A nitrogen-doped diamond porous titanium composite film electrode and its preparation method

Abstract

The present invention provides a nitrogen-doped diamond porous titanium composite film electrode and a preparation method thereof, which relates to the cross technical field of electrochemical sewage treatment and welding. The method uses a gold-based high-entropy alloy solder as an intermediate layer to perform diffusion welding on the nitrogen-doped diamond and the porous titanium; the diffusion welding is carried out in a vacuum furnace or a protective atmosphere furnace; by molar percentage, the composition of the gold-based high-entropy alloy solder is as follows: 25% - 30% Au, 15% - 20% Cu, 10% - 15% Cr, 10% - 15% Ti, 10% - 15% Ni, 10% - 15% Mn. For the first time, the present invention connects the nitrogen-doped diamond and the porous titanium by diffusion welding using an alloy solder, solves the problems such as the difficulty in depositing the diamond film on the porous titanium and the decrease in the bonding strength of the interface region, improves the bonding strength between the nitrogen-doped diamond film and the porous titanium, enhances the working efficiency and service life of the electrode, and reduces the sewage treatment cost.

Description

Technical Field

[0001] The present invention relates to the cross - technical field of electrochemical sewage treatment and welding, and in particular to a nitrogen - doped diamond porous titanium composite membrane electrode and a preparation method thereof. Background Art

[0002] With the rapid increase in population, the rapid development of the economy, and the inevitable requirement of sustainable development, environmental and resource protection has become an important issue in social and economic development. The water resources in our country are not abundant. Controlling and reducing sewage discharge is an important way to protect water resources and also a huge challenge faced by all mankind.

[0003] As a new type of sewage treatment process, the electrochemical method is regarded as a sewage treatment process with great application potential due to its advantages such as simple equipment required, easy operation, high energy efficiency, easy automation, and low cost. The applications of electrochemical water treatment technology in the environmental field mainly include electrochemical oxidation, electrochemical reduction, electrochemical deposition, electro - flotation, electro - adsorption, etc.

[0004] The electrode material restricts the further application of the electrochemical method for treating sewage. Commonly used electrode materials include graphite electrodes, metal electrodes, and boron - doped diamond electrodes. Diamond films have unique advantages in mechanics, optics, thermology, chemistry, electricity, etc., such as extremely high hardness, good chemical inertness, low friction coefficient, etc. Diamond films are insulators and can have good electrical conductivity by doping atoms such as boron and nitrogen. Compared with boron - doped diamond thin films, nitrogen - doped diamond thin film electrodes have a higher hydrogen evolution over - potential and show potential electro - catalytic reduction performance, and may be ideal cathode materials for the electrochemical reduction method, having broad application prospects in sewage treatment.

[0005] Titanium matrix is a good electrode matrix material with good electrical conductivity, high mechanical strength, low price, and porous titanium has a large surface area. However, due to different materials and a large difference in Young's modulus between the titanium matrix and the diamond thin film, there is a large stress between the two. Therefore, it is very difficult to deposit diamond thin films on porous titanium, and intermetallic compound TiC is easily generated between the titanium matrix and the diamond thin film under high - temperature fusion welding, greatly reducing the connection strength.

[0006] Improving the electrical conductivity, corrosion resistance, high - temperature resistance, and mechanical strength of diamond thin films at limited cost is one of the difficulties in the field of electrochemical sewage treatment. Therefore, it is urgent to propose a new method for preparing diamond composite thin films to improve the research in related fields, improve the working efficiency of electrodes, and reduce the cost of sewage treatment. The research on nitrogen - doped diamond thin films is less and has very broad prospects.

