Electrode for water electrolysis cell, water electrolysis cell, water electrolysis device, and method for manufacturing electrode for water electrolysis cell

Abstract

The water electrolysis cell electrode 1 comprises a conductive substrate 10, a first layer 11, and a second layer 12. The conductive substrate 10 includes a transition metal. The first layer 11 is disposed on the conductive substrate 10 and includes two or more transition metals and oxygen. The second layer 12 is disposed on the first layer 11 and includes a layered double hydroxide (LDH) that has two or more transition metals. The first layer 11 is disposed between the conductive substrate 10 and the second layer 12 in the thickness direction of the first layer 11. The first layer 11 includes a first transition metal and a second transition metal, wherein the first transition metal is the same kind as the transition metal included in the conductive substrate 10, and the second transition metal is the same kind as the transition metal included in the second layer 12 and is different from the first transition metal. The concentration of the first transition metal in the first layer 11 is higher than the concentration of the first transition metal in the second layer 12.

Description

[Technical field]

[0001] The present disclosure relates to an electrode for a water electrolysis cell, a water electrolysis cell, a water electrolysis device, and a method for manufacturing an electrode for a water electrolysis cell. [Background technology]

[0002] In recent years, there has been a demand for the development of electrodes for use in water electrolysis devices.

[0003] Patent Document 1 describes an electrode for electrolysis of water, in which NiO and a layered double hydroxide of Ni and Fe are formed on a nickel foam electrode substrate.

[0004] Patent Document 2 describes an anode for oxygen generation. In this anode for oxygen generation, a catalyst layer made of NiFe-ns (nanosheet) is formed on the surface of a specific intermediate body. The intermediate body is a nickel expanded mesh anode substrate having a surface on which a catalyst layer made of LiFe-ns (nanosheet) is formed. 0.5 Ni 1.5 An intermediate layer having a composition of O2 is formed.

[0005] Non-Patent Document 1 examines the activity of the oxygen evolution reaction (OER) of an electrode made of Ni-Fe layered double hydride (Ni-Fe LDH).

[0006] Non-Patent Document 2 describes that the local electronic structure of Ni-Fe LDH is adjusted by the interface interaction between FeOOH and Ni-Fe LDH, and the OER electrode catalytic action is enhanced. In alkaline water electrolysis, a problem is the outflow of the electrode catalyst or electrode substrate from the electrode due to the oxidation-reduction of the electrode substrate and the electrode caused by the reverse current generated by repeated operation stop cycles. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2020-12171 A [Patent Document 2] Patent Publication No. 2021-139027 [Non-patent literature]

[0008] [Non-Patent Document 1] Seyeong Lee et al., “Operational durability of three-dimensional Ni-Fe layered double hydroxide electrocatalyst for water oxidation,” Electrochimica Acta, 2019, Vol.315, p.94-101 [Non-Patent Document 2] Jiande Chen et al., “Interfacial Interaction between FeOOH and Ni-Fe LDH to Modulate the Local Electronic Structure for Enhanced OER Electrocatalysis,” ACS Catalysis, 2018, Vol.8, p.11342-11351 Summary of the Invention [Problem to be solved by the invention]

[0009] The descriptions in the above documents need to be reconsidered from the viewpoint of durability of electrodes used in water electrolysis devices. Therefore, the present disclosure provides a novel electrode for a water electrolysis cell that is advantageous from the viewpoint of durability. [Means for solving the problem]

[0010] The present disclosure relates to A conductive substrate containing a transition metal; a first layer including two or more transition metals and oxygen; a second layer comprising a layered double hydroxide having two or more transition metals; the first layer is disposed between the conductive substrate and the second layer in a thickness direction of the first layer, the first layer contains a first transition metal of the same type as the transition metal contained in the conductive substrate, and a second transition metal of the same type as the transition metal contained in the second layer but different from the first transition metal; a concentration of the first transition metal in the first layer is higher than a concentration of the first transition metal in the second layer; An electrode for a water electrolysis cell is provided. Effect of the Invention

[0011] According to the present disclosure, it is possible to provide a novel electrode for a water electrolysis cell that is advantageous in terms of durability. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view that illustrates a schematic diagram of an electrode for a water electrolysis cell according to a first embodiment. [Diagram 2] FIG. 2 is a diagram that illustrates an example of the crystal structure of a layered double hydroxide (LDH). [Diagram 3] FIG. 3 is a diagram illustrating a schematic mechanism for producing an electrode for a water electrolysis cell according to the first embodiment. [Figure 4] FIG. 4 is a cross-sectional view illustrating an example of a water electrolysis cell according to the second embodiment. [Diagram 5] FIG. 5 is a cross-sectional view that illustrates an example of a water electrolysis apparatus according to a third embodiment. [Figure 6A] FIG. 6A is a cross-sectional view illustrating an example of a water electrolysis cell according to a fourth embodiment. [Figure 6B] FIG. 6B is a cross-sectional view that illustrates a schematic diagram of another example of an electrode for a water electrolysis cell. [Figure 7] FIG. 7 is a cross-sectional view illustrating an example of a water electrolysis apparatus according to a fifth embodiment. [Figure 8] FIG. 8 is a transmission electron microscope (TEM) image of the electrode according to Example 1. [Figure 9A] FIG. 9A is a TEM image showing a portion of the electrode according to Example 1 for which electron beam diffraction results were obtained. [Figure 9B] FIG. 9B is an electron beam diffraction image obtained by TEM for the portion of the electrode shown in FIG. 9A. [Figure 10] FIG. 10 is a graph showing the results of line analysis of the electrode according to Example 1 by TEM-energy dispersive X-ray spectroscopy (TEM-EDX). [Figure 11] FIG. 11 is a TEM image of the electrode according to Comparative Example 3. [Figure 12A] FIG. 12A is a TEM image showing a portion of the electrode according to Comparative Example 3 for which an electron beam diffraction result was obtained. [Figure 12B] FIG. 12B is an electron beam diffraction image obtained by TEM for the portion of the electrode shown in FIG. 12A. [Figure 13] FIG. 13 is a graph showing the results of TEM-EDX line analysis of the electrode according to Comparative Example 3. [Figure 14] FIG. 14 is a graph showing the relationship between the OER overpotential and the number of cycles for the electrode according to Example 1 and the electrodes according to Comparative Examples 2 and 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] (Findings on which this disclosure is based) As a measure against global warming, the use of renewable energy such as solar and wind power has been attracting attention. However, power generation using renewable energy has the problem of surplus electricity being wasted. For this reason, the efficiency of renewable energy use is not necessarily sufficient. Therefore, a method of making effective use of surplus electricity by producing and storing hydrogen from the surplus electricity is being studied.

[0014] One method for producing hydrogen from surplus electricity is water electrolysis. To produce hydrogen cheaply and stably, there is a need to develop a highly efficient, long-life water electrolysis device.

[0015] In a water electrolysis device, oxygen is generated at the anode, and hydrogen is generated at the cathode. The reaction in which oxygen is generated at the anode is also called an anode reaction, and the reaction in which hydrogen is generated at the cathode is also called a cathode reaction. In order to provide a highly efficient water electrolysis device, it is desirable that the overvoltage is particularly low at the anode. In addition, it is also desirable that the overvoltage is low at the cathode. Thus, there is a demand for the development of high-performance electrodes for the anode reaction or cathode reaction in water electrolysis.

[0016] For example, LDH is considered to be a promising material for electrodes for water electrolysis cells in terms of its large specific surface area and various combinations of metal ions. In this case, it is considered to support LDH on a conductive substrate. For example, as described in Patent Document 1 and the like, it is considered to support LDH on a substrate such as nickel foam. However, this technology has room for reexamination in terms of durability against electrode reactions in water decomposition. As a result of extensive research, the present inventors have newly discovered that the durability of electrodes for water electrolysis cells is increased by the presence of a specific layer between a layer containing LDH and a conductive substrate, and have completed the electrode for water electrolysis cells disclosed herein.

[0017] Hereinafter, the embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments. The embodiments described below are all comprehensive or specific examples. Therefore, the numerical values, shapes, materials, components, arrangement positions and connection forms of the components shown in the following embodiments are examples and are not intended to limit the present disclosure. In addition, among the components in the following embodiments, components that are not described in the independent claims showing the highest concept are described as optional components. In addition, in the drawings, the description of components with the same reference numerals may be omitted. In addition, the drawings are schematic diagrams of each component for ease of understanding, and the shapes and dimensional ratios may not be displayed accurately.

