A method for reducing carbon dioxide to solid carbon using gallium-based liquid metal electrocatalysis

Abstract

This invention discloses a method for the electrocatalytic reduction of carbon dioxide to solid carbon using gallium-based liquid metal. The method employs a composite working electrode, using a platinum sheet electrode as the counter electrode and an Ag / AgCl electrode as the reference electrode. Solid carbon is prepared through an electrocatalytic reduction reaction in an organic electrolyte continuously purged with carbon dioxide until saturation. The composite working electrode is prepared as follows: using a copper sheet as a substrate, gallium-based liquid metal is treated with dilute hydrochloric acid to remove its surface oxide film, and then capillary action is used to uniformly coat the copper sheet surface. The gallium-based liquid metal is prepared by: mixing gallium, indium, and tin in a specific ratio and heating to obtain a gallium-indium-tin alloy; subsequently, under an inert atmosphere, vanadium powder is ground and mixed with the alloy to achieve uniform vanadium doping, forming more active sites, thereby significantly promoting the generation of solid carbon and effectively improving its Faraday efficiency, thus improving catalytic performance.

Description

Technical Field

[0001] This invention belongs to the field of carbon dioxide resource utilization and electrochemical catalysis technology. Specifically, it relates to a method for reducing carbon dioxide to solid carbon based on gallium-based liquid metal electrocatalysis. Background Technology

[0002] With the continued advancement of industrialization, the sustained increase in atmospheric carbon dioxide (CO2) concentration has become a major environmental problem leading to global climate change. Meanwhile, the pursuit of "carbon neutrality" has made the conversion of the greenhouse gas carbon dioxide into high-value-added chemical products or fuels a current hot topic in scientific research and technological development. Among numerous carbon dioxide conversion technologies, electrochemical catalysis technology, due to its advantages such as mild reaction conditions and controllable processes, demonstrates enormous development potential.

[0003] Currently, research on the electrocatalytic reduction of carbon dioxide mainly focuses on converting it into gaseous or liquid fuels such as carbon monoxide, formic acid, methane, and ethylene. However, these products typically face challenges such as high separation and purification costs and inconvenient storage and transportation. In contrast, directly converting carbon dioxide into solid carbon offers significant advantages, as the product is easy to store and transport and has wide applications in energy storage, composite materials, and other fields.

[0004] However, achieving efficient and low-energy electrocatalytic reduction of carbon dioxide to solid carbon remains a significant challenge. Traditional solid catalysts typically face the following key issues in this reaction:

[0005] 1. Catalyst deactivation and carbon buildup: During the reduction process, solid carbon products are very easy to deposit and cover on the surface of solid catalysts, blocking active sites, leading to rapid catalyst deactivation and difficulty in stable operation.

[0006] 2. High overpotential: Due to the stable chemical properties of carbon dioxide molecules, their activation requires overcoming a high energy barrier. Traditional solid catalysts have low catalytic efficiency for this process, necessitating a high overpotential for the reaction to proceed. This easily triggers side reactions such as hydrogen evolution, further impacting economic feasibility.

[0007] 3. Poor product selectivity: Due to the complexity of the carbon dioxide electroreduction process, traditional solid catalysts cannot selectively promote the conversion of carbon dioxide to solid carbon, resulting in the generation of a large number of by-products (such as carbon monoxide, formic acid, etc.), which significantly reduces the yield of the target product, solid carbon.

[0008] Therefore, there is an urgent need to develop a green and efficient catalyst to directly convert carbon dioxide into solid carbon, in order to solve the core problems of existing traditional solid catalysts, such as easy deactivation, high overpotential, and poor selectivity. In the prior art, Chinese invention patent application CN118047375A proposes a method for plasma-assisted liquid metal catalysis to synthesize solid carbon from carbon dioxide. This method uses cerium-containing liquid metal as an electrocatalyst to convert carbon dioxide into solid carbon at room temperature and introduces non-thermal plasma to lower the reaction energy barrier. Although this method attempts to combine the advantages of plasma and liquid metal, the introduction of the plasma device significantly increases the complexity and energy consumption of the system. Furthermore, the synergistic mechanism between plasma and liquid metal during the reaction is still unclear, which may cause instability at the reaction interface, affecting the uniformity and yield of the solid carbon product and limiting its feasibility for large-scale application. Chinese invention patent application CN115193372A relates to a wind / solar-assisted carbon dioxide conversion system, which uses an organic solution impregnated with liquid metal as the reaction medium. Although this invention attempts to drive the reaction process using renewable energy, its system configuration still relies on mechanical transmission devices, and the reaction system involves a multiphase interface between organic solutions and liquid metals, making process control complex. This complexity may cause uncertainties in the purity and yield of carbon products, and also poses challenges to the long-term stable operation of the system. Chinese invention patent application CN118007173A reports a gallium-based liquid alloy catalyst doped with cerium (Ce) via ball milling for the electrocatalytic reduction of carbon dioxide to elemental carbon. Although this invention utilizes the characteristic that liquid metal surfaces are not prone to carbon deposition, it still has the following significant limitations: First, although the cerium (Ce) active centers it relies on can drive carbon dioxide reduction through redox cycles, the system requires a high overpotential and has a large charge transfer resistance, which limits its catalytic efficiency and economy, and significantly affects the selectivity of the solid carbon pathway. Furthermore, catalyst preparation relies on high-energy ball milling processes, which may lead to metal contamination and uneven distribution of active sites; and the generated elemental carbon is easily detached into the electrolyte, requiring complex subsequent processing. Meanwhile, the invention directly uses liquid metal as the working electrode, and its inherent fluidity leads to unstable electrode shape, which is prone to short circuit risk during long-term electrolysis, thus limiting its large-scale application in industrial production. Summary of the Invention

