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Description
Proton exchange membrane fuel cells have attracted immense research activities from the inception of the technology due to its high stability and performance capabilities. The major obstacle from commercialization is the cost of the catalyst material in manufacturing the fuel cell. In the present study, the major focus in PEMFCs

Proton exchange membrane fuel cells have attracted immense research activities from the inception of the technology due to its high stability and performance capabilities. The major obstacle from commercialization is the cost of the catalyst material in manufacturing the fuel cell. In the present study, the major focus in PEMFCs has been in reduction of the cost of the catalyst material using graphene, thin film coated and Organometallic Molecular catalysts. The present research is focused on improving the durability and active surface area of the catalyst materials with low platinum loading using nanomaterials to reduce the effective cost of the fuel cells. Performance, Electrochemical impedance spectroscopy, oxygen reduction and surface morphology studies were performed on each manufactured material.

Alkaline fuel cells with anion exchange membrane get immense attention due to very attractive opportunity of using non-noble metal catalyst materials. In the present study, cathodes with various organometallic cathode materials were prepared and investigated for alkaline membrane fuel cells for oxygen reduction and performance studies. Co and Fe Phthalocyanine catalyst materials were deposited on multi-walled carbon nanotubes (MWCNTs) support materials. Membrane Electrode Assemblies (MEAs) were fabricated using Tokuyama Membrane (#A901) with cathodes containing Co and Fe Phthalocyanine/MWCNTs and Pt/C anodes. Fuel cell performance of the MEAs was examined.
ContributorsKolli, Sri Harsha (Author) / Madakannan, Arunachalanadar (Thesis advisor) / Nam, Changho (Committee member) / Peng, Xihong (Committee member) / Arizona State University (Publisher)
Created2014
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Description
Organic reactions in natural hydrothermal settings have relevance toward the deep carbon cycle, petroleum formation, the ecology of deep microbial communities, and potentially the origin of life. Many reaction pathways involving organic compounds under geochemically relevant hydrothermal conditions have now been characterized, but their mechanisms, in particular those involving

Organic reactions in natural hydrothermal settings have relevance toward the deep carbon cycle, petroleum formation, the ecology of deep microbial communities, and potentially the origin of life. Many reaction pathways involving organic compounds under geochemically relevant hydrothermal conditions have now been characterized, but their mechanisms, in particular those involving mineral surface catalysis, are largely unknown. The overall goal of this work is to describe these mechanisms so that predictive models of reactivity can be developed and so that applications of these reactions beyond geochemistry can be explored. The focus of this dissertation is the mechanisms of hydrothermal dehydration and catalytic hydrogenation reactions. Kinetic and structure/activity relationships show that elimination occurs mainly by the E1 mechanism for simple alcohols via homogeneous catalysis. Stereochemical probes show that hydrogenation on nickel occurs on the metal surface. By combining dehydration with and catalytic reduction, effective deoxygenation of organic structures with various functional groups such as alkenes, polyols, ketones, and carboxylic acids can be accomplished under hydrothermal conditions, using either nickel or copper-zinc alloy. These geomimetic reactions can potentially be used in biomass reduction to generate useful fuels and other high value chemicals. Through the use of earth-abundant metal catalysts, and water as the solvent, the reactions presented in this dissertation are a green alternative to current biomass deoxygenation/reduction methods, which often use exotic, rare-metal catalysts, and organic solvents.
ContributorsBockisch, Christiana (Author) / Gould, Ian R (Thesis advisor) / Hartnett, Hilairy E (Committee member) / Shock, Everett L (Committee member) / Arizona State University (Publisher)
Created2018
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Description
The search for highly active, inexpensive, and earth abundant replacements for existing transition metal catalysts is ongoing. Our group has utilized several redox non-innocent ligands that feature flexible arms with donor substituents. These ligands allow for coordinative flexibility about the metal centre, while the redox non-innocent core helps to overcome

