Water electrolysis cell electrode, water electrolysis cell, water electrolysis device, and method for producing water electrolysis cell electrode

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

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

[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.

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

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

[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 predetermined 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 investigates the activity of an electrode made of Ni-Fe layered double hydride (Ni-Fe LDH) in the oxygen evolution reaction (OER).

[0006] Non-Patent Document 2 describes that the interface interaction between FeOOH and Ni-Fe LDH adjusts the local electronic structure of Ni-Fe LDH and enhances the OER electrocatalytic activity. In alkaline water electrolysis, a problem is the effusion of the electrode catalyst or electrode substrate from the electrode due to the oxidation-reduction of the electrode substrate and electrode caused by a reverse current generated by repeated operation / shutdown cycles.

[0007] JP 2020-12171 A JP 2021-139027 A

[0008] Seyeong Lee et al., “Operational durability of three-dimensional Ni-Fe layered double hydroxide electrocatalyst for water oxidation,” Electrochimica Acta, 2019, Vol.315, p.94-101Jiande 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

[0009] The descriptions in the above documents need to be reconsidered from the viewpoint of the 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.

[0010] The present disclosure provides an electrode for a water electrolysis cell, comprising: a conductive substrate containing a transition metal; a first layer containing two or more types of transition metals and oxygen; and a second layer containing a layered double hydroxide having two or more types of transition metals, wherein 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; and the concentration of the first transition metal in the first layer is higher than the concentration of the first transition metal in the second layer.

[0011] According to the present disclosure, a novel electrode for a water electrolysis cell that is advantageous in terms of durability can be provided.

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

[0013] (Knowledge forming the basis of the present disclosure) The use of renewable energy such as solar and wind power has been attracting attention as a measure against global warming. Power generation using renewable energy has the problem of surplus electricity being wasted. For this reason, the utilization efficiency of renewable energy is not necessarily sufficient. Therefore, methods for effectively utilizing surplus electricity by producing and storing hydrogen from surplus electricity have been studied.

[0014] Electrolysis of water is one possible method for producing hydrogen from surplus electricity. 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 the anode reaction, and the reaction in which hydrogen is generated at the cathode is also called the cathode reaction. In order to provide a highly efficient water electrolysis device, it is desirable that the overvoltage at the anode is low. In addition, it is also desirable that the overvoltage at the cathode is low. Therefore, there is a need to develop 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 the wide variety of combinations of metal ions. In this case, it is conceivable to support LDH on a conductive substrate. For example, as described in Patent Document 1 and the like, it is conceivable to support LDH on a substrate such as nickel foam. However, this technology needs to be reconsidered from the perspective of durability against electrode reactions in water splitting. After extensive research, the present inventors have newly discovered that the presence of a specific layer between a layer containing LDH and a conductive substrate increases the durability of electrodes for water electrolysis cells, and have completed the electrodes for water electrolysis cells disclosed herein.

[0017] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments. Note that the embodiments described below are all comprehensive or specific examples. Therefore, the numerical values, shapes, materials, components, component placement positions, and connection configurations shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, components that are not recited in the independent claims that represent the highest concepts will be described as optional components. Furthermore, in the drawings, descriptions of components with the same reference numerals may be omitted. Furthermore, the drawings schematically illustrate each component to facilitate understanding, and the shapes, dimensional ratios, etc. may not be accurately represented.

