Method for manufacturing an electrode for water electrolysis

Abstract

This method for manufacturing a water electrolysis electrode 2 includes promoting mixing of a solution, which includes ions of a transition metal and chloride ions, in a state in which a conductive substrate 10 is immersed in the solution. In addition, the method for manufacturing the water electrolysis electrode 2 includes forming a layered double hydroxide layer 16 having two or more kinds of transition metals on the surface of the conductive substrate 10. The conductive substrate 10 has a mesh structure including a plurality of metal wires. The intersecting metal wires are joined to each other at intersections 3.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing an electrode for water electrolysis.

Background Art

[0002] Conventionally, electrodes for water electrolysis are known.

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

[0004] In Non-Patent Document 1, the activity of the oxygen evolution reaction (OER) of an electrode of Ni-Fe layered double hydride (Ni-Fe LDH) has been investigated.

[0005] Non-Patent Document 2 describes that the interfacial interaction between FeOOH and Ni-Fe LDH adjusts the local electronic structure of Ni-Fe LDH and enhances the OER electrode catalytic action.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Non-Patent Documents

[0007]

Non-Patent Document 1

[0008] The invention described in the above literature has room for reconsideration from the viewpoint of improving the performance of the electrode for water electrolysis. Therefore, the present disclosure provides a method for manufacturing an electrode for water electrolysis that is advantageous from the viewpoint of exhibiting excellent performance. [Means for Solving the Problems]

[0009] The present disclosure promotes the mixing of the solution in a state where a conductive substrate is immersed in a solution containing transition metal ions and chloride ions, and forms a layered double hydroxide layer having two or more types of transition metals on the surface of the conductive substrate, and the conductive substrate has a mesh structure including a plurality of metal wires, and the intersecting metal wires are joined to each other at the intersections, and provides a method for manufacturing an electrode for water electrolysis. [Effects of the Invention]

[0010] According to the present disclosure, a method for manufacturing an electrode for water electrolysis that is advantageous from the viewpoint of exhibiting excellent performance can be provided.

Brief Description of the Drawings

[0011]

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Figure 11B

Modes for Carrying Out the Invention

[0012] (Knowledge underlying the present disclosure) As a measure against global warming, the use of renewable energy such as sunlight and wind power has attracted attention. In power generation using renewable energy, a problem occurs in that surplus power is wasted. Therefore, the utilization efficiency of renewable energy is not always sufficient. Thus, a method of effectively utilizing surplus power by producing and storing hydrogen from surplus power has been studied.

[0013] As a method of producing hydrogen from surplus power, electrolysis of water is conceivable. In order to produce hydrogen inexpensively and stably, the development of a highly efficient and long-life water electrolysis device is required.

[0014] In a water electrolysis device, oxygen is generated at the anode and hydrogen is generated at the cathode. The reaction in which oxygen is generated at the anode is also called the anodic reaction, and the reaction in which hydrogen is generated at the cathode is also called the cathodic 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 desirable that the overvoltage at the cathode is also low. Therefore, the development of a high-performance electrode for the anodic reaction or cathodic reaction of water electrolysis is expected.

[0015] For example, layered double hydroxide (LDH) is considered promising as a material for an electrode for water electrolysis from the viewpoints of a large specific surface area and various combinations of metal ions. Patent Document 1 describes a method for producing an electrode for electrolysis of water including a layered double hydroxide represented by a predetermined composition formula by performing pulse electrodeposition treatment in an aqueous solution containing a compound containing a predetermined metal using a conductive substrate as an anode. On the other hand, the method for producing an electrode by pulse electrodeposition treatment described in Patent Document 1 is hardly simple.

[0016] The inventors have studied a method for manufacturing an electrode for water electrolysis by forming an LDH layer on a conductive substrate in a solution. In the method for manufacturing an electrode for water electrolysis found by the inventors, first, the conductive substrate is etched in a solution. Specifically, the metal contained in the conductive substrate elutes into the solution. Next, LDH is synthesized using the ions of the metal eluted into the solution and the ions of the metal that was present in the solution in advance, and an LDH layer is formed on the conductive substrate.

[0017] As the conductive substrate, candidates include a substrate having a non-porous structure such as a plate or a foil, and a substrate having a porous structure such as a mesh. A substrate having a non-porous structure such as a plate or a foil has a problem that it is difficult to increase the surface area of the substrate. On the other hand, a substrate having a porous structure such as a mesh has an advantage that the surface area of the substrate can be increased, and an advantage that the gas generated in the water electrolysis reaction diffuses easily.

