Zinc-tin alloy catalyst and preparation method and application thereof

Abstract

The invention belongs to the technical field of catalysts, and particularly relates to a zinc-tin alloy catalyst and a preparation method and application thereof. The zinc-tin alloy catalyst disclosed by the invention is prepared from Sn, Zn, ZnO, SnO and SnO2; sn and Zn are located in the zinc-tin alloy catalyst, and ZnO, SnO and SnO2 are located on the surface of the zinc-tin alloy catalyst. The zinc-tin alloy catalyst is prepared through alloying, tin-zinc alloying is beneficial for improving the catalytic activity and selectivity of the catalyst in preparation of formic acid through electroreduction, and good stability can be kept in an accelerated decay life test; the zinc-tin alloy catalyst has large-scale commercial application potential and prospect in preparation of formic acid through reduction of carbon dioxide.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts, and particularly relates to a zinc-tin alloy catalyst and a preparation method and application thereof. Background Art

[0002] At present, the widespread use of fossil fuels has led to the depletion of energy, and the excessive emission of carbon dioxide has caused a series of environmental and energy problems. Therefore, renewable green energy, such as solar energy, wind energy, tidal energy, etc., has received widespread attention. These renewable energy sources are often used in the form of electricity. However, due to the limitations of geography, climate, and temporal and spatial distribution, the electricity generated by the above renewable energy sources is unstable. Converting unstable electrical energy into easily storable chemical energy and releasing it when used is an important means of regulating uneven power distribution. At the same time, a series of carbon-containing molecules produced by the reduction of carbon dioxide are important fuels and chemical raw materials. Therefore, the emitted CO 2 Converting it into valuable carbon-containing molecules can reduce CO in the atmosphere 2 content, mitigate the environmental crisis, achieve "carbon neutrality", and produce useful fuels and chemical raw materials.

[0003] Formic acid is a useful monobasic organic acid that can be used as a raw material in light chemical industry, medicine, food additives, etc. At the same time, it is also an important energetic molecule and can be used as a good energy storage carrier. In fuel cells, formic acid can be directly used as fuel cell fuel, thereby realizing the conversion and storage of green energy based on carbon dioxide. However, the electrocatalyst for the reduction of formic acid by carbon dioxide has not yet been used on a large scale in commercial applications. This is because the final products obtained in the process of reducing carbon dioxide to formic acid are very diverse, including carbon monoxide (CO), methane (CH 4 ), methanol (CH 3 OH), ethylene (C 2 H 4 ), ethanol (C 2 H 5 OH), ethane (C 2 H 6 ) and n-propanol (C 3 H 7 Most importantly, since the reduction of carbon dioxide is carried out in water, the decomposition of water may lead to serious hydrogen evolution reaction, which reduces the Faradaic efficiency of carbon dioxide reduction to formic acid.

[0004] Therefore, it is of great significance to provide a catalyst for the electroreduction of carbon dioxide to formic acid with high activity, high selectivity and good stability. Summary of the invention

[0005] The present invention aims to solve one or more technical problems existing in the above-mentioned prior art and at least provide a beneficial option. Specifically, the present invention provides a zinc-tin alloy catalyst having high activity, high selectivity and good stability in the process of electroreduction of carbon dioxide to formic acid.

[0006] The inventive concept of the present invention is as follows: the zinc-tin alloy catalyst of the present invention comprises Sn, Zn, ZnO, SnO and SnO 2 The Sn and Zn are located inside the zinc-tin alloy catalyst, and the ZnO, SnO and SnO 2 Located on the surface of the zinc-tin alloy catalyst. In the zinc-tin alloy catalyst, metallic Sn and Zn are distributed inside as a substrate, that is, the internal SnZn alloy can provide electron transport and enhance conductivity; the surface ZnO, SnO and SnO 2 There is an interaction, and their combined effect can improve the performance of carbon dioxide reduction to formic acid.

[0007] Therefore, a first aspect of the present invention provides a zinc-tin alloy catalyst.

[0008] Specifically, the zinc-tin alloy catalyst includes Sn, Zn, ZnO, SnO and SnO 2 ;

[0009] The Sn and Zn are located inside the zinc-tin alloy catalyst, and the ZnO, SnO and SnO 2 Located on the surface of the zinc-tin alloy catalyst.