[0018] First Embodiment FIG. 1 is a cross-sectional view schematically illustrating a water electrolysis cell electrode according to a first embodiment. As shown 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 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 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 the water electrolysis cell electrode 1 more likely to exhibit high durability and high electrode activity. The thickness of the first layer 11 can be determined, for example, by performing 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. 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 in the results of the TEM-EDX line analysis. 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 maintaining 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 is conductive. The conductive substrate 10 may contain a metal other than the first transition metal or may contain a resin. The entire conductive substrate 10 may be made of metal. The conductive substrate 10 may have a configuration in which a metal-containing surface layer is formed on a resin member such as polypropylene or polyethylene. In this case, the metal-containing surface layer may be a plated film or a sputtered 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, the 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 or foil, or a porous structure such as a mesh, foam, or nonwoven fabric. The conductive substrate 10 may be made of particles such as metal particles. The conductive substrate 10 preferably has a porous structure. In this case, the surface area of ​​the conductive portion of the conductive substrate 10 tends to be large, and the water electrolysis cell electrode 1 tends to have high electrode activity. In addition, it is easy to prevent gas generated during 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 has a thickness of, for example, 0.02 mm or more. In this case, the conductive substrate 10 tends to be easy to handle. 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 illustrating an example of the crystal structure of LDH. LDH 20 is active in a reaction for producing gases such as hydrogen and oxygen at the anode or cathode of a water electrolysis cell. For example, in alkaline water electrolysis, LDH 20 can be converted into hydroxide by the water electrolysis reaction.

[0028] The LDH20 has, for example, a composition represented by the following formula (1): 2+ is a divalent transition metal ion. 3+ is a trivalent transition metal ion. n- is an anion between layers. x is a rational number satisfying the condition 0<x<1. y is a number corresponding to the amount of charge balance required. 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 the LDH 20 are not limited to specific transition metals. In other words, M1 and M2 in the composition shown in formula (1) are not limited to specific transition metals. 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 the LDH 20 may include, for example, Ni and Fe, and may be, for example, such that M1 is Ni and M2 is Fe in the composition shown in formula (1). In this case, the water electrolysis cell electrode 1 is more likely to have high electrode activity.

[0031] A is an interlayer anion n- may be an inorganic ion or an organic ion. An example of an inorganic ion is CO 2- , NO3 - , Cl - , SO4 2- ,Br - , O.H. - , F - , I - , Si2O5 2- , B4O5(OH)4 2- , and PO 3- An example of an organic ion is CH3(CH2) n SO 4- , CH3 (CH2) n COO - , CH3 (CH2) n P.O. 4- , and CH3(CH2) n NO 3- It is. 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- or a plurality of types of A n- may also include:

[0032] As shown in FIG. 2, LDH20 is a 2+ or M2 3+ OH at each vertex of the octahedron centered at- LDH20 contains [M1 2+ 1-x M2 3+ x (OH) x+ This metal hydroxide layer has a layered structure in which hydroxide octahedra are connected two-dimensionally, 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 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 metal hydroxide and an anion A n- The LDH 20 has a sheet-like structure in which M1 contained in the metal hydroxide layer and a guest layer 22 of water molecules are alternately stacked. 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 when forming 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, i.e., a multidentate ligand.

[0034] The chelating agent is not limited to a specific chelating agent. For example, the chelating agent is 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 chelating agents include β-diketones, β-ketoesters, hydroxycarboxylic acids, and hydroxycarboxylic acid salts. Examples of β-diketones include acetylacetone (ACAC), trifluoroacetylacetone, hexafluoroacetylacetone, benzoylacetone, thenoyltrifluoroacetone, dipyrrolylmethane, dibenzoylmethane, and ascorbic acid. Examples of β-ketoesters include methyl acetoacetate, ethyl acetoacetate, allyl acetoacetate, benzyl acetoacetate, n-propyl acetoacetate, isopropyl acetoacetate, n-butyl acetoacetate, isobutyl 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 salts thereof.

[0035] The chelating agent preferably contains at least one selected from the group consisting of acetylacetone and citrate, which is more likely to provide high electrode activity for the water electrolysis cell electrode 1. 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, for example, a portion having a thickness of 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 likely to have high electrode activity. In addition, the water electrolysis cell electrode 1 is likely to have high durability. The coverage can be determined, for example, according to the method described in the Examples.