The search for highly active, inexpensive, and earth abundant replacements for existing transition metal catalysts is ongoing. Our group has utilized several redox non-innocent ligands that feature flexible arms with donor substituents. These ligands allow for coordinative flexibility about the metal centre, while the redox non-innocent core helps to overcome the one electron chemistry that is prevalent in first row transition metals. This dissertation focuses on the use of Ph2PPrDI, which can adopt a κ4-configuration when bound to a metal. One reaction that is industrially useful is hydrosilylation, which allows for the preparation of silicones that are useful in the lubrication, adhesive, and cosmetics industries. Typically, this reaction relies on highly active, platinum-based catalysts. However, the high cost of this metal has inspired the search for base metal replacements. In Chapter One, an overview of existing alkene and carbonyl hydrosilylation catalysts is presented. Chapter Two focuses on exploring the reactivity of (Ph2PPrDI)Ni towards carbonyl hydrosilylation, as well as the development of the 2nd generation catalysts, (iPr2PPrDI)Ni and (tBu2PPrDI)Ni. Chapter Three presents a new C-O bond hydrosilylation reaction for the formation of silyl esters. It was found the (Ph2PPrDI)Ni is the most active catalyst in the literature for this transformation, with turnover frequencies of up to 900 h-1. Chapter Four explores the activity and selectivity of (Ph2PPrDI)Ni for alkene hydrosilylation, including the first large scope of gem-olefins for a nickel-based catalyst. Chapter Five explores the chemistry of (Ph2PPrDI)CoH, first through electronic structure determinations and crystallography, followed by an investigation of its reactivity towards alkyne hydroboration and nitrile dihydroboration. (Ph2PPrDI)CoH is the first reported cobalt nitrile dihydroboration catalyst.
ContributorsRock, Christopher L (Author) / Trovitch, Ryan J (Thesis advisor) / Kouvetakis, John (Committee member) / Pettit, George R. (Committee member) / Arizona State University (Publisher)
Created2018
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Description
The late first row transition metals, being inexpensive and environmentally benign, have become very attractive for sustainable catalyst development. However, to overcome the detrimental one electron redox processes exhibited by these metals, the employment of redox non-innocent chelates turned out to be very useful. The Trovitch group has designed a

The late first row transition metals, being inexpensive and environmentally benign, have become very attractive for sustainable catalyst development. However, to overcome the detrimental one electron redox processes exhibited by these metals, the employment of redox non-innocent chelates turned out to be very useful. The Trovitch group has designed a series of pentadentate bis(imino)pyridine ligands (pyridine diimine, PDI) that are capable of binding the metal center beyond their 3-N,N,N core and also possess coordination flexibility. My research is focused on developing PDI-supported manganese catalysts for organic transformations and renewable fuel production.

The thesis presents synthesis and characterization of a family of low valent (PDI)Mn complexes. Detailed electronic structure evaluation from spectroscopic and crystallographic data revealed electron transfer from the reduced metal center to the accessible ligand orbitals. One particular (PDI)Mn variant, (5-Ph2PPrPDI)Mn has been found to be the most efficient carbonyl hydrosilylation catalyst reported till date, achieving a maximum turnover frequency of up to 4950 min-1. This observation demanded a thorough investigation of the operative mechanism. A series of controlled stoichiometric reactions, detailed kinetic analysis, and relevant intermediate isolation suggest a mechanism that involves oxidative addition, carbonyl insertion, and reductive elimination. Noticing such remarkable efficiency of the (PDI)Mn system, it has been tested for application in renewable fuel generation. A modest efficiency for H2 production at an apparent pH of 8.4 have been achieved using a cationic Mn complex, [(Ph2PPrPDI)Mn(CO)]Br. Although, a detailed mechanistic investigation remained challenging due to complex instability, a set of relevant Mn(-I) intermediates have been isolated and characterized thoroughly.

The dissertation also includes synthesis, characterization, and electronic structure evaluation of a series of Triphos supported iron complexes. Using this pincer chelate and either 2,2’-bipyridine (bpy) or 1,3,5,7-cyclooctatetraene (COT), a set of electronically interesting complexes have been isolated. Detailed electronic structure investigation using spectroscopy, magnetometry, crystallography, and DFT calculations revealed redox non-innocent behavior in the Bpy and COT ligands. Additionally, CO binding to the (Triphos)Fe system followed by reaction with borohydride reagents allowed for the isolation of some catalytically relevant and reactive iron hydride complexes.
ContributorsMukhopadhyay, Tufan K (Author) / Trovitch, Ryan J (Thesis advisor) / Buttry, Daniel (Committee member) / Pettit, George (Committee member) / Arizona State University (Publisher)
Created2016
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Description
Operando transmission electron microscopy (TEM) is an extension of in-situ TEM in which the performance of the material being observed is measured simultaneously. This is of great value, since structure-performance relationships lie at the heart of materials science. For catalyst materials, like the SiO2-supported Ru nanoparticles studied, the important performance

Operando transmission electron microscopy (TEM) is an extension of in-situ TEM in which the performance of the material being observed is measured simultaneously. This is of great value, since structure-performance relationships lie at the heart of materials science. For catalyst materials, like the SiO2-supported Ru nanoparticles studied, the important performance metric, catalyst activity, is measured inside the microscope by determining the gas composition during imaging. This is accomplished by acquisition of electron energy loss spectra (EELS) of the gas in the environmental TEM while catalysis is taking place. In this work, automated methods for rapidly quantifying low-loss and core-loss EELS of gases were developed. A new sample preparation method was also established to increase catalytic conversion inside a differentially-pumped environmental TEM, and the maximum CO conversion observed was about 80%. A system for mixing gases and delivering them to the environmental TEM was designed and built, and a method for locating and imaging nanoparticles in zone axis orientations while minimizing electron dose rate was determined.

