Acidified electrode for anion exchange membrane water electrolysis

Abstract

The present invention provides a low-cost, high-performance, and highly stable oxidation electrode for anion-exchange membrane water electrolysis. Specifically, one embodiment of the present invention provides an oxidation electrode for anion-exchange membrane water electrolysis, comprising nickel metal and a monolayer layered double hydroxide (LDH) containing nickel and iron and located on one or both sides of the nickel metal.

Description

[Technical Field]

[0001] [Cross-reference to related applications] This application claims priority to Korean Patent Application No. 10-2020-0150363, filed November 11, 2020, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to an oxidation electrode for anion exchange membrane water electrolysis. [Background technology]

[0003] BACKGROUND ART There is increasing importance in technology that can produce hydrogen, a next-generation energy source that can solve the problems of fossil fuel depletion and environmental pollution, in an environmentally friendly manner.

[0004] According to the roadmap for revitalizing the hydrogen economy recently announced by the Ministry of Trade, Industry and Energy of South Korea, most hydrogen production is expected to be done in an environmentally friendly manner, and there is an even greater need for the development of water electrolysis, a representative technology for environmentally friendly hydrogen production.

[0005] In this regard, active research is being conducted on water electrolysis technology using electrolysis methods, and representative low-temperature water electrolysis technologies are known to be proton exchange membrane water electrolysis (PEMWE) and alkaline water electrolysis (AWE).

[0006] Among these, alkaline water electrolysis uses alkaline water as a reactant, requiring electrode materials with strong corrosion resistance to alkaline water. Candidate electrode materials include non-platinum metals such as nickel, iron, and cobalt, which are relatively low-cost electrode materials. Since electrodes account for a significant portion of the cost of water electrolysis, using non-platinum metals has the advantage of reducing hydrogen production costs. However, alkaline water electrolysis systems have the disadvantage of requiring a large space and low current per electrode area, resulting in reduced efficiency due to the high overpotential required for hydrogen production.

[0007] On the other hand, proton exchange membrane water electrolysis has the advantage of high energy density due to its compact system design, but has the disadvantage of increasing hydrogen production costs due to the necessity of platinum-based metals that can withstand the acidic atmosphere of the proton exchange membrane.

[0008] In contrast, anion exchange membrane water electrolysis (AEMWE) is a system that utilizes the advantages of existing systems while eliminating their disadvantages. Because it operates in an alkaline environment, non-platinum metals can be used as electrode materials, and a compact system design can achieve favorable energy density.

[0009] However, research into anion exchange membrane water electrolysis has not progressed as much as it has in existing systems, and as a result, the standard exchange membrane and electrode materials are not yet known. Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention provides a low-cost, high-performance, and highly stable oxidation electrode for anion-exchange membrane water electrolysis. [Means for solving the problem]

[0011] Specifically, one embodiment of the present invention provides an oxidation electrode for anion exchange membrane water electrolysis, comprising: nickel metal; and a monolayer layered double hydroxide (LDH) containing nickel and iron and located on one or both sides of the nickel metal.

[0012] In another embodiment of the present invention, there is provided a method for manufacturing an oxidation electrode for anion exchange membrane water electrolysis, which includes a series of steps of synthesizing a layered double hydroxide (LDH) containing nickel and iron into a monolayer structure using a bottom-up method, and then depositing nickel metal on one or both sides of the monolayer.

[0013] In yet another embodiment of the present invention, there is provided an anion exchange membrane water electrolysis cell comprising: an anion exchange membrane; and a reduction electrode and an oxidation electrode located on either side of the anion exchange membrane, respectively, wherein the oxidation electrode is the oxidation electrode of the above-described embodiment. [Effects of the Invention]

