>Magister Scientiae - MSc / In the current study, we give a report when oxalic acid was used as an electrolyte to synthesize an AAO template with hexagonal pore array. Optimum parameters were observed as 0.4 M of oxalic acid, anodizing voltage of 45 V, temperature of approximately 8 °C and the period of 120 minutes. Atomic force microscope (AFM) and High resolution scanning electron microscope (HRSEM) showed that template has an average pore diameter of 103 nm. Co and MnOx (x = 1,2) nanostructures were selectively deposited in the pores of the template using a novel atomic layer deposition (ALD) technique. The diameter sizes and the array of the nanostructures and the template were corresponding. Energy dispersive xrays (EDX) and X-ray photoelectron spectroscopy (XPS) confirmed the presence of Co and MnOx (x =1,2) on the samples while x-ray diffraction (XRD) provided an indication of their orientations. Magnetic force microscopy as main characterization tool showed the existence of multi-domains on both Co and MnOx (x =1,2) nanostructures. / South Africa

This graduate work deals with the study and preparation of gel polymer electrolytes with flame retardants for lithium-ion batteries. The theoretical part describes the types of electrolytes, their features, benefits, how they differ and where they are used in detail. The basis of this section is gel electrolytes with flame retardants, to measure their electrical and electrochemical properties. The experimental part deals with the preparation of samples of gel electrolytes with different percentages of flame retardant, where varied species of flame retardants and measuring their electrical conductivity and potential windows. Impedance spectroscopy, cyclic voltammetry and dynamic-analytical thermal analysis were selected as measuring methods.

This master's thesis deals with a topic of determination of the most suitable ratio of cathode materials for the lithium-sulfur systems. The first two chapters provide a general introduction to the topic of electrochemical energy sources and present the commonly used primary and secondary battery systems with emphasis on their characteristics and applications. The core of the theoretical part is dedicated to lithium-ion and lithium-sulfur batteries, their working principles along with the benefits or drawbacks related to the particular systems, and widely used materials. The experimental part briefly comments on determining the suitable electrode paste preparation method, the subsequent main part is focused on evaluation of electrochemical performance of cells using different ratios of cathode materials. Five samples of cathode materials were prepared, where the sulfur ratio is in range from 64 to 88 wt. %. Finally, the comparison of all prepared ratios in terms of their electrochemical properties is provided.

This diploma thesis deals with the description of individual types of batteries. The first part is focused to primary and secondary batteries, materials for their positive and negative electrodes with a focus on lithium-ion batteries and their changes over time. The next section focuses on a more detailed description of sodium-ion batteries, used electrode materials and to their problems. Practical part is focesed to preparing of electrode materials and to completing of measuring electrochemical cell and to discribing of measuring methodes and to evaluation of measured data.

Philosophiae Doctor - PhD / Ammonia has attracted attention as a possible fuel for direct fuel cells since it is easy to handle under low pressure, costs only slightly higher than methanol and can easily be cracked down into hydrogen and nitrogen. At low temperature, ammonia oxidation on noble metal electrodes is a sluggish reaction and efficient catalysts are required to convert ammonia to nitrogen and hydrogen at reasonable reaction rates. In this thesis, I present polycrystalline and oriented nanoalloys synthesised at room temperature in aqueous media and their catalytic effects on the oxidation of ammonia. The electro-oxidation of ammonia on palladium-goldsilver (PdAuAgNPs) ternary nanoalloys was systematically studied in alkaline solution of potassium hydroxide (KOH) by cyclic voltammetry (CV). The PdAuAg nanoalloys were prepared through a facile synthesis with ascorbic acid as a reductant and polyvinylpyrrolidone (PVP) as a stabilising agent from aqueous solutions of PdCh/HAuCI4.3H20/AgN03 mixtures. UV-visible spectroscopy was used to confirm the complete reduction of the metal ions; absorption peaks observed at 260 nm, 285 nm and 420 nm for Ag", Au3+ and Pd2+ ions respectively, disappeared after reduction indicating a complete reduction of the metal ions to zero-valent nanoparticles. High resolution transmission electron microscopy (HR TEM) revealed the formation of crystalline nonaggregated 25-35 nm sized nanoalloys. The elemental composition of the nanoalloys measured using energy dispersive X-ray spectroscopy (EDX) showed the presence of the three elements; Pd, Au and Ag. The well-dispersed non-agglomerated PdAuAg nanoalloys exhibited a reduced overpotential and a 33%, 400%,82% and 54% increase in current density for ammonia electro-oxidation compared to Pd, PdAg, PdAu nanoparticles and bare Pt electrode, respectively. The much improved current density of the well-dispersed PdAuAg nanoalloys is attributed to the increased electrochemically active surface area of the nanoalloys. This electro catalytic behaviour of the PdAuAg nanoalloys for ammonia oxidation in KOH solutions provides a promising route for development of low-cost and high performance electro catalyst for electro-oxidation of ammoniaMoreover, ammonia oxidation on platinum surfaces has been found to be a very structure sensitive reaction which takes place almost exclusively on Pt(100) surfaces. I report for the first time the preparation of sodium polyacrylate-capped Pt(100)Pd, pte 1OO)Au, pte 1OO)Ir, Pt(IOO)Rh, Pt(100)PdAu, Pt(100)IrAu, Pt(IOO)PdIr and Pt(IOO)RhAu nanoalloys. The reduction of the metal ions to nanoparticles was confirmed by UV-visible spectroscopy while the shapes and the structures of the nanoparticles were studied using HRTEM and CV. HRTEM analysis showed well distributed non-agglomerated 5-20 nm semi-spherical and cubic nanoalloys with lattice fridges on their surfaces indicating the crystalline nature of the nanoalloys. Pt(100) nanoalloy systems showed particles with triangular and cubic shapes. The existence of the preferentially cubic shaped nanoparticles in the samples indicated that the nanoalloys had some (100) sites orientation/a significant amount of (100) sites at their surfaces. The CV of the nanoparticles in the hydrogen adsorption/desorption region (-200 mV to 100 mV vs. Ag! AgCl) was used to obtain qualitative information about the surface structure of the nanoparticles. The voltammogram of oriented Pt(100) nanoparticles showed very clearly the presence of adsorption states associated with (110) sites, (100) domains and (l00) sites at -131 mV, -34 mV and 29 mV, respectively. The companson of this voltammetric profile with that obtained for a Pt(100) single crystal electrode clearly points out that the synthesised Pt nanoparticles have a high density of (100) sites. However, the peak that was observed at 29 mV in the CV of Pt(100) nanoparticles was not present in the vo ltammo grams of the Pt(100) nanoalloy systems confirming the formation of the nanoalloys. The results reported in this work demonstrate the importance of controlling the intrinsic structural properties of Pt nanoparticles; in terms of nature of the active sites and the effect of adding adatoms (such as Au, Pd, Rh, Ir) in order to understand their catalytic properties. The electrochemical activities of these nanoparticles for ammonia oxidation in basic medium showed an increase of over 100% current density compared to Pt electrode. Pt(lOO)RhAu nanoalloys showed the highest catalytic properties while Pt(lOO)PdAu had the lowest as shown in the trend: Pt(lOO)RhAu > Pt(lOO)PdIr > Pt(lOO) > Pt(lOO)IrAu > Pt(lOO)Pd> Pt(lOO)Rh > Pt(lOO)Au > Pt(lOO)Ir > Pt(lOO)PdAu. The synthesised oriented nanoalloys were further interrogated towards the oxidation of hydrazine as a fuel for hydrazine fuel cells. The oriented Pt(lOO) nanoparticles and Pt(lOO) nanoalloy systems exhibited over 1000% increase in current density and reduced oxidation overpotential compared to bare glassy carbon electrode. These excellent catalytic properties are attributed to the increased surface area and the presence of (100) sites which favour the oxidation of hydrazine.

