A method for quickly preparing a highly efficient hydrogen evolution catalyst on carbon steel

Abstract

The invention discloses a preparation method for quickly preparing an efficient hydrogen evolution catalyst on carbon steel. The method is prepared by treating empty carbon steel, preparing an electroplating solution and an electrodeposited catalyst. The preparation method is simple, the process is easy to control, the raw material source is wide, the cost is low, and the preparation cycle is short. In the preparation process, a dynamic hydrogen bubble template method is used to quickly and firmly grow a NiCoFe catalyst on a carbon steel substrate under a large current, which not only enhances the hydrophilicity and gas repellency of the carbon steel, but also improves the double electric layer capacitance of the material, reduces the hydrogen evolution overpotential of the material, and the prepared catalyst particle size is 1 μm, and the morphology is a three-dimensional porous spherical structure, which lays a foundation for its excellent hydrogen evolution catalytic performance. The catalyst prepared by the invention can be mass-produced, has good economic benefits, and is suitable for industrial application.

Description

Technical Field

[0001] The invention belongs to the field of electrochemical catalyst preparation, relates to a hydrogen evolution catalyst, and specifically relates to a preparation method for quickly preparing a high-efficiency hydrogen evolution catalyst on carbon steel. Background Art

[0002] As fossil fuels are depleted and the energy crisis becomes increasingly serious, people are paying more attention to the development of renewable energy. Since the early 1970s, hydrogen has been regarded as an ideal energy source. Hydrogen has the highest energy density among known fuels and is a clean energy source with zero carbon dioxide emissions. Electrolysis of water can also produce oxygen, which is necessary for human survival.

[0003] There are abundant water resources on the earth. If we can use renewable energy such as wind power and solar energy to generate electricity, we can directly electrolyze water to produce a large amount of clean fuel, which can effectively alleviate the energy crisis. Hydrogen production by water electrolysis includes alkaline water electrolysis and acidic water electrolysis. Electrocatalysts are easily corroded in the acidic electrolyte process, so the high-purity hydrogen produced in the alkaline water electrolysis process has no acid mist and is competitive in the market. The best electrocatalyst for hydrogen evolution reaction (HER) is platinum-based catalyst, but platinum metal is a precious metal and is expensive, so it is very expensive to use it as a catalyst. At present, researchers mostly use materials with 3D foam structures such as nickel foam and copper foam as substrate materials for research. Some people also use stainless steel wire mesh, copper mesh, etc. as substrate materials, and some people use carbon cloth and carbon paper as substrate materials for hydrogen evolution material modification research, and have made certain progress. However, industrial water electrolysis to produce hydrogen is definitely a large-scale industrialization process, and substrate materials such as nickel foam have a honeycomb structure, which will hinder the output of H2 after hydrogen evolution and increase the gas resistivity of the material. Due to the special chemical properties of hydrogen, it is bound to form a safety hazard over time. Secondly, if stainless steel wire mesh or copper mesh is used as the substrate, it is difficult to provide effective support because the substrate material is relatively soft and cannot be applied over a large area; finally, if carbon cloth or carbon paper is used as the substrate material, its price will inevitably rise, and the electrolytic water hydrogen evolution effect is average, which is not conducive to the development of the electrolytic water industry. Therefore, the preparation of self-supporting electrolytic water catalysts to promote the development of the hydrogen production industry, the selection of appropriate substrate materials and the preparation of efficient hydrogen evolution catalysts are of great practical significance.

[0004] At present, my country's steel industry has mature technology, low-priced carbon steel, excellent alkali corrosion resistance and good supporting performance. If it can be used and modified to prepare hydrogen evolution catalysts, it will greatly promote the industrialization process of hydrogen production under strong alkaline conditions, which is of great significance to the development of the industry. Summary of the invention

