A low-crystalline tin dioxide catalyst for electrocatalysis and a method for preparing the same

Abstract

The application belongs to the technical field of electrocatalysis, and particularly relates to a low-crystalline tin dioxide catalyst for electrocatalysis and a preparation method thereof. By regulating solute types, solvent ratios and other elements, the low-crystalline tin dioxide is prepared by a simple one-step precipitation method. The low-crystalline catalyst contains rich crystalline-amorphous heterojunctions and defects (such as oxygen vacancies), enhances carbon dioxide adsorption and activation, improves formic acid selectivity and catalytic reaction activity, maintains high Faraday efficiency under industrial current density, and overcomes problems such as poor stability of traditional SnO2 catalysts under large current, intensified hydrogen evolution side reactions and the like. In addition, the method of the application does not need high-temperature calcination, has low energy consumption, uses common reagents, and is suitable for industrial large-scale preparation. The low-crystalline tin dioxide shows excellent activity and selectivity in electrocatalytic CO2 reduction to produce formic acid.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalysis technology, specifically relating to a low-crystallinity tin dioxide catalyst for electrocatalysis and its preparation method. Background Technology

[0002] With the large-scale use of fossil fuels such as coal, oil, and natural gas, human society has entered a period of rapid development. However, the utilization of fossil fuels generates large amounts of carbon dioxide (CO2) emissions into the atmosphere, leading to increasingly severe environmental problems such as global warming and ocean acidification, seriously threatening the sustainable development of human society. Currently, carbon dioxide capture, utilization, and storage (CCUS) has received widespread attention as an effective way to reduce CO2 emissions. Among them, electrocatalytic CO2 reduction technology, as one of the CO2 utilization technologies, can electrochemically convert CO2 into high-value-added fuels and chemicals using renewable electricity as an energy source. It has advantages such as mild reaction conditions and controllable processes, and has great development potential. Electrocatalytic CO2 reduction produces many products, such as carbon monoxide, formic acid, ethylene, and ethanol. Among them, formic acid can be used as a chemical raw material and fuel cell feedstock, with broad market prospects and higher added value compared to other products.

[0003] Tin dioxide (SnO2) is a common electrocatalyst for the reduction of CO2 to formic acid. This catalyst has advantages such as high selectivity, low cost, and environmental friendliness in formic acid production. However, it also has limitations in industrial-scale applications requiring high currents (≥300 mA cm⁻¹). -2 Problems such as poor stability and intensified hydrogen evolution reaction urgently need to be addressed. Multiple studies have demonstrated that, compared to highly crystalline catalysts, low-crystalline catalysts possess a higher density of defects and an unsaturated coordination environment, resulting in a richer number of active sites and stronger adsorption and activation capabilities for CO2. Therefore, low-crystalline catalysts have higher electrocatalytic CO2 reduction potential. Developing efficient low-crystalline tin dioxide catalysts suitable for large-scale industrial production will be beneficial for promoting the industrial application of electrocatalytic CO2 reduction to formic acid. Summary of the Invention

[0004] The purpose of this invention is to provide a low-crystallinity tin dioxide catalyst for electrocatalysis and its preparation method, which exhibits excellent activity and selectivity in the electrocatalytic reduction of CO2 to formic acid.

[0005] A method for preparing a low-crystallinity tin dioxide catalyst for electrocatalysis includes the following steps:

[0006] S1. Mix tin salt with solvent A and stir at 300-500 rpm until completely dissolved to obtain substance one;

[0007] S2. Add solvent B to substance one and continue stirring at 300-500 rpm for 20-40 minutes to obtain substance two;

[0008] S3. Add an alkaline solution to substance 2, observe the formation of a white precipitate, and then stir at 300-500 rpm for 0.5-1.5 hours to obtain substance 3;

[0009] S4. Wash the substance three with anhydrous ethanol and deionized water in sequence, centrifuge 5-6 times (or vacuum filter), and then vacuum dry to obtain the final product.

[0010] Preferably, in step S1, the tin salt is any one of tin chloride and its hydrate.

[0011] Preferably, in step S1, solvent A is anhydrous ethanol or deionized water.

[0012] Preferably, the ratio of the tin salt to solvent A is 1 mmol: (0-10) mL.

[0013] Preferably, in step S2, solvent B is anhydrous ethanol or deionized water.

[0014] Preferably, the ratio of the tin salt to solvent B is 1 mmol: (0-10) mL.

[0015] Preferably, the ratio of the total amount of solvent A and solvent B added to the tin salt is (3-10) mL: 1 mmol.

[0016] In some preferred embodiments, solvent A and solvent B are ethanol and deionized water, respectively, in a volume ratio of 1:1.

[0017] Preferably, in step S3, the alkaline solution is one or more of ammonia, sodium hydroxide solution, and potassium hydroxide solution.

[0018] Preferably, the mass fraction of the ammonia solution is 28-30%; the molar concentration of both the sodium hydroxide solution and the potassium hydroxide solution is 0.1-10 mol / L.

[0019] Preferably, the ratio of the tin salt to ammonia is 1 mmol: (0-4) mL.

[0020] Preferably, the molar ratio of sodium hydroxide in the tin salt and sodium hydroxide solution is 1 mmol:(0-4) mmol; and the molar ratio of potassium hydroxide in the tin salt and potassium hydroxide solution is 1 mmol:(0-4) mmol.

