A two-dimensional MOFs / SnO2 quantum dot / MXene catalyst electrode and its preparation method

Abstract

This application relates to a two-dimensional MOFs / SnO2 quantum dot / MXene catalyst electrode and its preparation method. The method for preparing a two-dimensional MOFs / SnO2 quantum dot / MXene catalyst includes: Step 1: preparing SnO2 quantum dot / MXene material; Step 2: dissolving an inorganic metal salt and an organic ligand in an organic mixed solution, and then adding dropwise a dispersion containing SnO2 quantum dot / MXene material; Step 3: high-temperature reaction, centrifugation, washing, and drying to obtain the two-dimensional MOFs / SnO2 quantum dot / MXene catalyst. This application effectively overcomes the problems of low catalytic activity, excessively high reaction overpotential, poor solubility of N2 in aqueous solution, slow diffusion rate, and low activation efficiency of N2 in existing electrocatalytic N2 reduction, achieving efficient nitrogen reduction synthesis of ammonia at room temperature and pressure.

Description

Technical Field

[0001] This application relates to the field of catalyst electrodes, and more specifically, to a two-dimensional MOFs / SnO2 quantum dot / MXene catalyst electrode and its preparation method. Background Technology

[0002] Ammonia is not only a key raw material in fertilizer production, but also widely used in the manufacturing processes of explosives, plastics, dyes, and refrigerants. Nitrogen (N2) constitutes up to 78% of the air, making it an extremely abundant resource. However, due to the extremely high energy of the N≡N bond in the N2 molecule (approximately 941 kJ / mol), it is highly susceptible to oxidation. -1 The high activation energy barrier of nitrogen makes it difficult to directly convert into ammonia. Therefore, developing efficient and energy-saving nitrogen conversion technologies is of great significance for meeting the growing demand for ammonia.

[0003] Currently, the Haber–Bosch process is the main industrial method for ammonia synthesis. This process uses an iron-based catalyst to synthesize ammonia (NH3) from high-purity nitrogen (N2) and high-purity hydrogen (H2) under high temperature (over 300°C) and high pressure (over 100 atm) conditions. Although the Haber–Bosch process is widely used in industrial production, it has several drawbacks: demanding reaction conditions, high energy consumption and cost; and it emits large amounts of carbon dioxide (CO2) during production, causing environmental pollution.

[0004] Electrocatalytic nitrogen fixation, as an emerging ammonia synthesis technology, aims to directly reduce N2 to NH3 using electricity and water as a hydrogen source under environmental conditions. However, current electrocatalytic nitrogen fixation technology still faces many challenges: poor catalytic activity, excessively high reaction potential, low solubility of N2 in aqueous solution, slow diffusion rate, and easy deactivation of catalysts. These factors severely limit the conversion efficiency of electrocatalytic N2 reduction to ammonia synthesis.

[0005] Despite the great potential of metal-organic frameworks (MOFs) and SnO2 quantum dots in the field of catalysis, many challenges remain in the synthesis of ammonia.

[0006] For example, while two-dimensional (2D) MOF nanosheets have advantages such as a large aspect ratio and numerous exposed active sites, their poor conductivity limits their application in electrocatalysis. Although SnO2 quantum dots possess large specific surface area, interfacial effects of nanoparticles, and quantum size effects, how to effectively prevent their aggregation and improve their dispersibility in composite materials is also a problem that urgently needs to be solved.

[0007] MXene, as an emerging two-dimensional layered material, possesses advantages such as high specific surface area and high electrical conductivity, and has potential application value in the field of electrocatalysis. However, two-dimensional MXene sheets are prone to self-stacking, leading to increased electrode film thickness and decreased electron transport and ion diffusion capabilities, thereby affecting its catalytic activity.

[0008] Therefore, developing a novel catalyst with high catalytic activity and selectivity has become a difficult point and challenge in the field of ammonia synthesis technology. Summary of the Invention

[0009] To address the aforementioned issues, this application provides a two-dimensional MOFs / SnO2 quantum dot / MXene catalyst electrode and its preparation method.

[0010] In a first aspect, this application provides a method for preparing a two-dimensional MOFs / SnO2 quantum dot / MXene catalyst, employing the following technical solution:

[0011] A method for preparing a two-dimensional MOFs / SnO2 quantum dot / MXene catalyst includes the following steps:

[0012] Step 1: Preparation of SnO2 quantum dot / MXene materials:

[0013] Step 1a: Mix 1-8 parts by weight of Mo2CT x MXene was placed in anhydrous ethanol aqueous solution, magnetically stirred, and ultrasonically dispersed to obtain homogeneous Mo2CT. x MXene dispersion;

[0014] Step 1b: Dissolve 4-6 parts by weight of SnCl4·5H2O in an inorganic acid solution, stir magnetically, add 0.5-1.5 parts by weight of urea, and stir.