[0014] The oxidation electrode of the present embodiment includes non-precious metals nickel and iron, and therefore can be produced efficiently at low cost in a short time. The oxidation electrode includes a monolayer layered double hydroxide (LDH) containing nickel and iron, which ensures high performance and stability compared to multilayer structures. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram illustrating the principle of an anion exchange membrane water electrolysis device. [Figure 2a] FIG. 1 is a diagram showing a method for synthesizing B-NiFe-LDH. [Figure 2b] FIG. 1 is a diagram showing a method for synthesizing M-NiFe-LDH. [Figure 3a]FIG. 1 is a diagram illustrating a method for producing an oxidation electrode using B-NiFe-LDH. [Figure 3b] FIG. 1 is a diagram illustrating a method for producing an oxidation electrode using M-NiFe-LDH. [Figure 4a] 1 is a TEM image of Production Example 2 (B-NiFe-LDH). [Figure 4b] 1 is a TEM image of Production Example 2 (B-NiFe-LDH). [Figure 4c] EDS mapping images at the same scale. [Figure 4d] 1 is a TEM image of Production Example 1 (M-NiFe-LDH). [Figure 4e] 1 is a TEM image of Production Example 1 (M-NiFe-LDH). [Figure 4f] EDS mapping images at the same scale. [Figure 5] FIG. 1 shows XRD patterns of the catalyst (B-NiFe-LDH) of Comparative Example 1 in a powder state, the catalyst (M-NiFe-LDH) of Example 1 dispersed in water to form a colloidal state, and the catalyst (M-NiFe-LDH) of Example 1 dried in an oven to form a powder state. [Figure 6a] 1 is an SEM image of the oxidation electrode (B-NiFe-LDH on Ni foam) of Comparative Example 1. [Figure 6b] 1 is an SEM image of the oxidation electrode (B-NiFe-LDH on Ni foam) of Comparative Example 1. [Figure 6c] 1 is an SEM image of the oxidation electrode (B-NiFe-LDH on Ni foam) of Comparative Example 1. [Figure 6d] 1 is an SEM image of the oxidation electrode (M-NiFe-LDH on Ni foam) of Example 1. [Figure 6e] 1 is an SEM image of the oxidation electrode (M-NiFe-LDH on Ni foam) of Example 1. [Figure 6f] 1 is an SEM image of the oxidation electrode (M-NiFe-LDH on Ni foam) of Example 1. [Figure 7a] 1 is a current-voltage graph of each anion-exchange membrane water electrolysis cell of Comparative Examples 1 to 5. [Figure 7b] 1 is a current-voltage graph of each anion-exchange membrane water electrolysis cell of Examples 1 to 4. [Figure 7c] 1 is a current-voltage graph of the anion-exchange membrane water electrolysis cells of Example 3 and Comparative Examples 3 and 5. [Figure 8] 1 is a stability evaluation graph for each of the anion exchange membrane water electrolysis cells of Example 3, Comparative Example 3, and Comparative Example 6.

[0016] In the present invention, terms such as "first" and "second" are used to describe various components, and the terms are used only to distinguish one component from another.

[0017] Furthermore, the terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise. In this specification, the terms "comprise," "include," "comprise," "have," and the like are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, and should be understood as not precluding the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0018] Furthermore, in the present invention, when it is said that each layer or element is formed "on" or "on" another layer or element, it means that each layer or element is formed directly on the other layer or element, or that other layers or elements may be additionally formed between each layer, on the object, or on the substrate.

[0019] The present invention can be modified in various ways and can have various forms, so that the following detailed description will be given by way of example of a specific embodiment, but it is not intended to limit the present invention to the specific disclosed embodiment, and it should be understood that the present invention includes all modifications, equivalents, and alternatives within the spirit and technical scope of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] Anion exchange membrane oxidation electrode for water electrolysis One embodiment of the present invention provides an oxidation electrode for anion exchange membrane water electrolysis, comprising: nickel metal; and a monolayer layered double hydroxide (LDH) containing nickel and iron and located on one side of the nickel metal.

[0021] This material contains the non-precious metals nickel and iron, making it possible to produce it at low cost. The monolayer layered double hydroxide (LDH) containing nickel and iron ensures higher performance and stability than multilayer structures.

[0022] 1) In one embodiment of the oxidation electrode, a monolayer layered double hydroxide (LDH) containing nickel and iron is located on one or both sides of the nickel metal and functions as an oxygen generating catalyst.

[0023] In other words, the oxidation electrode of the embodiment includes a single-layer structure catalyst layer, and such a single-layer structure catalyst layer is a layered double hydroxide containing nickel and iron.

[0024] In general, layered double hydroxide (LDH) is a type of ionic solid with a two-dimensional structure.

[0025] Specifically, [(AcB)-Z-(AcB)] n where c represents a metal proton layer, A and B represent hydroxide ion (OH) layers, Z represents layers containing other anions and neutral molecules (e.g., water), and n represents the number of repeating layers.

[0026] In the [AcB-Z-AcB] unit, the inserted anion or neutral molecule (Z) is weakly bound and can be exchanged with other anions or neutral molecules. The distance between the AcB layers that separate the anions or neutral molecules (Z) is called the interlayer basal spacing.

[0027] 2) In the general catalytic field, bulk nickel-iron layered double hydroxides are known to produce high catalytic performance.

[0028] Here, the layered double hydroxide containing nickel and iron in a bulk state (NiFe-LDH), i.e., a multilayer layered double hydroxide containing nickel and iron, may be used. Hereinafter, the layered double hydroxide containing nickel and iron in a bulk state will be referred to as "B-NiFe-LDH."

[0029] Specifically, B-NiFe-LDH has a monolayer structure (monolayer) including a first hydroxide ion (OH-) layer (A), a metal layer (c) including nickel and iron, and a second hydroxide ion (OH-) layer (B) as one unit (AcB); between the two units (AcB), there is another anion, CO3 2- , O.H. - The structure (Z) contains neutral molecules such as water, and multiple units are stacked together [(AcB)-Z-(AcB)]. n It has.

[0030] Such B-NiFe-LDH has significant drawbacks for use as an anion exchange membrane water electrolysis catalyst, mainly due to its low electrical conductivity and low stability.

[0031] Specifically, in B-NiFe-LDH, the basal plane acts as a reaction site for the oxygen evolution reaction, and OH-, which is used as a reactant, cannot diffuse quickly into the multilayer structure, resulting in a partial acidic environment between the catalyst layers, causing the catalyst to dissolve. This presents a major problem in anion exchange membrane water electrolysis, which operates at higher temperatures and currents than alkaline water electrolysis.

