Bismuth oxide based electrolytes are well known for their high oxide ion conductivity at intermediate temperatures (300-700C). Indeed, the defect fluorite structured -phase of Bi2O3 shows the highest known oxide ion conductivity of any material. Unfortunately this phase is only stable above 730C and much research has been carried out on stabilising this phase to lower temperatures through solid solution formation with other oxides. The work described in this thesis examines the structure-conductivity relationships in several substituted bismuth oxide systems. The effects of Nb5+, Y3+ and Pb2+ substitutions for Bi3+ have been examined using a combination of neutron and X-ray diffraction. Conductivity measurements have been performed on selected compounds using a. c. impedance spectroscopy. Nb5+ substituted systems show extensive superlattice ordering of the fluorite subcell. Three structural types have been examined in the Bi2O3-Nb2O5 binary oxide system, the Type II (incommensurately modulated) structure, the Type III (commensurately modulated) tetragonal structure and the Type IV (Aurivillius) layered structure. The relationship between these structures and that of fluorite is discussed. A detailed investigation of the highly conducting phase -Bi3YO6 was carried out using total neutron scattering methods. The average structure shows oxide ions disordered on the crystallographic scale and distributed over 3 crystallographic sites in the Fm-3m cubic cell. Evidence from the total neutron scattering analysis reveals further detail on local ordering and has provided the first physical evidence of <110> vacancy ordering in a substituted bismuth oxide based fluorite. Double substitution in Bi2O3 has been examined in the systems Bi2O3-Nb2O5-Y2O3 and Bi2O3-PbO-Y2O3. In the Pb2+/Y3+ substituted system, three temperature regions were evident in the Arrhenius plots of total conductivity and were reflected in the thermal expansion of the cubic lattice parameter. The difference between these regions is less pronounced in the Bi2O3-Nb2O5-Y2O3 system with essentially two linear regions identified and an intermediate temperature region. Subtle redistributions of oxide ions are believed to be associated with these transitions. New phases have been examined in the Bi2O3-PbO system and initial structural characterisation of the high temperature phases at compositions Bi3PbO5.5 and Bi4PbO7 has been carried out.

Biofuel cells demand three-dimensional, “high” surface area electrodes with “high” electrical conductivity and structural integrity. The aim of this project is to design and fabricate porous carbon structures as electrodes for enzyme and microbe immobilisation in biofuel cells. These electrodes should have homogeneous pore size distributions, “high” electrical conductivity, “good” mechanical strength and a suitable surface for enzyme and microbe immobilisation. Various routes have been introduced to produce porous carbon electrodes with different ranges of pore sizes. In the case of microbial fuel cells where the pore sizes need to be in the micrometric ranges, a foaming method was adopted. To develop porous carbon electrodes with pore sizes in the nanometre ranges, a templating method was used. Highly ordered hierarchical mesoporous and macroporous carbon structures were obtained using the templating method. Ultimately, a polymer blend technique was developed to produce porous carbon electrodes in large-scales. Porous carbons prepared by this method composed of pores in the micrometric ranges and nanometre pores on the walls of the electrodes’ structures. Various methods to improve mechanical strength and electrical conductivity of the fabricated electrodes were examined. Successive impregnations of the samples in a resin improved the strength and the conductivity of the samples. Moreover, to increase the electrical conductivity of the electrodes, catalytic graphitisation was tested and different graphitic components were produced. The graphitised carbons exhibited electrical conductivities of up to fifty times larger than those obtained from the non-graphitised samples. Electrochemical behaviour of the amorphous and the graphitic carbon electrodes was investigated and it was found that the fabricated electrodes were electrochemically active.

