Porous electrode with controlled pore size and method for manufacturing same

Abstract

The present invention relates to a porous electrode having controlled pore size and a method for manufacturing same and, more particularly, to a method for manufacturing a water electrolysis electrode and a water electrolysis electrode manufactured by the method of the present invention, the method comprising the steps of: preparing mixed metal powder including nickel powder and aluminum powder; filling the mixed metal powder into a mold formed in the shape of an electrode; applying pressure to the filled mixed metal powder to form a molded body; subjecting the molded body to first heat treatment in a reducing atmosphere; treating the heat-treated molded body with a basic solution to leach an aluminum component; and performing second heat treatment in a reducing atmosphere.

Description

Porous electrode with controlled pore size and method for manufacturing the same

[0001] The present invention relates to a porous electrode with controlled pore size and a method for manufacturing the same, and more specifically, to manufacturing an electrode with controlled pore size so that hydrogen and oxygen gases formed by the electrolysis of water on the surface of the electrode can be easily discharged.

[0002] Efforts to reduce carbon dioxide emissions due to global warming and to use clean hydrogen as fuel are being made worldwide, and in particular, water electrolysis technology, which produces green hydrogen by electrolyzing water using renewable energy, is gaining attention as the most desirable method for producing clean hydrogen.

[0003] Methods used for water electrolysis include high-temperature electrolysis, which produces hydrogen by decomposing steam under high-temperature operating conditions, and low-temperature electrolysis, which decomposes water at low temperatures. Since high-temperature electrolysis operates at temperatures exceeding 700°C, it presents a high level of technical difficulty, and thus, it can be considered to be in the early stages of commercialization. Although there are concerns regarding the use of precious metals such as Pt and Ir as electrode catalysts and a short lifespan due to strong corrosiveness, a low-temperature electrolysis technology known as polymer electrolyte electrolysis, commercialization has recently begun. Meanwhile, alkaline electrolysis is a method in which electrodes come into contact with an alkaline electrolyte to electrolyze water. It has the advantages of not requiring the use of expensive precious metals, operating at low temperatures, making manufacturing and maintenance relatively easy, and having low equipment costs; consequently, it has been commercialized for a long time, with the largest capacity facilities distributed worldwide.

[0004] Nickel, which is stable even in high-concentration alkaline aqueous solutions, is the most widely used electrode material for such alkaline water electrolysis, and nickel-plated stainless steel is also used. Various electrode shapes, such as plate, mesh, porous plate, and foam types, are commonly used. Korean Patent Application No. 10-2022-0109869 discloses a technology for manufacturing an electrode with excellent specific surface area and porosity by forming a dendritic porous composite metal structure on a conductive substrate.

[0005] However, if a technology is provided that can easily control the pore size of the electrode without relying on steps such as forming a dendritic composite metal structure, it is expected to be widely applied in related fields.

[0006] [Prior Art Literature]

[0007] [Patent Document](Patent Document 1) Republic of Korea Application No. 10-2022-0109869

[0008] According to one embodiment of the present invention, a method for manufacturing an electrode capable of providing improved water electrolysis performance can be provided.

[0009] According to another embodiment of the present invention, an electrode capable of providing improved water electrolysis performance may be provided.

[0010] A method for manufacturing a water electrolysis electrode according to one embodiment of the present invention may be a method for manufacturing a water electrolysis electrode comprising: a step of preparing a mixed metal powder including nickel powder and aluminum powder; a step of filling the mixed metal powder into a mold made in the shape of an electrode; a step of manufacturing a molded body by applying pressure to the filled mixed metal powder; a step of performing a first heat treatment of the molded body in a reducing atmosphere; a step of leaching out aluminum components by treating the heat-treated molded body with a basic solution; and a step of performing a second heat treatment in a reducing atmosphere.

[0011] Based on the total weight of the above mixed metal powder, the nickel powder may be mixed in an amount of 50 to 90 weight percent.

[0012] The above nickel powder may be nickel powder in the shape of a filament.

[0013] The above filament-shaped nickel powder may have an aspect ratio of 1.5 to 10.

[0014] The above filament-shaped nickel powder may have a cross-sectional diameter of 1 to 3 μm and a length of 5 to 10 μm.

