The electrorefiner (ER) is the heart of pyroprocessing technology operating at a high-temperature (723 K – 773 K) to separate uranium from Experimental Breeder Reactor-II (EBR-II) used metallic fuel. One of the most common electroanalytical methods for determining the thermodynamic and electrochemical behavior of elemental species in the eutectic molten salt LiCl-KCl inside ER is cyclic voltammetry (CV). Information from CV can possibly be used to estimate diffusion coefficients, apparent standard potentials, transfer coefficients, and numbers of electron transferred. Therefore, predicting the trace of each species from the CV method in an absence of experimental data is important for safeguarding this technology. This work focused on the development an interactive computational design for the CV method by analyzing available uranium chloride data sets (1 to 10 wt%) in a LiCl-KCl molten salt at 773 K under different scan rates to help elucidating, improving, and providing robustness in detection analysis. A principle method and a computational code have been developed by using electrochemical fundamentals and coupling various variables such as: the diffusion coefficients, formal potentials, and process time duration. Although this developed computational model works moderately well with reported uranium data sets, it experiences difficulty in tracing zirconium data sets due to their complex CV structures. Therefore, an artificial neural intelligent (ANI) data analysis has been proposed to resolve this issue and to provide comparative study to the precursor computational modeling development. For this purpose, ANI has been applied on 0.5 to 5 wt% of zirconium chloride in LiCl-KCl eutectic molten salt at 773 K under different scan rates to mimic the system and provide current and potential simulated data sets for the unseen data. In addition, a Graphical User Interface (GUI) through the commercial software Matlab was created to provide a controllable environment for different users. The computational code shows a limitation in high concentration CV prediction, capturing the adsorption peaks, and provides a dissimilarity. However, the model is able to capture the important anodic and cathodic peaks of uranium chloride CV which is the main focus of this study. Furthermore, the developed code is able to calculate the concentration of each species as a function of time. Due to the complexity of the CV of zirconium chloride, the computational model is used to predict the probability reactions occurring at each peak. The resulting study reveals that the reaction at the highest anodic peak is related to the combination of 70% Zr/Zr+4 and 30% Zr/Zr+2 for the 1.07 wt% and 2.49 wt% zirconium chloride and 30% Zr/Zr+4 and 70% Zr/Zr+2 combination for 4.98 wt% ZrCl4. The proposed alternative ANI method has demonstrated its capability in predicting the trend of species in a new situation with a high accuracy on predictions without any dissimilarity. Two final structures from zirconium chloride study which high accuracy (that is, a low error) are related to [9, 15, 10]-18 and [10, 11, 25]-19. These two final structures have been applied on uranium chloride salt experimental data sets to further validate the ANI’s ability and concept. Three different fixed data combinations were considered. The result indicates that by increasing the number of training data sets it does not necessarily help improving the prediction process. ANI implementation outcome on uranium chloride data set illustrates a good prediction with a specific fixed data combination and [9, 15, 10]-18 structure. Thus, it can be concluded that ANI is a promising method for safeguarding pyroprocessing technology due to its robustness in predicting the CV plots with high accuracy.

