Electrochemical Control of Concentration of Silicon Ions During Electrolysis of Molten Electrolytes

Electrochemical Control of Concentration of Silicon Ions During Electrolysis of Molten Electrolytes | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Electrochemical Control of Concentration of Silicon Ions During Electrolysis of Molten Electrolytes Yulia Parasotchenko, Timofey Gevel, Andrey Suzdaltsev This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7360717/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Silicon and silicon-based materials are increasingly used, as this element is in demand in microelectronics, solar energy, as well as in lithium-ion batteries with improved anode capacity. To obtain silicon of the required morphology and dimensions, electrodeposition methods are promising. At the same time, in order to meet the requirements, electrodeposition should be performed at a stable concentration of silicon ions in electrolytes. In the present work possible ways are briefly discussed, and a method of electrochemical control of concentration of silicon ions during electrolysis of melts based on mixtures of LiCl, KCl, CsCl with the addition of K 2 SiF 6 in the range of operating temperatures from 550 to 790°C is proposed and tested. For three electrolyte compositions, empirical dependences of the current density of the electroreduction peak current of silicon ions as a function of their concentration in the melts were plotted using spectral analysis, voltametric measurements, and an electrochemical sensor. Based on the obtained dependences, the possibility of online control of silicon ion concentration during electrolysis of KCl-K 2 SiF 6 melt was demonstrated. electrochemical control voltametric sensor electrolysis silicon molten electrolyte voltammetry concentration Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Molten salts have a wide range of applications for the preparation of metals, alloys, and compounds by chemical and electrochemical synthesis [ 1 – 3 ]. For electrochemical methods, control and maintenance of a stable concentration of electroactive ions is important, since it affects both the technical and economic parameters of electrolysis and the quality of the product [ 4 – 6 ]. In a number of cases this problem has been safely solved in laboratory and industrial scales, while for some processes the relevance of developing methods and devices for controlling concentration of electroactive ions remains. In particular, this applies to silicon production by electrolysis of molten salts, which have a number of advantages in comparison with the traditional scheme of silicon production. Methods of silicon production are characterized by lower energy consumption and the possibility to obtain silicon with the required morphology (ingots, tubes, films, fibers) particle size (from nanoscale objects), as well as the content of functional micro-impurities in one or two stages [ 7 – 10 ]. However, the full realization of these advantages requires the organization of the process with the control of parameters of electrolysis of molten salts with silicon-containing additive. One of the most important parameters is the concentration of silicon-containing ions in the molten electrolyte, the stability of the value of which ensures the production of precipitates of the required size and morphology. To date, the main studies have focused on the electrodeposition of silicon from molten electrolytes based on the systems KF-KCl-K 2 SiF 6 [ 10 – 12 ] and CaCl 2 -CaO-SiO 2 [ 9 , 13 , 14 ]. Electrodeposition of silicon from ionic liquids and organic electrolytes can be considered as a separate promising direction [ 15 ]. Since each of these electrolytes has disadvantages, we have proposed methods of electrodeposition of silicon from melts based on mixtures of LiCl, KCl, CsCl with educed fluorine ion content [ 16 – 18 ]. Depending on the melt composition, the source of silicon can be metallurgical silicon (during electrorefining), K 2 SiF 6 , SiO 2 , and SiCl 4 (during electroextraction). From the analysis of literature data, it can be noted that many works are devoted to the study of electrodeposition patterns and electrolytic production of silicon. However, the stability and control of silicon ion concentration is practically not considered, except for a limited number of works [ 19 , 20 ]. According to [ 19 ], the concentration of silicon ions can decrease in fluoride melts due to thermal decomposition of K 2 SiF 6 , and the ionic composition of complex electroactive silicon ions can change when SiO 2 appears in the melt [ 20 ]. From the above, it can be assumed that more attention should be paid to the study of the stability of silicon ion concentration and ionic composition of molten salts with additions of silicon compounds. At the same time, for our proposed chloride melts the situation may be more critical due to the lower complexing ability [ 21 ]. The purpose of this work was to apply an electrochemical method for determining the concentration of silicon ions to the concentration of silicon ions directly during the electrodeposition of silicon. For this we briefly discuss possible variants, propose and test the method of electrochemical control of silicon ion concentration during electrolysis of molten salts. There are quite a lot of methods for controlling electrochemical processes, among which the simplest, fastest and quite accurate are methods using electrochemical sensors [ 22 – 26 ]. The principle of such devices is based on the registration of some signal (current, potential, etc.) in the investigated molten electrolyte, the value of which depends on the concentration of electroactive ions. Thus, potentiometric