Water electrolysis electrode, water electrolysis anode, water electrolysis cathode, water electrolysis cell, water electrolysis device, and method for producing water electrolysis electrode

Abstract

A water electrolysis electrode 1 comprises a conductive substrate 10 and a layered double hydroxide layer 11. The conductive substrate 10 has a surface 10a comprising nickel with a (111) plane orientation. The layered double hydroxide layer 11 includes a layered double hydroxide containing two or more transition metals. The layered double hydroxide layer 11 is provided on the surface 10a.

Description

Water electrolysis electrode, water electrolysis anode, water electrolysis cathode, water electrolysis cell, water electrolysis device, and method for producing water electrolysis electrode

[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, a water electrolysis device, and a method for manufacturing an electrode for water electrolysis.

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

[0003] Patent Document 1 describes a cathode for electrolyzing an aqueous solution. This cathode includes a conductive substrate having a nickel surface, a mixed layer formed on the surface of the conductive substrate, and an electrode catalyst layer provided on the mixed layer. The mixed layer contains metallic nickel, nickel oxide, and carbon atoms. The electrode catalyst layer is a layer containing a platinum group metal or a platinum group metal compound. The electrode substrate is manufactured by applying a nickel compound such as nickel formate or nickel acetate to the surface of a conductive substrate having a nickel surface and thermally decomposing the nickel compound under predetermined conditions to form a mixed layer.

[0004] Patent Document 2 describes a method for producing an electrode for water electrolysis, which includes a step of immersing an electrode substrate containing a predetermined layered double hydroxide in an organic solvent. In this production method, the electrode substrate is produced by 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. For example, an electrode in which a layered double hydroxide containing nickel and iron (NiFe-LDH) is formed on the surface of foamed nickel by electrodeposition is immersed in a predetermined formamide solution to peel off the NiFe-LDH layer.

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

[0006] Non-Patent Document 2 describes that the interface interaction between FeOOH and Ni-Fe LDH adjusts the local electronic structure of Ni-Fe LDH and enhances the OER electrocatalytic activity. In alkaline water electrolysis, a problem is the effusion of the electrode catalyst or electrode substrate from the electrode due to the oxidation-reduction of the electrode substrate and electrode caused by a reverse current generated by repeated operation / shutdown cycles.

[0007] JP 2011-190534 A International Publication No. 2017 / 154134

[0008] Electrochimica Acta, (UK), 2019, Vol.315, p.94-101ACS Catalysis, (US), 2018, Vol.8, p.11342-11351

[0009] The descriptions in the above documents need to be reconsidered from the viewpoint of the durability of electrodes used in water electrolysis devices. Therefore, the present disclosure provides a novel water electrolysis electrode that is advantageous from the viewpoint of durability.

[0010] The present disclosure provides an electrode for water electrolysis comprising: a conductive substrate; and a layered double hydroxide layer containing two or more transition metals, wherein the conductive substrate has a surface made of nickel with a (111) orientation, and the layered double hydroxide layer is provided on the surface.

[0011] According to the present disclosure, it is possible to provide a novel electrode for water electrolysis that is advantageous in terms of durability.

[0012] FIG. 1 is a cross-sectional view schematically showing a water electrolysis electrode according to the first embodiment. FIG. 2 is a view schematically showing an example of the crystal structure of a layered double hydroxide (LDH). FIG. 3 is a view schematically showing a mechanism for producing a water electrolysis electrode according to the first embodiment. FIG. 4 is a cross-sectional view schematically showing an example of a water electrolysis cell according to the second embodiment. FIG. 5 is a cross-sectional view schematically showing an example of a water electrolysis apparatus according to the third embodiment. FIG. 6 is a cross-sectional view schematically showing an example of a water electrolysis cell according to the fourth embodiment. FIG. 7 is a cross-sectional view schematically showing an example of a water electrolysis apparatus according to the fifth embodiment. FIG. 8 is a graph showing the relationship between OER overpotential and the number of cycles for the electrode according to Example 1 and the electrodes according to Comparative Examples 2 and 3. FIG. 9A is a transmission electron microscope (TEM) image of the electrode according to Example 1. FIG. 9B is an electron diffraction image related to the TEM image shown in FIG. 9A. FIG. 9C is an electron diffraction image related to the TEM image shown in FIG. 9A. FIG. 9D is another TEM image of the electrode according to Example 1. Fig. 10A is a TEM image of an electrode according to Example 3. Fig. 10B is an electron beam diffraction image related to the TEM image shown in Fig. 10A. Fig. 10C is an electron beam diffraction image related to the TEM image shown in Fig. 10A. Fig. 11A is a TEM image of an electrode according to Comparative Example 3. Fig. 11B is an electron beam diffraction image related to the TEM image shown in Fig. 11A. Fig. 11C is an electron beam diffraction image related to the TEM image shown in Fig. 11A. Fig. 11D is another TEM image of the electrode according to Comparative Example 3.

[0013] (Knowledge forming the basis of the present disclosure) The use of renewable energy such as solar and wind power has been attracting attention as a measure against global warming. In power generation using renewable energy, attention has been focused on improving energy utilization efficiency by utilizing surplus electricity. Therefore, methods for producing and storing hydrogen from surplus electricity have been studied.

[0014] Electrolysis of water is one possible method for producing hydrogen from surplus electricity. To produce hydrogen cheaply and stably, there is a need to develop a highly efficient, long-life water electrolysis device.

[0015] Water electrolysis mainly includes alkaline water electrolysis, polymer water electrolysis, and high-temperature steam electrolysis, with alkaline water electrolysis being the most commonly used method at present. In water electrolysis, 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 particularly desirable that the overvoltage at the anode is low. In addition, it is also desirable that the overvoltage at the cathode is low. Therefore, there is a need to develop high-performance electrodes for the anode reaction or cathode reaction in water electrolysis.

[0016] For example, LDH is considered to be a promising material for water electrolysis electrodes in terms of its large specific surface area and diverse combinations of metal ions. In this case, it is conceivable to support LDH on a conductive substrate. As described above, in Patent Document 2, an electrode in which NiFe-LDH is formed on the surface of foamed nickel by electrodeposition is immersed in a predetermined formamide solution to peel off the NiFe-LDH layer. On the other hand, the above-mentioned documents, including Patent Document 2, do not fully consider the durability of water electrolysis electrodes during repeated operation and shutdown cycles of a water electrolysis device, and the techniques described in the above documents have room for reexamination from this perspective. As a result of extensive research, the present inventors have newly discovered that the durability of water electrolysis electrodes is enhanced by forming nickel with a predetermined orientation on the surface of a conductive substrate and providing a layer containing LDH on the surface. Based on this new finding, the water electrolysis electrode of the present disclosure has been completed.

[0017] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments. Note that the embodiments described below are all comprehensive or specific examples. Therefore, the numerical values, shapes, materials, components, component placement positions, connection configurations, etc. shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, components that are not recited in the independent claims that represent the highest concept are described as optional components. Furthermore, in the drawings, descriptions of components with the same reference numerals may be omitted. Furthermore, for ease of understanding, the drawings schematically illustrate each component, and the shapes, dimensional ratios, etc. may not be accurately depicted. Furthermore, in the manufacturing method, the order of steps may be changed or known steps may be added as necessary.

