A method for preparing a high-efficiency twinned copper-tin alloy catalyst based on pulse electrodeposition-annealing process

Abstract

The invention discloses a method for preparing a high-efficiency twinned copper-tin alloy catalyst based on a pulse electrodeposition-annealing process. The method comprises the following steps: step 1, preparing an acidic electrolyte containing copper sulfate, stannous sulfate and sulfuric acid, depositing the copper sulfate, stannous sulfate and sulfuric acid on a predetermined deposition substrate using a pulse electrodeposition technique, and preparing a high-quality twinned copper-tin electrocatalyst foil with controllable density in the acidic electrolyte under a predetermined pulse electrodeposition cycle, a predetermined pulse time, a predetermined duration, a predetermined pulse current density and a predetermined counter electrode; and step 2, placing the twinned copper-tin catalyst foil in a low-pressure, high-vacuum annealing furnace, and performing an annealing treatment under inert or reducing atmosphere protection at a predetermined annealing temperature and for a predetermined annealing time to obtain a high-efficiency twinned copper-tin alloy catalyst.

Description

Technical Field

[0001] The present invention relates to the field of pulse electrodeposition-annealing technology, and in particular to a method for preparing a high-efficiency twinned copper-tin alloy catalyst based on the pulse electrodeposition-annealing technology. Background Art

[0002] Global climate change and energy shortages have prompted more than 120 countries to develop blueprints. Electrocatalytic carbon dioxide reduction reaction (CO2RR) can reduce CO2 emissions and is an effective way to help achieve this. In addition, converting CO2 into high-value-added chemicals can effectively store abundant intermittent energy in the form of liquid fuels, such as formic acid, alcohols, etc. (Dinh CT, Science, 360, 783-787 (2018)), and using them as liquid fuels can alleviate energy shortages. Formic acid is one of the most promising bulk chemicals for electrocatalytic carbon dioxide reduction so far. However, due to the lack of efficient, stable, low-cost and large-scale electrocatalysts, the application of CO2RR technology to the synthesis of bulk chemicals is challenging.

[0003] Currently, research on formic acid catalysts for CO2RR is booming. For example, Bi-, Sn-, Pd-, and In-based electrocatalysts have been reported. However, the nanoelectrocatalysts obtained by currently reported synthesis methods suffer from cumbersome synthesis processes, high synthesis costs, and poor stability, hindering their further large-scale application in the preparation of efficient formic acid catalysts. Meanwhile, currently reported bulk alloy catalysts offer the advantages of mature preparation processes, low costs, excellent performance, and good stability. However, these conventional bulk alloy electrocatalysts cannot be coupled with existing commercial gas diffusion electrodes, limiting their potential for high current density applications. Therefore, there is an urgent need to develop a method for the synthesis of formic acid catalysts using efficient alloy catalysis that can be coupled with gas diffusion electrodes. Summary of the Invention

[0004] The present invention is made to solve the above problems, and its purpose is to provide a method for preparing a high-efficiency twinned copper-tin alloy catalyst based on a pulse electrodeposition-annealing process.

[0005] The present invention provides a preparation method of a high-efficiency twinned copper-tin alloy catalyst based on a pulse electrodeposition-annealing process. The method comprises the following steps: step 1, preparing an acidic electrolyte containing copper sulfate, stannous sulfate and sulfuric acid, and depositing the copper sulfate, stannous sulfate and sulfuric acid on a predetermined deposition substrate by using a pulse electrodeposition technology; and preparing a high-quality twinned copper-tin electrocatalyst foil with controllable density in the acidic electrolyte under a predetermined pulse electrodeposition cycle, a predetermined pulse time, a predetermined duration, a predetermined pulse current density and a predetermined counter electrode; and step 2, placing the twinned copper-tin catalyst foil in a low-pressure and high-vacuum annealing furnace, and performing an annealing treatment under inert or reducing atmosphere protection at a predetermined annealing temperature and for a predetermined annealing time to obtain a high-efficiency twinned copper-tin alloy catalyst.

[0006] The preparation method of a high-efficiency twinned copper-tin alloy catalyst based on a pulse electrodeposition-annealing process provided by the present invention may also have the following characteristics: wherein, in step 1, the concentration of sulfuric acid in the acidic electrolyte is 0.05M to 1M, the concentration range of copper sulfate is 0.5M to 1.5M, the concentration of stannous sulfate is 0.1M to 0.5M, and the pH value of the acidic electrolyte is less than 1.

