A multi-level porous metal catalytic electrode and a preparation method thereof

Abstract

The application discloses a kind of multi-level hole metal catalytic electrode and preparation method thereof, and preparation method includes using physical vapor deposition on foam nickel substrate magnetron sputtering film forming, forms nickel coating;Nickel coating is deposited in electrode in lye and is soaked, cleaning, i.e. the multi-level hole catalytic electrode with microporous and nanopore structure is obtained.The application constructs the microporous structure of nanometer grade on the flat skeleton of foam nickel substrate by magnetron sputtering and the post-processing method of lye soaking, significantly increases specific surface area.It is rich in surface structure, increases the active area of catalytic electrode, and then realizes the significant promotion of utilization efficiency and hydrogen evolution catalytic performance of nickel catalyst, and has better binding force simultaneously.

Description

Technical Field

[0001] This invention relates to the field of catalyst hydrogen production electrode technology, specifically to a hierarchical porous metal catalytic electrode and its preparation method. Background Technology

[0002] Catalysts have been widely used in industry. Taking hydrogen production as an example, methods such as natural gas-to-hydrogen, methanol-to-hydrogen, and water electrolysis all rely on catalyst selection to reduce production costs and achieve efficient hydrogen production. While noble metals, such as platinum, exhibit significant hydrogen evolution catalytic activity, their high cost limits their widespread industrial application. Therefore, current research focuses on finding non-noble metal catalytic electrodes as alternatives. Nickel, with its high conductivity and catalytic activity, has become a mainstream non-noble metal electrode for hydrogen evolution catalysis. Research has found that in addition to the inherent electrocatalytic activity of the catalyst material, the effective surface area of ​​the electrode participating in the electrochemical reaction—the electrochemically active area—significantly affects electrochemical performance. For catalysts of the same composition, increasing their surface structure and surface area yields more active sites for catalytic reactions, thus significantly increasing catalyst utilization efficiency. Currently, porous nickel foam is widely used industrially as an electrode material for water electrolysis to produce hydrogen. However, its active area at the microscopic level is still relatively small, and the reaction rate and current density of the water electrolysis process are still relatively low, resulting in high energy consumption and failing to meet the needs of industrial applications.

[0003] Currently, the preparation methods for metal framework catalytic electrodes with microporous structures mainly focus on plasma spraying and thermal spraying after melting and crushing. These methods are difficult to achieve large-area controllable preparation and have obvious binding force problems, which limit their industrial application. In addition, such metal framework catalytic electrodes still have the problem of poor catalytic performance. Summary of the Invention

[0004] To address the aforementioned technical problems of the current microporous metal framework catalytic electrodes, such as the difficulty in large-area controllable fabrication and poor catalytic performance, this invention provides a hierarchical porous metal catalytic electrode and its preparation method.

[0005] The first objective of this invention is to provide a method for preparing a hierarchical porous metal catalytic electrode, comprising: A nickel coating is formed by magnetron sputtering on a nickel foam substrate using physical vapor deposition. The electrode with a nickel coating is immersed in an alkaline solution and then cleaned to obtain a hierarchical porous catalytic electrode with microporous and nanoporous structures.

[0006] This invention employs magnetron sputtering to deposit a nickel coating on a substrate surface. This method enables the controllable preparation of large-area, high-purity nickel coatings, and significantly enhances the adhesion between the nickel coating and the substrate. Simultaneously, the nickel coating is immersed in an alkaline solution after deposition, forming numerous nanoscale nickel pores on the coating surface. This results in a nickel substrate with micron-sized pores and nanoscale nickel pores, achieving a multi-level porous electrochemical active area, which significantly improves the catalytic performance of the electrode.

[0007] As a preferred design, during the physical vapor deposition process, the surface of the nickel foam substrate is first pretreated. The pretreatment process is as follows: (1) Place the substrate in the cleaning agent, use an ultrasonic vibration frequency of 28kHz, ultrasonic cleaning time of 5~10min, and temperature of 50~70℃; (2) Remove the substrate from the cleaning agent and rinse it with deionized water; (3) Use anhydrous ethanol to perform ultrasonic cleaning on the substrate. The ultrasonic vibration frequency is 28kHz and the ultrasonic cleaning time is 5~10min.

