Electrode for water electrolysis, anode for water electrolysis, cathode for water electrolysis, water electrolysis unit, and water electrolysis device

Abstract

An electrode (1) for water electrolysis is provided with a conductive substrate (10) and a layered double hydroxide layer (20). The conductive substrate (10) contains Ni. The layered double hydroxide layer (20) is provided on the surface of the conductive substrate (10). The layered double hydroxide layer (20) contains Ni. The ratio (P003 / P111) of the intensity (P003) of the diffraction peak of the (003) plane of the layered double hydroxide to the intensity (P111) of the diffraction peak of the (111) plane of Ni is 0.025 or less in an XRD pattern obtained by X-ray diffraction at a small angle of the electrode (1) for water electrolysis.

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

[0002] An electrode for water electrolysis has been known in the past.

[0003] In Patent Literature 1, a method for manufacturing an electrode for electrolysis of water is described, which includes a step of impregnating an electrode substrate containing a prescribed 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 a metal M1 and a compound containing a metal M2, while using an electrically conductive substrate as an anode.

[0004] In Patent Literature 2, an oxygen evolution catalyst is described, which has a graphene oxide layer and a nickel-iron layered double hydroxide layer supported on the surface of the graphene oxide layer, and the average thickness of the graphene oxide layer is 0.33 to 4 nm.

[0005] In Non-Patent Literature 1, the activity of an oxygen evolution reaction (OER) of an electrode of a Ni-Fe layered double hydroxide (Ni-Fe LDH) was studied.

[0006] In Non-Patent Literature 2, it is described that the electronic structure of a local portion of a Ni-Fe LDH is adjusted by a boundary surface interaction between FeOOH and the Ni-Fe LDH, and the OER electrode catalysis is improved.

[0007] PRIOR ART DOCUMENTS

[0008] PATENT LITERATURE

[0009] Patent Literature 1: International Publication No. 2017 / 154134

[0010] Patent Literature 2: Japanese Patent Application Publication No. 2018-043193

[0011] NON-PATENT LITERATURE

[0012] Non-Patent Literature 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

[0013] Non-Patent Literature 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 SUMMARY

[0014] From the viewpoint of improving the performance of an electrode for water electrolysis, the above-described documents leave room for further research. Therefore, the present disclosure provides a novel electrode for water electrolysis that is advantageous from the viewpoint of exhibiting high performance.

[0015] The present disclosure provides an electrode for water electrolysis including a conductive substrate containing Ni, and a layered double hydroxide layer containing Ni provided on a surface of the conductive substrate,

[0016] In an X-ray diffraction pattern of the electrode for water electrolysis by micro-angle incident X-ray diffraction, the ratio of the intensity of the diffraction peak of the (003) plane of the layered double hydroxide to the intensity of the diffraction peak of the (111) plane of Ni is 0.025 or less.

[0017] According to the present disclosure, it is possible to provide a novel electrode for water electrolysis that is advantageous from the viewpoint of exhibiting high performance. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a cross-sectional view showing an example of the electrode for water electrolysis of the present disclosure.

[0019] Figure 2 is a diagram schematically showing an example of the crystal structure of a layered double hydroxide (LDH).

[0020] Figure 3 is a view schematically showing an example of a manufacturing mechanism of an electrode for water electrolysis.

[0021] Figure 4 is a cross-sectional view showing an example of a water electrolysis unit of the present disclosure.

[0022] Figure 5 is a cross-sectional view showing an example of a water electrolysis device of the present disclosure.

[0023] Figure 6 is a cross-sectional view showing another example of a water electrolysis unit of the present disclosure.

[0024] Figure 7 is a cross-sectional view showing another example of a water electrolysis device of the present disclosure.

[0025] Figure 8 is a view showing an X-ray diffraction pattern of micro-angle incident X-ray diffraction (GIXD) of an electrode related to Example 1.

[0026] Figure 9 is a view showing an X-ray diffraction pattern of GIXD of an electrode related to Example 2.

[0027] Figure 10 is a view showing an X-ray diffraction pattern of GIXD of an electrode related to Example 3.

[0028] Figure 11 is a view showing an X-ray diffraction pattern of GIXD of an electrode related to Example 4.

[0029] Figure 12 is a view showing an X-ray diffraction pattern of GIXD of an electrode related to Example 5.

[0030] Figure 13 is a view showing an X-ray diffraction pattern of GIXD of an electrode related to a comparative example. DETAILED DESCRIPTION

[0031] (Insight that is the basis of the present disclosure)

[0032] As a measure against global warming, the use of renewable energy such as sunlight and wind power is attracting attention. In power generation based on renewable energy, there is a problem that surplus electric power is wasted. Therefore, the efficiency of use of renewable energy is not necessarily sufficient. Therefore, a method of efficiently using surplus electric power by producing hydrogen from surplus electric power and storing it is being studied.

[0033] As a method of producing hydrogen from surplus electric power, electrolysis of water can be considered. In order to produce hydrogen inexpensively and stably, development of a water electrolysis device with high efficiency and long life is required. In a water electrolysis device, oxygen is generated at an anode, and hydrogen is generated at a cathode. The reaction in which oxygen is generated at the anode is also referred to as an anode reaction, and the reaction in which hydrogen is generated at the cathode is also referred to as a cathode reaction. In order to increase the hydrogen production speed in a water electrolysis device, particularly in a case where a prescribed voltage is applied between the anode and the cathode, it is desirable that a current, that is, a current density, flowing per unit electrode area in the anode be large. In addition, it is desirable that a current, that is, a current density, flowing per unit electrode area in the cathode be large. Therefore, development of an electrode with high performance for an anode reaction or a cathode reaction of water electrolysis is expected.

[0034] For example, from the viewpoint of a large specific surface area and a variety of combinations of metal ions, it is considered that LDH is promising as a material of an electrode for water electrolysis. For example, according to Patent Literature 1, an electrode substrate containing a prescribed layered double hydroxide is produced by performing an electrodeposition treatment in an aqueous solution containing a compound containing a metal M1 and a compound containing a metal M2, with a conductive substrate as an anode. On the other hand, the performance of an electrode produced by the electrodeposition treatment is insufficient, and there is room for improvement. As a result of repeated intensive studies by the present inventors, it has been newly found that, by adjusting the crystallinity of a water electrolysis electrode having a layer containing LDH to a prescribed state, the performance of the water electrolysis electrode is improved, and thus the electrode for water electrolysis of the present disclosure has been completed.

[0035] Embodiments of the present disclosure will be described below with reference to the accompanying drawings. The present disclosure is not limited to the following embodiments. Furthermore, the embodiments described below are embodiments that show general or specific examples. Therefore, the values, shapes, materials, constituent elements, arrangement positions of constituent elements, connection modes, and the like shown in the following embodiments are examples, and are not intended to limit the present disclosure. In addition, with respect to constituent elements among the constituent elements in the following embodiments that are not recited in the independent claims that represent the most general concept, the constituent elements are described as arbitrary constituent elements. In addition, in the drawings, portions to which the same reference numerals are attached are sometimes omitted from the description. In addition, the drawings are drawings in which each constituent element is schematically shown in order to facilitate understanding, and sometimes do not accurately show the shape and the size ratio, and the like.

