Water electrolysis electrode, water electrolysis cell, and water electrolysis apparatus

Abstract

To provide a novel electrode for water electrolysis which is advantageous from the viewpoint of exhibiting higher durability than before.SOLUTION: The water electrolysis electrode 1 includes a conductive substrate 10 and a layered double hydroxide (LDH) layer 20. The LDH layer 20 is disposed on the conductive substrate 10. The LDH layer 20 has a crack frequency of less than 0.18 cracks / μm. The crack frequency of the LDH layer 20 is the number of cracks in the LDH layer 20 per unit interface length between the conductive substrate 10 and the LDH layer 20.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

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

[0003] Patent Document 1 describes a method for producing an electrode for water electrolysis, which includes a step of immersing an electrode substrate containing a predetermined layered double hydroxide in an organic solvent. In this production method, the electrode substrate is produced by electrodeposition treatment in an aqueous solution containing a compound containing metal M1 and a compound containing metal M2, using the conductive substrate as the anode.

[0004] Patent Document 2 describes an oxygen generating catalyst that includes a graphene oxide layer and a nickel-iron layered double hydroxide layer supported on the surface of the graphene oxide layer, where the graphene oxide layer has an average thickness of 0.33 to 4 nm.

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

[0006] Non-Patent Document 2 describes that the interface interaction between FeOOH and Ni-Fe LDH adjusts the local electronic structure of Ni-Fe LDH, enhancing the OER electrocatalytic activity. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2017 / 154134 [Patent Document 2] Japanese Patent Application Publication No. 2018-043193 [Non-patent literature]

[0008] [Non-Patent Document 1] Seyeong Lee et al., “Operational durability of three-dimensional Ni-Fe layered double hydroxide electrocatalyst for water oxidation,” Electrochimica Acta, 2019, Vol.315, p.94-101 [Non-patent document 2] Jiande Chen et al., “Interfacial Interaction between FeOOH and Ni-Fe LDH to Modulate the Local Electronic Structure for Enhanced OER Electrocatalysis,” ACS Catalysis, 2018, Vol.8, p.11342-11351 [Non-patent document 3] PWTLu, S.Srinivasan, J.Electrochem.Soc.,125, 1416 (1978) [Non-patent document 4] CT Bowen, Int.J.Hydrogen Energy,9,59 (1984) Summary of the Invention [Problem to be solved by the invention]

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

[0010] The present disclosure provides: A conductive substrate; a layered double hydroxide layer provided on the conductive substrate, the crack frequency of the layered double hydroxide layer, which is the number of cracks in the layered double hydroxide layer per unit interface length between the conductive substrate and the layered double hydroxide layer, is less than 0.18 cracks / μm; An electrode for water electrolysis is provided. [Effects of the Invention]

[0011] According to the present disclosure, it is possible to provide a novel electrode for water electrolysis that is advantageous in terms of exhibiting higher durability than conventional electrodes. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view showing an example of an electrode for water electrolysis according to the present disclosure. [Figure 2] FIG. 2 is a diagram schematically illustrating an example of the crystal structure of a layered double hydroxide (LDH). [Figure 3] FIG. 3 is a diagram schematically illustrating an example of the mechanism for producing electrodes for water electrolysis. [Figure 4] FIG. 4 is a cross-sectional view showing an example of a water electrolysis cell according to the present disclosure. [Figure 5] FIG. 5 is a cross-sectional view showing an example of a water electrolysis apparatus according to the present disclosure. [Figure 6] FIG. 6 is a cross-sectional view showing another example of a water electrolysis cell according to the present disclosure. [Figure 7] FIG. 7 is a cross-sectional view showing another example of a water electrolysis apparatus according to the present disclosure. [Figure 8A] FIG. 8A is a scanning electron microscope (SEM) photograph of a cross section of the electrode according to Example 1. FIG. [Figure 8B] FIG. 8B is an SEM photograph of a cross section of the electrode according to Example 2. [Figure 8C] FIG. 8C is an SEM photograph of a cross section of the electrode according to Example 3. [Figure 8D] FIG. 8D is an SEM photograph of a cross section of the electrode according to Comparative Example 1. [Figure 8E] FIG. 8E is an SEM photograph of a cross section of the electrode according to Comparative Example 2. [Figure 9A]FIG. 9A is an SEM photograph of a cross section of the electrode according to Example 1. FIG. [Figure 9B] FIG. 9B is an SEM photograph of a cross section of the electrode according to Example 1. [Figure 9C] FIG. 9C is an SEM photograph of a cross section of the electrode according to Example 1. [Figure 9D] FIG. 9D is an SEM photograph of a cross section of the electrode according to Example 1. [Figure 9E] FIG. 9E is an SEM photograph of a cross section of the electrode according to Example 1. [Figure 9F] FIG. 9F is an SEM photograph of a cross section of the application electrode according to Example 1. [Figure 10A] FIG. 10A is an SEM photograph of a cross section of the electrode according to Example 2. FIG. [Figure 10B] FIG. 10B is an SEM photograph of a cross section of the electrode according to Example 2. [Figure 10C] FIG. 10C is an SEM photograph of a cross section of the electrode according to Example 2. [Figure 10D] FIG. 10D is an SEM photograph of a cross section of the electrode according to Example 2. [Figure 10E] FIG. 10E is an SEM photograph of a cross section of the electrode according to Example 2. [Figure 10F] FIG. 10F is an SEM photograph of a cross section of the electrode according to Example 2. [Figure 11A] FIG. 11A is an SEM photograph of a cross section of the electrode according to Example 3. FIG. [Figure 11B] FIG. 11B is an SEM photograph of a cross section of the electrode according to Example 3. [Figure 11C] FIG. 11C is an SEM photograph of a cross section of the electrode according to Example 3. [Figure 11D] FIG. 11D is an SEM photograph of a cross section of the electrode according to Example 3. [Figure 11E] FIG. 11E is an SEM photograph of a cross section of the electrode according to Example 3. [Figure 11F] FIG. 11F is an SEM photograph of a cross section of the electrode according to Example 3. [Figure 12A] FIG. 12A is an SEM photograph of a cross section of an electrode according to Comparative Example 1. FIG. [Figure 12B] FIG. 12B is an SEM photograph of a cross section of the electrode according to Comparative Example 1. [Figure 12C] FIG. 12C is an SEM photograph of a cross section of the electrode according to Comparative Example 1. [Figure 12D] FIG. 12D is an SEM photograph of a cross section of the electrode according to Comparative Example 1. [Figure 12E] FIG. 12E is an SEM photograph of a cross section of the electrode according to Comparative Example 1. [Figure 12F] FIG. 12F is an SEM photograph of a cross section of the electrode according to Comparative Example 1. [Figure 13A] FIG. 13A is an SEM photograph of a cross section of an electrode according to Comparative Example 2. FIG. [Figure 13B] FIG. 13B is an SEM photograph of a cross section of the electrode according to Comparative Example 2. [Figure 13C] FIG. 13C is an SEM photograph of a cross section of the electrode according to Comparative Example 2. [Figure 13D] FIG. 13D is an SEM photograph of a cross section of the electrode according to Comparative Example 2. [Figure 13E] FIG. 13E is an SEM photograph of a cross section of the electrode according to Comparative Example 2. [Figure 13F] FIG. 13F is an SEM photograph of a cross section of the electrode according to Comparative Example 2. [Figure 14] FIG. 14 is a graph showing the relationship between the ratio of the current density at the 35th cycle to the initial current density and the minimum thickness of the LDH layer in the electrodes according to the examples and the comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0013] (Findings that formed the basis of this disclosure) The use of renewable energy sources such as solar and wind power has been attracting attention as a measure against global warming. However, power generation using renewable energy sources has the problem of surplus electricity being wasted. As a result, the efficiency of renewable energy utilization is not necessarily sufficient. Therefore, methods for effectively utilizing surplus electricity by producing and storing hydrogen from surplus electricity are being considered.