sensor (or reference electrode) function according to the concentration of electroactive ions or partial pressure of gases according to the Nernst equation [ 26 , 27 ], and amperometric sensor register the magnitude of current related to the concentration of electroactive ions by one of the known expressions of electrochemical kinetics [ 27 ]. In molten electrolytes, when studying kinetics and electrodeposition of silicon, rods made of platinum, glass carbon (quasi-electrodes of comparison) or silicon are usually used as potentiometric sensors. On platinum and glass-carbon will realize the redox potential of the electrolyte under study, which is extremely sensitive to impurities. On the other hand, silicon in silicon-containing molten electrolytes can undergo dissolution by the disproportionation reaction Si 4+ + Si 0 = 2Si 2+ . This means that the sensor potential of these materials can be determined with high error. Gas chlorine electrodes [ 28 ] and metal reference electrodes [ 29 ] appear to be excellent options for monitoring silicon concentration from a thermodynamic point of view. However, the sensor designs for these electrodes are challenging for practical and widespread use. Electrochemical sensors that fix the value of critical or peak current of reduction or oxidation of electroactive ions are seems more simpler for practical application. Thus, a method of determining and controlling concentration of electroactive ions in the electrolytic production of aluminum using a voltametric sensor was tested on an industrial scale [ 30 ]. The principle of operation of such a sensor includes the construction of an empirical dependence of the peak current of the voltametric dependence on a reliably known concentration of electroactive ions in the melt [ 3 , 5 , 30 , 31 ]. Subsequently, the obtained empirical dependence is used for online nondestructive control of the concentration of electroactive ions using an electrochemical sensor. A similar technique was chosen to control the concentration of silicon ions in the present work. Although the method and techniques for its use are well-known, they have not previously been used to analyze and control the concentration of silicon ions in molten salts. Experimental The studies were carried out in molten electrolytes based on mixtures of LiCl, KCl, CsCl with K 2 SiF 6 addition in the range of operating temperatures from 550 to 790°C (mol%): 1) 58.4CsCl-25.1LiCl-16.5KCl, 550°C; 2) 83.5CsCl-16.5KCl, 660°C; 3) 100.0KCl, 790°C. Monitoring concentration of silicon ions in molten chloride electrolytes with a reduced content of fluorine ions is very relevant, since it seems that the stability of silicon-containing ions in them is lower than in fluoride and fluoride-chloride electrolytes. Nevertheless, the determination of the concentration of silicon-containing ions in other electrolytes also seems to be an interesting study that can be performed in the future. Electrolytes were prepared from individual chlorides with purity above 99.0 wt%. The salts were dried, remelted, and recrystallized via zone recrystallization method to purify them from residual impurities. After preparation, all salts were transferred to a sealed glove box with argon atmosphere, mixed in the required ratio and melted in a glass-carbon container with a capacity of up to 500 g of electrolyte. K 2 SiF 6 was purified from impurities by hydrofluorination [ 32 ], stored in a glove box and added to the studied melts after melting of electrolyte. To obtain an empirical dependence, voltammetry was used to record voltammetry at different concentrations of silicon ions in the studied melts. The polarization of the sensor was carried out both in the cathodic and anodic regions in order to dissolve the precipitate appearing on the sensor surface. A potential sweep rate of 0.1 V s − 1 was chosen for fixation. When sweep speed is decreased, the probability of cathode sediment formation on the sensor surface increases, which significantly changed actual surface. In parallel, a melt sample was taken for spectral analysis of silicon content in it. Electrochemical measurements were carried out using PGSTAT AutoLab 302N (MetrOhm, Netherlands) in a three-electrode cell, schematically presented in Fig. 1 . The working electrode was an electrochemical (voltametric) sensor represented by a glassy carbon rod with a fixed surface. To fix the surface, the rod was placed in a pyrolytic boron nitride tube as shown in Fig. 1 . After each series of measurements, the working surface of the electrode was renewed by grinding. In the electrochemical measurements, polycrystalline silicon (99.95%) was used both as a counter and quasi-reference electrode. Subsequently, all electrodes can be placed in one compact device [ 30 ]. The silicon content in electrolyte samples was carried out by ICP-AES method using Plasma 3000 atomic emission spectrometer (NCS, China). For this purpose, samples of heated melt were taken, cooled, taken out of the glove box, and immediately dissolved in a mixture of concentrated nitric and hydrofluoric acids. After complete dissolution of the sample, the solution was brought to a volume of 50 ml with distilled/deionized water. A series of solutions with different concentrations of the elements to be determined was used to construct the calibration characteristic. The series of solutions was usually prepared by dilution of the standard silicon-containing solution (MES-1, MES-2, “Scat”, Novosibirsk). Results and Discussion Voltametric dependences Figure 2 shows the cathodic regions of the voltametric dependences obtained using electrochemical sensor in the studied melts based on mixtures of LiCl, KCl, CsCl with the addition