Bi-SnO2 / C catalyst as well as preparation method and application thereof

Abstract

The invention provides a Bi-SnO2 / C catalyst as well as a preparation method and application thereof, and belongs to the technical field of electrocatalysts. The preparation method comprises the following steps: carrying out hydrothermal reaction by taking D-glucose as a carbon source to prepare a porous carbon precursor; mixing the porous carbon precursor and an alkali activator, and calcining to obtain porous carbon spheres; the preparation method comprises the following steps: mixing tin salt, bismuth salt and an ethylene glycol solution, and adding a precipitator for hydrothermal reaction to obtain a Bi-Sn precursor; and mixing the Bi-Sn precursor and the porous carbon spheres, adding a precipitant to carry out precipitation reaction, and calcining the product of the precipitation reaction to obtain the Bi-SnO2 / C catalyst. Porous carbon spheres with rich pore structures are prepared through an alkali activation method and serve as carriers of Bi-SnO2, the carrier effect between catalyst active components and the carriers is utilized, the electronic structure on the surface of Sn is adjusted, the charge transfer performance of Bi-SnO2 is improved, and therefore the electro-catalytic performance is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalysts, and in particular to a Bi-SnO2 / C catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, with the continuous development of modern industry, the combustion of a large amount of fossil fuels globally has caused the continuous increase of the CO2 concentration in the atmosphere. The observation results in June 2022 showed that the CO2 concentration in the atmosphere reached 420 ppm, far exceeding the safe concentration upper limit of 350 ppm and still showing a continuous growth trend. The excessive emission of CO2 has led to the imbalance of the carbon cycle, causing a series of environmental problems such as global warming and sea-level rise. In the past few decades, numerous methods have been proposed to convert CO2 into high-value chemicals or renewable energy and minimize its adverse impact on the environment. Among them, the main methods include thermal catalytic conversion, photocatalytic conversion, and electrocatalytic conversion.

[0003] The thermal catalytic CO2 technology is a process that uses a catalyst to promote the conversion of CO2 molecules under high-temperature conditions. It generally includes two main steps: CO2 adsorption and catalytic reaction. By regulating the composition, structure, and active sites of the catalyst, CO2 can be selectively converted into target products, such as organic compounds like hydrocarbons, alcohols, and carboxylic acids. However, the thermal catalytic CO2 technology may cause catalyst deactivation or structural degradation due to the high-temperature environment, affecting the lifespan and stability of the catalyst.

[0004] The photocatalytic technology is a green technology that can directly utilize solar energy to convert CO2 into chemical energy and can convert CO2 into other products under sunlight. In the photocatalytic reaction, the selection of the photocatalyst is crucial. Reported photocatalyst materials include various types such as semiconductor materials, perovskite materials, metal complexes, bioenzymes, and metal-organic frameworks. Nevertheless, achieving large-scale photocatalytic reduction of CO2 still has a long way to go. Among them, developing highly efficient, inexpensive, and easily industrially applicable catalysts is the key to improving the photocatalytic application process.

[0005] The electrocatalytic CO2 reaction is a method that uses electrical energy to reduce CO2 into substances such as alkanes, alkenes, alcohols, and acids. The electrochemical CO2 reduction reaction involves a multi-step proton-coupled electron transfer process and has multiple possible reaction paths, capable of producing a series of different reduction products, including carbon monoxide, formic acid, methane, ethylene, ethane, etc.

[0006] Compared with other methods, the electrocatalytic CO2 technology has many significant advantages. First of all, during the electrocatalytic conversion process, no additional heating or high-temperature and high-pressure conditions are required, and the reaction can be carried out under relatively mild conditions, thus reducing energy consumption and production costs. In addition, the electrocatalytic technology can also achieve the selective conversion of CO2 to produce high-value-added chemicals or renewable energy, further improving the resource utilization efficiency. By reasonably designing the catalyst and adjusting the reaction conditions, the selective synthesis of different products can be realized, and it has great development potential. Tin-based materials that are rich in resources and non-toxic can effectively electrocatalytically reduce CO2 to formic acid, and have good prospects for industrial application.