[0032] On the other hand, M-NiFe-LDH has a structure in which all basal planes are exposed to the reactant (OH-), unlike B-NiFe-LDH. - In other words, M-NiFe-LDH can solve the problem of low stability caused by B-NiFe-LDH.

[0033] In one embodiment, the oxidation electrode includes a monolayer layered double hydroxide (LDH) containing nickel and iron, hereinafter referred to as "M-NiFe-LDH."

[0034] M-NiFe-LDH contains only one unit (AcB), which overcomes the problems of low electrical conductivity and low stability of B-NiFe-LDH. Specifically, M-NiFe-LDH has a higher intrinsic oxygen evolution reaction activity (OER) than B-NiFe-LDH due to its single-layer structure, improving the performance of anion exchange membrane water electrolysis.

[0035] Meanwhile, in the oxidation electrode of the embodiment, the M-NiFe-LDH may be prepared using a bottom-up method or a top-down method.

[0036] Among these, the bottom-up method has a simpler manufacturing process and allows for more efficient electrode manufacturing than the top-down method.

[0037] The method for producing the M-NiFe-LDH will be described later.

[0038] 3) Furthermore, the electrical conductivity can be further enhanced by using nickel metal as a substrate.

[0039] Specifically, M-NiFe-LDH is more susceptible to the influence of the substrate due to its thinner thickness compared to B-NiFe-LDH. In this regard, the electrical conductivity of the oxidation electrode can be further enhanced by using a highly electrically conductive material such as nickel metal (e.g., nickel foam) as the substrate.

[0040] 4) Therefore, the oxidation electrode of the present embodiment includes the M-NiFe-LDH prepared by the bottom-up method as a catalyst layer and nickel metal as a substrate, thereby improving stability and electrical conductivity.

[0041] Therefore, compared with an oxidation electrode that does not include any catalyst layer at all, an oxidation electrode that includes B-NiFe-LDH as a catalyst layer, or an oxidation electrode that includes M-NiFe-LDH manufactured by the top-down method as a catalyst layer, the optimal catalyst amount can be increased, thereby improving the performance of the water electrolysis cell.

[0042] The oxidation electrode of the embodiment will be described in more detail below.

[0043] Nickel / iron weight ratio in layered double hydroxide The weight ratio of nickel / iron in the layered double hydroxide (M-NiFe-LDH) may be 15 / 85 to 85 / 15.

[0044] Within this range, as the nickel / iron weight ratio approaches 25 / 75, the overvoltage during the oxygen generation reaction decreases and catalytic performance may improve. As the ratio increases or decreases, the overvoltage during the oxygen generation reaction increases and catalytic performance deteriorates. The nickel / iron weight ratio can be controlled taking this into consideration.

[0045] For example, the weight ratio of nickel / iron in the layered double hydroxide (M-NiFe-LDH) can be controlled within the range of 25 / 85 to 85 / 25.

[0046] Layered double hydroxide loading amount The loading amount of the layered double hydroxide (M-NiFe-LDH) per one side of the nickel metal is 0.1 to 5 mg / cm 2 It could be.

[0047] Within this range, the performance of the anion exchange membrane water electrolysis cell improves as the loading amount of the layered double hydroxide (M-NiFe-LDH) increases, and the loading amount is 3 mg / cm. 2 The highest performance was achieved at 3 mg / cm 2 To the extent that it is exceeded, performance may be reduced.

[0048] Considering this tendency, the loading amount of the layered double hydroxide (M-NiFe-LDH) per one side of the nickel metal was set to 0.1 mg / cm. 2 More than 0.3mg / cm 2 More than 0.6mg / cm 2 or more, or 1 mg / cm 2 or more and 5 mg / cm 2 Below, 4.5 mg / cm 2 or less than 4 mg / cm 2 It can be controlled within the following range.

[0049] The thickness of the layered double hydroxide (M-NiFe-LDH) can increase in proportion to its loading amount.

[0050] Nickel metal The nickel metal may be nickel foam having a large number of pores therein. For example, the porosity of the nickel metal may be 50 to 200 PPI (pores per inch), specifically 70 to 170 PPI, e.g., 110 PPI.

[0051] The thickness of the nickel metal may be 150 to 350 μm, specifically 200 to 300 μm, for example 250 μm.

[0052] Method for manufacturing an oxidation electrode for anion exchange membrane water electrolysis In another embodiment of the present invention, there is provided a method for manufacturing an oxidation electrode for anion exchange membrane water electrolysis, which includes a series of steps of synthesizing a layered double hydroxide (LDH) containing nickel and iron into a monolayer structure using a bottom-up method, and then depositing nickel metal on one or both sides of the monolayer.

[0053] As a method for synthesizing M-NiFe-LDH, a top-down method and a bottom-up method are considered. Among them, the bottom-up method is used in the embodiment because the manufacturing process is simpler and more efficient than the top-down method.

[0054] Specifically, the method for manufacturing an oxidation electrode according to the embodiment includes the steps of: preparing a raw material mixture solution by adding an alkaline aqueous solution and an aqueous metal solution containing a nickel source and an iron source to an aqueous formamide solution; reacting the raw material mixture solution to produce a monolayer layered double hydroxide (LDH) containing nickel and iron; and coating the layered double hydroxide on one or both sides of a nickel metal.

