This thesis describes optimization and modification of standard thick-film electrochemical sensor to be able to be used for detection in microvolumes. In the theoretical part, the thick film technology is described. The work is then focused on the wettability of surfaces followed by introduction to electrochemistry and electro-analytical methods. In the experimental part, screen-printing of various types of thick film pastes on ceramic substrates for determination of their wettability and the following modification of the sensors with thick-film paste and with Parylene vaporization can be found, as well as the basic electrochemical measurements in microvolume using the modified sensor. Finally the results are summarized in conclusion.

The thesis is focused on the electrodeposition of tantalum from ionic solution 1-butyl-1- methylpyrrolidinium bis(trifluoromethylsulfonyl) imide, ([BMP]Tf2N) at 200°C and description of related transfer and kinetic phenomena on the interface between the ionic solution and working electrode. Furthermore, the electrodeposition of tantalum layers in different ionic solutions containing tantalum salts and especially in ([BMP]Tf2N) is introduced. In the last part of the thesis, results of cyclic voltammetry, surface analysis SEM and elemental analysis EDX are discussed. MIS (metal-insulator-semiconductor) structure was determined comprising porous anodic alumina as the insulator and semiconductive TaxOy on the top of the insulator. The electric conductivity of the MIS structures was studied by using amper-volt IV and CV characteristics. The results of the cyclic voltametry, impedance spectroscopy and chronoamperometry are discussed.

Die Elektrochemie und die Spektroelektrochemie von selbst-organisiererten Monoschichten (selfassembled monolayers, SAMs) gebildet aus 2-Mercaptopyridin (2MP) und 4-Mercaptopyridin (4MP) wurden an polykristallinen Goldelektroden in wässrigen Elektrolytlösungen untersucht. Folgende Untersuchungsmethoden wurden angewandt: zyklische Voltammetrie, elektrochemische Impedanzmessungen (EIM) und oberflächenverstärkte Raman Streuung (surface-enhanced Raman scattering, SERS). Die elektrochemischen Untersuchungen von 2MP und 4MP in wässriger saurer Lösung (0.5 M H2SO4) zeigten, dass 2MP stärker adsorbiert wird als 4MP aufgrund der Bildung eines S-Au-N Chelates, wobei die S-Au-Interaktionen bei 4MP stärker sind. Die Bildung eines Chelates im Falle von 2MP verringert die Wahrscheinlichkeit der Bildung eines Dimers. In sauren Lösungen wird das N-Atom von 2MP protoniert, was zu einer schwächeren Bindung von 2MP-Molekülen zur Substratoberfläche führt. Die Ergebnisse der SERS-Untersuchungen stimmen mit den Resultaten aus der zyklischen Voltammetrie überein. Man erhält eine Au-S-Streckschwingungsbande für 2MP zwischen 225 bis 250 cm-1 bei Abscheidung aus wässriger oder saurer Lösung und für 4MP bei ca. 263 cm-1 in beiden Lösungen. Die SERS-Experimente ergaben eine senkrechte Orientierung zur Goldoberfläche sowohl für 2MP als auch für 4MP. Die Thion-Thiol-Tautomerie von 2- Mercaptopyridinen wurde ebenfalls in Betracht gezogen. Die Unter- und Überpotentialabscheidung von Kupfer auf einer polykristallinen Goldelektrode in wässriger 0.1 M Schwefelsäure in An- und Abwesenheit von SAMs von 2- und 4- Mercaptopyridin wurde mit zyklischer Voltammetrie untersucht. Es zeigte sich, daß bei Vorhandensein der SAMs die Elektrodeposition von Kupfer verhindert wird, was auf starke Wechselwirkungskräfte zwischen dem Adsorbat (MP) und der Goldoberfläche zurückzuführen ist. 2MP zeigt eine grössere Inhibierung, was höchstwahrscheinlich auf die Bildung der Chelatstruktur zurückzuführen ist. Es wurden ebenso Untersuchungen zum Einfluss von 2MP und 4MP auf die abgeschiedene Kupfermonolage auf der Goldelektrode durchgeführt. Es zeigte sich, daß die Kupfermonolage teilweise durch 2MP oder 4MP ersetzt wird. Die Elektronenaustauschgeschwindigkeit für das Fe2+/Fe3+-Redoxsystem in An- und Abwesenheit von 2MP- oder 4MP-Monolagen wurde mit zyklischer Voltammetrie und elektrochemischen Impedanzmessungen (EIM) untersucht. Es stellte sich heraus, dass der Elektronenaustausch höchstwahrscheinlich über Defektstellen in der Monolage (Pinholes) erfolgt. In einer wässrigen Lösung verringert 4MP den Elektronenaustausch stärker als 