[0005] The present invention aims to provide a preparation method for quickly preparing an efficient hydrogen evolution catalyst on carbon steel. The method is prepared by treating empty carbon steel, preparing an electroplating solution and an electrodeposited catalyst. The preparation method is simple, the process is easy to control, the raw material source is wide, the cost is low, and the preparation cycle is short. During the preparation process, a dynamic hydrogen bubble template is used to quickly and firmly grow a NiCoFe catalyst on a carbon steel substrate under a large current, which not only enhances the hydrophilicity and gas repellency of the carbon steel, but also improves the double-layer capacitance of the material and reduces the hydrogen evolution overpotential of the material. The prepared catalyst has a particle size of 1 μm and a three-dimensional porous spherical structure, which lays a foundation for its excellent hydrogen evolution catalytic performance.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing a highly efficient hydrogen evolution catalyst that can be quickly prepared on carbon steel, characterized in that the following preparation steps are carried out in sequence:

[0008] S1. Processing of bare carbon steel: Cut the carbon steel into pieces with a wire cutting machine to a size of 0.8 cm*1.0 cm*0.8 mm, remove rust and polish, and then place in anhydrous ethanol for ultrasonic cleaning;

[0009] S2, preparing an electroplating solution: taking a nickel source solution and a cobalt source solution, wherein the molar ratio of the nickel source to the cobalt source is 4:1, stirring and mixing them evenly, adding a composite buffer solution and adjusting the pH of the electroplating solution to 5.5-6;

[0010] In the present invention, the formula of the electroplating solution is relatively critical, which affects the three-dimensional porous spherical structure of the product. When the molar ratio of the nickel source to the cobalt source is 4:1, the particle size of the particles formed is small and uniform, and the particle size is 1 μm. However, at other ratios, the catalyst morphology obtained by electrodeposition is broken and uneven, which is not conducive to the electrolysis of water and hydrogen evolution reaction.

[0011] S3. Electrodeposition catalyst: Using Pt mesh as anode and carbon steel treated in S1 as cathode, electroplating was performed continuously for 10 to 20 minutes using a double electrode system in an electrolyte at -10 to -5 V and 2 to 5 A to obtain a highly efficient hydrogen evolution catalyst.

[0012] In the process of electrodeposition, the three metal elements are active, reducible, and k sp The chemical properties are different, and the reduction potential response competition will occur under the deposition conditions. Under the conditions of this electrolysis system, not only can the three metal elements be deposited quickly and evenly, preventing local unevenness or too little content of a certain metal element after deposition, but also the morphology and structure of the product after formation are further guaranteed during the preparation process, which will lay the foundation for its excellent hydrogen evolution catalytic performance.

[0013] As a first limitation of the present invention: in step S1, the empty carbon steel is 86CrMoV, which is a low-carbon steel, an iron-carbon alloy with a carbon content of 0.0218-2.11%, wherein the iron content is about 91%.

[0014] As a second limitation of the present invention, in step S2, the nickel source is H 12 N2NiO 10 S2 or NiCl2, and the cobalt source is CoSO4 or CoCl2.

[0015] As a third limitation of the present invention, in step S2, the composite buffer solution is a buffer solution prepared by mixing citric acid and sodium citrate in a molar ratio of 1:1, and the concentration of the buffer solution is 0.1 mol / L.

[0016] As a fourth limitation of the present invention, in step S1, the ultrasonic power is 360 W and the ultrasonic time is 20 min.

[0017] The present invention has another limitation that the high-efficiency hydrogen evolution catalyst has a three-dimensional spherical structure and a particle size of 1 μm.

[0018] As is known to all, the morphology and particle size of a material are closely related to its performance. This is mainly because the catalyst with a small particle size of 1 μm prepared by the present invention has a larger specific surface area, which can expose more active sites suitable for catalytic reactions, promote water electrolysis, and thus improve its hydrogen evolution catalytic performance.

[0019] The above technical solution of the present invention is taken as a whole, and its various steps are closely related to each other, forming an organic whole, and are inseparable and cannot be separated.

