Abstract—Under the conditions of resource saving and decreasing carbon footprint, the development of oxygen-releasing anodes for manufacturing technologies of important metals and alloys by the electrolysis of molten salts seems to be an urgent task. Data on the kinetics and mechanism of the anodic process on a material that is not prone to oxidation are needed to determine the degree of “inertness” of a particular anode material. In this connection, the anodic process on gold in the KF–AlF3–Al2O3 melt for electrolytic aluminum production is studied by cyclic voltammetry (CV) and square-wave voltammetry. The influence of temperature (715 and 775°C) of the melt, Al2O3 content in the melt (from 0.1 to saturation), and polarization rate (0.05–1 V/s) on the kinetics and some features of the mechanism of the studied process is determined. An oxygen release on gold without dissolution of the substrate is assumed to take place in the overvoltage range from 0 to 0.8 V. The process is shown to consist of the stages of electrochemical adsorption and desorption of the intermediate product, the first of which is limited by the diffusion of electroactive anions to the anode.

Abstract—The electrochemical behavior of scandium in halide melts is of interest from the viewpoint of developing new electrochemical approaches to produce scandium and related materials. In addition, scandium is used to simulate the electrochemical behavior of fission products at nuclear waste pyrochemical reprocessing in molten layers. The electrolytic reduction of scandium ions versus the parameters of LiF–CaF2–ScF3 melt electrolysis has been studied by means of cyclic voltammetry, square wave voltammetry, and chronopotentiometry at 800°C. It has been shown that electrochemical reduction of scandium in the given melt takes place at a potential more negative than –0.45 V relative to the potential of the aluminum electrode. In this case, the scandium reduction on the electrode favors the reduction of lithium cations with depolarization. The analysis of polarization dependences has shown that the scandium reduction has one three-electrode stage and is not electrochemically reversible. It has been supposed that irreversibility is the result of new phase formation. The conclusion has been drawn that owing to a wide electrochemical window, LiF–CaF2 melt may be used for electrochemical synthesis of scandium and analysis of joint or selective electrochemical reduction of many actinides and lanthanides.

Abstract—Electrolysis of molten salts is one of the promising methods for the preparation of silicon and its materials due to a possibility of controlling the composition and morphology. However, data on the influence of various factors on the kinetics of silicon electrodeposition are needed. The influence of the material of the cathode support on the kinetics of silicon ion electroreduction in the low-fluoride 57KCl–43CsCl (wt

Currently, there is an active search for suitable anode materials for a lithium-ion power source. Lithium-ion power sources are the subject of extensive research due to their superior properties, including energy density and power, making them suitable for a wide range of modern applications, including in electric vehicles, medicine, and energy storage systems. One of the attractive anode materials for lithium-ion power sources are NiO/C mixtures or NiO@C composites. However, the existing schemes for their production seem to be complicated, expensive, and time-consuming, which may complicate their realization on a semi-industrial scale. The present work investigates the behavior of a NiO/C anode, which was obtained in the simplest and most accessible way via thermally synthesis. The anode was used to create experimental half-cell lithium-ion power source samples. The performance and energy characteristics of NiO/C mixtures with the different NiO content were studied by means cyclic voltammetry, galvanostatic testing, and EIS. The stability of the discharge capacity of NiO/C anode samples of 355–370 mAh g−1 as well as the stability of ohmic resistance during repeated cycling was shown. The paper also analyses ways for further optimizing the NiO/C anode composition.

The methods of electrolytic production of silicon and materials based on it with controlled morphology, particle size, and trace element content are important for the development of new microelectronic and renewable energy devices. In this work, the possibility of silicon production by the electrolysis of the KCl–K2SiF6 chloride melt with a low content of fluorine ions using quartz (silicon oxide) as a starting material is studied. Cyclic chronovoltammetry is used to determine the silicon electrodeposition parameters (cathode current density) and the recommended SiO2 content in the melt, which allows stable electrolysis without electrode passivation. A series of experiments on silicon electrodeposition from the melt using a graphite anode and a graphite cathode is performed at various cathode current densities (10–50 mA/cm2). Silicon deposits are formed, and their composition and morphology are studied by scanning electron microscopy, energy dispersive analysis, and X-ray diffraction analysis. Predominant silicon deposition in the form of fibers with an average diameter of 0.3–0.8 μm and larger particles of an arbitrary shape is observed. As the cathode current density increases, the amount of β quartz in the deposit is found to increase, and its appearance is likely to be caused by the codeposition of potassium in the form of silicides and their subsequent hydrolysis during the separation of salts from the deposit in distilled water. The measurement results are used to propose a method for continuous electrolytic silicon production from quartz; it includes periodic removal of the cathode with a deposit from an electrolysis cell and loading quartz into the melt.