2MP. Da die Packungsdichte bei 4MP größer ist als bei 2MP ist wahrscheinlich auch die Zahl der Pinholes geringer in der 4MP-Monolage. In saurer Lösung liegen die N-Atome protoniert vor. Man kann davon ausgehen, dass in saurer Lösung zwei Prozesse gleichzeitig ablaufen, die für den Elektronenaustausch entscheidend sind. Erstens kommt es zu einer Abstoßung zwischen der positiv geladenen Monolage und den positiv geladenen Redoxionen. Und zweitens erfolgt eine Abstoßung zwischen den positiv geladenen Molekülen der SAMs, was zu einer geringeren Packungsdichte führt. Der Ladungsaustausch wird dominiert durch den zweiten Effekt. Mit Hilfe von EIM wurden die Elektronenaustauschgeschwindigkeit und der Bedeckungsgrad bestimmt. Die korrosionshemmende Wirkung von 2MP und 4MP auf Stahl in 3.5 % wässriger NaCl-Lösung wurde mit Hilfe der EIM untersucht. 2MP zeigte eine grössere Hemmung als 4MP. / The electrochemistry and spectroelectrochemistry of the self-assembled monolayers (SAMs) prepared of 2-mercaptopyridine (2MP) and 4-mercaptopyridine (4MP) dissolved either in water or 0.1 M H2SO4 have been investigated at polycrystalline gold electrodes in aqueous electrolyte solutions using cyclic voltammetry, electrochemical impedance measurements (EIM) and surface enhanced Raman spectroscopy (SERS). Electrochemical studies of 2MP and 4MP monolayers in aqueous acidic solution (0.5 M H2SO4) suggest that 2MP is adsorbed more strongly than 4MP due to the formation of S-Au-N chelate. However, the S-Au bond was found to be stronger in 4MP as compared with 2MP. The formation of the chelate in case of 2MP diminishes the probability of dimer formation. In the acidic solvent, the N-atom of 2MP molecule will be protonated leading to a weaker interaction of 2MP molecules with the substrate surface. The SERS results are in good agreement with the cyclic voltammetry results. The Au-S stretching band was obtained in the region from 215 to 245 cm-1 for 2MP deposited from water and acidic solvent and around 263 cm-1 for 4MP in both solvents. The SERS measurements showed also a perpendicular orientation of both 2MP and 4MP on the gold surface. In explaining the SERS results, the thione-thiol tautomerisations of the mercaptopyridines were also taken into consideration. The under- and overpotential deposition of copper on a polycrystalline gold electrode in aqueous 0.1 M sulfuric acid in the presence and in the absence of SAMs of 2- and 4-mercaptopyridine has been studied using cyclic voltammetry. In general, the presence of these SAMs has been found to inhibit the electrodeposition process of copper, suggesting very strong interactions between these adsorbates and the Au surface. 2MP shows a higher degree of inhibition, which is due to a stronger interaction probably due to the formation of the chelate structure. Studies have also been made of the influence of mercaptopyridines SAMs on the copper monolayer electrodeposited on the gold surface. The copper adlayer was found to be partially displaced by 2MP and 4MP monolayers. The rate of electron transfer for the Fe3+/2+ redox system on the gold electrode has been probed in the absence and presence of 2MP and 4MP monolayers by cyclic voltammetry and electrochemical impedance measurements (EIM). The charge transfer process was suggested to occur through the defects (pinholes) in the monolayer. In case of aqueous solvent 4MP decreases the electron transfer reaction stronger than 2MP. Since the packing density for 4MP is higher than that of 2MP the number of pinholes might be lower in 4MP monolayer. In acidic solvent the N-atoms of the mercaptopyridines will be protonated. It is proposed that two effects, which exist at the same time, are responsible for the electron transfer process in acidic solution. First, there will be a repulsive interaction between the positively charged monolayer and the positively charged redox probe. Second, there is a repulsion among the positively charged monolayer molecules that results in a less compact monolayer. The charge transfer is dominated due to the latter effect. With the EIM the rate of electron transfer and the surface coverage were determined. 2MP and 4MP were examined as steel corrosion inhibitors in 3.5% aqueous NaCl solution using EIM. 2MP shows higher inhibition efficiency than 4MP.

