Snncn catalyst and method of making and use in electrocatalytic reduction of co2

Abstract

The application belongs to the technical field of catalytic preparation of formate from CO2, and particularly relates to a SnNCN catalyst, a preparation method and application of the SnNCN catalyst in electrocatalytic reduction of CO2. The preparation method comprises the following steps: (1) mixing a tin source and melamine, and obtaining an intermediate product after reaction; and (2) calcining. The preparation method overcomes the problem that the catalyst with an oxidation state metal active center in the prior art has poor stability when used in electrocatalytic reduction of CO2 under an industrial-grade current, and the oxidation state metal active center of the obtained catalyst can remain stable under long-time electrolysis conditions.

Description

Technical Field

[0001] This invention belongs to the field of CO2 catalytic production of formate technology, specifically relating to a SnNCN catalyst, its preparation method, and its application in electrocatalytic reduction of CO2. Background Technology

[0002] Electrocatalytic reduction of CO2 is a low-carbon technology that can reduce CO2 to various high-value-added products, such as CO, CH4, HCOOH, C2H5OH, and CH3COOH, in the presence of electricity. Electrocatalytic reduction of CO2 is typically carried out at room temperature and pressure, with a simple process flow and equipment, offering advantages such as mild reaction conditions and a straightforward process.

[0003] Formic acid and formate products are currently the most valuable electrocatalytic CO2 reduction products for electron utilization. The main challenges in achieving high-performance electrocatalytic CO2 reduction to produce formic acid and formate are high selectivity for formic acid and formate, and an industrial-grade current density (>200 mA·cm⁻¹). -2 Excellent stability is a key characteristic of catalysts with oxidized metal active centers. These catalysts, such as indium and lead, exhibit high selectivity for the electrocatalytic reduction of CO2 to formic acid and formate, but also exhibit two side reactions: hydrogen evolution reaction and electrocatalytic reduction of CO2 to CO. However, these catalysts with oxidized metal active centers struggle to maintain excellent stability at high current densities. This is because the potential required for the oxidized metal active center to self-reduction to a zero-valent metal is lower than the overpotential for CO2 electroreduction. The reduction of the oxidized metal to a zero-valent metal significantly enhances the competing hydrogen evolution side reaction. Therefore, constructing stable oxidized metal active centers, suppressing their self-reduction in the electrochemical process, achieving high selectivity for formic acid and formate while simultaneously realizing industrial-grade current, and stabilizing the catalyst for the electrocatalytic reduction of CO2 have become a major research focus. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the shortcomings of existing electrocatalytic reduction of CO2 to formate catalysts, such as difficulty in maintaining excellent stability at high current densities and serious hydrogen evolution reactions, and to provide a SnNCN catalyst, preparation method and application of electrocatalytic reduction of CO2.

[0005] To this end, the present invention provides the following technical solution.

[0006] The first aspect of this invention provides a method for preparing a SnNCN catalyst, comprising the following steps:

[0007] (1) A mixture of tin source and melamine was reacted to obtain an intermediate product;

[0008] (2) Calcination.

[0009] The specific steps of the calcination include: heating to 550-650°C at a heating rate not exceeding 8°C / min and then holding at that temperature for 1-3 hours.

[0010] The molar ratio of the tin source to the melamine is (4-5.5):(11-13).

[0011] In step (1), the reaction temperature is 150-170℃ and the time is 10-14h.

[0012] The tin source is stannous salt;

[0013] Preferably, the stannous salt is stannous chloride and / or stannous nitrate;

[0014] Preferably, the stannous salt is stannous chloride.

[0015] Step (1) further includes adding a dispersant when mixing the tin source and melamine;

[0016] Preferably, the specific steps of step (1) include: mixing tin source, melamine and dispersant, separating after reaction to obtain precipitate, drying, i.e. intermediate product.

[0017] In the preparation method of SnNCN catalyst, the dispersant can be, but is not limited to, methanol. This invention does not impose specific requirements on the amount of dispersant added, as long as it can disperse the tin source and melamine.

[0018] Preferably, in step (2), the calcination is carried out under conditions of air isolation;

[0019] Preferably, the calcination is carried out under air-isolated conditions; preferably, the calcination is carried out under a nitrogen and / or argon atmosphere.

[0020] A second aspect of the present invention provides a SnNCN catalyst prepared by the above-described preparation method.

