Electrode for water electrolysis unit, water electrolysis unit, water electrolysis device, and method for producing electrode for water electrolysis unit

Abstract

An electrode (1) for a water electrolysis unit is provided with a conductive substrate (10), a first layer (11), and a second layer (12). The conductive substrate 10 contains a transition metal. The first layer (11) is disposed on the conductive substrate (10) and contains two or more transition metals and oxygen. The second layer (12) is disposed on the first layer (11) and contains a layered double hydroxide (LDH) having two or more transition metals. The first layer (11) is disposed between the conductive substrate (10) and the second layer (12) in the thickness direction of the first layer (11). The first layer (11) contains a first transition metal of the same type as the transition metal contained in the conductive substrate (10), and a second transition metal of the same type as the transition metal contained in the second layer (12) and of a different type from the first transition metal. The concentration of the first transition metal in the first layer (11) is higher than the concentration of the first transition metal in the second layer (12).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an electrode for a water electrolysis unit, a water electrolysis unit, a water electrolysis device, and a method for manufacturing an electrode for a water electrolysis unit. BACKGROUND

[0002] In recent years, development of an electrode used for a water electrolysis device is expected.

[0003] In Patent Literature 1, an electrode for water electrolysis in which a layer of NiO and a layered double hydroxide of Ni and Fe is formed on an electrode substrate that is a nickel foam is described.

[0004] In Patent Literature 2, an oxygen-evolving anode is described. In the oxygen-evolving anode, a catalyst layer composed of NiFe-ns (nanosheets) is formed on the surface of a prescribed intermediate. The intermediate, on the surface of an anode substrate that is a nickel-expanded mesh, has Li 0.5 Ni 1.5 O2-composed intermediate layer.

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

[0006] In Non-Patent Literature 2, it is described that the electronic structure of a local part of a Ni-Fe LDH is adjusted by a boundary surface interaction between FeOOH and the Ni-Fe LDH, and the OER electrode catalysis is improved. In alkaline water electrolysis, the outflow of an electrode catalyst or an electrode substrate from an electrode caused by oxidation and reduction of the electrode substrate and the electrode caused by a reverse current generated by a repeated operation stop cycle is a problem.

[0007] PRIOR ART DOCUMENTS

[0008] PATENT LITERATURE

[0009] Patent Literature 1: Japanese Patent Application Publication No. 2020-12171

[0010] Patent Literature 2: Japanese Patent Application Publication No. 2021-139027

[0011] NON-PATENT LITERATURE

[0012] Non-Patent Literature 1: Seyeong Lee et al., "Operational durability of three-dimensional Ni-Fe layered double hydroxide electrocatalyst for water oxidation", Electrochimica Acta, 2019, Vol. 315, p. 94-101

[0013] Non-Patent Literature 2: Jiande Chen et al., "Interfacial Interaction between FeOOH and Ni-Fe LDH to Modulate the Local Electronic Structure for Enhanced OER Electrocatalysis", ACS Catalysis, 2018, Vol. 8, p. 11342-11351 SUMMARY

[0014] From the viewpoint of durability of an electrode used for a water electrolysis device, the above-described literatures have room for further study. Therefore, the present disclosure provides a novel electrode for a water electrolysis unit that is advantageous from the viewpoint of durability.

[0015] The present disclosure provides an electrode for a water electrolysis unit, which includes a conductive substrate containing a transition metal, a first layer containing two or more kinds of transition metals and oxygen, and a second layer containing a layered double hydroxide having two or more kinds of transition metals,

[0016] The first layer is disposed between the conductive substrate and the second layer in the thickness direction of the first layer,

[0017] The first layer contains a first transition metal and a second transition metal, the first transition metal being a transition metal of the same kind as the transition metal contained in the conductive substrate, and the second transition metal being a transition metal of the same kind as the transition metal contained in the second layer and different from the first transition metal,

[0018] The concentration of the first transition metal in the first layer is higher than the concentration of the first transition metal in the second layer,

[0019] According to the present disclosure, a novel electrode for a water electrolysis unit that is advantageous from the viewpoint of durability can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a cross-sectional view schematically showing an electrode for a water electrolysis unit according to the first embodiment.

[0021] Figure 2 is a view schematically showing an example of a crystal structure of a layered double hydroxide (LDH).

[0022] Figure 3 is a view schematically showing a manufacturing mechanism of an electrode for a water electrolysis unit according to the first embodiment.

[0023] Figure 4 is a cross-sectional view schematically showing an example of a water electrolysis unit according to the second embodiment.

[0024] Figure 5 is a cross-sectional view schematically showing an example of a water electrolysis device according to the third embodiment.

[0025] Figure 6A is a cross-sectional view schematically showing an example of a water electrolysis unit according to the fourth embodiment.

[0026] Figure 6B is a cross-sectional view schematically showing another example of an electrode for a water electrolysis unit.

[0027] Figure 7 is a cross-sectional view schematically showing an example of a water electrolysis device according to the fifth embodiment.

[0028] Figure 8 is a transmission electron microscope (TEM) image of the electrode according to Example 1.

[0029] Figure 9A is a TEM image of a portion where electron diffraction results were obtained in the electrode according to Example 1.

[0030] Figure 9B is an electron diffraction image obtained by TEM for a portion of the electrode shown in Figure 9A

[0031] is a graph showing the results of line analysis by energy dispersive X-ray spectroscopy (TEM-EDX) using TEM for the electrode according to Example 1. Figure 10

[0032] is a TEM image of the electrode according to Comparative Example 3. Figure 11

[0033] Figure 12A ​is a TEM image of a portion of the electrode relating to Comparative Example 3, which shows the result of electron diffraction.

[0034] Figure 12B is a TEM image of a portion of the electrode relating to Figure 12A is an electron diffraction image of a portion of the electrode shown in FIG. 6.

[0035] Figure 13 is a graph showing the result of line analysis of TEM-EDX of the electrode relating to Comparative Example 3.

[0036] Figure 14 is a graph showing the relationship between OER overvoltage and cycle number of the electrode relating to Example 1 and the electrodes relating to Comparative Examples 2 and 3. DETAILED DESCRIPTION

[0037] (Insight that is the basis of the present disclosure)

[0038] As a measure against global warming, the use of renewable energy such as sunlight and wind power is attracting attention. In power generation based on renewable energy, there is a problem that surplus electric power is wasted. Therefore, the efficiency of the use of renewable energy is not necessarily sufficient. Thus, a method of efficiently using surplus electric power by producing hydrogen from surplus electric power and storing it is being studied.

[0039] As a method of producing hydrogen from surplus electric power, electrolysis of water can be considered. In order to produce hydrogen inexpensively and stably, development of a water electrolysis device with high efficiency and long life is required.

[0040] In a water electrolysis device, oxygen is generated at an anode, and hydrogen is generated at a cathode. The reaction in which oxygen is generated at the anode is also referred to as an anode reaction, and the reaction in which hydrogen is generated at the cathode is also referred to as a cathode reaction. In order to provide a water electrolysis device with high efficiency, it is particularly desirable that the anode overvoltage be low. In addition, it is desirable that the cathode overvoltage also be low. Therefore, development of an electrode with high performance for an anode reaction or a cathode reaction of water electrolysis is expected.

[0041] For example, from the viewpoint of a large specific surface area and a variety of combinations of metal ions, it is considered that LDH is promising as a material of an electrode for a water electrolysis unit. In this case, it is possible to consider that LDH is supported on a substrate having conductivity. For example, it is possible to consider that LDH is supported on a substrate such as a nickel foam as described in Patent Literature 1 or the like. On the other hand, from the viewpoint of durability with respect to an electrode reaction in water splitting, there is room for further study of this technology. As a result of repeated intensive studies by the present inventors, it has been newly found that, by the presence of a prescribed layer between a layer containing LDH and a conductive substrate, the durability of an electrode for a water electrolysis unit is improved, and thus the electrode for a water electrolysis unit of the present disclosure has been completed.

[0042] Embodiments of the present disclosure will be described below with reference to the accompanying drawings. The present disclosure is not limited to the following embodiments. Furthermore, the following described embodiments are all illustrative embodiments showing general or specific examples. Therefore, the values, shapes, materials, component elements, arrangement positions of component elements, connection modes, and the like shown in the following embodiments are examples, and are not intended to limit the present disclosure. In addition, regarding the component elements among the component elements in the following embodiments, the component elements not recited in the independent claims that represent the most general concept are described as arbitrary component elements. In addition, in the drawings, the portions annotated with the same reference numerals are sometimes omitted from the description. In addition, the drawings are drawings that schematically show the component elements in order to facilitate understanding, and sometimes do not show the shapes and the dimensional ratios, and the like accurately.