[0015] The above aluminum powder may be spherical aluminum powder with a particle size of 10 to 100 μm.

[0016] The step of manufacturing the above molded body is 100 to 900 kg / cm² 2 It may be performed by a compression step that applies pressure.

[0017] The above first heat treatment step may be performed in a temperature range of 300 to 550°C.

[0018] The above second heat treatment step may be performed in a temperature range of 650 to 950°C.

[0019] The above basic solution may be an aqueous solution containing at least one metal hydroxide base selected from sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium hydroxide (LiOH), and calcium hydroxide (Ca(OH)₂).

[0020] A water electrolysis electrode according to another embodiment of the present invention is manufactured by the method of the present invention and is a water electrolysis electrode having a bimodal distribution pore structure having micropores with a diameter of less than 10 μm and pores with a diameter of 10 to 100 μm together.

[0021] According to the present invention, an electrode is provided in which the specific surface area of ​​the electrode is widened so that an electrolytic solution can easily penetrate the electrode, and according to the present invention, the size of the pores can be easily controlled so that hydrogen and oxygen gases formed by the electrolysis of water on the surface of the electrode can be easily discharged.

[0022] Figure 1 is a photograph of the shape of the nickel powder used in the present invention using a scanning electron microscope.

[0023] Figure 2 shows photographs of Comparative Examples 1 to 3 after first heat treatment at temperatures of 550°C, 650°C, and 750°C, respectively, and it can be seen that the shape of the specimens is changed and fine pores disappear as excessive interdiffusion occurs between nickel and aluminum.

[0024] Figure 3 is a scanning electron microscope image taken at a magnification of ×300 of the fracture surface and surface of the specimens of Examples 1, 2, and 3, which were subjected to a first heat treatment at 525°C.

[0025] Figure 4 is a scanning electron microscope image taken at a magnification of ×300 of the fracture surface and surface of Examples 1, 2, and 3 after leaching was completed.

[0026] Figure 5 shows a comparison of the phases obtained by X-ray diffraction analysis before (top) and after (bottom) leaching of the test specimen of Example 3.

[0027] Figure 6 is a scanning electron microscope image of the fracture surface and the surface of Examples 1, 2, and 3, each of which had undergone secondary heat treatment, taken at a magnification of ×300.

[0028] Figure 7 is a graph showing the results of comparing the hydrogen generation activity when test specimens of Examples 1 to 3 and Comparative Examples 4 and 5 were used as electrode materials.

[0029] Preferred embodiments of the present invention will be described below with reference to the attached drawings. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0030] In addition, embodiments of the present invention are provided to more fully explain the present invention to those with average knowledge in the relevant technical field.

[0031] In drawings, the shapes and sizes of elements may be exaggerated for clearer explanation.

[0032] In describing the embodiments of the present invention, if it is determined that a detailed description of known technology related to the present invention may unnecessarily obscure the essence of the present invention, such detailed description will be omitted. Furthermore, the terms described below are defined considering their functions in the present invention, and these may vary depending on the intentions or conventions of the user or operator. Therefore, such definitions should be based on the content throughout this specification. The terms used in the detailed description are merely for describing the embodiments of the present invention and should not be limited in any way. Unless explicitly stated otherwise, expressions in the singular form include the meaning of the plural form.

[0033] In this description, expressions such as “include” or “equipped” are intended to refer to certain characteristics, numbers, steps, actions, elements, parts or combinations thereof, and should not be interpreted to exclude the existence or possibility of one or more other characteristics, numbers, steps, actions, elements, parts or combinations thereof other than those described.

[0034] Unless otherwise specifically defined in the specification of the present invention, % units mean weight %.

[0035] Additionally, throughout the specification, when it is said that one part is 'connected' to another part, this includes not only cases where they are 'directly connected,' but also cases where they are 'indirectly connected' with other elements in between.

[0036] The present invention will be described in detail below through each embodiment or example of the invention. It should be noted that each embodiment or example described in this specification is not limited to a single embodiment or example, but may also be combined with other embodiments or examples. Accordingly, the citation of claims in the patent claims is merely an example of an embodiment, and the technical concept of the present invention should not be interpreted as being limited only to a combination with the cited claims; rather, combinations with various claims are also included within the scope of the technical concept of the present invention.