In recent developments of mixed potential gas sensors based on Yttrium Stabilized Zirconia (YSZ), the combination of Au/AuPt-admixtures and oxides was found to be promising electrode materials. With this material combination, satisfactory sensing characteristics were achieved, but the role of Au addition, especially its effect on the processes contributing to the mixed potential formation, has not yet been well understood. Deeper insights of the influence of Au on the electrochemical behaviors of this kind of electrodes are necessary for better understanding of the sensing behaviors and for achieving further technological improvements, as for instance, enhancement of the long-term stability. This situation motivated studies of a layered Au,Pt-YSZ mixed potential gas sensing electrode and its dependence on the thickness of the Au-layer and the sintering conditions. In this work, for the first time three variations of this kind of electrode, which generally comprises a thick-film Pt-YSZ electrode and a thin-film Au layer deposited on top, were studied by different kinds of material analytical approaches and electrochemical methods. These studies elucidated the correlation among the electrochemical behaviors of the electrodes, the amount of gold deposition and its non-uniform distribution over the electrode. Based on these structural and electrochemical data, a qualitative model for the first time is proposed to interpret the sensing mechanism of the layered Au,Pt-YSZ electrodes. In the past such a theory was only available for the electrodes at which the Au was homogeneously admixed with the Pt-YSZ composite. From the structural studies including the ESEM, the XRD and the Glow Discharge-Optical Emission Spectroscopy analysis (GD-OES), it was shown that the thin film Au layer at the layered Au,Pt-YSZ electrodes is not uniformly admixed with the Pt-YSZ bulk after firing, but results in a non-uniform lateral distribution on the electrode surface and a concentration gradient of Au from top over the thickness of the electrode. This Au distribution is strongly affected by the sintering temperature. The higher sintering temperature (1050 °C) results in not only a more uniform morphology of the electrode surface without a separate crystalline phase of gold , but also a better alloying of Au and Pt in the inner parts of the electrode during the sintering process, compared to the electrodes sintered at a lower temperature (850 °C). These clear structural differences of the electrodes fired at different temperatures are related to different catalytic activities over the electrode layer, and accordingly affect their open circuit potential (OCP) sensing behaviors and other electrochemical properties. With respect to selectivity and stability of the sensors, the highest sensing response was observed in the H2 containing gases compared to the other gas species like CO, CH4, and C3H6 for both the type II (low temperature sintered) and the type III (high temperature sintered) sensors. However, clear response and potential stability losses were observed at exposure to C3H6. Formation of coking layers on the electrode seems to be correlated with this response decrease. Surprisingly, the response degradation was even observed by aging the sensors at 600 °C in ambient air. Combined OCP, CV and EIS studies revealed that, the aging process results in some minor irreversible but mainly reversible changes at the electrode/electrolyte interface. Both induce the response degradation which is well correlated with an impedance increase and a CV current decrease. The reversible changes are assumed to be attributed to the formation of an oxidation phase of the metallic parts at the TPB, which is well described in literature. Now, for the first time in this work it could be demonstrated that this reversible response degradation can be nearly fully recovered by the application of cathodic polarization sequences. Consequently, due to the strong correlation between the OCP response to CO and the dynamic electrochemical behaviors ((EIS and CV)) at ambient air, both the EIS and the CV method can be used as efficient tools to check the sensitivity of the sensor at ambient air conditions. In case of OCP response degradation, the sensitivity can be almost fully regenerated by application of cathodic polarization at enhanced temperatures (T700°C). This combination of OCP measurements with dynamic electrochemical methods and the application of cathodic polarization procedures is of enormous practical relevance and was filed for a patent. It excited high interest of the sensor chip producer (Lamtec Meß- und Regeltechnik für Feuerungen GmbH, Walldorf) because it allows sensitivity estimation and regeneration of layered Au,Pt-YSZ gas sensing electrodes whenever ambient air conditions are given. For instance, in case of long-term CO/HC-monitoring for improvement of automated combustion process control of firing appliances, this procedure could be carried out in breaks between firing batches without the need of de-installation of the sensor and, indeed, without any exposure to model gases.