[0015] Step 1c: Mo2CT x The MXene dispersion was added to the material from step 1b and stirred; then the mixture was reacted at 175-185℃ for 8-16 hours.

[0016] Step 1d: After the reaction in step 1c is completed, the impurities in the precipitate are washed away, and the precipitate is frozen and dried to obtain SnO2 quantum dot / MXene material;

[0017] Step 2: Place the SnO2 quantum dot / MXene material in anhydrous ethanol and stir magnetically and disperse ultrasonically until a uniform SnO2 quantum dot / MXene material dispersion is obtained;

[0018] Step 3: Dissolve the inorganic metal salt and organic ligand in the organic mixed solution, stir, and dropwise add the SnO2 quantum dot / MXene material dispersion while stirring;

[0019] The molar ratio of inorganic metal salt to organic ligand is 1:(2-4);

[0020] Organic mixed solutions include one of DMF / CH3OH and DMF / CH3CH2OH;

[0021] Inorganic metal salts include one of bismuth nitrate, zinc nitrate, zinc acetate, copper nitrate, and copper acetate;

[0022] Organic ligands include one of terephthalic acid, 4,4-bipyridine, and dimethylimidazole;

[0023] Step 4: React the material from Step 3 at 140-180℃ for 8-16 hours, then collect the powder by centrifugation, wash and dry to obtain the two-dimensional MOFs / SnO2 quantum dot / MXene catalyst.

[0024] MXene, a highly conductive two-dimensional material, is used as a component of catalysts to significantly improve the overall conductivity of the catalyst. Although MOFs themselves have poor conductivity, their combination with MXene leverages MXene's excellent conductivity, facilitating electron transport within the catalyst and thus improving catalytic efficiency. SnO2 quantum dot / MXene materials, obtained through reactions under specific conditions, help to uniformly disperse SnO2 quantum dots on the MXene surface or between layers, preventing SnO2 quantum dot aggregation. Simultaneously, the two-dimensional structure of MXene provides more attachment sites for SnO2 quantum dots, further reducing the possibility of aggregation. Regarding the problem of self-stacking between MXene sheets, the introduction of SnO2 quantum dots and the growth of MOFs both play a role in suppressing MXene sheet self-stacking. SnO2 quantum dots can fill the spaces between MXene sheets, increasing interlayer interactions and preventing sheet stacking. At the same time, the growth of MOFs occupies space on the surface of MXene sheets, further preventing tight stacking.

[0025] The specially prepared catalyst contains MOFs, SnO2 quantum dots, and MXene, each with different hydrophilic and hydrophobic properties. This facilitates the formation of a hydrophilic-hydrophobic interface within the catalyst. This interfacial structure promotes the adsorption of reactants and the desorption of products, thereby enhancing catalytic activity and selectivity.

[0026] Preferably, the inorganic acid solution in step 1b is an HCl solution with a concentration of 0.1-0.3 mol / L.

[0027] Preferably, in step 1d, the precipitate is soaked in water and anhydrous ethanol to wash away impurities, and then the washed product is frozen for 24 hours and then dried by hot air vacuum.

[0028] Preferably, in the DMF / CH3OH mixture, the volume ratio of DMF to CH3OH is 1:(0.5-2); in the DMF / CH3CH2OH mixture, the volume ratio of DMF to CH3CH2OH is 1:(0.5-2).

[0029] Secondly, this application provides a two-dimensional MOFs / SnO2 quantum dot / MXene catalyst.

[0030] The 2D-0D-2D structure (two-dimensional MOFs, zero-dimensional SnO2 quantum dots, and two-dimensional MXene) proposed in this application fully utilizes the synergistic effect between its components through rational structural design. This structure not only improves the conductivity and stability of the catalyst but also optimizes the transport pathway of reactants and the distribution of catalytic active sites, thereby achieving good catalytic activity and selectivity for the N2 reduction to ammonia synthesis reaction.

[0031] Thirdly, this application provides a method for preparing a two-dimensional MOFs / SnO2 quantum dot / MXene catalyst electrode, employing the following technical solution:

[0032] A method for preparing a two-dimensional MOFs / SnO2 quantum dot / MXene catalyst electrode includes the following steps:

[0033] Step A: Pretreatment of the electrode substrate:

[0034] Step A1: Sonicate the carbon paper in deionized ethanol and distilled water respectively;

[0035] Step A2: Immerse the carbon paper treated in step A1 in acid solution and rinse; then immerse it in alkaline solution and rinse; then immerse it in water.

[0036] Step A3: Place the carbon paper treated in step A2 into a mixed solution of nitric acid and hydrogen peroxide, and sonicate it at 50-70℃ and 80-100Hz.

