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Shen, Dai - Dissertation.pdf (3.62 MB)

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Investigation of Charge Transfer Kinetics in Non–Aqueous Electrolytes Using Voltammetric Techniques and Mathematical Modeling

Shen, Dai
http://orcid.org/0000-0003-2747-9771
http://rave.ohiolink.edu/etdc/view?acc_num=case1574762430962913

Abstract Details

2020, Doctor of Philosophy, Case Western Reserve University, Chemical Engineering.
Deep eutectic solvents (DES) are attracting attention for their potential use in energy storage applications such as redox flow battery. In such application, knowledge of the transport and electrochemical kinetics properties of DES is critically important. To date, attempts to measure the kinetics parameters of the Cu2++e <-> Cu1+ reaction in ethaline DES have yielded unreliable kinetic results. In this work, detailed recommendations are developed and verified for avoiding pitfalls in kinetics analysis of highly resistive DES electrolytes. Incorporating these recommendations, a comprehensive study of the kinetics and transport properties of the aforementioned redox reaction was carried out. Using steady–state and transient polarization measurements on RDE and microelectrodes combined with diffusion–reaction modeling, we demonstrate that the Cu2+/Cu1+ transition exhibits a charge transfer coefficient in the range of 0.49 – 0.54 and a reaction rate constant in the range (1.78 – 1.95) × 10-4 cm/s. The result indicates that the Cu2+/Cu1+ redox reaction in chloride–containing DES media suffers from sluggish charge transfer kinetics. The effects of DES composition and temperature on kinetics provided insights into the origins of the sluggish kinetics. Specifically, species complexation with Cl– which is present in excess in the chosen DES systems is shown to be the reason for slow charge transfer. For potential application in rare-earth metal recovery from spent waste, the electrodeposition of neodymium (Nd) metal from NdCl3–containing molten LiCl–KCl eutectic melts was investigated using voltammetry and diffusion–reaction modeling. Voltammetry studies confirmed that Nd electrodeposition is a two–step reduction process involving first a reversible one–electron transfer reduction of Nd3+ to Nd2+, followed by quasi–reversible reduction of Nd2+ to Nd metal. In the electrode potential range where Nd3+ is reduced to Nd2+, the peak current density measured in a voltammetry scan showed good agreement with the classical Randles–Sevcik model for reversible soluble–soluble redox transitions. However, in the potential range where Nd2+ is reduced to Nd metal, the experimentally measured peak currents in the voltammogram were substantially lower than those predicted by applying the Berzins–Delahay model for reversible soluble–insoluble redox transitions. This discrepancy was addressed using transient diffusion–reaction modeling, which accounted for the multivalent (Nd2+ and Nd3+) species transport and their multi–step reduction to Nd metal. The diffusion–reaction model accurately predicts the voltammetric response during Nd electrodeposition in a broad range of operating conditions (species concentrations and voltammetry scan rates), while providing access to the kinetic parameters governing Nd electrodeposition from halide melts.
Rohan Akolkar, Ph.D. (Committee Chair)
Robert Savinell, Ph.D. (Committee Member)
Uziel Laudau, Ph.D. (Committee Member)
Mark De Guire, Ph.D. (Committee Member)
136 p.
Chemical Engineering
deep eutectic solvents; high temperature molten salts; ethaline; electrochemical kinetics; electrochemical engineering; electrochemical redox reactions; complexation; diffusion-reaction modeling; molten salt electrolysis; neodymium;

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Citations

  • Shen, D. (2020). Investigation of Charge Transfer Kinetics in Non–Aqueous Electrolytes Using Voltammetric Techniques and Mathematical Modeling [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1574762430962913

    APA Style (7th edition)

  • Shen, Dai. Investigation of Charge Transfer Kinetics in Non–Aqueous Electrolytes Using Voltammetric Techniques and Mathematical Modeling. 2020. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1574762430962913.

    MLA Style (8th edition)

  • Shen, Dai. "Investigation of Charge Transfer Kinetics in Non–Aqueous Electrolytes Using Voltammetric Techniques and Mathematical Modeling." Doctoral dissertation, Case Western Reserve University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1574762430962913

    Chicago Manual of Style (17th edition)

case1574762430962913
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© 2020, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.