[0018] First Embodiment FIG. 1 is a cross-sectional view schematically illustrating a water electrolysis electrode according to a first embodiment. As shown in FIG. 1 , the water electrolysis electrode 1 includes a conductive substrate 10 and a layered double hydroxide (LDH) layer 11. The conductive substrate 10 has a surface 10a made of nickel with a (111) orientation. The LDH layer 11 contains a layered double hydroxide containing two or more transition metals. The LDH layer 11 can function as a catalyst for the anodic reaction or cathodic reaction of water electrolysis. The LDH layer 11 is provided on the surface 10a. Thus, even when a water electrolysis device including the water electrolysis electrode 1 is repeatedly operated and stopped, the LDH layer 11 provided on the surface 10a of the conductive substrate 10 is unlikely to separate from the conductive substrate 10. This allows the water electrolysis electrode 1 to exhibit high durability. LDH can be converted to hydroxide during the water electrolysis process.

[0019] The ratio of the area of ​​nickel having a (111) orientation on the surface 10a to the area of ​​the surface 10a is not limited to a specific value. For example, this ratio is 70% or more. This allows the water electrolysis electrode 1 to exhibit high durability. This ratio may be 80% or more, or may be 90% or more.

[0020] When the potential of the water electrolysis electrode 1 is changed to cause a reduction reaction of nickel, the integral value I of the current density corresponding to this reduction reaction is Ni is not limited to a specific value. Ni is, for example, 200 mA / cm 2 This makes it easier for the water electrolysis electrode 1 to exhibit high durability. Ni can be determined by referring to the method described in the Examples.

[0021] At the water electrolysis electrode 1, the integral value I Ni is 398mA / cm 2 The integral value I Ni is 803mA / cm 2 It may be more than that.

[0022] The purity of the nickel constituting the surface 10a is not limited to a specific value. The purity is, for example, 90% by mass or more. In this case, the water electrolysis electrode 1 is more likely to exhibit high durability. In addition, the conductive substrate 10 is more likely to have high alkali resistance. The method for determining the purity of the nickel constituting the surface 10a is not limited to a specific method. The purity of the nickel constituting the surface 10a may be determined by elemental analysis such as X-ray fluorescence spectroscopy (XRF) and energy dispersive X-ray spectroscopy (EDX). For example, the purity of nickel may be determined by completely dissolving the conductive substrate 10 in aqua regia and analyzing the resulting extract using a method such as inductively coupled plasma atomic emission spectroscopy (ICP-AES). When the purity of nickel is high, the purity of nickel may be determined by comparing the specific gravity of the conductive substrate 10 with that of pure nickel.

[0023] The purity of the nickel constituting the surface 10a is preferably 95% by mass or more, more preferably 97% by mass or more, even more preferably 98% by mass or more, and particularly preferably 99% by mass or more.

[0024] The conductive substrate 10 is not limited to a specific substrate as long as its surface 10a is made of nickel with a (111) plane orientation. The conductive substrate 10 may contain a metal other than nickel or may contain a resin. The entire conductive substrate 10 may be made of nickel. The conductive substrate 10 may have a configuration in which a nickel-containing surface layer is formed along the surface of a resin member such as polypropylene or polyethylene. In this case, the nickel-containing surface layer may be a plated film or a sputtered film. The metal contained in the conductive substrate 10 may be a pure metal such as nickel or iron, or an alloy such as stainless steel or Inconel. Inconel is a registered trademark.

[0025] The shape of the conductive substrate 10 is not limited to a specific shape. The conductive substrate 10 may be particles. The conductive substrate 10 may be in a sheet form. The sheet-like conductive substrate 10 may have a non-porous structure such as a plate or foil, or a porous structure such as an expanded metal, mesh, foam, or nonwoven fabric. The conductive substrate 10 preferably has a porous structure. In this case, the surface area of ​​the conductive portion of the conductive substrate 10 is likely to be large, and the water electrolysis electrode 1 is likely to have high electrode activity. In addition, it is easy to prevent gas generated during the water electrolysis reaction from escaping.

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

[0027] As described above, the LDH layer 11 contains LDH. Fig. 2 is a diagram schematically illustrating an example of the crystal structure of LDH. The LDH 20 is active in a reaction for producing gases such as hydrogen and oxygen at the anode or cathode of the water electrolysis cell. For example, in alkaline water electrolysis, the LDH 20 can be converted into hydroxide by the water electrolysis reaction.

[0028] The LDH20 has, for example, a composition represented by the following formula (1): 2+is a divalent transition metal ion. 3+ is a trivalent transition metal ion. n- is an anion between layers. x is a rational number satisfying the condition 0<x<1. y is a number corresponding to the amount of charge balance required. n is an integer. m is an appropriate rational number. [M1 2+ 1-x M2 3+ x (OH)2][yA n- ・mH2O] Formula (1)

[0029] The two or more transition metals in the LDH 20 are not limited to specific transition metals. In other words, M1 and M2 in the composition represented by formula (1) are not limited to specific transition metals. The two or more transition metals include, for example, at least two selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. In this case, the water electrolysis electrode 1 is likely to have high electrode activity.

[0030] The two or more transition metals in the LDH 20 may include, for example, at least one selected from the group consisting of Ni and Fe. In this case, the water electrolysis electrode 1 is more likely to have high electrode activity. For example, in the composition represented by formula (1), M1 may be Ni and M2 may be Fe.

[0031] A is an interlayer anion n- may be an inorganic ion or an organic ion. An example of an inorganic ion is CO 2- , NO3 - , Cl - , SO4 2- ,Br - , O.H. - , F - , I - , Si2O5 2- , B4O5(OH)4 2- , and PO 3- An example of an organic ion is CH3(CH2) n SO 4- , CH3 (CH2) n COO - , CH3 (CH2) n P.O. 4- , and CH3(CH2)n NO 3- It is. A n- can be intercalated between the layers of the metal hydroxide along with water molecules. n- The charge and ion size of LDH20 are not limited to a specific value. n- or a plurality of types of A n- may also include:

[0032] As shown in FIG. 2, LDH20 is a 2+ or M2 3+ OH at each vertex of the octahedron centered at - LDH20 contains [M1 2+ 1-x M2 3+ x (OH) x+ This metal hydroxide has a layered structure in which hydroxide octahedra are connected two-dimensionally, sharing edges. Between the metal hydroxide layers, anions A n- and water molecules are present. The metal hydroxide layer functions as a host layer 21, and anions A n- and a guest layer 22 containing water molecules is disposed between the host layers 21. In other words, the LDH 20 as a whole is composed of a host layer 21 of metal hydroxide and an anion A n- The LDH 20 has a sheet-like structure in which M1 contained in the metal hydroxide layer and a guest layer 22 of water molecules are alternately stacked. 2+ Part of M2 3+ It has a structure substituted with

[0033] The LDH layer 11 may contain a chelating agent. The chelating agent may be coordinated to a transition metal ion contained in the LDH 20. This allows the LDH 20 to be stably present in the LDH layer 11. In addition, the LDH 20 is easily synthesized to have a small particle size. In addition, the LDH 20 nucleated on the conductive substrate 10 is likely to undergo slow crystal growth, so that a dense LDH layer 11 with few voids containing the LDH 20 is likely to have a desired thickness relative to the conductive substrate 10. This allows the LDH layer 11 to effectively contribute to the anode reaction or the cathode reaction, and the water electrolysis electrode 1 is likely to have high electrode activity. The LDH layer 11 does not necessarily need to contain a chelating agent.