Currently, the development of oxygen-evolving anodes for eco-friendly technologies to produce important metals and alloys by electrolysis of molten salts seems to be an urgent task. To determine the degree of “inertness” of a particular anode material, data on the kinetics and mechanism of the anode process on an ideal material not subject to oxidation are required. In this connection, the anode process on gold in the low-temperature KF-AlF3-Al2O3 melt for electrolytic aluminum production was investigated in this work by cyclic and square-wave voltammetry methods. The influence of temperature (715 and 775°C) of the melt, the content of Al2O3 in it (from 0.1 to saturation), as well as the polarization rate (0.05–1 V s−1) on the kinetics and some features of the mechanism of the investigated process was determined. An assumption is made that oxygen release on gold without dissolution of the substrate takes place in the region of overvoltages from 0 to 0.8 V. It is shown that the process includes the stages of electrochemical adsorption and desorption of the intermediate product, the first of which is limited by the diffusion of electroactive anions to the anode.

The unique properties of zirconium silicides attract the attention of a large number of authors from various scientific fields. Expansion of application methods also poses the challenge of developing new, more environmentally friendly and affordable methods of production. The most environmentally friendly method without equipment requirements is the electrolysis of the molten salt. The work proposes a method for producing zirconium silicides by electrolysis of the KCl–K2SiF6–ZrO2 melt. In order to substantiate the electrolysis parameters, the kinetics of cathodic reduction was studied and the limiting stage of the process was determined. The structure and phase composition of the cathode deposit were studied using X-ray diffraction and electron scanning microscopy. In the course of the work, conclusions were drawn about the change in the content of the ZrO2 additives on the morphology of the sediment, and it was also suggested that it was possible to obtain zirconium silicides from more accessible raw materials, such as zircon.

The possibility of using silicon-based anodes in lithium-ion power sources is actively investigated due to the increased lithium capacitance of silicon. This work reports the preparation of submicron silicon fibers on glassy carbon in KI–KF–KCl–K2SiF6 melt at 720°C. For this purpose, the parameters of silicon electrodeposition in the form of fibers were determined by cyclic voltammetry, experimental batches of ordered silicon fibers with an average diameter from 0.1 to 0.3 μm were obtained under galvanostatic electrolysis conditions, and using the obtained silicon fibers, anode half-cells of lithium-ion current sources were fabricated and their electrochemical behavior and behavior under multiple lithiation and delithiation were studied. By means of voltammetric studies, it is observed that charging and discharging of the anode based on the obtained silicon fibers occurs at potentials from 0.2 to 0.05 V and from 0.2 to 0.5 V, respectively. Cycling of electrodeposited silicon fibers in anode half-cells of lithium-ion power source was carried out. Depending on the charge current, the discharge capacity ranged from 200 to 500 mAh/g at Coulomb efficiency of 98–100 %. Also, multiple cycling of the sample of lithium-ion power source with a lithium counter electrode was performed. In the course of 800 cycling with current 0.5C, the discharge capacity of the sample decreased from 165 to 65 mAh/g. Scanning electron microscopy shows the volumetric expansion of the of silicon fibers during cycling.