[0010] Preferably, in the zinc-tin alloy catalyst, the mass ratio of Sn element, Zn element and oxygen element is (1.2-1.6):(20-28):64.48.

[0011] Further preferably, in the zinc-tin alloy catalyst, the mass ratio of Sn element, Zn element and oxygen element is (1.3-1.5):(22-26):64.48.

[0012] More preferably, in the zinc-tin alloy catalyst, the mass ratio of Sn element, Zn element and oxygen element is 1.42:24.5:64.48.

[0013] Specifically, the Sn element, Zn element and oxygen element are evenly distributed.

[0014] Preferably, in the zinc-tin alloy catalyst, the Sn, Zn, ZnO, SnO and SnO 2 The mass ratio is 1:(6-8):(1.3-1.4):(40-46.7).

[0015] Preferably, the zinc-tin alloy catalyst has a flake structure.

[0016] Preferably, the side length and thickness of the sheet-like structure are both 0.1-4 μm.

[0017] The second aspect of the present invention provides a method for preparing the zinc-tin alloy catalyst described in the first aspect of the present invention.

[0018] Specifically, the preparation method of the zinc-tin alloy catalyst comprises the following steps:

[0019] Sn and Zn are mixed and melted to obtain the zinc-tin alloy catalyst.

[0020] The invention obtains a zinc-tin alloy as a catalyst by melting metal Sn and Zn, and has good catalytic activity, selectivity and stability when preparing formic acid by electro-reduction of carbon dioxide.

[0021] Preferably, the mass ratio of Sn to Zn is 1:(0.38-3.3); further preferably, the mass ratio of Sn to Zn is 1:(0.43-3); further preferably, the mass ratio of Sn to Zn is 1:1.

[0022] Specifically, the Sn and Zn are commercial metal Sn and Zn, and the purity of each is greater than 99.9%.

[0023] Preferably, the mixing further comprises a process of adding a co-solvent.

[0024] Preferably, the co-solvent comprises ammonium chloride; further preferably, the co-solvent comprises an aqueous solution of ammonium chloride.

[0025] Preferably, the mass fraction of the aqueous ammonium chloride solution is 4-6%; further preferably, the mass fraction of the aqueous ammonium chloride solution is 4.5-5.5%; further preferably, the mass fraction of the aqueous ammonium chloride solution is 5%.

[0026] Preferably, the melting temperature is 450-550°C, and the melting time is 20-50 min; further preferably, the melting temperature is 480-520°C, and the melting time is 20-40 min; further preferably, the melting temperature is 500°C, and the melting time is 30 min.

[0027] Preferably, the heating rate during melting is 8-12°C / min; further preferably, the heating rate during melting is 9-11°C / min; further preferably, the heating rate during melting is 10°C / min.

[0028] Preferably, the melting is carried out in air.

[0029] Preferably, the melting process further includes cooling, pressing and hydrothermal treatment.

[0030] Preferably, during the cooling, the temperature is first lowered to 100° C. at a certain cooling rate, and then cooled naturally.

[0031] Preferably, the cooling rate is 8-12°C / min; further preferably, the cooling rate is 9-11°C / min; further preferably, the cooling rate is 10°C / min.

[0032] Preferably, the compression is performed using a tablet press.

[0033] Preferably, after the pressing, a flake with a thickness of 0.15-0.25 mm is obtained; further preferably, after the pressing, a flake with a thickness of 0.18-0.22 mm is obtained; further preferably, after the pressing, a flake with a thickness of 0.2 mm is obtained.

[0034] Preferably, the temperature of the hydrothermal treatment is 125-145°C, and the time of the hydrothermal treatment is 11-13h; further preferably, the temperature of the hydrothermal treatment is 130-140°C, and the time of the hydrothermal treatment is 11.5-12.5h; further preferably, the temperature of the hydrothermal treatment is 135°C, and the time of the hydrothermal treatment is 12h.

[0035] Specifically, the hydrothermal treatment is carried out in a hydrothermal kettle, with the purpose of removing potential impurities such as oil stains on the surface of the zinc-tin alloy catalyst.

[0036] Preferably, the hydrothermal treatment is followed by natural cooling and then washing to obtain the zinc-tin alloy catalyst.

[0037] The third aspect of the present invention provides a use of the zinc-tin alloy catalyst described in the first aspect of the present invention in the electroreduction of carbon dioxide to prepare formic acid.

