Thesis advisor: Matthias M. Waegele / Studying the adsorption and reaction kinetics of surface-bound chemical species, on different metal catalysts or electrodes, is of paramount importance in the development of inhomogeneous catalytic methodology. Our study of the oxidation of CO on platinum was accomplished by designing a thin layer flow cell in an external reflection configuration. A charge-injection circuit was successfully implemented which decreased the time required to charge the double layer in the electrochemical cell. We were able to obtain a signal via Stark shift spectrum, of the adsorbed CO, using the thin layer cell configuration. Additionally, electrochemical impedance spectroscopy was used as a diagnostic tool to assess the effect of electrode geometry, on the voltage response, in the thin layer cell. The coupling of visible light-driven photoexciation with transition metal catalytic plat- forms is emerging as a synthetic strategy to achieve unique reactivity that has previously been inaccessible. One such example is the iridium/nickel-dipyridyl system discovered recently. Characterizing the interactions between the iridium and nickel catalysts, under reaction conditions, is important to develop a better understanding of the system. In order to apply infrared spectroscopic measurement techniques, in-situ, we made modifications to the synthetic scheme by changing the solvent and by utilizing different iridium catalysts for the synthesis of the desired methyl 4-(benzoyloxy)benzoate product. Using our trans- mission infrared setup we effectively demonstrated in-situ product detection of the aryl- ester coupled product. Additionally, after constructing a transient infrared pump-probe setup, we collected preliminary results of the triplet state lifetime of the iridium dye. The surface morphology of copper has been shown to affect the electrochemical reduction of CO2. Using surface-enhanced Raman spectroscopies, the reversible formation of nanoscale metal clusters on a copper electrode was revealed at sufficiently cathodic potentials where we observed the appearance of a new band at 2080 cm-1 corresponding to C≡O adsorbed to undercoordinated copper defect sites. The formation of new undercoordinated sites additionally resulted in the surface enhancement of the Raman scattering which amplified the intensity of the other spectral bands. / Thesis (MS) — Boston College, 2019. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

With the growing global population comes the ever-increasing consumption of energy in powering cities, electric vehicles, and portable devices such as cell-phones. While the power grid is used to distribute energy to consumers, the energy sources needed to power the grid itself are unsustainable and inefficient. The primary energy sources powering the grid, being fossil fuels, natural gas, and nuclear, are unsustainable as the economically-accessible reserves are continually depleted in exchange for detrimental emissions and air-pollutants. Cleaner, renewable sources, such as solar, wind, and hydroelectric, are intermittent and unreliable during the peak hours of energy usage, that is dawn and dusk. However, during waking hours and nighttime sleeping hours, energy consumption plummets resulting in substantial losses of potential energy as these intermittent energy providers do not have the infrastructure to store unused energy. Therefore, the research and development of efficient energy storage materials and renewable energy sources is critical to meet the needs of society in their fundamental operation while reducing harmful emissions. The research presented in this thesis focuses on selected energy storage materials and electrocatalysts as attractive technology for sustainable and benign renewable energy chemistry. Specifically, (1) theoretical studies on magnesium chloride / aluminum chloride electrolytes provide insight for further development of Mg batteries; (2) theoretical and experimental studies on viologen derivatives for organic redox flow batteries advance the development of these two-electron storage systems; and (3) a new iron(II) polypyridine catalyst that was found to electrochemically reduce CO2 to produce renewable fuels such as carbon monoxide (CO), hydrogen (H2), and methane (CH4), as well as promote the photochemical CO2-to-methane conversion with visible light.

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第21132号 / 農博第2258号 / 新制||農||1056(附属図書館) / 学位論文||H30||N5106(農学部図書室) / 京都大学大学院農学研究科応用生命科学専攻 / (主査)教授 加納 健司, 教授 小川 順, 教授 三芳 秀人 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

This dissertation presents studies electrodeposited MoS2 and metal-doped MoS2 thin films, and their performance for energy storage, catalysis, and biosensor applications. Ni-doped MoS2 thin films were fabricated by electrodeposition from electrolytes containing both MoS42- and varying concentrations of Ni2+, followed by annealing at 400 ºC for 2 h in an Ar atmosphere. The film resistivity increased from 11.3 µΩ-cm for un-doped MoS2 to 32.8 µΩ-cm for Ni-doped MoS2 containing 9 atom% Ni. For all Ni dopant levels studied, only the x-ray diffraction (XRD) pattern expected for MoS2 is observed, with the average grain size increases with increasing Ni content. Ni-doped MoS2 thin films were tested for their activity towards the hydrogen evolution reaction (HER) in 0.5M H2SO4. Tafel equation fits reveal that the catalytic activity for HER, as measured by the exchange current density, increases up to 6 atom% Ni, and then decreases slightly for 9 atom% Ni. Ni-doped MoS2 thin films were also tested in 1.0 M Na2SO4 for use within electrochemical supercapacitors, and the capacitance per unit area increases by 2-3x for 9 atom% Ni-doped MoS2 relative to un-doped MoS2. The highest specific capacitance obtained for Ni-doped MoS2 during galvanostatic charge-discharge measurements is ~300 F/g

