CuS nanosheet, preparation method thereof and electrode material

Abstract

The invention provides a CuS nanosheet, a preparation method thereof and an electrode material. The preparation method comprises the following steps: mixing a cuprous source, a sulfur source and a solvent to form a reaction solution; the molar ratio of the cuprous source to the sulfur source is (1.5-2.5): 1, and the solvent comprises water; the reaction liquid is frozen, the frozen reaction liquid is heated in the atmosphere of protective gas for a reaction, a reaction product is washed and dried, and the CuS nanosheet is obtained. The invention also provides the CuS nanosheet obtained by the preparation method and an electrode material containing the nanosheet. The thickness of the CuS nanosheet is as low as atomic scale, the specific surface area is large, and the CuS nanosheet has high catalytic activity and catalytic stability.

Description

Technical Field

[0001] This invention relates to the field of electrochemical technology, and in particular to a CuS nanosheet, its preparation method, and electrode material. Background Technology

[0002] In electrocatalytic reactions, catalytic properties are influenced by the interaction between reactants and the catalyst surface. Therefore, the performance of an electrocatalyst primarily depends on its surface chemical structure, geometry, atomic arrangement, and electronic structure. Catalyst design is crucial for achieving good CO2 electrochemical reduction performance.

[0003] Currently, metal-based catalysts in heterogeneous electrocatalysts have been extensively studied, including transition metals and main group metals, and are classified according to the strength of their bonding with CO2 reduction intermediates and the type of products. Metal-based catalysts such as Ti, Ni, and Pt exhibit low CO2 reduction activity, primarily favoring H2 formation. Metal-based catalysts such as In, Sn, and Hg can catalyze the reduction of CO2 to *OCHO or *COOH, further generating HCOOH or HCOO-. Metal catalysts such as Pd, Ag, and Au can reduce the *COOH intermediate to *CO, but due to the weak bonding between *CO and the metal surface, they cannot further reduce *CO to other products to generate CO. Compared to other metals, copper is unique in that copper-based catalysts can reduce CO2 to HCOOH and *CO to generate CO, or through further reduction and *CO dimerization, generate various hydrocarbon products.

[0004] The application of CuS in electrocatalytic CO2 reduction is being gradually developed. CuS is a transition metal sulfide with the following advantages: 1. High abundance, low cost, and environmentally friendly, being green and pollution-free. 2. Excellent intrinsic properties, such as a tunable band gap (1.2-2.4 eV), significant carrier mobility, high carrier concentration, and low thermal conductivity. 3. Rich structure, possessing various non-stoichiometric phases. Two-dimensional CuS, with its unique anisotropy and electronic structure, can endow it with unique electrocatalytic performance. Its large specific surface area provides numerous surface active sites, and catalytic activity and stability can be controlled by adjusting electronic properties, which is of great significance for further improving the electrochemical performance of CO2 selectivity and efficiency.

[0005] The existing technique Graphdiyne enables Cu nanoparticles for highly selective electroreduction of CO2 to form CuS (ACS Appl. Mater. Interfaces, 2018, 10, 34, 28572-81) to synthesize CuS via electrodeposition.x S-doped and undoped Cu-based catalysts were obtained through electroreduction treatment. The S-doped Cu exhibited high selectivity and activity for the electrocatalytic reduction of CO2 to formate, achieving a formate FE of 75% and a local current density of -9.0 mA·cm⁻¹ at -0.9 V vs RHE. -2 However, the vapor deposition process of this technology is demanding, the preparation method is complex, and the cost is high, which is not conducive to industrial production.

[0006] Existing techniques, such as Sulfur-modified copper catalysts for the electrochemical reduction of carbon dioxide to formate (ACS Catal., 2018, 8, 2 837-844), have shown that the formate produced by synthesizing Cu-S particles of varying sizes is proportional to the particle size, and that S-modified Cu (Cu-S) catalysts can be used for the electrocatalytic reduction of CO2. However, this preparation method is complex, has poor selectivity, and is inefficient.