[0043] (First Embodiment)

[0044] Figure 1 is a schematic cross-sectional view of an electrode for a water electrolysis cell to which the first embodiment is applied. As shown in Figure 1 , the electrode for a water electrolysis cell 1 includes an electrically conductive substrate 10, a first layer 11, and a second layer 12. The first layer 11 is arranged between the electrically conductive substrate 10 and the second layer 12 in the thickness direction thereof. The electrically conductive substrate 10 includes a transition metal. The first layer 11 is arranged on the electrically conductive substrate 10 and includes two or more kinds of transition metals and oxygen. The second layer 12 is arranged on the first layer 11 and includes a layered double hydroxide (LDH) having two or more kinds of transition metals. The first layer 11 includes a first transition metal of the same kind as the transition metal included in the electrically conductive substrate 10, and a second transition metal of the same kind as the transition metal included in the second layer 12 and different from the first transition metal. The concentration of the first transition metal in the first layer 11 is higher than the concentration of the first transition metal in the second layer 12. As shown in Figure 1 , the first layer 11 is present between the second layer 12 including the LDH and the electrically conductive substrate 10 in the thickness direction of the first layer 11. Specifically, the second layer 12 including the LDH is joined to the electrically conductive substrate 10 via the first layer 11. Thereby, the second layer 12 is easily firmly fixed to the electrically conductive substrate 10, and the electrode for a water electrolysis cell 1 easily exhibits high durability.

[0045] In the electrode for water electrolysis unit 1, the thickness of the first layer 11 is not limited to a particular value. The first layer 11 has, for example, a thickness of 10 nm or less. Thereby, the electrode for water electrolysis unit 1 easily exhibits high durability, and the electrode for water electrolysis unit 1 easily has high electrode activity. The thickness of the first layer 11 can be determined, for example, by performing line analysis of TEM-EDX in a region of a TEM image of a cross section of the electrode for water electrolysis unit 1 that contains the second layer 12, the first layer 11, and the electrically conductive substrate 10. In the results of the line analysis of TEM-EDX, the thickness of the first layer 11 can be determined by focusing on the counts of the first transition metal, the second transition metal, and oxygen. The thickness of the first layer 11 is, for example, 1 nm or more.

[0046] In the electrode for water electrolysis unit 1, the first transition metal and the second transition metal are not limited to particular metals. The first transition metal is, for example, Ni. The second transition metal is, for example, a transition metal selected from V, Cr, Mn, Fe, Co, Cu, W, and Ru. According to such a configuration, the electrode for water electrolysis unit 1 has high electrode activity and more easily exhibits high durability.

[0047] In the electrode for water electrolysis unit 1, the second transition metal is preferably Fe. In this case, the electrode for water electrolysis unit 1 more easily has high electrode activity, and more easily exhibits high durability. Also, the manufacturing cost of the electrode for water electrolysis unit 1 easily decreases.

[0048] The electrically conductive substrate 10 is not limited to a particular substrate as long as it contains the first transition metal and has electrical conductivity. The electrically conductive substrate 10 can contain a metal other than the first transition metal, and can contain a resin. The entirety of the electrically conductive substrate 10 can also be composed of a metal. The electrically conductive substrate 10 can have a configuration in which a surface layer containing a metal is formed on a member made of a resin such as polypropylene or polyethylene. In this case, the surface layer containing a metal can be a plating film or a sputtering film. The metal contained in the electrically conductive substrate 10 can be a pure metal such as nickel, or an alloy such as stainless steel or Inconel (chromium-nickel-iron heat- and corrosion-resistant alloy). Inconel is a registered trademark.

[0049] The surface of the electrically conductive substrate 10 preferably contains at least one selected from nickel and nickel oxide. In this case, the electrically conductive substrate 10 easily has high alkali resistance. In the case where the surface of the electrically conductive substrate 10 contains at least one selected from nickel and nickel oxide, the entirety of the electrically conductive substrate 10 can be composed of nickel. The electrically conductive substrate 10 can have a surface layer containing at least one selected from nickel and nickel oxide. The surface layer is, for example, a sputtering film or a plating film.

[0050] In the case where the surface of the electrically conductive substrate 10 contains at least one selected from nickel and nickel oxide, the nickel and the nickel oxide can also have a prescribed orientation.

[0051] The shape of the conductive substrate 10 is not limited to a particular shape. The conductive substrate 10 can have, for example, a non-porous structure such as a plate and a foil, or a porous structure such as a mesh, a foam, and a non-woven fabric. The conductive substrate 10 can also be a particle such as a metal particle. The conductive substrate 10 preferably has a porous structure. In this case, the surface area of the portion of the conductive substrate 10 having conductivity easily becomes large, and the water electrolysis cell electrode 1 easily has high electrode activity. Furthermore, the escape of gas generated in the water electrolysis reaction is easily prevented.

[0052] The thickness of the conductive substrate 10 is not limited to a particular value. The conductive substrate 10 is, for example, 0.02 mm or more. In this case, the handling of the conductive substrate 10 easily becomes easy. The thickness of the conductive substrate 10 is, for example, 10 mm or less.

[0053] As described above, the second layer 12 contains an LDH. Figure 2 is a diagram schematically showing an example of the crystal structure of an LDH. The LDH 20 has activity with respect to the generation reaction of gas such as hydrogen and oxygen at the anode or the cathode of a water electrolysis cell. For example, in alkaline water electrolysis, the LDH 20 can change into a hydroxide by a water electrolysis reaction.

[0054] The LDH 20 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 of 0 < x < 1. y is a number corresponding to the necessary amount of the balance charge. n is an integer. M is an appropriate rational number.

[0055] [M1 2+ 1-x M2 3+ x (OH)2][yA n- · mH2O] Formula (1)

[0056] The two or more kinds of transition metals in the LDH 20 are not limited to particular transition metals. In other words, M1 and M2 in the composition represented by formula (1) are not limited to particular transition metals. The two or more kinds of transition metals contain, for example, at least two kinds selected from V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. In this case, the water electrolysis cell electrode 1 easily has high electrode activity.

[0057] The LDH20 contains two or more transition metals, such as Ni and Fe. For example, in the composition shown in formula (1), M1 can be Ni and M2 can be Fe. In this case, the water electrolysis unit electrode 1 is more likely to have high electrode activity.

[0058] A as an interlayer anion n- These can be inorganic or organic ions. An example of an inorganic ion is CO3. 2- NO3 - Cl - SO4 2- ,Br - OH - F - I - Si2O5 2- B4O5(OH)4 2- and PO4 3- Examples of organic ions include CH3 (CH2). n SO 4- CH3 (CH2) n COO - CH3 (CH2) n PO 4- and CH3 (CH2) n NO 3- A n- It can embed itself between metal hydroxide layers along with water molecules. A n- The charge and size of the ions are not limited to specific values. LDH20 can contain one type of A n- It can also contain multiple A's. n- .

[0059] like Figure 2 As shown, LDH20 in M1 2+ or M2 3+ The vertices of the octahedron centered on the center have OH - Ions. Contained in LDH20 with [M1] 2+ 1-x M2 3+ x [(OH)2] x+ The diagram shows a metal hydroxide layer. This metal hydroxide layer forms a two-dimensionally connected layered structure with octahedral shared edges. Anions A are present between the metal hydroxide layers. n- And water molecules. The metal hydroxide layer functions as the host layer 21, containing anions A. n- Guest layers 22 containing water molecules are disposed between each other in the host layer 21. In other words, LDH20, as a whole, has a host layer 21 containing metal hydroxide and anions An- and water molecules. The LDH20 has a structure in which a part of M1 2+ in the metal hydroxide layer is substituted with M2 3+ .

[0060] The second layer 12 can contain a chelating agent. The chelating agent can coordinate with the transition metal ion contained in the LDH20. Thereby, the LDH20 is easily synthesized in a manner of having a small particle diameter in the formation of the second layer 12. Accordingly, the specific surface area of the LDH20 is easily made high, and the electrode 1 for a water electrolysis unit more easily has a high electrode activity. The chelating agent is a ligand having a plurality of coordination sites, i.e., a polydentate ligand.

[0061] The chelating agent is not limited to a particular chelating agent. The chelating agent is, for example, an organic compound capable of coordinating with the transition metal ion in the LDH20. The chelating agent can be at least one selected from a bidentate organic ligand and a tridentate organic ligand. Examples of the chelating agent are β-diketone, β-ketoester, hydroxycarboxylic acid, and hydroxycarboxylic acid salt. Examples of the β-diketone are acetylacetone (ACAC), trifluoroacetylacetone, hexafluoroacetylacetone, benzoylacetone, thienoyltrifluoroacetone, di-tert-amylmethane, dibenzoylmethane, and ascorbic acid. Examples of the β-ketoester are methyl acetoacetate, ethyl acetoacetate, allyl acetoacetate, benzyl acetoacetate, n-propyl acetoacetate, isopropyl acetoacetate, n-butyl acetoacetate, isobutyl acetoacetate, t-butyl acetoacetate, 2-methoxyethyl acetoacetate, and methyl 3-oxopentanoate. Examples of the hydroxycarboxylic acid and the salt thereof are tartaric acid, citric acid, malic acid, gluconic acid, ferulic acid, lactic acid, glucuronic acid, and salts thereof.

