A sulfur-modified modified electrode for electrochemical reduction of carbon dioxide and a preparation method thereof

Abstract

The application discloses a sulfur-modified electrode for electrochemical reduction of carbon dioxide and a preparation method thereof, relates to the field of sulfur-modified electrodes, and comprises the following steps: in-situ depositing and growing a core-shell structure Cu2O-Cu2S-Cu(V) / Cu on a copper substrate by means of electrochemical pulse deposition and electrochemical constant-potential deposition reconstruction technology on the surface of a substrate layer of the copper substrate x O-Cu x S / CM catalyst. In the growth process, Cu x S-Cu x O is prepared on the surface of the substrate by pulse deposition; then, Cu x O and Cu x S on the surface layer of the catalyst are reconstructed and reduced by means of electrochemical constant-potential structure reconstruction, Cu2O-Cu2S-Cu(V) is grown on the surface, and the sulfur-modified electrode is formed. The sulfur-modified electrode is prepared by coupling pulse electrodeposition and constant-potential deposition reconstruction, the preparation method is simple, raw materials are widely available, the electrode prepared has good selectivity, high catalytic activity and stability, the structure reconstruction enlarges the solid-liquid-gas three-phase interface area, and the electrocatalyst has more active sites and a larger specific surface area.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sulfur-modified electrodes, and particularly relates to a sulfur-modified electrode for electrochemical reduction of carbon dioxide and a preparation method. BACKGROUND

[0002] Under the background of increasingly severe global climate change, carbon dioxide (CO2) as the main greenhouse gas, its emission reduction and conversion has become an important scientific research topic. In order to cope with this challenge, researchers continue to explore innovative methods to achieve efficient conversion and utilization of CO2. Among them, electrochemical reduction of carbon dioxide (ECR-CO2) technology as a promising solution has received extensive attention. ECR-CO2 technology uses electrical energy to convert CO2 into valuable chemicals such as methanol, ethanol, carbon monoxide, etc., which not only reduces CO2 emissions, but also produces renewable fuels and raw materials. This technology provides potential wide application in the field of climate change, energy security and sustainable chemistry.

[0003] Copper-based materials exhibit unique advantages in the process of electrochemical ECR-CO2 conversion, especially their binding ability to key reaction intermediates such as *COOH, *CO, *CHO and *COH. The core-shell structure formed in the present application not only effectively promotes the adsorption of *COOH intermediates, compared with Cu catalysts, Cu x S catalysts have higher binding energy with *OCHO due to the stabilizing effect of negatively charged S atoms. Cu x S promotes the dissociation of H2O into adsorbed H, and the two synergistically reduce the formation energy barrier of formic acid, thereby promoting the efficient conversion of CO2 to HCOOH, and can significantly inhibit the H2 and CO pathways. However, a key challenge lies in the stability and selectivity of the catalyst: under cathodic conditions, sulfur is prone to dissolve in the electrolyte, which directly affects the composition stability and structural integrity of the catalyst, and the selectivity of the product of copper-based materials is unstable, which becomes a major obstacle in the practical application and commercialization of the technology. Therefore, exploring methods to improve the stability of sulfur or developing alternative catalyst design strategies is of great significance to promote the practical process of electrochemical ECR-CO2 technology.

[0004] To this end, we provide a sulfur-modified electrode for electrochemical reduction of carbon dioxide and a preparation method to solve the above problems. SUMMARY

[0005] In view of the problems existing in the prior art, the present application provides a sulfur-modified electrode for electrochemical reduction of carbon dioxide and a preparation method, which solves the problem that the method for improving the stability of sulfur or the development of alternative catalyst design strategies is still insufficient in the prior art.

[0006] To achieve the above objectives, this invention employs a sulfur-modified electrode for the electrochemical reduction of carbon dioxide, wherein Cu₂O-Cu₂S-Cu(V) / Cu is deposited and reconstructed on the surface of a copper substrate through electrochemical deposition, electrochemical reduction techniques, and subsequent growth. x O-Cu x S / CM catalyst;

[0007] A sulfur-modified electrode for the electrochemical reduction of carbon dioxide, characterized in that,

[0008] A core-shell structure Cu2O-Cu2S-Cu(V) / Cu was in situ deposited and grown on a copper substrate using electrochemical pulse deposition and electrochemical potentiostatic deposition reconstruction techniques. x O-Cu x S / CM catalyst;

[0009] During the growth process, Cu is first deposited on the substrate surface. x O-Cu x S;

[0010] Then, the developed catalyst was deposited and reconstructed using electrochemical potentiostatic deposition and reconstruction technology, and the Cu on the surface layer was... x O and Cu x S is reduced and reconstructed, and Cu2O-Cu2S is grown on the surface to form a sulfur-modified electrode.

[0011] A method for preparing a sulfur-modified electrode for the electrochemical reduction of carbon dioxide, characterized in that: the preparation of the sulfur-modified electrode for the electrochemical reduction of carbon dioxide includes the following steps:

[0012] S1: Soak the copper mesh, copper foam, and copper plate substrate in water, hydrochloric acid with a mass concentration of 25%, ethanol, or acetone in sequence, clean them in an ultrasonic cleaner, and then clean and dry them for later use.