[0021] A third aspect of this invention provides a method for the electrocatalytic reduction of CO2 to prepare formate, comprising the following steps:

[0022] (1) The SnNCN catalyst prepared by the above preparation method is used as a working electrode and assembled into a gas diffusion flow cell; wherein, in the electrocatalytic reduction of CO2 to prepare formate, Pt sheet is used as auxiliary electrode and saturated silver chloride electrode is used as reference electrode.

[0023] (2) Introduce CO2 and react.

[0024] The method for preparing the working electrode includes: mixing the catalyst, conductive agent, binder solution and dispersion to obtain a catalyst solution, spraying it onto the substrate surface, and drying it to obtain the working electrode;

[0025] In the method for preparing formate by electrocatalytic reduction of CO2, the specific steps for preparing the working electrode include: adding a catalyst and a conductive agent to a dispersion, ultrasonically dispersing for 4-6 minutes, then adding a binder solution, continuing ultrasonic dispersion to obtain a catalyst solution, spraying it onto the substrate surface, and drying to obtain the working electrode.

[0026] The conductive agent can be carbon black; the binder solution can be Nafion solution; and the dispersion can be anhydrous ethanol. In this invention, materials commonly used in the art, such as carbon paper and carbon cloth, are employed as the substrate.

[0027] Preferably, the mass ratio of the catalyst to the conductive agent is (1.5–2.5):1;

[0028] Preferably, the ratio of the mass (mg) of the catalyst to the volume (ml) of the dispersion is (35-45):5;

[0029] Preferably, the volume ratio of the binder solution to the dispersion is (40-60):1000; wherein the solid content of the binder solution is 5-15 wt%.

[0030] Preferably, the catalyst solution is sprayed onto the substrate at a rate of 1.0–2.0 mg / cm². 2 .

[0031] Preferably, when carrying out the reaction described in step (2), the CO2 flow rate is 40-60 sccm;

[0032] Preferably, the voltage is -0.7 to -0.9 V (compared to the reversible hydrogen electrode) during the reaction described in step (2).

[0033] Furthermore, in the electrocatalytic reduction of CO2 to prepare formate, the electrolyte can be, but is not limited to, a neutral electrolyte, such as a potassium bicarbonate solution. Preferably, the electrolyte is a potassium bicarbonate solution with a concentration of 0.8-1.2 mol / L.

[0034] The technical solution of this invention has the following advantages:

[0035] 1. The preparation method of the SnNCN catalyst provided by the present invention includes (1) mixing a tin source and melamine, and obtaining an intermediate product after reaction; (2) calcination. This preparation method overcomes the problem of poor stability of catalysts with oxidized metal active centers in the prior art when used for electrocatalytic reduction of CO2 under industrial-grade current. The oxidized metal active centers of the obtained catalyst can remain stable under long-term electrolysis conditions. The cyanide ion of stannous cyanide, as a strong σ-bond donor, can enhance the covalent interaction between stannous ions and cyanide ions, making the structure more stable and maintaining activity over a long period of time. This allows the catalyst to maintain high stability while obtaining high selectivity and high current density of formate products. In addition, the cyanide ion structure has special characteristics, and [N=C=N] exists in the electrocatalytic process. 2- and [N≡CN] 2- The two forms allow the cyanamide ion to act as a proton relay station, promoting the electron coupling process of proton transfer. The relatively large pore size of the cyanamide compound SnNCN facilitates contact between CO2 and the active metal center. The π-π interaction between the cyanamide ion and CO2 promotes CO2 adsorption on the catalyst, enhancing catalytic activity and increasing the reaction current density. Therefore, the SnNCN catalyst prepared in this invention can achieve high selectivity for formate products while maintaining high stability at industrial-grade current densities.

[0036] Furthermore, in the preparation of formate, the key intermediate is ·OCHO. When the intermediate is ·COOH, the final product is CO. Therefore, controlling the formation of the intermediate ·OCHO is crucial. The SnNCN catalyst prepared in this invention can control the formation of the intermediate ·OCHO, thus improving the high selectivity of the formate product and avoiding the formation of CO. The coordination of cyanamide ions with stannous ions can make the stannous ions more stable in their oxidized state during the electrochemical process, preventing them from being reduced to elemental tin.

[0037] 2. The SnNCN catalyst preparation method provided by the present invention can further optimize the performance of the catalyst by optimizing the reaction conditions, such as controlling the calcination process to further improve the crystallinity of the catalyst.