[0009] To address the problems existing in the prior art, the present invention aims to provide a method for the electrocatalytic reduction of carbon dioxide to solid carbon based on gallium-based liquid metal. This invention employs a composite electrode with a copper sheet as the supporting substrate and a vanadium-doped gallium-indium-tin alloy as the catalytic active layer as the working electrode. This method can efficiently and stably reduce carbon dioxide to solid carbon, solving problems such as catalyst deactivation, high reaction overpotential, and poor product selectivity in the electrocatalytic reduction process. The present invention uses a catalyst preparation and electrode construction method combining grinding and copper sheet substrate coating. By systematically optimizing the vanadium doping amount and electrochemical reaction conditions, it achieves efficient and stable reduction of carbon dioxide to solid carbon products under mild conditions.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows.

[0011] This invention provides a method for the electrocatalytic reduction of carbon dioxide to solid carbon using gallium-based liquid metal. The method employs a composite electrode with a copper sheet as the supporting substrate and a vanadium-doped gallium-indium-tin alloy as the catalytic active layer as the working electrode, a platinum sheet electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode. Solid carbon is prepared through an electrocatalytic reduction reaction in an organic electrolyte in which carbon dioxide is continuously passed until saturation. The method for preparing the gallium-based liquid metal includes: (1) Gallium, indium and tin are mixed in proportion and heated to a molten state in a crucible to prepare gallium indium tin alloy; (2) After pre-treating the mortar and pestle, transfer them to a glove box filled with inert gas. Then place the vanadium powder and gallium indium tin alloy in the mortar and grind and mix them so that the vanadium powder is evenly dispersed in the gallium indium tin alloy matrix. (3) Transfer the mixture obtained after grinding to a sealed reagent bottle to obtain gallium-based liquid metal.

[0012] In this invention, the working electrode is prepared as follows: a copper sheet is used as a substrate, and gallium-based liquid metal is treated with dilute hydrochloric acid (0.1-1 mol / L) to remove the oxide film on its surface. The gallium-based liquid metal is then uniformly covered on the surface of the copper sheet by capillary action. The thickness of the gallium-based liquid metal layer is 0.1-1 mm.

[0013] In this invention, the organic electrolyte is composed of an electrolyte, a solvent, and a small amount of water; wherein the electrolyte is tetrabutylammonium hexafluorophosphate, tetrabutylperchloride, or tetraethylhexafluorophosphate, and the corresponding solvents are N,N-dimethylformamide, acetonitrile, or propylene carbonate, respectively.

[0014] In this invention, the concentration of the electrolyte in the organic electrolyte is 0.1-0.2 mol / L, and the water content is 2-3 mol / L.

[0015] In this invention, the electrocatalytic reduction reaction is carried out at room temperature and pressure using constant potential electrolysis. The reaction voltage, relative to the Ag / AgCl reference electrode, is between -1.8 V and -2.4 V. Most preferably, the reaction voltage is -2.4 V.

[0016] In this invention, in step (1), the melting temperature is 200-250 ℃; based on the mass of gallium indium tin alloy being 100%, the mass of gallium is 60-75 wt%, the mass of indium is 15-30 wt%, and the mass of tin is 5-15 wt%.

[0017] In this invention, in step (2), vanadium powder accounts for 0.5-3 wt% of the total mass of vanadium powder and gallium indium tin alloy, and the continuous grinding time is 20-30 min; preferably, vanadium powder accounts for 1-3 wt% of the total mass of vanadium powder and gallium indium tin alloy.

[0018] In this invention, the working principle of the gallium-based liquid metal electrocatalytic reduction of carbon dioxide to solid carbon is as follows: The catalyst used is a vanadium-doped gallium-indium-tin alloy. Because the vanadium (V) on the surface of the liquid alloy is in prolonged contact with air, it easily forms V₂O₅, resulting in the catalyst surface initially being dominated by V₂O₅. When a sufficiently negative electrochemical potential is applied, some V₂O₅ is reduced to metallic V. This metallic V has high redox activity, capable of reducing CO₂ to solid C, while V is oxidized to VO₂. Under the influence of a negative potential, VO₂ is continuously reduced to metallic V, forming a cyclic process that ensures the continuous progress of the reaction.

