Microfluidic flow devices coupled with quantitative Raman spectroscopy are able to provide a deep insight into the reaction mechanism and kinetics of electrocatalytic reactions. With a microfluidic flow device made with glass microscope slides and polymer building blocks, the feasibility of this technique was examined by methanol electrooxidation reaction with a Pt working electrode. Pre-calibration of the Raman peak area was done with solutions of known concentrations of methanol and its major oxidation product, i.e., formate, which enabled the time-dependent Raman spectra taken during the reaction to be converted to time-dependent concentrations. These were interpreted in terms of a model with one-dimensional convection and the reaction kinetics. An improved version of this technique was then applied to a comparative study of different alcohols with Ni-based electrodes. This showed the production of formate as the major product from the oxidation of alcohols with vicinal OH groups, leading to the discovery that C-C bond dissociation is a major reaction pathway for vicinal diols and triols if Ni electrocatalysts are used. It is also suggested that the cleavage of C-C bonds is the rate-determining step. The potential use of printed circuit boards (PCB) in the next generation of a novel microfluidic device was explored, as PCB have advantages over regular electrochemical microfluidic substrates, such as simpler electrode fabrication strategies, more wiring layers, and customization of size and shape of electrodes. Pretreatments and electrodeposition protocols of nickel, silver, palladium and platinum on PCB were successfully developed, together with four types of PCB-based microfluidic devices designed with an open-source PCB design software. This work establishes a new electrochemical microfluidic platform for online and in-situ monitoring of electrocatalytic reactions, which can quickly determine the reaction mechanism and kinetics. / Graduate

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For more than a decade, since 2009, biodiesel production has led to excessive production of its by-product, glycerol, consequently decreasing its market value and creating waste issues for the biodiesel industry. Valorization of glycerol is a promising strategy to enhance the sustainability of the biodiesel industry. Electrochemical oxidation of glycerol stands out among the other methods (i.e., hydrogenolysis, dehydration, and catalytic oxidation) due to its simplicity, eco-friendliness, and cost-effectiveness. Glycerol electrooxidation reaction has a wide range of products including C3 (i.e., glyceric acid), C2 (i.e., glycolic acid) and C1 (i.e., formic acid) products, and a complex reaction pathway. Moreover, some of the products spontaneously convert to each other or form decomposition products in the strong alkaline medium, making the product analysis challenging. Therefore, this thesis started by establishing a foundation for the quantitative technical analysis method of glycerol electrooxidation products. Proton Nuclear Magnetic Resonance (H-NMR) was developed as an alternative to High-Performance Liquid Chromatography (HPLC) by providing the capability to assess the products in their medium and detect the chemical conversions in alkaline medium. Additionally, H-NMR is a highly sensitive technique with a low detection limit of 0.01mM for the GOR product, and its accuracy was confirmed with less than 8% error by using a sample product mixture with known concentrations. Most importantly, the proposed chemical pathways were determined by using H-NMR, assisting in a deeper understanding of the glycerol electrooxidation mechanism in an alkaline medium. Subsequently, this thesis explores an efficient catalyst for the glycerol electrooxidation reaction since the state-of-the-art catalysts developed for the glycerol electrooxidation reaction mostly include noble metals hindering their commercialization due to their high price and low stability resulting from susceptibility to CO poisoning. Specifically, catalysts that can hinder the C-C cleavage provide more economic advantages since C3 products have higher market prices than the C2 and C1 products. Thus, the primary aim of this thesis is to develop a cost-effective catalyst with high selectivity towards C3 products, by demonstrating high activity, and stability to make the glycerol electrooxidation reaction economically feasible. This thesis uses the catalyst development strategy of alloying the noble metal with the transition metal, where Pt and Cu were chosen, respectively. PtxCu100-x/C bimetallic alloy catalysts were prepared using the chemical reduction method. The effect of Pt:Cu ratio on the electrochemical performance was studied by using a three-electrode cell in an alkaline medium, revealing the