[0062] The chelating agent preferably contains at least one selected from acetylacetone and citrate. In this case, the electrode 1 for a water electrolysis unit more easily has a high electrode activity. An example of the citrate is trisodium citrate.

[0063] The thickness of the second layer 12 is not limited to a particular value. The second layer 12 has, for example, a thickness of 35 nm or more. According to such a configuration, the electrode 1 for a water electrolysis unit more easily has a high electrode activity. The second layer 12 contains, for example, a site having a thickness of 35 nm or more. The thickness of the second layer 12 can be determined, for example, by TEM observation of a cross section of the electrode 1 for a water electrolysis unit. The thickness of the second layer 12 is, for example, 210 nm or less.

[0064] The second layer 12, for example, covers the surface of the conductive substrate 10. The coverage rate of the second layer 12 over the surface of the conductive substrate 10 is not limited to a specific value. Preferably, the coverage rate is 99% or higher. In this case, the electrode 1 for the water electrolysis unit tends to have high electrode activity. Furthermore, the electrode 1 for the water electrolysis unit tends to have higher durability. The coverage rate can be determined, for example, according to the method described in the embodiments.

[0065] The method for manufacturing electrode 1 for a water electrolysis unit is not limited to a specific method. Electrode 1 for a water electrolysis unit can be manufactured, for example, according to the methods comprising (I) and (II) below.

[0066] (I) In a state in which the conductive substrate 10 containing the first transition metal is immersed in a solution S containing a second transition metal of a different kind than the first transition metal and chloride ions, the mixing of the solution S is promoted.

[0067] (II) A layer containing LDH is formed on a conductive substrate 10, wherein the LDH has a second transition metal and a third transition metal of a different kind than the second transition metal.

[0068] In step (I) above, the first transition metal contained in the conductive substrate 10 can interact with the second transition metal contained in the solution S and the chloride. This facilitates the formation of a layer that firmly fixes the LDH-containing layer formed in step (II) to the conductive substrate 10. As a result, the electrode 1 for the water electrolysis unit readily exhibits high durability.

[0069] The mixing of solution S can be promoted, for example, by vibrating the conductive substrate 10, oscillating the container containing S and the conductive substrate 10, or stirring the solution S using a stirrer or agitator. According to such methods, forced convection of solution S can be generated, thus promoting the mixing of solution S.

[0070] (I) The temperature of solution S in the process is not limited to a specific temperature. (I) The temperature of solution S in the process is, for example, room temperature 20℃±15℃. In this case, it is easy to obtain electrode 1 for water electrolysis unit with high electrode activity.

[0071] The solvent of solution S can be water, an organic solvent, or a mixture of water and an organic solvent.

[0072] Solution S may further contain a chelating agent, for example. Therefore, the particle size of LDH synthesized in step (II) can be easily reduced, and the specific surface area of ​​LDH20 can be easily increased. Electrode 1 for the water electrolysis unit is more likely to have high electrode activity.

[0073] In the case where the solution S contains a chelating agent, the solution S can further contain a third transition metal. In this case, a complex formed by the third transition metal and the chelating agent contained in the solution S can contribute to the synthesis of LDH20.

[0074] In the case where the solution S contains a chelating agent, the third transition metal can be a transition metal of the same kind as the first transition metal. In this case, the manufacturing method of the water electrolysis unit electrode 1 can easily become simple.

[0075] The chelating agent contained in the solution S can be selected with reference to the above-described examples of the chelating agent contained in the second layer 12. The chelating agent contained in the solution S preferably contains at least one selected from acetylacetone and citrate. Thereby, the stability of dispersion of the complex in the solution S becomes high, and the second layer 12 is easily formed in a desired state in the water electrolysis unit electrode 1. As a result, the water electrolysis unit electrode 1 more easily has high electrode activity.

[0076] In the (II) process, the method of forming the layer containing LDH is not limited to a particular method. For example, the layer containing LDH can be formed by adjusting the solution S to be basic. Thereby, the water electrolysis unit electrode 1 more easily exhibits high durability.

[0077] The method of adjusting the solution S to be basic is not limited to a particular method. For example, the solution can be adjusted to be basic by mixing the above-described solution S with an alkaline solution. Alternatively, a pH-raising agent can be added to the above-described solution to adjust the solution to be basic. In this case, the pH-raising agent is not limited to a particular compound. The pH-raising agent is, for example, a compound having an epoxy group. Examples of the pH-raising agent are propylene oxide, ethylene oxide, and butylene oxide.

[0078] If the pH-raising agent having an epoxy group such as propylene oxide is added to the solution S, in the presence of a nucleophile such as chloride ion, the pH-raising agent can capture a hydrogen ion present in the solution S with ring-opening reaction of the epoxy group. Thereby, the pH value of the solution S rises, and the solution S can have basicity. The pH value of the solution S is, for example, 1. When the pH-raising agent is added to this solution S, the pH value of the solution S gradually rises, for example, from 1, and finally the solution S can have basicity. The final pH value of the solution S is, for example, 8 or more and 12 or less. By adding the pH-raising agent to the solution, the reaction of capturing the hydrogen ion in the solution S proceeds. Thereby, the pH value of the solution S gradually rises. The time from the addition of the pH-raising agent to the solution S to the time when the pH value of the solution S becomes a stable state is not limited to a particular time. The time is, for example, 24 hours or more, and can be several days.

[0079] The temperature of the solution S when the solution S is adjusted to be alkaline is not limited to a particular temperature. The temperature of the solution S is, for example, normal temperature of 20°C ± 15°C. In this case, the water electrolysis cell electrode 1 having high electrode activity is easily obtained.

[0080] In the above production method, the first transition metal and the second transition metal are not limited to particular transition metals. For example, the first transition metal is Ni, and the second transition metal is a transition metal selected from V, Cr, Mn, Fe, Co, Cu, W, and Ru. In this case, the water electrolysis cell electrode having high electrode activity and more easily exhibiting high durability is easily produced.

[0081] The second transition metal is preferably Fe. In this case, the water electrolysis cell electrode having high electrode activity and more easily exhibiting high durability is easily produced.

[0082] In the case where the first transition metal is Ni and the second transition metal is Fe, for example, the reaction of the following formula (2) can occur in the (I) process. Thereby, the conductive substrate 10 can be etched. Also, it is considered that, in the (I) process, Fe 3+ diffuses to the vicinity of the surface of the conductive substrate 10, and a part of Fe 3+ and a part of Ni 2+ together with oxygen form a layer containing Ni, Fe, and oxygen on the surface of the conductive substrate 10. Then, in the (II) process, a layer containing LDH is formed on the layer. Thereby, the water electrolysis cell electrode 1 in which the layer containing Ni, Fe, and oxygen is formed between the layer containing LDH and the conductive substrate 10 is obtained.

[0083] 4Ni 2+ Cl - 2+2Fe 3+ Cl - 3+2Ni→5Ni 2+ Cl - 2+2Fe 2+ Cl - 2+1Ni Formula (2)

[0084] In the case where the first transition metal is Ni and the second transition metal is Fe, in the production of the water electrolysis cell electrode 1, the molar ratio of the content of Fe ions to the content of Ni contained in the conductive substrate 10 is not limited to a particular value. The molar ratio is, for example, 0.75 or less. In this case, it is possible to prevent the nickel contained in the conductive substrate 10 from dissolving by the reaction shown by formula (2) and thereby making it difficult to produce the water electrolysis cell electrode 1.

[0085] The molar ratio described above is preferably 0.05 to 0.25. In this case, a layer containing Ni, Fe, and oxygen can be easily formed on the surface of the conductive substrate 10 in a desired state, and an electrode 1 for a water electrolysis unit with high durability can be easily obtained. Moreover, a second layer 12 can be easily formed uniformly on the conductive substrate 10, making it easier to manufacture an electrode 1 for a water electrolysis unit with high electrode activity.

[0086] When the first transition metal is Ni and the second transition metal is Fe, the value obtained by dividing the molar content of Fe ions by the surface area of ​​the conductive substrate 10 during the manufacture of electrode 1 for the water electrolysis unit is not limited to a specific value. This value is, for example, 0.29 mmol / cm². 2 In this case, it is possible to prevent the nickel in the conductive substrate 10 from dissolving through the reaction shown in formula (2), thereby making it difficult to manufacture the electrode 1 for the water electrolysis unit.

