Matching Items (8)
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- All Subjects: electrochemistry
- All Subjects: Electrolytes
- Creators: Friesen, Cody
- Creators: Buttry, Daniel A.
Description
Dealloying, the selective dissolution of an elemental component from an alloy, is an important corrosion mechanism and a technological significant means to fabricate nanoporous structures for a variety of applications. In noble metal alloys, dealloying proceeds above a composition dependent critical potential, and bi-continuous structure evolves "simultaneously" as a result of the interplay between percolation dissolution and surface diffusion. In contrast, dealloying in alloys that show considerable solid-state mass transport at ambient temperature is largely unexplored despite its relevance to nanoparticle catalysts and Li-ion anodes. In my dissertation, I discuss the behaviors of two alloy systems in order to elucidate the role of bulk lattice diffusion in dealloying. First, Mg-Cd alloys are chosen to show that when the dealloying is controlled by bulk diffusion, a new type of porosity - negative void dendrites will form, and the process mirrors electrodeposition. Then, Li-Sn alloys are studied with respect to the composition, particle size and dealloying rate effects on the morphology evolution. Under the right condition, dealloying of Li-Sn supported by percolation dissolution results in the same bi-continuous structure as nanoporous noble metals; whereas lattice diffusion through the otherwise "passivated" surface allows for dealloying with no porosity evolution. The interactions between bulk diffusion, surface diffusion and dissolution are revealed by chronopotentiometry and linear sweep voltammetry technics. The better understanding of dealloying from these experiments enables me to construct a brief review summarizing the electrochemistry and morphology aspects of dealloying as well as offering interpretations to new observations such as critical size effect and encased voids in nanoporous gold. At the end of the dissertation, I will describe a preliminary attempt to generalize the morphology evolution "rules of dealloying" to all solid-to-solid interfacial controlled phase transition process, demonstrating that bi-continuous morphologies can evolve regardless of the nature of parent phase.
ContributorsChen, Qing (Author) / Sieradzki, Karl (Thesis advisor) / Friesen, Cody (Committee member) / Buttry, Daniel (Committee member) / Chan, Candace (Committee member) / Arizona State University (Publisher)
Created2013
Description
The electrode-electrolyte interface in electrochemical environments involves the understanding of complex processes relevant for all electrochemical applications. Some of these processes include electronic structure, charge storage, charge transfer, solvent dynamics and structure and surface adsorption. In order to engineer electrochemical systems, no matter the function, requires fundamental intuition of all the processes at the interface. The following work presents different systems in which the electrode-electrolyte interface is highly important. The first is a charge storage electrode utilizing percolation theory to develop an electrode architecture producing high capacities. This is followed by Zn deposition in an ionic liquid in which the deposition morphology is highly dependant on the charge transfer and surface adsorption at the interface. Electrode Architecture: A three-dimensional manganese oxide supercapacitor electrode architecture is synthesized by leveraging percolation theory to develop a hierarchically designed tri-continuous percolated network. The three percolated phases include a faradaically-active material, electrically conductive material and pore-former templated void space. The micropores create pathways for ionic conductivity, while the nanoscale electrically conducting phase provides both bulk conductivity and local electron transfer with the electrochemically active phase. Zn Electrodeposition: Zn redox in air and water stable N-ethyl-N-methylmorpholinium bis(trifluoromethanesulfonyl)imide, [C2nmm][NTf2] is presented. Under various conditions, characterization of overpotential, kinetics and diffusion of Zn species and morphological evolution as a function of overpotential and Zn concentration are analyzed. The surface stress evolution during Zn deposition is examined where grain size and texturing play significant rolls in compressive stress generation. Morphological repeatability in the ILs led to a novel study of purity in ionic liquids where it is found that surface adsorption of residual amine and chloride from the organic synthesis affect growth characteristics. The drivers of this work are to understand the processes occurring at the electrode-electrolyte interface and with that knowledge, engineer systems yielding optimal performance. With this in mind, the design of a bulk supercapacitor electrode architecture with excellent composite specific capacitances, as well as develop conditions producing ideal Zn deposition morphologies was completed.