[0007] In view of this, the present invention is specifically proposed. Summary of the Invention

[0008] The object of the present invention is to provide a nitrogen-doped diamond porous titanium composite film electrode and a preparation method thereof. For the first time, the present invention uses a gold-based alloy solder to perform diffusion welding on nitrogen-doped diamond and porous titanium by means of diffusion welding, solves the problems such as the difficulty in depositing diamond thin films on porous titanium and the decrease in the bonding force in the interface region, improves the bonding strength between the nitrogen-doped diamond thin film and porous titanium, enhances the working efficiency and service life of the electrode, and reduces the sewage treatment cost.

[0009] The technical solution provided by the present invention is as follows:

[0010] In one aspect, the present invention provides a preparation method of a nitrogen-doped diamond porous titanium composite film electrode, using a gold-based high-entropy alloy solder as an intermediate layer to perform diffusion welding on the precision-processed nitrogen-doped diamond and porous titanium; the diffusion welding is carried out in a vacuum furnace or a protective atmosphere furnace;

[0011] By molar percentage, the composition of the gold-based high-entropy alloy solder is as follows: 25% - 30% Au, 15% - 20% Cu, 10% - 15% Cr, 10% - 15% Ti, 10% - 15% Ni, 10% - 15% Mn;

[0012] Wherein, the precision processing is to process the workpiece to be welded into a precision workpiece to be welded with dislocation channels by means of precision ultrasonic processing or laser processing before the diffusion welding is carried out.

[0013] The present invention adopts the diffusion welding method, uniformly coats the nitrogen-doped diamond paste on the surface of the porous titanium with a high-entropy alloy solder interlayer, and uses a vacuum furnace or an atmosphere furnace to carry out diffusion welding tests to prepare a nitrogen-doped diamond porous titanium composite film electrode. The nitrogen-doped diamond thin film prepared by the traditional deposition method has defects such as poor mechanical strength and poor conductivity; and the traditional method cannot overcome problems such as large stress caused by using porous titanium. The present invention uses a gold-based high-entropy solder AuCuMnCrTiNi with a specific ratio as an intermediate layer, and welds the nitrogen-doped diamond film and porous titanium together well through a diffusion process, greatly improving the bonding strength between the nitrogen-doped diamond and porous titanium, and the prepared nitrogen-doped diamond porous Ti composite film electrode has good performance and development and application potential.

[0014] In one embodiment, the present invention performs vacuum diffusion welding in a vacuum furnace or an atmosphere furnace, and the conditions of the vacuum furnace are: the vacuum degree is less than 5×10 -3 Pa, the heating temperature is 700 - 800 °C, the holding time is 20 - 30 min, and it is cooled with the furnace;

[0015] Alternatively, the conditions of the atmosphere furnace are: using an inert gas as a protective gas, the welding temperature is 800 - 900 °C, the holding time is 0.5 - 1 h, and it is cooled naturally; preferably, the inert gas is argon.

[0016] In one embodiment, the diffusion welding comprises the following steps:

[0017] (a) Raise the welding temperature from 20°C to 600°C at a rate of 10°C / min and preheat it under a high pressure of 30 MPa for 10 - 20 min (to ensure close contact of the joint surfaces);

[0018] (b) Heat the sample from step (a) to the welding temperature at a rate of 50°C / min and maintain the holding time under an axial pressure of 15 MPa.

[0019] In one embodiment, after welding, the obtained joint is cooled to room temperature.

[0020] The above - specific vacuum brazing conditions in the present invention are set for the brazing filler metal to be brazed in the present invention. Under the vacuum brazing conditions defined in the present invention, the melting degree of the brazing filler metal is appropriate, so that the nitrogen - doped diamond and the porous titanium are bonded with a relatively high strength. If the vacuum brazing conditions are not suitable, the performance of the prepared nitrogen - doped diamond porous titanium composite film electrode will be affected and even greatly reduced.

[0021] In one embodiment, the preparation method includes the preparation of porous titanium, the preparation of a gold - based high - entropy alloy brazing filler metal, and the preparation of the diffusion welding of the nitrogen - doped diamond porous titanium composite thin film electrode.