[0021] In some preferred embodiments, step S2 can be omitted, and an alkaline solution can be added directly to substance one.

[0022] The addition of alkaline solution introduces hydroxyl groups into the catalyst. Vacuum drying is insufficient to destroy the hydroxyl bonds in the precursor; instead, it rapidly removes free water, ultimately retaining the hydroxyl groups within the formed low-crystalline tin dioxide. The introduction of hydroxyl groups leads to the formation of a Sn-OH structure in the low-crystalline tin dioxide. Compared to Sn-O, Sn-OH is less easily reduced to metallic Sn during electrocatalytic CO2 reduction, which is beneficial for CO2 adsorption and activation, inhibiting the hydrogen evolution reaction. This allows the low-crystalline tin dioxide to maintain high formic acid selectivity even at high current densities. However, the amount of alkaline solution added must be appropriate; excessive alkaline solution will cause the generated tin hydroxide to further react with the alkali and dissolve to form stannate.

[0023] Preferably, in step S4, the specific conditions for centrifugation are: a rotation speed of 7000-12000 rpm and a time of 5-10 min.

[0024] Preferably, in step S4, the specific conditions for vacuum drying are: vacuum degree of 0.08-0.1 MPa, temperature of 50-80℃, and time of 5-12h.

[0025] By controlling the vacuum drying conditions, the prepared catalyst can be in a low-crystallinity state, which helps to improve the catalyst's activity and selectivity in the electrocatalytic reduction of formic acid by CO2. This is likely because vacuum drying at temperatures of 50-80℃ can only remove physically adsorbed water and ethanol, as well as some structural water, and the energy provided is far from sufficient to remove all structural water and achieve sufficient crystal growth. The atoms within the catalyst can only undergo localized, short-range ordering, and cannot form long-range periodic arrangements. The low-crystallinity catalyst possesses abundant defects, enhancing CO2 adsorption and activation, and improving the selectivity of the electrocatalytic reduction of formic acid by CO2.

[0026] The low-crystalline tin dioxide catalyst prepared by the method described above is a low-crystalline tin dioxide catalyst for electrocatalysis.

[0027] Preferably, the surface of the low-crystallinity tin dioxide catalyst contains hydroxyl groups, and the particle size is in the nanometer range.

[0028] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0029] 1. This invention provides a low-crystallinity tin dioxide catalyst for electrocatalysis. A simple one-step precipitation method is used to synthesize an electrocatalyst for the reduction of CO2 to formic acid with excellent performance at industrial-grade current densities. It does not require high-temperature calcination, has low energy consumption, and is suitable for large-scale industrial preparation.

[0030] 2. By controlling experimental factors such as the type of solute and the ratio of solvent, this invention can prepare a catalyst in a low-crystallinity state, which helps to improve the activity and selectivity of the catalyst in the electrocatalytic reduction of CO2 to formic acid.

[0031] 3. The low-crystallinity tin dioxide catalyst synthesized in this invention has abundant crystalline-amorphous heterostructures and defects (such as oxygen vacancies), which enhance CO2 adsorption and activation.

[0032] 4. The low-crystallinity tin dioxide catalyst synthesized in this invention has a Sn-OH structure. The Sn-OH structure is more difficult to reduce than the Sn-O structure. Therefore, the low-crystallinity tin dioxide catalyst is more difficult to be reduced to metallic tin (Sn) during the electrocatalytic CO2 reduction process, thereby inhibiting the occurrence of hydrogen evolution reaction. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0034] Figure 1 The XRD patterns are of the SnO2-OH-1 catalyst of Example 1, SnO2-OH-2 catalyst of Example 2, SnO2-OH-3 catalyst of Example 3 and SnO2 catalyst of Comparative Example 1 prepared by the present invention.

[0035] Figure 2 TGA images of the SnO2-OH-3 catalyst of Example 3 and the SnO2 catalyst of Comparative Example 1 prepared by the present invention;

[0036] Figure 3 The FTIR spectra of the SnO2-OH-4 catalyst of Example 4 and the SnO2 catalyst of Comparative Example 1 prepared by the present invention are shown below.

[0037] Figure 4 The EPR test results are shown for the SnO2-OH-1 catalyst of Example 1 and the SnO2 catalyst of Comparative Example 1 prepared by the present invention.

[0038] Figure 5 This is a SEM image of the SnO2 catalyst prepared in Comparative Example 1 according to the present invention;

[0039] Figure 6 The image shows a SEM image of the SnO2-OH-1 catalyst prepared in Example 1 according to the present invention.

[0040] Figure 7 This is a SEM image of the SnO2-OH-5 catalyst prepared in Example 5 of this invention;

[0041] Figure 8 The EDS diagram of the SnO2-OH-1 catalyst prepared in Example 1 according to the present invention;

[0042] Figure 9Here is an HRTEM image of the SnO2 catalyst prepared in Comparative Example 1 according to the present invention;

[0043] Figure 10 The image shows an HRTEM image of the SnO2-OH-1 catalyst prepared in Example 1 according to the present invention.

[0044] Figure 11 The image shows the HRTEM image of the SnO2-OH-4 catalyst prepared in Example 4 according to the present invention.