[0055] In the top-down method, a monolayer NiFe-LDH can be produced from B-NiFe-LDH by increasing the interlayer basal spacing of B-NiFe-LDH through intercalated anion exchange, dispersing it in formamide solvent, and then exfoliating each layer through sonication (exfoliation), which takes a long time of about 1-2 weeks.

[0056] When using this top-down method, the final M-NiFe-LDH is dispersed in a formamide solvent, which can cause problems during the solvent removal process. Formamide is a low-volatility liquid, making it impossible to dry quickly. Therefore, when using the top-down method, there is a fatal problem in that efficient electrode production is impossible.

[0057] In contrast, the bottom-up method simplifies the manufacturing process by producing M-NiFe-LDH through a one-step reaction, and the synthesis can be completed within about an hour, significantly shortening the manufacturing time.

[0058] In addition, when synthesized using the bottom-up method, the final M-NiFe-LDH is dispersed in distilled water, which allows for faster drying compared to the formamide solvent used in the top-down method, enabling efficient electrode production.

[0059] Manufacturing raw material mixture solution The aqueous metal solution may contain, based on a total amount (100% by weight), 0.5 to 1.5% by weight, for example 0.7 to 1.3% by weight, of a nickel source; 0.1 to 1.0% by weight, for example 0.2 to 0.7% by weight, of an iron source; and the remainder being water.

[0060] By adjusting the contents of the nickel source and the iron source, the contents of nickel and iron in the final product (ie, M-NiFe-LDH) can be controlled.

[0061] The nickel source can be nickel nitrate (Ni(NO3)2) or its hydrate (Ni(NO3)2·6H2O), and the iron source can be iron nitrate (Fe(NO3)3) or its hydrate (Fe(NO3)3·9H2O).

[0062] The alkaline aqueous solution may be an aqueous sodium hydroxide solution.

[0063] Specifically, the molar concentration of the aqueous sodium hydroxide solution may be 0.05 to 5 M, for example, 0.1 to 3 M; the remainder may be water.

[0064] The sodium hydroxide solution is used to synthesize the OH - and can adjust the pH to 9 to 11. When the content of sodium hydroxide in the aqueous sodium hydroxide solution satisfies the above range, the desired shape, size, etc. of the catalyst can be obtained.

[0065] The aqueous formamide solution may contain 15 to 40% by volume, for example 20 to 30% by volume, of formamide in a total amount (100% by volume), with the remainder being water.

[0066] The formamide aqueous solution can interact with hydroxide during catalyst synthesis to inhibit growth on the z-axis (layered structure). Therefore, when the formamide content in the formamide aqueous solution satisfies the above range, the layered double hydroxide (M-NiFe-LDH) can be obtained.

[0067] When preparing the raw material mixed solution, 50 to 200 parts by weight, for example, 70 to 130 parts by weight, of the aqueous alkali solution and 50 to 200 parts by weight, for example, 70 to 130 parts by weight, of the aqueous metal solution may be mixed with 100 parts by weight of the aqueous formamide solution.

[0068] Reaction of raw material mixture solution (production of M-NiFe-LDH) During the reaction of the raw material mixed solution, the pH of the raw material mixed solution can be controlled within the range of 9 to 11, for example, 9.5 to 10.5, using the alkaline aqueous solution.

[0069] During the reaction of the mixed solution of raw materials, the pH can affect the final form of the catalyst. As long as the pH is maintained within the above range, the layered double hydroxide (M-NiFe-LDH) is successfully synthesized.

[0070] The reaction of the raw material mixed solution can be carried out within a temperature range of 70 to 90°C, for example, 75 to 85°C.

[0071] During the reaction of the raw material mixture solution, the temperature may affect the rate at which the catalyst is synthesized and may also affect the shape and size of the catalyst.

[0072] The reaction of the raw material mixed solution can be carried out for 1 to 20 minutes, for example, 5 to 15 minutes.

[0073] During the reaction of the raw material mixture solution, the reaction time may affect the crystallinity of the catalyst.

[0074] Post-treatment of the reaction (production of M-NiFe-LDH) After the reaction of the raw material mixed solution, the method may further include washing the layered double hydroxide (M-NiFe-LDH) with a washing solvent; and dispersing the washed layered double hydroxide (M-NiFe-LDH) in water.

[0075] Specifically, the layered double hydroxide (M-NiFe-LDH) is washed with a washing solvent (e.g., a mixture of water and ethanol) to dissolve impurities remaining in the layered double hydroxide (M-NiFe-LDH) in the solvent, and then the solvent containing the dissolved impurities can be removed by centrifugation.

[0076] The washed layered double hydroxide (M-NiFe-LDH) can then be dispersed in water to finally obtain an aqueous solution containing the layered double hydroxide (M-NiFe-LDH) and water.

[0077] Application of M-NiFe-LDH When applying the layered double hydroxide onto one surface of the nickel metal, an aqueous solution containing the layered double hydroxide and water may be applied.

