Liquid-metal Cathode Research Articles

CuGa2 transition phase anchored liquid GaSn achieves high-performance liquid metal battery cathode

Severe volume expansion will cause the gallium-based liquid metal cathode material to detach from the collector thus deteriorating performance. Here, we propose a strategy for preparing electrodes by anchoring the liquid metal with an intermetallic compound transition phase to avoid the problem of liquid metal shedding during cycling. The good reactive wetting between the CuGa2 transition phase and gallium can firmly anchor the liquid metal to prevent the electrode material exfoliating from the collector. On the other hand, the unique two-dimensional layer structure of CuGa2 can also limit the lithiation volume expansion of liquid gallium. Density functional theory (DFT) reveals the anchoring mechanism of the CuGa2 transition layer to liquid gallium and the reaction mechanism of Li with CuGa2 during the electrochemical reaction. As a result, O-GaSn/CF cathodes exhibit low resistance, fast ion diffusion, high reversible capacity, excellent rate performance and outstanding cycling stability.

(Invited) Magnesium Production By MgO Reduction in Molten CaF2-MgF2 Salt with Reactive Liquid Metal Cathode and Consumable Carbon Anode or Nonconsumable Zirconia Solid Oxide Membrane

A process for magnesium production is proposed beginning with MgO electrolysis in molten MgF2-CaF2 salt with a reactive liquid metal cathode, followed by efficient multiple effect distillation to separate the magnesium from the cathode. Experiments with a liquid tin cathode and carbon anode show over 90% current efficiency; with a yttria-stabilized zirconia (YSZ) solid oxide membrane (SOM) between the bath and anode, current efficiency is above 80%. A detailed mass balance estimates the amount of MgF2 and tin required to maintain steady bath and cathode chemistry with CaO and other impurities in the MgO feedstock. A detailed energy balance describes the relationship between applied potential and cell thermal balance over a range of process temperatures, including minimum energy losses through cell leads. Emissions analysis shows a range of greenhouse emissions depending on the raw material type, MgO separation and calcination method, anode type (carbon or YSZ SOM), and electrical energy source.

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.

Selective extraction of Sm from LiCl-KCl molten salt into wasteforms via liquid bismuth

The electrorefining of spent nuclear fuels in a molten LiCl-KCl salt electrolyte recovers the valuable actinides but also releases radioactive fission products in the salt. To minimize the nuclear waste volume, dissolved fission products such as rare earths (REs) must be removed from the electrorefining salt and immobilized into proper wasteforms. Here we propose a two-step approach for treating the electrorefining waste salt by (i) the electrolytic recovery of REs from the salt using a liquid metal cathode; and subsequent (ii) oxidative extraction of REs from the liquid metal into durable wasteforms. Experimental demonstration using rare earth element samarium (Sm) and liquid metal (Bi) was successful. The Sm ions dissolved in the salt can be selectively recovered as dendrite Sm-Bi intermetallic products on the top of liquid bismuth cathode through electrolysis at appropriate applied currents or potentials. Then the Sm in the Sm-Bi alloy was efficiently extracted into both zinc-in-titania (ZIT) glass ceramic and lanthanide aluminoborosilicate (LABS) glass wasteforms through selective oxidation at Sm2O3 loadings of 18–25 wt% and 50 wt%, respectively. Recycling of the electrorefining salt with minimum nuclear waste generation is foreseeable with the use of this simple, efficient, and highly compatible process.