[0008] Pretreatment is performed before coating to remove grease and rust from the material surface, ensuring a strong coating adhesion.

[0009] As a preferred design, the substrate is pretreated followed by plasma cleaning. During plasma cleaning, the vacuum level of the deposition chamber is 5 × 10⁻⁶. -5 Pa~5×10 -3 Pa, the vacuum degree of the chamber reaction is 0.1Pa~2Pa; And / or, the plasma cleaning power is 800W~2000W, and the cleaning time is 10~20min.

[0010] As a preferred design, during physical vapor deposition of nickel layers, the reaction vacuum degree of the chamber during the deposition process is 1 Pa to 2 Pa, the DC magnetron sputtering power is 1 to 5 kW, and the deposition time is 60 to 180 min. And / or the thickness of the deposited nickel layer is 2~4μm.

[0011] During magnetron sputtering of metals, the metal material is deposited onto the sample substrate in atomic form. As deposition continues, the particles on the coating gradually stack, diffuse, and become denser. Magnetron sputtering process parameters such as reaction vacuum and power affect the coating deposition quality, while deposition time affects the deposition thickness. This invention preferably utilizes the current process, which yields a high-quality nickel coating, thereby positively impacting the subsequent hydrogen evolution catalysis process.

[0012] The coating thickness directly affects the catalytic active area, charge transfer rate, and also the stability and cycle life of the electrode. An excessively thin coating may lead to insufficient catalytically active material, reducing catalytic efficiency. While increasing the coating thickness can improve the durability and long-term cycling stability of the electrode material to some extent, an excessively thick coating can decrease conductivity, potentially increasing electron transport distance and affecting the electron transfer rate, resulting in decreased catalytic performance and cycle stability. Furthermore, it can increase internal resistance, thereby inhibiting electrochemical performance. Therefore, designing an appropriate coating thickness in this invention is beneficial for improving electrocatalytic performance and achieving a balance between electrocatalytic performance and conductivity.

[0013] As a preferred design, the alkaline solution used in the post-treatment process is either sodium hydroxide solution or potassium hydroxide solution.

[0014] As a preferred design, the concentration of the alkaline solution is 1 mol / L to 5 mol / L.

[0015] As a preferred design, the electrode is immersed in alkaline solution for 6 to 12 hours.

[0016] In this invention, alkaline immersion treatment is used to dissolve defects and impurities in the magnetron sputtered coating while preserving the strong nickel framework. The amount dissolved is affected by the immersion time and the concentration of the alkaline solution. If the time is too short or the concentration is too low, the amount of impurities dissolved will be insufficient, the nanopores will not form a three-dimensional structure, and this will interfere with the catalytic process, thus affecting performance. A sufficiently long immersion time is required to ensure complete dissolution of impurities.

[0017] As a preferred design, the foamed nickel substrate has dimensions of 800*500mm, a thickness of 0.3mm, and a porosity of 88.8%.

[0018] The second objective of this invention is to provide a hierarchical porous metal catalytic electrode, which is prepared by any of the preparation methods described above.

[0019] As a preferred design, the electrode has micron-sized pores and nanon-sized nickel pores; And / or, the pore size of the micron-sized pores is 50~200μm, and the pore size of the nano-sized nickel pores is 50~200nm.

[0020] Compared with the prior art, the present invention has the following advantages and beneficial effects: This invention utilizes a magnetron sputtering combined with alkaline immersion post-treatment to construct a nanoscale microporous structure on a flat framework of a nickel foam substrate, significantly increasing the specific surface area compared to a flat framework surface. This rich surface structure increases the active area of ​​the catalytic electrode, resulting in a larger surface area in contact with the electrolyte. Consequently, it significantly improves the utilization efficiency of the nickel catalyst and the hydrogen evolution catalytic performance, while also exhibiting superior adhesion. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 The electrochemical hydrogen evolution test curves corresponding to the catalytic electrodes obtained in Examples 1, 2 and Comparative Example 1 are shown, where (a) is the LSV curve and (b) is the overpotential value measurement.