[0007] The method for preparing a high-efficiency twinned copper-tin alloy catalyst based on a pulse electrodeposition-annealing process provided by the present invention may also have the following characteristics: wherein, in step 1, the predetermined pulse electrodeposition period is 1s to 4s, the predetermined pulse time is 20 to 200ms, the predetermined duration is 6h to 20h, and the predetermined pulse current density is 1A cm -2 ~2A cm -2 , the predetermined deposition substrate is graphite paper, and the predetermined counter electrode is copper foil.

[0008] The method for preparing a high-efficiency twinned copper-tin alloy catalyst based on a pulse electrodeposition-annealing process provided by the present invention may also have the following characteristics: wherein the size of the predetermined pulse current density is determined by the size of the exposed area of ​​the graphite paper.

[0009] The preparation method of a high-efficiency twinned copper-tin alloy catalyst based on a pulse electrodeposition-annealing process provided by the present invention may also have the following characteristics: wherein, in step 2, the inert or reducing atmosphere is hydrogen, the flow rate of hydrogen is adjusted by a mass flow meter and is 10 to 2000 sccm, the predetermined annealing temperature is 200 to 600°C, and the predetermined annealing time is 0.5 to 10 hours.

[0010] The preparation method of a high-efficiency twinned copper-tin alloy catalyst based on a pulse electrodeposition-annealing process provided by the present invention may also have the following characteristics: wherein, in step 1, the predetermined deposition substrate is replaced with a gas diffusion electrode carbon paper to prepare a high-efficiency twinned copper-tin alloy catalyst, and the high-efficiency twinned copper-tin alloy catalyst is a twinned copper-tin alloy gas diffusion electrode, and the gas transmission side of the gas diffusion electrode carbon paper is encapsulated with silica gel and PET materials, while keeping the hydrophobic side of the gas transmission side of the gas diffusion electrode carbon paper exposed to the acidic electrolyte.

[0011] The present invention provides an application of a high-efficiency twinned copper-tin alloy catalyst based on a pulse electrodeposition-annealing process in electrocatalytic carbon dioxide reduction synthesis of formic acid. The application method has the following characteristics: a specific method of encapsulating the high-efficiency twinned copper-tin alloy catalyst in a common electrochemical device, conducting an electrochemical carbon dioxide reduction test under neutral electrolyte conditions, and efficiently catalyzing the conversion of carbon dioxide into formic acid; the common electrochemical device is encapsulated with silicone sealant; the contact resistance between the wire in the common electrochemical device and the high-efficiency twinned copper-tin alloy catalyst is less than 100Ω; the neutral electrolyte is a potassium bicarbonate or sodium bicarbonate solution saturated with carbon dioxide, the concentration of the potassium bicarbonate or sodium bicarbonate is from 0.1M to saturation, and the flow rate of carbon dioxide is from 1 to 5000sccm.

[0012] The present invention provides an application of a high-efficiency twinned copper-tin alloy catalyst based on a pulse electrodeposition-annealing process in electrocatalytic carbon dioxide reduction synthesis of formic acid. The catalyst has the following characteristics: a specific application method comprises assembling a twinned copper-tin alloy gas diffusion electrode in an exchange membrane electrode group, adopting ion exchange membrane technology, electrolyzing carbon dioxide in a potassium bicarbonate electrolyte, and applying the catalyst to the production of formic acid chemicals; the concentration of potassium bicarbonate in the potassium bicarbonate electrolyte is 0.1M to 2M, the flow rate of the potassium bicarbonate electrolyte is 10 to 5000 sccm, the gas supply flow rate of carbon dioxide is 10 to 5000 sccm, the electrolysis test counter electrode is either iridium oxide or a metal platinum catalyst, and the anode adopts a gas-liquid mixed flow pump to maintain electrolyte circulation.