[0038] The method for producing the water electrolysis cell electrode 1 is not limited to any particular method. The water electrolysis cell electrode 1 can be produced, for example, by a method including the following steps (I) and (II): (I) A conductive substrate 10 containing a first transition metal is immersed in a solution S containing a second transition metal different from the first transition metal and chloride ions, and mixing of the solution S is promoted. (II) A layer containing an LDH having the second transition metal and a third transition metal different from the second transition metal is formed on the conductive substrate 10.

[0039] In the step (I), the first transition metal contained in the conductive substrate 10 may interact with the second transition metal and chloride contained in the solution S. This facilitates the formation of a layer for firmly immobilizing the LDH-containing layer formed in the step (II) on the conductive substrate 10. As a result, the water electrolysis cell electrode 1 is 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 sealed, or stirring the solution S using a stirrer piece or a stirrer. Such methods cause forced convection of the solution S, which can promote 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 likely to be 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 increase the specific surface area of ​​the LDH 20. This tends to further increase the electrode activity of the water electrolysis cell electrode 1.

[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 for producing the water electrolysis cell electrode 1.

[0046] The chelating agent contained in the 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 the 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 the solution S, making it easier to form the second layer 12 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 step (II), the method for forming the LDH-containing layer is not limited to a specific method. For example, the LDH-containing layer 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 for adjusting the solution S to be alkaline is not limited to a specific method. For example, the solution S may be adjusted to be alkaline by mixing the solution S with an alkaline solution. 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 solution S, in the presence of a nucleophile, such as chloride ion, a ring-opening reaction of the epoxy group occurs, and the pH-raising agent captures hydrogen ions present in solution S. This increases the pH of solution S, making solution S alkaline. The pH of solution S is, for example, 1. When a pH-raising agent is added to solution S, the pH of solution S gradually increases from, for example, 1, and eventually solution S may become alkaline. The final pH of solution S is, for example, 8 or more and 12 or less. The addition of the pH-raising agent to the solution S causes a reaction to capture hydrogen ions in solution S. This gradually increases the pH of solution S. The time from the addition of the pH-raising agent to solution S until the pH of solution S reaches a steady state is not limited to a specific time. This time may be, for example, 24 hours or more, or 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 likely to be obtained.

[0051] In the above-described production method, the first transition metal and the second transition metal are not limited to specific transition metals. 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 etch the conductive substrate 10. In addition, in step (I), the Fe contained in the solution S may 3+ is diffused near the surface of the conductive substrate 10 and becomes Fe 3+ Part of and Ni 2+It is believed that a portion of the 4Ni, together with oxygen, can 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. 2+ Cl - 2+ 2Fe 3+ Cl - 3 + 2Ni → 5Ni 2+ Cl - 2+ 2Fe 2+ Cl - 2 + 1Ni formula (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 may be, for example, 0.29 mmol / cm. 2 In this case, it is possible to prevent the nickel contained in the conductive substrate 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 schematically illustrating an example of the mechanism for manufacturing the electrode for a water electrolysis cell according to the first embodiment. As shown in FIG. 3, the conductive substrate 10 is immersed in a solution S containing ions of a second transition metal TM2, chloride ions (not shown), ions of a third transition metal TM3, and a chelating agent 30. For example, the ions of the second transition metal TM2 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 eluted 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 may 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 types of transition metal ions. A portion 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, forming a complex C1 between the ions TM1 of the first transition metal derived from the conductive substrate 10 and the chelating agent 30. 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 an alkaline state, the complexes C1, C2, and C3 react on the surface of the conductive substrate 10, synthesizing LDH 20 along the surface of the conductive substrate 10. Because the complexes C1, C2, and C3 contain the chelating agent 30, the effect of the chelating agent 30 suppresses crystal growth of LDH 20. As a result, the second layer 12 containing the LDH 20 and the chelating agent 30 is formed on the conductive substrate 10, and the water electrolysis cell electrode 1 is obtained.