ContributorsEngstrom, Erika (Author) / Friesen, Cody (Thesis advisor) / Buttry, Daniel (Committee member) / Sieradzki, Karl (Committee member) / Arizona State University (Publisher)
Created2011
Description
This work investigates in-situ stress evolution of interfacial and bulk processes in electrochemical systems, and is divided into two projects. The first project examines the electrocapillarity of clean and CO-covered electrodes. It also investigates surface stress evolution during electro-oxidation of CO at Pt{111}, Ru/Pt{111} and Ru{0001} electrodes. The second project explores the evolution of bulk stress that occurs during intercalation (extraction) of lithium (Li) and formation of a solid electrolyte interphase during electrochemical reduction (oxidation) of Li at graphitic electrodes. Electrocapillarity measurements have shown that hydrogen and hydroxide adsorption are compressive on Pt{111}, Ru/Pt{111}, and Ru{0001}. The adsorption-induced surface stresses correlate strongly with adsorption charge. Electrocatalytic oxidation of CO on Pt{111} and Ru/Pt{111} gives a tensile surface stress. A numerical method was developed to separate both current and stress into background and active components. Applying this model to the CO oxidation signal on Ru{0001} gives a tensile surface stress and elucidates the rate limiting steps on all three electrodes. The enhanced catalysis of Ru/Pt{111} is confirmed to be bi-functional in nature: Ru provides adsorbed hydroxide to Pt allowing for rapid CO oxidation. The majority of Li-ion batteries have anodes consisting of graphite particles with polyvinylidene fluoride (PVDF) as binder. Intercalation of Li into graphite occurs in stages and produces anisotropic strains. As batteries have a fixed size and shape these strains are converted into mechanical stresses. Conventionally staging phenomena has been observed with X-ray diffraction and collaborated electrochemically with the potential. Work herein shows that staging is also clearly observed in stress. The Li staging potentials as measured by differential chronopotentiometry and stress are nearly identical. Relative peak heights of Li staging, as measured by these two techniques, are similar during reduction, but differ during oxidation due to non-linear stress relaxation phenomena. This stress relaxation appears to be due to homogenization of Li within graphite particles rather than viscous flow of the binder. The first Li reduction wave occurs simultaneously with formation of a passivating layer known as the solid electrolyte interphase (SEI). Preliminary experiments have shown the stress of SEI formation to be tensile (~+1.5 MPa).
ContributorsMickelson, Lawrence (Author) / Friesen, Cody (Thesis advisor) / Sieradzki, Karl (Committee member) / Buttry, Daniel (Committee member) / Venables, John (Committee member) / Arizona State University (Publisher)
Created2011
Description
The electrochemical behavior of nanoscale solids has become an important topic to applications, such as catalysis, sensing, and nano–electronic devices. The electrochemical behavior of elemental metal and alloy particles was studied in this work both theoretically and experimentally. A systematic thermodynamic derivation for the size–dependent Pourbaix Diagram for elemental metal particles is presented. The stability of Pt particles was studied by in situ electrochemical scanning tunneling microscopy (ECSTM). It is shown that small Pt particles dissolve at a lower potential than the corresponding bulk material. For the alloy particles, two size ranges of AuAg particles, ∼4 nm and ∼45 nm in diameter, were synthesized by co–reduction of the salts of Au and Ag from an aqueous phase. The alloy particles were dealloyed at a series of potential by chronoamperometry in acid, and the resulting morphology and composition were characterized by electron microscopy, energy dispersive X–ray spectroscopy (EDX). In the case of the smaller particles, only surface dealloying occurred yielding a core–shell structure. A porous structure was observed for the larger particles when the potential was larger than a critical value that was within 50 mV of the thermodynamic prediction.
