The active region of the dissolution of zinc in flowing electrolyte has been examined. In certain circumstances the active dissolution is extended indefinitely when silicate ion is present. Double-layer capacitance measurements have been made and the results confirm earlier observations that it is possible to study the electrode/electrolyte solution interphase free from the intrusion of adsorbed anions. It is also shown that the silicate ion is adsorbed at the electrode at potentials close to the dissolution potential. The exchange reaction has been studied and improvements made to earlier reported data. A proposed mechanism consistent with the new kinetic data appears to be satisfactory.

The theory and application of anodic oxidation is summarized and the literature relevant to this study is briefly reviewed. The synthesis of several dibenz[c,e]azocin-7-ones and dibenz[c,e]azepin-5-ones is described (Chapter 1). Practical difficulties were encountered during the oxidation of some secondary amides and esters, and with the evidence supplied from cyclic voltammetry, benzylic oxidation is proposed as a major problem. Attempts to synthesise the alkaloid, lycorine, by the oxidative coupling of several 1-substituted oxindoles were unsuccessful but the anodic oxidation of 3-substituted oxindoles and indoles afforded several compounds of novel structure. The first reported electrochemical oxidation of an indoline to an indole is described. Anodic oxidation of diarylesters yielded only intermolecularly coupled products, some of which proved to be ortho and para quinones. A mechanism for their formation based upon cyclic voltammetric evidence is proposed.

No description available.

This thesis is devoted to the characterisation of redox-active metal-coordination complexes containing the N-bipy chromophore; where M = metal and bipy = 2,2'-bipyridine. Their electronic structural formulations have been closely defined by comparative examination of their absorption spectra in sequences of one-electron related oxidation states. We have found that such a series of related complexes offers a far greater chance of successful analysis of the absorption spectra than if the spectra are approached in isolation. The redox changes were generally achieved by controlled electrogeneration using an optically transparent thin layer electrode (O.T.T.L.E.) directly placed in the spectrophotometer beam, so that the absorption spectra of the unstable low-oxidation state complexes could be unambiguously recorded. It was found necessary to develop such 'spectroelectrochemical techniques' because of the extreme sensitivity to oxygen of the reduced complexes. In particular, we have shown that for reduced metal-biayridyl complexes the spectroelectrochemical results can only be rationalised using a trapped-electron model; for example the tris-bipy complexes should be formulated as follows: [M(bipy) ]2+ = [M(bipy )]2+, [M(bipy)31 (2-1)+ = IM(bipy0) 2 (bipy 1 )) (2-1)(M(bipy) 31 (2-2)+ _[M(bipy°)(bipy )21(2-2)+, IM(bipy)31(2-3)+ _ [M(bipy )3] (2-3)+Thus we infer that in[M(bipy)3]2+ and [M(bipy)2L2]2+ complexes the bipy ligands are non-interacting. We also discuss the metal-to-ligand charge transfer excited state of [Ru(bipy) 31 2+ in which we find the optically transferred electron to be exclusively located on one ligand; best formulated as[Ru(III)(bipy°)2(bipy )]2+. This complex is, therefore, an example of a symmetric D3 ground state complex giving rise to a highly unsymmetric excited state. The detailed analysis of characteristic electrode potentials (for metal-based versus ligand-based reductions) and the spectroscopic recognition of bipy and bipy chromophores have provided complementary and consistent electronic structural elucidations, from which molecular orbital energy diagrams can be usefully constructed, and a simple correlation between central metal charge and ligand-based reduction potentials can be identified.