[0045] Figure 12 The image shows the HRTEM image of the SnO2-OH-5 catalyst prepared in Example 5 of this invention.

[0046] Figure 13 The image shows the HRTEM image of the SnO2-OH-6 catalyst prepared in Example 6 of this invention.

[0047] Figure 14 The LSV test results of the SnO2-OH-1 catalyst of Example 1 and the SnO2 catalyst of Comparative Example 1 prepared by the present invention are shown without iR correction.

[0048] Figure 15 The LSV test results of the SnO2-OH-1 catalyst of Example 1 and the SnO2 catalyst of Comparative Example 1 prepared by the present invention are shown in the iR-corrected LSV test results.

[0049] Figure 16 The LSV test results of the SnO2-OH-1 catalyst of Example 1 and the SnO2-C catalyst of Comparative Example 2 prepared by the present invention are without iR correction.

[0050] Figure 17 The image shows the liquid chromatogram of a standard formic acid solution (20.0 mmol / L).

[0051] Figure 18 The SnO2 catalyst prepared for Comparative Example 1 of this invention was subjected to a reaction at 1000 mA cm⁻¹. -2 Liquid chromatogram of the electrolyte obtained after reacting at current density for 2500 s.

[0052] Figure 19 Example 1 SnO2-OH-1 prepared according to the present invention was subjected to a reaction at 1000 mA cm⁻¹ -2 Liquid chromatogram of the electrolyte obtained after reacting at current density for 2500 s.

[0053] Figure 20 Example 2 SnO2-OH-2 prepared according to the present invention was subjected to a reaction at 1000 mA cm⁻¹ -2 Liquid chromatogram of the electrolyte obtained after reacting at current density for 2500 s.

[0054] Figure 21 Example 3 SnO2-OH-3 prepared according to the present invention was subjected to a reaction at 1000 mA cm⁻¹ -2 Liquid chromatogram of the electrolyte obtained after reacting at current density for 2500 s.

[0055] Figure 22 Example 4 SnO2-OH-4 prepared according to the present invention was subjected to a reaction at 1000 mA cm⁻¹ -2 Liquid chromatogram of the electrolyte obtained after reacting at current density for 2500 s.

[0056] Figure 23 Example 5 SnO2-OH-5 prepared according to the present invention was subjected to a reaction at 1000 mA cm⁻¹ -2 Liquid chromatogram of the electrolyte obtained after reacting at current density for 2500 s.

[0057] Figure 24 Example 6 SnO2-OH-6 prepared according to the present invention was subjected to a reaction at 1000 mA cm⁻¹ -2 Liquid chromatogram of the electrolyte obtained after reacting at current density for 2500 s.

[0058] Figure 25 The formic acid Faraday efficiency diagrams are obtained by constant current testing of electrocatalytic CO2 reduction of the SnO2-OH-1 catalyst of Example 1 and the SnO2 catalyst of Comparative Example 1 prepared by the present invention.

[0059] Figure 26 The SnO2-OH-1 catalyst prepared in Example 1 of this invention was subjected to a reaction at 400 mA cm⁻¹. -2 Stability test results of electrocatalytic CO2 reduction reaction at current density.

[0060] Figure 27 The CO2 isothermal adsorption test results are shown for the SnO2-OH-1 catalyst of Example 1 and the SnO2 catalyst of Comparative Example 1 prepared by the present invention.

[0061] Figure 28 The cyclic voltammetry (CV) curves of the SnO2-OH-1 catalyst of Example 1 and the SnO2 catalyst of Comparative Example 1 prepared by the present invention are shown.

[0062] Figure 29 The image shows the XRD pattern of the SnO2 catalyst prepared in Comparative Example 1 after electrocatalytic CO2 reduction reaction at a specific current density.

[0063] Figure 30The image shows the XRD pattern of the SnO2-OH-1 catalyst prepared in Example 1 of this invention after electrocatalytic CO2 reduction reaction at a specific current density.

[0064] Figure 31 This is a comparison chart showing the yield of the SnO2-OH-4 catalyst prepared in Example 4 and the SnO2-OH-7 catalyst prepared in Comparative Example 3. Detailed Implementation

[0065] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0066] All raw materials used in this invention are commercially available, as detailed below.

[0067] Example 1

[0068] This embodiment provides a low-crystallinity tin dioxide catalyst SnO2-OH-1 for electrocatalysis, and its preparation method includes the following steps:

[0069] S1. Mix 4 mmol of SnCl4·5H2O with 18 mL of anhydrous ethanol and stir at 400 rpm until completely dissolved to obtain substance one;

[0070] S2. Add 18 mL of deionized water to substance one and continue stirring at 400 rpm for 30 min to obtain substance two;

[0071] S3. Add 4 mL of ammonia water to substance 2, observe the formation of a white precipitate, and then stir at 400 rpm for 1 hour to obtain substance 3.

[0072] S4. Wash the substance three with anhydrous ethanol and deionized water in sequence, centrifuge 5 times, and then dry under vacuum to obtain the final product.

[0073] The ammonia solution has a mass fraction of 28%.

[0074] In step S4, the specific conditions for centrifugation are: a rotation speed of 8000 rpm and a time of 8 min.

