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

Abstract

In the present invention, a water electrolysis electrode 1 comprises an electroconductive substrate 10 and a layered double hydroxide layer 20. The layered double hydroxide layer 20 is provided on a surface of the conductive substrate 10. The layered double hydroxide layer 20 has two or more types of transition metals. The contact angle of the surface of the layered double hydroxide layer 20 is 20° to 100°. The contact angle of the surface of the layered double hydroxide layer 20 may be 26° or greater.

Description

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

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

[0002] Layered double hydroxides (LDHs), for example, are known as electrode catalysts for water electrolysis electrodes.

[0003] Non-Patent Document 1 investigates the activity of an electrode with Ni-Fe layered double hydride (Ni-Fe LDH) for the oxygen evolution reaction (OER).

[0004] Non-Patent Document 2 describes that the interface interaction between FeOOH and Ni-Fe LDH adjusts the local electronic structure of Ni-Fe LDH, thereby enhancing the OER electrocatalytic activity.

[0005] 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

[0006] The present disclosure provides an electrode for water electrolysis that is advantageous from the viewpoint of suppressing an increase in overpotential.

[0007] The present disclosure provides an electrode for water electrolysis, comprising: a conductive substrate; and a layered double hydroxide layer containing two or more types of transition metals, provided on the surface of the conductive substrate; wherein the contact angle of the surface of the layered double hydroxide layer with a 6 mol / L aqueous potassium hydroxide solution is 20 degrees or more and 100 degrees or less.

[0008] According to the present disclosure, it is possible to provide an electrode for water electrolysis that is advantageous from the viewpoint of suppressing an increase in overvoltage.

[0009] FIG. 1 is a cross-sectional view schematically showing an example of a water electrolysis electrode according to the present disclosure. FIG. 2 is a diagram schematically showing the relationship between bubbles generated by a water electrolysis reaction and the water electrolysis electrode. FIG. 3 is a cross-sectional view schematically showing an example of an optical model of a water electrolysis electrode obtained by spectroscopic ellipsometry. FIG. 4 is a diagram schematically showing an example of the crystal structure of a layered double hydroxide (LDH). FIG. 5 is a flowchart showing an example of a method for producing a water electrolysis electrode. FIG. 6 is a diagram schematically showing an example of the mechanism for producing a water electrolysis electrode. FIG. 7 is a cross-sectional view schematically showing an example of a water electrolysis cell according to the present disclosure. FIG. 8 is a cross-sectional view schematically showing an example of a water electrolysis apparatus according to the present disclosure. FIG. 9 is a cross-sectional view schematically showing an example of a water electrolysis cell according to the present disclosure. FIG. 10 is a cross-sectional view schematically showing an example of a water electrolysis apparatus according to the present disclosure. FIG. 11 is a graph showing the relationship between contact angle and overvoltage in each example and comparative example.

[0010] (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.

[0011] 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 water electrolysis device.

[0012] In a water electrolysis device, oxygen is generated at the anode and hydrogen is generated at the cathode. The reaction that generates oxygen at the anode is also called the anode reaction, and the reaction that generates hydrogen at the cathode is also called the cathode reaction. To provide a water electrolysis device with excellent electrode efficiency, 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 an electrode catalyst for water electrolysis electrodes that is suitable for suppressing an increase in overvoltage.

[0013] For example, layered double hydroxides (LDHs) containing two or more transition metals are promising as electrode catalysts for water electrolysis electrodes due to their large specific surface area and diverse combinations of metal ions. The water electrolysis electrode includes, for example, a conductive substrate and an LDH layer containing two or more transition metals provided on the surface of the conductive substrate. In a water electrolysis device including such a water electrolysis electrode, bubbles generated by the water electrolysis reaction may cause a voltage drop, resulting in a decrease in electrolysis efficiency. Specifically, bubbles of oxygen, hydrogen, and the like generated by the water electrolysis reaction may adhere to the surface of the water electrolysis electrode. In addition, the size of the bubbles may increase when the bubbles adhere to the surface of the water electrolysis electrode. The adhesion of bubbles to the surface of the water electrolysis electrode or an increase in the size of the bubbles attached to the surface of the water electrolysis electrode reduces the effective area of ​​the water electrolysis electrode. This increases the reaction resistance of the water electrolysis reaction. The reaction resistance of the water electrolysis reaction increases the overvoltage, resulting in a decrease in electrolysis efficiency. As a result of extensive investigations, the present inventors have newly discovered that in a water electrolysis electrode, an increase in overvoltage can be suppressed by appropriately adjusting the contact angle on the surface of an LDH layer. Based on this new finding, the present inventors have completed the water electrolysis electrode according to the present disclosure.

[0014] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the embodiments described below are all comprehensive or specific examples. Therefore, the numerical values, shapes, materials, components, component placement positions, connection configurations, etc. 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 concept are described as optional components. Furthermore, in the drawings, descriptions of components with the same reference numerals may be omitted. Furthermore, for ease of understanding, the drawings schematically illustrate each component, and the shapes, dimensional ratios, etc. may not be accurately depicted. Furthermore, in the manufacturing method, the order of steps may be changed, or known steps may be added, as necessary.

[0015] First Embodiment Fig. 1 is a cross-sectional view schematically illustrating an example of a water electrolysis electrode according to the present disclosure. As shown in Fig. 1 , the water electrolysis electrode 1 includes a conductive substrate 10 and a layered double hydroxide (LDH) layer 20. The LDH layer 20 is provided on the surface of the conductive substrate 10. For example, the surface of the conductive substrate 10 is coated with the LDH layer 20. The LDH layer 20 can function as a catalyst for the anode reaction or cathode reaction in water electrolysis. The LDH layer 20 contains LDH as a catalyst for water electrolysis.

[0016] In the water electrolysis electrode 1, the contact angle of the surface of the LDH layer 20 is 20 degrees or more and 100 degrees or less. The contact angle is a value measured using a droplet of a 6 mol / L (mol / L) aqueous potassium hydroxide solution. This configuration can provide a water electrolysis electrode 1 that is suitable for suppressing an increase in overvoltage.