Pt31Cu69/C as the best-performing catalyst with the highest Pt-mass normalized current density (5.9 mA μgPt-1), highest geometrical current density (75.3 mA cm-2), and low onset potential (~0.38V vs RHE) among Pt/C and other PtxCu100-x/C catalysts. Conducting parametric studies on the electrolyte concentrations and applied potential, the C3 selectivity of Pt31Cu69/C catalyst demonstrated the highest selectivity to GLY (75 %) and C3 (86 %) after 10 h chronoamperometry at optimal conditions. Subsequently, the impact of the metal oxide effect on the Pt-based catalyst, PtCu/C-CeO2, and Pt/C-CeO2 were prepared using the ball milling method. The CeO2 impact on the selectivity towards C3 products was investigated. PtCu/C-CeO2 showed the highest selectivity and concentration for C3 products compared to Pt/C-CeO2, Pt/C and PtCu/C. Additionally, temperature impact on the performance towards glycerol electrooxidation reaction was studied, revealing temperature increase further increases the selectivity and concentration for C3 products (90%, and 18.4 mM). All the catalysts prepared in this thesis were characterized physically using analytical techniques of transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and inductively coupled plasma optical emission spectroscopy (ICP-OES). / Thesis / Doctor of Philosophy (PhD) / Fossil fuels need to be replaced by clean alternatives due to sustainability concerns. Consequently, as a renewable energy source, biodiesel production has been booming since 2009, producing large amounts of glycerol as a side-product. This overproduction devalorizes glycerol, creating a disposal problem for the biodiesel industry. Electrochemical valorization is a sustainable approach to upgrade glycerol into useful compounds such as glyceric acid and tartronic acid that have medical, food and cosmetic applications. However, glycerol electrooxidation reaction (GOR) has a complex reaction pathway with a wide range of products that can be converted to each other spontaneously in an alkaline medium, making it challenging to fully understand the GOR mechanism, thereby negatively impacts GOR catalyst development. This thesis develops the proton nuclear magnetic resonance method for quantitative analysis of GOR products, highlights the chemical reaction pathways in alkaline electrolyte, and develops PtCu/C and PtCu/C-CeO2 catalysts as selective GOR catalysts towards the valuable C3 products.

Electrochemical diazonium grafting offers versatile functionalization of chemically inert graphite under mild condition, which is particularly suitable for CNT composite modification. Tetrafluorinated carboxylphenyl diazonium grafting provides the most controllable functionalization chemistry allowing near monolayer levels of functionality on carbon nanotubes. The functional density was successfully quantified by anion selective dye-assay and X-ray photoelectron spectroscopy (XPS) of thiol-Au self-assembled monolayers (SAM) as a calibration reference. This technique enables monolayer functionality at the tips of carbon nanotube membranes for biomimetic pumps and valves as well as thin conductive layers for CNT-based high area electrochemical support electrodes. Double-walled carbon nanotube (DWCNT) membranes were functionalized with sterically bulky dye molecules with amine termination in a single step functionalization process. Non-faradic (EIS) spectra indicated that the functionalized gatekeeper by single-step modification can be actuated to mimic protein channel under bias. This functional chemistry on membranes resulted in rectification factors of up to 14.4 with potassium ferricyanide in trans-membrane electrochemical measurements. One step functionalization by electrooxidation of amines provides simple and promising functionalization chemistry for the application of CNT membranes. Carbon nanotubes (CNTs) are considered a promising catalyst support due to high surface area, conductivity and stability. But very few cases of asymmetric catalysis have been reported using CNTs as support. Three noncovalent functionalization approaches have been carried out to immobilize Rh-Josiphos complex on CNTs for asymmetric hydrogenation of dimethyl itaconate. Coordinated Rh catalyst on CNTs exhibited excellent activity and reuse ability even after seventh run in hydrogenation but no enantiomeric excess as expected for lacking a chiral directing ligand. The catalyst using pyrene absorption gave 100% yield and excellent enantiomer excess (>90%) but suffered from leaching into solution. The phosphotungstic acid (PTA) anchored catalyst gave 100% yield and higher ee (99%) and better reusability over pyrene absorbed catalyst but had significant leaching after the second run. At this point it remains a significant challenge to utilize CNTs as a chiral catalyst support.

