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.

This dissertation presents my efforts to use viologens to improve the performance of glucose fuel cells and aqueous redox flow batteries. These two electrochemical systems have the potential to efficiently exploit renewable sources of energy. The contributions and significance of this work are briefly described below. Glucose Fuel cells. For glucose fuel cells, viologens were adopted as an electron mediator to facilitate the transfer of electrons from glucose to electrodes for power generation. Use of a mediator circumvents the need for precious metal electrodes to catalyze glucose oxidation. Both the oxidation efficiency and rate of glucose oxidation are important to the viability of glucose fuel cells. Oxidation efficiency is defined as the extent to which the carbons of a carbohydrate (glucose for instance) are oxidized relative to full oxidation to carbon dioxide. The efficiency measured in this study depended on the initial molar ratio of viologen to glucose and also on the rate of the regeneration of the mediator. The maximum conversion efficiency observed was ~22%, which is about three times larger than the values observed for precious-metal-based fuel cells. Rate performance is another important aspect of a glucose fuel cell. Detailed simulations demonstrated that rate performance of viologen-mediated cells was limited principally by mass transfer. The maximum obtainable current density was ~200 mA/cm2, which is significantly higher than the rates available from biological fuel cells and comparable to the values observed for precious-metal-based fuel cells. Viologen-mediated fuel cells offer the potential for higher oxidation efficiency and high current densities at a significantly lower cost. This makes viologen-mediated cells an appealing option for future development of glucose fuel cells. Redox Flow Battery. An asymmetric viologen called MMV was assessed for potential use in aqueous flow batteries to improve performance. With an asymmetric structure, MMV demonstrated one of the most negative redox potentials reported to date for organic electroactive compounds. MMV also showed a relatively high solubility in neutral electrolytes. The electrochemical reaction of MMV involved a reversible single electron transfer with fast kinetics. These characteristics support MMV as a promising anolyte for flow battery applications to improve capacity, energy density, and cell potential. MMV, however, exhibited poor cycling performance at elevated concentrations since it underwent irreversible or partially reversible side reactions. Signs of dimerization and precipitation were observed during cycling. These undesired reactions can be potentially mitigated by synthesizing asymmetric MMV derivatives that possess a higher charge than that possessed by MMV (+1). This modification can reduce the extent of dimerization by increasing repulsive forces between the monomers, and it also has the potential to reduce precipitation by increasing the solubility limit of the compounds.

Actuellement, l'élaboration de matériaux nanohybrides organiques/inorganiques suscite l'engouement de nombreux chercheurs du fait de leurs diverses applications potentielles. Le but de ce projet de thèse a été de préparer et caractériser de nouveaux éléments inorganiques et organiques permettant la conception de nanohybrides multi-fonctionnels possédant des propriétés répondant aux problématiques actuelles. Dans cet objectif, nous avons préparé des nanoparticules d'oxyde de zinc (ZnO) en tant que composant inorganique par ablation laser. La surface de ces NPs peut être modifiée par des composés organiques possédant un groupe d'ancrage acide carboxylique. Nous avonssynthétisé et caractérisé des dérivés viologènes, bien connu comme de forts accepteurs d'électron, possédant le groupe d'ancrage. Les nanohybrides de ZnO/viologènes ont été préparés et caractérisés par diverses techniques de spectroscopie. Nous avons développé des voies de synthèse efficaces permettant d'obtenir une série de nouveaux hétérocycles possédant des propriétés de donneur d'électron : dérivés de dibenzo[2,3:5,6]pyrrolizino[1,7-bc]indolo[1,2,3-lm]carbazole. Ces nouvelles molécules présentent une forte stabilité thermique et une forte fluorescence dans le domaine du visible. Leurs propriétés d'absorption à un et deux photons (Proche-infrarouge) ainsi que leur habilité de donneur d'électron ont été étudiés expérimentalement et à l'aide de calculs de mécanique quantique. Les éléments organiques et inorganiques étudiés sont des motifs de choix pour l'élaboration future de nanohybrides utilisables pour diverses applications comme dans le domaine de l'énergie photovoltaïque ou encore l'imagerie médicale. / Currently, the development of organic/inorganic nanohybrid materials arouses the enthusiasm of many researchers owing to their potential applications. The aim of this thesis was to prepare and characterize new inorganic and organic components for the future design of new multi-functional nanohybrids with properties responding to the current challenges. For this purpose, we have prepared nanoparticles of zinc oxide (ZnO) as the inorganic component by laser ablation. The surface of these nanoparticles can be modified by an organic component bearing the carboxylic group as an anchor. We synthesized and characterized a number of viologen derivatives, well known as strong electron acceptors, involving the anchoring groups. The nanohybrids of ZnO/viologens were prepared and characterized by various spectroscopic techniques. We have developed efficient synthetic routes toward a series of new heterocycles possessing the electron donating properties: derivatives of dibenzo[2,3:5,6]pyrrolizino[1,7-bc]indolo[1,2,3-lm]carbazole. These new molecules exhibit high thermal stability and strong fluorescence in the visible range. Their one- and two-photon (Near-infrared) absorption properties and electron donor ability were investigated experimentally and by means of quantum mechanical calculations. The studied organic and inorganic components can serve as promising building blocks of choice for the future development of nanohybrids used in various application domains such as in the fields of photovoltaics and medical imaging.