[0014] Water electrolysis is one possible method for producing hydrogen from surplus electricity. To produce hydrogen inexpensively and stably, there is a need for the development of a highly efficient, long-life water electrolysis device. In a water electrolysis device, oxygen is generated at the anode, and hydrogen is generated at the cathode. The reaction by which oxygen is generated at the anode is also called the anode reaction, and the reaction by which hydrogen is generated at the cathode is also called the cathode reaction. To provide a highly efficient water electrolysis device, it is desirable that the overvoltage at the anode is low. Additionally, it is also desirable that the overvoltage at the cathode is low. Therefore, there is a need for the development of high-performance electrodes for the anode reaction or cathode reaction in water electrolysis.

[0015] It is conceivable to use nickel-based materials, which are stable in highly concentrated alkaline aqueous solutions, as anodes for alkaline water electrolysis. In the case of alkaline water electrolysis using a stable power source, it has been reported that nickel-based anodes have a lifespan of several decades or more (see Non-Patent Documents 3 and 4). However, water electrolysis using renewable energy as a power source is often carried out under harsh conditions, such as frequent start-stops and load fluctuations, and deterioration of the performance of nickel-based anodes can be a problem (see Non-Patent Document 3).

[0016] For example, LDHs are considered promising materials for electrodes for water electrolysis due to their large specific surface area and diverse combinations of metal ions. According to Patent Document 1, an electrode substrate containing a predetermined LDH is produced by performing an electrodeposition process in an aqueous solution containing a compound containing metal M1 and a compound containing metal M2, using a conductive substrate as the anode. However, no study has been conducted on the deterioration of electrode performance in water electrolysis using renewable energy as the power source.

[0017] The present disclosure has been made in consideration of these problems of the conventional art. An object of the present disclosure is to provide an electrode for water electrolysis that is less likely to deteriorate in performance than conventional electrodes and that exhibits higher durability than conventional electrodes, even when water electrolysis is performed using a power source with large output fluctuations, such as renewable energy. After extensive investigations, the present inventors have newly discovered that having an LDH layer in a predetermined state is advantageous in terms of exhibiting higher durability than conventional electrodes, and have completed the water electrolysis electrode of the present disclosure.

[0018] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments. Note that the embodiments described below are all comprehensive or specific examples. Therefore, the numerical values, shapes, materials, components, component placement positions, and connection configurations shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, components that are not recited in the independent claims that represent the highest concepts will be described as optional components. Furthermore, in the drawings, descriptions of components with the same reference numerals may be omitted. Furthermore, the drawings schematically illustrate each component to facilitate understanding, and the shapes, dimensional ratios, etc. may not be accurately represented.

[0019] (First embodiment) FIG. 1 is a cross-sectional view showing a water electrolysis electrode according to a first embodiment. 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 conductive substrate 10 and contains a layered double hydroxide (LDH). The LDH layer 20 is bonded to the conductive substrate 10. The LDH layer 20 is directly bonded to the surface of the conductive substrate 10 without an adhesive containing an organic material such as a polymer. The crack frequency of the LDH layer 20 is less than 0.18 cracks / μm. This configuration makes it easier for the water electrolysis electrode 1 to exhibit higher durability than conventional electrodes. The crack frequency of the LDH layer 20 is the number of cracks in the LDH layer 20 per unit interface length between the conductive substrate 10 and the LDH layer 20. The crack frequency of the LDH layer 20 can be determined, for example, by observing a cross section of the central portion of the water electrolysis electrode 1 extending in the thickness direction of the water electrolysis electrode 1 using an SEM. The central portion of the water electrolysis electrode 1 may be, for example, a region surrounded by a square with a side length of 3 mm that includes the center of the water electrolysis electrode 1 in a plan view of the water electrolysis electrode 1. The center of the square region, which is the intersection of a pair of diagonals, is, for example, the center of the water electrolysis electrode 1 in a plan view of the water electrolysis electrode 1. The center of the water electrolysis electrode 1 in a plan view of the water electrolysis electrode 1, is the center of gravity of the plan view visible in the plan view of the water electrolysis electrode 1. As shown in FIG. 1 , gaps penetrating the LDH layer 20 in a cross section extending along the thickness direction of the water electrolysis electrode 1 are identified as cracks. Note that gaps that extend from the surface of the LDH layer 20 toward the interface between the LDH layer 20 and the conductive substrate 10 but do not reach the interface are not considered to be cracks. Similarly, gaps that extend from the interface between the LDH layer 20 and the conductive substrate 10 to the surface of the LDH layer 20 but do not reach the surface are also not considered to be cracks. Furthermore, voids present within the LDH layer 20 are also not considered to be cracks. To determine the frequency of cracks in the LDH layer 20, for example, a cross section of the interface between the LDH layer 20 and the conductive substrate 10 in the above region where the length is 20 μm or more is observed.The length of the interface between the LDH layer 20 and the conductive substrate 10 can be determined, for example, by processing an SEM photograph of a cross section extending in the thickness direction of the water electrolysis electrode 1 using image processing software such as Image J.

