Proton exchange membrane electrolysers (PEMEs) constitute the state-of-the-art in electrolytic water splitting, capable of producing H2 at high current density and efficiency. However, when operating at low current or under increased pressure, H2 and O2 can cross through the membrane which separates the electrodes, creating a potentially explosive gas mixture and reducing the efficiency. Electron-coupled proton buffers (ECPBs) provide a solution to the issues of gas crossover in electrolytic water splitting, by breaking up the oxygen and hydrogen evolution reactions (OER and HER) into two separate steps. This provides benefits to gas purity and improves the operational safety of the electrolyser. Initially, ECPBs were limited to polyoxometalate (POM) compounds, which contain expensive transition metals and have high molecular weights. The use of a cheap organic species as an ECPB was later introduced using hydroquinone sulfonate (HQS); however, this compound was found to be unstable under extended redox cycling, making it unsuitable for practical applications. This thesis details the examination of a host of organic molecules for use as ECPBs, and their development into practical PEME systems. In the first section of work, several classes of organic compounds were investigated to determine their suitability for different modes of ECPB operation. This included anthraquinone-2,7-disulfonic acid (AQDS), which was found to be exceptionally stable under extended redox cycling, providing a lifetime 17 times greater than the previously published HQS. Biphenyl tetrasulfonic acid (BPTS) was found to have a redox potential of 1.037 V vs. the standard hydrogen electrode (SHE), and was subsequently used in a photoelectrochemical cell (PEC). This PEC was able to operate at currents of 0.9 mA∙cm−2 under 1 Sun illumination with zero applied external bias, and the removal of H2 production from the cell eliminates the possibility of explosive gas combinations forming. A sulfonated viologen molecule ((SPr)2V), was found to have a redox potential of −0.392 V vs. SHE, making it capable, in theory, of evolving H2 spontaneously from the reduced solution. Unfortunately, this was not possible due to the chemical stability of the compound. Organic molecules with high pKa functional groups were then investigated at high pH, in the hope of identifying the first ECPB for alkaline water splitting. Although no suitable molecule was identified in the course of this research, the work detailed here provides a solid foundation for future studies. In the second section of work, an ECPB-mediated PEME cell was developed for the first time. This system utilised the AQDS molecule identified in the first section, implementing it into a dual cell PEME which produced H2 and O2 in separate locations. This electrolyser was shown to operate at a similar level to a conventional PEME (in excess of 1.5 A∙cm−2), while producing H2 at higher purity and without cross contamination of the product gases. Through operating the cells independently of one another, H2 was able to be produced at current densities of up to 3.71 A∙cm−2 at 2.0 V. In the third section, similar systems were constructed using the polyoxometalate ECPBs, phosphomolybdic acid (PMA) and silicotungstic acid (STA). These systems were developed to a similar level as the AQDS electrolyser, before being directly compared in terms of performance and cost. Although the conventional PEME was found to have the highest voltage efficiency of the four systems (78.65% at 1 A∙cm−2), it was also found to have the lowest Faradaic efficiency (92.82%), and was the only system examined where crossover of the product gases was observed. Of the three ECPB-based systems, the AQDS PEME was found to have the highest voltage efficiency (54.70% at 1 A∙cm−2) and Faradaic efficiency (>99%), as well as being able to operate at the highest current densities. A mole-for-mole cost-comparison of the different ECPBs revealed AQDS to be just 2.11% and 1.02% of the cost of PMA and STA, respectively. In the final results section, the AQDS PEME was adapted so that the AQDS oxidation cell provided an energy output instead of producing H2, thereby moving away from water splitting and towards electrochemical energy storage. The system developed here is a hybrid between redox flow battery and fuel cell technology, utilising a rechargeable liquid electrolyte alongside the H2O/O2 redox couple. Charging the device proceeded in the same manner as O2 evolution in the AQDS PEME, but the subsequent oxidation of AQDS was then coupled to O2 reduction (forming H2O) instead of proton reduction (forming H2). The system was developed to produce a maximum power density of 124 mW∙cm−2, with a great deal of scope for further improvements.

