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

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

Technical Field

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

Background Art

[0002] As an electrode catalyst for water electrolysis, for example, layered double hydroxide (LDH) is known.

[0003] In Non-Patent Document 1, the activity of an oxygen evolution reaction (OER) of an electrode provided with Ni-Fe layered double hydride (Ni-Fe LDH) has been studied.

[0004] Non-Patent Document 2 describes that the interfacial interaction between FeOOH and Ni-Fe LDH adjusts the local electronic structure of Ni-Fe LDH and enhances the OER electrode catalysis.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

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

Means for Solving the Problems

[0007] The present disclosure provides a conductive substrate, a layered double hydroxide layer having two or more transition metals provided on the surface of the conductive substrate, and 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, an electrode for water electrolysis.

Effects of the Invention

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

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

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Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Mode for Carrying Out the Invention

[0010] (Knowledge on which the present disclosure is based) As a measure against global warming, the use of renewable energy such as sunlight and wind power has attracted attention. In power generation using renewable energy, there is a problem that surplus power is wasted. For this reason, the utilization efficiency of renewable energy is not always sufficient. Therefore, a method of effectively utilizing surplus power by producing and storing hydrogen from surplus power has been studied.

[0011] As a method for producing hydrogen from surplus power, electrolysis of water can be considered. In order to produce hydrogen inexpensively and stably, the development of a highly efficient water electrolysis apparatus is required.

[0012] 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 anodic reaction, and the reaction in which hydrogen is generated at the cathode is also called the cathodic reaction. In order to provide a water electrolysis device with excellent electrode efficiency, it is particularly desirable that the overvoltage is low at the anode. In addition, it is desirable that the overvoltage is also low at the cathode. Therefore, the development of an electrode catalyst for water electrolysis suitable for suppressing an increase in overvoltage is expected.

[0013] For example, a layered double hydroxide (LDH) containing two or more transition metals is promising as an electrode catalyst for a water electrolysis electrode from the viewpoints of a large specific surface area and various 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 equipped with such a water electrolysis electrode, bubbles generated by the water electrolysis reaction may cause a voltage drop. As a result, the electrolysis efficiency decreases. Specifically, bubbles such as oxygen and hydrogen 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 while the bubbles are attached to the surface of the water electrolysis electrode. When bubbles adhere to the surface of the water electrolysis electrode or the size of the bubbles attached to the surface of the water electrolysis electrode increases, the effective area of the water electrolysis electrode decreases. As a result, the reaction resistance of the water electrolysis reaction increases. The reaction resistance of the water electrolysis reaction increases the overvoltage, and as a result, the electrolysis efficiency decreases. As a result of intensive studies, the present inventors have newly found that an increase in overvoltage can be suppressed by appropriately adjusting the contact angle of the surface of the LDH layer in the water electrolysis electrode. 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 specifically described with reference to the drawings. Note that all the embodiments described below show comprehensive or specific examples. Therefore, the numerical values, shapes, materials, components, arrangement positions of the components, connection forms, etc. shown in the following embodiments are merely examples and are not intended to limit the present disclosure. In addition, among the components in the following embodiments, the components not described in the independent claims indicating the most general concept are described as optional components. In the drawings, components with the same reference numerals may be omitted from the description. In addition, for ease of understanding, the drawings schematically show each component, and the shapes, dimensional ratios, etc. may not be accurately shown. In the manufacturing method, the order of the steps may be changed or known steps may be added as necessary.

[0015] (First Embodiment) FIG. 1 is a cross-sectional view schematically showing an example of an electrode for water electrolysis of the present disclosure. As shown in FIG. 1, the electrode 1 for water electrolysis 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 covered by the LDH layer 20. The LDH layer 20 can function as a catalyst for the anodic reaction or cathodic reaction of water electrolysis. The LDH layer 20 contains LDH as a catalyst for water electrolysis.

[0016] In the electrode 1 for water electrolysis, 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 / liter (mol / L) potassium hydroxide aqueous solution. According to such a configuration, an electrode 1 for water electrolysis suitable for suppressing an increase in overvoltage can be provided.