[0007] SnO2 is a semiconductor oxide with a rutile structure as the main structure. Due to its low cost and non-toxicity, it has broad prospects in electrocatalytic CO2. However, due to the low conductivity of the SnO2 material, it often exhibits problems such as high required potential, low selectivity, and poor stability. Therefore, its modification is particularly important. Doping SnO2 with a metal with high conductivity can improve the conductivity of the SnO2 catalyst, which is beneficial to the charge transport performance in the electrocatalytic reduction reaction. Summary of the Invention

[0008] The purpose of the present invention is to provide a Bi-SnO2 / C catalyst, its preparation method and application, in order to solve the problems of high required potential, low selectivity and poor stability of the SnO2 catalyst in the prior art.

[0009] In order to achieve the above invention purpose, the present invention provides the following technical solutions:

[0010] The present invention provides a preparation method of a Bi-SnO2 / C catalyst, which includes the following steps:

[0011] (1) Using D-glucose as a carbon source for hydrothermal reaction to prepare a porous carbon precursor;

[0012] (2) Mixing the porous carbon precursor and an alkali activator and then performing calcination to obtain porous carbon spheres;

[0013] (3) Mixing a tin salt, a bismuth salt and an ethylene glycol solution, adding a precipitating agent and performing hydrothermal reaction to obtain a Bi-Sn precursor;

[0014] (4) Mixing the Bi-Sn precursor and the porous carbon spheres, adding a precipitating agent for precipitation reaction, and calcining the product of the precipitation reaction to obtain a Bi-SnO2 / C catalyst.

[0015] Preferably, in step (1), the temperature of the hydrothermal reaction is 150-180 °C, and the time of the hydrothermal reaction is 12-20 h.

[0016] Preferably, in step (2), the alkali activator includes potassium hydroxide or sodium hydroxide; the mass ratio of the porous carbon precursor to the alkali activator is 1:0.5 - 1.5.

[0017] Preferably, in step (2), the calcination temperature is 600 - 700 °C, and the calcination time is 1 - 2 h.

[0018] Preferably, in step (3), the addition amount of the bismuth salt is 6.25% - 50% of the molar amount of the tin salt; the hydrothermal reaction temperature is 170 - 190 °C, and the hydrothermal reaction time is 14 - 26 h.

[0019] Preferably, in step (4), the mass ratio of the Bi-Sn precursor to the porous carbon spheres is 2 - 5:1; the pH value after adding the precipitant is 6 - 9.

[0020] Preferably, in step (4), the calcination temperature is 600 - 700 °C, and the calcination time is 1 - 2 h.

[0021] The present invention also provides a Bi-SnO2 / C catalyst prepared by the preparation method of the Bi-SnO2 / C catalyst described above.

[0022] The present invention also provides an application of the Bi-SnO2 / C catalyst described above in carbon dioxide reduction. The Bi-SnO2 / C catalyst is made into an electrode, and carbon dioxide can be electrocatalyzed.

[0023] Preferably, the preparation method of the electrode is: dispersing the Bi-SnO2 / C catalyst in a mixed solution, and then dropping it on a carbon cloth and drying it.

[0024] The mixed solution is made of ethanol and Nafion solution.

[0025] Advantages of the present invention:

[0026] The present invention prepares porous carbon spheres with a rich pore structure by an alkali activation method. As a carrier of Bi-SnO2, the carrier effect between the catalyst active component and the carrier is utilized to adjust the electronic structure on the surface of Sn, improve the charge transport performance of Bi-SnO2, and thus improve the electrocatalytic performance.

[0027] The present invention uses Bi-doped SnO2 to construct more active sites. Compared with the SnO2 catalyst, the Bi-Sn bimetallic oxide has a synergistic effect and can improve the catalytic activity. The optimal potential of the Bi-SnO2 / C catalyst prepared by the present invention is -0.6 V, and the FE is 84.3%. It can operate stably for more than 20 h. Description of the drawings

[0028] Figure 1 SEM image of the porous carbon spheres prepared in Example 1;

[0029] Figure 2 SEM image of the 12.5% Bi-SnO2 / C catalyst of Example 1;

[0030] Figure 3 XRD patterns of Bi-SnO2 / C catalysts with different doping amounts;

[0031] Figure 4 Long-term stability test curve of FE using the 12.5% Bi-SnO2 / C catalyst HCOOH ;

[0032] Figure 5 IT curve of FE using the 12.5% Bi-SnO2 / C catalyst HCOOH ;

[0033] Figure 6 EIS diagrams of Bi-SnO2 / C catalysts with different doping amounts;

[0034] Figure 7 ECSA diagrams of Bi-SnO2 / C catalysts with different doping amounts;

[0035] Figure 8 Tafel slope diagrams of Bi-SnO2 / C catalysts with different doping amounts. Detailed implementation method