A recyclable method for titanium extraction and oxygen evolution from Ti−bearing slags

Despite its existence for more than 80 years, the titanium industry is still challenged by massive carbon emissions, high production costs, and large resource waste. More than one hundred million tons of Ti−bearing blast furnace slag (TB−slag) has been discarded in China because of the difficulty of reutilization, which requires efficient titanium extraction and recovery technologies. This paper describes a low−cost, carbon−emission−free method for Ti extraction and oxygen evolution via molten oxide electrolysis (MOE) vacuum distillation. After a comprehensive analysis of the binding energies and activities of liquid metals, the highlights of our study are as follows. 1) Sb has the best preferential deposition of Ti among a series of high−Ti−affinitive liquid metal cathodes (Cu, Ni, Pb, Sn, and Sb). 2) The Ir anode was first used in TB−slag with IrO2 formed on its surface to protect it from further corrosion. 3) An alloy containing Ti and Ca can be obtained by MOE, and Ti and Ca metals can be refined by further vacuum distillation. 4) A closed loop is formed in the overall process owing to the recyclable Sb cathode and continuous feeding of TB−slag into the electrolyte. This simple, low−cost, and environmentally friendly method can realize the efficient utilization of Ti resources and achieve carbon neutrality.

Fully rubbery Schottky diode and integrated devices.

A fully rubbery stretchable diode, particularly entirely based on stretchy materials, is a crucial device for stretchable integrated electronics in a wide range of applications, ranging from energy to biomedical, to integrated circuits, and to robotics. However, its development has been very nascent. Here, we report a fully rubbery Schottky diode constructed all based on stretchable electronic materials, including a liquid metal cathode, a rubbery semiconductor, and a stretchable anode. The rubbery Schottky diode exhibited a forward current density of 6.99×10-3 A/cm2 at 5 V and a rectification ratio of 8.37×104 at ±5 V.Stretchy rectifiers and logic gates based on the rubbery Schottky diodes were developed and could retain their electrical performance even under 30% tensile stretching. With the rubbery diodes, fully rubbery integrated electronics, including an active matrix multiplexed tactile sensor and a triboelectric nanogenerator-based power management system, are further demonstrated.

Electrochemical recovery of Nd using liquid metals (Bi and Sn) in LiCl-KCl-NdCl3

• Thermochemical properties of Nd in liquid Bi and Sn via reliable emf measurements • Highly-efficient electrochemical recovery of Nd using liquid metal cathodes • Facile charge-transfer kinetics (high exchange current) of Nd 3+ /Nd in liquid metals • High recovery capacity of liquid metals for Nd (20 mol%) beyond the solubility limit Highly efficient recovery of Nd into liquid metals of Bi and Sn was achieved in molten LiCl-KCl-NdCl 3 electrolyte at 773–973 K by leveraging the strong interactions of Nd with liquid metals. Based on the emf measurements of Nd-Sn and Nd-Bi alloys, the activity values of Nd were determined as low as 1.1‒5.8×10 –13 in both liquid metals at 973 K while the solubility of Nd was found to be 1.46 mol% in Sn and 5.65 mol% in Bi. Both liquid metals demonstrated high round-trip coulombic efficiencies (>99.3%) during deposition-removal cycles of 10‒50 mA cm ‒2 and high recovery capacity up to approximately 20 mol% Nd beyond the solubility limit. In addition, a high Nd recovery yield (84–90%) with respect to the applied charge was confirmed based on chemical analysis of electrolysis products in Bi after constant current electrolysis (–50 mA cm –2 ) at 873‒973 K. Overpotentials during the Nd deposition process were attributed to charge-transfer and mass-transport resistances based on the current-potential curve and electrochemical impedance spectroscopy. The charge-transfer kinetics of Nd deposition into liquid metals was facile with high exchange current densities at ∼220 mA cm ‒2 . The exceptionally high recovery efficiency for Nd in the molten chloride is thought to result from strong chemical interactions (i.e., low activity) of Nd in liquid metals that encourage one-step reduction, i.e., Nd 3+ + 3e → Nd(in Bi or Sn) by effectively suppressing side reaction pathways from multivalent states (Nd 2+ and Nd 3+ ).