[0018] The inventors have found a problem that when an electrode for water electrolysis is manufactured by the above-described manufacturing method using a conductive substrate having a mesh structure, it is difficult to improve the performance of the electrode for water electrolysis. In the above-described manufacturing method, when the conductive substrate is etched, the metal contained in the conductive substrate elutes into the solution. In a conductive substrate having a mesh structure, the metal contained in the metal wire constituting the conductive substrate elutes into the solution and the wire diameter of the metal wire decreases. For this reason, when a conductive substrate having a mesh structure is etched, a gap is generated between the metal wires at the intersection where the metal wires intersect. When a gap is generated between the metal wires, the contact resistance between the intersecting metal wires increases compared to before etching, so it is difficult to improve the performance of the electrode for water electrolysis. Further, even if an LDH layer is formed in the gap, generally, the conductivity of the LDH layer is lower than the conductivity of the metal wire, so the contact resistance between the intersecting metal wires increases and it is difficult to improve the performance of the electrode for water electrolysis. Based on this new finding, the inventors have completed the method for manufacturing an electrode for water electrolysis according to the present disclosure.

[0019] 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 each of the embodiments described below shows comprehensive or specific examples. Therefore, numerical values, shapes, materials, components, arrangement positions of components, connection forms, etc. shown in the following embodiments are merely examples and are not intended to limit the present disclosure. In addition, among the components in the following embodiments, components not described in the independent claims indicating the most general concept are described as optional components. Also, in the drawings, components with the same reference numerals may be omitted from the description. In addition, for ease of understanding, the drawings schematically show each component, and the shape, dimensional ratio, etc. may not be accurately shown.

[0020] (Embodiment) FIG. 1 is a flowchart showing an example of a method for manufacturing an electrode for water electrolysis. The electrode for water electrolysis obtained by the manufacturing method according to the present embodiment includes a conductive substrate and a layered double hydroxide (LDH) layer having two or more types of transition metals. The conductive substrate has a mesh structure including a plurality of metal wires. The LDH layer is formed on the surface of the conductive substrate. The LDH layer can function as a catalyst for the anodic reaction or cathodic reaction of water electrolysis.

[0021] As shown in FIG. 1, the method for manufacturing an electrode for water electrolysis includes step S10, step S11, and step S12. Step S10 is a step of preparing a solution. Step S11 is a step of immersing the conductive substrate in the solution. Step S12 is a step of promoting the mixing of the solution. As a result, in the solution, LDH is synthesized while the LDH layer is formed on the conductive substrate. As a result, an electrode for water electrolysis can be manufactured in the solution.

[0022] In step S10, a solution S is prepared. In step S10, a solution for synthesizing a layered double hydroxide is prepared.

[0023] Solution S contains ions of a first transition metal and chloride ions. The ions of the first transition metal include, for example, the ions of the transition metal contained in the layered double hydroxide described later. The ions of the first transition metal include, for example, at least one ion of a transition metal selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru. According to the layered double hydroxide containing these transition metals, an electrode for water electrolysis having more excellent electrode activity can be obtained.

[0024] The ions of the first transition metal contained in solution S preferably include at least one ion of a transition metal selected from the group consisting of Ni and Fe. In this case, an electrode for water electrolysis having more excellent electrode activity can be manufactured.

[0025] The ions of the first transition metal preferably include Fe ions. In this case, an electrode for water electrolysis having more excellent electrode activity and more excellent durability can be manufactured.

[0026] The solvent of solution S may be water, an organic solvent, or a mixed solvent of water and an organic solvent.

[0027] Solution S may contain a chelating agent. The chelating agent is, for example, an organic compound that coordinates with transition metal ions in a layered double hydroxide. 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 are β-diketones, β-ketoesters, hydroxycarboxylic acids, and hydroxycarboxylates. Examples of β-diketones are acetylacetone (ACAC), trifluoroacetylacetone, hexafluoroacetylacetone, benzoylacetone, thenoyltrifluoroacetone, dipyrovilmethane, dibenzoylmethane, and ascorbic acid. Examples of β-ketoesters are methyl acetoacetate, ethyl acetoacetate, allyl acetoacetate, benzyl acetoacetate, n-propyl acetoacetate, iso-propyl acetoacetate, n-butyl acetoacetate, iso-butyl acetoacetate, tert-butyl acetoacetate, 2-methoxyethyl acetoacetate, and methyl 3-oxopentanoate. Examples of hydroxycarboxylic acids and their salts are tartaric acid, citric acid, malic acid, gluconic acid, ferulic acid, lactic acid, glucuronic acid, and their salts. The chelating agent contained in solution S preferably contains at least one selected from the group consisting of acetylacetone and citrate. Thereby, the stability of the dispersion of the complex in solution S is increased, and the LDH layer is likely to be formed in a desired state on the electrode for water electrolysis. As a result, the electrode for water electrolysis can have more excellent electrode activity. An example of the citrate is trisodium citrate.