[0019] This is based on V 0 The VO2 cycle mechanism, compared to the Ce element system, is more conducive to the breaking of CO bonds and coupling of carbon atoms in CO2 molecules, fundamentally ensuring the high selectivity of solid carbon products.

[0020] The above process can be represented by the following chemical reaction equation: (1) (2) (3) (4)

[0021] In this invention, the Faraday efficiency of solid carbon is calculated as follows: The gaseous products (CO and H2) generated during the reaction are detected using a gas chromatograph, and their Faraday efficiency is calculated. The Faraday efficiency of solid carbon is derived indirectly based on the principle of charge conservation, using the following specific formula: (1) (2) (3) in, and These represent the amounts of carbon monoxide and hydrogen, respectively (in moles), where F is the Faraday constant (96485 C / mol). The total charge (C) passing through during electrolysis, and 2 represents the number of electrons transferred to produce 1 mol of the target product (CO or H2) in the reaction. , and These represent the Faraday efficiencies for carbon monoxide, hydrogen, and solid carbon, respectively.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. Innovation of active elements and highly selective catalysis

[0024] This is the first time that vanadium (V) has been used as an active dopant in a gallium-based liquid metal electrocatalytic reduction of CO2 system. The unique V... 0 The / VO2 redox cycle, compared to elements such as cerium (Ce) commonly used in existing technologies, can more efficiently activate CO2 molecules and promote their complete reduction, significantly inhibiting the generation of gaseous byproducts such as CO, and playing an important role in improving the selectivity of the target product (solid C).

[0025] 2. Simplification and optimization of catalyst preparation process

[0026] This invention employs a grinding and mixing method to replace the traditional high-energy mechanical ball milling method. This method is carried out in an inert atmosphere, is simple to operate, requires minimal equipment, and effectively avoids metal contamination that may occur during high-energy ball milling. Simultaneously, it promotes the uniform dispersion and alloying of vanadium powder in the gallium-indium-tin alloy, thereby avoiding the problem of uneven distribution of active sites. This lays the foundation for obtaining highly active and stable catalysts, making the catalyst preparation process simpler and more controllable.

[0027] 3. Electrode structure optimization

[0028] This invention innovatively uses a copper (Cu) sheet as a supporting substrate to construct a composite working electrode. The specific preparation method is as follows: using a copper sheet as a substrate, gallium-based liquid metal is treated with dilute hydrochloric acid to remove its surface oxide film, and capillary action is used to uniformly cover the copper sheet surface with the liquid metal. This design effectively improves the shape instability problem caused by the easy flow of pure liquid metal electrodes, ensuring the long-term operational stability of the system. Simultaneously, this composite structure constructs a stable interface conducive to the directional deposition and growth of solid carbon products, allowing the reduced carbon to gradually form a firmly attached continuous solid carbon layer during electrolysis. After electrolysis, the copper sheet with the attached solid carbon can be directly removed, washed with anhydrous ethanol, dried, and stored, thus achieving integrated collection of solid carbon. This significantly simplifies the subsequent processing steps required in traditional processes due to carbon products falling into the electrolyte, and improves overall process efficiency.

[0029] 4. Optimization of catalytic reaction conditions and improvement of efficiency

[0030] By synergistically optimizing key parameters such as vanadium doping amount (0.5-3 wt%) and operating potential (-1.8 V ~ -2.4 V vs. Ag / AgCl), the selectivity of the catalyst for the reduction of carbon dioxide to solid carbon was significantly enhanced, and side reactions such as hydrogen evolution were effectively suppressed. Thus, the efficient generation of solid carbon was achieved under mild conditions, while maintaining a high current density.

[0031] In summary, this invention, by selecting metallic V as the active dopant element and employing a novel grinding and mixing method, designs a composite working electrode with a Cu sheet as the substrate, thus constructing a new, efficient, stable, and easily collectable electrocatalytic reduction system for CO2 to produce solid carbon. Specifically, the V element ensures high selectivity in the direction of solid carbon formation; the grinding and mixing method effectively promotes the uniform dispersion of the active components; and the copper sheet substrate effectively alleviates the stability issues of the liquid metal electrode, utilizing its surface properties to achieve in-situ, firm adhesion, and integrated collection of solid carbon. This new system effectively improves upon the shortcomings of existing liquid metal catalytic systems in terms of product selectivity and electrode stability, providing a new technological solution with practical application potential for CO2 resource utilization. Attached Figure Description

[0032] Figure 1 Characterization images of the gallium-based liquid metal prepared in Example 1 of this invention: (a) surface SEM image; (b) macroscopic surface morphology image; (c) EDS elemental composition analysis image.

[0033] Figure 2 This is a comparison image of the copper sheet surface before and after the reaction in Example 1 of the present invention.

