In this dissertation electrochemical nickel oxide formation in alkaline solution and the electro-oxidation of glycerol on polycrystalline electrodes are studied as a function of temperature. This is done using electrochemical impedance spectroscopy (EIS), Tafel analysis, cyclic voltammetry, chronoamperometry, and chronopotentiometry among other techniques. Additionally, in order to facilitate the study of aqueous alkaline systems beyond the normal boiling point of water, an electrochemical cell was designed utilizing a self-pressurizing autoclave. This allowed for the study of aqueous alkaline systems up to 140 °C. Product analysis of glycerol electro-oxidation on nickel was performed at various temperatures using HPLC. A reaction pathway for the organic products was determined. At su ciently high temperatures a polymer was discovered. This polymer product was characterized by DLS, DSC, CP-MAS NMR, and ATR-IR and determined to likely be a pseudo-polysaccharide. DSC analysis suggests that the polymer exists as three distinct structures, and DLS analysis suggests that the polymer exists in three di erent size distributions. The lack of a glass transition temperature in the DSC spectrum indicates that it is likely thoroughly cross-linked. The aging process of alpha-Ni(OH)2 to beta-Ni(OH)2 was studied as a function of temperature using cyclic voltammetry and dynamic EIS. This lead to the observation that beta-Ni(OH)2 does not appear to form on the oxide surface at 100 °C and above. A methodology was developed for preferentially stabilizing either beta-NiOOH or gamma-NiOOH on the electrode surface. This methodology was used to determine that beta-NiOOH is the better oxygen evolution catalyst of the two oxide phases. The reversible potential of Ni(OH)2 oxidation was observed to have a shift of -1:14 mV K-1, and this data was used in a thermodynamic analysis to identify the nickel species involved in the reaction. Based on data from the literature the oxidation of NiO or Ni(OH)2 to NiO2 appears to best match the observed data. Mechanistic analysis was performed for glycerol on nickel in alkaline solution using a combination of Tafel analysis, cyclic voltammetry, AC voltammetry, and EIS. This study indicates that glycerol oxidation behaves differently on gamma-NiOOH and beta-NiOOH, perhaps explaining the discrepancy between various pieces of data found in the literature. Tafel analysis led to the observation that there appear to be two di erent glycerol oxidation regimes. Below 80 °C, alpha = 0.5, indicating that the rate determining step is an electron transfer step with no pre-equilibrium electron transfers. At 80 °C and above alpha = 1, indicating that the rate determining step has no electron transfer and one pre-equilibrium electron transfer. This was determined to be caused by the transition of the underlying nickel oxide phase from gamma-NiOOH to beta-NiOOH because the change is retained upon cooling. Additionally, EIS showed two semicircles which indicates the presence of one kinetically signifficant adsorbed intermediate. These observations were incorporated into a detailed proposed reaction mechanism. / Graduate

Experiments were designed for an undergraduate instrumental analysis laboratory course, two in X-ray diffraction and two in electrochemistry. Those techniques were chosen due their underrepresentation in the Journal of Chemical Education. Paint samples (experiment 1) and pennies (experiment 2) were characterized using x-ray diffraction to teach students how to identify different metals and compounds in a sample. in the third experiment, copper from a penny was used to perform stripping analyses at different deposition times. As the deposition time increases, the current of the stripping peak also increases. the area under the stripping peak gives the number of coulombs passed, which allows students to calculate the mass of copper deposited on the electrode surface. the fourth experiment was on the effects of variable scan rates on a chemical system. This type of experiment gives valuable mechanistic information about the chemical system being studied.

