Electrode for water electrolysis, electrode for water electrolysis, electrode for water electrolysis, electrolysis cel, and water electrolysis apparatus

Abstract

This electrode 1 for water electrolysis comprises a conductive base material 10 and a layered double hydroxide layer 20. The catalyst layer 20 is provided on the surface of the conductive base material 10. The layered double hydroxide layer 20 comprises a roughness layer 20r. With respect to the layered double hydroxide layer 20, the ratio Ptr of the thickness t20r of the roughness layer 20r to the thickness t20 of the layered double hydroxide layer 20 is 4.8% or more.

Description

Technical Field

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

Background Art

[0002] Conventionally, electrodes for water electrolysis have been known.

[0003] Patent Document 1 describes a method for manufacturing an electrode for electrolysis of water, including a step of immersing an electrode substrate containing a predetermined layered double hydroxide in an organic solvent. In this manufacturing method, the electrode substrate is manufactured by performing an electrodeposition treatment in an aqueous solution containing a compound containing metal M1 and a compound containing metal M2 with a conductive substrate as an anode. [[ID=1​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​

[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 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The descriptions in the above-mentioned literature warrant reconsideration from the perspective of improving the performance of water electrolysis electrodes. Therefore, this disclosure provides a novel water electrolysis electrode that is advantageous from the perspective of achieving high performance. [Means for solving the problem]

[0010] This disclosure is, A conductive substrate and The conductive substrate comprises a layered double hydroxide layer provided on its surface, The aforementioned layered double hydroxide layer comprises a roughness layer, The ratio of the thickness of the roughness layer to the thickness of the layered double hydroxide layer is 4.8% or more. We provide electrodes for water electrolysis. [Effects of the Invention]

[0011] According to this disclosure, it is possible to provide a novel electrode for water electrolysis that is advantageous in terms of achieving high performance. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a cross-sectional view showing an example of a water electrolysis electrode according to the present disclosure. [Figure 2] Figure 2 is a schematic cross-sectional view showing an example of an optical model of a water electrolysis electrode obtained by spectroscopic ellipsometry. [Figure 3] Figure 3 is a schematic diagram showing an example of the crystal structure of a layered double hydroxide (LDH). [Figure 4] Figure 4 is a schematic diagram illustrating an example of the manufacturing mechanism of electrodes for water electrolysis. [Figure 5] Figure 5 is a cross-sectional view showing an example of a water electrolysis cell according to the present disclosure. [Figure 6] Figure 6 is a cross-sectional view showing an example of a water electrolysis apparatus according to the present disclosure. [Figure 7] Figure 7 is a cross-sectional view showing another example of a water electrolysis cell according to the present disclosure. [Figure 8] Figure 8 is a cross-sectional view showing another example of a water electrolysis apparatus according to the present disclosure. [Modes for carrying out the invention]

[0013] (Knowledge that forms the basis of this disclosure) As a measure against global warming, the use of renewable energy sources such as solar and wind power is attracting attention. However, a problem arises with renewable energy generation: surplus electricity goes to waste. Therefore, the utilization efficiency of renewable energy is not always sufficient. As a result, methods are being considered to effectively utilize surplus electricity by producing and storing hydrogen from it.

[0014] Electrolysis of water is a possible method for producing hydrogen from surplus electricity. To produce hydrogen cheaply and stably, there is a need for the development of highly efficient and long-lasting water electrolysis devices. In a water electrolysis device, oxygen is generated at the anode and hydrogen at the cathode. The reaction in which oxygen is generated at the anode is called the anodic reaction, and the reaction in which hydrogen is generated at the cathode is called the cathode reaction. To provide a highly efficient water electrolysis device, it is desirable that the current density per unit electrode area at the anode is high, especially when a predetermined voltage is applied between the anode and cathode. In addition, it is desirable that the current density per unit electrode area at the cathode is also high in this case. Therefore, the development of high-performance electrodes for the anodic or cathode reaction of water electrolysis is highly anticipated.

[0015] For example, LDH is considered promising as a material for water electrolysis electrodes due to its large specific surface area and diverse combinations of metal ions. For example, according to Patent Document 1, an electrode substrate containing a predetermined layered double hydroxide is manufactured by electrodeposition treatment in an aqueous solution containing a compound containing metal M1 and a compound containing metal M2, with a conductive substrate as the anode. On the other hand, the performance of electrodes manufactured by electrodeposition treatment was not sufficient, and there was room for improvement. As a result of diligent research, the present inventors have newly discovered that the performance of a water electrolysis electrode can be improved by forming the layer containing LDH such that it has a predetermined roughness layer, and have completed the water electrolysis electrode of the present disclosure.

[0016] The embodiments of this disclosure will be described below with reference to the drawings. This disclosure is not limited to the embodiments described below. The embodiments described below are all comprehensive or specific examples. Therefore, the numerical values, shapes, materials, components, arrangement positions of components, and connection configurations shown in the embodiments below are examples and are not intended to limit this disclosure. In addition, components in the embodiments below that are not described in an independent claim indicating the highest-level concept will be described as optional components. Also, in the drawings, components with the same reference numerals may not be described. Furthermore, the drawings are schematic representations of each component for ease of understanding, and the shapes and dimensional ratios may not be accurately represented.

[0017] (First Embodiment) Figure 1 is a cross-sectional view showing a water electrolysis electrode according to the first embodiment. Figure 2 is a schematic cross-sectional view showing an example of an optical model of the water electrolysis electrode obtained by spectroscopic ellipsometry. As shown in Figure 1, the water electrolysis electrode 1 comprises 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. The LDH layer 20 can function as a catalyst layer for the anode or cathode reaction of water electrolysis. As shown in Figure 2, the LDH layer 20 comprises a roughness layer 20r. In the LDH layer 20, the layer thickness t of the LDH layer 20 20 Thickness t of the roughness layer 20r 20r The proportion P tr This is 4.8% or more. With this configuration, when a predetermined voltage is applied between the anode and cathode during water electrolysis, the current density per unit electrode area at the anode or cathode tends to increase, allowing the water electrolysis electrode 1 to exhibit high performance.