[0037] Step A4: Calcine the carbon paper after ultrasonic treatment in step A3 at 400-500℃ for 20-40 min to obtain the electrode substrate; Step B: Add the two-dimensional MOFs / SnO2 quantum dot / MXene catalyst described in claim 5 to the dispersion and ultrasonically mix to obtain a suspension of 20-30 mg / mL.

[0038] Step C: The suspension is uniformly drop-coated onto the surface of the electrode substrate, and then 0.01-0.1 wt% Nafion solution is coated onto the surface of the electrode substrate and dried to obtain a two-dimensional MOFs / SnO2 quantum dot / MXene catalyst electrode.

[0039] By adopting the above technical solution, the pretreatment process of the electrode substrate ensures the cleanliness and hydrophilicity of the electrode surface, providing a good foundation for the uniform coating of the catalyst. Ultrasonic treatment with deionized ethanol and distilled water, followed by soaking and rinsing with acid and alkali solutions, effectively removes impurities from the carbon paper surface and improves its surface properties. Subsequent ultrasonic treatment with a mixed solution of nitric acid and hydrogen peroxide, and high-temperature calcination, further enhance the stability and conductivity of the electrode substrate, providing strong support for the efficient operation of the catalyst.

[0040] Preferably, the dispersion includes one of methanol and ethanol.

[0041] Preferably, in step A2, the acid solution includes an HCl solution with a concentration of 0.5-1 mol / L; the alkaline solution includes a NaOH solution with a concentration of 0.5-1 mol / L.

[0042] Preferably, the volume ratio of nitric acid to hydrogen peroxide in the mixed solution is 1:(0.8-1.2).

[0043] Fourthly, this application provides a MOFs / SnO2 quantum dot / MXene catalyst electrode.

[0044] The specially structured two-dimensional MOFs / SnO2 quantum dots / MXene catalyst can effectively improve the conductivity and stability of the catalyst electrode. Furthermore, the unique structure allows for a more complete distribution of catalytic active sites on the catalyst electrode surface, enabling the catalyst electrode to more effectively adsorb and activate nitrogen molecules in the N2 reduction to ammonia reaction, thus significantly improving catalytic activity and selectivity, and also effectively reducing the reduction potential required for reduction.

[0045] In summary, this application has the following beneficial effects:

[0046] 1. The two-dimensional MOFs / SnO2 quantum dot / MXene catalyst of this application, through rational structural design, achieves a 2D-0D-2D structure (two-dimensional MOFs, zero-dimensional SnO2 quantum dots, and two-dimensional MXene), thereby fully utilizing the synergistic effect between the components. This structure not only improves the conductivity and stability of the catalyst, but also optimizes the transport pathway of reactants and the distribution of catalytic active sites, thus achieving good catalytic activity and selectivity for the N2 reduction to ammonia synthesis reaction.

[0047] 2. The MOFs / SnO2 quantum dot / MXene catalyst electrode provided in this application can overcome the problems of low catalytic activity, excessively high reaction overpotential, poor solubility and slow diffusion rate of N2 in aqueous solution, and low activation efficiency of N2 in existing electrocatalytic N2 reduction methods, and realize efficient nitrogen reduction synthesis of ammonia at room temperature and pressure. Attached Figure Description

[0048] Figure 1 This is a SEM image of the two-dimensional Bi-BDC / SnO2 quantum dot / MXene catalyst prepared in Example 1.

[0049] Figure 2 This is an LSV curve of the two-dimensional Bi-BDC / SnO2 quantum dot / MXene catalyst electrode prepared in Example 1 under Ar and N2 atmospheres.

[0050] Figure 3 The graph shows the ammonia yield and Faraday efficiency of the two-dimensional Bi-BDC / SnO2 quantum dot / MXene catalyst electrode prepared in Example 1 under different reduction potentials.

[0051] Figure 4 This is a performance comparison chart of the two-dimensional MOFs / SnO2 quantum dot / MXene catalyst electrode prepared in Examples 1-3 and the SnO2 quantum dot / MXene catalyst electrode in Comparative Example 1. Detailed Implementation

[0052] The present application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0053] The raw materials used in the following examples and comparative examples are all commercially available products.

[0054] Preparation Example

[0055] Preparation Example 1

[0056] Mo2CT x Preparation of MXene:

[0057] Mo2CT was prepared based on the literature (Chemical Engineering Journal, 2021, 410, 128349). x MXene material, specifically:

[0058] 1.0 g of Mo2Ga2C was weighed and placed in 50 mL of a mixed solution of hydrofluoric acid (49% by mass) and concentrated hydrochloric acid at a volume ratio of 3:2. The mixture was reacted at 35 °C for 72 hours under stirring to exfoliate layered Mo2CTx MXene. After etching, the obtained solid was centrifuged, thoroughly washed with distilled water and ethanol, and then vacuum dried at 60 °C to obtain the target product Mo2CTx MXene.

