A method for recovering silicon from silicon tetrachloride, a by-product of the silicon industry, by electrodeposition using a copper-based gallium-indium alloy electrode

Abstract

The present application relates to a method for recovering silicon from silicon industry by-product silicon tetrachloride by using copper-based gallium-indium alloy electrode electro-deposition. The present application dissolves silicon industry by-product containing silicon tetrachloride in a eutectic solvent system to prepare an electrolyte; loads gallium-indium alloy on the surface of a copper substrate to obtain a working electrode of copper-based gallium-indium alloy; uses a three-electrode system to carry out constant potential electro-deposition reaction; washes and peels the electro-deposition product of the working electrode of copper-based gallium-indium alloy to obtain crystalline silicon. The gallium-indium alloy electrode of the present application combines the excellent conductivity and structural stability of the copper substrate, significantly enhances the interface reaction kinetics in the electro-deposition process, realizes high-efficiency reaction at normal pressure and low temperature, and significantly reduces energy consumption and equipment requirements. The present application realizes high-value resource utilization of hazardous waste, and the copper-based gallium-indium alloy electrode can be recycled, which meets the principle of green chemistry.

Description

Technical Field

[0001] This invention relates to the field of high-value resource recovery and electrochemical synthesis technology of industrial by-products, and in particular to a method for recovering elemental silicon from silicon tetrachloride, a by-product of the silicon industry, by electrodeposition using copper-based gallium-indium alloy electrodes. Background Technology

[0002] Silicon tetrachloride (SiCl4) is a major byproduct of the semiconductor industry and polysilicon production. SiCl4 is a colorless, transparent liquid with a strong, pungent odor. It readily hydrolyzes in air, producing hydrogen chloride (HCl) fumes and silicic acid, posing a serious threat to the environment and human health. Furthermore, SiCl4 itself contains valuable silicon and chlorine elements; failure to effectively recycle and utilize these elements would result in enormous resource waste and significantly increase the production cost of polysilicon. Therefore, achieving efficient, economical, and green conversion and resource recovery of SiCl4 is of great practical significance for promoting the sustainable development of the photovoltaic and semiconductor industries.

[0003] In recent years, electrochemical deposition has gradually become a research hotspot for the resource recovery of SiCl4 due to its mild reaction conditions, low energy consumption, and high controllability. This method uses electrical energy to drive the reduction deposition of silicon ions, avoiding the high energy consumption and stringent equipment requirements of traditional high-temperature pyrolysis or hydrogenation reduction processes. However, early electrodeposition studies mostly used pure liquid metal electrodes, especially liquid gallium electrodes, which were widely studied due to their certain solubility for silicon and low reduction potential. But liquid gallium electrodes have obvious limitations in practical applications, such as high fluidity leading to unstable electrode shape, difficulty in constructing regular electrode structures, difficulty in controlling the reaction interface, and difficulty in separating deposition products, which seriously restricts their prospects for industrial application. Summary of the Invention

[0004] To address the technical problems of low recovery efficiency, difficulty in controlling the reaction interface, difficulty in separating deposited products, complex operation, high cost, and safety risks in existing silicon tetrachloride (SiCl4) recovery methods, this invention provides a method for recovering elemental silicon from silicon tetrachloride, a byproduct of the silicon industry, using copper-based gallium-indium alloy electrodes via electrodeposition. The method creatively employs a copper sheet as a substrate, on which a layer of gallium-indium (Ga-In) alloy is constructed through a scraping process. The copper substrate provides excellent conductivity and mechanical support, while the gallium-indium alloy, with its high atomic mobility, self-renewing surface properties, and silicon dissolution ability, acts as a highly active catalytic layer, greatly promoting the reduction reaction of silicon tetrachloride and effectively preventing passivation of the electrode surface caused by solid silicon deposition. This invention achieves direct and efficient electrochemical conversion of SiCl4 to high-purity silicon under near-room temperature and atmospheric pressure conditions, providing a green, low-energy-consumption, and high-value-added new technical route for the resource recovery of SiCl4.

