The rapid development of modern society has been met by a fierce and overwhelming increase in fossil fuel utilization and the mass production of nonrenewable/recyclable materials. The escalating usage of fossil fuels results in rising greenhouse gas (GHG) emissions, while mass production of non-recyclable materials has led to unimaginable amounts of waste, which ultimately ends up in landfills or in the ocean. If we seek a sustainable future, it is imperative that we develop methods that can harness \u201cgreen\u201d electrons to generate power, particularly synthetic routes that selectively generate renewable materials via these electrons.
\r\n\r\nIn this thesis, we leverage theoretical methods to investigate several platforms for the conversion of GHGs to value-added products such as methanol, ethylene, methylacetic acid, styrene, etc. To generate these products, we use heterogeneous and homogeneous catalysts, with and without the assistance of an applied potential. The overarching goal of these methods is to remediate carbon and nitrogen cycles, such that generation of harmful carbon and nitrogen-based products is immediately followed by conversion of said products back to useful reactant species.
\r\n\r\nIn summation, this thesis provides several catalytic platforms for the selective and efficient production of useful fuels and feedstocks from harmful GHGs.
", "doi": "10.7907/hnc1-je90", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17192", "collection": "thesis", "collection_id": "17192", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05022025-025023583", "type": "thesis", "title": "Beyond Li: Challenges in Moving Towards Earth-Abundant Battery Materials", "author": [ { "family_name": "Qian", "given_name": "Michelle Dena", "orcid": "0000-0002-4815-1014", "clpid": "Qian-Michelle-Dena" } ], "thesis_advisor": [ { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" } ], "thesis_committee": [ { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" }, { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" }, { "family_name": "Hadt", "given_name": "Ryan G.", "orcid": "0000-0001-6026-1358", "clpid": "Hadt-Ryan-G" }, { "family_name": "Manthiram", "given_name": "Karthish", "orcid": "0000-0001-9260-3391", "clpid": "Manthiram-Karthish" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Batteries are a necessary component towards the advancement and proliferation of modern day technology, and are also an essential piece of the transition towards renewable energy. The lithium-ion battery (LIB) is the most common type of rechargeable battery, and the archetype relies on a traditional layered transition metal oxide cathode, organic electrolyte with a lithium salt, and a graphite anode. The design of these cells has been optimized to the point that the energy densities in these batteries are approaching their theoretical capacities. Combined with the supply chain challenges associated with many typical cathode elements and increasing energy demand, this highlights the need for new earth-abundant, high energy density battery technology. This thesis addresses challenges in two such systems: Mg-S and sodium-ion batteries (SIBs). Mg-S batteries suffer from capacity fade related to the polysulfide shuttle effect, which results in loss of active material and passivation of the anode. Here, we demonstrate that the rate of passivation is inversely proportional to the chain length of the polysulfides present in solution, and that passivation can be slowed or even reversed through addition of S\u2088 and the consequent perturbation of existing polysulfide speciation equilibria. SIBs are frequently touted as a \"drop-in\" technology for LIBs due to both systems relying on mobile alkali ions, but SIBs have inherently lower energy densities due to larger Na\u207a ion. In Chapters 3 and 4 we explore anion redox as a method of increasing energy densities in SIBs--Chapter 3 shows that in LiNaFeS\u2082, the charge compensation mechanisms from Li and Na cycling are identical. However, Na\u207a cycling is worsened compared to Li\u207a by structural degradation from the removal and insertion of the bulky Na\u207a ion, emphasizing the differences that exist between optimizing SIB cathode performance compared with that of LIBs. In Chapter 4, we aim to develop structure-property relationships that enable a stronger understanding of anion redox that can be leveraged to design high energy density, multielectron redox cathodes. Through the examination of the electrochemically inactive NaCu1.5Fe0.5S\u2082 and its vacancy-containing derivative NaCu1.125Fe0.625S\u2082, we show that vacancies in the transition metal layer enable redox although the redox is observed occurs on the transition metals. The study also demonstrates potential limitations of ideal model systems and bulk spectroscopic analysis techniques in materials with low degrees of redox.