A universal study of liquid metal cathodes for direct extraction of titanium within a closed loop

Due to the environmental pollution, long process, and high cost of the current titanium recycling technologies, hundred million tons of titanium containing blast furnace slag generated in the iron making process are abandoned, which calls for urgent and effective utilization. Herein, we report a universal study of a series of high titanium affinitive liquid metal cathodes coupled with graphite anode for direct titanium extraction from titanium containing slag in a molten oxide electrolysis method. Two cost free slags, titanium containing blast furnace slag and electroslag remelting slag, serve as the electrolytes, and a series of liquid cathode metals are tuned to reveal the depolarization effect. Through thermodynamic and experimental analyses and kinetic calculations, we find binding energy, work function, and activities of titanium in liquid metal cathodes can synergistically affect the preferential deposition of titanium. After galvanostatic electrolysis, titanium–rich alloy cathodes are obtained, which can be directly used as industrial products or further distillated in vacuum to separate pure titanium and recyclable cathode metals, forming a closed loop throughout its life cycle. An ultrahigh cathodic current efficiency (∼64%) with short process and low energy consumption is achieved in this work. The outcomes reveal this environmentally friendly strategy can achieve efficient utilization of titanium resources, significantly reduce the loss of energy in the extraction process and lower the industrial production costs, and the breakthrough of directly extracting titanium from titanium containing oxides in this work is of great importance to titanium industry.

Ultra‐High Temperature Molten Oxide Electrochemistry

AbstractRecently, the ultra‐high temperature electrochemistry (UTE, about >1000 °C) has emerged, which represents an exploration to extend the temperature limit of human technology in electrochemical engineering. UTE has far‐reaching impact on revolutionary low‐carbon metal extraction and the in situ production of oxygen for deep‐space exploration. It is hence of urgency to systematically summarize the development of UTE. In this Review, the basic concepts of UTE and the physicochemical properties of molten oxides are analyzed. The principles in the design of inert anodes for the oxygen evolution reaction in molten oxides are discussed, which forms a solid basis for the in situ production of oxygen from simulated lunar regolith by UTE. Furthermore, liquid metal cathodes for revolutionary titanium extraction and ironmaking/steelmaking are highlighted. With emphasis on the key challenges and perspectives, the Review can provide valuable inspiration for the rapid advancement of UTE.

Ultra-High Temperature Molten Oxide Electrochemistry.

Recently, the ultra-high temperature electrochemistry (UTE, about >1000 °C) has emerged, which represents an exploration to extend the temperature limit of human technology in electrochemical engineering. UTE has far-reaching impact on revolutionary low-carbon metal extraction and the in situ production of oxygen for deep-space exploration. It is hence of urgency to systematically summarize the development of UTE. In this Review, the basic concepts of UTE and the physicochemical properties of molten oxides are analyzed. The principles in the design of inert anodes for the oxygen evolution reaction in molten oxides are discussed, which forms a solid basis for the in situ production of oxygen from simulated lunar regolith by UTE. Furthermore, liquid metal cathodes for revolutionary titanium extraction and ironmaking/steelmaking are highlighted. With emphasis on the key challenges and perspectives, the Review can provide valuable inspiration for the rapid advancement of UTE.

Electrochemical Separation of Ag2S and Cu2S from Molten Sulfide Electrolyte

The production of precious metals from Cu-rich sources such as ore products or secondary sources is slow and complex largely due to limited solubility in aqueous electrolytes. This results in sequential processing with various electrolytes and chemistries, where first Cu is electrorefined, followed by Ag, followed by Au and the platinum group metals. These are separate processes, often conducted in separate electrorefining and electrowinning facilities. The chemical properties of molten sulfides, and their ability to operate at a temperature where liquid metal cathodes are used, suggest the possibility of an alternative, streamlined processing route for Cu and precious metals. Unfortunately, little thermodynamic or electrochemical information is available regarding the behavior of Cu and precious metal sulfides in molten sulfide electrolytes. Herein, the relative activity of the Cu2S-Ag2S pseudobinary dissolved in a BaS-La2S3 supporting electrolyte is measured at 1523 K. It was found that the supporting electrolyte favors mixing with Ag2S over Cu2S. Molten sulfide electrolysis of Cu and Ag was conducted, with results in good agreement with the thermodynamic model. It is found that the Ag-Cu cathode chemistry will influence the electrochemical selectivity in the Ag-Cu-Ba-La-S system.