[0017] The contact angle of the surface of the LDH layer 20 can be measured using a contact angle meter. The contact angle of a 6 mol / L potassium hydroxide aqueous solution on the surface of the LDH layer 20 can be determined according to the θ / 2 method. Specifically, first, a 0.2 microliter (μL) droplet of a 6 mol / L potassium hydroxide aqueous solution is deposited on the surface of the LDH layer 20 of the water electrolysis electrode 1. The contact angle of the surface of the LDH layer 20 can be measured by measuring the angle between the tangent of the droplet and the surface of the LDH layer 20 using a contact angle meter. A microcontact angle meter or an extremely small contact angle meter may be used to measure the contact angle. The microcontact angle meter or the extremely small contact angle meter can form an extremely small droplet, on the order of nanoliters to picoliters, on the surface of the LDH layer 20. Therefore, even when the LDH layer 20 is formed on a conductive substrate 10 having a mesh structure including fine metal wires, such as a mesh or expanded metal, droplets can be formed on the surface of this LDH layer 20.

[0018] FIG. 2 is a schematic diagram illustrating the relationship between bubbles generated by the water electrolysis reaction and the water electrolysis electrode. As shown in FIG. 2 , the water electrolysis electrode 1 includes a conductive substrate 10 and an LDH layer 20 provided on the surface of the conductive substrate 10, and the LDH layer 20 contains LDH. The LDH can contribute to the water electrolysis reaction. The inventors have found that by controlling the wettability of the surface of the LDH layer 20, specifically by adjusting the contact angle of the surface of the LDH layer 20 to 20 degrees or more and 100 degrees or less, bubbles 7 generated from the water electrolysis electrode 1 are likely to detach from the surface of the LDH layer 20. As shown in FIG. 2 , when bubbles 7 are generated on the surface of the LDH layer 20 by the water electrolysis reaction, the bubbles 7 adhere to the surface of the LDH layer 20. In this state, when the surface of the LDH layer 20 is easily wetted, i.e., when the contact angle of the surface of the LDH layer 20 is 20 degrees or more and 100 degrees or less, the electrolyte solution 8 is likely to spread on the surface of the LDH layer 20. Therefore, the electrolyte solution 8 easily enters between the surface of the LDH layer 20 and the gas bubbles 7. When the electrolyte solution 8 enters between the surface of the LDH layer 20 and the gas bubbles 7, the contact area between the LDH layer 20 and the gas bubbles 7 can be reduced. This makes it easier for the gas bubbles 7 to detach from the surface of the LDH layer 20. As a result, the effective area of ​​the water electrolysis electrode 1 is less likely to decrease in the water electrolysis reaction, and the reaction resistance of the water electrolysis reaction is less likely to increase. On the other hand, if the wettability of the surface of the LDH layer 20 is poor, i.e., if the contact angle of the surface of the LDH layer 20 exceeds 100 degrees, the electrolyte solution 8 is less likely to spread on the surface of the LDH layer 20. Therefore, the electrolyte solution 8 is less likely to enter between the surface of the LDH layer 20 and the gas bubbles 7, and the gas bubbles 7 are less likely to detach from the surface of the LDH layer 20. As a result, the effective area of ​​the water electrolysis electrode 1 is more likely to decrease in the water electrolysis reaction, and the reaction resistance of the water electrolysis reaction is more likely to increase.

[0019] In the water electrolysis electrode 1, the contact angle on the surface of the LDH layer 20 may be 26 degrees or more. This configuration provides a water electrolysis electrode 1 that is more suitable for suppressing an increase in overvoltage.

[0020] In the water electrolysis electrode 1, the contact angle of the surface of the LDH layer 20 may be 26 degrees or more and 94 degrees or less, 30 degrees or more and 80 degrees or less, or 40 degrees or more and 65 degrees or less. This configuration makes it possible to obtain a water electrolysis electrode 1 that is more suitable for suppressing an increase in overvoltage.

[0021] The LDH layer 20 is bonded to, for example, the conductive substrate 10. For example, no adhesive layer containing an organic material such as a polymer is disposed between the LDH layer 20 and the conductive substrate 10, and the LDH layer 20 is bonded directly to the surface of the conductive substrate 10.

[0022] In the water electrolysis electrode 1, the thickness of the LDH layer 20 is, for example, 1800 nm or less. This structure can increase the amount of LDH that contributes to the water electrolysis reaction and suppress an increase in resistance in the water electrolysis electrode 1. As a result, a water electrolysis electrode 1 that is more suitable for suppressing an increase in overvoltage can be obtained.

[0023] The thickness of the LDH layer 20 may be 500 nm or more, or may be 1000 nm or more. With such a structure, an increase in overvoltage in the anode reaction and the cathode reaction of water electrolysis can be further suppressed.

[0024] [Layered Double Hydroxide Layer] The thickness of the LDH layer 20 can be calculated by steps S1 to S4.

[0025] Step S1 is a step of measuring the reflection spectrum of the water electrolysis electrode 1 by spectroscopic ellipsometry to obtain measurement data E of the polarization parameters of the water electrolysis electrode 1. Step S2 is a step of creating an optical model of the water electrolysis electrode 1 and obtaining simulation data M of the polarization parameters based on the optical model. Step S3 is a step of fitting the simulation data M of the polarization parameters to the measurement data E of the polarization parameters. Step S4 is a step of calculating the thickness of the LDH layer 20 using the results of the fitting calculation according to the following formula (1):

[0026] T 20 [nm] = T 28 +T 27 +T 26 Formula (1)

[0027] In formula (1), T 20 indicates the thickness of the LDH layer 20. 28 indicates the thickness [nm] of the surface roughness layer 28. 27 indicates the thickness [nm] of the dense layer 27. 26 indicates the thickness [nm] of the interface layer 26.

[0028] In step S1, the reflection spectrum of the water electrolysis electrode 1 is measured by spectroscopic ellipsometry. In step S1, measurement data E of the polarization parameters of the water electrolysis electrode 1 can be obtained.

