Method for preparing tetramethylammonium hydroxide through underpotential electrolysis

Abstract

The invention belongs to the technical field of separation and purification, and particularly relates to a method for preparing tetramethylammonium hydroxide through underpotential electrolysis. The method is carried out in a diaphragm electrolytic cell and comprises the following steps: step 1, preparation of a capacitor electrode: sequentially carrying out roughening treatment and high-temperature activation treatment on a porcelain tube, and then carrying out chemical nickel plating to obtain the capacitor electrode which serves as an anode and a cathode at the same time; and 2, underpotential electrolysis: adding a tetramethylammonium bicarbonate solution into the anode chamber, adding a tetramethylammonium hydroxide solution into the cathode chamber, and then carrying out underpotential electrolysis reaction to obtain the tetramethylammonium hydroxide solution. According to the method, the tetramethylammonium hydroxide solution product is high in purity, and the operation cost is low.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrolytic purification, and particularly relates to a production and purification method of tetramethylammonium hydroxide. BACKGROUND

[0002] Electronic-grade tetramethylammonium hydroxide (TMAH) is a strong alkaline chemical and is usually used as an alkaline developer. At present, the main methods for preparing TMAH include the silver chloride method, ion exchange resin method, alkali displacement method and electrolysis method. Among them, the production method of high-purity TMAH is the ion membrane electrolysis method, which meets the requirements of the electronic industry by using the combination of electrolysis and ion membrane. The electrolytic raw material mainly used in China is tetramethylammonium bicarbonate, which belongs to an environmentally friendly green production process.

[0003] Electronic chemicals have the characteristics of many varieties, high quality requirements, small amount of use, and harsh environmental cleanliness requirements, and these characteristics are becoming more and more obvious with the development of microfabrication technology. The separation and purification process is the key unit of the production of electronic-grade chemicals, and electronic-grade chemicals are often obtained by purifying industrial-grade chemicals. The purification process usually uses multiple separation technologies such as rectification, adsorption, crystallization, extraction, ion membrane, etc. in combination, among which the ion membrane technology has the outstanding advantages of high separation efficiency, high product purity and strong controllability, and is a commonly used technology and key technology for the purification of electronic-grade chemicals.

[0004] In recent years, with the rapid development of the semiconductor industry, the quality requirements of electronic-grade chemicals are becoming higher and higher. Based on the characteristics of extremely high purity and strict impurity control, the traditional electrolysis technology used in the preparation of electronic-grade chemicals in the prior art cannot meet the higher use requirements of electronic-grade chemicals. SUMMARY

[0005] Therefore, the technical problem to be solved by the present application is to overcome the defects in the prior art, such as high metal ion content in electronic-grade tetramethylammonium hydroxide and inability to meet higher use requirements, so as to provide a method for preparing tetramethylammonium hydroxide by under-potential electrolysis, so as to meet different production requirements.

[0006] Under-potential electrolysis is a technology for realizing water decomposition to produce hydrogen through step-by-step operation. The core is to decouple the traditional electrolysis process: first, charge the porous electrode at a voltage lower than the water decomposition voltage, so that the electrode adsorbs charged ions and solvent water; then separate and stand the electrode, and gradually increase the double-layer voltage by solvent evaporation until the water decomposition potential is reached, so as to realize the electrolysis of water under the condition that the input electric energy is lower than the theoretical value.

[0007] The advantage is that the electrical energy required by the conventional electrolysis process must be higher than the theoretical voltage required for water decomposition, which means that in actual operation, relatively more electrical energy will be consumed, and thus the under-potential electrolysis can be carried out at the theoretical voltage point, avoiding the energy consumption loss at a higher voltage and the pollution caused by other electrical damage.

[0008] To achieve the above technical effects, the present application provides the following technical solutions:

[0009] A method for preparing tetramethylammonium hydroxide by under-potential electrolysis, the method is carried out in a diaphragm electrolytic cell, and the method steps include:

[0010] Step 1, preparation of a capacitive electrode: roughening treatment, high-temperature activation treatment, and then chemical nickel plating are sequentially performed on a porcelain tube to obtain a capacitive electrode, which simultaneously serves as an anode and a cathode.