[0078] Alternatively, a Nafion solution may be added to the layered double hydroxide before coating.

[0079] Here, Nafion is dispersed and applied together with the catalyst, so it can act as a binder to prevent the catalyst from being detached during the reaction. The Nafion solution can have a Nafion content of 5 to 10 wt % based on the total amount (100 wt %).

[0080] When applying the layered double hydroxide, a spray drying method can be used.

[0081] Furthermore, when the layered double hydroxide is applied, the nickel metal may be placed on a hot plate at 70 to 90°C.

[0082] The spray drying method is advantageous for uniformly applying the catalyst. In this case, when the temperature of the nickel metal is within the above range, the evaporation rate of the solvent can be well controlled, allowing the catalyst to be uniformly applied.

[0083] Anion exchange membrane water electrolysis cell In another embodiment of the present invention, there is provided an anion exchange membrane water electrolysis cell comprising: an anion exchange membrane; and a reduction electrode and an oxidation electrode located on either side of the anion exchange membrane, respectively, wherein the oxidation electrode is the oxidation electrode of the above-described embodiment.

[0084] This may be because the water electrolysis performance is improved by including the oxidation electrode according to the embodiment described above.

[0085] Hereinafter, the description of the oxidation electrode of the above-described embodiment will be omitted, and the other components will be described in detail.

[0086] FIG. 1 is a diagram showing a water electrolysis cell according to the embodiment.

[0087] The water electrolysis cell of the embodiment may include a potentiostat connected to the reduction electrode and the oxidation electrode, respectively.

[0088] The oxidation electrode may be the oxidation electrode of the above-described embodiment, and the reduction electrode may be a composite electrode of platinum (Pt) and carbon (C) coated on carbon paper.

[0089] Although only one water electrolysis cell is shown in FIG. 1, a water electrolysis stack can be constructed by stacking a plurality of unit cells in series, each unit cell being a single water electrolysis cell.

[0090] The water electrolysis stack may include an electrolyte tank (not shown), which may store an alkaline aqueous solution such as potassium hydroxide (KOH) or sodium hydroxide (NaOH) and supply the alkaline aqueous solution to the anion exchange membrane.

[0091] When an alkaline aqueous solution is supplied from the electrolyte tank to the anion exchange membrane and a DC power supply is applied to the oxidation electrode and the reduction electrode, hydroxide ions (OH - ) reacts catalytically on the surface of the oxidation electrode to generate oxygen, water, and electrons, which can then travel along an external wire to the reduction electrode. On the surface of the reduction electrode, the electrons and water react catalytically to generate hydrogen and hydroxide ions (OH - The oxygen generated at the oxidation electrode and the hydrogen generated at the reduction electrode can be transferred to and stored in a storage tank (not shown) outside the unit cell.

[0092] Other aspects can be realized with reference to water electrolysis cells and water electrolysis stacks that are well known in the art. [Example]

[0093] Preferred examples are presented below to aid in understanding the invention, but the following examples are for illustrative purposes only and are not intended to limit the invention.

[0094] <Production example> Production Example 1: Production of M-NiFe-LDH by bottom-up method Solution A (metal solution) was prepared by dissolving 218.1 mg of Ni(NO3)2·6H2O and 101.0 mg of Fe(NO3)3·9H2O in 20 ml of deionized water, where the metal weight ratio of Ni:Fe was 3:1.

[0095] Separately, Solution B (alkaline aqueous solution) was prepared by dissolving NaOH in 20 ml of ultrapure water (deionized water) at a concentration of 0.25 M.

[0096] The internal temperature of the water bath was set to 80°C.

[0097] A 100 ml round-bottom flask was charged with 15 ml of deionized water and 5 ml of formamide, and the flask was immersed in a water bath whose internal temperature was maintained at 80°C and stirred at 600 rpm to prepare an aqueous formamide solution. The mixture was then left to stand for about 5 minutes.

[0098] Solution A and Solution B were simultaneously added to the round-bottom flask in an air atmosphere at room temperature, while maintaining the pH at 10. Each solution was added drop-by-drop, and the addition was completed within 10 minutes.

[0099] After the addition of each solution was completed, the mixture was stirred at 600 rpm for 10 minutes.

[0100] Then, the mixture was cooled down at room temperature for 30 minutes, and then washed three times with deionized water and once with ethanol using a centrifuge.

[0101] If gel precipitates during washing using the centrifuge, it can be thoroughly dispersed by bath sonication and then washed again.

[0102] After the washing process is completed, the product is dispersed in water and stored, and the concentration can be confirmed by ICP.

[0103] As a result, an aqueous solution containing M-NiFe-LDH and water (hereinafter referred to as "M-NiFe-LDH aqueous solution of Preparation Example 1") was obtained. The solid content in the M-NiFe-LDH aqueous solution of Preparation Example 1 was approximately 88.33 wt% based on 100 wt% of the total aqueous solution.

[0104] Production Example 2: Production of B-NiFe-LDH Solution C was prepared by adding 32 mmol of NiCl2·6H2O and 10.7 mmol of FeCl3 to 40 ml of deionized water and dispersing thoroughly by bath sonication. The metal weight ratio of Ni:Fe was 3:1.