[0059] The water electrolysis cell electrode 1 according to this embodiment can be used as an electrode of a water electrolysis cell in, for example, an alkaline water electrolysis apparatus or an anion exchange membrane water electrolysis apparatus. 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 apparatus. This tends to increase the activity of the anode reaction or the cathode reaction in water electrolysis.

[0060] Second Embodiment Fig. 4 is a cross-sectional view schematically illustrating an example of a water electrolysis cell according to a second embodiment. As shown 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 a potassium hydroxide aqueous solution and a sodium hydroxide aqueous solution.

[0062] 4 , the water electrolysis cell 2 includes, for example, an electrolytic cell 2s, a first chamber 2m, and a second chamber 2n. A diaphragm 2p is disposed inside the electrolytic cell 2s, separating the interior of the electrolytic cell 2s into the first chamber 2m and the second chamber 2n. An anode 2a is disposed in the first chamber 2m, and a 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 pores that serve as passages for ions or the electrolyte. The material of the diaphragm 2p is not limited to a specific material. Examples of materials for the diaphragm 2p include 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 materials for the diaphragm 2p include 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, i.e., 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 alkali metal or 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 material for alkaline water electrolysis cells.

[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 material for alkaline water electrolysis cells. 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 2 a and the cathode 2 b includes the water electrolysis cell electrode 1, and therefore the water electrolysis cell 2 can exhibit high durability.

[0069] Third Embodiment Fig. 5 is a cross-sectional view schematically illustrating an example of a water electrolysis apparatus according to a third embodiment. As shown 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 supply. The power-type power supply adjusts the voltage applied between the anode 2a and the cathode 2b and the current flowing between the anode 2a and the cathode 2b so that the power supplied to the water electrolysis device 3 becomes a predetermined set value.

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

[0072] Fourth Embodiment Fig. 6A is a cross-sectional view schematically illustrating an example of a water electrolysis cell according to the fourth embodiment. As shown 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 mixing of oxygen gas generated at the anode 4a and hydrogen gas generated at the cathode 4b. The oxygen gas passes through the gas diffusion layer 4n and is guided to the outside of the anode 4a. The hydrogen gas passes through the gas diffusion layer 4k and is guided 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 AEM-type water electrolysis cells. 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 according to 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 (conductive substrate 10) is coated 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 coated with the second layer 12 containing LDH, or only a portion of the surface of the metal particle may be coated with the second layer 12 containing LDH. The second layer 12 covers, for example, 70% or more of the surface of the metal particle (conductive substrate 10). The second layer 12 may cover most of the surface of the metal particle (conductive substrate 10), specifically 90% or more. The water electrolysis cell electrode 1 may have a cross section whose surface is coated 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 substrate 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 forming the conductive substrate 10 is not limited to a specific shape. The shape of the metal particles is, for example, granular. When the metal particles are 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 sufficient to support a sufficient amount of LDH. This makes it difficult for the LDH-containing second layer 12 and the metal particles forming the conductive substrate 10 to separate even when a voltage is applied to the water electrolysis cell electrode 1, thereby making the water electrolysis cell electrode 1 more likely to have high durability. In addition, with 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 that can be observed in their entirety, after determining 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 schematically illustrating an example of a water electrolysis apparatus according to a fifth embodiment. As shown 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 supply. In the power-type power supply, 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 reaches a predetermined set value.

