The main aim and ultimate final goal of the work carried out in this thesis is a drive towards a feasible system for light harvesting, which is in short, using the Sun’s energy to create electricity or a fuel for our energy requirements here on Earth. This work will see an approach using the triple phase boundary afforded by a microdroplet array. Although light harvesting is an ambition which has seen decades of work and uncountable man-hours, approaching it from the angle of utilizing the triple phase boundary between two immiscible liquids and a solid electrode is a new, and novel concept. Before any attempts towards a light harvesting technique can be made, we will need to have characterized and fully understood the mechanisms and nuances, both for dark and light processes, that are observed at the triple phase boundary. This initial process will start by selection of a suitable redox molecule, and exploring its reactivity in microdroplets under dark conditions. Once this has been achieved, an attempt can be made to use this knowledge, and implement it towards light harvesting. This will eventually include an attempt to couple photo-excited states with other molecules, this will be an important step if energy is ever able to be stored from such a system. This early phase will also see the need to employ many other techniques other than electrochemistry in an effort to aid in the understanding and characterization of the triple phase boundary at microdroplets. This will include travelling to other laboratories in search of specialized scientific skills and apparatus, such as electron paramagnetic resonance, or photocurrent spectroscopy. It will also see the need to build new equipment needed to conduct tests such as surface tension visualization, or new electrochemical cells for photocurrent measurement. In summary, this report will see initial characterization of the processes, both light and dark, that occur within the triple phase boundary of a microdroplet for a given redox molecule dissolved within. Early attempts at coupling excited states with other molecules are also explored. Serendipity has always played a part in scientific discovery and the work outlined in this report was no different. The choice of oil used for the organic phase microdroplet deposits yielded some interesting and unexpected results, and has been implicated as one of the key aspects of the photoreactions that have been explored.

by Chow Lap-wai. / Thesis (M.A.)--Chinese University of Hong Kong, 1980. / Bibliography: leaves 185-188.

The characteristics of a Zinc/Air (Zn/Air) primary cell are discussed. In addition, current technologies and the corresponding electrical performance are introduced. The basic principles of operation of a Zn/Air primary cell are discussed, focusing on the anode, cathode, and electrolyte. Basic kinetic and transport expressions are developed for the two main components of the cell: the anode and cathode compartments, based on which an overall formula for the cell polarization is developed. Input parameters are selected and approximated where possible to observe the model¡¦s ability to predict potential versus current density. Time-dependent anode performance is accomplished through the use of the shrinking core reaction model for the discharge of the zinc particles. The time-dependent dimensionless radius of the zinc particle (ď) is then used in conjunction with the developed transport and kinetic expressions for the prediction of the overall cell performance as a function of time. Plots of cell voltage prediction versus time and percent capacity versus time are presented. The simulations indicate an adequate approximate analytic model valid for a variety of drain rates corresponding to current hearing instrument devices in the market.

This thesis reports the design and development of novel voltammetric pH sensors for buffered, low-buffered and unbuffered media. pH sensors in stagnant and hydrodynamic environments were designed and developed for performing measurements using square wave voltammetry. Chapter 1 introduces the motivation of this project, the current development of electrochemical sensors, and the basic theory and techniques of electrochemistry concerned within the thesis. The existing development of carbon-based electrochemical sensors and the application of screen-printing technology in sensor fabrication are highlighted. Chapter 2 introduces the screen-printing technology and the fundamental methods of numerical simulation. In addition, reagents, equipment and software packages used in the thesis are listed in this chapter. In Chapter 3, a novel design of quinone derivative-based pH probes is presented for the application in stagnant weakly buffered media (< 1mM), based on previous studies of quinone compounds in buffered media. The results from the weakly buffered system is consistent with the results in buffered systems. To further extend the application of this design in unbuffered media, a numerical model of a pH-sensitive redox particle immobilised on an electrode was developed, which predicted that the accumulation of hydrogen ions near the electrode is the possible limiting factor for the performance of this design in unbuffered media. To develop a pH-monitoring technology for unbuffered media, Chapter 4 reports on the design, fabrication and testing of different electropolymerised-phenol derivative modified electrodes, which overcome the limitation of hydrogen ions accumulation. The results revealed that 2-(methylthio)phenol graphite resin electrodes have high accuracy (ca. 1% error) in unbuffered media, benchmarked by a commercial glass pH meter. This is the first detailed study on the v application of the economical and scalable technology in pH sensing in unbuffered environment. Chapter 5 presents a unique design of electrochemical pH sensors, free from the need to use a glass reference electrode. This design integrates a pH indicator and an internal reference electrode. Different designs of ferrocene screen-printed electrodes were tested as the internal reference electrode. The nafion-coated ferrocene screen-printed electrode showed stable peak potential in a wide pH range (pH 1 - 12) with good durability (stable in 500+ cycles of test). It was then cross connected with an alizarin electrode, forming the pH sensor free from a glass reference electrode. Chapter 6 describes novel designs of hydrodynamic pH sensors. The design of a microfluidic pH sensor modified by poly-sodium salicylate was firstly demonstrated. The sensor showed a Nernstian response in a wide pH range and, in hydrodynamic conditions, provided improved accuracy in unbuffered media compared to the stagnant state. For more convenient measurements, a novel rocking disc electrode was studied for pH sensing, modified with alizarin and poly-salicylic acid as pH indicators. The electrodes modified by both chemicals showed a Nernstian response in buffered media and the highest accuracy in unbuffered media was reached at 50 rpm.