Silicon and its materials are widely used in metallurgy, micro- and nano-electronics, solar energy, and are also promising materials for anodes of lithium-ion power sources with increased specific capacity. The expansion of application areas of silicon with controlled morphology necessitates the development of new energy–efficient methods of its production. In the present work, the influence of the mode as well as parameters of electrolysis of the LiCl–KCl–CsCl–K2SiF6 melt with a temperature of 545 оC on the morphology of electrolytic precipitation of silicon on glassy carbon has been studied. The galvanostatic mode of electrodeposition, widely used in industry, as well as the pulsed mode, which is actively investigated at present, were used for the electrolysis. Silicon electrodeposition was carried out by varying such parameters as cathodic current density (from 3 to 50 mA/cm2) and electrolysis duration (from 30 to 180 min) in the galvanostatic mode, as well as by varying the density and duration of the cathodic current pulse, the duration of current pauses and the total duration of electrolysis in the pulsed mode. It is shown that electrodeposition of silicon on glassy carbon is accompanied by the formation of a continuous sediments of hemispherical nuclei with a diameter of about 1 micron on the electrode surface. An increase in the cathodic current density and an increase in the cathodic current pulse pause frequency contribute to the disruption of the sediment continuity and the growth of dendrites of ordered or arbitrary shape. At the same time, the pulsed mode allows to increase the cathode current density at silicon electrodeposition (from 25–30 to 250–500 mA/cm2) and stabilize the value of the cathode potential during electrolysis.

Multilayer structures based on semiconductor materials are being actively studied for their use in various solar energy detectors and converters. Due to the combination of properties of individual materials, an overall improvement of performance characteristics can be achieved in their multilayer design. In the present work, a technique for the preparation of layered structures based on PbS on the surface of silicon substrates has been tested for the first time. The principal possibility of chemical deposition of lead sulfide films from aqueous media at 80 °C by varying the initial state of the silicon substrate and the presence of the sensitive NH 4 Cl addition is presented. The morphology, elemental and phase composition, structural, and optical characteristics of the obtained lead sulfide films were studied by ICP, SEM-EDX, XRD and Raman spectroscopy. The photoelectrochemical effect of initial silicon substrates and layered PbS/Si structures was obtained using a solar simulator.

In this work, we studied the kinetics of the cathodic process and the regularities of the initial stages of silicon electrodeposition with methods of cyclic voltammetry, square-wave voltammetry, and chronoamperometry on a glassy carbon substrate from a LiCl-KCl-CsCl melt with K 2 SiF 6 at a temperature of 545 ± 5°C. It is shown that the cathodic process of silicon reduction proceeds in one stage, and it is not electrochemically reversible. The diffusion coefficient of silicon ions found by CV and chronoamperometry was 8.44·10 −11 and 1.00·10 −10 m 2 s −1 , respectively. It was also found that the nucleation of silicon on glassy carbon is progressive; the formation of new nuclei proceeds continuously against the background of the growth of existing ones. Based on electrochemical measurements, various modes of silicon electrodeposition in the form of thin films were chosen: potentiostatic, pulse, reverse and galvanostatic with preliminary anodizing. As a result of electrolysis, silicon films were obtained, which were analyzed by SEM and XRD methods. The thickness of such deposits during electrolysis reaches several microns, and it consists of many spherical nuclei up to 0.7 microns in diameter. The content of impurities in deposits is extremely low, and the main contaminant is oxygen (0.4–1.2 wt%).

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.

The electrochemical behavior of scandium in halide melts is of interest both from the point of view of developing new electrochemical methods for producing scandium and its materials, and from the point of view of simulating electrochemical behavior of fission products during pyrochemical processing of spent nuclear fuel in molten salts. Using the methods of cyclic voltammetry, square-wave voltammetry and chronopotentiometry, the regularities of electrical reduction of scandium ions depending on the electrolysis parameters of the LiF–CaF2–ScF3 melt at a temperature of 800°C were studied. It is shown that the electrical reduction of scandium in the melt under study occurs at potentials more negative than –0.45 V relative to the potential of the aluminum electrode, while the electrodeposition of scandium on the electrode contributes to the electrical reduction of lithium cations with depolarization. When analyzing the obtained polarization dependences, it was noted that the process of electroreduction of scandium proceeds in one 3-electrode stage, while it is not electrochemically reversible. It has been suggested that the cause of irreversibility is the stage of formation of a new phase. As a result of electrochemical measurements, it was concluded that, due to the wide “electrochemical window”, the LiF–CaF2 melt can be used both for the electrochemical synthesis of scandium and studying regularities of the selective electroreduction or co-electroreduction of minor actinides and lanthanides.