[0036] (First Embodiment)

[0037] Figure 1 is a cross-sectional view that shows the electrode for water electrolysis according to the first embodiment. As shown in FIG. 1, the electrode for water electrolysis according to the first embodiment includes a substrate 1, a first layer 2, and a second layer 3. The substrate 1 is a conductive substrate. The first layer 2 is a layer containing LDH. The second layer 3 is a layer containing a compound containing a metal M1 and a compound containing a metal M2. Figure 1As shown, the water electrolysis electrode 1 includes a conductive substrate 10 and a layered double hydroxide (LDH) layer 20. The conductive substrate 10 contains Ni. The LDH layer 20 contains Ni and is disposed on the surface of the conductive substrate 10. The LDH layer 20 can function as a catalyst for the anodic or cathodic reaction in water electrolysis. In the small angle incident X-ray diffraction (GIXD) X-ray diffraction (XRD) pattern of the water electrolysis electrode 1, the intensity P of the diffraction peak of the (003) plane of LDH is... 003 The intensity P of the diffraction peak relative to the (111) plane of Ni 111 The ratio of P 003 / P 111 The value is below 0.025. This suggests that crystal growth in the direction perpendicular to the (003) plane is suppressed in the LDH contained in the LDH layer 20. With such a structure, the current density in the anode or cathode tends to increase when a specified voltage is applied between the anode and cathode in water electrolysis, and the hydrogen production rate in water electrolysis tends to increase. Therefore, the electrode 1 for water electrolysis can achieve high performance. The (111) plane of Ni is the (111) plane of Ni in the conductive substrate 10. The (003) plane of LDH is the (003) plane of the LDH contained in the LDH layer 20.

[0038] The GIXD measurement described above is performed as follows. With X-rays incident on the sample at a predetermined angle to the sample surface, the sample is rotated 360° in-plane to determine the direction in which the diffraction peak intensity of the (111) plane of Ni from the conductive substrate 10 is maximized within the sample plane. Then, in this determined in-plane direction, the detector position is adjusted to correspond to the diffraction angle 2θ to obtain the aforementioned XRD pattern.

[0039] P 003 / P 111 The lower bound is not limited to a specific value. (Compared to P) 003 / P 111 It can be greater than 0.0015, greater than 0.0016, greater than 0.0064, or greater than 0.015.

[0040] In the XRD diagram above, as long as it is greater than P 003 / P 111 If it is below 0.025, then it is more than P. 003 / P 111 Compared to P 012 / P 111 The sum S is not limited to a specific value. Compared to P 012 / P 111 The intensity P of the diffraction peak on the (012) plane of LDH 012the intensity P of the diffraction peak of the (111) plane of Ni 111 the ratio. The (012) plane of the LDH is the (012) plane of the LDH contained in the LDH layer 20. S is, for example, 0.0015 or more. It is considered that if the ratio P 003 111 P is 0.025 or less, and S is 0.0015 or more, in the LDH layer 20, there are more LDHs in which the growth of the crystal in the direction perpendicular to the (003) plane of the LDH is suppressed. The direction perpendicular to the (003) plane of the LDH corresponds to the direction perpendicular to the bulk layer of the LDH described later. It is considered that if the growth of the crystal in this direction is suppressed, the thickness of the layered structure of the LDH is difficult to increase, and the resistance of the LDH layer 20 is difficult to increase. Thus, in the water electrolysis, in the case where a prescribed voltage is applied between the anode and the cathode, the current density in the anode or the cathode is likely to increase, and the hydrogen production rate in the water electrolysis is likely to increase. Therefore, the electrode 1 for water electrolysis can exhibit high performance.

[0041] S is preferably 0.0016 or more, more preferably 0.0075 or more, further preferably 0.021 or more, and particularly preferably 0.026 or more.

[0042] The conductive substrate 10 is not limited to a particular substrate as long as it contains Ni. The conductive substrate 10 can contain a metal other than Ni, and can contain a resin. The entire conductive substrate 10 can also be composed of a metal. The conductive substrate 10 can have a configuration in which a surface layer containing a metal is formed on a member made of a resin such as polypropylene or polyethylene. In this case, the surface layer containing a metal can be a plating film or a sputtering film. The metal contained in the conductive substrate 10 can be a pure metal such as Ni and Fe, or an alloy such as stainless steel and Inconel (registered trademark). Inconel is a registered trademark.

[0043] The conductive substrate 10 has, for example, a surface composed of Ni. In this case, the conductive substrate 10 is more likely to have characteristics that are advantageous from the viewpoint of combining corrosion resistance and conductivity in the alkaline water electrolysis. In this case, the entire conductive substrate 10 can be composed of Ni, or the conductive substrate 10 can have a surface layer composed of Ni. The surface layer composed of Ni is, for example, a sputtering film or a plating film.

[0044] ​In the case where the electrically conductive substrate 10 has a surface composed of Ni, the purity of the Ni constituting the surface is not limited to a particular value. The purity is, for example, 90% by mass or more. In this case, the electrically conductive substrate 10 more easily has characteristics favorable from the viewpoint of combining corrosion resistance and electric conductivity in alkaline water electrolysis. The method of determining the purity of the Ni constituting the surface of the electrically conductive substrate 10 is not limited to a particular method. The purity of the Ni constituting the surface of the electrically conductive substrate 10 can be determined by an elemental analysis method such as fluorescent X-ray spectroscopy (XRF) and energy dispersive X-ray spectroscopy (EDX). The purity of the Ni constituting the surface of the electrically conductive substrate 10 can also be determined by analyzing an extract obtained by completely dissolving the electrically conductive substrate 10 with aqua regia using a method such as inductively coupled plasma atomic emission spectroscopy (ICP-AES). In the case where the purity of the Ni is high, the purity of the Ni constituting the surface of the electrically conductive substrate 10 can also be determined by comparing the specific gravity of the electrically conductive substrate 10 with the specific gravity of pure Ni.

[0045] The purity of the Ni constituting the surface of the electrically conductive substrate 10 is preferably 95% by mass or more, more preferably 97% by mass or more, further preferably 98% by mass or more, and particularly preferably 99% by mass or more.

[0046] The shape of the electrically conductive substrate 10 is not limited to a particular shape. The electrically conductive substrate 10 is, for example, in a sheet shape. The electrically conductive substrate 10 can have a non-porous structure such as a plate and a foil, or a porous structure such as a porous metal mesh (expanded metal), a mesh, a foam, and a non-woven fabric. The electrically conductive substrate 10 preferably has a porous structure. In this case, the surface area of the site having electric conductivity in the electrically conductive substrate 10 easily becomes large, and the gas generated in the water electrolysis reaction easily diffuses.