[0029] In step S2, an optical model of the water electrolysis electrode 1 is created. In step S2, simulation data M of polarization parameters based on the optical model can be obtained.

[0030] 3 is a cross-sectional view schematically illustrating an example of an optical model of a water electrolysis electrode obtained by spectroscopic ellipsometry. As shown in FIG. 3, the optical model 1m includes an LDH layer 20 and a conductive substrate 10. The LDH layer 20 has a predetermined thickness T 20 The LDH layer 20 has a surface roughness layer 28, a dense layer 27, and an interface layer 26. The surface roughness layer 28 has voids 25. The surface roughness layer 28 has a predetermined thickness T 28 The dense layer 27 has a predetermined thickness T 27 The interface layer 26 has a predetermined thickness T 26 It has.

[0031] Thickness T of the surface roughness layer 28 28 , the thickness T of the dense layer 27 27 , and the thickness T of the interface layer 26 26is determined by fitting, which will be described later. As shown in FIG. 3 , in the optical model 1m, the LDH layer 20 includes an interface layer 26, a dense layer 27, and a surface roughness layer 28, in that order from closest to the conductive substrate 10 in the thickness direction. The interface layer 26 is composed of the material of the conductive substrate 10 and the LDH contained in the LDH layer 20. The dense layer 27 is composed only of the LDH contained in the LDH layer 20. The surface roughness layer 28 is composed of air that may be present in the voids 25 and the LDH contained in the LDH layer 20. The volume proportions of the material of the conductive substrate 10 and the LDH in the interface layer 26 can be predetermined proportions. The volume proportions of the LDH and the air in the surface roughness layer 28 can be predetermined proportions.

[0032] In step S3, a fitting calculation is performed, in which simulation data M of the polarization parameters is fitted to measurement data E of the polarization parameters.

[0033] Based on the above optical model 1m, a fitting calculation is performed. 28 , thickness T 27 , and thickness T 26 can be determined.

[0034] The fitting calculation can be performed using, for example, predetermined software, and is performed so that the mean square error between the simulation data calculated from the optical model 1m and the measurement data is 10 degrees or less. For example, the fitting calculation may be performed using the New Amorphous equation proposed by Horiba Jobin Yvon and the Tauc-Lorentz equation, and the calculation result with the smaller mean square error may be adopted.

[0035] In step S4, the thickness T of the LDH layer 20 is calculated by the above-described formula (1) using the fitting result obtained in step S3. 20 Calculate.

[0036] [Layered double hydroxide] Fig. 4 is a diagram schematically illustrating an example of the crystal structure of an LDH. The LDH 20a contained in the LDH layer 20 is active in a reaction for producing gases such as hydrogen and oxygen at the anode or cathode of water electrolysis. For example, the LDH 20a can be converted to hydroxide during alkaline water electrolysis.

[0037] The LDH 20a has, for example, a composition represented by the following formula (2): 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.

[0038] [M1 2+ 1-x M2 3+ x (OH)2][yA n- ・mH2O] Formula (2)

[0039] The LDH 20a contains two or more types of transition metals. The two or more types of transition metals in the LDH 20a are not limited to specific transition metals. In other words, M1 and M2 in the composition represented by formula (2) are not limited to specific transition metals. The LDH 20a contains, for example, at least two transition metals selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. In this case, the water electrolysis electrode 1 can have better electrode activity.

[0040] The LDH 20a preferably contains at least one transition metal selected from the group consisting of Fe and Ni. In this case, the water electrolysis electrode 1 can have better electrode activity. In addition, the production cost of the water electrolysis electrode 1 can be easily reduced.

[0041] The LDH 20a may contain Ni and Fe, and for example, in the composition shown in formula (2), M1 may be Ni and M2 may be Fe. In this case, the water electrolysis electrode can have better electrode activity.

[0042] In LDH20a, the interlayer anion A 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 SO4 - , CH3 (CH2) n COO - , CH3 (CH2) n PO4 2- , and CH3(CH2) n No. 3 - It is. A n- can be intercalated between the layers of the metal hydroxide along with water molecules. n- The charge and ion size of LDH20a are not limited to a specific value. n- or a plurality of types of A n- may also include:

[0043] As shown in FIG. 4, LDH20a is a soluble form of M1 2+ or M2 3+ OH at each vertex of the octahedron centered at - LDH20a contains [M1 2+ 1-x M2 3+ x (OH) x+ This metal hydroxide 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 acts 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 20a as a whole is composed of a host layer 21 of metal hydroxide and an anion A n- The LDH 20a 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

[0044] The crystal structure and crystallinity of LDH20a can be qualitatively and quantitatively analyzed by X-ray diffraction measurement (XRD).

[0045] [Chelating Agent] The LDH layer 20 may contain a chelating agent. The chelating agent may be coordinated to a transition metal ion contained in the LDH 20a. This allows the LDH 20a to be stably present in the LDH layer 20. In addition, the LDH 20a is likely to have a small particle size. In addition, the LDH layer 20 is likely to be a dense layer containing the LDH 20a with few voids, and is likely to be firmly fixed to the conductive substrate 10 with a desired thickness. This is because, when the LDH layer 20 is formed on the conductive substrate 10, nucleated LDH is likely to undergo slow crystal growth. As a result, the LDH layer 20 is likely to effectively contribute to the anode reaction or cathode reaction of water electrolysis, and the water electrolysis electrode 1 can have superior electrode activity.

[0046] 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 LDH20a. 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 hydroxycarboxylate 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.

[0047] The chelating agent preferably contains at least one selected from the group consisting of acetylacetone and citrate, which can improve the electrode activity of the water electrolysis electrode 1. An example of the citrate is trisodium citrate.

[0048] [Conductive Substrate] The shape of the conductive substrate 10 is not limited to a specific shape. The conductive substrate 10 is, for example, sheet-shaped. 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 preferably has a porous structure. In this case, the surface area of ​​the conductive substrate 10 can be increased, and gas generated in the water electrolysis reaction can be easily diffused.

[0049] The conductive substrate 10 is not limited to a specific substrate as long as it is conductive. The conductive substrate 10 may contain a metal or 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 iron, or an alloy such as stainless steel or Inconel. Inconel is a registered trademark.