[0018] (First embodiment) FIG. 1 is a cross-sectional view that typically illustrates a water electrolysis cell electrode according to a first embodiment. As illustrated in FIG. 1, the water electrolysis cell electrode 1 includes a conductive substrate 10, a first layer 11, and a second layer 12. The first layer 11 is disposed between the conductive substrate 10 and the second layer 12 in the thickness direction. The conductive substrate 10 includes a transition metal. The first layer 11 is disposed on the conductive substrate 10, and includes two or more kinds of transition metals and oxygen. The second layer 12 is disposed on the first layer 11, and includes a layered double hydroxide (LDH) having two or more kinds of transition metals. The first layer 11 includes a first transition metal of the same type as the transition metal contained in the conductive substrate 10, and a second transition metal of the same type as the transition metal contained in the second layer 12 but different from the first transition metal. The concentration of the first transition metal in the first layer 11 is higher than the concentration of the first transition metal in the second layer 12. 1 , the first layer 11 is present between the second layer 12 containing LDH and the conductive substrate 10 in the thickness direction of the first layer 11. Specifically, the second layer 12 containing LDH is bonded to the conductive substrate 10 via the first layer 11. This makes it easier for the second layer 12 to be firmly fixed to the conductive substrate 10, and makes it easier for the water electrolysis cell electrode 1 to exhibit high durability.

[0019] In the water electrolysis cell electrode 1, the thickness of the first layer 11 is not limited to a specific value. The first layer 11 has a thickness of, for example, 10 nm or less. This makes it easier for the water electrolysis cell electrode 1 to exhibit high durability and high electrode activity. The thickness of the first layer 11 can be determined, for example, by performing a TEM-EDX line analysis on a region including the second layer 12, the first layer 11, and the conductive substrate 10 in a TEM image of a cross section of the water electrolysis cell electrode 1. In the results of the TEM-EDX line analysis, the thickness of the first layer 11 can be determined by focusing on the counts of the first transition metal, the second transition metal, and oxygen. The thickness of the first layer 11 is, for example, 1 nm or more.

[0020] In the water electrolysis cell electrode 1, the first transition metal and the second transition metal are not limited to specific metals. The first transition metal is, for example, Ni. The second transition metal is, for example, a transition metal selected from the group consisting of V, Cr, Mn, Fe, Co, Cu, W, and Ru. With this configuration, the water electrolysis cell electrode 1 is more likely to exhibit high durability while having high electrode activity.

[0021] In the water electrolysis cell electrode 1, the second transition metal is preferably Fe. In this case, the water electrolysis cell electrode 1 is more likely to have high electrode activity and high durability. In addition, the production cost of the water electrolysis cell electrode 1 is likely to be low.

[0022] The conductive substrate 10 is not limited to a specific substrate as long as it contains a first transition metal and has conductivity. The conductive substrate 10 may contain a metal other than the first transition metal, or may contain a resin. The conductive substrate 10 may be entirely made of metal. The conductive substrate 10 may have a configuration in which a surface layer containing a metal is formed on a resin member such as polypropylene or polyethylene. In this case, the surface layer containing a metal may be a plating film or a sputtering film. The metal contained in the conductive substrate 10 may be a pure metal such as nickel, or an alloy such as stainless steel or Inconel. Inconel is a registered trademark.

[0023] The surface of the conductive substrate 10 preferably contains at least one selected from the group consisting of nickel and nickel oxide. In this case, the conductive substrate 10 is likely to have high alkali resistance. When the surface of the conductive substrate 10 contains at least one selected from the group consisting of nickel and nickel oxide, the entire conductive substrate 10 may be made of nickel. The conductive substrate 10 may have a surface layer containing at least one selected from the group consisting of nickel and nickel oxide. The surface layer is, for example, a sputtered film or a plated film.

[0024] When the surface of the conductive substrate 10 contains at least one selected from the group consisting of nickel and nickel oxide, nickel and nickel oxide may have a predetermined orientation.

[0025] The shape of the conductive substrate 10 is not limited to a specific shape. The conductive substrate 10 may have a non-porous structure such as a plate and a foil, or may have a porous structure such as a mesh, a foam, and a non-woven fabric. The conductive substrate 10 may be particles such as metal particles. The conductive substrate 10 preferably has a porous structure. In this case, the surface area of the conductive part in the conductive substrate 10 tends to be large, and the electrode 1 for a water electrolysis cell tends to have high electrode activity. In addition, it is easy to prevent the gas generated in the water electrolysis reaction from escaping.

[0026] The thickness of the conductive substrate 10 is not limited to a specific value. The conductive substrate 10 is, for example, 0.02 mm or more. In this case, the handling of the conductive substrate 10 tends to be easy. The thickness of the conductive substrate 10 is, for example, 10 mm or less.

[0027] As described above, the second layer 12 contains LDH. FIG. 2 is a diagram schematically showing an example of the crystal structure of LDH. LDH20 is active with respect to the generation reaction of gases such as hydrogen and oxygen at the anode or cathode of the water electrolysis cell. For example, in alkaline water electrolysis, LDH20 can be changed to a hydroxide by the water electrolysis reaction.

[0028] LDH20 has, for example, a composition represented by the following formula (1). In formula (1), M1 2+ is a divalent transition metal ion. M2 3+ is a trivalent transition metal ion. A n- is an interlayer anion. x is a rational number satisfying the condition 0 <x <1. y is a number corresponding to the required amount of charge balance. n is an integer. m is an appropriate rational number. [M1 2+ 1-x M2 3+ x (OH)2][yA n-·mH2O] Formula (1)

[0029] The two or more transition metals in LDH20 are not limited to a specific transition metal. In other words, M1 and M2 in the composition shown in formula (1) are not limited to a specific transition metal. The two or more transition metals include, for example, at least two selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. In this case, the water electrolysis cell electrode 1 is likely to have high electrode activity.

[0030] The two or more transition metals in LDH20 include, for example, Ni and Fe, and may be, for example, in the composition shown in formula (1), where M1 is Ni and M2 is Fe. In this case, the water electrolysis cell electrode 1 is more likely to have high electrode activity.

[0031] Interlayer anions, A n- may be an inorganic ion or an organic ion. An example of an inorganic ion is CO3 2- , NO3 - , Cl - , SO4 2- , Br - , O.H. - , F - , I - , Si2O5 2- , B4O5(OH)4 2- , and PO4 3- An example of an organic ion is CH3(CH2) n SO 4- , CH3(CH2) n COO - , CH3(CH2) n PO 4- , and CH3(CH2) n NO 3- A n- can be inserted between the metal hydroxide layers along with water molecules. n- The charge and ion size of LDH20 are not limited to a specific value. n- may contain multiple types of A n- may also include

[0032] As shown in Figure 2, LDH20 is a 2+ Or M2 3+ At each vertex of the octahedron with - LDH20 has [M1 2+ 1-x M2 3+ x (OH)2] x+ The metal hydroxide layer is composed of a layer structure in which hydroxide octahedra are connected two-dimensionally by sharing edges. Between the metal hydroxide layers, anions A n- and water molecules are present. The metal hydroxide layer functions as a host layer 21, and the anions A n- and a guest layer 22 containing water molecules is disposed between the host layers 21. In other words, the LDH 20 as a whole is composed of a host layer 21 of a metal hydroxide and an anion A n- The LDH 20 has a sheet-like structure in which the guest layer 22 of water molecules and the guest layer 23 of metal hydroxide are alternately laminated. 2+ Part of M2 3+ It has a structure substituted with:

[0033] The second layer 12 may contain a chelating agent. The chelating agent may be coordinated to a transition metal ion contained in the LDH 20. This makes it easier to synthesize the LDH 20 to have a small particle size in the formation of the second layer 12. This makes it easier for the specific surface area of ​​the LDH 20 to be increased, and makes it easier for the water electrolysis cell electrode 1 to have high electrode activity. The chelating agent is a ligand having multiple conformations, that is, a multidentate ligand.