of K 2 SiF 6 in the range of operating temperatures from 550 to 790°C. On all dependences cathodic peaks were observed, and with increasing concentration of silicon ions in the melts the peak currents increased. This indicates the possibility of constructing empirical dependences of peak current density on the concentration of silicon ions in electrolytes. From the presented voltametric dependences, it can be noted that in addition to the main process of silicon ion discharge, there is a discharge of alkali metal ions (potassium) at potentials negative to the main peak potential. Moreover, with the increase of KCl share in the electrolyte the influence of alkali metal ions discharge on the kinetics of the cathodic process becomes more significant. In spite of this, the investigated sensor responds to the change in the concentration of silicon ions, which is more important. Empirical dependences j p - C The peak current densities obtained from the voltammetric dependences for melts with different composition and concentration of silicon ions were used to construct empirical dependences j p - C , which are summarized in Fig. 3 . From them it can be seen that the current densities of the electroreduction peak currents of silicon ions depend almost linearly on their concentration in the studied melts. The dependences cross the origin of coordinates or the current density axis at a value not higher than − 0.015 A cm − 2 (which is associated with side processes). The mean square deviation was above 99%. The error in determining concentration of silicon ions in the studied melts by five parallel measurements was 0.02×10 − 4 mol cm − 3 , which does not exceed 10% of the absolute measured values. Workability of the sensor during electrolysis Based on the obtained results, it follows that the selected method and its implementation allow controlling silicon concentration in the studied melts directly during their electrolysis (in the region of the studied concentration values). This position was verified in the process of electrodeposition of silicon from KCl-K 2 SiF 6 melt using soluble silicon anode and insoluble graphite anode at cathodic current density of 50 mA cm − 2 and initial content of 5 wt% K 2 SiF 6 . During electrolysis, the potential of the graphite working electrode was measured relative to a silicon quasi-reference electrode. Periodically the electrolysis was stopped and the voltametric dependences were recorded, from which the current density of the silicon ion reduction peak was determined. Melt samples for determining concentration of silicon ions in it were taken only before and after electrolysis. Figure 4 shows the time dependence of the working electrode potential change during electrolysis of KCl melt with the addition of 5 wt% K 2 SiF 6 at a cathodic current density of 50 mA cm − 2 . Expectedly, when the soluble anode was used, the working electrode potential was stable and was about − 0.07 V, while when the graphite anode was used, the working electrode potential gradually shifted to the region of negative values from − 0.08 to -0.28 V, then abruptly to the region of -0.38 V. In the first case, this indicates a stable concentration of silicon ions in the melt, while in the second case it indicates a decrease in the concentration of silicon ions and the beginning of potassium release. This is confirmed by the results of silicon ion concentration measurement by electrochemical sensor and spectral analysis, shown in Fig. 5 . So, the possibility of determining silicon concentration was shown using voltametric sensor. In the case of electrolysis with a soluble anode concentration remained almost constant, while with the graphite anode, the concentration of silicon ions decreased to a certain value, after which potassium began to be released. Apparently, the residual silicon ion concentration is due to the partial dissolution of silicon from the quasi-reference electrode. Although the results indicate that it is fundamentally possible to control the silicon ion concentration during electrodeposition, it should be noted that: - individual empirical dependence j p - C is required for each specific sensor and system under study; - when oxygen-containing ions and other impurities appear in the melt, the dependence may be more complicated than linear; - when varying composition of the investigated melt, an individual choice of the material shielding working surface of the sensor is necessary. Consequently, further work can be aimed at clarifying and expanding the data on the method of application of the voltametric sensor, as well as at studying possibility of its application for studying interaction of silicon and its compounds with halide melts. Conclusion In this work we propose a method of controlling concentration of electroactive silicon-containing ions in molten salts during electrodeposition of silicon of the required morphology and size. The method includes the obtaining empirical dependence of the current density of the electroreduction peak of silicon ions depending on their concentration in the melt under study. The proposed method is experimentally tested in melts based on mixtures of LiCl, KCl, CsCl with different content of K 2 SiF 6 in the temperature range from 550 to 790°C. Sets of voltametric dependences at different K 2 SiF 6 content in the melts were obtained for the investigated melt compositions in a series of measurements. From them empirical dependences of current density of the peak electroreduction peak of silicon ions on their concentration were obtained, which for the studied systems are close to linear. Using obtained empirical dependences, the principal possibility of online control of silicon ion