After atomic resolution images of Ru nanoparticles observed during CO oxidation were obtained, the shape and surface structures of these particles was investigated. A Wulff model structure for Ru particles was compared to experimental images both by manually rotating the model, and by automatically determining a matching orientation using cross-correlation of shape signatures. From this analysis, it was determined that most Ru particles are close to Wulff-shaped during CO oxidation. While thick oxide layers were not observed to form on Ru during CO oxidation, thin RuO2 layers on the surface of Ru nanoparticles were imaged with atomic resolution for the first time. The activity of these layers is discussed in the context of the literature on the subject, which has thus far been inconclusive. We conclude that disordered oxidized ruthenium, rather than crystalline RuO2 is the most active species.
ContributorsMiller, Benjamin (Author) / Crozier, Peter (Thesis advisor) / Liu, Jingyue (Committee member) / McCartney, Martha (Committee member) / Rez, Peter (Committee member) / Arizona State University (Publisher)
Created2016
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Description
New sol-gel routes were developed to fabricate transparent conducting oxide coatings for energy applications. Sol-gel synthesis was chosen because the metal oxide products have high surface area and porosity. Titanium sol-gel chemistry was the main focus of the studies, and the synthesis of macroporous antimony-doped tin oxide was

New sol-gel routes were developed to fabricate transparent conducting oxide coatings for energy applications. Sol-gel synthesis was chosen because the metal oxide products have high surface area and porosity. Titanium sol-gel chemistry was the main focus of the studies, and the synthesis of macroporous antimony-doped tin oxide was also explored. The surface chemistry and band characteristics of anatase TiO2 show promise for solar energy purposes as photoelectrodes in DSSCs and as photocatalysts to degrade organic dyes and to split water. Modifying the band structure by increasing the conduction band edge energy is specifically of interest for reducing protons in water. To this end, a new sol-gel method was developed for incorporating Zr-dopant in nanoporous anatase TiO2. The products follow Vegard’s law up to 20 atom%, exhibiting surface area of 79 m2/g and pore volume of 0.20 cm3/g with average pore diameter of 10.3 nm; the conduction band edge energy increased by 0.22 eV and the band gap increased by 0.1 eV.

In pursuit of a greener sol-gel route for TiO2 materials, a solution of TiOSO4 in water was explored. Success in obtaining a gel came by utilizing hydrogen peroxide as a ligand that suppressed precipitation reactions. Through modifying this sol-gel chemistry to obtain a solid acid, the new material hydrogen titanium phosphate sulfate, H1-xTi2(PO4)3-x(SO4)x, (0 < x < 0.5) was synthesized and characterized for the first time. From the reported synthetic route, this compound took the form of macroscopic agglomerates of nanoporous aggregates of nanoparticles around 20 nm and the product calcined at 600 °C exhibited surface area of 78 m2/g, pore volume of 0.22 cm3/g and an average pore width of 11 nm. This solid acid exhibits complete selectivity for the non-oxidative dehydrogenation of methanol to formaldehyde and hydrogen gas, with >50% conversion at 300 °C.

Finally, hierarchically meso-macroporous antimony doped tin oxide was synthesized with regular macropore size around 210 nm, determined by statistical dye trajectory tracking, and also with larger pores up to micrometers in size. The structure consisted of nanoparticles around 4 nm in size, with textural mesopores around 20 nm in diameter.
ContributorsMieritz, Daniel (Author) / Seo, Dong-Kyun (Thesis advisor) / Petuskey, William (Committee member) / Herckes, Pierre (Committee member) / Arizona State University (Publisher)
Created2016
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Description
Development of efficient and renewable electrocatalytic systems is foundational to creation of effective means to produce solar fuels. Many redox enzymes are functional electrocatalysts when immobilized on an electrode, but long-term stability of isolated proteins limits use in applications. Thus there is interest in developing bio-inspired functional catalysts or electrocatalytic

Development of efficient and renewable electrocatalytic systems is foundational to creation of effective means to produce solar fuels. Many redox enzymes are functional electrocatalysts when immobilized on an electrode, but long-term stability of isolated proteins limits use in applications. Thus there is interest in developing bio-inspired functional catalysts or electrocatalytic systems based on living organisms. This dissertation describes efforts to create both synthetic and biological electrochemical systems for electrocatalytic hydrogen production.