[0013] S2: Prepare a mixed solution of bicarbonate, carbonate, and sodium sulfide as the electrolyte, and stir it thoroughly for 20 minutes under a magnetic stirrer. The concentrations of sodium bicarbonate and carbonate are 0.1M to 1M, preferably 0.1M to 0.5M; the concentration of sulfur is 0.3mM to 2.0mM, preferably 0.5mM to 1mM.

[0014] S3: Under the protection of inert gas, the oxidation potential Ea of the cyclic voltage pulse is -0.2V to -0.6V; the reduction potential Ec is -1.2V to -0.6V.

[0015] The absolute value of the oxidation potential is always set to be less than the absolute value of the reduction potential;

[0016] The oxidation time Δta is 1 to 5 seconds, with a preferred time of 2 to 4 seconds;

[0017] The reduction time Δtc is 2 to 8 seconds, with the preferred time being 4 to 8 seconds;

[0018] The number of cycles is 50 to 400, and the number of optimization cycles is 100 to 200.

[0019] S4: Under the protection of an inert gas, the electrode prepared in step S3 is used to perform surface reconstruction of the electrodeposited catalyst on the substrate surface using electrochemical potentiostatic reconstruction under the same electrolyte.

[0020] S5: The electrode prepared in S4 is rinsed clean and dried in a vacuum drying oven at 40-60°C to obtain a sulfur-modified electrode.

[0021] The method for preparing a sulfur-modified electrode for the electrochemical reduction of carbon dioxide is characterized in that: the concentration of sodium bicarbonate and carbonate is 0.1M to 1M, preferably 0.1M to 0.5M; the concentration of sulfur is 0.3mM to 2mM, preferably 0.5mM to 1mM.

[0022] The method for preparing a sulfur-modified electrode for the electrochemical reduction of carbon dioxide is characterized in that: the oxidation time Δta in S3 is 1 to 10 seconds, preferably 2 to 4 seconds;

[0023] The reduction time Δtc is 2 to 8 seconds, with a preferred time of 4 to 8 seconds; the number of cycles is 50 to 400, with a preferred number of cycles of 100 to 200.

[0024] The method for preparing a sulfur-modified electrode for the electrochemical reduction of carbon dioxide is characterized in that the molar ratio of sodium bicarbonate or carbonate to sodium sulfide is 117:1 to 200:1, preferably 150:1 to 180:1.

[0025] The method for preparing a sulfur-modified electrode for the electrochemical reduction of carbon dioxide is characterized in that: the sodium bicarbonate salt and carbonate of the electrolyte solution of the cyclic voltage pulse are one or more of KHCO3, NaHCO3, Na2CO3 and K2CO3.

[0026] The method for preparing a sulfur-modified electrode for the electrochemical reduction of carbon dioxide is characterized in that: the concentration of the electrolyte is 0.1M to 1M, preferably 0.1M to 0.5M.

[0027] The method for preparing a sulfur-modified electrode for the electrochemical reduction of carbon dioxide is characterized in that the constant potential method uses the constant voltage method.

[0028] The sulfur-modified electrode for electrochemical reduction of carbon dioxide and its preparation method are characterized in that: the voltage used in the constant voltage method is set to -2.0V to -1.0V, and the deposition time is 800 to 2000 seconds.

[0029] As a further optimization of the above scheme, the concentration of sodium bicarbonate and carbonate is 0.1M to 0.5M;

[0030] The concentration of the sulfide is 0.5 mM to 1.0 mM.

[0031] As a further optimization of the above scheme, the oxidation time Δta in S3 is 2 to 4 seconds;

[0032] The restoration time Δtc is 4 to 8 seconds;

[0033] Repeat 100 to 200 times.

[0034] As a further optimization of the above scheme, the molar ratio of sodium bicarbonate or carbonate to sodium sulfide is 150:1 to 180:1.

[0035] As a further optimization of the above scheme, the electrolyte solution of the cyclic voltage pulse is composed of sodium bicarbonate, carbonate, KHCO3, NaHCO3, Na2CO3, or K2CO3, or one or more of these.

[0036] As a further optimization of the above scheme, the concentration of the electrolyte is 0.1M to 0.5M.

[0037] As a further optimization of the above scheme, the voltage used in the constant voltage method is set to -2.0V to -0.5V, and the deposition time is 800 to 2000 seconds.

[0038] The present invention provides a sulfur-modified electrode for the electrochemical reduction of carbon dioxide and its preparation method, which has the following beneficial effects:

[0039] This invention focuses on performance optimization strategies for copper-based metal catalysts, and delves into ways to enhance catalytic performance by modulating their crystal facet properties and grain boundary structure. An electrocatalyst was prepared using a cyclic pulse voltage combined with a constant voltage method, forming a core-shell structure, resulting in a sulfur-modified electrode for the electrochemical reduction of carbon dioxide.

[0040] The preparation method of this invention is simple, the raw materials are widely available, and it has high catalytic activity and stability. It can be prepared by cyclic pulse voltage and constant voltage method in alkaline and sulfur-containing electrolytes. By increasing the interface area of ​​solid, liquid and gas three phases, the electrocatalyst can have more active sites and a larger specific surface area.