[0022] Figure 2 The images are SEM images of the electrodes of Comparative Example 1, Example 1, and Example 2 at different magnifications. (a) to (c) correspond to Comparative Example 1, (d) to (f) correspond to Example 1, and (g) to (i) correspond to Example 2.

[0023] Figure 3 SEM images of the electrodes obtained in Comparative Example 2 and Example 1 at different magnifications. (a)~(c) correspond to Comparative Example 2, (d)~(f) correspond to Example 1.

[0024] Figure 4 The image shows the SEM image of the electrode obtained in Comparative Example 3. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. The illustrative embodiments and descriptions of this invention are only used to explain this invention and are not intended to limit this invention.

[0026] This invention proposes a plasma vapor deposition method for preparing a catalytic electrode with a large-area microporous structure, resulting in a nickel metal framework catalytic electrode. This method includes the following steps: 1. Substrate cleaning A specific concentration of 1003A cleaning agent is prepared in an ultrasonic cleaning tank and heated to a suitable temperature. The substrate is then placed inside for ultrasonic cleaning. The concentration of 1003A cleaning agent is 10-20%, the tank temperature is 50-70℃, and the cleaning time is 5-10 minutes. The substrate is then removed from the cleaning solution and rinsed with deionized water until the 1003A cleaning agent is completely removed. Next, anhydrous ethanol is used to ultrasonically clean the substrate to remove any moisture adhering from the previous step. The ultrasonic cleaning time is 5-10 minutes. Finally, anhydrous ethanol is used to ultrasonically clean the substrate again to further ensure surface cleanliness. The ultrasonic cleaning time is 5-10 minutes. After ultrasonic cleaning, the substrate is removed and dried with nitrogen.

[0027] 2. Substrate clamping The mesh substrate is installed and fixed using clamps. After fixing, the workpiece is placed in the vacuum chamber of the magnetron sputtering coating system and adjusted to a suitable position. After confirming that all components of the coating system are functioning properly, the vacuum chamber door is closed.

[0028] 3. Magnetron sputtering coating The magnetron sputtering coating process involves two main steps, namely: (1) Hall plasma cleaning; (2) nickel coating deposition.

[0029] The mechanical pump, Roots pump, and molecular pump of the magnetron sputtering coating system are started sequentially to begin evacuating the vacuum chamber. Once the chamber vacuum reaches the background vacuum level, high-purity argon gas (99.99% purity) is introduced to adjust the reaction vacuum level in the chamber.

[0030] 3.1 First, the unipolar HALL source is activated, and the workpiece rotation is started to perform plasma cleaning on the substrate surface. The chamber's background vacuum level is 5 × 10⁻⁶. -4 Pa~5×10 -3 Pa, the chamber reaction vacuum degree is 0.1Pa~1Pa, the plasma cleaning power is 800W~2000W, and the cleaning time is 10~20min. 3.2 After plasma cleaning, turn off the HALL power supply and turn on the DC magnetron sputtering power supply to perform nickel coating deposition. The workpiece is kept rotating during the process. The chamber vacuum level is 1 Pa to 2 Pa, the DC magnetron sputtering power is 1 to 5 kW, and the deposition time is 60 to 180 min.

[0031] After deposition is complete, turn off the magnetron power supply, and then turn off the molecular pump, Roots pump, mechanical pump, etc. in sequence to shut down the magnetron sputtering coating system.

[0032] 4. Post-processing After the nickel coating is prepared, the electrode is post-processed to obtain a nickel metal framework structure with microporous structure that meets the requirements.

[0033] 4.1 Prepare the solution: Weigh an appropriate amount of potassium hydroxide or sodium hydroxide solid (analytical grade) and deionized water to prepare an alkaline solution of 1 mol / L to 5 mol / L.

