Electrode for water electrolysis, anod for water electrolysis, cartridge for water electrolysis, water electrolysis cell, and water electrolysis device

Abstract

The water electrolysis electrode 1 comprises a conductive substrate 10 and a layered double hydroxide layer 20. The layered double hydroxide layer 20 is provided on the surface of the conductive substrate 10. The layered double hydroxide layer 20 contains Ni. In a diffraction pattern of the layered double hydroxide layer 20 obtained by grazing incidence X-ray diffraction measurement, the diffraction peak height P 012 is the diffraction peak height P of the 003 plane 003 Higher than.

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 technology]

[0002] Electrodes for water electrolysis are conventionally known.

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

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

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

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

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

[0008] [Non-Patent Document 1] Seyeong Lee et al., “Operational durability of three-dimensional Ni-Fe layered double hydroxide electrocatalyst for water oxidation,” Electrochimica Acta, 2019, Vol.315, p.94-101 [Non-Patent Document 2] Jiande Chen et al., “Interfacial Interaction between FeOOH and Ni-Fe LDH to Modulate the Local Electronic Structure for Enhanced OER Electrocatalysis,” ACS Catalysis, 2018, Vol.8, p.11342-11351 Summary of the Invention [Problem to be solved by the invention]

[0009] The descriptions in the above documents need to be reconsidered from the viewpoint of improving the performance of electrodes for water electrolysis. Therefore, the present disclosure provides a novel electrode for water electrolysis that is advantageous in terms of achieving high performance. [Means for solving the problem]

[0010] The present disclosure relates to A conductive substrate; A layered double hydroxide layer containing Ni is provided on a surface of the conductive substrate, In a diffraction pattern obtained by grazing incidence X-ray diffraction measurement of the layered double hydroxide layer, the height of the diffraction peak of the 012 plane is higher than the height of the diffraction peak of the 003 plane. An electrode for water electrolysis is provided. Effect of the Invention

[0011] According to the present disclosure, it is possible to provide a novel water electrolysis electrode that is advantageous in terms of exerting high performance. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view illustrating an example of a water electrolysis electrode according to the present disclosure. [Diagram 2] FIG. 2 is a diagram that illustrates an example of the crystal structure of a layered double hydroxide (LDH). [Diagram 3] FIG. 3 is a diagram illustrating an example of a mechanism for producing an electrode for water electrolysis. [Figure 4] FIG. 4 is a cross-sectional view showing an example of a water electrolysis cell according to the present disclosure. [Diagram 5] FIG. 5 is a cross-sectional view illustrating an example of a water electrolysis apparatus according to the present disclosure. [Figure 6] FIG. 6 is a cross-sectional view showing another example of a water electrolysis cell according to the present disclosure. [Figure 7] FIG. 7 is a cross-sectional view showing another example of a water electrolysis apparatus according to the present disclosure. [Figure 8] FIG. 8 is a graph showing a diffraction pattern of the electrode according to Example 1 measured by grazing incidence X-ray diffraction (GIXD). [Figure 9] FIG. 9 is a graph showing a diffraction pattern of the electrode according to Example 2 in the GIXD measurement. [Figure 10] FIG. 10 is a graph showing a diffraction pattern of the GIXD measurement of the electrode according to Example 3. [Figure 11] FIG. 11 is a graph showing a diffraction pattern of the electrode according to Comparative Example 1 in the GIXD measurement. [Figure 12] FIG. 12 is a graph showing a diffraction pattern of the electrode according to Comparative Example 2 in the GIXD measurement. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] (Findings on which this disclosure is based) As a measure against global warming, the use of renewable energy such as solar and wind power has been attracting attention. However, power generation using renewable energy has the problem of surplus electricity being wasted. For this reason, the efficiency of renewable energy use is not necessarily sufficient. Therefore, a method of effectively utilizing surplus electricity by producing and storing hydrogen from the surplus electricity is being considered.

[0014] Electrolysis of water is considered as a method for producing hydrogen from surplus electricity. In order to produce hydrogen cheaply and stably, there is a demand for the development of a highly efficient and long-life water electrolysis device. In a water electrolysis device, oxygen is generated at the anode, and hydrogen is generated at the cathode. The reaction in which oxygen is generated at the anode is also called the anode reaction, and the reaction in which hydrogen is generated at the cathode is also called the cathode reaction. In order to provide a highly efficient water electrolysis device, it is desirable that the overvoltage is particularly low at the anode. In addition, it is also desirable that the overvoltage is low at the cathode. Therefore, there is a demand for the development of high-performance electrodes for the anode reaction or cathode reaction in water electrolysis.

[0015] For example, LDH is considered to be a promising material for electrodes for water electrolysis in terms of its large specific surface area and the variety of combinations of metal ions. For example, according to Patent Document 1, an electrode substrate containing a specific layered double hydroxide is produced by performing an electrodeposition process in an aqueous solution containing a compound containing metal M1 and a compound containing metal M2, using a conductive substrate as the anode. However, the performance of the electrode produced by the electrodeposition process is not sufficient, and there is room for improvement. As a result of extensive investigations, the present inventors have newly discovered that an LDH layer with crystallinity adjusted to a specific state enhances the performance of a water electrolysis electrode, and have completed the water electrolysis electrode of the present disclosure.

[0016] Hereinafter, the embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments. The embodiments described below are all comprehensive or specific examples. Therefore, the numerical values, shapes, materials, components, arrangement positions and connection forms of the components shown in the following embodiments are examples and are not intended to limit the present disclosure. In addition, among the components in the following embodiments, components that are not described in the independent claims showing the highest concept are described as optional components. In addition, in the drawings, the description of components with the same reference numerals may be omitted. In addition, the drawings are schematic diagrams of each component for ease of understanding, and the shapes and dimensional ratios may not be displayed accurately.