[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 droplet of 0.2 microliters (μL) of a 6 mol / L potassium hydroxide aqueous solution is attached to the surface of the LDH layer 20 of the water electrolysis electrode 1. Then, the contact angle of the surface of the LDH layer 20 can be measured by measuring the angle formed between the tangent of this droplet and the surface of the LDH layer 20 with a contact angle meter. For the measurement of the contact angle, a micro contact angle meter or a ultra-micro contact angle meter may be used. With a micro contact angle meter or an ultra-micro contact angle meter, a very small amount of droplets in the nanoliter to picoliter order can be formed 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 containing 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 diagram schematically showing the relationship between the 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. 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 be 20 degrees or more and 100 degrees or less, the bubbles 7 generated from the water electrolysis electrode 1 are likely to separate 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 wettable, that is, when the contact angle of the surface of the LDH layer 20 is 20 degrees or more and 100 degrees or less, the electrolytic solution 8 is likely to spread on the surface of the LDH layer 20. Therefore, the electrolytic solution 8 is likely to enter between the surface of the LDH layer 20 and the bubbles 7. When the electrolytic solution 8 enters between the surface of the LDH layer 20 and the bubbles 7, the contact area between the LDH layer 20 and the bubbles 7 can be reduced. As a result, the bubbles 7 are likely to separate from the surface of the LDH layer 20. As a result, in the water electrolysis reaction, the effective area of the water electrolysis electrode 1 is less likely to be reduced, and the reaction resistance of the water electrolysis reaction is less likely to increase. On the other hand, when the wettability of the surface of the LDH layer 20 is poor, that is, when the contact angle of the surface of the LDH layer 20 exceeds 100 degrees, the electrolytic solution 8 is unlikely to spread on the surface of the LDH layer 20. Therefore, the electrolytic solution 8 is unlikely to enter between the surface of the LDH layer 20 and the bubbles 7, and the bubbles 7 are unlikely to separate from the surface of the LDH layer 20. As a result, in the water electrolysis reaction, the effective area of the water electrolysis electrode 1 is likely to be reduced, and the reaction resistance of the water electrolysis reaction is likely to increase.

[0019] In the water electrolysis electrode 1, the contact angle of the surface of the LDH layer 20 may be 26 degrees or more. According to such a configuration, a water electrolysis electrode 1 more suitable for suppressing the increase in overvoltage can be obtained.

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

[0021] The LDH layer 20 is bonded to the conductive substrate 10, for example. For example, an adhesive layer containing an organic material such as a polymer is not disposed between the LDH layer 20 and the conductive substrate 10, and the LDH layer 20 is directly bonded to the surface of the conductive substrate 10.

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

[0023] The thickness of the LDH layer 20 may be 500 nm or more or 1000 nm or more. According to such a structure, an increase in overvoltage in the anodic reaction and cathodic 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 electrode 1 for water electrolysis by spectroscopic ellipsometry and obtaining measurement data E of the polarization parameters of the electrode 1 for water electrolysis. Step S2 is a step of creating an optical model of the electrode 1 for water electrolysis 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 by the following formula (1) using the result of the fitting calculation.

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

[0027] In Formula (1), T 20 represents the thickness of the LDH layer 20. T 28 represents the thickness [nm] of the surface roughness layer 28. T 27 represents the thickness [nm] of the dense layer 27. T 26 represents 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. Through step S1, the 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. Through step S2, the simulation data M of the polarization parameters based on the optical model can be obtained.

[0030] FIG. 3 is a cross-sectional view schematically showing an example of the optical model of the 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 .

[0031] The 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 26It is determined by the fitting 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 this order from the side closer 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 of only 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 ratio of the material of the conductive substrate 10 and the LDH in the interface layer 26 can be a predetermined ratio. The volume ratio of the LDH and the volume ratio of the air in the surface roughness layer 28 can be a predetermined ratio.

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

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

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

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

[0036] [Layered double hydroxide] Figure 4 is a diagram schematically showing an example of the crystal structure of LDH. LDH20a contained in the LDH layer 20 is active with respect to the gas generation reaction such as hydrogen and oxygen at the anode or cathode of water electrolysis. For example, LDH20a can be changed to a hydroxide in alkaline water electrolysis.

[0037] LDH20a has a composition represented by, for example, the following formula (2). In formula (2), M1 2+ is a divalent transition metal ion. M2 3+ is a trivalent transition metal ion. A n- is an interlayer anion. x is a rational number satisfying the condition 0 < x < 1. y is a number corresponding to the required amount of charge balance. n is an integer. m is an appropriate rational number.

[0038] [M1 2+ 1-x M2 3+ x (OH) 2 [yA n- ·mH 2 O] Formula (2)

[0039] LDH20a contains two or more types of transition metals. The two or more types of transition metals in LDH20a are not limited to specific transition metals. In other words, M1 and M2 in the composition shown in formula (2) are not limited to specific transition metals. LDH20a 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 more excellent electrode activity.

[0040] LDH20a desirably 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 more excellent electrode activity. In addition, the manufacturing cost of the water electrolysis electrode 1 can be easily reduced.

[0041] LDH20a may contain Ni and Fe. For example, in the composition shown in formula (2), M1 may be Ni and M2 may be Fe. In this case, the electrode for water electrolysis can have more excellent electrode activity.