[0011] Step 2, under-potential electrolysis: tetramethylammonium bicarbonate solution is added to the anode chamber, and tetramethylammonium hydroxide solution is added to the cathode chamber, and then under-potential electrolysis reaction is carried out to obtain tetramethylammonium hydroxide solution.

[0012] In an embodiment, the porcelain tube in step 1 is a ceramic tube, which is used as a tubular ceramic medium in the present application, and a metal electrode nickel is coated on the inner wall and the outer wall thereof, which can be used as a capacitive electrode. The capacitance can be adjusted by controlling the overlapping area of the electrodes. The ceramic tube has a high dielectric constant (ε r up to 12,000) and high voltage resistance (~500V).

[0013] The porcelain tube is a product obtained by firing after extrusion or dry pressing forming by using a known conventional method. The present application does not have specific requirements for the source thereof, and can be a common commercially available product, such as the AEC-Q200 series product of the TY brand or the C series product of the TDK brand. Alternatively, it can be prepared by referring to the existing method, for example, according to the method disclosed in CN202111352511.6.

[0014] In an embodiment, the roughening treatment in step 1 is to immerse the porcelain tube in hydrofluoric acid with a concentration of 2-15wt%, such as 2wt%, 4wt%, 6wt%, 8wt%, 10wt%, 12wt%, 14wt%, 15wt%, etc., for 30-90min, such as 30min, 40min, 50min, 60min, 70min, 80min, 90min, etc. Then, the porcelain tube is taken out, washed with water, dehydrated with alcohol, and dried (loss on drying method, weight loss ratio <0.1% within 1h at 105℃), to complete the roughening treatment.

[0015] In one embodiment, the high-temperature activation treatment in step 1 involves immersing the roughened ceramic tube in an aqueous solution of tetrabutylammonium hydroxide with a concentration of 5–20 g / L, and then heating it to 120–180°C, for example, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, etc., for 2–6 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, etc., and then taking it out and washing it with water (preferably using 3 times the amount of water to wash 3 times) to complete the high-temperature activation treatment.

[0016] In one embodiment, the electroless nickel plating in step 1 uses water as the solvent and includes the following raw materials in the following amounts: nickel sulfate 5-80 g / L, for example 5 g / L, 20 g / L, 40 g / L, 60 g / L, 80 g / L, etc.; sodium hypophosphite 10-60 g / L, for example 10 g / L, 20 g / L, 30 g / L, 50 g / L, 60 g / L, etc.

[0017] The electroless nickel plating method used in this invention is a conventional operation in the field. Its related operations, process conditions, and the equipment used can all be selected using conventional methods in the field, and there are no particular limitations. Those skilled in the art can optimize the process based on existing technology and known processes according to actual needs. Specifically, for example, the conditions listed below in this invention can be used for operation:

[0018] Optionally, the specific operating conditions for the electroless nickel plating (refer to "Electroplating & Finishing" | 2021, No. 13 | pp. 1012-1017) include:

[0019] 1) Preprocessing

[0020] Degreasing: Soak in an alkaline solution (60-80℃) for 2-8 hours;

[0021] Pickling and activation: Treat with 10-15wt% hydrochloric acid for 2-6 hours to remove the oxide layer;

[0022] 2) Electroless nickel plating

[0023] Plating solution preparation: Nickel sulfate as the main salt, sodium hypophosphite as the reducing agent, pH value 4.5-5.5, temperature 85-95℃, treatment time 4-12h;

[0024] 3) Post-processing

[0025] Cleaning and drying: Rinse with running water and then blow dry with hot air (measured by weight loss method, at 105℃, the weight loss ratio is <0.1% within 1 hour).

[0026] In one embodiment, the tetramethylammonium bicarbonate solution in step 2 is an aqueous solution;

[0027] Optionally, the initial concentration of the tetramethylammonium bicarbonate solution is 22-28 wt%, such as 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, etc.

[0028] In one embodiment, the tetramethylammonium hydroxide solution in step 2 is an aqueous solution;

[0029] Optionally, the initial concentration of the tetramethylammonium hydroxide is 18 to 23 wt%, such as 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, etc.

[0030] In one embodiment, the underpotential electrolysis reaction in step 2 is carried out at an electrolysis temperature of 40–60°C, such as 40°C, 45°C, 50°C, 55°C, 60°C, etc.

[0031] In one embodiment, the underpotential electrolysis reaction in step 2 has an electrolysis time of 30 to 60 minutes, such as 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, 60 minutes, etc.