Este trabalho investigou a oxidação eletroquímica do ácido tânico em eletrodos do tipo Ânodo Dimensionalmente Estáveis (ADE) a base de SnO2 e IrO2 e eletrodos de Diamante Dopado com Boro (BDD). As eletrólises foram feitas em modo galvanostático em função de parâmetros como densidade de corrente e concentração de cloreto. A oxidação eletroquímica do ácido tânico foi capaz de promover a diminuição da concentração de fenóis totais, Carbono Orgânico Total (COT) e Demanda Química de oxigênio (DQO). Para os ADE os melhores resultados de remoção de Carbono Orgânico Total (COT) foram nas condições em que se utilizou 300 mg L-1 de cloreto e densidade de corrente de 25 mA cm-2. No entanto houve a formação de compostos organoclorados que não foram degradados com maiores tempo de reação. Para os eletrodos de BDD, obteve-se a remoção de aproximadamente 98% de COT após 10 horas de reação à 75 mA cm-2, na ausência de cloreto. Maiores remoções de COT são obtidas com o aumento da densidade de corrente. Eletrólises na presença de cloreto removeram quase 100% do COT em tempos menores de reação. Análises de compostos organohalogenados (AOX) mostraram que não houve a formação de compostos organoclorados. Menores densidades de corrente apresentaram maiores Eficiência de Corrente (EC) e menor Consumo de Energia (CE). As eletrólises na presença de cloro apresentaram melhores resultados de EC que na ausência do mesmo. A oxidação fotoeletroquímia do ácido tânico em eletrodos do tipo ADE de composição nominal Ti/ Sn0,7 Ir0,3 O2 também foi investigada nesse trabalho. O tratamento fotoeletroquímico foi realizado utilizando uma lâmpada de vapor de mercúrio de alta pressão de 125 W como fonte de irradiação. A variação da corrente não mostrou diferença significativa na oxidação do ácido tânico. A variação da concentração de cloreto no eletrólito suporte influenciou de forma acentuada a oxidação do ácido tânico. O tratamento fotoeletroquímico se mostrou mais eficiente na remoção de COT que os tratamentos eletroquímico e fotoquímico. No tratamento fotoeletroquímico ocorreu a formação de AOX no início da reação, no entanto com o passar do tempo esses compostos foram degradados. / This study investigated the electrochemical oxidation of tannic acid on electrodes of the Dimensionally Stable Anode (DSA) type based on SnO2 and IrO2 as well as on boron doped diamond (BDD) electrodes. The electrolyses were performed in the galvanostatic mode, as a function of such parameters as current density and chloride concentration. The electrochemical oxidation of tannic acid was able to promote the reduction of the concentration of total phenolics, total organic carbon (TOC), and chemical oxygen demand (COD). For the DSA the best results of Total Organic Carbon (TOC) removal were achieved at 300 ppm chloride and current density of 25 mA cm-2. However, organochlorine compounds were formed and were not degraded with increased reaction times. For the BDD electrodes, the removal of approximately 98% TOC was obtained after 10 hours of reaction at 75 mA cm-2, in the absence of chloride. Major TOC removals were obtained with increasing current density. Electrolyses in the presence of chloride removed almost 100% TOC in shorter reaction times. Analysis of organohalogen compounds (AOX) showed no formation of organochlorine compounds. Lower current densities led to higher current efficiency (CE) and lower Energy Consumption (EC). The electrolyses in the presence of chlorine produced better CE results than those performed in the absence of chlorine. The photoelectrochemical oxidation of tannic acid in ADE-type electrodes of nominal composition Ti / Sn0.9 Ir0.3 O2 was also investigated in this work. The photoelectrochemical treatment was performed using a high pressure mercury vapor lamp 125 W as the source of irradiation. The variation in current revealed no significant difference in the oxidation of tannic acid. The variation in chloride concentration in the electrolyte markedly influenced the oxidation of tannic acid. The photoelectrochemical treatment was more efficient for TOC removal than the electrochemical and photochemical treatments. Formation of AOX occurred at the beginning of the photoelectrochemical treatment, but over time these compounds were degraded.