[0059] Example

[0060] Example 1

[0061] A method for preparing a two-dimensional MOFs / SnO2 quantum dot / MXene catalyst electrode includes the following steps:

[0062] Step 1: Preparation of two-dimensional MOFs / SnO2 quantum dots / MXene catalyst

[0063] Step 1: Preparation of SnO2 quantum dot / MXene materials:

[0064] Step 1a: 300 mg of Mo2CT prepared in Example 1 x MXene was placed in 10 mL of anhydrous ethanol aqueous solution, magnetically stirred for 1 h, and ultrasonically dispersed for 30 min. This process was repeated three times to obtain homogeneous Mo2CT. x MXene dispersion.

[0065] Step 1b: Dissolve 0.526g of SnCl4·5H2O in 30mL of 0.1mol / L hydrochloric acid solution and stir magnetically for 30 minutes. Add 0.1g of urea and stir for 1 hour.

[0066] Step 1c: Mo2CT x The MXene dispersion was added to the material from step 1b and stirred thoroughly for 1 hour. The mixture was then transferred to a high-pressure reactor lined with polytetrafluoroethylene and reacted at 180°C for 12 hours.

[0067] Step 1d: After natural cooling, the obtained precipitate was soaked and stirred in deionized water and anhydrous ethanol for 30 min respectively, and repeated 3 times. The obtained product was frozen for 24 h and then vacuum dried at 60 °C for 24 h to obtain SnO2 quantum dot / MXene material.

[0068] Step 2: Place the SnO2 quantum dot / MXene material in 20 mL of anhydrous ethanol, stir magnetically for 10 min, sonicate for 30 min, repeat three or more times until a uniform SnO2 quantum dot / MXene material dispersion is obtained.

[0069] Step 3: Dissolve 1 mmol of Bi(NO3)3·5H2O and 3 mmol of terephthalic acid (molar ratio 1:3) in 30 mL of a 1:2 DMF / CH3OH mixture and stir at room temperature for 30 min. Then, while stirring, add dropwise the prepared homogeneous SnO2 quantum dot / Mo2CT mixture. x The MXene material dispersion was dripped over 30 minutes.

[0070] Step 4: Transfer the material from Step 3 to a 100 mL polytetrafluoroethylene-lined reactor, react at 160 °C for 12 h, collect the resulting powder by centrifugation, and wash with ethanol.

[0071] Then, it was vacuum dried in an oven at 60℃ for 12 h to obtain a two-dimensional MOFs / SnO2 quantum dot / MXene catalyst, specifically a two-dimensional Bi-BDC / SnO2 quantum dot / Mo2CT catalyst. x Mxene catalyst.

[0072] SEM image of the two-dimensional Bi-BDC / SnO2 quantum dot / MXene catalyst (see reference) Figure 1 As can be seen from the figure, the prepared catalyst has a two-dimensional layered structure.

[0073] Step 2: Preparation of the catalyst electrode

[0074] Step A: Pretreatment of the electrode substrate:

[0075] Step A1: Cut the carbon paper to a suitable size, and then sonicate it in deionized ethanol and distilled water for 20 minutes at room temperature.

[0076] Step A2: Soak the carbon paper treated in step A1 in 50 mL of 0.5 mol / L HCl for 2 hours, then rinse it.

[0077] Then immerse it in 50 mL of 0.5 mol / L NaOH for 2 hours, followed by rinsing with deionized water.

[0078] Then soak in deionized water for 5 hours.

[0079] Step A3: Place the carbon paper treated in step A2 into a mixed solution of nitric acid and hydrogen peroxide with a volume ratio of 1:1, and sonicate it at 60℃ and 90Hz for 30 minutes.

[0080] Step A4: Calcine the carbon paper that has been ultrasonically treated in step A3 at 450°C for 30 minutes.

[0081] The calcined product was rinsed with deionized water until the pH reached 7 and then dried at 120°C for 12 hours to obtain the electrode substrate.

[0082] Step B: Add 10 mg of the two-dimensional Bi-BDC / SnO2 quantum dot / MXene catalyst prepared in Step 1 to 400 μL of ethanol, and sonicate for 30 min to obtain a uniformly mixed suspension of 25 mg / mL.

[0083] Step C: Use a 100μL pipette to draw 100μL of suspension and evenly drop it onto the surface of the electrode substrate, once on each side.

[0084] Then, 100 μL of Nafion solution (0.05 wt%) was uniformly drop-coated onto its surface and dried to obtain a two-dimensional Bi-BDC / SnO2 quantum dot / MXene catalyst electrode.