[0041] At the solid-liquid-gas three-phase interface, CO2 undergoes a reduction reaction (ECR-CO2), and the core-shell structure undergoes an instantaneous surface structure transformation. This process not only accelerates the formation of the key intermediate *OCHO, but also effectively blocks the competitive adsorption of *H and *COOH. This mechanism significantly enhances the selectivity of the electrochemical CO2 reduction reaction (ECR-CO2) to formic acid conversion, thereby achieving higher catalytic efficiency.

[0042] Compared to conventional electrochemical deposition methods, an innovative modification of copper mesh surfaces can be achieved by combining cyclic pulsed voltage with a constant voltage method in a sulfur-rich electrolyte solution. This method not only continuously exposes new interfaces but also effectively cleans the substrate. The constant voltage causes sulfur ions in the electrolyte to undergo an electrochemical reduction reaction on the copper mesh surface, firmly adhering to the surface and reducing copper oxides to cuprous oxide. During this process, the constant potential ensures the stability and uniformity of the deposition rate, avoiding inconsistent deposition quality or detachment problems caused by potential fluctuations.

[0043] This preparation method is simple, efficient, and utilizes abundant raw materials. The resulting electrocatalyst exhibits excellent catalytic activity and stability. Treatment with cyclic pulsed voltage and constant voltage in an alkaline sulfur-containing electrolyte promotes the formation of abundant active sites and an expanded specific surface area. This catalyst not only effectively suppresses the hydrogen evolution side reaction but also significantly improves the selectivity for formic acid formation. The overall preparation process is rapid, environmentally friendly, energy-efficient, and pollution-free, making it an ideal electrocatalyst preparation method.

[0044] Specific embodiments of the present invention are disclosed in detail with reference to the following description and accompanying drawings, indicating how the principles of the present invention can be adopted. It should be understood that the embodiments of the present invention are not limited in scope as a result, and that the embodiments of the present invention include many changes, modifications and equivalents within the spirit and scope of the appended claims. Attached Figure Description

[0045] Figure 1 X-ray energy dispersive spectroscopy (EDS) characterization of the sulfur-modified electrode material for the electrochemical reduction of carbon dioxide of the present invention;

[0046] Figure 2 X-ray energy dispersive spectroscopy (EDS) characterization of the sulfur-modified electrode material for the electrochemical reduction of carbon dioxide of the present invention (II);

[0047] Figure 3 X-ray energy dispersive spectroscopy (EDS) characterization of the sulfur-modified electrode material for the electrochemical reduction of carbon dioxide of the present invention;

[0048] Figure 4Scanning electron microscopy (SEM) characterization of the sulfur-modified electrode material for the electrochemical reduction of carbon dioxide of the present invention (Part IV);

[0049] Figure 5 Characterization of the sulfur-modified electrode material for the electrochemical reduction of carbon dioxide of the present invention by scanning electron microscopy (SEM) (Part 5);

[0050] Figure 6 This is a flowchart illustrating the preparation method of the sulfur-modified electrode for the electrochemical reduction of carbon dioxide according to the present invention. Detailed Implementation

[0051] Please refer to the instruction manual appendix. Figures 1-4 The present invention provides a technical solution: a sulfur-modified electrode for the electrochemical reduction of carbon dioxide and its preparation method.

[0052] Electrodeposition is a highly efficient, environmentally friendly, and flexible preparation method suitable for the preparation and modification of catalysts. This technology allows for precise control of the morphology, structure, and performance of Cu catalysts by adjusting electrodeposition parameters such as current, voltage, electrolyte composition, temperature, and deposition time. Adjustments to these parameters directly affect the deposition rate, grain size, and surface morphology of the catalyst, thereby influencing its catalytic activity and selectivity. By optimizing these parameters, the performance of the catalyst can be controlled, resulting in superior performance in electrocatalytic carbon dioxide reduction.

[0053] This invention utilizes an innovative method of cyclic voltage pulse combined with constant voltage modification on a copper substrate in a sulfur-rich electrolyte solution to successfully prepare a high-efficiency copper-based electrocatalyst. Cu₂O-Cu₂S-Cu(V) / Cu₂S is deposited and grown on the substrate surface using electrochemical deposition and electrochemical reduction techniques. x O-Cu x S / CM core-shell structure; during growth, Cu is first deposited on the substrate surface. x S-Cu x O; then, the developed catalyst was reconstructed using electrochemical reduction technology, and the copper oxide and Cu on the surface layer were removed. x S is reduced and reconstructed, allowing Cu2S-Cu2O to continue growing on the substrate, thus preparing a sulfur-modified electrode for the electrochemical reduction of carbon dioxide. Through chemical and electrochemical reduction techniques, the catalyst surface structure was tailored, inducing heterometallic inclusions to promote surface reconstruction. The outer Cu2O layer helps improve the catalyst's activity and selectivity, and the resulting Cu... xS vacancies lead to more electrons being donated to *OCHO, improving the selectivity for formic acid. Catalyst surface reconstruction involves adjusting the number and ratio of active sites on the catalyst surface using cyclic pulse technology and electrochemical reduction techniques, or introducing a small amount of functional modification layers and functional groups that can bond with C or O atoms onto the catalyst surface. These functional modification layers have the potential to form chemical bonds with reduction reaction intermediates (such as *COOH), thereby altering their adsorption and desorption strengths, ultimately improving the selectivity of reduction products. During the cyclic pulse voltage process, not only is the film structure and morphology precisely controlled, but the substrate is also effectively purified. Even with non-high-purity Cu metal substrates, it overcomes the limitations imposed by long-term deposition and high-concentration precursors, ensuring continuous optimization of catalyst performance. Constant voltage allows the copper oxide and Cu on the surface layer to... x S is reduced and reconstructed, thus forming a Cu x An S-Cu2O modified capping layer was used. A constant potential ensured the stability and uniformity of the deposition rate, avoiding inconsistencies in deposition quality or detachment caused by potential fluctuations. The electrocatalyst, prepared using a combination of cyclic voltage pulse and constant voltage methods, exhibited significant effects in the carbon dioxide electroreduction process, effectively suppressing the hydrogen evolution side reaction and significantly improving the selectivity of formic acid products, thereby optimizing the efficiency and product distribution of the catalytic reaction.