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

[0084] (Additional Notes) The above disclosure discloses the following technologies. (Technology 1) A water electrolysis cell electrode comprising: a conductive substrate containing a transition metal; a first layer containing two or more transition metals and oxygen; and a second layer containing a layered double hydroxide having two or more transition metals, wherein the first layer is disposed between the conductive substrate and the second layer in a thickness direction of the first layer, and 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, and the concentration of the first transition metal in the first layer is higher than the concentration of the first transition metal in the second layer. (Technology 2) The water electrolysis cell electrode according to Technology 1, wherein the conductive substrate has a porous structure. (Technology 3) The water electrolysis cell electrode according to Technology 1 or 2, wherein the first layer has a thickness of 10 nm or less. (Technology 4) The water electrolysis cell electrode according to any one of Technologies 1 to 3, wherein the second layer has a thickness of 35 nm or more. (Technology 5) The water electrolysis cell electrode according to any one of Technologies 1 to 4, wherein the second layer contains a chelating agent. (Technology 6) The water electrolysis cell electrode according to Technology 5, wherein the chelating agent contains at least one selected from the group consisting of acetylacetone and citrate. (Technology 7) The water electrolysis cell electrode according to any one of Technologies 1 to 6, wherein 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. (Technology 8) The water electrolysis cell electrode according to Technology 7, wherein the second transition metal is Fe. (Technology 9) A water electrolysis cell comprising an anode, a cathode, and a diaphragm, wherein 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 Technologies 1 to 8. (Technology 10) A water electrolysis cell comprising an anode, a cathode, and an anion exchange membrane, wherein 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 Technologies 1 to 8.(Technology 11) A water electrolysis device comprising the water electrolysis cell according to Technology 9 or 10, and a voltage applicator that applies a voltage between the cathode and the anode. (Technology 12) A method for manufacturing an electrode for a water electrolysis cell, comprising: promoting mixing of a conductive substrate containing a first transition metal while the conductive substrate is immersed in a solution containing a second transition metal different from the first transition metal and chloride ions; and forming, on the conductive substrate, a layer containing a layered double hydroxide having the second transition metal and a third transition metal different from the second transition metal. (Technology 13) A method for manufacturing an electrode for a water electrolysis cell according to Technology 12, wherein the solution further contains the third transition metal and a chelating agent. (Technology 14) A method for manufacturing an electrode for a water electrolysis cell according to Technology 12, wherein the third transition metal is the same type of transition metal as the first transition metal, and the solution further contains a chelating agent. (Technology 15) The method for producing an electrode for a water electrolysis cell according to any one of Techniques 12 to 14, wherein the layer containing the layered double hydroxide is formed by adjusting the solution to be alkaline. (Technology 16) The method for producing an electrode for a water electrolysis cell according to any one of Techniques 12 to 15, wherein 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. (Technology 17) The method for producing an electrode for a water electrolysis cell according to Technique 16, wherein the second transition metal is Fe, and 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. (Technology 18) The method for producing an electrode for a water electrolysis cell according to Technique 17, wherein the molar ratio is 0.05 to 0.25. (Technology 19) The second transition metal is Fe, and the molar content of Fe ions divided by the surface area of ​​the conductive substrate is 0.29 mmol / cm. 2 The method for manufacturing an electrode for a water electrolysis cell according to Technology 16, wherein the value is 0.01 mmol / cm or less. 2 to 0.1 mmol / cm 2(Technology 21) The method for producing an electrode for a water electrolysis cell according to Technology 13 or 14, wherein the chelating agent includes at least one selected from the group consisting of acetylacetone and citrate.

[0085] The present disclosure will be described in more detail below with reference to examples. Note that the following examples are 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. The volume ratio of water to ethanol in the mixed solvent 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. To this solution, 0.113 mL of acetylacetone (ACAC) was added as a chelating agent to obtain a chelating agent-containing solution. ACAC was purchased from Sigma-Aldrich. The amount of ACAC in the chelating agent-containing solution was 1 / 3.25 of the total amount of Ni ions and Fe ions. The chelating agent-containing solution was acidic.

[0087] Five Ni meshes manufactured by Nilaco Corporation were washed with acetone for 10 minutes and then with a 1M HCl aqueous solution for 10 minutes to degrease the Ni meshes and remove impurities. The Ni meshes had a wire diameter of 0.1 mm, 60 meshes, 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. The Ni meshes were then washed with water and dried to complete the cleaning process.