[0034] 4.2 Immersion of electrodes: Immerse the electrode workpiece with nickel coating in the prepared alkaline solution for 6-12 hours.

[0035] 4.3 Remove the electrode from the alkaline solution and rinse it with deionized water.

[0036] In practical applications, this invention strictly controls the magnetron sputtering process parameters, such as sputtering power and sputtering gas pressure, to obtain a microporous nickel coating with excellent electrolytic hydrogen catalytic performance.

[0037] The technical solution of the present invention will be further described below through specific embodiments. Example 1:

[0038] Nickel foam with dimensions of 800*500mm, a thickness of 0.3mm, and a porosity of 88.8% was selected as the substrate.

[0039] 1. Prepare a 10% concentration of 1003A cleaning agent, heat the ultrasonic bath to 60℃, set the ultrasonic vibration frequency to 28kHz, and perform ultrasonic cleaning for 10 minutes. For ultrasonic cleaning using anhydrous ethanol, the ultrasonic cleaning time is 5 minutes.

[0040] 2. Use a clamp to hold the nickel foam substrate in place. This clamp can rotate around its axis. The workpiece faces the molybdenum sulfide target as it rotates.

[0041] 3. Set the chamber's background vacuum level to 5×10⁻⁶. -4 Argon gas was introduced to create a reaction vacuum of 1 Pa in the chamber. The HALL plasma cleaning power was set to 1500 W, and the cleaning time was 20 min.

[0042] 4. Maintain the reaction vacuum in the chamber at 1 Pa, start the nickel target DC magnetron sputtering power supply, set the power to 3.0 kW, and the nickel deposition time to 60 min.

[0043] 5. After deposition is complete, turn off the magnetic power supply, molecular pump, Roots pump, and mechanical pump, and stop the machine to remove the sample.

[0044] 6. Immerse the deposited electrode in a prepared 5 mol / L potassium hydroxide solution for 6 hours. Then rinse the electrode with deionized water and dry it to obtain a nickel framework electrode with a microporous structure. Example 2:

[0045] Nickel foam with dimensions of 800*500mm, a thickness of 0.3mm, and a porosity of 88.8% was selected as the substrate.

[0046] 1. Prepare a 10% concentration of 1003A cleaning agent, heat the ultrasonic bath to 60℃, set the ultrasonic vibration frequency to 28kHz, and perform ultrasonic cleaning for 10 minutes. When using anhydrous ethanol for ultrasonic cleaning, the ultrasonic time is 5 minutes. 2. Use a clamp to hold the nickel foam substrate in place. This clamp can rotate around its axis. The workpiece faces the molybdenum sulfide target as it rotates.

[0047] 3. Set the chamber's background vacuum level to 5×10⁻⁶. -5 Argon gas was introduced to create a reaction vacuum of 2 Pa in the chamber. The HALL plasma cleaning power was set to 2000 W, and the cleaning time was 10 min.

[0048] 4. Maintain the reaction vacuum in the chamber at 2 Pa, start the nickel target DC magnetron sputtering power supply, set the power to 3.0 kW, and the nickel deposition time to 120 min.

[0049] 5. After deposition is complete, turn off the magnetic power supply, molecular pump, Roots pump, and mechanical pump, and stop the machine to remove the sample.

[0050] 6. Immerse the deposited electrode workpiece in a prepared 5 mol / L potassium hydroxide solution for 12 hours to completely dissolve the aluminum. Then rinse the electrode with deionized water and dry it to obtain a nickel skeleton electrode with a microporous structure.

[0051] Comparative Example 1: A conventional pure nickel non-porous skeletal electrode was used as a comparison. Furthermore, the nickel layer on this pure nickel non-porous electrode was applied directly to the electrode substrate using plasma spraying or thermal spraying methods.

[0052] Comparative Example 2: The difference from Example 1 is that no post-treatment alkaline soaking process was performed. Everything else is the same as Example 1.