[0034] The chelating agent is not limited to a specific chelating agent. For example, the chelating agent is an organic compound capable of coordinating with a transition metal ion in LDH20. The chelating agent may be at least one selected from the group consisting of bidentate organic ligands and tridentate organic ligands. Examples of chelating agents include β-diketones, β-ketoesters, hydroxycarboxylic acids, and hydroxycarboxylic acid salts. Examples of β-diketones include acetylacetone (ACAC), trifluoroacetylacetone, hexafluoroacetylacetone, benzoylacetone, thenoyltrifluoroacetone, dipyrrolylmethane, dibenzoylmethane, and ascorbic acid. Examples of β-ketoesters include methyl acetoacetate, ethyl acetoacetate, allyl acetoacetate, benzyl acetoacetate, n-propyl acetoacetate, isopropyl acetoacetate, n-butyl acetoacetate, isobutyl acetoacetate, tert-butyl acetoacetate, 2-methoxyethyl acetoacetate, and methyl 3-oxopentanoate. Examples of hydroxycarboxylic acids and their salts are tartaric acid, citric acid, malic acid, gluconic acid, ferulic acid, lactic acid, glucuronic acid, and salts thereof.

[0035] The chelating agent preferably contains at least one selected from the group consisting of acetylacetone and citrate. In this case, the water electrolysis electrode 1 is more likely to have high electrode activity. An example of the citrate is trisodium citrate.

[0036] The thickness of the LDH layer 11 is not limited to a specific value. The LDH layer 11 has a thickness of, for example, 35 nm or more. With such a configuration, the water electrolysis electrode 1 is more likely to have high electrode activity. The LDH layer 11 includes a portion having a thickness of, for example, 35 nm or more. The thickness of the LDH layer 11 can be determined, for example, by TEM observation of a cross section of the water electrolysis electrode 1. The thickness of the LDH layer 11 is, for example, 213 nm or less.

[0037] The coverage of the LDH layer 11 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 likely to have high electrode activity. In addition, the water electrolysis electrode 1 is likely to have high durability. The coverage can be determined, for example, according to the method described in the Examples.

[0038] The LDH layer 11 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 11 and the conductive substrate 10, and the LDH layer 11 is directly bonded to the surface of the conductive substrate 10. Here, "the LDH layer 11 is bonded to the conductive substrate 10" means that the LDH layer 11 is bonded to most of the surface of the conductive substrate 10. For example, the LDH layer 11 may be bonded to 90% or more of the surface of the conductive substrate 10.

[0039] The method for producing the electrode 1 for water electrolysis is not limited to any particular method. The electrode 1 for water electrolysis can be produced, for example, by a method including the following steps (I) and (II): (I) A conductive substrate 10 having a surface 10a made of nickel is immersed in a solution S containing transition metal ions and chloride ions, and mixing of the solution S is promoted. (II) An LDH layer 11 containing LDHs containing two or more types of transition metals is formed on the surface 10a of the conductive substrate 10.

[0040] Step (I) above facilitates a reaction involving transition metal ions and chloride ions contained in the solution S and nickel on the surface 10a of the conductive substrate 10, and part of the nickel on the surface 10a may be etched and eluted into the solution S. Therefore, step (I) facilitates obtaining the surface 10a made of nickel having a (111) orientation. This allows the LDH layer 11 containing LDH formed in step (II) to be provided on the surface 10a in a desired state, and the water electrolysis electrode 1 is likely to exhibit high durability.

[0041] In step (I), the mixing of the solution S can be promoted by, for example, vibrating the conductive substrate 10, shaking the container in which the solution S and the conductive substrate 10 are sealed, or stirring the solution S using a stirrer piece or a stirrer. Such methods cause forced convection of the solution S, which can promote the mixing of the solution S. As a result, the transition metal ions and chloride ions contained in the solution S move toward the surface 10a of the conductive substrate 10, and a reaction involving the transition metal ions and chloride ions contained in the solution S and nickel on the surface 10a can occur. The mixing of the solution can be promoted in a state in which the container containing the solution and the conductive substrate 11 is sealed, or in an inert gas atmosphere.

[0042] The temperature of the solution S in step (I) is not limited to a specific temperature. The temperature of the solution S in step (I) is, for example, room temperature (20° C.±15° C.). In this case, a water electrolysis electrode 1 having high electrode activity is likely to be obtained.

[0043] The solvent of the solution S may be water, an organic solvent, or a mixed solvent of water and an organic solvent.

[0044] The solution S may further contain, for example, a chelating agent. This allows the LDH 20 to be stably present in the LDH layer 11. In addition, the LDH 20 is easily synthesized to have a small particle size. In addition, the LDH 20 nucleated on the conductive substrate 10 is likely to undergo slow crystal growth, and therefore the dense LDH layer 11 containing the LDH 20 and having few voids is likely to have a desired thickness relative to the conductive substrate 10. This allows the LDH layer 11 to effectively contribute to the anode reaction or the cathode reaction, and the water electrolysis electrode 1 is likely to have high electrode activity. The solution S does not need to contain a chelating agent.

[0045] The chelating agent contained in the solution S may be selected with reference to the above examples of the chelating agent contained in the LDH layer 11. The chelating agent contained in the solution S 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 S, and facilitates the formation of the LDH layer 11 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.

[0046] In step (II), the method for forming the LDH layer 11 containing LDH is not limited to a specific method. The LDH layer 11 containing LDH can be formed, for example, by adjusting the solution S to be alkaline. This makes it easier for the water electrolysis electrode 1 to exhibit high durability.

[0047] The method for adjusting the solution S to be alkaline is not limited to a specific method. For example, the solution S may be adjusted to be alkaline by mixing the solution S with an alkaline solution. Alternatively, a pH-raising agent may be added to the solution to adjust the solution to be alkaline. 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 the pH-raising agent are propylene oxide, ethylene oxide, and butylene oxide.

[0048] When a pH-raising agent having an epoxy group, such as propylene oxide, is added to solution S, in the presence of a nucleophile, such as chloride ions, a ring-opening reaction of the epoxy group occurs, and the pH-raising agent can capture hydrogen ions present in solution S. This increases the pH of solution S, making solution S alkaline. The pH of solution S is, for example, acidic. When a pH-raising agent is added to solution S, the pH of solution S gradually increases, and solution S can eventually become alkaline. The addition of the pH-raising agent to the solution S causes a reaction to capture hydrogen ions in solution S. This gradually increases the pH of solution S. The time from the addition of the pH-raising agent to solution S until the pH of solution S reaches a steady state is not limited to a specific time. This time can be, for example, 24 hours or more, or several days.

[0049] The temperature of the solution S when the solution S is adjusted to be alkaline is not limited to a specific temperature. The temperature of the solution S is, for example, room temperature of 20° C.±15° C. In this case, a water electrolysis electrode 1 having high electrode activity is likely to be obtained.

[0050] In the above-described production method, the two or more transition metals in the LDH are not limited to specific transition metals. One of the two or more transition metals in the LDH is the same metal species as the transition metal ion contained in the solution S. In this case, the transition metal ion contained in the solution S can serve as a transition metal supply source for synthesizing the LDH. This tends to simplify the production method of the water electrolysis electrode 1.