[0050] The surface of the conductive substrate 10 is preferably made of nickel. In this case, the conductive substrate 10 tends to have excellent alkali resistance. When the surface of the conductive substrate 10 is made of nickel, the entire conductive substrate 10 may be made of nickel, or the conductive substrate 10 may have a surface layer made of nickel. The surface layer made of nickel is a sputtered film or a plated film.

[0051] [Manufacturing method of electrode for water electrolysis] Figure 5 is a flowchart showing an example of a method for manufacturing an electrode for water electrolysis. The method for manufacturing an electrode for water electrolysis according to this embodiment includes steps S10 to S13. Step S10 is a step of preparing a solution. Step S11 is a step of immersing a conductive substrate in the solution. Step S12 is a step of promoting mixing of the solution. Step S13 is a step of adjusting the solution to be alkaline at room temperature. As a result, a layered double hydroxide is synthesized in the solution, and an LDH layer containing the layered double hydroxide is formed on the surface of the conductive substrate. As a result, an electrode for water electrolysis can be manufactured in the solution.

[0052] "Room temperature" means a temperature range of 20°C ± 15°C as specified in Japanese Industrial Standards (JIS) Z 8703.

[0053] In step S10, a solution S is prepared. In step S10, a solution for synthesizing a layered double hydroxide is prepared.

[0054] The precursor solution for preparing solution S contains two or more types of transition metal ions. At least one of the two or more types of transition metal ions may be an ion of a transition metal contained in a layered double hydroxide described below. The two or more types of transition metal ions include, for example, ions of at least two transition metals selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. A water electrolysis electrode 1 having excellent electrode activity can be obtained by using a layered double hydroxide containing these transition metals.

[0055] The two or more types of transition metal ions preferably include ions of at least one transition metal selected from the group consisting of Ni and Fe. In this case, a water electrolysis electrode 1 having superior electrode activity can be produced.

[0056] The solvent for the precursor solution may be water, an organic solvent, or a mixed solvent of water and an organic solvent.

[0057] The solution S is prepared, for example, by adding a chelating agent to the precursor solution. The chelating agent may be selected with reference to the above examples of chelating agents contained in the LDH layer 20. 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 LDH layer 20 on the surface of the conductive substrate 10. As a result, the water electrolysis electrode 1 can have superior electrode activity. An example of the citrate is trisodium citrate.

[0058] By adjusting the content of the chelating agent in the solution S, the LDH layer 20 is likely to be formed in a desired state in the water electrolysis electrode 1. Specifically, by adjusting the content of the chelating agent in the solution S, the contact angle on the surface of the LDH layer 20 can be adjusted to 20 degrees or more and 100 degrees or less. This makes it possible to obtain a water electrolysis electrode 1 that is more suitable for suppressing an increase in overvoltage.

[0059] In step S11, the conductive substrate 10 is immersed in the solution S. In step S11, the metal contained in the conductive substrate 10 is dissolved into the solution S.

[0060] The surface of the conductive substrate 10 is preferably made of nickel. In this case, it is easy to produce a water electrolysis electrode 1 that has advantageous properties, for example, from the viewpoint of achieving both corrosion resistance and electrical conductivity in alkaline water electrolysis.

[0061] The conductive substrate 10 preferably contains Ni. The two or more types of transition metal ions contained in the solution S preferably contain Fe ions. The solution S preferably contains chloride ions. In this case, the reaction shown in formula (3) may occur. This may cause etching of the conductive substrate 10. Specifically, the Fe ions and chloride ions contained in the solution S react with the conductive substrate 10. This causes etching of the conductive substrate 10 by the Fe ions and chloride ions. As a result, Ni contained in the conductive substrate 10 is dissolved into the solution S.

[0062] 4Ni 2+ Cl - 2 + 2Fe 3+ Cl - 3 + 2Ni → 5Ni 2+ Cl - 2 + 2Fe 2+ Cl - 2 + Ni Equation (3)

[0063] In the production of the water electrolysis electrode 1, the ratio R of the amount of Fe ions in the solution S to the amount of Ni in the conductive base material 10 is not limited to a specific value. The ratio R is, for example, 0.75 or less. In this case, it is possible to prevent the nickel in the conductive base material 10 from dissolving due to the reaction represented by formula (3), which would make it difficult to produce the water electrolysis electrode 1. The lower limit of the ratio R is not particularly limited and is, for example, 0.02.

[0064] The ratio R is preferably 0.04 or more and 0.10 or less. In this case, the LDH layer 20 is more likely to be formed uniformly on the surface of the conductive substrate 10, and a water electrolysis electrode 1 having superior electrode activity can be produced.

[0065] In the production of the water electrolysis electrode 1, the value W obtained by dividing the amount of Fe ions contained in the solution S by the surface area of ​​the conductive substrate 10 is not limited to a specific value. The value W may be, for example, 0.29 millimoles (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 (3), which would make it difficult to manufacture the water electrolysis electrode. The lower limit of W is not particularly limited, and may be, for example, 0.05 mmol / cm 2 is.

[0066] The value W is preferably 0.01 mmol / cm 2 0.2 mmol / cm or more 2 In this case, the LDH layer 20 is likely to be formed uniformly on the surface of the conductive substrate 10, and a water electrolysis electrode 1 having excellent electrode activity is likely to be produced.

[0067] Next, in step S12, mixing of the solution S is promoted. In step S12, an LDH layer 20 is formed on the surface of the conductive substrate 10 to obtain a water electrolysis electrode 1.

[0068] By promoting the mixing of the solution S, the conductive substrate 10 is etched and an LDH layer 20 is formed on the surface of the conductive substrate 10 .

[0069] Methods for promoting the mixing of the solution S include vibrating the conductive substrate 10, shaking the container in which the solution S and the conductive substrate 10 are sealed, and stirring the solution S using a stirrer piece and a stirrer. Such methods cause forced convection of the solution S, promoting the mixing of the solution S. The promotion of the mixing of the solution S may be carried out while the container containing the solution S and the conductive substrate 10 is sealed, or may be carried out in an inert gas atmosphere.