[0038] 3. This invention provides a method for the electrocatalytic reduction of CO2 to prepare formate. Using the catalyst prepared according to this invention, high selectivity of formate products can be achieved while maintaining stability at industrial-grade current densities. The generation of byproducts CO and H2 is avoided during the preparation of formate products. Attached Figure Description

[0039] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0040] Figure 1 This is the XRD pattern of the catalyst prepared in Example 1 of this invention;

[0041] Figure 2 This is the XRD pattern of the catalyst prepared in Comparative Example 1 of this invention;

[0042] Figure 3 This refers to the current density and formate Faraday efficiency of the catalyst in Example 1 of this invention under different voltages;

[0043] Figure 4 This is the current density and formate Faraday efficiency of the catalyst in Comparative Example 1 of this invention under different voltages;

[0044] Figure 5 This is the current density and formate Faraday efficiency of the catalyst in Comparative Example 2 of this invention under different voltages;

[0045] Figure 6 The catalyst in Example 1 of this invention operates at a current density of 200 mA·cm⁻¹. -2 The following are the results after 110 hours of stability testing. Detailed Implementation

[0046] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0047] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0048] Example 1

[0049] This embodiment provides a method for preparing a SnNCN catalyst, including the following steps:

[0050] (1) Add 0.8g of anhydrous stannous chloride, 1.5g of melamine and 35mL of anhydrous methanol to the reaction vessel and stir at room temperature for 35min to obtain a mixed suspension;

[0051] The reaction vessel containing the mixed suspension was placed in an oven at 160°C and kept at that temperature for 11 hours to carry out the reaction. After the reaction was completed, the product was centrifuged, the lower precipitate was removed, and dried at 50°C for 6 hours to obtain the intermediate product.

[0052] (2) The intermediate product was heated to 600℃ at a heating rate of 5℃ / min and calcined for 2h under Ar atmosphere to obtain SnNCN catalyst.

[0053] This embodiment also provides a method for preparing formate, including the following steps:

[0054] (1) The above-mentioned SnNCN catalyst and carbon black were added to anhydrous ethanol. The mass ratio of SnNCN catalyst to carbon black was 2.2:1, and the mass ratio of SnNCN catalyst to anhydrous ethanol was 40 mg: 5 mL. After ultrasonic dispersion for 5 min, a Nafion solution with a solid content of 5 wt% was added. The volume ratio of the added Nafion solution to anhydrous ethanol was 50:1000. Ultrasonic dispersion was continued for 30 min to obtain a catalyst solution. The obtained catalyst solution was uniformly sprayed onto sheet carbon paper. The coating amount of SnNCN nanocatalyst on the carbon paper was 1.8 mg / cm³. 2 After drying, the working electrode is obtained.

[0055] (2) A 1.5cm×2.5cm working electrode was placed in the cathode chamber, with a contact area of ​​0.5cm×2.0cm with the gas diffusion layer. Saturated silver chloride was used as the reference electrode, and Pt sheet was used as the auxiliary electrode. The gas diffusion flow cell was assembled, and CO2 was introduced to react and synthesize formate. The electrolyte was a 1mol / L potassium bicarbonate solution, and the CO2 gas flow rate was 50sccm. Formate was synthesized under voltages of -0.7V, -0.75V, -0.8V, -0.85V and -0.9V (compared to the reversible hydrogen electrode).

[0056] Example 2

[0057] This embodiment provides a method for preparing a SnNCN catalyst, including the following steps:

[0058] (1) Add 0.9g of anhydrous stannous chloride, 1.45g of melamine and 45mL of anhydrous methanol to the reaction vessel and stir at room temperature for 25min to obtain a mixed suspension.

[0059] The reaction vessel containing the mixed suspension was placed in an oven at 165°C and kept at that temperature for 12 hours to carry out the reaction. After the reaction was completed, the product was centrifuged, the lower precipitate was removed, and dried at 60°C for 5 hours to obtain the intermediate product.

[0060] (2) The intermediate product was heated to 620℃ at a heating rate of 6℃ / min and calcined for 1h under Ar atmosphere to obtain SnNCN catalyst.

[0061] This embodiment also provides a method for preparing formate, including the following steps:

[0062] (1) The above-mentioned SnNCN catalyst and carbon black were added to anhydrous ethanol. The mass ratio of SnNCN catalyst to carbon black was 1.8:1, and the mass-to-volume ratio of SnNCN catalyst to anhydrous ethanol was 42 mg:5 mL. After ultrasonic dispersion for 6 min, a Nafion solution with a solid content of 5 wt% was added. The volume ratio of the added Nafion solution to anhydrous ethanol was 60:1000. Ultrasonic dispersion was continued for 30 min to obtain the catalyst solution. The obtained catalyst solution was uniformly sprayed onto sheet carbon paper. The coating amount of SnNCN nanocatalyst on the carbon paper was 1.5 mg / cm³. 2 After drying, the working electrode is obtained.