[0017] (First embodiment) Fig. 1 is a cross-sectional view showing an electrode for water electrolysis according to the first embodiment. As shown in Fig. 1, the electrode for water electrolysis 1 comprises a conductive substrate 10 and a Ni-containing layered double hydroxide (LDH) layer 20. The LDH layer 20 is provided on the surface of the conductive substrate. The LDH layer 20 can function as a catalyst for the anode reaction or cathode reaction of water electrolysis. In a diffraction pattern obtained by grazing incidence X-ray diffraction (GIXD) measurement of the LDH layer 20, the diffraction peak height P 012 is the diffraction peak height P of the 003 plane 003 This suggests that the crystallinity in the direction perpendicular to the 012 plane in the LDH layer 20 is higher than that in the direction perpendicular to the 003 plane. When the LDH layer 20 has such a structure, the overvoltage at the anode or cathode for water electrolysis tends to be low, and the water electrolysis electrode 1 can exhibit high performance.

[0018] The GIXD measurement is carried out, for example, as follows. A crystal plane in the conductive substrate 10 that has the maximum XRD diffraction peak intensity is identified, and the sample is rotated 360° in the plane while X-rays are incident on the sample so that the angle between the sample surface and the crystal plane is a predetermined angle, and the direction in the sample plane in which the diffraction peak intensity derived from the crystal plane is the largest is identified. Next, the position of the detector is adjusted to correspond to the diffraction angle 2θ in the in-plane direction of the sample thus identified, and the diffraction pattern is obtained. The diffraction peak height is the height of the diffraction peak from the baseline of the diffraction pattern.

[0019] Diffraction peak height P 012 is the diffraction peak height P 003 As long as the diffraction peak height P is higher than 003 Diffraction peak height P 012 Ratio of P 012 / P 003 is not limited to a specific value. 012 / P 003 is, for example, not less than 1.1. In this case, the overvoltage at the anode or cathode for water electrolysis is more likely to be lower, and the water electrolysis electrode 1 is more likely to exhibit high performance.

[0020] ratio P 012 / P 003 The ratio P is preferably 1.7 or more, and more preferably 2.4 or more. 012 / P 003 is, for example, 13 or less.

[0021] The conductive substrate 10 is not limited to a specific substrate as long as it has conductivity. The conductive substrate 10 may contain a metal or may contain a resin. The conductive substrate 10 may be entirely made of metal. The conductive substrate 10 may have a configuration in which a surface layer containing a metal is formed on a member made of resin such as polypropylene and polyethylene. In this case, the surface layer containing a metal may be a plating film or a sputtering 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.

[0022] The conductive base material 10 contains, for example, Ni. In this case, the conductive base material 10 tends to have advantageous properties in terms of achieving both corrosion resistance and electrical conductivity in alkaline water electrolysis.

[0023] The conductive substrate 10 has a surface made of, for example, Ni. In this case, the conductive substrate 10 is more likely to have advantageous properties in terms of achieving both corrosion resistance and conductivity in alkaline water electrolysis. 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 sputtered film or a plated film.

[0024] When the conductive substrate 10 has a surface made of Ni, the purity of the Ni constituting the surface is not limited to a specific value. The purity is, for example, 90 mass% or more. In this case, the conductive substrate 10 is more likely to have advantageous characteristics in terms of both corrosion resistance and conductivity in alkaline water electrolysis. The method for determining the purity of Ni constituting the surface of the conductive substrate 10 is not limited to a specific method. The purity of Ni constituting the surface of the conductive substrate 10 may be determined by elemental analysis such as X-ray fluorescence spectroscopy (XRF) and energy dispersive X-ray spectroscopy (EDX). The purity of Ni constituting the surface of the conductive substrate 10 may be determined by analyzing an extract obtained by completely dissolving the conductive substrate 10 in aqua regia using a method such as inductively coupled plasma atomic emission spectroscopy (ICP-AES). When the purity of Ni is high, the purity of Ni constituting the surface of the conductive substrate 10 may be determined by comparing the specific gravity of the conductive substrate 10 with the specific gravity of pure Ni.

[0025] The purity of Ni constituting the surface of the conductive base material 10 is desirably 95% by mass or more, more desirably 97% by mass or more, even more desirably 98% by mass or more, and particularly desirably 99% by mass or more.

[0026] The shape of the conductive substrate 10 is not limited to a specific shape. The conductive substrate 10 is, for example, in the form of a sheet. The conductive substrate 10 may have a non-porous structure such as a plate or foil, or may have a porous structure such as an expanded metal, a mesh, a foam, or a nonwoven fabric. The conductive substrate 10 preferably has a porous structure. In this case, the surface area of ​​the conductive portion of the conductive substrate 10 tends to be large, and gas generated in the water electrolysis reaction tends to diffuse.

[0027] The thickness of the conductive substrate 10 is not limited to a specific value. The thickness is, for example, 0.02 mm or more. In this case, the conductive substrate 10 tends to be easy to handle. The thickness of the conductive substrate 10 is, for example, 10 mm or less, and preferably 1 mm or less.

[0028] The LDH layer 20 is not limited to a specific layer as long as it contains an LDH containing Ni. For example, the thickness of the LDH layer 20 is not limited to a specific value. The thickness is, for example, 35 nm or more. With such a configuration, the water electrolysis electrode 1 is likely to have high electrode activity. The thickness of the LDH layer 20 can be determined, for example, by observation of a cross section of the water electrolysis electrode 1 with a transmission electron microscope (TEM).

[0029] The LDH layer 20 covers, for example, the surface of the conductive substrate 10. The coverage of the LDH layer 20 on the surface of the conductive substrate 10 is not limited to a specific value. The coverage is preferably 99% or more. In this case, the water electrolysis electrode 1 is more likely to have high electrode activity. In addition, the water electrolysis electrode 1 is more likely to have high durability.