[0047] The thickness of the electrically conductive substrate 10 is not limited to a particular value. The thickness is, for example, 0.02 mm or more. In this case, the processing of the electrically conductive substrate 10 easily becomes easy. The thickness of the electrically conductive substrate 10 is, for example, 10 mm or less, and is preferably 1 mm or less.

[0048] The LDH layer 20 is not limited to a particular layer as long as it contains Ni. For example, the thickness of the LDH layer 20 is not limited to a particular value. The thickness is, for example, 35 nm or more. According to such a configuration, the water electrolysis electrode 1 easily has high electrode activity. The LDH layer 20 contains, for example, a site having a thickness of 35 nm or more. The thickness of the LDH layer 20 can be determined, for example, by transmission electron microscope (TEM) observation of the cross section of the water electrolysis electrode 1. The thickness of the LDH layer 20 is, for example, 5000 nm or less.

[0049] The LDH layer 20 covers the surface of the conductive substrate 10, for example. The coverage ratio of the LDH layer 20 on the surface of the conductive substrate 10 is not limited to a particular value. The coverage ratio thereof is preferably 99% or more. In this case, the water electrolysis electrode 1 more easily has high electrode activity. Also, the water electrolysis electrode 1 easily has high durability.

[0050] The LDH layer 20 is joined to the conductive substrate 10, for example. For example, no adhesive layer containing an organic material such as a polymer is disposed between the LDH layer 20 and the conductive substrate 10, and the LDH layer 20 is directly joined to the surface of the conductive substrate 10.

[0051] The LDH layer 20 further contains a chelating agent, for example. In this case, the LDH layer 20 has a desired structure, and the water electrolysis electrode 1 more easily exhibits high performance.

[0052] Figure 2 is a diagram schematically showing an example of the crystal structure of an LDH. The LDH 20a contained in the LDH layer 20 has activity for a generation reaction of a gas such as hydrogen and oxygen in the anode or the cathode of water electrolysis. For example, in alkaline water electrolysis, the LDH 20a can be changed into a hydroxide by a water electrolysis reaction.

[0053] The LDH 20a has a composition represented by the following formula (1), for example. In formula (1), M1 2+ is a divalent transition metal ion. M2 3+ is a trivalent transition metal ion. A n- is an anion between layers. x is a rational number satisfying the condition of 0 < x < 1. y is a number corresponding to the necessary amount of a balance charge. n is an integer. m is an appropriate rational number.

[0054] [M1 2+ 1-x M2 3+ x (OH)2][yA n- · mH2O] Formula (1)

[0055] The LDH layer 20 can contain two or more kinds of transition metals including Ni. The two or more kinds of transition metals in the LDH 20a are not limited to particular transition metals as long as they include Ni. In other words, M1 and M2 in the composition represented by formula (1) are not limited to particular transition metals as long as they include Ni.

[0056] The LDH layer 20 further contains at least one kind selected from V, Cr, Mn, Fe, Co, Cu, W, and Ru in addition to Ni, for example. In this case, the water electrolysis electrode 1 more easily has high electrode activity.

[0057] The LDH layer 20 preferably contains Fe in addition to Ni. In this case, the water electrolysis electrode 1 is more likely to have high electrode activity. Moreover, the manufacturing cost of the water electrolysis electrode 1 is more likely to be lower. For example, in the composition shown in formula (1), M1 can be Ni, and M2 can be Fe. In this case, the water electrolysis electrode 1 is more likely to have high electrode activity.

[0058] In LDH20a, A acts as an interlayer anion. n- These can be inorganic or organic ions. An example of an inorganic ion is CO3. 2- NO3 - Cl - SO4 2- ,Br - OH - F - I - Si2O5 2- B4O5(OH)4 2- and PO4 3- Examples of organic ions include CH3 (CH2). n SO 4- CH3 (CH2) n COO - CH3 (CH2) n PO 4- and CH3 (CH2) n NO 3- A n- It can embed itself between layers of metal hydroxide along with water molecules. A n- The charge and size of the ions are not limited to specific values. LDH20a can contain one type of A. n- It can also contain multiple A's. n- .

[0059] like Figure 2 As shown, LDH20a in M1 2+ or M2 3+ The vertices of the octahedron centered on the center have OH - Ions. Contained in LDH20a with [M1] 2+ 1-x M2 3+ x [(OH)2] x+ The metal hydroxide is represented. This metal hydroxide forms a two-dimensional, layered structure where octahedrons share edges, thus connecting the layers. Anions A exist between the layers of the metal hydroxide. n- And water molecules. The metal hydroxide layer functions as the host layer 21, containing anions A n-The guest layers 22 of water molecules are arranged between the host layers. In other words, the LDH20a as a whole has the host layers 21 of metal hydroxides and the anion A n- and the guest layers 22 of water molecules are alternately laminated. The LDH20a has a structure in which a part of M1 2+ in the layer of metal hydroxides is substituted with M2 3+ .

[0060] The crystal structure and crystallinity of the LDH20a can be qualitatively and quantitatively analyzed by XRD. In the case of a thin LDH layer 20, the signals in the XRD become less, and it becomes difficult to perform analysis. Therefore, the crystal structure and crystallinity of the LDH20a are preferably qualitatively and quantitatively analyzed by grazing incidence X-ray diffraction (GIXD) measurement. The angle formed by the incident X-rays and the surface of the sample is fixed at 3°, the water electrolysis electrode 1 is horizontally rotated by 360°, and the intensity of the diffraction peak originating from the (111) plane of Ni contained in the conductive substrate 10 appearing in the range of 2θ = 42° to 46° is measured. In the surface direction of the water electrolysis electrode 1 in which the intensity of the diffraction peak originating from the (111) plane of Ni contained in the conductive substrate 10 becomes the largest, a diffraction pattern of the LDH20a originating from the LDH layer 20 is obtained by XRD. In this diffraction pattern, for example, the diffraction peaks originating from the (003) plane, the (012) plane, the (015) plane, and the (018) plane of the LDH20a are obtained in the range of 2θ = 10° to 12°, the range of 2θ = 33° to 36°, the range of 2θ = 38° to 40°, and the range of 2θ = 46° to 48°, respectively. The intensity of each diffraction peak is determined as the height of each diffraction peak from the baseline, that is, the diffraction peak height.

[0061] According to the research by the present inventors, it is considered that the ratio P 003 / P 111 is 0.025 or less as described above suggests that the growth of the crystal in the direction perpendicular to the (003) plane is suppressed in the LDH20a contained in the LDH layer 20. It is considered that this is because the chelating agent used when synthesizing the LDH20a contributes to the suppression of the crystalline growth of the LDH20a in the direction perpendicular to the (003) plane.

