Repository logo

Browsing by Author "Rappe, Anthony, committee member"

Now showing 1 - 10 of 10
  • Thumbnail Image
    ItemEmbargo
    Charge carrier dynamics of 2-dimensional photoelectrodes probed via ultrafast spectroelectrochemistry
    (Colorado State University. Libraries, 2024) Austin, Rachelle, author; Sambur, Justin, advisor; Krummel, Amber, advisor; Rappe, Anthony, committee member; Prieto, Amy, committee member; McNally, Andrew, committee member; Brewer, Samuel, committee member
    The integration of hot charge carrier-based energy conversion systems with two-dimensional (2D) semiconductors holds immense promise for enhancing the efficiency of solar energy technologies and enabling novel photochemical reactions. Current approaches, however, often rely on costly multijunction architectures. In this dissertation, I present research that combines spectroelectrochemical and in-operando transient absorption spectroscopy measurements to unveil ultrafast (<50 fs) hot exciton and free charge carrier extraction in a proof-of-concept photoelectrochemical solar cell constructed from earth-abundant monolayer (ML) MoS2. Theoretical analyses of exciton states reveal enhanced electronic coupling between hot exciton states and neighboring contacts, facilitating rapid charge transfer. Additionally, I discuss insights into the physical interpretation of transient absorption (TA) spectroscopy data in 2D semiconductors, comparing historical perspectives from physical chemistry and solid-state physics literature. My perspective encompasses various physical explanations for spectral features and experimental trends, particularly focusing on the contribution of trions to TA spectra. Furthermore, I examine how different physical interpretations and data analysis procedures can yield distinct timescales and mechanisms from the same experimental results, providing a comprehensive framework for understanding charge carrier dynamics in 2D semiconductor-based optoelectronic devices.
  • Thumbnail Image
    ItemOpen Access
    Electrochemically prepared metal antimonide nanostructures for lithium ion and sodium ion battery anodes
    (Colorado State University. Libraries, 2016) Jackson, Everett D., author; Prieto, Amy, advisor; Rappe, Anthony, committee member; Dandy, David, committee member; Bailey, Travis, committee member; Henry, Charles, committee member
    The use of energy fundamentally enables and globally supports post-industrial economies and is critical to all aspects of modern society. In recent years, it has become apparent that we will require superior energy technologies to support our society, including improved methods of generating, storing, and utilizing energy resources. Battery technology occupies a critical part of this new energy economy, and the development of electrochemical energy storage devices will be a critical factor for the successful implementation of renewable energy generation and efficiency strategies at the grid, transportation, and consumer levels. Current batteries suffer from limitations in energy density, power density, longevity, and overall cost. In addition, the inherent tradeoffs required in battery design make it impossible to create a single battery that is perfect for all applications. To overcome these issues, the development of low-cost and high-throughput methods, new strategies for materials design, and a comprehensive understanding of electrochemical mechanisms for battery performance is necessary. Herein, an in-depth study on the electrochemistry of a model anode system for rechargeable batteries based on metal antimony alloys produced through an electroplating approach is detailed. The first chapter of this dissertation provides a brief introduction of lithium ion and sodium ion battery technology. In the second chapter, a detailed review of the literature on antimony and metal antimonide alloys for battery anodes is provided. The third chapter details a study on copper antimonide thin films with varying stoichiometry produced through a facile electrodeposition process. In the fourth chapter, stoichiometric Cu2Sb thin films are studied as potential anodes for sodium ion batteries. The fifth chapter details the development of a process for electroplating zinc-antimony alloy thin films onto zinc and their electrochemical properties in sodium ion cells. The sixth and seventh chapters report the synthesis and characterization of copper-antimony alloy nanowire arrays produced through an alumina-templated process. These nanowire arrays are first used in an electrolyte-additive study to show the importance of surface stabilization for high surface area electrodes in chapter five. In chapter six, the rate performance is characterized under different thermal conditions for different compositions of copper-antimony alloy nanowire arrays as an assessment of the kinetic limitations of this electrode. The final chapter briefly describes some preliminary experiments that have been performed on characterizing the electrochemistry of metal salts in a deep eutectic solvent as a potential method for co-deposition of new metal antimonides.