[0087] The value obtained by dividing the molar amount of Fe ions by the surface area of ​​the conductive substrate 10 is preferably 0.01 mmol / cm². 2 ~0.1mmol / cm 2 In this case, a layer containing Ni, Fe, and oxygen can be easily formed on the surface of the conductive substrate 10 in a desired state, and an electrode 1 for a water electrolysis unit with high durability can be easily obtained. Moreover, a second layer 12 can be easily formed uniformly on the conductive substrate 10, making it easier to manufacture an electrode 1 for a water electrolysis unit with high electrode activity.

[0088] Figure 3 This diagram schematically illustrates an example of the manufacturing mechanism of the electrode for the water electrolysis unit according to the first embodiment. (See diagram below.) Figure 3 As shown, the conductive substrate 10 is immersed in a solution S containing ions TM2 of a second transition metal, chloride ions (not shown), ions TM3 of a third transition metal, and a chelating agent 30. For example, the ions TM2 of the second transition metal are Fe. 3+ The ion TM3 of the third transition metal is Ni. 2+ The conductive substrate 10, for example, contains Ni as a first transition metal. In step (I), ions TM2 of a second transition metal contained in solution S diffuse towards the vicinity of the surface of the conductive substrate 10 through the action of ions TM2. As a result, the conductive substrate 10 is etched, and the first transition metal contained in the conductive substrate 10 dissolves into solution S, generating ions TM1 originating from the first transition metal of the conductive substrate 10. Through the diffusion of ions TM2 towards the vicinity of the surface of the conductive substrate 10, a layer containing, for example, Fe, Ni, and oxygen can be formed along the surface of the conductive substrate 10. In this example, both ions TM1 and ions TM3 are Ni. 2+However, the ion TM1 and the ion TM3 can also be transition metal ions of mutually different kinds. A portion of the chelating agent 30 contained in the solution S reacts with the ion TM1 of the first transition metal eluted from the conductive substrate 10, forming a complex C1 of the ion TM1 of the first transition metal derived from the conductive substrate 10 and the chelating agent 30. In addition, a complex C2 of the ion TM2 of the second transition metal and the chelating agent 30, and a complex C3 of the ion TM3 of the third transition metal derived from the solution S and the chelating agent 30 are formed. Next, if the solution S is adjusted to be alkaline, the complexes C1, C2, and C3 react on the surface of the conductive substrate 10, and LDH20 is synthesized along the surface of the conductive substrate 10. Since the complexes C1, C2, and C3 contain the chelating agent 30, the crystallization growth of the LDH20 is suppressed by the effect of the chelating agent 30. Thus, the second layer 12 containing the LDH20 and the chelating agent 30 is formed on the conductive substrate 10, and the electrode 1 for a water electrolysis cell is obtained.

[0089] The electrode 1 for a water electrolysis cell according to the present embodiment can be used as an electrode of a water electrolysis cell of an alkaline water electrolysis device or an anion exchange membrane type water electrolysis device, for example. The electrode 1 for a water electrolysis cell is used in at least one selected from an anode and a cathode in these water electrolysis devices, for example. Thus, the activity of an anode reaction or a cathode reaction of water electrolysis easily becomes high.

[0090] (2nd Embodiment)

[0091] Figure 4 is a cross-sectional view schematically showing an example of a water electrolysis cell according to the 2nd embodiment. As shown in Figure 2 , the water electrolysis cell 2 includes an anode 2a, a cathode 2b, and a separator 2p. At least one selected from the anode 2a and the cathode 2b contains the electrode 1 for a water electrolysis cell according to the 1st embodiment, for example. In this case, the activity of an anode reaction or a cathode reaction in the water electrolysis cell 2 easily becomes high, and the anode 2a or the cathode 2b easily exhibits high durability.

[0092] The water electrolysis cell 2 is an alkaline water electrolysis cell using an aqueous alkali solution, for example. The aqueous alkali solution used in the water electrolysis cell 2 is not limited to a particular aqueous alkali solution. Examples of the aqueous alkali solution are an aqueous potassium hydroxide solution and an aqueous sodium hydroxide solution.

[0093] As shown in Figure 4 , the water electrolysis cell 2 includes an electrolytic tank 2s, a first chamber 2m, and a second chamber 2n, for example. The separator 2p is disposed inside the electrolytic tank 2s, and divides the inside of the electrolytic tank 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.

[0094] The separator 2p is, for example, a separator for alkaline water electrolysis. The separator 2p is, for example, a sheet-like porous membrane. The separator 2p has a thickness of, for example, 100 μm to 500 μm, and has pores that become channels for ions or electrolyte. The material of the separator 2p is not limited to a particular material. Examples of the material of the separator 2p are asbestos, polymer-reinforced asbestos, potassium titanate bonded with polytetrafluoroethylene (PTFE), zirconia bonded with PTFE, and antimony acid bonded with polysulfone and antimony oxide bonded with polysulfone. Another example of the material of the separator 2p is sintered nickel, nickel coated with ceramic, and nickel coated with nickel oxide, and polysulfone. The separator 2p can also be Zirfon Perl UTP 500 manufactured by AGFA.

[0095] The anode 2a can be configured in a state in contact with the separator 2p, that is, in a state of zero gap, or can be configured in a state of having a gap between the anode 2a and the separator 2p. The cathode 2b can be configured in a state in contact with the separator 2p, or can be configured in a state of having a gap between the cathode 2b and the separator 2p.

[0096] The water electrolysis unit 2 electrolyzes an aqueous alkali solution to produce hydrogen and oxygen. An aqueous solution containing a hydroxide of an alkali metal or an alkaline earth metal is supplied to the first chamber 2m. In addition, an aqueous alkali solution can be supplied to the second chamber 2n. Electrolysis is performed while discharging an aqueous alkali solution of a prescribed concentration from the first chamber 2m and the second chamber 2n, to produce hydrogen and oxygen.

[0097] In a case where the anode 2a includes the electrode 1 for water electrolysis unit, the cathode 2b can include, for example, an electrode material known as a cathode of an alkaline water electrolysis unit.

[0098] In the water electrolysis unit 2, in a case where the cathode 2b includes the electrode 1 for water electrolysis unit, the anode 2a can include an electrode material known as an anode of an alkaline water electrolysis unit. In the water electrolysis unit 2, both the anode 2a and the cathode 2b can include the electrode 1 for water electrolysis unit.

[0099] According to the above configuration, at least one selected from the anode 2a and the cathode 2b includes the electrode 1 for water electrolysis unit, and thus the water electrolysis unit 2 is able to exhibit high durability.

[0100] (3rd Embodiment)

[0101] Figure 5 is a cross-sectional view schematically showing an example of a water electrolysis device according to the 3rd embodiment. As shown in Figure 5 The water electrolysis device 3 includes the water electrolysis unit 2 according to the 2nd embodiment and a voltage applier 40. The voltage applier 40 applies a voltage between the cathode 2b and the anode 2a. The water electrolysis device 3 is an alkaline water electrolysis device that uses an aqueous alkali solution.

[0102] The voltage applier 40 is electrically connected to the anode 2a and the cathode 2b. The potential of the anode 2a becomes higher than the potential at the cathode 2b by the voltage applier 40. The voltage applier 40 is not limited to a specific kind of voltage applier as long as it can apply a voltage between the anode 2a and the cathode 2b. The voltage applier 40 can also be a device that adjusts the voltage applied between the anode 2a and the cathode 2b. In the case where the voltage applier 40 is connected to a direct-current power source such as a battery, a solar cell, and a fuel cell, the voltage applier 40 has, for example, a DC / DC converter. In the case where the voltage applier 40 is connected to an alternating-current power source such as an industrial power source, the voltage applier 40 has, for example, an AC / DC converter. The voltage applier 40 can also be, for example, a power supply type power source. In the power supply 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 electric power (power) supplied to the water electrolysis device 3 becomes a prescribed set value.

[0103] According to the above configuration, the water electrolysis device 3 can exhibit high durability.

[0104] (4th Embodiment)

[0105] Figure 6A is a cross-sectional view schematically showing an example of a water electrolysis cell according to the 4th embodiment. As shown in Figure 6A The water electrolysis cell 4 has an anode 4a, a cathode 4b, and an anion exchange membrane 4p. In the water electrolysis cell 4, at least one selected from the anode 4a and the cathode 4b contains, for example, the electrode 1 for water electrolysis cell according to the 1st embodiment. In this case, the activity of the anode reaction or the activity of the cathode reaction in the water electrolysis cell 4 easily becomes high, and the anode 4a or the cathode 4b easily exhibits high durability.

[0106] The water electrolysis cell is, for example, an anion exchange membrane (AEM) type water electrolysis cell. As shown in Figure 6A The anode 4a has, for example, a catalyst layer 4m and a gas diffusion layer 4n. The cathode 3b has, 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.