Carbon dioxide electroreduction (CO2R) is a promising and sustainable route to generate valuable feedstocks through the electrochemical conversion from CO2 with electricity generated by renewable energy resources, to reduce greenhouse gas emissions, thereby protecting the global environment. One of the critical challenges for developing practical CO2R developments is understanding the structures and chemistry of CO2R electrocatalysts, and then generating fundamental insights to guide the design and optimization of high-performance electrocatalysts. During my Ph.D. studies, synchrotron-based X-ray spectro-microscopy techniques, scanning transmission X-ray microscopy (STXM) and X-ray spectro-ptychography, were used to study nickel-nitrogen-carbon (Ni-N-C) and electrodeposited Cu-based CO2R electrocatalysts. STXM and ptychography were upgraded to in situ characterizations to provide spectroscopic characterization and quantitative, chemically selective imaging of these catalytic materials under CO2R conditions. To achieve in situ STXM and spectro-ptychography, a micro-fluidic based, liquid-flow electrochemical in situ device was developed, fabricated, and implemented. The in situ device is optimized from previous versions developed by Vinod Prabu, past graduate student of Hitchcock group, and the initial concept was provided by Pablo Ingino and Dr. Martin Obst, collaborators at the University of Bayreuth. In situ STXM and spectro-ptychography provided a detailed chemical and morphological evaluation of catalyst materials at different applied potentials during electrochemical processes. The in situ STXM studies of Cu-based catalysts showed that electrodeposited Cu2O particles are converted to metallic Cu with different reaction rates at applied potentials less negative than that for initiation of CO2R. The in situ STXM results show a degree of heterogeneity in the electrochemical response of discrete nanoparticles and metallic Cu as the active catalyst for CO2 reduction which is structurally relatively stable at CO2R-relevant potentials within the spatial resolution of STXM. In situ spectra-ptychography was used to follow morphological changes of a single Cu-based catalytic particle in the electrochemical regime of CO2R. Our results show that the Cu particle lost the initial cubic structure and formed irregular dendritic-like structures during the CO2R process. To the best of my knowledge, this is the first time in situ STXM has been applied to CO2R electrocatalysts under flow liquid and electrochemical conditions and the first report of in situ spectro-ptychography studies. In summary, my research has successfully achieved the in situ STXM and spectro-ptychography experiments and contributed to an improved understanding of Cu nanoparticle CO2R electrocatalysts. / Dissertation / Doctor of Philosophy (PhD)

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No / The emission of greenhouse gases on a global scale is predominantly caused by the utilization of fossil fuels. Various methods have been explored to address the recycling of CO2, which among, the CO2 conversion into high-value chemicals become so promising. The purpose of this book chapter evaluation is CO2 reduction and H2 evolution reactions for producing syngas. A comprehensive analysis shall highlight (i) the technical advantages and impediments of various reactor classifications, (ii) the effect of electrolytes on electrolyzers in the liquid phase, and (iv) the catalysts that are viable for the creation of important products such as CO.

Metal complexes of dipyrromethene (dipyrrins) used as sensitizers in photocatalysis offer a way to harness solar energy in chemical bonds to create new fuels. This offers the dual role of reducing fossil fuel dependence and atmospheric CO2 levels. Traditionally, metal dipyrrin complexes are synthesized using substituted pyrroles, aldehydes, and transition metals. Indoles have a more expanded pi-electron system and their dipyrrin-type complex may exhibit visible light absorption, suggesting that they can act as photosensitizers for CO2 reduction processes. A novel indoledipyrromethene was synthesized using unsubstituted indole and mesitaldehyde. The complex exhibits visible light absorption at 422 nm. Its Zn coordinated complex it likely to exhibit blue-green light absorption making it suitable as a sensitizer for CO2 photoreduction and other applications.