[0030] The LDH layer 20 is bonded to, for example, the conductive substrate 10. For example, no adhesive layer containing an organic material such as a polymer is disposed between the LDH layer 20 and the conductive substrate 10, and the LDH layer 20 is bonded directly to the surface of the conductive substrate 10.

[0031] Figure 2 schematically shows an example of the crystal structure of LDH. LDH 20a contained in the LDH layer 20 is active for gas generation reactions such as hydrogen and oxygen at the anode or cathode of water electrolysis. For example, LDH 20a can be changed to a hydroxide in alkaline water electrolysis.

[0032] LDH 20a has, for example, a composition represented by the following formula (1). In formula (1), M1 2+ is a divalent transition metal ion. M2 3+ is a trivalent transition metal ion. A n- is an interlayer anion. x is a rational number satisfying the condition 0 < x < 1. y is a number corresponding to the required amount of charge balance. n is an integer. m is an appropriate rational number. [M1 2+ 1-x M2 3+ x (OH)2][yA n- ·mH2O] Formula (1)

[0033] The LDH layer 20a may contain two or more transition metals including Ni. The two or more transition metals in LDH 20a are not limited to specific transition metals as long as they contain Ni. In other words, M1 and M2 in the composition shown in formula (1) are not limited to specific transition metals as long as they contain Ni.

[0034] In addition to Ni, the LDH layer 20 further contains at least one selected from the group consisting of, for example, V, Cr, Mn, Fe, Co, Cu, W, and Ru. In this case, the water electrolysis electrode 1 is more likely to have high electrode activity.

[0035] The LDH layer 20 preferably further contains Fe in addition to Ni. In this case, the water electrolysis electrode 1 is more likely to have high electrode activity. In addition, the manufacturing cost of the water electrolysis electrode 1 is likely to be low. For example, in the composition shown in formula (1), M1 may be Ni and M2 may be Fe.

[0036] In LDH 20a, A which is an interlayer anionn- may be an inorganic ion or an organic ion. An example of an inorganic ion is CO3 2- , NO3 - , Cl - , SO4 2- , Br - , O.H. - , F - , I - , Si2O5 2- , B4O5(OH)4 2- , and PO4 3- An example of an organic ion is CH3(CH2) n SO 4- , CH3(CH2) n COO - , CH3(CH2) n PO 4- , and CH3(CH2) n NO 3- A n- can be inserted between the layers of the metal hydroxide along with water molecules. n- The charge and ion size of LDH20a are not limited to a specific value. n- may contain multiple types of A n- may also include

[0037] As shown in Figure 2, LDH20a is a 2+ Or M2 3+ At each vertex of the octahedron with - LDH20a has the [M1 2+ 1-x M2 3+ x (OH)2] x+ This metal hydroxide has a layered structure in which hydroxide octahedra are connected two-dimensionally by sharing edges. Between the layers of the metal hydroxide, anions A n- and water molecules are present. The metal hydroxide layer acts as a host layer 21, and the anions A n- and a guest layer 22 containing water molecules is disposed between the host layers. In other words, the LDH 20a as a whole is composed of a host layer 21 of a metal hydroxide and an anion A n-The LDH 20a has a sheet-like structure in which a guest layer 22 of water molecules and a guest layer 23 of metal hydroxide are alternately laminated. 2+ Part of M2 3+ It has a structure substituted with:

[0038] The crystal structure and crystallinity of the LDH 20a can be analyzed qualitatively and quantitatively by XRD. When the LDH layer 20 is thin, the signal in XRD is small, making analysis difficult. For this reason, the LDH layer 20 is analyzed qualitatively and quantitatively by GIXD measurement. The angle between the incident X-ray and the sample surface is fixed at 3°, the electrode 1 for water electrolysis is rotated horizontally by 360°, and the diffraction peak intensity derived from the crystal plane of the conductive substrate 10 at which the diffraction peak intensity of XRD is maximum is measured. For example, when the conductive substrate 10 contains Ni, the diffraction peak intensity derived from the 111 plane of Ni appearing in the range of 2θ=42° to 46° is measured. The diffraction pattern of the LDH layer 20 is obtained by XRD in the surface direction of the electrode 1 for water electrolysis at which the diffraction peak intensity derived from the crystal plane of the conductive substrate 10 is maximum. In this diffraction pattern, for example, diffraction peaks originating from the 003, 012, 015, and 018 planes of LDH20a are obtained in the ranges of 2θ=10° to 12°, 2θ=33° to 36°, 2θ=38° to 40°, and 2θ=46° to 48°, respectively. The intensity of each diffraction peak is determined as the diffraction peak height, which is the height of each diffraction peak from the baseline.

[0039] According to the study by the present inventors, it is considered that in the LDH layer 20, the LDH 20a having the 012 crystal plane has a higher reactivity than the LDH 20a having the 003 crystal plane. 012 is the diffraction peak height P 003 It is understood that when the capacitance is higher than 100%, the overvoltage at the anode or cathode of water electrolysis is likely to be low, and the water electrolysis electrode 1 can exhibit high performance.

[0040] The LDH layer 20 may contain a chelating agent. The chelating agent may be coordinated to a transition metal contained in the LDH 20a. This allows the LDH 20a to be present stably in the LDH layer 20. In addition, the LDH 20a is likely to have a small particle size. In addition, the LDH layer 20 is likely to be firmly fixed to the conductive substrate 10 with a desired thickness as a dense layer containing the LDH 20a and with few voids. This is because, when the LDH layer 20 is formed on the conductive substrate 10, the nucleated LDH is likely to grow slowly into crystals. This allows the LDH layer 20 to effectively contribute to the anode reaction or cathode reaction of water electrolysis, and the water electrolysis electrode 1 is likely to have high electrode activity.