[0036] The present invention provides a preparation method of a Bi-SnO2 / C catalyst, comprising the following steps:

[0037] (1) Hydrothermal reaction is carried out using D-glucose as a carbon source to prepare a porous carbon precursor;

[0038] (2) The porous carbon precursor and an alkali activator are mixed and then calcined to obtain porous carbon spheres;

[0039] (3) A tin salt, a bismuth salt and an ethylene glycol solution are mixed, and a precipitating agent is added for hydrothermal reaction to obtain a Bi-Sn precursor;

[0040] (4) The Bi-Sn precursor and the porous carbon spheres are mixed, a precipitating agent is added for precipitation reaction, and the reaction product is placed in a tubular furnace for calcination to obtain a Bi-SnO2 / C catalyst.

[0041] In the present invention, it is preferred to dissolve D-glucose in water and then carry out hydrothermal reaction, wherein the mass-volume ratio of D-glucose to water is 10-20 g: 40-60 mL, preferably 15 g: 50 mL.

[0042] In the present invention, in step (1), the temperature of the hydrothermal reaction is 150 to 180 °C, preferably 150 °C, 160 °C, 170 °C, 180 °C; the time of the hydrothermal reaction is 12 to 20 h, preferably 12 h, 14 h, 16 h, 18 h, 20 h.

[0043] In the present invention, in step (2), the alkali activator includes potassium hydroxide or sodium hydroxide, preferably potassium hydroxide; the mass ratio of the porous carbon precursor to the alkali activator is 1:0.5 to 1.5, preferably 1:1.

[0044] In the present invention, it is preferred to mix the porous carbon precursor and the alkali activator and then dry them, and the drying temperature is 120 to 150 °C.

[0045] In the present invention, in step (2), the calcination temperature is 600 to 700 °C, preferably 650 °C; the calcination time is 1 to 2 h, preferably 1 h.

[0046] In the present invention, in step (2), the calcination is preferably carried out in a nitrogen atmosphere.

[0047] In the present invention, in step (3), the addition amount of the bismuth salt is 6.25 to 50% of the molar amount of the tin salt, preferably 6.25%, 12.5%, 25%, 50%.

[0048] In the present invention, in step (3), the ethylene glycol solution is prepared from deionized water and ethylene glycol, and the volume ratio of deionized water to ethylene glycol is 1:1 to 10.

[0049] In the present invention, in step (3), the pH value after adding the precipitant is 6 to 9.

[0050] In the present invention, in step (3), the temperature of the hydrothermal reaction is 170 to 190 °C, preferably 175 to 185 °C, more preferably 180 °C; the time of the hydrothermal reaction is 14 to 26 h, preferably 16 to 24 h, more preferably 18 to 22 h.

[0051] In the present invention, in step (4), the mass ratio of the Bi-Sn precursor to the porous carbon spheres is 2 to 5:1, preferably 3 to 4:1, more preferably 3.5:1; the pH value after adding the precipitant is 6 to 9, preferably 7 to 9, more preferably 8 to 9.

[0052] In the present invention, in step (4), the calcination temperature is 600 to 700 °C, preferably 600 °C, 650 °C, 700 °C; the calcination time is 1 to 2 h, preferably 2 h.

[0053] The present invention also provides a Bi-SnO2 / C catalyst prepared by the preparation method of the Bi-SnO2 / C catalyst described above.

[0054] The present invention also provides an application of the Bi-SnO2 / C catalyst described above in carbon dioxide reduction. The Bi-SnO2 / C catalyst is made into an electrode, and carbon dioxide can be electrocatalyzed.

[0055] In the present invention, the preparation method of the electrode is as follows: the Bi-SnO2 / C catalyst is dispersed in a mixed solution, and then dropped on a carbon cloth and dried.

[0056] The mixed solution is made of ethanol and Nafion solution.

[0057] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0058] Example 1

[0059] Dissolve 15 g of D-anhydrous glucose (>98%, Macklin) in 50 mL of deionized water, stir for 30 min, transfer to a 100 mL hydrothermal reaction kettle after complete dissolution, and carry out hydrothermal reaction at 180 °C for 12 h. After hydrothermal reaction, dry to obtain a porous carbon precursor. Mix the porous carbon precursor and KOH according to a mass ratio of 1:1, dry at 130 °C, transfer to a tubular furnace, raise the temperature to 650 °C in a nitrogen atmosphere, keep the temperature for 1 h, and obtain porous carbon spheres after grinding, denoted as C.