[0005] This invention utilizes silicon tetrachloride dissolved in a eutectic solvent composed of 1,3-dimethyl-2-imidazolinone and 1,3-dimethylurea to form an electrolyte. During electrodeposition, the deposition efficiency of this alloy system on silicon varies significantly with different gallium-indium (GaIn) mass ratios. When the GaIn ratios are 9:1, 8:2, 3:1, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, and 1:9, the current efficiencies of the electrolytic system are approximately 62%, 80%, 92%, 86%, 71%, 50%, 23%, 10%, 0%, and 0%, respectively. Among these, the deposition effect is optimal when the GaIn ratio is 3:1 (i.e., 75% Ga and 25% In), with a peak current efficiency of 92%. This ratio coincides with the lowest eutectic point of the GaIn alloy, which is beneficial for forming a uniform alloy layer and thus enhancing electrocatalytic activity.

[0006] In this invention, the high catalytic activity of the gallium-indium alloy and the suppression of hydrogen evolution side reactions are the two core factors for improving the utilization rate of electrodeposition current. These two factors work synergistically and are indispensable. Their working principle is as follows: Current utilization rate is essentially the proportion of electrons provided by the external circuit used for the target deposition reaction; the direction of electron distribution directly determines the current efficiency. On the one hand, the alloy's high catalytic activity exhibits clear selectivity, its core being a significant enhancement of its catalytic ability for the target deposition reaction. This lowers the activation energy barrier of the target reaction, accelerates the reaction rate, and allows electrons to be efficiently used for the reduction and deposition of metal ions, reducing electron waste. On the other hand, hydrogen evolution side reactions are the main source of current loss. Suppressing hydrogen evolution side reactions (e.g., by introducing indium to increase the alloy's hydrogen evolution overpotential) essentially reduces the alloy's catalytic activity for the hydrogen evolution reaction, reduces the competitiveness of hydrogen ions for electrons, and avoids a large number of electrons being consumed in the hydrogen generation reaction.

[0007] To ensure efficient electrodeposition, this invention optimized the electrodeposition conditions, particularly the voltage selection. Through multiple experiments and cyclic voltammetry (CV) analysis, a significant reduction peak was observed within the voltage range of -4V to 0V. At -1.2V, the deposition rate significantly increased, resulting in ideal silicon deposition. The effect diminished further away from this voltage range. This invention ultimately confirmed that the -4V to 0V voltage range is the optimal electrodeposition voltage range, ensuring high purity and stability of the silicon film. During the entire electrodeposition process, silicon ions in the solution are directly deposited on a copper-based gallium-indium alloy electrode, resulting in a uniform and dense silicon film. The film is then scraped off. The entire process is simple and efficient, achieving a highly efficient conversion from silicon tetrachloride to silicon film. The electrodeposition technique deposits crystalline silicon from ionic silicon in solution onto the working electrode in a one-step reaction: , The present invention achieves its objective through the following specific solutions: The purpose of this invention is to provide a method for recovering elemental silicon from silicon tetrachloride, a byproduct of the silicon industry, using copper-based gallium-indium alloy electrodes via electrodeposition, comprising the following steps: An electrolyte was prepared by dissolving silicon industry byproducts containing silicon tetrachloride in a eutectic solvent system. Gallium-indium alloy is loaded onto the surface of a copper substrate to obtain a copper-based gallium-indium alloy working electrode; A constant potential electrodeposition reaction was performed using a three-electrode system. The electrodeposition product of the copper-based gallium-indium alloy working electrode was cleaned and stripped to obtain crystalline silicon.

[0008] In some embodiments of the present invention, the eutectic solvent system comprises 1,3-dimethyl-2-imidazolinone and 1,3-dimethylurea. The present invention uses a eutectic solvent composed of 1,3-dimethyl-2-imidazolinone and 1,3-dimethylurea, thoroughly stirred with silicon tetrachloride to prepare an electrolyte. A copper-based gallium-indium alloy is used as the working electrode. This electrode combines the excellent conductivity and structural stability of the copper substrate with the stability and high catalytic activity of the gallium-indium alloy at room temperature, significantly enhancing the interfacial reaction kinetics during electrodeposition. This achieves highly efficient reactions at ambient pressure and medium-low temperatures, significantly reducing energy consumption and equipment requirements. Simultaneously, the deposit possesses the characteristic structure of crystalline silicon, indicating that this method can effectively achieve silicon deposition and collection.

[0009] In some embodiments of the present invention, the molar ratio of 1,3-dimethyl-2-imidazolinone and 1,3-dimethylurea is 1:1 to 3:1.