In this Diploma Thesis, an interaction of genotoxic environmental pollutant 2-nitrofluorene with a double-stranded calf thymus DNA has been studied using a hanging mercury drop electrode (HMDE) as an electrochemical sensor. Two types of DNA damage were investigated and electrochemically detected (using cyclic voltammetry and differential pulse voltammetry): (i) The DNA damage caused by the direct interaction with 2-nitrofluorene and (ii) the DNA damage caused by short-lived radicals generated by the electrochemical reduction of the nitro group in 2-nitrofluorene. For the study of direct interaction, HMDE was modified by DNA and the interaction of DNA with 2-nitrofluorene was studied, after their incubation, right at the HMDE surface (adsorptive transfer stripping technique) or the DNA was preincubated with 2-nitrofluorene and, subsequently, the interaction was studied voltammetrically (DNA titration technique). Using both detection techniques, the formation of DNA - 2-nitrofluorene complex was observed and the mutual interaction was interpreted as an intercalation between the DNA base pairs, although such interaction was not clearly confirmed by UV-visible absorption spectroscopy. An electrostatic binding of 2-nitrofluorene on DNA sugar-phosphate backbone was partially formed at low concentrations of...

In dieser Arbeit werden drei voneinander unabhängige Verfahren zur Diagnose von Alterungsvorgängen an automobilen Polymer-Elektrolyt-Membran-Brennstoffzellen-Stapeln und -Aggregaten entwickelt. Gemeinsam ermöglichen diese Methoden ein tieferes Verständnis für die elektrochemischen Schadensmechanismen und stellen Mittel zu deren Reduktion zur Verfügung. Die erste Methode behebt die an Stapeln auftretenden Probleme konventioneller Zyklovoltammetrie mittels gezielter Modifikation der Spannungstransienten. Dieses Vorgehen ermöglicht die exakte und sehr zuverlässig reproduzierbare Bestimmung von Wasserstoff- Crossoverstrom, Doppelschichtkapazität und aktiver Katalysator-Oberfläche im Stapel und stellt damit eine neue Art der Alterungsdiagnose an Stapeln dar. Der Zweck der zweiten Methode ist es, die systematische Entwicklung einer schonenden Betriebsstrategie für Luft-/Luft-Starts auf Aggregate-Ebene zu ermöglichen. Hierfür wird eine Reihe von Referenzelektroden in ein Fahrzeug-Aggregat eingebracht, um die im Stapel während des Starts ablaufenden elektrochemischen Vorgänge örtlich und zeitlich aufgelöst beobachten zu können. Auf diese Weise werden zwei Startprozeduren analysiert und bzgl. ihrer Eignung verglichen. Beim dritten Verfahren handelt es sich um eine Parameterschätzung, die die modellbasierte Diagnose und Regelung von schwer zu messenden Zustandsgrößen zum Ziel hat. Der echtzeitfähige Algorithmus schätzt die aktive Katalysator-Oberfläche, die Gaszusam- mensetzungen auf Anode und Kathode sowie den rezirkulierten Volumenstrom mittels verschiedener Modelle für Stapel und Systemkomponenten.:(1) Einleitung (2) Aufbau und elektrochemische Limitierungen von PEM-Brennstoffzellen (3) Aufbau von automobilen PEM-Brennstoffzellenaggregaten (4) Eine Übersicht bekannter Diagnosemethoden für PEM-Brennstoffzellen (5) In-situ-Charakterisierung von PEM-Brennstoffzellenstapeln (6) Bewertungsmethode für Startprozeduren von PEM-Brennstoffzellenaggregaten (7) Online-Diagnose mittels gekoppelter Echtzeit-Parameterschätzung (8) Zusammenfassung und Ausblick / This thesis presents three newly developed methods for the diagnosis of deterioration in automotive polymer electrolyte membrane fuel cell stacks and systems. The combination of these methods allows for a more comprehensive understanding of electrochemical degradation processes and provides means for their mitigation. The first technique aims at the elimination of problems associated with the application of conventional cyclic voltammetry on fuel cell stacks. This is achieved by specific modification of the voltage transients. The procedure enables the precise and highly reproducible measurement of the hydrogen crossover current, double layer capacity and the electrochemically active surface area within the stack and thus represents a completely new kind of stack diagnosis method. The intention of the