[0107] The anion exchange membrane 4p is not limited to a specific kind of anion exchange membrane. The anion exchange membrane 4p has conductivity of anions such as hydroxide ions. The anion exchange membrane 4p can prevent oxygen generated at the anode 4a from mixing with hydrogen generated at the cathode 4b. The oxygen is guided to the outside of the anode 4a through the gas diffusion layer 4n. The hydrogen is guided to the outside of the cathode 4b through the gas diffusion layer 4k.

[0108] In the water electrolysis unit 4, if the anode 4a includes the electrode 1 for the water electrolysis unit, the cathode 4b can also be a known cathode in an AEM-type water electrolysis unit.

[0109] In the water electrolysis unit 4, if the cathode 4b includes the electrode 1 for the water electrolysis unit, the anode 4a can also be a known anode in an AEM-type water electrolysis unit. In the water electrolysis unit 4, both the anode 4a and the cathode 4b may include the electrode 1 for the water electrolysis unit.

[0110] Based on the above configuration, at least one of the anode 4a and the cathode 4b includes the electrode 1 for the water electrolysis unit, thus enabling the water electrolysis unit 4 to exhibit high durability.

[0111] Figure 6B This illustrates another example of electrode 1 used in the water electrolysis unit according to the fourth embodiment. For example... Figure 6B As shown, the electrode 1 for a water electrolysis unit includes a conductive substrate 10, a first layer 11, and a second layer 12. The first layer 11 is disposed between the conductive substrate 10 and the second layer 12 in its thickness direction. The conductive substrate 10 is, for example, metal particles, with the first layer 11 positioned between the surface of the metal particles serving as the conductive substrate 10 and the second layer 12, and the surface of the metal particles is covered by the second layer 12 containing LDH. The entire surface of the metal particles may be covered by the second layer 12 containing LDH, or only a portion of the surface of the metal particles may be covered by the second layer 12 containing LDH. The second layer 12 covers, for example, more than 70% of the surface of the metal particles serving as the conductive substrate 10. The second layer 12 may cover most of the surface of the metal particles serving as the conductive substrate 10, specifically more than 90% of the surface. The electrode 1 for a water electrolysis unit may have a cross-section in which its surface is covered by LDH. In the electrode 1 for a water electrolysis unit, the ratio of the mass of the metal particles to the mass of LDH is not limited to a specific value. This ratio is, for example, 8.0 or less. Based on this configuration, the electrode 1 for the water electrolysis unit is more likely to have high durability.

[0112] The metal particles serving as the conductive substrate 10 contain one or more transition metals. Examples of transition metals include V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. The metal particles may contain Ni, and the metal particles may be Ni particles. The transition metals contained in the metal particles 11 may be the same type of metal as the two or more transition metals contained in the LDH of the second layer 12.

[0113] The shape of the metal particles that are the conductive base material 10 is not limited to a particular shape. The shape of the metal particles is, for example, granular. In the case where the shape of the metal particles is granular, the average particle diameter of the metal particles is not limited to a particular value. The average particle diameter of the metal particles can be 100 nm or less, and can be 50 nm or less. The average particle diameter of the metal particles can be 10 nm or more, and can be 20 nm or more. The metal particles can have, for example, an average particle diameter to the extent that a sufficient amount of LDH can be supported. Thereby, even in the case where a voltage is applied to the water electrolysis cell electrode 1, the second layer 12 containing the LDH and the metal particles that are the conductive base material 10 are difficult to separate, and thus the water electrolysis cell electrode 1 is more likely to have high durability. Further, according to such a configuration, the water electrolysis cell electrode 1 is, for example, more likely to have high durability in the anode reaction of water electrolysis. The average particle diameter of the metal particles can be found, for example, by observing the metal particles using a transmission electron microscope (TEM). Specifically, with respect to the average particle diameter, for each of any 50 metal particles of which the entirety can be observed, on the basis of determining the average of the maximum diameter and the minimum diameter thereof as the particle diameter of each metal particle, the arithmetic mean of the particle diameters thereof is determined.

[0114] (5th Embodiment)

[0115] Figure 7 is a cross-sectional view schematically showing an example of a water electrolysis device according to the 5th embodiment. As shown in Figure 7 , the water electrolysis device 5 includes a water electrolysis cell 4 and a voltage applier 40. The voltage applier 40 applies a voltage between the cathode 4b and the anode 4a. The water electrolysis device 5 is, for example, an AEM-type water electrolysis device.

[0116] The voltage applier 40 is electrically connected to the anode 4a and the cathode 4b. By the voltage applier 40, the potential of the anode 4a becomes higher than the potential at the cathode 4b. The voltage applier 40 is not limited to a particular kind of voltage applier as long as it can apply a voltage between the anode 4a and the cathode 4b. The voltage applier 40 can also be a device that adjusts the voltage applied between the anode 4a and the cathode 4b. In the case where the voltage applier 40 is connected to a direct-current power source such as a battery, a solar cell, and a fuel cell, the voltage applier 40 includes, for example, a DC / DC converter. In the case where the voltage applier 40 is connected to an alternating-current power source such as a commercial power source, the voltage applier 40 includes, for example, an AC / DC converter. The voltage applier 40 can also be, for example, a power-type power source. In the power-type power source, the voltage applied between the anode 4a and the cathode 4b and the current flowing between the anode 4a and the cathode 4b are adjusted so that the electric power (power) supplied to the water electrolysis device 5 becomes a predetermined set value.

[0117] According to the above configuration, the water electrolysis device 5 can exhibit high performance.

[0118] (Addendum)

[0119] According to the above description, the following technology is disclosed.

[0120] (Technology 1)

[0121] An electrode for a water electrolysis unit, comprising an electrically conductive substrate, a first layer, and a second layer, the electrically conductive substrate containing a transition metal, the first layer containing two or more kinds of transition metals and oxygen, the second layer containing a layered double hydroxide having two or more kinds of transition metals,

[0122] the first layer being disposed between the electrically conductive substrate and the second layer in a thickness direction of the first layer,

[0123] the first layer containing a first transition metal and a second transition metal, the first transition metal being a kind of transition metal that is the same as a kind of transition metal contained in the electrically conductive substrate, the second transition metal being a kind of transition metal that is the same as a kind of transition metal contained in the second layer and different from the first transition metal,

[0124] a concentration of the first transition metal in the first layer is higher than a concentration of the first transition metal in the second layer.

[0125] (Technology 2)

[0126] The electrode for a water electrolysis unit according to Technology 1, wherein the electrically conductive substrate has a porous structure.

[0127] (Technology 3)

[0128] The electrode for a water electrolysis unit according to Technology 1 or 2, wherein the first layer has a thickness of 10 nm or less.

[0129] (Technology 4)

[0130] The electrode for a water electrolysis unit according to any one of Technologies 1 to 3, wherein the second layer has a thickness of 35 nm or more.

[0131] (Technology 5)

[0132] The electrode for a water electrolysis unit according to any one of Technologies 1 to 4, wherein the second layer contains a chelating agent.

[0133] (Technology 6)

[0134] The electrode for a water electrolysis unit according to Technology 5, wherein the chelating agent contains at least one selected from the group consisting of acetylacetone and citrate.

[0135] (Technology 7)

[0136] The electrode for a water electrolysis unit according to any one of techniques 1 to 6,

[0137] The first transition metal is Ni,

[0138] The second transition metal is a transition metal selected from V, Cr, Mn, Fe, Co, Cu, W, and Ru.

[0139] (Technique 8)

[0140] The electrode for a water electrolysis unit according to technique 7, wherein the second transition metal is Fe.

[0141] (Technique 9)

[0142] A water electrolysis unit comprising an anode, a cathode, and a separator,

[0143] At least one selected from the anode and the cathode comprises the electrode for a water electrolysis unit according to any one of techniques 1 to 8.

[0144] (Technique 10)

[0145] A water electrolysis unit comprising an anode, a cathode, and a cation exchange membrane,

[0146] At least one selected from the anode and the cathode comprises the electrode for a water electrolysis unit according to any one of techniques 1 to 8.

[0147] (Technique 11)

[0148] A water electrolysis device comprising the water electrolysis unit according to technique 9 or 10, and a voltage applier that applies a voltage between the cathode and the anode.

[0149] (Technique 12)

[0150] A method for manufacturing an electrode for a water electrolysis unit, comprising the steps of:

[0151] promoting mixing of a solution in a state in which an electrically conductive substrate containing a first transition metal is immersed in the solution, the solution containing a second transition metal of a different kind from the first transition metal and chloride ions; and

[0152] forming a layer containing a layered double hydroxide on the electrically conductive substrate, the layered double hydroxide having the second transition metal and a third transition metal of a different kind from the second transition metal.