Electrochemical water splitting to hydrogen and oxygen is an attractive approach to store and convert intermittent renewable energy sources. Energy efficient, cost effective and durable electrochemical systems are highly required. Firstly, CeOx coated oxygen evolution electrocatalysts were developed to improve the stability. Unique permselectivity of the CeOx layer was disclosed, which helps to prevent dissolution of active metal site. Because oxygen evolution reaction requires a higher overpotential than hydrogen evolution reaction, kinetically facile oxidation of soluble redox ions was proposed as an alternative anodic reaction, in which the oxidized redox ions can be used for succeeding homogeneous reactions, such as treatment of H2S. How to tune the thermodynamics and the diffusion of candidate redox ions is discussed for a desired application. In addition to the anodic reaction, cathodic hydrogen evolution reaction has to be optimized. To maximize hydrogen evolution performance in near-neutral pH buffered conditions, concentration overpotentials from local pH and hydrogen on a Pt cathode are distinguished by mass transport modelling. Finally, stand-alone module was developed to perform solar-driven redox-mediated H2S splitting to H2 and S under natural solar irradiation.

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The need for accessible, safe and reliable energy storage solutions has been accentuated, in recent years, due to the shift from fossil to renewable energy sources. In this context, aluminum-based electrochemical systems have emerged as strong candidates for energy storage devices. Despite that, the successful translation from the laboratory and the commercialization of the technology faces critical challenges that must be overcome. This Dissertation explores carbon and carbon-inorganic cathodes for Al-based electrochemical energy storage devices. We start by understanding carbon cathodes in the presence of acidic ionic liquid electrolytes and draw relevant conclusions on how transition metal catalysts affect different facets of the cell's electrochemical performance. Then, we introduce sulfur and draw insights on the origin of poor cycling stability of carbon/sulfur cathodes as well as on how to extend their cycle life. Next, we focus on maximizing the pseudocapacitive contribution of carbons, and thus cathode capacity, through pore size engineering. Finally, we translate our findings to aqueous electrolytes and fabricate, for the first time, a superior rechargeable aluminum-carbon battery cathode by setting forward a hypothesis of a unique charge-storage mechanism.

Thesis (Nucl. E. and S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2005. / Includes bibliographical references. / Shadow corrosion of zirconium alloy fuel cladding in BWR environments, the phenomenon in which accelerated corrosion is experienced when the cladding surface is in close proximity to other metals, has become a potentially life-limiting issue for BWR fuel. Recent results from experimentation at MIT, Halden, and Studvik suggest that a galvanic coupling drives the phenomenon between the cladding and the adjacent material. However, the actual processes involved are not understood. One key parameter that would help in the understanding of the phenomenon would be a measurement of the actual corrosion current between fuel cladding and adjacent materials in the actual in-reactor environment. The limitations placed on the bum-up of uranium oxide fuel correlates to the amount of corrosion seen through a directly measurable oxide thickness on the waterside of the zirconium alloy cladding. This oxide corrosion product directly correlates to distance from structural components, leading to the effect commonly referred to as shadow corrosion. In recent experiments, Studvik determined that there are large ECP differences associated with Inconel and zirconium alloys that correlate to increased galvanic current density when the materials are coupled. / (cont.) In this thesis research, four electrode pairs were used to measure galvanic current densities in the irradiation environment: Pt-Pt, Zircaloy 2 (Zr-2)-Pt, Inconel (X-750)-Pt, and Zr-2-X-750. To determine the changes in the coolant water conductivity due to the presence of radiolysis products, electrochemical potential measurements of Pt-Pt coupled electrodes were analyzed. Finally, attempts to characterize the observed oxide behavior using measurements from Electrochemical Impedance Spectroscopy (EIS), also known as Alternating Current Impedance, were conducted. Through the measurements taken, analysis of the mechanisms potentially causing the shadow corrosion phenomenon was conducted. The results of the observations included: -- Measurement of increased conductivity of coolant water correlating to increases in reactor power. -- Measurement of increased galvanic current measurements correlating to increases in reactor power. / by Nicole M. Treeman. / Nucl.E.and S.M.

