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High Temperature Electrochemistry V: Session II
Sponsored by: TMS Extraction and Processing Division, TMS: Hydrometallurgy and Electrometallurgy Committee
Program Organizers: Prabhat Tripathy, Batelle Energy Alliance (Idaho National Laboratory); Guy Fredrickson, Idaho National Laboratory

Monday 2:00 PM
March 20, 2023
Room: 28B
Location: SDCC

Session Chair: Hojong Kim, Pennsylvania State University

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2:00 PM Introductory Comments

2:05 PM  Invited
Relative Performance of Platinum, Iridium, and Ruthenium as Oxygen-Evolving Anodes during the Electrolytic Reduction of Uranium Oxide in Molten LiCl-Li2O: Steven Herrmann¹; Prabhat Tripathy¹; James King¹; Guoping Cao¹; Kevin Tolman¹; ¹Idaho National Laboratory
    The performance of platinum, iridium, and ruthenium as oxygen-evolving anodes during the electrolytic reduction of uranium oxide in molten salt was investigated. Separate experiments were conducted with platinum-iridium, iridium-ruthenium, and platinum-ruthenium anode pairs, each of which was coupled to a common cathode with independent power supply units. The cathode, a permeable steel basket loaded with uranium oxide particulate, was suspended in a pool of LiCl – 1 wt% Li2O at 650 °C. A pair of 3-mm diameter by 100-mm long anode rods were suspended in the salt pool adjacent to the cathode basket. The power supply units were operated concurrently in a controlled potential mode to effect uranium oxide reduction at the cathode and oxygen gas formation at the anodes. Anode and cathode potentials and currents were plotted for each run to compare anode performance. Post-run anodes were subjected to dimensional and microscopic analyses to assess their relative robustness.

2:45 PM  
Evaluating the Electrochemical Recovery of Gd Using a Reactive Liquid Bi Electrode: Stephanie Castro Baldivieso¹; Sanghyeok Im¹; Nathan Smith¹; Hojong Kim¹; ¹Pennsylvania State University
    Electrochemical transition of Gd³⁺ ions in LiCl-KCl-GdCl₃ electrolyte was investigated using an inert W electrode at 700–1048 K and a liquid Bi electrode at 873 K. The Gd³⁺/Gd(s) transition was studied using cyclic voltammetry to characterize the peak potentials, currents, and the diffusivity of Gd³⁺ ions in molten salts. In contrast, the Gd³⁺/Gd(in Bi) transition was investigated at various current densities (10–150 mA/cm²) to estimate the coulombic efficiency and current-dependent overpotentials, in complement with electrochemical impedance spectroscopy (EIS). High coulombic efficiency of Gd deposition (>99%) was achieved based on deposition-removal of Gd into/from the liquid Bi electrode and facile charge transfer and mass transport kinetics was evident from EIS measurements. These findings suggest efficient recovery of Gd using liquid Bi, leveraging their strong interactions (i.e., low activity of Gd in liquid Bi) by mitigating side reactions, e.g., dissolution of Gd metal in molten salts.

3:05 PM  
Cyclic Voltammetry for Real-time Oxide Ion Concentration Measurements of a Molten CaCl2: Forest Felling¹; Olivia Dale¹; Mario Gonzalez¹; Michael Simpson¹; ¹University of Utah
    Salt-soluble CaO is generated during direct oxide reduction (DOR) of metal oxides with Ca dissolved in CaCl2. Real-time measurement of the CaO concentration could be used to track the DOR process’s progress. It was previously reported that a cyclic voltammetry (CV) oxidation peak using a tungsten working electrode had been correlated with CaO up to 4.0 wt.% CaO. More recently, a sintered CaO pellet was slowly dissolved in CaCl2 up to 12 wt% to emulate the slow increase in CaO concentration during DOR. At CaO concentrations above 5.6 wt%, the oxidation peak could not be resolved. Instead of determining peak height, the CV current was integrated over the range of potentials at which the oxidation reaction occurred. Below about 7 wt%, a good correlation was found between CaO concentration and the integrated oxidation current. Above this concentration, the integrated current decreases with increasing time. This behavior is not currently understood.

