Molten Salt Electrolysis Research Articles

System identification and artificial intelligent (AI) modelling of the molten salt electrolysis process for prediction of the anode effect

NdFeB magnets are widely used in various applications including electric and hybrid vehicles, wind turbines, and computer hard drives. They contain approximately 31–32 wt% Rare Earth Elements (REEs), mainly neodymium (Nd) and praseodymium (Pr), and are produced by molten salt electrolysis using fluoride electrolytes. However, anode passivation or anode effect may occur, generating greenhouse gases if insufficient amounts of metal oxides are available in the system. Therefore, in this study, a dynamic model of the electrochemical process was developed to estimate the system variables and predict the anode effect using several system identification methods. The Transfer Function (TF) estimation, Auto-Regressive with Extra inputs (ARX), Hammerstein-Weiner (HW), and Artificial Neural Network (ANN) models were used, and their results were compared based on the occurrence of the anode effect. The best model achieved an average accuracy of 96% in predicting the process output.

EFFECT OF THE SUBSTRATE MATERIAL ON THE KINETICS OF SILICON ELECTROREDUCTION IN THE KCl–CsCl–K<sub>2</sub>SiF<sub>6</sub> MELT

Due to the possibility of controlling composition and morphology, one of the promising methods for obtaining silicon and its materials is the electrolysis of molten salts. However, this requires data on the influence of various factors on the kinetics of silicon electrodeposition. In this work, an effect of the cathode substrate material on the kinetics of electroreduction of silicon ions in a low-fluoride melt (wt %) 57KCl–43CsCl with the addition of 2.8 wt % K2SiF6 at a temperature of 730°C was studied by cyclic voltammetry and chronoamperometry. Interacting and indifferent materials for silicon were chosen as substrates: glassy carbon, silver, and nickel. On the glassy carbon electrode, the electroreduction of silicon ions proceeds in the potential region more negative than –0.05 V, on the silver electrode, more negative than 0.05 V, and on the nickel electrode, more negative than 0.40 V relative to the potential of the silicon quasi-reference electrode. For all the studied substrates, a cathode process is observed, which is not electrochemically reversible. In this case, according to chronoamperometry measurements, the stage of nucleation of a new phase at the cathode does not affect the kinetics of the process under study. Presumably, in the case of glassy carbon and silver, irreversibility can be caused by a delayed discharge, while silicon electrodeposition on a nickel electrode is accompanied by the formation of nickel silicides. From the voltammetric and chronoamperometric dependences, the diffusion coefficient of silicon ions to the glassy carbon electrode was estimated, the values of which were 1.5 · 10–5 and 1.2 · 10–5 cm2/s, respectively.

Oreate - Oxide Reduction by Electrochemical Amalgamation and Thermal Extraction

Establishing a capability for generating consistent, small-scale, and high-purity metals (i.e., transition metals, lanthanides and actinides) would have significant impact in many levels from fundamental science to national security related applications. Among the many procedures to purify transition and f-block metals (direct oxide reduction, electrolysis in molten salts, etc), there does not exist a U.S. process that can respond to the diverse needs of small- and large-scale science campaigns. Hence, there is widespread need to develop a capability that can supply a broad range of customers with “craft” metals of interest. The main goal is to consistently convert metal oxides to chemically pure metals in near quantitative yield.Traditional separation methods of actinides and lanthanides from aqueous media has been based on structure and bonding differences between these metals with various ligands. Although liquid-liquid extractions have proven to be quite efficient, they are expensive and require complex engineering. On the other hand, separation by pyro-chemistry based on the difference of their reductive extraction to metallic phase provides a good separation performance but requires the use of high temperatures, which adds technological difficulties to the process. An alternative method that has grown interest in the last few years is the utilization of the difference in the reduction potentials from ionic state to metallic state. However, this electrochemical approach has been believed difficult because of the highly negative reduction potentials of these metals (more negative than hydrogen evolution) and the challenging control of their electrolytic deposition onto solid cathodes.In this work we present a process comprising the oxide reduction by electrochemical amalgamation and thermal extraction (OREATE) that intends to be an optimized version of the traditional electrochemical amalgamation process in aqueous medium for trivalent f-elements. A mercury pool is used as cathode material to overcome most of the difficulties related to the use of solid cathodes: (i) Once reduced to the metallic state, the metal quickly dissolves into the liquid mercury to form amalgam, which ensures more stable surface condition of the cathode. (ii) Higher hydrogen over-voltage on mercury enables more effective reduction of the metals in a slightly acidic solution. (iii) Mercury's high vapor pressure allows an easy thermal extraction process to obtain a highly pure metal.As part of our study, we have maximized the yield of the Ce electrochemical amalgamation (yield > 99%) by monitoring dissolved Ce3+ concentration in solution by UV-vis, optimized the mercury recycling process during the thermal extraction (Hg recycling > 99%), as well as improved the purity of the Ce content in the product (Ce purity > 99%). The proposed OREATE method appears easier and simpler than traditional separation and purification methods and is suitable for laboratory scale preparation of high purity metals.