concentration during its electrodeposition from KCl-K 2 SiF 6 melt using soluble silicon and insoluble graphite anode has been demonstrated. The ways of research development in this direction are defined. Declarations Acknowledgments This work was carried out in the frame of the agreement No. 075-03-2025-258 dated 17.01.2025 (theme number FEUZ-2025-0002). Funding None. Data Availability The authors declare that the data supporting the fundings of this study are available within the article and its supplementary information are available by request. Declarations Competing Interests The authors declare no competing interests. Ethical Approval Not Applicable. Consent for Publications All the authors of the manuscript mutually agree on submission and publication in the journal. Consent to Participate All the authors contributed to the work and revised the manuscript. Conflict of Interest The authors declare that they have no known competing fnancial interests or personal relationships that could have appeared to infuence the work reported in this paper References Kushkhov KB, Tlenkopachev MR (2021) Electrochemical synthesis of intermetallic and refractory compounds based on rare-earth metals in ionic melts: achievements and prospects, Rus. J. Gen. Chem. 91:251–272. https://doi.org/10.1134/S1070363221020146. Zaikov YuP, Batukhtin VP, Shurov NI, Suzdaltsev AV (2022) High-temperature electrochemistry of calcium, Electrochem. Mater. Technol. 1:20221007. https://doi.org/10.15826/elmattech.2022.1.007. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7360717","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":501179584,"identity":"cbbdd755-c1a9-4b8d-86eb-f7fdb70acce2","order_by":0,"name":"Yulia Parasotchenko","email":"","orcid":"","institution":"Ural Federal University","correspondingAuthor":false,"prefix":"","firstName":"Yulia","middleName":"","lastName":"Parasotchenko","suffix":""},{"id":501179585,"identity":"72e87b64-8ef0-472f-96bb-628919226e85","order_by":1,"name":"Timofey Gevel","email":"","orcid":"","institution":"Ural Federal 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04:38:24","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7360717/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7360717/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":89266307,"identity":"d127aff5-0c15-4836-a1f0-fe3aee2eccb0","added_by":"auto","created_at":"2025-08-18 08:13:54","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":19439,"visible":true,"origin":"","legend":"\u003cp\u003eScheme for the electrochemical measurements and electrolysis\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7360717/v1/5496c99a79e3b60566797e80.png"},{"id":89266305,"identity":"c0bdb3f2-5576-422f-9ead-4ba869c86bee","added_by":"auto","created_at":"2025-08-18 08:13:54","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":71304,"visible":true,"origin":"","legend":"\u003cp\u003eCathodic areas of voltammetric dependences obtained with a voltametric sensor in melts based on mixtures of LiCl, KCl, CsCl with different content of K\u003csub\u003e2\u003c/sub\u003eSiF\u003csub\u003e6\u003c/sub\u003e\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7360717/v1/e71b0b37ac5c8fa2c9124713.png"},{"id":89265574,"identity":"8b831d6c-07e4-44b3-94ce-9b2a9a43314a","added_by":"auto","created_at":"2025-08-18 08:05:54","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":40430,"visible":true,"origin":"","legend":"\u003cp\u003eEmpirical dependences \u003cem\u003ej\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e-\u003cem\u003eC\u003c/em\u003e for melts based on mixtures of LiCl, KCl, CsCl with different K\u003csub\u003e2\u003c/sub\u003eSiF\u003csub\u003e6\u003c/sub\u003e content\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7360717/v1/b85f718ab23efa92288ac66e.png"},{"id":89265576,"identity":"c92e3675-e8f2-48f3-881d-6d73e6f8da99","added_by":"auto","created_at":"2025-08-18 08:05:54","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":25296,"visible":true,"origin":"","legend":"\u003cp\u003eChange of working electrode potential during electrolysis of KCl melt with initial addition of 5 wt% K\u003csub\u003e2\u003c/sub\u003eSiF\u003csub\u003e6\u003c/sub\u003e at cathodic current density of 50 mA cm\u003csup\u003e-2\u003c/sup\u003e and temperature of 790°C\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7360717/v1/b9d57ce515be4f87ec587895.png"},{"id":89266315,"identity":"1d6f4a46-ed43-4694-a914-3a97a8b850b0","added_by":"auto","created_at":"2025-08-18 08:13:57","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":32543,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of peak current and silicon ion concentration according to sensor data (□) and ICP analysis (×) during electrolysis of KCl-K\u003csub\u003e2\u003c/sub\u003eSiF\u003csub\u003e6\u003c/sub\u003e melt at 790°C\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7360717/v1/2062d229c0760c87365d8f5c.png"},{"id":94013939,"identity":"61bc213c-4c50-4b7e-990e-f82e179944a5","added_by":"auto","created_at":"2025-10-21 10:46:37","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":621590,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7360717/v1/71ddcc6b-aafd-41c2-a57a-ccc5db9ec94c.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eElectrochemical Control of Concentration of Silicon Ions During Electrolysis of Molten Electrolytes\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eMolten salts have a wide range of applications for the preparation of metals, alloys, and compounds by chemical and electrochemical synthesis [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. For electrochemical methods, control and maintenance of a stable concentration of electroactive ions is important, since it affects both the technical and economic parameters of electrolysis and the quality of the product [\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. In a number of cases this problem has been safely solved in laboratory and industrial scales, while for some processes the relevance of developing methods and devices for controlling concentration of electroactive ions remains.