[0042] In LDH20a, A which is an anion between layers n- may be an inorganic ion or an organic ion. Examples of inorganic ions are CO 3 2- , NO 3 - , Cl - , SO 4 2- , Br - , OH - , F - , I - , Si 2 O 5 2- , B 4 O 5 (OH) 4 2- , and PO 4 3- . Examples of organic ions are CH 3 (CH 2 ) n SO 4 - , CH 3 (CH 2 ) n COO - , CH 3 (CH 2 ) n PO 4 2- , and CH 3 (CH 2 ) n NO 3 - . A n- can be inserted between the layers of the metal hydroxide together with water molecules. The charge and size of A n- are not limited to specific values. LDH20a may contain one type of A n- or may contain multiple types of A n- .

[0043] As shown in FIG. 4, LDH20a is a 2+ or M2 3+ At each vertex of the octahedron with - LDH20a has the [M1 2+ 1-x M2 3+ x (OH) 2 ] x+ This metal hydroxide has a layered structure in which hydroxide octahedra are connected two-dimensionally by sharing edges. Between the layers of the metal hydroxide, anions A n- and water molecules are present. The metal hydroxide layer acts as a host layer 21, and the anions A n- and a guest layer 22 containing water molecules is disposed between the host layers 21. In other words, the LDH 20a as a whole is composed of a host layer 21 of a metal hydroxide and an anion A n- The LDH 20a has a sheet-like structure in which a guest layer 22 of water molecules and a guest layer 23 of metal hydroxide are alternately laminated. 2+ Part of M2 3+ It has a structure substituted with:

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

[0045] [Chelating agents] 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 present stably 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 firmly fixed to the conductive substrate 10 with a desired thickness as a dense layer containing the LDH 20a and with few voids. This is because, when the LDH layer 20 is formed on the conductive substrate 10, the nucleated LDH is likely to grow slowly into crystals. 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 better 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 to transition metal ions 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 are β-diketones, β-ketoesters, hydroxycarboxylic acids, and hydroxycarboxylates. Examples of β-diketones are acetylacetone (ACAC), trifluoroacetylacetone, hexafluoroacetylacetone, benzoylacetone, thenoyltrifluoroacetone, dipyrovilmethane, dibenzoylmethane, and ascorbic acid. Examples of β-ketoesters are methyl acetoacetate, ethyl acetoacetate, allyl acetoacetate, benzyl acetoacetate, n-propyl acetoacetate, iso-propyl acetoacetate, n-butyl acetoacetate, iso-butyl acetoacetate, tert-butyl acetoacetate, 2-methoxyethyl acetoacetate, and methyl 3-oxopentanoate. Examples of hydroxycarboxylic acids and their salts are tartaric acid, citric acid, malic acid, gluconic acid, ferulic acid, lactic acid, glucuronic acid, and their salts.

[0047] The chelating agent preferably contains at least one selected from the group consisting of acetylacetone and citrate. In this case, the electrode 1 for water electrolysis can have more excellent electrode activity. 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 may have a porous structure such as a mesh, foam, or non-woven fabric. The conductive substrate 10 preferably has a porous structure. In this case, it is possible to increase the surface area of the conductive substrate 10, and the gas generated in the water electrolysis reaction is likely to diffuse.

[0049] The conductive substrate 10 is not limited to a specific substrate as long as it has conductivity. The conductive substrate 10 may contain a metal or a resin. The entire conductive substrate 10 may be composed of a metal. The conductive substrate 10 may have a configuration in which a surface layer containing a metal is formed on a resin member such as polypropylene or polyethylene. In this case, the surface layer containing a metal can be a plating film or a sputtering film. The metal contained in the conductive substrate 10 may be a pure metal such as nickel or 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 is likely to have excellent alkali resistance. When the surface of the conductive substrate 10 is made of nickel, the entire conductive substrate 10 may be composed of nickel, or the conductive substrate 10 may have a surface layer made of nickel. The surface layer made of nickel is a sputtering film or a plating film.

[0051] [Method for manufacturing an electrode for water electrolysis] FIG. 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 the present embodiment includes steps S10 to S13. Step S10 is a step of preparing a solution. Step S11 is a step of immersing the conductive substrate in the solution. Step S12 is a step of promoting the mixing of the solution. Step S13 is a step of adjusting the solution to be alkaline at room temperature. As a result, in the solution, a layered double hydroxide is synthesized while 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 defined in Japanese Industrial Standard (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 the ion of the transition metal contained in the layered double hydroxide described later. 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. According to the layered double hydroxide containing these transition metals, the water electrolysis electrode 1 having excellent electrode activity can be obtained.

[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, the water electrolysis electrode 1 having more excellent electrode activity can be manufactured.