Low-Cost Clean One-Step Production of Solar Silicon from Natural Quartzite

Despite the fact that many groups have tried to achieve solar silicon production using molten salt electrolysis, the motivation for this project is to build on a recent breakthrough in silicon molten salt chemistry. The novel molten salt bath comprised of MgF₂-CaF₂-YF₃-CaO-SiO₂ exhibits low volatility (<0.1 μg/cm2·s), low viscosity (<5 mPa·s), high ionic conductivity (>4 S/cm), SiO₂ solubility (>5 wt%), and yttria-stabilized zirconia (YSZ) solid oxide membrane (SOM) compatibility, which are all at least an order of magnitude better than prior works. Our goal is to produce high-purity silicon from natural 99.7-99.9% pure quartzite (SiO₂) in only one step, utilizing molten salt electrolysis with a state-of-the-art molten salt composition. This process can potentially produce silicon with 4-5N purity at $1.70/kg using <30 kWh/kg, with pure oxygen by-product and zero direct Greenhouse Gas (GHG) emissions. The 4-5N product purity would be sufficient for directional solidification, resulting in $2.20-2.70/kg solar-grade silicon cost, i.e., 90-95% lower than today. Besides considerable silicon price reduction, our novel technology provides a high level of scalability that can control solar silicon price fluctuations, while it is a "green" production.

Electrochemical Oxygen Evolution from Metal Oxides Using Perovskite Anodes Towards Lunar Resource Utilization

In-situ resource utilization (ISRU) has been proposed for realizing sustainable lunar development. One of the representative resources on the Moon is lunar regolith, which covers the lunar surface. The chemical composition of lunar regolith resembles the constituents of the Earth: silica (SiO2) is the most abundant oxides in the lunar regolith. Silicon, which can be produced by silica reduction, will be the material for solar cells, and oxygen is essential for manned space exploration. Enormous amounts of silicon and oxygen will be obtainable on the Moon without transportation from the Earth by establishing silicon reduction methods without consumables. However, the conventional silica reduction method consumes vast amounts of carbon, which cannot be mined on the Moon.For realizing carbon free silica reduction method consistent with the concept of ISRU, molten salt electrolysis processes using perovskite anodes has been researched. In this method, the silica dissolved in molten salts is electrolyzed using voltage with passage of direct current through electrodes, which generate oxygen gas and silicon by the electrochemical process. The perovskite oxides have high electrical conductivity and oxidation resistance. Therefore, the perovskite anodes have been expected as oxygen generation inert anodes.In this study, we report the characteristics of perovskite-type anodes for oxygen generation measured in the electrolysis experiments. In molten fluoride containing silica at a temperature over 500℃, the measured cyclic voltammograms with a perovskite-type anode show drastically increases of current density at 2.6 V vs K+/K, which was approximately same to the oxygen generation potential in the previous molten salt electrolysis result without the perovskite anodes. The characteristics of perovskite-type anodes for oxygen generation will be discussed from the results of electrochemical measurements and chemical analysis using XRD, SEM, EDX, and ICP-AES analysis.