[0018] Layer thickness t 20 and layer thickness t 20ris determined, for example, by spectroscopic ellipsometry. As shown in FIG. 2, in the optical model 1m, the LDH layer 20 includes an interface layer 20i, a dense layer 20f, and a roughness layer 20r in this order from the side closer to the conductive substrate 10 in the thickness direction. The interface layer 20i is composed of the material of the conductive substrate 10 and the LDH contained in the LDH layer 20. The dense layer 20f is composed only of the LDH contained in the LDH layer 20. The roughness layer 20r is a surface roughness layer and 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 20i may be a predetermined ratio. The volume ratio of the LDH and air in the roughness layer 20r may be a predetermined ratio. Based on the measurement data obtained by the spectroscopic ellipsometer, the above optical model 1m is created, and by performing fitting calculations, the layer thickness t 20 and the layer thickness t 20r can be determined. In addition, the layer thickness t 20i of the interface layer 20i, the layer thickness t 20f of the dense layer 20f, the volume ratio of the material of the conductive substrate 10 and the LDH in the interface layer 20i, and the volume ratio of the LDH and air in the roughness layer 20r can be determined to be predetermined ratios. This fitting calculation can be executed, for example, using predetermined software, and is performed so that the mean square error between the simulation data calculated from the optical model 1m and the measurement data is 10° 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.

[0019] The layer thickness t 20iWhen the layer thickness t is large, the bonding strength between the LDH layer 20 and the conductive substrate 10 tends to increase due to the anchoring effect, and the electronic conductivity at the boundary between the LDH layer 20 and the conductive substrate 10 tends to increase. For this reason, the water electrolysis electrode 1 is likely to exhibit high performance. In addition, when the bonding strength between the LDH layer 20 and the conductive substrate 10 is high, peeling of the LDH layer 20 due to gas generation in high temperature and alkaline environments during water splitting is less likely to occur, and the water electrolysis electrode 1 is less likely to deteriorate. For this reason, the water electrolysis electrode 1 tends to have high durability. 20i For example, it is 50 nm or more, and may be 60 nm or more. 20i For example, it is 80nm or less.

[0020] The dense layer 20f is thought to have the function of bonding the interface layer 20i and the roughness layer 20r. Layer thickness t 20f If it is greater than or equal to a predetermined value, the layer thickness t 20f The function can be fully demonstrated. On the other hand, the layer thickness t 20f If the value is below a predetermined value, the electronic conductivity of the LDH layer 20 may increase. From these perspectives, the layer thickness t 20f For example, it is 111 nm or more, and may be 250 nm or more or 490 nm or more, and the layer thickness t 20f For example, it may be less than 3000 nm, and may also be less than 2000 nm or 1830 nm or less.

[0021] The roughness layer 20r can provide a reaction field for the gas evolution reaction. The roughness layer 20r can increase the surface area of ​​the interface between the electrolyte and catalyst that contributes to the reaction per unit electrode area, thereby promoting the gas evolution reaction. In other words, the use of the water electrolysis electrode 1 tends to increase the gas generation rate per unit electrode area.

[0022] Layer thickness t 20 is, layer thickness t 20i and layer thickness t 20f and layer thickness t 20r It is the sum of the following. Layer thickness t 20 The layer thickness t may be above a predetermined value from the viewpoint of the LDH layer 20's function, and below a predetermined value from the viewpoint of material diffusion and electron conduction. 20For example, it is 200 nm or more, and may be 400 nm or more, 500 nm or more, 600 nm or more, or 1000 nm or more, and the layer thickness t 20 For example, it may be less than 4000 nm, and may also be less than 3000 nm or less than 2000 nm. (Ratio P) tr When expressed as a percentage, the layer thickness t 20r The layer thickness t 20 It can be calculated as the product of the value obtained by dividing by 100. Proportion P tr The larger the value, the higher the gas generation rate per unit electrode area tends to be, allowing the water electrolysis electrode 1 to exhibit high performance.

[0023] Proportion P tr This may be 7.3% or more, 17.7% or more, 39.4% or more, or 50.9% or more.

[0024] Proportion P tr The upper limit is not limited to a specific value. tr It may be 99% or less, 95% or less, 90% or less, or 86.0% or less.

[0025] The conductive substrate 10 is not limited to a specific substrate as long as it is conductive. The conductive substrate 10 may contain metal or resin. The entire conductive substrate 10 may be made of metal. The conductive substrate 10 may have a configuration in which a surface layer containing metal is formed on a resin component such as polypropylene and polyethylene. In this case, the surface layer containing metal 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 and Fe, or an alloy such as stainless steel and Inconel. Inconel is a registered trademark.

[0026] The conductive substrate 10 contains, for example, Ni. In this case, the conductive substrate 10 tends to have properties that are advantageous from the viewpoint of achieving both corrosion resistance and conductivity in alkaline water electrolysis.

[0027] The conductive substrate 10 has a surface made of, for example, Ni. In this case, the conductive substrate 10 tends to have high alkali resistance. In this case, 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 sputtering film or a plating film.

[0028] When the conductive substrate 10 has a surface made of Ni, the purity of the Ni forming that surface is not limited to a specific value. For example, the purity is 90% by mass or higher. In this case, the conductive substrate 10 is more likely to have high alkali resistance. The method for determining the purity of the Ni forming the surface of the conductive substrate 10 is not limited to a specific method. The purity 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 forming the surface of the conductive substrate 10 may also 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). If the purity of Ni is high, the purity of the Ni forming the surface of the conductive substrate 10 may also be determined by comparing the specific gravity of the conductive substrate 10 with the specific gravity of pure Ni.