Proton exchange membrane or anion exchange membrane water electrolyzers and fuel cells are still expensive for large-scale commercialization. It requires more investigation and research on finding more economical and efficient electrocatalysts for reactions in these devices. This thesis investigates the performance of metal-modified transition metal carbides on hydrogen evolution reaction (HER) and ethanol oxidation reaction (EOR). The catalysts screening principles for HER and EOR in acid and alkaline are examined and developed by correlating density functional theory (DFT) calculations with experimental results. Metal-modified transition metal carbides can reduce the amount of platinum group metals required for HER, but it is unclear what descriptors are relevant for these materials for the HER under alkaline conditions. Several transition metal carbides (Mo2C, NbC, TaC, WC, VC) thin films were synthesized and modified with monolayers of platinum or gold. The experimentally measured HER exchange current densities were compared with DFT calculations of adsorbed hydrogen and hydroxyl binding energies. The plot of HER activity versus hydrogen binding energy showed a volcano shape for catalysts in both acid and alkaline electrolytes, but the hydroxyl binding energy did not form a strong correlation with alkaline HER activity. Relatively high surface area molybdenum carbide (Mo2C) particles was modified with 5 wt % silver, copper, nickel, platinum, and palladium and subsequently assessed for their HER activity in alkaline and acid electrolytes. DFT‐calculated hydrogen binding energies predicted that Pt–Mo2C and Pd–Mo2C should be most active, which was confirmed with experimental results. Similar activity trends were observed at both high and low pH values, with Cu/Mo2C being the least active. X‐ray photoelectron spectroscopy (XPS) confirmed that metal particles remained on the sample before and after HER testing. Pt‐modified nanocrystalline Mo2C showed superior HER activity compared with Pt‐modified commercial Mo2C, making it a potential replacement for bulk Pt in alkaline membrane electrolyzers. The positive effect on the HER activity of the metal contact with non‐passivated Mo2C surfaces was also demonstrated. Ethanol is an ideal fuel in low-temperature fuel cells. The EOR on platinum-modified tantalum carbide (TaC) was investigated using both model thin films and powder catalysts. The results demonstrated that the 1.5 wt% Pt-modified TaC catalyst obtained enhanced EOR activity compared to Pt. In-situ infrared reflection absorption spectroscopy (IRRAS) study revealed that the Pt surface was less poisoned by EOR intermediates and a higher CO2 selectivity (7~9%) was achieved on the 1.5 wt% Pt/TaC catalyst, compared to the 40 wt% Pt/C. DFT calculations revealed that the binding energies of EOR intermediates on the Pt/TaC(111) surface a weaker than on Pt(111), suggesting an enhanced poison-tolerance from the adsorption of these intermediates. The combined experimental and theoretical investigations strongly suggested that Pt/TaC should be a promising electrocatalyst for EOR. Palladium-modified tungsten carbide (Pd/WC) as an efficient catalyst was investigated for EOR through combined DFT, surface science and electrochemical measurements. Compared to the Pd(111) surface, DFT calculations suggested that the Pd/WC(0001) surface should be less poisoned by the ethanol decomposition intermediates, consistent with surface science results that desorption temperatures of the detected intermediates were lower on the Pd/WC surface. Electrochemical evaluation coupled with in-situ IRRAS measurements of 5 wt% Pd/WC/C powder catalysts were then conducted. The EOR activity of the 5 wt% Pd/WC/C-op catalyst synthesized by the one-pot (op) method was noticeably enhanced, compared to the benchmark 40 wt% Pd/C and 5 wt% Pd/WC/C-iwi that was synthesized using a conventional incipient wetness impregnation (iwi) method. The IRRAS results showed that the EOR products were detected at a lower onset potential on 5 wt% Pd-WC/C-op than on 40 wt% Pd/C. Overall, results from the current thesis demonstrated the feasibility of using metal-modified transition metal carbides as lower-cost and more efficient electrocatalysts for HER and EOR. These results identified descriptors that can be potentially used to design more cost-effective catalysts. Furthermore, results from this thesis also revealed the general similarities and differences of the activity and stability of carbide-based catalysts in acid and alkaline electrolytes.