[0062] The chelating agent can coordinate with the transition metal contained in the LDH 20a. Thereby, the LDH 20a can stably exist in the LDH layer 20. Also, the LDH 20a easily has a small particle diameter. Also, the LDH layer 20 as a dense layer containing the LDH 20a with few voids easily becomes in a state of being firmly fixed to the conductive substrate 10 with a desired thickness. The reason is because, in a case where the LDH layer 20 is formed on the conductive substrate 10, the nucleated LDH easily slowly crystalline grows. Thereby, the LDH layer 20 easily effectively contributes to the anode reaction or the cathode reaction of water electrolysis, and the electrode for water electrolysis 1 more easily has a high electrode activity.

[0063] The chelating agent is not limited to a particular chelating agent. The chelating agent is, for example, an organic compound capable of coordinating with the transition metal ion in the LDH 20a. The chelating agent can be at least one selected from the group consisting of a bidentate organic ligand and a tridentate organic ligand. Examples of the chelating agent are β-diketone, β-ketoester, hydroxycarboxylic acid, and hydroxycarboxylic acid salt. Examples of the β-diketone are acetylacetone (ACAC), trifluoroacetylacetone, hexafluoroacetylacetone, benzoylacetone, thienyl trifluoroacetone, di-tert-amylmethane, dibenzoylmethane, and ascorbic acid. Examples of the β-ketoester are methyl acetoacetate, ethyl acetoacetate, allyl acetoacetate, benzyl acetoacetate, n-propyl acetoacetate, isopropyl acetoacetate, n-butyl acetoacetate, isobutyl acetoacetate, t-butyl acetoacetate, 2-methoxyethyl acetoacetate, and 3-oxopentanoic acid methyl ester. Examples of the hydroxycarboxylic acid and the salt thereof are tartaric acid, citric acid, malic acid, gluconic acid, ferulic acid, lactic acid, glucuronic acid, and salts thereof.

[0064] The chelating agent preferably contains at least one selected from the group consisting of acetylacetone and citrate. In this case, the electrode for water electrolysis 1 more easily has a high electrode activity. An example of the citrate is trisodium citrate.

[0065] The method of manufacturing the electrode for water electrolysis 1 is not limited to a particular method. The electrode for water electrolysis 1 is, for example, manufactured by adjusting a solution containing a chelating agent and two or more kinds of transition metal ions to be alkaline in a state where the conductive substrate 10 is immersed in the solution. According to such a method, the LDH layer 20 containing the LDH 20a and the chelating agent can be formed on the conductive substrate 10 with a simple method.

[0066] The temperature of the solution at the time of adjusting the solution to be alkaline is not limited to a particular temperature. The temperature of the solution is, for example, normal temperature of 20°C ± 15°C. In this case, the electrode for water electrolysis 1 having a high electrode activity is easily obtained.

[0067] The solvent of the solution can be water, can be an organic solvent, or can be a mixed solvent of water and an organic solvent.

[0068] The method for producing the electrode 1 for water electrolysis preferably includes a step of increasing the pH. By this, the LDH 20a can be formed on the conductive substrate 10 in a short period of time, and the electrode 1 for water electrolysis having high electrode activity can be easily obtained. Also, the electrode 1 for water electrolysis produced can easily have high durability.

[0069] The method of adjusting the solution to be basic is not limited to a particular method. For example, the solution can be adjusted to be basic by mixing the above-described solution with a basic solution. Alternatively, a pH-raising agent can be added to the above-described solution to adjust the solution to be basic. In this case, the pH-raising agent is not limited to a particular compound. The pH-raising agent is, for example, a compound having an epoxy group. Examples of the pH-raising agent are propylene oxide, ethylene oxide, and butylene oxide. If a pH-raising agent having an epoxy group such as propylene oxide is added to the solution, the pH-raising agent can capture hydrogen ions present in the solution due to ring-opening reaction of the epoxy group in the presence of a nucleophile such as chloride ion. By this, the pH of the solution increases, and the solution can become basic. The pH of the solution containing the chelating agent and the two or more kinds 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 from 1, and finally the solution can become basic. The final pH of the solution is, for example, 8 or more and 12 or less. By adding the pH-raising agent to the solution, a reaction of capturing hydrogen ions in the solution proceeds. By this, the pH of the solution gradually increases. The time from the addition of the pH-raising agent to the solution to the time when the pH of the solution becomes stable is not limited to a particular time. The time is, for example, 24 hours or more, and can be several days.

[0070] The two or more kinds of transition metal ions contained in the solution are not limited to particular transition metal ions. The two or more kinds of transition metal ions contained in the solution are, for example, ions of at least two kinds of transition metals selected from V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. In this case, the electrode 1 for water electrolysis having high electrode activity can be more easily produced.

[0071] The two or more kinds of transition metal ions contained in the solution preferably include ions of at least one kind of transition metal selected from Ni and Fe. In this case, the electrode 1 for water electrolysis having high electrode activity can be more easily produced.

[0072] The two or more kinds 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) can occur. Thereby, the conductive substrate 10 can be etched. The manufacturing method of the water electrolysis electrode 1 preferably contains a step of promoting mixing of the solution in a state where the conductive substrate 10 is immersed, before the solution is adjusted to be alkaline. The promotion of the mixing of the solution can be performed, for example, by vibration of the conductive substrate 10, oscillation of a container in which the solution and the conductive substrate 10 are housed, stirring of the solution using a stirring member and a stirrer. According to such a method, forced convection of the solution can be generated, and the mixing of the solution is promoted. Thereby, the conductive substrate 10 is etched in a desired state, and the LDH layer 20 can be formed on the conductive substrate 10 in a desired state. As a result, the water electrolysis electrode 1 easily has high durability. Further, the promotion of the mixing of the solution can be performed in a state where a container in which the solution and the conductive substrate 10 are housed is closed, or can be performed in a non-active gas atmosphere.

[0073] 4Ni 2+ Cl - 2+2Fe 3+ Cl - 3+2Ni→5Ni 2+ Cl - 2+2Fe 2+ Cl - 2+1Ni Formula (2)

[0074] In the manufacturing of the water electrolysis electrode 1, the molar ratio of the content of the Fe ions with respect to the content of the Ni contained in the conductive substrate 10 is not limited to a particular value. The molar ratio is, for example, 0.75 or less. In this case, it is possible to prevent the Ni contained in the conductive substrate 10 from dissolving by the reaction represented by formula (2) and thereby making it difficult to manufacture the water electrolysis electrode 1.

[0075] The above-described molar ratio is preferably 0.05 to 0.25. In this case, the LDH layer 20 is easily formed uniformly on the conductive substrate 10, and the water electrolysis electrode 1 more easily has high electrode activity.

[0076] The chelating agent contained in the solution can be selected with reference to the above-described 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. Thereby, the stability of the dispersion of the complex in the solution becomes high, and the LDH layer 20 is easily formed in a desired state in the water electrolysis electrode 1. As a result, the water electrolysis electrode 1 more easily has high electrode activity.