[0041] The chelating agent is not limited to a specific chelating agent. The chelating agent is, for example, an organic compound capable of coordinating with a transition metal ion in LDH20a. The chelating agent may be at least one selected from the group consisting of bidentate organic ligands and tridentate organic ligands. Examples of the chelating agent are β-diketones, β-ketoesters, hydroxycarboxylic acids, and hydroxycarboxylates. Examples of β-diketones are acetylacetone (ACAC), trifluoroacetylacetone, hexafluoroacetylacetone, benzoylacetone, thenoyltrifluoroacetone, dipyrrolylmethane, dibenzoylmethane, and ascorbic acid. Examples of β-ketoesters are methyl acetoacetate, ethyl acetoacetate, allyl acetoacetate, benzyl acetoacetate, n-propyl acetoacetate, iso-propyl acetoacetate, n-butyl acetoacetate, iso-butyl acetoacetate, tert-butyl acetoacetate, 2-methoxyethyl acetoacetate, and methyl 3-oxopentanoate. Examples of hydroxycarboxylic acids and their salts are tartaric acid, citric acid, malic acid, gluconic acid, ferulic acid, lactic acid, glucuronic acid, and their salts.

[0042] The chelating agent preferably contains at least one selected from the group consisting of acetylacetone and citrates. In this case, the water electrolysis electrode 1 is more likely to have high electrode activity. An example of the citrate is trisodium citrate.

[0043] The method for producing the water electrolysis electrode 1 is not limited to a specific method. The water electrolysis electrode 1 is produced, for example, by immersing the conductive substrate 10 in a solution containing a chelating agent and two or more types of transition metal ions and adjusting the solution to an alkaline state. According to such a method, the LDH layer 20 containing the LDH 20a and the chelating agent can be formed on the surface of the conductive substrate 10 in a simple manner.

[0044] The temperature of the solution when it is adjusted to be alkaline is not limited to a specific temperature. The temperature of the solution is, for example, room temperature of 20° C.±15° C. In this case, a water electrolysis electrode 1 having high electrode activity is easily obtained.

[0045] The solvent of the solution may be water, an organic solvent, or a mixed solvent of water and an organic solvent.

[0046] The method for producing the water electrolysis electrode 1 preferably includes increasing the pH. This allows the LDH 20a 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 produced water electrolysis electrode 1 is likely to have high durability.

[0047] The method of adjusting the 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. The 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 the solution, in the presence of a nucleophile such as chloride ion, the pH-raising agent may capture hydrogen ions present in the solution along with the ring-opening reaction of the epoxy group. This increases the pH of the solution, and the solution may have an alkaline property. The pH of a solution containing a chelating agent and 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, for example, from 1, and finally, the solution may have an alkaline property. The final pH of the solution is, for example, 8 or more and 12 or less. The addition of the pH-raising agent to the solution causes a reaction in which hydrogen ions in the solution are captured. This causes the pH of the solution to gradually increase. The time from the addition of the pH-raising agent to the solution until the pH of the solution reaches a steady state is not limited to a specific time. The time may be, for example, 24 hours or more, and may be several days.

[0048] The two or more types of transition metal ions contained in the solution are not limited to specific transition metal ions. For example, the two or more types of transition metal ions contained in the solution are ions of at least two transition metals selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. In this case, a water electrolysis electrode 1 having high electrode activity is more easily produced.

[0049] The two or more types of transition metal ions contained in the solution preferably include an ion of at least one transition metal selected from the group consisting of Ni and Fe. In this case, a water electrolysis electrode 1 having high electrode activity can be more easily produced.

[0050] The two or more kinds of transition metal ions contained in the solution preferably include Fe ions. The solution preferably includes chloride ions. In this case, the reaction shown in formula (2) may occur. As a result, the conductive substrate 10 may be etched. The method for producing the electrode 1 for water electrolysis preferably includes promoting mixing of the solution before adjusting the solution to be alkaline while the conductive substrate 10 is immersed in the solution. The promotion of mixing of the solution may be achieved, for example, by vibrating the conductive substrate 10, shaking the container containing the solution and the conductive substrate 10, or stirring the solution using a stirrer piece and a stirrer. According to such a method, forced convection of the solution occurs, and mixing of the solution may be promoted. As a result, the conductive substrate 10 is etched in a desired state, and the LDH layer 20 may be formed on the conductive substrate 10 in a desired state. As a result, the electrode 1 for water electrolysis is likely to have high durability. The promotion of mixing of the solution may be achieved while the container containing the solution and the conductive substrate 10 is sealed, or may be achieved 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)

[0051] In the production of the water electrolysis electrode 1, the molar ratio of the Fe ion content to the Ni content in the conductive base material 10 is not limited to a specific value. The molar ratio is, for example, 0.75 or less. In this case, it is possible to prevent the Ni contained in the conductive base material 10 from dissolving due to the reaction shown in formula (2), which would make it difficult to produce the water electrolysis electrode 1.

[0052] The molar ratio is preferably from 0.05 to 0.25. In this case, the LDH layer 20 is more likely to be formed uniformly on the surface of the conductive substrate 10, and the water electrolysis electrode 1 is more likely to have high electrode activity.

[0053] The chelating agent contained in the solution may be selected with reference to the above examples of the chelating agent contained in the LDH layer 20. The chelating agent contained in the solution preferably contains at least one selected from the group consisting of acetylacetone and citrate. This increases the stability of the dispersion of the complex in the solution, and makes it easier for the LDH layer 20 to be formed in a desired state in the water electrolysis electrode 1. As a result, the water electrolysis electrode 1 is more likely to have high electrode activity.