[0038] Preferably, the working electrode for electro-reduction is the zinc-tin alloy catalyst described in the first aspect of the present invention.

[0039] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0040] (1) The zinc-tin alloy catalyst of the present invention comprises Sn, Zn, ZnO, SnO and SnO 2 The Sn and Zn are located inside the zinc-tin alloy catalyst, and the ZnO, SnO and SnO 2The zinc-tin alloy catalyst of the present invention has good catalytic activity and selectivity. At a voltage of -0.63 to -1.13 V vs. RHE, the Faradaic efficiency of carbon dioxide reduction to generate formic acid is greater than 70%, and can reach a maximum of more than 90% (the corresponding Faradaic efficiency is 92% when the potential is -0.93 V, and the yield of formic acid is 0.79 mmol h -1 cm -2 The current density of carbon dioxide reduction to formic acid reaches its maximum value at -1.13 V, which is 61 mA cm -2 The larger the current density, the higher the yield. At this time, the yield of formic acid is 1.12 mmolh -1 cm -2 .

[0041] (2) The zinc-tin alloy catalyst of the present invention has good stability in the electroreduction of carbon dioxide to formic acid. At a potential of -0.93 V vs RHE, after a 400-hour on-off accelerated decay life test, the current density remains stable at 42 mA cm -2 There is no obvious attenuation, and the Faradaic efficiency of generating formic acid remains stable at around 90%.

[0042] (3) The preparation process of the present invention is simple, low in cost, and has a wide potential, which is convenient for large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is the X-ray diffraction pattern of the zinc-tin alloy catalyst of Example 1 of the present invention;

[0044] Figure 2 This is the element distribution diagram of the zinc-tin alloy catalyst in Example 1 of the present invention;

[0045] Figure 3 This is a scanning electron microscope image of the surface of the zinc-tin alloy catalyst of Example 1 of the present invention;

[0046] Figure 4 This is an X-ray photoelectron spectrum of the zinc-tin alloy catalyst of Example 1 of the present invention;

[0047] Figure 5 This is a diagram of the Faraday efficiency and the current density of the zinc-tin alloy catalyst for the electroreduction of carbon dioxide to formic acid in Example 1 of the present invention;

[0048] Figure 6 This is a diagram of the Faraday efficiency and the current density of the zinc-tin alloy catalyst for the electroreduction of carbon dioxide to formic acid in Example 2 of the present invention;

[0049] Figure 7This is a diagram of the Faraday efficiency and the partial current density of the electroreduction of carbon dioxide to formic acid using a zinc-tin alloy catalyst according to Example 3 of the present invention;

[0050] Figure 8 This is a diagram of the Faraday efficiency and the current density of the metal Zn catalyst for electroreduction of carbon dioxide to formic acid in Comparative Example 1 of the present invention;

[0051] Fig. 9 This is a diagram of the Faraday efficiency and the current density of the metal tin catalyst for the electroreduction of carbon dioxide to formic acid in Comparative Example 2 of the present invention;

[0052] Fig.10 This is a stability performance diagram of the zinc-tin alloy catalyst in Example 1 of the present invention. DETAILED DESCRIPTION

[0053] In order to make the technical scheme of the present invention more clearly understood by those skilled in the art, the following embodiments are listed for illustration. It should be pointed out that the following embodiments do not limit the protection scope of the present invention.

[0054] Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0055] Example 1

[0056] A zinc-tin alloy catalyst comprising Sn, Zn, ZnO, SnO and SnO 2 Sn and Zn are located inside the zinc-tin alloy catalyst, ZnO, SnO and SnO 2 Located on the surface of zinc-tin alloy catalyst.

[0057] A method for preparing a zinc-tin alloy catalyst comprises the following steps:

[0058] (1) Weigh a certain mass of metal tin (Sn, Sn>99.9%) and metal zinc (Zn, Zn>99.9%) particles in a mass ratio of 1:1, place them in a crucible, add a 5% ammonium chloride aqueous solution at a mass ratio of 1:10 to moisten them (the ratio of the co-solvent to the sum of the mass of metal tin and zinc is 1:10), heat the mixture to 500°C at a heating rate of 10°C / min in an air atmosphere, melt react for 30 min, then control the cooling rate to be 10°C / min, cool to 100°C, and finally cool naturally;