[0013] Functions and effects of the invention

[0014] According to the method for preparing a high-efficiency twinned copper-tin alloy catalyst based on a pulse electrodeposition-annealing process involved in the present invention, an acidic electrolyte containing copper sulfate, stannous sulfate and sulfuric acid is first prepared, and pulse electrodeposition technology is used to deposit them on a predetermined deposition substrate. Under a predetermined pulse electrodeposition cycle, a predetermined pulse time, a predetermined duration, a predetermined pulse current density and a predetermined counter electrode, a density-controllable, high-quality twinned copper-tin electrocatalyst foil is prepared in the acidic electrolyte; then, the twinned copper-tin catalyst foil is placed in a low-pressure, high-vacuum annealing furnace and annealed under inert or reducing atmosphere protection, a predetermined annealing temperature and a predetermined annealing time to obtain a high-efficiency twinned copper-tin alloy catalyst.

[0015] Therefore, the pulse electrodeposition-annealing process used in the preparation method of the high-efficiency twinned copper-tin alloy catalyst based on the pulse electrodeposition-annealing process involved in the present invention is a mature, stable, and cost-controllable two-step process. The subsequent annealing process can alloy the copper and tin, significantly improve the catalyst performance of the material, and is conducive to the large-scale expansion of the synthesis of other high-efficiency twinned alloy carbon dioxide reduction electrocatalysts.

[0016] In addition, the high-efficiency twinned copper-tin alloy electrocatalyst prepared by the preparation method of the high-efficiency twinned copper-tin alloy catalyst based on the pulse electrodeposition-annealing process involved in the present invention has excellent performance in reducing carbon dioxide to formic acid, and by combining with a gas diffusion electrode, a higher current density formic acid electrosynthesis can be obtained.

[0017] Finally, the catalyst preparation process and the method for producing formic acid chemicals by reducing carbon dioxide provided by the preparation method of the high-efficiency twinned copper-tin alloy catalyst based on the pulse electrodeposition-annealing process involved in the present invention can be used for large-scale production of formic acid chemicals. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the preparation method of a high-efficiency twinned copper-tin alloy catalyst based on a pulse electrodeposition-annealing process in Example 1 of the present invention;

[0019] Figure 2 TEM images of twinned copper-tin crystals before and after annealing in Example 1 of the present invention;

[0020] Figure 3 This is a bar graph of atomic ratios of twinned copper-tin crystals before and after annealing in Example 1 of the present invention;

[0021] Figure 4 HAADF atomic images of twinned copper-tin before and after annealing and their corresponding atomic brightness gradient images in Example 1 of the present invention;

[0022] Figure 5 1 is the X-ray diffraction pattern of the twinned copper-tin before and after annealing in Example 1 of the present invention;

[0023] Figure 6 This is a bar graph showing the performance of electrocatalytic reduction of carbon dioxide by twinned copper-tin before and after annealing in Example 1 of the present invention;

[0024] Figure 7 This is a bar graph of the carbon dioxide reduction current density before and after annealing of the twinned copper-tin in Example 1 of the present invention;

[0025] Figure 8 This is a graph showing the maximum carbon dioxide partial current density corresponding to different annealing temperatures of twinned copper-tin in Example 1 of the present invention;

[0026] Figure 9 Schematic diagram of the Faradaic efficiency of carbon dioxide reduction to produce formic acid at different polishing depths after annealing of twinned copper-tin in Example 1 of the present invention;

[0027] Figure 10 is a schematic diagram of the principle of a flow cell in embodiment 2 of the present invention; and

[0028] Figure 11 Schematic diagram of the current density distribution corresponding to the reduction of carbon dioxide to produce formic acid when the twinned copper-tin alloy is coupled to the gas diffusion electrode in Example 2 of the present invention. DETAILED DESCRIPTION

[0029] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the following examples and drawings specifically illustrate the preparation method of a high-efficiency twinned copper-tin alloy catalyst based on the pulse electrodeposition-annealing process of the present invention.

[0030] <Example 1>

[0031] This embodiment provides a method for preparing a high-efficiency twinned copper-tin alloy catalyst based on a pulse electrodeposition-annealing process.

[0032] The preparation method of the high-efficiency twinned copper-tin alloy catalyst based on the pulse electrodeposition-annealing process in this embodiment is:

[0033] In step S1, 9.987 g of copper sulfate pentahydrate and 1.72 g of stannous sulfate powder were weighed into a beaker using an analytical balance, 80 ml of deionized water was added, and the mixture was stirred to dissolve. The mixture was ultrasonicated for 30 min at a power of 200 W. Then, 2.25 ml of concentrated sulfuric acid (98%) was slowly added dropwise to the homogeneous solution and stirred for 5-10 min. The electrolyte for pulse electrodeposition was thus prepared.