[0029] 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.

[0030] The shape of the conductive substrate 10 is not limited to a specific shape. The conductive substrate 10 may be, for example, a sheet. The conductive substrate 10 may have a non-porous structure such as a plate or foil, or it may have a porous structure such as expanded metal, mesh, foam, or nonwoven fabric. Preferably, the conductive substrate 10 has a porous structure. In this case, the surface area of ​​the conductive parts of the conductive substrate 10 tends to be large, and the gas generated in the water electrolysis reaction diffuses easily.

[0031] The thickness of the conductive substrate 10 is not limited to a specific value. Its thickness is, for example, 0.02 mm or more. In this case, the conductive substrate 10 is easier to handle. The thickness of the conductive substrate 10 is, for example, 10 mm or less, and preferably 1 mm or less.

[0032] The LDH layer 20 covers, for example, the surface of the conductive substrate 10. The coverage rate of the LDH layer 20 on the surface of the conductive substrate 10 is not limited to a specific value. Preferably, the coverage rate is 99% or higher. In this case, the water electrolysis electrode 1 is likely to have high electrode activity. In addition, the water electrolysis electrode 1 is likely to have high durability.

[0033] The LDH layer 20 is bonded to, for example, the conductive substrate 10. For example, no other layer, such as an adhesive layer, is placed 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.

[0034] The near-infrared absorption characteristics of the LDH layer 20 can be quantitatively evaluated, for example, by spectroscopic ellipsometry. For example, the higher the extinction coefficient of the LDH layer 20 for near-infrared radiation at a wavelength of 800 nm, in other words, the greater the absorption of near-infrared radiation at a wavelength of 800 nm in the LDH layer 20, the more likely the water electrolysis electrode 1 is to exhibit high performance. The extinction coefficient of the LDH layer 20 for near-infrared radiation at a wavelength of 800 nm is, for example, 0.08 or higher, but may also be 0.1 or higher, 0.2 or higher, 0.3 or higher, or 0.4 or higher. High absorption of near-infrared radiation by the LDH layer 20 suggests that the LDH layer 20 has high conductivity. High conductivity of the LDH layer 20 makes it easier for the water electrolysis electrode 1 to exhibit high performance.

[0035] Figure 3 is a schematic diagram showing an example of the crystal structure of LDH. LDH20a contained in the LDH layer 20 is active in the gas generation reaction of hydrogen and oxygen, etc., at the anode or cathode of water electrolysis. For example, LDH20a can be converted to hydroxide in alkaline water electrolysis.

[0036] LDH20a has a composition represented by the following formula (1), for example. In formula (1), M12+ 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 charge balance. n is an integer. m is a suitable rational number. [M1 2+ 1-x M2 3+ x (OH)2][yA n- ·mH2O] Formula (1)

[0037] LDH20a may contain, for example, two or more types of transition metals. The two or more types of transition metals in LDH20a are not limited to specific transition metals. LDH20a contains, for example, at least two selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. In this case, the electrode 1 for water electrolysis is likely to have high electrode activity.

[0038] LDH20a preferably contains at least one transition metal selected from the group consisting of Fe and Ni. In this case, the electrode 1 for water electrolysis is more likely to have high electrode activity. In addition, the manufacturing cost of the electrode 1 for water electrolysis is likely to be low.

[0039] LDH20a may contain Fe and Ni. For example, in the composition shown in Formula (1), M1 may be Ni and M2 may be Fe. In this case, the electrode 1 for water electrolysis is more likely to have high electrode activity.

[0040] In LDH20a, A which is an interlayer anion n- may be an inorganic ion or an organic ion. Examples of inorganic ions are CO3 2- , NO3 - , Cl - , SO4 2- , Br - , OH - , F - , I - , Si2O5 2- , B4O5(OH)42- , 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- It can be inserted between layers of metal hydroxide along with water molecules. n- The charge and ion size are not limited to specific values. LDH20a is one type A n- It may include multiple types of A n- It may include.

[0041] As shown in Figure 3, LDH20a is M1 2+ or M2 3+ At each vertex of an octahedron centered at OH - It contains ions. LDH20a contains [M1 2+ 1-x M2 3+ x (OH)2] x+ It contains metal hydroxides represented by . These metal hydroxides have a layered structure in which octahedrons of hydroxide are linked together in two dimensions, sharing edges. Between the layers of metal hydroxide are anions A n- and water molecules are present. The metal hydroxide layer functions as the host layer 21, and anion A n- And a guest layer 22 containing water molecules is placed between the host layers. In other words, LDH20a as a whole consists of a host layer 21 of metal hydroxide and anion A n- It has a sheet-like structure in which the guest layer 22 of water molecules and the metal hydroxide are alternately stacked. LDH20a contains M1 2+ Part of M2 3+ It has a structure that has been replaced by [this].

[0042] The LDH layer 20 may contain a chelating agent. The chelating agent may be coordinated to the transition metal contained in LDH20a. This allows LDH20a to exist stably in the LDH layer 20. In addition, LDH20a tends to have a small particle size. Furthermore, the LDH layer 20 tends to become a dense layer with few voids containing LDH20a, and is firmly fixed to the conductive substrate 10 with the desired thickness. This is because when the LDH layer 20 is formed on the conductive substrate 10, the nucleated LDH tends to grow slowly as crystals. As a result, the LDH layer 20 tends to effectively contribute to the anode or cathode reaction of water electrolysis, and the water electrolysis electrode 1 tends to have higher electrode activity.