From Roxy to Mini-Roxy: The Next Step Towards an Efficient Method for Oxygen Extraction from Regolith

Future exploration missions to the Moon and beyond will be dependent on the use of lunar regolith to produce metals/alloys and oxygen, provided they can be produced very efficiently such that their mass exceeds the mass of any needed consumables or spares to sustain the process. Among the many methods that have been studied so far, molten salt electrolysis with solid oxide membranes appears to be most promising since it meets all of the viability criteria. A specific implementation of this method to lunar applications called ROXY (Regolith to Oxygen and Metals) has been developed and tested, and the design and operations of related demonstration and production facilities have been investigated. As a next step, a miniaturized version of the ROXY cell has been developed, leading to the Mini-ROXY concept and further improvements in terms of process efficiency, and is a new starting point for upscaling the technology.

Electrochemical Formation of Nd-Ni Alloys in a Molten Cesium Chloride System

We have been investigating a new recovery process of Dy and Nd from the magnet scraps using molten salt electrolysis and alloy diaphragms [1-14]. The key step in this process is the alloying and de-alloying of rare earth (RE) elements on both sides of the diaphragm in order to effectively separate them in the molten salt. Here, the alloying and de-alloying were termed electrochemical implantation and electrochemical displantation, respectively, in a molten LiCl–KCl [15]. The features of these alloying and dealloying were different from those expected from the ordinary concept of solid phase diffusion. The growth rate of DyNi2 phase was extremely high compared with the conventional solid phase diffusion at temperatures lower than half of the melting temperature of DyNi2, and the dissolution rate of Dy from the formed DyNi2 was also high. So far, we have reported that Dy can be selectively alloyed with Ni by potentiostatic electrolysis in a molten LiCl–KCl–DyCl3(0.50 mol%)–NdCl3(0.50 mol%) system at 723 K [5]. The selective permeation of Dy through the RE-Ni alloy diaphragm from an anolyte containing DyCl3 and NdCl3 to a catholyte has been also confirmed [14]. However, the current density was of the order of 10 mA cm-2 or less, which is insufficient for industrial electrolysis. So, in this study, we focused on the CsCl system as a candidate melt to achieve a higher current density due to its high operation temperature. Since the alloying and de-alloying of REs in this system is unknown, the electrochemical formation of Dy-Ni alloys was investigated in a molten CsCl–DyCl3 system at 973 K as a first step in studying this system. On the other hand, in this study electrochemical formation of Nd-Ni alloys was investigated in a molten CsCl-NdCl3 (0.50 mol%) system at 973 K. Open-circuit potentiometry tests were carried out with Mo and Ni flag electrodes after depositing Nd metal by potentiostatic electrolysis at -0.15 V (vs. Nd3+/Nd) for 150 s and at -0.10 V for 1 h, respectively. A potential plateau was observed at 0.00 V with a Mo electrode. Since Mo does not form any intermetallic compounds with Nd, the observed potential is interpreted as the Nd3+/Nd equilibrium potential. Also five potential plateaus were observed at 0.04 V, 0.11 V, 0.18 V, 0.38 V and 0.57 V with a Ni electrode, which possibly correspond to the potentials of two-phase coexisting states of different Nd–Ni alloys. The alloy samples were prepared by potentiostatic electrolysis at 0.08 V for 1 h with a Ni plate electrode. The XRD analysis of obtained sample indicated the formation of NdNi2. The formed NdNi2 layers at 0.08 V were transformed to other phases such as NdNi3 at 0.14 V, Nd2Ni7 at 0.22 V and NdNi5 at 0.44 V due to anodic dissolution of Nd, depending on the applied potentials.References Oishi, H. Konishi, T. Nohira, M. Tanaka and T. Usui, Kagaku Kogaku Ronbunshu, 36(4), 299 (2010). [in Japanese]H. Konishi, H.Ono, T. Nohira and T. Oishi, MOLTEN SALTS, 54(1), 21 (2011). [in Japanese]S. Kobayashi, K. Kobayashi, T. Nohira, R. Hagiwara, T. Oishi and H. Konishi, J. Electrochem. Soc., 158(12), E142 (2011).S. Kobayashi, T. Nohira, K. Kobayashi, K. Yasuda, R. Hagiwara, T. Oishi and H. Konishi, J. Electrochem. Soc., 159(12), E193 (2012).H. Konishi, H.Ono, T. Nohira and T. Oishi, ECS Trans., 50(11), 463 (2012).T. Nohira, S. Kobayashi, K. Kondo, K. Yasuda, R. Hagiwara, T. Oishi and H. Konishi, ECS Trans., 50(11), 473 (2012).H. Konishi, H.Ono, T. Nohira and T. Oishi, ECS Trans., 53(11), 37 (2013).H. Konishi, H. Ono, E. Takeuchi, T. Nohira and T. Oishi, ECS Trans., 61(28), 19 (2014).H. Konishi, H. Ono, E. Takeuchi, T. Nohira and T. Oishi, ECS Trans., 64(4), 593, (2014).H. Konishi, T. Oishi, T. Nohira, H. Ono and E. Takeuchi, ECS Trans., 75(15), 105 (2016).H. Konishi, H. Hua, H. Ono, Y. Koizumi, T. Oishi and T. Nohira, ECS Trans., 86(14), 321 (2018).Y. Watanabe, Y. Norikawa, K. Yasuda and T. Nohira, Mater. Trans. 60(3) 379 (2019).K. Yasuda, T. Enomoto, Y. Watanabe, T. Oishi and T. Nohira, Mater. Trans., 61(12), 2329 (2020).T. Oishi, M. Yaguchi, Y. Katasho, H. Konishi and T. Nohira, J. Electrochem. Soc., 167(16), 163505 (2020).H. Konishi, T. Nohira and Y. Ito, J. Electrochem. Soc., 148(7), C506 (2001).