[0085] Example 2

[0086] A method for preparing a two-dimensional MOFs / SnO2 quantum dot / MXene catalyst electrode differs from Example 1 in that some raw materials and parameters are different, as detailed below:

[0087] Step 1: Preparation of two-dimensional MOFs / SnO2 quantum dots / MXene catalyst

[0088] Step 1: Preparation of SnO2 quantum dot / MXene materials:

[0089] Step 1a: 800 mg of Mo2CT prepared in Example 1 x MXene was placed in 10 mL of anhydrous ethanol aqueous solution, magnetically stirred for 1 h, and ultrasonically dispersed for 30 min. This process was repeated three times to obtain homogeneous Mo2CT. x MXene dispersion.

[0090] Step 1b: Dissolve 0.4g of SnCl4·5H2O in 30mL of 0.3mol / L hydrochloric acid solution and stir magnetically for 30 minutes. Add 0.05g of urea and stir for 1 hour.

[0091] Step 1c: Mo2CT x The MXene dispersion was added to the material from step 1b and stirred thoroughly for 1 hour. The mixture was then transferred to a high-pressure reactor lined with polytetrafluoroethylene and reacted at 175°C for 16 hours.

[0092] Step 1d: After natural cooling, the obtained precipitate was soaked and stirred in deionized water and anhydrous ethanol for 30 min respectively, and repeated 3 times. The obtained product was frozen for 24 h and then vacuum dried at 60 °C for 24 h to obtain SnO2 quantum dot / MXene material.

[0093] Step 2: Place the SnO2 quantum dot / MXene material in 20 mL of anhydrous ethanol, stir magnetically for 10 min, sonicate for 30 min, repeat three or more times until a uniform SnO2 quantum dot / MXene material dispersion is obtained.

[0094] Step 3: Dissolve 1 mmol of Zn(NO3)2·6H2O and 2 mmol of terephthalic acid (molar ratio 1:2) in 30 mL of DMF / CH3CH2OH mixture (volume ratio 1:0.5), stir at room temperature for 30 min, and then, while stirring, add dropwise the prepared homogeneous SnO2 quantum dot / Mo2CT mixture. x The MXene material dispersion was dripped over 30 minutes.

[0095] Step 4: Transfer the material from Step 3 to a 100 mL polytetrafluoroethylene-lined reactor, react at 140 °C for 16 h, collect the resulting powder by centrifugation, and wash with ethanol.

[0096] Then, it was vacuum dried in an oven at 60℃ for 12 h to obtain a two-dimensional MOFs / SnO2 quantum dot / MXene catalyst, specifically a two-dimensional Zn-BDC / SnO2 quantum dot / Mo2CT catalyst. x Mxene catalyst.

[0097] Step 2: Preparation of the catalyst electrode

[0098] Step A: Pretreatment of the electrode substrate:

[0099] Step A1: Cut the carbon paper to a suitable size, and then sonicate it in deionized ethanol and distilled water for 20 minutes at room temperature.

[0100] Step A2: Soak the carbon paper treated in step A1 in 50 mL of 1 mol / L HCl for 2 hours, then rinse it.

[0101] Then immerse it in 50 mL of 1 mol / L NaOH for 2 hours, followed by rinsing with deionized water.

[0102] Then soak in deionized water for 5 hours.

[0103] Step A3: Place the carbon paper treated in step A2 into a mixed solution of nitric acid and hydrogen peroxide with a volume ratio of 1:0.8, and sonicate it at 50°C and 100Hz for 30 minutes.

[0104] Step A4: Calcine the carbon paper that has been ultrasonically treated in step A3 at 400℃ for 40 minutes.

[0105] The calcined product was rinsed with deionized water until the pH reached 7 and then dried at 120°C for 12 hours to obtain the electrode substrate.

[0106] Step B: Add 8 mg of the two-dimensional Zn-BDC / SnO2 quantum dot / MXene catalyst prepared in Step 1 to 400 μL of ethanol, and sonicate for 30 min to obtain a uniformly mixed suspension of 20 mg / mL.

[0107] Step C: Use a 100μL pipette to draw 100μL of suspension and evenly drop it onto the surface of the electrode substrate, once on each side.

[0108] Then, 100 μL of Nafion solution (0.01 wt%) was uniformly drop-coated onto its surface and dried to obtain a two-dimensional Zn-BDC / SnO2 quantum dot / MXene catalyst electrode.

[0109] Example 3

[0110] A method for preparing a two-dimensional MOFs / SnO2 quantum dot / MXene catalyst electrode differs from Example 1 in that some raw materials and parameters are different, as detailed below:

[0111] Step 1: Preparation of two-dimensional MOFs / SnO2 quantum dots / MXene catalyst

[0112] Step 1: Preparation of SnO2 quantum dot / MXene materials:

[0113] Step 1a: 200 mg of Mo2CT prepared in Example 1 was used to prepare the Mo2CT. x MXene was placed in 10 mL of anhydrous ethanol aqueous solution, magnetically stirred for 1 h, and ultrasonically dispersed for 30 min. This process was repeated three times to obtain homogeneous Mo2CT. x MXene dispersion.