Highly efficient and eco-friendly InP-based quantum dot light-emitting diodes with a synergetic combination of a liquid metal cathode and size-controlled ZnO nanoparticles

Colloidal quantum dot light-emitting diodes (QLEDs) are the most promising candidates for next-generation displays due to wide color gamut, high contrast ratio, and narrow bandwidth emission. However, high-efficiency QLEDs based on toxic cadmium-based quantum dots (QDs) are strictly regulated by environmental law, and therefore environmentally friendly fabrication methods using non-cadmium-based QDs are indispensable for industrial applications. In this study, an eco-friendly and scalable fabrication strategy based on a synergetic combination of colloidal InP QDs, a eutectic gallium-indium liquid metal, and size-controlled ZnO nanoparticles was developed to produce highly efficient, environmentally friendly, solution-processable QLEDs. The cathode electrode of a gallium alloy liquid metal was applied using a simple screen-printing method, and the InP/GaP/ZnS green QDs with an excellent photoluminescence quantum yield of 85% were facilely prepared and incorporated into the device through spin coating process, ensuring that high device efficiency of InP-based QLED was achieved through uniform electroluminescence of active area. In addition, a size-controlled synthetic method for ZnO nanoparticles as the electron transfer layer was developed to improve the quantum efficiency of InP QDs, and consequently the optoelectronic performance of the resulting device was higher than that of conventional device in terms of current density, luminance, and external quantum efficiency.

Core-shell GaSn@rGO nanoparticles as high-performance cathodes for room-temperature liquid metal batteries

Gallium-based liquid metals with high specific capacity and good self-healing properties are promising cathode materials for room-temperature liquid metal batteries (LMBs). Most liquid metal cathode materials, however, face critical challenges, including the large volume expansion, unstable solid electrolyte interface (SEI) layer, and serious capacity decay. Here, a facile coating strategy is shown to prepare GaSn nanoparticles encapsulated by reduced graphene oxide (rGO) with core–shell structures that exhibit high structural integrity and excellent electrochemical performance. The pleated rGO shell (≈6 nm) offers superior buffering properties and a stable SEI layer during charging and discharging processes, achieving excellent cycling stability. In situ X-ray diffraction patterns reveal that this novel GaSn@rGO NP electrode is based on an alloying/dealloying lithium storage mechanism. This study demonstrates that the rationally designed cathode material offers an unprecedented opportunity for room-temperature LMBs with high rate capability and cycling stability.

Recent Progress in Molten Salt Electrolysis Using a Liquid Metal Cathode and Vacuum Distillation for the Production of Ultra-High-Purity Mg Metal from MgO

In order to produce ultra-high-purity magnesium (Mg) metal from magnesium oxide (MgO), a novel and environmentally-sound process via molten salt electrolysis using a liquid metal cathode and vacuum distillation has been developed. The molten salt electrolysis of MgO in magnesium fluoride (MgF2) – lithium fluoride (LiF) molten salt is conducted at 1053 K using a tin (Sn), copper (Cu), or silver (Ag) cathode and a carbon (C) or platinum (Pt) anode for the production of Mg alloys. Subsequently, vacuum distillation of the obtained Mg alloys is carried out at 1200 – 1300 K to produce Mg metal with a purity of 99.999 %. In this study, the influence of the electrolysis temperature, concentration of Mg in the Mg alloys, and current density of the cathode on the faradaic efficiency was investigated. In addition, the reaction between the Mg alloys cathode and alumina (Al2O3) in contact with the cathode was analyzed. Recent results obtained by scale-up of the developed electrolytic and vacuum distillation processes and the use of secondary resources containing MgO as a feedstock for robustness and extension of the process will also be discussed. This study demonstrates the feasibility of an effective and environmentally-friendly Mg production process using MgO. Figure 1

Electrochemical Recovery of Rare-Earth Elements Using Liquid Metals in Molten Salts