[0037] Description of the invention

[0038] According to the present invention, an electrode with controlled pore size and a method for manufacturing the same are provided.

[0039] More specifically, the method for manufacturing a water electrolysis electrode of the present invention comprises the steps of: preparing a mixed metal powder comprising nickel powder and aluminum powder; filling the mixed metal powder into a mold made in the shape of an electrode; applying pressure to the filled mixed metal powder to produce a molded body; performing a first heat treatment of the molded body in a reducing atmosphere; treating the heat-treated molded body with a basic solution to leach out the aluminum component; and performing a second heat treatment in a reducing atmosphere.

[0040] Based on the total weight of the mixed metal powder, the nickel powder is mixed in an amount of 50 to 90 weight percent. For example, the nickel powder and aluminum powder may be mixed in a weight ratio of 9:1 to 5:5, and a more preferable weight ratio of nickel powder and aluminum powder may be 8:2 to 6:4. Meanwhile, if the content of aluminum powder is below the above range, the formation of coarse pores may be insufficient, and if it exceeds the above range, the strength of the electrode may be weakened.

[0041] Meanwhile, the metal powder comprises filament-shaped nickel powder, wherein the filament-shaped nickel powder may have an aspect ratio of 1.5 to 10, for example, 1.7 to 10, where the length of the filament is divided by the cross-sectional diameter. Additionally, since the filament shape is advantageous for forming a three-dimensional network structure, a pore structure can be formed stably and uniformly, and as a result, the electrolyte can diffuse more easily into the electrode, thereby improving electrolyte accessibility. Furthermore, release pathways for hydrogen and / or oxygen are efficiently formed, increasing gas release efficiency. Additionally, since the filament shape shrinks more uniformly throughout the entire particle than spherical particles during the heat treatment process, the stability of the formed structure can be ensured compared to spherical particles, which can increase the mechanical strength of the electrode.

[0042] When the aspect ratio of the filament-shaped nickel powder, calculated by dividing the length of the filament by the cross-sectional diameter, is less than 1.5, the effect caused by the filament formation described above may be minimal, and when the aspect ratio exceeds 10, dispersibility may be reduced, making it difficult to form a uniform molded body during the manufacturing process, and as a result, the stability of the electrode structure may be reduced.

[0043] For example, the filament-shaped nickel powder may have a cross-sectional diameter of 1 to 3 μm and a length of 5 to 10 μm.

[0044] Meanwhile, the aluminum powder may be spherical aluminum powder with a particle size of 10 to 100 μm, for example, 20 to 100 μm. According to the present invention, when the final electrode is manufactured, pores corresponding to the size of the aluminum particles are formed in the electrode, so the pore size of the final electrode can be controlled by changing the size of the aluminum particles.

[0045] Subsequently, a step of manufacturing a molded body by molding a porous nickel support coated with the metal powder; and a step of performing a first heat treatment of the molded body in a reducing atmosphere, wherein the molding step and the heat treatment step may be performed sequentially or simultaneously.

[0046] The step of manufacturing the above molded body is 100 to 900 kg / cm² 2 This may be performed by a compression step applying pressure, for example, 150 to 700 kg / cm² 2 , preferably 200 to 500 kg / cm² 2 It is performed within the pressure range.

[0047] The above first heat treatment step may be performed in a temperature range of 300°C or higher and less than 550°C, for example, in a temperature range of 450 to 540°C or 500 to 530°C. If the above first heat treatment step is performed at a temperature below 300°C, the heat-treated molded body may have difficulty maintaining its shape during subsequent leaching and first heat treatment processes, and if it is performed at a temperature exceeding 550°C, severe interdiffusion between nickel and aluminum may occur, causing the molded body to deform and the pore size to decrease.

[0048] In this way, when using a mixed metal powder of nickel and aluminum, controlled pores can be formed by selective leaching on a heat-treated molded body.

[0049] Selective leaching means leaching only aluminum without leaching nickel.