No presente trabalho estuda-se sistematicamente a influência orgânico axial R nos complexos (RCo(III)(SALEN)DMF) onde [Ver esquema no PDF] R = CH3, C2H5, n-C3H7, n-C4H9, s-C4H9, i-C4H9, CH2Cl, c-C6H11CH2, c-C6H11, C6H5CH2, p-CH3 C6H4CH2 e p-NO2 C6H4CH2, na oxidação eletroquímica destes compostos em dimetilformamida (DMF), 0,2M em perclorato de tetraetilamônio à temperatura ambiente e a -20&#176;C. O método da voltametria cíclica foi utilizado, sendo os eletrodos de disco de platina, Ag/AgCl e fio de platina, empregados como eletrodos de trabalho, referência e auxiliar, respectivamente. Pode-se agrupar os compostos acima em três conjuntos, de acordo com o comportamento eletroquímico: A - Os compostos com R = CH3, C2H5, n-C3H7, n-C4H9, c-C6H11CH2 são oxidados monoeletrônica e reversivelmente em velocidades de varredura de potenciais de 10 a 50 V.s-1 . A velocidades de varredura mais baixas constata-se que uma reação química de pseudo-primeira ordem de decomposição da forma oxidada segue a etapa primária eletroquímica. A baixa temperatura, a velocidade da reação química é diminuída e observa-se essencialmente a etapa monoeletrônica e reversível. B - Os compostos com R = CH2Cl, C6H5CH2, p-CH3 C6H4CH2 e p-NO2 C6H4CH2 são oxidados monoeletrônica e quase-reversivelmente à temperatura ambiente. Abaixando-se a temperatura, a reação eletroquímica torna-se irreversível. São calculados os parâmetros cinéticos para as quatro reaçoes. c - Os compostos com R = i-C4H9, s-C4H9 e c-C6H11 sao oxidados monoeletrônica e reversivelmente a -20 &#176;C. À temperatura ambiente a reação química que segue a etapa eletroquímica ée rápida demais para poder-se isolar a etapa primária. Analisando-se o efeito do ligante orgânico axial R sobre os potenciais de meia onda E1/2, idênticos aos potenciais padrão de eletrodo (para os compostos que sofrem oxidaçãoreversível) pois os coeficientes de difusão das formas oxidada e reduzida são iguais, verifica-se que os E1/2 são tanto menores quanto maior o poder de doação de elétrons do substituinte. Dentro do erro experimentar obtém-se uma correlaç~ão linear entre os E1/2 e os parâmetros polares de Taft, &#963;*, com &#961;* = (0,25 ± 0,03) para os grupos R apropriados. O mesmo tipo de correlação foi obtido para as organocobaloximas em HClO4 1M com um valor de &#961;* três vezes menor. Esta menor inclinação é parcialmente devida ao efeito do ligante equatorial e Sem dúvida à mudança do solvente. Enquanto no estudo das vinte e sete organocobaloximas todos os compostos eram oxidados monoeletrônica e reversivelmente,nos derivados de SALEN o efeito dos grupos R reflete-se também sobre a velocidade do processo de transferência de carga heterogênea. Para os derivados benzílicos e os dotados de baixa habilidade de doação de elétrons (CH2Cl) a etapa dominante da velocidade é a de transferência de carga heterogênea (a baixa temperatura). Propõe-se um paralelo entre os mecanismos de reações redox homogêneas de esfera externa e interna aos de eletrodo reversível e quase-reversível (a irreversível) respectivamente. Portanto, para os derivados de SALEN o efeito do ligante orgânico axial R reflete-se tanto na termodinâmica quanto na cinética da oxidação eletroquímica. / The influence of the axial organic ligand R on the electrochemical oxidation of the complexes (RCo(III)(SALEN)DMF) where [Ver esquema no PDF] R = CH3, C2H5, n-C3H7, n-C4H9, s-C4H9, i-C4H9, CH2Cl, c-C6H11CH2, c-C6H11, C6H5CH2, p-CH3 C6H4CH2 e p-NO2 C6H4CH2, was studied by means of cyclic voltammetry in dimethylformamide (DMF) containing O,2M in tetraethylammonium perchlorate at room temperature and at -20&#176;C. A platinum disk, Ag/AgCl, and a platinum wire were employed as the working, reference, and auxiliar electrodes, respectively. The above-mentioned compounds can be classified according to their electrochemical behavior: A) The complexes with R = CH3, C2H5, n-C3H7, n-C4H9, c-C6H11CH2 undergo a reversible one-electron oxidation in the 10-50 V.s-1 potential scan rate range. At slower scan rates, the oxidized product decomposes chemically, following the electrochemical step, via a solvent-assisted pseudo-first order reaction. At -20&#176;C, this chemical is slow and reversible one-electron