MD Simulation and Transport Property Analysis of Silicon in High-Temperature Molten Fluoride Salts Electrolyte

Silicon is the dominant solar material because of its abundance, low cost, and high solar efficiency. But manufacturing high-purity silicon required for solar energy is very complex, hard to scale, and unsafe since it involves dealing with toxic flammable gases. Therefore, a new solar silicon production technology based on molten salt electrolysis has been proposed. To comprehensively study the self-diffusion and deposition mechanism of silicon ions in high-temperature molten salt electrolyte and their composition and temperature dependence, both interatomic potential molecular dynamics (IPMD) and ab-initio molecular dynamics (AIMD) are introduced. Thermodynamics and transport properties of molten salt electrolyte such as density, heat capacity, viscosity etc. are investigated and compared to the existed experimental results. Also, local structural information and coordination number analysis are obtained and discussed.

Electrochemical Recovery of Lithium-Ion Battery Materials from Molten Salts: Microstructural Characterisation Using X-Ray Imaging

Recycling spent Li-ion batteries (LiBs) guarantees the conservation of important metal resources by reducing demands on raw supply and offsetting the energy and environmental costs associated with its manufacture. However, selecting practical end of life solutions for battery waste management remains a challenge. Molten salts, on the other hand, are a well-established group of inorganic compounds and are understood to be one of the leading candidates in the recovery of valuable metals. They offer a much greener and simpler route to metal recovery by electrochemical means compared with the use of reducing agents for hydrometallurgical recovery [1]. Yet, the current mechanistic understanding of the electrochemical recovery of metals in molten salts needs to be improved.SEM, EDS and XRD are some of the most employed characterisation techniques used to reveal material composition and surface topography; however, they are known to expose the final product to air and moisture obscuring the results. X-ray computed tomography offers a non-destructive approach for 3D microstructure visualisation and subsequent quantification [2]. This technique can be used to study the morphological evolution of metal deposits from their oxide particles in a representative high-temperature medium to provide a wealth of information on the fundamentals of the electrochemical reduction process.Here, we demonstrate a study into the electrochemical deposition of recovered Co metal from lithium cobalt oxide, LiCoO2 in LiCl-KCl eutectic (LKE) which has been previously studied by the authors’ using a fluidised cathode arrangement [3]. This novel diagnostic approach has been applied to LiCoO2-LKE samples before and after electrolysis at 450 °C, yielding key insights into the morphological evolution of product formation. Different morphologies of recovered Co metal such as dendrite features and agglomerates have been captured and quantified. It has also been observed that CO/CO2 gas formation occurs in copious quantities at the anode surface leading to operational consequences such as the required overpotential needed to drive the reaction. For the first time, the application of X-ray imaging offers the ability to understand the role of process conditions and cell configurations to optimise a pyro-electrochemical reprocessing technology that can play a key role in sustainable battery recycling as well as refractory metal recovery.