[0063] (2) A 1.5cm×2.5cm working electrode was placed in the cathode chamber, with a contact area of ​​0.5cm×2.0cm with the gas diffusion layer. Saturated silver chloride was used as the reference electrode, and Pt sheet was used as the auxiliary electrode. The gas diffusion flow cell was assembled, and CO2 was introduced to react and synthesize formate. The electrolyte was a 1mol / L potassium bicarbonate solution, and the CO2 gas flow rate was 50sccm. Formate was synthesized under voltages of -0.7V, -0.75V, -0.8V, -0.85V and -0.9V (compared to the reversible hydrogen electrode).

[0064] Example 3

[0065] This embodiment provides a method for preparing a SnNCN catalyst, including the following steps:

[0066] (1) Add 0.85g of anhydrous stannous chloride, 1.55g of melamine and 40mL of anhydrous methanol to the reaction vessel and stir at room temperature for 30min to obtain a mixed suspension.

[0067] The reaction vessel containing the mixed suspension was placed in an oven at 160°C and kept at that temperature for 13 hours to carry out the reaction. After the reaction was completed, the product was centrifuged, the lower precipitate was removed, and dried at 80°C for 3 hours to obtain the intermediate product.

[0068] (2) The intermediate product was heated to 580℃ at a heating rate of 5℃ / min and calcined for 2.5h under Ar atmosphere to obtain SnNCN catalyst.

[0069] This embodiment also provides a method for preparing formate, including the following steps:

[0070] (1) The above-mentioned SnNCN catalyst and carbon black were added to anhydrous ethanol. The mass ratio of SnNCN catalyst to carbon black was 2.3:1, and the mass-to-volume ratio of SnNCN catalyst to anhydrous ethanol was 45 mg:5 mL. After ultrasonic dispersion for 4 min, a Nafion solution with a solid content of 5 wt% was added. The volume ratio of the added Nafion solution to anhydrous ethanol was 45:1000. Ultrasonic dispersion was continued for 30 min to obtain the catalyst solution. The obtained catalyst solution was uniformly sprayed onto sheet carbon paper. The coating amount of SnNCN nanocatalyst on the carbon paper was 1.2 mg / cm³. 2 After drying, the working electrode is obtained.

[0071] (2) A 1.5cm×2.5cm working electrode was placed in the cathode chamber, with a contact area of ​​0.5cm×2.0cm with the gas diffusion layer. Saturated silver chloride was used as the reference electrode, and Pt sheet was used as the auxiliary electrode. The gas diffusion flow cell was assembled, and CO2 was introduced to react and synthesize formate. The electrolyte was a 1mol / L potassium bicarbonate solution, and the CO2 gas flow rate was 50sccm. Formate was synthesized under voltages of -0.7V, -0.75V, -0.8V, -0.85V and -0.9V (compared to the reversible hydrogen electrode).

[0072] Comparative Example 1

[0073] This comparative example provides a method for preparing a catalyst, comprising the following steps:

[0074] Take 10 mmol of cyanamide and 10 ml of octadecene in a flask, stir at 60 °C, and evacuate for 20 min.

[0075] 3.5 mmol of TOPO (dissolved in 10 mL of octadecene) and 1 mmol of anhydrous SnCl2 were mixed and stirred at 120 °C under vacuum for 20 min. Then, 4 mL of oleylamine was added, the temperature was raised to 140 °C, and 5 mL of cyanamide in octadecene was added. Stirring was continued for another 30 min. After the reaction was complete, the mixture was washed with ethanol and water and dried to obtain the SnNCN catalyst.

[0076] This comparative example also provides a method for preparing formate, using the SnNCN catalyst prepared in this comparative example to prepare formate according to the method of Example 1.

[0077] Comparative Example 2

[0078] This comparative example also provides a method for preparing formate, using stannous oxide SnO (manufactured by McLean) as a catalyst, and preparing formate according to the method of Example 1.

[0079] Test case

[0080] This experimental example provides performance tests of the catalysts in the examples and comparative examples, as detailed below:

[0081] (1) Figure 1 This is the XRD pattern of the catalyst prepared in Example 1. From Figure 1 As can be seen, the SnNCN catalyst of this invention corresponds to the standard card, indicating that this invention can produce SnNCN catalysts without other impurities.

[0082] Figure 2 This is the XRD pattern of the catalyst prepared in Comparative Example 1. Figure 2 It can be seen that SnNCN prepared using HCN as a raw material has poor crystallinity.