[0054] FIG. 3 is a schematic diagram showing the mechanism of manufacturing the water electrolysis electrode 1. As shown in FIG. 3, the conductive substrate 10 is immersed in a solution containing transition metal ions TM1, transition metal ions TM2, and a chelating agent CH. For example, the transition metal ions TM1 are Ni ions, and the transition metal ions TM2 are Fe ions. In addition, Ni is present on the surface of the conductive substrate 10. A part of the transition metal ions TM2 etches and dissolves Ni present on the surface of the conductive substrate 10. A part of the chelating agent reacts with the surface of the conductive substrate 10 to form a complex C1 between the transition metal ions TM1 and the chelating agent CH derived from the conductive substrate 10. In addition, when the solution is adjusted to be alkaline, a complex C1 derived from the transition metal ions TM1 and the chelating agent CH derived from the solution is formed in the solution, and a complex C2 between the transition metal ions TM2 and the chelating agent CH is formed. Next, the complexes C1 and C2 react on the surface of the conductive substrate 10 to synthesize LDH 20a along the surface of the conductive substrate 10. In addition, since the complexes C1 and C2 contain the chelating agent CH, crystal growth of the LDH 20a is suppressed. As a result, an LDH layer 20 containing the LDH 20a and the chelating agent CH is formed on the surface of the conductive substrate 10, and a water electrolysis electrode 1 is obtained.

[0055] The water electrolysis electrode 1 according to this embodiment can be used, for example, as an electrode of a 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 an anode and a cathode in these water electrolysis apparatuses. In other words, at least one selected from the group consisting of a water electrolysis anode including the water electrolysis electrode 1 and a water electrolysis cathode including the water electrolysis electrode 1 can be provided. This tends to increase the activity of the anode reaction or cathode reaction in water electrolysis.

[0056] Second embodiment Fig. 4 is a cross-sectional view illustrating an example of a water electrolysis cell according to the second embodiment. As illustrated in Fig. 4, the water electrolysis cell 2 includes an anode 2a, a cathode 2b, and a diaphragm 2p. At least one selected from the group consisting of the anode 2a and the cathode 2b includes, for example, the water electrolysis electrode 1 according to the first embodiment. In this case, the activity of the anode reaction or the cathode reaction in the water electrolysis cell is likely to be high, and the anode 2a or the cathode 2b is likely to exhibit high performance.

[0057] The water electrolysis cell 2 is, for example, an alkaline water electrolysis cell that uses an alkaline aqueous solution. The alkaline aqueous solution used in the water electrolysis cell 2 is not limited to a specific alkaline aqueous solution. Examples of the alkaline aqueous solution include an aqueous potassium hydroxide solution and an aqueous sodium hydroxide solution.

[0058] 4, the water electrolysis cell 2 includes, for example, an electrolytic cell 2s, a first chamber 2m, and a second chamber 2n. The diaphragm 2p is disposed inside the electrolytic cell 2s and separates the inside of the electrolytic cell 2s into the first chamber 2m and the second chamber 2n. The anode 2a is disposed in the first chamber 2m, and the cathode 2b is disposed in the second chamber 2n.

[0059] 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 holes that serve as passages for ions or an electrolyte. The material of the diaphragm 2p is not limited to a specific material. Examples of the material of the diaphragm 2p are asbestos, polymer-reinforced asbestos, potassium titanate bound with polytetrafluoroethylene (PTFE), zirconia bound with PTFE, and antimonic acid and antimony oxide bound with polysulfone. Other examples of the material of the diaphragm 2p are sintered nickel, nickel coated with ceramics and nickel oxide, and polysulfone. The diaphragm 2p may be Zirfon Perl UTP 500 manufactured by AGFA.

[0060] The anode 2a may be disposed in a zero-gap state in which it is in contact with the diaphragm 2p, or may be disposed with a gap between it and the diaphragm 2p. The cathode 2b may be disposed in a contact state with the diaphragm 2p, or may be disposed with a gap between it and the diaphragm 2p.

[0061] The water electrolysis cell 2 electrolyzes an alkaline aqueous solution to produce hydrogen and oxygen. An aqueous solution containing a hydroxide of an alkaline metal or an alkaline earth metal is supplied to the first chamber 2m. In addition, an alkaline aqueous solution can be supplied to the second chamber 2n. Electrolysis is performed while an alkaline aqueous solution of a predetermined concentration is discharged from the first chamber 2m and the second chamber 2n, and hydrogen and oxygen are produced.

[0062] When the anode 2a includes the electrode 1 for water electrolysis, the cathode 2b may include, for example, a known electrode material for the cathode of an alkaline water electrolysis cell. When the cathode 2b includes the electrode 1 for water electrolysis, the anode 2a may include a known electrode material for the anode of an alkaline water electrolysis cell. In the water electrolysis cell 2, both the anode 2a and the cathode 2b may include the electrode 1 for water electrolysis.

[0063] According to the above configuration, at least one selected from the group consisting of the anode 2a and the cathode 2b includes the water electrolysis electrode 1, so that the water electrolysis cell 2 can exhibit high performance.

[0064] Third embodiment Fig. 5 is a cross-sectional view illustrating an example of a water electrolysis apparatus according to the third embodiment. As illustrated in Fig. 5, the water electrolysis apparatus 3 includes the water electrolysis cell 2 according to the second embodiment and a voltage applicator 40. The voltage applicator 40 applies a voltage between the cathode 2b and the anode 2a. The water electrolysis apparatus 3 is an alkaline water electrolysis apparatus that uses an alkaline aqueous solution.

[0065] The voltage applicator 40 is electrically connected to the anode 2a and the cathode 2b. The voltage applicator 40 makes the potential of the anode 2a higher than the potential of the cathode 2b. The voltage applicator 40 is not limited to a specific type of voltage applicator as long as it can apply a voltage between the anode 2a and the cathode 2b. The voltage applicator 40 may be a device that adjusts the voltage applied between the anode 2a and the cathode 2b. When the voltage applicator 40 is connected to a DC power source such as a battery, a solar cell, or a fuel cell, the voltage applicator 40 includes, for example, a DC / DC converter. When the voltage applicator 40 is connected to an AC power source such as a commercial power source, the voltage applicator 40 includes, for example, an AC / DC converter. The voltage applicator 40 may be, for example, a power-type power source. In the power-type power source, the voltage applied between the anode 2a and the cathode 2b and the current flowing between the anode 2a and the cathode 2b are adjusted so that the power supplied to the water electrolysis device 3 becomes a predetermined set value.