[0043] The chelating agent is not limited to any particular chelating agent. A chelating agent is, for example, an organic compound that can coordinate to transition metal ions in LDH20a. The chelating agent may be at least one selected from the group consisting of bidentate organic ligands and tripidentate organic ligands. Examples of chelating agents are β-diketones, β-ketoesters, hydroxycarboxylic acids, and hydroxycarboxylate salts. Examples of β-diketones are acetylacetone (ACAC), trifluoroacetylacetone, hexafluoroacetylacetone, benzoylacetone, tenoyltrifluoroacetone, dipyrobilmethane, 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 include tartaric acid, citric acid, malic acid, gluconic acid, ferulic acid, lactic acid, glucuronic acid, and their salts.

[0044] The chelating agent preferably includes 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.

[0045] The method for manufacturing the water electrolysis electrode 1 is not limited to a specific method. For example, the water electrolysis electrode 1 can be manufactured by immersing a conductive substrate 10 in a solution containing a chelating agent and two or more transition metal ions, and then adjusting the solution to be alkaline. With such a method, an LDH layer 20 containing LDH 20a and a chelating agent can be formed on the surface of the conductive substrate 10 in a simple manner.

[0046] The temperature of the solution when adjusting it to an alkaline state is not limited to a specific temperature. For example, the temperature of the solution can be room temperature, 20°C ± 15°C. In this case, a water electrolysis electrode 1 with high electrode activity is easily obtained.

[0047] The solvent in the solution may be water, an organic solvent, or a mixed solvent of water and an organic solvent.

[0048] The method for manufacturing the water electrolysis electrode 1 preferably includes increasing the pH. This allows LDH20a to be formed on the surface of the conductive substrate 10 in a short period of time, making it easier to obtain a water electrolysis electrode 1 with high electrode activity. In addition, the manufactured water electrolysis electrode 1 tends to have high durability.

[0049] The method for adjusting a solution to be alkaline is not limited to a specific method. For example, the solution may be adjusted to be alkaline by mixing the above solution with an alkaline solution. Alternatively, the solution may be adjusted to be alkaline by adding a pH-raising agent to the above solution. In this case, the pH-raising agent is not limited to a specific compound. A pH-raising agent is, for example, a compound having an epoxy group. Examples of pH-raising agents are propylene oxide, ethylene oxide, and butylene oxide. When a pH-raising agent having an epoxy group, such as propylene oxide, is added to a solution, in the presence of a nucleophile such as a chloride ion, the pH-raising agent may capture hydrogen ions present in the solution through a ring-opening reaction of the epoxy group. This can raise 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-raising agent is added to this solution, the pH of the solution may gradually rise from, for example, 1, and eventually the solution may become alkaline. The final pH of the solution may be, for example, between 8 and 12. When a pH-raising agent is added to a solution, a reaction occurs in which hydrogen ions in the solution are captured. This gradually increases the pH of the solution. The time it takes for the pH of the solution to reach a steady state after adding the pH-raising agent is not limited to a specific time. This time could be, for example, 24 hours or more, or even several days.

[0050] The two or more transition metal ions contained in the solution are not limited to specific transition metal ions. For example, the two or more transition metal ions contained in the solution are at least two transition metal ions selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. In this case, it is easier to manufacture a water electrolysis electrode 1 with high electrode activity.

[0051] The solution preferably contains two or more transition metal ions, including at least one transition metal ion selected from the group consisting of Ni and Fe. In this case, a water electrolysis electrode 1 with high electrode activity is more easily manufactured.

[0052] The conductive substrate 10 contains, for example, Ni. The solution contains two or more transition metal ions, preferably Fe ions. The solution preferably contains chloride ions. In this case, the reaction shown in formula (2) may occur. This may etch the conductive substrate 10. The method for manufacturing the water electrolysis electrode 1 preferably includes promoting the mixing of the solution before adjusting the solution to alkaline while the conductive substrate 10 is immersed in it. Promoting the mixing of the solution can be done, for example, by vibrating the conductive substrate 10, shaking the container containing the solution and the conductive substrate 10, or stirring the solution using a stirrer piece and a stirrer. Such methods can cause forced convection of the solution and promote the mixing of the solution. This may etch the conductive substrate 10 to the desired state and form the LDH layer 20 on the conductive substrate 10 to the desired state. As a result, the water electrolysis electrode 1 is likely to have high durability. The promotion of the mixing of the solution may be done with the container containing the solution and the conductive substrate 10 sealed, or under an inert gas atmosphere. 4Ni 2+ Cl - 2 + 2Fe 3+ Cl - 3+ 2Ni → 5Ni 2+ Cl - 2 + 2Fe 2+ Cl - 2+ 1Ni Equation (2)

[0053] In the manufacture of the water electrolysis electrode 1, the molar ratio of Fe ions to Ni in the conductive substrate 10 is not limited to a specific value. For example, the molar ratio is 0.75 or less. In this case, it is possible to prevent the Ni in the conductive substrate 10 from dissolving due to the reaction shown in equation (2), which would make the manufacture of the water electrolysis electrode 1 difficult.

[0054] The above molar ratio is, for example, 0.03 or higher. In this case, the LDH layer 20 is more easily formed uniformly on the surface of the conductive substrate 10, and the water electrolysis electrode 1 is more likely to have high electrode activity.

[0055] The chelating agent included in the solution may be selected with reference to the above examples of chelating agents included in the LDH layer 20. Preferably, the chelating agent included in the solution 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 for the LDH layer 20 to form in the desired state on the water electrolysis electrode 1. As a result, the water electrolysis electrode 1 is more likely to have high electrode activity.