[0083] (2) The current density corresponding to voltages of -0.8V and -0.9V (compared to the reversible hydrogen electrode) during the synthesis of formate in Examples 1, Comparative Example 1 and Comparative Example 2 was determined using Chenhua 1140E. Under the same voltage, the higher the current density, the higher the activity of the catalyst.

[0084] The Faraday efficiency of Example 1, Comparative Example 1, and Comparative Example 2 in the synthesis of formate was determined respectively. The Faraday efficiency was tested by determining the formate concentration in the solution after the reaction using nuclear magnetic resonance spectroscopy, and then calculating the Faraday efficiency using the formula:

[0085]

[0086] Where FE is the Faraday efficiency; F is the Faraday constant; Q is the actual amount of electricity passing through the circuit, in C; and n is the amount of substance of the product, in mol. In this invention, n is the amount of formate produced.

[0087] The current densities of Examples 1, 1, and 2 at different voltages, and the Faraday efficiency of formate are shown in the figures. Figure 3-5 .from Figure 3-5 It can be seen that the catalyst in this embodiment has better activity, better selectivity of formate, and higher Faraday efficiency.

[0088] (3) Figure 6 The catalyst prepared in Example 1 was used at a current density of 200 mA·cm⁻¹ -2 The following are the results of the cycle stability test after 110 hours. Figure 6 It can be seen that the catalyst in Example 1 operates at 200 mA·cm⁻¹ -2 Even after 110 hours at a current density of [insert current density here], the SnNCN catalyst prepared in this invention still maintains high activity and Faradaic efficiency, demonstrating good stability and catalytic activity. The cycle stability was tested at 200 mA·cm⁻¹. -2The test was conducted at a current density, and the change in the Faraday efficiency of the formate product was monitored to test its stability until the Faraday efficiency decreased.

[0089] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a SnNCN catalyst, characterized by, The method comprises the following steps: (1) mixing a tin source and melamine to obtain an intermediate product; (2) calcining; The step (1) further comprises a step of adding a dispersant when mixing the tin source and melamine. The specific steps of the step (1) comprise: mixing the tin source, melamine and dispersant, separating after reaction, drying the precipitate to obtain the intermediate product. The tin source is stannous salt.

2. The production method according to claim 1, characterized by, The specific steps of the calcining comprise: heating at a heating rate of not higher than 8 ℃ / min to 550-650 ℃ and then keeping the temperature for 1-3 h.

3. The preparation method according to claim 1, characterized in that, The molar ratio of the tin source to the melamine is (4-5.5):(11-13).

4. The method of claim 1, wherein, The temperature of the reaction in the step (1) is 150-170 ℃, and the time is 10-14 h.

5. The preparation method according to claim 1, characterized in that, The stannous salt is stannous chloride and / or stannous nitrate.

6. The method of claim 1, wherein, The stannous salt is stannous chloride.

7. The preparation method according to claim 1, characterized in that, The calcining in the step (2) is carried out in an air-isolated condition.

8. The method of claim 1, wherein, The calcining is carried out in a nitrogen and / or argon atmosphere.

9. A method for electrocatalytic reduction of CO2 to form formate salt, characterized by, The method comprises the following steps: (1) preparing a working electrode by using the SnNCN catalyst prepared by the preparation method in any one of claims 1-8, and assembling a gas diffusion flow cell; (2) introducing CO2 and reacting.

10. The method of claim 9, wherein, The preparation method of the working electrode comprises: mixing the catalyst, conductive agent, binder solution and dispersion liquid to obtain a catalyst solution, spraying the catalyst solution on the surface of a substrate, and drying to obtain the working electrode.

11. The method of claim 10, wherein, The mass ratio of the catalyst to the conductive agent is (1.5-2.5):

1.

12. The method of claim 10, wherein, The ratio of the mass (mg) of the catalyst to the volume (ml) of the dispersion liquid is (35-45):

5.

13. The method of claim 10, wherein, The volume ratio of the binder solution to the dispersion liquid is (40-60):1000; wherein the solid content of the binder solution is 5-15 wt%.

14. The method of claim 10, wherein, The catalyst solution is sprayed on the substrate in an amount of 1.0 to 2.0 mg / cm 2 .

15. The method of claim 9, wherein, When the reaction in the step (2) is carried out, the amount of introduced CO2 is 40-60 sccm.

16. The method of claim 9, wherein, When the reaction in the step (2) is carried out, the voltage is-0.7--0.9 V.

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