[0088] Next, the Ni mesh after the cleaning treatment was immersed in the 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 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 taking into consideration the wire diameter, the number of meshes, 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-raising 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 the POX gradually captured hydrogen ions in the mixed solution, and the pH of the mixed solution gradually increased and became alkaline. After 72 hours of shaking and stirring, the Ni mesh was recovered, washed with water, and dried. In this way, the electrode according to Example 1 was obtained.

[0090] Example 2 An electrode according to Example 2 was fabricated in the same manner as Example 1, except for the following points. 0.535 mL of water and 0.803 mL of ethanol were mixed to prepare a mixed solvent. The ratio of the volume of water to the volume of ethanol in the mixed solvent was 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. The amount of ACAC added to prepare the chelating agent-containing solution was 0.009 mL, and the amount of ACAC in the chelating agent-containing solution was 1 / 3.25 of the total 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. When the chelating agent-containing solution containing the Ni meshes was shaken and stirred, the molar ratio of the Fe ion content to the Ni contained in the Ni meshes was 0.05. In addition, the molar content of Fe ions divided 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 fabricated in the same manner as Example 1, except for the following points. In preparing 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 was 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 preparing the chelating agent-containing solution, the amount of ACAC added was 1.164 mL, and the amount of ACAC in the chelating agent-containing solution was 1 / 3.25 of the total 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 had a square shape with a side length of 20 mm in 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 ion content in the Ni mesh when the chelating agent-containing solution containing the Ni mesh was shaken and stirred 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. 2The 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 would be 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. The volume ratio of water to ethanol in the mixed solvent was 2:3. 5.8654 g of nickel chloride hexahydrate and 3.3351 g of iron chloride hexahydrate were dissolved in the mixed solvent to prepare a solution. 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 the solution as a chelating agent to obtain a chelating agent-containing solution. ACAC was purchased from Sigma-Aldrich. The amount of ACAC in the chelating agent-containing solution was 1 / 3.25 of the total amount of Ni ions and Fe ions. The pH of the chelating agent-containing solution was 1.

[0093] A Ni mesh manufactured by Nilaco Corporation was washed with acetone for 10 minutes and then 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 a square shape 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.

[0094] Next, the Ni mesh after the cleaning process was immersed in the 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 formula (2). Therefore, in Comparative Example 1, an evaluable electrode 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 the cleaning treatment in the same manner as in Example 1 were used as electrodes in Comparative Example 2.

[0096] Comparative Example 3 An electrode according to Comparative Example 3 was fabricated in the same manner as in Example 1, except for the following points. The Ni mesh after the cleaning treatment 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 (FIB) processing and observation system (FB-2200) manufactured by Hitachi High-Technologies Corporation. Next, the sample for morphological observation was thinned using an 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 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 from which electron beam diffraction results were 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 was 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, electron beam diffraction of this layer revealed lattice spacings of 0.14 nm, 0.19 nm, and 0.22 nm derived from the LDH lattice, and diffraction interference fringes corresponding to (113), (015), and (012), respectively, were confirmed. This confirmed that a layer containing LDH was formed on the surface of the Ni mesh.