[0060] Weigh 2 g of SnCl4·5H2O (AR>98.0%, aladdin), weigh Bi(NO3)3·5H2O (>99%, Macklin) according to a molar ratio of 12.5%, dissolve it in 50 mL of ethylene glycol solution (the ethylene glycol solution is prepared from deionized water and ethylene glycol according to a volume ratio of 1:1), stir and ultrasonic until completely dissolved, then use 2.5 mol / L NaOH solution as a precipitant to adjust the pH to 9, transfer to a reaction kettle with a polytetrafluoroethylene lining, carry out hydrothermal reaction at 180 °C for 20 h, naturally cool after the reaction, and finally wash the reaction product 4 times with deionized water and dry it in a vacuum drying oven at 80 °C to obtain a Bi-Sn precursor.

[0061] Mix 600 mg of porous carbon spheres and 2.1 g of Bi-Sn precursor in 75 ml of deionized water, and mix them evenly by ultrasonic and stirring. Use 2.5 mol / L NaOH solution as a precipitant to adjust the pH to 9. Wash, filter, and separate the obtained precipitate. Finally, place it in a muffle furnace, raise the temperature to 700 °C at a heating rate of 5 °C / min, calcine for 2 h, cool to room temperature, and grind to obtain the Bi-SnO2 / C catalyst, denoted as 12.5% Bi-SnO2 / C.

[0062] Example 2

[0063] The difference from Example 1 is that the molar ratio of Bi(NO3)3·5H2O to SnCl4·5H2O is 6.25%, and other conditions are the same. The Bi-SnO2 / C catalyst is obtained, denoted as 6.25% Bi-SnO2 / C.

[0064] Example 3

[0065] The difference from Example 1 is that the molar ratio of Bi(NO3)3·5H2O to SnCl4·5H2O is 25%, and other conditions are the same. The Bi-SnO2 / C catalyst is obtained, denoted as 25% Bi-SnO2 / C.

[0066] Example 4

[0067] The difference from Example 1 is that the molar ratio of Bi(NO3)3·5H2O to SnCl4·5H2O is 50%, and other conditions are the same. The Bi-SnO2 / C catalyst is obtained, denoted as 50% Bi-SnO2 / C.

[0068] Comparative Example 1

[0069] The difference from Example 1 is that Bi(NO3)3·5H2O is not added, and other conditions are the same. The SnO2 / C catalyst is obtained, denoted as 0% Bi-SnO2 / C.

[0070] Application Example 1

[0071] Cut the carbon cloth (model WOS1011) into rectangular pieces of 1 cm × 1.5 cm as the independent working electrode, and its active area is 1 cm 2 (1 cm × 1 cm), and the excess part of the bare carbon cloth is covered with Teflon tape and clips.

[0072] The catalysts prepared in Examples 1-4 were made into carbon cloth electrodes. The specific process was as follows: 10 mg of the catalyst was dispersed in a mixed solution of ethanol and 0.5 wt.% Nafion solution (the volume of ethanol was 950 μL and the volume of Nafion solution was 50 μL), and ultrasonicated for 30 min to obtain a catalyst dispersion. 100 μL of the catalyst dispersion was dropped onto the cut carbon cloth and dried under infrared light. The catalyst loading on the carbon cloth was 1 mg / cm 2 , and carbon cloth electrodes were made.

[0073] Using the above carbon cloth electrode as the working electrode, graphite as the counter electrode, and Ag / AgCl as the reference electrode, a three-electrode system was formed, and electrocatalytic reduction of carbon dioxide to synthesize formic acid was carried out under the assistance of an electric field. A KHCO3 solution with a concentration of 0.5 mol / L was used as the electrolyte, and carbon dioxide was introduced throughout the process. The electric field voltage was -0.4 to -0.8 V (vs RHE).

[0074] Figure 1 SEM image of the porous carbon spheres prepared in Example 1. From Figure 1 it can be seen that: the porous carbon sphere support is composed of several carbon spheres with a diameter of about 2-6 μm. These carbon spheres have a spherical structure, and this spherical structure usually has a larger specific surface area and can provide more active sites in the catalyst.

[0075] Figure 2 SEM image of the 12.5% Bi-SnO2 / C catalyst. From Figure 2 it can be seen that: 12.5% Bi-SnO2 / C presents an amorphous shape, and its particle size distribution is between 5-12 nm.