[0066] With the above configuration, the water electrolysis device 3 can exhibit high performance.

[0067] (Fourth embodiment) Fig. 6 is a cross-sectional view illustrating an example of a water electrolysis cell according to the fourth embodiment. As illustrated in Fig. 6, the water electrolysis cell 4 includes an anode 4a, a cathode 4b, and an anion exchange membrane 4p. In the water electrolysis cell 4, at least one selected from the group consisting of the anode 4a and the cathode 4b includes, for example, the water electrolysis electrode 1 according to the first embodiment. In this case, the activity of the anode reaction or the cathode reaction in the water electrolysis cell 4 is likely to be high, and the anode 4a or the cathode 4b is likely to exhibit high performance.

[0068] The water electrolysis cell 4 is, for example, an anion exchange membrane (AEM) type water electrolysis cell. As shown in Fig. 6, the anode 4a includes, for example, an electrode catalyst layer 4m and a gas diffusion layer 4n. The cathode 4b includes, for example, an electrode catalyst layer 4j and a gas diffusion layer 4k. The electrode catalyst layer 4m of the anode 4a is in contact with one main surface of the anion exchange membrane 4p, and the electrode catalyst layer 4j of the cathode 4b is in contact with the other main surface of the anion exchange membrane 4p.

[0069] The anion exchange membrane 4p is not limited to a specific type of anion exchange membrane. The anion exchange membrane 4p has conductivity of anions such as hydroxide ions. The anion exchange membrane 4p can prevent the oxygen gas generated at the anode 4a from mixing with the hydrogen gas generated at the cathode 4b. The oxygen gas passes through the gas diffusion layer 4n and is led to the outside of the anode 4a. The hydrogen gas passes through the gas diffusion layer 4k and is led to the outside of the cathode 4b.

[0070] In the water electrolysis cell 4, when the anode 4a includes the water electrolysis electrode 1, the cathode may be a known cathode for AEM-type water electrolysis cells. In this case, the LDH layer 20 of the water electrolysis electrode 1 can function as the electrode catalyst layer 4m, and the conductive substrate 10 of the water electrolysis electrode 1 can function as the gas diffusion layer 4n. In the water electrolysis cell 4, when the cathode 4b includes the water electrolysis electrode 1, the anode 4a may be a known anode for AEM-type water electrolysis cells. In this case, the LDH layer 20 of the water electrolysis electrode 1 can function as the electrode catalyst layer 4j, and the conductive substrate 10 of the water electrolysis electrode 1 can function as the gas diffusion layer 4k. In the water electrolysis cell 4, both the anode 4a and the cathode 4b may include the water electrolysis electrode 1.

[0071] According to the above configuration, at least one selected from the group consisting of the anode 4a and the cathode 4b includes the water electrolysis electrode 1, so that the water electrolysis cell 4 can exhibit high performance.

[0072] Fifth embodiment Fig. 7 is a cross-sectional view illustrating an example of a water electrolysis apparatus according to a fifth embodiment. As illustrated in Fig. 7, the water electrolysis apparatus 5 includes a water electrolysis cell 4 and a voltage applicator 40. The voltage applicator 40 applies a voltage between the cathode 4b and the anode 4a. The water electrolysis apparatus 5 is, for example, an AEM type water electrolysis apparatus.

[0073] The voltage applicator 40 is electrically connected to the anode 4a and the cathode 4b. The voltage applicator 40 makes the potential of the anode 4a higher than the potential of the cathode 4b. The voltage applicator 40 is not limited to a specific type of voltage applicator as long as it can apply a voltage between the anode 4a and the cathode 4b. The voltage applicator 40 may be a device that adjusts the voltage applied between the anode 4a and the cathode 4b. When the voltage applicator 40 is connected to a DC power source such as a battery, a solar cell, or a fuel cell, the voltage applicator 40 includes, for example, a DC / DC converter. When the voltage applicator 40 is connected to an AC power source such as a commercial power source, the voltage applicator 40 includes, for example, an AC / DC converter. The voltage applicator 40 may be, for example, a power-type power source. In the power-type power source, the voltage applied between the anode 4a and the cathode 4b and the current flowing between the anode 4a and the cathode 4b are adjusted so that the power supplied to the water electrolysis device 5 becomes a predetermined set value.

[0074] With the above configuration, the water electrolysis device 5 can exhibit high performance.

[0075] (Additional Note) From the above description, the following techniques are disclosed. (Technology 1) A conductive substrate; A layered double hydroxide layer containing Ni is provided on a surface of the conductive substrate, In a diffraction pattern obtained by grazing incidence X-ray diffraction measurement of the layered double hydroxide layer, the height of the diffraction peak of the 012 plane is higher than the height of the diffraction peak of the 003 plane. Electrode for water electrolysis. (Technology 2) a ratio of the height of the diffraction peak of the 012 plane to the height of the diffraction peak of the 003 plane is 1.1 or more; The electrode for water electrolysis according to claim 1. (Technology 3) The ratio is 1.7 or more. The water electrolysis electrode according to claim 2. (Technology 4) The ratio is equal to or greater than 2.4. The water electrolysis electrode according to claim 3. (Technology 5) The layered double hydroxide layer further contains at least one transition metal selected from the group consisting of V, Cr, Mn, Fe, Co, Cu, W, and Ru. 5. An electrode for water electrolysis according to any one of claims 1 to 4. (Technology 6) The layered double hydroxide layer further contains Fe. The water electrolysis electrode according to claim 5. (Technology 7) The conductive substrate contains Ni. 7. An electrode for water electrolysis according to any one of claims 1 to 6. (Technology 8) The conductive substrate has a surface made of Ni. The water electrolysis electrode according to claim 7. (Technology 9) The layered double hydroxide layer contains a chelating agent. 9. An electrode for water electrolysis according to any one of claims 1 to 8. (Technology 10) The chelating agent includes at least one selected from the group consisting of acetylacetone and citrate. The electrode for water electrolysis according to claim 9. (Technology 11) Provided with the water electrolysis electrode according to any one of techniques 1 to 10. Anode for water electrolysis. (Technology 12) Provided with the water electrolysis electrode according to any one of techniques 1 to 10. Cathode for water electrolysis. (Technology 13) An anode; A cathode; a diaphragm; At least one selected from the group consisting of the anode and the cathode comprises the water electrolysis electrode according to any one of techniques 1 to 10. water electrolysis cell. (Technology 14) A water electrolysis cell according to Technical 13; A voltage applicator that applies a voltage between the cathode and the anode. Water electrolysis equipment. (Technology 15) An anode; A cathode; an anion exchange membrane, At least one selected from the group consisting of the anode and the cathode comprises the water electrolysis electrode according to any one of techniques 1 to 10. water electrolysis cell. (Technology 16) A water electrolysis cell according to Technical 15; A voltage applicator that applies a voltage between the cathode and the anode. Water electrolysis equipment. EXAMPLES