>Magister Scientiae - MSc / In the wide search for advanced materials for next generation lithium-ion batteries, lithium manganese orthosilicate, Li₂MnSiO₄ is increasingly gaining attention as a potential cathode material by virtue of its ability to facilitate the extraction of two lithium ions per formula unit, resulting in a two-electron redox process involving Mn²⁺/Mn³⁺ and Mn³⁺/Mn⁴⁺ redox couples. This property confers on it, a higher theoretical specific capacity of 333 mAhg⁻¹ which is superior to the conventional layered LiCoO₂ at 274 mAhg⁻¹ and the commercially available olivine LiFePO₄ at 170 mAhg⁻¹. Its iron analogue, Li₂FeSiO₄ has only 166 mAhg⁻¹ capacity as the Fe⁴⁺ oxidation state is difficult to access. However, the capacity of Li₂MnSiO₄ is not fully exploited in practical galvanostatic charge-discharge tests due to the instability of the delithiated material which causes excessive polarization during cycling and its low intrinsic electronic conductivity. By reducing the particle size, the electrochemical performance of this material can be enhanced since it increases the surface contact between the electrode and electrolyte and further reduces the diffusion pathway of lithium ions. In this study, a versatile hydrothermal synthetic pathway was employed to produce nanoparticles of Li₂MnSiO₄, by carefully tuning the reaction temperature and the concentration of the metal precursors. The nanostructured cathode material was further coated with a thin film of aluminium oxide in order to modify its structural and electronic properties. The synthesized materials were characterized by microscopic (HRSEM and HRTEM), spectroscopic (FTIR, XRD, SS-NMR, XPS) and electrochemical techniques (CV, SWV and EIS). Microscopic techniques revealed spherical morphologies with particle sizes in the range of 21-90 nm. Elemental distribution maps obtained from HRSEM for the novel cathode material showed an even distribution of elements which will facilitate the removal/insertion of Li-ions and electrons out/into the cathode material. Spectroscopic results (FTIR) revealed the vibration of the Si-Mn-O linkage, ascertaining the complete insertion of Mn ions into the SiO₄⁴⁻ tetrahedra. XRD and ⁷Li MAS NMR studies confirmed a Pmn21 orthorhombic crystal pattern for the pristine Li₂MnSiO₄ and novel Li₂MnSiO₄/Al₂O₃ which is reported to provide the simplest migratory pathway for Li-ions due to the high symmetrical equivalence of all Li sites in the unit cell, thus leading to high electrochemical reversibility and an enhancement in the overall performance of the cathode materials. The divalent state of manganese present in Li₂Mn²⁺SiO₄ was confirmed by XPS surface analysis. Scan rate studies performed on the novel cathode material showed a quasi-reversible electron transfer process. The novel cathode material demonstrated superior electrochemical performance over the pristine material. Charge/discharge capacity values calculated from the cyclic voltammograms of the novel and pristine cathode materials showed a higher charge and discharge capacity of 209 mAh/g and 107 mAh/g for the novel cathode material compared to 159 mAh/g and 68 mAh/g for the pristine material. The diffusion coefficient was one order of magnitude higher for the novel cathode material (3.06 x10⁻⁶ cm2s⁻¹) than that of the pristine material (6.79 x 10⁻⁷ cm2s⁻¹), with a charge transfer resistance of 1389 Ω and time constant (τ) of 1414.4 s rad⁻¹ for the novel cathode material compared to 1549 Ω and 1584.4 s rad-1 for the pristine material. The higher electrochemical performance of the novel Li₂MnSiO₄/All₂O₃ cathode material over the pristine Li₂MnSiO₄ material can be attributed to the alumina nanoparticle surface coating which considerably reduced the structural instability intrinsic to the pristine Li₂MnSiO₄ cathode material and improved the charge transfer kinetics.

The electrochemical investigation of nickel, copper and silver thin films interfaced with yttria stabilized zirconia (YSZ) solid electrolyte was accomplished to determine their response to polarization in dilute oxygen environments at 350 °C and assess their viability for electrochemical promotion of catalysis (EPOC). Polycrystalline YSZ (8 mol % Y2O3-ZrO2) pellets were synthesized in the lab and films deposited onto them using evaporative physical vapor deposition (PVD). The critical thickness of copper, silver and nickel thin films were foundusing in-situ resistance measurements. Following this, 50 and 100 nm copper and nickel films were studied using solid electrolyte cyclic voltammetry (SECV) to determine their response to polarization. Given that silver thin films at such thicknesses are thermally unstable, a film of 800 nm was used in this study. The materials were found to respond to polarization in different ways, forming oxides according to Wagner and Mott-Cabrera oxidation models.

The electrochemical oxidation of CoCl2(PPh3)2 was investigated in a mixture of acetonitrile and pentanol (1:1) at a platinum disk working electrode using Cyclic Voltammetry (CV) and Chronoamperometry. Elemental Analysis and Infrared Spectroscopy were used to characterise the synthesized compounds i.e. CoCl2(PPh3)2 and CoCl(PPh3)3. Cyclic Voltammetry was utilised for the examination of different working electrode materials that could be used for the anodic voltammetric studies of CoCl2 (PPh3)2, to characterise the reactants and products of each electrode reaction, to investigate the chloride binding ability to a CoCl(PPh3)3 complex, and to evaluate the electrocatalytic substitution of chloride by PPh3 from the complex CoCl2(PPh3)2. Use of ferrocene as an internal standard during the anodic studies of CoCl2(PPh3)2 was also evaluated. The number of electron involved in the electrode process, CoII to CoIII from CoCl2(PPh3)2 and diffusion coefficient of ferrocene in a mixture of acetonitrile and pentanol (1:1) were determined using Chronoamperometry. Ultraviolet-Visible (UV-Vis) and 31P Nuclear Magnetic Resonance (31P NMR) spectra were used to assist with the characterisation of the electrode reactions involved during oxidation of CoCl2(PPh3)2. / Dissertation (MSc (Chemistry))--University of Pretoria, 2008. / Chemistry / unrestricted

This master thesis deals with supercapacitors based on electrical double layer and proper carbon electrodes for this type of supercapacitors. In theoretical part of work is described theory of supercapacitors, energy storage principles and their properties. In the next part are described carbon materials, their properties and electrochemical methods of measurements that we used. In the experimental part is described preparation of electrodes, results and conclusion.

The diploma thesis deals with researching electrodeposition of silicon in anhydrous solutions. As electrolyte was used EC:DMC (1:1) with (C2H5)4NBF4, LiPF6 and LiClO4. Research was measured by cyclic voltammetry and XRD.