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

[0057] 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 the chelating agent contained in the LDH layer 20. The chelating agent contained in solution S preferably contains at least one selected from the group consisting of acetylacetone and citrate. Thereby, the stability of the dispersion of the complex in solution S is increased, and the LDH layer 20 is likely to be formed on the surface of the conductive substrate 10. As a result, the water electrolysis electrode 1 can have more excellent electrode activity. An example of the citrate is trisodium citrate.

[0058] By adjusting the content of the chelating agent contained in 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 contained in solution S, the contact angle of the surface of the LDH layer 20 can be adjusted to 20 degrees or more and 100 degrees or less. Thereby, a water electrolysis electrode 1 more suitable for suppressing an increase in overvoltage can be obtained.

[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 eluted into the solution S.

[0060] The surface of the conductive substrate 10 is preferably made of nickel. In this case, for example, it is easy to manufacture the electrode 1 for electrolysis having advantageous characteristics from the viewpoint of achieving both corrosion resistance and conductivity in alkaline electrolysis.

[0061] The conductive substrate 10 preferably contains Ni. The two or more transition metal ions contained in the solution S preferably contain Fe ions. The solution S preferably contains chloride ions. In this case, the reaction represented by formula (3) can occur. Thereby, the conductive substrate 10 can be etched. Specifically, the Fe ions and chloride ions contained in the solution S react with the conductive substrate 10. Thereby, the conductive substrate 10 is etched by the Fe ions and chloride ions. As a result, the Ni contained in the conductive substrate 10 is eluted into the solution S.

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

[0063] In the production of the electrode 1 for electrolysis, the ratio R of the amount of substance of Fe ions contained in the solution S to the amount of substance of Ni contained in the conductive substrate 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 contained in the conductive substrate 10 from dissolving due to the reaction represented by formula (3) and making it difficult to manufacture the electrode 1 for electrolysis. The lower limit value of the ratio R is not particularly limited and is, for example, 0.02.

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

[0065] In the production of the water electrolysis electrode 1, the value W obtained by dividing the amount of substance 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 is, for example, 0.29 millimoles (mmol) / cm 2 or less. In this case, it is possible to prevent the nickel contained in the conductive substrate 10 from being dissolved by the reaction shown in the formula (3) and making it difficult to manufacture the water electrolysis electrode. The lower limit value of the value W is not particularly limited, and is, for example, 0.05 mmol / cm 2 or the like.

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

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

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

[0069] Examples of the method 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 enclosed, stirring the solution S using a stirrer piece and a stirrer, and the like. According to such a method, forced convection of the solution S occurs and the mixing of the solution S is promoted. The promotion of the mixing of the solution S may be performed in a state where the container containing the solution S and the conductive substrate 10 is sealed, or may be performed in an inert gas atmosphere.

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

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

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

[0073] The method of adjusting solution S to be alkaline, that is, the method of adjusting the pH of the solution to a value greater than 7, is not limited to a specific method. For example, solution S may be adjusted to be alkaline by mixing the above solution S and an alkaline solution. Alternatively, a pH increasing agent may be added to the above solution S to adjust solution S to be alkaline. In this case, the pH increasing agent is not limited to a specific compound. The pH increasing agent is, for example, a compound having an epoxy group. Examples of the pH increasing agent are propylene oxide (POX), ethylene oxide, and butylene oxide.

[0074] When a pH increasing agent having an epoxy group such as propylene oxide is added to solution S, in the presence of a nucleophile such as chloride ion, hydrogen ions present in solution S can be captured by the ring-opening reaction of the epoxy group. Thereby, the pH of solution S increases and solution S has alkalinity. The pH of solution S is, for example, 1. When the pH increasing agent is added to this solution S, the pH of solution S gradually increases from, for example, 1, and finally, solution S has alkalinity. The final pH of solution S is, for example, 8 or more and 12 or less. By adding the pH increasing agent to the solution, the reaction in which hydrogen ions in solution S are supplemented proceeds. Thereby, the pH of solution S gradually increases. The time from the addition of the pH increasing agent to solution S until the pH of solution S reaches a steady state is not limited to a specific time. That time is, for example, 24 hours or more and can be several days.

[0075] When adjusting the solution S to be alkaline, the temperature of the solution S is not limited to a specific temperature. The temperature of the solution S is, for example, room temperature. In this case, it is easy to obtain the water electrolysis electrode 1 having excellent electrode activity.

[0076] Step S13 preferably includes increasing the pH. Thereby, a layered double hydroxide can be formed on the surface of the conductive substrate 10 in a short period of time, and it is easy to obtain the water electrolysis electrode 1 having excellent electrode activity. In addition, the manufactured water electrolysis electrode 1 is likely to have excellent durability.