[0034] The chelating agent is not limited to a specific chelating agent. The chelating agent is, for example, an organic compound capable of coordinating with a transition metal ion in LDH20. The chelating agent may be at least one selected from the group consisting of bidentate organic ligands and tridentate organic ligands. Examples of the chelating agent are β-diketones, β-ketoesters, hydroxycarboxylic acids, and hydroxycarboxylates. Examples of β-diketones are acetylacetone (ACAC), trifluoroacetylacetone, hexafluoroacetylacetone, benzoylacetone, thenoyltrifluoroacetone, dipyrrolylmethane, dibenzoylmethane, and ascorbic acid. Examples of β-ketoesters are methyl acetoacetate, ethyl acetoacetate, allyl acetoacetate, benzyl acetoacetate, n-propyl acetoacetate, iso-propyl acetoacetate, n-butyl acetoacetate, iso-butyl acetoacetate, tert-butyl acetoacetate, 2-methoxyethyl acetoacetate, and methyl 3-oxopentanoate. Examples of hydroxycarboxylic acids and their salts are tartaric acid, citric acid, malic acid, gluconic acid, ferulic acid, lactic acid, glucuronic acid, and their salts.

[0035] The chelating agent preferably contains at least one selected from the group consisting of acetylacetone and citrate. In this case, the water electrolysis cell electrode 1 is more likely to have high electrode activity. An example of the citrate is trisodium citrate.

[0036] The thickness of the second layer 12 is not limited to a specific value. The second layer 12 has a thickness of, for example, 35 nm or more. With such a configuration, the water electrolysis cell electrode 1 is more likely to have high electrode activity. The second layer 12 includes a portion having a thickness of, for example, 35 nm or more. The thickness of the second layer 12 can be determined, for example, by TEM observation of a cross section of the water electrolysis cell electrode 1. The thickness of the second layer 12 is, for example, 210 nm or less.

[0037] The second layer 12 covers, for example, the surface of the conductive substrate 10. The coverage of the second layer 12 with respect to the surface of the conductive substrate 10 is not limited to a specific value. The coverage is preferably 99% or more. In this case, the water electrolysis cell electrode 1 is more likely to have high electrode activity. In addition, the water electrolysis cell electrode 1 is more likely to have high durability. The coverage can be determined, for example, according to the method described in the Examples.

[0038] There is no particular limitation on the method for producing the water electrolysis cell electrode 1. The water electrolysis cell electrode 1 can be produced, for example, according to a method including the following (I) and (II). (I) Mixing of the solution S is promoted while the conductive substrate 10 containing a first transition metal is immersed in the solution S containing a second transition metal different from the first transition metal and chloride ions. (II) A layer including an LDH having a second transition metal and a third transition metal different from the second transition metal is formed on the conductive substrate 10 .

[0039] In the above step (I), an interaction may occur between the first transition metal contained in the conductive substrate 10 and the second transition metal and chloride contained in the solution S. This makes it easier to form a layer for firmly fixing the layer containing LDH formed in step (II) to the conductive substrate 10. As a result, the water electrolysis cell electrode 1 is more likely to exhibit high durability.

[0040] The mixing of the solution S can be promoted by, for example, vibrating the conductive substrate 10, shaking the container in which the solution S and the conductive substrate 10 are enclosed, or stirring the solution S using a stirrer piece or a stirrer. Such a method can generate forced convection of the solution S, promoting the mixing of the solution S.

[0041] The temperature of the solution S in step (I) is not limited to a specific temperature. The temperature of the solution S in step (I) is, for example, room temperature of 20° C.±15° C. In this case, a water electrolysis cell electrode 1 having high electrode activity is easily obtained.

[0042] The solvent of the solution S may be water, an organic solvent, or a mixed solvent of water and an organic solvent.

[0043] The solution S may further contain, for example, a chelating agent, which tends to reduce the particle size of the LDH synthesized in step (II) and tends to increase the specific surface area of ​​the LDH 20. The water electrolysis cell electrode 1 is more likely to have high electrode activity.

[0044] When the solution S contains a chelating agent, the solution S may further contain a third transition metal. In this case, a complex formed by the third transition metal contained in the solution S and the chelating agent may contribute to the synthesis of LDH20.

[0045] When the solution S contains a chelating agent, the third transition metal may be the same type of transition metal as the first transition metal, which tends to simplify the method of producing the water electrolysis cell electrode 1.

[0046] The chelating agent contained in solution S may be selected with reference to the above examples of the chelating agent contained in the second layer 12. The chelating agent contained in solution S preferably contains at least one selected from the group consisting of acetylacetone and citrate. This increases the stability of the dispersion of the complex in solution S, making it easier for the second layer 12 to be formed in a desired state in the water electrolysis cell electrode 1. As a result, the water electrolysis cell electrode 1 is more likely to have high electrode activity.

[0047] In the step (II), the method for forming the layer containing LDH is not limited to a specific method. For example, the layer containing LDH can be formed by adjusting the solution S to be alkaline. This makes it easier for the water electrolysis cell electrode 1 to exhibit high durability.

[0048] The method of adjusting the solution S to be alkaline is not limited to a specific method. For example, the solution S may be mixed with an alkaline solution to adjust the solution to be alkaline. Alternatively, a pH-raising agent may be added to the solution to adjust the solution to be alkaline. In this case, the pH-raising agent is not limited to a specific compound. The pH-raising agent is, for example, a compound having an epoxy group. Examples of the pH-raising agent are propylene oxide, ethylene oxide, and butylene oxide.

[0049] When a pH-raising agent having an epoxy group such as propylene oxide is added to the solution S, the pH-raising agent may capture hydrogen ions present in the solution S in the presence of a nucleophile such as chloride ions, accompanying a ring-opening reaction of the epoxy group. As a result, the pH of the solution S increases, and the solution S may have an alkaline property. The pH of the solution S is, for example, 1. When a pH-raising agent is added to this solution S, the pH of the solution S may increase gradually from, for example, 1, and finally, the solution S may have an alkaline property. The final pH of the solution S is, for example, 8 or more and 12 or less. The addition of the pH-raising agent to the solution progresses a reaction in which hydrogen ions in the solution S are captured. As a result, the pH of the solution S gradually increases. The time from the addition of the pH-raising agent to the solution S until the pH of the solution S reaches a steady state is not limited to a specific time. The time may be, for example, 24 hours or more, and may be several days.

[0050] The temperature of the solution S when the solution S is adjusted to be alkaline is not limited to a specific temperature. The temperature of the solution S is, for example, room temperature of 20° C.±15° C. In this case, a water electrolysis cell electrode 1 having high electrode activity is easily obtained.

[0051] In the above-mentioned production method, the first transition metal and the second transition metal are not limited to a specific transition metal. For example, the first transition metal is Ni, and the second transition metal is a transition metal selected from the group consisting of V, Cr, Mn, Fe, Co, Cu, W, and Ru. In this case, a water electrolysis cell electrode that has high electrode activity and is more likely to exhibit high durability can be produced.

[0052] The second transition metal is preferably Fe. In this case, a water electrolysis cell electrode that has high electrode activity and is more likely to exhibit high durability can be produced.

[0053] When the first transition metal is Ni and the second transition metal is Fe, for example, a reaction represented by the following formula (2) may occur in step (I). This may cause etching of the conductive substrate 10. In addition, in step (I), the Fe contained in the solution S may be 3+ is diffused near the surface of the conductive substrate 10. 3+ Part of and Ni 2+ It is believed that a part of the Ni, Fe, and oxygen may form a layer containing Ni, Fe, and oxygen on the surface of the conductive substrate 10. Then, in step (II), a layer containing LDH is formed on this layer. This results in a water electrolysis cell electrode 1 in which a layer containing Ni, Fe, and oxygen is formed between the layer containing LDH and the conductive substrate 10. 4Ni 2+ Cl - 2+ 2Fe 3+ Cl - 3+ 2Ni→5Ni 2+ Cl - 2+ 2Fe 2+ Cl - 2+ 1Ni Equation (2)

[0054] When the first transition metal is Ni and the second transition metal is Fe, the molar ratio of the Fe ion content to the Ni content in the conductive substrate 10 in the production of the water electrolysis cell electrode 1 is not limited to a specific value. The molar ratio is, for example, 0.75 or less. In this case, it is possible to prevent the nickel in the conductive substrate 10 from being dissolved by the reaction shown in formula (2), which would make it difficult to produce the water electrolysis cell electrode 1.

[0055] The molar ratio is preferably 0.05 to 0.25. In this case, a layer containing Ni, Fe, and oxygen is likely to be formed in a desired state on the surface of the conductive substrate 10, and a water electrolysis cell electrode 1 having high durability is likely to be obtained. In addition, the second layer 12 is likely to be formed uniformly on the conductive substrate 10, and a water electrolysis cell electrode 1 having high electrode activity is more likely to be produced.