[0114] Step 1b: Dissolve 0.6g of SnCl4·5H2O in 30mL of 0.1mol / L hydrochloric acid solution and stir magnetically for 30 minutes. Add 0.15g of urea and stir for 1 hour.

[0115] Step 1c: Mo2CT x The MXene dispersion was added to the material from step 1b and stirred thoroughly for 1 hour. The mixture was then transferred to a high-pressure reactor lined with polytetrafluoroethylene and reacted at 185°C for 8 hours.

[0116] Step 1d: After natural cooling, the obtained precipitate was soaked and stirred in deionized water and anhydrous ethanol for 30 min respectively, and repeated 3 times. The obtained product was frozen for 24 h and then vacuum dried at 60 °C for 24 h to obtain SnO2 quantum dot / MXene material.

[0117] Step 2: Place the SnO2 quantum dot / MXene material in 20 mL of anhydrous ethanol, stir magnetically for 10 min, sonicate for 30 min, repeat three or more times until a uniform SnO2 quantum dot / MXene material dispersion is obtained.

[0118] Step 3: Dissolve Zn(CH3COO)2 (1 mmol) and 4,4'-bipyridine (4 mmol) in a molar ratio of 1:4 in 30 mL of a DMF / CH3OH mixture with a volume ratio of 1:1. Stir at room temperature for 30 min. Then, while stirring, add the prepared homogeneous SnO2 quantum dot / Mo2CT mixture dropwise. x The MXene material dispersion was dripped over 30 minutes.

[0119] Step 4: Transfer the material from Step 3 to a 100 mL polytetrafluoroethylene-lined reactor, react at 180 °C for 8 h, collect the resulting powder by centrifugation, and wash with ethanol.

[0120] Then, it was vacuum dried in an oven at 60℃ for 12 h to obtain a two-dimensional MOFs / SnO2 quantum dot / MXene catalyst, specifically a two-dimensional Zn-(4,4,-Bpy) / SnO2 quantum dot / Mo2CT catalyst. x Mxene catalyst.

[0121] Step 2: Preparation of the catalyst electrode

[0122] Step A: Pretreatment of the electrode substrate:

[0123] Step A1: Cut the carbon paper to a suitable size, and then sonicate it in deionized ethanol and distilled water for 20 minutes at room temperature.

[0124] Step A2: Soak the carbon paper treated in step A1 in 50 mL of 0.5 mol / L HCl for 2 hours, then rinse it.

[0125] Then immerse it in 50 mL of 0.5 mol / L NaOH for 2 hours, followed by rinsing with deionized water.

[0126] Then soak in deionized water for 5 hours.

[0127] Step A3: Place the carbon paper treated in step A2 into a mixed solution of nitric acid and hydrogen peroxide with a volume ratio of 1:1.2, and sonicate it at 70℃ and 80Hz for 30 minutes.

[0128] Step A4: Calcine the carbon paper that has been ultrasonically treated in step A3 at 500℃ for 20 minutes.

[0129] The calcined product was rinsed with deionized water until the pH reached 7 and then dried at 120°C for 12 hours to obtain the electrode substrate.

[0130] Step B: Add 12 mg of the two-dimensional Zn-(4,4,-Bpy) / SnO2 quantum dot / MXene catalyst prepared in Step 1 to 400 μL of ethanol, and sonicate for 30 min to obtain a uniformly mixed suspension of 30 mg / mL.

[0131] Step C: Use a 100μL pipette to draw 100μL of suspension and evenly drop it onto the surface of the electrode substrate, once on each side.

[0132] Then, 100 μL of Nafion solution (0.1 wt%) was uniformly drop-coated onto its surface and dried to obtain a two-dimensional Zn-(4,4,-Bpy) / SnO2 quantum dot / MXene catalyst electrode.

[0133] Comparative Example

[0134] Comparative Example 1

[0135] A method for preparing a SnO2 quantum dot / MXene catalyst electrode includes the following steps:

[0136] Step 1: Preparation of SnO2 quantum dot / MXene materials:

[0137] Step 1a: 300 mg of Mo2CT prepared in Example 1 x MXene was placed in 10 mL of anhydrous ethanol aqueous solution, magnetically stirred for 1 h, and ultrasonically dispersed for 30 min. This process was repeated three times to obtain homogeneous Mo2CT. x MXene dispersion.

[0138] Step 1b: Dissolve 0.526g of SnCl4·5H2O in 30mL of 0.1mol / L hydrochloric acid solution and stir magnetically for 30 minutes. Add 0.1g of urea and stir for 1 hour.

[0139] Step 1c: Mo2CT x The MXene dispersion was added to the material from step 1b and stirred thoroughly for 1 hour. The mixture was then transferred to a high-pressure reactor lined with polytetrafluoroethylene and reacted at 180°C for 12 hours.