[0075] In step S4, the specific conditions for vacuum drying are: vacuum degree of 0.09 MPa, temperature of 60°C, and time of 8 hours.

[0076] Example 2

[0077] This embodiment provides a low-crystallinity tin dioxide catalyst SnO2-OH-2 for electrocatalysis, and its preparation method includes the following steps:

[0078] S1. Mix 4 mmol of SnCl4·5H2O with 36 mL of deionized water and stir at 400 rpm until completely dissolved to obtain substance one;

[0079] S2. Add 4 mL of ammonia water to substance 1, observe the formation of a white precipitate, and then stir at 400 rpm for 1 hour to obtain substance 3.

[0080] S3. Wash the substance three with anhydrous ethanol and deionized water in sequence, centrifuge 5 times, and then dry under vacuum to obtain the final product.

[0081] The ammonia solution has a mass fraction of 28%.

[0082] In step S3, the specific conditions for centrifugation are: a rotation speed of 8000 rpm and a time of 8 minutes.

[0083] In step S3, the specific conditions for vacuum drying are: vacuum degree of 0.09 MPa, temperature of 60°C, and time of 8 hours.

[0084] Example 3

[0085] This embodiment provides a low-crystallinity tin dioxide catalyst SnO2-OH-3 for electrocatalysis, and its preparation method includes the following steps:

[0086] S1. Mix 4 mmol of SnCl4·5H2O with 36 mL of anhydrous ethanol and stir at 400 rpm until completely dissolved to obtain substance one;

[0087] S2. Add 4 mL of ammonia water to substance 1, observe the formation of a white precipitate, and then stir at 400 rpm for 1 hour to obtain substance 3.

[0088] S3. Wash the substance three with anhydrous ethanol and deionized water in sequence, centrifuge 5 times, and then dry under vacuum to obtain the final product.

[0089] The ammonia solution has a mass fraction of 28%.

[0090] In step S3, the specific conditions for centrifugation are: a rotation speed of 8000 rpm and a time of 8 minutes.

[0091] In step S3, the specific conditions for vacuum drying are: vacuum degree of 0.09 MPa, temperature of 60°C, and time of 8 hours.

[0092] Example 4

[0093] This embodiment provides a low-crystallinity tin dioxide catalyst SnO2-OH-4 for electrocatalysis, and its preparation method includes the following steps:

[0094] S1. Mix 4 mmol of SnCl4·5H2O with 18 mL of anhydrous ethanol and stir at 400 rpm until completely dissolved to obtain substance one;

[0095] S2. Add 18 mL of deionized water to substance one and continue stirring at 400 rpm for 30 min to obtain substance two;

[0096] S3. Add 4 mL of potassium hydroxide solution to substance 2, observe the formation of a white precipitate, and then stir at 400 rpm for 1 hour to obtain substance 3.

[0097] S4. Wash the substance three with anhydrous ethanol and deionized water in sequence, centrifuge 5 times, and then dry under vacuum to obtain the final product.

[0098] The molar concentration of the potassium hydroxide solution is 4 mol / L.

[0099] In step S4, the specific conditions for centrifugation are: a rotation speed of 8000 rpm and a time of 8 min.

[0100] In step S4, the specific conditions for vacuum drying are: vacuum degree of 0.09 MPa, temperature of 60°C, and time of 8 hours.

[0101] Example 5

[0102] This embodiment provides a low-crystallinity tin dioxide catalyst SnO2-OH-5 for electrocatalysis, and its preparation method includes the following steps:

[0103] S1. Mix 4 mmol of SnCl4·5H2O with 18 mL of anhydrous ethanol and stir at 400 rpm until completely dissolved to obtain substance one;

[0104] S2. Add 18 mL of deionized water to substance one and continue stirring at 400 rpm for 30 min to obtain substance two;

[0105] S3. Add 4 mL of ammonia water to substance 2, observe the formation of a white precipitate, and then stir at 400 rpm for 1 hour to obtain substance 3.

[0106] S4. Wash the substance three with anhydrous ethanol and deionized water in sequence, centrifuge 5 times, and then dry under vacuum to obtain the final product.

[0107] The ammonia solution has a mass fraction of 28%.

[0108] In step S3, the specific conditions for centrifugation are: a rotation speed of 8000 rpm and a time of 8 minutes.

[0109] In step S3, the specific conditions for vacuum drying are: vacuum degree of 0.09 MPa, temperature of 60℃, and time of 12h.

[0110] Example 6

[0111] This embodiment provides a low-crystallinity tin dioxide catalyst SnO2-OH-6 for electrocatalysis, and its preparation method includes the following steps:

[0112] S1. Mix 4 mmol of SnCl4·5H2O with 16 mL of anhydrous ethanol and stir at 400 rpm until completely dissolved to obtain substance one;

[0113] S2. Add 16 mL of deionized water to substance one and continue stirring at 400 rpm for 30 min to obtain substance two;

[0114] S3. Add 8 mL of ammonia water to substance 2, observe the formation of a white precipitate, and then stir at 400 rpm for 1 hour to obtain substance 3.

[0115] S4. Wash the substance three with anhydrous ethanol and deionized water in sequence, centrifuge 5 times, and then dry under vacuum to obtain the final product.

[0116] The ammonia solution has a mass fraction of 28%.