electrochemical oxidation is observed. B) The compounds with R = CH2Cl, C6H5CH2, p-CH3 C6H4CH2 and p-NO2 C6H4CH2 undergo a quasi-reversible one-electron electrochemical oxidation at room temperature. At -20&#176;C the electrochemical process becomes totally irreversible. Kinetic parameters are calculated for the heterogeneous electron transfers. C) The compounds with R = i-C4H9, s-C4H9 and c-C6H11 undergo a reversible one-electron oxidation at -20&#176;C. At room temperature, the irreversible chemical reaction following the electron transfer step is too fast to allow the isolation of the electrochemical step. The effect of the organic ligands R on the half-wave potentials, E1/2, was studied. For the compounds which exhibit reversible electrochemical oxidation, the E1/2 are identical to the standard electrode potentials, the diffusion coefficients of the reduced and oxidized species being identical. The E1/2 decreases with increasing electron-donating ability of the ligands R. Within the experimental error, a linear free-energy relationship between E1/2 and the Taft polar parameters &#963;* is obtained with &#961;* = 0.25 ± 0.03. The same type of correlation was previously obtained for organocobaloximes in 1M HclO4, but with a &#963;* value three times smaller. The different slopes are attributable in part to the effect of the equatorial ligand and, of course, to the change of solvent. Whereas all 27 of the organocobaloximes previously studied exhibited reversible one-electron electrooxidation, the electrochemical behavior of the ALEN derivatives depends on the nature of the axial organic ligand R. At low temperatures, the rate determining step for the benzyl derivatives and the CH2Cl (electron withdrawing group) derivative is a heterogeneous charge transfer reaction. A parallel between the homogeneous outer- and inner-sphere redox mechanisms and reversible and quasi-reversible (to irreversible) electrochemical mechanisms is proposed. Therefore, for the SALEN derivatives, the axial organic ligand R exerts its influence on both the thermodynamic and kinetic aspects of the electrochemical oxidation.

This thesis is concerned with modelling natural convective flows and specifically with their role in electrochemistry. The studies described here demonstrate that many electroanalytical techniques are prone to non-negligible natural convective effects, thus making the standard assumption for purely diffusional mass transport inapplicable. The chosen approach focusses on investigating idealized systems and establishing orders of magnitude for the quantities of interest. The complexity of the observed natural convective flows and their strong dependence on factors such as container geometry serve as compelling arguments for rigorously excluding natural convection in experimental measurements. The text is structured as follows. Chapter 1 introduces the theoretical framework used in the rest of the text and gives an outline of the electrochemical techniques to which the results in later chapters apply. Chapter 2 surveys the literature on natural convection in electrochemistry and emphasizes recent developments. Chapter 3 studies the natural convection induced by the intrinsic heat of an electrochemical reaction, specifically its effect on mass transport in chronoamperometry and cyclic voltammetry. Chapters 4-6 deal exclusively with coupled heat and momentum transport. Chapter 4 considers the thermal convective flows that arise in an idealized cell for scanning electrochemical microscopy (SECM) and the surrounding air under conditions of imperfect thermostating. Chapter 5 is dedicated to thermal convection in an SECM cell that is being thermostated from below through a solid substrate. This chapter demonstrates the influence of the spatial distribution of substrate thermal conductivity on the observed flows and highlights this effect by using a simpler model of the SECM cell than Chapter 4. Chapter 6 investigates the thermal convection in a novel thermostated cell for electrochemical measurements. Chapter 7 contains the main conclusions from the studies described in the thesis. Appendices A, B and C provide additional data for Chapters 3, 5 and 6, respectively.