[0010] In some embodiments of the present invention, the concentration of silicon tetrachloride in the electrolyte is 0.027–0.081 mol / L.

[0011] In some embodiments of the present invention, the electrolyte is prepared at a temperature of 80~100°C.

[0012] In some embodiments of the present invention, the copper substrate is pretreated by: mechanically polishing the copper sheet with sandpaper, ultrasonically cleaning it in an acid solution for 5-15 minutes to remove surface oxides, increasing its surface roughness, enhancing the stability of the gallium indium alloy coating, rinsing it with deionized water and drying it to obtain a clean and activated copper substrate.

[0013] Furthermore, the acid is selected from one or more of hydrochloric acid and sulfuric acid; In some embodiments of the present invention, the thickness of the gallium indium alloy in the copper-based gallium indium alloy is 0.1~0.3 mm.

[0014] In some embodiments of the present invention, the mass ratio of gallium to indium in the gallium-indium alloy is 8:2 to 7:3. Exemplarily, it can be 9:1, 8:2, 3:1, 7:3, 6:4, 5:5, 4:6, 3:7, or any range between any two values. More preferably, it is 8:2, 3:1, 7:3, or 6:4, or it can be 3:1 to 7:3. The lower eutectic point component within this ratio range is used to coat the gallium-indium alloy onto the surface of the copper substrate to form a firmly bonded gallium-indium alloy layer.

[0015] The gallium-indium alloy is applied to the copper-based surface by a scraping method.

[0016] In some embodiments of the present invention, the temperature of the constant potential electrodeposition reaction is 50~100℃, the working voltage is -4~4V, exemplary values ​​are -4, -3, -2, -1, 0, 1, 2, 3, 4, etc., or any interval value between any two numerical ranges, preferably -4V~0V; the deposition time is 0.5~2h.

[0017] In some embodiments of the present invention, the three-electrode system further includes a counter electrode and an auxiliary electrode; the counter electrode is a graphite electrode, and the auxiliary electrode is a silver / saturated silver chloride electrode.

[0018] In this invention, the electrodeposited product is sequentially subjected to acetone cleaning, cooling crystallization, and ethanol cleaning; wherein, cooling causes the electrolyte on the surface of the working electrode to form crystals, and then ethanol cleaning causes the crystals to fall off.

[0019] In this invention, a scraper is used to scrape off the black substance on the surface of the cleaned working electrode to achieve crystalline silicon extraction.

[0020] This invention employs a copper-based gallium-indium alloy as the working electrode, firmly anchoring the gallium-indium alloy onto the surface of a copper sheet to form a stable composite electrode. The Ga-In alloy loaded on this electrode provides extremely high electrocatalytic activity. The combination of these two elements achieves synergy between a "high-speed conductive channel" and a "highly active catalytic site," significantly reducing the reaction overpotential, accelerating the reduction rate of silicon tetrachloride, and improving current efficiency. This provides a new, green, low-energy-consumption, and high-value-added technological pathway for the resource recovery of SiCl4.

[0021] The technical solution of the present invention has the following advantages compared with the prior art: 1) Improved deposition efficiency: Copper-based gallium-indium alloy electrodes possess the excellent conductivity of copper substrates and the stability and high catalytic activity of gallium-indium alloys at room temperature, which enhances the interfacial reaction kinetics during electrodeposition, resulting in a significant improvement in the deposition efficiency of crystalline silicon.

[0022] 2) Improved electrode stability and lifespan: The formation of fixed electrodes solves the core pain points of unstable shape and difficulty in large-scale production of pure liquid electrodes, and significantly improves electrode lifespan and reusability.

[0023] 3) Significant advantages in cost and practicality: The method of this invention only coats a thin layer of Ga-In alloy on the copper surface, which greatly reduces the amount of precious metals gallium and indium used. While ensuring high performance, it significantly reduces the raw material cost of the electrode, making the technology more industrially viable.

[0024] 4) Further improvement in resource utilization: The entire process is mild, simple, uses readily available raw materials, and has no pollutant emissions, making it suitable for large-scale production. This greatly improves the recovery and reuse rate, fundamentally reducing the environmental pressure caused by its emissions.