[0007] It can be seen that the existing synthesis methods for copper-based catalysts are complex and costly; the resulting copper-based catalysts are mostly particulate, and their specific surface area needs further improvement. Furthermore, the existing copper-based catalysts exhibit low catalytic selectivity and efficiency.

[0008] Therefore, it is necessary to design a Cu-based catalyst with a small thickness and a large specific surface area to improve its CO2 electroreduction performance. Summary of the Invention

[0009] To address the aforementioned problems, the present invention aims to provide a CuS nanosheet, its preparation method, and an electrode material thereof. This CuS nanosheet has a thickness down to the atomic level, a large specific surface area, and exhibits high catalytic activity and stability.

[0010] To achieve the above objectives, the present invention provides a method for preparing CuS nanosheets, the method comprising:

[0011] A reaction solution is formed by mixing a cuprous source, a sulfur source, and water; the molar ratio of the cuprous source to the sulfur source is 2-2.5:1, and the solvent is water.

[0012] The reaction solution was frozen, and then heated in a protective gas atmosphere to carry out the reaction. The reaction product was washed and dried to obtain the CuS nanosheets.

[0013] In the above preparation method, the cuprous source may include one or a combination of two or more of cuprous chloride, cuprous sulfate, and cuprous oxide. In some specific embodiments, by adjusting the type of cuprous source, the structural dimensions of the nanosheets, such as thickness and lateral dimensions, can be significantly adjusted.

[0014] In the above preparation method, the sulfur source may include thiourea.

[0015] In the above preparation method, the copper source and sulfur source can be added to the reaction solution in the form of vacuum-dried powder. Vacuum drying eliminates the influence of moisture on the quality of the raw materials.

[0016] In the above preparation method, the preparation method includes: after freezing the reaction solution, placing the frozen reaction solution into a sealed container, removing the air from the sealed container, then introducing a protective gas, and then heating the reaction solution in the sealed container to carry out the reaction. By removing the air from the sealed container, the influence of gases such as moisture and oxygen on the formation of the material can be avoided, thus promoting the formation of low-thickness nanosheets.

[0017] In the above preparation method, the molar ratio of the cuprous source to the sulfur source can be controlled to be 1.5-2.5:1, specifically 1.5:1, 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, etc., and any two of the above specific values ​​as endpoints; further, it can be controlled to be 2-2.5:1. By controlling the ratio of components in the reaction solution, the morphology of the reaction product can be adjusted. In some specific embodiments, by reducing the ratio of the cuprous source to the sulfur source, the thickness of the nanosheets can be reduced.

[0018] In the above preparation method, the solvent can be a polar solvent, such as water. This invention has found that when a solvent with low polarity and viscosity is used, the obtained CuS is granular rather than flake-like; when a solvent with high polarity and viscosity is used, the obtained CuS nanosheets are thick and aggregate. This invention, by using water as the solvent for the reaction liquid, can provide the reaction system with suitable viscosity and polarity, and can also rapidly freeze the reaction liquid to obtain smaller ice crystals, promoting the formation of nanosheets with a large specific surface area.

[0019] In the above preparation method, the molar ratio of the solvent to the cuprous source can be controlled to be 15-50:1, specifically 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, 50:1, etc., and any two of the above specific values ​​as endpoints; further, it can be controlled to be 30-50:1. In some specific embodiments, the amount of solvent added can be 70mL-150mL. In some specific embodiments, by increasing the ratio of solvent to cuprous source, the thickness of the nanosheets can be reduced.

[0020] In the above preparation method, the mixing time for forming the reaction solution can be 1h-5h, for example, specific values ​​such as 1h, 2h, 3h, 4h, 5h, and a range with any two of the above specific values ​​as endpoints.

[0021] In the above preparation method, the mixing process used to form the reaction solution may include stirring.