[0077] Figure 3 is a diagram schematically representing a manufacturing mechanism of the water electrolysis electrode 1. As Figure 3As shown, a conductive substrate 10 is immersed in a solution containing transition metal ions TM1, TM2, and a chelating agent CH. For example, transition metal ion TM1 is Ni ions, and transition metal ion TM2 is Fe ions. For example, Ni is present on the surface of the conductive substrate 10. A portion of the transition metal ions TM2 etches and dissolves the Ni present on the surface of the conductive substrate 10. A portion of the chelating agent reacts with the surface of the conductive substrate 10 to form a complex C1 of transition metal ions TM1 and chelating agent CH originating from the conductive substrate 10. Furthermore, if the solution is adjusted to alkaline, complex C1 of transition metal ions TM1 and chelating agent CH originating from the solution is formed in the solution, and complex C2 of transition metal ions TM2 and chelating agent CH is formed. Subsequently, complexes C1 and C2 react on the surface of the conductive substrate 10 to synthesize LDH20a along the surface of the conductive substrate 10. Furthermore, since complexes C1 and C2 contain the chelating agent CH, the crystal growth of LDH20a is suppressed. Thus, an LDH layer 20 containing LDH20a and chelating agent CH is formed on the conductive substrate 10, resulting in an electrode 1 for water electrolysis.

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

[0079] (Second Implementation)

[0080] Figure 4 This is a cross-sectional view schematically illustrating an example of a water electrolysis unit according to the second embodiment. For example... Figure 4 As shown, the water electrolysis unit 2 includes an anode 2a, a cathode 2b, and a diaphragm 2p. At least one of the anode 2a and cathode 2b is selected, for example, the water electrolysis electrode 1 according to the first embodiment. In this case, the activity of the anodic or cathodic reaction in the water electrolysis unit is easily increased, and the anode 2a or cathode 2b is likely to exhibit high performance.

[0081] Water electrolysis unit 2 is, for example, an alkaline water electrolysis unit that uses an alkaline aqueous solution. The alkaline aqueous solution used in water electrolysis unit 2 is not limited to a specific type. Examples of alkaline aqueous solutions include potassium hydroxide aqueous solution and sodium hydroxide aqueous solution.

[0082] like Figure 4As shown, the water electrolysis unit 2 includes, for example, an electrolytic cell 2s, a first chamber 2m, and a second chamber 2n. A separator 2p is disposed inside the electrolytic cell 2s to divide the inside of the electrolytic cell 2s into the first chamber 2m and the second chamber 2n. The anode 2a is disposed in the first chamber 2m, and the cathode 2b is disposed in the second chamber 2n.

[0083] The separator 2p is, for example, a separator for alkaline water electrolysis. The separator 2p is, for example, a sheet-like porous membrane. The separator 2p has a thickness of, for example, 100 μm to 500 μm and has pores that serve as passages for ions or electrolyte. The material of the separator 2p is not limited to a particular material. Examples of the material of the separator 2p are asbestos, polymer-reinforced asbestos, potassium titanate bonded with polytetrafluoroethylene (PTFE), zirconia bonded with PTFE, and antimony acid bonded with polysulfone and antimony oxide bonded with polysulfone. Another example of the material of the separator 2p is sintered nickel, nickel coated with ceramic, and nickel coated with nickel oxide, and polysulfone. The separator 2p can also be Zirfon Perl UTP 500 manufactured by AGFA.

[0084] The anode 2a can be disposed in a state in contact with the separator 2p, that is, in a state of zero gap, or can be disposed in a state of having a gap between the anode 2a and the separator 2p. The cathode 2b can be disposed in a state in contact with the separator 2p, or can be disposed in a state of having a gap between the cathode 2b and the separator 2p.

[0085] The water electrolysis unit 2 electrolyzes an aqueous alkali solution to produce hydrogen and oxygen. An aqueous solution containing a hydroxide of an alkali metal or an alkaline earth metal is supplied to the first chamber 2m. In addition, an aqueous alkali solution can be supplied to the second chamber 2n. Electrolysis is performed while an aqueous alkali solution of a prescribed concentration is discharged from the first chamber 2m and the second chamber 2n, to produce hydrogen and oxygen.

[0086] In the case where the anode 2a includes the water electrolysis electrode 1, the cathode 2b can include, for example, an electrode material known as a cathode of an alkaline water electrolysis unit. In the case where the cathode 2b includes the water electrolysis electrode 1, the anode 2a can include an electrode material known as an anode of an alkaline water electrolysis unit. In the water electrolysis unit 2, both the anode 2a and the cathode 2b can include the water electrolysis electrode 1.

[0087] According to the above configuration, at least one selected from the anode 2a and the cathode 2b includes the water electrolysis electrode 1, and thus the water electrolysis unit 2 is able to exhibit high performance.

[0088] (3rd Embodiment)

[0089] Figure 5 is a cross-sectional view schematically showing an example of a water electrolysis device according to the 3rd embodiment. As shown, the water electrolysis device 1 includes, for example, an electrolytic cell 1s, a first chamber 1m, and a second chamber 1n. A separator 1p is disposed inside the electrolytic cell 1s to divide the inside of the electrolytic cell 1s into the first chamber 1m and the second chamber 1n. The anode 1a is disposed in the first chamber 1m, and the cathode 1b is disposed in the second chamber 1n. Figure 5As shown, the water electrolysis apparatus 3 includes the water electrolysis unit 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.

[0090] The voltage applicator 40 is electrically connected to the anode 2a and the cathode 2b. Through the voltage applicator 40, the potential of the anode 2a becomes higher than the potential of the cathode 2b. The voltage applicator 40 is not limited to a specific type, as long as it can apply a voltage between the anode 2a and the cathode 2b. The voltage applicator can also be a device for adjusting the voltage applied between the anode 2a and the cathode 2b. When the voltage applicator 40 is connected to a DC power source such as a battery, solar cell, or fuel cell, the voltage applicator 40 may include a DC / DC converter, for example. When the voltage applicator 40 is connected to an AC power source such as an industrial power source, the voltage applicator 40 may include an AC / DC converter, for example. The voltage applicator 40 may also be a power source, for example. In a power source, the voltage applied between the anode 2a and the cathode 2b, and the current flowing between the anode 2a and the cathode 2b, are adjusted so that the power supplied to the water electrolysis device 3 is a predetermined set value.

[0091] Based on the above configuration, the water electrolysis device 3 can achieve high performance.

[0092] (Fourth implementation)

[0093] Figure 6 This is a cross-sectional view schematically illustrating an example of a water electrolysis unit according to the fourth embodiment. For example... Figure 6 As shown, the water electrolysis unit 4 includes an anode 4a, a cathode 4b, and an anion exchange membrane 4p. In the water electrolysis unit 4, at least one of the anode 4a and the cathode 4b is, for example, the water electrolysis electrode 1 according to the first embodiment. In this case, the activity of the anodic reaction or the cathodic reaction in the water electrolysis unit 4 is easily increased, and the anode 4a or the cathode 4b is likely to exhibit high performance.