[0025] In summary, this invention proposes a method for recovering elemental silicon from silicon tetrachloride, a byproduct of the silicon industry, using a copper-based gallium-indium alloy electrode via electrodeposition, significantly improving silicon deposition efficiency. Compared to the pure liquid gallium electrode used in CN120384314A, the copper-based gallium-indium alloy electrode used in this invention has more prominent structural and catalytic advantages. Its core mechanism lies in the fact that the introduction of indium (In) significantly optimizes the surface electronic structure and interfacial reaction characteristics of the alloy. Indium can effectively increase the hydrogen evolution overpotential of the alloy, suppress the side reaction of hydrogen ion reduction during electrodeposition, reduce current loss, and allow more electrons to be used for the selective reduction of silicon tetrachloride. At the same time, indium can lower the eutectic point of the gallium-indium alloy, enabling it to maintain a uniform and stable liquid surface under medium and low temperature conditions, increasing the dissolution and migration rate of silicon atoms in the alloy, and avoiding passivation caused by rapid coverage of solid silicon on the electrode surface. In addition, the synergistic electronic effect formed by indium and gallium can regulate the surface adsorption energy and promote the Si... 4+ The interfacial charge transfer accelerates reduction kinetics, resulting in a more stable deposition process, more uniform products, and higher purity. This mechanism makes copper-based gallium-indium alloy electrodes significantly superior to pure liquid gallium electrodes in terms of reactivity, selectivity, and stability. Furthermore, the introduction of a copper substrate effectively overcomes the inherent limitations of pure liquid electrodes in terms of mechanical stability, operability, and cost, playing a crucial role in promoting sustainable development and a circular economy. Attached Figure Description

[0026] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein... Figure 1 This is a technical circuit diagram of the present invention for recovering silicon tetrachloride, a byproduct of the silicon industry, by electrodeposition.

[0027] Figure 2 This is a comparison diagram of the working electrode before and after operation in Embodiment 1 of the present invention.

[0028] Figure 3 This is a SEM image of the deposited silicon in Example 1 of the present invention.

[0029] Figure 4 This is a cyclic voltammetry (CV) curve of the deposited silicon in Example 1 of the present invention.

[0030] Figure 5 EDS elemental analysis of the deposited silicon in Example 1 of this invention. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0032] This invention employs a copper-based gallium-indium alloy (GaIn) as the working electrode. The copper substrate possesses excellent conductivity and structural stability, providing reliable support for the electrodeposition process. The GaIn alloy layer exhibits highly efficient catalytic activity, accelerating the target reaction process. The two work synergistically to significantly optimize the reaction kinetics of the electrodeposition system. Simultaneously, this copper-based GaIn alloy electrode effectively solves the technical challenges of easy flow and difficult deposit extraction associated with pure liquid metal electrodes. Furthermore, the copper-based GaIn alloy exhibits good conductivity and chemical stability, and its electrode structure is simple and rationally designed, easy to operate and maintain, and suitable for large-scale, high-efficiency recycling scenarios. During electrodeposition, reaction conditions can be precisely controlled, simplifying the operation process and significantly reducing production costs, thereby significantly optimizing the energy consumption and equipment requirements of the entire process. Compared to pure liquid gallium electrodes, the GaIn alloy has a lower melting point, higher atomic mobility, and stronger resistance to passivation, effectively preventing deactivation of the electrode surface due to solid silicon deposition, and significantly improving reaction kinetics and deposition efficiency.

[0033] This invention provides a method for recovering elemental silicon from silicon tetrachloride, a byproduct of the silicon industry, using copper-based gallium-indium alloy electrodes via electrodeposition. The specific steps are as follows: First, a eutectic solvent is prepared in a vacuum glove box, using a specific mass ratio of 2:1 for 1,3-dimethyl-2-imidazolinone and 1,3-dimethylurea.

[0034] Next, the prepared eutectic solvent was heated to 60°C, stirred with a glass rod for 3 minutes, and then placed in a vacuum drying oven at 100°C for 12 hours to reduce the water and oxygen content in the system. The dried eutectic solvent was then placed in a vacuum glove box and SiCl4 was added at 80°C-100°C. The mixture was stirred thoroughly until dissolved, thus preparing the electrolyte.