[0022] In one embodiment, the preparation method of the porous titanium includes: depositing titanium on the surface of a porous silicon array by radio - frequency magnetron sputtering to prepare a porous titanium substrate;

[0023] Preferably, the pore diameter of the porous silicon array is 2 - 10 μm;

[0024] Preferably, the porous silicon array is prepared by electrochemical corrosion;

[0025] Preferably, during the radio - frequency magnetron sputtering process, a DC self - bias voltage is applied; more preferably, the power of the DC self - bias voltage system is 1 - 3 kw.

[0026] In the present invention, titanium is deposited on the surface of porous silicon arrays with pore diameters of 2, 5, and 10 μm respectively by radio - frequency magnetron sputtering, and a certain self - bias voltage is applied to ensure uniform magnetron sputtering and reduce the deposition thickness on the surface and in the pores. The radio - frequency magnetron sputtering process is a conventional technical process in the art and can be carried out according to the conventional methods in the art. The preparation of the porous silicon array by electrochemical corrosion is a conventional technical process in the art and can be carried out according to the conventional methods in the art.

[0027] In one embodiment, the method further includes boiling the porous titanium substrate in hydrochloric acid, successively performing ultrasonic treatment in distilled water, diamond powder, acetone, and water, and finally drying;

[0028] Preferably, the porous titanium substrate is boiled in hydrochloric acid for 15 min, ultrasonically cleaned with secondary distilled water for 5 min, ultrasonically cleaned in diamond powder for 40 min, then ultrasonically cleaned with acetone and water for 5 min respectively, and finally dried by passing nitrogen and subjected to physical polishing.

[0029] In one embodiment, before diffusion welding, after polishing and ultrasonically cleaning the joint surfaces of the high-entropy alloy solder, nitrogen-doped diamond, and porous titanium, nitrogen is passed through to dry them.

[0030] Preferably, the joint surfaces of the high-entropy alloy solder, nitrogen-doped diamond, and porous titanium are polished with silicon carbide paper, and then ultrasonically cleaned in acetone, alcohol, and water respectively.

[0031] In a specific embodiment, for the porous titanium (porous Ti film) prepared in the experiment, the joint surfaces of the base metal and the solder participating in diffusion welding are polished with silicon carbide paper to 2000 mesh, then ultrasonically cleaned in acetone, alcohol, and water for 10 min to remove dust, and then dried by passing nitrogen. This step can eliminate the influence of other factors on the prepared specimens.

[0032] In one embodiment, the preparation method of the gold-based high-entropy alloy solder includes: simultaneously depositing metals Au, Cu, Mn, Cr, Ti, and Ni on the surface of a Si wafer substrate by multi-target ultra-high vacuum magnetron sputtering to form a gold-based high-entropy alloy solder.

[0033] In one embodiment, the raw materials of Au, Cu, Mn, Cr, Ti, and Ni are Au powder, Cu powder, MnO2 powder, Cr powder, Ti powder, and Ni powder with a purity of more than 99%, and are prepared into target materials by powder metallurgy.

[0034] In one embodiment, the method further includes steps of surface structure characterization, performance testing, and electrochemical property analysis of the nitrogen-doped diamond porous titanium composite film electrode.

[0035] Specifically, the surface structure characterization of the nitrogen-doped diamond porous titanium composite film electrode can be analyzed by atomic force microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), polycrystalline X-ray diffraction (XRD), Raman spectroscopy (Raman), etc.; the mechanical properties are measured using a nanoindenter (Nano Indenter); the electrochemical property analysis test includes electrochemical window testing and electrochemical impedance spectroscopy measurement.

[0036] In another aspect, a nitrogen-doped diamond porous titanium composite film electrode prepared by the preparation method.

[0037] In another aspect, the present invention provides the application of the nitrogen-doped diamond porous titanium composite film electrode in sewage treatment, which can be used as a cathode for electrochemical reduction.