", "doi": "10.7907/s5ws-m162", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17282", "collection": "thesis", "collection_id": "17282", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05282025-142549821", "type": "thesis", "title": "Catalytic Proton-Coupled Reductions of Dinitrogen and Cyanide", "author": [ { "family_name": "Johansen", "given_name": "Christian Marinelli", "orcid": "0000-0003-0066-4424", "clpid": "Johansen-Christian-Marinelli" } ], "thesis_advisor": [ { "family_name": "Peters", "given_name": "Jonas C.", "orcid": "0000-0002-6610-4414", "clpid": "Peters-J-C" } ], "thesis_committee": [ { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" }, { "family_name": "Fu", "given_name": "Gregory C.", "orcid": "0000-0002-0927-680X", "clpid": "Fu-G-C" }, { "family_name": "Manthiram", "given_name": "Karthish", "orcid": "0000-0001-9260-3391", "clpid": "Manthiram-Karthish" }, { "family_name": "Peters", "given_name": "Jonas C.", "orcid": "0000-0002-6610-4414", "clpid": "Peters-J-C" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This thesis, directly and indirectly, focuses on mechanisms and strategies for the 6H\u207a/6e\u207b reduction of N\u2082 to NH\u2083 (nitrogen reduction; N\u2082R) using well-defined molecular catalysts. In nature, nitrogenases reduce N\u2082 to NH\u2083, but nitrogenases can also reduce cyanide to CH\u2084 and NH\u2083, making CN\u207b and N\u2082 reduction interesting to compare. We describe the highly selective catalytic reduction of CN\u207b to NH\u2083 and CH\u2084 by a mononuclear Fe-catalyst related to Fe-based N\u2082R systems. Mechanistic studies suggest several intermediates, including iron isocyanides (FeCNH), aminocarbynes (FeCNH\u2082), and aminocarbenes (FeC(H)NH\u2082\u207a), allowing a comparison to N\u2082R. We then show the 2H\u207a/2e\u207b equilibration of iron cyanide to the iron aminocarbyne complexes of these early intermediates of catalysis. Such reversible triple bond activations are rare. We show that key to this transformation is the H-bond facilitated multisite proton-coupled electron transfer (MS-PCET).
\r\n\r\nNext, seeking alternative ways to drive N\u2082R, a photodriven approach is explored. The Hantzsch ester (HEH\u2082), a dihydropyridine, is utilized as a 2H\u207a/2e\u207b photoreductant, and when partnered with a suitable catalyst (Mo) and an organic buffer (collidine/collidinium; Col/ColH\u207a) under blue light irradiation allows for photodriven N\u2082R. Catalysis is enhanced by addition of a photoredox catalyst (Ir). This photodriven N\u2082R is thermodynamically comparable to the industrial hydrogenation of N\u2082, but light is used to drive the reaction. Mechanistic studies of the Ir-free conditions show that Col-buffer is essential for transferring H\u207a/e\u207b from HEH\u2082 to N\u2082. An H-bonded pre-association can form between [ColH]\u207a and HEH\u2082, allowing for rapid oxidative quenching of the excited HEH\u2082. Subsequently, the base deprotonates HEH\u2082\u2022\u207a, circumventing back electron transfer. In net ColH\u2022 and HEH\u2022, two potent H-atom donors are generated. This reagent combination is competent for the photoreduction of organic substrates as well. Lessons from this mechanistic study drove the development of photodriven methods for SmIII-to-SmII reduction, an appealing prospect given SmI\u2082 being a potent and selective reductant, including for N\u2082R. HEH\u2082 can serve either as a direct photoreductant or as the reductive quencher for an Ir photoredox catalyst. Both methods for SmI\u2082 generation translate to proof-of-concept photodriven, Sm-catalyzed reductive cross-coupling reactions.
", "doi": "10.7907/jrh7-2a15", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17298", "collection": "thesis", "collection_id": "17298", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05292025-183641323", "type": "thesis", "title": "Synthesis and Spectroscopy of Open-Shell Complexes Bearing Unusual M-E (E = N, C) Bonding Motifs and Synthesis of Novel Weakly-Coordinating Anions with Applications in Coordination Chemistry and Electrochemistry", "author": [ { "family_name": "He", "given_name": "Tianyi", "orcid": "0000-0002-8191-188X", "clpid": "He-Tianyi" } ], "thesis_advisor": [ { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" } ], "thesis_committee": [ { "family_name": "Peters", "given_name": "Jonas C.", "orcid": "0000-0002-6610-4414", "clpid": "Peters-J-C" }, { "family_name": "Hadt", "given_name": "Ryan G.", "orcid": "0000-0001-6026-1358", "clpid": "Hadt-Ryan-G" }, { "family_name": "Gray", "given_name": "Harry B.", "orcid": "0000-0002-7937-7876", "clpid": "Gray-H-B" }, { "family_name": "Manthiram", "given_name": "Karthish", "orcid": "0000-0001-9260-3391", "clpid": "Manthiram-Karthish" }, { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This dissertation focuses on a diverse range of topics centered around inorganic synthesis, ranging from spectroscopic studies of rare bonding motifs (Chapter 3 and Chapter 4) and applications of novel weakly-coordinating anions in applications in coordination chemistry and electrochemistry (Chapter 1 and Chapter 2). While the projects described herein are distinct in the nature of their execution, the utility and applications of synthetic inorganic chemistry are highlighted in all of the projects.\r\nChapter 1 describes the design principles and the synthesis a novel weakly-coordinating anion based on alkyl or aryl substituted silicates bearing fluorinated pinacolate ligands. A wide range of anions bearing distinct R groups were prepared, enabling facile tuning of anion sterics and solubility. A range of cations invoked in chemical reactivity studies supported by these novel anions was prepared, highlighting the utility of these novel anions in both coordination and catalysis. Cations relevant to electrochemical studies were also accessed, wherein the exceptionally wide stability window for the methyl-substituted variant was demonstrated. Reversible magnesium deposition and stripping supported by these anions were also shown, demonstrating the utility of these novel anions in next-generation battery chemistry applications.