[0117] In step S3, the specific conditions for centrifugation are: a rotation speed of 8000 rpm and a time of 8 minutes.

[0118] In step S3, the specific conditions for vacuum drying are: vacuum degree of 0.09 MPa, temperature of 60°C, and time of 8 hours.

[0119] Comparative Example 1

[0120] The difference between this comparative example and Example 1 is that the SnO2-OH-1 prepared in Example 1 was placed in a muffle furnace and calcined at 500°C for 3 hours to obtain a crystalline SnO2 catalyst.

[0121] Comparative Example 2

[0122] This comparative example uses SnO2-C (commercial tin dioxide) catalyst. This catalyst can be purchased directly from chemical procurement platforms.

[0123] Comparative Example 3

[0124] This comparative example provides a low-crystallinity tin dioxide catalyst SnO2-OH-7 for electrocatalysis, and its preparation method includes the following steps:

[0125] S1. Mix 4 mmol of SnCl4·5H2O with 18 mL of anhydrous ethanol and stir at 400 rpm until completely dissolved to obtain substance one;

[0126] S2. Add 18 mL of deionized water to substance one and continue stirring at 400 rpm for 30 min to obtain substance two;

[0127] S3. Add 5 mL of potassium hydroxide solution to substance 2, observe the formation of a white precipitate, and then stir at 400 rpm for 1 hour to obtain substance 3.

[0128] S4. Wash substance three five times with anhydrous ethanol and deionized water in sequence, then filter, centrifuge, and vacuum dry to obtain the product.

[0129] The molar concentration of the potassium hydroxide solution is 4 mol / L.

[0130] In step S4, the specific conditions for centrifugation are: a rotation speed of 8000 rpm and a time of 8 min.

[0131] In step S4, the specific conditions for vacuum drying are: vacuum degree of 0.09 MPa, temperature of 60°C, and time of 8 hours.

[0132] Characterization and performance testing

[0133] (1) X-ray diffraction (XRD) test: In order to determine the phase of the catalyst, the catalyst prepared in this invention was subjected to XRD test, and the results are shown in the figure. Figure 1 .from Figure 1 As can be seen from the comparison with the standard PDF card, the catalyst of Comparative Example 1, which underwent muffle furnace calcination, is a SnO2 catalyst with good crystallinity. The catalysts of Example 1 (SnO2-OH-1), Example 2 (SnO2-OH-2), and Example 3 (SnO2-OH-3), which were not calcined in a muffle furnace, showed no sharp diffraction peaks and were low-crystallinity tin dioxide. To investigate the phase evolution of the catalyst during the electrocatalytic CO2 reduction reaction, XRD tests were performed on the catalysts after the electrocatalytic CO2 reduction reaction. The results are shown in [Figure number missing]. Figures 29-30 .from Figure 29 As can be seen from the comparison with the standard PDF card, the SnO2 catalyst in Comparative Example 1 was reduced to metallic tin (Sn) during the electrocatalytic CO2 reduction process. Furthermore, the changes in diffraction peak intensity indicate that the degree of reduction of the SnO2 catalyst in Comparative Example 1 gradually increased with increasing current density. Figure 30As can be seen from the comparison with the standard PDF card, the SnO2-OH-1 catalyst of Example 1 was also reduced to metallic Sn during the electrocatalytic CO2 reduction process. Furthermore, the change in diffraction peak intensity shows that the degree of reduction of SnO2-OH-1 in Example 1 gradually increases with increasing current density. Comparing the diffraction peak intensities of metallic Sn generated by the SnO2 catalyst of Comparative Example 1 and the SnO2-OH-1 catalyst of Example 1 during the electrocatalytic CO2 reduction process, it is clear that the SnO2-OH-1 catalyst of Example 1 is more difficult to reduce to metallic Sn compared to the SnO2 catalyst of Comparative Example 1. This is because the low-crystallinity tin dioxide catalyst has a Sn-OH structure, and the Sn-OH structure is more difficult to reduce than the Sn-O structure. Therefore, the low-crystallinity tin dioxide catalyst is more difficult to reduce to metallic Sn during the electrocatalytic CO2 reduction process, which is beneficial for inhibiting the hydrogen evolution reaction and has greater potential for electrocatalytic CO2 reduction to formic acid.

[0134] (2) Thermogravimetric analysis (TGA) test: The catalyst prepared in this invention was subjected to TGA test, and the results are shown in the figure. Figure 2 .from Figure 2 It can be seen that under a nitrogen atmosphere, the mass of the SnO2 catalyst in Comparative Example 1 did not change significantly with increasing temperature, while the mass of the SnO2-OH-3 catalyst in Example 3 decreased by 16%. This indicates that, unlike the SnO2 catalyst in Comparative Example 1, the SnO2-OH-3 catalyst in Example 3 may contain hydroxyl groups. Increased temperature causes the hydroxyl groups in the SnO2-OH-3 catalyst in Example 3 to volatilize in the form of water, resulting in a significant decrease in its mass.

[0135] (3) Fourier Transform Infrared (FTIR) Spectroscopy: To determine the structure of the catalyst, FTIR spectroscopy was performed on the catalyst prepared in this invention. The results are shown in […]. Figure 3 .from Figure 3 It can be seen that, unlike the SnO2 catalyst in Comparative Example 1 which only has peaks corresponding to O-Sn-O, the SnO2-OH-4 catalyst in Example 4 not only has peaks corresponding to O-Sn-O, but also peaks corresponding to -OH and Sn-OH, indicating that the SnO2-OH-4 catalyst in Example 4 contains hydroxyl groups.