[0077] FIG. 6 is a diagram schematically showing the mechanism of manufacturing the water electrolysis electrode. As shown in FIG. 6, the conductive substrate 10 is immersed in a solution containing transition metal ion TM1, transition metal ion TM2, and chelating agent 30. For example, the transition metal ion TM1 is a Ni ion, and the transition metal ion TM2 is an Fe ion. In addition, Ni is present on the surface of the conductive substrate 10. A part of the transition metal ion TM2 etches and elutes the Ni present on the surface of the conductive substrate 10. A part of the chelating agent 30 reacts with the surface of the conductive substrate 10, and a complex C1 of the transition metal ion TM1 derived from the conductive substrate 10 and the chelating agent 30 is formed. In addition, when the solution is adjusted to be alkaline, in the solution, a complex C1 derived from the transition metal ion TM1 derived from the solution and the chelating agent 30 is formed, and a complex C2 of the transition metal ion TM2 and the chelating agent 30 is formed. Next, the complexes C1 and C2 react on the surface of the conductive substrate 10, and LDH20a is synthesized along the surface of the conductive substrate 10. In addition, since the complexes C1 and C2 contain the chelating agent 30, the crystal growth of LDH20a is suppressed. Thereby, the LDH layer 20 containing LDH20a and the chelating agent 30 is formed on the conductive substrate 10, and the water electrolysis electrode 1 is obtained.

[0078] The water electrolysis electrode 1 according to this embodiment can be used, for example, as an electrode of an alkaline water electrolysis device or an anion exchange membrane type water electrolysis cell. The water electrolysis electrode 1 is used, for example, in at least one selected from the group consisting of anodes and cathodes in these water electrolysis devices. In other words, at least one selected from the group consisting of a water electrolysis anode provided with the water electrolysis electrode 1 and a water electrolysis cathode provided with the water electrolysis electrode 1 can be provided. Thereby, the activity of the anodic reaction or cathodic reaction of water electrolysis tends to be high.

[0079] (Second Embodiment) FIG. 7 is a cross-sectional view schematically showing an example of a water electrolysis cell according to the second embodiment. As shown in FIG. 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, in the water electrolysis cell 2, the activity of the anodic reaction or the cathodic reaction 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 in which an alkaline aqueous solution is used. 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 are an aqueous potassium hydroxide solution and an aqueous sodium hydroxide solution.

[0081] As shown in FIG. 7, the water electrolysis cell 2 includes, for example, an electrolytic cell 2s, a first chamber 2m, and a second chamber 2n. The diaphragm 2p is disposed inside the electrolytic cell 2s and separates the inside of the electrolytic cell 2s into the first chamber 2m and the second chamber 2n. The anode 2a is disposed in the first chamber 2m, and the cathode 2b is disposed in the second chamber 2n.

[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, from 100 μm to 500 μm and has pores that serve as passageways for ions or electrolytic solution. The material of the diaphragm 2p is not limited to a specific material. Examples of the material of the diaphragm 2p are asbestos, polymer-reinforced asbestos, potassium titanate bound with polytetrafluoroethylene (PTFE), zirconia bound with PTFE, and antimonic acid and antimony oxide bound with polysulfone. Another example of the material of the diaphragm 2p is 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 arranged in a zero-gap state in contact with the diaphragm 2p, or may be arranged in a state having a gap with the diaphragm 2p. The cathode 2b may be arranged in a state in contact with the diaphragm 2p, or may be arranged in a state having a gap with 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 an alkaline earth metal is supplied to the first chamber 2m. In addition, an alkaline aqueous solution may be supplied to the second chamber 2n. Electrolysis is performed while discharging an alkaline aqueous solution having a predetermined concentration 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, an electrode material known as a cathode of an alkaline water electrolysis cell. When the cathode 2b includes the water electrolysis electrode 1, the anode 2a may include an electrode material known as an 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, since at least one selected from the group consisting of the anode 2a and the cathode 2b includes the water electrolysis electrode 1, the water electrolysis cell 2 can exhibit excellent performance.

[0087] (Third Embodiment) FIG. 8 is a cross-sectional view schematically showing an example of a water electrolysis apparatus according to the 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 in which an alkaline aqueous solution is used.