[0059] (2) using a tablet press to press the sample naturally cooled in step (1) into a thin slice with a thickness of 0.2 mm, using anhydrous ethanol to remove surface oil stains, using 200-mesh sandpaper to polish to remove solid impurities such as surface oxide film, then using anhydrous ethanol to remove organic pollutants caused by surface polishing, and further cleaning the surface of the slice with deionized water;

[0060] (3) The thin slice obtained in step (2) was cut into samples of 3×3 cm in size, placed in a 50 mL hydrothermal kettle, 20 mL of deionized water was mixed with the sample, the temperature was raised to 135° C., and the hydrothermal treatment was performed for 12 hours. After the reaction was completed, the temperature was naturally lowered, and then the surface was washed with deionized water, and excess surface water was absorbed with filter paper to obtain a zinc-tin alloy catalyst.

[0061] Example 2

[0062] The only difference between Example 2 and Example 1 is that in Example 2, the mass ratio of Zn to Sn is 3:7, and the rest is the same as Example 1.

[0063] Example 3

[0064] The only difference between Example 3 and Example 1 is that in Example 3, the mass ratio of Zn to Sn is 7:3, and the rest is the same as Example 1.

[0065] Comparative Example 1

[0066] Comparative Example 1 uses metal Zn as a catalyst for preparing formic acid by electrocatalytic reduction of carbon dioxide.

[0067] Comparative Example 2

[0068] In Comparative Example 2, metallic Sn was used as a catalyst for preparing formic acid by electrocatalytic reduction of carbon dioxide.

[0069] Performance Testing

[0070] 1. X-ray diffraction analysis

[0071] The zinc-tin alloy catalyst prepared in Example 1 was subjected to X-ray diffraction (XRD) analysis. The X-ray diffraction pattern is as follows: Figure 1 shown.

[0072] Depend on Figure 1 It can be seen that the zinc-tin alloy catalyst prepared by the present invention contains Sn, Zn, ZnO and SnO 2 Polyphase.

[0073] 2. Energy spectrum analysis

[0074] The zinc-tin alloy catalyst prepared in Example 1 was subjected to energy spectrum analysis (EDS) to observe the element distribution in the zinc-tin alloy catalyst. The element distribution in the zinc-tin alloy catalyst is as follows: Figure 2shown.

[0075] Energy spectrum analysis shows that in the zinc-tin alloy catalyst prepared by the present invention, the Sn element, the Zn element and the oxygen element are uniformly distributed, and the mass ratio of the Sn element, the Zn element and the oxygen element is 1.42:24.5:64.48.

[0076] 3. Scanning electron microscopy observation

[0077] The surface of the zinc-tin alloy catalyst prepared in Example 1 was observed by scanning electron microscopy (SEM). The surface of the zinc-tin alloy catalyst is shown in the SEM image. Figure 3 As shown. Among them, Figure 3 Figure (a) is a scanning electron microscope image of the surface of the zinc-tin alloy catalyst at a low magnification. Figure 3 Figure (b) is a scanning electron microscope image of the surface of the zinc-tin alloy catalyst at high magnification.

[0078] Depend on Figure 3 It can be seen that the zinc-tin alloy catalyst prepared in the present invention is a flake structure, and the flake structure is square, and the side length of the flake structure is 2 μm.

[0079] 4. X-ray photoelectron spectroscopy test

[0080] The zinc-tin alloy catalyst prepared in Example 1 was subjected to an X-ray photoelectron spectroscopy (XPS) test. The X-ray photoelectron spectrum of the zinc-tin alloy catalyst is shown in FIG. Figure 4 As shown. Among them, Figure 4 Figure (a) shows the photoelectron spectrum formed by the transition of the 1s orbital electrons of the oxygen element in the zinc-tin alloy catalyst under X-ray irradiation; Figure 4 Figure (b) shows the photoelectron spectrum formed by the transition of the 2p orbital electrons of the zinc element in the zinc-tin alloy catalyst under X-ray irradiation; Figure 4 Figure (c) shows the photoelectron spectrum formed by the transition of 3d orbital electrons of the tin element in the zinc-tin alloy catalyst under X-ray irradiation.