[0034] Figure 3This is a scanning electron microscope (SEM) image of the deposits on the surface of the copper sheet after the reaction, as shown in Example 1 of the present invention.

[0035] Figure 4 This is an energy dispersive spectroscopy (EDS) analysis diagram of the deposits on the surface of the copper sheet after the reaction in Example 1 of the present invention.

[0036] Figure 5 This is a SEM image showing the microstructure of the solid carbon product prepared in Example 1 of the present invention.

[0037] Figure 6 This is an energy dispersive spectroscopy (EDS) analysis diagram of the solid carbon product prepared in Example 1 of the present invention.

[0038] Figure 7 This is the chronocurrent curve of constant potential electrolysis performed at different potentials when the vanadium powder mass percentage is 1 wt% in Example 2 of the present invention.

[0039] Figure 8 The chronoamperometry curves are obtained for constant potential electrolysis at the same potential (-2.4 V) in Examples 1, 2, 3 and Comparative Example 1 of the present invention when different vanadium powder mass percentages (0 wt%, 0.5 wt%, 1 wt%, 3 wt%) are used.

[0040] Figure 9 This is a comparison chart of the Faraday efficiency of solid carbon after constant potential electrolysis at the same potential (-2.4 V) for different vanadium powder mass percentages (0 wt%, 0.5 wt%, 1 wt%, 3 wt%) in Examples 1, 2, 3 and Comparative Example 1 of the present invention. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0042] This invention provides a method for the electrocatalytic reduction of carbon dioxide to solid carbon using gallium-based liquid metals. First, vanadium (V) is selected as the key doping element, due to its unique V... 0The VO2 redox cycle exhibits superior electrochemical activity compared to the traditional Ce element system. The vanadium-doped catalyst displays a lower onset potential and significantly reduced charge transfer resistance, which thermodynamically favors the breaking of CO bonds and coupling with carbon atoms in the CO2 molecule, thereby selectively driving the reaction towards the formation of solid carbon. Secondly, in terms of preparation process, this invention uses a simplified grinding and mixing method instead of high-energy ball milling, achieving uniform doping of vanadium powder in gallium-indium-tin alloy under an inert atmosphere. This effectively avoids the contamination and uneven distribution of active sites that may result from ball milling, making catalyst preparation simpler and more controllable. Finally, regarding electrode structure, this invention innovatively uses a copper (Cu) sheet as a supporting substrate to construct a composite working electrode. This design not only effectively solves the problem of shape instability caused by the easy flow of pure liquid metal electrodes, ensuring the stability and uniformity of the electrode / electrolyte interface, but also successfully constructs a stable interface conducive to the directional deposition and growth of solid carbon products by coating liquid metal onto the surface of the copper sheet. In actual electrocatalysis, the reduced carbon elemental can continuously grow at the interface, forming a continuous and firmly attached solid carbon layer, rather than detaching into the electrolyte in fragments, greatly simplifying the subsequent processing. After the reaction is complete, the copper sheet with the attached solid carbon can be directly removed, washed with anhydrous ethanol, dried, and stored, thus achieving integrated collection of solid carbon.

[0043] Example 1

[0044] I. Preparation of Gallium-based Liquid Metal

[0045] (1) After mixing gallium, indium and tin, place them in a crucible and heat them at 200-250 °C. After they are completely melted, cool them to room temperature to obtain a gallium-indium-tin alloy. In the gallium-indium-tin alloy, gallium, indium and tin account for 68.5%, 21.5% and 10%, respectively. Then transfer it to a reagent bottle and seal it for storage for later use.

[0046] (2) The mortar and pestle were alternately cleaned with 1 mol / L hydrochloric acid solution and 1 mol / L potassium hydroxide solution to remove surface impurities and achieve surface activation. Then, an appropriate amount of gallium indium tin alloy was added to the mortar and ground thoroughly to uniformly cover the surface of the mortar and pestle, forming a mirror-like alloy layer. The treated mortar and pestle were transferred to a glove box filled with high-purity argon gas, and excess alloy was removed, leaving only the surface mirror-like alloy layer. Finally, in the glove box, a measured amount of gallium indium tin alloy and vanadium powder were added to the pretreated mortar, with the vanadium powder accounting for 0.5 wt% of the total mass of the gallium indium tin alloy and vanadium powder; grinding was continued for 20-30 min until uniformly mixed, and the vanadium powder was uniformly dispersed in the gallium indium tin alloy matrix, forming a uniform and stable gallium-based liquid alloy; the gallium-based liquid alloy was transferred to a sealed reagent bottle using a pipette. Figure 1As shown, the surface of the gallium-based liquid alloy is uniform and dense, exhibiting typical liquid metal surface morphology and corresponding elemental composition. This helps to form a stable working interface during the electrochemical process, which is of great significance for maintaining the stability of the catalyst.