Chapter 1 introduces the phenomenon of Magnetic Chiral Anisotropy in chiral conductors and reviews the current literature on chiral charge transfer molecular conductors and synthetic routes towards them. The second part of the chapter focuses on examples of chiral anionic species reported in the literature. Chapter 2 describes the synthesis and improvements to the literature procedures for organic donor molecules: tetrathiafulvalene, tetraselenafulvalene and bis(ethylenedithio)tetraselenafulvalene. The synthesis and characterisation of new chiral TTF imine systems are also reported. A stable TTF imine derivative of chiral biphenyl amine was used in the synthesis of a homochiral bimetallic helicate with copper(I). Unusual structural and magnetic properties of this compound are reported. Chapter 3 focuses on the synthesis and properties of optically pure anionic complexes, [MIII(Ln)2]-(M = Co, Fe), of chiral pyridinecarboxamide ligands (Ln). The complexes show interesting extended structures ranging from 0D discrete units through 1D zigzag chains to 2D honeycomb layers. The complex anions were used in the synthesis of radical cation salts with tetrathiafulvalene (TTF). The salts (TTF)[CoIII(R,R-L1)2] and (TTF)[CoIII(S,S-L2)2]·EtOAc were characterised by single crystal X-ray diffraction and conductivity measurements. Solution spectroscopic and cyclic voltammetric evidence points to the formation of soluble assemblies between TTF+ and the counterion which correspond to the stoichiometry observed by crystallography and other methods in the solid state. Chapter 4 describes the synthesis of the first diastereomerically pure, organicsoluble salts of cobalt, iron and chromium complexes of optically pure chelate: H4EDDS. A number of synthetic approaches were attempted, but finally the PPh4[MIII(EDDS)]·2H2O series emerged providing readily accessible compounds in reasonable yields via the silver salts. The species are very soluble in methanol, acetonitrile and even THF and isolation of highly crystalline solids is possible upon addition of water. The structures of the three compounds are isomorphous and comprise of H2O-bridged extended hydrogen bonded structures with large channels occupied by the counterion molecules. The magnetic properties and circular dichroism spectra are reported. The diastereomeric purity in the paramagnetic systems is assessed through powder XRD. Chapter 5 focuses on the use of organic-soluble EDDS complexes in the resolution of optically active cations and as a chiral NMR shift agent. The initial results of the resolution of (±)-[RuII(bpy)3]2+ are reported along with the crystal structure of the {Λ-[RuII(bpy)3]}{Λ-[FeIII(S,S-EDDS)]}Cl·H2O adduct. The result of testing of the diamagnetic PPh4[CoIII(S,S-EDDS)] salt as·a 1H NMR shift agent for chiral complex cations: [ML3]2+, (M = Co, Ru, Fe; L = bpy, phen, en) and small organic molecules are also reported. Chapter 6 describes the electrochemical synthesis of a new family of conductive optically pure tetrathiafulvalenium and tetraselenafulvalenium salts D3[MIII(S,S-EDDS)]2·nH2O (where D = TTF, TSF; M = Co, Fe, Cr). The compounds are characterised by single crystal X-ray diffraction, conductivity measurements and elemental microanalysis and exhibit well-behaved semiconductor behaviour with conductivities up to 2.8·10-4 S·cm-1 (Ea ca 0.1 eV). Computational work indicates that it is feasible to generate metallic conductors with similar structures. Initial results for an ET analogue showing metallic conductivity are also reported. Chapter 7 details the experimental procedures used to carry out the work in this thesis.

The field of carbon nanotube (CNT) electrochemistry has received increasing attention from the scientific community since 1996, when the first CNT electrode displaying electrocatalytic properties was reported. However, the large majority of the field functions on the assumption that the sidewalls of CNTs, both multi-walled (MWNTs) and single-walled (SWNTs), are electrochemically inert and only edgeplane- like defects, open ends and catalytic nanoparticles (NPs) are responsible for the impressive electrochemistry observed at CNT electrodes. This thesis aims to elucidate the fundamental electrochemical properties of SWNTs. Random, highly interconnected 2D SWNT networks (either as <1% or ~ 100% surface coverage) grown using catalysed chemical vapour deposition (cCVD) on an insulating support are used throughout. Unlike other growth methods, cCVD results in clean SWNTs, without the need for further purification and with limited metal NP content. Chemical functionalisation of <1% SWNT networks indicates that the main effect of introducing defects (either as sidewall addends or open ends) is a dramatic decrease in the conductivity of the SWNT network, with repercussions on the electrochemical performance of SWNTs. Disk-shaped ultramicroelectrodes (UMEs) fabricated using pristine <1% SWNT networks shows superb electrochemistry for simple outersphere redox couples and superior characteristics over solid conventional UMEs, such as lower background currents and faster response times. Importantly, reversible cyclic voltammetry (CV) obtained under high mass transport conditions suggests that the SWNT sidewall is more electroactive than previously thought. In addition, electrochemical impedance spectroscopy (EIS) coupled with SWNT UMEs is shown to be a powerful method for determining all parameters of an electrochemical reaction in a single experiment. EIS also offers tremendous promise as a detection strategy for sensing applications. The use of a thin-layer cell (TLC) configuration, generating high mass transport rates to the SWNTs, allows for the quantitative determination of electron transfer (ET) kinetics at SWNTs. The value obtained for the rate of ET again provides strong evidence that the SWNT sidewall must be electrochemically active. While <1% SWNT networks are suitable for low concentration electrochemical detection and for the investigation of ET kinetics at SWNTs, a 100% CNT material, or CNT mat, is preferred for the detection of challenging redox molecules, such as dopamine, known to foul the surface of conventional carbon electrodes. CNT mat UMEs can be used for the electrochemical detection of dopamine at micro-molar concentrations in in-vivo mimics, with no decrease in electrode performance after extensive use, outperforming any other carbon electrode material currently available.