ContributorsLi, Xiaoqian (Author) / Sieradzki, Karl (Thesis advisor) / Crozier, Peter (Committee member) / Buttry, Daniel (Committee member) / Friesen, Cody (Committee member) / Arizona State University (Publisher)
Created2012
Description
Structural details of phosphonic acid functionalized nanomaterials and protic ionic liquids (PILs) were characterized using nuclear magnetic resonance (NMR) spectroscopy. It is well known that ligands play a critical role in the synthesis and properties of nanomaterials. Therefore, elucidating the details of ligand-surface and ligand-ligand interactions is crucial to understanding nanomaterial systems more completely.
In an effort to further the understanding of ligand-surface interactions, a combination of multi-nuclear (1H, 29Si, 31P) and multi-dimensional solid-state NMR techniques were utilized to characterize the phosphonic acid functionalization of fumed silica nanoparticles using methyl phosphonic acid (MPA) and phenyl phosphonic acid (PPA). Quantitative 31P MAS solid-state NMR measurements indicate that ligands favor a monodentate binding mode. Furthermore, 1H-1H single quantum-double quantum (SQ-DQ) back-to-back (BABA) 2D NMR spectra of silica functionalized with MPA and PPA indicate that the MPA and PPA are within 4.2±0.2 Å on the surface of the nanomaterial.
The ligand capping of phosphonic acid (PA) functionalized CdSe/ZnS core-shell quantum dots (QDs) was investigated with a combination of ligand exchange, solution and solid-state 31P NMR spectroscopy. In order to quantify the ligand populations on the surface of the QDs, ligand exchange facilitated by PPA resulted in the displacement of the PAs, and allowed for quantification of the free ligands using 31P liquid state NMR.
In addition to characterizing nanomaterials, the ionicity and transport properties of a series of diethylmethylamine (DEMA) based protic ionic liquids (PILs) were characterized, principally utilizing NMR. Gas phase proton affinity was shown to be a better predictor for the extent of proton transfer, and in turn the ionicity of the PIL, than using ∆pKa. Furthermore, pulsed field gradient (PFG) NMR was used to determine that the exchangeable proton diffuses with the cation or the anion based on the strength of the acid used to generate the PILs.
In an effort to further the understanding of ligand-surface interactions, a combination of multi-nuclear (1H, 29Si, 31P) and multi-dimensional solid-state NMR techniques were utilized to characterize the phosphonic acid functionalization of fumed silica nanoparticles using methyl phosphonic acid (MPA) and phenyl phosphonic acid (PPA). Quantitative 31P MAS solid-state NMR measurements indicate that ligands favor a monodentate binding mode. Furthermore, 1H-1H single quantum-double quantum (SQ-DQ) back-to-back (BABA) 2D NMR spectra of silica functionalized with MPA and PPA indicate that the MPA and PPA are within 4.2±0.2 Å on the surface of the nanomaterial.
The ligand capping of phosphonic acid (PA) functionalized CdSe/ZnS core-shell quantum dots (QDs) was investigated with a combination of ligand exchange, solution and solid-state 31P NMR spectroscopy. In order to quantify the ligand populations on the surface of the QDs, ligand exchange facilitated by PPA resulted in the displacement of the PAs, and allowed for quantification of the free ligands using 31P liquid state NMR.
In addition to characterizing nanomaterials, the ionicity and transport properties of a series of diethylmethylamine (DEMA) based protic ionic liquids (PILs) were characterized, principally utilizing NMR. Gas phase proton affinity was shown to be a better predictor for the extent of proton transfer, and in turn the ionicity of the PIL, than using ∆pKa. Furthermore, pulsed field gradient (PFG) NMR was used to determine that the exchangeable proton diffuses with the cation or the anion based on the strength of the acid used to generate the PILs.