[0022] In the above preparation method, the reaction solution is usually rapidly frozen. Rapid freezing allows the reaction solution to form uniform and fine ice crystals; during the subsequent heating reaction, these ice crystals can be transformed into uniformly distributed reaction nuclei, thereby obtaining CuS nanosheets with atomic-level thickness and micron-level lateral dimensions, resulting in a large specific surface area.

[0023] In the above preparation method, the freezing method may include liquid nitrogen freezing and / or liquid helium freezing, etc., to achieve rapid freezing.

[0024] In the above preparation method, the protective gas may include one or a combination of two or more of argon, nitrogen, and helium. This invention has found that reacting the reaction solution in air leads to the formation of a thin film of alkaline copper carbonate on the surface of CuS nanosheets, which affects the performance of the CuS nanosheets. By reacting the reaction solution in a protective gas environment, the formation of this alkaline copper carbonate film can be avoided.

[0025] In the above preparation method, the pressure of the protective gas can be controlled between 1 MPa and 3 MPa, for example, specific values ​​such as 1 MPa, 1.5 MPa, 2 MPa, 2.5 MPa, and 3 MPa, or a range with any two of these specific values ​​as endpoints. By controlling the pressure of the introduced protective gas, the growth, morphology, and structure of CuS nanosheets can be adjusted, promoting the formation of nanosheets with sub-nanometer thickness.

[0026] According to a specific implementation plan, the above preparation method further includes: after introducing a protective gas into the sealed container, waiting for the temperature of the reaction liquid in the sealed container to reach room temperature, and then heating the reaction liquid in the sealed container to carry out the reaction. Heating the frozen reaction liquid only after it has reached room temperature avoids damage to the container with a certain pressure during rapid heating, and also promotes uniform nucleation of the reaction liquid in the initial stage of the reaction, which is beneficial for forming nanosheet materials with low thickness and large specific surface area. In this invention, the room temperature is typically 20℃-25℃.

[0027] In the above preparation method, the reaction temperature can be controlled between 130℃ and 180℃, for example, specific values ​​such as 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, 170℃, 175℃, and 180℃, as well as a range with any two of the above specific values ​​as endpoints; it can be further controlled between 130℃ and 150℃. In some specific embodiments, by lowering the reaction temperature, the thickness of the nanosheets can be reduced.

[0028] The reaction time is 4h-12h, for example, specific values ​​such as 4h, 5h, 6h, 7h, 8h, 10h, 12h, and a range with any two of the above specific values ​​as endpoints; it can be further controlled to 4h-8h.

[0029] In the above preparation method, the heating rate during the heating process is 5℃ / min-10℃ / min, for example, specific values ​​such as 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, etc., and a range with any two of the above specific values ​​as endpoints.

[0030] In the above preparation method, the reaction process is stirred at a speed of 100 rpm to 1000 rpm.

[0031] In the above preparation method, after the reaction is completed, the temperature and pressure of the sealed container can be reduced to room temperature and pressure before the reaction product is taken out.

[0032] In the above preparation method, the reaction product can be washed with ethanol and water.

[0033] In the above preparation method, the reaction product can be dried by vacuum drying.

[0034] The present invention also provides a CuS nanosheet obtained by the above preparation method. The CuS nanosheet provided by the present invention can achieve an atomic (angstrom) thickness. The thinned nanosheet has an increased specific surface area, which can expose more active sites and enhance catalytic activity.

[0035] This invention modulates the catalytic performance of CuS nanosheets through morphological and structural control and crystal facet modulation. The resulting CuS nanosheets can serve as a highly efficient Cu-based catalyst, and the CO2 electroreduction performance is improved. The active sites of this Cu-based catalyst in the electrocatalytic reduction of carbon dioxide are mainly affected by crystal facets, grain boundaries, and valence states. Crystal facets affect product selectivity; for example, a higher Cu(100) content or a higher Cu(100) / Cu(111) ratio favors ethylene production, while a higher Cu(110) / Cu(100) ratio favors ethanol production. The activity of the aforementioned CuS nanosheet catalyst in the electrochemical reduction of CO2 can be influenced by electronic structure modulation controlled by external voltage and by modification of the local surface environment.