[0153] (Technique 13)

[0154] The method for manufacturing an electrode for a water electrolysis unit according to technique 12,

[0155] The solution further contains the third transition metal and a chelating agent.

[0156] (Technique 14)

[0157] The manufacturing method of an electrode for a water electrolysis unit according to any one of Techniques 12 to 14,

[0158] The third transition metal is a transition metal of the same kind as the first transition metal,

[0159] The solution further contains a chelating agent.

[0160] (Technique 15)

[0161] The manufacturing method of an electrode for a water electrolysis unit according to any one of Techniques 12 to 14,

[0162] The layer containing the layered double hydroxide is formed by adjusting the solution to be alkaline.

[0163] (Technique 16)

[0164] The manufacturing method of an electrode for a water electrolysis unit according to any one of Techniques 12 to 15,

[0165] The first transition metal is Ni,

[0166] The second transition metal is a transition metal selected from V, Cr, Mn, Fe, Co, Cu, W, and Ru.

[0167] (Technique 17)

[0168] The manufacturing method of an electrode for a water electrolysis unit according to Technique 16,

[0169] The second transition metal is Fe,

[0170] The molar ratio of the content of Fe ions to the content of Ni contained in the electrically conductive substrate is 0.75 or less.

[0171] (Technique 18)

[0172] The manufacturing method of an electrode for a water electrolysis unit according to Technique 17,

[0173] The molar ratio is 0.05 to 0.25.

[0174] (Technique 19)

[0175] The manufacturing method of an electrode for a water electrolysis unit according to Technique 16,

[0176] The second transition metal is Fe,

[0177] The value obtained by dividing the content of the Fe ions on a molar basis by the surface area of the electrically conductive substrate is 0.29 mmol / cm 2 The following.

[0178] (Technique 20)

[0179] The manufacturing method of the electrode for a water electrolysis unit according to Technique 19,

[0180] The value is 0.01 mmol / cm 2 ~0.1 mmol / cm 2 .

[0181] (Technique 21)

[0182] The manufacturing method of the electrode for a water electrolysis unit according to Technique 13 or 14,

[0183] The chelating agent includes at least one selected from acetylacetone and citrate.

[0184] Example

[0185] The present disclosure is further explained in detail by the following examples. Furthermore, the following examples are one example of the present disclosure, and the present disclosure is not limited to the following examples.

[0186] (Example 1)

[0187] A mixed solvent was prepared by mixing 6.688 milliliters (mL) of water and 10.032 mL of ethanol. The ethanol was purchased from FUJIFILM and Otsuka Pharmaceutical Co., Ltd. In the mixed solvent, the volume of water: the volume of ethanol = 2:3. A solution was prepared by dissolving 0.5685 g of nickel chloride hexahydrate and 0.3233 g of ferric chloride hexahydrate in the mixed solvent. The nickel chloride hexahydrate and the ferric chloride hexahydrate were purchased from FUJIFILM and Otsuka Pharmaceutical Co., Ltd. To the solution, 0.113 mL of acetylacetone (ACAC) was added as a chelating agent, to obtain a chelating agent-containing solution. The ACAC was purchased from Sigma-Aldrich Co. Ltd. The amount of substance of the ACAC in the chelating agent-containing solution was 1 / 3.25 of the total amount of substance of Ni ions and Fe ions. The chelating agent-containing solution was acidic.

[0188] Degreasing and impurity removal of the Ni mesh were performed by subjecting five Ni meshes manufactured by Nilaco Co., Ltd. to 10 minutes of acetone cleaning and 10 minutes of 1M HCl aqueous solution cleaning. The wire diameter of the Ni mesh was 0.1 mm, the mesh count of the Ni mesh was 60, and each of the Ni meshes was circular with a diameter of 15 mm in plan view. The total weight of the five Ni meshes was 0.281 g. Next, water washing and drying of the Ni mesh were performed, and the cleaning treatment of the Ni mesh was completed.

[0189] Next, the Ni mesh after the cleaning treatment was immersed in the above-mentioned chelate agent-containing solution. In this state, the chelate agent-containing solution with the Ni mesh was subjected to 24 hours of shaking agitation at 25°C. At this time, the surface of the Ni mesh was etched according to the formula of the above-mentioned formula (2). In this case, the molar ratio of the content of Fe ions to the content of Ni contained in the Ni mesh was 0.25. Further, the value obtained by dividing the content of Fe ions on a molar basis by the surface area of the Ni mesh was 0.0942 mmol / cm 2 The surface area of the Ni mesh was determined taking into account the geometry of the Ni mesh based on the wire diameter, mesh count, and diameter.

[0190] Next, 1.216 mL of propylene oxide (POX) was added as a pH raiser to the chelate agent-containing solution. The amount of POX added was adjusted so that the ratio of the amount of substance of POX to the amount of substance of chloride ions in the mixed solution would be 2. The resulting mixed solution was subjected to 72 hours of shaking agitation at 25°C. During the shaking agitation of the mixed solution, it is understood that POX slowly captures hydrogen ions in the mixed solution, the pH of the mixed solution gradually rises, and becomes alkaline. After 72 hours of shaking agitation, the Ni mesh was recovered, and water washing and drying of the Ni mesh were performed. In this way, the electrode relating to Example 1 was obtained.

[0191] (Example 2)

[0192] The electrode relating to Example 2 was produced in the same manner as in Example 1, except for the following points. In the preparation of the mixed solvent, 0.535 mL of water and 0.803 mL of ethanol were mixed. In the mixed solvent, the volume of water:volume of ethanol = 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 in the preparation of the chelate agent-containing solution was 0.009 mL, and the amount of substance of ACAC in the chelate agent-containing solution was 1 / 3.25 of the total amount of substance of Ni ions and Fe ions. Two pieces of nickel mesh were used, and the total mass of the two pieces of nickel mesh was 0.112 g. The molar ratio of the content of Fe ions to the content of Ni contained in the Ni mesh in the shaking agitation of the chelate agent-containing solution with the Ni mesh was 0.05. Further, the value obtained by dividing the content of Fe ions on a molar basis by the surface area of the Ni mesh was 0.0188 mmol / cm 2 .

[0193] (Example 3)

[0194] An electrode related to Example 3 was produced in the same manner as Example 1 except for the following points. In the preparation of the mixed solvent, 6.900 mL of water and 10.351 mL of ethanol were mixed. In the mixed solvent, the volume of water : the volume of ethanol = 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. The amount of ACAC added in the preparation of the chelate-containing solution was 1.164 mL, and the amount of substance of ACAC in the chelate-containing solution was 1 / 3.25 of the total amount of substance of Ni ions and Fe ions. Four pieces of Ni mesh were used, and the total mass of the four pieces of Ni mesh was 0.96 g. Each piece of Ni mesh was a square shape with a length of 20 mm on a side when viewed from above, and was single-edged. The amount of POX added to the chelate-containing solution was 12.545 mL. The molar ratio of the content of Fe ions in the oscillatory stirring of the chelate-containing solution with the Ni mesh to the content of Ni in the Ni mesh was 0.75. Furthermore, the value obtained by dividing the content of Fe ions on a molar basis by the surface area of the Ni mesh was 0.2844 mmol / cm2. 2 The amount of POX added was adjusted in such a manner that the ratio of the amount of substance of POX to the amount of substance of chloride ions in the mixed solution of the chelate-containing solution and POX became 2.

[0195] (Comparative Example 1)

[0196] A mixed solvent was prepared by mixing 6.900 mL of water and 10.351 mL of ethanol. The ethanol was purchased from FUJIFILM Wako Pure Chemical Corporation. In the mixed solvent, the volume of water : the volume of ethanol = 2 : 3. A solution was prepared by dissolving 5.8654 g of nickel chloride hexahydrate and 3.3351 g of iron chloride hexahydrate in the mixed solvent. The nickel chloride hexahydrate and the iron chloride hexahydrate were purchased from FUJIFILM Wako Pure Chemical Corporation. To the solution, 1.164 mL of acetylacetone (ACAC) as a chelating agent was added to obtain a chelate-containing solution. The ACAC was purchased from Sigma-Aldrich. The amount of substance of ACAC in the chelate-containing solution was 1 / 3.25 of the total amount of substance of Ni ions and Fe ions. The pH of the chelate-containing solution was 1.

[0197] A piece of Ni mesh manufactured by Nilaco was subjected to degreasing and impurity removal by acetone cleaning for 10 minutes and 1M aqueous HCl cleaning for 10 minutes. The wire diameter of the Ni mesh was 0.1 mm, the mesh count of the Ni mesh was 60, and the Ni mesh was a square shape with a length of 20 mm on a side when viewed from above, and was single-edged. The weight of the Ni mesh was 0.25 g. Next, the Ni mesh was subjected to water washing and drying, and the cleaning treatment of the Ni mesh was completed.