[0056] When the first transition metal is Ni and the second transition metal is Fe, the value obtained by dividing the molar content of Fe ions by the surface area of ​​the conductive substrate 10 in the production of the water electrolysis cell electrode 1 is not limited to a specific value. The value is, for example, 0.29 mmol / cm 2 In this case, it is possible to prevent the nickel contained in the conductive base material 10 from dissolving due to the reaction shown in formula (2), which would make it difficult to manufacture the water electrolysis cell electrode 1.

[0057] The molar content of Fe ions divided by the surface area of ​​the conductive substrate 10 is preferably 0.01 mmol / cm 2 to 0.1 mmol / cm 2 In this case, a layer containing Ni, Fe, and oxygen is likely to be formed in a desired state on the surface of the conductive substrate 10, and a water electrolysis cell electrode 1 having high durability is likely to be obtained. In addition, the second layer 12 is likely to be formed uniformly on the conductive substrate 10, and a water electrolysis cell electrode 1 having high electrode activity is more likely to be produced.

[0058] 3 is a diagram illustrating an example of the mechanism for producing the electrode for a water electrolysis cell according to the first embodiment. As illustrated in FIG. 3, a conductive substrate 10 is immersed in a solution S containing ions TM2 of a second transition metal, chloride ions (not shown), ions TM3 of a third transition metal, and a chelating agent 30. For example, the ions TM2 of the second transition metal are Fe 3+ and the third transition metal ion TM3 is Ni 2+The conductive substrate 10 contains, for example, Ni as the first transition metal. Due to the action of the ions TM2, in step (I), the ions TM2 of the second transition metal contained in the solution S diffuse near the surface of the conductive substrate 10. As a result, the conductive substrate 10 is etched, the first transition metal contained in the conductive substrate 10 is dissolved into the solution S, and ions TM1 of the first transition metal derived from the conductive substrate 10 are generated. As the ions TM2 diffuse near the surface of the conductive substrate 10, a layer containing, for example, Fe, Ni, and oxygen can be formed along the surface of the conductive substrate 10. In this example, the ions TM1 and TM3 are both Ni. 2+ However, the ions TM1 and TM3 may be different kinds of transition metal ions. A part of the chelating agent 30 contained in the solution S reacts with the ions TM1 of the first transition metal eluted from the conductive substrate 10, and a complex C1 between the ions TM1 of the first transition metal derived from the conductive substrate 10 and the chelating agent 30 is formed. In addition, a complex C2 between the ions TM2 of the second transition metal and the chelating agent 30 and a complex C3 derived from the ions TM3 of the third transition metal derived from the solution S and the chelating agent 30 are formed. Next, when the solution S is adjusted to be alkaline, the complexes C1, C2, and C3 react on the surface of the conductive substrate 10, and the LDH 20 is synthesized along the surface of the conductive substrate 10. Since the complexes C1, C2, and C3 contain the chelating agent 30, the crystal growth of the LDH 20 is suppressed by the effect of the chelating agent 30. As a result, a second layer 12 containing the LDH 20 and the chelating agent 30 is formed on the conductive substrate 10, and an electrode 1 for a water electrolysis cell is obtained.

[0059] The water electrolysis cell electrode 1 according to this embodiment can be used, for example, as an electrode of a water electrolysis cell in an alkaline water electrolysis device or an anion exchange membrane type water electrolysis device. The water electrolysis cell electrode 1 is used, for example, in at least one selected from the group consisting of an anode and a cathode in these water electrolysis devices. This tends to increase the activity of the anode reaction or cathode reaction in water electrolysis.

[0060] Second embodiment Fig. 4 is a cross-sectional view illustrating an example of a water electrolysis cell according to the second embodiment. As illustrated in Fig. 2, the water electrolysis cell 2 includes an anode 2a, a cathode 2b, and a diaphragm 2p. At least one selected from the group consisting of the anode 2a and the cathode 2b includes, for example, the water electrolysis cell electrode 1 according to the first embodiment. In this case, the activity of the anode reaction or the cathode reaction in the water electrolysis cell 2 is likely to be high, and the anode 2a or the cathode 2b is likely to exhibit high durability.

[0061] The water electrolysis cell 2 is, for example, an alkaline water electrolysis cell that uses an alkaline aqueous solution. The alkaline aqueous solution used in the water electrolysis cell 2 is not limited to a specific alkaline aqueous solution. Examples of the alkaline aqueous solution include an aqueous potassium hydroxide solution and an aqueous sodium hydroxide solution.

[0062] 4, the water electrolysis cell 2 includes, for example, an electrolytic cell 2s, a first chamber 2m, and a second chamber 2n. The diaphragm 2p is disposed inside the electrolytic cell 2s and separates the inside of the electrolytic cell 2s into the first chamber 2m and the second chamber 2n. The anode 2a is disposed in the first chamber 2m, and the cathode 2b is disposed in the second chamber 2n.

[0063] The diaphragm 2p is, for example, a diaphragm for alkaline water electrolysis. The diaphragm 2p is, for example, a sheet-like porous membrane. The diaphragm 2p has a thickness of, for example, 100 μm to 500 μm and has holes that serve as passages for ions or an electrolyte. The material of the diaphragm 2p is not limited to a specific material. Examples of the material of the diaphragm 2p are asbestos, polymer-reinforced asbestos, potassium titanate bound with polytetrafluoroethylene (PTFE), zirconia bound with PTFE, and antimonic acid and antimony oxide bound with polysulfone. Other examples of the material of the diaphragm 2p are sintered nickel, nickel coated with ceramics and nickel oxide, and polysulfone. The diaphragm 2p may be Zirfon Perl UTP 500 manufactured by AGFA.

[0064] The anode 2a may be disposed in a zero-gap state in which it is in contact with the diaphragm 2p, or may be disposed with a gap between it and the diaphragm 2p. The cathode 2b may be disposed in a contact state with the diaphragm 2p, or may be disposed with a gap between it and the diaphragm 2p.

[0065] The water electrolysis cell 2 electrolyzes an alkaline aqueous solution to produce hydrogen and oxygen. An aqueous solution containing a hydroxide of an alkaline metal or an alkaline earth metal is supplied to the first chamber 2m. In addition, an alkaline aqueous solution can be supplied to the second chamber 2n. Electrolysis is performed while an alkaline aqueous solution of a predetermined concentration is discharged from the first chamber 2m and the second chamber 2n, and hydrogen and oxygen are produced.

[0066] When the anode 2a includes the water electrolysis cell electrode 1, the cathode 2b may include, for example, an electrode material known as a cathode for an alkaline water electrolysis cell.

[0067] In the water electrolysis cell 2, when the cathode 2b includes the water electrolysis cell electrode 1, the anode 2a may include an electrode material known as an anode for an alkaline water electrolysis cell. In the water electrolysis cell 2, both the anode 2a and the cathode 2b may include the water electrolysis cell electrode 1.

[0068] According to the above configuration, at least one selected from the group consisting of the anode 2a and the cathode 2b includes the water electrolysis cell electrode 1, so that the water electrolysis cell 2 can exhibit high durability.

[0069] Third embodiment Fig. 5 is a cross-sectional view illustrating an example of a water electrolysis apparatus according to the third embodiment. As illustrated in Fig. 5, the water electrolysis apparatus 3 includes the water electrolysis cell 2 according to the second embodiment and a voltage applicator 40. The voltage applicator 40 applies a voltage between the cathode 2b and the anode 2a. The water electrolysis apparatus 3 is an alkaline water electrolysis apparatus that uses an alkaline aqueous solution.

[0070] The voltage applicator 40 is electrically connected to the anode 2a and the cathode 2b. The voltage applicator 40 makes the potential of the anode 2a higher than the potential of the cathode 2b. The voltage applicator 40 is not limited to a specific type of voltage applicator as long as it can apply a voltage between the anode 2a and the cathode 2b. The voltage applicator 40 may be a device that adjusts the voltage applied between the anode 2a and the cathode 2b. When the voltage applicator 40 is connected to a DC power source such as a battery, a solar cell, or a fuel cell, the voltage applicator 40 includes, for example, a DC / DC converter. When the voltage applicator 40 is connected to an AC power source such as a commercial power source, the voltage applicator 40 includes, for example, an AC / DC converter. The voltage applicator 40 may be, for example, a power-type power source. In the power-type power source, the voltage applied between the anode 2a and the cathode 2b and the current flowing between the anode 2a and the cathode 2b are adjusted so that the power supplied to the water electrolysis device 3 becomes a predetermined set value.

[0071] With the above configuration, the water electrolysis apparatus 3 can exhibit high durability.