[0036] According to a specific embodiment of the present invention, the thickness of the CuS nanosheet is 0.7 nm to 50 nm, for example, specific values ​​such as 0.7 nm, 3 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, and 50 nm, and a range with any two of the above specific values ​​as endpoints. In some specific embodiments, the thickness of the CuS nanosheet can be 0.7-30 nm, further can be 0.7-10 nm, even further can be 0.7-5 nm, and still further can be 0.7-3 nm.

[0037] According to a specific embodiment of the present invention, the lateral dimension of the CuS nanosheet is 0.5μm-3μm, for example, specific values ​​such as 1μm, 1.5μm, 2μm, 2.5μm, 3μm, etc., and a range with any two of the above specific values ​​as endpoints; further, it can be 1μm-3μm. In the present invention, the lateral dimension is the dimension perpendicular to the thickness direction, such as length, width, diameter, etc.

[0038] This invention also provides an electrode material, the raw material of which includes the aforementioned CuS nanosheets. This electrode material can be applied to electrocatalytic CO2 reduction processes. The CuS nanosheets have a thickness down to the atomic level and a lateral dimension reaching the micrometer level, resulting in a larger specific surface area compared to other multidimensional materials. This not only exposes more active sites but also significantly alters the electronic structure (electronic state) of surface ions, facilitating the generation and activation of more C intermediates, thus significantly improving catalytic activity and selectivity.

[0039] The beneficial effects of this invention include:

[0040] This invention synthesizes atomically thin CuS nanosheets using a wet chemical synthesis method. These nanosheets have a thickness on the angstrom scale (single-atom layer thickness) and a lateral dimension on the micrometer scale, exhibiting a large specific surface area. Compared to existing two-dimensional materials, these nanosheets show a significantly reduced thickness and a substantial increase in surface area. This not only implies an influence on the two-dimensional wavefunction through quantum confinement but also suggests a greater number of potential active sites that can enhance physicochemical reactions and achieve highly efficient catalysis. Compared to ordinary two-dimensional materials, these nanosheets expose more active sites, exhibiting high electrocatalytic activity. Furthermore, due to the atomic confinement, the electronic structure of surface ions undergoes significant changes, which is more conducive to the activation of multi-carbon intermediates, resulting in higher selectivity and stability. Attached Figure Description

[0041] Figure 1 This is a SEM image of the CuS nanosheets from Example 1.

[0042] Figure 2 The image shows the SEM image of sample a in Comparative Example 2.

[0043] Figure 3 This is the SEM image of sample b from Comparative Example 2.

[0044] Figure 4 The image shows the SEM image of the CuS sample from Comparative Example 3.

[0045] Figure 5 The image shows the SEM image of sample a from Comparative Example 4.

[0046] Figure 6 This is a SEM image of sample b from Comparative Example 4.

[0047] Figure 7 The LSV curves of CuS nanosheets from Example 1 and CuS nanospheres from Comparative Example 1 in CO2-saturated 0.5M KHCO3 electrolyte are shown. Detailed Implementation

[0048] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0049] Example 1

[0050] This embodiment provides a CuS nanosheet, the preparation method of which includes:

[0051] A reaction solution was prepared by mixing CuCl powder and thiourea powder (molar ratio 2.3:1, vacuum-dried) with deionized water for 3 hours and stirring for 3 hours. The molar ratio of deionized water to CuCl was 45:1. The reaction solution was then frozen with liquid nitrogen and placed in a sealed container. The air in the sealed container was evacuated, and then an inert protective gas (nitrogen or helium) at 20 atmospheres (2 MPa) was introduced. After the reaction solution in the sealed container returned to room temperature, it was heated at a heating rate of 5 °C / min, while simultaneously stirring the reaction solution at 500 rpm. The reaction solution was heated to 150 °C and held at this temperature for 6 hours. After the reaction was completed, the solution was placed at room temperature and pressure, removed, and washed 3-7 times with a mixture of water and ethanol. After vacuum drying, a black powder, namely CuS nanosheets, was obtained.