[0034] Next, cut the copper foil of appropriate size to be used as the anode and seal the graphite paper with insulating silicone to make the exposed window 1×1.5cm 2, ensure that the area of ​​the anode copper foil is larger than the exposed window area of ​​the cathode graphite paper, connect the copper foil and graphite paper electrodes with stainless steel electrode clamps, immerse them in the above-prepared electrolyte, and connect the anode and cathode.

[0035] Then, a Geely 2612B source meter was used to apply a constant pulse current with a pulse period of 2 seconds, a pulse time of 40 ms, a duration of 6 hours, and a pulse current of 1.5 A. During the deposition process, the solution was stirred and the rotation speed was controlled at 400 rpm.

[0036] Finally, the pulse-deposited sample was peeled off the graphite paper, washed with deionized water, blown dry with a nitrogen gun, and sealed for storage to obtain a density-controlled, high-quality twinned copper-tin electrocatalyst foil for further testing and characterization.

[0037] In step S2, the dried sample is placed in a CVD tube furnace with adjustable vacuum and annealed in a hydrogen atmosphere. The annealing conditions are: a system pressure of <30 mtor, a hydrogen flow rate of 200 sccm, a temperature of 300°C, an annealing time of 1 hour, and slow cooling to obtain a twinned copper-tin alloy sample.

[0038] In this embodiment, the performance of the twinned copper-tin alloy sample prepared by the above process was tested, and the specific method was as follows:

[0039] First, a wire was welded to the prepared twinned copper-tin alloy sample as the working electrode and sealed with silicone rubber so that the sample exposed area was 0.5 cm 2 The actual contact resistance between the wire and the catalyst measured by an ohmmeter is less than 5Ω.

[0040] The working electrode was then used for electrochemical carbon dioxide reduction testing. The electrolyte was a carbon dioxide-saturated 0.2M KHCO3 solution. The carbon dioxide flow rate was maintained at 200 sccm. The counter electrode was a commercial iridium oxide-coated titanium mesh. The reference electrode was an Ag / AgCl electrode. After a period of reaction, the electrolyte was collected for product detection.

[0041] Figure 1 Schematic diagram of the preparation method of a high-efficiency twinned copper-tin alloy catalyst based on a pulse electrodeposition-annealing process in this embodiment.

[0042] like Figure 1 As shown, the copper-tin alloy synthesized by pulse electrodeposition does not contain tin at the twin boundaries, resulting in low selectivity for catalytic CO2 conversion. After heating and annealing, tin atoms are enriched at the twin boundaries, forming a highly efficient copper-tin twin formic acid catalyst that achieves specific formic acid selectivity.

[0043] Figure 2 1 and 2 are transmission electron microscope images of the twinned copper-tin crystals before and after annealing in this embodiment.

[0044] like Figure 2 As shown, a large number of twin boundaries can be seen.

[0045] Figure 3 This is a bar chart of the atomic ratio of twinned copper and tin before and after annealing in this embodiment.

[0046] like Figure 3 As shown, the mass fraction of tin is about 1.1%.

[0047] Figure 4 These are the HAADF atomic images of the twinned copper-tin crystals before and after annealing and their corresponding atomic brightness gradient images in this embodiment.

[0048] like Figure 4 As shown, it can be seen that the tin content at the twin boundary is very low before heating, while a negative tin electrode appears after heating.

[0049] Figure 5 1 is the X-ray diffraction pattern of the twinned copper-tin before and after annealing in this embodiment.

[0050] like Figure 5 As shown, there is no obvious change in the crystal orientation of the catalyst before and after heating.

[0051] Figure 6 4 is a bar graph showing the performance of electrocatalytic reduction of carbon dioxide before and after annealing of the twinned copper-tin crystals in this embodiment.

[0052] like Figure 6 As shown, the main products of the twin catalyst before heating include CO, CH4, formic acid and C2 products, and the main product of CO2 reduction catalyzed by the heated catalyst is formic acid.