[0094] Water electrolysis unit 4 is, for example, an anion exchange membrane (AEM) type water electrolysis unit. Figure 6 As shown, 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.

[0095] The anion exchange membrane 4p is not limited to a specific kind of anion exchange membrane. The anion exchange membrane 4p has conductivity of anions such as hydroxide ions. The anion exchange membrane 4p can prevent oxygen generated at the anode 4a from mixing with hydrogen generated at the cathode 4b. Oxygen is guided to the outside of the anode 4a through the gas diffusion layer 4n. Hydrogen is guided to the outside of the cathode 4b through the gas diffusion layer 4k.

[0096] In the water electrolysis unit 4, in a case where the anode 4a includes the water electrolysis electrode 1, the cathode can be a publicly known cathode in an AEM-type water electrolysis unit. At this time, the LDH layer 20 of the water electrolysis electrode 1 can function as the electrode catalyst layer 4m, and the electrically conductive substrate 10 of the water electrolysis electrode 1 can function as the gas diffusion layer 4n. In the water electrolysis unit 4, in a case where the cathode 4b includes the water electrolysis electrode 1, the anode 4a can be a publicly known anode in an AEM-type water electrolysis unit. At this time, the LDH layer 20 of the water electrolysis electrode 1 can function as the electrode catalyst layer 4j, and the electrically conductive substrate 10 of the water electrolysis electrode 1 can function as the gas diffusion layer 4k. In the water electrolysis unit 4, both the anode 4a and the cathode 4b can include the water electrolysis electrode 1.

[0097] According to the above configuration, at least one selected from the anode 4a and the cathode 4b includes the water electrolysis electrode 1, and thus the water electrolysis unit 4 can exhibit high performance.

[0098] (5th Embodiment)

[0099] Figure 7 is a cross-sectional view schematically showing an example of a water electrolysis device according to the 5th embodiment. As shown in Figure 7 The water electrolysis device 5 includes the water electrolysis unit 4 and a voltage applier 40. The voltage applier 40 applies a voltage between the cathode 4b and the anode 4a. The water electrolysis device 5 is, for example, an AEM-type water electrolysis device.

[0100] The voltage applier 40 is electrically connected to the anode 4a and the cathode 4b. The potential of the anode 4a becomes higher than the potential of the cathode 4b by the voltage applier 40. The voltage applier 40 is not limited to a specific kind of voltage applier as long as it can apply a voltage between the anode 4a and the cathode 4b. The voltage applier 40 can also be a device that adjusts the voltage applied between the anode 4a and the cathode 4b. In the case where the voltage applier 40 is connected to a direct-current power source such as a battery, a solar cell, and a fuel cell, the voltage applier 40 has, for example, a DC / DC converter. In the case where the voltage applier 40 is connected to an alternating-current power source such as a commercial power source, the voltage applier 40 has, for example, an AC / DC converter. The voltage applier 40 can also be, for example, a power-type power source. In the power-type power source, the voltage applied between the anode 4a and the cathode 4b and the current flowing between the anode 4a and the cathode 4b are adjusted so that the electric power (power) supplied to the water electrolysis device 5 becomes a predetermined set value.

[0101] According to the above configuration, the water electrolysis device 5 can exhibit high performance.

[0102] (Postscript)

[0103] According to the above description, the following technology is disclosed.

[0104] (Technology 1)

[0105] An electrode for water electrolysis includes a conductive substrate including Ni, and a layered double hydroxide layer including Ni provided on a surface of the conductive substrate,

[0106] In an X-ray diffraction pattern of the electrode for water electrolysis in which a small-angle X-ray is incident, a ratio of an intensity of a diffraction peak of a (003) plane of the layered double hydroxide to an intensity of a diffraction peak of a (111) plane of the Ni is 0.025 or less.

[0107] (Technology 2)

[0108] The electrode for water electrolysis according to Technology 1,

[0109] In the X-ray diffraction pattern, a sum of a ratio of an intensity of a diffraction peak of a (003) plane of the layered double hydroxide to an intensity of a diffraction peak of a (111) plane of the Ni and a ratio of an intensity of a diffraction peak of a (012) plane of the layered double hydroxide to the intensity of the diffraction peak of the (111) plane of the Ni is 0.0015 or more.

[0110] (Technology 3)

[0111] The electrode for water electrolysis according to Technology 2,

[0112] The sum is 0.0016 or more.

[0113] (Technique 4)

[0114] The electrode for water electrolysis according to Technique 3,

[0115] The sum is 0.0075 or more.

[0116] (Technique 5)

[0117] The electrode for water electrolysis according to Technique 4,

[0118] The sum is 0.021 or more.

[0119] (Technique 6)

[0120] The electrode for water electrolysis according to Technique 5,

[0121] The sum is 0.026 or more.

[0122] (Technique 7)

[0123] The electrode for water electrolysis according to any one of Techniques 1 to 6,

[0124] The layered double hydroxide layer further contains at least one transition metal selected from V, Cr, Mn, Fe, Co, Cu, W, and Ru.

[0125] (Technique 8)

[0126] The electrode for water electrolysis according to Technique 7,

[0127] The layered double hydroxide layer further contains Fe.

[0128] (Technique 9)

[0129] The electrode for water electrolysis according to any one of Techniques 1 to 8,

[0130] The electrically conductive substrate has a surface composed of Ni.

[0131] (Technique 10)

[0132] The electrode for water electrolysis according to Technique 9,

[0133] The Ni constituting the surface of the electrically conductive substrate has a purity of 90 mass% or more.

[0134] (Technique 11)

[0135] The electrode for water electrolysis according to any one of Techniques 1 to 10,

[0136] The layered double hydroxide layer further contains a chelating agent.

[0137] (Technique 12)

[0138] The electrode for water electrolysis according to Technical 11,

[0139] The chelating agent contains at least one selected from the group consisting of acetylacetone and citrate.

[0140] (Technical 13)

[0141] An anode for water electrolysis, comprising the electrode for water electrolysis according to any one of Technical 1 to 12.

[0142] (Technical 14)

[0143] A cathode for water electrolysis, comprising the electrode for water electrolysis according to any one of Technical 1 to 12.

[0144] (Technical 15)

[0145] A water electrolysis unit, comprising an anode, a cathode, and a separator,

[0146] satisfies at least one condition selected from the group consisting of:

[0147] The anode is the anode for water electrolysis according to Technical 13;

[0148] The cathode is the cathode for water electrolysis according to Technical 14.

[0149] (Technical 16)

[0150] A water electrolysis unit, comprising an anode, a cathode, and an anion exchange membrane,

[0151] satisfies at least one condition selected from the group consisting of:

[0152] The anode is the anode for water electrolysis according to Technical 13;

[0153] The cathode is the cathode for water electrolysis according to Technical 14.