[0050] Selective leaching can be performed by contacting, for example, immersing a molded body that has undergone primary heat treatment in a basic solution, and the basic solution may be an aqueous solution with a pH of 8 to 14 containing at least one metal hydroxide base among sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium hydroxide (LiOH), and calcium hydroxide (Ca(OH)₂).

[0051] More specifically, the leaching can be carried out at a temperature of 10 to 90°C, for example, at room temperature of 20 to 40°C or at a temperature of 50 to 90°C for 1 to 24 hours. As the leaching solution used for selective leaching, an aqueous solution containing the metal hydroxide base can be used, for example, 10 wt% to 40 wt% or 10 to 30 v / v% of KOH, etc., but the present invention is not limited thereto, and any alkaline solution capable of selective leaching can be used.

[0052] Nickel hydroxide may be formed during the process of forming a porous layer by performing a selective leaching step in this manner.

[0053] Meanwhile, the second heat treatment step may be performed in a temperature range of 600 to 950°C, for example, in a temperature range of 700 to 850°C. Sintering may be performed by the second heat treatment step; if sintering is performed at a temperature below 600°C, the bonding force between nickel powder particles may be insufficient, resulting in a decrease in strength, and if it is performed at a temperature exceeding 950°C, the porosity may be excessively reduced due to over-sintering. The strength of the electrode can be secured by performing the second heat treatment as described above. If the temperature is below or above the above range, the strength of the electrode may be insufficient or the porosity may decrease.

[0054] The first and second heat treatment steps above may each be performed independently in a reducing atmosphere, and the reducing atmosphere may be an atmosphere containing hydrogen (H₂) gas, for example, under an inert mixed gas containing 5 to 40 v / v% or 10 to 30 v / v% of hydrogen. The inert gas may be, for example, argon, but is not limited thereto.

[0055] The water electrolysis electrode of the present invention obtained by such a method may have a bimodal pore structure having coarse pores with a diameter of 10 to 100 μm formed by the selective dissolution of aluminum powder mixed with fine pores with a diameter of less than 10 μm through inter-particle bonding achieved by heat treatment of nickel particles.

[0056] The total thickness of the electrode may be 0.1 mm to 3 mm.

[0057] The present invention will be described in detail below through examples. However, it should be noted that the examples described below are intended merely to illustrate and embody the present invention and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the patent claims and matters reasonably inferred therefrom.

[0058] Examples

[0059] 1. Manufacturing of electrodes

[0060] Examples

[0061] (1) Preparation of metal powder

[0062] Nickel powder in the form of filaments with a thickness of 1 to 3 μm and a length of 5 to 10 μm was used. Figure 1 is a photograph of the shape of the nickel powder used in the present invention taken using a scanning electron microscope.

[0063] Meanwhile, in the case of aluminum powder, a powder having a particle size distribution of 20 to 100 μm was selected, which allows for the control of pore formation corresponding to the size of the aluminum particles in the electrode when the final electrode is manufactured.

[0064] The nickel powder and aluminum powder were selected and mixed in weight ratios of 8:2, 7:3, and 6:4, respectively. A uniformly mixed powder was obtained by mixing for more than one hour using a powder mixer. The amount of pores formed on the electrode can be controlled by varying the mixing ratio of the aluminum powder.

[0065] (2) Plastic surgery

[0066] The above mixed powder is filled into a mold measuring 40mm × 40mm × 3mm, and then molded using a press at a pressure of 350 kg / cm² 2 It was compressed and molded in.

[0067] (3) 1st heat treatment

[0068] The molded body obtained in this way was subjected to a primary heat treatment to ensure that the molded body could be maintained during subsequent leaching and secondary heat treatment processes. At this time, to prevent oxidation, the heat treatment was performed in a reducing gas atmosphere in which hydrogen was mixed with argon at 10 v / v%. The heating rate was set to 10°C / min, and the target temperatures were changed to 525, 550, 650, and 750°C, respectively, while the holding time for each was fixed at 1 hour. In Table 1 below, nickel powder and aluminum powder were mixed in weight ratios of 8:2, 7:3, and 6:4, respectively; Comparative Examples 1 to 3 represent cases where heat treatment was performed at 650°C, and Examples 1 to 3 represent cases where heat treatment was performed at 525°C.