[0070] "Promoting the mixing of the solution S" means promoting the diffusion of Ni ions eluted from the conductive substrate 10 into the solution S by the above-mentioned method.

[0071] Step S13 is a step of adjusting the solution S to be alkaline. In step S13, an LDH layer 20 is formed on the conductive substrate 10 to obtain a water electrolysis electrode 1.

[0072] Step S13 forms the LDH layer 20. The LDH layer 20 is formed on the surface of the conductive substrate 10.

[0073] The method for adjusting the solution S to alkaline, i.e., the method for adjusting the pH of the solution to a value greater than 7, is not limited to a specific method. For example, the solution S may be adjusted to alkaline by mixing the solution S with an alkaline solution. Alternatively, the solution S may be adjusted to alkaline by adding a pH-raising agent to the solution S. 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 (POX), ethylene oxide, and butylene oxide.

[0074] 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 ions, 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 this solution S, the pH of solution S gradually increases from, for example, 1, and eventually, solution S becomes 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 may take several days.

[0075] The temperature of the solution S when adjusted to be alkaline is not limited to a specific temperature. The temperature of the solution S is, for example, room temperature. In this case, a water electrolysis electrode 1 having excellent electrode activity is likely to be obtained.

[0076] Step S13 preferably includes increasing the pH. This allows a layered double hydroxide to be formed on the surface of the conductive substrate 10 in a short period of time, making it easier to obtain a water electrolysis electrode 1 with excellent electrode activity. In addition, the produced water electrolysis electrode 1 is likely to have excellent durability.

[0077] FIG. 6 is a schematic diagram illustrating the mechanism of manufacturing a water electrolysis electrode. As shown in FIG. 6 , a conductive substrate 10 is immersed in a solution containing transition metal ions TM1, TM2, and a chelating agent 30. For example, the transition metal ions TM1 are Ni ions, and the transition metal ions TM2 are Fe ions. In addition, Ni is present on the surface of the conductive substrate 10. Some of the transition metal ions TM2 etch and dissolve the Ni present on the surface of the conductive substrate 10. Some of the chelating agent 30 reacts with the surface of the conductive substrate 10 to form a complex C1 between the transition metal ions TM1 derived from the conductive substrate 10 and the chelating agent 30. In addition, when the solution is adjusted to an alkaline pH, a complex C1 derived from the transition metal ions TM1 derived from the solution and the chelating agent 30 is formed in the solution, and a complex C2 between the transition metal ions TM2 and the chelating agent 30 is formed. Next, the complexes C1 and C2 react on the surface of the conductive substrate 10, synthesizing LDH 20a along the surface of the conductive substrate 10. In addition, the crystal growth of the LDH 20a is suppressed because the complexes C1 and C2 contain the chelating agent 30. As a result, an LDH layer 20 containing the LDH 20a and the chelating agent 30 is formed on the conductive substrate 10, and a water electrolysis electrode 1 is obtained.

[0078] The water electrolysis electrode 1 according to this embodiment can be used, for example, as an electrode in a water electrolysis cell of an alkaline water electrolysis apparatus or an anion exchange membrane water electrolysis apparatus. The water electrolysis 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 apparatuses. In other words, at least one selected from the group consisting of a water electrolysis anode including the water electrolysis electrode 1 and a water electrolysis cathode including the water electrolysis electrode 1 can be provided. This tends to increase the activity of the anode reaction or the cathode reaction in water electrolysis.

[0079] Second Embodiment Figure 7 is a cross-sectional view schematically illustrating an example of a water electrolysis cell according to a second embodiment. As shown in Figure 7, 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 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 improved, and the anode 2a or the cathode 2b is likely to exhibit excellent performance.

[0080] 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 alkaline aqueous solutions include a potassium hydroxide aqueous solution and a sodium hydroxide aqueous solution.

[0081] 7 , 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] When the anode 2a includes the water electrolysis electrode 1, the cathode 2b may include, for example, a known electrode material for the cathode of an alkaline water electrolysis cell. When the cathode 2b includes the water electrolysis electrode 1, the anode 2a may include a known electrode material for the anode of an alkaline water electrolysis cell. In the water electrolysis cell 2, both the anode 2a and the cathode 2b may include the water electrolysis electrode 1.

[0086] 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 electrode 1, and therefore the water electrolysis cell 2 can exhibit excellent performance.

[0087] Third Embodiment Fig. 8 is a cross-sectional view schematically illustrating an example of a water electrolysis apparatus according to a third embodiment. As shown in Fig. 8, 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.

[0088] 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. In the power-type power supply, 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 apparatus 3 reaches a predetermined set value.

[0089] With the above configuration, the water electrolysis device 3 can exhibit excellent performance.

[0090] Fourth Embodiment Figure 9 is a cross-sectional view schematically illustrating an example of a water electrolysis cell according to a fourth embodiment. As shown in Figure 9, the water electrolysis cell 4 includes an anode 4a, a cathode 4b, and an electrolyte 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 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 excellent performance.

[0091] The water electrolysis cell 4 is, for example, an anion exchange membrane (AEM)-type water electrolysis cell. As shown in Fig. 9 , 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 electrolyte membrane 4p, and the catalyst layer 4j of the cathode 4b is in contact with the other main surface of the electrolyte membrane 4p. The electrolyte membrane 4p is, for example, an anion exchange membrane.

[0092] The electrolyte membrane 4p is not limited to a specific type of electrolyte membrane. The electrolyte membrane 4p may include an anion exchange membrane. The electrolyte membrane 4p may be an anion exchange membrane. When the electrolyte membrane 4p is an anion exchange membrane, the electrolyte membrane 4p is not limited to a specific type of anion exchange membrane. The anion exchange membrane has conductivity of anions such as hydroxide ions. The anion exchange membrane 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.