second method is to facilitate the purposeful development of damage mitigating air-/air-startup operating strategies on system level. To that intent, a number of dynamic hydrogen reference electrodes are positioned within the stack of a vehicle system, which allows for locally and temporally resolved observation of the electrochemical processes. Using this method, two startup procedures are analysed and compared with regard to their suitability. The third technique is an online parameter estimation aiming at the model based diagnosis and control of quantities, which can only be measured with difficulty. The algorithm estimates the electrochemically active surface area, the gas compositions on anode and cathode and the recirculated volumetric flow using various models for stack and system components. With these three methods, all relevant parameters for the intrinsical quantification of the degradation of each single cell within the stack can be precisely quantified. The methods thus enable a direct observation of the deterioration of the fuel cell and contribute to a further increase in durability as well as faster and more efficient development processes.:(1) Einleitung (2) Aufbau und elektrochemische Limitierungen von PEM-Brennstoffzellen (3) Aufbau von automobilen PEM-Brennstoffzellenaggregaten (4) Eine Übersicht bekannter Diagnosemethoden für PEM-Brennstoffzellen (5) In-situ-Charakterisierung von PEM-Brennstoffzellenstapeln (6) Bewertungsmethode für Startprozeduren von PEM-Brennstoffzellenaggregaten (7) Online-Diagnose mittels gekoppelter Echtzeit-Parameterschätzung (8) Zusammenfassung und Ausblick

This thesis is concentrated on the optimization of conditions for determination of genotoxic environmental pollutants whitch belong to derivatives of polycyclic aromatic hydrocarbons − 1-nitropyrene (1-NP), 1-aminopyrene (1-AP) and 1-hydroxypyrene (1-HP). All three compounds were determined by differential pulse voltammetry (DPV) at boron-doped diamond film electrode in water-methanolic solutions. Further, 1-AP and 1-HP were determined in a model sample of urine. For this purpose, effective separative techniques such as solid phase extraction and high performance liquid chromatography with reverse phase and amperometric detection at above mentioned type of electrode were used. Limits of detection of all tested compounds in water-methanolic solutions are 9⋅10−8 −3⋅10−7 mol dm−3 using DPV and 1⋅10−8 mol dm−3 for 1-HP and 1-AP in model sample of urine determined by HPLC with amperometric detection.

El conocimiento de las características interfaciales es de suma importancia para poder desarrollar materiales que sean capaces de dar lugar a reacciones electrocatalíticas eficientes. Por esta razón, en esta tesis se muestran diferentes estudios interfaciales sobre superficies monocristalinas de platino y cobre en diferentes electrolitos. Además se estudian las características de la interfase electrodoldisolución con superficies de platino modificadas con adátomos de hierro, cobalto y níquel. Para ello, se han empleado las técnicas de voltametría cíclica, espectroscopía infrarroja con transformada de Fourier, desplazamiento de carga con CO y salto de temperatura inducido por láser. Los resultados muestran cómo varía el campo eléctrico interfacial disminuye al aumentar el recubrimiento de hierro y níquel en la superficie de platino. Este efecto tiene un gran impacto en la reacción de evolución de hidrógeno, ya que la mejora electrocatalítica de esta reacción está relacionada con la energía de reorganización de las moléculas de agua, la cual, depende de la fortaleza del campo eléctrico interfacial. Los estudios realizados en medio alcalino para las diferentes superficies de cobre y platino sin modificar muestran una correlación entre el potencial de máxima entropía y las funciones de trabajo para cada una de las diferentes orientaciones atómicas superficiales. Por otro lado, debido a la aplicabilidad de las nanopartículas en los sistemas reales de conversión de energía, se realizaron experimentos de sincrotrón empleando la técnica de Bragg coherent difraction imaging con el objetivo de estudiar el deterioro de las nanopartículas en condiciones operando.