[0032] In one embodiment, the underpotential electrolysis reaction in step 2 has an initial electrolysis voltage of 0.6 to 1.1V, such as 0.6V, 0.7V, 0.8V, 0.9V, 1.0V, 1.1V, etc.

[0033] In one embodiment, the underpotential electrolysis reaction in step 2 has an electrolysis current density of 500-2000 A / m. 2 For example, 500A / m 2 700A / m 2 1000A / m 2 1300A / m 2 1500A / m 2 1800A / m 2 2000A / m 2 wait.

[0034] In one embodiment, the initial liquid levels of the anode chamber and cathode chamber in step 2 are both 20% to 40% of the height of the electrolytic cell, such as 20%, 25%, 30%, 35%, 40%, etc.

[0035] The method of the present invention does not impose any restrictions on the specific shape and arrangement of the electrodes in the diaphragm electrolytic cell. All electrode shapes and cathode and anode arrangements that can realize the electrolysis function based on ceramic tubes are covered within the method of the present invention.

[0036] In one embodiment, the diaphragm electrolyzer uses a cation exchange membrane, preferably a perfluorosulfonic acid cation exchange membrane, such as DuPont N551 or DuPont N324 membranes.

[0037] In one embodiment, the membrane electrolyzer is made of titanium.

[0038] In this invention, after the electrolysis reaction is completed, an aqueous solution of tetramethylammonium hydroxide is obtained from the cathode chamber, with a concentration of approximately 25wt% ± 2wt%, and the content of metal ions such as K ions, Na ions, Fe ions, and Ni ions can be as low as below 0.1ppb.

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

[0040] 1) It can be used to prepare electronic-grade TMAH;

[0041] 2) The low electrolysis potential greatly reduces metal contamination in the electrodes;

[0042] 3) The operating voltage is low, and the operating cost of electrolysis is 20-30% lower. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the underpotential electrolysis device provided in the embodiments of the present invention. Detailed Implementation

[0044] The following embodiments are provided to better understand this application and are not limited to the preferred embodiments described herein. They do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the scope of protection of this application.

[0045] It should be noted that the endpoints and any values ​​of the ranges disclosed in this specification are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0047] Where specific experimental steps or conditions are not specified in the examples, they can be performed according to the conventional experimental steps or conditions described in the literature in this field. Unless otherwise specified, the reagents, materials, and instruments used in the following examples are all conventional reagents, materials, and instruments in this field, and are all commercially available. The reagents involved can also be synthesized by conventional methods in this field.

[0048] The sources of the main raw materials used in the various embodiments and comparative examples of this invention are as follows:

[0049] Porcelain tubes: TY brand AEC-Q200 series, Xiangyang New City distributor;

[0050] Hydrofluoric acid: Inokai;

[0051] Tetrabutylammonium hydroxide: Inokai;

[0052] Tetramethylammonium bicarbonate: Hubei Nuona;

[0053] Tetramethylammonium hydroxide: Hubei Nuona;

[0054] DSA anode: U-Chuang Technology;

[0055] Cathode nickel plate: Jiangsu Ankait;

[0056] Diaphragm electrolyzer: made of titanium, plate and frame electrolyzer body, two chambers and one membrane tank, 1.5m*2m.

[0057] The main analytical methods used in the embodiments and comparative examples of this invention are as follows:

[0058] Tetramethylammonium hydroxide product content: acid-base neutralization titration method;

[0059] K ion, Na ion, Fe ion, and Ni ion content determination: Inductively coupled plasma mass spectrometry;

[0060] The above methods adopt the GB / T 37403-2019 standard.

[0061] Conversion rate: Conversion rate = (Amount of reactants converted / Total amount of initial reactants) × 100%. The amount of reactants is quantified using the acid-base neutralization titration method described above.

[0062] Selectivity: Selectivity = (Tetramethylammonium hydroxide obtained from the reaction / Total amount of all products) × 100%, the selectivity of this reaction is >99%.

[0063] Current efficiency: η=m'÷(I·t·k)×100%, where η is the current efficiency; m' is the actual product mass; I is the current intensity (A); t is the energizing time (h); and k is the electrochemical equivalent (g· / (A·h)).