ContributorsDavidowski, Stephen (Author) / Yarger, Jeffery L. (Thesis advisor) / Holland, Gregory P (Thesis advisor) / Angell, Charles A. (Committee member) / Buttry, Daniel A. (Committee member) / Arizona State University (Publisher)
Created2015
Description
Palladium metal in its various forms has been heavily studied for many catalytic, hydrogen storage and sensing applications and as an electrocatalyst in fuel cells. A short review on various applications of palladium and the mechanism of Pd nanoparticles synthesis will be discussed in chapter 1. Size dependent properties of various metal nanoparticles and a thermodynamic theory proposed by Plieth to predict size dependent redox properties of metal nanoparticles will also be discussed in chapter 1.
To evaluate size dependent stability of metal nanoparticles using electrochemical techniques in aqueous media, a synthetic route was designed to produce water soluble Pd nanoparticles. Also, a purification technique was developed to obtain monodisperse metal nanoparticles to study size dependent stability using electrochemical methods. Chapter 2 will describe in detail the synthesis, characterization and size dependent anodic dissolution studies of water soluble palladium nanoparticles.
The cost associated with using expensive metal catalysts can further decreased by using the underpotential deposition (UPD) technique, in which one metal is electrodeposited in monolayer or submonolayer form on a different metal substrate. Electrochemically, this process can be detected by the presence of a deposition peak positive to the bulk deposition potential in a cyclic voltammetry (CV) experiment. The difference between the bulk deposition potential and underpotential deposition peak (i.e. the UPD shift), which is a measure of the energetics of the monolayer deposition step, depends on the work function difference between the metal pairs. Chapter 3 will explore how metal nanoparticles of different sizes will change the energetics of the UPD phenomenon, using the UPD of Cu on palladium nanoparticles as an example. It will be shown that the UPD shift depends on the size of the nanoparticle substrate in a way that is understandable based on the Plieth model.
High electrocatalytic activity of palladium towards ethanol oxidation in an alkaline medium makes it an ideal candidate for the anode electrocatalyst in direct ethanol based fuel cells (DEFCs). Chapter 4 will explore the poisoning of the catalytic activity of palladium in the presence of halide impurities, often used in synthesis of palladium nanoparticles as precursors or shape directing agents.
To evaluate size dependent stability of metal nanoparticles using electrochemical techniques in aqueous media, a synthetic route was designed to produce water soluble Pd nanoparticles. Also, a purification technique was developed to obtain monodisperse metal nanoparticles to study size dependent stability using electrochemical methods. Chapter 2 will describe in detail the synthesis, characterization and size dependent anodic dissolution studies of water soluble palladium nanoparticles.
The cost associated with using expensive metal catalysts can further decreased by using the underpotential deposition (UPD) technique, in which one metal is electrodeposited in monolayer or submonolayer form on a different metal substrate. Electrochemically, this process can be detected by the presence of a deposition peak positive to the bulk deposition potential in a cyclic voltammetry (CV) experiment. The difference between the bulk deposition potential and underpotential deposition peak (i.e. the UPD shift), which is a measure of the energetics of the monolayer deposition step, depends on the work function difference between the metal pairs. Chapter 3 will explore how metal nanoparticles of different sizes will change the energetics of the UPD phenomenon, using the UPD of Cu on palladium nanoparticles as an example. It will be shown that the UPD shift depends on the size of the nanoparticle substrate in a way that is understandable based on the Plieth model.
High electrocatalytic activity of palladium towards ethanol oxidation in an alkaline medium makes it an ideal candidate for the anode electrocatalyst in direct ethanol based fuel cells (DEFCs). Chapter 4 will explore the poisoning of the catalytic activity of palladium in the presence of halide impurities, often used in synthesis of palladium nanoparticles as precursors or shape directing agents.