\u003c/p\u003e\u003cp\u003eIn particular, this applies to silicon production by electrolysis of molten salts, which have a number of advantages in comparison with the traditional scheme of silicon production. Methods of silicon production are characterized by lower energy consumption and the possibility to obtain silicon with the required morphology (ingots, tubes, films, fibers) particle size (from nanoscale objects), as well as the content of functional micro-impurities in one or two stages [\u003cspan additionalcitationids=\"CR8 CR9\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. However, the full realization of these advantages requires the organization of the process with the control of parameters of electrolysis of molten salts with silicon-containing additive. One of the most important parameters is the concentration of silicon-containing ions in the molten electrolyte, the stability of the value of which ensures the production of precipitates of the required size and morphology.\u003c/p\u003e\u003cp\u003eTo date, the main studies have focused on the electrodeposition of silicon from molten electrolytes based on the systems KF-KCl-K\u003csub\u003e2\u003c/sub\u003eSiF\u003csub\u003e6\u003c/sub\u003e [\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] and CaCl\u003csub\u003e2\u003c/sub\u003e-CaO-SiO\u003csub\u003e2\u003c/sub\u003e [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Electrodeposition of silicon from ionic liquids and organic electrolytes can be considered as a separate promising direction [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Since each of these electrolytes has disadvantages, we have proposed methods of electrodeposition of silicon from melts based on mixtures of LiCl, KCl, CsCl with educed fluorine ion content [\u003cspan additionalcitationids=\"CR17\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Depending on the melt composition, the source of silicon can be metallurgical silicon (during electrorefining), K\u003csub\u003e2\u003c/sub\u003eSiF\u003csub\u003e6\u003c/sub\u003e, SiO\u003csub\u003e2\u003c/sub\u003e, and SiCl\u003csub\u003e4\u003c/sub\u003e (during electroextraction).\u003c/p\u003e\u003cp\u003eFrom the analysis of literature data, it can be noted that many works are devoted to the study of electrodeposition patterns and electrolytic production of silicon. However, the stability and control of silicon ion concentration is practically not considered, except for a limited number of works [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. According to [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], the concentration of silicon ions can decrease in fluoride melts due to thermal decomposition of K\u003csub\u003e2\u003c/sub\u003eSiF\u003csub\u003e6\u003c/sub\u003e, and the ionic composition of complex electroactive silicon ions can change when SiO\u003csub\u003e2\u003c/sub\u003e appears in the melt [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eFrom the above, it can be assumed that more attention should be paid to the study of the stability of silicon ion concentration and ionic composition of molten salts with additions of silicon compounds. At the same time, for our proposed chloride melts the situation may be more critical due to the lower complexing ability [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe purpose of this work was to apply an electrochemical method for determining the concentration of silicon ions to the concentration of silicon ions directly during the electrodeposition of silicon. For this we briefly discuss possible variants, propose and test the method of electrochemical control of silicon ion concentration during electrolysis of molten salts.\u003c/p\u003e\u003cp\u003eThere are quite a lot of methods for controlling electrochemical processes, among which the simplest, fastest and quite accurate are methods using electrochemical sensors [\u003cspan additionalcitationids=\"CR23 CR24 CR25\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. The principle of such devices is based on the registration of some signal (current, potential, etc.) in the investigated molten electrolyte, the value of which depends on the concentration of electroactive ions. Thus, potentiometric sensor (or reference electrode) function according to the concentration of electroactive ions or partial pressure of gases according to the Nernst equation [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], and amperometric sensor register the magnitude of current related to the concentration of electroactive ions by one of the known expressions of electrochemical kinetics [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn molten electrolytes, when studying kinetics and electrodeposition of silicon, rods made of platinum, glass carbon (quasi-electrodes of comparison) or silicon are usually used as potentiometric sensors. On platinum and glass-carbon will realize the redox potential of the electrolyte under study, which is extremely sensitive to impurities. On the other hand, silicon in silicon-containing molten electrolytes can undergo dissolution by the disproportionation reaction Si\u003csup\u003e4+\u003c/sup\u003e + Si\u003csup\u003e0\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;2Si\u003csup\u003e2+\u003c/sup\u003e. This means that the sensor potential of these materials can be determined with high error. Gas chlorine electrodes [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] and metal reference electrodes [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e] appear to be excellent options for monitoring silicon concentration from a thermodynamic point of view. However, the sensor designs for these electrodes are challenging for practical and widespread use.