in the fuel cell to carbon monoxide, the hydrogen must be extremely pure (typically <50 ppm CO). Due to a lack of hydrogen infrastructure, it is envisaged that a medium term solution will be the reforming of more conventional fuels such as gasoline. The gas mixture produced however, contains impurities such as CO, CO₂ and CH₄. Purification may be achieved using palladium membranes, which allow selective permeation of hydrogen. This thesis describes the research carried out in conjunction with Johnson Matthey on thin (typically 7.5 μm) palladium/silver alloy membranes supported on both ceramic and stainless steel porous tubular substrates. Extensive experimental flow testing has been performed to assess the effect of temperature, feed composition, including wet feeds, and membrane thickness on the hydrogen purification properties. An existing Fortran based model was validated and revised to accurately account for the effects of operating conditions such as temperature and carbon monoxide concentration. This work provided excellent correlation between experimental and simulated results. The validated and improved model was incorporated in the design of a hydrogen refuelling station in Aspen Plus and the palladium membrane requirements assessed to supply 650 fuel cell vehicles per day. The system incorporated a steam reformer, membrane clean-up module, water trap and high pressure compressor for hydrogen storage at 1000 bara. Operating conditions such as system pressure, fuel feed and steam to carbon ratio were investigated and adjusted to optimise the overall system efficiency. An efficiency of 52% was achieved with a steam to carbon ratio of SCR = 2.5. A membrane requirement of 6000 standard tubes was found to provide a 90% hydrogen recovery efficiency.

Proton Exchange Membrane Fuel Cells (PEMFCs) are widely regarded as the next generation of portable power production devices, with uses ranging from powering automotive vehicles to laptops and smartphones. PEMFCs convert oxygen and hydrogen into water and usable electricity and have no moving parts, meaning that they can reach overall efficiencies of 60%. However current Polymer Electrolyte Membranes only work efficiently below 80 C and at high humidity. At this low temperature, CO poisoning of the Pt electrocatalysts means that only high-grade fuel (low CO concentration ≤ 2 ppm) and high catalyst loading are required. This means that the overall cost of a PEMFC is prohibitively expensive. To dramatically the reduce cost and increase the efficiency of a PEMFC, new membranes are required which work at 120 C, at which point CO poisoning is no longer a dominating issue. In this thesis, the synthesis of novel organic/inorganic hybrid polyurethane Polymer Electrolyte Membranes (PEMs) with covalently bound phosphonic acid moieties (PA) made from cheap source materials have been reported, which, for the first time, demonstrate high conductivities at high temperatures, for example a PEM made from triethoxysilylpropyl isocyanate, polyethylene glycol, 4,4’-methylene diphenyl diisocyanate and PA displayed a conductivity of 3  10-2 S cm-1 at 120 C and 100% RH. The membranes also display good mechanical, thermal and chemical stability making them ideal candidate PEMs for the use in PEMFCs. However further work needs to be done to reduce the thickness of the membranes from their current thickness of 200 m to just 20-30 m, which would dramatically increase their efficiency when used in a PEMFC, by reducing the Area Specific Resistance and increasing the output (usable) power.

This thesis presents an experimental investigation into the feasibility of using a functionally thermal fluid to enhance the performance of a Proton Exchange Membrane (PEM) Fuel Cell. Specifically, a fluid was developed that utilised a liquid-solid phase change to enhance heat transport within the fuel cell. Increasing the convective heat transfer coefficient could permit the use of smaller volumetric flow rates and reduce pumping power. The objective of the thermal fluid was to create isothermal conditions across a fuel cell and to reduce parasitic loadings from pumps and other components to enhance the overall system performance. Additionally, the fluid could reduce the system size and component cost, and stabilise temperature fluctuations within the system. The thermal fluid that was developed constituted a mix of fine, Microencapsulated Phase Change Material (MicroPCM) particles suspended in a single-phase working fluid. For successful integration with the fuel cell, the microPCMs thermal and fluid properties, and their effectiveness in transferring heat, had to be fully characterised and understood. Research consisted of experimental investigations of the fuel cell, followed by microPCM development. Experimentation on the fuel cell stack revealed a requirement for thermal stability and reduction in parasitic load from the pumps. Quantitative characterisation and development of the microPCM properties involved state of the art equipment to measure the latent heat of fusion, melting and freezing points, surface morphology and viscosity of the microPCM slurry. The effects of repeated use of solid to liquid phase change particles upon melting and solidification were studied. This lead to the further development of microPCM particles and experimentally examined in a fuel cell system. The use of MicroPCM developed in this study balanced the improvement in thermal capacity of the fluid with the increase in pumping load, when compared to the use of water alone. The study suggested that with further development of the microPCM slurry, it has the potential to significantly increase the thermal capacity of the fluid and stabilise temperatures across the fuel cell, which in turn would results in improved stack performance and electrical conversion efficiency.