[0035] Next, the copper-based gallium-indium alloy working electrode is prepared: the copper sheet is polished to a mirror finish with 800-grit and 2000-grit sandpaper, then ultrasonically cleaned in 10% hydrochloric acid solution for 10 minutes to remove the surface oxide layer, then rinsed with deionized water and dried to obtain a clean and activated copper substrate. The liquid alloy is then gently scraped onto the surface of the copper sheet using a tool (PTFE scraper) to prepare the working electrode.

[0036] Finally, an electrochemical device with a three-electrode system was used, with a copper-based gallium-indium alloy as the working electrode, a graphite electrode as the counter electrode, and a silver / saturated silver chloride electrode as the auxiliary electrode. The electrodeposition reaction was carried out under precisely controlled electrochemical conditions, with a working voltage of -4 to 4V and a deposition time of 0.5 to 2 hours. After the electrodeposition was completed, the working electrode was removed, and the electrodeposition product was cleaned with acetone and ethanol in sequence. Then, a polytetrafluoroethylene scraper was used to scrape off the silicon film on the surface of the cleaned working electrode. Example 1

[0037] This embodiment provides a method for recovering elemental silicon from silicon tetrachloride, a byproduct of the silicon industry, using copper-based gallium-indium alloy electrodes via electrodeposition, as detailed below: 1. Prepare a eutectic solvent in a vacuum glove box: Weigh 22.83 g of 1,3-dimethyl-2-imidazolinone and 8.81 g of 1,3-dimethylurea and add them to a 200 ml beaker. Heat the prepared eutectic solvent to 60 °C and stir with a glass rod for 3 min. Then place it in a vacuum drying oven and set the drying temperature to 100 °C for 12 h. After drying, the solution will be pale yellow. Quickly transfer the dried and cooled eutectic solvent to a vacuum glove box and conduct the experiment in an environment where the water content and oxygen content are less than 1 ppm.

[0038] 2. Prepare a gallium-indium alloy with a mass ratio of 3:1, and then use a polytetrafluoroethylene (PTFE) scraper to coat a copper sheet with a liquid gallium-indium alloy to a thickness of 0.1~0.3 mm to prepare the working electrode. Heat the eutectic solvent dried in step 1 to 100℃, and use a 1000uL pipette to add 99% pure silicon tetrachloride dropwise until the solvent is saturated. During the dropwise addition, the solution is light pink. After the solution is stirred evenly and the surface foam disappears, the solution is used in a three-electrode electrochemical device. The working electrode is a copper-based gallium-indium alloy, the other working electrode is a 10mm×10mm copper sheet, the counter electrode is a 5mm diameter×90mm high graphite electrode, and the auxiliary electrode is a 5mm diameter×80mm high silver / saturated silver chloride electrode. Before use, the graphite electrodes need to be polished. The counter and auxiliary electrodes are ultrasonically cleaned for 10 minutes with anhydrous ethanol, followed by ultrasonic cleaning with deionized water for another 10 minutes. After the electrode assembly is dry, it can be installed and used. Electrodeposition is carried out under precisely controlled electrochemical conditions. When the deposition temperature is 90℃ and the electrode voltage is adjusted to -2~2V, obvious reduction and oxidation peaks are observed. Subsequently, electrodeposition is performed for 7200 seconds based on the lowest point of the CV curve, which is -1.2V. After deposition begins, the upper layer of the solution, far from the electrode, contains a small amount of low-valence silicon and therefore appears dark yellow. The lower layer of the solution appears dark brown, with the portion near the working electrode containing a higher concentration of Si. 4+ Therefore, the solution color is darker, and after deposition for 3600 seconds, Si... 4+ Black substances begin to appear on the surface dissolved and absorbed by the working electrode, and the solution color gradually fades until it becomes clear and transparent. The copper sheet pretreatment involves polishing it to a mirror finish with 800-grit and 2000-grit sandpaper, followed by ultrasonic cleaning in a 10% hydrochloric acid solution for 10 minutes to remove the surface oxide layer. It is then rinsed with deionized water and dried to obtain a clean, activated copper substrate.