  • Thumbnail Image
    ItemOpen Access
    Exploring gas-phase plasma chemistry and plasma-surface interactions: progress in plasma-assisted catalysis
    (Colorado State University. Libraries, 2020) Hanna, Angela R., author; Fisher, Ellen R., advisor; Levinger, Nancy E., committee member; Rappe, Anthony, committee member; Bradley, R. Mark, committee member
    To view the abstract, please see the full text of the document.
  • Thumbnail Image
    ItemOpen Access
    I. Ground-state association between phenothiazine and tris(diimine)ruthenium(II) complexes: its role in highly efficient photoinduced charge separation. II. Ligand modifications of cobalt complexes to increase efficiency of electron-transfer mediators in dye-sensitized solar cells
    (Colorado State University. Libraries, 2012) Weber, John, author; Elliott, C. Michael, advisor; Rappe, Anthony, committee member; Levinger, Nancy, committee member; Woody, Robert, committee member; Van Orden, Alan, committee member
    Supramolecular triad assemblies consisting of a central trisbipyridineruthenium(II) chromophore (C2+), with one or more appended phenothiazine electron donors (D) and a diquat-type electron acceptor (A2+) have been shown to form long-lived photoinduced charge separated states (CSS) with unusually high quantum efficiency. Up to now, there has been no explanation for why such large efficiencies (often close to unity) are achieved from these systems when other, seemingly similar, systems are often much less efficient. In the present study, using a bimolecular system consisting of chromophore-acceptor diad (C2+-A2+) and an N-methylphenothiazine donor we demonstrate that a ground-state association exists between the RuL32+ and the phenothiazine prior to photoexcitation. It is this association process that is responsible for the efficient CSS formation in the bimolecular system and, by inference, also must be an essential factor in the fully intramolecular process occurring with the D-C2+-A2+ triad analogs. Alkyl-substituted bipyridine ligands in cobalt II/III complexes were modified in order to serve as efficient electron-transfer mediators in dye-sensitized solar cells. Attempts at halogen substitution reactions are described. Ultimately isopropyl groups appended to bipyridine ligands were modified by introducing a hydroxyl group at the benzylic position. The electrochemical behavior of the modified ligand is described, as well as its performance as part of a cobalt complex electron-transfer mediator in dye-sensitized solar cells.
  • Thumbnail Image
    ItemEmbargo
    Investigating the role of chemical additives in the structure and dynamics of electrolyte mixtures via 2D infrared spectroscopy and microscopy
    (Colorado State University. Libraries, 2022) Tibbetts, Clara Anne, author; Krummel, Amber T., advisor; Wilson, Jesse, committee member; Levinger, Nancy, committee member; Rappe, Anthony, committee member
    The research in this dissertation is focused on the impact that additives have on the chemical structure and dynamics of electrolyte solutions that can be used in electrochemical devices such as batteries or solar devices. Two-dimensional infrared spectroscopy (2D IR) has been used in conjunction with linear Fourier Transform infrared spectroscopy (FTIR), rheology, molecular dynamics, and density functional theory to study organic carbonate and ionic liquid mixtures. In addition, 2D IR microscopy is successfully implemented to study ionic liquid mixtures in different environments including a microdroplet and a copper electrochemical cell. 2D IR and molecular dynamics simulations of organic carbonate mixtures with varied amounts of a common additive, fluoroethylene carbonate (FEC), show that even in small quantities FEC can induce changes in the solvent structure. Experimental results demonstrated that at low concentrations FEC slows spectral diffusion. Cylindrical distribution functions calculated from molecular dynamics simulations in conjunction with experimental results suggest the slowing is due to significant changes in the behavior of one of the solution components, ethylene carbonate. Furthermore, a combination of experimental anisotropy