[0056] Figure 4 is a schematic diagram illustrating the manufacturing mechanism of the water electrolysis electrode 1. As shown in Figure 4, a conductive substrate 10 is immersed in a solution containing transition metal ions TM1, transition metal ions TM2, and a chelating agent CH. For example, transition metal ion TM1 is a Ni ion, and transition metal ion TM2 is an Fe ion. For example, Ni is present on the surface of the conductive substrate 10. Some of the transition metal ions TM2 etch and dissolve the Ni present on the surface of the conductive substrate 10. Some of the chelating agent reacts with the surface of the conductive substrate 10, forming a complex C1 between the transition metal ions TM1 derived from the conductive substrate 10 and the chelating agent CH. In addition, when the solution is adjusted to be alkaline, a complex C1 derived from the transition metal ions TM1 derived from the solution and the chelating agent CH is formed in the solution, and a complex C2 between the transition metal ions TM2 and the chelating agent CH is formed. Next, 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 complexes C1 and C2 contain the chelating agent CH, the crystal growth of LDH20a is suppressed. As a result, an LDH layer 20 containing LDH20a and the chelating agent CH is formed on the surface of the conductive substrate 10, and an electrode 1 for water electrolysis is obtained.

[0057] The water electrolysis electrode 1 according to this embodiment can be used, for example, as an electrode in the water electrolysis cell of an alkaline water electrolysis apparatus or an anion exchange membrane type water electrolysis apparatus. The water electrolysis electrode 1 is used, for example, in at least one selected from the group consisting of anode and cathode in these water electrolysis apparatuses. In other words, at least one selected from the group consisting of a water electrolysis anode equipped with the water electrolysis electrode 1 and a water electrolysis cathode equipped with the water electrolysis electrode 1 can be provided. This makes it easier to increase the activity of the anodic or cathode reaction of water electrolysis.

[0058] (Second Embodiment) Figure 5 is a schematic cross-sectional view showing an example of a water electrolysis cell according to the second embodiment. As shown in Figure 5, the water electrolysis cell 2 comprises an anode 2a, a cathode 2b, and a diaphragm 2p. At least one selected from the group consisting of anode 2a and 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 cathode reaction in the water electrolysis cell tends to be high, and anode 2a or cathode 2b tends to exhibit high performance.

[0059] Water electrolysis cell 2 is, for example, an alkaline water electrolysis cell that uses an alkaline aqueous solution. The alkaline aqueous solution used in water electrolysis cell 2 is not limited to a specific alkaline aqueous solution. Examples of alkaline aqueous solutions are potassium hydroxide aqueous solution and sodium hydroxide aqueous solution.

[0060] As shown in Figure 5, the water electrolysis cell 2 comprises, for example, an electrolytic cell 2s, a first chamber 2m, and a second chamber 2n. The diaphragm 2p is located inside the electrolytic cell 2s, dividing the inside of the electrolytic cell 2s into the first chamber 2m and the second chamber 2n. The anode 2a is located in the first chamber 2m, and the cathode 2b is located in the second chamber 2n.

[0061] 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 electrolytes. The material of the diaphragm 2p is not limited to a specific material. Examples of materials for the diaphragm 2p are asbestos, polymer-reinforced asbestos, potassium titanate bonded with polytetrafluoroethylene (PTFE), zirconia bonded with PTFE, and antimony acid and antimony oxide bonded with polysulfone. Another example of materials for the diaphragm 2p is sintered nickel, nickel coated with ceramics and nickel oxide, and polysulfone. The diaphragm 2p may also be Zirfon Perl UTP 500 manufactured by AGFA.

[0062] The anode 2a may be positioned in a zero-gap state, in contact with the diaphragm 2p, or it may be positioned with a gap between it and the diaphragm 2p. The cathode 2b may be positioned in contact with the diaphragm 2p, or it may be positioned with a gap between it and the diaphragm 2p.

[0063] The water electrolysis cell 2 produces hydrogen and oxygen by electrolyzing an alkaline aqueous solution. An aqueous solution containing an alkali metal or alkaline earth metal hydroxide is supplied to the first chamber 2m. In addition, an alkaline aqueous solution may be supplied to the second chamber 2n. Electrolysis is carried out while alkaline aqueous solutions of a predetermined concentration are discharged from the first chamber 2m and the second chamber 2n, and hydrogen and oxygen are produced.

[0064] If the anode 2a includes the water electrolysis electrode 1, the cathode 2b may include, for example, an electrode material known as the cathode of an alkaline water electrolysis cell. If the cathode 2b includes the water electrolysis electrode 1, the anode 2a may include an electrode material known as 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.

[0065] With the above configuration, at least one selected from the group consisting of anode 2a and cathode 2b includes the water electrolysis electrode 1, so the water electrolysis cell 2 can exhibit high performance.

[0066] (Third embodiment) Figure 6 is a schematic cross-sectional view showing an example of a water electrolysis apparatus according to the third embodiment. As shown in Figure 6, the water electrolysis apparatus 3 comprises a water electrolysis cell 2 according to the second embodiment and a voltage inductor 40. The voltage inductor 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.

[0067] The voltage inductor 40 is electrically connected to the anode 2a and the cathode 2b. The voltage inductor 40 raises the potential of the anode 2a above the potential of the cathode 2b. The voltage inductor 40 is not limited to any particular type of voltage inductor, as long as it can apply a voltage between the anode 2a and the cathode 2b. The voltage inductor 40 may also be a device that adjusts the voltage applied between the anode 2a and the cathode 2b. When the voltage inductor 40 is connected to a DC power source such as a battery, solar cell, and fuel cell, the voltage inductor 40 includes, for example, a DC / DC converter. When the voltage inductor 40 is connected to an AC power source such as a commercial power supply, the voltage inductor 40 includes, for example, an AC / DC converter. The voltage inductor 40 may also be, for example, a power supply. In a 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 device 3 is a predetermined set value.

[0068] With the above configuration, the water electrolysis device 3 can exhibit high performance.

[0069] (Fourth Embodiment) Figure 7 is a schematic cross-sectional view showing an example of a water electrolysis cell according to the fourth embodiment. As shown in Figure 7, the water electrolysis cell 4 comprises 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 anode 4a and 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 tends to be high, and the anode 4a or cathode 4b tends to exhibit high performance.