[0140] Step 1d: After natural cooling, the obtained precipitate was soaked and stirred in deionized water and anhydrous ethanol for 30 min respectively, and repeated 3 times. The obtained product was frozen for 24 h and then vacuum dried at 60 °C for 24 h to obtain SnO2 quantum dot / MXene material.

[0141] Step 2: Preparation of the catalyst electrode

[0142] Step A: Pretreatment of the electrode substrate:

[0143] Step A1: Cut the carbon paper to a suitable size, and then sonicate it in deionized ethanol and distilled water for 20 minutes at room temperature.

[0144] Step A2: Soak the carbon paper treated in step A1 in 50 mL of 0.5 mol / L HCl for 2 hours, then rinse it.

[0145] Then immerse it in 50 mL of 0.5 mol / L NaOH for 2 hours, followed by rinsing with deionized water.

[0146] Then soak in deionized water for 5 hours.

[0147] Step A3: Place the carbon paper treated in step A2 into a mixed solution of nitric acid and hydrogen peroxide with a volume ratio of 1:1, and sonicate it at 60℃ and 90Hz for 30 minutes.

[0148] Step A4: Calcine the carbon paper that has been ultrasonically treated in step A3 at 450°C for 30 minutes.

[0149] The calcined product was rinsed with deionized water until the pH reached 7 and then dried at 120°C for 12 hours to obtain the electrode substrate.

[0150] Step B: Add 10 mg of the SnO2 quantum dot / MXene material prepared in Step 1 to 400 μL of ethanol, and sonicate for 30 min to obtain a uniformly mixed suspension of 25 mg / mL.

[0151] Step C: Use a 100μL pipette to draw 100μL of suspension and evenly drop it onto the surface of the electrode substrate, once on each side.

[0152] Then, 100 μL of Nafion solution (0.05 wt%) was uniformly drop-coated onto its surface and dried to obtain the SnO2 quantum dot / MXene catalyst electrode.

[0153] Performance testing

[0154] The two-dimensional Bi-BDC / SnO2 quantum dot / MXene catalyst electrode from Example 1 was used as the working electrode. An H-type electrolyzer with a cation-separated membrane was selected. 60 mL of 0.1 mol / L NaSO4 electrolyte was added to each of the cathode and anode chambers. N2 gas was bubbled through the cathode chamber at a rate of 5 mL / s for 30 min. The electrocatalytic performance of the catalyst electrode from Example 1 was tested within a potential window of (-0.8)–0 V. Finally, the cathode electrolyte after a 2-hour It test was analyzed using a UV spectrophotometer and the Nash reagent method to determine the ammonia yield and FE of the catalyst.

[0155] The LSV curves of the two-dimensional Bi-BDC / SnO2 quantum dot / MXene catalyst electrode in Ar (the test method is the same as the one described above with N2 introduced, except for the gas introduced, all other operations are the same) and N2 atmospheres are referenced. Figure 2 .

[0156] according to Figure 2 It can be seen that the reduction current density in the N2 atmosphere is significantly higher than that in Ar, indicating that the material has good selectivity for the N2 reduction reaction.

[0157] For details on ammonia yield and FE results, please refer to [link / reference]. Figure 3 The results are summarized in Table 1.

[0158] Table 1

[0159]

[0160]

[0161] According to the test data, the Faraday efficiency reaches a maximum of 37.80% at -0.2V, and the ammonia yield is highest at -0.5V, reaching 16.67 μg·h⁻¹. -1 mg -1 This indicates that the material has a good catalytic effect on the N2 reduction reaction.

[0162] The above method was used to test the two-dimensional MOFs / SnO2 quantum dot / MXene catalyst electrodes of Examples 2-3 and the SnO2 quantum dot / MXene catalyst electrode of Comparative Example 1. The electrocatalytic performance of different catalysts was tested at a reduction potential of -0.5V vs RHE.

[0163] For detailed results, please see [link to results]. Figure 4 The results are summarized in Table 2.

[0164] Table 2

[0165] Group code name <![CDATA[Ammonia production rate (μg·h -1 mg -1 )]]> FE (%) Example 1 Catalyst 3 16.67 24.10 Example 2 Catalyst 2 14.46 20.09 Example 3 Catalyst 4 15.02 21.43 Comparative Example 1 Catalyst 1 5.91 10.51

[0166] The test data show that the catalytic performance of catalysts 2-4 is significantly higher than that of catalyst 1, and catalyst 3 (Example 1) has the best catalytic performance.