This work is focused on optimalisation of coposite materials for civil engineering. In the theoretical part of the project is introduction of the composite materials and materials which are used for their production. There are also concerned their properties and possible application areas. In conclusion of theoretical part this project is a summary of the possible use of composite materials. The practical part compares the characteristics of the different types of composites made in terms of conductivity and the rate of corrosion.

This thesis deals with the mixing of liquids issues. The simulation of structure for mixing of liquids and evaluation of parametres which have most significant influence on mixing of liquids was made with help of COMSOL programm. In the next section of thesis the quality of electrodes used for cyclic voltammetry made on LTCC by thick layer technology was determined. In the end of this thesis the 3D structure for mixing of liquids was made. The quality of mixing was controlled by cyclic voltammetry.

This work deals with the preparation of gold nanostructures for future usage in electrochemical sensors and biosensors, methods for their characterization and production. The emphasis is focused on the template-based electrodeposition method of gold and on study of the effect of manufacturing conditions on physical properties, mainly electrical and topological of nanostructures. Thesis is focused also on overall function and sensitivity of the gold nanostructured electrode.

A series of Fischer mono- and biscarbene complexes of the type [MLn{C=(XR)R'}] was synthesized and characterized. The redox behavior of the complexes was studied by different techniques, including cyclic voltammetry, spectroelectrochemistry, ESR and computational methods. Different transition metals (M) and carbene substituents (XR, R') were employed to compare both the effect of the central metal atom as well as the carbene substituent. Thienyl, furyl and ferrocenyl chromium(0) mono- and biscarbene complexes with ethoxy and amino substituents were electrochemically studied in CH2Cl2. Results were mutually consistent with computational data showing that the carbene double bond of all complexes is reduced pseudo reversibly to an anion radical, -Cr-C•. The Cr centers are oxidized in two successive one electron transfer steps to Cr(II) via the Cr(I) intermediate. For all ferrocenyl carbene complexes the Fe(II) is oxidized after the first oxidation of Cr. It was found that with respect to the aryl substituents the donating effect decreases from Fc>Fu>Th. Stabilization from the XR substituent, where XR = NHR, also resulted in lower redox potentials compared to their OEt analogues. The inclusion of ferrocene in the carbene substituent was done, as its redox activity and increased donating effect are well known. Mono- and biscarbene complexes with ethoxy and amino substituents of both chromium and tungsten were electrochemically studied. Again experimental data were supported by computational studies. Similar to the ethoxy chromium complexes, reduction of the W=C fragment to -W-C• was observed. However oxidation of the Fc group occurred first before the electrochemically irreversible oxidation process for W(0) involving a three electron-mediated process as seen in chronocoulometric analyses. The tungsten oxidation was restricted to a W0/II, consistent with computational studies, by the use of the electrolyte [NnBu4][B(C6F5)4]. The short-lived W(II) species were calculated to be stabilized by agostic CH···W interactions, similar to the chromium analogues. To extend linkers between the metal-carbene termini and investigate metal-metal interaction, biferrocenyl and 2,5-thienylbiferrocenyl tungsten(0) mono-and biscarbene complexes were synthesized and studied by spectroelectrochemistry. A metal-metal charge transfer transition between the tungsten carbonyl increment and the biferrocenyl / 2,5-thienylbiferrocenyl unit was confirmed by infrared spectroelectrochemical studies. The electronic interaction in the corresponding cationic species can be described as weakly coupled class II systems according to Robin and Day. The cymantrenyl moiety, Mn(η5-C5H4)(CO)3, provides an interesting alternative to ferrocene as an organometallic molecular tag, however the instability of the radical cation impairs its use. Improved stability of the cation, monitored by electrochemical measurements, was accomplished by substituting a carbonyl with a ferrocenyl Fischer carbene ligand resulting in Mn(I) oxidation occuring at lower potentials than ferrocenyl oxidation. These uncommon Fischer carbene complexes is the first organometallic multi-tags reported. The mono cationic species, [CpMn(CO)2{=C(OEt)Fc}][PF6], could be isolated and characterized with ESR analysis. Finally, transmetallation from the tungsten(0) Fischer carbene complexes yielded examples of rare acyclic alkoxy- and aminocarbene complexes of gold(I). Single x-ray structures for all complexes could be obtained including the novel ferrocenophane dinuclear biscarbene Au(I) complex. All structures display unsupported aurophilic interactions, while the bridging biscarbene shows a semi-supported Au-Au interaction. In the case of the furanyl/thienyl methoxy monocarbene complexes, extended Au-Au interactions result in oligomeric structures. Although this study is of a fundamental nature, it is imperative for the understanding and design of gold compounds with specific applications. / Thesis (PhD)--University of Pretoria, 2013. / gm2014 / Chemistry / unrestricted