[0070] The water electrolysis cell 4 is, for example, an anion exchange membrane (AEM) type water electrolysis cell. As shown in Figure 7, the anode 4a comprises, for example, an electrode catalyst layer 4m and a gas diffusion layer 4n. The cathode 4b comprises, 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.

[0071] The anion exchange membrane 4p is not limited to a specific type of anion exchange membrane. The anion exchange membrane 4p is conductive to anions such as hydroxide ions. The anion exchange membrane 4p can prevent the mixing of oxygen gas produced at anode 4a and hydrogen gas produced at cathode 4b. The oxygen gas is guided outside anode 4a through the gas diffusion layer 4n. The hydrogen gas is guided outside cathode 4b through the gas diffusion layer 4k.

[0072] In the water electrolysis cell 4, if the anode 4a includes the water electrolysis electrode 1, the cathode may be a known cathode in an AEM-type water electrolysis cell. In the water electrolysis cell 4, if the cathode 4b includes the water electrolysis electrode 1, the anode 4a may be a known anode in an AEM-type water electrolysis cell. In the water electrolysis cell 4, both the anode 4a and the cathode 4b may include the water electrolysis electrode 1.

[0073] With the above configuration, at least one selected from the group consisting of anode 4a and cathode 4b includes the water electrolysis electrode 1, so the water electrolysis cell 4 can exhibit high performance.

[0074] (Fifth embodiment) Figure 8 is a schematic cross-sectional view showing an example of a water electrolysis apparatus according to the fifth embodiment. As shown in Figure 8, the water electrolysis apparatus 5 comprises a water electrolysis cell 4 and a voltage injector 40. The voltage injector 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.

[0075] The voltage inductor 40 is electrically connected to the anode 4a and the cathode 4b. The voltage inductor 40 raises the potential of the anode 4a above the potential of the cathode 4b. The voltage inductor 40 is not limited to any particular type of voltage inductor, as long as it can apply a voltage between the anode 4a and the cathode 4b. The voltage inductor 40 may also be a device that adjusts the voltage applied between the anode 4a and the cathode 4b. When the voltage inductor 40 is connected to a DC power source such as a battery, solar cell, or fuel cell, the voltage inductor 40 includes, for example, a DC / DC converter. When the voltage inductor 40 is connected to an AC power source such as a commercial power supply, the voltage inductor 40 includes, for example, an AC / DC converter. The voltage inductor 40 may also be, for example, a power supply. In a power supply, the voltage applied between the anode 4a and the cathode 4b, and the current flowing between the anode 4a and the cathode 4b are adjusted so that the power supplied to the water electrolysis device 5 is a predetermined set value.

[0076] With the above configuration, the water electrolysis device 5 can exhibit high performance.

[0077] (Note) Based on the above description, the following technologies are disclosed. (Technology 1) A conductive substrate and The conductive substrate comprises a layered double hydroxide layer provided on its surface, The aforementioned layered double hydroxide layer comprises a roughness layer, The ratio of the thickness of the roughness layer to the thickness of the layered double hydroxide layer is 4.8% or more. Electrode for water electrolysis. (Technology 2) The aforementioned percentage is 7.3% or more. Electrodes for water electrolysis as described in Technology 1. (Technology 3) The aforementioned percentage is 17.7% or more. Electrodes for water electrolysis as described in Technology 2. (Technology 4) The aforementioned percentage is 39.4% or higher. Electrodes for water electrolysis as described in Technical 3. (Technology 5) The aforementioned percentage is 50.9% or more. Electrodes for water electrolysis as described in Technical 4. (Technology 6) 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. An electrode for water electrolysis as described in any one of the technical items 1 to 5. (Technology 7) The layered double hydroxide layer contains at least one transition metal selected from the group consisting of Fe and Ni. An electrode for water electrolysis as described in Technical 6. (Technology 8) The aforementioned layered double hydroxide layer contains a chelating agent. An electrode for water electrolysis as described in any one of the technical items 1 to 7. (Technology 9) The chelating agent comprises at least one selected from the group consisting of acetylacetone and citrate. Electrodes for water electrolysis as described in Technical 8. (Technology 10) Equipped with an electrode for water electrolysis as described in any one of Technical Items 1 to 9, Anode for water electrolysis. (Technology 11) Equipped with an electrode for water electrolysis as described in any one of Technical Items 1 to 9, Cathode for water electrolysis. (Technology 12) A-scatter, Cathode and, Equipped with a diaphragm, At least one selected from the group consisting of the anode being an anode for water electrolysis described in Technology 10 and the cathode being a cathode for water electrolysis described in Technology 11 is satisfied. water electrolysis cell. (Technology 13) A-scatter, Cathode and, It comprises an anion exchange membrane, At least one selected from the group consisting of the anode being an anode for water electrolysis described in Technology 10 and the cathode being a cathode for water electrolysis described in Technology 11 is satisfied. water electrolysis cell. (Technology 14) A water electrolysis cell as described in Technology 12 or 13, A voltage injector that applies a voltage between the cathode and the anode is provided. Water electrolysis equipment. [Examples]

[0078] The present disclosure will be described in more detail below with reference to examples. Note that the following examples are merely examples of the present disclosure and are not limited to these examples.

[0079] (Example 1) A solution was prepared by dissolving 0.151 g of nickel chloride hexahydrate and 0.043 g of iron chloride hexahydrate in 3.64 ml (mL) of water in a perfluoroalkoxyalkane (PFA) mini-vial OD-98-5MV manufactured by Taiyo Co., Ltd. The nickel chloride hexahydrate and iron chloride hexahydrate were purchased from Fujifilm Wako Pure Chemical Industries, Ltd. To this solution, 0.025 mL of acetylacetone (ACAC) was added as a chelating agent to obtain the chelating agent-containing solution according to Example 1. The ACAC was purchased from Sigma-Aldrich.