[0020] The crack frequency in the LDH layer 20 is preferably 0.15 cracks / μm or less, more preferably 0.10 cracks / μm or less, and may be 0 cracks / μm. In this case, the water electrolysis electrode 1 is more likely to exhibit higher durability than conventional electrodes.

[0021] 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 Ni or Fe, or an alloy such as stainless steel or Inconel. Inconel is a registered trademark.

[0022] The conductive substrate 10 preferably has a surface made of Ni. In this case, the conductive substrate 10 is likely to have high alkali resistance. When the conductive substrate 10 has a surface made of Ni, the entire conductive substrate 10 may be made of Ni, or the conductive substrate 10 may have a surface layer made of Ni. The surface layer made of Ni is, for example, a sputtered film or a plated film.

[0023] When the conductive substrate 10 has a surface made of Ni, the purity of the Ni constituting the surface is not limited to a specific value. The purity is, for example, 90% by mass or more. In this case, the conductive substrate 10 is more likely to have high alkali resistance. The method for determining the purity of the Ni constituting the surface of the conductive substrate 10 is not limited to a specific method. The purity of the Ni constituting the surface of the conductive substrate 10 may be determined by elemental analysis such as X-ray fluorescence spectroscopy (XRF) and energy dispersive X-ray spectroscopy (EDX). The purity of the Ni constituting the surface of the conductive substrate 10 may be determined by analyzing the extract obtained by completely dissolving the conductive substrate 10 in aqua regia using a method such as inductively coupled plasma atomic emission spectroscopy (ICP-AES). When the purity of Ni is high, the purity of the Ni constituting the surface of the conductive substrate 10 may be determined by comparing the specific gravity of the conductive substrate 10 with that of pure Ni.

[0024] The purity of Ni forming the surface of the conductive substrate 10 is preferably 95% by mass or more, more preferably 97% by mass or more, even more preferably 98% by mass or more, and particularly preferably 99% by mass or more.

[0025] The conductive substrate 10 is, for example, in the form of a sheet. The conductive substrate 10 may have a non-porous structure such as a plate or foil, or a porous structure such as an expanded metal, mesh, foam, or nonwoven fabric. The conductive substrate 10 preferably has a porous structure. In this case, the surface area of ​​the conductive portion of the conductive substrate 10 tends to be large, and gas generated in the water electrolysis reaction tends to diffuse easily.

[0026] The thickness of the conductive substrate 10 is not limited to a specific value. The thickness is, for example, 0.02 mm or more. In this case, the conductive substrate 10 tends to be easy to handle. The thickness of the conductive substrate 10 is, for example, 10 mm or less, and preferably 1 mm or less.

[0027] The LDH layer 20 contains, for example, a chelating agent. This allows the chelating agent to adjust the crystal growth of LDH during the formation of the LDH layer 20, making it easier for the LDH layer 20 containing LDH to exist in a desired state on the conductive substrate 10, and making it easier for the water electrolysis electrode 1 to have high electrode activity.

[0028] The LDH layer 20 covers, for example, the surface of the conductive substrate 10. The coverage of the LDH layer 20 on the surface of the conductive substrate 10 is not limited to a specific value. The coverage is preferably 99% or more. In this case, the water electrolysis electrode 1 is more likely to have high electrode activity.

[0029] The minimum thickness t of the LDH layer 20 20 is not limited to a specific value. 20 With this configuration, the water electrolysis electrode 1 is more likely to exhibit higher durability than conventional electrodes. 20 can be determined, for example, by observing a cross section of the central part of the water electrolysis electrode 1, extending in the thickness direction of the water electrolysis electrode 1, using an SEM. The central part of the water electrolysis electrode 1 may be, for example, a square region with a side length of 3 mm that includes the center of the water electrolysis electrode 1 in a plan view of the water electrolysis electrode 1. The center of the square region, which is the intersection of a pair of diagonal lines, is, for example, the center of the water electrolysis electrode 1 in a plan view of the water electrolysis electrode 1. The center of the water electrolysis electrode 1 in a plan view of the water electrolysis electrode 1 is the center of gravity of the plan view visible when the water electrolysis electrode 1 is viewed in plan. As shown in Figure 1, there may be irregularities on the surface of the LDH layer 20. The minimum thickness t 20 can be determined by paying attention to the convex portions of the unevenness on the surface of the LDH layer 20. The distance between the boundary surface between the conductive substrate 10 and the LDH layer 20 and the apex of the convex portion in the normal direction of the boundary surface is specified as the thickness of the convex portion. The minimum value of the thicknesses of the multiple convex portions is the minimum thickness t 20 is determined as follows.

[0030] Minimum thickness t 20is desirably 500 nm or less. In this case, the electrode 1 for water electrolysis is more likely to exhibit higher durability than conventional ones. The minimum thickness t 20 is more desirably 480 nm or less, still more desirably 450 nm or less, and particularly desirably 420 nm or less.