\r\nChapter 2 describes efforts towards developing reproducible and stable magnesium deposition and stripping chemistry supported by a novel silicon-based weakly-coordinating anion. Aspects that impact reproducible and stable magnesium electrochemistry described in prior literature were studied in detail. Emphasis was placed on probing the prevalent hypothesis in magnesium electrolyte literature that magnesium alkyl, aryl, and amido additives improve electrochemical performance by acting as water or impurity scavengers. A range of magnesium additives were tested, wherein the identity of the additives was shown to dictate magnesium deposition and stripping behavior. An unconventional magnesium hydrocarbyl species was identified as the active species responsible for improved Mg deposition/stripping performance, highlighting the utility of synthetic inorganic chemistry in elucidating fundamental electrochemistry.\r\nChapter 3 describes the synthesis and the spectroscopy of an unusual molybdenum para-terphenyl diphosphine complex bearing a terminal nitride and a parent amide motif. Detailed continuous wave- and pulse-electron paramagnetic resonance techniques were employed the interrogate the electronic structure of this unusual open-shell motif, revealing significant radical character on the amide motif. On the other hand, the terminal nitride motif showed negligible spin density. With further insight obtained from density functional theory calculations, the high spin density on the terminal amide motif was attributed to significant orbital overlap between the amide nitrogen py orbital with the Mo dxy orbital.\r\nChapter 4 describes the synthetic, spectroscopic, and computational studies of a pentametallic molybdenum-iron-sulfur cluster of MoS3Fe3CMo composition with \u03bc4-carbide and \u03bc2-CO motifs that resembles the lo-CO form of nitrogenase. The cluster was accessed via carbide transfer from a Mo carbide complex supported by a para-terphenyl diphosphine ligand. Different isotopologues of this cluster were accessed by selectively labelling the molybdenum para-terphenyl diphosphine precursor. This cluster displays an S = \u00bd ground spin state amenable for pulse electron paramagnetic resonance spectroscopy. Detailed spectroscopic studies reveal a significantly larger carbide hyperfine interaction than any observed for various states of nitrogenase studied thus far, thereby providing benchmarking information for metal-carbon interactions studied by electron paramagnetic resonance methods.\r\nAppendix A describes the synthesis and preliminary reactivity studies of a heterometallic molybdenum-iron-nickel cubane supported by a bulky bisphenoxide ligand with a central anthracene linker, relevant to the active site of the nickel-iron carbon monoxide dehydrogenase. Preliminary electron paramagnetic resonance studies on this cubane were suggestive of an S = 2 ground state, wherein incorporation of a formal closed-shell nickel site into a trimetallic cluster significantly perturbs the electronic structure.\r\nAppendix B describes efforts towards accessing molybdenum para-terphenyl disphosphine carbyne complexes with no bound carbon monoxide ligands. Preliminary studies on the molybdenum carbyne complexes showed that molybdenum complexes with a terminal carbide and a terminal chloride can be accessed.\r\nAppendix C describes the synthesis and preliminary electrochemical studies of novel dianonic silicates supported by fluorinated pinacolate ligands, wherein magnesium deposition and stripping supported by a novel dianion was demonstrated.", "doi": "10.7907/27c4-ey05", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:16249", "collection": "thesis", "collection_id": "16249", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11172023-202811116", "type": "thesis", "title": "Development of Microcrystal Electron Diffraction Techniques for the Characterization of Small Molecules and Novel Materials", "author": [ { "family_name": "Jones", "given_name": "Christopher Glenn", "orcid": "0000-0003-4308-1368", "clpid": "Jones-Christopher-Glenn" } ], "thesis_advisor": [ { "family_name": "Nelson", "given_name": "Hosea M.", "orcid": "0000-0002-4666-2793", "clpid": "Nelson-H-M" } ], "thesis_committee": [ { "family_name": "Stoltz", "given_name": "Brian M.", "orcid": "0000-0001-9837-1528", "clpid": "Stoltz-B-M" }, { "family_name": "Rees", "given_name": "Douglas C.", "orcid": "0000-0003-4073-1185", "clpid": "Rees-D-C" }, { "family_name": "Manthiram", "given_name": "Karthish", "orcid": "0000-0001-9260-3391", "clpid": "Manthiram-Karthish" }, { "family_name": "Nelson", "given_name": "Hosea M.", "orcid": "0000-0002-4666-2793", "clpid": "Nelson-H-M" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Traditional techniques for structural analysis, such as X-ray crystallography and Nuclear Magnetic Resonance (NMR), have been invaluable in understanding the composition of various substances. However, these methods often encounter challenges when applied to the analysis of small molecules and certain novel materials, particularly those that cannot form large, high-quality crystals. The research presented here focuses on the evolution and applications of Microcrystal Electron Diffraction (MicroED), a transformative technique that has expanded the boundaries of structural analysis. We trace the developmental trajectory of MicroED, exploring its underlying principles, technological advancements, and comparative advantages over conventional methods. A variety of data from several key studies was collected through a series of experiments utilizing MicroED to analyze a range of substances, from small organic molecules to complex novel materials and innovative inorganic complexes. MicroED offers unprecedented resolution and sensitivity, capable of structural elucidation where other methods fail. In particular, MicroED has been successful in determining the structures of several novel materials and small molecules with applications in areas such as renewable energy, advanced manufacturing, and pharmaceuticals. Furthermore, this technique is highly amenable to integration with other analytical and computational methods, including machine learning algorithms for data interpretation, enhancing its applicability and efficiency. This research contends