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Electrochemistry of macrocyclic complexes
Kaďorková, Veronika ; Liška, Alan (advisor) ; Kotek, Jan (referee)
The present thesis summarizes fundamental electrochemical properties of copper(II) complexes derived from three cyclame-like macrocyclic ligands. Target application of the studied complexes is radioimaging in medicine. The complexes were studied by means of DC-polarography and cyclic voltammery on mercury hanging drop electrode in buffered media (0.1M sodium acetate, pH 5) upon mixing of the ligand and copper(II) sulfate stock solutions. All three complexes undergo a single two-electron irreversible reduction process yielding free ligand and copper amalgam. The apparent thermodynamic stability of the investigated complexes (expressed as negative shift of the observed reduction potentials relatively to copper(II) sulfate) correlates to structural motifs employed in the individual ligand molecules. Presence of the bridged moiety as well as the carboxylate group seems to enhance the overall stability whereas the phenolic oxygen atoms in role of donor atoms seem to be less efficient.
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Development and characterization of micro-reference electrodes for bioelectronics applications
Florian, Vojtěch ; Glowacki, Eric Daniel (referee) ; Ehlich, Jiří (advisor)
The subject of this work was the construction and long term stability measurement of micro-reference electrodes based on anodized silver wire and titanium wire with Ag/AgCl paste. A measuring apparatus, with which the long term stability was measured, was constructed as a part of this work. These days, commercial reference electrodes are available on the market. These reference electrodes are characterized by their excellent long term stability, however, they are too large and too expensive to be used in bioelectronic systems. Because of this, the science community has been trying to miniaturize reference electrodes in the past years. Without reference electrodes, it is impossible to do most electrochemical measurements. Based on the long term stability of measured samples it was determined which of the samples meet the criteria for bioelectronic measurements. It was also determined which of the studied samples were most suitable. The last result of this work is a measuring apparatus that can measure the long term stability of up to thirty-two electrodes.
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Thermodynamic modelling of hydrogen fuel cells
Nováček, Marek ; Pavelka, Michal (advisor) ; Němec, Tomáš (referee)
In this thesis, proton exchange membrane fuel cells are studied. At the beginning, the ideas underlying their function are exposed and some possibilities of usage are pre- sented. Thereafter, we aim to describe the processes inside the fuel cells with the aid of thermodynamics and in agreement with constitutive relations that have been obtained experimentally. Namely, we are interested in the fluxes of water and protons inside the membrane, where they are acted upon by thermodynamic forces, and the electrochemical reactions at the electrodes, which can be described by the Butler-Volmer equations. Also do we study the efficiency of the fuel cell by evaluating the production of entropy due to the diverse processes that take place in the fuel cell. It is the goal of the computational part of this thesis to propose a zero-dimensional model and compare it with the results provided in the supervisor's doctoral thesis. 1
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Electrochemical studies of the analytical utilization of self-assembled monolayers of calix[4]arene on the surface of polycrystalline gold electrode
Hrdlička, Vojtěch ; Navrátil, Tomáš (advisor) ; Ludvík, Jiří (referee)
This MSc. Thesis deals with electrochemical studies of the analytical utilization of self-assembled monolayers of thiolated calix[4]arene (C4A) and/or undecanthiole (C11SH) on the surface of a polycrystalline gold electrode. Hydroquinone, nitrobenzene, 2-nitrophenole and 4-nitrophenole have been used as tested model compounds. The real surface area of the electrode was determined using these two methods: From the charge of desorption peak of α-gold oxides (5.72±0.48 mm2 ) and using the Randles- Ševčík equation. (6.14±0.59 mm2 ). The preparation of the electrode consisted of polishing on alumina, immersing into piranha solution and cyclic voltammetry. The area of electrode surface was well reproducible. Stability of thiol monolayer in the area of negative potentials was tested. The C11SH layer is very stable; the desorption peak was recorded in basic solutions only (at −1.3 V vs. 3M Ag/AgCl). The position of the desorption peak of C4A is more pH dependent and it was recorded at −1.08 V at pH 13. The properties of the electrode modified by C11SH and or C4A were investigated using the model compound hydroquinone. It is assumed that the oxidation of the hydroquinone does not take place inside the C4A cavity; hence the hydroquinone molecule is too big to pass through the cavity. C11SH and C4 + C11SH act...