[0052] Figure 1 The SEM image of CuS obtained in this embodiment shows that the CuS is in the form of nanosheets. Measurements show that the thickness of the CuS nanosheets obtained in this embodiment is 0.7 nm-3 nm, and the lateral dimension is 1 μm-3 μm.

[0053] Example 2

[0054] This embodiment provides a CuS nanosheet, the preparation method of which includes:

[0055] A reaction solution was prepared by mixing CuCl powder and thiourea powder (molar ratio 2.3:1, vacuum-dried) with deionized water for 3 hours and stirring for 3 hours. The molar ratio of deionized water to CuCl was 45:1. The reaction solution was then frozen with liquid nitrogen and placed in a sealed container. The air in the sealed container was evacuated, and then an inert protective gas (nitrogen or helium) at 20 atmospheres (2 MPa) was introduced. After the reaction solution in the sealed container returned to room temperature, it was heated at a heating rate of 5 °C / min while being stirred at 500 rpm. The reaction solution was heated to 180 °C and held at this temperature for 6 hours. After the reaction was completed, the solution was placed at room temperature and pressure, removed, and washed 3-7 times with a mixture of water and ethanol. After vacuum drying, a black powder, namely CuS nanosheets, was obtained.

[0056] The CuS obtained in this embodiment is in the form of nanosheets. Measurements show that the thickness of the CuS nanosheets obtained in this embodiment is 3nm-5nm, and the lateral dimension is 0.5μm-1μm.

[0057] Example 3

[0058] This embodiment provides a CuS nanosheet, the preparation method of which includes:

[0059] A reaction solution was prepared by mixing vacuum-dried CuCl powder and thiourea powder in a molar ratio of 1.5:1 with deionized water and stirring for 3 hours. The molar ratio of deionized water to CuCl was 15:1. The reaction solution was then frozen with liquid nitrogen and placed in a sealed container. The air in the sealed container was evacuated, and then an inert protective gas (nitrogen or helium) at a pressure of 20 atmospheres (2 MPa) was introduced. After the reaction solution in the sealed container returned to room temperature, it was heated at a heating rate of 5 °C / min, while the reaction solution was stirred at 500 rpm during heating. The reaction solution was heated to 150 °C and held at this temperature for 6 hours. After the reaction was completed, the solution was placed at room temperature and pressure, removed, and washed 3-7 times with a mixture of water and ethanol. After vacuum drying, a black powder, namely CuS nanosheets, was obtained.

[0060] The CuS obtained in this embodiment is in the form of nanosheets. Measurements show that the thickness of the CuS nanosheets obtained in this embodiment is 2nm-5nm, and the lateral dimension is 1μm-3μm.

[0061] Example 4

[0062] This embodiment provides a CuS nanosheet, the preparation method of which includes:

[0063] A reaction solution was prepared by stirring deionized water (45:1 molar ratio) with cuprous sulfate powder and thiourea powder (1.5:1 molar ratio) in deionized water for 3 hours after vacuum drying. The reaction solution was then frozen with liquid nitrogen and placed in a sealed container. The air in the sealed container was evacuated, and then an inert protective gas (nitrogen or helium) at 20 atmospheres (2 MPa) was introduced. After the reaction solution in the sealed container returned to room temperature, it was heated at a heating rate of 5 °C / min while being stirred at 500 rpm. The reaction solution was heated to 150 °C and held at this temperature for 6 hours. After the reaction was completed, the solution was placed at room temperature and pressure, removed, washed 3-7 times with a mixture of water and ethanol, and then vacuum dried to obtain CuS nanosheets.

[0064] The CuS obtained in this embodiment is a nanosheet with a thickness of 30nm-50nm and a lateral dimension of 1μm-3μm.

[0065] The main reaction parameters and product structural parameters of the above embodiments are summarized in Table 1.