[0051] The two or more transition metals in the LDH include, for example, at least two selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. This facilitates the production of a water electrolysis electrode 1 that is more likely to exhibit high durability while maintaining high electrode activity.

[0052] The transition metal ions contained in the solution S are not limited to specific ions. The ions are preferably iron ions. In this case, step (I) more easily provides the surface 10a made of nickel with a (111) orientation. As a result, the water electrolysis electrode 1 is more likely to exhibit high durability.

[0053] When the transition metal ions contained in the solution S are iron ions, for example, the reaction represented by the following formula (2) may occur. As a result, the surface 10a of the conductive substrate 10 can be etched to a desired state. 2+ Cl - 2+ 2Fe 3+ Cl - 3 + 2Ni → 5Ni 2+ Cl - 2+ 2Fe 2+ Cl - 2 + 1Ni formula (2)

[0054] When the transition metal ions contained in the solution S are iron ions, the molar ratio of the Fe ion content to the nickel content in the conductive substrate 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 nickel contained in the conductive substrate 10 from dissolving due to the reaction represented by formula (2), which would make it difficult to produce the water electrolysis electrode 1.

[0055] The molar ratio is preferably 0.05 to 0.25. In this case, the LDH layer 11 is likely to be formed in a desired state on the surface 10a of the conductive substrate 10, and a water electrolysis electrode 1 having high durability is likely to be obtained. In addition, the LDH layer 11 is likely to be formed uniformly on the conductive substrate 10, and a water electrolysis electrode 1 having high electrode activity is likely to be produced.

[0056] When the transition metal ions contained in the solution S are iron ions, the value obtained by dividing the molar content of Fe ions by the surface area of ​​the conductive substrate 10 is not limited to a specific value. The value is, for example, 0.29 mmol / cm 2 In this case, it is possible to prevent the nickel contained in the conductive substrate 10 from being dissolved by the reaction shown in formula (2), which would make it difficult to manufacture the water electrolysis electrode 1.

[0057] The molar content of Fe ions divided by the surface area of ​​the conductive substrate 10 is preferably 0.01 mmol / cm 2 to 0.1 mmol / cm 2In this case, the LDH layer 11 is likely to be formed in a desired state on the surface 10a of the conductive substrate 10, and a water electrolysis electrode 1 having high durability is likely to be obtained. In addition, the LDH layer 11 is likely to be formed uniformly on the conductive substrate 10, and a water electrolysis electrode 1 having high electrode activity is likely to be produced.

[0058] 3 is a diagram schematically illustrating an example of the mechanism for producing the water electrolysis electrode according to the first embodiment. As shown in FIG. 3, the conductive substrate 10 is immersed in a solution S containing first transition metal ions TM1, second transition metal ions TM2, chloride ions (not shown), and a chelating agent 30. For example, the ions TM1 are Ni ions. 2+ and ion TM2 is Fe 3+ The surface 10a of the conductive substrate 10 is made of nickel. In step (I), ions TM1, ions TM2, and chloride ions contained in the solution S diffuse near the surface 10a of the conductive substrate 10, etching the conductive substrate 10 according to the reaction shown in formula (2), and a portion of the nickel constituting the surface 10a is eluted into the solution S. When the solution S is adjusted to an alkaline state, a portion of the chelating agent 30 reacts with the nickel eluted from the conductive substrate 10, forming a complex C1 between the ion TM1, which is a nickel ion derived from the conductive substrate 10, and the chelating agent 30. In addition, a complex C1 between the ion TM1 derived from the solution S and the chelating agent 30 is formed, and a complex C2 between the ion TM2 and the chelating agent 30 is formed. Next, the complexes C1 and C2 react on the surface 10a of the conductive substrate 10, synthesizing LDH 20 along the surface 10a of the conductive substrate 10. Because the complexes C1 and C2 contain the chelating agent 30, crystal growth of LDH 20 is suppressed. As a result, an LDH layer 11 containing the LDH 20 is formed on the conductive substrate 10, and a water electrolysis electrode 1 is obtained.

[0059] The water electrolysis electrode 1 according to this embodiment can be used to provide an anode or cathode for water electrolysis. The water electrolysis electrode 1 can be used, for example, as an electrode for a water electrolysis cell in an alkaline water electrolysis apparatus or an anion exchange membrane water electrolysis apparatus. The water electrolysis electrode 1 is used, for example, in at least one selected from the group consisting of an anode and a cathode in these water electrolysis apparatuses. This tends to increase the activity of the anode reaction or the cathode reaction in water electrolysis. In addition, the durability of the anode or cathode in the water electrolysis apparatus tends to be increased.

[0060] Second Embodiment Figure 4 is a cross-sectional view schematically illustrating an example of a water electrolysis cell according to a second embodiment. As shown in Figure 4, the water electrolysis cell 2 includes an anode 2a, a cathode 2b, and a diaphragm 2p. At least one selected from the group consisting of the anode 2a and the cathode 2b includes, for example, the water electrolysis electrode 1 according to the first embodiment. In this case, the activity of the anode reaction or the cathode reaction in the water electrolysis cell 2 is likely to be high, and the anode 2a or the cathode 2b is likely to exhibit high durability.

[0061] 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 a potassium hydroxide aqueous solution and a sodium hydroxide aqueous solution.

[0062] 4 , the water electrolysis cell 2 includes, for example, an electrolytic cell 2s, a first chamber 2m, and a second chamber 2n. A diaphragm 2p is disposed inside the electrolytic cell 2s, separating the interior of the electrolytic cell 2s into the first chamber 2m and the second chamber 2n. An anode 2a is disposed in the first chamber 2m, and a cathode 2b is disposed in the second chamber 2n.

[0063] The diaphragm 2p is, for example, a diaphragm for alkaline water electrolysis. The diaphragm 2p is, for example, a sheet-like porous membrane. The diaphragm 2p has a thickness of, for example, 100 μm to 500 μm and has pores that serve as passages for ions or the electrolyte. The material of the diaphragm 2p is not limited to a specific material. Examples of materials for the diaphragm 2p include asbestos, polymer-reinforced asbestos, potassium titanate bound with polytetrafluoroethylene (PTFE), zirconia bound with PTFE, and antimonic acid and antimony oxide bound with polysulfone. Other examples of materials for the diaphragm 2p include sintered nickel, nickel coated with ceramics and nickel oxide, and polysulfone. The diaphragm 2p may be Zirfon Perl UTP 500 manufactured by AGFA.

[0064] The anode 2a may be disposed in a zero-gap state, i.e., 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.

[0065] The water electrolysis cell 2 electrolyzes an alkaline aqueous solution to produce hydrogen and oxygen. An aqueous solution containing a hydroxide of an alkali metal or alkaline earth metal is supplied to the first chamber 2m. In addition, an alkaline aqueous solution can be supplied to the second chamber 2n. Electrolysis is performed while an alkaline aqueous solution of a predetermined concentration is discharged from the first chamber 2m and the second chamber 2n, and hydrogen and oxygen are produced.

[0066] When the anode 2a includes the water electrolysis electrode 1, the cathode 2b may include, for example, an electrode material known as a cathode material for alkaline water electrolysis cells.