[0053] Comparative Example 3: The difference from Example 1 is that only the process of magnetron sputtering nickel plating is omitted; the rest is the same as Example 1.

[0054] test: 1. Electrochemical tests were performed on the substrate with the prepared coating to determine the electrochemical hydrogen evolution performance of the coating obtained in the examples. The nickel metal frameworks with different micropore sizes obtained according to the above steps in Examples 1 and 2 exhibited different hydrogen evolution catalytic properties, such as… Figure 1 As shown in a and b in the diagram.

[0055] The electrodes of Comparative Example 1 were also tested. The results are shown below. Figure 1 As shown in (a) and (b) in the figure. In (b), NF represents the electrode sample without microporous structure of Comparative Example 1, while Ni-1 and Ni-2 are the electrode samples of Example 1 and Example 2, respectively.

[0056] according to Figure 1 As can be seen from the LSV curves and overpotential values, the electrolytic hydrogen desorption performance of the multi-level porous structure electrodes obtained in Examples 1 and 2 is significantly better than the electrolytic performance of the electrode without microporous structure in Comparative Example 1.

[0057] 2. The surface morphology of the electrodes in Examples 1, 2, and Comparative Example 1 was characterized using a scanning electron microscope (SEM) of a ZEISS Sigma 360. The SEM image of the non-porous electrode of Comparative Example 1 is shown below. Figure 2 In the diagram, (a)~(c), (d)~(f), and (g)~(i) are SEM images of the electrodes of Example 1 and Example 2 at different magnifications, respectively.

[0058] Depend on Figure 2 It can be seen that Examples 1 and 2 prepared electrode frameworks with obvious nanoscale micropores. Compared with the flat framework surface of Comparative Example 1, the specific surface area was significantly increased, thereby improving the catalytic activity. Figure 1 The test results correspond to those in the [reference / reference].

[0059] 3. The morphology of the electrode obtained in Comparative Example 2 was also characterized, and the results are as follows: Figure 3 As shown, Figure 3 Images (a) to (c) show the morphology of the electrode surface of Comparative Example 2 at different magnifications, while images (d) to (f) show the SEM images of the electrode of Example 1 at different magnifications. In Comparative Example 2, the electrode was not subjected to alkaline soaking. The resulting sample surface exhibited significant large-particle defects and areas of poor adhesion after nickel magnetron sputtering. After alkaline soaking, these defects dissolved, and the poorly adhered coating detached with stress release, leaving only the areas with the best adhesion. On the other hand, alkaline solutions may chemically react with certain particles on the coating surface, causing changes in the crystal structure or morphology of the coating surface. This chemical corrosion makes the coating surface rougher, forming specific microstructures such as corrosion pits. Figure 3 It is known that the surface corrosion pits after alkali soaking are at the nanometer level. Therefore, in this invention, after magnetron sputtering of the nickel layer, alkali soaking not only forms a large number of nanometer-sized pores, but also eliminates large particles and areas of poor adhesion on the coating surface formed after nickel magnetron sputtering. This is helpful in improving the coating adhesion and catalytic performance.

[0060] The inventors also investigated electrodes obtained by directly alkali immersion of nickel foam, and characterized the surface morphology of these electrodes. The results are shown in [Figure number missing]. Figure 4 The SEM image shows that if the nickel foam is directly soaked in alkali, the corrosion pits shown in Example 1 cannot be obtained. Therefore, this layer of nickel deposited by magnetron sputtering is necessary.

[0061] This invention has the following technical advantages: 1. This invention employs a physical preparation method, plasma vapor deposition, for coating preparation. This method enables the preparation of high-purity, large-area coatings with good process controllability and repeatability, low preparation cost, and suitability for large-area catalytic electrode manufacturing processes in industrial applications. This invention also effectively improves the adhesion between the coating and the substrate to meet the requirements of industrial applications.