[0072] (Fourth embodiment) Fig. 6A is a cross-sectional view illustrating an example of a water electrolysis cell according to the fourth embodiment. As illustrated in Fig. 6A, the water electrolysis cell 4 includes an anode 4a, a cathode 4b, and an anion exchange membrane 4p. In the water electrolysis cell 4, at least one selected from the group consisting of the anode 4a and the cathode 4b includes, for example, the water electrolysis cell electrode 1 according to the first embodiment. In this case, the activity of the anode reaction or the cathode reaction in the water electrolysis cell 4 is likely to be high, and the anode 4a or the cathode 4b is likely to exhibit high durability.

[0073] The water electrolysis cell is, for example, an anion exchange membrane (AEM) type water electrolysis cell. As shown in Fig. 6A, the anode 4a includes, for example, a catalyst layer 4m and a gas diffusion layer 4n. The cathode 3b includes, for example, a catalyst layer 4j and a gas diffusion layer 4k. The catalyst layer 4m of the anode 4a is in contact with one main surface of the anion exchange membrane 4p, and the catalyst layer 4j of the cathode 4b is in contact with the other main surface of the anion exchange membrane 4p.

[0074] The anion exchange membrane 4p is not limited to a specific type of anion exchange membrane. The anion exchange membrane 4p has conductivity of anions such as hydroxide ions. The anion exchange membrane 4p can prevent the oxygen gas generated at the anode 4a from mixing with the hydrogen gas generated at the cathode 4b. The oxygen gas passes through the gas diffusion layer 4n and is led to the outside of the anode 4a. The hydrogen gas passes through the gas diffusion layer 4k and is led to the outside of the cathode 4b.

[0075] In the water electrolysis cell 4, when the anode 4a includes the water electrolysis cell electrode 1, the cathode 4b may be a known cathode for AEM-type water electrolysis cells.

[0076] In the water electrolysis cell 4, when the cathode 4b includes the water electrolysis cell electrode 1, the anode 4a may be a known anode for an AEM-type water electrolysis cell. In the water electrolysis cell 4, both the anode 4a and the cathode 4b may include the water electrolysis cell electrode 1.

[0077] According to the above configuration, at least one selected from the group consisting of the anode 4a and the cathode 4b includes the water electrolysis cell electrode 1, so that the water electrolysis cell 4 can exhibit high durability.

[0078] FIG. 6B shows another example of the water electrolysis cell electrode 1 in the fourth embodiment. As shown in FIG. 6B, the water electrolysis cell electrode 1 includes a conductive substrate 10, a first layer 11, and a second layer 12. The first layer 11 is disposed between the conductive substrate 10 and the second layer 12 in the thickness direction. The conductive substrate 10 is, for example, a metal particle, and the surface of the metal particle, which is the conductive substrate 10, is covered with the second layer 12 containing LDH with the first layer 11 interposed between the surface of the metal particle and the second layer 12. The entire surface of the metal particle may be covered with the second layer 12 containing LDH, or only a part of the surface of the metal particle may be covered with the second layer 12 containing LDH. The second layer 12 covers, for example, 70% or more of the surface of the metal particle, which is the conductive substrate 10. The second layer 12 may cover most of the surface of the metal particle, which is the conductive substrate 10, specifically 90% or more. The water electrolysis cell electrode 1 may have a cross section whose surface is covered with LDH. In the water electrolysis cell electrode 1, the ratio of the mass of the metal particles to the mass of the LDH is not limited to a specific value. The ratio is, for example, 8.0 or less. With this configuration, the water electrolysis cell electrode 1 is more likely to have high durability.

[0079] The metal particles of the conductive base material 10 contain one or more types of transition metals. Examples of the transition metals are V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. The metal particles may contain Ni, or may be Ni particles. The transition metal contained in the metal particles 11 may be the same type of metal as the two or more types of transition metals contained in the LDH of the second layer 12.

[0080] The shape of the metal particles that are the conductive substrate 10 is not limited to a specific shape. The shape of the metal particles is, for example, granular. When the shape of the metal particles is granular, the average particle size of the metal particles is not limited to a specific value. The average particle size of the metal particles may be 100 nm or less, or 50 nm or less. The average particle size of the metal particles may be 10 nm or more, or 20 nm or more. The metal particles may have an average particle size that can support a sufficient amount of LDH, for example. As a result, even when a voltage is applied to the water electrolysis cell electrode 1, the second layer 12 containing LDH and the metal particles that are the conductive substrate 10 are unlikely to separate, so that the water electrolysis cell electrode 1 is more likely to have high durability. In addition, according to this configuration, the water electrolysis cell electrode 1 can more reliably have high durability, for example, in the anode reaction of water electrolysis. The average particle size of the metal particles can be determined by observing the metal particles using, for example, a transmission electron microscope (TEM). Specifically, the average particle size can be determined as the arithmetic mean of the particle sizes of any 50 metal particles for which the entire metal particle can be observed, after defining the average of the maximum and minimum diameters as the particle size of each metal particle.

[0081] Fifth embodiment Fig. 7 is a cross-sectional view illustrating an example of a water electrolysis apparatus according to a fifth embodiment. As illustrated in Fig. 7, the water electrolysis apparatus 5 includes a water electrolysis cell 4 and a voltage applicator 40. The voltage applicator 40 applies a voltage between the cathode 4b and the anode 4a. The water electrolysis apparatus 5 is, for example, an AEM type water electrolysis apparatus.

[0082] The voltage applicator 40 is electrically connected to the anode 4a and the cathode 4b. The voltage applicator 40 makes the potential of the anode 4a higher than the potential of the cathode 4b. The voltage applicator 40 is not limited to a specific type of voltage applicator as long as it can apply a voltage between the anode 4a and the cathode 4b. The voltage applicator 40 may be a device that adjusts the voltage applied between the anode 4a and the cathode 4b. When the voltage applicator 40 is connected to a DC power source such as a battery, a solar cell, or a fuel cell, the voltage applicator 40 includes, for example, a DC / DC converter. When the voltage applicator 40 is connected to an AC power source such as a commercial power source, the voltage applicator 40 includes, for example, an AC / DC converter. The voltage applicator 40 may be, for example, a power-type power source. In the power-type power source, the voltage applied between the anode 4a and the cathode 4b and the current flowing between the anode 4a and the cathode 4b are adjusted so that the power supplied to the water electrolysis device 5 becomes a predetermined set value.

[0083] With the above configuration, the water electrolysis device 5 can exhibit high performance.

[0084] (Additional Note) From the above description, the following techniques are disclosed. (Technology 1) A conductive substrate containing a transition metal; a first layer including two or more transition metals and oxygen; a second layer comprising a layered double hydroxide having two or more transition metals; the first layer is disposed between the conductive substrate and the second layer in a thickness direction of the first layer, the first layer contains a first transition metal of the same type as the transition metal contained in the conductive substrate, and a second transition metal of the same type as the transition metal contained in the second layer but different from the first transition metal; a concentration of the first transition metal in the first layer is higher than a concentration of the first transition metal in the second layer; Electrode for water electrolysis cells. (Technology 2) The conductive substrate has a porous structure. An electrode for a water electrolysis cell according to claim 1. (Technology 3) The first layer has a thickness of 10 nm or less. An electrode for a water electrolysis cell according to claim 1 or 2. (Technology 4) The second layer has a thickness of 35 nm or more. An electrode for a water electrolysis cell according to any one of claims 1 to 3. (Technology 5) the second layer comprises a chelating agent; An electrode for a water electrolysis cell according to any one of claims 1 to 4. (Technology 6) The chelating agent includes at least one selected from the group consisting of acetylacetone and citrate. An electrode for a water electrolysis cell according to claim 5. (Technology 7) The first transition metal is Ni; The second transition metal is a transition metal selected from the group consisting of V, Cr, Mn, Fe, Co, Cu, W, and Ru; An electrode for a water electrolysis cell according to any one of claims 1 to 6. (Technology 8) The second transition metal is Fe; An electrode for a water electrolysis cell according to claim 7. (Technology 9) An anode; A cathode; a diaphragm; At least one selected from the group consisting of the anode and the cathode includes the water electrolysis cell electrode according to any one of techniques 1 to 8. water electrolysis cell. (Technology 10) An anode; A cathode; an anion exchange membrane, At least one selected from the group consisting of the anode and the cathode includes the water electrolysis cell electrode according to any one of techniques 1 to 8. water electrolysis cell. (Technology 11) A water electrolysis cell according to any one of claims 9 to 10, A voltage applicator that applies a voltage between the cathode and the anode. Water electrolysis equipment. (Technology 12) Promoting mixing of a solution containing a second transition metal different from the first transition metal and chloride ions while a conductive substrate containing a first transition metal is immersed in the solution; forming a layer containing a layered double hydroxide having the second transition metal and a third transition metal different from the second transition metal on the conductive substrate; A method for producing electrodes for water electrolysis cells. (Technology 13) the solution further comprises the third transition metal and a chelating agent; A method for producing an electrode for a water electrolysis cell according to claim 12. (Technology 14) the third transition metal is a transition metal of the same kind as the first transition metal; The solution further comprises a chelating agent. A method for producing an electrode for a water electrolysis cell according to claim 12. (Technology 15) The solution is adjusted to be alkaline, thereby forming a layer containing the layered double hydroxide. 15. A method for producing an electrode for a water electrolysis cell according to any one of claims 12 to 14. (Technology 16) The first transition metal is Ni; The second transition metal is a transition metal selected from the group consisting of V, Cr, Mn, Fe, Co, Cu, W, and Ru; 16. A method for producing an electrode for a water electrolysis cell according to any one of claims 12 to 15. (Technology 17) the second transition metal is Fe; The molar ratio of the Fe ion content to the Ni content contained in the conductive base material is 0.75 or less. A method for producing an electrode for a water electrolysis cell according to claim 16. (Technology 18) the molar ratio is from 0.05 to 0.25; A method for producing an electrode for a water electrolysis cell according to claim 17. (Technology 19) the second transition metal is Fe; The molar content of Fe ions divided by the surface area of ​​the conductive substrate is 0.29 mmol / cm 2 Below is the A method for producing an electrode for a water electrolysis cell according to claim 16. (Technology 20) The value is 0.01 mmol / cm 2 to 0.1 mmol / cm 2 That is, A method for producing an electrode for a water electrolysis cell according to claim 19. (Technology 21) The chelating agent includes at least one selected from the group consisting of acetylacetone and citrate. 15. A method for producing an electrode for a water electrolysis cell according to claim 13 or 14. EXAMPLES