[0099] TEM-EDX line analysis was performed from the LDH-containing layer 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 represents the net counts of Fe, O, and Ni, and the horizontal axis represents the distance from a specific point in the LDH-containing layer where the line analysis was started. Focusing on the Ni net count in FIG. 10 reveals a point where the net count begins to rise steeply, indicating that as the line analysis progresses, the interface between the LDH-containing layer and the substrate is reached. The Ni net count increases within a range corresponding to a distance of approximately 5 nm from that point, reaching a saturation point. Focusing on the Fe net count within this range reveals that the net count gradually decreases within a range corresponding to a distance of 4 nm. This indicates the presence of a 4 nm layer in which Fe is diffused. Meanwhile, focusing on the oxygen spectrum reveals that the net count gradually decreases within a range corresponding to a distance of 5 nm. Therefore, it can be understood that Fe diffuses into the interface region between the LDH-containing layer and the substrate, resulting in the continuous presence of a 4 nm-thick layer containing Ni, Fe, and oxygen and a layer approximately 1 nm-thick layer containing Ni and oxygen. The portion corresponding to a distance equal to or greater than the saturation point of the increase in the Ni net count is considered to be a Ni mesh. Taking these results together, the electrode according to Example 1 contains a layer a1 containing LDH having Ni and Fe, a layer a2 containing Ni, Fe, and oxygen, a Ni native oxide film a3, and a Ni mesh a4, 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 from which electron beam diffraction results were obtained. FIG. 12B is an electron beam diffraction image obtained by TEM of the portion of the electrode shown in FIG. 12A. FIG. 12B shows the electron beam diffraction results obtained for the region indicated by the white dashed line in FIG. 12A. As shown in FIG. 11, it can be seen that LDH is present on a portion 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, the reaction represented by the above formula (2) is unlikely to occur, and the Ni source for LDH synthesis is insufficient, which is thought to have resulted in insufficient LDH synthesis. Furthermore, because the reaction represented by formula (2) did not occur sufficiently, it is thought that the formation of an intermediate layer containing Ni, Fe, and oxygen due to the diffusion of Fe is unlikely to occur, and LDH is not firmly fixed to the Ni mesh. As a result, it is thought that numerous voids are generated between the LDH and the Ni mesh.

[0101] 12A and 12B, the lattice spacings of 0.14 nm, 0.17 nm, 0.19 nm, and 0.22 nm, which are derived from the LDH lattice, were observed, and diffraction interference fringes corresponding to (113), (110), (015), and (012), respectively, were confirmed, confirming the presence of LDH on the surface of the Ni mesh.

[0102] TEM-EDX line analysis was performed from the LDH-containing layer of the electrode according to Comparative Example 3 toward the Ni mesh. Figure 13 is a graph showing the results of TEM-EDX line analysis of the electrode according to Example 1. In Figure 13, the vertical axis represents the net counts of Fe, O, and Ni, and the horizontal axis represents the distance from a specific point in the LDH-containing layer where the line analysis began. Focusing on the Ni net count in Figure 13 reveals a point where the net count begins to increase sharply, indicating that the line analysis reached the interface between the LDH-containing layer and the substrate. The Ni net count continues to increase from that point. Focusing on the Fe net count in this region reveals that the presence of a layer containing Ni, Fe, and oxygen, as in the electrode according to Example 1, is not confirmed. It is understood that in the electrode according to Example 1, a layer (native oxide film) b2 containing Ni and oxygen, corresponding to a distance of approximately 2 nm, exists between the LDH-containing layer b1 and the substrate b3. This result is thought to be related to the numerous voids between the LDH and the Ni mesh observed in FIG.

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

[0104] Current density at the fifth cycle: 10 mA / cm 2The 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 stirred 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 at a potential of 1.38 V to 1.48 V, and S Ni is the integral value of the current density at a potential of 1.35 V to 1.38 V. The current density peak at a potential of 1.38 V to 1.48 V is a peak derived from nickel and iron hydroxides, and the current density peak at a potential of 1.35 V to 1.38 V is a peak derived from pure nickel. Coverage = S NiOx / (S Ni + S NiOx )×100 Formula (3)

[0106] As shown in Table 1, the OER overvoltages of the electrodes according to Examples 1 to 3 are lower than the OER overvoltage of the electrode according to Comparative Example 2, and it can be seen 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 the Ni becomes intense, causing the entire Ni mesh to dissolve, making it impossible to produce an electrode. For this reason, it can be seen 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 is 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 were particularly low. Therefore, it was suggested that, from the viewpoint of electrode activity, the molar ratio of the Fe ion content to the Ni content contained in the Ni mesh should be in the range of 0.05 to 0.25. In addition, the molar content of Fe ions divided by the surface area of ​​the Ni mesh was 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 1,000 cycles to evaluate the electrode durability. For the measurement, a potentiostat VersaSTAT4 manufactured by Princeton Applied Research, a 200 mL alkali sample vial manufactured by BAS, a 200 mL Teflon® cap manufactured by BAS, and an AE-2 plate electrode manufactured by EC Frontier were used as the working electrode fixture. The working electrodes of Example 1 and Comparative Examples 2 and 3 were fixed to this fixture. A Metrohm double platinum wire counter electrode D.6.0305.200J was used as the counter electrode. The current derived from the anodic reaction of the water electrolysis cell was measured using a three-electrode method under the following measurement conditions. The anodic reaction was an oxygen evolution reaction. (Measurement conditions) Solution: 1 M KOH solution Potential to RHE: 1.0 V to 1.7 V Maximum number of cycles: 1000 cycles Potential sweep rate: 100 mV / sec Temperature: 25°C