[0047] II. Preparation of the working electrode

[0048] First, the copper sheet is mechanically polished until a uniform luster is achieved. Then, it is placed in anhydrous ethanol and ultrasonically cleaned for 5-10 minutes to thoroughly remove organic contaminants, grease, and polishing residue from the surface. After cleaning, the surface is rinsed with deionized water to remove residual impurities (such as anhydrous ethanol), and then placed in a drying oven for drying, ultimately obtaining a clean copper substrate.

[0049] A suitable amount of the prepared gallium-based liquid metal is treated with dilute hydrochloric acid and then uniformly coated onto the surface of a pretreated copper sheet to form a dense catalytic layer with a thickness of approximately 0.1-1 mm. This results in a composite working electrode with a copper sheet as the supporting substrate and a vanadium-doped gallium-indium-tin alloy as the catalytic active layer.

[0050] III. Electrocatalytic Reduction Process

[0051] An H-type electrolytic cell was used as the reaction apparatus. The composite working electrode and the Ag / AgCl electrode (reference electrode) prepared above were placed in the cathode chamber, and the platinum sheet electrode (counter electrode) was placed in the anode chamber, forming a three-electrode system. The electrolyte used was an N,N-dimethylformamide (DMF) solution containing 0.1 mol / L tetrabutylammonium hexafluorophosphate and 2 mol / L water.

[0052] During the reaction, carbon dioxide is continuously introduced into the electrolyte to ensure it remains saturated. A gas chromatograph is connected to the end of the reactor to detect the carbon monoxide and hydrogen produced in the reaction. An electrochemical workstation is then connected to perform potentiostatic electrolysis at room temperature and pressure, and a potential of -2.4 V.

[0053] IV. Calculation of Faraday efficiency in solid carbon

[0054] After the reaction, the products were analyzed using gas chromatography to obtain the peak areas of carbon monoxide and hydrogen, and the corresponding amounts of substance were calculated based on their respective standard curves. Then, the obtained amounts of substance were substituted into the following formulas to calculate the Faraday efficiencies of carbon monoxide and hydrogen, respectively: (1) (2)

[0055] Among them, total charge The Faraday efficiency of solid carbon is obtained by integrating the current-time curves recorded by an electrochemical workstation. It is calculated indirectly by the following formula:

[0056] Calculations show that the Faraday efficiency of solid carbon is approximately 71.5%, indicating that with 0.5 wt% vanadium doping and a reaction potential of -2.4 V, this method can efficiently and selectively reduce CO2 to solid carbon and effectively suppress competing side reactions such as hydrogen evolution.

[0057] In Example 1, after the electrolysis reaction was completed, a dense and firmly adhered black solid product was observed to the surface of the copper sheet, such as... Figure 2 As shown in the figure. At this point, the copper sheet can be directly removed for drying. Simultaneously, SEM and EDS analyses are performed on the surface deposits to characterize their morphology and elemental composition, respectively. The results are as follows: Figure 3 and Figure 4 As shown, the copper substrate was completely covered by a continuous and uniform layer of solid carbon, and the original metal substrate surface was no longer visible. This product layer was macroscopically smooth and dense, indicating that the effective conversion and deposition of carbon dioxide into solid carbon was successfully achieved on the copper substrate surface, greatly simplifying the operation steps and eliminating the need to filter and collect the carbon product from the electrolyte. This phenomenon further confirms the crucial role of the copper substrate in guiding the in-situ adhesion and growth of solid carbon. EDS analysis results showed that carbon had the highest content and was the main component; the detected fluorine mainly originated from electrolyte residue. To reduce the interference of residues on subsequent characterization, the copper substrate surface was gently rinsed with anhydrous ethanol to ensure that the solid carbon remained firmly attached, followed by drying.

[0058] To further characterize the structure and composition of the aforementioned solid carbon, the dried copper sheet was sequentially subjected to ultrasonic dispersion and centrifugation to obtain a cleaner solid carbon product. Subsequent SEM morphology analysis and EDS analysis were performed, and the results are as follows: Figure 5 and Figure 6 As shown. From Figure 5 It can be observed that the product is composed of irregularly aggregated particles. Its basic carbonaceous unit is a spherical particle with uneven size. These particles are stacked and in close contact with each other, forming abundant gaps and pores, thus constituting a loose porous aggregate with a large active surface and abundant pore channels.

[0059] Meanwhile, EDS quantitative analysis showed that the carbon content was 83.6 wt%. This data fully demonstrates that the obtained solid carbon product has high purity, and the catalyst has good chemical stability during the reaction process, effectively avoiding interference from metal impurities on the product.

[0060] Example 2

[0061] I. Preparation of Gallium-based Liquid Metal

[0062] (1) After mixing gallium, indium and tin, place them in a crucible and heat them at 200-250 °C. After they are completely melted, cool them to room temperature to obtain a gallium-indium-tin alloy. In the gallium-indium-tin alloy, gallium, indium and tin account for 68.5%, 21.5% and 10%, respectively. Then transfer it to a reagent bottle and seal it for storage for later use.