[0198] Next, the Ni mesh after the cleaning treatment was immersed in the above-mentioned chelating agent-containing solution. In this state, the chelating agent-containing solution with the Ni mesh put therein was subjected to oscillatory agitation for 24 hours at 25°C. At this time, the entire Ni mesh was etched and dissolved according to the formula of formula (2) above. Therefore, in Comparative Example 1, an electrode that could be evaluated could not be obtained. The molar ratio of the content of Fe ions to the content of Ni contained in the Ni mesh was 2.9. Further, the value obtained by dividing the content of Fe ions on a molar basis by the surface area of the Ni mesh was 1.0919 mmol / cm2. 2 .

[0199] (Comparative Example 2)

[0200] Five Ni meshes for which the cleaning treatment was completed in the same manner as in Example 1 were used as electrodes relating to Comparative Example 2.

[0201] (Comparative Example 3)

[0202] An electrode relating to Comparative Example 3 was produced in the same manner as in Example 1 except for the following point. The Ni mesh after the cleaning treatment was put into the above-mentioned chelating agent-containing solution, and then POX was immediately added to the chelating agent-containing solution. In other words, in Comparative Example 3, oscillatory agitation of the chelating agent-containing solution with the Ni mesh put therein was not performed before the addition of POX.

[0203] [Identification of the structure of the electrode and observation of the morphology]

[0204] Pickup processing of a sample for observation of the morphology was performed using a focused ion beam processing observation device (FIB) FB-2200 manufactured by Hitachi High-Technologies Co., Ltd. Next, using an FIB NX5000 manufactured by Hitachi High-Tech Science Co., Ltd., a sample for observation of the morphology was thinned to obtain a sample for observation of the morphology. The obtained sample was subjected to observation based on a transmission electron microscope (TEM) JEM-F200 manufactured by JEOL Ltd. and electron diffraction based on the TEM to perform identification of the structure of the electrode and observation of the morphology of the electrode relating to each of the examples and the comparative examples. The state of the LDH in the electrode relating to each of the examples and the comparative examples was evaluated in this way.

[0205] Figure 8 is a TEM image of the electrode relating to Example 1. Figure 9A is a TEM image showing a portion for which an electron diffraction result was obtained in the electrode relating to Example 1. Figure 9B is an electron diffraction image obtained by TEM for a portion of the electrode shown in Figure 9A As shown in Figure 8As shown, it is understood that a prescribed layer is formed on the surface of the Ni mesh. The layer has a thickness of 35 nm or more. As shown in Figure 9A and Figure 9B As shown, from the electron diffraction of the layer, the interplanar spacing of the lattice derived from the LDH, 0.14 nm, 0.19 nm, and 0.22 nm, were observed, and it was confirmed that the diffraction interference fringes coincided with (113), (015), and (012), respectively. Thus, it was confirmed that a layer containing the LDH was formed on the surface of the Ni mesh.

[0206] Line analysis by TEM-EDX was performed on the layer containing the LDH from the electrode involved in Example 1 toward the Ni mesh. Figure 10 is a graph showing the results of line analysis by TEM-EDX of the electrode involved in Example 1. In Figure 10 , the vertical axis shows the net count of Fe, O, and Ni, and the horizontal axis shows the distance from a specific point of the layer containing the LDH from which the line analysis was started. In Figure 10 , if the net count of Ni is focused on, it is understood that there is a point at which the net count of Ni starts to sharply rise, and as the line analysis proceeds, the region of the interface between the layer containing the LDH and the substrate is reached. From this point, in the range of a distance of about 5 nm, the net count of Ni rises and reaches a saturation point. In this range, if the net count of Fe is focused on, it is understood that in the range of a distance of 4 nm, the net count gradually decreases. It is thus shown that there is a layer of 4 nm in which Fe diffuses. On the other hand, if the spectrum of oxygen is focused on, it is understood that in the range of a distance of 5 nm, the net count gradually decreases. Thus, it is understood that Fe diffuses in the region of the interface between the layer containing the LDH and the substrate, and there are a layer containing Ni, Fe, and oxygen having a thickness of 4 nm, and a layer containing Ni and oxygen having a thickness of about 1 nm, which are present continuously. It is considered that the portion corresponding to the distance above the distance of the saturation point of the rise of the net count of Ni is the Ni mesh. From these results collectively, in the electrode involved in Example 1, there are, in order, a layer al containing the LDH having Ni and Fe, a layer a2 containing Ni, Fe, and oxygen, a natural oxidation film a3 of Ni, and a Ni mesh a4.

[0207] Figure 11 is a TEM image of the electrode involved in Comparative Example 3. Figure 12A is a TEM image showing a portion in which electron beam diffraction results were obtained in the electrode involved in Comparative Example 3. Figure 12B is an electron diffraction image obtained by TEM for the portion shown in Figure 12A . Figure 12B shows the results of electron beam diffraction obtained for the region indicated by a white dotted line in Figure 12A . As shown in Figure 11As shown, it can be understood that in the electrode involved in Comparative Example 3, LDH exists on a portion of the surface of the Ni mesh. On the other hand, in the electrode involved in Comparative Example 3, voids are generated between the LDH and the Ni mesh. It is believed that in Comparative Example 3, the reaction shown in Equation (2) above is difficult to occur, the Ni source for LDH synthesis is insufficient, and the synthesis of LDH is not fully carried out. In addition, it is believed that because the reaction of Equation (2) is not fully carried out, it is difficult to form an intermediate layer containing Ni, Fe and oxygen associated with Fe diffusion, and the LDH is not firmly fixed to the Ni mesh. As a result, it is believed that multiple voids are generated between the LDH and the Ni mesh.

[0208] like Figure 12A and Figure 12B As shown, interplanar spacings of 0.14 nm, 0.17 nm, 0.19 nm, and 0.22 nm from the LDH lattice were observed, and diffraction interference fringes consistent with (113), (110), (015), and (012) were confirmed. The presence of LDH on the surface of the Ni mesh was confirmed.

[0209] Linear TEM-EDX analysis was performed on the LDH-containing layer of the electrode involved in Comparative Example 3, directed toward the Ni mesh. Figure 13 This is a graph showing the results of TEM-EDX line analysis of the electrode involved in Example 1. In Figure 13 In the diagram, the vertical axis represents the net count of Fe, O, and Ni, and the horizontal axis represents the distance from the specific location in the LDH-containing layer where the line analysis began. Focusing on... Figure 13 The net Ni count reveals a point where its net count begins to increase sharply, reaching the region at the interface between the LDH-containing layer and the substrate as the line analysis progresses. The net Ni count continues to rise from this point. If the net Fe count is examined in this region, the presence of a layer containing Ni, Fe, and oxygen cannot be confirmed as in the electrode of Example 1. It can be understood that in the electrode of Example 1, there is a layer (native oxide film) b2 containing Ni and oxygen with a distance of approximately 2 nm between the LDH-containing layer b1 and the substrate b3. This result is considered to be consistent with... Figure 11 The LDH identified is related to multiple voids between the Ni mesh.

[0210] [Electrode Evaluation]

[0211] The oxygen evolution (OER) overvoltage of the electrodes involved in each of the examples and Comparative Examples 2 and 3 was evaluated. In the measurement, a potentiostat VersaSTAT4 manufactured by Princeton Applied Research, an alkaline sample bottle (200 mL) manufactured by BAS, a Teflon (registered trademark) cap (200 mL) manufactured by BAS, and a plate electrode AE-2 manufactured by EC-Frontier as a jig for a working electrode were used. The electrodes involved in each of the examples and Comparative Examples 2 and 3 as working electrodes were fixed to the jig. As a counter electrode, a double platinum wire counter electrode D.6.0305.200J manufactured by Metrohm was used. The current derived from the anode reaction of a water electrolysis cell was measured in a three-electrode system under the following measurement conditions. The anode reaction was an oxygen evolution reaction.

[0212] (Measurement conditions)

[0213] Solution: 1M KOH solution

[0214] Potential relative to a reversible hydrogen electrode (RHE): 1.0 V to 1.7 V

[0215] Number of cycles: 5 cycles

[0216] Potential scan rate: 10 mV / sec

[0217] Temperature: 25°C

[0218] The voltage corresponding to the current density of 10 mA / cm 2 The OER overvoltage was determined by subtracting the theoretical potential of 1.229 V required for the oxygen evolution reaction from the corresponding voltage. The results are shown in Table 1. In Table 1, the molar ratio of the content of Fe ions to the content of Ni contained in the Ni mesh in the production of the electrode, and the value obtained by dividing the content of Fe ions on a molar basis by the surface area of the Ni mesh are also shown. In addition, in Table 1, whether or not the electrode could be produced, the presence or absence of oscillatory stirring of the solution containing the chelating agent into which the Ni mesh was immersed before the POX addition, and the like are also shown.