[0066] Table 1

[0067]

[0068] Comparing Example 2 with Example 1, it can be seen that in Example 2, increasing the reaction temperature leads to an increase in the thickness of the nanosheets and a decrease in their lateral dimensions. Comparing Example 3 with Example 1, it can be seen that reducing the molar ratio of the cuprous source to the sulfur source and the molar ratio of water to the cuprous source in Example 3 increases the thickness of the nanosheets. Comparing Example 4 with Example 1, it can be seen that changing the type of cuprous source has a significant impact on the thickness of the nanosheets. Furthermore, this invention also found that the thickness of the nanosheets increases with decreasing pressure. In summary, the cuprous source is the decisive factor affecting the thickness of the nanosheets.

[0069] The above results demonstrate that by adjusting the type of cuprous source, reaction temperature, pressure, ratio of cuprous source to sulfur source, and ratio of water to cuprous source (which affects the concentration of the reaction solution), the present invention can adjust the thickness and lateral dimensions of the nanosheets, thereby adjusting the specific surface area of ​​the nanosheets.

[0070] Comparative Example 1

[0071] This comparative example provides a CuS material, the preparation method of which includes:

[0072] A reaction solution was prepared by stirring CuCl2 divalent copper salt powder and thiourea powder (with a molar ratio of 2.3:1) in deionized water for 3 hours. The molar ratio of deionized water to divalent copper salt was 45:1. The reaction solution was then frozen with liquid nitrogen and placed in a sealed container. The air in the sealed container was evacuated, and then an inert protective gas (nitrogen or helium) at a pressure of 20 atmospheres (2 MPa) was introduced. After the reaction solution in the sealed container returned to room temperature, it was heated at a heating rate of 5 °C / min, while the reaction solution was stirred at 500 rpm during heating. The reaction solution was heated to 150 °C and held at this temperature for 6 hours. After the reaction was completed, the solution was placed at room temperature and pressure, removed, washed 3-7 times with a mixture of water and ethanol, and then vacuum dried to obtain CuS material.

[0073] The main difference between this comparative example and Example 1 is that an equimolar amount of divalent copper salt was used instead of CuCl in this comparative example. The CuS obtained in this comparative example were nanospheres with a particle size of 10 nm-50 nm.

[0074] Comparative Example 2

[0075] This comparative example provides a method for preparing CuS material, which includes:

[0076] CuCl powder and thiourea powder, dried under vacuum with a molar ratio of 2.3:1, were placed in n-hexane and stirred for 3 hours to obtain a reaction solution. The molar ratio of n-hexane to CuCl was 45:1. The reaction solution was frozen with liquid nitrogen and then placed in a sealed container. The air in the sealed container was evacuated, and then an inert protective gas (nitrogen or helium) at a pressure of 20 atmospheres (2 MPa) was introduced. After the reaction solution in the sealed container returned to room temperature, it was heated at a heating rate of 5 °C / min, while the reaction solution was stirred at 500 rpm during heating. The reaction solution was heated to 150 °C and held at this temperature for 6 hours to carry out the reaction. After the reaction was completed, it was placed at room temperature and pressure, and the reaction solution was removed, washed 3-7 times with a mixture of water and ethanol, and then dried under vacuum to obtain sample a.

[0077] The main difference between this comparative example and Example 1 is that this comparative example uses an equimolar amount of n-hexane instead of water as a solvent.

[0078] Figure 2 The SEM image of sample a shows that sample a consists of CuS particles with a diameter of less than 10 nm.