that MicroED is not merely an alternative but a substantial upgrade to existing methodologies, holding the potential to revolutionize fields as diverse as materials science, chemistry, and medicine.", "doi": "10.7907/cfnr-f362", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16190", "collection": "thesis", "collection_id": "16190", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09272023-154324412", "type": "thesis", "title": "Organic Films at the Electrode-Electrolyte Interface in CO\u2082 Reduction", "author": [ { "family_name": "Watkins", "given_name": "Nicholas Bret", "orcid": "0000-0001-7251-9387", "clpid": "Watkins-Nicholas-Bret" } ], "thesis_advisor": [ { "family_name": "Peters", "given_name": "Jonas C.", "orcid": "0000-0002-6610-4414", "clpid": "Peters-J-C" }, { "family_name": "Gregoire", "given_name": "John M.", "orcid": "0000-0002-2863-5265", "clpid": "Gregoire-J-M" } ], "thesis_committee": [ { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" }, { "family_name": "Reisman", "given_name": "Sarah E.", "orcid": "0000-0001-8244-9300", "clpid": "Reisman-S-E" }, { "family_name": "Manthiram", "given_name": "Karthish", "orcid": "0000-0001-9260-3391", "clpid": "Manthiram-Karthish" }, { "family_name": "Peters", "given_name": "Jonas C.", "orcid": "0000-0002-6610-4414", "clpid": "Peters-J-C" }, { "family_name": "Gregoire", "given_name": "John M.", "orcid": "0000-0002-2863-5265", "clpid": "Gregoire-J-M" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This thesis focuses on the use of use high-throughput experimentation and analytical electrochemistry techniques to understand how organic films on (photo)electrode surfaces alter catalyst selectivity. Specifically, the objective has been to deconvolute effects associated with the organic film from the atomic identity of the catalyst, reactant and intermediate concentration polarization effects, and temperature in the context of electrochemical CO\u2082 reduction. The first chapter provides the motivations behind the transformation of CO\u2082 into value-added materials using electricity and the challenges that the field faces. The second chapter introduces the data-driven identification of a scaling relationship between the partial current densities of methane and C\u2082\u208a products among 14 bulk copper bimetallic alloys. This strict dependence represents an intrinsic limitation of selectivity tuning through alloying. However, it can be disrupted to favor C\u2082\u208a products by the presence of an organic additive, highlighting the potential of hybrid organic\u2013inorganic catalysts to tune branching ratios in the CO\u2082R reaction network. The third chapter highlights that with the wide band gap CuGa\u2083Se\u2085 chalcopyrite absorber, organic coatings can not only provide dramatic increases in selectivity toward CO\u2082R products compared to the unmodified system, but also and significantly moderate catalyst corrosion. The fourth chapter unveils a new class of molecular films on polycrystalline copper, derived from aryl diazonium and iodonium salts, that are corrosion resistant even at pH 1 and have the potential for many future electrochemical applications. In the fifth chapter, we demonstrate that increased mass transport at the electrode surface directly resulted in changes to the ethylene and methane Tafel slope values on copper electrodes. These findings emphasize that the apparent Tafel slope reported for any copper system is not necessarily representative of the catalyst\u2019s intrinsic kinetics alone, but also contains information about the cell geometry and electrolyte convective transport. The final chapter investigates the combined effect of organic films, mass transport, and electrode heating on electrocatalysis. We find that we can use surface heating to replace bulk heating, but that the complexity of CO\u2082R prevents predictable behavior. However, the addition of additive films to the electrode surface enables idealized electrochemical CO\u2082 reduction kinetics, and therefore the calculation of important parameters such as the activation energy for C\u2082\u208a product formation.", "doi": "10.7907/7t8e-7j20", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16362", "collection": "thesis", "collection_id": "16362", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04292024-055507772", "type": "thesis", "title": "Altering Framework Topology and Heteroatom Distributions of Molecular Sieves by Designed Organic Structure-Directing Agents", "author": [ { "family_name": "Park", "given_name": "Youngkyu", "orcid": "0000-0001-7328-7565", "clpid": "Park-Youngkyu" } ], "thesis_advisor": [ { "family_name": "Davis", "given_name": "Mark E.", "orcid": "0000-0001-8294-1477", "clpid": "Davis-M-E" } ], "thesis_committee": [ { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" }, { "family_name": "Manthiram", "given_name": "Karthish", "orcid": "0000-0001-9260-3391", "clpid": "Manthiram-Karthish" }, { "family_name": "Stoltz", "given_name": "Brian M.", "orcid": "0000-0001-9837-1528", "clpid": "Stoltz-B-M" }, { "family_name": "Zones", "given_name": "Stacey I.", "clpid": "Zones-S-I" }, { "family_name": "Davis", "given_name": "Mark E.", "orcid": "0000-0001-8294-1477", "clpid": "Davis-M-E" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The growing demand for chemical production combined with the urgent need to mitigate the accelerated climate and environmental changes motivates efforts to create highly efficient and selective catalysts and adsorbents. Zeolites and molecular sieves are a key class of materials for addressing these needs because of their high activity and selectivity with catalytic reactions. Additionally, they can show superior adsorption properties because of their structure and surface polarity that can also give shape selectivity with molecules smaller than ca. 1 nanometer. Further advancements in molecular sieve properties will rely on advancements in preparation methods. To this end, the research results presented here explore synthetic approaches for controlling the framework topology and the heteroatom incorporation within silicate-based molecular sieves by means of the strategic design of their organic structure-directing agents (OSDAs).