[1] B. Zhang, H. Xie, B. Lu, X. Chen, P. Xing, J. Qu, Q. Song, H. Yin, A Green Electrochemical Process to Recover Co and Li from Spent LiCoO2-Based Batteries in Molten Salts, ACS Sustain Chem Eng. 7 (2019) 13391–13399.[2] P.J. Withers, C. Bouman, S. Carmignato, V. Cnudde, D. Grimaldi, C.K. Hagen, E. Maire, M. Manley, A. du Plessis, S.R. Stock, X-ray computed tomography, Nature Reviews Methods Primers. 1 (2021) 1–21.[3] M. Mirza, R. Abdulaziz, W.C. Maskell, C. Tan, P.R. Shearing, D.J.L. Brett, Recovery of cobalt from lithium-ion batteries using fluidised cathode molten salt electrolysis, Electrochim Acta. 391 (2021) 138846.

Recovering rare earths, lithium and fluorine from rare earth molten salt electrolytic slag using sub-molten salt method

Viewing the problem of high energy consumption in the process of recovering rare earths from rare earth molten salt electrolysis slag, an environmentally friendly and low carbon process by sub-molten salt decomposition was developed. The thermodynamic analysis of sub-molten salt reaction indicates that the recovery of rare earths from the slag using sub-molten salt medium is thermodynamically feasible. In this process, the rare earth fluoride and lithium in the slag are almost transformed into rare earth hydroxide, sodium fluoride and lithium hydroxide, fluorine and lithium are transferred into the washing solution, and the rare earths in the residues can be leached into solution by acid leaching. Under the optimum reaction conditions of reaction temperature 200 °C, reaction time 3 h, NaOH initial concentration 80%, NaOH-Slag mass ratio 3:1, the leaching efficiency of rare earths, fluorine and lithium can reach to 99.05%, 98.23% and 99.22%. After evaporation, the fluorine and lithium in the washing solution can be obtained in the forms of sodium fluoride and lithium fluoride, the recovery efficiency reach 95.5% and 92.8%, respectively. The RE oxides (99.53%) can be obtained from the leaching solution after precipitation and roasting.

Electrochemical separation of Fe and Ti from ilmenite via molten salt electrolysis and its mechanism

A green separation routes for Fe and Ti from ilmenite via molten salt electrolysis is proposed in CaCl2-NaCl-CaO molten salt. FeTiO3 powder can be dissolved into the molten salt, directly. In the process, CaTiO3 is formed by the reaction of TiO32- and Ca2+ in molten salt components. Pure iron is obtained under the controllable regulation of electrolysis parameters such as cell voltage or electrolysis temperature. Fe is deposited on the cathode by the selective electroreduction of Fe2+ with 2 electrons transfer process. Ti through the consecutive two-steps with 4 electrons transfer electroreduction process of TiO32- is obtained: TiO32- → TiO →Ti. FeTi and Fe2Ti alloy is also obtained through reaction of Fe and Ti. The electroreduction of Fe2+ and TiO32- is limited by its diffusion. This approach provides a one-step green and sustainable separation of Fe and Ti from ilmenite (FeTiO3). The main product of Fe and CaTiO3 can be used for the field of catalyst, architecture, aerospace and energy storage materials.