[0020] The present invention uses carbon steel as a substrate carrier, and the carbon steel contains Fe elements. The prepared catalyst is a NiCoFe hydrogen evolution catalyst. According to the metal material catalytic volcano diagram ( Figure 1 As shown in Figure 2, it can be found that transition metals such as Ni, Co, and Fe exhibit catalytic activity second only to that of precious metals near the equilibrium potential. The outer electron configurations of Ni, Co, and Fe are 3d 8 4s 2 ,3d 7 4s 2 ,3d 6 4s 2, after the transition metal with unpaired d electrons or d empty orbital forms an alloy or alloy compound, it will form an MH bond with the adsorbed hydrogen, and the MH bond with a moderate bond energy will greatly improve the adsorption and desorption process of hydrogen, thereby accelerating the water decomposition reaction. In addition, a synergistic catalytic effect will be produced between the metals in the NiCoFe catalyst prepared by the present invention, which will jointly improve the activity of the hydrogen evolution reaction and promote the electrolysis of water. In the preparation process of the present invention, carbon steel is used as a substrate carrier and provides an iron source. In addition, carbon steel has good alkali resistance and can be stored for a long time in an alkaline electrolyte with good stability. The in-situ growth method is used to grow a transition metal-based catalyst on a self-supporting electrode, which will greatly improve the activity of the catalyst. At the same time, it also makes the self-supporting electrode have good conductivity and is not easy to fall off.

[0021] The present invention uses a dynamic hydrogen bubble template method, and utilizes that in an acidic solution containing metal ions, the cathode will continuously precipitate its hydrogen bubbles under a relatively negative potential, and then the hydrogen bubbles are used as a "dynamic template" during metal deposition, and the metal ions are reduced between the gaps of the hydrogen bubbles to form a porous structure. The porous metal prepared by the hydrogen bubble dynamic template method has a large specific surface area and is conducive to the rapid transmission of substances. Since high melting point metals such as Ni and Co have a low exchange current density, the deposition kinetics are slow, so that the prepared catalyst is a three-dimensional porous spherical morphology. NiCoFe catalysts are quickly and firmly grown on carbon steel (CS) substrates under high currents. After the NiCoFe catalysts are deposited on carbon steel, the ternary metals can not only synergistically catalyze hydrogen evolution, but also the deposited catalysts enhance the hydrophilic and gas-repellent properties of carbon steel, which is beneficial to the rapid desorption of H2 from the electrode surface, and at the same time, the double electric layer capacitance of the material is also improved, and the hydrogen evolution overpotential of the material is reduced.

[0022] The beneficial effects achieved by adopting the above technical solution of the present invention are as follows:

[0023] 1. The present invention uses carbon steel as the base material, which is not only inexpensive, but also uses a dynamic hydrogen bubble template during its preparation process, which further ensures the three-dimensional spherical morphology of the prepared catalyst, so that it has a larger specific surface area, laying the foundation for excellent catalytic hydrogen evolution.

[0024] 2. The present invention adopts an electrodeposition method to in-situ grow a NiCoFe catalyst on a carbon steel substrate. The ternary metals can not only synergistically catalyze hydrogen evolution during the hydrogen evolution process, but also, due to the hydrophilicity and gas repellency of carbon steel, it is beneficial for H2 to quickly desorb from the electrode surface, thereby reducing the hydrogen evolution overpotential of the material. The material has good stability and lifespan, and good acid and alkali resistance.

[0025] 3. The preparation method of the present invention has high speed, simple operation process, low raw material cost, can be produced on a large scale, has good economic benefits, and is suitable for industrial application.

[0026] The invention is suitable for rapidly preparing a high-efficiency hydrogen evolution catalyst on carbon steel.

[0027] The specific implementation of the present invention will be further described in detail below with reference to the accompanying drawings.

[0028] Instruction Manual

[0029] Figure 1 This is the volcano diagram of pure metal in hydrogen evolution reaction;

[0030] Figure 2 The preparation flow chart and product SEM image of Example 1 of the present invention;

[0031] Figure 3 Surface scan distribution diagram of carbon steel 86CrMoV used in Example 1 of the present invention, wherein Figure a is a HAADF-STEM image of carbon steel 86CrMoV; Figure b is a Fe element distribution mapping diagram in carbon steel 86CrMoV; Figure c is a Cr element distribution mapping diagram in carbon steel 86CrMoV; Figure d is an EDS spectrum of carbon steel 86CrMoV; Figure e is a Mo element distribution mapping diagram in carbon steel 86CrMoV; Figure f is a V element distribution mapping diagram in carbon steel 86CrMoV;

[0032] Figure 4 XRD patterns of the catalysts prepared in Examples 1 and 2 of the present invention;

[0033] Figure 5 is the test result of the contact angle of carbon steel in Example 3 of the present invention;

[0034] Figure 6 3 is the test result of the contact angle of the material after the Ni-Co electroplating solution is electroplated in Example 3 of the present invention, wherein, Figure a is the water contact angle image at 0s; Figure b is the water contact angle image at 1s; Figure c is the water contact angle image at 2s; Figure d is the water contact angle image at 2.5s;

[0035] Figure 7 These are the test results of the double-layer capacitance of the products prepared in Examples 2-4 of the present invention and the carbon steel used in Example 1.