[0105] Separately, Solution D was prepared by dissolving 68.3 mmol of NaOH and 21.3 mmol of Na2CO3 in 40 ml of deionized water.

[0106] 80 ml of deionized water was placed in a 250 ml round bottom flask and stirred at 600 rpm.

[0107] The round-bottom flask was simultaneously charged with Solution C and Solution D in an air atmosphere at room temperature, while maintaining the pH at 8.5.

[0108] After the addition of each solution was completed, the mixture was stirred at 600 rpm for 24 hours.

[0109] Then, the mixture was centrifuged and washed three times with deionized water and once with ethanol.

[0110] After washing using the centrifuge, the mixture was dried in a convection oven at 60° C. for 24 hours.

[0111] Then, the mixture was finely crushed into powder using a pestle and mortar, and then stored under vacuum conditions.

[0112] <Example> Example 1 (1) Fabrication of oxidation electrode 10 mL of the M-NiFe-LDH aqueous solution of Preparation Example 1 and 158.730 mL of a Nafion aqueous solution containing 10 wt % Nafion were placed in a vial and subjected to ultrasonic treatment at 20 Hz for 1 hour.

[0113] A nickel foam with a porosity of 110 PPI and a thickness of 250 μm was placed on a hot plate at 80° C. The ultrasonically treated aqueous solution was uniformly sprayed onto the nickel foam to form a catalyst layer.

[0114] At this time, spraying was performed at a spray rate of 2 L / min using a spray dryer (product name: INFINITY CR plus 0,4 [v2.0], manufacturer: INFINITY), and the loading amount of the catalyst layer per side of the nickel foam was 1.0 mg / cm. 2 An oxidation electrode of Example 1 was produced.

[0115] (2) Manufacturing of anion exchange membrane water electrolysis cells Using the oxidation electrode of Example 1, each water electrolysis cell was manufactured.

[0116] Specifically, the reduction electrode is a carbon paper coated with platinum catalyst-supported carbon (40 wt% Pt / C), and an anion exchange membrane (Sustainion TM , Dioxide Material Co., Ltd.) was used.

[0117] The anion exchange membrane was placed between the two electrodes, with the oxidation electrode and the reduction electrode positioned on either side of the anion exchange membrane to form a stack in this order: oxidation electrode / anion exchange membrane / reduction electrode. A gasket was then placed in place, and the stack was pressurized at a torque of 100 kg f cm to complete the anion exchange membrane water electrolysis cell of Example 1.

[0118] The cell is 5 cm 2The reaction area was 1000 m / s. A titanium block with a single serpentine flow pattern was used as a channel for transporting the reactant (1 M KOH) and product (oxygen) to the oxidation electrode, and a graphite block with a single serpentine flow pattern was used as a channel for transporting the reactant (1 M KOH) and product (hydrogen) to the reduction electrode. This block abutted against a gold-plated current collector, which was connected to a potentiostat. The rest of the process followed the manufacturing method of an anion exchange membrane water electrolysis cell commonly known in the art.

[0119] Example 2 The catalyst layer loading per side of the nickel foam is 2.0 mg / cm 2 An oxidation electrode and an anion exchange membrane water electrolysis cell of Example 2 were manufactured in the same manner as in Example 1, except that the above-mentioned procedure was changed to the above.

[0120] Example 3 The catalyst layer loading per side of the nickel foam is 3.0 mg / cm 2 An oxidation electrode and an anion exchange membrane water electrolysis cell of Example 3 were manufactured in the same manner as in Example 1, except that the above-mentioned procedure was changed to the above.

[0121] Example 4 The catalyst layer loading per side of the nickel foam is 4.0 mg / cm 2 An oxidation electrode and an anion exchange membrane water electrolysis cell of Example 4 were manufactured in the same manner as in Example 1, except that the above-mentioned procedure was changed to the above.

[0122] Comparative Example 1 (1) Fabrication of oxidation electrode 50 mg of the B-NiFe-LDH powder of Preparation Example 2 and 158.730 mL of a Nafion aqueous solution containing 10 wt % Nafion were placed in a vial and subjected to ultrasonic treatment at 20 Hz for 1 hour.

[0123] A nickel foam with a porosity of 110 PPI and a thickness of 250 μm was placed on a hot plate at 80° C. The ultrasonically treated aqueous solution was uniformly sprayed onto the nickel foam to form a catalyst layer.

[0124] At this time, spraying was performed at a spray rate of 2 L / min using a spray dryer (product name: INFINITY CR plus 0,4 [v2.0], manufacturer: INFINITY), and the loading amount of the catalyst layer per side of the nickel foam was 1.0 mg / cm. 2 An oxidation electrode of Comparative Example 1 was produced.

[0125] (2) Manufacturing of anion exchange membrane water electrolysis cells A water electrolysis cell of Comparative Example 1 was prepared in the same manner as in Example 1, except that the oxidation electrode of Comparative Example 1 was used instead of the oxidation electrode of Example 1.

