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Kasun Dadallagei Thesis10.03 MB
Embargoed Access, Embargo ends: 01/26/2026
Dissertation
Exploring heterogeneous rate constants, lanthanide separation, catalysis, and baseline correction with graphical methods
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Autumn 2023
DOI: 10.25820/etd.006844
Abstract
Electrochemical experimentation plays a pivotal role in the analysis of catalysis and provides valuable insights into rate constants and electrochemical processes. This study aims to enhance the understanding of electrochemical data analysis by employing both classical and graphical methods. By delving into the intricacies of electrochemical analysis, the study seeks to refine the approach to experimentation, ultimately advancing knowledge and capabilities in the field of electrochemistry.
Electrochemical impedance spectroscopy (EIS) analysis of iron (III) perchlorate: Electrochemical impedance spectroscopy (EIS) is employed to investigate the effects of magnetic fields on iron(III) perchlorate electrochemical systems. Previous studies have shown that the introduction of magnetic micro particles into ion exchange polymers on electrode surfaces can significantly enhance the catalytic activity of metal tris bipyridine complexes. This enhancement is attributed to improved kinetics in both heterogeneous exchange rate and self exchange rate processes. In this research, the focus is on quantifying the impact of magnetic fields on heterogeneous rates by comparing magnetically modified electrodes with the demagnetized magnetic counterparts using EIS analysis.
Lanthanide separation an application of the optimized waveforms: The increasing utilization of lanthanides in various applications, including catalysis and electronics, has led to a growing accumulation of lanthanide waste materials. Developing an efficient and precise method for lanthanide separation is essential to address this issue. Electrochemical separation methods offer advantages such as precision, lower maintenance requirements, and simplified production line setup compared to alternative approaches. However, conventional thermodynamic limitations pose challenges to achieving a 99% separation of certain lanthanides. This work explores the application of optimized waveforms, as developed by Dr. Daniel Parr IV, to overcome the thermodynamic limitations associated with lanthanide separation. By leveraging kinetic parameters, these optimized waveforms aim to achieve separations in cases where conventional thermodynamics fall short. Experimental results obtained through the application of these waveform approximations suggest the effectiveness in lanthanide separation, offering a promising solution to address the increasing accumulation of lanthanide waste materials.
Lanthanide mixtures in oxygen reduction reaction: This thesis chapter delves into the exploration of lanthanide mixtures as potential catalysts for the oxygen reduction reaction (ORR), a key process in fuel cells and other electrochemical applications. The primary objective is to identify cost effective alternatives to platinum based catalysts, which, despite the platinum based catalysts efficiency, platinum based catalysts are economically prohibitive as the end goal of the study is to create a cost effective ethanol fuel cell. This research focuses on utilizing lanthanide based catalysts, specifically combinations of ytterbium and lanthanum, to enhance ORR. The experimental approach involves electrochemical testing using glassy carbon electrodes modified with a lanthanide mixture. Various electrochemical techniques, including chronocoulometry (CC) and linear sweep voltammetry (LSV), are employed to assess the catalytic activity and efficiency of these lanthanide mixtures. The results indicate notable improvements in current density and inconsistent improvements of onset potentials when lanthanides are used, suggesting lanthanides mixtures potential as effective ORR catalysts. The findings present an initial step towards more sustainable and cost effective solutions for ORR catalysis, with lanthanide mixtures offering a promising avenue for future research in energy conversion technologies.
Development of polymer electrodes for 3D printing and molding: The field of electrochemistry continually seeks cost effective electrode materials tailored to diverse applications requiring versatile shapes and forms. Polymer electrodes emerge as promising solutions to address these varied requirements, with a primary focus on two polymers, ABS (acrylonitrile butadiene styrene) and PLA (polylactic acid). These polymers offer affordability and versatility and can be readily modified with carbon or graphene to provide conductivity. This research presents preliminary research on the behavior and potential applications of ABS and PLA polymer electrodes. The study explores suitability for use in electrochemical systems, with a particular emphasis on adaptability to 3D printing and molding processes, providing insights into practicality and feasibility in various electrochemical applications.
New perspectives from classical transition state theory: The hydrogen evolution reaction on metal electrodes: A fresh perspective on hydrogen evolution reactions (HER) emerges when classical transition state theory is applied to this field. Trasatti's groundbreaking work revealed that the exchange current density, denoted as j_{0}, exhibits an exponential increase in relation to the metal electrode work function, represented as \Phi. This observation is rooted in the description of the elementary electron transfer step: M(e)+H_{ads}^{+}\rightleftarrows M(0)+H_{ads}^{\bullet} which highlights the crucial role of the metal in the transition state. Leads to the formulation of rate equations that explicitly incorporate the material specific physiochemical property \Phi. One striking finding is the linear correlation between the logarithm of j_{0} and \Phi, a quantifiable relationship that sheds light on the influence of \Phi on j_{0}. Specifically, \Phi elevates j_{0} by reducing the activation energy required for electrocatalysis. These rate expressions, enriched with material specific physiochemical properties, open up exciting opportunities for a priori electrocatalyst design and offer profound insights into the intricate realm of electron transfer kinetics. By revisiting established HER data through the lens of classical transition state theory, this research presents novel perspectives that enrich our understanding of this critical electrochemical process.