The first part of this dissertation describes the preparation of three different types of proton reduction catalysts. First, four bioinspired diiron complexes of the form (μ-SRS)Fe(CO)3[Fe(CO)(N-N)] for SRS = 1,2-benzenedithiolate (bdt) and 1,3-propanedithiolate (pdt) and N-N = 2,2’-bipyridine (bpy) and 2,2’-bypyrimidine (bpym), are described. Electrocatatlytic experiments show that although the byprimidinal complexes are not catalysts, the bipyridyl complexes produce hydrogen from acetic acid under reducing conditions. Second, three new mononuclear FeII carbonyl complexes of the form [Fe(CO)(bdt)(PPh2)2] in which P2 = bis-phosphine: 4,5-Bis(diphenylphosphino)- 9,9-dimethylxanthene (Xantphos), 1,2-Bis(diphenylphosphino)benzene (dppb), or cis- 1,2-Bis(diphenylphosphino)ethylene (dppv) are described. All are functional bio-inspired models of the distal Fe site of [FeFe]-hydrogenases. Of these, the Xanthphos complex is the most stable to redox reactions and active as an electrocatalyst. Third, a molybdenum catalyst based on the redox non-innocent PDI ligand framework is also shown to produce hydrogen in the presence of acid.

The second part of this dissertation describes creating functional interfaces between chemical and biological models at electrode surfaces to create electroactive systems. First, covalent tethering of the redox probe ferrocene to thiol-functionalized reduced graphene oxide is demonstrated. I demonstrate that this attachment is via the thiol functional groups. Second, I demonstrate the ability to use electricity in combination with light to drive production of hydrogen by the anaerobic, phototrophic microorganism Heliobacterium modesticaldum.
ContributorsLaureanti, Joseph Anthony (Author) / Jones, Anne K. (Thesis advisor) / Moore, Thomas (Committee member) / Redding, Kevin E. (Committee member) / Arizona State University (Publisher)
Created2017
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Description
This thesis develops molecular models for electron transport in molecular junctions and intra-molecular electron transfer. The goal is to identify molecular descriptors that afford a substantial simplification of these electronic processes.

First, the connection between static molecular polarizability and the molecular conductance is examined. A correlation emerges whereby the measured

This thesis develops molecular models for electron transport in molecular junctions and intra-molecular electron transfer. The goal is to identify molecular descriptors that afford a substantial simplification of these electronic processes.

First, the connection between static molecular polarizability and the molecular conductance is examined. A correlation emerges whereby the measured conductance of a tunneling junction decreases as a function of the calculated molecular polarizability for several systems, a result consistent with the idea of a molecule as a polarizable dielectric. A model based on a macroscopic extension of the Clausius-Mossotti equation to the molecular domain and Simmon’s tunneling model is developed to explain this correlation. Despite the simplicity of the theory, it paves the way for further experimental, conceptual and theoretical developments in the use of molecular descriptors to describe both conductance and electron transfer.

Second, the conductance of several biologically relevant, weakly bonded, hydrogen-bonded systems is systematically investigated. While there is no correlation between hydrogen bond strength and conductance, the results indicate a relation between the conductance and atomic polarizability of the hydrogen bond acceptor atom. The relevance of these results to electron transfer in biological systems is discussed.

Hydrogen production and oxidation using catalysts inspired by hydrogenases provides a more sustainable alternative to the use of precious metals. To understand electrochemical and spectroscopic properties of a collection of Fe and Ni mimics of hydrogenases, high-level density functional theory calculations are described. The results, based on a detailed analysis of the energies, charges and molecular orbitals of these metal complexes, indicate the importance of geometric constraints imposed by the ligand on molecular properties such as acidity and electrocatalytic activity. Based on model calculations of several intermediates in the catalytic cycle of a model NiFe complex, a hypothetical reaction mechanism, which very well agrees with the observed experimental results, is proffered.