[0053] Figure 7 4 is a bar graph of the carbon dioxide reduction current density before and after annealing of the twinned copper-tin in this embodiment.

[0054] like Figure 7 As shown in the figure, the partial current density of formic acid is greatly improved after the twin catalyst is heated and annealed.

[0055] Figure 8 This is a graph showing the maximum carbon dioxide partial current density corresponding to different annealing temperatures of the twinned copper-tin in Example 1 of the present invention.

[0056] like Figure 8 As shown, 300℃ is the optimal annealing temperature.

[0057] Figure 9 Schematic diagram of the Faraday efficiency of carbon dioxide reduction to produce formic acid at different polishing depths after annealing of twinned copper-tin in Example 1 of the present invention.

[0058] like Figure 9As shown in the figure, electrolytic polishing is used to control the polishing time so that the atoms on the catalyst surface can be continuously renewed, thereby maintaining its high catalytic activity.

[0059] <Example 2>

[0060] This embodiment provides a method for preparing a high-efficiency twinned copper-tin alloy catalyst based on a pulse electrodeposition-annealing process.

[0061] The preparation method of the high-efficiency twinned copper-tin alloy catalyst based on the pulse electrodeposition-annealing process in this embodiment is similar to that in Example 1, except that:

[0062] The graphite paper in the second step was replaced with commercial gas diffusion electrode carbon paper. The pulse electrodeposition time was 6 h. The rest was the same as in Example 1. Finally, a twinned copper-tin alloy electrocatalytic electrode with gas diffusion function was prepared, ensuring that the catalytic surface window size was 1×2.5 cm.

[0063] In this embodiment, the performance of the twinned copper-tin alloy electrocatalytic electrode with gas diffusion function prepared by the above process was tested. The specific method is as follows:

[0064] The electrode prepared as above was used as the working electrode to carry out carbon dioxide electroreduction in a flow cell electrolytic cell. An anion exchange membrane was used to separate the anode and cathode. The cathode electrolyte was 1M KHCO3, the anolyte was 1M KOH, and the anode catalyst was a homemade hydrophilic carbon paper electrode uniformly loaded with iridium oxide. The cathode carbon dioxide supply rate was 30sccm, the cathode electrolyte was maintained at a flow rate of 40sccm by a peristaltic pump (EC-200), and the anolyte was maintained in circulation by a gas-liquid mixed flow pump. After a period of reaction, the cathode electrolyte was collected for product detection.

[0065] Figure 10 Schematic diagram of the principle of the flow cell in this embodiment.

[0066] like Figure 10 As shown, the gas diffusion electrode used includes an anode catalyst, an anion exchange membrane, a cathode catalyst, an anode electrolyte and a cathode electrolyte. The carbon dioxide supply gas is introduced from the back side of the cathode catalyst. Due to its hydrophobic ventilation effect, a high current density can be achieved.

[0067] Figure 11 Schematic diagram of the current density distribution corresponding to the reduction of carbon dioxide to produce formic acid when the twinned copper-tin alloy is coupled under the gas diffusion electrode in this embodiment.

[0068] like Figure 11 As shown, at different potentials, the liquid phase product formic acid is collected and the current density of the reaction is recorded at the same time, so the partial current of formic acid at different potentials is calculated.

[0069] Functions and Effects of the Embodiments

[0070] According to the preparation method of a high-efficiency twinned copper-tin alloy catalyst based on a pulse electrodeposition-annealing process involved in this embodiment, an acidic electrolyte containing copper sulfate, stannous sulfate and sulfuric acid is first prepared, and pulse electrodeposition technology is used to deposit it on a predetermined deposition substrate. Under a predetermined pulse electrodeposition cycle, a predetermined pulse time, a predetermined duration, a predetermined pulse current density and a predetermined counter electrode, a density-controllable, high-quality twinned copper-tin electrocatalyst foil is prepared in the acidic electrolyte; then the twinned copper-tin catalyst foil is placed in a low-pressure, high-vacuum annealing furnace, and annealed under inert or reducing atmosphere protection, a predetermined annealing temperature and a predetermined annealing time to obtain a high-efficiency twinned copper-tin alloy catalyst.