[0085] The present disclosure will be described in more detail below with reference to examples. Note that the following examples are merely examples of the present disclosure, and the present disclosure is not limited to the following examples.

[0086] Example 1 A mixed solvent was prepared by mixing 6.688 milliliters (mL) of water and 10.032 mL of ethanol. Ethanol was purchased from Fujifilm Wako Pure Chemical Industries, Ltd. In the mixed solvent, the volume of water:volume of ethanol was 2:3. A solution was prepared by dissolving 0.5685 g of nickel chloride hexahydrate and 0.3233 g of iron chloride hexahydrate in the mixed solvent. Nickel chloride hexahydrate and iron chloride hexahydrate were purchased from Fujifilm Wako Pure Chemical Industries, Ltd. 0.113 mL of acetylacetone (ACAC) was added to this solution as a chelating agent to obtain a chelating agent-containing solution. ACAC was purchased from Sigma-Aldrich. The substance amount of ACAC in the chelating agent-containing solution was 1 / 3.25 of the total substance amount of Ni ions and Fe ions. The chelating agent-containing solution was acidic.

[0087] Five Ni meshes manufactured by Nilaco were washed with acetone for 10 minutes and with a 1M HCl aqueous solution for 10 minutes to degrease the Ni meshes and remove impurities. The wire diameter of the Ni meshes was 0.1 mm, the number of meshes was 60, and each Ni mesh was circular with a diameter of 15 mm in plan view. The total weight of the five Ni meshes was 0.281 g. Next, the Ni meshes were washed with water and dried to complete the cleaning process of the Ni meshes.

[0088] Next, the Ni mesh after the cleaning process was immersed in the above-mentioned chelating agent-containing solution. In this state, the chelating agent-containing solution containing the Ni mesh was shaken and stirred at 25°C for 24 hours. At this time, the outermost surface of the Ni mesh was etched according to the above-mentioned formula (2). In this case, the molar ratio of the Fe ion content to the Ni content contained in the Ni mesh was 0.25. In addition, the value obtained by dividing the molar content of Fe ions by the surface area of ​​the Ni mesh was 0.0942 millimoles (mmol) / cm. 2 The surface area of ​​the Ni mesh was determined by considering the wire size, mesh number, and the geometric shape of the Ni mesh based on the diameter.

[0089] Next, 1.216 mL of propylene oxide (POX) was added to the chelating agent-containing solution as a pH-increasing agent. The amount of POX added was adjusted so that the ratio of the amount of POX to the amount of chloride ions in the mixed solution was 2. The resulting mixed solution was shaken and stirred at 25°C for 72 hours. During the shaking and stirring of the mixed solution, it was understood that POX gradually captured hydrogen ions in the mixed solution, and the pH of the mixed solution gradually increased and became alkaline. After shaking and stirring for 72 hours, the Ni mesh was collected, washed with water and dried. In this way, the electrode according to Example 1 was obtained.

[0090] Example 2 The electrode according to Example 2 was prepared in the same manner as in Example 1, except for the following points. In the preparation of the mixed solvent, 0.535 mL of water and 0.803 mL of ethanol were mixed. In the mixed solvent, the volume of water:volume of ethanol=2:3. The amount of nickel chloride hexahydrate dissolved in the mixed solvent was 0.0455 g, and the amount of iron chloride hexahydrate dissolved in the mixed solvent was 0.0259 g. In the preparation of the chelating agent-containing solution, the amount of ACAC added was 0.009 mL, and the substance amount of ACAC in the chelating agent-containing solution was 1 / 3.25 of the total substance amount of Ni ions and Fe ions. Two Ni meshes were used, and the total mass of the two Ni meshes was 0.112 g. The molar ratio of the content of Fe ions to Ni contained in the Ni mesh in the shaking and stirring of the chelating agent-containing solution containing the Ni mesh was 0.05. In addition, the value obtained by dividing the molar content of Fe ions by the surface area of ​​the Ni mesh was 0.0188 mmol / cm 2 It was.

[0091] Example 3 An electrode according to Example 3 was prepared in the same manner as in Example 1, except for the following points. In the preparation of the mixed solvent, 6.900 mL of water and 10.351 mL of ethanol were mixed. In the mixed solvent, the volume of water:volume of ethanol=2:3. The amount of nickel chloride hexahydrate dissolved in the mixed solvent was 5.8654 g, and the amount of iron chloride hexahydrate dissolved in the mixed solvent was 3.3351 g. In the preparation of the chelating agent-containing solution, the amount of ACAC added was 1.164 mL, and the substance amount of ACAC in the chelating agent-containing solution was 1 / 3.25 of the total substance amount of Ni ions and Fe ions. Four Ni meshes were used, and the total mass of the four Ni meshes was 0.96 g. Each Ni mesh was a square with a side length of 20 mm in a plan view. The amount of POX added to the chelating agent-containing solution was 12.545 mL. The molar ratio of the Fe ion content to the Ni content in the Ni mesh in the chelating agent-containing solution containing the Ni mesh when it was shaken was 0.75. In addition, the molar content of Fe ions divided by the surface area of ​​the Ni mesh was 0.2844 mmol / cm 2 The amount of POX added was adjusted so that the ratio of the amount of POX to the amount of chloride ions in the mixed solution of the chelating agent-containing solution and POX was 2.

[0092] Comparative Example 1 A mixed solvent was prepared by mixing 6.900 mL of water and 10.351 mL of ethanol. Ethanol was purchased from Fujifilm Wako Pure Chemical Industries, Ltd. In the mixed solvent, the volume of water:volume of ethanol was 2:3. A solution was prepared by dissolving 5.8654 g of nickel chloride hexahydrate and 3.3351 g of iron chloride hexahydrate in the mixed solvent. Nickel chloride hexahydrate and iron chloride hexahydrate were purchased from Fujifilm Wako Pure Chemical Industries, Ltd. 1.164 mL of acetylacetone (ACAC) was added to this solution as a chelating agent to obtain a chelating agent-containing solution. ACAC was purchased from Sigma-Aldrich. The substance amount of ACAC in the chelating agent-containing solution was 1 / 3.25 of the total substance amount of Ni ions and Fe ions. The pH of the chelating agent-containing solution was 1.

[0093] A Ni mesh manufactured by Nilaco was washed with acetone for 10 minutes and with a 1M HCl aqueous solution for 10 minutes to degrease the Ni mesh and remove impurities. The Ni mesh had a wire diameter of 0.1 mm, 60 meshes, and was a square with a side length of 20 mm in plan view. The Ni mesh weighed 0.25 g. The Ni mesh was then washed with water and dried to complete the cleaning process of the Ni mesh.