[0067] In the water electrolysis cell 2, when the cathode 2b includes the water electrolysis electrode 1, the anode 2a may include an electrode material known as an anode material for alkaline water electrolysis cells. In the water electrolysis cell 2, both the anode 2a and the cathode 2b may include the water electrolysis electrode 1.

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

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

[0070] The voltage applicator 40 is electrically connected to the anode 2a and the cathode 2b. The voltage applicator 40 makes the potential of the anode 2a higher than the potential of the cathode 2b. The voltage applicator 40 is not limited to a specific type of voltage applicator as long as it can apply a voltage between the anode 2a and the cathode 2b. The voltage applicator 40 may be a device that adjusts the voltage applied between the anode 2a and the cathode 2b. When the voltage applicator 40 is connected to a DC power 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 supply. The power-type power supply adjusts the voltage applied between the anode 2a and the cathode 2b and the current flowing between the anode 2a and the cathode 2b so that the power supplied to the water electrolysis device 3 becomes a predetermined set value.

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

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

[0073] The water electrolysis cell is, for example, an anion exchange membrane (AEM)-type water electrolysis cell. As shown in Fig. 6 , the anode 4a includes, for example, a catalyst layer 4m and a gas diffusion layer 4n. The cathode 3b includes, for example, a catalyst layer 4j and a gas diffusion layer 4k. The catalyst layer 4m of the anode 4a is in contact with one main surface of the anion exchange membrane 4p, and the catalyst layer 4j of the cathode 4b is in contact with the other main surface of the anion exchange membrane 4p.

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

[0075] In the water electrolysis cell 4, when the anode 4a includes the water electrolysis electrode 1, the cathode 4b may be a known cathode for AEM-type water electrolysis cells. The LDH layer 11 of the water electrolysis electrode 1 can function as the catalyst layer 4m, and the conductive substrate 10 of the water electrolysis electrode 1 can function as the gas diffusion layer 4n.

[0076] 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. The LDH layer 11 of the water electrolysis electrode 1 may function as the catalyst layer 4j, and the conductive substrate 10 of the water electrolysis electrode 1 may function as the gas diffusion layer k. In the water electrolysis cell 4, both the anode 4a and the cathode 4b may include the water electrolysis electrode 1.

[0077] According to the above configuration, at least one selected from the group consisting of the anode 4a and the cathode 4b includes the water electrolysis electrode 1, and therefore the water electrolysis cell 4 can exhibit high durability.

[0078] Fifth Embodiment Fig. 7 is a cross-sectional view schematically illustrating an example of a water electrolysis apparatus according to a fifth embodiment. As shown in Fig. 7, the water electrolysis apparatus 5 includes a water electrolysis cell 4 and a voltage applicator 40. The voltage applicator 40 applies a voltage between the cathode 4b and the anode 4a. The water electrolysis apparatus 5 is, for example, an AEM-type water electrolysis apparatus.

[0079] 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 supply. In the power-type power supply, the voltage applied between the anode 4a and the cathode 4b and the current flowing between the anode 4a and the cathode 4b are adjusted so that the power supplied to the water electrolysis device 5 reaches a predetermined set value.

[0080] With the above configuration, the water electrolysis device 5 can exhibit high durability.

[0081] (Additional Notes) The above disclosure discloses the following technologies. (Technology 1) A water electrolysis electrode comprising a conductive substrate and a layered double hydroxide layer containing two or more transition metals, wherein the conductive substrate has a surface made of nickel with a (111) orientation, and the layered double hydroxide layer is provided on the surface. Here, "the layered double hydroxide layer is provided on the surface" means that the layered double hydroxide layer is provided over most of the surface. For example, the layered double hydroxide layer may be provided over 90% or more of the surface of the conductive substrate. (Technology 2) When the potential of the water electrolysis electrode is changed to cause a reduction reaction of nickel, the integrated value of the current density corresponding to the reduction reaction is 200 mA / cm 2The water electrolysis electrode according to Technology 1, wherein the nickel forming the surface has a purity of 90 mass% or more. (Technology 3) The water electrolysis electrode according to Technology 1 or 2, wherein the nickel forming the surface has a purity of 90 mass% or more. (Technology 4) The water electrolysis electrode according to any one of Technology 1 to 3, wherein the layered double hydroxide layer contains a chelating agent. (Technology 5) The water electrolysis electrode according to Technology 4, wherein the chelating agent contains at least one selected from the group consisting of acetylacetone and citrate. (Technology 6) The water electrolysis electrode according to any one of Technology 1 to 5, wherein the layered double hydroxide layer has a thickness of 35 nm or more. (Technology 7) The water electrolysis electrode according to any one of Technology 1 to 6, wherein the two or more transition metals include at least two selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. (Technology 8) The water electrolysis electrode according to Technology 7, wherein the two or more transition metals include at least one selected from the group consisting of Ni and Fe. (Technology 9) An anode for water electrolysis, comprising the electrode for water electrolysis according to any one of Technologies 1 to 8. (Technology 10) A cathode for water electrolysis, comprising the electrode for water electrolysis according to any one of Technologies 1 to 8. (Technology 11) A water electrolysis cell, comprising an anode, a cathode, and a diaphragm, wherein at least one selected from the group consisting of the anode being the anode for water electrolysis according to Technology 9 and the cathode being the cathode for water electrolysis according to Technology 10 is satisfied. (Technology 12) A water electrolysis cell, comprising an anode, a cathode, and an anion exchange membrane, wherein at least one selected from the group consisting of the anode being the anode for water electrolysis according to Technology 9 and the cathode being the cathode for water electrolysis according to Technology 10 is satisfied. (Technology 13) A water electrolysis device, comprising the water electrolysis cell according to Technology 11 or 12, and a voltage applicator for applying a voltage between the cathode and the anode. (Technology 14) A method for producing an electrode for water electrolysis, comprising: promoting mixing of a solution containing transition metal ions and chloride ions while immersing a conductive substrate having a surface made of nickel in the solution; and forming a layered double hydroxide layer containing two or more types of transition metals on the surface of the conductive substrate.(Technology 15) The method for producing an electrode for water electrolysis according to Technology 14, wherein one of the two or more transition metals in the layered double hydroxide is the same metal species as the transition metal ion contained in the solution. (Technology 16) The method for producing an electrode for water electrolysis according to Technology 14 or 15, wherein the layered double hydroxide layer is formed by adjusting the solution to be alkaline. (Technology 17) The method for producing an electrode for water electrolysis according to any one of Technology 14 to 16, wherein the two or more transition metals include at least two selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. (Technology 18) The method for producing an electrode for water electrolysis according to any one of Technology 14 to 17, wherein the transition metal ion contained in the solution is an iron ion. (Technology 19) The method for producing an electrode for water electrolysis according to Technology 18, wherein the molar ratio of the iron ion content to the nickel content in the conductive base material is 0.75 or less. (Technology 20) The method for producing an electrode for water electrolysis according to Technology 19, wherein the molar ratio is 0.05 to 0.25. (Technology 21) A value obtained by dividing the molar content of Fe ions by the surface area of ​​the conductive substrate is 0.29 mmol / cm. 2 The method for producing an electrode for water electrolysis according to Technology 18, wherein the value is 0.01 mmol / cm or less. 2 to 0.1 mmol / cm 2 The method for producing an electrode for water electrolysis according to Technology 21, wherein the solution further contains a chelating agent. (Technology 23) The method for producing an electrode for water electrolysis according to any one of Technology 14 to 22, wherein the solution further contains a chelating agent. (Technology 24) The method for producing an electrode for water electrolysis according to Technology 23, wherein the chelating agent contains at least one selected from the group consisting of acetylacetone and citrate.