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As society continues to develop, demand for energy is destined to increase. Energy production and consumption are responsible for a majority of greenhouse gas emissions that cause climate change, biodiversity loss, and can generate toxic waste. Today, much of our energy demands are met via nonrenewable resources, particularly by the combustion of fossil fuels. In order to correct recent fluxes of manmade species into the geochemical cycles, we must transition to alternate forms of energy production and consumption that do not imbalance the environment. The transition to a solar hydrogen economy is attractive because it utilizes sunlight and water—virtually unlimited resources, to produce hydrogen fuel and gaseous oxygen as a by-product. Efficient and affordable catalytic systems are necessary to establish a solar-hydrogen economy. Industrial nitrogen fixation plants require an immense amount of energy for maintaining operations aimed at the production of ammonia, an essential chemical for society. Further development of catalytic materials may serve to facilitate the process under less taxing conditions.Nature has resulted in the evolution of a wide variety of enyzmes to catalytically carry out chemical reactions. Billions of years of evolution have resulted in the incorporation of metals readily available in the environment. Enzymes may provide inspiration for the design of novel catalytic systems utilizing abundant elements to result in efficient and affordable materials. To this breath, to understand the structure and function of enzymes of interest, particularly the active sites of metalloenzymes. A useful tool is the comparison of native systems to molecular model complexes. It is thus imperative to synthesize and characterize model complexes that are both structurally and functionally relevant. Of interest to this work are the oxygen-evolving complex (OEC) of photosystem II and the iron-molybdenum cofactor (FeMoco) of molybdenum dependent nitrogenase enzymes. Model complexes of these active sites have been widely investigated, however, OEC and FeMoco model complexes generally fall into one category or the other: structural or functional models. The aim of this work is to synthesize and study synthetic multinuclear metallocomplexes to model the structure and function of the OEC and FeMoco. The lessons learned from these systems could contribute to the understanding and design of catalysts and help progress toward viable catalysts. Presented here is the synthesis and characterization of a series of OEC structural models with hemicubane geometry, derived from self-assembled precursor fragments. In chapter 2, a series of Ca-Mn clusters, with the ligand 2-pyridinemethoxide (Py-CH2O), have been prepared with varying degrees of topological similarity to the CaMn4 oxygen evolving complex (OEC) of photosystem II. Through variation of reagent stoichiometry, Mn4, CaMn3, CaMn5, Ca2Mn4, and Ca4Mn3 clusters are prepared via self-assembled precursor fragments and fully characterized. All products feature a hemicubane motif (a heterocubane structure minus one corner metal ion) with Mn or Ca atoms bridged by oxygen, while containing water-accessible metal coordination sites. In chapter 3, the catalytic activation of water as a substrate in the oxidative degradation of stable propylene carbonate into CO2 is discussed. The propensity of these clusters to activate water in this oxidation reaction is correlated with increasing topological similarity to the OEC. In chapter 4, a series of analogous molecules have been explored with the incorporation of calcium, cobalt, and iron metal centers. Preliminary studies indicate the ability to perform water oxidation by a calcium complex with redox-active ligands. The synthesis, characterization, and electrocatalytic water activation chemistry will be discussed. Chapter 5 focuses on the synthesis and characterization of a [FeII(NR2)2]2CS3 complex, resulting from the activation of CS2 by an FeI(NR2)3 precursor species. This work is an extension of attempts toward achieving a synthetic central carbide included within a synthetic Fe-S cluster, which previously resulted in the activation of CS2 by a reduced FeI(NR2)3 species to obtain {[Fe(NR2)2]2CS2}[K(18-crown-6)1.5]2, where a bridging CS2 group assumes a bent geometry. Understanding the electronic structure and magnetic properties of this model complex is relevant towards the design and development of catalysts used in the production of ammonia via industrial nitrogen fixation. Presented in chapter 6 is the discovery of a layered Fe-S material that consists of alternating sheets of an Fe-S layer and a potassium layer. The crystallographic structure suggests the inclusion of periodic carbon atoms with in the Fe-S layer, although these sites may also be modeled with partial Fe occupancy. X-ray diffraction methods (single crystal and powder diffraction) and X-ray photoelectron spectroscopy were employed to investigate the composition of this material. / Chemistry

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