[0054] The electrode was grown by depositing Cu on the substrate surface using pulsed electrochemical deposition. x S-Cu x O / substrate layer; potentiostatic method to make Cu x S-Cu x Electrochemical reduction and reconstruction occur in the O / substrate layer, allowing for continued growth of Cu2O-Cu2S-Cu(V) / Cu. x O-Cu x S / CM core-shell structure. The electrocatalyst is prepared according to the following steps:

[0055] S1: Soak the copper mesh, copper foam, and copper plate substrate in water, hydrochloric acid with a mass concentration of 25%, ethanol, or acetone in sequence, clean them in an ultrasonic cleaner, and then clean and dry them for later use.

[0056] S2: Prepare a mixed solution of bicarbonate, carbonate, and sodium sulfide as the electrolyte, and stir it thoroughly for 20 minutes under a magnetic stirrer. The concentrations of sodium bicarbonate and carbonate are 0.1M to 1M, preferably 0.1M to 0.5M; the concentration of sulfur is 0.3mM to 2.0mM, preferably 0.5mM to 1mM.

[0057] S3: Under the protection of inert gas, the oxidation potential Ea of the cyclic voltage pulse is -0.2V to -0.6V; the reduction potential Ec is -1.2V to -0.6V.

[0058] The absolute value of the oxidation potential is always set to be less than the absolute value of the reduction potential;

[0059] The oxidation time Δta is 1 to 5 seconds, with a preferred time of 2 to 4 seconds;

[0060] The reduction time Δtc is 2 to 8 seconds, with the preferred time being 4 to 8 seconds;

[0061] The number of cycles is 50 to 400, and the number of optimization cycles is 100 to 200.

[0062] S4: Under the protection of an inert gas, the electrode prepared in step S3 is used to perform surface reconstruction of the electrodeposited catalyst on the substrate surface using electrochemical potentiostatic reconstruction under the same electrolyte.

[0063] S5: The electrode prepared in S4 is rinsed clean and dried in a vacuum drying oven at 40-60°C to obtain a sulfur-modified electrode.

[0064] Electrocatalysts can act as cathode catalysts in the electrochemical reduction reaction of carbon dioxide.

[0065] Example 1

[0066] The copper mesh substrate was sequentially immersed in hydrochloric acid, water, ethanol, or acetone with a molar concentration of 2–5 mol / L, and ultrasonically cleaned for 15 minutes. Afterward, it was cleaned and dried for later use. A mixed solution of sodium bicarbonate (0.1 M) and sodium sulfide (0.85 mM) was prepared and stirred with a magnetic stirrer for 20 minutes to ensure thorough mixing. Under inert gas protection at room temperature, using an Ag / AgCl electrode as a reference electrode, the treated copper mesh substrate was placed in the mixed solution for cyclic voltage pulses. The voltage Ea was set to -0.2 V for a duration Δta = 2 seconds; the potential Ec was set to -0.6 V for a duration Δtc = 4 seconds, and the number of cycles was 100. Immediately after the cyclic pulses ended, constant-pressure reduction was performed, with a reduction voltage of -1.5 V and a time of 1200 seconds. The prepared electrocatalyst was dried at room temperature in a vacuum drying oven to prevent oxidation, thus obtaining a sulfur-modified electrode material catalyst for the electrochemical reduction of carbon dioxide.

[0067] Example 2

[0068] The copper mesh substrate was sequentially immersed in hydrochloric acid, water, ethanol, or acetone with a molar concentration of 2–5 mol / L, ultrasonicated for 15 minutes in an ultrasonic cleaner, and then cleaned and dried for later use. A certain amount of mixed solution of sodium bicarbonate and sodium sulfide was prepared, with a sodium bicarbonate concentration of 0.1M and a sodium sulfide concentration of 0.35mM, and stirred with a magnetic stirrer for 20 minutes to ensure thorough mixing. Under the protection of an inert gas at room temperature, using an Ag / AgCl electrode as a reference electrode, the treated copper mesh substrate was placed in the mixed solution for cyclic voltage pulses. The voltage Ea was set to -0.2V, and the duration Δta = 2 seconds; the potential Ec was set to -0.6V, and the duration Δtc = 4 seconds, with 100 cycles. After the cyclic pulses ended, constant pressure reduction was immediately performed, with the reduction voltage set to -1.5V and the time set to 1200 seconds. The prepared electrocatalyst was dried in a vacuum drying oven at room temperature to prevent catalyst oxidation, thus obtaining the catalyst.