[0079] In this comparative example, ethylene glycol was used instead of water as the solvent in an equimolar amount to obtain sample b. The specific preparation method is as follows:

[0080] CuCl powder and thiourea powder, dried under vacuum and in a molar ratio of 2.3:1, were placed in ethylene glycol and stirred for 3 hours to obtain a reaction solution. The molar ratio of ethylene glycol to CuCl was 45:1. The reaction solution was frozen with liquid nitrogen and then placed in a sealed container. The air in the sealed container was evacuated, and then an inert protective gas (nitrogen or helium) at a pressure of 20 atmospheres (2 MPa) was introduced. After the reaction solution in the sealed container returned to room temperature, it was heated at a heating rate of 5 °C / min, while the reaction solution was stirred at 500 rpm during heating. The reaction solution was heated to 150 °C and held at this temperature for 6 hours to carry out the reaction. After the reaction was completed, it was placed at room temperature and pressure, and the reaction solution was removed, washed 3-7 times with a mixture of water and ethanol, and then dried under vacuum to obtain a black powder, which is CuS nanosheets.

[0081] Figure 3 The SEM image of sample b shows that sample b is CuS nanosheets, but the nanosheets are relatively thick and show obvious aggregation.

[0082] Hexane has a lower viscosity and less polarity than water, while ethylene glycol has a higher viscosity and greater polarity than water. Figure 1 and Figure 2 , Figure 3 The comparison shows that, compared with solvents with high viscosity and polarity, and solvents with low viscosity and polarity, the solvent with moderate viscosity and polarity used in this invention can promote the synthesis of thin CuS nanosheets, avoid agglomeration, and ensure that the nanosheets have a large specific surface area.

[0083] Comparative Example 3

[0084] This comparative example provides a method for preparing CuS material, which includes:

[0085] A reaction solution was prepared by mixing vacuum-dried CuCl powder and thiourea powder in a molar ratio of 2.3:1 (45:1) with deionized water for 3 hours. The reaction solution was then frozen with liquid nitrogen and placed in a sealed container under an air atmosphere. After the reaction solution in the sealed container returned to room temperature, it was heated at a rate of 5°C / min while being stirred at 500 rpm. The reaction solution was heated to 150°C and held at this temperature for 6 hours. After the reaction was completed, the solution was placed at room temperature and pressure, removed, and washed 3-7 times with a mixture of water and ethanol. After vacuum drying, CuS material was obtained.

[0086] The main difference between this comparative example and Example 1 is that air was retained in the sealed container of this comparative example and no protective gas was introduced, resulting in a CuS sample with a SEM image of [image details missing]. Figure 4 .from Figure 4 It can be seen that the CuS obtained in this comparative example is in the form of nanosheets, but the surface of the nanosheets is covered with a layer of basic copper carbonate, which affects the performance of the CuS nanosheets. Figure 1 and Figure 4 The comparison shows that by introducing a protective gas, the present invention can prevent the formation of a basic copper carbonate layer on the surface of the nanosheets, thus ensuring that the performance of the CuS nanosheets is not affected.

[0087] Comparative Example 4

[0088] This comparative example provides a method for preparing CuS material. Compared to Example 1, this comparative example reduces the pressure of the protective gas to 0.5 MPa to obtain sample a. The specific preparation method is as follows:

[0089] A reaction solution was prepared by mixing vacuum-dried CuCl powder and thiourea powder in a molar ratio of 2.3:1 (45:1) with deionized water for 3 hours. The reaction solution was then frozen with liquid nitrogen and placed in a sealed container. The air in the sealed container was evacuated, and then an inert protective gas (nitrogen or helium) at 0.5 MPa was introduced. After the reaction solution in the sealed container returned to room temperature, it was heated at a rate of 5 °C / min while being stirred at 500 rpm. The reaction solution was heated to 150 °C and held at this temperature for 6 hours. After the reaction was completed, the solution was placed at room temperature and pressure, removed, washed 3-7 times with a mixture of water and ethanol, and then vacuum-dried to obtain sample a.

[0090] Figure 5Here is the SEM image of sample a, from Figure 5 It can be seen that the CuS in sample a is in the form of nanospheres.