[0219] Based on the following formula (3), the coverage ratio of the layer containing the LDH to the surface of the Ni mesh was determined from the results of the measurement for evaluating the OER overvoltage. The results are shown in Table 1. In formula (3), S NiOx is the integral value of the current density at a potential of 1.38 V to 1.48 V, S Ni is the integral value of the current density at a potential of 1.35 V to 1.38 V. The peak of the current density at a potential of 1.38 V to 1.48 V is derived from the hydroxide of nickel and iron, and the peak of the current density at a potential of 1.35 V to 1.38 V is derived from pure nickel.

[0220] Coverage = S NiOx / (S Ni + S NiOx ) x 100 Equation (3)

[0221] As shown in Table 1, the OER overvoltage of the electrode related to Examples 1 to 3 is lower than that of the electrode related to Comparative Example 2, and it is understood that the electrode has high electrode activity by virtue of the electrode having a layer containing LDH. On the other hand, according to the comparison between each of the examples and Comparative Example 1, when the molar ratio of the content of Fe ions to the content of Ni contained in the Ni mesh is large, the chemical reaction that dissolves Ni becomes intense, and the entire Ni mesh dissolves, and the electrode cannot be produced. Therefore, it is understood that the molar ratio of the content of Fe ions to the content of Ni contained in the Ni mesh is preferably 0.75 or less. Furthermore, it is understood that the value obtained by dividing the content of Fe ions on a molar basis by the surface area of the Ni mesh is preferably 0.29 mmol / cm 2 or more.

[0222] As shown in Table 1, the OER overvoltage of the electrode related to Examples 1 and 2 is particularly low. Therefore, it is suggested that the molar ratio of the content of Fe ions to the content of Ni contained in the Ni mesh is more preferably in the range of 0.05 to 0.25 from the viewpoint of electrode activity. Furthermore, it is suggested that the value obtained by dividing the content of Fe ions on a molar basis by the surface area of the Ni mesh is more preferably 0.01 mmol / cm 2 or more. 2 .

[0223] [Durability evaluation of electrode]

[0224] The OER overvoltage of the electrode related to Example 1 and Comparative Examples 2 and 3 was measured for 1000 cycles, and the durability of the electrode was evaluated. In the measurement, a potentiostat VersaSTAT4 manufactured by Princeton Applied Research, an alkaline sample bottle (200 mL) manufactured by BAS, a Teflon (registered trademark) cap (200 mL) manufactured by BAS, and a plate electrode AE-2 manufactured by EC-Frontier as a jig for a working electrode were used. The electrode related to Example 1 and Comparative Examples 2 and 3 as a working electrode was fixed to the jig. As a counter electrode, a double platinum wire counter electrode D.6.0305.200J manufactured by Metrohm was used. The current derived from the anode reaction of a water electrolysis unit was measured under the following measurement conditions using a three-electrode method. The anode reaction is an oxygen evolution reaction.

[0225] (Measurement conditions)

[0226] Solution: 1M KOH solution

[0227] Potential vs. RHE: 1.0 V to 1.7 V

[0228] Maximum cycle number: 1000 cycles

[0229] Potential scan rate: 100 mV / sec

[0230] Temperature: 25°C

[0231] Figure 14 is a graph showing the relationship between the OER overvoltage and the cycle number of the electrode involved in Example 1 and the electrodes involved in Comparative Examples 2 and 3. In this graph, the OER overvoltage per 50 cycles is shown. Each cycle simulates the start and stop of water electrolysis.

[0232] According to the comparison between Example 1 and Comparative Examples 2 and 3, in the electrode involved in Example 1, the OER overvoltage did not rise before the 50th cycle. On the other hand, in the electrodes involved in Comparative Examples 2 and 3, the OER overvoltage rose before the 50th cycle. Therefore, from the viewpoint of the durability of the electrode, it is important to promote the mixing of the solution in the state where the Ni mesh is immersed in the solution containing the chelating agent before the solution is adjusted to be basic, as in the oscillatory agitation of the solution containing the chelating agent with the Ni mesh.

[0233] Further, in light of the above description, many modifications and other embodiments of the present disclosure will be apparent to those skilled in the art from this disclosure. Therefore, the above description should not be construed as limiting, but merely as illustrative, and the present disclosure is provided for the purpose of teaching those skilled in the art the best way known to the inventors to make and use the present disclosure. Substantial equivalents of the operations, compositions, structures, and / or functions described herein can be substituted without departing from the true spirit of the present disclosure.

[0234]

[0235] Industrial Applicability

[0236] The electrode for water electrolysis unit of the present disclosure can be utilized as an anode or a cathode for water electrolysis.

Claims

1. An electrode for a water electrolysis unit, comprising a conductive substrate, a first layer, and a second layer, wherein the conductive substrate comprises a transition metal, the first layer comprises two or more transition metals and oxygen, and the second layer comprises a layered double hydroxide having two or more transition metals. The first layer is disposed between the conductive substrate and the second layer in the thickness direction of the first layer. The first layer comprises a first transition metal and a second transition metal, wherein the first transition metal is of the same type as the transition metal contained in the conductive substrate, and the second transition metal is of the same type as the transition metal contained in the second layer but a different type from the first transition metal. The concentration of the first transition metal in the first layer is higher than the concentration of the first transition metal in the second layer.

2. The electrode for a water electrolysis unit according to claim 1, wherein the conductive substrate has a porous structure.

3. The electrode for a water electrolysis unit according to claim 1 or 2, wherein the first layer has a thickness of less than 10 nm.

4. The electrode for a water electrolysis unit according to any one of claims 1 to 3, wherein the second layer has a thickness of 35 nm or more.

5. The electrode for a water electrolysis unit according to any one of claims 1 to 4, wherein the second layer comprises a chelating agent.

6. The electrode for a water electrolysis unit according to claim 5, wherein the chelating agent comprises at least one selected from acetylacetone and citrate.

7. The electrode for a water electrolysis unit according to any one of claims 1 to 6, The first transition metal is Ni. The second transition metal is selected from V, Cr, Mn, Fe, Co, Cu, W and Ru.

8. The electrode for the water electrolysis unit according to claim 7, wherein the second transition metal is Fe.

9. A water electrolysis unit comprising an anode, a cathode, and a diaphragm. The electrode selected from at least one of the anode and the cathode comprises the electrode for the water electrolysis unit as described in any one of claims 1 to 8.

10. A water electrolysis unit comprising an anode, a cathode, and an anion exchange membrane. The electrode selected from at least one of the anode and the cathode comprises the electrode for the water electrolysis unit as described in any one of claims 1 to 8.

11. A water electrolysis apparatus comprising the water electrolysis unit as described in claim 9 or 10, and a voltage applicator for applying a voltage between the cathode and the anode.

12. A method for manufacturing an electrode for a water electrolysis unit, comprising the following steps: The mixing of the solution is promoted while a conductive substrate containing a first transition metal is immersed in the solution, the solution containing a second transition metal of a different kind than the first transition metal and chloride ions; and A layer comprising a layered double hydroxide is formed on the conductive substrate, the layered double hydroxide having the second transition metal and a third transition metal of a different kind than the second transition metal.

13. The method for manufacturing electrodes for a water electrolysis unit according to claim 12 The solution also contains the third transition metal and a chelating agent.

14. The method for manufacturing electrodes for a water electrolysis unit according to claim 12. The third transition metal is a transition metal of the same kind as the first transition metal. The solution also contains a chelating agent.

15. A method for manufacturing electrodes for a water electrolysis unit according to any one of claims 12 to 14, A layer containing the layered double hydroxide is formed by adjusting the solution to alkalinity.

16. A method for manufacturing electrodes for a water electrolysis unit according to any one of claims 12 to 15, The first transition metal is Ni. The second transition metal is selected from V, Cr, Mn, Fe, Co, Cu, W and Ru.

17. The method for manufacturing electrodes for a water electrolysis unit according to claim 16, The second transition metal is Fe. The molar ratio of Fe ion content to Ni content in the conductive substrate is 0.75 or less.

18. The method for manufacturing electrodes for a water electrolysis unit according to claim 17, The molar ratio is 0.05~0.

25.

19. The method for manufacturing electrodes for a water electrolysis unit according to claim 16, The second transition metal is Fe. The value obtained by dividing the molar concentration of Fe ions by the surface area of ​​the conductive substrate is 0.29 mmol / cm². 2 the following.

20. The method for manufacturing electrodes for a water electrolysis unit according to claim 19, The value was 0.01 mmol / cm. 2 ~0.1mmol / cm 2 .

21. The method for manufacturing electrodes for a water electrolysis unit according to claim 13 or 14, The chelating agent comprises at least one selected from acetylacetone and citrate.

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