[0069] Example 3

[0070] The copper mesh substrate was sequentially immersed in hydrochloric acid, water, ethanol, or acetone at a concentration of 2–5 mol / L, ultrasonicated for 15 minutes in an ultrasonic cleaner, and then cleaned and dried for later use. A mixed solution of sodium bicarbonate and sodium sulfide was prepared, with a sodium bicarbonate concentration of 0.1 M and a sodium sulfide concentration of 0.65 mM, and stirred with a magnetic stirrer for 20 minutes to ensure thorough mixing. Under inert gas protection at room temperature, using an Ag / AgCl electrode as a reference electrode, the treated copper mesh substrate was placed in the mixed solution for cyclic voltage pulses. The voltage Ea was set to -0.2 V, and the duration Δta = 2 seconds; the potential Ec was set to -0.6 V, and the duration Δtc = 4 seconds, with 100 cycles. After the cyclic pulses ended, constant pressure reduction was immediately performed, with the reduction voltage set to -1.5 V and the time set to 1200 seconds. The prepared electrocatalyst was then dried in a vacuum drying oven at room temperature to prevent oxidation, thus obtaining the catalyst.

[0071] Example 4

[0072] The copper mesh substrate was sequentially immersed in hydrochloric acid, water, ethanol, or acetone at a concentration of 2–5 mol / L, ultrasonicated for 15 minutes in an ultrasonic cleaner, and then cleaned and dried for later use. A mixed solution of sodium bicarbonate and sodium sulfide was prepared, with a sodium bicarbonate concentration of 0.1 M and a sodium sulfide concentration of 1 mM, and stirred with a magnetic stirrer for 20 minutes to ensure thorough mixing. Under inert gas protection at room temperature, using an Ag / AgCl electrode as a reference electrode, the treated copper mesh substrate was placed in the mixed solution for cyclic voltage pulses. The voltage Ea was set to -0.2 V, and the duration Δta = 2 seconds; the potential Ec was set to -0.6 V, and the duration Δtc = 4 seconds, with 100 cycles. After the cyclic pulses ended, constant pressure reduction was immediately performed, with the reduction voltage set to -1.5 V and the time set to 1200 seconds. The prepared electrocatalyst was then dried in a vacuum drying oven at room temperature to prevent oxidation, thus obtaining the catalyst.

[0073] Example 5

[0074] The copper mesh substrate was sequentially immersed in hydrochloric acid, water, ethanol, or acetone at a concentration of 2–5 mol / L, and ultrasonically cleaned for 15 minutes. Afterward, it was cleaned and dried for later use. A mixed solution of sodium bicarbonate (0.1 M) and sodium sulfide (0.85 mM) was prepared and stirred with a magnetic stirrer for 20 minutes to ensure thorough mixing. Under inert gas protection at room temperature, using an Ag / AgCl electrode as a reference electrode, the treated copper mesh substrate was placed in the mixed solution for cyclic voltage pulses. The voltage Ea was set to -0.2 V for a duration Δta = 2 seconds; the potential Ec was set to -0.6 V for a duration Δtc = 4 seconds, and the number of cycles was 50. Immediately after the cyclic pulses ended, constant-pressure reduction was performed, with a reduction voltage of -1.5 V and a time of 1200 seconds. The prepared electrocatalyst was dried at room temperature in a vacuum drying oven to prevent oxidation, thus obtaining a sulfur-modified electrode material catalyst for the electrochemical reduction of carbon dioxide.

[0075] Example 6

[0076] The copper mesh substrate was sequentially immersed in hydrochloric acid, water, ethanol, or acetone at a concentration of 2–5 mol / L, and ultrasonically cleaned for 15 minutes. Afterward, it was cleaned and dried for later use. A mixed solution of sodium bicarbonate (0.1 M) and sodium sulfide (0.85 mM) was prepared and stirred with a magnetic stirrer for 20 minutes to ensure thorough mixing. Under inert gas protection at room temperature, using an Ag / AgCl electrode as a reference electrode, the treated copper mesh substrate was placed in the mixed solution for cyclic voltage pulses. The voltage Ea was set to -0.2 V for a duration Δta = 2 seconds; the potential Ec was set to -0.6 V for a duration Δtc = 4 seconds, and the number of cycles was 150. Immediately after the cyclic pulses ended, constant-pressure reduction was performed, with a reduction voltage of -1.5 V and a time of 1200 seconds. The prepared electrocatalyst was dried at room temperature in a vacuum drying oven to prevent oxidation, thus obtaining a sulfur-modified electrode material catalyst for the electrochemical reduction of carbon dioxide.