\r\n\r\nPart I presents the synthesis of STW-type germanosilicate molecular sieves with high-silica framework compositions and the enrichment of chirality. A chiral OSDA is computationally designed based on the predicted stabilization energy toward the pure-silica STW framework. An improved synthesis route for both enantiomers of the OSDA is developed. The enantiopure OSDA is capable of crystallizing a high-silica STW-type germanosilicate molecular sieve that shows distinct framework compositions from previously reported germanium-rich STW. The enantiomeric enrichment of powdered samples without occluded enantiopure OSDAs is characterized by the dynamical refinement of microcrystal electron diffraction data. The high-silica, enantiomerically enriched STW exhibits the framework stability upon thermal treatment and the enantioselective adsorption of 2-butanol. The results in Part I demonstrate the design strategy of OSDAs for crystallizing stable, enantio-enriched molecular sieves for enantioselective chemical separations and catalysis.
\r\n\r\nIn Part II, the distribution of heteroatoms incorporated within borosilicate molecular sieves is studied with regard to its control by cationic OSDAs. To aid in the characterization of the heteroatom sites within borosilicate molecular sieves, the relationship between the 11B NMR chemical shift and the local geometry of boron within tetrahedrally coordinated silicate frameworks is first investigated. From crystalline borosilicate minerals with highly ordered, tetrahedrally coordinated boron atoms, it is revealed that the chemical shifts from 11B NMR linearly correlate with the local geometric parameters. Further studies on the borosilicate molecular sieves that possess more open space and wider angles suggest that the correlation between the average bond angles and 11B NMR chemical shifts can be employed for the entire class of three-dimensional, crystalline borosilicates. Two structurally similar quaternary ammonium OSDAs with different locations of positive charge are designed and synthesized. MWW-type borosilicate molecular sieves are crystallized by both OSDAs, and the quaternary ammonium moieties in the two OSDAs are found to interact with boron species with significantly different 11B NMR chemical shifts. Using the correlation developed here, the characterization results demonstrate that the heteroatom siting within the molecular sieve framework can be selectively altered by tailoring the OSDA structure in terms of the position of positive charge.
", "doi": "10.7907/d1xj-kn25", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16343", "collection": "thesis", "collection_id": "16343", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03302024-040656026", "primary_object_url": { "basename": "HeimGavinThesis.pdf", "content": "final", "filesize": 78661523, "license": "other", "mime_type": "application/pdf", "url": "/16343/1/HeimGavinThesis.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Molecular Tuning of Electrocatalysts for Generation of Commodity Chemicals", "author": [ { "family_name": "Heim", "given_name": "Gavin Paul", "orcid": "0000-0002-9244-6565", "clpid": "Heim-Gavin-Paul" } ], "thesis_advisor": [ { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" } ], "thesis_committee": [ { "family_name": "Peters", "given_name": "Jonas C.", "orcid": "0000-0002-6610-4414", "clpid": "Peters-J-C" }, { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" }, { "family_name": "Stoltz", "given_name": "Brian M.", "orcid": "0000-0001-9837-1528", "clpid": "Stoltz-B-M" }, { "family_name": "Manthiram", "given_name": "Karthish", "orcid": "0000-0001-9260-3391", "clpid": "Manthiram-Karthish" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Improving our understanding of electrocatalytic transformations is envisioned to facilitate society\u2019s implementation of technologies that achieve a net zero carbon footprint. Carbon dioxide is one of the most emitted greenhouse gases, and improvement in CO\u2082 capture technologies along with decreasing costs of renewable energy provide an opportunity to convert this species to value-added chemicals using electrochemical processes. Tuning homogeneous and heterogeneous electrocatalyst performance with well-defined molecular species can render systems more selective and active while also allowing us to readily predict variables crucial in achieving these transformations. This thesis investigates 1) molecular and polymeric species as electrode coatings for enhanced generation of carbon-coupled products and 2) discrete electrocatalyst active sites for formation CO\u2082 reduction products at low overpotentials; generation of highly reduced liquid fuels is observed with molecular electrocatalysts supported on electrodes.\r\nChapter I provides context and background to the contents of this thesis.