Since the first reported use of carbon nanotubes (CNTs) as an electrode material in 1996 the use of CNTs within electrochemistry has grown rapidly. Single walled carbon nanotubes offer bio-compatibility combined with nano-scale dimensions and low background currents in the pristine state. Over the past decade the quantity of SWNTs synthesised globally has greatly increased making the material available for a variety of studies and potentially a feasible material for commercial electrodes. Despite this rise in popularity there is still an on going debate about the sites of electron transfer (ET) at a carbon nanotube. Some reports claim that the sidewall of the carbon nanotube exhibits sluggish ET rates with the majority of the ET occurring at defect sites and the end of the CNT. In contrast there is also evidence that suggests that ET at the sidewall is facile and not sluggish. The origin of ET is investigated using both theoretical and experimental data to probe the developing diffusion profiles to active ET sites. This is achieved on the timescale of a typical voltammetric experiment by significantly reducing the rate of diffusion to the electroactive sites using a NafionTM film. The reduced rate of diffusion allows the developing diffusion profiles to the individual sites to be decoupled. The use of convection and diffusion is a proven electrochemical technique to increase the sensitivity of analytical measurements and to probe reaction rates and mechanisms. The well-defined mass transport within a channel flow cell or an impinging jet electrode, combined with the continual replacement of solution, makes this geometry amenable to online studies, e.g. bedside or industrial monitoring, or a combination with chromatography. One draw back of conventional channel flow and impinging jet electrode set-ups is the need for specialist equipment or calibration steps each time the system is assembled. The use of microstereo lithography (MSL) to construct custom designed cells for use with a variety of planar electrodes is investigated. The hydrodynamics within the proposed designs are theoretically tested and verified experimentally. The devices constructed are easily assembled using a wide range of electrode materials and the computer aided manufacture provides flexibility in critical dimensions. Importantly, the devices only require a one-off determination of the height prior to assembly, removing the need for an electrochemical calibration step as the cells do not distort during assembly. Of particular interest for analytical studies is the greatly reduced background currents provided by a carbon nanotube network compared to an equivalent size carbon macroelectrode. The lower background signal allows small Faradaic currents to be observed experimentally, allowing lower concentrations to be distinguished. The enhanced sensitivity is combined with the increased mass transport of channel flow and impinging jet convective systems to determine the limit of detection for particular channel and impinging jet geometries under constant flow rates. This approach allows the successful detection of nano-molar concentrations under hydrodynamic control using standard voltammetric techniques.