\u003c/p\u003e\u003cp\u003eElectrochemical sensors that fix the value of critical or peak current of reduction or oxidation of electroactive ions are seems more simpler for practical application. Thus, a method of determining and controlling concentration of electroactive ions in the electrolytic production of aluminum using a voltametric sensor was tested on an industrial scale [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. The principle of operation of such a sensor includes the construction of an empirical dependence of the peak current of the voltametric dependence on a reliably known concentration of electroactive ions in the melt [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. Subsequently, the obtained empirical dependence is used for online nondestructive control of the concentration of electroactive ions using an electrochemical sensor. A similar technique was chosen to control the concentration of silicon ions in the present work. Although the method and techniques for its use are well-known, they have not previously been used to analyze and control the concentration of silicon ions in molten salts.\u003c/p\u003e"},{"header":"Experimental","content":"\u003cp\u003eThe studies were carried out in molten electrolytes based on mixtures of LiCl, KCl, CsCl with K\u003csub\u003e2\u003c/sub\u003eSiF\u003csub\u003e6\u003c/sub\u003e addition in the range of operating temperatures from 550 to 790\u0026deg;C (mol%):\u003c/p\u003e\u003cp\u003e1) 58.4CsCl-25.1LiCl-16.5KCl, 550\u0026deg;C;\u003c/p\u003e\u003cp\u003e2) 83.5CsCl-16.5KCl, 660\u0026deg;C;\u003c/p\u003e\u003cp\u003e3) 100.0KCl, 790\u0026deg;C.\u003c/p\u003e\u003cp\u003eMonitoring concentration of silicon ions in molten chloride electrolytes with a reduced content of fluorine ions is very relevant, since it seems that the stability of silicon-containing ions in them is lower than in fluoride and fluoride-chloride electrolytes. Nevertheless, the determination of the concentration of silicon-containing ions in other electrolytes also seems to be an interesting study that can be performed in the future. Electrolytes were prepared from individual chlorides with purity above 99.0 wt%. The salts were dried, remelted, and recrystallized via zone recrystallization method to purify them from residual impurities. After preparation, all salts were transferred to a sealed glove box with argon atmosphere, mixed in the required ratio and melted in a glass-carbon container with a capacity of up to 500 g of electrolyte. K\u003csub\u003e2\u003c/sub\u003eSiF\u003csub\u003e6\u003c/sub\u003e was purified from impurities by hydrofluorination [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e], stored in a glove box and added to the studied melts after melting of electrolyte.\u003c/p\u003e\u003cp\u003eTo obtain an empirical dependence, voltammetry was used to record voltammetry at different concentrations of silicon ions in the studied melts. The polarization of the sensor was carried out both in the cathodic and anodic regions in order to dissolve the precipitate appearing on the sensor surface. A potential sweep rate of 0.1 V s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was chosen for fixation. When sweep speed is decreased, the probability of cathode sediment formation on the sensor surface increases, which significantly changed actual surface. In parallel, a melt sample was taken for spectral analysis of silicon content in it.\u003c/p\u003e\u003cp\u003eElectrochemical measurements were carried out using PGSTAT AutoLab 302N (MetrOhm, Netherlands) in a three-electrode cell, schematically presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The working electrode was an electrochemical (voltametric) sensor represented by a glassy carbon rod with a fixed surface. To fix the surface, the rod was placed in a pyrolytic boron nitride tube as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. After each series of measurements, the working surface of the electrode was renewed by grinding.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn the electrochemical measurements, polycrystalline silicon (99.95%) was used both as a counter and quasi-reference electrode. Subsequently, all electrodes can be placed in one compact device [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe silicon content in electrolyte samples was carried out by ICP-AES method using Plasma 3000 atomic emission spectrometer (NCS, China). For this purpose, samples of heated melt were taken, cooled, taken out of the glove box, and immediately dissolved in a mixture of concentrated nitric and hydrofluoric acids. After complete dissolution of the sample, the solution was brought to a volume of 50 ml with distilled/deionized water. A series of solutions with different concentrations of the elements to be determined was used to construct the calibration characteristic. The series of solutions was usually prepared by dilution of the standard silicon-containing solution (MES-1, MES-2, \u0026ldquo;Scat\u0026rdquo;, Novosibirsk).