Increasingly global warming and air pollution caused by the consumption of fossil fuel have imposed the priority of using green energy. As a result, the use of rechargeable lithium-ion batteries (LIBs) has increased rapidly Olivine-structured LiFePO4 is considered as one of the most promising positive electrode materials owing to its significant advantages of nontoxicity, low cost of raw materials, good structural stability at high temperature, excellent safety performance, and relatively high theoretical specific capacity (170 mAhg-1) with a flat discharge-charge potential (3.45V vs. Li+/Li). Therefore, LiFePO4 battery becomes a reliable material for energy storage system used in hybrid electric vehicles (HEVs), full electric vehicles (EVs), plug-in hybrid electric vehicles (PHEVs), and portable devices. However, the poor rate performance of LiFePO4, resulting from its intrinsic low Li+ diffusivity (10-17 to 10-14 cm2s-1) and low electronic conductivity (10-9 to 10-8 S cm-1), has become a technical bottleneck to confine its widely practical applications. Following previous studies, a systematic study on controllable preparation of LiFePO4 positive electrode material with nanoscale size, or hierarchical micro/nano mesoporous structure has been carried out using various synthesis methods, including impinging stream reaction (ISR), ultrasonic-intensified impinging stream reaction (UISR), two-step co-precipitation method, and two-step hydrothermal method (UIHT). The physical and chemical properties of as-synthesized products are measured by XRD, FTIR, SEM, TEM, BET, Mastersizer, CV, and charge-discharge test. Based on these observations, the relationship among particle morphology, electrochemical performance, and impacts of fluid dynamics is evaluated in this work.

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The aim of this thesis work has been focused on the development of Li-rich complex oxide materials and their advanced characterisation by a wide range of techniques for their application in Li batteries. To achieve this ultimate goal, it is necessary to consider the material design and discovery, the synthetic routes employed, and the characterisation of these materials to unpick the underpinning structure-property relations which govern functionality. Chapter 1 introduces the basic aspects of current Li-ion battery technologies and their limitations. This is followed by a description of the all-solid-state battery concept and an examination of solid electrolyte candidate materials. Lithium-rich garnet materials are described in the following section with the conductivity-crystal structure relationship detailed. The role of lithium-excess in complex oxides for battery applications is explored followed by a section introducing the novel concept of lithium-rich double perovskites and the Li6Hf2O7 system. Finally, a section reviewing the microwave and sol-gel synthetic pathways employed for battery materials will conclude this introductory chapter. The chemicals and synthetic approaches employed in this thesis to develop the materials under study are detailed in Chapter 2. The basics behind the characterisation techniques employed in this thesis, including powder X-ray diffraction (PXRD) and neutron powder diffraction (NPD) techniques for structural characterisation, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and galvanostatic cycling with potential limitation (GCPL) for electrochemical analyses, X-ray absorption spectroscopy (XAS) synchrotron-based techniques for local structure analyses and muon-spin relaxation (μ+SR) for local Li+ diffusion studies, among others, are also detailed. The first results chapter, Chapter 3, details the studies performed on Zn-, Ga-, Al-doped Li6BaLa2Ta2O12 (LBLTO) garnet materials as solid-state electrolytes. The achievement of shorter reaction times and temperatures compared to conventional solid-state chemistry methods is detailed. The role of the dopant in the structure is analysed by PXRD and XAS studies and its influence on the ionic conductivity of the materials is examined. For the undoped material, local Li+ diffusion analyses by μ+SR are also evaluated and discussed. Chapter 4 presents a novel microwave-assisted synthesis for Al- and Ga-doped Li7La3Zr2O12 (LLZO) garnets. The chapter discusses the stabilisation of the cubic phase of the LLZO garnet at lower temperatures and shorter reaction times. The structure of the material and dopant positions are analysed by PXRD, XAS and PND studies. The macro and micro ionic transport properties of the materials are examined by EIS and μ+SR and related to the macrostructure and dopant positions within the garnet structure. The preparation of the homologous Al-doped LLZO cubic garnet by sol-gel chemistry is explored in Chapter 5. The stabilisation of the highly conducting cubic phase even at lower temperatures is analysed by conventional PXRD, advanced in-situ NPD and Raman spectroscopy. The reasons behind the ionic transport behaviour of this sol-gel prepared material are analysed by EIS and local Li+ diffusion studied with μ+SR. Chapter 6 focuses on the synthesis and ionic conductivity studies of the novel Li-rich complex oxides In-and Y-doped Li6Hf2O7 as solid-state electrolytes for lithium-ion batteries. The analysis of this new family of materials and their crystallographic structures are presented. The transport properties and the role of the dopant is discussed, with the ionic conductivity and activation energy for macroscopic ionic conduction presented. In Chapter 7, a new family of Li-rich double perovskites as versatile novel materials for all-solid-state Li batteries is presented. The synthesis and structural characterisation of the Li1.5La1.5WO6 (LLWO) and Li1.5La1.5TeO6 (LLTeO) novel compounds by PXRD, NPD and XAS analyses is described. Investigation of Li1.5La1.5WO6 as a candidate negative insertion electrode was analysed by CV and GCPL experiments, as well as the macro and microscopic study of their transport properties by EIS and μ+SR techniques respectively. The chapter also includes the study and discussion of the redox stability and Li+ conduction properties of Li1.5La1.5TeO6 as a solid-state electrolyte and preliminary studies of a pseudo solid-state battery formed by these two novel Li-rich double perovskites. In Chapter 8, the homologous Na-rich double perovskite Na1.5La1.5TeO6 is presented. The crystal structure has been explored by PXRD, Raman spectroscopy and in-situ variable-temperature PXRD experiments. The transport properties have also been explored at the macroscopic and local level by EIS and μ+SR and its compatibility with Na metal electrodes analysed in symmetrical cells. To conclude, a summary of the main conclusions obtained from the work presented in this thesis, together with further lines of research to explore, are discussed in Chapter 9.