[0076] Figure 3 XRD patterns of Bi-SnO2 / C catalysts with different doping amounts. From Figure 3 it can be seen that: at 2θ angles of 26.5°, 33.8° and 51.7°, except for the 50% doping ratio, three obvious diffraction peaks are presented. These peaks correspond to the (110), (101) and (211) crystal planes of rutile structure SnO2 respectively. This result indicates that at lower doping ratios, SnO2 with high crystallinity can be formed. At 2θ angles of 27.1°, 37.9° and 64.5°, except for the 50% doping ratio, three obvious diffraction peaks are presented. These peaks correspond to the (012), (104), and (122) crystal planes of triclinic Bi metal element respectively. From Figure 3It can be clearly seen that the diffraction peaks with a 50% ratio are relatively small, possibly due to the excessive doping ratio causing crystal collapse, or the excessive doping ratio leading to partial amorphization of the crystal structure, and the degree of amorphization increases with the increase of the doping amount. At the same time, by analyzing the positions of the diffraction peaks of the prepared catalyst and the standard card, it can be known that the XRD diffraction peak position of the Bi-SnO2 / C sample shifts to the left when the 2θ angle is 33.8°, indicating that Bi is doped into the interior of SnO2 and the lattice constant becomes larger because heteroatoms with a larger atomic radius than the main atoms are incorporated.

[0077] The stability of the electrode material is also one of the important parameters for evaluating the performance of the catalyst. The CV curves of the 12.5% Bi-SnO2 / C catalyst before and after electrolysis at -0.6V for 20h were analyzed, and the results are as Figure 4 shown. From Figure 4 it can be seen that the cyclic voltammograms before and after electrolysis can basically coincide, and the current density decay is within 10%, indicating that after a period of electrolysis, the surface structure and state of the electrode have not changed significantly, and it has good electrochemical stability.

[0078] To detect the long-term stability of the catalyst, the change curve of the current density of the 12.5% Bi-SnO2 / C catalyst with time was tested at -0.6V, as Figure 5 shown: the current density shows an increasing trend during the 2-hour electrolysis. It may be that the HER reaction is relatively intense during electrolysis, resulting in an increase in the current density. However, the it-current density always remains within 2.4 - 2.5 mA within 2h, indicating its better stability.

[0079] To verify the charge transfer performance of the Bi-SnO2 / C catalyst in the electrolyte, electrochemical impedance spectroscopy (EIS) tests were carried out in a 0.5 mol / L KHCO3 solution saturated with CO2, and the results are as Figure 6 shown. From Figure 6 it can be seen that when using the 12.5% Bi-SnO2 / C catalyst, the solution resistance and charge transfer resistance are the smallest, which indicates that in this catalytic system, it has the smallest electron migration resistance, thus showing the fastest electron transfer rate.

[0080] Figure 7 are the double-layer capacitance values of Bi-SnO2 / C catalysts with different doping amounts. From Figure 7 it can be seen that the Cdl values of 6.25% Bi-SnO2 / C, 12.5% Bi-SnO2 / C, 25% Bi-SnO2 / C, and 50% Bi-SnO2 / C are 0.65 mF / cm 2 , 1.75 mF / cm 2 , 1.25 mF / cm 2 , 0.52 mF / cm2 , the order of the electrochemically active surface area is

[0081] 12.5% Bi-SnO2 / C > 25% Bi-SnO2 / C > 6.25% Bi-SnO2 / C > 50% Bi-SnO2 / C, indicating that the catalyst of 12.5% Bi-SnO2 / C has a higher ECSA value. The higher the ECSA, the more exposed active sites, which is beneficial to improving the CO2 catalytic performance.

[0082] Figure 8 is the Tafel slope diagram of Bi-SnO2 / C catalysts with different doping amounts. From Figure 8 it can be seen that the Tafel slopes of 6.25% Bi-SnO2 / C, 12.5% Bi-SnO2 / C, 25% Bi-SnO2 / C, and 50% Bi-SnO2 / C are 152 mV / dec, 128 mV / dec, 138 mV / dec, and 197 mV / dec, respectively. These values are all relatively close to the theoretical value of 116 mV / dec, indicating that the rate-determining step in the reaction process is the conversion process in which CO2 obtains an electron to generate a CO2 radical intermediate. Among them, the Tafel slope value of 12.5% Bi-SnO2 / C is the smallest, which means it has the fastest reaction rate. This further shows that 12.5% Bi-SnO2 / C exhibits high catalytic activity and good electrochemical performance in the CO2 electrocatalytic reaction.