[0036] Figure 8 It is a comparison chart of the HER performance of the product prepared in the embodiment of the present invention and the catalyst prepared in Comparative Example 1. DETAILED DESCRIPTION

[0037] In the following examples, the reagents described are all commercially available unless otherwise specified, and the following experimental methods and detection methods are all based on existing experimental methods and detection methods unless otherwise specified.

[0038] Example 1

[0039] This embodiment is a method for quickly preparing an efficient hydrogen evolution catalyst on carbon steel. The preparation method is carried out in the following steps:

[0040] S1. Processing of bare carbon steel (86CrMoV): The carbon steel purchased from Shandong Zhongxin Metal Materials Co., Ltd. was cut into 0.8 cm*1.0 cm*0.8 mm size using a wire cutting machine (the wire cutting machine model for cutting carbon steel is DK7763), rust removed and polished, and then ultrasonically cleaned in anhydrous ethanol at 360 W for 20 min;

[0041] S2. Prepare plating solution: prepare 25 ml of 2M H 12 N2NiO 10 S2 solution and 0.5M CoSO4 solution are mixed and stirred evenly, and then a composite buffer solution is added to adjust the pH of the plating solution to 5.5. The concentration of the composite buffer solution is 0.1 mol / L. The composite buffer solution is a buffer prepared by citric acid and sodium citrate in a molar ratio of 1:1.

[0042] S3. Electrodeposition catalyst: Pt mesh is used as anode, and the cathode is made of carbon steel treated in S1. Electrolysis is performed using the plating solution prepared in S2. Under the conditions of -5V and 2A, a double electrode system is used to perform continuous electrodeposition for 10 minutes to obtain the final hydrogen evolution catalyst.

[0043] Figure 2 This is a flow chart of Example 1. The left side is 86CrMoV bare carbon steel, which is cut into small pieces and subjected to rust removal and polishing treatment. The right side is an electron scanning microscope picture after electrodeposition. It can be seen from the picture that the morphology of the catalyst prepared by the present invention is a three-dimensional porous sphere.

[0044] Example 2

[0045] This embodiment is a method for quickly preparing an efficient hydrogen evolution catalyst on carbon steel. The preparation method is carried out in the following steps:

[0046] S1. Processing of bare carbon steel (86CrMoV): Cut the carbon steel wire purchased from Shandong Zhongxin Metal Materials Co., Ltd. into a size of 0.8 cm*1.0 cm*0.8 mm, remove rust and polish, and then ultrasonically clean it in anhydrous ethanol at 360 W for 20 min. The wire cutting machine model for cutting carbon steel is DK7763;

[0047] S2, prepare electroplating solution: prepare 25ml, 2M NiCl2 and 0.5M CoCl2 solution, mix and stir evenly, then add composite buffer solution to adjust the pH of the electroplating solution to 6, the concentration of the composite buffer solution is 0.1mol / L, and the composite buffer solution is a buffer solution prepared by citric acid and sodium citrate in a molar ratio of 1:1;

[0048] S3. Electrodeposition catalyst: Pt mesh is used as anode, and the cathode is made of carbon steel treated in S1. Electrolysis is performed using the plating solution prepared in S2. Under the conditions of -10V and 5A, a double electrode system is used to perform continuous electrodeposition for 20 minutes to obtain the final hydrogen evolution catalyst.

[0049] Figure 3 This is a surface scanning distribution diagram of 86CrMoV used in Example 2 of the present invention. It can be analyzed from the figure that the main component of bare carbon steel is Fe, which contains a small amount of Cr, Mo, and V elements.

[0050] Figure 4 The XRD diagram of the catalyst prepared in Examples 1 and 2 of the present invention shows that compared with the empty carbon steel CS ( Figure 4 As for the top curve, the NiCoFe catalysts prepared in Example 1 and Example 2 were grown on a carbon steel substrate CS (86CrMoV), respectively.