O glicerol, 1,2,3-propanotriol, é o principal subproduto da indústria do biodiesel, cerca de 10% em massa. Apesar das inúmeras aplicações que o glicerol tem na indústria, a oferta desse poliálcool, devido ao grande aumento da produção de biodiesel nos últimos anos, tem crescido tanto que o produto tem se acumulado nas usinas, levando a um desequilíbrio entre produção e consumo. Dessa forma, muita pesquisa vem sendo feita na tentativa de utilizar essa abundante, barata e não tóxica matéria prima como base para a obtenção de energia e outros produtos de maior valor agregado. Dentre os vários processos para a conversão do glicerol, a eletro-oxidação recebe atenção especial devido à sua versatilidade, simplicidade e baixo custo. Neste trabalho, utilizou-se a voltametria cíclica para a análise do comportamento eletroquímico do glicerol e dos possíveis produtos obtidos pela sua eletro-oxidação sobre diversos eletrodos e a influência de variáveis experimentais, tais como, solvente, eletrólito de suporte, concentrações de substrato e eletrólito de suporte, na atividade eletrocatalítica do sistema. As técnicas de eletroforese capilar, coulometria e voltametria cíclica foram utilizadas para a determinação da taxa de conversão e análise quantitativa do glicerol e dos produtos obtidos por meio de eletrólise exaustiva e como esses parâmetros são influenciados pelas variáveis experimentais. Além disso, é importante citar que o método analítico baseado na técnica de eletroforese capilar com detecção condutométrica sem contato foi desenvolvido e otimizado durante o projeto de mestrado e tem grande relevância para este trabalho / Glycerol, 1,2,3-propanetriol, is the main by-product of biodiesel industry, around 10% w/w. Despite of several glycerol applications in industry, the offer of this polyalcohol has increased so much in the last years that it has accumulated in the mills, leading to an unbalance between its production and consumption. Thus, a lot of research has been done trying to use this abundant, cheap and non-toxic raw material as the basis for energy production and synthesis of other more value-added compounds. Among the several conversion processes, the electrooxidation has drawn attention due to its versatility, simplicity and low cost. Cyclic voltammetry is used for analyzing the electrochemical behavior of glycerol and the possible electroconversion products on several electrodes, as well as the influence of experimental variables, such as, solvent, supporting electrolyte and its concentration, substrate concentration on the electrocatalytic activity of the system. Capillary electrophoresis, coulometry and cyclic voltammetry were used for determination of rate conversion and quantitative analyses of glycerol and the obtained products through bulk electrolysis and how these parameters are influenced by experimental conditions. Besides, it is noteworthy that the analytical method based on capillary electrophoresis technique with contactless conductometric detection was developed and optimized along this Master project and it has large relevance for this work.

Este trabalho descreve estudos eletroquímicos e espectroscópicos da eletrooxidação de etanol, acetaldeído e ácido acético sobre uma superfície de platina monocristalina de baixo índice de Miller 110 modificada por ósmio (Os). O eletrodo monocristalino de Pt(110) foi modificado por Os espontaneamente e pela aplicação de potencial. Os eletrodos foram caracterizados eletroquimicamente, de forma que foram obtidos valores baixos, intermediários e altos de Os sobre a superfície de Pt(110). A eletrooxidação de etanol sobre Pt(110) e Pt(110)/Os, analisada pelas técnicas de voltametria cíclica e cronoamperometria, mostrou que as densidades de corrente para essa reação foram maiores nos graus de recobrimento entre 0,51 – 0,61 ML. A partir dos resultados de FTIR in situ, verificou-se que a reação de oxidação de etanol difere em seus caminhos de acordo com o grau de recobrimento de Os. O caminho um sugere a quebra da ligação C—C com maior intensidade em graus de recobrimento entre 0,36 – 0,80 ML, formando espécies como COlinear, CHx e, posteriormente, CO2. O caminho dois mostra a formação de acetaldeído a partir de 0,4 V sobre os eletrodos Pt(110) e Pt(110)/Os, e que pode haver ainda a produção de CO e ácido acético a partir desse orgânico sobre eletrodos com HOs > 0,80 ML, a baixos potenciais. O estudo realizado com acetaldeído mostrou que o desempenho na oxidação desse orgânico foi sutilmente maior para os eletrodos modificados por Os. O caminho três apresenta a produção de CO2 proveniente da oxidação de etanol diretamente a ácido acético sobre eletrodos com alto grau de recobrimento. Durante a oxidação ocorre a formação a baixos potenciais de COlinear em grandes quantidades. Além disso, há produção de ácido acético e posteriormente de CO2. Ainda nos eletrodos espessos, a produção de CO2 ocorre sem que se observe a presença de COlinear, indicando a possibilidade da oxidação de ácido acético a CO2. A eletrooxidação de ácido acético sobre os diversos eletrodos de Pt(110)/Os mostra que ocorre a quebra dessa molécula para formar CO2, embora de forma