[0088] The voltage applicator 40 is electrically connected to the anode 2a and the cathode 2b. By the voltage applicator 40, the potential of the anode 2a becomes higher than the potential at the cathode 2b. The voltage applicator 40 is not limited to a specific type of voltage applicator as long as it can apply a voltage between the anode 2a and the cathode 2b. The voltage applicator 40 may be a device that adjusts the voltage applied between the anode 2a and the cathode 2b. When the voltage applicator 40 is connected to a DC power source such as a battery, a solar cell, or a fuel cell, the voltage applicator 40 includes, for example, a DC / DC converter. When the voltage applicator 40 is connected to an AC power source such as a commercial power source, the voltage applicator 40 includes, for example, an AC / DC converter. The voltage applicator 40 may be, for example, a power type power source. In the power type power source, the voltage applied between the anode 2a and the cathode 2b and the current flowing between the anode 2a and the cathode 2b are adjusted so that the power supplied to the water electrolysis apparatus 3 becomes a predetermined set value.

[0089] According to the above configuration, the water electrolysis apparatus 3 can exhibit excellent performance.

[0090] (Fourth Embodiment) FIG. 9 is a cross-sectional view schematically showing an example of a water electrolysis cell according to the fourth embodiment. As shown in FIG. 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, in the water electrolysis cell 4, the activity of the anodic reaction or the cathodic reaction 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 for anions such as hydroxide ions. The anion exchange membrane can prevent the oxygen gas generated at the anode 4a and the hydrogen gas generated at the cathode 4b from mixing. The oxygen gas is guided to the outside of the anode 4a through the gas diffusion layer 4n. The hydrogen gas is guided to the outside of the cathode 4b through the gas diffusion layer 4k.

[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 in an AEM type water electrolysis cell. At this time, the LDH layer 20 of the water electrolysis electrode 1 can function as the catalyst layer 4m, and the conductive substrate 10 of the water electrolysis electrode 1 can 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 in an AEM type water electrolysis cell. At this time, the LDH layer 20 of the water electrolysis electrode 1 can function as the catalyst layer 4j, and the conductive substrate 10 of the water electrolysis electrode 1 can 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, since at least one selected from the group consisting of the anode 4a and the cathode 4b includes the water electrolysis electrode 1, the water electrolysis cell 4 can exhibit excellent performance.

[0095] (Fifth Embodiment) FIG. 10 is a cross-sectional view schematically showing an example of a water electrolysis apparatus according to the 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 at 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 supply, the voltage applicator 40 includes, for example, an AC / DC converter. The voltage applicator 40 may be, for example, a power-type power source. In the power-type power source, the voltage applied between the anode 4a and the cathode 4b and the current flowing between the anode 4a and the cathode 4b are adjusted so that the power supplied to the water electrolysis device 5 becomes a predetermined set value.

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

[0098] (Other Embodiments) (Supplementary Note) From the above description, the following technologies are disclosed.

[0099] (Technology 1) A conductive substrate, A layered double hydroxide layer having two or more types of transition metals provided on the surface of the conductive substrate, and 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, An electrode for water electrolysis.

[0100] According to Technology 1, an electrode for water electrolysis advantageous from the viewpoint of suppressing an increase in overvoltage can be provided.

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

[0102] According to Technology 2, an electrode for water electrolysis that is more suitable for suppressing an increase in overvoltage can be provided.

[0103] (Technology 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 Technology 1 or 2. According to Technology 3, the electrode for water electrolysis is likely to have excellent electrode activity.

[0104] (Technology 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 any one of Technologies 1 to 3. According to Technology 4, the electrode for water electrolysis can have more excellent electrode activity.

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

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

[0107] According to Technologies 5 and 6, the electrode for water electrolysis can have more excellent electrode activity.

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

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

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

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

[0112] According to Technologies 9 and 10, the activity of the anodic reaction or cathodic reaction of water electrolysis is likely to increase.

[0113] (Technology 11) An anode, A cathode, A diaphragm, and comprising, At least one selected from the group consisting of the anode being the anode for water electrolysis described in Technology 9 and the cathode being the cathode for water electrolysis described in Technology 10 is satisfied, Water electrolysis cell.

[0114] (Technology 12) An anode, A cathode, An electrolyte membrane, and comprising, At least one selected from the group consisting of the anode being the anode for water electrolysis described in Technology 9 and the cathode being the cathode for water electrolysis described in Technology 10 is satisfied, Water electrolysis cell.

[0115] According to Technologies 11 and 12, in the water electrolysis cell, the activity of the anodic reaction or the cathodic reaction is likely to be improved.

[0116] (Technology 13) The water electrolysis cell according to Technology 11 or 12, and A voltage applicator that is connected to the cathode and the anode and applies a voltage between the cathode and the anode. Water electrolysis device.

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

[0118] (Technique 14) A method for manufacturing an electrode for water electrolysis, comprising a conductive substrate and a layered double hydroxide layer provided on the surface of the conductive substrate, Preparing a solution containing a chelating agent and two or more types of transition metal ions; Immersing the conductive substrate containing 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 the mixing of the solution; Adjusting the solution to be alkaline at room temperature, and including that 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. Method for manufacturing an electrode for water electrolysis.