[0069] Comparative Example 4

[0070] An electrode was manufactured by the same process as in the example, except that only nickel powder was used instead of a mixed powder of nickel powder and aluminum powder.

[0071] The conditions of the examples and comparative examples manufactured according to specific examples are summarized in Table 1 below.

[0072] Powder Composition, Ni : Al (Weight Ratio) 1st Heat Treatment Temperature (°C) Comparative Example 18:2650 Comparative Example 27:3650 Comparative Example 36:4650 Example 18:2525 Example 27:3525 Example 36:4525

[0073] In the case of Comparative Examples 1 to 3, which underwent primary heat treatment at 550, 650, and 750°C, respectively, it was observed that excessive interdiffusion between nickel and aluminum occurred, causing the shape of the specimen to change and the fine pores to disappear, as shown in Fig. 2. On the other hand, it was confirmed that when the primary heat treatment was performed at 525°C, the original shape could be maintained while maintaining appropriate strength. Through this, it was confirmed that the appropriate primary heat treatment temperature condition should be 550°C or lower. Fig. 3 shows scanning electron microscope images of the fracture surfaces and surfaces of Examples 1, 2, and 3, which underwent primary heat treatment at 525°C, at a magnification of ×300, respectively. In the images, the particles appearing relatively darker are aluminum, and the fine particles surrounding them are nickel particles. It can be observed that as the aluminum content increases, the area occupied by aluminum expands.

[0074] (4) Aluminum leaching

[0075] Aluminum leaching is a process in which a molded body is immersed in a basic solution to leach and remove aluminum components, thereby enabling the creation of pores within the molded body that correspond to the size of aluminum powder.

[0076] Aqueous solutions such as NaOH and KOH can be used as basic solutions, and in this experiment, aluminum leaching was performed by immersing in a 30 wt% KOH aqueous solution at room temperature for more than 2 hours.

[0077] Figure 4 is a scanning electron microscope image taken at a magnification of ×300 of the fracture surfaces and surfaces of Examples 1, 2, and 3 after leaching was completed. Compared to Figure 3, which was before aluminum leaching, it can be seen that the sites where aluminum was present have been converted into pores. In the case of Example 3, which had a high initial aluminum content, it can be confirmed that significantly more pores were formed compared to Example 1.

[0078] In Examples 1, 2, and 3, nickel powder was mixed with aluminum powder and heat-treated, and after leaching the aluminum, X-ray diffraction analysis was performed to compare the phases. Figure 5 shows the results before and after leaching in Example 3.

[0079] In the case of Example 3 before leaching, both nickel and aluminum could be identified, and although the small peaks with low intensity were not shown in Figure 5, they were identified as Al3Ni and Al3Ni2. It is understood that only a portion of the nickel particles in contact with the aluminum particles formed trace amounts of intermetallic compounds through interdiffusion.

[0080] After aluminum leaching was performed, it was confirmed that all the aluminum was dissolved by the basic solution, and since no intermetallic compounds of Al3Ni and Al3Ni2 were detected, it was found that the state was almost pure nickel. Accordingly, in the example classification in Table 1, it can be understood that the chemical composition after aluminum leaching is 100 wt% nickel.

[0081] (5) Secondary heat treatment

[0082] A second heat treatment is performed to impart strength sufficient for the molded body to be used as a water electrolysis electrode, and a range of 600 to 950°C is appropriate, but in this embodiment, it was performed at 750°C for 1 hour in a reducing gas atmosphere.

[0083] Figure 6 is a scanning electron microscope image of the fracture surface and the surface of Examples 1, 2, and 3, each of which had undergone secondary heat treatment, taken at a magnification of ×300. Compared to Figure 4, it can be confirmed that the portion occupied by aluminum remains as a pore even after the secondary heat treatment.

[0084] By going through the steps described above, it was possible to manufacture a metal sintered electrode having a shape in which fine pores of 10 μm or less and coarse pores of about 10 μm to 100 μm exist together between the bonds of nickel particles.