[0136] (4) Electron paramagnetic resonance (EPR) test: The catalyst prepared in this invention was subjected to EPR test, and the results are shown in the figure. Figure 4 .from Figure 4 It can be seen that, compared with the SnO2 catalyst of Comparative Example 1, the SnO2-OH-1 catalyst of Example 1 has a more significant peak at g = 2.003, indicating that the oxygen vacancy concentration of the SnO2-OH-1 catalyst of Example 1 is higher.

[0137] (5) Scanning Electron Microscopy (SEM) Test: To determine the morphology of the catalyst, SEM tests were performed on the catalyst prepared in this invention. The results are shown in [Figure number missing]. Figures 5-7 .from Figure 5 It can be seen that the SnO2 catalyst in Comparative Example 1 has spherical particles with a diameter of approximately 30 nm; from Figure 6 - Figure 7 It can be seen that the SnO2-OH-1 catalyst in Example 1 and the SnO2-OH-5 catalyst in Example 5 are spherical particles with a diameter of about 30 nm.

[0138] (6) Energy-dispersive X-ray spectroscopy (EDS) test: In order to determine the elemental composition of the catalyst, the catalyst prepared in this invention was subjected to EDS test, and the results are shown in […]. Figure 8 .from Figure 8 It can be seen that the SnO2-OH-1 catalyst in Example 1 contains tin (Sn) and oxygen (O) elements, and the Sn and O elements are evenly distributed.

[0139] (7) High-power transmission electron microscopy (HRTEM) test: The catalyst prepared in this invention was subjected to HRTEM test, and the results are shown in the figure. Figure 9 - Figure 13 .from Figure 9 It can be seen that the lattice fringes of the SnO2 catalyst in Comparative Example 1 are clear, with a region having a lattice spacing of 0.33 nm, corresponding to the (110) crystal plane of SnO2, and a region having a lattice spacing of 0.26 nm, corresponding to the (101) crystal plane of SnO2. From Figure 10 It can be seen that the lattice fringes of the SnO2-OH-1 catalyst in Example 1 are blurred and disordered, with crystalline and amorphous regions coexisting, exhibiting abundant crystalline-amorphous heterointerfaces, consistent with its low crystallinity characteristics. Among these, there exists a region with a lattice spacing of 0.33 nm, corresponding to the (110) crystal plane of SnO2. From... Figure 11 It can be seen that the lattice fringes of the SnO2-OH-4 catalyst in Example 4 are blurred and disordered, with crystalline and amorphous regions coexisting, exhibiting abundant crystalline-amorphous heterointerfaces, consistent with its low crystallinity characteristics. Among these, there exists a region with a lattice spacing of 0.23 nm, corresponding to the (200) crystal plane of SnO2. From... Figure 12 It can be seen that the lattice fringes of the SnO2-OH-5 catalyst in Example 5 are blurred and disordered, with crystalline and amorphous regions coexisting, exhibiting abundant crystalline-amorphous heterojunctions, consistent with its low crystallinity characteristics. Among these, there exists a region with a lattice spacing of 0.33 nm, corresponding to the (110) crystal plane of SnO2. From... Figure 13It can be seen that the lattice stripes of the SnO2-OH-6 catalyst in Example 6 are blurred and disordered, with crystalline and amorphous regions coexisting, and have abundant crystalline-amorphous heterostructures, which is consistent with its low crystallinity characteristics. There is a region with a lattice spacing of 0.33 nm, which corresponds to the (110) crystal plane of SnO2.

[0140] (8) Linear sweep voltammetry (LSV) test for electrocatalytic CO2 reduction: The catalyst prepared in this invention was tested using a flow electrolyzer, Hg / HgO reference electrode, anion exchange membrane, and platinum sheet counter electrode in 1 M KOH electrolyte. The results are shown in […]. Figures 14-16 .from Figure 14 It can be seen that, under conditions without iR compensation, within the same potential range, compared to the reaction in an argon (Ar) atmosphere, the SnO2 catalyst of Comparative Example 1 and the SnO2-OH-1 catalyst of Example 1 achieve larger reaction currents in a CO2 atmosphere, indicating that both catalysts possess electrocatalytic CO2 reduction activity. Furthermore, in a CO2 atmosphere, over a wide potential range, the SnO2-OH-1 catalyst of Example 1 achieves a larger reaction current than the SnO2 catalyst of Comparative Example 1, preliminarily suggesting that the SnO2-OH-1 catalyst of Example 1 may have stronger electrocatalytic CO2 reduction activity. Figure 15 It can be seen that, under iR compensation conditions, in a CO2 atmosphere, and over a wide potential range, the SnO2-OH-1 catalyst of Example 1 achieves a larger reaction current than the SnO2 catalyst of Comparative Example 1, further demonstrating that the SnO2-OH-1 catalyst of Example 1 possesses stronger electrocatalytic CO2 reduction activity. Figure 16 It can be seen that, under conditions without iR compensation, within the same potential range, the Comparative Example 2 SnO2-C catalyst achieves a larger reaction current in a CO2 atmosphere compared to the reaction in an argon (Ar) atmosphere, indicating that the Comparative Example 2 SnO2-C catalyst possesses electrocatalytic CO2 reduction activity. Furthermore, within a CO2 atmosphere and over a wide potential range, the Example 1 SnO2-OH-1 catalyst achieves a larger reaction current than the Comparative Example 2 SnO2-C catalyst, further demonstrating that the Example 1 SnO2-OH-1 catalyst exhibits superior electrocatalytic CO2 reduction activity.