[0031] The minimum thickness t 20 is, for example, 230 nm or more. According to such a configuration, the LDH layer 20 is likely to be stably present in the electrode 1 for water electrolysis, and the electrode 1 for water electrolysis is likely to have high electrode activity.

[0032] FIG. 2 is a diagram schematically showing an example of the crystal structure of LDH. The LDH 20a 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, the LDH 20a can be changed to a hydroxide in alkaline water electrolysis.

[0033] The LDH 20a has, for example, a composition represented by the following formula (1). In formula (1), M1 2+ is a divalent transition metal ion. M2 3+ is a trivalent transition metal ion. A n- is an interlayer anion. x is a rational number satisfying the condition 0 < x < 1. y is a number corresponding to the required amount of charge balance. n is an integer. m is an appropriate rational number. [M1 2+ 1-x M2 3+ x (OH)2][yA n- ·mH2O] Formula (1)

[0034] The LDH 20a may contain 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 shown in formula (1) are not limited to specific transition metals.

[0035] The LDH 20a contains, for example, at least one element selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. In this case, the water electrolysis electrode 1 is more likely to have high electrode activity.

[0036] The LDH 20a preferably contains at least one element selected from the group consisting of Ni and Fe. In this case, the water electrolysis electrode 1 is more likely to have high electrode activity. In addition, the production cost of the water electrolysis electrode 1 is likely to be low. For example, in the composition represented by formula (1), M1 may be Ni and M2 may be Fe. In this case, the water electrolysis electrode 1 is more likely to have high electrode activity.

[0037] In LDH20a, the interlayer anion A n- may be an inorganic ion or an organic ion. An example of an inorganic ion is CO3 2- , NO3 - , Cl - , SO4 2- , Br - , O.H. - , F - , I - , Si2O5 2- , B4O5(OH)4 2- , and PO4 3- An example of an organic ion is CH3(CH2) n SO 4- , CH3(CH2) n COO - , CH3(CH2) n PO 4- , and CH3(CH2) n NO 3- A n- can be inserted between the metal hydroxide layers along with water molecules. n- The charge and size of the ions are not limited to a specific value. n- It may contain multiple types of A n- may also include:

[0038] As shown in Figure 2, LDH20a is a 2+ or M2 3+OH at each vertex of the octahedron centered at - LDH20a contains [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, 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. 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 guest layers 22 of water molecules and guest layers 22 of metal hydroxide molecules are alternately laminated. 2+ Part of M2 3+ The crystal structure and crystallinity of LDH20a can be analyzed qualitatively and quantitatively by X-ray diffraction (XRD).

[0039] As described above, the LDH layer 20 contains, for example, 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 can be easily synthesized to have a small particle size. Furthermore, since the LDH 20a nucleated on the conductive substrate 10 is likely to undergo slow crystal growth, the dense LDH layer 20 with few voids containing the LDH 20a is likely to have a desired thickness and be firmly fixed to the conductive substrate 10. This allows the LDH layer 20 to effectively contribute to the anode reaction or the cathode reaction, and the water electrolysis electrode 1 is likely to have high electrode activity.

[0040] The chelating agent is not limited to a specific chelating agent. For example, the chelating agent may be an organic compound capable of coordinating with the 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 hydroxycarboxylic acid salts. Examples of β-diketones include acetylacetone (ACAC), trifluoroacetylacetone, hexafluoroacetylacetone, benzoylacetone, thenoyltrifluoroacetone, dipyrrolylmethane, dibenzoylmethane, and ascorbic acid. Examples of β-ketoesters include methyl acetoacetate, ethyl acetoacetate, allyl acetoacetate, benzyl acetoacetate, n-propyl acetoacetate, isopropyl acetoacetate, n-butyl acetoacetate, isobutyl acetoacetate, tert-butyl acetoacetate, 2-methoxyethyl acetoacetate, and methyl 3-oxopentanoate. Examples of hydroxycarboxylic acids and their salts are tartaric acid, citric acid, malic acid, gluconic acid, ferulic acid, lactic acid, glucuronic acid, and salts thereof.

[0041] The chelating agent preferably contains at least one selected from the group consisting of acetylacetone and citrate. In this case, the water electrolysis electrode 1 is more likely to have high electrode activity. An example of a citrate is trisodium citrate.

[0042] The method for producing the water electrolysis electrode 1 is not limited to a specific method. The water electrolysis electrode 1 is produced, for example, by immersing the conductive substrate 10 in a solution containing a chelating agent and two or more types of transition metal ions and adjusting the solution to an alkaline state. This method allows, for example, the LDH layer 20 containing the LDH 20a and the chelating agent to be formed on the conductive substrate 10 in a simple manner.

[0043] The temperature of the solution when adjusted to an alkaline state is not limited to a specific temperature. The temperature of the solution is, for example, room temperature of 20° C.±15° C. In this case, a water electrolysis electrode 1 having high electrode activity is likely to be obtained.

[0044] The solvent of the solution may be water, an organic solvent, or a mixed solvent of water and an organic solvent.

[0045] The method for producing the water electrolysis electrode 1 preferably includes increasing the pH. This allows the LDH layer 20 to be formed on the conductive substrate 10 in a short period of time, making it easier to obtain a water electrolysis electrode 1 with high electrode activity. In addition, the produced water electrolysis electrode 1 is likely to have higher durability than conventional electrodes.

[0046] The method for adjusting the solution to alkaline is not limited to a specific method. For example, the solution may be adjusted to alkaline by mixing the above solution with an alkaline solution. Alternatively, the solution may be adjusted to alkaline by adding a pH-increasing agent to the above solution. 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, ethylene oxide, and butylene oxide.