This thesis focuses on the synthesis and characterisation of catalyst free, vertically aligned, Few Layered Graphene Nanoflakes (FLGs) and investigates associated field emission properties and inherent and applied electrochemical properties. The catalyst-free synthesis of FLGs was carried out using the Microwave Plasma Enhanced Chemical Vapour Deposition (MPECVD) technique on heavily doped Si substrates. To understand their growth mechanism, an in-depth study of FLGs was carried out using a combination of Raman spectroscopy, X-ray diffraction (XRD) and electron microscopy. These were studied over a range of growth times. The XRD analysis revealed that the increase in the growth time, promoted an enhanced vertical orientation of the flakes and was accompanied by the structural transformation of nanocrystalline turbostratic graphite to highly-ordered few layered graphene nanoflakes. The transformation involves the release of internal stress at nanocrystalline turbostratic graphite nucleation sites as measured by Raman spectroscopy, where a 5 cm-1 reduction in the G band position was observed. The Nitrogen doping of FLGs was carried out using in-situ low pressure Electron Cyclotron Resonance (ECR) plasma. As compared to pristine FLGs, the N doped FLGs displayed a significant improvement in the field emission characteristics where the turn-on field reduced from 1.94 Vμm-1 for pristine FLGs to 0.85 Vμm-1 for N doped FLGs. This was accompanied by an increase in the emission current density, where the pristine FLGs showed a maximum current density of 17μAcm-2 (at 2.1 Vμm-1), while the N-doped FLGs displayed 297 μAcm-2 (at 1.08 Vμm-1). The change in the field emission behaviour of pristine and N doped FLGs is explained in terms of microstructural changes as well as a reduction in the work function, probed using Valence Band X-ray Photoelectron Spectroscopy. Due to the large number of exposed edge planes and associated high electronic Density of States (DOS), the FLGs exhibited excellent reversible electrochemical behaviour. The FLGs demonstrated fast electron transfer rates, with near ideal peak-to-peak separation of 60 mV for redox peaks, thus exhibiting ideal Nerstian behaviour. The quantification of edge plane sites revealed that with the increasing growth time, the contributing sites actually reduce. The ECR plasma treatment provided a facile route to prepare N-doped FLGs for applications such as Oxygen Reduction Reaction (ORR) and H2O2 reduction. The increase in the defect density, localised electronic DOS and grafting of favourable N-moieties such as pyridinic nitrogen, increased the ORR activity of N-doped FLGs as compared to the pristine FLGs. Excellent long term stability was also observed for these materials in chrono-amperometric studies, making them a potential candidate for metal-catalyst free ORR electrodes. Nitrogen doped FLGs also exhibited excellent sensitivity towards the reduction of H2O2 at much lower applied potentials as compared to pristine FLGs. The FLGs provide an ideal, high surface area platform for sputter deposition of Pt and RuO2 nanoparticles for methanol oxidation and supercapacitor applications, respectively. Addition of pseudo-capacitive RuO2 nanoparticles to FLGs resulted in a significant enhancement of capacitance of RuO2-FLG nanocomposite structures. The RuO2-FLG nanocomposites not only exhibited higher capacitance but also significant improvements in charging-discharging characteristics as well as long operational stability. Ultra-low catalyst loadings of Pt on FLGs exhibited high performance for efficient oxidation of methanol with high mass specific current densities and a high tolerance towards CO poisoning. The enhancement in the electrochemical behaviour was attributed to the synergistic effects of FLGs, which resulted in a high dispersion of the catalyst nanoparticles, thereby increasing their effective surface area and rate of electron transfer through the FLGs.

A fundamental study in to the correlation of nucleation mechanism with deposit morphology using silver salts as a well behaved system has been carried out in deep eutectic solvents i.e. mixtures of choline chloride (ChCl) with firstly ethylene glycol and secondly urea in a 1:2 molar ratio. The nucleation and growth kinetics of silver deposition were measured as a function of liquid type, deposition potential and silver salt type. The effect of different additives including surfactants (SDS and CTAB) and aqueous brightener (cresyl fast violet-CFV and crystal violet-CV) on nucleation was determined using electrochemical techniques such as cyclic voltammetery and chronoamperometery. Electrogravimetric studies were carried out using electrochemical quartz crystal microbalance (EQCM) to correlate the deposited mass of silver with findings from the electrochemical studies in both solvents. A qualitative evaluation of the nucleation and growth mechanism and quantitative estimation of the kinetic parameters of silver electrocrystallization process was carried out using the existing theoretical formalisms. A computer simulation was used to extract the nuclear number density, rate of nucleation, diffusion co-efficient and influence of the double layer charging by fitting the whole potentiostatic current transients using a ‘non-linear best fitting’ method. The analysis of the development of the surface by nucleation and growth of the silver deposition in real time was studied using the ex-situ AFM and in-situ DHM. The latter of these was the first demonstration of this technique for the study of nucleation and growth mechanism of metal deposition and the results showed good agreement with the ex-situ AFM findings.

No description available.

No description available.

No description available.

No description available.