[0091] In addition, the pressure of the protective gas was increased to 4 MPa in this comparative example to obtain sample b. The specific preparation method is as follows:

[0092] A reaction solution was prepared by mixing vacuum-dried CuCl powder and thiourea powder in a molar ratio of 2.3:1 (45:1) with deionized water for 3 hours. The reaction solution was then frozen with liquid nitrogen and placed in a sealed container. The air in the sealed container was evacuated, and then an inert protective gas (nitrogen or helium) at 4 MPa was introduced. After the reaction solution in the sealed container returned to room temperature, it was heated at a rate of 5 °C / min while being stirred at 500 rpm. The reaction solution was heated to 150 °C and held at this temperature for 6 hours. After the reaction was completed, the solution was placed at room temperature and pressure, removed, washed 3-7 times with a mixture of water and ethanol, and then vacuum-dried to obtain sample b.

[0093] Figure 6 Here is the SEM image of sample b, from Figure 6 It can be seen that the CuS in sample b is in the form of chains.

[0094] Will Figure 5 , Figure 6 and Figure 1 The comparison shows that neither excessively high nor low pressure of the protective gas can yield CuS nanosheets. This invention, by controlling the pressure of the protective gas, can obtain CuS nanosheets with a large specific surface area.

[0095] Test Example 1

[0096] The performance of the CuS nanosheets from Example 1 was tested. The testing apparatus was an H-type electrolytic cell, and the testing process employed a three-electrode system: an Ag / AgCl electrode and a CuS / carbon paper (1×1 cm⁻¹) electrode. 2 The electrode sheet and graphite rod electrode serve as the reference electrode, working electrode, and counter electrode, respectively, with a scan rate set to 10 mV·s. -1 Linear sweep voltammetry curves were collected in CO2-saturated 0.5M KHCO3 (pH=7.2) electrolyte, with a potential range of 0V to -1.2V.

[0097] Figure 7 The LSV curves of CuS nanosheets from Example 1 and CuS nanospheres from Comparative Example 1 in CO2-saturated 0.5 M KHCO3 electrolyte are shown. Figure 7 It can be seen that at 20mA·cm -2The CuS nanosheets prepared in Example 1 showed a lower potential (0.45V) compared to the nanospheres obtained in Comparative Example 1. This indicates that the CuS nanosheets provided by the present invention have a larger specific surface area and thus higher electrocatalytic CO2 reduction activity compared to the nanospheres.

[0098] The above results demonstrate that the preparation method provided by this invention can obtain ultrathin CuS nanosheets with a large specific surface area, which can expose more active sites and is conducive to the activation of multi-C intermediates. The catalytic activity and catalytic stability are significantly improved, exhibiting high electrocatalytic CO2 reduction activity.

Claims

1. A method for preparing CuS nanosheets, the method comprising: mixing a cuprous source, a sulfur source and a solvent to form a reaction solution; the molar ratio of the cuprous source to the sulfur source being 1.5-2.5: 1, and the solvent being water; freezing the reaction solution, heating the frozen reaction solution in an atmosphere of a protective gas to perform a reaction, washing and drying the reaction product to obtain the CuS nanosheets. The cuprous source comprises one or a combination of two or more of cuprous chloride, cuprous sulfate and cuprous oxide. The sulfur source comprises thiourea.

2. The production method according to claim 1, wherein The molar ratio of the solvent to the cuprous source is 15-50:

1.

3. The production method according to claim 1, wherein The freezing mode comprises liquid nitrogen freezing and / or liquid helium freezing.

4. The production method according to claim 1, wherein The pressure of the protective gas is 1-3 MPa.

5. The production method according to claim 1, wherein The temperature of the reaction is 130-180℃, and the reaction time is 4-12 h.

6. The production method according to claim 1, wherein 8.A CuS nanosheet obtained by the method of any one of claims 1-7.

7. The production method according to claim 1, wherein The CuS nanosheet has a thickness of 0.7-50 nm and a lateral size of 0.5-3 μm. 10.An electrode material, the raw material of the electrode material comprising the CuS nanosheet of claim 8 or 9.

9. The CuS nanoplatelets of claim 8, wherein, ​ ​

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