[0093] In the water electrolysis cell 4, when the anode 4a includes the water electrolysis electrode 1, the cathode 4b may be a known cathode for AEM-type water electrolysis cells. In this case, the LDH layer 20 of the water electrolysis electrode 1 may function as the catalytic layer 4m, and the conductive substrate 10 of the water electrolysis electrode 1 may function as the gas diffusion layer 4n. In the water electrolysis cell 4, when the cathode 4b includes the water electrolysis electrode 1, the anode 4a may be a known anode for AEM-type water electrolysis cells. In this case, the LDH layer 20 of the water electrolysis electrode 1 may function as the catalytic layer 4j, and the conductive substrate 10 of the water electrolysis electrode 1 may function as the gas diffusion layer 4k. In the water electrolysis cell 4, both the anode 4a and the cathode 4b may include the water electrolysis electrode 1.

[0094] 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 electrode 1, and therefore the water electrolysis cell 4 can exhibit excellent performance.

[0095] Fifth Embodiment Fig. 10 is a cross-sectional view schematically illustrating an example of a water electrolysis apparatus according to a fifth embodiment. As shown in Fig. 10, 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.

[0096] 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.

[0097] With the above configuration, the water electrolysis device 5 can exhibit excellent performance.

[0098] (Other Embodiments) (Additional Notes) From the above description, the following techniques are disclosed.

[0099] (Technology 1) An electrode for water electrolysis, comprising: a conductive substrate; and a layered double hydroxide layer containing two or more types of transition metals provided on the surface of the conductive substrate, wherein the contact angle of the surface of the layered double hydroxide layer with a 6 mol / L aqueous potassium hydroxide solution is 20 degrees or more and 100 degrees or less.

[0100] According to technique 1, it is possible to provide an electrode for water electrolysis that is advantageous from the viewpoint of suppressing an increase in overvoltage.

[0101] (Technology 2) The electrode for water electrolysis according to Technology 1, wherein the contact angle of the surface of the layered double hydroxide layer is 26 degrees or more.

[0102] According to the second technique, it is possible to provide an electrode for water electrolysis that is more suitable for suppressing an increase in overvoltage.

[0103] (Technology 3) The electrode for water electrolysis according to Technology 1 or 2, wherein the layered double hydroxide layer contains at least two transition metals selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. Technology 3 makes it likely that the electrode for water electrolysis will have excellent electrode activity.

[0104] (Technology 4) The water electrolysis electrode according to any one of Technologies 1 to 3, wherein the layered double hydroxide layer contains at least one transition metal selected from the group consisting of Ni and Fe. Technology 4 allows the water electrolysis electrode to have better electrode activity.

[0105] (Technology 5) The electrode for water electrolysis according to any one of Technologies 1 to 4, wherein the layered double hydroxide layer contains a chelating agent.

[0106] (Technology 6) The electrode for water electrolysis according to Technology 5, wherein the chelating agent includes at least one selected from the group consisting of acetylacetone and citrate.

[0107] According to Techniques 5 and 6, the water electrolysis electrode can have better electrode activity.

[0108] (Technology 7) The electrode for water electrolysis according to any one of Technologies 1 to 6, wherein the layered double hydroxide layer has a thickness of 500 nm or more. Technology 7 can further suppress an increase in overvoltage in the anodic reaction and cathodic reaction of water electrolysis.

[0109] (Technology 8) The electrode for water electrolysis according to any one of Technologies 1 to 7, wherein the layered double hydroxide layer has a thickness of 1800 nm or less. According to Technology 8, the electrode for water electrolysis can have better electrode activity.

[0110] (Technology 9) An anode for water electrolysis, comprising the electrode for water electrolysis according to any one of Technologies 1 to 8.

[0111] (Technology 10) A cathode for water electrolysis, comprising the electrode for water electrolysis according to any one of Technologies 1 to 8.

[0112] Techniques 9 and 10 tend to increase the activity of the anode reaction or cathode reaction in water electrolysis.

[0113] (Technology 11) A water electrolysis cell comprising: an anode; a cathode; and a diaphragm, wherein at least one selected from the group consisting of the anode being the anode for water electrolysis according to Technology 9 and the cathode being the cathode for water electrolysis according to Technology 10 is satisfied.

[0114] (Technology 12) A water electrolysis cell comprising: an anode; a cathode; and an electrolyte membrane, wherein the anode is the anode for water electrolysis according to Technology 9; and the cathode is the cathode for water electrolysis according to Technology 10.

[0115] Techniques 11 and 12 tend to improve the activity of the anode reaction or the cathode reaction in a water electrolysis cell.

[0116] (Technology 13) A water electrolysis device comprising: the water electrolysis cell according to Technology 11 or 12; and a voltage applicator connected to the cathode and the anode, for applying a voltage between the cathode and the anode.

[0117] According to Technique 13, the water electrolysis device can exhibit excellent performance.

[0118] (Technology 14) A method for producing an electrode for water electrolysis, comprising a conductive substrate and a layered double hydroxide layer provided on a surface of the conductive substrate, the method comprising: preparing a solution containing a chelating agent and two or more types of transition metal ions; immersing the conductive substrate, which contains a transition metal of the same type as at least one of the two or more types of transition metal ions, in the solution; promoting mixing of the solution; and adjusting the solution to be alkaline at room temperature, wherein the contact angle of the surface of the layered double hydroxide layer with a 6 mol / L aqueous potassium hydroxide solution is 20 degrees or more and 100 degrees or less.

[0119] According to Technique 14, the water electrolysis electrode of the present disclosure can be produced.

[0120] (Technology 15) The method for producing an electrode for water electrolysis according to Technology 14, further comprising increasing the pH of the solution. According to Technology 15, a layered double hydroxide can be formed on the conductive substrate in a short period of time.

[0121] (Technology 16) The method for producing an electrode for water electrolysis according to Technology 14 or 15, wherein the two or more types of transition metal ions include ions of at least two transition metals selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru.

[0122] (Technology 17) The method for producing an electrode for water electrolysis according to any one of Techniques 14 to 16, wherein the two or more types of transition metal ions include an ion of at least one transition metal selected from the group consisting of Ni and Fe.

[0123] (Technology 18) The method for producing an electrode for water electrolysis according to any one of Techniques 14 to 17, wherein the conductive substrate contains Ni.