[0080] A single nickel plate manufactured by Nilaco was subjected to a 10-minute acetone wash followed by a 10-minute wash in a 1M HCl aqueous solution to degrease and remove impurities. The nickel plate had a thickness of 0.2 mm and was circular in shape with a diameter of 15 mm in plan view. The weight of the nickel plate was 0.315 g. Next, the nickel plate was washed with water and dried to complete the cleaning process.

[0081] Next, the Ni plate after the cleaning process was immersed in the chelating agent-containing solution according to Example 1. In this state, the chelating agent-containing solution containing the Ni plate was shaken and stirred at 25°C for 24 hours. At this time, the outermost surface of the Ni plate was etched according to equation (2) above. Next, 0.254 mL of propylene oxide (POX) was added to the chelating agent-containing solution as a pH raising agent. The resulting mixed solution was shaken and stirred at 25°C for 72 hours. After 72 hours of shaking and stirring, the Ni plate was collected, washed with water, and dried. In this way, the electrode according to Example 1 was obtained.

[0082] (Example 2) An electrode according to Example 2 was prepared in the same manner as in Example 1, except for the points described below. A mixed solvent was prepared by mixing 1.50 mL of water and 2.25 mL of ethanol in a PFA mini vial OD-98-5MV. The ethanol was purchased from Fujifilm Wako Pure Chemical Industries, Ltd. A solution was prepared by dissolving 0.128 g of nickel chloride hexahydrate and 0.073 g of iron chloride hexahydrate in the mixed solvent. 0.0253 mL of ACAC was added to this solution as a chelating agent to obtain the chelating agent-containing solution according to Example 2. An electrode according to Example 2 was obtained in the same manner as in Example 1, except that the chelating agent-containing solution according to Example 2 was used instead of the chelating agent-containing solution according to Example 1, and 0.136 mL of POX was added to the chelating agent-containing solution as a pH raising agent.

[0083] (Example 3) An electrode according to Example 3 was prepared in the same manner as in Example 1, except for the points described below. A mixed solvent was prepared by mixing 1.45 mL of water and 2.17 mL of ethanol in a PFA mini vial OD-98-5MV. The ethanol was purchased from Fujifilm Wako Pure Chemical Industries, Ltd. A solution was prepared by dissolving 0.123 g of nickel chloride hexahydrate and 0.070 g of iron chloride hexahydrate in the mixed solvent. 0.0365 mL of ACAC was added to this solution as a chelating agent to obtain the chelating agent-containing solution according to Example 3. An electrode according to Example 3 was obtained in the same manner as in Example 1, except that the chelating agent-containing solution according to Example 3 was used instead of the chelating agent-containing solution according to Example 1, and 0.263 mL of POX was added to the chelating agent-containing solution as a pH raising agent.

[0084] (Example 4) An electrode according to Example 4 was prepared in the same manner as in Example 1, except for the points described below. A mixed solvent was prepared by mixing 1.45 mL of water and 2.18 mL of ethanol in a PFA mini vial OD-98-5MV. The ethanol was purchased from Fujifilm Wako Pure Chemical Industries, Ltd. A solution was prepared by dissolving 0.123 g of nickel chloride hexahydrate and 0.070 g of iron chloride hexahydrate in the mixed solvent. 0.0200 mL of ACAC was added to this solution as a chelating agent to obtain the chelating agent-containing solution according to Example 4. An electrode according to Example 4 was obtained in the same manner as in Example 1, except that the chelating agent-containing solution according to Example 4 was used instead of the chelating agent-containing solution according to Example 1, and 0.260 mL of POX was added to the chelating agent-containing solution as a pH raising agent.

[0085] (Example 5) An electrode according to Example 5 was prepared in the same manner as in Example 1, except for the points described below. A mixed solvent was prepared by mixing 1.46 mL of water and 2.19 mL of ethanol in a PFA mini vial OD-98-5MV. The ethanol was purchased from Fujifilm Wako Pure Chemical Industries, Ltd. A solution was prepared by dissolving 0.124 g of nickel chloride hexahydrate and 0.070 g of iron chloride hexahydrate in the mixed solvent. 0.0061 mL of ACAC was added to this solution as a chelating agent to obtain the chelating agent-containing solution according to Example 5. An electrode according to Example 5 was obtained in the same manner as in Example 1, except that the chelating agent-containing solution according to Example 5 was used instead of the chelating agent-containing solution according to Example 1, and 0.265 mL of POX was added to the chelating agent-containing solution as a pH raising agent.

[0086] (Example 6) An electrode according to Example 6 was prepared in the same manner as in Example 1, except for the points described below. 3.64 mL of water was placed in a PFA mini vial OD-98-5MV. 0.124 g of nickel chloride hexahydrate and 0.07 g of iron chloride hexahydrate were dissolved in the water to prepare a solution. 0.0123 mL of ACAC was added to this solution as a chelating agent to obtain the chelating agent-containing solution according to Example 6. An electrode according to Example 6 was obtained in the same manner as in Example 1, except that the chelating agent-containing solution according to Example 6 was used instead of the chelating agent-containing solution according to Example 1, and 0.265 mL of POX was added to the chelating agent-containing solution as a pH raising agent.

[0087] (Comparative Example 1) An electrode according to Comparative Example 1 was prepared in the same manner as in Example 1, except for the points described below. A solution was prepared by dissolving 0.226 g of nickel chloride hexahydrate and 0.128 g of iron chloride hexahydrate in 3.32 mL of water placed in a PFA mini vial OD-98-5MV. To this solution, 0.0400 mL of ACAC was added as a chelating agent to obtain the chelating agent-containing solution according to Comparative Example 1. An electrode according to Comparative Example 1 was obtained in the same manner as in Example 1, except that the chelating agent-containing solution according to Comparative Example 1 was used instead of the chelating agent-containing solution according to Example 1, and 0.480 mL of POX was added to the chelating agent-containing solution as a pH raising agent.