During the course of this PhD, a number of potential PET and SPECT imaging agents were synthesised for particular in vivo targets. The first targets were monocarboxylate transporters 1 and 2 (MCT 1 and 2) which are responsible for the transport of moncarboxylates such as lactate and pyruvate across plasma membranes. The generation of imaging agents which bind to these MCTs could lead to the effective molecular imaging of epileptogenic regions of the brain. A potent and selective inhibitor of MCT 1 and 2 was previously synthesised by AstraZeneca (AR-C155858). In this project, a library of analogues of this compound was synthesised, containing potential sites for radiolabelling. A group of these compounds underwent preliminary biological evaluation to determine the inhibitory effect on lactate uptake against MCT 1, 2 and 4 (the most active being thienopyrimidine 73). The second target was poly(ADP-ribose) polymerase-1 (PARP-1), an enzyme used in the repair of DNA. Targeting PARP-1 with radiotracers could aid the diagnosis and monitoring of various tumours. A small library of potential PET imaging agents, which have the potential to undergo facile radiofluorination, were synthesised based on the PARP-1 inhibitor olaparib. This series of compounds were subject to a PARP-1 immunofluorescence assay and the most potent compound in the series was found to be phthalazinone 147. The second part of this thesis describes the development of novel radioiododeboronation methods using both gold(I) and potassium acetate catalysis. These methods were used in the radiosynthesis of a number of aromatic iodides, giving the radiolabelled products in high radiochemical yields. SPECT imaging agents [125I]MIBG and a PARP-1 tracer were also generated under these conditions.

This thesis reports the selective oxidation of alkyl aromatic substrates under mild ‘green’ conditions, with a particular emphasis on developing alternatives to established gold-based catalysts. Three alkyl aromatics were chosen for investigation: toluene, ethylbenzene and 2-ethylnapthalene; so differences due to increased alkyl chain length and extended aromaticity could be explored. The oxidation of toluene using tertiary-butyl hydroperoxide (tBHP) was carried out with a ruthenium-palladium catalyst. This catalyst was found to be highly active, more so than a gold-palladium equivalent, and further optimised in terms of molar ratio of Ru : Pd, wt.% metal loading, reducing temperature and support material. The resulting catalyst was found to be reusable with little loss of conversion, though selectivity changed significantly. This was the case despite notable metal leaching. Finally, the catalyst was explored via experiments varying substrate : metal molar ratio and time-on-line studies, revealing unusual behaviour. The ruthenium-palladium catalyst was also applied to the oxidation of 2-ethylnapthalene with tBHP. Extensive comparisons were drawn between this catalyst and gold-palladium equivalents. Sol immobilisation, conventional impregnation and modified impregnation were tested as preparation methods. Once again, the ruthenium-palladium bimetallic catalyst proved to be more active than the gold-palladium, even at very low wt.% loadings. Finally, an iron-palladium catalyst was applied to the oxidation of ethylbenzene with molecular oxygen. High molar ratios of substrate : metal were explored, and conversion found to be highly dependent on this factor. The catalyst was optimised in terms of molar ratio of Fe : Pd, wt.% metal loading, preparation method and reducing temperature. The resulting iron-palladium catalyst achieved activity exceeding that of gold-palladium in similar conditions. This activity was attributed to radical chemistry, explored via studies with initiators and scavengers.