[0141] (9) Electrocatalytic CO2 reduction constant current test: A flow electrolytic cell, Hg / HgO reference electrode, anion exchange membrane, and platinum sheet counter electrode were used. The CO2 gas flow rate was maintained at 20 mL / min. The catalyst prepared in this invention was subjected to constant current test in 1 M KOH electrolyte. The electrolyte collected after the test was detected by liquid chromatography. The results are shown in the figure. Figures 17-25.from Figure 17 It can be seen that the peak position of the formic acid standard solution (20.0 mmol / L) on the spectrum is at 3.9 min, proving that this peak corresponds to formic acid. From Figure 18 It can be seen that the SnO2 catalyst in Comparative Example 1 at 1000 mA cm⁻¹ -2 The electrolyte obtained after reacting at a current density for 2500 s showed a peak position at 3.9 min in the spectrum, confirming the presence of formate ions in the electrolyte. The formate concentration after dilution was determined to be 6.9 mmol / L using a calibration curve. Figure 19 It can be seen that the SnO2-OH-1 catalyst in Example 1 at 1000 mA cm⁻¹ -2 The electrolyte obtained after reacting at a current density for 2500 s showed a peak position at 3.9 min in the spectrum, confirming the presence of formate ions in the electrolyte. The formate concentration after dilution was determined to be 13.7 mmol / L using a calibration curve. Figure 20 It can be seen that the SnO2-OH-2 catalyst in Example 2 at 1000 mA cm⁻¹ -2 The electrolyte obtained after reacting at a current density for 2500 s showed a peak position at 3.9 min in the spectrum, confirming the presence of formate ions in the electrolyte. The formate concentration after dilution was determined to be 12.5 mmol / L using a calibration curve. Figure 21 It can be seen that the SnO2-OH-3 catalyst in Example 3 at 1000 mAcm -2 The electrolyte obtained after reacting at a current density for 2500 s showed a peak position at 3.9 min in the spectrum, confirming the presence of formate ions in the electrolyte. The formate concentration after dilution was determined to be 12.7 mmol / L using a calibration curve. Figure 22 It can be seen that the SnO2-OH-4 catalyst in Example 4 at 1000 mA cm⁻¹ -2 The electrolyte obtained after reacting at a current density for 2500 s showed a peak position at 3.9 min in the spectrum, confirming the presence of formate ions in the electrolyte. The formate concentration after dilution was determined to be 12.2 mmol / L using a calibration curve. Figure 23 It can be seen that the SnO2-OH-5 catalyst in Example 5 at 1000 mA cm⁻¹ -2 The electrolyte obtained after reacting at a current density for 2500 s showed a peak position at 3.9 min in the spectrum, confirming the presence of formate ions in the electrolyte. The formate concentration after dilution was determined to be 13.5 mmol / L using a calibration curve. Figure 24 It can be seen that the SnO2-OH-6 catalyst in Example 6 at 1000 mA cm⁻¹ -2The electrolyte obtained after reacting at a current density for 2500 s showed an elution position of 3.9 min in the chromatogram, confirming the presence of formate ions in the electrolyte. The formate concentration after dilution was determined to be 12.9 mmol / L using a calibration curve. These liquid chromatography results preliminarily indicate that, compared to the SnO2 catalyst in Comparative Example 1, the SnO2-OH-1 catalyst in Examples 1, SnO2-OH-2 catalyst in Examples 2, SnO2-OH-3 catalyst in Examples 3, SnO2-OH-4 catalyst in Examples 4, SnO2-OH-5 catalyst in Examples 5, and SnO2-OH-6 catalyst in Examples 6 exhibit superior electrocatalytic performance in the reduction of CO2 to formate. Figure 25 It can be seen that the SnO2 catalyst in Comparative Example 1 operates at -600 mA cm⁻¹. -2 At a given current density, the formic acid faradaic efficiency can reach 92.5%; however, when the current density reaches -800 mA cm⁻¹, the efficiency is significantly lower. -2 At this point, the hydrogen evolution reaction intensifies, and the formic acid Faraday efficiency decreases to 64.8%; when the current density reaches -1000 mA cm⁻¹ -2 At that time, the formic acid faradaic efficiency was only 38.2%. Example 1: SnO2-OH-1 catalyst at -400 to -1000 mA cm⁻¹ -2 The formic acid production faradaic efficiency is greater than 93% within the current density range; when the current density reaches -800 mA cm⁻¹ -2 At the specified current, the formic acid faradaic efficiency reached 95.8%. Comparison showed that, under the test current, the SnO2-OH-1 catalyst of Example 1 exhibited a higher formic acid faradaic efficiency than the SnO2 catalyst of Comparative Example 1. This result indicates that the low-crystallinity SnO2-OH-1 catalyst possesses superior electrocatalytic CO2 reduction formic acid production performance compared to the crystalline SnO2 catalyst.