[0051] Example 3

[0052] This embodiment is a method for quickly preparing an efficient hydrogen evolution catalyst on carbon steel. The preparation method is carried out in the following steps:

[0053] S1. Processing of empty carbon steel (CS): The carbon steel purchased from Shandong Zhongxin Metal Materials Co., Ltd. was cut into 0.8 cm*1.0 cm*0.8 mm size by wire cutting, rust removal and polishing, and then ultrasonically cleaned in anhydrous ethanol at 360 W for 20 minutes. The wire cutting machine model for cutting carbon steel was DK7763;

[0054] S2. Prepare plating solution: prepare 25 ml of 2M H 12 N2NiO 10 S2 and 0.5M CoSO4 solution are mixed and stirred evenly, and then a composite buffer solution is added to adjust the pH of the plating solution to 5.7. The concentration of the composite buffer solution is 0.1 mol / L. The composite buffer solution is a buffer prepared by citric acid and sodium citrate in a molar ratio of 1:1.

[0055] S3. Electrodeposition catalyst: Pt mesh is used as the anode, and the cathode is made of carbon steel treated in S1. The electrolysis is the plating solution prepared in S2. Under the conditions of -8V and 3A, a double electrode system is used to carry out continuous electrodeposition for 15 minutes to obtain the final hydrogen evolution catalyst.

[0056] Figure 5 is the test result of the contact angle of carbon steel in Example 3 of the present invention, Figure 5 The left picture shows the water contact angle image at 0.5s, and the right picture shows the water contact angle image at 3s. It can be seen from the pictures that water droplets have always existed on the CS surface.

[0057] Figure 6This is the test result of the contact angle of the NiCoFe catalyst material prepared in Example 3 of the present invention. It can be seen from the figure that Figure ad takes 0.25s, and the water droplet is completely immersed in a very short time. Figure 5 and Figure 6 The comparison fully demonstrates that the material prepared by the present invention significantly improves the hydrophilicity of empty carbon steel, which will be beneficial to its catalytic hydrogen evolution process.

[0058] Example 4

[0059] This embodiment prepares a highly efficient hydrogen evolution catalyst that can be quickly prepared on carbon steel. The preparation method is carried out in the following steps:

[0060] S1. Processing of empty carbon steel (CS): The carbon steel purchased from Shandong Zhongxin Metal Materials Co., Ltd. was cut into 0.8cm*1.0cm*0.8mm size by wire cutting, rust removal and polishing, and then ultrasonically cleaned in anhydrous ethanol at 360W for 20min. The wire cutting machine model for cutting carbon steel was DK7763;

[0061] S2. Prepare electroplating solution: prepare 25 ml of 2M NiCl2 and 0.5M CoSO4 solution, mix and stir evenly, then add composite buffer solution to adjust the pH of the electroplating solution to 6, the concentration of the composite buffer solution is 0.1 mol / L, and the composite buffer solution is a buffer solution prepared by citric acid and sodium citrate in a molar ratio of 1:1;

[0062] S3. Electrodeposition catalyst: Pt mesh is used as the anode, and the cathode is made of carbon steel treated in S1. The electrolysis is the plating solution prepared in S2. Under the conditions of -7V and 4A, a double electrode system is used for continuous deposition for 18 minutes to obtain the final hydrogen evolution catalyst.

[0063] Figure 7 The double-layer capacitance test results of the products prepared in Examples 2-4 of the present invention and the carbon steel used in the preparation process can be analyzed from the figure. Compared with the bare carbon steel, the double-layer capacitance of the material after preparing NiCoFe is significantly increased, and the electrochemical active area calculated from it is also increased. The increase in active area is more conducive to its catalytic hydrogen evolution. The electrochemical active area of ​​the catalyst is calculated according to the following equation:

[0064] ECSA=Cdl / Cs

[0065] ECSA: Electrochemically Active Area

[0066] Cdl: electrochemical double layer capacitance

[0067] Cs: Specific capacitance of the corresponding smooth surface sample under the same conditions

[0068] Comparative Example 1

[0069] In this example, a series of hydrogen evolution catalysts were prepared. The specific preparation process was similar to that of Example 1, except that the base materials were different during the preparation process, as follows:

[0070] Group A: The substrate is nickel foam (NF);

[0071] Group B: substrate is copper foam (CF);

[0072] Group C: substrate is foamed iron (FF);

[0073] Group D: substrate is carbon cloth (CC);

[0074] Group E: The base is stainless steel wire mesh (SS316L).