3:25 PM  
Electrochemical Behavior of Bismuth in molten LiCl-KCl-CaCl2: Greg Chipman¹; Bryant Johnson¹; Devin Rappleye¹; ¹Brigham Young University
    Bismuth has been investigated as a potential liquid electrode for molten salt electrorefining, but its electrochemical behavior has received scant attention in eutectic LiCl-KCl melts and no studies were found in the ternary LiCl-KCl-CaCl2 melts. LiCl-KCl-CaCl2 melts offer some advantages over eutectic LiCl-KCl, such as lower melting point and higher oxide solubility. To better understand bismuth’s electrochemical parameters, electrochemical techniques such as cyclic voltammetry, square wave voltammetry, and electrochemical impedance spectroscopy will be used to measure electrochemical parameters, such as diffusivity, exchange current density, standard reduction potential. While the effect of deposition has been well characterized for cyclic and square wave voltammetry, electrochemical impedance spectroscopy has largely been used in soluble-soluble systems. This study aims to see if electrochemical impedance spectroscopy can be used in systems with deposition to measure any of the above parameters while also identifying possible differences or challenges in calculating parameters.

3:45 PM Break

4:05 PM  
Electrochemical Properties of Ca-Sb Metal Battery with a Molten Chloride Electrolyte: Peyman Asghari-Rad¹; Sanghyeok Im¹; Kelly Elizabeth Varnell¹; Hojong Kim¹; ¹Pennsylvania State University
    The electrochemical performance of the Ca||Sb metal battery was investigated in a calcium-chloride based molten salt electrolyte at 450–550 ºC to determine the cell voltage, round-trip current and voltage efficiencies, as well as discharge capacity. For this study, a three-electrode cell was developed using a binary Ca-Bi alloy (35 mol% Ca) as the reference electrode for reliable electrochemical measurements, leveraging the stability of two-phase behavior with solid Ca₁₁Bi₁₀ and liquid Bi. The cell voltage of the positive electrode (Sb) was determined at various current densities of 50–500 mA cm^-2 to verify facile charge transfer and rapid mass transport near the electrode-electrolyte interface in complement with electrochemical impedance spectroscopy measurements. The measured electrochemical properties were corroborated by the post-mortem characterization of Sb electrodes at various states of discharge using scanning electron microscopy, powder X-ray diffraction, and inductively-coupled plasma mass spectrometry.

4:25 PM  
Numerical Modelling and Phase Field Modelling of Silicon Electrodeposition for Solar Cells at High Temperatures using Molten Salts: Aditya Moudgal¹; Tyler Melo¹; Alexander Alonzo¹; Andrew Charlebois¹; Evan Costa¹; Peter Catalino¹; Adam Powell¹; Yu Zhong¹; Uday Pal²; ¹Worcester Polytechnic Institute; ²Boston University
    Solid oxide membrane (SOM) molten salt electrolysis is a promising process in primary metals production. It is seen as a one step, environmentally clean, direct reduction process. This method has been demonstrated to produce pure magnesium and silicon using liquid cathodes. The scientific challenge that remains are non-uniform and non-planar growth of the silicon deposit on a suitable solid cathode. This presentation provides a numerical model and phase field model to understand deposition characteristics. A macroscopic finite element model considering conservation equations and solving for anodic current distribution, magnetohydrodynamic effects, and heat transfer is described. A phase field model solving the Cahn-Hilliard equation to understand interface stability is also shown. Experimentally, design and development of high-power switch to perform pulsed electrolysis will be presented. A cradle to gate life cycle analysis quantifying material inputs related to the mass balances in the electrolyte will also be presented.

4:45 PM  
Evaluating the Effects of Mixed Cation Molten Salt Electrolytes within the Li-Sb-Sn Liquid Metal Battery System: Kelly Varnell¹; Sanghyeok Im¹; Peyman Asghari-Rad¹; Hojong Kim¹; ¹Pennsylvania State University
    The coupling of renewable energy technologies (e.g., wind, solar, and nuclear) with large-scale stationary energy storage technologies such as liquid metal batteries (LMBs) has the potential to stabilize an electrical grid less reliant on carbon-based technologies. However, the energy produced from such systems must be cost competitive with current carbon-based energy. The Li(l)|LiF-LiCl-LiBr|Sb-Sn(l) LMB system may be utilized as a high-performance option for such applications by employing an antimony-tin (Sb-Sn) fusible alloy to lower the necessary operating temperature. However, lithium salts are significantly more expensive than other alkali or alkaline earth metal salts (e.g., KCl, SrCl₂) making production less economically viable. Techniques such as coulometric titration at various current densities and electrochemical impedance spectroscopy are employed to observe changes in coulombic efficiency, current-overpotential relationships, and theoretical capacity as well as the effects of cation co-deposition as mixed cation molten salts are introduced to the Li-Sb-Sn system.

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