[0126] Comparative Example 2 The loading amount of the catalyst layer per side of the nickel foam is 1.5 mg / cm 2 An oxidation electrode and an anion exchange membrane water electrolysis cell of Comparative Example 2 were manufactured in the same manner as in Comparative Example 1, except that the above-mentioned procedure was changed to the following.

[0127] Comparative Example 3 The catalyst layer loading per side of the nickel foam is 2.0 mg / cm 2 An oxidation electrode and an anion exchange membrane water electrolysis cell of Comparative Example 3 were manufactured in the same manner as in Comparative Example 1, except that the above-mentioned procedure was changed to the following.

[0128] Comparative Example 4 The catalyst layer loading per side of the nickel foam is 3.0 mg / cm 2 An oxidation electrode and an anion exchange membrane water electrolysis cell of Comparative Example 4 were manufactured in the same manner as in Comparative Example 1, except that the above-mentioned procedure was changed to the following.

[0129] Comparative Example 5 An oxidation electrode and an anion exchange membrane water electrolysis cell of Comparative Example 5 were prepared in the same manner as in Comparative Example 1, except that nickel foam itself was used as the oxidation electrode.

[0130] Comparative Example 6 Commercially available iridium oxide (IrOx) was used instead of the M-NiFe-LDH powder of Comparative Example 1. Except for this, an oxidation electrode and an anion-exchange membrane water electrolysis cell of Comparative Example 6 were produced in the same manner as in Comparative Example 1.

[0131] Experimental Example 1: Evaluation of binder for oxidation electrode (1)TEM TEM (Transmission Electron Microscope) images and element distribution images of Preparation Example 1 (M-NiFe-LDH) and Preparation Example 2 (B-NiFe-LDH) were obtained and are shown in FIGS. 4a to 4f.

[0132] Specifically, Figures 4a and 4b are TEM images of Production Example 2 (B-NiFe-LDH), Figure 4c shows the element distribution evaluated on the same scale, and Figures 4d and 4e are TEM images of Production Example 1 (M-NiFe-LDH), Figure 4f shows the element distribution evaluated on the same scale.

[0133] Figures 4a and 4b show that the thickness of Preparation Example 2 (B-NiFe-LDH) is relatively thick, indicating that it exists as a layered structure, whereas Figures 4d and 4e show that the thickness of Preparation Example 1 (M-NiFe-LDH) is relatively thin (~1 nm), indicating that it exists as a monolayer structure.

[0134] (2) XRD FIG. 5 shows XRD patterns of the catalyst (B-NiFe-LDH) of Comparative Example 1 in a powder state, the catalyst (M-NiFe-LDH) of Example 1 dispersed in water to form a colloidal state, and the catalyst (M-NiFe-LDH) of Example 1 dried in an oven to form a powder state.

[0135] For reference, the catalyst (M-NiFe-LDH) of Example 1 is applied in a colloidal form in the manufacturing process of the oxidation electrode, and the catalyst (M-NiFe-LDH) of Example 1 is present in a dried state in the dried oxidation electrode after manufacturing.

[0136] In the XRD pattern, the catalyst (B-NiFe-LDH) of Comparative Example 1 clearly exhibits a (003) peak, whereas the colloidal catalyst (M-NiFe-LDH) of Example 1 does not exhibit a (003) peak. This proves that the growth of NiFe-LDH along the z-axis was suppressed by formamide during the synthesis of the catalyst (M-NiFe-LDH) of Example 1, resulting in the synthesis of a monolayer.

[0137] Meanwhile, when the colloidal catalyst (M-NiFe-LDH) of Example 1 was dried, the single-layer structure was changed to a layered structure through stacking, and a (003) peak similar to that of the catalyst (B-NiFe-LDH) of Comparative Example 1 was observed to be generated. However, the peak intensity was lower than that of the catalyst (B-NiFe-LDH) of Comparative Example 1, which may cause a difference in performance when applied to an anion exchange membrane water electrolysis cell.

[0138] Experimental Example 2: Evaluation of oxidation electrode Scanning electron microscope (SEM) images were obtained for each of the oxidation electrodes of Example 1 and Comparative Example 1 and are shown in FIGS. 6a and 6f.

[0139] The distribution of the catalyst on the electrode surface can be confirmed by SEM.

[0140] Specifically, Figures 6a to 6c are SEM images of the oxidation electrode (B-NiFe-LDH on Ni foam) of Comparative Example 1, and it can be seen that bulk nanoparticles are present in a solidified state.

[0141] In contrast, Figures 6d to 6f are SEM images of the oxidation electrode (M-NiFe-LDH on Ni foam) of Example 1, and show that the monolayer structure of NiFe-LDH is densely attached and has a smooth surface.

[0142] In this regard, the use of M-NiFe-LDH has excellent contact characteristics with nickel metal (specifically, Ni foam) and anion exchange membranes, thereby improving the performance of anion exchange membrane water electrolysis cells.

[0143] More specifically, the performance of the anion exchange membrane water electrolysis cell was evaluated in Experimental Example 3 below.