[0076] 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 the present disclosure is not limited to the following examples.

[0077] Example 1 A solution was prepared by dissolving 0.120 g of nickel chloride hexahydrate and 0.070 g of iron chloride hexahydrate in 3.63 milliliters (mL) of water. Nickel chloride hexahydrate and iron chloride hexahydrate were purchased from Fujifilm Wako Pure Chemical Industries, Ltd. 0.020 mL of acetylacetone (ACAC) was added to this solution as a chelating agent to obtain a chelating agent-containing solution. ACAC was purchased from Sigma-Aldrich.

[0078] A Ni plate manufactured by Nilaco was washed with acetone for 10 minutes and with a 1M HCl aqueous solution for 10 minutes to degrease the Ni plate and remove impurities. The Ni plate had a thickness of 0.2 mm and was circular with a diameter of 15 mm in plan view. The Ni plate weighed 0.335 g. The Ni plate was then washed with water and dried to complete the cleaning process.

[0079] After the cleaning process, the Ni plate was immersed in the above-mentioned chelating agent-containing solution. In this state, the Ni plate and the chelating agent-containing solution were shaken and stirred at 25°C for 24 hours. At this time, the outermost surface of the Ni plate was etched according to the above formula (2).

[0080] Next, 0.260 mL of propylene oxide (POX) was added to the chelating agent-containing solution as a pH-increasing agent. The resulting mixed solution was shaken and stirred at 25° C. for 72 hours. After shaking and stirring for 72 hours, the Ni plate was collected, washed with water, and dried. In this way, the electrode according to Example 1 was obtained.

[0081] Example 2 An electrode according to Example 2 was prepared in the same manner as in Example 1, except for the following points. 0.230 g of nickel chloride hexahydrate and 0.130 g of iron chloride hexahydrate were dissolved in 3.32 mL of water to prepare a solution. 0.040 mL of acetylacetone (ACAC) was added to this solution as a chelating agent to obtain a chelating agent-containing solution. 0.480 mL of propylene oxide (POX) was added to the chelating agent-containing solution as a pH-increasing agent.

[0082] Example 3 An electrode according to Example 3 was prepared in the same manner as in Example 1, except for the following points. 0.090 g of nickel chloride hexahydrate and 0.100 g of iron chloride hexahydrate were dissolved in 3.62 mL of water to prepare a solution. 0.020 mL of acetylacetone (ACAC) was added as a chelating agent to this solution to obtain a chelating agent-containing solution. 0.280 mL of propylene oxide (POX) was added as a pH-raising agent to the chelating agent-containing solution.

[0083] Comparative Example 1 An electrode according to Comparative Example 1 was prepared in the same manner as in Example 1, except for the following points. 1.52 mL of water and 2.28 mL of isopropyl alcohol (IPA) were mixed to prepare a mixed solvent. IPA was purchased from Fujifilm Wako Pure Chemical Industries, Ltd. 0.07 g of nickel chloride hexahydrate and 0.043 g of iron chloride hexahydrate were dissolved in this mixed solvent to prepare a solution. 0.010 mL of acetylacetone (ACAC) was added to this solution as a chelating agent to obtain a chelating agent-containing solution. 0.140 mL of propylene oxide (POX) was added to the chelating agent-containing solution as a pH-raising agent.

[0084] Comparative Example 2 An electrode according to Comparative Example 1 was prepared in the same manner as in Example 1, except for the following points. 1.45 mL of water and 2.18 mL of ethanol were mixed to prepare a mixed solvent. Ethanol was purchased from Fujifilm Wako Pure Chemical Industries, Ltd. 0.15 g of nickel chloride hexahydrate and 0.043 g of iron chloride hexahydrate were dissolved in this mixed solvent to prepare a solution. 0.020 mL of acetylacetone (ACAC) was added to this solution as a chelating agent to obtain a chelating agent-containing solution. 0.25 mL of propylene oxide (POX) was added to the chelating agent-containing solution as a pH-raising agent.