[0094] Next, the Ni mesh after the cleaning process was immersed in the above-mentioned chelating agent-containing solution. In this state, the chelating agent-containing solution containing the Ni mesh was shaken and stirred at 25°C for 24 hours. At this time, the entire Ni mesh was etched and dissolved according to the above-mentioned formula (2). For this reason, in Comparative Example 1, an electrode that could be evaluated was not obtained. The molar ratio of the Fe ion content to the Ni content contained in the Ni mesh was 2.9. In addition, the value obtained by dividing the molar content of Fe ions by the surface area of ​​the Ni mesh was 1.0919 mmol / cm 2 It was.

[0095] Comparative Example 2 Five Ni meshes that had been subjected to a cleaning treatment in the same manner as in Example 1 were used as electrodes according to Comparative Example 2.

[0096] Comparative Example 3 An electrode according to Comparative Example 3 was prepared in the same manner as in Example 1, except for the following points. The Ni mesh after the cleaning process was placed in the chelating agent-containing solution, and immediately thereafter, POX was added to the chelating agent-containing solution. In other words, in Comparative Example 3, the chelating agent-containing solution containing the Ni mesh was not shaken or stirred before the addition of POX.

[0097] [Identification of electrode structure and morphological observation] A sample for morphological observation was picked up and processed using a focused ion beam processing and observation device (FIB) FB-2200 manufactured by Hitachi High-Technologies Corporation. Next, the sample for morphological observation was sliced ​​using a FIB NX5000 manufactured by Hitachi High-Tech Science Corporation to obtain a sample for morphological observation. The obtained sample was observed using a transmission electron microscope (TEM) JEM-F200 manufactured by JEOL Ltd., and the structure of the electrode according to each example and each comparative example was identified and the morphology of the electrode was observed by electron beam diffraction using the TEM. In this way, the state of LDH in the electrodes according to the examples and comparative examples was evaluated.

[0098] FIG. 8 is a TEM image of the electrode according to Example 1. FIG. 9A is a TEM image showing a portion of the electrode according to Example 1 where an electron beam diffraction result was obtained. FIG. 9B is an electron beam diffraction image obtained by TEM for the portion of the electrode shown in FIG. 9A. As shown in FIG. 8, it can be seen that a predetermined layer is formed on the surface of the Ni mesh. This layer had a thickness of 35 nm or more. As shown in FIGS. 9A and 9B, according to the electron beam diffraction of this layer, lattice spacings of 0.14 nm, 0.19 nm, and 0.22 nm derived from the LDH lattice were observed, and diffraction interference fringes corresponding to (113), (015), and (012), respectively, were confirmed. Therefore, it was confirmed that a layer containing LDH was formed on the surface of the Ni mesh.

[0099] A TEM-EDX line analysis was performed from the layer containing LDH of the electrode according to Example 1 toward the Ni mesh. FIG. 10 is a graph showing the results of the TEM-EDX line analysis of the electrode according to Example 1. In FIG. 10, the vertical axis shows the net counts of Fe, O, and Ni, and the horizontal axis shows the distance from a specific point in the layer containing LDH where the line analysis was started. In FIG. 10, when focusing on the net count of Ni, there is a point where the net count starts to rise steeply, and it can be understood that as the line analysis progresses, it has reached the region of the interface between the layer containing LDH and the substrate. The net count of Ni increases in a range corresponding to a distance of about 5 nm from that point and reaches a saturation point. In this range, when focusing on the net count of Fe, it can be understood that the net count gradually decreases in a range corresponding to a distance of 4 nm. This indicates that a layer in which Fe is diffused exists of 4 nm. On the other hand, when focusing on the spectrum of oxygen, it can be understood that the net count gradually decreases in a range corresponding to a distance of 5 nm. Therefore, it is understood that Fe is diffused in the region of the interface between the layer containing LDH and the substrate, and a layer containing Ni, Fe, and oxygen having a thickness of 4 nm and a layer containing Ni and oxygen having a thickness of about 1 nm are continuously present. The part corresponding to the distance equal to or greater than the distance of the saturation point of the increase in the net count of Ni is considered to be Ni mesh. Taking these results together, in the electrode according to Example 1, a layer a1 containing LDH having Ni and Fe, a layer a2 containing Ni, Fe, and oxygen, a Ni natural oxide film a3, and a Ni mesh a4 are present in this order.

[0100] FIG. 11 is a TEM image of the electrode according to Comparative Example 3. FIG. 12A is a TEM image showing a portion of the electrode according to Comparative Example 3 where the electron beam diffraction results were obtained. FIG. 12B is an electron beam diffraction image obtained by TEM for the portion of the electrode shown in FIG. 12A. FIG. 12B shows the result of electron beam diffraction obtained for the region shown by the white dashed line in FIG. 12A. As shown in FIG. 11, it is understood that LDH is present on a part of the surface of the Ni mesh in the electrode according to Comparative Example 3. On the other hand, in the electrode according to Comparative Example 3, voids are generated between the LDH and the Ni mesh. In Comparative Example 3, it is considered that the reaction shown in the above formula (2) is difficult to occur, the Ni source for LDH synthesis is insufficient, and LDH synthesis is not sufficiently performed. In addition, since the reaction of formula (2) does not occur sufficiently, it is considered that the formation of an intermediate layer containing Ni, Fe, and oxygen accompanying the diffusion of Fe is difficult to occur, and LDH is not firmly fixed to the Ni mesh. As a result, it is considered that a large number of voids are generated between the LDH and the Ni mesh.

[0101] As shown in Figures 12A and 12B, the interplanar spacings of 0.14 nm, 0.17 nm, 0.19 nm, and 0.22 nm due to the LDH lattice were observed, and the diffraction interference fringes corresponding to (113), (110), (015), and (012), respectively, were confirmed. It was confirmed that the LDH was present on the surface of the Ni mesh.

[0102] TEM-EDX line analysis was performed from the layer containing LDH of the electrode according to Comparative Example 3 toward the Ni mesh. FIG. 13 is a graph showing the results of the TEM-EDX line analysis of the electrode according to Example 1. In FIG. 13, the vertical axis shows the net counts of Fe, O, and Ni, and the horizontal axis shows the distance from a specific point in the layer containing LDH where the line analysis was started. Focusing on the Ni net count in FIG. 13, there is a point where the net count starts to increase steeply, and it can be understood that as the line analysis progresses, it has reached the interface region between the layer containing LDH and the substrate. The Ni net count continues to increase from that point. Focusing on the Fe net count in this region, the presence of a layer containing Ni, Fe, and oxygen cannot be confirmed as in the electrode according to Example 1. It can be understood that in the electrode according to Example 1, a layer (natural oxide film) b2 containing Ni and oxygen equivalent to a distance of about 2 nm exists between the layer b1 containing LDH and the substrate b3. This result is also thought to be related to the numerous voids between the LDH and Ni mesh confirmed in FIG. 11.

[0103] [Electrode evaluation] The oxygen evolution (OER) overvoltage of the electrodes according to each Example and Comparative Examples 2 and 3 was evaluated. For the measurement, a potentiostat VersaSTAT4 manufactured by Princeton Applied Research, an alkali sample vial (200 mL) manufactured by BAS, a Teflon (registered trademark) cap (for 200 mL) manufactured by BAS, and a plate electrode AE-2 manufactured by EC Frontier were used as a jig for the working electrode. The electrodes according to each Example and Comparative Examples 2 and 3, which are the working electrodes, were fixed to this jig. A double platinum wire counter electrode D.6.0305.200J manufactured by Metrohm was used as the counter electrode. The current derived from the anode reaction of the water electrolysis cell was measured by the three-electrode method under the following measurement conditions. The anode reaction is an oxygen evolution reaction. (Measurement conditions) Solution: 1M KOH solution Potential vs. reversible hydrogen electrode (RHE): 1.0V to 1.7V Number of cycles: 5 cycles Potential sweep speed: 10mV / sec Temperature: 25℃

[0104] Current density at 5th cycle: 10mA / cm 2 The OER overpotential was determined by subtracting the theoretical potential of 1.229 V required to cause the oxygen evolution reaction to proceed from the voltage corresponding to the potential. The results are shown in Table 1. Table 1 also shows the molar ratio of the Fe ion content to the Ni content contained in the Ni mesh in the preparation of the electrode, and the value obtained by dividing the molar content of Fe ions by the surface area of ​​the Ni mesh. Table 1 also shows whether the chelating agent-containing solution containing the Ni mesh was shaken or not before the addition of POX, and whether the electrode could be prepared.