A crescente emissão do CO2 para a atmosfera, causada pela matriz energética dependente dos combustíveis fósseis tem gerado a necessidade de sistemas que o utilizem como matéria-prima para a produção ou armazenamento de energia. Em vista disso, este trabalho teve como objetivo o estudo do ciclo de estocagem de hidrogênio baseado em etapas eletrocatalíticas da eletro-redução e eletro-oxidação do par CO2/HCOO-. Para o processo de eletro-redução, foram utilizados eletrocatalisadores suportados em pó de carbono formados à base de estanho (Sn/C) e de estanho modificado com cobalto (Co-Sn/C), cobre (Cu-Sn/C) e paládio (Sn-Pd/C). Os materiais foram sintetizados pelo método de impregnação seguido por tratamento térmico e caracterizados fisicamente por Difratometria de Raios X (DRX) e Espectroscopia por energia Dispersiva de Raios X (EDX). Os testes eletroquímicos foram realizados via cronoamperometria (eletrólise) e a quantificação dos íons formato por Cromatografia Líquida de Alta Eficiência (CLAE) e voltametria cíclica (VC). Os resultados obtidos mostraram que os materiais nanoestruturados sintetizados apresentaram estruturas cristalinas, sendo que o estanho apresentou-se na forma de SnO2, mas sofrendo eletro-redução em condições in situ para SnO ou SnOH. Os resultados eletroquímicos mostraram que o Sn/C eletrocatalisa a redução do CO2 para HCOO-, sendo que a quantificação por VC utilizando eletrodos de paládio e platina indicaram correntes de pico crescentes até o potencial de eletrólise de -1,6 V vs. Ag/AgCl/Cl-. Ademais, experimentos de eletrólise evidenciaram o aumento linear da concentração de HCOO- após 6 horas de polarização, indicando alta estabilidade do eletrocatalisador de Sn/C. A atividade eletrocatalítica dos eletrocatalisadores à base de estanho frente a redução de CO2 para HCOO- foi atribuída a dois aspectos: (i) o estanho favorece a adsorção ou interação do CO2 através dos átomos de oxigênio, possibilitando a transferência de prótons e elétrons sem a quebra da ligação C-O e/ou; (ii) a presença de espécies SnOH na superfície, mesmo em baixos potenciais, permite a interação com o CO2 e leva à formação de intermediários adsorvidos reativos, que sofrem a adição de prótons e elétrons para a formação de HCOO-. A eficiência máxima de corrente faradaica para a formação de HCOO- foi de aproximadamente 7 % tendo a reação de desprendimento de hidrogênio (HER) como rota paralela. A investigação da influência da natureza do eletrocatalisador mostrou inatividade do material de Co-Sn/C, mas com aumento da atividade de Cu-Sn/C para a eletro-redução de CO2, quando comparado com Sn/C puro. / With the increase CO2 emissions into atmosphere caused mainly by the energy dependence on fossil fuels, systems for generation or storage of clean energy has been studied to couple CO2 as feedstock. This work proposed a hydrogen storage cycle based on electrocatalytic steps of pair CO2/HCOO-, such electroreduction and electrooxidation. For electroreduction process were used carbon-supported tin-based electrocatalysts (Sn/C) and tin modified with cobalt (Co-Sn/C), copper (Cu-Sn/C) and palladium (Sn-Pd/C). The materials were synthesized by impregnation method followed of thermal treatment, and X Ray Diffraction (XRD) and Energy Dispersive X-ray Spectroscopy (EDS) techniques were used for physical characterization. Electrochemical tests were performed via chronoamperometry (electrolysis) and the quantification of formate ions by High Performance Liquid Chromatography (HPLC) and cyclic voltammetry (CV). Results of synthesized nanostructured materials showed crystalline structures with tin as SnO2 species, but tin oxide suffering electroreduction to SnO or SnOH in situ conditions. Electrochemical results presented that the Sn/C catalyzes the CO2 reduction to HCOO-, with an increase peak current until electrolysis potential of -1.6 V vs. Ag/AgCl/Cl- quantified by CV on palladium and platinum electrodes. Moreover, electrolysis measurements demonstrated the linear increase of HCOO- concentration after polarization for 6 hours, which indicates the high stability of Sn/C electrocatalyst. The electrocatalytic activity of tin-based electrocatalysts for CO2 reduction into HCOO- was attributed to two aspects: (i) tin favors the adsorption or interaction of CO2 through oxygen atoms, which enables the proton and electron transfer without breaking C-O bond and/or; (ii) the presence on surface of SnOH species allows the interaction with CO2 even at low potential, and leads to the formation of reactive intermediates adsorbed that undergo addition of protons and electrons to form HCOO-. Maximum Faradaic efficiency for HCOO- formation was near 7% with Hydrogen Evolution Reaction (HER) as parallel route. Investigation of the influence of the electrocatalyst nature showed inactivity of CO-Sn/C material, but the activity of CO2 electroreduction increased on Cu-Sn/C material as compared to Sn/C pure.