[0167] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing a two-dimensional MOFs / SnO2 quantum dot / MXene catalyst, characterized in that, Includes the following steps: Step 1: Preparation of SnO2 quantum dot / MXene materials: Step 1a: Mix 1-8 parts by weight of Mo2CT x MXene was placed in anhydrous ethanol aqueous solution, magnetically stirred, and ultrasonically dispersed to obtain homogeneous Mo2CT. x MXene dispersion; Step 1b: Dissolve 4-6 parts by weight of SnCl4·5H2O in an inorganic acid solution, stir magnetically, add 0.5-1.5 parts by weight of urea, and stir. Step 1c: Mo2CT x The MXene dispersion was added to the material from step 1b and stirred; then the mixture was reacted at 175-185℃ for 8-16 hours. Step 1d: After the reaction in step 1c is completed, the impurities in the precipitate are washed away, and the precipitate is frozen and dried to obtain SnO2 quantum dot / MXene material; Step 2: Place the SnO2 quantum dot / MXene material in anhydrous ethanol and stir magnetically and disperse ultrasonically until a uniform SnO2 quantum dot / MXene material dispersion is obtained; Step 3: Dissolve the inorganic metal salt and organic ligand in the organic mixed solution, stir, and dropwise add the SnO2 quantum dot / MXene material dispersion while stirring; The molar ratio of inorganic metal salt to organic ligand is 1:(2-4); Organic mixed solutions include one of DMF / CH3OH and DMF / CH3CH2OH; Inorganic metal salts include one of bismuth nitrate, zinc nitrate, zinc acetate, copper nitrate, and copper acetate; Organic ligands include one of terephthalic acid, 4,4-bipyridine, and dimethylimidazole; Step 4: React the material from Step 3 at 140-180℃ for 8-16 hours, then collect the powder by centrifugation, wash and dry to obtain the two-dimensional MOFs / SnO2 quantum dot / MXene catalyst.

2. The method for preparing the two-dimensional MOFs / SnO2 quantum dot / MXene catalyst according to claim 1, characterized in that: The inorganic acid solution in step 1b is an HCl solution with a concentration of 0.1-0.3 mol / L.

3. The method for preparing the two-dimensional MOFs / SnO2 quantum dot / MXene catalyst according to claim 1, characterized in that: In step 1d, the precipitate is soaked in water and anhydrous ethanol to wash away impurities, and then the washed product is frozen and dried.

4. The method for preparing the two-dimensional MOFs / SnO2 quantum dot / MXene catalyst according to claim 1, characterized in that: In the DMF / CH3OH mixture, the volume ratio of DMF to CH3OH is 1:(0.5-2); in the DMF / CH3CH2OH mixture, the volume ratio of DMF to CH3CH2OH is 1:(0.5-2).

5. A two-dimensional MOFs / SnO2 quantum dot / MXene catalyst prepared by the preparation method of the two-dimensional MOFs / SnO2 quantum dot / MXene catalyst according to claims 1-4.

6. A method for preparing a two-dimensional MOFs / SnO2 quantum dot / MXene catalyst electrode, characterized in that, Includes the following steps: Step A: Pretreatment of the electrode substrate: Step A1: Sonicate the carbon paper in deionized ethanol and distilled water respectively; Step A2: Immerse the carbon paper treated in step A1 in acid solution and rinse; then immerse it in alkaline solution and rinse; then immerse it in water. Step A3: Place the carbon paper treated in step A2 into a mixed solution of nitric acid and hydrogen peroxide, and sonicate it at 50-70℃ and 80-100Hz. Step A4: Calcine the carbon paper that has been ultrasonically treated in step A3 at 400-500℃ for 20-40 minutes to obtain the electrode substrate; Step B: Add the two-dimensional MOFs / SnO2 quantum dot / MXene catalyst described in claim 5 to the dispersion and mix ultrasonically to obtain a suspension of 20-30 mg / mL; Step C: The suspension is uniformly drop-coated onto the surface of the electrode substrate, and then 0.01-0.1 wt% Nafion solution is coated onto the surface of the electrode substrate and dried to obtain a two-dimensional MOFs / SnO2 quantum dot / MXene catalyst electrode.

7. The method for preparing the two-dimensional MOFs / SnO2 quantum dot / MXene catalyst electrode according to claim 6, characterized in that: The dispersion includes one of methanol and ethanol.

8. The method for preparing the two-dimensional MOFs / SnO2 quantum dot / MXene catalyst electrode according to claim 6, characterized in that: In step A2, the acid solution includes an HCl solution with a concentration of 0.5-1 mol / L; the alkaline solution includes a NaOH solution with a concentration of 0.5-1 mol / L.

9. The method for preparing a two-dimensional MOFs / SnO2 quantum dot / MXene catalyst electrode according to claim 6, characterized in that: In the mixed solution, the volume ratio of nitric acid to hydrogen peroxide is 1:(0.8-1.2).

10. A two-dimensional MOFs / SnO2 quantum dot / MXene catalyst electrode prepared by the preparation method of the two-dimensional MOFs / SnO2 quantum dot / MXene catalyst electrode according to any one of claims 6-9.

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