Due to its abundance in nature as well as its properties, silicon is one of the most demanded materials in various industry areas. Currently, metallurgical silicon is obtained by carbothermic reduction of quartz. In order to obtain solar grade silicon, the last should be treated by hydrochlorination and multiple chlorination. This brief review presents an analysis of alternative methods for obtaining silicon by electrolysis of molten salts. The factors that determine the choice of the composition of molten salts, typical silicon deposits obtained by electrolysis of molten salts are shown. An assessment of the results and prospects for further use of electrodeposited silicon in lithium-ion power sources and representative test results on the use of electrolytic silicon for solar energy conversion devices were presented. The problems that need to be solved for the practical implementation of methods for the electrolytic production of silicon samples suitable for new devices and materials for energy conversion and storage are noted.

The development of methods for producing silicon and materials based on it with controllable morphology and composition of microimpurities is a challenging problem, since such materials are widely used in modern microelectronics and power engineering. In this work, the influence of the substrate material and the parameters of silicon electrodeposition from a low-melting low-fluoride LiCl–KCl–CsCl melt with a K 2 SiF 6 addition at a temperature of 545°C on the morphology of the deposit is studied. To determine the range of electrodeposition parameters, the regularities in the cathodic process in this melt are studied on glassy carbon, molybdenum, and nickel using cyclic voltammetry and square-wave voltammetry. This process is shown not to be electrochemically reversible on all the substrates and to proceed in two stages. Varying the electrodeposition parameters, three silicon deposits are formed for each of the substrates. On glassy carbon, a silicon film in the form of spherical dendrites uniformly distributed over the electrode surface and silicon fibers are deposited depending on the electrodeposition conditions. On molybdenum, silicon is deposited in the form of ordered dendrites, fibers, and a continuous coating consisting of spherical particles, as in the case of glassy carbon, depending on the electrolysis conditions. On nickel electrodes, nickel silicides and also silicon dendrites and fibers are deposited.

Silicon and silicon-based materials find extensive applications in metallurgy, microelectronics, and other emerging industries. The field of use of synthesized silicon varies based on its morphology and purity. This study employs voltammetry, galvanostatic electrolysis, and scanning electron microscopy to examine the impact of KI surfactant (in mol %) to 66.5KF–33.3KCl–0.23K2SiF6 melt at 750°C on the electrowinning kinetics of silicon ions and the morphology of silicon deposits formed on a glassy carbon electrode. The findings demonstrate that the addition of potassium iodide to the KF–KCl–K2SiF6 melt at a concentration of 2 mol % induces changes in interfacial tension at the boundary between the glassy carbon, melt, and atmosphere. Consequently, the wetting of the glassy carbon with the melt decreases, leading to a reduction in the actual working surface area and, consequently, a decrease in cathode current while maintaining current density. Taking into account this effect and employing an algebraic estimation of the influence of the melt meniscus shape, it is postulated that the addition of KI does not significantly affect the kinetics of the cathode process. Nevertheless, the impact of KI addition on the morphology of electrodeposited silicon is mentioned. During the electrolysis of the KF–KCl–K2SiF6 melt, fibrous silicon deposits with arbitrary shapes are formed on the glassy carbon electrode, whereas the addition of 2 and 4 mol % of potassium iodide to the melt leads to the agglomeration and smoothing of silicon deposits under the same electrolysis conditions (cathode current density: 0.02 A/cm2, electrolysis duration: 2 h). The obtained results indicate the potential to manipulate the morphology of electrodeposited silicon for specific applications in various fields.

Silicon and silicon-based materials find extensive applications in metallurgy, microelectronics, and other emerging industries. The field of use of synthesized silicon varies based on its morphology and purity. This study employs voltammetry, galvanostatic electrolysis, and scanning electron microscopy to examine the impact of KI surfactant (in mol %) to 66.5KF–33.3KCl–0.23K 2 SiF 6 melt at 750°C on the electrowinning kinetics of silicon ions and the morphology of silicon deposits formed on a glassy carbon electrode. The findings demonstrate that the addition of potassium iodide to the KF–KCl–K 2 SiF 6 melt at a concentration of 2 mol % induces changes in interfacial tension at the boundary between the glassy carbon, melt, and atmosphere. Consequently, the wetting of the glassy carbon with the melt decreases, leading to a reduction in the actual working surface area and, consequently, a decrease in cathode current while maintaining current density. Taking into account this effect and employing an algebraic estimation of the influence of the melt meniscus shape, it is postulated that the addition of KI does not significantly affect the kinetics of the cathode process. Nevertheless, the impact of KI addition on the morphology of electrodeposited silicon is mentioned. During the electrolysis of the KF–KCl–K 2 SiF 6 melt, fibrous silicon deposits with arbitrary shapes are formed on the glassy carbon electrode, whereas the addition of 2 and 4 mol % of potassium iodide to the melt leads to the agglomeration and smoothing of silicon deposits under the same electrolysis conditions (cathode current density: 0.02 A/cm 2 , electrolysis duration: 2 h). The obtained results indicate the potential to manipulate the morphology of electrodeposited silicon for specific applications in various fields.