This work presents electrodeposition of rare-earth elements (Nd and Gd) in molten salts using liquid metal cathodes (Bi and Sn) at 773–973 K with an aim enhance the recovery of rare-earth elements. Recovery of rare-earth elements from molten salts is technically challenging due to high reactivity of rare-earth metals, multivalency of rare-earth cations in electrolytes that can results in a disproportionation reaction (e.g., Nd + 2NdCl3 → 3NdCl2), and dissolution of rare-earth metals in molten salts (e.g., 9 mol% La metal in LaCl3 at 1099 K). Improved rare-earth recovery is discussed based on round-trip coulombic efficiencies using liquid metal electrodes in molten salts and the electromotive force (emf) measurements of rare-earth alloys (e.g., Nd-Bi, Nd-Sn, and Gd-Bi). The rare-earth alloys are also characterized using X-ray diffraction, electron microscopy, and differential scanning calorimetry to determine their phase behavior during electrodeposition processes. The use of two-phase rare-earth alloys, e.g., Nd-Sn alloy (10-90 mol%), as a stable reference electrode is discussed within the context of reliable electrochemical characterization of rare-earth alloys.

Investigation of Electrowinning of Mg from MgO Using a Liquid Metal Cathode in MgF2-CaF2-NaF or MgF2-LiF Molten Salt

A novel magnesium (Mg) production process utilizing an electrolytic method was investigated for the direct reduction of magnesium oxide (MgO). Electrolysis of MgO was carried out with an applied voltage of 3.0 V using a copper (Cu), silver (Ag), or tin (Sn) cathode and carbon (C) or platinum (Pt) anode in magnesium fluoride (MgF2)−calcium fluoride (CaF2)−sodium fluoride (NaF) at 1273 K or MgF2− lithium fluoride (LiF) at 1083−1093 K. After the electrolysis of MgO in MgF2−CaF2−NaF molten salt, Mg alloys such as Mg2Cu, Cu2Mg, or Mg2Sn phases were produced with current efficiencies of 75.8−85.6% when the concentration of Mg in Mg alloys was 9.1−14.6 mass%. In addition, when the electrolysis of MgO was conducted in MgF2–LiF molten salt, Mg alloys such as Mg2Cu or AgMg phase were produced with current efficiencies of 76.2−81.7% when the concentration of Mg in the Mg alloys was 12.5−13.2 mass%. In addition, to produce high-purity Mg metal from Mg alloys, vacuum distillation was conducted. When vacuum distillation was conducted at 1100−1400 K for a duration of 5 h, the concentration of Mg in the Mg alloys feed decreased from 30.2−34.1 mass% to 0.64−1.75 mass%, and Mg metal with a purity of 99.998−99.999% was obtained under certain conditions. Therefore, the molten salt electrolysis using liquid metal cathode (MSE-LMC) process developed here is feasible for the direct reduction of MgO using an effective and environmentally sound method.

Electrochemical Liquid Liquid Synthesis of Semiconductor and Intermetallic Nanomaterials

This presentation describes the hybrid methodology of electrochemical liquid-liquid-solid (ec-LLS) crystal growth for the synthesis of semiconductor and intermetallic nanostructures. The premise of ec-LLS is that electrodeposition can be coupled with melt-crystal growth through the use of liquid metal cathodes. Electrodeposition of zero-valent metals and metalloids, followed by dissolution into and then precipitation out of the liquid metal, affords low-temperature and rapid crystal growth. This presentation first describes our latest understanding of the governing factors of ec-LLS processes for the preparation of semiconductor nanowires. Following, our latest results for the synthesis of intermetallic nanoparticles by ec-LLS will be demonstrated. The operative design rules for optimal liquid metal cathodes that afford tailored binary and ternary intermetallic nanoparticles will be discussed. An emphasis will be placed on ec-LLS reactions that produce catalytic intermetallic nanomaterials.