The present work deals with the use of manganese oxide as a catalyst for positive electrode of fuel cells. The theoretical part is to analyze the problem of fuel cells, focusing on lowtemperature fuel cells. Are discussed and the methods of measurement and evaluation of properties of manganese oxide layer. The practical part deals with doping electrolytic manganese dioxide salts of divalent metals and monitoring their behavior in the cyclic voltammetry by the EQCM method.

Nowadays it is attached to a major effort to study applications of nanoparticles in biosensors technology. We studied the effect of gold nanoparticles on the surface of the electrodes by Electrochemical Impedance Spectroscopy method and Cyclic Voltammetry. For impedance measurements was proposed substitute electrical model and cyclic voltammetry method was used to determine the electroactive surface of electrodes.

The present work deals with the research and development of gel polymer electrolytes and their applications. Thesis talks about the mechanisms that take place in gel electro-lytes. It also discusses the electroanalytical methods used in assessing the gel electro-lytes. The main focus of the work is the preparation of gel polymer electrolytes and compared their properties using methods of impedance spectroscopy, cyclic voltam-metry and methods of measurement of transference numbers. KEYWORDS

This dissertation work deals with analysis of nickel hydroxide phases, their oxidation compounds, their stability and degradation mechanisms of electrochemically more active alpha phase on standard beta phase. The active material was prepared by both methods, electrodeposition and chemical precipitation. Main analysis method was Electrochemical Quartz Crystal Microbalance in combination with common analytical methods (cyclic voltammetry, potenciometry) can resolute between alpha and beta phases and quantitatively describe differences in main reaction by monitoring mass changes in the active material. Poor stability of the ?-Ni(OH)2 were improved by adding cations with valence two three and four into the structure instead of Ni atoms. The most important role plays cobalt and its hydroxide. Totally new way is to use titanium in combination with other cations. In electrolyte the most significant addition is LiOH, which has beneficial influent on cycle ability, stability in strong alkaline medium and cycle life.

Nowadays, nanostructures fixed on solid substrates and colloidal nanoparticles permeate through all areas of human life, in area of sensors and detection as well. This dissertation thesis deals with the fabrication of nanostructures on the surface of planar electrodes via self-ordered nanoporous template of aluminum trioxide. The nanofabrication, as one of many possible techniques, is used to increase the active surface area of electrodes by creating unique surface types with specific properties. These electrodes are very perspective in the applications, such as biomolecules electrochemical detection and measurement. The transformation of aluminum layer into non-conductive nanoporous template in the process of anodic oxidation is a fundamental technique employed to obtain the array of nanostructures in this thesis. The fabrication of high quality nanoporous membranes with narrow pore size distribution on various types of metallic multilayers is one of the key experimental parts in this work. Several problems associated with the production of the thin-film systems, including the dissolving the barrier oxide layer, are discussed and solved. Another part of this work deals with the use of nanoporous membrane as a template for the production of metallic nanostructures via electrochemical metal ions deposition directly into the pores. The obtained nanostructures as nanowires, nanorods or nanodots are characterized by the scanning electron microscopy and energy-dispersive or wavelength X-ray spectroscopy. The electrode surface, modified by gold nanostructures suitable for the detection of biomolecules, has been chosen for the electrochemical measurements, due to the gold biocompatibility. The nanostructured electrodes were characterized by electrochemical impedance spectroscopy and cyclic voltammetry. The effect of nanostructured surface geometrical parameters, including the size of the electrochemically active area, on the results of electrochemical measurements has been observed and compared to flat gold electrodes. Two model biomolecules, namely guanine and glutathione, have been chosen for the study of potential application of these nanostructures in biosensors.