Hydrogen has long been considered an ideal energy carrier for a sustainable energy economy, for both direct combustion and as a fuel for polymer-electrolyte fuel cells. One of the main challenges associated with the use of hydrogen is to find efficient methods of storage. Any method must be safe, reversible, cost-effective and practical. In this thesis, a general introduction to hydrogen energy and the hydrogen economy is provided, together with descriptions of incumbent and emerging storage methods. A mathematical framework for simulating sorption isotherms in microporous materials is developed. This framework provides explicit expressions for the excess, condensed, compressed and absolute hydrogen masses. Furthermore, key parameters such as the surface area and adsorption volume can be estimated (for the first time) using a single-step nonlinear regression analysis, with the use of any isotherm model. Values are derived for three classes of porous materials, showing consistency with experimental data. A novel composite consisting of titanate nanotubes decorated with nanostructured metal cyanide frameworks, e.g., cadmium ferricyanide (Cd3[Fe(CN)6]2), are synthesised. The equilibrium and kinetic hydrogen sorption properties of the titanate-nanotube/Cd3[Fe(CN)6]2 composite are studied at low, intermediate and high pressure (up to 150 bar), revealing uptake values of ca. 14 weight %, which compare favourably with known materials for hydrogen storage. The role of mass transport in the sorption process is investigated, including the effects of boundary-layer diffusion and intraparticle diffusion. The results suggest that the composite possesses good hydrogen mass transfer characteristics. The effects of the reaction environment during synthesis are explored and the samples are thoroughly characterised. Significant differences in the loading of Cd3[Fe(CN)6]2 on the titanate nanotubes are seen. Hydrogen and nitrogen sorption analyses reveal the role of the pore size distribution on the effective surface area for adsorption and, therefore, the hydrogen uptake.

No description available.

MgH2 is considered to be one of the most promising options for a solid state hydrogen storage material. For practical use it is still imperative to find a convenient means of overcoming its slow kinetics and high stability. In this investigation, a range of binary and ternary metal oxides of aluminium, silicon, titanium, and zirconium, as well as Pd-modified Ti02 samples, were prepared and characterised. The prepared oxides were ball milled with MgH2, and the hydrogen sorption behaviour of the ball milled mixtures was investigated using DSC-TGA-MSS, Sieverts and IGA. Thermodynamic parameters including enthalpies and entropies of hydrogen desorption were determined from experimental data, and activation energy calculations along with modelling of the kinetics were used to understand the mechanism and rate-limiting step of dehydrogenation. Oxide components, calcination temperature, and surface area were found to have a significant impact on the hydrogen sorption behaviour of MgH2 in the ball milled mixtures. Of the prepared binary and ternary oxides, Ti02 and mixed oxides with a Ti02 component were found to lower the dehydrogenation onset temperature by as much as 100°C, while additions of Pd-modified Ti02 resulted in the lowest dehydrogenation onset temperature of 205°C, compared to 360°C for ball milled MgH2. In addition, rates of hydrogen desorption and absorption were significantly increased as a result of the Ti02 and Ti02 - Pd additives. Dehydrogenation of 90 % of the full H2 capacity took 6 min at 300°C, compared to 230 min for milled MgH2 at 350°C. It was found that a reduction of the Ti02 oxide resulted in the active species responsible for the enhanced dehydrogenation behaviour. Through analysis of the reaction kinetics, the mechanism of dehydrogenation was found to change from a surface controlled, contracting volume model for ball milled MgH2 to one of a Johnson-Mehl-Avrami model of two - dimensional nucleation and growth upon addition of Ti02 and Ti02 - Pd.