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Electrochemistry of Nitrocalixarenes
Liška, Alan ; Vojtíšek, Pavel (advisor) ; Cibulka, Radek (referee)
In this diploma thesis a detailed investigation of the step-by-step reduction mechanism of cone-mono-, di-, tri and tetranitrocalix[4]arenes (in non-aqueous DMF) is presented. The intramolecular interaction of reducible (and reduced) centers and its consequences for the geometry of the starting molecule was discussed including the character of radicalic intermediates and their spin state. It was found, that the electrochemically generated radical anions of nitrogroups (unlike their starting electroneutral state) can act as ligands. Therefore, a study of complex formation equilibria of cone-tetranitrocalix[4]arenes with alkali metal cations followed. The possible use of a "stereoelectrochemical" approach (the relationship between geometry or conformation of the molecule and its electrochemical data) was demonstrated in describing and explaining conformational and electrochemical differences between two isomeric dinitrocalix[4]arenes. Finally, a new series of 1,3-alt-tetranitrothiacalix[4]arenes was electrochemically characterized and compared with the "classic" calixarene derivatives. Key words: electrochemistry, calixarenes, stereochemistry
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Exectrochemical methods as tools for study complex macrocyclic moleculs
Liška, Alan ; Vojtíšek, Pavel (advisor) ; Liška, František (referee)
By means of electrochemical techniques, the electroreduction of polynitrocalix[4]arenes - molecules with multiple redox centers - was investigated and described. Based on interpretation of experimental data and on their correlation with quantum chemical calculations the relationship between structure and redox properties of the title molecules was revealed and discussed. It was shown that the tetranitrocalix[4]arenes involve two different couples of equivalent nitrogroups, what confirms experimentally the pinched shape of the molecule even in solution. The sequence of reduction steps was determined and the corresponding mechanism described. In the first part of the thesis different reduction mechanisms of p-substituted nitroaromates were found in dependence on substitution. It points to an important influence of lower ring substitution on the redox properties of the whole tetranitrocalix[4]arene.
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Investigation of new catalysts for polymer membrane fuel cells
Fiala, Roman ; Matolín, Vladimír (advisor) ; Bystroň, Tomáš (referee) ; Napporn, Teko Wilhelmin (referee)
Fuel cells are a promising alternate power source of electricity. Despite of sig- nificant improvement that was reached by research throughout recent decades, the technology is not still ready to large scale commercial use. The catalyst of fuel cell (FC) should be still investigated due to fact that the only reliable functional catalyst is Platinum, a noble and expensive metal, which makes the use of this technology not competitive. In this thesis, investigation of Platinum doped ceria catalyst and its modification prepared by physical technique of deposition which is magnetron sputtering is presented. The catalyst was studied using standard sur- face analytic techniques (PES, SEM, AFM, XANES) as well as electrochemical measurement (CV, PEIS). The principal part of this thesis reports direct analyses of catalyst in fuel cell using an individually designed fuel cell test station. Con- sidering the high power density (PD) about 1 W cm−2 and substantially higher specific power per gram of Platinum (SP) 1.6 kW mg−1 in comparison with com- mercial Pt-Ru/Pt-C reference catalyst and additionally the relatively longtime stability, the sputtered Platinum doped cerium oxide based catalyst was found a suitable catalyst for PEM FC. Moreover, possible substitution of Pt and CeO2 by other elements was shown. Beside of...
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Voltammetric Determination of Nimesulide Using Graphite Composite Electrode
Hubáčková, Monika ; Vyskočil, Vlastimil (advisor) ; Fischer, Jan (referee)
This Diploma Thesis deals with the study of the electrochemical behaviour of the nonsteroidal anti-inflammatory drug nimesulide. The aim of this work is to find optimal conditions for the determination of nimesulide using voltammetric techniques direct current voltammetry (DCV) and differential pulse voltammetry (DPV) in oxidation and reduction potential regions. An ultra-trace graphite electrode (UTGE) was used as the working electrode. The pH dependence was measured to select the optimal pH, the probable mechanism of reactions was determined, the repeatability of the measurements was checked, and finally the calibration dependences were constructed and evaluated in the selected media. BR buffer media of pH 2 and 4 for DCV and pH 2 and 5 for DPV were selected to measure calibration curves in the concentration range of 0.1-100 µmol L−1 . The detection limits for both methods DCV and DPV at the UTGE were in order of about 10−7 mol L−1 , which are values corresponding to alternative voltametric methods that also use unmodified working electrodes.
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Preparation of electrodes of Li-S batteries using inversely vulcanized sulfur
Trochta, David ; Kunický, Daniel (referee) ; Čech, Ondřej (advisor)
This work focuses on research of lithium-sulfur batteries, which are a promising battery type due to their theoretically high capacity and low environmental impact. Steering away from the commonly used elementary sulfur as the electroactive material of the cathode, inversely vulcanized sulfur with amorphic structure was utilized instead, while the manufacturing process of which was improved and optimized during the research. A series of samples of inversely vulcanized sulfur was synthesised, each containing a different ratio of the input precursors. X-ray diffraction was used to verify the amorphic structure of the material, which simultaneously also ruled out the presence of crystalline sulfur. Additionally, this work presents the results of Raman spectroscopy. At the same time, the possibility of utilization of Raman spectroscopy to identify the exact quantitative ratios of the used precursors was presented for the first time. Specific samples were also handpicked to undertake a dissolution test involving procedural solvents. Electrodes for electrochemical cells (Li-S battery) were manufactured based upon the knowledge gathered. The distribution homogeneity of the electroactive material of the electrode was observed through creation of an elemental map using the EDS technique. Electrochemical characterization of the selected inversely vulcanized sulfur electrode samples was measured using various methods: cyclical voltammetry, electrochemical impedance spectroscopy and galvanostatic cycling with potential limitation.
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