[0038] Beneficial effects:

[0039] (1) For the first time, the present invention uses a gold-based high-entropy alloy solder to perform diffusion welding between nitrogen-doped diamond and porous titanium by means of vacuum welding, solving problems such as the difficulty of depositing diamond thin films on porous titanium and the decrease in the bonding strength in the interface region, improving the bonding strength between the nitrogen-doped diamond thin film and porous titanium, enhancing the working efficiency and service life of the electrode, and reducing the sewage treatment cost.

[0040] (2) The gold-based high-entropy solder AuCuMnCrTiNi prepared in the present invention has a suitable melting temperature, uniform structure and unique high-entropy effect. Using it as an intermediate layer and connecting the nitrogen-doped diamond film and porous titanium by diffusion welding process can effectively solve problems such as the difficulty of depositing diamond thin films on porous titanium and the decrease in bonding strength caused by the formation of TiC in the interface region.

[0041] (3) Titanium has an air absorption tendency, and an oxide layer is easily formed on the lower surface in air. During actual use, the oxide layer will fall off when the electrode is electrified, indicating that the titanium electrode has the ability of self-protection during shutdown. Compared with other metal materials, titanium has higher mechanical strength and smaller density. The diamond thin film under the same area has a smaller mass than other metals, and the price of titanium metal is low, which greatly reduces the use cost and is easy to be popularized and used.

[0042] (4) In addition to the metal properties of titanium metal itself, due to the presence of a large number of pores inside, porous titanium exhibits many excellent properties of porous materials, such as high specific strength, large specific surface area, good energy absorption, high heat transfer and heat dissipation capacity, low thermal conductivity, and good processability. Preparing a diamond porous titanium thin film can make the diamond extend from the surface into the pores, presenting a porous structure, enabling the sewage to be quickly filtered, reducing its turbidity, and expanding its application fields.

[0043] (5) Compared with the boron-doped diamond thin film electrode, the nitrogen-doped diamond thin film has extremely excellent performance in terms of reducibility, has great development potential in the aspect of electrochemical reduction method as a cathode, and the nitrogen-doped diamond thin film has high energy efficiency, has unique advantages in sewage treatment, and also has very remarkable performance in terms of economic benefits.

[0044] (6) The high-entropy alloy solder has the sluggish diffusion effect of high-entropy alloys, which can effectively regulate the interfacial reaction between diamond and porous titanium. The sluggish diffusion effect can ensure the penetration and filtration effect of the nitrogen-doped diamond thin film in the field of sewage treatment. Description of the drawings

[0045] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0046] Figure 1 Schematic diagram of the preparation process of the nitrogen-doped diamond porous titanium composite film electrode by diffusion welding provided by an embodiment of the present invention;

[0047] Figure 2 Schematic diagram of the principle of radio frequency magnetron sputtering used for the preparation of the porous titanium film provided by an embodiment of the invention;

[0048] Figure 3 Schematic diagram of the principle of multi-target ultra-high vacuum DC magnetron sputtering used for the gold-based high-entropy alloy solder provided by an embodiment of the invention;

[0049] Figure 4 Schematic diagram of the diffusion welding of the nitrogen-doped diamond film and the porous titanium film electrode provided by an embodiment of the invention. Specific embodiments

[0050] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the described embodiments are some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0051] Example 1

[0052] Figure 1 Schematic diagram of the preparation process of the nitrogen-doped diamond porous titanium composite film electrode.

[0053] (a) Preparation of porous titanium

[0054] Titanium is deposited on the surface of a porous silicon array with pore diameters of 5 microns respectively by radio frequency magnetron sputtering. A certain self-bias voltage is applied to ensure uniform magnetron sputtering and reduce the deposition thickness on the surface and in the pores. The applied DC bias voltage is 1.5 kw. The porous silicon array is prepared by electrochemical etching.