and viscosity, and computational rotational correlation functions shows that local solvent rigidity increases with high amounts of FEC. Moreover, these results show that additional FEC increases macroscopic viscosity which is correlated to global solvent orientational relaxation. In functional batteries FEC is shown to dramatically impact how the solid electrolyte interphase forms, a layer that impacts battery metrics such as lifetime and safety.1–3 Therefore, it is possible that the observed changes in the solvent structure upon addition of FEC has implications in how the solid electrolyte interphase forms. The combination of linear and 2D IR spectroscopy with viscosity measurements is used to study the impact of small amounts of water (between ~1.32 and 21.6% mole fraction water) on the structure and dynamics of room-temperature ionic liquid mixtures. Specifically, the effects of water on a mixture of 1-butyl-3-methylimidazolium tetrafluoroborate (BmimBF4) and 1-butyl-3-methylimidazolium dicyanamide (BmimDCA) room-temperature ionic liquid (RTIL) was investigated by tracking changes in the vibrational features of the dicyanamide anion (DCA). Shifts in the infrared peak frequencies of DCA indicated the formation of water-associated and non-water-associated DCA populations. Time-dependent 2D IR shows differences in the dynamic behavior of the water-associated and non-water-associated populations of DCA at low (below 2.5% χWater), mid (between 2.5% χWater and 9.6% χWater), and high (between 11.6% χWater and 21.6% χWater) water concentrations. The vibrational relaxation occurs more quickly with increasing water content for water-associated populations of DCA, indicating water introduces additional pathways for relaxation, possibly via new bath modes. On the other hand, spectral diffusion of water-associated populations slows significantly with more water, suggesting water induces the formation of distinct and non- or very slowly interchangeable local environments. It is possible that in a functional electrochemical device with a water and RTIL electrolyte the introduction of these diverse local solvent environments might impact device performance. If water could be introduced in a system in a way that increased ion-mobility but does not cause undesirable interfacial interactions near an electrode this could improve device efficiency. Therefore, determining if and how this local heterogeneity presents itself in an operational electrochemical cell is an important next step. Ultrafast 2D IR microscopy is discussed as an emerging imaging platform that is a promising tool for investigating heterogeneous samples across multiple time scales and length scales, including electrochemical devices. However, there are numerous practical considerations in the implementation of 2D IR microscopy. Some of these considerations include mid-IR laser sources, repetition rates, mid-IR pulse shaping, noise reduction, microscope design, and detection limitations. In this work we show the implementation of improvements in spectral resolution and noise reduction and the consequent successful imaging of a BmimDCA:BmimBF4 electrolyte in two different scenarios—a droplet and a copper electrochemical cell. Imaging the BmimDCA:BmimBF4 microdroplet shows how 2D IR imaging can be used to probe dynamics on a spatial scale. Results indicate the solvent dynamics in the microdroplet are spatially homogenous. Imaging experiments of the RTIL electrolyte in a copper cell, demonstrates a practical application of ultrafast 2D IR microscopy to study functional electrochemical devices. 2D IR spectra collected between the copper counter electrode and working electrode showed dramatic changes in peak positions and shapes suggesting the formation of DCA copper complexes. These results suggest 2D IR microscopy will allow chemical exchange dynamics of different species involved in the electrochemical reactions to be monitored as they evolve from the counter electrode to the working electrode. This work establishes 2D IR microscopy as a tool well equipped to connect molecular level condensed phase reaction dynamics to micro- and mesoscale spatial dependence in an electrochemical cell.