Development of Numerical Analysis Model for New Magnesium Electrolysis Process Using COMSOL

Magnesium (Mg) has good physical properties including light weight, excellent specific strength and high stiffness, and Mg is used in many fields. But current production methods of Mg have disadvantages, such as the generation of sulfur oxide and chlorine gas. In this situation, The Korea Institute of Geoscience and Mineral Resources (KIGAM) developed a Molten Salt Electrolysis Using Liquid Metal Cathode (MSELMC) method to produce high-purity magnesium. The MSE-LMC method can obtain 99.998-99.999% highpurity magnesium by the electrolysis of MgO dissolved in (MgF2)-LiF molten salt at 1053-1083 K, and by vacuum distilling an alloy generated by reacting with a metallic liquid cathode at 1200-1300 K. This study developed a numerical analysis model using COMSOL Multiphysics electrodeposition module to optimize the design of the electrolysis process. The model temperature was 1053K and molten salt was 54MgF2-46LiF with a 0.6wt% MgO system. 10A constant current was applied at the anode. This model uses the Butler-Volmer equation and the Nernst equation for the electric reaction. The Stokes-Einstein equation and Nernst-Einstein relation were used to calculate the diffusivity and electric mobility of salts. Unlike the experiment, in this model chlorine gas was generated. However, this model satisfied Faraday’s law. Therefore we define a new parameter using electric flux and voltage to conduct a quantitative evaluation according to the electrode shape, and compared that parameter by the changing angle of the anode.

Electrochemical synthesis of Co–Pr intermetallic compounds by the co-reduction of Co(II) and Pr(III) ions in a molten LiCl–KCl eutectic

For effective recovery of the fission element Pr from spent nuclear fuel (SNF) by using molten salt electrolysis technology, the electrochemical behavior of Pr(III) on inert Mo electrode in the molten LiCl–KCl system was investigated by cyclic voltammetry (CV) and square wave voltammetry (SWV) techniques, indicating that the reduction of Pr(III) on the Mo electrode is a one-step reaction process with three electrons. Subsequently, electrochemical methods were used to reveal and calculate the kinetic and thermodynamic parameters of the Pr(III) ion reduction process. The co-reduction reaction of Pr(III) and Co(II) ions was explored, and five different CoxPry intermetallic compounds were detected. Meanwhile, only one Co2Pr intermetallic compound was obtained by galvanostatic and potentiostatic electrolysis with the best electrochemical parameters, and the thermodynamic properties of the Co2Pr intermetallic compound were calculated at different temperatures. The co-reduction product was verified using X-ray diffraction (XRD), and the composition was determined by scanning electron microscopy (SEM) with energy spectrum analysis (EDS) and X-ray photoelectron spectroscopy (XPS). In addition, the produced Co2Pr intermetallic compound has magnetic properties with a saturation magnetization of 10.3 emu/g.

High‐Capacity Sub‐Nano Divalent Silicon from Biosilicification

AbstractIn terms of high capacity and reliable safety, low‐valent silicon‐based composites with small grain sizes are practicable anode materials for lithium‐ion batteries. However, robust tetravalent silicon precursors make the synthesis hard to be green. Using biosilicification in water hyacinth (Eichhornia crassipes), it is found to be a superior natural precursor of low‐valent silicon. The biogenic sub‐nano (0.5 nm) siliceous dots composite (EC‐SiOC) shows a reversible conversion mechanism between Si─O and C─O bonds, unlike previous lithium storage mechanisms associated with alloying reactions. Due to the homogeneous biogenic structure facilitating the solid‐phase reaction, the normalized energy consumption of pyrolytic EC‐SiOC is about 80% lower than the carbothermic reduction of silica, similar to molten salt electrolysis. Statistically, the sampling survey of EC‐SiOC from different regions shows a high average capacity of 749.9 mAh g−1 under a current density of 100 mA g−1. This study reveals the great potential of biomass precursors for synthesizing Si─O─C materials.