[0064] Example 1

[0065] The ceramic tube was immersed in 2wt% hydrofluoric acid for 90 minutes. Then the ceramic tube was taken out and washed with water, followed by alcohol dehydration and drying (measured by weight loss method, at 105℃, the weight loss ratio within 1 hour was <0.1%), thus completing the roughening process.

[0066] The roughened ceramic tube was then immersed in a 5 g / L tetrabutylammonium hydroxide aqueous solution, heated to 180°C, and heat-treated for 2 hours before being removed and washed three times with three times the volume of water.

[0067] The ceramic tubes, after being washed with water, were subjected to electroless nickel plating. The nickel plating solution used water as a solvent and included the following raw materials in the following proportions: nickel sulfate 80 g / L and tetrabutylammonium hydroxide 10 g / L. The nickel plating conditions were: 1) Immersion in an alkaline solution (60℃) for 2 hours, followed by treatment with 10% hydrochloric acid for 2 hours to remove the oxide layer; 2) Treatment with nickel sulfate as the main salt, sodium hypophosphite as the reducing agent, pH 4.5, temperature 85℃, for 4 hours. Finally, the tubes were rinsed with running water and dried with hot air (measured by weight loss method; weight loss ratio <0.1% within 1 hour at 105℃) to obtain the capacitor electrode, which served as both the anode and cathode.

[0068] In the diaphragm electrolyzer, the diaphragm was DuPont N551. The initial concentration of tetramethylammonium bicarbonate aqueous solution in the anode chamber was 28 wt%, and the initial concentration of tetramethylammonium hydroxide aqueous solution in the cathode chamber was 18 wt%. The initial liquid levels in both the anode and cathode chambers were 40% of the electrolyzer height. The electrolyzer was heated to 60°C to initiate the underpotential electrolysis reaction. The initial electrolysis voltage was 0.6 V, and the electrolysis current density was 1200 A / m. 2 The underpotential electrolysis time was 30 min, and a tetramethylammonium hydroxide solution was obtained with a purity of 25.02%. The metal ion content is shown in Table 1 below.

[0069] In this embodiment, the conversion rate of the raw material tetramethylammonium bicarbonate is 18%, the selectivity of tetramethylammonium hydroxide is 99.96%, and the current efficiency is 78%.

[0070] Example 2

[0071] The ceramic tube was immersed in 15wt% hydrofluoric acid for 30 minutes. Then the ceramic tube was taken out, washed with water, dehydrated with alcohol, and dried to complete the roughening process.

[0072] The roughened ceramic tube was then immersed in a 20 g / L tetrabutylammonium hydroxide aqueous solution, heated to 120°C, and heat-treated for 6 hours before being removed and washed three times with three times the volume of water.

[0073] The ceramic tubes, after being washed with water, were subjected to electroless nickel plating. The nickel plating solution used water as a solvent and contained the following raw materials in the following proportions: nickel sulfate 80 g / L and tetrabutylammonium hydroxide 10 g / L. The nickel plating conditions were: 1) Immersion in an alkaline solution (80℃) for 8 hours, followed by treatment with 15% hydrochloric acid for 6 hours to remove the oxide layer; 2) Treatment with nickel sulfate as the main salt, sodium hypophosphite as the reducing agent, pH 5.5, temperature 95℃, for 12 hours. Finally, the tubes were rinsed with running water and dried with hot air (measured by weight loss method; at 105℃, the weight loss ratio was <0.1% within 1 hour), yielding a capacitor electrode, which served as both the anode and cathode.

[0074] In the diaphragm electrolyzer, the diaphragm was DuPont N551. The initial concentration of tetramethylammonium bicarbonate aqueous solution in the anode chamber was 22 wt%, and the initial concentration of tetramethylammonium hydroxide aqueous solution in the cathode chamber was 23 wt%. The initial liquid levels in both the anode and cathode chambers were 20% of the electrolyzer height. The electrolyzer was heated to 40°C to initiate the underpotential electrolysis reaction. The initial electrolysis voltage was 1.1 V, and the electrolysis current density was 500 A / m. 2 The underpotential electrolysis time was 60 min, and a tetramethylammonium hydroxide solution was obtained with a purity of 25.04%. The metal ion content is shown in Table 1 below.

[0075] In this embodiment, the conversion rate of the raw material tetramethylammonium bicarbonate is 21%, the selectivity of tetramethylammonium hydroxide is 99.97%, and the current efficiency is 80%.