[0085] 2. Evaluation of Hydrogen Generation Characteristics

[0086] To evaluate the hydrogen generation characteristics of the porous nickel powder sintered electrode prepared according to 1. above, a potentiodynamic polarization test of the water electrolysis reaction in an alkaline aqueous solution was performed.

[0087] The experiment was conducted by constructing a 3-electrode electrochemical cell using the electrodes of the examples prepared under the conditions of 1. as the working electrodes, a platinum electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode.

[0088] A 30 wt% KOH aqueous solution at 70°C was used as the electrolyte. The potential applied to the graph was converted to RHE (Reversible Hydrogen Electrode) and plotted. To compare the relative effects of the fabricated electrodes, the performance of nickel foam was also compared, with a pore size of 450 μm, a thickness of 1.5 mm, and a yield of 420 g / m². 2 A commercial nickel foam having density specifications was used as Comparative Example 5, and the performance of the electrode of Comparative Example 4, which was prepared using pure nickel powder under the same conditions as the example, was also compared.

[0089] Figure 7 is a graph showing the results of comparing the activity of hydrogen generation. When the same current density is applied, the closer the potential is to 0, the lower the overvoltage, which indicates superior performance. The electrodes prepared in Examples 1 to 3 show superior performance compared to the nickel foam of Comparative Example 5, and it was confirmed that the higher the aluminum content (Examples 1, 2, and 3), the relatively superior performance is shown.

[0090] Meanwhile, Table 2 below shows the current density at 100 mA / cm² 2 This compares the overvoltage of the electrode under the application conditions.

[0091] Test Specimen Classification Overvoltage (mV) Comparative Example 5315 Comparative Example 4228 Example 1180 Example 2164 Example 3138

[0092] Compared to Comparative Example 5, which is nickel foam, all metal sintered electrodes manufactured according to the embodiments of the present invention exhibited excellent characteristics, and in particular, the electrodes of Examples 1 to 3, which had large pores formed, showed lower overpotential compared to Comparative Example 4, which had no large pores.

Claims

1. A step of preparing a mixed metal powder comprising nickel powder and aluminum powder; A step of filling a mold made in the shape of an electrode with mixed metal powder; A step of manufacturing a molded body by applying pressure to a filled mixed metal powder; Step of primary heat treatment of the molded body in a reducing atmosphere; A step of treating a heat-treated molded body with a basic solution to leach out aluminum components; and Step of secondary heat treatment in a reducing atmosphere; A method for manufacturing a water electrolysis electrode comprising 2. A method for manufacturing a water electrolysis electrode according to claim 1, wherein the nickel powder is mixed in an amount of 50 to 90 weight% based on the total weight of the mixed metal powder.

3. A method for manufacturing a water electrolysis electrode according to claim 1, wherein the nickel powder is a filament-shaped nickel powder.

4. A method for manufacturing a water electrolysis electrode, wherein, in paragraph 3, the filament-shaped nickel powder has an aspect ratio of 1.5 to 10.

5. A method for manufacturing a water electrolysis electrode according to claim 3, wherein the filament-shaped nickel powder has a cross-sectional diameter of 1 to 3 μm and a length of 5 to 10 μm.

6. A method for manufacturing a water electrolysis electrode according to claim 1, wherein the aluminum powder is spherical aluminum powder with a particle size of 10 to 100 μm.

7. In claim 1, the step of manufacturing the molded body is 100 to 900 kg / cm² 2 A method for manufacturing a water electrolysis electrode, performed by a compression step that applies pressure.

8. A method for manufacturing a water electrolysis electrode according to claim 1, wherein the first heat treatment step is performed in a temperature range of 300 to 550°C.

9. A method for manufacturing a water electrolysis electrode according to claim 1, wherein the step of secondary heat treatment is performed in a temperature range of 600 to 950°C.

10. A method for manufacturing a water electrolysis electrode according to claim 1, wherein the basic solution is an aqueous solution comprising at least one metal hydroxide base selected from sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium hydroxide (LiOH), and calcium hydroxide (Ca(OH)₂). A water electrolysis electrode having a bimodal pore structure having micropores with a diameter of less than 11.10 μm and pores with a diameter of 10 to 100 μm.

Images