[0081] Depend on Figure 4 It can be seen that on the surface of the zinc-tin alloy catalyst, tin, zinc and oxygen elements coexist. (a) The oxygen 1s spectrum shows that tin and zinc exist in the form of oxides, and (b) the 2p 3 / 2 The spectrum shows that the zinc element in the catalyst is +2 valence. (c) The 3d 3 / 2 The spectrum shows that the tin element in the catalyst has +4 and +2 valences, but the XRD does not show the diffraction peak of +2 valence tin compounds, proving that the +2 valence tin in the zinc-tin alloy catalyst enters SnO in the form of doping. 2 In the lattice.

[0082] In summary, the structure of the zinc-tin alloy catalyst is as follows: metallic Sn and Zn are distributed inside the zinc-tin alloy catalyst as a substrate, and the surface layer of the zinc-tin alloy catalyst is +4-valent tin oxide (SnO 2 ) and ZnO, and the mass ratio of Sn element, Zn element and oxygen element is Sn:Zn:O=1.42:24.5:64.48.

[0083] 5. Performance test of preparing formic acid by electroreduction of carbon dioxide

[0084] The performance of the zinc-tin alloy catalysts of Examples 1-3, the metal Zn catalyst of Comparative Example 1, and the metal tin catalyst of Comparative Example 2 in electro-reducing carbon dioxide to prepare formic acid was tested, and the test method was as follows:

[0085] The electrochemical test was carried out using a three-electrode system at 25 °C, 100 kPa pressure, and 0.5 M KHCO saturated with carbon dioxide. 3 The electrolytic solution was carried out. Carbon dioxide was continuously introduced during the test to achieve and maintain carbon dioxide saturation. A Ti mesh coated with Ru-Ir oxide was used as an anode, a saturated calomel electrode was used as a reference electrode, and zinc-tin alloy catalysts of Examples 1-3, metal Zn catalysts of Comparative Example 1, and metal tin catalysts of Comparative Example 2 were used as working electrodes. After 180 minutes of reaction, the solution was extracted and the formic acid concentration was characterized by high performance liquid chromatography, and the Faraday efficiency and yield of formic acid generation were calculated.

[0086] Wherein, the yield of formic acid = Q / zFt; Q is the coulomb number C; z is the number of electron transfers; for formic acid z = 2; t is the test time; F is the Faraday constant, F = 96485 C / mol.

[0087] The results of the Faraday efficiency and the current density of the zinc-tin alloy catalyst for the electroreduction of carbon dioxide to prepare formic acid in Example 1-3 are as follows: Figure 5-7 shown.

[0088] The Faraday efficiency and current density of the metal Zn catalyst in Comparative Example 1 and the metal tin catalyst in Comparative Example 2 for the electroreduction of carbon dioxide to prepare formic acid are shown in Table 1. Figure 8 and 9 shown.

[0089] Figure 5-9 The bar graph in the figure is the Faraday efficiency result of electroreduction of carbon dioxide to formic acid, the curve is the formic acid distribution current density result, and V vs. RHE in the abscissa represents the voltage relative to the reversible hydrogen electrode.

[0090] Depend on Figure 5It can be seen that the zinc-tin alloy catalyst with a zinc to tin mass ratio of 1:1 generates formic acid in the carbon dioxide reduction. In the range of -0.63 to -1.13 V vs. RHE, the Faradaic efficiency of carbon dioxide reduction to formic acid is greater than 70%, and the highest yield is 1.12 mmol h -1 cm -2 (-1.13 V vs. RHE). At a voltage of -0.93 V vs. RHE, the catalyst achieved the best formic acid production Faradaic efficiency of 92%, and the formic acid yield was 0.79 mmol h -1 cm -2 When the potential is above -0.73 V, the Faradaic efficiency of carbon dioxide reduction to formic acid is greater than 80%. The partial current density of carbon dioxide reduction to formic acid reaches the highest value at -1.13 V, which is 61 mA cm -2 .

[0091] Depend on Figure 5-7 It can be seen that the zinc-tin alloy catalysts of Examples 1-3 have good catalytic activity and selectivity when preparing formic acid by electro-reduction of carbon dioxide. Compared with the catalyst samples with other zinc to tin mass ratios in Examples 2-3, the zinc-tin alloy catalyst obtained in Example 1 with a zinc to tin mass ratio of 1:1 has a higher Faraday efficiency and formic acid current density for the reduction of formic acid by carbon dioxide. Therefore, the zinc-tin alloy catalyst with a tin to zinc mass ratio of 1:1 has the best activity and selectivity for catalyzing the generation of formic acid by carbon dioxide.