[0142] (10) Electrocatalytic CO2 reduction stability test: A flow electrolyzer, Hg / HgO reference electrode, anion exchange membrane, and platinum sheet counter electrode were used. The CO2 gas flow rate was maintained at 20 mL / min, and the current density was -400 mA cm⁻¹. -2 The stability of the SnO2-OH-1 catalyst prepared in Example 1 according to the present invention was tested in 1 M KOH electrolyte, and the results are shown in [the table below]. Figure 26 .from Figure 26 It can be seen that the SnO2-OH-1 catalyst in Example 1 operates at -400 mA cm⁻¹ -2 Even after 15 hours of reaction at the current density, the formic acid production efficiency remains above 80%, the hydrogen production efficiency is below 8%, and the carbon monoxide production efficiency is below 6%, indicating that this low-crystallinity tin dioxide catalyst has good stability.

[0143] (11) CO2 isothermal adsorption test: CO2 isothermal adsorption tests were performed on the SnO2-OH-1 catalyst of Example 1 and the SnO2 catalyst of Comparative Example 1 using a surface area and pore size analyzer (BET). The results are shown in the figure. Figure 27 .from Figure 27 It can be seen that, under the same test temperature, the CO2 adsorption capacity of the SnO2-OH-1 catalyst in Example 1 is five times that of the SnO2 catalyst in Comparative Example 1, indicating that the low-crystallinity tin dioxide catalyst has a superior CO2 adsorption capacity. This result also explains why the low-crystallinity tin dioxide catalyst has superior electrocatalytic performance in the reduction of CO2 to formic acid.

[0144] (12) Cyclic voltammetry (CV) test: A flow electrolytic cell, Hg / HgO reference electrode, anion exchange membrane, and platinum sheet counter electrode were used in an argon atmosphere at -400 mA cm⁻¹. -2 At a current density, the CV test was performed on the SnO2-OH-1 catalyst of Example 1 and the SnO2 catalyst of Comparative Example 1 prepared by the present invention in 1 M KOH electrolyte. The results are shown in the figure. Figure 28 .from Figure 28 It can be seen that, compared with the SnO2 catalyst of Comparative Example 1, the SnO2-OH-1 catalyst of Example 1 has a lower reduction peak current density, indicating that the SnO2-OH-1 catalyst of Example 1 is more difficult to be reduced in the electrocatalytic CO2 reduction reaction.

[0145] (13) Yield Test: During the synthesis of SnO2-OH-4 in Example 4, the amount of precipitate gradually increased with the addition of potassium hydroxide solution. After centrifugation, washing, and vacuum drying, the precipitate was weighed, and the yield of SnO2-OH-4 was determined to be 0.834 g ( Figure 31 In the synthesis of Comparative Example 3, SnO2-OH-7, the precipitate initially increased gradually with the addition of potassium hydroxide solution; however, the precipitate gradually decreased as excess potassium hydroxide solution was added. After centrifugation, washing, and vacuum drying, the precipitate was weighed, and the yield of SnO2-OH-7 was determined to be 0.169 g. Figure 31 Comparative studies revealed that adding excessive amounts of potassium hydroxide solution reduced the yield of low-crystalline tin dioxide.

[0146] In summary, the low-crystallinity tin dioxide catalyst prepared using the raw materials and methods described in this application has uniform and nanoscale particle size, contains abundant crystalline-amorphous interfaces, defects, and hydroxyl groups, and exhibits excellent activity and selectivity in the electrocatalytic reduction of CO2 to formic acid.

[0147] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. The use of a low-crystallinity tin dioxide catalyst in electrocatalysis, characterized in that, The preparation method of the low-crystallinity tin dioxide catalyst includes the following steps: S1. Mix tin salt with solvent A at a ratio of 1 mmol: (0-10) mL with the endpoint values ​​not being 0, and stir at 300-500 rpm until completely dissolved to obtain substance 1; the tin salt is any one of tin chloride and its hydrate; S2. Add solvent B to substance 1 and continue stirring at 300-500 rpm for 20-40 min to obtain substance 2; the ratio of tin salt to solvent B is 1 mmol: (0-10) mL and the endpoint value is not 0; The ratio of the total amount of solvent A and solvent B to the tin salt is (3-10) mL: 1 mmol; Solvent A and solvent B are ethanol and deionized water, respectively, with a volume ratio of 1:1; S3. Add an alkaline solution to substance 2, observe the formation of a white precipitate, and then stir at 300-500 rpm for 0.5-1.5 h to obtain substance 3; the alkaline solution is ammonia or potassium hydroxide solution; the ratio of tin salt to ammonia is 1 mmol: (0-4) mL and the endpoint value is not 0; the molar ratio of potassium hydroxide in the tin salt and potassium hydroxide solution is 1 mmol: (0-4) mmol and the endpoint value is not 0; S4. Wash substance 3 with anhydrous ethanol and deionized water sequentially, centrifuge 5-6 times or vacuum filter, and then vacuum dry to obtain the product. The vacuum drying conditions are: vacuum degree of 0.08-0.1 MPa, temperature of 50-80℃, and time of 5-12h.

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