This thesis is concerned with understanding and directing the functionalisation of solid surfaces with materials: molecules, nanoparticles and crystals. Both conducting (electrode) and insulating surfaces are of interest. For molecular functionalisation, a sweep potential procedure has been developed to assist the formation of self assembled monolayers (SAMs) of a ruthenium thiolated complex. Electrochemical investigations were employed to characterised the SAM formed on a platinum electrode. Nanoparticles formation explored two distinct routes. First Pd nanoparticles were successfully formed within ultra-thin Nafion films via impregnation and a chemical reduction method. Morphological investigations utilised atomic force microscopy. The electrocatalytic properties of the nanocomposite material were elucidated for the hydrogen oxidation reaction. The methodology used for the preparation of this nanocomposite material shows promise for applications in sensors and fuel cells. Second, the potential-assisted deposition of pre–formed perthiolated-ß-cyclodextrin-capped Pt nanoparticles method is described. Pt nanoparticles (5 nm diameter) were deposited in a controlled fashion on indium tin oxide and highly oriented pyrolytic graphite electrodes. The Pt nanoparticles formed in this way were electrocatalytically active towards hydrogen generation and oxidation. This new approach for the deposition of metal nanoparticles with controlled surface density provides a new tool for the investigation of electrocatalytic processes. A major focus of the second part of the thesis has been the development of methods to study crystal deposition at extreme supersaturation. For this purpose a delivery system for calcium carbonate at high-supersaturation ion has been coupled with a quartz crystal microbalance and in–situ optical microscopy. The dynamics and quantitative evaluation of calcium carbonate deposition onto foreign solid substrates, and the effect of various additives, are described. Ex– situ studies, scanning electron microscopy and microRaman spectroscopy, allowed the morphological characterisation of the phases deposited. The transformation of ACC to calcite has been explored in details. In the study of additives, a significant finding was that citrate concentration shows a nonmonotonic behaviour on the amount of scale deposited. Fast screening of different additives (polymeric and molecular) and a quantitative ranking of their inhibitory properties on calcium carbonate deposition on a gold surface is described. Molecular and polymeric additives showed different inhibitory mechanisms on the scaling process and the technique employed gave a better insight into their mode of action.

This thesis is concerned with the application of evanescent wave cavity ring-down spectroscopy (EW-CRDS) and evanescent wave broadband cavity enhanced absorption spectroscopy (EW-BB-CEAS) for studies of electrochemical and interfacial processes. These include nanoparticle adsorption/dissolution, polymer nanoparticle formation and surface-bound electrochemical redox reactions. Different experimental setups have been designed to investigate these systems. EW-CRDS is a surface sensitive technique, which allows absorption measurements at solid/liquid and solid/air interfaces. Surface reactions can easily be monitored in real time. A pulsed or modulated laser beam is coupled into an optical cavity which consists of at least one optical element, in which the beam is total internal reflected. At the position of total internal reflection (TIR), an evanescent field is established with the amplitude decaying exponentially with distance from the boundary. The evanescent field can be exploited to investigate the absorbance properties of the liquid phase in the first few hundred nanometres of the solution above the silica surface. These types of instruments have high temporal resolution (up to 2 kHz repetition rate), coupled with high sensitivity (minimum detectable interfacial absorbance per pass: ~80 ppm) which enables the investigation of a variety of processes relating to fundamental questions in the field of physical chemistry and materials science. The aforementioned sensitivity and resolution make EW-CRDS an ideal tool for those investigations, especially if combined with other techniques such as electrochemistry or microfluidic and hydrodynamic techniques. In this thesis, different instrumentational setups will be discussed. EW-BB-CEAS is another example for a TIR based absorption spectroscopic technique and can give additional spectral information about the investigated surface processes by employing broadband light such as supercontinuum radiation. In this case, the amplified light intensity within the optical cavity is measured rather than the light decay. By employing complementary techniques, such as electrochemistry and atomic force microscopy and by fitting experimental data using finite-element modelling, surface processes can not only be described accurately but also kinetic information such as rate constants for the aforementioned systems can be calculated.

Interactions at the nanoscale are governed almost exclusively by electromagnetic forces, but the interplay between different scaling laws produces a vast array of behaviours. We investigate radically different systems spanning almost three orders of magnitude of length scales, and use a variety of experimental techniques to determine the forces present in each regime, and the interplay between them. An important prototypical surface in SPM science has been the Si(100) surface, which due to it’s unstable buckling and complex electronic structure has fostered considerable debate in the surface science community. We have used small amplitude, high sensitivity combined qPlus STM/AFM to investigate tip -- sample interactions on the Si(100) surface at low-temperature in UHV, with a focus on the chemical, and electronic properties of the system and how these are modified by the probe. We present the first atomic resolution combined force/tunnel current results on the surface and show that great care must be taken in interpreting either pure AFM or pure STM data. We also examine tip -- sample interactions on arrays of thiol passivated spin-cast nanoparticles in both UHV and ambient conditions and show for the first time how minor modifications to the experimental parameters can radically alter the data collected, most likely due to the thiol -- surface -- tip interaction. We also present SKPM and voltage spectroscopy of the same samples and show the importance of electrostatic interactions in correct height determination of these network arrays, in parallel with the caution that must be maintained in interpreting CPD data. A key mechanism for the manipulation of meso-scale objects in solution is Dielelectrophoresis, which offers strong material and size specificity and a high degree of spatial control. In the final experimental chapter we investigate the effect of inhomogenous electric fields on nanoparticles in aqueous solution, and reveal how previously uninvestigated electrochemical effects can become important even at high frequencies, and may offer a new and exciting route for the control of self organised nanowires in solution.