[0082] The present disclosure will be described in more detail below with reference to examples. Note that the following examples are examples of the present disclosure, and the present disclosure is not limited to the following examples.

[0083] Example 1: A mixed solvent was prepared by mixing 6.688 milliliters (mL) of water and 10.032 mL of ethanol. Ethanol was purchased from Fujifilm Wako Pure Chemical Industries, Ltd. The volume ratio of water to ethanol in the mixed solvent was 2:3. A solution was prepared by dissolving 0.5685 g of nickel chloride hexahydrate and 0.3233 g of iron chloride hexahydrate in the mixed solvent. Nickel chloride hexahydrate and iron chloride hexahydrate were purchased from Fujifilm Wako Pure Chemical Industries, Ltd. To this solution, 0.113 mL of acetylacetone (ACAC) was added as a chelating agent to obtain a chelating agent-containing solution. ACAC was purchased from Sigma-Aldrich. The amount of ACAC in the chelating agent-containing solution was 1 / 3.25 of the total amount of Ni ions and Fe ions. The chelating agent-containing solution was acidic.

[0084] Five Ni meshes manufactured by Nilaco Corporation were washed with acetone for 10 minutes and then with a 1M HCl aqueous solution for 10 minutes to degrease the Ni meshes and remove impurities. The Ni meshes had a wire diameter of 0.1 mm, a mesh count of 60, and each Ni mesh was circular with a diameter of 15 mm in plan view. The total weight of the five Ni meshes was 0.281 g. The Ni meshes were then washed with water and dried to complete the cleaning process. The purity of the Ni meshes was 99% by mass.

[0085] Next, the Ni mesh after the cleaning treatment was immersed in the chelating agent-containing solution. In this state, the chelating agent-containing solution containing the Ni mesh was shaken and stirred at 25°C for 24 hours. At this time, the outermost surface of the Ni mesh was etched according to the reaction of the above formula (2). In this case, the molar ratio of the Fe ion content to the Ni content contained in the Ni mesh was 0.25. In addition, the value obtained by dividing the molar content of Fe ions by the surface area of ​​the Ni mesh was 0.0942 millimoles (mmol) / cm. 2 The surface area of ​​the Ni mesh was determined by taking into consideration the wire diameter, the number of meshes, and the geometric shape of the Ni mesh based on the diameter.

[0086] Next, 1.216 mL of propylene oxide (POX) was added to the chelating agent-containing solution as a pH-raising agent. The amount of POX added was adjusted so that the ratio of the amount of POX to the amount of chloride ions in the mixed solution was 2. The resulting mixed solution was shaken and stirred at 25°C for 72 hours. During the shaking and stirring of the mixed solution, it was understood that the POX gradually captured hydrogen ions in the mixed solution, and the pH of the mixed solution gradually increased and became alkaline. After 72 hours of shaking and stirring, the Ni mesh was recovered, washed with water, and dried. In this way, the electrode according to Example 1 was obtained.

[0087] Example 2 An electrode according to Example 2 was fabricated in the same manner as Example 1, except for the following points. 0.535 mL of water and 0.803 mL of ethanol were mixed to prepare a mixed solvent. The ratio of the volume of water to the volume of ethanol in the mixed solvent was 2:3. The amount of nickel chloride hexahydrate dissolved in the mixed solvent was 0.0455 g, and the amount of iron chloride hexahydrate dissolved in the mixed solvent was 0.0259 g. The amount of ACAC added to prepare the chelating agent-containing solution was 0.009 mL, and the amount of ACAC in the chelating agent-containing solution was 1 / 3.25 of the total amount of Ni ions and Fe ions. Two Ni meshes were used, and the total mass of the two Ni meshes was 0.112 g. When the chelating agent-containing solution containing the Ni meshes was shaken and stirred, the molar ratio of the Fe ion content to the Ni contained in the Ni meshes was 0.05. In addition, the molar content of Fe ions divided by the surface area of ​​the Ni mesh was 0.0188 mmol / cm 2 It was.

[0088] Example 3 An electrode according to Example 3 was fabricated in the same manner as Example 1, except for the following points. In preparing the mixed solvent, 6.900 mL of water and 10.351 mL of ethanol were mixed. In the mixed solvent, the volume of water:volume of ethanol was 2:3. The amount of nickel chloride hexahydrate dissolved in the mixed solvent was 5.8654 g, and the amount of iron chloride hexahydrate dissolved in the mixed solvent was 3.3351 g. In preparing the chelating agent-containing solution, the amount of ACAC added was 1.164 mL, and the amount of ACAC in the chelating agent-containing solution was 1 / 3.25 of the total amount of Ni ions and Fe ions. Four Ni meshes were used, and the total mass of the four Ni meshes was 0.96 g. Each Ni mesh had a square shape with a side length of 20 mm in plan view. The amount of POX added to the chelating agent-containing solution was 12.545 mL. The molar ratio of the Fe ion content to the Ni ion content in the Ni mesh when the chelating agent-containing solution containing the Ni mesh was shaken and stirred was 0.75. In addition, the molar content of Fe ions divided by the surface area of ​​the Ni mesh was 0.2844 mmol / cm. 2 The amount of POX added was adjusted so that the ratio of the amount of POX to the amount of chloride ions in the mixed solution of the chelating agent-containing solution and POX would be 2.

[0089] Comparative Example 1: A mixed solvent was prepared by mixing 6.900 mL of water and 10.351 mL of ethanol. Ethanol was purchased from Fujifilm Wako Pure Chemical Industries, Ltd. The volume ratio of water to ethanol in the mixed solvent was 2:3. 5.8654 g of nickel chloride hexahydrate and 3.3351 g of iron chloride hexahydrate were dissolved in the mixed solvent to prepare a solution. Nickel chloride hexahydrate and iron chloride hexahydrate were purchased from Fujifilm Wako Pure Chemical Industries, Ltd. 1.164 mL of acetylacetone (ACAC) was added to the solution as a chelating agent to obtain a chelating agent-containing solution. ACAC was purchased from Sigma-Aldrich. The amount of ACAC in the chelating agent-containing solution was 1 / 3.25 of the total amount of Ni ions and Fe ions. The pH of the chelating agent-containing solution was 1.

[0090] A Ni mesh manufactured by Nilaco Corporation was washed with acetone for 10 minutes and then with a 1M HCl aqueous solution for 10 minutes to degrease the Ni mesh and remove impurities. The Ni mesh had a wire diameter of 0.1 mm, 60 meshes, and a square shape with a side length of 20 mm in plan view. The Ni mesh weighed 0.25 g. The Ni mesh was then washed with water and dried to complete the cleaning process.

[0091] Next, the Ni mesh after the cleaning treatment was immersed in the chelating agent-containing solution. In this state, the chelating agent-containing solution containing the Ni mesh was shaken and stirred at 25°C for 24 hours. During this time, the entire Ni mesh was etched and dissolved according to the reaction of the above formula (2). Therefore, in Comparative Example 1, an evaluable electrode was not obtained. The molar ratio of the Fe ion content to the Ni content contained in the Ni mesh was 2.9. In addition, the value obtained by dividing the molar content of Fe ions by the surface area of ​​the Ni mesh was 1.0919 mmol / cm 2 It was.