[0063] (2) The mortar and pestle were alternately cleaned with 1 mol / L hydrochloric acid solution and 1 mol / L potassium hydroxide solution to remove surface impurities and achieve surface activation. Then, an appropriate amount of gallium indium tin alloy was added to the mortar and ground thoroughly to make it uniformly cover the surface of the mortar and pestle, forming a mirror-like alloy layer. The treated mortar and pestle were transferred into a glove box filled with high-purity argon gas, and the excess alloy was removed, leaving only the surface mirror-like alloy layer. Finally, in the glove box, a certain amount of gallium indium tin alloy and vanadium powder were added to the pretreated mortar, with the vanadium powder accounting for 1 wt% of the total mass of the gallium indium tin alloy and vanadium powder; grinding was continued for 20-30 min until the mixture was uniform and the vanadium powder was uniformly dispersed in the gallium indium tin alloy matrix to form a uniform and stable gallium-based liquid alloy; the gallium-based liquid alloy was transferred to a sealed reagent bottle using a pipette.

[0064] II. Preparation of the working electrode

[0065] First, the copper sheet is mechanically polished until a uniform luster is achieved. Then, it is placed in anhydrous ethanol and ultrasonically cleaned for 5-10 minutes to thoroughly remove organic contaminants, grease, and polishing residue from the surface. After cleaning, the surface is rinsed with deionized water to remove residual impurities (such as anhydrous ethanol), and then placed in a drying oven for drying, ultimately obtaining a clean copper substrate.

[0066] A suitable amount of the prepared gallium-based liquid metal is treated with dilute hydrochloric acid and then uniformly coated onto the surface of a pretreated copper sheet to form a dense catalytic layer with a thickness of approximately 0.1-1 mm. This results in a composite working electrode with a copper sheet as the supporting substrate and a vanadium-doped gallium-indium-tin alloy as the catalytic active layer.

[0067] III. Electrocatalytic Reduction Process

[0068] An H-type electrolytic cell was used as the reaction apparatus. The composite working electrode and the Ag / AgCl electrode (reference electrode) prepared above were placed in the cathode chamber, and the platinum sheet electrode (counter electrode) was placed in the anode chamber, forming a three-electrode system. The electrolyte used was an N,N-dimethylformamide (DMF) solution containing 0.1 mol / L tetrabutylammonium hexafluorophosphate and 2 mol / L water.

[0069] During the reaction, carbon dioxide was continuously introduced into the electrolyte to ensure it remained saturated. A gas chromatograph was connected to the end of the reactor to detect the carbon monoxide and hydrogen produced in the reaction. An electrochemical workstation was connected, and constant-potential electrolysis was performed at multiple potential points (including -1.8 V, -2.0 V, -2.2 V, and -2.4 V) within the range of -1.8 V to -2.4 V (relative to the Ag / AgCl reference electrode) at ambient temperature and pressure. The corresponding chronoamperometry curves are shown below. Figure 7 As shown.

[0070] Depend on Figure 7 It can be seen that, under the condition of 1 wt% vanadium doping, when constant potential electrolysis is performed at different potentials, the current density gradually increases with the negative shift of the applied potential, indicating a significant enhancement of reaction kinetics. In particular, the system exhibits the highest current density at -2.4 V.

[0071] IV. Calculation of Faraday efficiency in solid carbon

[0072] Based on the product analysis and calculation methods in Example 1, the reaction results at the optimal potential of -2.4 V were systematically examined. The calculated Faraday efficiency for solid carbon was approximately 76.8%, which fully demonstrates that when the vanadium doping concentration is optimized to 1 wt%, the catalyst exhibits optimal selectivity and catalytic activity for the reduction of CO2 to solid carbon.

[0073] Example 3

[0074] I. Preparation of Gallium-based Liquid Metal

[0075] (1) After mixing gallium, indium and tin, place them in a crucible and heat them at 200-250 °C. After they are completely melted, cool them to room temperature to obtain a gallium-indium-tin alloy. In the gallium-indium-tin alloy, gallium, indium and tin account for 68.5%, 21.5% and 10%, respectively. Then transfer it to a reagent bottle and seal it for storage for later use.

[0076] (2) The mortar and pestle were alternately cleaned with 1 mol / L hydrochloric acid solution and 1 mol / L potassium hydroxide solution to remove surface impurities and achieve surface activation. Then, an appropriate amount of gallium indium tin alloy was added to the mortar and ground thoroughly to uniformly cover the surface of the mortar and pestle, forming a mirror-like alloy layer. The treated mortar and pestle were transferred to a glove box filled with high-purity argon gas, and the excess alloy was removed, leaving only the surface mirror-like alloy layer. Finally, in the glove box, a quantitative amount of gallium indium tin alloy and vanadium powder was added to the pretreated mortar, with the vanadium powder accounting for 3 wt% of the total mass of the gallium indium tin alloy and vanadium powder; grinding was continued for 20-30 min until the mixture was uniform and the vanadium powder was uniformly dispersed in the gallium indium tin alloy matrix to form a uniform and stable gallium-based liquid alloy; the gallium-based liquid alloy was transferred to a sealed reagent bottle using a pipette.