[0055] In the preparation steps of the porous titanium sample, the porous titanium substrate needs to be boiled in hydrochloric acid for 15 min, then ultrasonically treated in secondary distilled water for 5 min, ultrasonically treated in diamond powder for 40 min, then ultrasonically treated in acetone and water for 5 min respectively, and finally dried by introducing nitrogen and subjected to physical polishing.

[0056] Figure 2Schematic diagram of the principle of radio frequency magnetron sputtering for the preparation of porous titanium thin films.

[0057] (b) Preparation of gold-based high-entropy alloy solder

[0058] Six metals, namely Au, Cu, Mn, Cr, Ti, and Ni, are simultaneously deposited on the substrate surface by using a multi-target ultra-high vacuum magnetron sputtering device to prepare a gold-based six-component high-entropy alloy solder.

[0059] The specific molar percentages of the selected target materials are as follows: 30% Au; 20% Cu; 15% Cr; 15% Ti, 10% Ni, 10% Mn.

[0060] In the preparation steps of the gold-based high-entropy alloy solder, the selected Au powder, Cu powder, MnO2 powder, Cr powder, Ti powder, and Ni powder are all commercially available, with a purity of over 99%, and are prepared into target materials by powder metallurgy.

[0061] Figure 3 Schematic diagram of the principle of multi-target ultra-high vacuum DC magnetron sputtering for gold-based high-entropy alloy solder.

[0062] (c) Preparation of diffusion welding of nitrogen-doped diamond porous titanium composite film electrode

[0063] The diffusion welding method is used to uniformly coat a nitrogen-doped diamond paste on the surface of the porous titanium with a gold-based high-entropy alloy solder interlayer, and a diffusion welding test is carried out using a vacuum furnace.

[0064] Before implementing diffusion welding, the workpiece to be welded is processed into a precision workpiece with dislocation channels by using precision ultrasonic machining or laser machining.

[0065] In the diffusion welding step of the nitrogen-doped diamond paste and porous titanium, a gold-based high-entropy alloy solder is used as the intermediate layer, and the welding process is set in two steps.

[0066] First, the temperature is raised from 20°C to 600°C at a rate of 10°C / min and preheated under a high pressure of 30 MPa for 20 min to ensure close contact of the joint surface. Subsequently, the tightly bonded sample is heated to the welding temperature at a rate of 50°C / min and kept warm under an axial pressure of 15 MPa. After welding, the obtained joint is cooled to room temperature.

[0067] In the diffusion welding step of the nitrogen-doped diamond film and porous titanium, the conditions of the vacuum furnace are as follows: the vacuum degree B < 5×10 - 3 Pa, the welding temperature T = 700°C, the holding time t = 20 min, and it is cooled with the furnace.

[0068] In the diffusion welding process of the nitrogen-doped diamond film and the porous titanium, to eliminate the influence of other factors on the prepared specimens, the prepared porous titanium film in the experiment and the bonding surfaces of the diffusion welding gold-based high-entropy alloy solder are polished to 2000 mesh with silicon carbide paper, and then ultrasonically cleaned in acetone, alcohol, and water for 10 minutes respectively to remove dust, and then dried by passing nitrogen gas.

[0069] Figure 4 It is a schematic diagram of the diffusion welding of the nitrogen-doped diamond film porous titanium film electrode.

[0070] (d) Surface structure characterization, performance testing, and electrochemical property analysis of the diamond porous titanium composite film.

[0071] The surface structure of the nitrogen-doped diamond porous titanium composite film electrode can be characterized by atomic force microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), polycrystalline X-ray diffraction (XRD), Raman spectroscopy (Raman), etc.; the mechanical properties are measured using a nanoindentation instrument (Nano Indenter); the electrochemical property analysis test includes electrochemical window testing and electrochemical impedance spectroscopy measurement.