[0077] Example 7

[0078] The copper mesh substrate was sequentially immersed in hydrochloric acid, water, ethanol, or acetone with a molar concentration of 2–5 mol / L, ultrasonicated for 15 minutes in an ultrasonic cleaner, and then cleaned and dried for later use. A certain amount of mixed solution of sodium bicarbonate and sodium sulfide was prepared, with a sodium bicarbonate concentration of 0.1M and a sodium sulfide concentration of 0.85mM, and stirred with a magnetic stirrer for 20 minutes to ensure thorough mixing. Under the protection of an inert gas at room temperature, using an Ag / AgCl electrode as a reference electrode, the treated copper mesh substrate was placed in the mixed solution for cyclic voltage pulses. The voltage Ea was set to -0.2V, and the duration Δta = 2 seconds; the potential Ec was set to -0.6V, and the duration Δtc = 4 seconds, with 100 cycles. After the cyclic pulses ended, constant pressure reduction was immediately performed, with the reduction voltage set to -1.5V and the time set to 800 seconds. The prepared electrocatalyst was dried at room temperature in a vacuum drying oven to prevent oxidation, thus obtaining a sulfur-modified electrode material catalyst for the electrochemical reduction of carbon dioxide.

[0079] Example 8

[0080] The copper mesh substrate was sequentially immersed in hydrochloric acid, water, ethanol, or acetone at a concentration of 2–5 mol / L, and ultrasonically cleaned for 15 minutes. Afterward, it was cleaned and dried for later use. A mixed solution of sodium bicarbonate (0.1 M) and sodium sulfide (0.85 mM) was prepared and stirred with a magnetic stirrer for 20 minutes to ensure thorough mixing. Under inert gas protection at room temperature, using an Ag / AgCl electrode as a reference electrode, the treated copper mesh substrate was placed in the mixed solution for cyclic voltage pulses. The voltage Ea was set to -0.2 V for a duration Δta = 2 seconds; the potential Ec was set to -0.6 V for a duration Δtc = 4 seconds, and the number of cycles was 100. Immediately after the cyclic pulses ended, constant-pressure reduction was performed, with a reduction voltage of -1.5 V and a time of 1600 seconds. The prepared electrocatalyst was dried at room temperature in a vacuum drying oven to prevent oxidation, thus obtaining a sulfur-modified electrode material catalyst for the electrochemical reduction of carbon dioxide.

[0081] Comparative Example 1

[0082] The copper mesh substrate was sequentially immersed in hydrochloric acid, water, ethanol, or acetone at a concentration of 2–5 mol / L, ultrasonicated for 15 minutes in an ultrasonic cleaner, and then cleaned and dried for later use. A mixed solution of sodium bicarbonate and sodium sulfide was prepared, with a sodium bicarbonate concentration of 0.1 M and a sodium sulfide concentration of 0.85 mM, and stirred with a magnetic stirrer for 20 minutes to ensure thorough mixing. Under inert gas protection at room temperature, using an Ag / AgCl electrode as a reference electrode, the treated copper mesh substrate was placed in the mixed solution for cyclic voltage pulses. The voltage Ea was set to -0.2 V, and the duration Δta = 2 seconds; the potential Ec was set to -0.6 V, and the duration Δtc = 4 seconds, with 100 cycles. After the cyclic pulses, the prepared electrocatalyst was dried in a vacuum drying oven at room temperature to prevent catalyst oxidation, thus obtaining the catalyst.

[0083] Comparative Example 2

[0084] The copper mesh substrate was sequentially immersed in hydrochloric acid, water, ethanol, or acetone at concentrations of 2–5 mol / L, ultrasonicated for 15 min in an ultrasonic cleaner, and then cleaned and dried for later use. A mixed solution of sodium bicarbonate and sodium sulfide was prepared, with a sodium bicarbonate concentration of 0.1 M and a sodium sulfide concentration of 0.85 mM, and stirred with a magnetic stirrer for 20 min to ensure thorough mixing. Under inert gas protection at room temperature, using an Ag / AgCl electrode as a reference electrode, the treated copper mesh substrate was placed in the mixed solution for constant-pressure reduction, with the reduction voltage set to -1.5 V and the time set to 1600 seconds. The prepared electrocatalyst was then dried in a vacuum drying oven at room temperature to prevent catalyst oxidation, thus preparing a sulfur-modified electrode material catalyst for the electrochemical reduction of carbon dioxide.

[0085] Table 1. Distribution of reduction products in Examples 1, 2, 3, 4, 5, 6, 7, 8, Comparative Example 1, and Comparative Example 2.

[0086]

[0087]

[0088] The prepared electrocatalyst was used as the cathode in the electrochemical catalytic reduction of carbon dioxide reaction system. Electrochemical tests were conducted using a three-electrode system, with the prepared 1cm × 1cm electrode material used as the working electrode and an Ag / AgCl reference electrode used as the reference electrode. 2 A platinum sheet electrode was used as the counter electrode. The cathode chamber contained 65 mL of 0.1 M NaHCO3 solution, and the anode chamber contained 65 mL of 0.1 M NaHCO3 solution. During the electrocatalytic reduction of CO2, the CO2 flow rate was set to 50 mL / min. The catalytic reduction product was detected every 15 min.