\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003eVoltametric dependences\u003c/h2\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e shows the cathodic regions of the voltametric dependences obtained using electrochemical sensor in the studied melts based on mixtures of LiCl, KCl, CsCl with the addition of K\u003csub\u003e2\u003c/sub\u003eSiF\u003csub\u003e6\u003c/sub\u003e in the range of operating temperatures from 550 to 790\u0026deg;C. On all dependences cathodic peaks were observed, and with increasing concentration of silicon ions in the melts the peak currents increased. This indicates the possibility of constructing empirical dependences of peak current density on the concentration of silicon ions in electrolytes. From the presented voltametric dependences, it can be noted that in addition to the main process of silicon ion discharge, there is a discharge of alkali metal ions (potassium) at potentials negative to the main peak potential. Moreover, with the increase of KCl share in the electrolyte the influence of alkali metal ions discharge on the kinetics of the cathodic process becomes more significant. In spite of this, the investigated sensor responds to the change in the concentration of silicon ions, which is more important.\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eEmpirical dependences\u003c/strong\u003e \u003cstrong\u003ej\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003ep\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003eThe peak current densities obtained from the voltammetric dependences for melts with different composition and concentration of silicon ions were used to construct empirical dependences \u003cem\u003ej\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e-\u003cem\u003eC\u003c/em\u003e, which are summarized in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. From them it can be seen that the current densities of the electroreduction peak currents of silicon ions depend almost linearly on their concentration in the studied melts. The dependences cross the origin of coordinates or the current density axis at a value not higher than \u0026minus;\u0026thinsp;0.015 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (which is associated with side processes). The mean square deviation was above 99%. The error in determining concentration of silicon ions in the studied melts by five parallel measurements was 0.02\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e mol cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e, which does not exceed 10% of the absolute measured values.\u003c/p\u003e\n\u003c/div\u003e\n\u003ch3\u003eWorkability of the sensor during electrolysis\u003c/h3\u003e\n\u003cp\u003eBased on the obtained results, it follows that the selected method and its implementation allow controlling silicon concentration in the studied melts directly during their electrolysis (in the region of the studied concentration values). This position was verified in the process of electrodeposition of silicon from KCl-K\u003csub\u003e2\u003c/sub\u003eSiF\u003csub\u003e6\u003c/sub\u003e melt using soluble silicon anode and insoluble graphite anode at cathodic current density of 50 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and initial content of 5 wt% K\u003csub\u003e2\u003c/sub\u003eSiF\u003csub\u003e6\u003c/sub\u003e. During electrolysis, the potential of the graphite working electrode was measured relative to a silicon quasi-reference electrode. Periodically the electrolysis was stopped and the voltametric dependences were recorded, from which the current density of the silicon ion reduction peak was determined. Melt samples for determining concentration of silicon ions in it were taken only before and after electrolysis.\u003c/p\u003e\n\u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e shows the time dependence of the working electrode potential change during electrolysis of KCl melt with the addition of 5 wt% K\u003csub\u003e2\u003c/sub\u003eSiF\u003csub\u003e6\u003c/sub\u003e at a cathodic current density of 50 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. Expectedly, when the soluble anode was used, the working electrode potential was stable and was about \u0026minus;\u0026thinsp;0.07 V, while when the graphite anode was used, the working electrode potential gradually shifted to the region of negative values from \u0026minus;\u0026thinsp;0.08 to -0.28 V, then abruptly to the region of -0.38 V. In the first case, this indicates a stable concentration of silicon ions in the melt, while in the second case it indicates a decrease in the concentration of silicon ions and the beginning of potassium release. This is confirmed by the results of silicon ion concentration measurement by electrochemical sensor and spectral analysis, shown in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003eSo, the possibility of determining silicon concentration was shown using voltametric sensor. In the case of electrolysis with a soluble anode concentration remained almost constant, while with the graphite anode, the concentration of silicon ions decreased to a certain value, after which potassium began to be released. Apparently, the residual silicon ion concentration is due to the partial dissolution of silicon from the quasi-reference electrode.\u003c/p\u003e\n\u003cp\u003eAlthough the results indicate that it is fundamentally possible to control the silicon ion concentration during electrodeposition, it should be noted that:\u003c/p\u003e\n\u003cp\u003e- individual empirical dependence \u003cem\u003ej\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e-\u003cem\u003eC\u003c/em\u003e is required for each specific sensor and system under study;\u003c/p\u003e\n\u003cp\u003e- when oxygen-containing ions and other impurities appear in the melt, the dependence may be more complicated than linear;\u003c/p\u003e\n\u003cp\u003e- when varying composition of the investigated melt, an individual choice of the material shielding working surface of the sensor is necessary.