[0047] When a pH-elevating agent having an epoxy group, such as propylene oxide, is added to a solution, the epoxy group undergoes a ring-opening reaction in the presence of a nucleophile, such as chloride ion, and the pH-elevating agent captures hydrogen ions present in the solution. This increases the pH of the solution, making it alkaline. The pH of a solution containing a chelating agent and two or more transition metal ions is, for example, 1. When a pH-elevating agent is added to this solution, the pH of the solution gradually increases from, for example, 1, and the solution may eventually become alkaline. The final pH of the solution is, for example, 8 or more and 12 or less. The addition of the pH-elevating agent to the solution causes a reaction that captures hydrogen ions in the solution. This gradually increases the pH of the solution. The time required for the pH of the solution to reach a steady state after the addition of the pH-elevating agent to the solution is not limited to a specific time. This time may be, for example, 24 hours or more, or even several days.

[0048] The pH-elevating agent may be an organic compound having an epoxy group and a hydroxy group, such as glycidol. In this case, the water electrolysis electrode 1 is also likely to have high electrode activity. In the presence of a nucleophile, such as chloride ions, the pH-elevating agent may capture hydrogen ions present in the solution as a result of a ring-opening reaction of the epoxy group of glycidol. This increases the pH of the solution, potentially making the solution alkaline. The interaction of the ring-opening compound of glycidol with transition metal ions makes it easier for the LDH layer 20 to assume a desired state, and the water electrolysis electrode 1 is also likely to have high electrode activity. Even when an organic compound having an epoxy group and a hydroxy group other than glycidol is used, the water electrolysis electrode 1 is also likely to have high electrode activity.

[0049] Organic compounds having epoxy and hydroxy groups, such as glycidol, have a higher flash point, are less flammable, and are less expensive than other epoxides. Therefore, using such organic compounds as pH-increasing agents can eliminate the need for explosion-proof specifications in the manufacturing equipment for the water electrolysis electrodes 1, which tends to reduce the manufacturing costs of the water electrolysis electrodes 1.

[0050] The pH increasing agent may be sodium carbonate.

[0051] The pH of a solution containing two or more types of transition metal ions is, for example, 1. When a pH-raising agent is added to this solution, the pH of the solution gradually increases, for example, from 1, and the solution may eventually become alkaline. The final pH of the solution is, for example, 8 or more and 12 or less. The addition of the pH-raising agent to the solution causes a reaction in which hydrogen ions in the solution are captured. This causes the pH of the solution to gradually increase. The time from the addition of the pH-raising agent to the solution until the pH of the solution reaches a steady state is not limited to a specific time. This time may be, for example, one hour or more, or several days.

[0052] The two or more types of transition metal ions contained in the solution are not limited to specific transition metal ions. For example, the two or more types of transition metal ions contained in the solution may be ions of at least two transition metals selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. In this case, a water electrolysis electrode 1 having high electrode activity can be more easily produced.

[0053] The two or more types of transition metal ions contained in the solution 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 with high electrode activity can be more easily produced.

[0054] As described above, the conductive base material 10 has a surface made of, for example, Ni. In this case, it is easy to produce a water electrolysis electrode that has advantageous properties from the viewpoint of achieving both corrosion resistance and conductivity in alkaline water electrolysis.

[0055] The conductive substrate 10 preferably contains Ni. The two or more types of transition metal ions contained in the solution preferably contain Fe ions. The solution preferably contains chloride ions. In this case, the reaction represented by formula (2) may occur, which may etch the conductive substrate 10. The method for producing the water electrolysis electrode 1 preferably includes promoting mixing of the solution before adjusting the solution to an alkaline state while the conductive substrate 10 is immersed in the solution. The promotion of mixing of the solution may be achieved, for example, by vibrating the conductive substrate 10, shaking a container containing the solution and the conductive substrate 10, or stirring the solution using a stirrer piece or a stirrer. Such a method may generate forced convection in the solution, which may promote mixing of the solution. This allows the conductive substrate 10 to be etched in a desired state, and the LDH layer 20 to be formed on the conductive substrate 10 in a desired state. As a result, the water electrolysis electrode 1 is likely to have higher durability than conventional electrodes. The promotion of mixing of the solution may be achieved while the container containing the solution and the conductive substrate 10 is sealed, or may be achieved in an inert gas atmosphere. 4Ni 2+ Cl - 2+ 2Fe 3+ Cl -3+ 2Ni → 5Ni 2+ Cl - 2+ 2Fe 2+ Cl - 2+ 1Ni Equation (2)

[0056] In the production of the water electrolysis electrode 1, the molar ratio of the Fe ion content to the Ni content in the conductive base material 10 is not limited to a specific value. The molar ratio is, for example, 0.75 or less. This prevents the dissolution of Ni in the conductive base material 10 due to the reaction shown in formula (2), which makes it difficult to produce the water electrolysis electrode 1.

[0057] The molar ratio is preferably 0.05 to 0.25. In this case, the LDH layer 20 is more likely to be formed uniformly on the conductive substrate 10, and the water electrolysis electrode 1 is more likely to have high electrode activity.

[0058] The chelating agent contained in the solution may be selected with reference to the above examples of the chelating agent contained in the LDH layer 20. The chelating agent contained in the solution 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, making it easier to form the LDH layer 20 in a desired state in the water electrolysis electrode 1. As a result, the water electrolysis electrode 1 is more likely to have high electrode activity.

[0059] FIG. 3 is a schematic diagram illustrating the mechanism of manufacturing a water electrolysis electrode. As shown in FIG. 3, a conductive substrate 10 is immersed in a solution containing transition metal ions TM1, TM2, and a chelating agent CH. For example, the transition metal ions TM1 are nickel ions, and the transition metal ions TM2 are iron ions. In addition, nickel is present on the surface of the conductive substrate 10. Some of the transition metal ions TM2 etch and dissolve the nickel present on the surface of the conductive substrate 10. Some of the chelating agent CH reacts with the surface of the conductive substrate 10 to form a complex C1 between the transition metal ions TM1 and the chelating agent CH derived from the conductive substrate 10. In addition, when the solution is adjusted to an alkaline pH, a complex C1 derived from the transition metal ions TM1 and the chelating agent CH derived from the solution is formed in the solution, and a complex C2 between the transition metal ions TM2 and the chelating agent CH is formed. Next, the complexes C1 and C2 react on the surface of the conductive substrate, synthesizing LDH 20a along the surface of the conductive substrate 10. In addition, since the complexes C1 and C2 contain the chelating agent CH, crystal growth of the LDH 20a is suppressed. As a result, an LDH layer 20 containing the LDH 20a and the chelating agent CH is formed on the conductive substrate 10, and a water electrolysis electrode 1 is obtained.