\r\n\r\nChapter II discusses novel, polyaromatic molecular additives utilized for low pH CO\u2082 reduction on Cu electrodes. N-phenyl isoquinolinium triflate film facilitates high selectivity for C\u2082+ products in 0.1 M H\u2083PO\u2084/KH\u2082PO\u2084, suggesting enhancement in CO\u2082 mass transport rather than limiting proton carrier diffusion. Improvement in long-term stability and tolerance to lower pH compared to previous films is observed.
\r\n\r\nChapter III reports on a series of polystyrene-based ionomers to probe the effect of local [K\u207a] in the Cu electrode microenvironment on CO\u2082R performance. Partial current density towards C\u2082\u208a products (|jC\u2082\u208a|) increases monotonically with [K\u207a] in ionomer, up to 225 mA cm\u207b\u00b2. Replacing K\u207a with [Me4N]\u207a lowers performance to the level of bare Cu, highlighting the crucial role of K\u207a in improving C\u2082\u208a product selectivity. Molecular dynamics simulations and partial pressure CO\u2082 electrolysis experiments are consistent with enhanced CO\u2082 mass transport due to K\u207a in the film.
\r\n\r\nChapter IV discusses variation of ionomer/polymer structures to maximize CO\u2082R performance. Incorporation of neutral comonomers bearing cross-linking units rich in biphenyl and terphenyl motifs result in high current densities (~270 mA cm\u207b\u00b2) towards C\u2082\u208a products with 82% Faradaic efficiency. The analogous neutral variants (i.e., those lacking the charged comonomer) show comparable |jC\u2082\u208a| to the K\u207a-containing polymers, suggesting a non-innocent role of the aryl-rich polymers in boosting performance.
\r\n\r\nChapter V presents novel four-coordinate, dicationic Co complexes supported on carbon nanotubes capable of generating MeOH from CO\u2082. Electrolysis with CO also leads to formation of MeOH, suggesting a CO-bound complex to be a crucial intermediate in CO\u2082R to MeOH. This work highlights rare examples of molecular systems facilitating multi-electron electrochemical transformations to highly demanded commodity chemicals.
\r\n\r\nChapter VI presents work on molecular electrocatalysts bearing novel polyaromatic ligands that lower the electrocatalytic potential (Ecat) of CO\u2082R by ~310 mV compared to state-of-the-art complexes as determined via cyclic voltammetry. The extended \u03c0 system motif is more proximal to the metal center relative to previously reported nanographene-containing electrocatalysts. Well-defined characterization was obtained via single-crystal X-ray diffraction in addition to solution-state techniques. Density functional theory calculations reveal significant ligand contributions in the frontier orbitals of relevant CO\u2082R intermediates.
\r\n\r\nChapter VII highlights a polycyclic aromatic hydrocarbon (PAH) bearing twelve edge nitrogen atoms. Spectroscopy, electrochemistry, and computational results suggest a significant narrowing of the HOMO-LUMO gap compared to the N-free analogue owing to the electron-deficient extended \u03c0 system imposed by the nitrogen dopants. Changes to absorption and emission spectra from titration of the PAH with metal salts suggest that coordination chemistry provides an additional degree of freedom towards tuning electronic structure. Dramatic changes from addition of trifluoromethanesulfonic acid suggest this material to be a possible pH sensor. This approach in judiciously tuning the band gap of bulk graphene materials via saturation of the nanographene edge sites with nitrogen atoms gives rise to a novel compound with intriguing electronic properties.
\r\n\r\nAppendix A describes systematic attempts in demonstrating cascade electrocatalysis between molecular CO\u2082-to-CO complexes and pyridinium film-modified Cu towards enhanced rates of C\u2082\u208a products formation.
\r\n\r\nAppendix B provides results coupling electrodeposited imidazolium-derived films with pyridinium towards enhanced CO\u2082R to C\u2082\u208a on Cu. While promising performance is achieved, the difficulty in characterizing the films limits the tractability of these systems with respect to their impacts on the microenvironment.
\r\n\r\nAppendix C discusses developing coordination complexes of heteroatom containing polyaromatic hydrocarbons. Several examples characterized via X-ray crystallography are reported.
\r\n\r\nAppendix D shows CO\u2082R data on K\u207a ionomer-coated Au. Elevation in |jCO| is demonstrated as a function of potassium content in the electrode-electrolyte interface provided by the film.
\r\n\r\nAppendix E discusses attempts to determine and CO\u2082 uptake by K\u207a ionomers via solid state NMR spectroscopy.