Study on the mechanism of preparing metallic iron from soluble anode

The optimization of the ironmaking process for the preparation of high-purity metallic iron has become an important part of the production of the iron and steel industry due to the increasing demand for steel in the modern industry. This article adopted the soluble anode molten salt electrolysis process to prepare a soluble anode with excellent conductivity by mixing Fe2O3 and C in a molar ratio of 1:3, sintering at 1073 K for 6 h. The metal iron was electrolytically deposited on the cathode by applying a constant current of 0.1 A for 6 h in the NaCl-CaCl2 molten salt system. The anode dissolution and cathode deposition mechanisms were analyzed based on the electrolysis U-t curve. The experimental results showed that the presence of C after sintering reduces the impedance value by reducing Fe2O3 to Fe3O4. During the electrolysis process, Fe2+ in Fe3O4 oxidized to Fe3+ and entered the molten salt, migrated to the vicinity of the cathode, and underwent the reduction process of Fe3+-Fe2+-Fe during the cathodic reduction process. The deposited Fe on the cathode exhibited a dendritic crystal structure with a purity of 99.51%.

Magnesium production by molten salt electrolysis with liquid tin cathode and multiple effect distillation.

Low-cost clean primary production of magnesium metal is important for its use in many applications, from light-weight structural components to energy technologies. This work describes new experiments and cost and emissions analysis for a magnesium metal production process. The process combines molten salt electrolysis of MgO using MgF₂-CaF₂ electrolyte and a reactive liquid tin cathode, with gravity-driven multiple effect thermal system (G-METS) distillation to separate out the magnesium product, and re-use of the tin. Electrolysis experiments with carbon anodes showed current yield above 90%, while a yttria-stabilized zirconia solid oxide membrane (SOM) anode experiment showed 84% current yield. G-METS distillation is an important component of the envisioned process. It can potentially lower costs and energy use considerably compared with conventional magnesium distillation. Techno-economic analysis including detailed mass and energy balances shows that this electrolyte composition could lower costs by utilizing CaO, which is the primary impurity in MgO, as the Hall-Héroult process uses the sodium impurity in alumina. Analysis options include: raw material types (magnesite rock vs. brine or seawater), drying and calcining using electricity vs. natural gas, and carbon vs. SOM anode type. Using SOM inert anodes results in a cost premium around 10%-15%, mostly due to higher electrical energy usage resulting from membrane resistance, and reduces GHG emissions by approximately 1kg CO₂/kg Mg product. Capital and operating cost estimates, and cradle to gate greenhouse gas (GHG) emissions analysis under several raw material and process technology scenarios, show comparable costs and emissions to those of aluminum production.

Electrochemical and kinetic analysis of Ce recovery using Ga electrode in LiCl-KCl melt

Electrode material is an obstacle to the application of molten salt electrolysis in Ce recovery. Liquid Ga is a potential candidate for the cathode, but the corresponding reaction process on the electrode in the melt has yet to be fully understood and systematically studied. Herein, the electrochemical reaction and the kinetics of recovering Ce using Ga electrodes were investigated by various electrochemical methods. A concentration-dependent test of the co-deposition reaction revealed the continuous alloying process of reduced Ce. The electrolytic reduction of Ce ions on liquid Ga was studied by electrochemical impedance spectroscopy (EIS). The result shows that the reaction is controlled by diffusion. In addition, some important parameters such as exchange current density, activity coefficient and solubility were determined by pulsed electrolysis and coulomb titration, allowing a preliminary assessment of the electrolytic extraction of Ce on the Ga electrode.