[0089] Specifically, the differences in the reduction product distributions of Examples 1 and 2, and Examples 3 and 4 in Table 1 are as follows: the concentration of sodium sulfide during electrodeposition is different. In Example 1, when the sodium sulfide concentration is 0.85 mM, the highest Faradaic efficiency for formic acid formation at -1.9 V is 88.54%, and the Faradaic efficiency for hydrogen is 20.98%. In Example 2, when the sodium sulfide concentration is 0.35 mM, the highest Faradaic efficiency for formic acid formation at -1.9 V is 79.53%, and the Faradaic efficiency for hydrogen is 25.16%. In Example 3, when the sodium sulfide concentration is 0.65 mM, the highest Faradaic efficiency for formic acid formation at -1.9 V is 82.97%, and the Faradaic efficiency for hydrogen is 24.38%. In Example 4, when the sodium sulfide concentration is 1 mM, the highest Faradaic efficiency for formic acid formation at -1.9 V is 67.83%, and the Faradaic efficiency for hydrogen is 35.31%. Overall, the Faradaic efficiency of formic acid initially increases and then decreases with increasing sodium sulfide concentration, with almost no byproducts detected except for hydrogen gas. The Faradaic efficiency of formic acid is highest at -1.9V. At a sodium sulfide concentration of 0.85mM, formic acid exhibits the highest Faradaic efficiency of 88.54%, with reduced side reactions such as hydrogen evolution. This indicates that at -1.9V and a sodium sulfide concentration of 0.85mM, the active sites provided by the core-shell structure on the copper substrate surface can adsorb more CO2. The S vacancies formed on the surface lead to the transfer of more electrons from Cu sites, improving their selectivity, thereby expanding the three-phase interface area, accelerating the formation of the key intermediate *OCHO, effectively regulating product selectivity, and promoting the conversion of CO2 to formic acid.

[0090] Specifically, the differences in the distribution of reduction products in Examples 1, 5, and 6 of Table 1 lie in the number of cycles during cyclic pulse deposition. In Example 1, with 100 cycles during cyclic pulse deposition, the highest Faradaic efficiency for formic acid formation at -1.9V was 88.54%, and the Faradaic efficiency for hydrogen was 20.98%. In Example 5, with 50 cycles during cyclic pulse deposition, the highest Faradaic efficiency for formic acid formation at -1.9V was 67.25%, and the Faradaic efficiency for hydrogen was 26.33%. In Example 6, with 150 cycles during cyclic pulse deposition, the highest Faradaic efficiency for formic acid formation at -1.9V was 60.32%, and the Faradaic efficiency for hydrogen was 35.32%. The comparison shows that the Faradaic efficiency for formic acid is highest when the number of cycles is 100. This indicates that Cu was not completely reacted in the first step. x S-Cu x The O structure prevented the removal of Cu from the catalyst surface layer during the second step of electrochemical potentiostatic structural reconstruction. x O and Cu x S was reconstructed but not reduced, failing to form a good Cu2O-Cu2S-Cu(V) / Cu x O-Cux S / CM core-shell structure catalysts. Influence the selectivity of the catalyst for formic acid formation.

[0091] Specifically, the difference in the reduction product distributions of Examples 1, 7, and 8 in Table 1 lies in the different durations of the constant-potential reduction. In Example 1, when the constant-potential voltage was applied for 1200 seconds, the highest Faradaic efficiency for formic acid formation at -1.9V was 88.54%, and the Faradaic efficiency for hydrogen was 20.98%. In Example 7, when the constant-potential voltage was applied for 800 seconds, the highest Faradaic efficiency for formic acid formation at -1.9V was 68.22%, and the Faradaic efficiency for hydrogen was 28.38%. In Example 8, when the constant-potential voltage was applied for 1600 seconds, the highest Faradaic efficiency for formic acid formation at -1.9V was 48.36%, and the Faradaic efficiency for hydrogen was 45.63%. The comparison shows that the Faradaic efficiency for formic acid was highest when the constant-potential voltage was applied for 1200 seconds. This indicates that the preparation of Cu in the first step... x S-Cu x After the O structure is formed, the optimal time for the second step of electrochemical potential reconstruction is 1200 seconds. This forms a relatively complete core-shell structure on the copper substrate surface, providing more active sites for CO2 adsorption and dissociation, which helps convert carbon dioxide into formic acid.

[0092] Specifically, the difference in the reduction product distribution between Example 1 and Comparative Example 1 in Table 1 is as follows: In Comparative Example 1, a constant voltage method was not used during electrodeposition compared to Example 1. In Example 1, the highest Faradaic efficiency for formic acid generation at -1.9V was 88.54%, and the Faradaic efficiency for hydrogen was 20.98%. In Example 2, the highest Faradaic efficiency for formic acid generation at -1.9V was 79.53%, and the Faradaic efficiency for hydrogen was 25.16%. This comparison demonstrates that the lack of a constant voltage method prevented the formation of a complete core-shell structure. S ions in the solution failed to be reduced to the copper substrate surface, and the Faradaic efficiency of formic acid on the sulfur-modified Cu2O electrocatalyst was highly dependent on the crystal facets of Cu2O. The lack of a constant voltage method prevented the surface layer of copper oxide and Cu... x S is reduced and reconstructed, but Cu cannot be obtained. x O-Cu x The S / Cu2O-Cu2S-Cu(V) core-shell structure. When the number of active sites decreases, the overall catalytic activity weakens accordingly. Simultaneously, the reduced proportion of edge active sites also leads to decreased selectivity in the catalytic process.