  • Thumbnail Image
    ItemOpen Access
    Investigation of the growth mechanism of highly branched silica nanowires grown using in-situ Cu-catalyst loading, and the development of electrochemical anodization synthetic methods specifically targeting solid ionically conducting materials
    (Colorado State University. Libraries, 2023) Boissiere, Jacob Daniel, author; Prieto, Amy, advisor; Finke, Richard, committee member; Rappe, Anthony, committee member; Dandy, David, committee member
    Gaining a better understanding of the world around us is the fundamental objective of science, with chemistry looking to better understand the processes and applications that occur on a molecular and sub-molecular scale. Developing this better understanding has allowed us to create medicine and computers, begin exploring space and understanding the atom and is a never-ending process of asking questions and testing hypotheses as we work toward an increasingly objective answer. The best that I can hope for, not only in my time in graduate school, but as I move forward in life, is that I have moved this understanding, even in the slightest, in the correct direction. This may be a small impact, but much of the work presented in this dissertation will focus on small things. Two significant research directions will be presented along with work on device and process development for characterization. The first major system that will be discussed is the chemical vapor deposition of highly branched silica nanowires that were grown in a single synthetic step as a result of in-situ Cu-catalyst loading. The second research direction involves the investigation into using electrochemical anodization synthesis as a way to target the formation and discovery of ionically conducting materials. The overall link between these research topics involves the focus on solid inorganic materials, with a broad direction of understanding materials systems, process development and optimization, careful characterization, hypothesis generation, and considerations of potential applications and future directions of the materials and techniques being investigated. Systems of interest could loosely be classified as energy related materials. Both systems provided unique and challenging aspects to understanding the synthetic processes involved as products were formed under highly dynamic environments. Additionally, device and process developments were perused to address systematic variables such as instability of products and improve overall reaction design and therefore reproducibility and significance of results. The first system investigated involved the chemical vapor deposition of silicon-based nanowire products. The initial objective of the project was to investigate the unique structures of highly branched nanowires that were grown through in-situ doping of Cu, and investigate their properties and performance as a potential anode material for use in Li-ion battery devices. The synthetic method used, and the unique structures observed were previously reported by the Prieto research group. The hypothesis was that these products were grown as crystalline Si and being catalytically oxidized due to the presence of Cu and Cu3Si post synthesis. The work presented here disproves this hypothesis, instead proposing that the product is grown as the oxide. Due to this new conclusion, the battery application study was no longer pursued, and investigation instead focused on developing and proposing a new growth hypothesis. This new hypothesis involves the formation of a multi-wire backbone, which is believed to be the first report to directly investigate and explain this phenomenon. The second research direction outlines the motivation, theory, and initial outcomes of attempting to develop a new synthetic methodology for ionically conducting materials through electrochemical anodization. While anodization is itself far from a new synthetic method, it has never been used to synthesize the targeted material systems, nor has it been used to pursue the synthesis of ionically conducting materials generally. Much of the discussion will revolve around the background, motivation, and hypotheses relating to this project. This focus is partially due to the limited success of certain research objectives, but the intention is to hopefully highlight the intrinsic value of the synthetic concept and theory behind it, as well as direct future potential research based on what has been learned. The synthetic results and discussion focus on the anodization synthesis of AgI, the morphologies and crystallographic properties of the materials formed, and insights into the synthetic process. The related systems of CuI and CuxS will also be touched upon, as well as attempts to pursue the synthesis of Na3PS4. Throughout these investigations, a variety of side project and collaborations were worked on, but the one of significance that will be included in the final chapter relates to the development of an air-free sample transfer holder. This was developed to allow the air-free transfer of a surface sensitive material between a glove-box and an X-ray photoelectron spectroscopy instrument. This enables more accurate and meaning data to be collected on samples that could otherwise be modified or compromised through exposure to ambient air before analysis.