[0088] [Evaluation of LDH layer thickness] Using a UVISEL2 spectroscopic ellipsometer manufactured by Horiba, Ltd., measurements were taken at the center point of each electrode under the conditions of an incident angle of 70 degrees, a measurement wavelength range of 0.6 to 5.5 eV, and a spot diameter of 1 mm × 2 mm. The measurement data was analyzed using Delta Psi2 software included with UVISEL2, and the layer thicknesses of the LDH layer, interface layer, dense layer, and roughness layer were determined using the optical model shown in Figure 2. For the fitting calculations in this analysis, the New Amorphous equation proposed by Horiba-Jovin Yvon and the Tauc-Lorentz equation were used, and the result with the smallest mean squared error between the simulation data calculated from the optical model and the measurement data was adopted. In addition, the fitting calculations were performed so that the mean squared error was 10° or less.

[0089] [Evaluation of electrode current density and overvoltage] The current density during oxygen evolution (OER) of the electrodes in each example and comparative example was evaluated. For the measurements, a Princeton Applied Research VersaSTAT4 potentiostat, a BAS alkaline sample vial (200 mL), a BAS Teflon® cap (for 200 mL), and an EC Frontier AE-2 plate electrode were used as the working electrode fixture. The electrodes in each example and comparative example, which served as the working electrodes, were fixed to this fixture. A Metrohm double platinum wire counter electrode D.6.0305.200J was used as the counter electrode. The current derived from the anode reaction of the water electrolysis cell was measured using the three-electrode method under the following measurement conditions. The anode reaction is the oxygen evolution reaction. (Measurement conditions) Solution: 1M KOH solution Potential relative to the reversible hydrogen electrode (RHE): 1.0V to 1.7V Number of cycles: 5 cycles Potential sweep speed: 10mV / sec Temperature: 25℃

[0090] Current density in the 5th cycle: 10 mA / cm² 2 The overpotential was determined by subtracting the theoretical potential of 1.229V required to advance the oxygen evolution reaction from the voltage corresponding to the overpotential. The current value corresponding to the voltage of 1.6V in the 5th cycle was calculated by viewing the area of ​​the Ni plate electrode in a planar view of 1.767cm². 2 The current density was determined by dividing by [the specified value].

[0091] Table 1 shows the ratio of the roughness layer thickness to the LDH layer thickness, the roughness layer thickness, the dense layer thickness, the interface layer thickness, the LDH layer thickness, the current density, and the overvoltage for each example and comparative example electrode. Although the overvoltages for each example and Comparative Example 1 are similar, the current density in each example is greater than that of Comparative Example 1. In the electrodes of each example, the ratio of the roughness layer thickness to the LDH layer thickness is greater than that of the electrode of Comparative Example 1. From these results, it can be understood that in a water electrolysis electrode equipped with an LDH layer containing LDH, if the ratio of the roughness layer thickness to the LDH layer thickness is 4.8% or more, the water electrolysis electrode can exhibit high performance.

[0092] [Table 1]

[0093] Furthermore, many improvements and other embodiments of the disclosure will be apparent to those skilled in the art from the above description. Therefore, the above description should be interpreted as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the disclosure. The operating conditions, composition, structure and / or function can be substantially modified without departing from the spirit of the disclosure. [Industrial applicability]

[0094] The electrode for water electrolysis disclosed herein can be used as an anode or cathode for water electrolysis.

Claims

1. A conductive substrate having a surface made of Ni, The conductive substrate comprises a layered double hydroxide layer provided on the surface thereof, The aforementioned layered double hydroxide layer comprises an interface layer, a dense layer, and a roughness layer. The ratio of the thickness of the roughness layer to the thickness of the layered double hydroxide layer and the thickness of the interface layer, as determined by spectroscopic ellipsometry, are 4.8% or more and 50 nm or more, respectively. Electrode for water electrolysis.

2. The aforementioned percentage is 7.3% or more. The electrode for water electrolysis according to claim 1.

3. The aforementioned percentage is 17.7% or more. The electrode for water electrolysis according to claim 2.

4. The aforementioned percentage is 39.4% or more. The electrode for water electrolysis according to claim 3.

5. The aforementioned percentage is 50.9% or more. The electrode for water electrolysis according to claim 4.

6. The aforementioned layered double hydroxide layer is made of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. A system comprising at least two transition metals selected from the group, The electrode for water electrolysis according to claim 1.

7. The layered double hydroxide layer is composed of at least one transition selected from the group consisting of Fe and Ni. Including metals, The electrode for water electrolysis according to claim 6.

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

9. The chelating agent is selected from the group consisting of acetylacetone and citrate, and is at least one of the following: Including one more, The electrode for water electrolysis according to claim 8.

10. A water electrolysis electrode as described in claim 1, Anode for water electrolysis.

11. A water electrolysis electrode as described in claim 1, Cathode for water electrolysis.

12. A-scatter, Cathode and, Equipped with a diaphragm, The anode is the anode for water electrolysis described in claim 10 and the cathode is At least one selected from the group consisting of the water electrolysis cathodes described in item 11 is I am satisfied. water electrolysis cell.

13. A-scatter, Cathode and, It comprises an anion exchange membrane, The anode is the anode for water electrolysis described in claim 10 and the cathode is At least one selected from the group consisting of the water electrolysis cathodes described in item 11 is I am satisfied. water electrolysis cell.

14. The water electrolysis cell according to claim 12, A voltage injector that applies a voltage between the cathode and the anode is provided. Water electrolysis equipment.

15. The water electrolysis cell according to claim 13, A voltage injector that applies a voltage between the cathode and the anode is provided. Water electrolysis equipment.

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