[0105] From the measurement results for evaluating the OER overpotential, the coverage of the LDH-containing layer on the surface of the Ni mesh was determined based on the following formula (3). The results are shown in Table 1. In formula (3), S NiOx is the integral of the current density from 1.38 V to 1.48 V, and S Ni is the integral value of the current density at a potential from 1.35 V to 1.38 V. The current density peak at a potential from 1.38 V to 1.48 V is a peak derived from nickel and iron hydroxides, and the current density peak at a potential from 1.35 V to 1.38 V is a peak derived from pure nickel. Coverage rate = S NiOx / (S Ni + S NiOx )×100 Equation (3)

[0106] As shown in Table 1, the OER overpotential of the electrodes according to Examples 1 to 3 is lower than that of the electrode according to Comparative Example 2, and it is understood that the electrodes have high electrode activity due to the presence of a layer containing LDH. On the other hand, a comparison between each Example and Comparative Example 1 shows that if the molar ratio of the Fe ion content to the Ni content contained in the Ni mesh is large, the chemical reaction that dissolves Ni becomes intense, and the entire Ni mesh dissolves, making it impossible to fabricate an electrode. For this reason, it is understood that the molar ratio of the Fe ion content to the Ni content contained in the Ni mesh is preferably 0.75 or less. In addition, the value obtained by dividing the molar content of Fe ions by the surface area of ​​the Ni mesh was 0.29 mmol / cm. 2 It is understood that it is desirable that:

[0107] As shown in Table 1, the OER overpotentials of the electrodes according to Examples 1 and 2 are particularly low. Therefore, it was suggested that the molar ratio of the Fe ion content to the Ni content contained in the Ni mesh is more preferably in the range of 0.05 to 0.25 from the viewpoint of electrode activity. In addition, the molar content of Fe ions divided by the surface area of ​​the Ni mesh is more preferably 0.01 mmol / cm. 2 to 0.1 mmol / cm 2 It was suggested that it would be more desirable to

[0108] [Electrode durability evaluation] The OER overpotential of the electrodes according to Example 1 and Comparative Examples 2 and 3 was measured for 1000 cycles to evaluate the durability of the electrodes. For the measurement, a potentiostat VersaSTAT4 manufactured by Princeton Applied Research, an alkali sample vial (200 mL) manufactured by BAS, a Teflon (registered trademark) cap (for 200 mL) manufactured by BAS, and a plate electrode AE-2 manufactured by EC Frontier were used as a jig for the working electrode. The electrodes according to Example 1 and Comparative Examples 2 and 3, which are the working electrodes, were fixed to this jig. A double platinum wire counter electrode D.6.0305.200J manufactured by Metrohm was used as the counter electrode. The current derived from the anode reaction of the water electrolysis cell was measured by the three-electrode method under the following measurement conditions. The anode reaction is an oxygen evolution reaction. (Measurement conditions) Solution: 1M KOH solution Potential vs. RHE: 1.0V to 1.7V Maximum number of cycles: 1000 cycles Potential sweep speed: 100mV / sec Temperature: 25℃

[0109] 14 is a graph showing the relationship between the OER overpotential and the number of cycles for the electrode according to Example 1 and the electrodes according to Comparative Examples 2 and 3. In this graph, the OER overpotential is shown for every 50 cycles. Each cycle simulates the start and stop of water electrolysis.

[0110] Comparing Example 1 with Comparative Examples 2 and 3, the OER overpotential did not increase by the 50th cycle in the electrode of Example 1. On the other hand, the OER overpotential increased by the 50th cycle in the electrodes of Comparative Examples 2 and 3. For this reason, from the viewpoint of electrode durability, it is important to promote mixing of the solution before adjusting the solution to be alkaline while immersing the Ni mesh in the chelating agent-containing solution, such as by shaking and stirring the chelating agent-containing solution containing a Ni mesh.

[0111] However, from the above description, many improvements and other embodiments of the present disclosure will be apparent to those skilled in the art. Therefore, the above description should be interpreted as merely illustrative and is provided for the purpose of teaching those skilled in the art the best mode for carrying out the present disclosure. Substantially alterations in operating conditions, composition, structure and / or function can be made without departing from the spirit of the present disclosure.

[0112] [Table 1] [Industrial Applicability]

[0113] The water electrolysis cell electrode of the present disclosure can be used as an anode or a cathode for water electrolysis.

Claims

1. A conductive substrate containing a transition metal; a first layer comprising two or more transition metals and oxygen; a second layer comprising a layered double hydroxide having two or more transition metals; the first layer is disposed between the conductive substrate and the second layer in a thickness direction of the first layer, the first layer includes a first transition metal of the same type as the transition metal included in the conductive substrate, and a second transition metal of the same type as the transition metal included in the second layer but different from the first transition metal; a concentration of the first transition metal in the first layer is higher than a concentration of the first transition metal in the second layer; Electrode for water electrolysis cells.

2. The conductive substrate has a porous structure. The electrode for a water electrolysis cell according to claim 1 .

3. The first layer has a thickness of 10 nm or less. The electrode for a water electrolysis cell according to claim 1 .

4. The second layer has a thickness of 35 nm or more. The electrode for a water electrolysis cell according to claim 1 .

5. the second layer comprises a chelating agent; The electrode for a water electrolysis cell according to claim 1 .

6. The chelating agent includes at least one selected from the group consisting of acetylacetone and citrate. The electrode for a water electrolysis cell according to claim 5 .

7. The first transition metal is Ni; The second transition metal is a transition metal selected from the group consisting of V, Cr, Mn, Fe, Co, Cu, W, and Ru; The electrode for a water electrolysis cell according to claim 1 .

8. The second transition metal is Fe. The electrode for a water electrolysis cell according to claim 7.

9. An anode; A cathode; a diaphragm; At least one selected from the group consisting of the anode and the cathode comprises the water electrolysis cell electrode according to any one of claims 1 to 8. water electrolysis cell.

10. An anode; A cathode; an anion exchange membrane, At least one selected from the group consisting of the anode and the cathode comprises the water electrolysis cell electrode according to any one of claims 1 to 8. water electrolysis cell.

11. The water electrolysis cell according to claim 9 ; A voltage applicator that applies a voltage between the cathode and the anode. Water electrolysis equipment.

12. The water electrolysis cell according to claim 10; A voltage applicator that applies a voltage between the cathode and the anode. Water electrolysis equipment.

13. In a state where a conductive substrate including a first transition metal is immersed in a solution including a second transition metal different from the first transition metal and chloride ions, promoting mixing of the solution before the solution is adjusted to an alkaline state; and after promoting mixing of the solution, adjusting the solution to be alkaline to form a layer containing a layered double hydroxide having the second transition metal and a third transition metal different from the second transition metal on the conductive substrate. A method for producing electrodes for water electrolysis cells.

14. The solution comprising the third transition metal and a chelating agent. The method for producing the electrode for a water electrolysis cell according to claim 13.

15. The third transition metal is a transition metal of the same type as the first transition metal, The solution comprises a chelating agent. The method for producing the electrode for a water electrolysis cell according to claim 13.

16. The method of claim 1, wherein the first transition metal is Ni; The second transition metal is a transition metal selected from the group consisting of V, Cr, Mn, Fe, Co, Cu, W, and Ru; A method for producing the electrode for a water electrolysis cell according to any one of claims 13 to 15.

17. The method of claim 1, wherein the second transition metal is Fe; The molar ratio of the content of Fe ions to the content of Ni contained in the conductive base material is 0.75 or less. The method for producing the electrode for a water electrolysis cell according to claim 16.

18. The molar ratio is greater than or equal to 0.05 and less than or equal to 0.

25. The method for producing the electrode for a water electrolysis cell according to claim 17.

19. The method of claim 1, wherein the second transition metal is Fe; the molar content of Fe ions divided by the surface area of ​​the conductive substrate is 0.29 mmol / cm2 or less; The method for producing the electrode for a water electrolysis cell according to claim 16.

20. The value is from 0.01 mmol / cm2 to 0.1 mmol / cm2. A method for producing the electrode for a water electrolysis cell according to claim 19.

21. The chelating agent includes at least one selected from the group consisting of acetylacetone and citrate. A method for producing the electrode for a water electrolysis cell according to claim 14 or 15.

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