[0060] 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.

[0061] (Second embodiment) Figure 4 is a cross-sectional view schematically illustrating an example of a water electrolysis cell according to the second embodiment. As shown in Figure 4, 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 high, and the anode 2a or the cathode 2b is likely to exhibit high performance.

[0062] 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 an aqueous potassium hydroxide solution and an aqueous sodium hydroxide solution.

[0063] 4, the water electrolysis cell 2 includes, for example, an electrolytic cell 2s, a first chamber 2m, and a second chamber 2n. A diaphragm 2p is disposed inside the electrolytic cell 2s, separating the interior of the electrolytic cell 2s into the first chamber 2m and the second chamber 2n. An anode 2a is disposed in the first chamber 2m, and a cathode 2b is disposed in the second chamber 2n.

[0064] 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.

[0065] The anode 2a may be disposed in a zero-gap state, in which the anode 2a is in contact with the diaphragm 2p, or may be disposed with a gap between the anode 2a 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 the cathode 2b and the diaphragm 2p.

[0066] 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, producing hydrogen and oxygen.

[0067] 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.

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

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

[0070] The voltage applicator 40 is electrically connected to the anode 2a and the cathode 2b. The voltage applicator 40 makes the potential of the anode 2a higher than the potential of the cathode 2b. The voltage applicator 40 is not limited to a specific type of voltage applicator as long as it can apply a voltage between the anode 2a and the cathode 2b. The voltage applicator 40 may be a device that adjusts the voltage applied between the anode 2a and the cathode 2b. When the voltage applicator 40 is connected to a DC power supply 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 supply 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 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.

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

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

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

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

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

[0076] 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 high performance.

[0077] (Fifth embodiment) Fig. 7 is a cross-sectional view schematically illustrating an example of a water electrolysis apparatus according to a fifth embodiment. As shown in Fig. 7, the water electrolysis apparatus 5 includes a water electrolysis cell 4 and a voltage applicator 40. The voltage applicator 40 applies a voltage between the cathode 4b and the anode 4a. The water electrolysis apparatus 5 is, for example, an AEM-type water electrolysis apparatus.

[0078] 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 supply 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 supply 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 supply. The power-type power supply adjusts the voltage applied between the anode 4a and the cathode 4b and the current flowing between the anode 4a and the cathode 4b so that the power supplied to the water electrolysis device 5 becomes a predetermined set value.

[0079] With the above configuration, the water electrolysis device 5 can exhibit high performance.

[0080] (Addendum) From the above description, the following techniques are disclosed. (Technology 1) A conductive substrate; a layered double hydroxide layer provided on the conductive substrate, the crack frequency of the layered double hydroxide layer, which is the number of cracks in the layered double hydroxide layer per unit interface length between the conductive substrate and the layered double hydroxide layer, is less than 0.18 cracks / μm; Electrode for water electrolysis. (Technology 2) The layered double hydroxide contains at least one selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. The electrode for water electrolysis according to Technical 1. (Technology 3) The layered double hydroxide contains at least one selected from the group consisting of Ni and Fe, The water electrolysis electrode according to claim 2. (Technology 4) The layered double hydroxide contains a chelating agent. 4. The electrode for water electrolysis according to any one of claims 1 to 3. (Technology 5) The chelating agent includes at least one selected from the group consisting of acetylacetone and citrate. The water electrolysis electrode according to claim 4. (Technology 6) The conductive substrate has a surface made of Ni. 6. The electrode for water electrolysis according to any one of claims 1 to 5. (Technology 7) an anode; a cathode; a diaphragm; At least one selected from the group consisting of the anode and the cathode comprises the water electrolysis electrode according to any one of techniques 1 to 6. water electrolysis cell. (Technology 8) an anode; a cathode; an anion exchange membrane, At least one selected from the group consisting of the anode and the cathode comprises the water electrolysis electrode according to any one of techniques 1 to 6. water electrolysis cell. (Technology 9) The water electrolysis cell according to Technical Example 7 or 8, a voltage applicator that applies a voltage between the cathode and the anode; Water electrolysis equipment. [Example]

[0081] 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.

[0082] Example 1 A solution was prepared by dissolving 0.208 g of nickel chloride hexahydrate and 0.118 g of iron chloride hexahydrate in 3.33 milliliters (mL) of water. Nickel chloride hexahydrate and iron chloride hexahydrate were purchased from Fujifilm Wako Pure Chemical Industries, Ltd. 0.020 mL of acetylacetone (ACAC) was added to this solution as a chelating agent to obtain a chelating agent-containing solution. ACAC was purchased from Fujifilm Wako Pure Chemical Industries, Ltd.

[0083] A single Ni plate manufactured by Nilaco Corporation was prepared. The Ni plate had a thickness of 0.2 mm, and in plan view had a shape in which a square A with a side length of 10 mm was connected to a square B with a side length of 2 mm. The Ni plate had a mass of 0.195 g. Next, the Ni plate was washed with water and dried, completing the cleaning process of the Ni plate.

[0084] Next, the Ni plate after the cleaning process was immersed in the chelating agent-containing solution. In this state, the chelating agent-containing solution containing the Ni plate was shaken and stirred at 25°C for 1 hour. During this time, the outermost surface of the Ni plate was etched according to the above formula (2).