[0062] 2. In both embodiments, this invention utilizes a magnetron sputtering combined with an alkaline immersion post-treatment method to construct a nanoscale microporous structure on a flat framework of a nickel foam substrate. This structure significantly increases the specific surface area compared to a flat framework surface. Its rich surface structure increases the active area of ​​the catalytic electrode, resulting in a larger surface area in contact with the electrolyte. This leads to a significant improvement in the utilization efficiency of the nickel catalyst and the hydrogen evolution catalytic performance, while also exhibiting better adhesion.

[0063] 3. The electrode surface formed by this invention has multiple levels of pores. One type consists of large pores of tens of micrometers in size inherent in the nickel foam itself, while the other type consists of corrosion pits of tens of nanometers in size obtained after alkali washing on the nickel foam skeleton. Compared to nickel foam materials with only micrometer-level pores, the material with nanometer-level corrosion pits has a larger specific surface area, thus improving catalytic performance. Furthermore, alkali immersion not only forms nanometer-level corrosion pits but also causes poorly bonded coatings in the magnetron sputtering film to fall off, improving the adhesion between the coating and the nickel foam substrate.

[0064] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a hierarchical porous metal catalytic electrode, characterized in that, include: A nickel coating is formed by magnetron sputtering on a nickel foam substrate using physical vapor deposition. The electrode with a nickel coating is immersed in an alkaline solution and then cleaned to obtain a hierarchical porous catalytic electrode with microporous and nanoporous structures.

2. The method for preparing a hierarchical porous metal catalytic electrode according to claim 1, characterized in that, During the physical vapor deposition process, the surface of the nickel foam substrate is first pretreated. The pretreatment process is as follows: (1) Place the substrate in the cleaning agent, use an ultrasonic vibration frequency of 28kHz, ultrasonic cleaning time of 5~10min, and temperature of 50~70℃; (2) Remove the substrate from the cleaning agent and rinse it with deionized water; (3) Use anhydrous ethanol to perform ultrasonic cleaning on the substrate. The ultrasonic vibration frequency is 28kHz and the ultrasonic cleaning time is 5~10min.

3. The method for preparing a hierarchical porous metal catalytic electrode according to claim 1, characterized in that, After pretreatment of the substrate, plasma cleaning is performed. During plasma cleaning, the vacuum level of the deposition chamber is 5 × 10⁻⁶. -5 Pa~5×10 - 3 Pa, the vacuum degree of the chamber reaction is 0.1Pa~2Pa; And / or, the plasma cleaning power is 800W~2000W, and the cleaning time is 10~20min.

4. The method for preparing a hierarchical porous metal catalytic electrode according to claim 1, characterized in that, When physical vapor deposition of nickel layers, the reaction vacuum degree of the chamber during the deposition process is 1 Pa to 2 Pa, the DC magnetron sputtering power is 1 to 5 kW, and the deposition time is 60 to 180 min. And / or the thickness of the deposited nickel layer is 2~4μm.

5. A method for preparing a hierarchical porous metal catalytic electrode according to any one of claims 1 to 4, characterized in that, The alkaline solution used in the post-treatment process is either sodium hydroxide solution or potassium hydroxide solution.

6. The method for preparing a hierarchical porous metal catalytic electrode according to claim 5, characterized in that, The concentration of the alkaline solution is 1 mol / L to 5 mol / L.

7. The method for preparing a hierarchical porous metal catalytic electrode according to claim 1, characterized in that, The electrodes are immersed in alkaline solution for 6 to 12 hours.

8. The method for preparing a hierarchical porous metal catalytic electrode according to claim 1, characterized in that, The foamed nickel substrate has dimensions of 800*500mm, a thickness of 0.3mm, and a porosity of 88.8%.

9. A hierarchical porous nickel catalytic electrode, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 8.

10. A hierarchical porous nickel catalytic electrode according to claim 9, characterized in that, The electrode has micron-sized pores and nanon-sized nickel pores; And / or, the pore size of the micron-sized pores is 50~200μm, and the pore size of the nano-sized nickel pores is 50~200nm.

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