  • Thumbnail Image
    ItemOpen Access
    Part I: Structural characterization of doped nanostructured magnesium: understanding disorder for enhanced hydrogen absorption kinetics. Part II: Synthesis, film deposition, and characterization of quaternary metal chalcogenide nanocrystals for photovoltaic applications
    (Colorado State University. Libraries, 2017) Braun, Max B., author; Prieto, Amy, advisor; Finke, Richard, committee member; Rappe, Anthony, committee member; Neilson, James, committee member; de la Venta, Jose, committee member
    The production, storage, and subsequent consumption of energy are at the foundation of all human activity and livelihood. The theme of this dissertation is the pursuit of fundamentalunderstanding of the chemistry of materials that are used for energy production and storage. A strong emphasis is placed on a synthetic foundation that allows for systematic investigation into the fundamental chemistry that controls the applicable properties of the materials of interest. This dissertation is written in the "journals format" style—which is accepted by the Graduate School at Colorado State University—and is based on one peer-reviewed publication that has appeared in Chemistry of Materials as well as two manuscripts to be submitted, one to The Journal of Physical Chemistry C, and one to ACS Applied Materials and Interfaces. In order to create a context forthese publications, Chapters 1 and 3 provide an overview of the motivations for the projects, and then continue to detail the initial synthetic investigations and considerations for the two projects. In addition to recounting Mg nanocrystals synthetic refinement that was necessary for reproducible hydride kinetic analysis, Chapter 1 also briefly introduces some of the conventional models used for fitting of the hydriding kinetics data. Furthermore, initial investigations into the use of these models for our system are presented. Chapter 2 is a paper to be submitted to The Journal of Physical Chemistry C that describes the local and extended structure characterization of Mg nanocrystals (NCs) with a small amount of nickel added during synthesis. Ni has a dramatic effect on the de/hydriding kinetics of Mg NCs, and this chapter describes the use of a combination of multiple state-of-the-art characterization techniques to gain insight into the structural perturbations due to Ni inclusion in the Mg NCs. This insight is then used to establish the characteristics of Ni inclusion that results in the enhanced hydrogen absorption processes. Chapter 3 introduces the many considerations needed to be taken into account during the development of a novel synthesis for copper zinc tin chalcogenide colloidal nanocrystals. In addition to introducing synthetic approaches to achieve this goal, Chapter 3 also describes essential characteristics that need to be considered for further investigation into the properties of films made from the nanocrystals. Chapter 4 is a publication that appeared in Chemistry of Materials, that describes an approach to tuning the surface and ligand chemistry of Cu2ZnSnS4 nanocrystals for use as an absorber layer in next generation photovoltaic devices. The publication describes ligand exchange chemistry achieved via layer-by-layer dip-casting of nanocrystal thin films, and the effects that this exchange chemistry has on the resulting films. It also details the fabrication of full photovoltaic (PV) devices to characterize the benefits of controlling the surface chemistry can have on PV performance. Chapter 5 is a paper—to be submitted to ACS Applied Materials and Interfaces—that describes the investigations into how varying the chalcogen ratio (i.e., S:Se) leads to changes in the physical and electrical properties of thin films made from Cu2ZnSn(S1-xSex)4 (where 0 < x < 1) NCs. It highlights the novel synthetic procedure (detailed in chapter 3) that was required for a systematic, deconvoluted evaluation of S:Se composition on the materials optical and electronic properties. Moreover, the characteristics of full PV devices based on thin films of each stoichiometry (x=0 to x=1) are assessed to establish a relationship between composition and the materials performance.
  • Thumbnail Image
    ItemOpen Access
    Software to design crosslinks for protein crystal stabilization
    (Colorado State University. Libraries, 2015) Sebesta, Jacob Christopher, author; Snow, Christopher, advisor; Fisk, Nick, committee member; Rappe, Anthony, committee member
    Programmable materials allow properties as specific locations in the material to be modified through reliable encoding. One class of such materials are protein crystals that allow changes to be made through genetic manipulation. Protein crystals are well-ordered and highly porous materials, but they are also easily dissolved, limiting their utility. Crosslinking techniques previously developed often have a deleterious effects on the crystal order. In this work, we introduce software to design specific crosslinks across protein crystal interfaces using disulfide and dityrosine crosslinks as well as a variety of small molecule crosslinkers used in protein conjugation. The software is a general tool for specific crosslinking that introduces a number of improvements on previous disulfide design software. Several of the disulfide and dityrosine designs were assembled in the lab and one of the disulfide crosslink designs was confirmed using X-ray diffraction.