[0154] (Technical 17)

[0155] A water electrolysis device, comprising the water electrolysis unit according to Technical 15 or 16, and a voltage applier that applies a voltage between the cathode and the anode.

[0156] Embodiment

[0157] The present disclosure is further explained in detail by the following examples. Furthermore, the following examples are one example of the present disclosure, and the present disclosure is not limited to the following examples.

[0158] (Embodiment 1)

[0159] A solution was prepared by charging a perfluoroalkoxy alkane (PFA) mini-vial OD-98-5MV manufactured by Too Yoko Corporation with 2.18 milliliters (mL) of water and 3.26 mL of ethanol, and dissolving 0.185 g of nickel chloride hexahydrate and 0.105 g of ferric chloride hexahydrate. The ethanol was purchased from Fuji Photo Film Co., Ltd. and Wako Pure Chemical Industries, Ltd. The nickel chloride hexahydrate and the ferric chloride hexahydrate were purchased from Fuji Photo Film Co., Ltd. and Wako Pure Chemical Industries, Ltd. To the solution was added 0.0367 mL of acetylacetone (ACAC) as a chelating agent, to obtain a chelating agent-containing solution related to Example 1. The ACAC was purchased from Sigma-Aldrich Corporation.

[0160] For one Ni plate manufactured by Nilaco Corporation, degreasing and impurity removal of the Ni plate were performed by acetone cleaning for 10 minutes and 1M aqueous HCl cleaning for 10 minutes. The Ni plate had a thickness of 0.2 mm, and was circular in plan view with a diameter of 15 mm. The weight of the Ni plate was 0.315 g. Subsequently, water washing and drying of the Ni plate were performed, to complete the cleaning treatment of the Ni plate.

[0161] Subsequently, the Ni plate after completion of the cleaning treatment was immersed in the chelating agent-containing solution related to Example 1. In this state, the chelating agent-containing solution into which the Ni plate was put was subjected to oscillatory agitation at 25°C for 24 hours. Subsequently, 0.396 mL of propylene oxide (POX) was added to the chelating agent-containing solution as a pH raiser. The resulting mixed solution was subjected to oscillatory agitation at 25°C for 72 hours. After the oscillatory agitation for 72 hours, the Ni plate was recovered, and subjected to water washing and drying. In this way, the electrode related to Example 1 was obtained.

[0162] (Example 2)

[0163] The electrode related to Example 2 was produced in the same manner as in Example 1, except for the following points. A solution was prepared by charging a PFA mini-vial OD-98-5MV with 1.46 mL of water and 2.18 mL of ethanol, and dissolving 0.124 g of nickel chloride hexahydrate and 0.070 g of ferric chloride hexahydrate. To the solution was added 0.0123 mL of ACAC as a chelating agent, to obtain a chelating agent-containing solution related to Example 2. The chelating agent-containing solution related to Example 2 was used instead of the chelating agent-containing solution related to Example 1, and 0.265 mL of POX was used as a pH raiser, and otherwise in the same manner as in Example 1, to obtain the electrode related to Example 2.

[0164] (Example 3)

[0165] Example 3 was produced in the same manner as Example 1 except for the following. A solution was prepared by charging 1.45 mL of water and 2.18 mL of ethanol in a PFA mini-vial OD-98-5MV and dissolving 0.123 g of nickel chloride hexahydrate and 0.070 g of ferric chloride hexahydrate. To this solution, 0.020 mL of ACAC was added as a chelating agent to obtain a chelating agent-containing solution relating to Example 3. The chelating agent-containing solution relating to Example 3 was used instead of the chelating agent-containing solution relating to Example 1, and 0.260 mL of POX was used as a pH raiser, and otherwise, Example 1 was followed to obtain the electrode relating to Example 3.

[0166] (Example 4)

[0167] Example 4 was produced in the same manner as Example 1 except for the following. A solution was prepared by charging 1.44 mL of water and 2.16 mL of ethanol in a PFA mini-vial OD-98-5MV and dissolving 0.123 g of nickel chloride hexahydrate and 0.070 g of ferric chloride hexahydrate. To this solution, 0.0486 mL of ACAC was added as a chelating agent to obtain a chelating agent-containing solution relating to Example 4. The chelating agent-containing solution relating to Example 4 was used instead of the chelating agent-containing solution relating to Example 1, and 0.262 mL of POX was used as a pH raiser, and otherwise, Example 1 was followed to obtain the electrode relating to Example 4.

[0168] (Example 5)

[0169] Example 5 was produced in the same manner as Example 1 except for the following. A solution was prepared by charging 3.80 mL of water in a PFA mini-vial OD-98-5MV and dissolving 0.065 g of nickel chloride hexahydrate and 0.037 g of ferric chloride hexahydrate. No ethanol was used. To this solution, 0.0100 mL of acetylacetone (ACAC) was added as a chelating agent to obtain a chelating agent-containing solution relating to Example 5. The chelating agent-containing solution relating to Example 5 was used instead of the chelating agent-containing solution relating to Example 1, and 0.262 mL of POX was used as a pH raiser, and otherwise, Example 1 was followed to obtain the electrode relating to Example 5.

[0170] (Comparative Example)

[0171] A solution relating to Comparative Example was prepared by charging 3.65 milliliters (mL) of water into a PFA mini-vial OD-98-5MV, dissolving 0.124 g of nickel chloride hexahydrate and 0.071 g of ferric chloride hexahydrate. No chelating agent was added. The solution relating to Comparative Example was used instead of the chelating agent-containing solution relating to Example 1, and 0.265 mL of POX was used as the pH raiser, and otherwise, the same as Example 1 was performed, to obtain an electrode relating to Comparative Example.

[0172] [Crystallinity Evaluation of Electrode]