[0093] Specifically, the difference in the reduction product distribution between Example 1 and Comparative Example 2 in Table 1 is that, in Comparative Example 2, the cyclic voltage pulse method was not added during electrodeposition compared to Example 1. In Example 1, the highest Faradaic efficiency for formic acid formation at -1.9V was 88.54%, and the Faradaic efficiency for hydrogen was 20.98%. In Comparative Example 2, the highest Faradaic efficiency for formic acid formation at -1.9V was 25.32%, and the Faradaic efficiency for hydrogen was 48.39%. Without the first-step cyclic voltage pulse, Cu was not formed. x S-Cu x The O-structure prevents the formation of a core-shell structure during catalyst surface reconstruction. Without S vacancies to provide active sites for CO2 adsorption and electron transfer, the conversion rate of formic acid is significantly reduced. The decrease in active sites and the reduced proportion of edge sites together lead to weakened catalytic activity and decreased selectivity.

[0094] Specifically, attached Figure 1 Appendix Figure 2 and attached Figure 3 Note: Cyclic voltage pulses and constant voltage methods can uniformly disperse the core-shell structure into the copper-based catalyst. The elements in the sample are uniformly distributed, with no local enrichment or deficiency observed. The elemental content fluctuations in different regions of the sample are small, indicating good uniformity. This demonstrates that this preparation method can effectively control the composition and distribution of the catalyst, thus contributing to improved catalyst performance. Simultaneously, the uniform elemental distribution reduces the risk of localized over-reaction or corrosion, thereby improving the catalyst's lifespan and stability.

[0095] Specifically, attached Figure 4 This is a SEM image of the catalyst prepared using the cyclic voltage pulse method. (Attached) Figure 5 This is a SEM image of the catalyst prepared using a cyclic pulse voltage method coupled with a potentiostatic method. (Attached) Figure 4 The preparation method exhibits a sheet-like stacked structure; attached Figure 5 The preparation method yielded a nanoparticle structure; by comparing the morphology of catalysts prepared by the two different methods, the attached... Figure 5 The prepared catalyst exhibits a tightly packed, loosely porous structure, which implies high density and good structural stability. Furthermore, it possesses a larger surface active area and a higher specific surface area, thereby expanding the three-phase interface area, which is beneficial for CO2 adsorption, conduction, and diffusion.

[0096] Tests have shown that this catalyst exhibits excellent catalytic activity and good selectivity for a single product. Compared with existing technologies, the raw materials of this invention are widely available, inexpensive, and simple to prepare, which is beneficial for improving carbon dioxide conversion efficiency. The electrocatalyst can act as the cathode in the electrochemical reduction reaction of carbon dioxide.

Claims

1. A method for preparing a sulfur-modified electrode for the electrochemical reduction of carbon dioxide, characterized in that: Includes the following steps: S1: Soak the copper mesh, copper foam or copper plate substrate in water, hydrochloric acid with a mass concentration of 25%, ethanol or acetone in sequence, clean it in an ultrasonic cleaner, and then clean and dry it for later use. S2: Prepare a solution of bicarbonate and sodium sulfide as the electrolyte, and stir it thoroughly for 20 min under a magnetic stirrer. The concentration of bicarbonate is 0.1 M to 1 M; the concentration of sodium sulfide is 0.3 mM to 2.0 mM. S3: Under the protection of inert gas, the oxidation potential Ea of the cyclic voltage pulse is -0.2 V to -0.6 V; the reduction potential Ec is -1.2 V to -0.6 V. The absolute value of the oxidation potential is always set to be less than the absolute value of the reduction potential; The oxidation time Δta is 1 to 5 seconds; The restoration time Δtc is 2 to 8 seconds; The number of cycles is 50 to 400; Cu is deposited and grown on the surface of the substrate using this voltage pulse deposition method. x O-Cu x S; S4: Under the protection of an inert gas, the electrode prepared in step S3 is used to perform surface reconstruction of the electrodeposited catalyst on the substrate surface using electrochemical potentiostatic reconstruction under the same electrolyte. The constant potential method uses the constant voltage method; the voltage used in the constant voltage method is set to -2.0 V to -1.0 V, and the deposition time is 800 to 2000 seconds; The copper on the surface was converted into Cu2O-Cu2S by a constant voltage method; S5: The electrode prepared in S4 is rinsed clean and dried in a vacuum drying oven at 40-60°C to obtain a sulfur-modified electrode.

2. The method for preparing a sulfur-modified electrode for the electrochemical reduction of carbon dioxide according to claim 1, characterized in that: The molar ratio of sodium bicarbonate salt to sodium sulfide solution is 117:1 to 200:

1.

3. The method for preparing a sulfur-modified electrode for the electrochemical reduction of carbon dioxide according to claim 1, characterized in that: The sodium bicarbonate salt of the electrolyte solution of the cyclic voltage pulse is one or more of KHCO3 and NaHCO3.

4. The method for preparing a sulfur-modified electrode for the electrochemical reduction of carbon dioxide according to claim 1, characterized in that: The concentration of the electrolyte is 0.1M to 1M.

5. A sulfur-modified electrode for the electrochemical reduction of carbon dioxide, characterized in that: The electrode is prepared according to the method described in claim 1, which is a sulfur-modified electrode for the electrochemical reduction of carbon dioxide.

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