[0039] III. After deposition is complete, the working electrode is removed, and 20 ml of acetone is added for ultrasonic cleaning three times, each time for 5 minutes, to ensure the removal of residual eutectic solvents on the surface. Subsequently, the cleaned working electrode is immersed in anhydrous ethanol to remove surface residues. A polytetrafluoroethylene (PTFE) scraper is used to scrape and collect the silicon film. The product shows no obvious impurities or byproducts and has high purity. The electrodeposition efficiency is calculated to be 92% according to Faraday's law. The silicon product sample is placed in a sealed sample bag to ensure its stability in an oxygen-free environment. The structure and properties of the obtained silicon product are characterized, and the results are shown below. Figures 2-5 .

[0040] Figure 2 This is a comparison image of the working electrode before and after operation in Example 1. After the coating is completed, the electrode surface is bright silver-white. After deposition, the working electrode surface is black, and a clear black silicon deposition layer can be seen attached to the electrode surface after deposition.

[0041] Figure 3 The image shows the SEM morphology of the deposited silicon in Example 1. It can be observed from the image that the surface morphology of the deposited layer is relatively dense and uniform.

[0042] Figure 4 The figure shows the cyclic voltammetry (CV) curve of the deposited silicon in Example 1. It can be observed from the figure that there is a clear reduction peak in a specific voltage range, which reflects the reduction reaction characteristics of SiCl4 in a low-melting-point solvent system.

[0043] Figure 5 EDS elemental analysis of the deposited silicon in Example 1 shows that a significant characteristic peak of Si appears in the product, indicating it is the main constituent element. Simultaneously, characteristic peaks of Ga and In from the gallium-indium alloy working electrode, as well as trace impurity peaks such as Cl from the electrolyte precursor SiCl4, C from residual eutectic solvent, and O from natural oxidation of the silicon surface, were detected. The elemental composition perfectly matches the experimental system of this invention, verifying the effectiveness of the electrodeposition process and the core chemical composition of the product. Semi-quantitative analysis results show that silicon atoms are significantly dominant, with a main component purity ≥95%, fully confirming that the product prepared by electrodepositing silicon tetrachloride using a eutectic solvent system is high-purity crystalline silicon. Example 2

[0044] This embodiment provides a method for recovering elemental silicon from silicon tetrachloride, a byproduct of the silicon industry, using copper-based gallium-indium alloy electrodes via electrodeposition, as detailed below: 1. Prepare a eutectic solvent in a vacuum glove box: Weigh 22.83 g of 1,3-dimethyl-2-imidazolinone and 8.81 g of 1,3-dimethylurea and add them to a 200 ml beaker. Heat the prepared eutectic solvent to 60 °C and stir with a glass rod for 3 min. Then place it in a vacuum drying oven and set the drying temperature to 100 °C for 12 h. After drying, the solution will be pale yellow. Quickly transfer the dried and cooled eutectic solvent to a vacuum glove box and conduct the experiment in an environment where the water content and oxygen content are less than 1 ppm.

[0045] 2. Prepare a working electrode by preparing a gallium-indium alloy with a mass ratio of 7:3. Apply a 0.1-0.3 mm thick layer of liquid gallium-indium alloy to the surface of a copper sheet using a polytetrafluoroethylene (PTFE) scraper. Heat the dried eutectic solvent to 90°C and add silicon tetrachloride dropwise using a 1000 μL pipette until the solution is saturated. The solution will be pale pink during the addition process. Once the solution is thoroughly stirred and the system is stable, use a three-electrode electrochemical device. The working electrode is a copper-based gallium-indium alloy, using a 10 mm × 10 mm copper sheet. The counter electrode is a 5 mm diameter × 90 mm high graphite electrode, and the auxiliary electrode is a 5 mm diameter × 80 mm high silver / saturated silver chloride electrode. Before use, the graphite electrode needs to be polished. The counter and auxiliary electrodes are ultrasonically cleaned with anhydrous ethanol for 10 min, followed by ultrasonic cleaning with deionized water for 10 min. After the electrode assembly is dry, it can be installed and used for electrodeposition under precisely controlled electrochemical conditions. When the deposition temperature was 90℃ and the electrode voltage was adjusted to -2~3V, obvious reduction and oxidation peaks were observed. Subsequently, electrodeposition was performed for 5400s based on the lowest point of the CV curve, i.e., -0.6V. After the start of deposition, trace amounts of water, oxygen-containing impurities, and the solvent itself in the electrolyte underwent reduction on the working electrode surface, accompanied by the production of a small amount of gas that accumulated on the electrode surface to form white foam. After 1800s of deposition, the white foam disappeared, and black substances were generated on the working electrode surface. After 3600s of deposition, the surface was basically covered by black substances, which aggregated together. With continued deposition, the black substances began to disperse. The copper sheet pretreatment involved polishing the copper sheet sequentially with 800-grit and 2000-grit sandpaper until a mirror finish, followed by ultrasonic cleaning in a 10% hydrochloric acid solution for 10 minutes to remove the surface oxide layer, and then rinsing with deionized water and drying to obtain a clean and activated copper substrate.