Future work related to this thesis may involve the systematic analysis of chemical reactivity in constrained geometries, a subject of importance if the context of enzymatic activity. Another, more intriguing direction is related to the fundamental issue of reformulating Marcus theory in terms of the molecular dielectric response function.
ContributorsKhezr Seddigh Mazinani, Shobeir (Author) / Mujica, Vladimiro (Thesis advisor) / Pilarisetty, Tarakeshwar (Committee member) / Angell, Charles A (Committee member) / Jones, Anne K (Committee member) / Arizona State University (Publisher)
Created2015
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Description
Non-stoichiometric oxides play a critical role in many catalytic, energy, and sensing technologies, providing the ability to reversibly exchange oxygen with the ambient environment through the creation and annihilation of surface oxygen vacancies. Oxygen exchange at the surfaces of these materials is strongly influenced by atomic structure, which varies significantly

Non-stoichiometric oxides play a critical role in many catalytic, energy, and sensing technologies, providing the ability to reversibly exchange oxygen with the ambient environment through the creation and annihilation of surface oxygen vacancies. Oxygen exchange at the surfaces of these materials is strongly influenced by atomic structure, which varies significantly across nanoparticle surfaces. The studies presented herein elucidate the relationship between surface structure behaviors and oxygen exchange reactions on ceria (CeO2) catalyst materials. In situ aberration-corrected transmission electron microscopy (AC-TEM) techniques were developed and employed to correlate dynamic atomic-level structural heterogeneities to local oxygen vacancy activity.

A model Ni/CeO2 catalyst was used to probe the role of a ceria support during hydrocarbon reforming reactions, and it was revealed that carbon formation was inhibited on Ni metal nanoparticles due to the removal of lattice oxygen from the ceria support and subsequent oxidation of adsorbed decomposed hydrocarbon products. Atomic resolution observations of surface oxygen vacancy creation and annihilation were performed on CeO2 nanoparticle surfaces using a novel time-resolved in situ AC-TEM approach. Cation displacements were found to be related to oxygen vacancy creation and annihilation, and the most reactive surface oxygen sites were identified by monitoring the frequency of cation displacements. In addition, the dynamic evolution of CeO2 surface structures was characterized with high temporal resolution AC-TEM imaging, which resulted in atomic column positions and occupancies to be determined with a combination of spatial precision and temporal resolution that had not previously been achieved. As a result, local lattice expansions and contractions were observed on ceria surfaces, which were likely related to cyclic oxygen vacancy activity. Finally, local strain fields on CeO2 surfaces were quantified, and it was determined that local strain enhanced the ability of a surface site to create oxygen vacancies. Through the characterization of dynamic surface structures with advanced AC-TEM techniques, an improvement in the fundamental understanding of how ceria surfaces influence and control oxygen exchange reactions was obtained.
ContributorsLawrence, Ethan Lee (Author) / Crozier, Peter A. (Thesis advisor) / Lin, Jerry (Committee member) / Liu, Jingyue (Committee member) / Petuskey, William (Committee member) / Arizona State University (Publisher)
Created2019
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Description
Redox enzymes represent a big group of proteins and they serve as catalysts for

biological processes that involve electron transfer. These proteins contain a redox center

that determines their functional properties, and hence, altering this center or incorporating

non-biological redox cofactor to proteins has been used as a means to generate redox

proteins with

Redox enzymes represent a big group of proteins and they serve as catalysts for

biological processes that involve electron transfer. These proteins contain a redox center

that determines their functional properties, and hence, altering this center or incorporating

non-biological redox cofactor to proteins has been used as a means to generate redox

proteins with desirable activities for biological and chemical applications. Porphyrins and

Fe-S clusters are among the most common cofactors that biology employs for electron

transfer processes and there have been many studies on potential activities that they offer

in redox reactions.

In this dissertation, redox activity of Fe-S clusters and catalytic activity of porphyrins

have been explored with regard to protein scaffolds. In the first part, modular property of

repeat proteins along with previously established protein design principles have been

used to incorporate multiple Fe-S clusters within the repeat protein scaffold. This study is

the first example of exploiting a single scaffold to assemble a determined number of

clusters. In exploring the catalytic activity of transmetallated porphyrins, a cobalt-porphyrin

binding protein known as cytochrome c was employed in a water oxidation

photoelectrochemical cell. This system can be further coupled to a hydrogen production

electrode to achieve a full water splitting tandem cell. Finally, a cobalt-porphyrin binding

protein known as cytochrome b562 was employed to design a whole cell catalysis system,

and the activity of the surface-displayed protein for hydrogen production was explored

photochemically. This system can further be expanded for directed evolution studies and

high-throughput screening.
ContributorsBahrami Dizicheh, Zahra (Author) / Ghirlanda, Giovanna (Thesis advisor) / Allen, James P. (Committee member) / Seo, Dong Kyun (Committee member) / Arizona State University (Publisher)
Created2019