Zirconium is one of the widely demanded materials, while the existing methods of its production are multistage and energy-intensive. The paper proposes a method for extracting zirconium from its oxide by electrolysis of low-temperature oxide-fluoride melt KF–AlF 3 –Al 2 O 3 –ZrO 2 with a temperature of 750°C. For this purpose, the potentials for the electroreduction of zirconium and aluminum ions on a glassy carbon electrode have been determined by means of voltammetric methods. It was shown that the electroreduction of aluminum ions in the KF–AlF 3 –Al 2 O 3 melt occurs at a potential more negative than –0.05 V relative to the aluminum electrode with the formation of a cathode peak in the potential range from –0.18 to –0.2 V. With the addition of 1 wt % of ZrO 2 , cathode current on the voltammogram begins at a potential more negative than 0 V, and the cathode peak is formed at a potential of about –0.1 V. Similar results were observed in the study of the cathode process in the KF–AlF 3 –Al 2 O 3 melt with and without the addition of ZrO 2 by means of square-wave voltammetry. It has been suggested that, because of the lower bond energy, zirconium-containing electroactive ions are discharged at a potential that is 0.05–0.08 V more positive than the discharge potential of aluminum-containing ions. At a graphite cathode potential of –0.1 and –0.3 V relative to the aluminum electrode, the electrolysis of the KF–AlF 3 –Al 2 O 3 –ZrO 2 melt was carried out, and the elemental and phase composition of the obtained deposits was determined by X-ray phase analysis, scanning electron microscopy, and energy dispersive microanalysis. It was shown that, at a potential of –0.1 V, a deposit with 98.5–99.5 wt % zirconium can be obtained. This indicates a reliable possibility of selective extraction of zirconium by the proposed method.

An installation for purifying alkali-metal chlorides, by means of zone recrystallization, for use in the basic operations of the pyrochemical processing of spent fuel from fast reactors is considered. The main technological operations for purifying chlorides at the proposed installation, which contains units for preparation, primary remelting, zone recrystallization, and packaging of finished salts, are described. The installation allows alkali-metal chlorides to be obtained very efficiently and with the lowest possible content of oxygen-containing impurities because all purification operations are performed in a way where the salt to be purified does not come into contact with a humid atmosphere. By way of an example, experimental confirmation was obtained for the purification of 100 kg lithium chloride and the optimal parameters for the purification of the salt were determined.

Abstract—Silicon and its composites are widely used to manufacture new electrochemical devices for energy conversion and storage. Current research is being actively conducted and aimed at developing methods for the preparation of micro- and nanosized silicon from molten salts. Therefore, the basic regularities of silicon electrodeposition on glassy carbon from the KCl–CsCl–K2SiF6 melt at a temperature of 690°C are studied by cyclic chronovoltammetry and square-wave voltammetry. The electroreduction of silicon ions on glassy carbon under experimental conditions is shown to proceed in one electrochemically reversible four-electron stage. The formal kinetic parameters of the electroreduction of silicon ions under the nonstationary polarization conditions are determined. The diffusion coefficient of electroactive silicon ions is estimated by the Berzins–Delahay equation for an electrochemically reversible process and is equal to 2.75 × 10–5 cm2/s. Silicon is electrodeposited on glassy carbon in the galvanostatic mode at a cathodic current density of 25 and 50 mA/cm2. As a result, deposits of fibrous morphology with the average diameter from 0.12 to 0.80 μm are formed.