[0046] 3. After deposition, the working electrode was removed, and 20 ml of acetone was added for ultrasonic cleaning three times, each time for 5 minutes, to ensure the removal of residual eutectic solvents on the surface. Subsequently, the cleaned working electrode was immersed in anhydrous ethanol to remove surface residues, yielding a crystalline silicon product. According to Faraday's law, the electrodeposition efficiency reached 86%. This system exhibits high deposition efficiency, sufficient silicon ion reduction, and stable and significant deposition results. Example 3

[0047] This embodiment provides a method for recovering elemental silicon from silicon tetrachloride, a byproduct of the silicon industry, using copper-based gallium-indium alloy electrodes via electrodeposition, as detailed below: 1. Prepare the eutectic solvent in a vacuum glove box: Weigh 45.66 g of 1,3-dimethyl-2-imidazolinone and 17.62 g of 1,3-dimethylurea and add them to a 500 ml beaker. Heat the prepared eutectic solvent to 60 °C and stir with a glass rod for 3 min. Then place it in a vacuum drying oven and set the drying temperature to 100 °C for 12 h. After drying, the solution will be pale yellow. Quickly transfer the dried and cooled eutectic solvent to a vacuum glove box and conduct the experiment in an environment where the water content and oxygen content are less than 1 ppm.

[0048] 2. Prepare a gallium-indium alloy with a mass ratio of 8:2, and then gently coat the liquid alloy (0.1~0.3 mm thick) onto the copper sheet surface using a polytetrafluoroethylene (PTFE) scraper to prepare the working electrode. Heat the dried eutectic solvent to 100℃, and add silicon tetrachloride dropwise using a 1000 μL pipette until the solution is saturated. The solution will be pale pink during the dropwise addition process. After the solution is stirred evenly and the temperature stabilizes, use a three-electrode electrochemical device. The working electrode is a copper-based gallium-indium alloy, the counter electrode is a 5 mm diameter × 90 mm high graphite electrode, and the auxiliary electrode is a silver / saturated silver chloride electrode. Before use, the graphite electrode needs to be polished and then ultrasonically cleaned with anhydrous ethanol for 10 min. After cleaning, it is ultrasonically cleaned with deionized water for 10 min. After the electrode device is dried, it can be installed and used. Under precisely controlled electrochemical conditions, the electrodeposition reaction is carried out. When the deposition temperature is 100℃ and the electrode voltage is adjusted to -3~1V, obvious reduction and oxidation peaks are observed. Subsequently, electrodeposition was performed for 7200 seconds based on the lowest point of the CV curve, which was -2V. After deposition began, the color gradually became clear and transparent, and black substances were generated on the surface of the working electrode. The copper sheet pretreatment involved polishing it to a mirror finish with 800-grit and 2000-grit sandpaper, followed by ultrasonic cleaning in a 10% hydrochloric acid solution for 10 minutes to remove the surface oxide layer. It was then rinsed with deionized water and dried to obtain a clean and activated copper substrate.

[0049] 3. After deposition is completed, remove the working electrode, add 20ml of acetone, and perform ultrasonic cleaning 3 times, each time for 5 minutes, to ensure that the residual eutectic solvent on the surface is removed. Scrape the electrode surface to obtain crystalline silicon product. According to Faraday's law, the electrodeposition efficiency reaches 80%.

[0050] Comparative Example 1 Similar to Example 1, the difference is that the copper-based gallium-indium alloy working electrode is replaced with liquid gallium metal from patent CN120384314A.