Molten Salt Electrolysis of Magnesium Oxide Using a Liquid–Metal Cathode for the Production of Magnesium Metal

A novel electrolytic process that uses a liquid–metal cathode was investigated to produce high-purity magnesium (Mg) metal using magnesium oxide (MgO). Electrolysis of MgO in a magnesium fluoride (MgF2)-lithium fluoride (LiF) molten salt was carried out with applied voltages of 2.5 V to 3.0 V at 1053 K to 1083 K using tin (Sn), silver (Ag), or copper (Cu) as the cathode and graphite or platinum (Pt) as the anode. After electrolysis, Mg alloys with Mg2Sn, AgMg, and Cu2Mg phases were produced with current efficiencies of 77.2 to 83.8 pct when the concentration of Mg in the Mg alloys was 11.9 to 12.9 mass pct. For the production of high-purity Mg metal directly from the Mg alloys, vacuum distillation was performed. When vacuum distillation was conducted at 1200 K to 1300 K, the concentration of Mg in the Mg alloys feed decreased from 30.2 to 34.1 mass pct to 0.32 to 1.75 mass pct, and Mg metal with a purity of 99.975 to 99.999 pct was obtained. Therefore, this study demonstrates that the production of high-purity Mg metal through an efficient and environmentally sound method using the electrolysis of MgO is feasible.

A review on liquid metals as cathodes for molten salt/oxide electrolysis

Compared with solid metals, liquid metals are considered more promising cathodes for molten slat/oxide electrolysis due to their fascinating advantages, which include strong depolarization effect, strong alloying effect, excellent selective separation, and low operating temperature. In this review, we briefly introduce the properties of the liquid metal cathodes and their selection rules, and then summarize development in liquid metal cathodes for molten salt electrolysis, specifically the extraction of Ti and separation of actinides and rare-earth metals in halide melts. We also review recent attractive progress in the preparation of liquid Ti alloys via molten oxide electrolysis by using liquid metal cathodes. Problems related to high-quality alloy production and large-scale applications are cited, and several research directions to further improve the quality of alloys are also discussed to realize the industrial applications of liquid metal cathodes.

EXPERIMENTAL AND MODEL EVALUATION OF DIFFUSION COEFFICIENTS OF BARIUM IN LIQUID GALLIUM AND LEAD

Gallium and lead are used as liquid cathodes to produce alloys of alkaline earth metals, including barium. Data on the diffusion coefficients of barium (DBa) in liquid metals obtained by anodic chronopotentiometry are very limited. In this paper, an experimental evaluation of DBa in liquid gallium and lead was carried out by a combined method. It is based on the joint processing of the measurement data of the cathode chronopotentiometry in the coordinates E–ln√τ and the equations of the isotherms of the potentials of the alloys of the E–lnXBa obtained under the same conditions. Measurements were carried out in the melt KCl– 26 mol % BaCl2, at temperatures from 953 to 1073 K. The basis for the calculation of DBa is the Sanda equation. The features of electrode processes on liquid metal cathodes in barium-containing chloride melts are taken into account. The values of stabilized residual current densities depending on the temperature are established. It is shown that at the beginning of the process of barium separation into alloys, the effect of joint potassium deposition is manifested, especially on the lead cathode. The contribution of barium current output is proposed to be estimated by the current selectivity index, which depends on the potential of the alloy. It is shown that the joint discharge of potassium and barium into alloys leads to an overestimation of dva on gallium and lead from 5 to 12%. The activation energies of barium diffusion in gallium and lead, respectively 20.7 and 16.2 kJ/mol, were calculated on the basis of the obtained temperature dependences of DBa. Calculations show that on liquid thallium, bismuth, antimony measurement of cathode chronopotentiograms for barium is impossible, because of significant potassium co-deposition. Based on the data on the structure of dilute alloys and thermodynamic characteristics of alkaline earth metals, the method of calculation of reduced radii of microgroups-diffusers in the Stokes – Einstein equation is proposed. The DMe values calculated using the reduced radii are in satisfactory agreement with the majority of experimental data. These facts confirm the validity of the model of collective diffusion of barium and other alkaline earth metals in alloys as part of microgroups by translational mechanism.