[0085] [Evaluation of electrode crystallinity] For the electrodes according to each of the examples and comparative examples, a crystallinity evaluation was performed by a small angle X-ray diffraction (GIXD) measurement, and the diffraction peak intensity of the 012 plane and the diffraction peak intensity of the 003 plane were specified. For this measurement, an X-ray diffractometer Smartlab manufactured by Rigaku Corporation was used. Cu was used as the anticathode of the X-ray generating section. For this measurement, a parallel beam method was used. As the scanning conditions, the electrode was placed on the sample stage, the angle between the incident X-ray and the sample surface was fixed at 3°, and the diffraction angle 2θ was fixed at the diffraction peak of the (111) plane of Ni. In this state, the electrode was rotated 360° in the horizontal direction, and the peak intensity derived from the 111 plane of Ni that appeared in the range of 2θ = 42° to 46° was measured. Next, the diffraction angle 2θ was changed in the range of 5° to 60° in a continuous scanning mode in the direction in which the diffraction peak intensity of the 111 plane of Ni was maximized, and a GIXD measurement was performed. The step width was set to 0.04°, and the scanning speed was set to 3° / min. FIG. 8 is a graph showing a diffraction pattern of the GIXD measurement of the electrode according to Example 1. FIG. 9 is a graph showing a diffraction pattern of the GIXD measurement of the electrode according to Example 2. FIG. 10 is a graph showing a diffraction pattern of the GIXD measurement of the electrode according to Example 3. FIG. 11 is a graph showing a diffraction pattern of the GIXD measurement of the electrode according to Comparative Example 1. FIG. 12 is a graph showing a diffraction pattern of the GIXD measurement of the electrode according to Comparative Example 2. In the obtained diffraction pattern, a baseline position that does not overlap with the tail of the diffraction peak was specified, and the baseline was determined by interpolating the baseline with a spline function. The intensity of each peak was calculated by determining the height from the baseline. The results are shown in Table 1.

[0086] [Electrode overpotential evaluation] The oxygen evolution (OER) overvoltage of the electrodes according to each Example and Comparative Example was evaluated. For the measurement, a potentiostat VersaSTAT4 manufactured by Princeton Applied Research, an alkali sample vial (200 mL) manufactured by BAS, a Teflon (registered trademark) cap (for 200 mL) manufactured by BAS, and a plate electrode AE-2 manufactured by EC Frontier were used as a jig for the working electrode. The electrodes according to each Example and Comparative Example, which are the working electrodes, were fixed to this jig. A double platinum wire counter electrode D.6.0305.200J manufactured by Metrohm was used as the counter electrode. The current derived from the anode reaction of the water electrolysis cell was measured by the three-electrode method under the following measurement conditions. The anode reaction is an oxygen evolution reaction. (Measurement conditions) Solution: 1M KOH solution Potential vs. reversible hydrogen electrode (RHE): 1.0V to 1.7V Number of cycles: 5 cycles Potential sweep speed: 10mV / sec Temperature: 25℃

[0087] Current density at 5th cycle: 10mA / cm 2 The overpotential was determined by subtracting the theoretical potential of 1.229 V required to drive the oxygen evolution reaction from the voltage corresponding to the reaction. The results are shown in Table 1.

[0088] As shown in Table 1, in the electrodes according to Examples 1 to 3, the diffraction peak intensity (diffraction peak height) of the 012 plane is higher than that of the 003 plane. It is considered that the 012 plane and the 003 plane are derived from the LDH formed in the electrode. According to Examples 1 to 3, it is understood that the greater the ratio of the diffraction peak intensity of the 012 plane to that of the 003 plane, the lower the overvoltage of the electrode. It was suggested that a high-performance electrode capable of reducing the power consumption of water electrolysis can be obtained by adjusting the crystalline state of the LDH so that the diffraction peak intensity of the 012 plane is higher than that of the 003 plane. For example, according to a comparison between the Examples and the Comparative Examples, it is understood that when the chelating agent-containing solution contains water but does not contain IPA or ethanol, the crystalline state of the LDH is easily adjusted so that the diffraction peak intensity of the 012 plane is higher than that of the 003 plane.

[0089] [Table 1]

[0090] From the above description, many improvements and other embodiments of the present disclosure will be apparent to those skilled in the art. Therefore, the above description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the present disclosure. Substantial changes in its operating conditions, composition, structure and / or function can be made without departing from the spirit of the present disclosure. [Industrial Applicability]

[0091] The water electrolysis electrode of the present disclosure can be used as an anode or a cathode in water electrolysis.

Claims

1. A conductive substrate; A layered double hydroxide layer containing Ni is provided on a surface of the conductive substrate, In a diffraction pattern obtained by grazing incidence X-ray diffraction measurement of the layered double hydroxide layer, the height of the diffraction peak of the 012 plane is higher than the height of the diffraction peak of the 003 plane. Electrode for water electrolysis.

2. a ratio of the height of the diffraction peak of the 012 plane to the height of the diffraction peak of the 003 plane is 1.1 or more; The electrode for water electrolysis according to claim 1 .

3. The ratio is equal to or greater than 1.

7. The electrode for water electrolysis according to claim 2.

4. The ratio is equal to or greater than 2.

4. The electrode for water electrolysis according to claim 3.

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

6. The layered double hydroxide layer further contains Fe. The electrode for water electrolysis according to claim 5 .

7. The conductive substrate contains Ni. The electrode for water electrolysis according to claim 1 .

8. The conductive substrate has a surface made of Ni. The electrode for water electrolysis according to claim 7.

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

10. The chelating agent includes at least one selected from the group consisting of acetylacetone and citrate. The electrode for water electrolysis according to claim 9.

11. A water electrolysis device comprising the water electrolysis electrode according to any one of claims 1 to 10. Anode for water electrolysis.

12. A water electrolysis device comprising the water electrolysis electrode according to any one of claims 1 to 10. Cathode for water electrolysis.

13. An anode; A cathode; a diaphragm; At least one selected from the group consisting of the anode and the cathode comprises the water electrolysis electrode according to any one of claims 1 to 10. water electrolysis cell.

14. The water electrolysis cell according to claim 13 ; A voltage applicator that applies a voltage between the cathode and the anode. Water electrolysis equipment.

15. An anode; A cathode; an anion exchange membrane, At least one selected from the group consisting of the anode and the cathode comprises the water electrolysis electrode according to any one of claims 1 to 10. water electrolysis cell.

16. The water electrolysis cell according to claim 15 ; A voltage applicator that applies a voltage between the cathode and the anode. Water electrolysis equipment.

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