[0173] Crystallinity evaluation based on micro- angle X-ray diffraction (GIXD) measurement was performed to measure the intensity of the diffraction peak of the (012) plane and the intensity of the diffraction peak of the (003) plane of the LDH. The device used was Smartlab manufactured by Rigaku Corporation. Cu was used for the X-ray generating portion. Parallel beam method was used. As the scanning conditions, the electrode was placed on the sample stage, the angle formed by the incident X-rays and the sample surface was fixed at 3°, and the diffraction angle 2 theta was fixed at the angle range where the diffraction peak of the (111) plane of Ni appeared. The diffraction angle 2 theta where the diffraction peak of the (111) plane of Ni appeared was determined by performing XRD measurement while changing the diffraction angle 2 theta in the range of 5 to 60 degrees. In this state, the peak intensity originating from the (111) plane of Ni appearing in the range of 2 theta = 42° to 46° was measured by rotating 360° in the horizontal direction. Next, diffraction measurement was performed in the range of 2 theta = 5° to 60° in the continuous scanning mode in the direction where the intensity of the diffraction peak of the (111) plane of Ni became the largest. The step was set to 0.04°, and the scanning speed was set to 3° / minute. Figure 8 is a graph showing the X-ray diffraction pattern of GIXD of the electrode relating to Example 1. Figure 9 is a graph showing the X-ray diffraction pattern of GIXD of the electrode relating to Example 2. Figure 10 is a graph showing the X-ray diffraction pattern of GIXD of the electrode relating to Example 3. Figure 11 is a graph showing the X-ray diffraction pattern of GIXD of the electrode relating to Example 4. Figure 12 is a graph showing the X-ray diffraction pattern of GIXD of the electrode relating to Example 5. Figure 13 is a graph showing the X-ray diffraction pattern of GIXD of the electrode relating to Comparative Example. The diffraction peak originating from the (003) plane of the LDH appeared in the range of 2 theta = 10° to 12°, and the diffraction peak originating from the (012) plane of the LDH appeared in the range of 2 theta = 33° to 36°. The baseline position not overlapping with the tail of the obtained diffraction peak was specified, the baseline was supplemented with a spline function, and thus the baseline was determined. The peak intensity of each peak was calculated by finding the height from the baseline. The results are shown in Table 1.

[0174] [Current Density Evaluation of Electrode]

[0175] The current density in oxygen evolution (OER) of the electrodes involved in each embodiment and comparative example was evaluated. In the measurements, a Princeton Applied Research VersaSTAT4 potentiostat, a BAS alkali sample vial (200 mL), a BAS Teflon cap (200 mL), and an EC-Frontier AE-2 plate electrode jig were used as the working electrode. The electrodes involved in each embodiment and comparative example, serving as the working electrode, were fixed to this jig. A Metrohm double platinum wire counter electrode D.6.0305.200J was used as the counter electrode. The current originating from the anodic reaction of the water electrolysis unit was measured using a three-electrode method under the following conditions. The anodic reaction was the oxygen evolution reaction.

[0176] (Measurement conditions)

[0177] Solution: 1M KOH solution

[0178] Potential relative to the reversible hydrogen electrode (RHE): 1.0 V to 1.7 V

[0179] Number of loops: 5

[0180] Potential scan rate: 10mV / second

[0181] Temperature: 25℃

[0182] The current value corresponding to a voltage of 1.6V in the 5th cycle is divided by the area of ​​the Ni plate electrode when viewed from above, which is 1.767 cm². 2 The current density was then determined. The results are shown in Table 1.

[0183] The electrodes described in Examples 1-5, compared to the electrodes described in the Comparative Examples, have a higher ratio P of peak intensity from the (003) plane of LDH to peak intensity from the (111) plane of Ni. 003 / P 111 The current density increases when a voltage of 1.6 V is applied, which is lower than that of P. 003 / P 111 The low value suggests that crystal growth in the direction perpendicular to the (003) plane of LDH is suppressed. It is believed that by suppressing crystal growth in this way, the electrode can achieve high performance. Current density is the current value per unit electrode area; a high current density indicates a high hydrogen production rate.

[0184] When comparing between Examples 1-5, the ratio of P is... 003 / P 111 Compared to P 012 / P 111The greater the sum is, the higher the current density is, and the higher the ratio P 012 / P 111 is the ratio of the peak intensity derived from the (012) plane of the LDH to the peak intensity derived from the (111) plane of Ni. From this result, it can be understood that in the LDH in which the crystal growth of the (003) plane is inhibited, the higher the sum of the presence ratio of the LDH having crystallinity of the (003) plane and the LDH having crystallinity of the (012) plane is, the higher the performance of the electrode can be exerted.

[0185]

[0186] Many modifications and other embodiments of the present disclosure will be apparent to those of ordinary skill in the art having the benefit of this disclosure. Therefore, the foregoing description should be taken only as illustrative and not as limiting of the scope of the disclosure, which is defined by the appended claims. Changes in and / or additions to the

[0187] Industrial Applicability

[0188] The electrode for water electrolysis of the present disclosure can be utilized as an anode or a cathode for water electrolysis.

Claims

1. An electrode for water electrolysis, comprising a conductive substrate containing Ni and a layered double hydroxide layer containing Ni disposed on the surface of the conductive substrate. In the X-ray diffraction pattern of the small angle incident X-ray diffraction of the electrode for water electrolysis, the ratio of the intensity of the diffraction peak of the (003) plane of the layered double hydroxide to the intensity of the diffraction peak of the (111) plane of Ni is less than 0.

025.

2. The electrode for water electrolysis according to claim 1, In the X-ray diffraction pattern, the sum of the ratio of the intensity of the diffraction peak of the (003) plane of the layered double hydroxide to the intensity of the diffraction peak of the (111) plane of Ni and the ratio of the intensity of the diffraction peak of the (012) plane of the layered double hydroxide to the intensity of the diffraction peak of the (111) plane of Ni is 0.0015 or more.

3. The electrode for water electrolysis according to claim 2, The sum is greater than or equal to 0.0016.

4. The electrode for water electrolysis according to claim 3, The sum is greater than 0.0075.

5. The electrode for water electrolysis according to claim 4, The sum is greater than or equal to 0.

021.

6. The electrode for water electrolysis according to claim 5, The sum is greater than 0.

026.

7. The electrode for water electrolysis according to any one of claims 1 to 6, The layered double hydroxide layer further comprises at least one transition metal selected from V, Cr, Mn, Fe, Co, Cu, W, and Ru.

8. The electrode for water electrolysis according to claim 7, The layered double hydroxide layer also contains Fe.

9. The electrode for water electrolysis according to any one of claims 1 to 8, The conductive substrate has a surface made of Ni.

10. The electrode for water electrolysis according to claim 9, The Ni constituting the surface of the conductive substrate has a purity of 90% by mass or more.

11. The electrode for water electrolysis according to any one of claims 1 to 10, The layered double hydroxide layer also contains a chelating agent.

12. The electrode for water electrolysis according to claim 11, The chelating agent comprises at least one selected from acetylacetone and citrate.

13. An anode for water electrolysis, comprising the electrode for water electrolysis as described in any one of claims 1 to 12.

14. A cathode for water electrolysis, comprising the electrode for water electrolysis as described in any one of claims 1 to 12.

15. A water electrolysis unit comprising an anode, a cathode, and a diaphragm. At least one of the following conditions must be met: The anode is the anode for water electrolysis as described in claim 13; The cathode is the cathode for water electrolysis as described in claim 14.

16. A water electrolysis unit comprising an anode, a cathode, and an anion exchange membrane. At least one of the following conditions must be met: The anode is the anode for water electrolysis as described in claim 13; The cathode is the cathode for water electrolysis as described in claim 14.

17. A water electrolysis apparatus comprising a water electrolysis unit as described in claim 15 or 16, and a voltage applicator for applying a voltage between the cathode and the anode.

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