[0077] II. Preparation of the working electrode

[0078] First, the copper sheet is mechanically polished until a uniform luster is achieved. Then, it is placed in anhydrous ethanol and ultrasonically cleaned for 5-10 minutes to thoroughly remove organic contaminants, grease, and polishing residue from the surface. After cleaning, the surface is rinsed with deionized water to remove residual impurities (such as anhydrous ethanol), and then placed in a drying oven for drying, ultimately obtaining a clean copper substrate.

[0079] A suitable amount of the prepared gallium-based liquid metal is treated with dilute hydrochloric acid and then uniformly coated onto the surface of a pretreated copper sheet to form a dense catalytic layer with a thickness of approximately 0.1-1 mm. This results in a composite working electrode with a copper sheet as the supporting substrate and a vanadium-doped gallium-indium-tin alloy as the catalytic active layer.

[0080] III. Electrocatalytic Reduction Process

[0081] An H-type electrolytic cell was used as the reaction apparatus. The composite working electrode and the Ag / AgCl electrode (reference electrode) prepared above were placed in the cathode chamber, and the platinum sheet electrode (counter electrode) was placed in the anode chamber, forming a three-electrode system. The electrolyte used was an N,N-dimethylformamide (DMF) solution containing 0.1 mol / L tetrabutylammonium hexafluorophosphate and 2 mol / L water.

[0082] During the reaction, carbon dioxide is continuously introduced into the electrolyte to ensure it remains saturated. A gas chromatograph is connected to the end of the reactor to detect the carbon monoxide and hydrogen produced in the reaction. An electrochemical workstation is then connected to perform potentiostatic electrolysis at room temperature and pressure, and a potential of -2.4 V.

[0083] IV. Calculation of Faraday efficiency in solid carbon

[0084] The analytical method was the same as in Example 1. Calculations showed that when the vanadium doping concentration increased to 3 wt%, the Faraday efficiency of solid carbon was approximately 73.2%. Compared to Example 2 (1 wt%), the selectivity decreased, mainly because excessively high vanadium doping concentrations easily induce local agglomeration of active components, leading to a reduction in effective active sites.

[0085] Comparative Example 1

[0086] I. Preparation of Gallium-based Liquid Metal

[0087] Gallium, indium, and tin are mixed and placed in a crucible, then heated and melted at 200-250 °C. After complete melting, the mixture is cooled to room temperature to obtain a gallium-indium-tin alloy (as a gallium-based liquid metal). In the gallium-indium-tin alloy, gallium, indium, and tin account for 68.5%, 21.5%, and 10%, respectively. The alloy is then transferred to a reagent bottle, sealed, and stored for later use.

[0088] II. Preparation of the working electrode

[0089] First, the copper sheet is mechanically polished until a uniform luster is achieved. Then, it is placed in anhydrous ethanol and ultrasonically cleaned for 5-10 minutes to thoroughly remove organic contaminants, grease, and polishing residue from the surface. After cleaning, the surface is rinsed with deionized water to remove residual impurities (such as anhydrous ethanol), and then placed in a drying oven for drying, ultimately obtaining a clean copper substrate.

[0090] A suitable amount of the prepared gallium-based liquid metal is treated with dilute hydrochloric acid and then uniformly coated onto the surface of a pretreated copper sheet to form a dense catalytic layer with a thickness of approximately 0.1-1 mm. This results in a composite working electrode with a copper sheet as the supporting substrate and a gallium-indium-tin alloy as the catalytic active layer.

[0091] III. Electrocatalytic Reduction Process

[0092] An H-type electrolytic cell was used as the reaction apparatus. The composite working electrode and the Ag / AgCl electrode (reference electrode) prepared above were placed in the cathode chamber, and the platinum sheet electrode (counter electrode) was placed in the anode chamber, forming a three-electrode system. The electrolyte used was an N,N-dimethylformamide (DMF) solution containing 0.1 mol / L tetrabutylammonium hexafluorophosphate and 2 mol / L water.

[0093] During the reaction, carbon dioxide is continuously introduced into the electrolyte to ensure it remains saturated. A gas chromatograph is connected to the end of the reactor to detect the carbon monoxide and hydrogen produced in the reaction. An electrochemical workstation is then connected to perform potentiostatic electrolysis at room temperature and pressure, and a potential of -2.4 V.