Цель работы состояла в определении оптимальных значений диаметра и массы углеродных нанотрубок (УНТ) в нафионсодержащей модифицирующей пленке для получения наилучших электрохимических и аналитических характеристик толстопленочных углеродсодержащих электродов (ТУЭ). В ходе работы синтезированы многостенные УНТ со средним диаметром dср ≈ 23 нм методом каталитического пиролиза этанола и проведена кислотная очистка полученного материала от металлических частиц катализатора и других модификаций углерода. Аналогичным способом обработаны коммерческие УНТ с dср ≈ 147 и 16 нм от Sigma-Aldrich. Успешно изготовлены 36 типов ТУЭ без УНТ и на основе УНТ в условиях варьирования массового содержания УНТ в диапазоне MУНТ = 0,3-10,0 мкг на поверхности ТУЭ. Аттестация поверхностей электродов проведена методами оптической и электронной микроскопии. Изучены электрохимические характеристики изготовленных ТУЭ методами циклической вольтамперометриии и импедансной спектроскопии. Выполнено определение ионов железа (III) в модельном растворе методом адсорбционной инверсионной вольтамперометрии. Установлены оптимальные значения среднего диаметра УНТ dср ≥ 23 нм и массы УНТ MУНТ = 5,0-10,0 мкг на поверхности ТУЭ для получения наилучших электрохимические и аналитические характеристики. Разработанные ТУЭ на основе УНТ могут применяться для определения ионов тяжелых металлов в реальных водах с концентрацией меньшей предельно-допустимых значений, установленных нормативными документами. / The aim is to determine the optimal values of the diameter and weight of carbon nanotubes (CNT) in modifier film containing Nafion for the best electrochemical and analytical characteristics of the thick film of carbon-containing electrodes (TFCE). Multi-walled CNT with an average diameter dav ≈ 23 nm were synthesized by the catalytic pyrolysis of ethanol and purified from the metal catalyst particles and other modifications of carbon, using mixture of concentrated sulfuric and nitric acids. Commercial CNT with dav ≈ 147 and 16 nm from Sigma-Aldrich were treated by a similar procedure. The batch of 36 types of TFCE without CNT and based on CNT varied by weight of CNT (MCNT) on TFCE surface in the range of 0,3-10,0 μg was made. The electrode surfaces were studied by optical and electron microscopy. The electrochemical characteristics of obtained TFCE by cyclic voltammetry and electrochemical impedance spectroscopy were investigated. The detection of Fe (III) ions in a model solution was carried out by adsorptive stripping voltammetry. The optimal values of the average diameter of CNT dav ≥ 23 nm and a weight of CNT on TFCE surfaces MCNT = 5,0-10,0 μg were determined. These parameters allow us to reach the best electrochemical and analytical characteristics of modified TFCE. Developed TFCE based on CNT may be used for the detection of heavy metal ions in real water with a concentration of less maximum permissible values, established by regulations.

Объектами исследования являются полифенольные антиоксиданты. Целью выпускнoй квалификационной работы является исследование антиоксидантных свойств полифенольных соединений с позиции механизмов их действия. В работе рассмотрены причины возникновения окислительного стресса, система антиоксидантной защиты и существующие методы исследования антиоксидантных свойств соединений. В процессе работы предложенными методами оценена хелатирующая способность полифенолов по отношению к ионам железа (II) и (III), исследована зависимость антиоксидантных свойств от рН, определены значения условных констант устойчивости и их зависимость от рН. / The objects of research are polyphenolic antioxidants. The purpose of the final qualifying work is to study the antioxidant properties of polyphenolic compounds from the perspective of their mechanisms of action. The paper considers the causes of oxidative stress, the system of antioxidant protection and existing methods for studying the antioxidant properties of compounds. In the process of work, the proposed methods evaluated the chelating ability of polyphenols with respect to iron (II) and (III) ions, investigated the dependence of antioxidant properties on pH, determined the values of conditional stability constants and their dependence on pH.