[0092] Depend on Figure 5 and Figure 8 , 9 It can be seen from the comparison that in the range of -0.63 to -1.13 Vvs. RHE, the Faraday efficiency and formic acid current density of the zinc-tin alloy catalyst in Example 1 during the electroreduction of carbon dioxide to prepare formic acid are significantly greater than those of Comparative Examples 1 and 2, that is, relative to unalloyed tin and zinc elements, the zinc-tin alloy catalyst has higher formic acid conversion Faraday efficiency and formic acid current density, proving that tin-zinc alloying is beneficial to the process of carbon dioxide reduction to generate formic acid, and is beneficial to improving the catalytic activity and selectivity of the catalyst.

[0093] The zinc-tin alloy catalyst of Example 1 was subjected to an accelerated decay life test of on-off circuit at a voltage of -0.93 V vs RHE for 400 hours to test the stability performance of the zinc-tin alloy catalyst.

[0094] The stability test results of the zinc-tin alloy catalyst in the accelerated decay life test of Example 1 of the present invention are as follows: Fig.10 shown.

[0095] Depend on Fig.10The curve of current and Faraday efficiency over time shows that the zinc-tin alloy catalyst has a stable current density of 42 mA cm-2 at a potential of -0.93 V vs RHE after a 400-hour on-off accelerated decay life test. -2 There is no obvious attenuation, and the Faraday efficiency of generating formic acid is stable at around 90%, which proves that the zinc-tin alloy catalyst of the present invention has good stability when producing formic acid by electroreduction of carbon dioxide.

[0096] In addition, the inventors found in long-term experimental research that other low-cost metal elements, such as copper, aluminum, and antimony, could not form uniform and continuous alloys during the experiment, and the finished products were in powder form, making subsequent performance tests impossible.

[0097] In summary, the present invention prepares a zinc-tin alloy catalyst by alloying. Tin-zinc alloying is beneficial to improving the catalytic activity and selectivity of the catalyst in the electroreduction of formic acid, and can maintain good stability in the accelerated decay life test, so that the zinc-tin alloy catalyst has the potential and prospect for large-scale commercial application in the carbon dioxide reduction of formic acid.

[0098] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A zinc-tin alloy catalyst, characterized in that Including Sn, Zn, ZnO, SnO and SnO2; The Sn and Zn are located inside the zinc-tin alloy catalyst, and the ZnO, SnO and SnO2 are located on the surface of the zinc-tin alloy catalyst.

2. The zinc-tin alloy catalyst according to claim 1, characterized in that In the zinc-tin alloy catalyst, the mass ratio of Sn element, Zn element and oxygen element is (1.2-1.6):(20-28):64.48; and / or, in the zinc-tin alloy catalyst, the mass ratio of Sn, Zn, ZnO, SnO and SnO2 is 1:(6-8):(1.4-1.3):(40-46.7).

3. The zinc-tin alloy catalyst according to claim 1, characterized in that The zinc-tin alloy catalyst has a flake structure.

4. The zinc-tin alloy catalyst according to claim 3, characterized in that The side length and thickness of the sheet structure are both 0.1-4 μm.

5. The method for preparing the zinc-tin alloy catalyst according to any one of claims 1 to 4, characterized in that: The following steps are involved: Sn and Zn are mixed and melted to obtain the zinc-tin alloy catalyst.

6. The preparation method according to claim 5, characterized in that: The mass ratio of Sn to Zn is 1:(0.38-3.3); and / or, the mixing also includes a process of adding a co-solvent; and / or, the melting temperature is 450-550°C, and the melting time is 20-50min; and / or, after melting, the process also includes cooling, pressing and hydrothermal treatment.

7. The preparation method according to claim 6, characterized in that: The melting is carried out in air; and / or the co-solvent comprises ammonium chloride.

8. The preparation method according to claim 6, characterized in that: The temperature of the hydrothermal treatment is 125-145° C., and the time of the hydrothermal treatment is 11-13 hours.

9. Use of the zinc-tin alloy catalyst according to any one of claims 1 to 4 in the preparation of formic acid by electroreduction of carbon dioxide.

10. The use according to claim 9, characterized in that: The working electrode for electroreduction is the zinc-tin alloy catalyst according to any one of claims 1 to 4.

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