[0094] IV. Calculation of Faraday efficiency in solid carbon

[0095] The analytical method was the same as in Example 1. Indirect calculations showed that the Faraday efficiency of solid carbon was only 12.4%, far lower than the results of Examples 1, 2, and 3. This directly confirms that undoped vanadium liquid metal cannot effectively reduce CO2 to solid carbon, and the reaction is dominated by hydrogen evolution as a side reaction.

[0096] Figure 8These are the chronoamperometry curves obtained by constant potential electrolysis at the same potential (-2.4 V) for different vanadium powder mass percentages (0 wt%, 0.5 wt%, 1 wt%, 3 wt%) in Examples 1, 2, 3, and Comparative Example 1 of the present invention. Figure 8 It is evident that vanadium doping concentration significantly affects electrocatalytic performance: the undoped catalyst exhibits lower current density and faster decay; at a doping concentration of 0.5 wt%, the current density does not show a significant increase due to the inability to form a sufficient number of highly active sites on the catalyst surface, remaining comparable to the undoped sample; however, when the doping concentration increases to 1 wt% and 3 wt%, the current density shows a significant increase. Therefore, precisely controlling the vanadium doping concentration is crucial for optimizing catalyst performance.

[0097] Figure 9 The figure shows the numerical values ​​and trends of the solid carbon Faraday efficiency at the same potential (-2.4 V) with different vanadium doping amounts. It can be seen from the figure that vanadium doping is key to achieving high selectivity in the conversion of CO2 to solid carbon, but there is an optimal concentration window; excessive vanadium doping (e.g., 3 wt%) is not conducive to further improving the solid carbon Faraday efficiency.

Claims

1. A method for the electrocatalytic reduction of carbon dioxide to solid carbon based on gallium-based liquid metals, characterized in that, It uses a composite electrode with a copper sheet as the supporting substrate and a vanadium-doped gallium-indium-tin alloy as the catalytic active layer as the working electrode, a platinum sheet electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode. Solid carbon is prepared by electrocatalytic reduction in an organic electrolyte continuously purged with carbon dioxide until saturation. The method for preparing the gallium-based liquid metal includes: (1) Gallium, indium and tin are mixed in proportion and heated to a molten state in a crucible to prepare gallium indium tin alloy; (2) After pre-treating the mortar and pestle, transfer them to a glove box filled with inert gas. Then place the vanadium powder and gallium indium tin alloy in the mortar and grind and mix them so that the vanadium powder is evenly dispersed in the gallium indium tin alloy matrix. (3) Transfer the mixture obtained after grinding to a sealed reagent bottle to obtain gallium-based liquid metal.

2. The method for reducing carbon dioxide to solid carbon based on gallium-based liquid metal electrocatalysis according to claim 1, characterized in that, The working electrode is prepared as follows: a copper sheet is used as a substrate, and gallium-based liquid metal is treated with dilute hydrochloric acid to remove its surface oxide film. The gallium-based liquid metal is then uniformly covered on the surface of the copper sheet by capillary action. The thickness of the gallium-based liquid metal layer is 0.1-1 mm.

3. The method for reducing carbon dioxide to solid carbon based on gallium-based liquid metal electrocatalysis according to claim 1, characterized in that, The organic electrolyte is composed of an electrolyte, a solvent, and a small amount of water; wherein the electrolyte is tetrabutylammonium hexafluorophosphate, tetrabutylperchloride, or tetraethylhexafluorophosphate, and the corresponding solvents are N,N-dimethylformamide, acetonitrile, or propylene carbonate, respectively.

4. The method for reducing carbon dioxide to solid carbon based on gallium-based liquid metal electrocatalysis according to claim 3, characterized in that, In the organic electrolyte, the concentration of the electrolyte is 0.1-0.2 mol / L, and the water content is 2-3 mol / L.

5. The method for reducing carbon dioxide to solid carbon based on gallium-based liquid metal electrocatalysis according to claim 1, characterized in that, The electrocatalytic reduction reaction was carried out at room temperature and pressure using constant potential electrolysis, with the reaction voltage ranging from -1.8 V to -2.4 V relative to the Ag / AgCl reference electrode.

6. The method for reducing carbon dioxide to solid carbon based on gallium-based liquid metal electrocatalysis according to claim 1, characterized in that, In step (1), the melting temperature is 200-250 ℃; based on the mass of gallium-indium-tin alloy as 100%, the mass of gallium is 60-75 wt%, the mass of indium is 15-30 wt%, and the mass of tin is 5-15 wt%.

7. The method for reducing carbon dioxide to solid carbon based on gallium-based liquid metal electrocatalysis according to claim 1, characterized in that, In step (2), vanadium powder accounts for 0.5-3 wt% of the total mass of vanadium powder and gallium indium tin alloy, and the grinding time is 20-30 min.

8. The method for reducing carbon dioxide to solid carbon based on gallium-based liquid metal electrocatalysis according to claim 1, characterized in that, In step (2), vanadium powder accounts for 1-3 wt% of the total mass of vanadium powder and gallium indium tin alloy.

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