The work described herein is concerned with Lewis acidic triarylboranes for synthetic and catalytic transformations where the influence of different substitution pattern and substituents were crucial in determining the resulting reactivity. Chapter 1 will provide a general introduction into acidity and will lay the theoretical foundation for the ensuing chapters. Chapter 2 introduces the boranes utilised in this work and will give literature examples describing reactivities of the currently known boranes. Besides providing several crystal structures, this chapter will discuss the Lewis acidity of these boranes. Chapter 3 explores the hydroboration of imines catalysed by tris[3,5-bis(trifluoromethyl)-phenyl]borane. By testing a variety of various Lewis acids further insight into the mechanism of this hydroboration is gained. Chapter 4 further investigates borane imine adducts and the impact of the adduct formation on the electronic transitions within the imines. The photoactive adducts are then explored as vapochromic materials towards various solvent vapours. Chapter 5 focuses on the formation of pyrones, dihydropyrones and isocoumarins catalysed by tris(pentafluorophenyl)borane. A cross over experiment reveals the nature of this cyclisation reaction. Chapter 6 investigates the radical character of a frustrated Lewis pairs and their resulting reactivity. A novel protocol for a radical Heck-type reaction is provided and the mechanism was investigated. Finally, Chapter 7 will show the ambiguity between 1,1-carboboration and 1,3-haloboration in the reaction of propargyl esters with dichlorophenylborane.

The objective of this work is to present formic acid as a suitable compound to be used in a hydrogen economy. Catalytic decomposition of formic acid at mild conditions is evaluated as a model reaction for hydrogen generation, making emphasis on the productivity, reusability of the catalysts, and quantification of concomitant CO evolved from the reaction. Characterisation of the fresh and used catalysts is performed to study the activity/structure relationship and investigate the possible reasons for its deactivation. Computational calculations are used to support experimental data and correlate productivity and CO evolution with the elementary steps of the reaction and the most common surfaces of the catalyst. Synthesis of materials with different surface properties and preparation methods is a fundamental part of this work. In Chapter 3, a commercial Pd/C catalyst is used as a reference to establish the reaction conditions that lead to a kinetically limited reaction. Reusability tests and subsequent characterisation of the used catalyst in conjunction with computational studies are performed to investigate its stability. Continuous flow experiments are carried out as a preliminary test to improve the reusability. Following the identification of the main parameters and characteristics of the catalysts involved in formic acid decomposition, in Chapter 4, materials with different properties (graphitisation degree and acid/base surface functionalisation) are synthesised by two preparation methods (sol-immobilisation and impregnation) using carbon nanofibers as supports. Once the optimal preparation method is identified, a set of parameters are modified in Chapter 5 to investigate the effects it has on the structure and morphology of the catalysts. Besides this optimisation, two supports (activated charcoal and titania) are investigated and an initial study of bimetallic catalysts and its properties is explored. Chapter 6 presents the main consequences of these results and a set of possibilities to continue this research.

The selective oxidation of methane, which is the primary component of natural gas, isone of the most important challenges in catalysis. While the search for catalysts capable of converting methane to higher value commodity chemicals and liquid fuels such as methanol has been ongoing for over a century, an industrially viable process has not yet been developed. Currently, large scale upgradation of natural gas proceeds indirectly employing high temperature conversion to syngas which is then processed to synthesise fuels and chemicals. Different catalysts are currently being studied for direct low temperature selective oxidation of methane to liquid oxygenates primarily methanol. One of the systems studied is based on gold-palladium supported nanoparticles using hydrogen peroxide. Though the catalyst was shown to be active, high wastage of hydrogen peroxide was observed along with low productivities. The work in this thesis shows the removal of support can be used to increase the activity and efficiency of the reaction. By tuning the amount of hydrogen peroxide, high productivities and selectivities were observed. Further optimisation of catalyst preparation and methane oxidation were also performed. A theoretical study based on density functional theory into interactions between metal particles, such as gold and palladium and substrates such as oxygen, hydrogen and water was also carried out to identify the active sites and reaction mechanism underway with hydrogen peroxide and these metal particles.