", "doi": "10.7907/dm95-6856", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:15109", "collection": "thesis", "collection_id": "15109", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02162023-233344819", "type": "thesis", "title": "Advancement of Asymmetric Bipolar Membranes for Tailoring Chemical Environments in Electrochemical Systems", "author": [ { "family_name": "Lucas", "given_name": "\u00c9owyn", "orcid": "0000-0002-8743-5722", "clpid": "Lucas-\u00c9owyn" } ], "thesis_advisor": [ { "family_name": "Atwater", "given_name": "Harry Albert", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" } ], "thesis_committee": [ { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Manthiram", "given_name": "Karthish", "orcid": "0000-0001-9260-3391", "clpid": "Manthiram-Karthish" }, { "family_name": "Atwater", "given_name": "Harry Albert", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Under reverse bias, bipolar membranes (BPMs) enhance water dissociation (WD) at the junction between a cation exchange layer (CEL) and an anion exchange layer (AEL), often with additional improvement from an integrated WD catalyst. Recent research has shown promise for developing and implementing BPMs in renewable energy systems, such as carbon removal, water and CO\u2082 electrolysis, and energy storage. The economic feasibility of these carbon capture and conversion systems with incorporated BPMs, however, relies on BPMs to maintain stable operation at high current densities (>100 mA cm\u207b\u00b2) and low overpotentials. Existing commercial BPMs are limited to current densities of \u2264100 mA cm\u207b\u00b2 as water transport through the CEL and AEL cannot keep up with the increased rate of WD at the junction at higher current densities. In this work, we present a freestanding, high current density BPM (HCD-BPM) with a thin AEL (15 \u03bcm, PiperION 15R), a graphene oxide (GrOx) catalyst layer, and a mechanically supportive CEL (50 \u03bcm, Nafion 212) specifically designed to overcome water transport limitations. When tested under reverse bias in a custom electrodialysis cell with Luggin capillaries, this HCD-BPM demonstrates the lowest published overpotentials up to 1 A cm\u207b\u00b2. Furthermore, the HCD-BPM exhibits stabilities of >1000 hour at 80 mA cm\u207b\u00b2, >100 hours at 500 mA cm\u207b\u00b2, and >60 hours at 1 A cm\u207b\u00b2, Faradaic efficiencies for H\u207a and OH\u207b of >95%, and successful implementation into a multi-cell electrodialysis stack designed for integration into a DOC system. Additional characterization, such as SEM, Confocal microscopy, and titration, was performed to understand the structure and performance of the HCD-BPM. Additionally, the BPM was tested in forward bias to investigate its use for acid/base flow batteries. Overall, this thesis presents a novel BPM with record performance in multiple electrochemical systems that mitigate anthropogenic CO\u2082 emissions.
", "doi": "10.7907/jken-ty64", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:15139", "collection": "thesis", "collection_id": "15139", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04142023-055704455", "primary_object_url": { "basename": "Faisal Alshafei - PhD Thesis - FINAL V1.pdf", "content": "final", "filesize": 13075550, "license": "other", "mime_type": "application/pdf", "url": "/15139/1/Faisal Alshafei - PhD Thesis - FINAL V1.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Enhancing the Ethylene and Propylene Selectivities in the Methanol-to-Olefins Reaction by Exploiting the Intricate Relationship between Framework Topology and Acidity", "author": [ { "family_name": "Alshafei", "given_name": "Faisal H.", "orcid": "0000-0003-1808-1374", "clpid": "Alshafei-Faisal-H" } ], "thesis_advisor": [ { "family_name": "Davis", "given_name": "Mark E.", "orcid": "0000-0001-8294-1477", "clpid": "Davis-M-E" } ], "thesis_committee": [ { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" }, { "family_name": "Manthiram", "given_name": "Karthish", "orcid": "0000-0001-9260-3391", "clpid": "Manthiram-Karthish" }, { "family_name": "Zones", "given_name": "Stacey I.", "clpid": "Zones-S-I" }, { "family_name": "Davis", "given_name": "Mark E.", "orcid": "0000-0001-8294-1477", "clpid": "Davis-M-E" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This thesis describes and presents results from several related projects within the theme of molecular sieve synthesis and catalysis. The early part of the thesis focuses on understanding the link between cage size/dimension and acidity (i.e., acid site density and strength) in the methanol-to-olefins (MTO) reaction. This relationship between cage size and acidity, once identified and investigated, is exploited in the latter parts of the thesis to rationally design materials that are able to steer the light olefins product distribution toward either more ethylene or propylene in a significant improvement over SAPO-34 (CHA), the commercial catalyst.
\r\n \r\nIn Chapters 2, 44 zeolites and silicoaluminophosphates (SAPOs) belonging to five frameworks (AEI, CHE, LEV, SWY, and ERI) with a wide range of Si/Al=4-31 and Si/(Al+P)=0.04-0.3, are synthesized and characterized using a myriad of techniques. Their MTO behavior is then systematically investigated to rationalize the effect of cage dimensions on the olefins product distribution as a function of acid site density and strength. The results from this study show that changes in acid site density and strength play a secondary role to the dominating influence of cage architecture on product distribution in AEI- and CHA-type molecular sieves. Decreasing the cage size, in going from AEI and CHA to LEV, SWY, and ERI, however, results in substantial changes in the ethylene-to-propylene ratio (E/P) as a function of acidity. These changes are attributed to differences in the identity and concentration of the hydrocarbon-pool (HP) species that form, particularly in early stages of the reaction.