[0075] The materials prepared by the AE group were tested for hydrogen evolution catalytic performance on a CHI660E electrochemical workstation using a traditional three-electrode system. The working electrode was the carbon steel with NiCoFe electrodeposited in the present invention, and the reference electrode was a Hg / HgO electrode. The counter electrode was a Pt sheet. The specific results are shown in Figure 8 . Figure 8 It is a comparison chart of the HER performance of the product prepared in Example 1 of the present invention and the catalyst prepared in Comparative Example AE group. From the analysis of the figure, it can be seen that the material obtained by in-situ growing the NiCoFe catalyst on the carbon steel (CS) substrate has the best hydrogen evolution performance. This is mainly because the present invention utilizes a dynamic hydrogen bubble template method to quickly and firmly grow the NiCoFe catalyst on the carbon steel (CS) substrate under a large current. After the NiCoFe catalyst is deposited on the carbon steel, the ternary metal can not only synergistically catalyze hydrogen evolution, but also the deposited catalyst enhances the hydrophilicity and gas repellency of the carbon steel, which is beneficial to the rapid desorption of H2 from the electrode surface. At the same time, it also improves the double layer capacitance of the material and reduces the hydrogen evolution overpotential of the material.

[0076] Comparative Example 2

[0077] In this embodiment, a series of hydrogen evolution catalysts were prepared. The specific preparation process was similar to that of Example 1, except that the substrate material or the electroplating solution was different during the preparation process, as follows:

[0078] Group F: The substrate is nickel foam (NF), and 0.5 M ferric nitrate is added to the electroplating solution;

[0079] Group G: The substrate is iron sheet;

[0080] Group H: The substrate is nickel sheet, and 0.5M ferric nitrate is added to the electroplating solution;

[0081] Group I: carbon cloth substrate, 0.5 M ferric nitrate was added to the plating solution;

[0082] The materials prepared by the FI group were tested for their hydrogen evolution catalytic performance at a scan rate of 2 mV / s and 100 mA / cm 2 The electrochemical catalytic hydrogen evolution test was carried out under the current density test conditions. The specific test results are shown in the table below.

[0083] Group Hydrogen evolution overpotential (mV) Group F 305 Group G 334 Group H 297 Group I 318

[0084] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of protection of the claims of the present invention.

Claims

1. A method for quickly preparing an efficient hydrogen evolution catalyst on carbon steel, characterized in that: The preparation steps are carried out in sequence as follows: S1. Processing of bare carbon steel: Cut the carbon steel into pieces with a wire cutting machine to a size of 0.8 cm × 1.0 cm × 0.8 mm, remove rust and polish, and then place in anhydrous ethanol for ultrasonic cleaning; S2, preparing an electroplating solution: taking a nickel source solution and a cobalt source solution, wherein the molar ratio of the nickel source to the cobalt source is 4:1, stirring and mixing them evenly, adding a composite buffer solution and adjusting the pH of the electroplating solution to 5.5-6; S3, electro-deposition preparation of catalyst: using Pt mesh as anode and carbon steel treated in S1 as cathode, electro-deposition was performed continuously for 10 to 20 minutes using a double electrode system in an electroplating solution at -10 to -5 V and 2 to 5 A to obtain a highly efficient hydrogen evolution catalyst; In step S1, the air carbon steel is 86 CrMoV; In step S2, the nickel source is H 12 N2NiO 10 S2 or NiCl2, the cobalt source is CoSO4 or CoCl2; In step S2, the composite buffer solution is a buffer solution prepared by mixing citric acid and sodium citrate in a molar ratio of 1:1, and the concentration of the buffer solution is 0.1 mol / L; The high-efficiency hydrogen evolution catalyst has a three-dimensional porous spherical structure and a particle size of 1 μm.

2. The method for quickly preparing a highly efficient hydrogen evolution catalyst on carbon steel according to claim 1, characterized in that: In step S1, the ultrasonic power is 360W and the ultrasonic time is 20min.

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