[0144] Experimental Example 3: Evaluation of anion exchange membrane water electrolysis cell (1) Current-voltage graph The current-voltage graphs of the anion exchange membrane water electrolysis cells of Comparative Examples 1 to 5 are shown in Figure 7a; the current-voltage graphs of the anion exchange membrane water electrolysis cells of Examples 1 to 4 are shown in Figure 7b; and the current-voltage graphs of Example 3, which showed the highest efficiency among the Examples, Comparative Example 3, which showed the highest efficiency among the Comparative Examples, and Comparative Example 5 are shown in Figure 7c. The operating conditions for each were 50°C, 1 A / cm 2 is.

[0145] Here, "Energy conversion efficiency" can be calculated using the following formula: [Formula 1]η[=E]_0 / V [Equation 2] E_0 = -ΔG / ηF [Equation 3] ΔG = ΔH - TΔS In the formulas 1 to 3, η is the energy conversion efficiency, E0 is the thermodynamic voltage required for water electrolysis (H2O → H2 + 1 / 2 O2), V is the measured voltage, ΔG is the free energy that changes after the water electrolysis reaction, n is the number of participating electrons (2), F is the faradaic constant (96485 C / mol).

[0146] Calculations using the above formulas 1 to 3 show that at 50°C, 1 A / cm 2 It can be seen that the maximum efficiency of B-NiFe-LDH is 69.5%, that of M-NiFe-LDH is 71.3%, and that of Ni foam is 53.2% under the same conditions.

[0147] (2) Time-voltage graph The stability of each anion exchange membrane water electrolysis cell was evaluated for Example 3, which showed the highest efficiency among the Examples, Comparative Example 3, which showed the highest efficiency among the Comparative Examples, and Comparative Example 6, which used a commercially available iridium oxide (IrOx) catalyst.

[0148] Specifically, for each anion exchange membrane water electrolysis cell, 50°C, 1 A / cm 2 Galvanostatic experiments were carried out under these conditions to measure the change in overpotential, and the results are shown in Figure 8.

[0149] In FIG. 8, it can be seen that in Comparative Example 6, which used a commercially available iridium oxide (IrOx) catalyst, the overvoltage increased rapidly, resulting in a rapid drop in performance.

[0150] In contrast, in the cases of Example 3 and Comparative Example 3, driving was more stable than in Comparative Example 6. Among them, it can be seen that driving in Example 3 was more stable.

Claims

1. adding an aqueous alkali solution and an aqueous metal solution containing a nickel source and an iron source to an aqueous formamide solution to prepare a raw material mixed solution; reacting the raw material mixture solution to produce a monolayered layered double hydroxide (LDH) containing nickel and iron; and a step of applying the layered double hydroxide to one or both surfaces of a nickel metal.

2. The metal aqueous solution is 2. The method for producing an oxidation electrode for anion exchange membrane water electrolysis according to claim 1, comprising, based on a total amount (100 wt%), 0.5 to 1.5 wt% of a nickel source, 0.1 to 1.0 wt% of an iron source, and the remainder being water.

3. The alkaline aqueous solution is The method for producing an oxidation electrode for anion exchange membrane water electrolysis according to claim 1 , wherein the anion exchange membrane is an aqueous sodium hydroxide solution.

4. The molar concentration of the sodium hydroxide aqueous solution is The method for producing an oxidation electrode for anion exchange membrane water electrolysis according to claim 3, wherein the concentration is 0.05 to 5 M.

5. The formamide aqueous solution is 2. The method for producing an oxidation electrode for anion exchange membrane water electrolysis according to claim 1, wherein the total amount (100% by volume) contains 15 to 40% by volume of formamide and the remainder is water.

6. When producing the raw material mixed solution, 2. The method for producing an oxidation electrode for anion exchange membrane water electrolysis according to claim 1, wherein 50 to 200 parts by weight of the alkaline aqueous solution and 50 to 200 parts by weight of the metal aqueous solution are mixed with 100 parts by weight of the formamide aqueous solution.

7. The reaction of the raw material mixed solution is The anion exchange membrane water electrolysis oxidation electrode according to claim 1, wherein the electrolysis is carried out in a pH range of 9 to 11. Manufacturing method.

8. The reaction of the raw material mixed solution is The method for producing an oxidation electrode for anion exchange membrane water electrolysis according to claim 1, wherein the process is carried out at a temperature within a range of 70 to 90°C.

9. The reaction of the raw material mixed solution is The method for producing an oxidation electrode for anion exchange membrane water electrolysis according to claim 1, wherein the oxidation is carried out for 1 to 20 minutes.

10. After the reaction of the raw material mixed solution, washing the layered double hydroxide with a washing solvent; and The method for producing an oxidation electrode for anion exchange membrane water electrolysis according to claim 1 , further comprising: dispersing the washed layered double hydroxide in water.

11. When applying the layered double hydroxide, The method for producing an oxidation electrode for anion exchange membrane water electrolysis according to claim 1 , wherein a Nafion solution is added to the layered double hydroxide before coating.

12. When applying the layered double hydroxide, The method for producing an oxidation electrode for anion exchange membrane water electrolysis according to claim 1, wherein a spray drying method is used.

13. When applying the layered double hydroxide, 2. The method for manufacturing an oxidation electrode for anion exchange membrane water electrolysis according to claim 1, wherein the nickel metal is placed on a hot plate at 70 to 90°C.

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