Pure and Metal‐confining Carbon Nanotubes through Electrochemical Reduction of Carbon Dioxide in Ca‐based Molten Salts

AbstractTo be successfully implemented, an efficient conversion, affordable operation and high values of CO2‐derived products by electrochemical conversion of CO2 are yet to be addressed. Inspired by the natural CaO‐CaCO3 cycle, we herein introduce CaO into electrolysis of SnO2 in affordable molten CaCl2‐NaCl to establish an in situ capture and conversion of CO2. In situ capture of anodic CO2 from graphite anode by the added CaO generates CaCO3. The consequent co‐electrolysis of SnO2 and CaCO3 confines Sn in carbon nanotube (Sn@CNT) in cathode and increases current efficiency of O2 evolution in graphite anode to 71.9 %. The intermediated CaC2 is verified as the nuclei to direct a self‐template generation of CNT, ensuring a CO2‐CNT current efficiency and energy efficiency of 85.1 % and 44.8 %, respectively. The Sn@CNT integrates confined responses of Sn cores to external electrochemical or thermal stimuli with robust CNT sheaths, resulting in excellent Li storage performance and intriguing application as nanothermometer. The versatility of the molten salt electrolysis of CO2 in Ca‐based molten salts for template‐free generation of advanced carbon materials is evidenced by the successful generation of pure CNT, Zn@CNT and Fe@CNT.

Pure and Metal-confining Carbon Nanotubes through Electrochemical Reduction of Carbon Dioxide in Ca-based Molten Salts.

To be successfully implemented, an efficient conversion, affordable operation and high values of CO2 -derived products by electrochemical conversion of CO2 are yet to be addressed. Inspired by the natural CaO-CaCO3 cycle, we herein introduce CaO into electrolysis of SnO2 in affordable molten CaCl2 -NaCl to establish an in situ capture and conversion of CO2 . In situ capture of anodic CO2 from graphite anode by the added CaO generates CaCO3 . The consequent co-electrolysis of SnO2 and CaCO3 confines Sn in carbon nanotube (Sn@CNT) in cathode and increases current efficiency of O2 evolution in graphite anode to 71.9 %. The intermediated CaC2 is verified as the nuclei to direct a self-template generation of CNT, ensuring a CO2 -CNT current efficiency and energy efficiency of 85.1 % and 44.8 %, respectively. The Sn@CNT integrates confined responses of Sn cores to external electrochemical or thermal stimuli with robust CNT sheaths, resulting in excellent Li storage performance and intriguing application as nanothermometer. The versatility of the molten salt electrolysis of CO2 in Ca-based molten salts for template-free generation of advanced carbon materials is evidenced by the successful generation of pure CNT, Zn@CNT and Fe@CNT.

Eliminating carbon contamination with improved one-step electrochemical preparation of refractory high-entropy alloy TiZrHfNbTa

Creating refractory high-entropy alloys (RHEAs) effectively without impurities is a momentous challenge. Conventional methods for the preparation of RHEAs have exacting requirements for raw material purity and energy consumption. Molten salt electrolytic oxides are applied to the preparation of HEAs by virtue of their low cost and high efficiency. However, the use of graphite anodes in electrolysis will result in the carbon contamination of the products due to the deposition of CO32− at the cathode. Increasing the reaction temperature accelerates the deoxidation of the oxide, thus reducing the amount of carbide but not eliminating it. Switching HfH2 instead of HfO2 and using Nb2O5 to shield the precursor can effectively remove carbon contamination. However, this leads to a complicated preparation process and energy waste. Herein, we use the solid oxygen ion-conducting membrane (SOM) containing graphite and Sn (named as SOM@C/Sn) anode to separate the carbon from the molten salt and prevent the circulation of CO32−. The pure single-phase TiZrHfNbTa RHEA can be produced in only one-step with the SOM@C/Sn anode, which completely solves the problem of carbon contamination in the molten salt electrolysis preparation of HEAs. This work provides a feasible solution for the preparation of novel complex alloys such as carbon-free RHEAs in a low-cost short process.