\u003c/p\u003e\n\u003cp\u003eConsequently, further work can be aimed at clarifying and expanding the data on the method of application of the voltametric sensor, as well as at studying possibility of its application for studying interaction of silicon and its compounds with halide melts.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn this work we propose a method of controlling concentration of electroactive silicon-containing ions in molten salts during electrodeposition of silicon of the required morphology and size. The method includes the obtaining empirical dependence of the current density of the electroreduction peak of silicon ions depending on their concentration in the melt under study.\u003c/p\u003e\u003cp\u003eThe proposed method is experimentally tested in melts based on mixtures of LiCl, KCl, CsCl with different content of K\u003csub\u003e2\u003c/sub\u003eSiF\u003csub\u003e6\u003c/sub\u003e in the temperature range from 550 to 790\u0026deg;C. Sets of voltametric dependences at different K\u003csub\u003e2\u003c/sub\u003eSiF\u003csub\u003e6\u003c/sub\u003e content in the melts were obtained for the investigated melt compositions in a series of measurements. From them empirical dependences of current density of the peak electroreduction peak of silicon ions on their concentration were obtained, which for the studied systems are close to linear.\u003c/p\u003e\u003cp\u003eUsing obtained empirical dependences, the principal possibility of online control of silicon ion concentration during its electrodeposition from KCl-K\u003csub\u003e2\u003c/sub\u003eSiF\u003csub\u003e6\u003c/sub\u003e melt using soluble silicon and insoluble graphite anode has been demonstrated. The ways of research development in this direction are defined.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was carried out in the frame of the agreement No. 075-03-2025-258 dated 17.01.2025 (theme number FEUZ-2025-0002).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNone.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that the data supporting the fundings of this study are available within the article and its supplementary information are available by request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclarations Competing Interests\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical Approval\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot Applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for Publications\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll the authors of the manuscript mutually agree on submission and publication in the journal.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Participate\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll the authors contributed to the work and revised the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing fnancial interests or personal relationships that could have appeared to infuence the work reported in this paper\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eKushkhov KB, Tlenkopachev MR (2021) Electrochemical synthesis of intermetallic and refractory compounds based on rare-earth metals in ionic melts: achievements and prospects, Rus. 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Soc., 166:D784\u0026ndash;D791. https://doi.org/10.1149/2.0521915jes.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"electrochemical control, voltametric sensor, electrolysis, silicon, molten electrolyte, voltammetry, concentration","lastPublishedDoi":"10.21203/rs.3.rs-7360717/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7360717/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSilicon and silicon-based materials are increasingly used, as this element is in demand in microelectronics, solar energy, as well as in lithium-ion batteries with improved anode capacity. To obtain silicon of the required morphology and dimensions, electrodeposition methods are promising. At the same time, in order to meet the requirements, electrodeposition should be performed at a stable concentration of silicon ions in electrolytes. In the present work possible ways are briefly discussed, and a method of electrochemical control of concentration of silicon ions during electrolysis of melts based on mixtures of LiCl, KCl, CsCl with the addition of K\u003csub\u003e2\u003c/sub\u003eSiF\u003csub\u003e6\u003c/sub\u003e in the range of operating temperatures from 550 to 790\u0026deg;C is proposed and tested. For three electrolyte compositions, empirical dependences of the current density of the electroreduction peak current of silicon ions as a function of their concentration in the melts were plotted using spectral analysis, voltametric measurements, and an electrochemical sensor. Based on the obtained dependences, the possibility of online control of silicon ion concentration during electrolysis of KCl-K\u003csub\u003e2\u003c/sub\u003eSiF\u003csub\u003e6\u003c/sub\u003e melt was demonstrated.\u003c/p\u003e","manuscriptTitle":"Electrochemical Control of Concentration of Silicon Ions During Electrolysis of Molten Electrolytes","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-18 08:05:50","doi":"10.21203/rs.3.rs-7360717/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"314b7d7e-b658-477a-bffb-4322ae864f1a","owner":[],"postedDate":"August 18th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-10-21T10:38:18+00:00","versionOfRecord":[],"versionCreatedAt":"2025-08-18 08:05:50","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7360717","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7360717","identity":"rs-7360717","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}