[0072] Example 2

[0073] (a) Preparation of porous titanium

[0074] Titanium is deposited on the surface of a porous silicon array with pore diameters of 10 microns respectively by radio frequency magnetron sputtering process, and a certain self-bias voltage is applied to ensure uniform magnetron sputtering and reduce the deposition thickness on the surface and in the pores. The applied DC bias voltage is 2 kw. The porous silicon array is prepared by electrochemical corrosion.

[0075] In the preparation process of the porous titanium specimen, the porous titanium substrate needs to be boiled in hydrochloric acid for 15 minutes, then ultrasonically treated in secondary distilled water for 5 minutes, ultrasonically treated in diamond powder for 40 minutes, then ultrasonically treated in acetone and water for 5 minutes respectively, and finally dried by passing nitrogen gas and subjected to physical polishing.

[0076] (b) Preparation of gold-based high-entropy alloy solder

[0077] Six metals, Au, Cu, Mn, Cr, Ti, and Ni, are simultaneously deposited on the substrate surface by a multi-target ultra-high vacuum magnetron sputtering device to prepare a gold-based six-component high-entropy alloy solder.

[0078] The specific target materials used are as follows in terms of molar percentage: 25% Au; 15% Cu; 15% Cr; 15% Ti, 15% Ni, 15% Mn.

[0079] In the preparation steps of the gold-based high-entropy alloy solder, the selected Au powder, Cu powder, MnO2 powder, Cr powder, Ti powder, and Ni powder are all commercially available with a concentration of over 99%, and are prepared into a target by powder metallurgy.

[0080] (c) Preparation of a diffusion-welded diamond-doped porous titanium composite film electrode

[0081] A diffusion welding method is used to uniformly coat a diamond-doped porous titanium surface with a high-entropy alloy solder interlayer, and a diffusion welding test is carried out using an atmosphere furnace.

[0082] Before performing diffusion welding, the workpiece to be welded is processed into a precision workpiece with dislocation channels by precision ultrasonic machining or laser machining.

[0083] In the diffusion welding step of the diamond-doped porous titanium, a high-entropy alloy solder is used as the intermediate layer, and the welding process is set in two steps.

[0084] First, the temperature is raised from 20°C to 600°C at a rate of 10°C / min and preheated under a high pressure of 30 MPa for 20 min to ensure close contact of the joint surface. Subsequently, the tightly bonded sample is heated to the welding temperature at a rate of 50°C / min and held under an axial pressure of 15 MPa. After welding, the obtained joint is cooled to room temperature.

[0085] In the diffusion welding step of the diamond-doped porous titanium, the atmosphere furnace conditions are as follows: argon is used as the protective gas, the welding temperature T = 900°C, the holding time t = 30 min, and natural cooling is carried out.

[0086] In the diffusion welding step of the diamond-doped porous titanium, to eliminate the influence of other factors on the prepared samples, the porous titanium thin film prepared in the experiment and the bonding surface of the diffusion-welded gold-based high-entropy alloy solder are polished to 2000 mesh with silicon carbide paper, and then ultrasonically cleaned in acetone, alcohol, and water for 10 min to wash away the dust, and then dried by passing nitrogen.

[0087] (d) Surface structure characterization, performance testing, and electrochemical property analysis of the diamond-doped porous titanium composite film

[0088] The surface structure of the diamond-doped porous titanium composite film electrode can be characterized by atomic force microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), polycrystalline X-ray diffraction (XRD), Raman spectroscopy (Raman), etc.; the mechanical properties are measured using a nanoindenter; the electrochemical property analysis test includes electrochemical window testing and electrochemical impedance spectroscopy measurement.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of a nitrogen-doped diamond porous titanium composite film electrode, characterized in that, Using a gold-based high-entropy alloy solder as an intermediate layer, diffusion welding is carried out between precisely machined nitrogen-doped diamond and porous titanium; the diffusion welding is carried out in a vacuum furnace or a protective atmosphere furnace; By molar percentage, the composition of the gold-based high-entropy alloy solder is as follows: 25-30% Au, 15-20% Cu, 10%-15% Cr, 10%-15% Ti, 10%-15% Ni, 10%-15% Mn; Among them, the precise machining is to use precise ultrasonic machining or laser machining to machine the workpiece to be welded into a precise workpiece to be welded with dislocation channels before diffusion welding.