  • Thumbnail Image
    ItemOpen Access
    Tuning optoelectronic properties and understanding charge transport in nanocrystal thin films of earth abundant semiconducting materials
    (Colorado State University. Libraries, 2011) Riha, Shannon C., author; Parkinson, Bruce A., advisor; Prieto, Amy L., advisor; Elliott, C. Michael, committee member; Field, Stuart, committee member; Henry, Charles, committee member; Rappe, Anthony, committee member
    With the capability of producing nearly 600 TW annually, solar power is one renewable energy source with the potential to meet a large fraction of the world's burgeoning energy demand. To make solar technology cost-competitive with carbon-based fuels, cheaper devices need to be realized. Solution-processed solar cells from nanocrystal inks of earth abundant materials satisfy this requirement. Nonetheless, a major hurdle in commercializing such devices is poor charge transport through nanocrystal thin films. The efficiency of charge transport through nanocrystal thin films is strongly dependent on the quality of the nanocrystals, as well as their optoelectronic properties. Therefore, the first part of this dissertation is focused on synthesizing high quality nanocrystals of Cu2ZnSnS4, a promising earth abundant photovoltaic absorber material. The optoelectronic properties of the nanocrystals were tuned by altering the copper to zinc ratio, as well as by introducing selenium to create Cu2ZnSn(S1-xSex)4 solid solutions. Photoelectrochemical characterization was used to test the Cu2ZnSnS4 and Cu2ZnSn(S1-xSex)4 nanocrystal thin films. The results identify minority carrier diffusion and recombination via the redox shuttle as the major loss mechanisms hindering efficient charge transport through the nanocrystal thin films. One way to solve this issue is to sinter the nanocrystals together, creating large grains for efficient charge transport. Although this may be quick and effective, it can lead to the formation of structural defects, among other issues. To this end, using a different copper-based material, namely Cu2Se, and simple surface chemistry treatments, an alternative route to enhance charge transport through nanocrystals thin films is proposed.
  • Thumbnail Image
    ItemOpen Access
    Using X-ray photoelectron spectroscopy to understand the solid electrolyte interphase formation in sodium ion batteries
    (Colorado State University. Libraries, 2022) Gimble, Nathan Jacob, author; Prieto, Amy, advisor; Ackerson, Christopher, committee member; Rappe, Anthony, committee member; Popat, Ketul, committee member
    Sodium-ion batteries offer a more sustainable energy storage alternative to lithium while maintaining many of lithium's important characteristics. The solid electrolyte interphase (SEI) forms on the surface of the anode in both sodium and lithium-ion batteries. The SEI effects battery performance, particularly in sodium batteries, and understanding how it forms is critical for developing sodium ion batteries. Chapter I of this dissertation motivates sodium ion batteries, outlines the important differences between sodium and lithium, introduces the SEI, and establishes how the SEI is studied, ultimately placing this work in context with the field. As the SEI is derived from the electrolyte and is affected by electrolyte additives, the small molecule electrolyte additive fluoroethylene carbonate (FEC) is introduced as it is investigated throughout the dissertation. Chapter II explains how X-ray photoelectron spectroscopy can be used to study the SEI, providing examples of important protocols and pitfalls. Chapter III examines SEI formation by correlating electrochemistry from differential capacity with X-ray photoelectron spectroscopy (XPS). It is revealed that SEI species appear as a result of applied chemistry when the small molecule additive FEC is present. Without FEC, the SEI is present without significant electrochemistry in the differential capacity. Chapter IV builds off the results in Chapter III, identifying the conditions of spontaneous SEI formation due to sodium metal reactivity with the electrolyte. The spontaneous formation of the SEI is mitigated by FEC, the role of which is understood to be pre-passivation of sodium metal to prevent further electrolyte decomposition. Chapter V summarizes the work in this dissertation and outlines different directions the work can take moving forward.