ContributorsKumar, Ashok (Author) / Buttry, Daniel A. (Thesis advisor) / Gould, Ian R. (Committee member) / Ghirlanda, Giovanna (Committee member) / Arizona State University (Publisher)
Created2016
Description
This investigation is divided into two portions linked together by the momentous reaches of electrochemistry science, principles influencing everyday phenomena as well as innovative research in the field of energy transformation. The first portion explores the strategies for flue gas carbon dioxide capture and release using electrochemical means. The main focus is in the role thiolates play as reversible strong nucleophiles with the ability to capture CO2 and form thiocarbonates. Carbon dioxide in this form is transported and separated from thiocarbonate through electrochemical oxidation to complete the release portion of this catch-and-release approach. Two testing design systems play a fundamental role in achieving an efficient CO2 catch and release process and were purposely build and adapted for this work. A maximum faradaic efficiency of seventeen percent was attained in the first membrane tests whose analysis is presented in this work. An efficiency close to thirty percent was attained with the membrane cell in recent experiments but have not been included in this manuscript.
The second portion of this manuscript studies bulk stress evolution resulting from insertion/extraction of lithium in/from a lithium manganese oxide spinel cathode structure. A cantilever-based testing system uses a sophisticated, high resolution capacitive technique capable of measuring beam deflections of the cathode in the subnanometer scale. Tensile stresses of up to 1.2 MPa are reported during delithiation along with compressive stresses of 1.0 MPa during lithiation. An analysis of irreversible charge loss is attributed to surface passivation phenomena with its associated stresses of formation following patterns of tensile stress evolution.
The second portion of this manuscript studies bulk stress evolution resulting from insertion/extraction of lithium in/from a lithium manganese oxide spinel cathode structure. A cantilever-based testing system uses a sophisticated, high resolution capacitive technique capable of measuring beam deflections of the cathode in the subnanometer scale. Tensile stresses of up to 1.2 MPa are reported during delithiation along with compressive stresses of 1.0 MPa during lithiation. An analysis of irreversible charge loss is attributed to surface passivation phenomena with its associated stresses of formation following patterns of tensile stress evolution.
ContributorsCastro De la Torre, Helme Atic (Author) / Friesen, Cody (Thesis advisor) / Buttry, Daniel (Committee member) / Bautista Martinez, Jose A (Committee member) / Arizona State University (Publisher)
Created2016
Description
Over the last decade copper electrodeposition has become the dominant process by which microelectronic interconnects are made. Replacing ultra-high vacuum evaporative film growth, the technology known as the Cu damascene process has been widely implemented in the microelectronics industry since the early 2000s. The transition from vacuum film growth to electrodeposition was enabled by solution chemistries that provide "bottom-up" or superfilling capability of vias and trenches. While the process has been and is used widely, the actual mechanisms responsible for superfilling remain relatively unknown. This dissertation presents and discusses the background and results of experimental investigations that have been done using in situ electrochemical surface stress monitoring techniques to study the evolution of stress on Cu{111} thin film electrodes. Because of its extreme sensitivity to the structure on both the electrode and solution sides of the interface, surface stress monitoring as analytical technique is well suited for the study of electrodeposition. These ultra-high resolution stress measurements reveal the dynamic response of copper electrodes to a number of electrochemical and chemical experimental variables. In the case of constant current pulsed deposition and stripping, the surface stress evolution depends not only on the magnitude of the current pulse, but also shows a marked response to plating bath composition. The plating bath chemistries used in this work include (1) additive free, (2) deposition suppressing solutions that include polyethylene glycol (PEG) and sodium chloride (NaCl) as well as (3) full additive solution combinations which contain PEG, NaCl, and a one of two deposition accelerating species (bis-(sodiumsulfopropyl)disulfide (SPS) or mercaptopropane sulfonic acid (MPS)). The development of thin film stress is further investigated through a series of solution exchange experiments that correlate the magnitude of electrode exchange current density and the stress state of the film. Remarkably, stress changes as large as ~8.5 N/m are observed during solution exchanges at the open circuit potential. Overall, this research demonstrates that solution chemistry can have a large impact on thin film stress evolution, even for very small deposition thicknesses (e.g. <10 ML) or in the absence of net addition or removal of material from the electrode.
ContributorsHeaton, Thomas Stanley (Author) / Friesen, Cody (Thesis advisor) / Buttry, Daniel (Committee member) / Sieradzki, Karl (Committee member) / Arizona State University (Publisher)
Created2011