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

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

[0121] (Technique 16) 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. The method for manufacturing an electrode for water electrolysis according to Technique 14 or 15.

[0122] (Technique 17) The above two or more types of transition metal ions include ions of at least one transition metal selected from the group consisting of Ni and Fe. The method for manufacturing an electrode for water electrolysis according to any one of Technologies 14 to 16.

[0123] (Technology 18) The conductive substrate contains Ni. The method for manufacturing an electrode for water electrolysis according to any one of Technologies 14 to 17.

[0124] According to Technologies 16 to 18, an electrode for water electrolysis having more excellent electrode activity can be manufactured.

Example

[0125] Hereinafter, the present disclosure will be described in more detail by way of 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) 0.226 g of nickel chloride hexahydrate and 0.128 g of iron chloride hexahydrate were dissolved in 3.32 milliliters (mL) of water to prepare a solution. Nickel chloride hexahydrate and iron chloride hexahydrate were purchased from Fujifilm Wako Pure Chemical Corporation. To this solution, 0.04 mL of acetylacetone (ACAC) was added as a chelating agent to obtain a chelating agent-containing solution. Acetylacetone was purchased from Sigma-Aldrich. The amount of substance of acetylacetone in the chelating agent-containing solution was 1 / 3.65 of the total amount of substance of Ni ions and Fe ions.

[0127] One Ni plate manufactured by Niraco was washed with acetone for 10 minutes and washed with a 1 mol / L aqueous HCl solution for 10 minutes to degrease the Ni plate and remove impurities. The thickness of the Ni plate was 0.2 mm, and the Ni plate was columnar with a diameter of 15 mm in plan view. The surface area of the Ni plate was 3.63 cm 2 It was. The mass of the Ni plate was 0.335 g. Next, the Ni plate was washed with water and dried to complete the washing process of the Ni plate.

[0128] Next, the Ni plate after the completion of the cleaning treatment was immersed in the above chelating agent-containing solution. In this state, the chelating agent-containing solution including the Ni plate was shaken and stirred at room temperature for 24 hours. At this time, in accordance with the above formula (3), the outermost surface of the Ni plate was etched. 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] Thereafter, as a pH increasing agent, 0.480 mL of propylene oxide (POX) was added to the chelating agent-containing solution. The obtained mixed solution was shaken and stirred at room temperature for 72 hours. At this time, since POX gradually captures hydrogen ions in the solution, the pH of the solution gradually increases. After 72 hours of shaking and stirring, the Ni plate was recovered and 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 produced in the same manner as in Example 1 except for the following points. 0.124 g of nickel chloride hexahydrate and 0.07 g of iron chloride hexahydrate were dissolved in 3.64 mL of water to prepare a solution. To this solution, 0.0061 mL of ACAC was added as a chelating agent to obtain a chelating agent-containing solution. The amount of substance of ACAC in the chelating agent-containing solution was 1 / 13 of the total amount of substance of Ni ions and Fe ions. The mass of the Ni plate was 0.315 g. As a pH increasing agent, 0.265 mL of POX was added to the chelating agent-containing solution. 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 in Example 1, except for the following points. 0.124 g of nickel chloride hexahydrate and 0.07 g of iron chloride hexahydrate were dissolved in 3.64 mL of water to prepare a solution. To this solution, 0.123 mL of ACAC was added as a chelating agent to obtain a chelating agent-containing solution. The amount of substance of ACAC in the chelating agent-containing solution was 1.5 times the total amount of substance of Ni ions and Fe ions. The mass of the Ni plate was 0.315 g. As a pH increasing agent, 0.265 mL of POX was added to the chelating agent-containing solution. 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 in Example 1, except for the following points. 0.123 g of nickel chloride hexahydrate and 0.07 g of iron chloride hexahydrate were dissolved in 3.61 mL of water to prepare a solution. To this solution, 0.486 mL of ACAC was added as a chelating agent to obtain a chelating agent-containing solution. The amount of substance of ACAC in the chelating agent-containing solution was 6.1 times the total amount of substance of Ni ions and Fe ions. The mass of the Ni plate was 0.315 g. As a pH increasing agent, 0.262 mL of POX was added 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 fabricated in the same manner as in Example 1, except for the following points. 0.065 g of nickel chloride hexahydrate and 0.037 g of iron chloride hexahydrate were dissolved in 3.80 mL of water to prepare a solution. To this solution, 0.0128 mL of ACAC was added as a chelating agent to obtain a chelating agent-containing solution. The amount of substance of ACAC in the chelating agent-containing solution was 1 / 3.27 of the total amount of substance of Ni ions and Fe ions. The mass of the Ni plate was 0.335 g. As a pH increasing agent, 0.138 mL of POX was added to the chelating agent-containing solution. The ratio R was 0.02. The value W was 0.08 mmol / cm 2 It was.