Graphical method to correct for baselines distorted by subsequent electrochemical processes using the cyclic voltammetric origami method: In a typical cyclic voltammetric (CV) experiment aimed at determining peak currents, it is crucial to establish a baseline. Traditionally, this baseline is derived from the forward direction of the potential sweep. However, scenarios may arise where determining the baseline becomes challenging or even impossible. In cases where voltammograms exhibit significant symmetry, a clever approach can be employed: flipping the voltammograms to deduce the forward baseline from the reverse baseline. This operation relies on fundamental mathematical transformations. To apply this method successfully it is essential that the peak symmetry is symmetric, which is typically the case for reversible to quasireversible electron transfer processes. For highly irreversible transfer processes, the effectiveness of this correction method diminishes. This correction technique is demonstrated through digital simulations for both single (E) and sequential (EE) electron transfer reactions. The practical utility of using flipped axes as a valuable tool becomes evident in situations where establishing the baseline poses challenges for example, where the voltammogram is recorded on approach to the solvent window.
Details
- Title: Subtitle
- Exploring heterogeneous rate constants, lanthanide separation, catalysis, and baseline correction with graphical methods
- Creators
- Kasun Saweendra Rathnatunga Dadallagei
- Contributors
- Johna Leddy (Advisor)Mark Arnold (Committee Member)Edward Gillan (Committee Member)Gary Small (Committee Member)Syed Mubeen (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Chemistry
- Date degree season
- Autumn 2023
- Publisher
- University of Iowa
- DOI
- 10.25820/etd.006844
- Number of pages
- xxviii, 159 pages
- Copyright
- Copyright 2023 Kasun S. R. Dadallagei
- Grant note
- The support of the National Science Foundation (CHE-0809745; CHE-1309366) and Army Research Office (W911NF-19-1-0208) and Johna Leddy’s time as a Fellow at the University of Iowa, Obermann Center for Advanced Study are gratefully acknowledged.
- Language
- English
- Date submitted
- 12/04/2023
- Description illustrations
- illustrations, tables, graphs
- Description bibliographic
- Includes bibliographical references (pages 155-159).
- Public Abstract (ETD)
- Electrochemical research plays a crucial role in advancing our understanding of catalysis and various electrochemical processes. These studies provide valuable insights into the rates of chemical reactions and how different factors affect rates. The primary objective of this research is to refine and enhance our methods for electrochemical analysis, ultimately leading to a deeper understanding of these processes and to promote efficiency. Recent work has shown that the magnetic properties of electrodes, catalysts, and chemical species impact rates of reaction. Introduction of magnetic microparticles to electrode surfaces can increase rates to improve efficiency and reduce costs. Magnetoelectrocatalysis is achieved when magnetic fields are introduced and controlled to increase the rate. To build better catalysts, good measurements must be made to develop an understanding of the process. The reaction rate of iron ions increases in the presence of a magnetic gradient observed during the experiments. To characterize this magnetic effect, rates of iron reactions are measured by an AC technique (electrochemical impedance spectroscopy) to verify the magnetic impacts on rate and to quantify the effect. Lanthanides are rare earth elements important in advanced technologies for communications, displays, sensors, and electrochemical energy systems such as batteries. Lanthanides are identified as critical materials by the US government. Although not rare, separation of lanthanides from mixed materials and separation of one lanthanide from another is challenging when separations are based on equilibrium, thermodynamic methods. A new separation method based on time dependent kinetics is given a first proof of concept for separation of one lanthanide from another. In fuel cells and some battery technologies, oxygen in the air provides the oxidant for the reaction. But, kinetics for the oxygen reduction reaction (ORR) is slow. Rates are increased at costly catalysts, such as platinum. Lanthanides are less expensive and more abundant. Lanthanides and selected mixtures of lanthanides are identified as electrocatalysts for ORR. Measurements determine rates and lay the foundation for understanding why lanthanides are good ORR catalysts. As a cost effective alternative, lanthanides and their mixtures serve as effective ORR catalysts, contributing to the goal of more affordable fuel cells. Furthermore, the field of electrochemistry continuously seeks cost effective electrode materials that can be tailored to various applications, especially those that require versatile shapes and forms. The ability to produce low resistance electrodes by 3D printing provides rapid prototyping of electrochemical devices. Two common conductive polymers, PLA and ABS are evaluated and modified to design better low resistance electrodes. The polymers can be modified with additives to enhance conductivity and to a add catalysts. Hydrogen is an excellent fuel for combustion and fuel cells. But currently, H2 is produced by steam reforming methane, an energy and environmentally taxing process. if catalysts were available, hydrogen would be more easily produced by electrolysis in the hydrogen evolution reaction, HER. Understanding of materials properties that lead to design of better HER catalysts would enable electrolysis. Fundamental properties of work function and hardness are identified as important material specific parameters for the design of good electrocatalysts. These insights provide the basis for a priori catalyst design. Finally, to make good measurements, experimental tools are needed to make the measurements. A protocol is developed to extract experimental parameters from electrochemical voltammetric data when the data are incomplete. The method relies on flipping the experimental data about the current and potential axes. The method works for one and two electron processes and relies on the symmetry of the data. This dissertation provides a means to improve electrochemical systems and measurements through combined experimental and modeling studies of reactions and catalysts.
- Academic Unit
- Chemistry
- Record Identifier
- 9984546848402771
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