[0124] According to Techniques 16 to 18, electrodes for water electrolysis having superior electrode activity can be produced.

[0125] 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.

[0126] Example 1: A solution was prepared by dissolving 0.226 g of nickel chloride hexahydrate and 0.128 g of iron chloride hexahydrate in 3.32 milliliters (mL) of water. Nickel chloride hexahydrate and iron chloride hexahydrate were purchased from Fujifilm Wako Pure Chemical Industries, Ltd. 0.04 mL of acetylacetone (ACAC) was added to this solution as a chelating agent to obtain a chelating agent-containing solution. Acetylacetone was purchased from Sigma-Aldrich. The amount of acetylacetone in the chelating agent-containing solution was 1 / 3.65 of the total amount of Ni ions and Fe ions.

[0127] A Ni plate manufactured by Nilaco Corporation was cleaned with acetone for 10 minutes and then with a 1 mol / L HCl aqueous solution for 10 minutes to degrease the Ni plate and remove impurities. The Ni plate had a thickness of 0.2 mm and a cylindrical shape with a diameter of 15 mm in plan view. The surface area of ​​the Ni plate was 3.63 cm. 2 The mass of the Ni plate was 0.335 g. Next, the Ni plate was washed with water and dried, completing the cleaning process of the Ni plate.

[0128] Next, the Ni plate 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 plate was shaken and stirred at room temperature for 24 hours. At this time, the outermost surface of the Ni plate was etched according to the above-mentioned formula (3). In this case, the ratio R of the amount of substance of Fe ions contained in the chelating agent-containing solution to the amount of substance of Ni contained in the Ni plate was 0.083. The value W obtained by dividing the amount of substance of Fe ions contained in the chelating agent-containing solution by the surface area of ​​the Ni plate was 0.13 mmol / cm 2 It was.

[0129] Then, 0.480 mL of propylene oxide (POX) was added to the chelating agent-containing solution as a pH-raising agent. The resulting mixed solution was shaken and stirred at room temperature for 72 hours. During this time, the POX gradually captured hydrogen ions in the solution, causing the pH of the solution to gradually increase. After 72 hours of shaking and stirring, the Ni plate was recovered, washed with water, and dried. In this way, the electrode according to Example 1 was obtained.

[0130] Example 2 An electrode according to Example 2 was fabricated in the same manner as Example 1, except for the following points. A solution was prepared by dissolving 0.124 g of nickel chloride hexahydrate and 0.07 g of iron chloride hexahydrate in 3.64 mL of water. 0.0061 mL of ACAC was added to this solution as a chelating agent to obtain a chelating agent-containing solution. The substance amount of ACAC in the chelating agent-containing solution was 1 / 13 of the total substance amount of Ni ions and Fe ions. The mass of the Ni plate was 0.315 g. 0.265 mL of POX was added to the chelating agent-containing solution as a pH-increasing agent. The ratio R was 0.049. The value W was 0.07 mmol / cm. 2 It was.

[0131] Example 3 An electrode according to Example 3 was fabricated in the same manner as Example 1, except for the following points. A solution was prepared by dissolving 0.124 g of nickel chloride hexahydrate and 0.07 g of iron chloride hexahydrate in 3.64 mL of water. 0.123 mL of ACAC was added to this solution as a chelating agent to obtain a chelating agent-containing solution. The substance amount of ACAC in the chelating agent-containing solution was 1.5 times the total substance amount of Ni ions and Fe ions. The mass of the Ni plate was 0.315 g. 0.265 mL of POX was added to the chelating agent-containing solution as a pH-increasing agent. The ratio R was 0.049. The value W was 0.07 mmol / cm. 2 It was.

[0132] Example 4 An electrode according to Example 4 was fabricated in the same manner as Example 1, except for the following points. A solution was prepared by dissolving 0.123 g of nickel chloride hexahydrate and 0.07 g of iron chloride hexahydrate in 3.61 mL of water. 0.486 mL of ACAC was added as a chelating agent to this solution to obtain a chelating agent-containing solution. The substance amount of ACAC in the chelating agent-containing solution was 6.1 times the total substance amount of Ni ions and Fe ions. The mass of the Ni plate was 0.315 g. 0.262 mL of POX was added as a pH-increasing agent to the chelating agent-containing solution. The ratio R was 0.049. The value W was 0.07 mmol / cm. 2 It was.

[0133] Comparative Example 1 An electrode according to Comparative Example 1 was prepared in the same manner as in Example 1, except for the following points. A solution was prepared by dissolving 0.065 g of nickel chloride hexahydrate and 0.037 g of iron chloride hexahydrate in 3.80 mL of water. 0.0128 mL of ACAC was added to this solution as a chelating agent to obtain a chelating agent-containing solution. The substance amount of ACAC in the chelating agent-containing solution was 1 / 3.27 of the total substance amount of Ni ions and Fe ions. The mass of the Ni plate was 0.335 g. 0.138 mL of POX was added to the chelating agent-containing solution as a pH-increasing agent. The ratio R was 0.02. The value W was 0.08 mmol / cm. 2 It was.

[0134] [Evaluation of Layered Double Hydroxide Layer Thickness] Measurements were performed on a single central point of each electrode using a Horiba UVISEL2 spectroscopic ellipsometer under the following conditions: an incident angle of 70°, a measurement wavelength range of 0.6 eV to 5.5 eV, and a spot diameter of 1 mm x 2 mm. This resulted in measurement data E of the polarization parameters. Next, an optical model such as that shown in Figure 3 was created, and simulation data M of the polarization parameters based on the optical model was obtained. The simulation data M of the polarization parameters was then fitted to the measurement data E of the polarization parameters. Specifically, the measurement data E was analyzed using Delta Psi2 software included with the UVISEL2, and the thicknesses of the interface layer, dense layer, and surface roughness layer were determined using the optical model shown in Figure 3. The fitting calculations in this analysis used the New Amorphous equation proposed by Horiba Jobin-Yvon and the Tauc-Lorentz equation. The result with the smallest mean square error between the simulation data M calculated from the optical model and the measurement data E was adopted. In addition, the fitting calculation was performed so that the mean square error was less than 10 degrees.