2. The preparation method according to claim 1, wherein The conditions of the vacuum furnace are as follows: the vacuum degree is less than 5×10 -3 Pa, the welding temperature is 700 - 800 °C, the heat preservation time is 20 - 30 min, and it is cooled in the furnace; Alternatively, the conditions of the atmosphere furnace are: using an inert gas as the protective gas, the welding temperature is 800-900 °C, the holding time is 0.5-1 h, and natural cooling is carried out.

3. The preparation method according to claim 2, wherein The inert gas is argon.

4. The preparation method according to claim 2, characterized in that, The diffusion welding includes the following steps: (a) Raise the welding temperature from 20 °C to 600 °C at a rate of 10 °C / min and preheat for 10-20 min under a high pressure of 30 MPa; (b) Heat the sample in step (a) to the welding temperature at a rate of 50 °C / min and hold the holding time under an axial pressure of 15 MPa.

5. The preparation method according to claim 1, characterized in that, The preparation method of the porous titanium includes: depositing titanium on the surface of a porous silicon array by radio frequency magnetron sputtering to prepare a porous titanium substrate.

6. The preparation method according to claim 5, characterized in that, The pore diameter of the porous silicon array is 2-10 μm.

7. The preparation method according to claim 5, characterized in that, The porous silicon array is prepared by electrochemical corrosion.

8. The preparation method according to claim 5, characterized in that, During the radio frequency magnetron sputtering process, a DC self-bias voltage is applied.

9. The preparation method according to claim 8, characterized in that, The power of the DC self-bias voltage system is 1-3 kw.

10. The preparation method according to claim 5, wherein The method also includes boiling the porous titanium substrate in hydrochloric acid, successively performing ultrasonic treatment in distilled water, diamond powder, acetone and water, and finally drying.

11. The preparation method according to claim 10, characterized in that, The porous titanium substrate is boiled in hydrochloric acid for 10-15 min, ultrasonically treated in secondary distilled water for 5-10 min, ultrasonically treated in diamond powder for 30-40 min, and then ultrasonically treated in acetone and water for 5-10 min respectively.

12. According to the preparation method described in claim 1, characterized in that, Before diffusion welding, after polishing and ultrasonic cleaning the bonding surfaces of the gold-based high-entropy alloy solder, nitrogen-doped diamond and porous titanium, nitrogen is introduced to dry.

13. The preparation method according to claim 12, characterized in that, The bonding surfaces of the gold-based high-entropy alloy solder, nitrogen-doped diamond and porous titanium are polished with silicon carbide paper, and then ultrasonically cleaned in acetone, alcohol and water respectively.

14. The preparation method according to claim 1, characterized in that, The preparation method of the gold-based high-entropy alloy solder includes: simultaneously depositing metals Au, Cu, Mn, Cr, Ti, Ni on the surface of a Si wafer substrate by multi-target ultra-high vacuum magnetron sputtering to make a gold-based high-entropy alloy solder.

15. The preparation method according to claim 14, wherein The raw materials of Au, Cu, Mn, Cr, Ti, Ni are Au powder, Cu powder, MnO2 powder, Cr powder, Ti powder, Ni powder with a purity of more than 99%, and are prepared into target materials by powder metallurgy.

16. The preparation method according to claim 1, characterized in that, The method also includes the steps of surface structure characterization, performance testing and electrochemical characteristic analysis of the nitrogen-doped diamond porous titanium composite film electrode.

17. A nitrogen-doped diamond porous titanium composite film electrode prepared by the preparation method according to any one of claims 1-16.

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