[0134] [Evaluation of the Thickness of the Layered Double Hydroxide Layer] Using a spectroscopic ellipsometer UVISEL2 manufactured by Horiba, Ltd., measurements were carried out on one point at the center of each electrode under the conditions of an incident angle of 70 degrees, a measurement wavelength range of 0.6 eV to 5.5 eV, and a spot diameter of 1 mm × 2 mm. As a result, measurement data E of the polarization parameters was obtained. Next, an optical model as shown in Fig. 3 was created, and simulation data M of the polarization parameters based on the optical model was obtained. Then, the simulation data M of the polarization parameters was fitted to the measurement data E of the polarization parameters. Specifically, the measurement data E was analyzed by the software Delta Psi2 attached to UVISEL2, and using the optical model as shown in Fig. 3, the thickness of the interfacial layer, the thickness of the dense layer, and the thickness of the surface roughness layer were determined. For the fitting calculation in this analysis, the New Amorphous formula and the Tauc-Lorentz formula proposed by Horiba Jobin Yvon were used, and the result with a smaller 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 10 degrees or less.

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

[0136] [Measurement of Contact Angle] For the measurement of the contact angle, a contact angle measuring instrument DM-501 manufactured by Kyowa Interface Science Co., Ltd. was used, and the measurement was carried out by the θ / 2 method. The contact angle was evaluated by dropping 0.2 microliters (μL) of an aqueous potassium hydroxide solution onto the surface of the electrode. The concentration of the aqueous potassium hydroxide solution was 6 mol / L. The results are shown in Table 1. The measurement of the contact angle was carried out 3 times for the electrodes according to each example and comparative example. The contact angle values shown in Table 1 are the average values of the values obtained by the 3 measurements.

[0137] [Evaluation of Overpotential of Electrodes] The oxygen evolution (OER) overpotentials of the electrodes according to each example and comparative example were evaluated. For the measurement, a potentiostat VersaSTAT4 manufactured by Princeton Applied Research, an alkaline sample vial (200 mL) manufactured by BAS, and a Teflon cap (for 200 mL) manufactured by BAS were used. As a jig for the working electrode, a plate electrode AE-2 manufactured by Easy-Flo Frontier was used. The electrodes according to each example and comparative example, which were the working electrodes, were fixed to this jig. As the counter electrode, a double platinum wire counter electrode D.6.0305.200J manufactured by Metrohm was used. By the three-electrode method, the current derived from the anodic reaction of the water electrolysis cell was measured under the following measurement conditions. The anodic reaction is an oxygen evolution reaction.

[0138] (Measurement Conditions) Solution: 1 mol / L KOH solution Potential with respect to the reversible hydrogen electrode (RHE): 1.0 V to 1.7 V Number of cycles: 5 cycles Potential sweep rate: 10 mV / second Temperature: 25 °C

[0139] Overpotential was determined by subtracting the theoretical potential of 1.229 V required to proceed the oxygen evolution reaction from the voltage corresponding to the current density of 10 mA / cm at the 5th cycle. The results are shown in Table 1. 2

[0140] [Table 1]

[0141] As shown in Table 1, for the electrodes according to each example, the contact angle on the surface of the layered double hydroxide layer was 20 degrees or more and 100 degrees or less. In addition, for the electrodes according to each example, the overpotential was 255 mV or less, and the increase in overpotential was suppressed. This result indicates that the water electrolysis electrodes used in each example are excellent from the viewpoint of electrode activity.

[0142] ​ FIG. 11 is a graph showing the relationship between the contact angle and the overvoltage in each example and comparative example. In FIG. 11, the horizontal axis represents the contact angle, and the vertical axis represents the overvoltage. In addition, curve X represents an approximate curve of the plots in each example and comparative example. A straight line Y parallel to the horizontal axis represents a straight 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. Therefore, it can be understood that by appropriately adjusting the contact angle, an increase in the overvoltage can be suppressed. In addition, as is apparent from curve X and straight line Y, it is presumed that if the contact angle is 20 degrees or more and 100 degrees or less, the overvoltage will be 255 mV or less. That is, it can be presumed that if the contact angle is 20 degrees or more and 100 degrees or less, it is possible to obtain an electrode for water electrolysis in which an increase in the overvoltage can be suppressed.

Industrial Applicability

[0144] The electrode for water electrolysis 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 layered double hydroxide layer has a thickness of 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. Raising the pH of the solution to between 8 and 12, 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.

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