This thesis is concerned with the electrochemical and spectroelectrochemical characterisation of cyano (CN) and trifluoromethyl (CF3) substituted polypyridine ligands and their metal complexes. The ligands investigated were X-CN-py (X = 3, 4 and 5, py = pyridine), X,X´-(CN)2-bpy) (X,X´ = 3,3´, 4,4´ and 5,5´ bpy = 2,2´- bipyridine) and X,X´-(CF3)2-bpy (X,X´ = 3,3´, 4,4´ and 5,5´). The Pt(II) complexes of the X-CN-py and X,X´-(CN)2-bpy ligands were studied along with the Fe(II) complexes of the X,X´-(CN)2-bpy and X,X´-(CF3)2-bpy ligands. Electrochemical studies of the X-CN-py ligands indicated that 2-CN-py and 4-CN-py have one reversible 1e- reduction and 3-CN-py has one quasi-reversible reduction. 4-CN-py is more easily reduced than 2-CN-py. EPR experiments on [2-CN-py]1- and [4-CN-py]1- combined with DFT calculations have indicated that the semi-occupied molecular orbital (SOMO) is delocalised over the entire molecule. The complex [Pt(4-CN-py)2Cl2] undergoes two reversible 1e- reductions, attributed to the sequential reduction of the two 4-CN-py ligands. [Pt(3-CN-py)2Cl2] was found to exhibit one irreversible reduction. The electrochemistry of the X,X´-(CN)2-bpy ligands indicated that 3,3´-(CN)2-bpy and 5,5´-(CN)2-bpy have two reversible 1e- reductions while 4,4´-(CN)2-bpy has only one reversible 1e- reduction. The reductions of 5,5´-(CN)2-bpy occur at significantly less negative potentials than those in 3,3´ or 4,4´ analogue. In-situ UV/Vis/NIR and EPR experiments on the X,X´-(CN)2-bpy ligands indicate that the reduction electron is delocalised over both the CN-py rings with the SOMO being spread across the entire molecule. [Pt(3,3´-(CN)2-bpy)Cl2] and [Pt(5,5´-(CN)2-bpy)Cl2] undergo two reversible 1e- reductions, attributed to the sequential reduction of the X,X´-(CN)2-bpy ligand. 4,4´-(CF3)2-bpy and 5,5´-(CF3)2-bpy, whose X-ray crystallographically determined structures are reported, both have one reversible 1e- reduction while 3,3´-(CF3)2-bpy exhibits an irreversible reduction. Again the 5,5´ analogue is the most easily reduced. Spectroelectrochemical results indicate that the reduction electron enters a SOMO that is delocalised over both the CF3-py rings. Substitution in the 5,5´ positions is determined to be electronically most significant. Complexes of the general formula [Fe(II)(X2-bpy)3][BF4] (where X = CN or CF3 in the 4,4´ or 5,5´ positions) exhibit three reversible ligand based reduction processes and a metal based oxidation. UV/Vis/NIR and EPR studies have confirmed that the reduction electron in each case enters a molecular orbital that is predominantly based on a bpy ligand. The redox potentials of 4-CN-py and 5,5´-(CN)2-bpy are solvent dependent with 1e- reduction of 4-CN-py and the two 1e- reductions of 5,5´-(CN)2-bpy moving to less negative potentials as the acceptor number (AN) of the solvent increases. A computational model has been developed for the study of the electronic properties of substituted bipyridines using DFT methods. This model has been used to aid the analysis of the EPR and UV/Vis/NIR spectra of the X2-bpys studied.

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