[0076] Example 3

[0077] The ceramic tube is immersed in 10% hydrofluoric acid for 60 minutes. Then the ceramic tube is taken out, washed with water, dehydrated with alcohol, and dried to complete the roughening process.

[0078] The roughened ceramic tube was then immersed in a 10 g / L tetrabutylammonium hydroxide aqueous solution, heated to 160°C, and heat-treated for 4 hours before being removed and washed three times with three times the volume of water.

[0079] The ceramic tubes, after being washed with water, were subjected to electroless nickel plating. The nickel plating solution used water as a solvent and contained the following raw materials in the following proportions: nickel sulfate 80 g / L and tetrabutylammonium hydroxide 10 g / L. The nickel plating conditions were: 1) Immersion in an alkaline solution (70°C) for 6 hours, followed by treatment with 12% hydrochloric acid for 4 hours to remove the oxide layer; 2) Treatment with nickel sulfate as the main salt, sodium hypophosphite as the reducing agent, pH 5, temperature 90°C, for 8 hours. Finally, the tubes were rinsed with running water and dried with hot air (measured by weight loss method; at 105°C, the weight loss percentage within 1 hour was <0.1%), yielding a capacitor electrode, which served as both the anode and cathode.

[0080] In the diaphragm electrolyzer, the diaphragm was DuPont N551. The initial concentration of tetramethylammonium bicarbonate aqueous solution in the anode chamber was 28 wt%, and the initial concentration of tetramethylammonium hydroxide aqueous solution in the cathode chamber was 24 wt%. The initial liquid levels in both the anode and cathode chambers were 30% of the electrolyzer height. The electrolyzer was heated to 50°C to initiate the underpotential electrolysis reaction. The initial electrolysis voltage was 0.8 V, and the electrolysis current density was 2000 A / m. 2 The underpotential electrolysis time was 40 min, and a tetramethylammonium hydroxide solution was obtained with a purity of 25.04%. The metal ion content is shown in Table 1 below.

[0081] In this embodiment, the conversion rate of the raw material tetramethylammonium bicarbonate is 18%, the selectivity of tetramethylammonium hydroxide is 99.98%, and the current efficiency is 81%.

[0082] Example 4

[0083] The ceramic tube is immersed in 6% hydrofluoric acid for 80 minutes. Then the ceramic tube is taken out, washed with water, dehydrated with alcohol, and dried to complete the roughening process.

[0084] The roughened ceramic tube was then immersed in an aqueous solution of tetrabutylammonium hydroxide with a concentration of 8 g / L, then heated to 150°C and heat-treated for 3 hours before being removed and washed three times with three times the amount of water.

[0085] The ceramic tubes, after being washed with water, were subjected to electroless nickel plating. The nickel plating solution used water as a solvent and contained the following raw materials in the following proportions: nickel sulfate 80 g / L and tetrabutylammonium hydroxide 10 g / L. The nickel plating conditions were: 1) Immersion in an alkaline solution (65°C) for 4 hours, followed by treatment with 12% hydrochloric acid for 3 hours to remove the oxide layer; 2) Treatment with nickel sulfate as the main salt, sodium hypophosphite as the reducing agent, pH 4.7, temperature 88°C, for 6 hours. Finally, the tubes were rinsed with running water and dried with hot air (measured by weight loss method; weight loss ratio <0.1% within 1 hour at 105°C) to obtain the capacitor electrode, which served as both the anode and cathode.

[0086] In the diaphragm electrolyzer, the diaphragm was DuPont N551. The initial concentration of tetramethylammonium bicarbonate aqueous solution in the anode chamber was 26 wt%, and the initial concentration of tetramethylammonium hydroxide aqueous solution in the cathode chamber was 20 wt%. The initial liquid levels in both the anode and cathode chambers were 22% of the electrolyzer height. The electrolyzer was heated to 45°C to initiate the underpotential electrolysis reaction. The initial electrolysis voltage was 1.0 V, and the electrolysis current density was 1800 A / m. 2 The underpotential electrolysis time was 55 min, and a tetramethylammonium hydroxide solution was obtained with a purity of 24.97%. The metal ion content is shown in Table 1 below.