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by Roger Chun Wang Liu. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (leaves 98-108). / ACKNOWLEDGEMENTS --- p.i / CONTENTS --- p.ii / ABBREVIATIONS --- p.v / LIST OF FIGURES --- p.vi / LIST OF TABLES --- p.vii / Chapter I. --- THE CHEMISTRY OF METALLO-PHTHALOCYANINES AND -NAPHTHALOCYANINES --- p.1 / ABSTRACT --- p.2 / Chapter 1. --- SANDWICH-LIKE BIS(PHTHALOCYANINATO)LANTHANIDE COMPLEXES / Chapter 1.1. --- Introduction --- p.3 / Chapter 1.2. --- Preparation of Substituted Phthalonitriles --- p.8 / Chapter 1.3. --- Condensation of Phthalonitrile --- p.9 / Chapter 1.4. --- Condensation of Substituted Phthalonitriles --- p.10 / Chapter 1.5. --- Spectroscopic and Electrochemical Properties --- p.12 / Chapter 1.6. --- Conclusion --- p.21 / Chapter 2. --- "SUBSTITUTED 2,3-NAPHTHALOCYANINES" / Chapter 2.1. --- Introduction --- p.22 / Chapter 2.2. --- Preparation of Alkyl-Substituted Dicyanonaphthalenes --- p.26 / Chapter 2.3. --- Preparation of Halo-Substituted Dicyanonaphthalenes --- p.30 / Chapter 2.4. --- Condensation of Alkyl-Substituted Dicyanonaphthalenes --- p.30 / Chapter 2.5. --- Condensation of Halo-Substituted Dicyanonaphthalenes --- p.35 / Chapter 2.6. --- Conclusion --- p.38 / Chapter 3. --- EXPERIMENTAL SECTION / Chapter 3.1. --- General Directions --- p.39 / Chapter 3.2. --- Preparation of Substituted Phthalonitriles --- p.40 / Chapter 3.3. --- Condensation of Phthalonitrile --- p.43 / Chapter 3.4. --- Condensation of Substituted Phthalonitriles --- p.44 / Chapter 3.5. --- Preparation of Alkyl-Substituted Dicyanonaphthalenes --- p.46 / Chapter 3.6. --- Preparation of Halo-Substituted Dicyanonaphthalenes --- p.49 / Chapter 3.7. --- Condensation of Alkyl-Substituted Dicyanonaphthalenes --- p.51 / Chapter 3.8. --- Condensation of Halo-Substituted Dicyanonaphthalenes --- p.52 / Chapter II. --- "SYNTHETIC STUDIES OF MIXED AZA-, OXA-, AND THIA-CROWN ETHERS" --- p.55 / ABSTRACT --- p.56 / Chapter 1. --- INTRODUCTION --- p.57 / Chapter 2. --- RESULTS AND DISCUSSION --- p.64 / Chapter 2.1. --- Preparation of Diols and Dithiols --- p.64 / Chapter 2.2. --- Preparation of Ditosylates --- p.66 / Chapter 2.3. --- 1:1 Cyclization -- Preparation of Monoaza- 15-crown-5 --- p.68 / Chapter 2.4. --- Crystal Structure of N-(4-methoxyphenyl) benzomonoaza-15- crown-5 (112) --- p.76 / Chapter 2.5. --- Complexation of Monoaza-15-crown-5 --- p.79 / Chapter 2.6. --- Conclusion --- p.80 / Chapter 3. --- MISCELLANEOUS SYNTHESES --- p.81 / Chapter 3.1. --- Preparation of Tetrabromodibenzo-24-crown-8 --- p.81 / Chapter 3.2. --- Complexation of Tetrabromodibenzo-24-crown-8 --- p.82 / Chapter 4. --- EXPERIMENTAL SECTION --- p.84 / Chapter 4.1. --- General Directions --- p.84 / Chapter 4.2. --- Preparation of Diols and Dithiols --- p.84 / Chapter 4.3. --- Preparation of Ditosylates --- p.88 / Chapter 4.4. --- 1:1 Cyclization -- Preparation of Monoaza- 15-crown-5 --- p.89 / Chapter 4.5. --- Complexation of Monoaza-15-crown-5 --- p.94 / Chapter 4.6. --- Preparation of Tetrabromodibenzo-24-crown-8 --- p.95 / Chapter 4.7. --- Complexation of Tetrabromodibenzo-24-crown-8 --- p.97 / REFERENCES AND NOTES --- p.98 / APPENDIX --- p.109

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