[0083] In the above embodiments, porous carbon spheres with rich pore structures were prepared by the KOH activation method as the support of the Bi-SnO2 catalyst and used for CO2RR. Through the structural and morphological characterization of the materials, it can be seen that Bi-SnO2 nanoparticles are uniformly loaded on the porous carbon spheres. The porous carbon spheres with rich pore structures as the support provide more active sites and reaction sites for the electroreduction reaction, thereby increasing the contact area and opportunity between the reactants and the catalyst. Through the electrocatalytic CO2 performance test of the catalyst, the prepared 12.5% Bi-SnO2 / C catalyst exhibits excellent CO2 catalytic activity and high selectivity for HCOOH. In a 0.5 M KHCO3 solution, at a potential of -0.6 V (vs RHE), the selectivity for HCOOH reaches 84.3%. In the 20-hour stability test, the 12.5% Bi-SnO2 / C catalyst shows high CO2 reduction stability. This excellent catalytic performance may be attributed to the interaction between Bi-SnO2 nanoparticles and the porous carbon sphere support. The pore structure and high specific surface area of the support provide good support for the loading of nanoparticles, keeping them uniformly dispersed and increasing the stability of the catalyst. In addition, the support can also promote the charge transfer on the surface of the Bi-SnO2 catalyst, regulate the charge transport performance of the catalyst by changing the electronic state and distribution on the surface of the nanoparticles, and has excellent application value.

[0084] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of Bi-SnO2 / C catalyst, characterized in that, It includes the following steps: (1) Hydrothermal reaction is carried out using D-glucose as a carbon source to obtain a porous carbon precursor; (2) The porous carbon precursor and an alkali activator are mixed and then calcined to obtain porous carbon spheres; (3) A tin salt, a bismuth salt and an ethylene glycol solution are mixed, and a precipitating agent is added for hydrothermal reaction to obtain a Bi-Sn precursor; (4) The Bi-Sn precursor and the porous carbon spheres are mixed, a precipitating agent is added for precipitation reaction, and the product of the precipitation reaction is calcined to obtain a Bi-SnO2 / C catalyst.

2. The preparation method of the Bi-SnO2 / C catalyst according to claim 1, characterized in that, In step (1), the temperature of the hydrothermal reaction is 150-180 °C, and the time of the hydrothermal reaction is 12-20 h.

3. The preparation method of the Bi-SnO2 / C catalyst according to claim 1 or 2, characterized in that, In step (2), the alkali activator includes potassium hydroxide or sodium hydroxide; the mass ratio of the porous carbon precursor to the alkali activator is 1:0.5-1.

5.

4. The preparation method of the Bi-SnO2 / C catalyst according to claim 3, characterized in that, In step (2), the temperature of the calcination is 600-700 °C, and the time of the calcination is 1-2 h.

5. The preparation method of the Bi-SnO2 / C catalyst according to claim 1 or 2 or 4, characterized in that, In step (3), the addition amount of the bismuth salt is 6.25-50% of the molar amount of the tin salt; the temperature of the hydrothermal reaction is 170-190 °C, and the time of the hydrothermal reaction is 14-26 h.

6. The preparation method of the Bi-SnO2 / C catalyst according to claim 5, wherein, In step (4), the mass ratio of the Bi-Sn precursor to the porous carbon spheres is 2-5:1; the pH value after adding the precipitating agent is 6-9.

7. The preparation method of the Bi-SnO2 / C catalyst according to claim 4 or 6, characterized in that, In step (4), the temperature of the calcination is 600-700 °C, and the time of the calcination is 1-2 h.

8. The Bi-SnO2 / C catalyst prepared by the preparation method of the Bi-SnO2 / C catalyst according to any one of claims 1-7.

9. Use of the Bi-SnO2 / C catalyst according to claim 8 in carbon dioxide reduction, characterized in that, The Bi-SnO2 / C catalyst is made into an electrode, and electrocatalysis of carbon dioxide can be carried out.

10. Use of the Bi-SnO2 / C catalyst according to claim 9 in carbon dioxide reduction, characterized in that, The preparation method of the electrode is: dispersing the Bi-SnO2 / C catalyst in a mixed solution, and then dropping it on a carbon cloth and drying it; The mixed solution is made of ethanol and a Nafion solution.

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