[0085] Next, 0.424 mL of glycidol (GL) was added to the chelating agent-containing solution as a pH-increasing agent, and the solution was shaken and stirred at 25°C for another 4 hours. After 4 hours of shaking and stirring, the Ni plate was recovered, washed with water, and dried. In this way, an electrode according to Example 1 was obtained in which an LDH layer was formed on the Ni plate.

[0086] Example 2 An electrode according to Example 2 was prepared in the same manner as Example 1, except for the following points. A solution was prepared by dissolving 0.646 g of nickel chloride hexahydrate and 0.368 g of iron chloride hexahydrate in 3.36 mL of water. To this solution, 0.063 mL of acetylacetone (ACAC) was added as a chelating agent to obtain a chelating agent-containing solution. 0.132 mL of GL was added as a pH-raising agent to the chelating agent-containing solution.

[0087] Example 3 An electrode according to Example 3 was prepared in the same manner as in Example 1, except for the following points. A solution was prepared by dissolving 0.303 g of nickel chloride hexahydrate and 0.172 g of iron chloride hexahydrate in 3.39 mL of water. 0.029 mL of ACAC was added to this solution as a chelating agent to obtain a chelating agent-containing solution. 0.296 mL of GL was added to the chelating agent-containing solution as a pH-raising agent.

[0088] (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 0.557 g of nickel chloride hexahydrate and 0.317 g of iron chloride hexahydrate in 3.35 mL of water. 0.054 mL of ACAC was added to this solution as a chelating agent to obtain a chelating agent-containing solution. 0.216 mL of GL was added to the chelating agent-containing solution as a pH-raising agent.

[0089] (Comparative Example 2) An electrode according to Comparative Example 2 was prepared in the same manner as in Example 1, except for the following points. A solution was prepared by dissolving 0.429 g of nickel chloride hexahydrate and 0.244 g of iron chloride hexahydrate in 3.17 mL of water. 0.042 mL of ACAC was added to this solution as a chelating agent to obtain a chelating agent-containing solution. 0.419 mL of GL was added to the chelating agent-containing solution as a pH-raising agent.

[0090] [Crack frequency and minimum thickness of LDH layer] The cross section of the electrode in each example and comparative example was exposed by ion polishing to prepare a sample for observing the electrode cross section. Ion polishing was performed on a square portion of the electrode with a side length of 1 mm including the center of a 10 mm square A in a plan view. The sample thus prepared was attached to a sample stage. Secondary electron images of the electrode cross section were observed at an accelerating voltage of 2 kV using a Hitachi High-Technologies Corporation field emission scanning electron microscope (FE-SEM) SU8220, and the minimum thickness of the LDH layer formed on the Ni substrate (Ni plate) was calculated. In secondary electron images of the cross section of the electrode where the interface length between the Ni substrate and the LDH layer was 20 μm or longer, the number of cracks, which are gaps penetrating the LDH layer, was identified. The interface length between the Ni substrate and the LDH layer was determined by processing the secondary electron images using the open-source image processing software Image J. The number of identified cracks was divided by the interface length between the Ni substrate and the LDH layer to determine the crack frequency in the LDH layer as the number of cracks per unit interface length (1 μm). The results are shown in Table 1.

[0091] In the secondary electron image, the distance between the apex of the convex portion of the irregularities observed on the surface of the LDH layer in the normal direction to the interface between the Ni substrate and the LDH layer was determined as the thickness of the convex portion. The minimum thickness of the multiple convex portions was determined as the minimum thickness of the LDH layer.

[0092] FIG. 8A is an SEM photograph of a cross section of an electrode according to Example 1. FIG. 8B is an SEM photograph of a cross section of an electrode according to Example 2. FIG. 8C is an SEM photograph of a cross section of an electrode according to Example 3. FIG. 8D is an SEM photograph of a cross section of an electrode according to Comparative Example 1. FIG. 8E is an SEM photograph of a cross section of an electrode according to Comparative Example 2. In FIGS. 8A to 8E, the boundary between the LDH layer and the Ni substrate (Ni plate) is indicated by a black line, and the length of the boundary is shown. Additionally, cracks observed in the LDH layer are indicated by white triangles. In FIGS. 8A to 8C, no cracks were observed in the LDH layer. Meanwhile, five cracks were observed in FIG. 8D, and 11 cracks were observed in FIG. 8E.

[0093] 9A, 9B, 9C, 9D, 9E, and 9F are SEM photographs of the cross section of the electrode according to Example 1. FIG. 9B is an SEM photograph showing an enlargement of the portion surrounded by the white line in FIG. 9A. FIG. 9C is an SEM photograph showing an enlargement of the portion surrounded by the white line in FIG. 9B. FIG. 9E is an SEM photograph showing an enlargement of the portion surrounded by the white line in FIG. 9D. FIG. 9F is an SEM photograph showing an enlargement of the portion surrounded by the white line in FIG. 9E. According to these SEM photographs, the minimum thickness of the LDH layer in the electrode according to Example 1 was 230 nm.

[0094] 10A, 10B, 10C, 10D, 10E, and 10F are SEM photographs of the cross section of the electrode according to Example 2. FIG. 10B is an SEM photograph showing an enlargement of the portion surrounded by the white line in FIG. 10A. FIG. 10C is an SEM photograph showing an enlargement of the portion surrounded by the white line in FIG. 10B. FIG. 10E is an SEM photograph showing an enlargement of the portion surrounded by the white line in FIG. 10D. FIG. 10F is an SEM photograph showing an enlargement of the portion surrounded by the white line in FIG. 10E. According to these SEM photographs, the minimum thickness of the LDH layer in the electrode according to Example 2 was 300 nm.