[0092] Comparative Example 2 Five Ni meshes that had been subjected to the cleaning treatment in the same manner as in Example 1 were used as electrodes in Comparative Example 2.

[0093] (Comparative Example 3) An electrode according to Comparative Example 3 was produced in the same manner as in Example 1, except for the following points: The chelating agent-containing solution containing the Ni mesh was not shaken or stirred before the pH-increasing agent was added, and the pH-increasing agent was added to the chelating agent-containing solution immediately after the Ni mesh was immersed in the chelating agent-containing solution.

[0094] [Electrode Evaluation] The oxygen evolution (OER) overpotential of the electrodes according to each Example and Comparative Examples 2 and 3 was evaluated. For the measurements, a potentiostat VersaSTAT4 manufactured by Princeton Applied Research, an alkali sample vial (200 mL) manufactured by BAS, a Teflon® cap (for 200 mL) manufactured by BAS, and an EC Frontier plate electrode AE-2 were used as the working electrode fixture. The working electrodes of each Example and Comparative Examples 2 and 3 were fixed to this fixture. A Metrohm double platinum wire counter electrode D.6.0305.200J was used as the counter electrode. The current derived from the anode reaction of the water electrolysis cell was measured using a three-electrode method under the following measurement conditions. The anode reaction was the oxygen evolution reaction. (Measurement conditions) Solution: 1 M KOH solution Potential to reversible hydrogen electrode (RHE): 1.0 V to 1.7 V Number of cycles: 5 cycles Potential sweep rate: 10 mV / sec Temperature: 25°C

[0095] Current density at the fifth cycle: 10 mA / cm 2 The OER overpotential was determined by subtracting the theoretical potential of 1.229 V required to cause the oxygen evolution reaction to proceed from the voltage corresponding to the electrode. The results are shown in Table 1. Table 1 also shows the molar ratio of the Fe ion content to the Ni content contained in the Ni mesh in the electrode preparation, and the value obtained by dividing the molar content of Fe ions by the surface area of ​​the Ni mesh. Table 1 also shows whether the electrode could be prepared.

[0096] From the measurement results for evaluating the OER overpotential, the coverage of the LDH-containing layer on the surface of the Ni mesh was determined based on the following formula (3). The results are shown in Table 1. In addition, from the measurement results for evaluating the OER overpotential, the coverage of the Ni 3+ →Ni 2+ The integral value I of the current density at a potential of 1.45 V to 1.2 V corresponds to the reduction reaction of Ni The current density was calculated by dividing the current value by the apparent electrode area of ​​the Ni mesh. NiOx is the integral of the current density at a potential of 1.38 V to 1.48 V, and S Niis the integral value of the current density at a potential between 1.35 V and 1.38 V. The peak of the current density at a potential between 1.38 V and 1.48 V is due to Ni hydroxides derived from nickel and iron. 2+ →Ni 3+ The current density peak at 1.35 V to 1.38 V is due to the oxidation reaction of Ni derived from pure nickel. 2+ →Ni 3+ This is a peak associated with the oxidation reaction of the coating ratio S NiOx / (S Ni +S NiOx )×100 Formula (3)

[0097] As shown in Table 1, the OER overvoltages of the electrodes according to Examples 1 to 3 are lower than the OER overvoltage of the electrode according to Comparative Example 2, and it is understood that the electrodes according to Examples 1 to 3 have high electrode activity. On the other hand, a comparison between each Example and Comparative Example 1 shows that if the molar ratio of the Fe ion content to the Ni content contained in the Ni mesh is large, the chemical reaction that dissolves the Ni becomes intense, causing the entire Ni mesh to dissolve, making it impossible to fabricate an electrode. For this reason, it is understood that the molar ratio of the Fe ion content to the Ni content contained in the Ni mesh is preferably 0.75 or less. In addition, the value obtained by dividing the molar content of Fe ions by the surface area of ​​the Ni mesh is 0.29 mmol / cm 2 It is understood that it is desirable that:

[0098] As shown in Table 1, the OER overpotentials of the electrodes according to Examples 1 and 2 were particularly low. Therefore, it was suggested that, from the viewpoint of electrode activity, the molar ratio of the Fe ion content to the Ni content contained in the Ni mesh should be in the range of 0.05 to 0.25. In addition, the molar content of Fe ions divided by the surface area of ​​the Ni mesh was 0.01 mmol / cm. 2 to 0.1 mmol / cm 2 It was suggested that it would be more desirable to

[0099] Comparing Example 1 and Comparative Example 3, the OER overpotential of the electrode according to Example 1 is lower than the OER overpotential of the electrode according to Comparative Example 3. Therefore, it is understood that the electrode according to Example 1 has higher electrode activity than the electrode according to Comparative Example 3. In addition, the coverage of the electrode according to Example 1 is higher than the coverage of the electrode according to Comparative Example 3. It is understood that the treatment of shaking and stirring the chelating agent-containing solution containing the Ni mesh before adding the pH-raising agent tends to improve the condition of the LDH-containing layer formed on the surface of the Ni mesh.

[0100] [Electrode Durability Evaluation] The OER overpotential of the electrodes according to Example 1 and Comparative Examples 2 and 3 was measured for 1,000 cycles to evaluate the electrode durability. For the measurement, a potentiostat VersaSTAT4 manufactured by Princeton Applied Research, a 200 mL alkali sample vial manufactured by BAS, a 200 mL Teflon® cap manufactured by BAS, and an AE-2 plate electrode manufactured by EC Frontier were used as the working electrode fixture. The working electrodes of Example 1 and Comparative Examples 2 and 3 were fixed to this fixture. A Metrohm double platinum wire counter electrode D.6.0305.200J was used as the counter electrode. The current derived from the anodic reaction of the water electrolysis cell was measured using a three-electrode method under the following measurement conditions. The anodic reaction was an oxygen evolution reaction. (Measurement conditions) Solution: 1 M KOH solution Potential to RHE: 1.0 V to 1.7 V Number of cycles: 1000 cycles Potential sweep rate: 100 mV / sec Temperature: 25°C

[0101] 8 is a graph showing the relationship between the OER overpotential and the number of cycles for the electrode according to Example 1 and the electrodes according to Comparative Examples 2 and 3. In this graph, the OER overpotential is shown every 50 cycles. Each cycle simulates the start and stop of water electrolysis.

[0102] Comparing Example 1 with Comparative Examples 2 and 3, the OER overpotential did not increase by the 50th cycle in the electrode of Example 1. On the other hand, the OER overpotential increased by the 50th cycle in the electrodes of Comparative Examples 2 and 3. This suggests that the electrode of Example 1 has higher durability than the electrodes of Comparative Examples 2 and 3. Therefore, from the viewpoint of electrode durability, it is understood that it is important to promote mixing of the solution containing Fe ions and chloride ions before forming a layer containing LDH while the Ni mesh is immersed in the solution.