[0135] The thickness T of the interface layer obtained by the above method 26 , the thickness of the dense layer T 27 , and the thickness of the surface roughness layer T 26 Based on the above formula (1), the thickness T of the layered double hydroxide layer is calculated. 20 The results are shown in Table 1.

[0136] [Contact Angle Measurement] The contact angle was measured by the θ / 2 method using a contact angle measuring instrument DM-501 manufactured by Kyowa Interface Science Co., Ltd. The contact angle was evaluated by dropping 0.2 microliters (μL) of potassium hydroxide aqueous solution onto the surface of the electrode. The concentration of the potassium hydroxide aqueous solution was 6 mol / L. The results are shown in Table 1. The contact angle measurement was performed three times for the electrodes according to each example and comparative example. The contact angle values ​​shown in Table 1 are the average values ​​obtained from the three measurements.

[0137] [Evaluation of Electrode Overpotential] The oxygen evolution (OER) overpotential of the electrodes in each Example and Comparative Example was evaluated. For the measurements, a potentiostat VersaSTAT4 manufactured by Princeton Applied Research, an alkali sample vial (200 mL) manufactured by BAS, and a Teflon cap (for 200 mL) manufactured by BAS were used. An AE-2 plate electrode manufactured by EC Frontier was used as the working electrode fixture. The working electrodes of each Example and Comparative Example 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.

[0138] (Measurement conditions) Solution: 1 mol / L 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

[0139] Current density at the fifth cycle: 10 mA / cm 2 The overpotential was determined by subtracting the theoretical potential of 1.229 V required for the oxygen evolution reaction to proceed from the voltage corresponding to the reaction. The results are shown in Table 1.

[0140]

[0141] As shown in Table 1, the electrodes according to each Example had a contact angle of 20 degrees or more and 100 degrees or less on the surface of the layered double hydroxide layer. In addition, the electrodes according to each Example had an overvoltage of 255 mV or less, and an increase in the overvoltage was suppressed. This result indicates that the water electrolysis electrodes used in each Example were excellent in terms of electrode activity.

[0142] 11 is a graph showing the relationship between contact angle and overvoltage in each example and comparative example. In FIG. 11, the horizontal axis represents contact angle, and the vertical axis represents overvoltage. In addition, curve X represents an approximation curve of the plots in each example and comparative example. Line Y, parallel to the horizontal axis, represents the line where the overvoltage is 255 mV.

[0143] As shown in Fig. 11 , curve X has a minimum value when the contact angle is around 60 degrees. This shows that an increase in overvoltage can be suppressed by appropriately adjusting the contact angle. In addition, as is clear from curve X and line Y, it is estimated that the overvoltage will be 255 mV or less if the contact angle is 20 degrees or more and 100 degrees or less. In other words, it is estimated that a water electrolysis electrode that can suppress an increase in overvoltage can be obtained if the contact angle is 20 degrees or more and 100 degrees or less.

[0144] The water electrolysis electrode of the present disclosure can be used as an anode or a cathode for water electrolysis.

Claims

1. A conductive substrate; a layered double hydroxide layer having two or more types of transition metals provided on a surface of the conductive substrate, the contact angle of the surface of the layered double hydroxide layer with respect to a 6 mol / L aqueous potassium hydroxide solution is 20 degrees or more and 100 degrees or less; Electrode for water electrolysis.

2. the contact angle on the surface of the layered double hydroxide layer is 26 degrees or more; The electrode for water electrolysis according to claim 1 .

3. The layered double hydroxide layer contains at least two transition metals selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. The electrode for water electrolysis according to claim 1 .

4. The layered double hydroxide layer contains at least one transition metal selected from the group consisting of Ni and Fe. The electrode for water electrolysis according to claim 1 .

5. The layered double hydroxide layer contains a chelating agent. The electrode for water electrolysis according to claim 1 .

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

7. The thickness of the layered double hydroxide layer is 500 nm or more. The electrode for water electrolysis according to claim 1 .

8. The thickness of the layered double hydroxide layer is 1800 nm or less. The electrode for water electrolysis according to claim 1 .

9. Equipped with the water electrolysis electrode according to claim 1, Anode for water electrolysis.

10. Equipped with the water electrolysis electrode according to claim 1, Cathode for water electrolysis.

11. An anode; A cathode; a diaphragm; the anode is the anode for water electrolysis according to claim 9, and the cathode is the cathode for water electrolysis according to claim 10. water electrolysis cell.

12. An anode; A cathode; An electrolyte membrane; the anode is the anode for water electrolysis according to claim 9, and the cathode is the cathode for water electrolysis according to claim 10. water electrolysis cell.

13. The water electrolysis cell according to claim 11; a voltage applicator connected to the cathode and the anode and applying a voltage between the cathode and the anode; Water electrolysis equipment.

14. The water electrolysis cell according to claim 12, a voltage applicator connected to the cathode and the anode and applying a voltage between the cathode and the anode; Water electrolysis equipment.

15. A method for producing an electrode for water electrolysis comprising a conductive substrate and a layered double hydroxide layer provided on a surface of the conductive substrate, comprising: preparing a solution containing a chelating agent and two or more transition metal ions; Immersing the conductive substrate containing the same transition metal as at least one of the two or more transition metal ions in the solution; promoting mixing of the solution; and Adjusting the solution to be alkaline at room temperature; the contact angle of the surface of the layered double hydroxide layer with respect to a 6 mol / L aqueous potassium hydroxide solution is 20 degrees or more and 100 degrees or less; A method for manufacturing an electrode for water electrolysis.

16. increasing the pH of the solution. The method for producing the water electrolysis electrode according to claim 15.

17. The two or more transition metal ions include ions of at least two transition metals selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru; The method for producing the water electrolysis electrode according to claim 15.

18. The two or more transition metal ions include at least one transition metal ion selected from the group consisting of Ni and Fe. The method for producing the water electrolysis electrode according to claim 15.

19. The conductive substrate contains Ni. The method for producing the water electrolysis electrode according to claim 15.