[0095] 11A, 11B, 11C, 11D, 11E, and 11F are SEM photographs of the cross section of the electrode according to Example 3. FIG. 11B is an SEM photograph showing an enlargement of the portion surrounded by the white line in FIG. 11A. FIG. 11C is an SEM photograph showing an enlargement of the portion surrounded by the white line in FIG. 11B. FIG. 11E is an SEM photograph showing an enlargement of the portion surrounded by the white line in FIG. 11D. FIG. 11F is an SEM photograph showing an enlargement of the portion surrounded by the white line in FIG. 11E. According to these SEM photographs, the minimum thickness of the LDH layer in the electrode according to Example 3 was 420 nm.

[0096] 12A, 12B, 12C, 12D, 12E, and 12F are SEM photographs of the cross section of the electrode according to Comparative Example 1. FIG. 12B is an SEM photograph showing an enlargement of the portion surrounded by the white line in FIG. 12A. FIG. 12C is an SEM photograph showing an enlargement of the portion surrounded by the white line in FIG. 12B. FIG. 12E is an SEM photograph showing an enlargement of the portion surrounded by the white line in FIG. 12D. FIG. 12F is an SEM photograph showing an enlargement of the portion surrounded by the white line in FIG. 12E. According to these SEM photographs, the minimum thickness of the LDH layer in the electrode according to Comparative Example 1 was 540 nm.

[0097] 13A, 13B, 13C, 13D, 13E, and 13F are SEM photographs of the cross section of the electrode according to Comparative Example 2. FIG. 13B is an SEM photograph showing an enlargement of the portion surrounded by the white line in FIG. 13A. FIG. 13C is an SEM photograph showing an enlargement of the portion surrounded by the white line in FIG. 13B. FIG. 13E is an SEM photograph showing an enlargement of the portion surrounded by the white line in FIG. 13D. FIG. 13F is an SEM photograph showing an enlargement of the portion surrounded by the white line in FIG. 13E. According to these SEM photographs, the minimum thickness of the LDH layer in the electrode according to Comparative Example 2 was 690 nm.

[0098] [Electrode overpotential evaluation] The oxygen evolution (OER) overpotential of the electrodes according to each example and comparative example was evaluated. For the measurements, a potentiostat (ivium-n-stat) manufactured by Ivium, a custom-made cell manufactured by EC Frontier, and working electrodes fabricated by welding nickel wire to each electrode were used. Additionally, a nickel coil was used as the counter electrode. A HydroFlex electrode manufactured by Gaskatal was used as the reference electrode. The current resulting 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 an oxygen evolution reaction. (Measurement conditions) Solution: 6M KOH solution Potential vs. reversible hydrogen electrode (RHE): 0.5V to 1.7V Number of cycles: 35 cycles Potential sweep speed: 0.5V / sec Temperature: 80℃

[0099] To evaluate the durability of the electrodes, the ratio of the current density at the 35th cycle to the initial current density at a voltage of 1.7 V was determined. The results are shown in Table 1. As shown in Table 1, the ratios of the current density at the 35th cycle to the initial current density were high in the electrodes of Examples 1 to 3, and it is understood that these electrodes have high durability. On the other hand, the ratios of the current density at the 35th cycle to the initial current density in the electrodes of Comparative Examples 1 and 2 were not high. A comparison between the Examples and Comparative Examples suggested that when the frequency of cracks in the LDH layer is less than 0.18 cracks / µm, the durability of the water electrolysis electrode is likely to be higher than conventional electrodes.

[0100] FIG. 14 is a graph showing the relationship between the ratio of the current density at the 35th cycle to the initial current density and the minimum thickness of the LDH layer in the electrodes according to the examples and the comparative examples.

[0101] It should be noted that many modifications and other embodiments of the present disclosure will be apparent to those skilled in the art from the above description. Accordingly, the above description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the present disclosure. Substantial changes can be made in the operating conditions, composition, structure, and / or function thereof without departing from the spirit of the present disclosure.

[0102] It should be noted that many modifications and other embodiments of the present disclosure will be apparent to those skilled in the art from the above description. Accordingly, the above description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the present disclosure. Substantial changes can be made in the operating conditions, composition, structure, and / or function thereof without departing from the spirit of the present disclosure.

[0103] [Table 1] [Industrial Applicability]

[0104] The water electrolysis electrode of the present disclosure can be used as an anode or a cathode for water electrolysis. [Explanation of symbols]

[0105] 1 Electrode for water electrolysis 2 Water electrolysis cell 2a Anode 2b cathode 2p septum 3 Water electrolysis device 4 Water electrolysis cell 4a Anode 4b Cathode 4p Anion Exchange Membrane 5 Water electrolysis equipment 10 Conductive base material 20 Layered double hydroxide (LDH) layer 20a Layered double hydroxide (LDH) 40 Voltage Applicator

Claims

1. A conductive substrate; a layered double hydroxide layer provided on the conductive substrate, the crack frequency of the layered double hydroxide layer, which is the number of cracks in the layered double hydroxide layer per unit interface length between the conductive substrate and the layered double hydroxide layer, is less than 0.18 cracks / μm; Electrode for water electrolysis.

2. The layered double hydroxide contains at least one 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.

3. The layered double hydroxide contains at least one selected from the group consisting of Ni and Fe. The electrode for water electrolysis according to claim 2.

4. The layered double hydroxide contains a chelating agent. The electrode for water electrolysis according to any one of claims 1 to 3.

5. The chelating agent includes at least one selected from the group consisting of acetylacetone and citrate. The electrode for water electrolysis according to claim 4.

6. The conductive substrate has a surface made of Ni. The electrode for water electrolysis according to any one of claims 1 to 5.

7. an anode; a cathode; a diaphragm; at least one selected from the group consisting of the anode and the cathode comprises the water electrolysis electrode according to any one of claims 1 to 6; water electrolysis cell.

8. an anode; a cathode; an anion exchange membrane, at least one selected from the group consisting of the anode and the cathode comprises the water electrolysis electrode according to any one of claims 1 to 6; water electrolysis cell.

9. The water electrolysis cell according to claim 7 or 8; a voltage applicator that applies a voltage between the cathode and the anode; Water electrolysis equipment.

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