[0103] [Identification of Electrode Structure and Morphological Observation] A sample for morphological observation was picked up and processed using a focused ion beam (FIB) processing and observation system (FB-2200) manufactured by Hitachi High-Technologies Corporation. Next, the sample for morphological observation was thinned using an FIB NX5000 manufactured by Hitachi High-Tech Science Corporation to obtain a sample for morphological observation. The structure of the electrodes according to each example and each comparative example was identified and the morphology of the electrodes was observed by cross-sectional observation using a transmission electron microscope (TEM) JEM-F200 manufactured by JEOL Ltd. and electron beam diffraction using the TEM. In this way, the state of LDH in the electrodes according to the examples and comparative examples was evaluated.

[0104] FIG. 9A is a TEM image of the electrode according to Example 1. FIGS. 9B and 9C are electron beam diffraction images of the entire TEM image shown in FIG. 9A. FIG. 9C shows a diagram obtained by connecting the diffraction spots observed in the electron beam diffraction image of FIG. 9B. FIG. 9D is another TEM image of the electrode according to Example 1. As shown in FIGS. 9A, 9B, and 9C, it can be seen that LDH is formed on the surface of the Ni mesh, and that nickel having a (111) plane orientation is present on the surface of the Ni mesh. Furthermore, in FIG. 9B, diffraction interference fringes originating from LDH are also observed, and it can be seen that the surface of the Ni mesh and the LDH are present in close proximity.

[0105] As shown in FIG. 9D, a layer containing LDH was uniformly formed on the surface of the Ni mesh, and the thickness of the layer was 35 nm or more.

[0106] FIG. 10A is a TEM image of the electrode according to Example 3. FIGS. 10B and 10C are electron beam diffraction images of the area surrounded by the white dashed line in FIG. 10A in the TEM image shown in FIG. 10A. FIG. 10C shows a diagram obtained by connecting the diffraction spots observed in the electron beam diffraction image of FIG. 10B. As shown in FIGS. 10A, 10B, and 10C, it can be seen that nickel having a (111) plane orientation is present on the surface of the Ni mesh in the electrode according to Example 3. In addition, significant irregularities appear on the surface of the Ni mesh. In Example 3, the molar ratio of the Fe ion content to the Ni content contained in the Ni mesh is higher than in Example 1. Therefore, it can be seen that etching of the Ni mesh progressed more when the chelating agent-containing solution containing the Ni mesh was shaken and stirred before the pH-raising agent was added.

[0107] Fig. 11A is a TEM image of an electrode according to Comparative Example 3. Figs. 11B and 11C are electron beam diffraction images related to the TEM image shown in Fig. 11A, and are electron beam diffraction images of the area surrounded by the white dashed line in Fig. 11A. Fig. 11C shows a diagram obtained by connecting the diffraction spots observed in the electron beam diffraction image of Fig. 11B. Fig. 11D is another TEM image of the electrode according to Comparative Example 3.

[0108] 11A, 11B, and 11C, it can be seen that nickel with a (111) plane orientation is present on the surface of the Ni mesh. On the other hand, it can be seen from FIG. 11D that voids have formed between the LDH-containing layer and the Ni mesh. In other words, in Comparative Example 3, no LDH-containing layer is provided on the Ni mesh surface. In Comparative Example 3, the chelating agent-containing solution containing the Ni mesh was not shaken or stirred before the pH-raising agent was added, and the pH-raising agent was added to the chelating agent-containing solution immediately after the Ni mesh was immersed in the chelating agent-containing solution. Therefore, it can be seen that the LDH was not firmly fixed to the surface of the Ni mesh, resulting in voids.

[0109] It should be noted that many modifications and other embodiments of the present disclosure will be apparent to those skilled in the art from the above description. Accordingly, the above description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the present disclosure. Substantial changes in operating conditions, composition, structure, and / or function can be made without departing from the spirit of the present disclosure.

[0110]

[0111] The water electrolysis electrode of the present disclosure can be used as an anode or a cathode for water electrolysis.

Claims

1. An electrode for water electrolysis comprising: a conductive substrate; and a layered double hydroxide layer containing two or more types of transition metals, wherein the conductive substrate has a surface made of nickel having a (111) orientation, and the layered double hydroxide layer is provided on the surface.

2. When the potential of the water electrolysis electrode is changed to cause a reduction reaction of nickel, the integral value of the current density corresponding to the reduction reaction is 200 mA / cm 2 The electrode for water electrolysis according to claim 1 , 3. The water electrolysis electrode according to claim 1 or 2, wherein the nickel constituting the surface has a purity of 90 mass % or more.

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

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

6. The water electrolysis electrode according to any one of claims 1 to 5, wherein the layered double hydroxide layer has a thickness of 35 nm or more.

7. The water electrolysis electrode according to any one of claims 1 to 6, wherein the two or more transition metals include at least two selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru.

8. The water electrolysis electrode according to claim 7, wherein the two or more transition metals include at least one selected from the group consisting of Ni and Fe.

9. An anode for water electrolysis comprising the electrode for water electrolysis according to any one of claims 1 to 8.

10. A cathode for water electrolysis comprising the electrode for water electrolysis according to any one of claims 1 to 8.

11. A water electrolysis cell comprising an anode, a cathode, and a diaphragm, wherein at least one selected from the group consisting of the anode being the anode for water electrolysis according to claim 9 and the cathode being the cathode for water electrolysis according to claim 10 is satisfied.

12. A water electrolysis cell comprising an anode, a cathode, and an anion exchange membrane, wherein at least one selected from the group consisting of the anode being the anode for water electrolysis according to claim 9 and the cathode being the cathode for water electrolysis according to claim 10 is satisfied.

13. A water electrolysis device comprising: the water electrolysis cell according to claim 11 or 12; and a voltage applicator that applies a voltage between the cathode and the anode.

14. A method for manufacturing an electrode for water electrolysis, comprising: promoting mixing of a solution containing transition metal ions and chloride ions while immersing a conductive substrate having a surface made of nickel in the solution; and forming a layered double hydroxide layer containing two or more types of transition metals on the surface of the conductive substrate.

15. The method for producing an electrode for water electrolysis according to claim 14, wherein one of the two or more transition metals in the layered double hydroxide is the same metal species as the transition metal ion contained in the solution.

16. The method for producing an electrode for water electrolysis according to claim 14 or 15, wherein the layered double hydroxide layer is formed by adjusting the solution to an alkaline state.

17. The method for producing a water electrolysis electrode according to any one of claims 14 to 16, wherein the two or more transition metals include at least two selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru.

18. The method for producing a water electrolysis electrode according to any one of claims 14 to 17, wherein the transition metal ions contained in the solution are iron ions.

19. The method for producing an electrode for water electrolysis according to claim 18, wherein the molar ratio of the content of iron ions to the content of nickel contained in the conductive base material is 0.75 or less.

20. The method for producing an electrode for water electrolysis according to claim 19, wherein the molar ratio is from 0.05 to 0.

25.

21. The molar content of Fe ions divided by the surface area of ​​the conductive substrate is 0.29 mmol / cm 2 The method for producing an electrode for water electrolysis according to claim 18, wherein the electrode is:

22. The value is 0.01 mmol / cm 2 to 0.1 mmol / cm 2 The method for producing an electrode for water electrolysis according to claim 21 , 23. The method for producing a water electrolysis electrode according to any one of claims 14 to 22, wherein the solution further contains a chelating agent.

24. The method for producing an electrode for water electrolysis according to claim 23, wherein the chelating agent includes at least one selected from the group consisting of acetylacetone and citrate salts.

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