[0087] In this embodiment, the conversion rate of the raw material tetramethylammonium bicarbonate is 16%, the selectivity of tetramethylammonium hydroxide is 99.97%, and the current efficiency is 81%.

[0088] Comparative Example 1

[0089] The conventional electrolysis process was used, with a DSA anode and a nickel plate as the cathode. The electrolysis voltage was 4.2V, and other conditions were the same as in Example 3. A tetramethylammonium hydroxide solution was obtained with a purity of 24.98%, and the metal ion content is shown in Table 1 below.

[0090] The conversion rate of the raw material tetramethylammonium bicarbonate was 17%, the selectivity of tetramethylammonium hydroxide was 99.92%, and the current efficiency was 61%.

[0091] Comparative Example 2

[0092] Referring to the electrolysis method in Example 3, the difference is that the ceramic tube is replaced with a nickel plate, while other operations and conditions remain unchanged, resulting in a tetramethylammonium hydroxide solution with a purity of 25.03%. The metal ion content is shown in Table 1 below.

[0093] In this comparative example, the conversion rate of the raw material tetramethylammonium bicarbonate was 18%, the selectivity of tetramethylammonium hydroxide was 99.6%, and the current efficiency was 62%.

[0094] Table 1. Metal ion content in the tetramethylammonium hydroxide solutions prepared in the examples and comparative examples.

[0095]

[0096]

Claims

1. A method for preparing tetramethylammonium hydroxide by underpotential electrolysis, characterized in that, The method is carried out in a diaphragm electrolyzer and includes the following steps: Step 1, preparation of capacitor electrode: The ceramic tube is subjected to roughening treatment, high-temperature activation treatment and then electroless nickel plating to obtain capacitor electrode, which serves as both anode and cathode; Step 2, underpotential electrolysis: Tetramethylammonium bicarbonate solution is added to the anode chamber and tetramethylammonium hydroxide solution is added to the cathode chamber. Then, underpotential electrolysis is carried out to obtain tetramethylammonium hydroxide solution.

2. The method according to claim 1, characterized in that, The ceramic tube is a product obtained by extrusion or dry pressing followed by firing, and can be selected from TY brand AEC-Q200 series products or TDK brand C series products.

3. The method according to claim 1 or 2, characterized in that, The roughening process described in step 1 involves immersing the ceramic tube in hydrofluoric acid with a concentration of 2-15 wt% for 30-90 minutes, then removing the tube, washing it with water, dehydrating it with alcohol, and drying it to complete the roughening process.

4. The method according to any one of claims 1-3, characterized in that, The high-temperature activation treatment described in step 1 involves immersing the roughened ceramic tube in an aqueous solution of tetrabutylammonium hydroxide with a concentration of 5–20 g / L, then heating it to 120–180°C for 2–6 hours. After heat treatment, the tube is removed, washed with water, and the high-temperature activation treatment is completed.

5. The method according to any one of claims 1-4, characterized in that, The electroless nickel plating described in step 1 uses water as a solvent and comprises the following raw materials in the following proportions: Nickel sulfate 5-80 g / L, sodium hypophosphite 10-60 g / L.

6. The method according to any one of claims 1-5, characterized in that, The tetramethylammonium bicarbonate solution mentioned in step 2 is an aqueous solution; Optionally, the initial concentration of the tetramethylammonium bicarbonate solution is 22–28 wt%.

7. The method according to any one of claims 1-6, characterized in that, The tetramethylammonium hydroxide solution mentioned in step 2 is an aqueous solution; Optionally, the initial concentration of the tetramethylammonium hydroxide is 18–23 wt%.

8. The method according to any one of claims 1-7, characterized in that, The underpotential electrolysis reaction described in step 2 is carried out at an electrolysis temperature of 40–60°C; and / or, Electrolysis time is 30–60 min; and / or, The initial electrolysis voltage is 0.6–1.1 V; and / or, Electrolysis current density is 500-2000 A / m 2 .

9. The method according to any one of claims 1-8, characterized in that, In step 2, the initial liquid levels in both the anode and cathode chambers are 20-40% of the electrolytic cell height.

10. The method according to any one of claims 1-9, characterized in that, The diaphragm electrolyzer uses a cation exchange membrane, preferably a perfluorosulfonic acid cation exchange membrane, such as DuPont N551 or DuPont N324 membranes.

Images