[0071] Therefore, the pulse electrodeposition-annealing two-step process used in the preparation method of the high-efficiency twinned copper-tin alloy catalyst based on the pulse electrodeposition-annealing process involved in the above embodiment is mature, stable, and cost-controllable. The subsequent annealing process can alloy the copper and tin, significantly improve the catalyst performance of the material, and is conducive to the large-scale expansion of the synthesis of other high-efficiency twinned alloy carbon dioxide reduction electrocatalysts.

[0072] In addition, the high-efficiency twinned copper-tin alloy electrocatalyst prepared by the preparation method of the high-efficiency twinned copper-tin alloy catalyst based on the pulse electrodeposition-annealing process involved in the above-mentioned embodiment has excellent performance in reducing carbon dioxide to formic acid, and by combining with a gas diffusion electrode, a higher current density formic acid electrosynthesis can be obtained.

[0073] Finally, the catalyst preparation process and the method for producing formic acid chemicals by reducing carbon dioxide provided by the preparation method of the high-efficiency twinned copper-tin alloy catalyst based on the pulse electrodeposition-annealing process involved in the above embodiment can be used for large-scale production of formic acid chemicals.

[0074] The above embodiments are preferred examples of the present invention and are not intended to limit the scope of protection of the present invention.

Claims

1. A method for preparing a high-efficiency twinned copper-tin alloy catalyst based on a pulse electrodeposition-annealing process, characterized in that: The following steps are involved: Step 1: Prepare an acidic electrolyte containing copper sulfate, stannous sulfate and sulfuric acid, and use pulse electrodeposition technology to deposit them on a predetermined deposition substrate. Under a predetermined pulse electrodeposition cycle, a predetermined pulse time, a predetermined duration, a predetermined pulse current density and a predetermined counter electrode, prepare a density-controllable, high-quality twinned copper-tin electrocatalyst foil in the acidic electrolyte. The concentration of the sulfuric acid in the acidic electrolyte is 0.05 M~1 M, the concentration range of the copper sulfate is 0.5 M~1.5 M, the concentration of the stannous sulfate is 0.1 M~0.5 M, the pH value of the acidic electrolyte is less than 1, the predetermined pulse electrodeposition cycle is 1 s~4 s, the predetermined pulse time is 20~200 ms, the predetermined duration is 6 h~20 h, and the predetermined pulse current density is 1 A cm -2 ~2 A cm -2 ; Step 2: placing the twinned copper-tin catalyst foil in a low-pressure, high-vacuum annealing furnace, and annealing it under inert or reducing atmosphere protection at a predetermined annealing temperature and for a predetermined annealing time to obtain a high-efficiency twinned copper-tin alloy catalyst in which tin atoms are enriched at the twin boundaries. The predetermined annealing temperature is 200-600°C, and the predetermined annealing time is 0.5-10 h.

2. The method for preparing a high-efficiency twinned copper-tin alloy catalyst based on a pulse electrodeposition-annealing process according to claim 1, characterized in that: in, In step 1, the predetermined deposition substrate is graphite paper, and the predetermined counter electrode is copper foil.

3. The method for preparing a high-efficiency twinned copper-tin alloy catalyst based on a pulse electrodeposition-annealing process according to claim 1, characterized in that: in, In step 2, the inert or reducing atmosphere is hydrogen, The flow rate of the hydrogen gas was adjusted by a mass flow meter and was 10-2000 sccm.

4. Use of a high-efficiency twinned copper-tin alloy catalyst prepared by the method for preparing a high-efficiency twinned copper-tin alloy catalyst based on a pulse electrodeposition-annealing process as claimed in any one of claims 1 to 3 in electrocatalytic carbon dioxide reduction synthesis of formic acid, characterized in that: The specific application method is: the high-efficiency twinned copper-tin alloy catalyst is packaged in a common electrochemical device, and an electrochemical carbon dioxide reduction test is performed under neutral electrolyte conditions to catalytically convert carbon dioxide into formic acid. The conventional electrochemical device is sealed with silicone, and the contact resistance between the wire in the conventional electrochemical device and the high-efficiency twinned copper-tin alloy catalyst is less than 100 Ω. The neutral electrolyte is a solution of potassium bicarbonate or sodium bicarbonate saturated with carbon dioxide, and the concentration of the potassium bicarbonate or sodium bicarbonate is from 0.1 M to saturation. The flow rate of the carbon dioxide is 1-5000 sccm.

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