[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 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. Therefore, from the viewpoint of electrode durability, it is important to promote mixing of the solution before adjusting the solution to alkaline while the Ni mesh is immersed in the chelating agent-containing solution, such as by shaking and stirring the chelating agent-containing solution containing the Ni mesh.

[0111] It should be noted that many modifications and other embodiments of the present disclosure will be apparent to those skilled in the art from the above description. Accordingly, the above description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the present disclosure. Substantial changes in operating conditions, composition, structure, and / or function can be made without departing from the spirit of the present disclosure.

[0112]

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

13. 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; and after promoting mixing of the solution, forming a layer on the conductive substrate, the layer including a layered double hydroxide having the second transition metal and a third transition metal different from the second transition metal; the solution comprises the third transition metal and a chelating agent; A method for producing electrodes for water electrolysis cells.

14. A method for producing a conductive substrate comprising a first transition metal, the conductive substrate being immersed in a solution comprising a second transition metal different from the first transition metal and chloride ions, the method comprising: promoting mixing of the solution; and after promoting mixing of the solution, forming a layer on the conductive substrate, the layer including a layered double hydroxide having the second transition metal and a third transition metal different from the second transition metal; the third transition metal is a transition metal of the same type as the first transition metal; The solution comprises a chelating agent. A method for producing electrodes for water electrolysis cells.

15. A method for producing a conductive substrate comprising a first transition metal, the conductive substrate being immersed in a solution comprising a second transition metal different from the first transition metal and chloride ions, the method comprising: promoting mixing of the solution; and after promoting mixing of the solution, forming a layer on the conductive substrate, the layer including a layered double hydroxide having the second transition metal and a third transition metal different from the second transition metal; The solution is adjusted to be alkaline, thereby forming a layer containing the layered double hydroxide. A method for producing electrodes for water electrolysis cells.

16. A method for producing a conductive substrate comprising a first transition metal, the conductive substrate being immersed in a solution comprising a second transition metal different from the first transition metal and chloride ions, the method comprising: promoting mixing of the solution; and after promoting mixing of the solution, forming a layer on the conductive substrate, the layer including a layered double hydroxide having the second transition metal and a third transition metal different from the second transition metal; The first transition metal is Ni; 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 0.05 or more and 0.25 or less; A method for producing electrodes for water electrolysis cells.

17. A method for producing a conductive substrate comprising a first transition metal, the conductive substrate being immersed in a solution comprising a second transition metal different from the first transition metal and chloride ions, the method comprising: promoting mixing of the solution; and after promoting mixing of the solution, forming a layer on the conductive substrate, the layer including a layered double hydroxide having the second transition metal and a third transition metal different from the second transition metal; The first transition metal is Ni; The second transition metal is Fe; the molar content of Fe ions divided by the surface area of ​​the conductive substrate is 0.01 mmol / cm 2 to 0.1 mmol / cm 2 ; A method for producing electrodes for water electrolysis cells.

18. 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.

19. 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 18.

20. 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 The method for producing the electrode for a water electrolysis cell according to claim 18.

21. The chelating agent includes at least one selected from the group consisting of acetylacetone and citrate. A method for producing an electrode for a water electrolysis cell according to claim 13 or 14.