[0051] The performance test results of Example 1 and Comparative Example 1 are compared as follows: SEM morphology shows that the silicon deposition layer obtained by using a copper-based gallium-indium alloy electrode in Example 1 has a dense and uniform surface, regular particles, good continuity, and no obvious pores or cracks. In contrast, the deposition layer obtained by using a pure liquid gallium electrode in Comparative Example 1 is loose and uneven, with obvious local agglomeration, poor surface smoothness, and significantly lower overall structural integrity. Cyclic voltammetry (CV) curves show that the Si of Example 1... 4+ The reduction peak is more negative, the peak current is higher, and the response is more significant, which can effectively reduce the reduction overpotential and improve the interfacial reaction kinetics. The reduction peak of Comparative Example 1 is weak, the current density is low, and the response is delayed, indicating that the electrodeposition driving force and reaction activity are significantly weaker. EDS elemental analysis shows that the Si element content in the product of Example 1 is ≥95%, and it contains only trace amounts of Ga, In, C, O, and Cl impurities, indicating higher purity. The Si content in the product of Comparative Example 1 is low, and it is accompanied by a large amount of Ga element residue and impurity peaks, indicating higher impurity content and significantly lower purity. In terms of electrodeposition efficiency, Example 1 can reach 92%, which is significantly higher than Comparative Example 1, further proving that the copper-based gallium indium alloy electrode is significantly better than the pure liquid gallium electrode in terms of catalytic activity, stability, and silicon deposition selectivity.

[0052] The copper-based gallium-indium alloy electrode used in this invention combines the excellent conductivity, mechanical strength, and cost advantages of copper substrates with the stability and high catalytic activity of gallium-indium alloys at room temperature, resulting in a significant improvement in deposition efficiency. This composite structure not only solves the bottleneck of the difficulty in forming and stabilizing pure liquid metals, but also fundamentally avoids the passivation problem caused by solid silicon deposition on the electrode surface through the in-situ dissolution of silicon atoms by the gallium-indium alloy, ensuring the continuous and efficient progress of the reaction. Simultaneously, this design enables simple separation of silicon products from the electrode medium after the reaction, providing key technical support for the efficient and low-energy resource recovery of silicon tetrachloride.

[0053] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for recovering elemental silicon from silicon tetrachloride, a byproduct of the silicon industry, using copper-based gallium-indium alloy electrodes by electrodeposition, characterized in that, Includes the following steps: An electrolyte was prepared by dissolving silicon industry byproducts containing silicon tetrachloride in a eutectic solvent system. Gallium-indium alloy is loaded onto the surface of a copper substrate to obtain a copper-based gallium-indium alloy working electrode; A three-electrode system was used to perform a constant potential electrodeposition reaction. The electrodeposition product of the copper-based gallium-indium alloy working electrode was cleaned and stripped to obtain crystalline silicon.

2. The method according to claim 1, characterized in that, The eutectic solvent system comprises 1,3-dimethyl-2-imidazolinone and 1,3-dimethylurea.

3. The method according to claim 2, characterized in that, The molar ratio of 1,3-dimethyl-2-imidazolinone to 1,3-dimethylurea is 1:1 to 3:

1.

4. The method according to claim 1, characterized in that, The concentration of silicon tetrachloride in the electrolyte is 0.027–0.081 mol / L.

5. The method according to claim 1, characterized in that, The electrolyte is prepared at a temperature of 80~100℃.

6. The method according to claim 1, characterized in that, Pretreatment of copper substrate: The copper sheet is mechanically polished with sandpaper, ultrasonically cleaned in acid solution for 5-15 minutes to remove surface oxides, increase its surface roughness, enhance the stability of gallium indium alloy coating, rinsed with deionized water and dried to obtain a clean and activated copper substrate.

7. The method according to claim 1, characterized in that, The thickness of the gallium indium alloy in copper-based gallium indium alloys is 0.1~0.3 mm.

8. The method according to claim 1, characterized in that, The mass ratio of gallium to indium in the gallium-indium alloy is 8:2 to 7:

3. The gallium-indium alloy is applied to the copper-based surface by a scraping method.

9. The method according to claim 1, characterized in that, The constant potential electrodeposition reaction has a temperature of 50~100℃, a working voltage of -4~4V, and a deposition time of 0.5~2h.

10. The method according to claim 1, characterized in that, The three-electrode system also includes a counter electrode and an auxiliary electrode; the counter electrode is a graphite electrode, and the auxiliary electrode is a silver / saturated silver chloride electrode.

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