menos expressiva que as demais moléculas estudadas. Sendo que parte do CO2 produzido provavelmente tem sua origem no grupo COO- que está adsorvido sobre a superfície do eletrodo. / This work reports the electrochemical and spectroscopic results of ethanol, acetaldehyde and acetic acid electrooxidation onto low index platinum single crystal surface (110) modified by osmium (Os). The Pt(110) electrode was modified by spontaneous and electroless Os deposition and checked electrochemically in order to obtain low, intermediate and high Os coverages on Pt(110). The ethanol electrooxidation on Pt(110) and Pt(110)/Os, which used voltammetric cycle and cronoamperometric techniques, showed higher currents toward this reaction on Os coverage between 0.51-0.61 ML. The FTIR results reveal that ethanol oxidation has different pathways according to Os coverage. The step one suggests that the cleavage of ethanol C—C bond occurs with major intensity forming species such as COlinaer and CHx when the reached coverage is 0.36 – 0.80 ML and further producing CO2. At the step two, acetaldehyde formation is improved above 0.4 V on Pt(110) and Pt(110)/Os, and at low potentials on HOs > 0.80 ML, this molecule can oxidize and form CO and acetic acid. Studies on acetaldehyde showed that the catalytic activity is slightly higher on electrodes modified by Os. The step three presents the CO2 production through acetic acid onto electrodes with high Os coverage. During the oxidation of this molecule, COlinear is produced in large quantities at low potentials; there is formation of acetic acid and thereupon CO2. Onto Os thick electrode, CO2 production occurs without the presence of COlinear, indicating the possibility of acetic acid oxidation directly to CO2. The acetic acid oxidation on various electrodes modified by Os is possible with cleavage of C—C bond to form CO2, though this process is less significant than others organic molecules studied. Since the amount of CO2 produced can arise through the acetate group once this specie is adsorbed onto the electrode surface.

O glicerol, 1,2,3-propanotriol, é o principal subproduto da indústria do biodiesel, cerca de 10% em massa. Apesar das inúmeras aplicações que o glicerol tem na indústria, a oferta desse poliálcool, devido ao grande aumento da produção de biodiesel nos últimos anos, tem crescido tanto que o produto tem se acumulado nas usinas, levando a um desequilíbrio entre produção e consumo. Dessa forma, muita pesquisa vem sendo feita na tentativa de utilizar essa abundante, barata e não tóxica matéria prima como base para a obtenção de energia e outros produtos de maior valor agregado. Dentre os vários processos para a conversão do glicerol, a eletro-oxidação recebe atenção especial devido à sua versatilidade, simplicidade e baixo custo. Neste trabalho, utilizou-se a voltametria cíclica para a análise do comportamento eletroquímico do glicerol e dos possíveis produtos obtidos pela sua eletro-oxidação sobre diversos eletrodos e a influência de variáveis experimentais, tais como, solvente, eletrólito de suporte, concentrações de substrato e eletrólito de suporte, na atividade eletrocatalítica do sistema. As técnicas de eletroforese capilar, coulometria e voltametria cíclica foram utilizadas para a determinação da taxa de conversão e análise quantitativa do glicerol e dos produtos obtidos por meio de eletrólise exaustiva e como esses parâmetros são influenciados pelas variáveis experimentais. Além disso, é importante citar que o método analítico baseado na técnica de eletroforese capilar com detecção condutométrica sem contato foi desenvolvido e otimizado durante o projeto de mestrado e tem grande relevância para este trabalho / Glycerol, 1,2,3-propanetriol, is the main by-product of biodiesel industry, around 10% w/w. Despite of several glycerol applications in industry, the offer of this polyalcohol has increased so much in the last years that it has accumulated in the mills, leading to an unbalance between its production and consumption. Thus, a lot of research has been done trying to use this abundant, cheap and non-toxic raw material as the basis for energy production and synthesis of other more value-added compounds. Among the several conversion processes, the electrooxidation has drawn attention due to its versatility, simplicity and low cost. Cyclic voltammetry is used for analyzing the electrochemical behavior of glycerol and the possible electroconversion products on several electrodes, as well as the influence of experimental variables, such as, solvent, supporting electrolyte and its concentration, substrate concentration on the electrocatalytic activity of the system. Capillary electrophoresis, coulometry and cyclic voltammetry were used for determination of rate conversion and quantitative analyses of glycerol and the obtained products through bulk electrolysis and how these parameters are influenced by experimental conditions. Besides, it is noteworthy that the analytical method based on capillary electrophoresis technique with contactless conductometric detection was developed and optimized along this Master project and it has large relevance for this work.