\r\n \r\nIn Chapters 3 and 4, ERI-type molecular sieves (e.g., SSZ-98, UZM-12, ERI-type zeolites, and SAPO-17) are thoroughly investigated as promising methanol-to-ethylene materials due to their narrow cage size. Specifically, numerous ERI-type molecular sieves are synthesized using several organic structure-directing agents (OSDAs) with varied Si/Al or Si/T-atoms ratios. The list of ERI-related materials synthesized and tested in MTO included a new disordered SAPO, denoted as CIT-16P, which upon thermal treatment in air transforms to SAPO-17 (ERI). The reaction results show that decreasing the Si/Al (or increasing the Si/T) ratio, irrespective of other material properties, improves the E/P of ERI-type molecular sieves (E/P=1.1-1.9) over CHA-type molecular sieves (E/P=0.82-0.85) in MTO. Dissolution-extraction experiments reveal that the rapid formation of cyclic intermediates and the shift in their composition toward less-methylated methylbenzenes and methylnaphthalenes are found to be key to enhancing the ethylene selectivity in ERI-type molecular sieves.
\r\n \r\nIn Chapter 5, several SAT-type molecular sieves are investigated as promising methanol-to-propylene catalysts. This effort entails the synthesis of CIT-17, an SAT SAPO-type molecular sieve, which is isostructural to STA-2 (MgAPO-SAT). Following the successful synthesis of CIT-17, the MTO behavior of several SAT-type molecular sieves (MgAPO, CoAPO, and SAPO) are investigated in MTO. The combination of low acidity of CIT-17 and unique structural features of the narrow SAT-cage lead to a catalytic pathway and mechanism that predominantly favors propylene (propylene-to-ethylene ratios (P/E) of 2-4.2; propylene selectivity of 40-50%). Indeed, CIT-17 achieves one of the highest P/E ratio values reported for this class of materials.
", "doi": "10.7907/btcj-w948", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:14953", "collection": "thesis", "collection_id": "14953", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06062022-211326081", "primary_object_url": { "basename": "Saccone_Max_Thesis_2022.pdf", "content": "final", "filesize": 54345211, "license": "other", "mime_type": "application/pdf", "url": "/14953/1/Saccone_Max_Thesis_2022.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Vat Photopolymerization Additive Manufacturing of Functional Materials: from Batteries to Metals and Alloys", "author": [ { "family_name": "Saccone", "given_name": "Max Anthony", "orcid": "0000-0003-3846-2908", "clpid": "Saccone-Max-Anthony" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Manthiram", "given_name": "Karthish", "orcid": "0000-0001-9260-3391", "clpid": "Manthiram-Karthish" }, { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" }, { "family_name": "Kornfield", "given_name": "Julia A.", "orcid": "0000-0001-6746-8634", "clpid": "Kornfield-J-A" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "Resnick Sustainability Institute" }, { "literal": "div_chem" } ], "abstract": "In recent years, additive manufacturing (AM), also known as 3D printing, has emerged as a uniquely powerful tool for rapid prototyping and for creating complex, high value structures. Vat polymerization (VP) is an AM technique which forms parts through light-initiated polymerization, capable of achieving both high resolution and high throughput. While VP has been utilized to fabricate a wide variety of polymeric materials, fabricating functional materials such as ceramics, metals, and inorganic composites has remained a challenge. This thesis focuses on developing fabrication methods for a range of functional materials, from battery active materials to metals and ceramics, via vat polymerization additive manufacturing, taking advantage of chemical reactions within an AM part after fabrication to form target materials in situ.
\r\n\r\nWe demonstrate the use of emulsions to introduce aqueous active material precursors into organic photopolymer resins to create architected lithium sulfide/carbon composites for use as lithium-sulfur battery cathodes. Such architected cathode materials are promising for mitigating mechanical degradation in high volume-change battery materials such as the sulfur cathode. We additionally performed nanome- chanical experiments on lithium sulfide powders to determine how lithium sulfide yields, deforms, and fails in the context of volume-change-induced stress during battery cycling. Because lithium sulfide is present as a discharge product in all lithium sulfur batteries, these nanomechanical particle compressions have bearing on the entire field, beyond the realm of 3D architected cathodes.
\r\n\r\nWe additionally demonstrate the use of organogel templates to streamline the AM process by enabling the fabrication of many materials starting with a single resin composition, followed by infiltration of appropriate metal precursors and post-processing heat treatment to convert the polymer/precursor matrix to the target metal via calcination and reduction reactions. We fabricate and characterize copper, nickel, silver, cobalt, cupronickel alloys, tungsten, and more to highlight the wide-ranging versatility of achievable materials and microstructures.
", "doi": "10.7907/v3cn-8h28", "publication_date": "2022", "thesis_type": "phd", "thesis_year": "2022" } ]