[0028] In step S11, the conductive substrate is immersed in solution S. In step S11, the metal contained in the conductive substrate is eluted into solution S.

[0029] By step S11, solution S and the conductive substrate react, and the conductive substrate is etched. Specifically, the ions of the first transition metal and chloride ions contained in solution S react with the conductive substrate. Thereby, the conductive substrate is etched by the ions of the first transition metal and chloride ions. As a result, the metal contained in the conductive substrate is eluted into solution S.

[0030] FIG. 2A is a perspective view schematically showing the conductive substrate 10. The conductive substrate 10 includes a plurality of metal wires. The plurality of metal wires have horizontal lines and vertical lines. As shown in FIG. 2A, the conductive substrate 10 has a plurality of horizontal lines 11 and a plurality of vertical lines 12. The conductive substrate 10 has a mesh structure formed by combining the plurality of horizontal lines 11 and the plurality of vertical lines 12. Thereby, since the conductive substrate 10 has a porous structure, the surface area of the conductive substrate 10 can be increased.

[0031] The conductive substrate 10 includes, for example, a plurality of first lines extending in a first direction and a plurality of second lines extending in a second direction. The first direction and the second direction are directions intersecting each other. The angle at which the first line and the second line intersect is not particularly limited and may be any angle. The first line is, for example, the horizontal line 11 shown in FIG. 2A. The second line is, for example, the vertical line 12 shown in FIG. 2A.

[0032] Each horizontal line 11 intersects a plurality of vertical lines 12. The horizontal line 11 intersects, for example, the first vertical line 12 and the second vertical line 12. The horizontal line 11 may intersect the first vertical line 12 above the first vertical line 12 and intersect the second vertical line 12 below the second vertical line 12. The first vertical line 12 and the second vertical line 12 may be two adjacent vertical lines.

[0033] Each vertical line 12 intersects a plurality of horizontal lines 11. The vertical line 12 intersects, for example, the first horizontal line 11 and the second horizontal line 11. The vertical line 12 may intersect the first horizontal line 11 above the first horizontal line 11 and intersect the second horizontal line 11 below the second horizontal line 11. The first horizontal line 11 and the second horizontal line 11 may be two adjacent horizontal lines.

[0034] The conductive substrate 10 may have a structure in which a plurality of metal wires are woven. The conductive substrate 10 may have a fabric structure in which the horizontal lines 11 and the vertical lines 12 are woven according to a certain rule. Thereby, the strength of the conductive substrate 10 can be improved.

[0035] Examples of the fabric structure of the conductive substrate 10 are plain woven wire mesh, twill woven wire mesh, and tabby woven wire mesh described in Japanese Industrial Standard (JIS) G3555:2004. In particular, since the conductive substrate 10 has the structure of plain woven wire mesh, it becomes possible to further increase the surface area of the conductive substrate 10, and the gas generated in the water electrolysis reaction easily diffuses.

[0036] FIG. 2B is a cross-sectional view schematically showing the conductive substrate 10 before etching. The conductive substrate 10 has horizontal lines 11 and vertical lines 12. The horizontal line 11 and the vertical line 12 intersect at an intersection 3. At the intersection 3, the horizontal line 11 and the vertical line 12 are joined to each other by a joint portion 13. As a result, at the intersection 3, the state where the horizontal line 11 and the vertical line 12 are fixed is maintained. As a result, the mechanical strength of the conductive substrate 10 is improved, and thus the mechanical strength of the water electrolysis electrode is also improved.

[0037] The conductive substrate 10 includes a plurality of metal wires. The metal wire contains a metal. The metal wire may contain a resin. The entire conductive substrate 10 may be composed of metal. The conductive substrate 10 may have a configuration in which a surface layer containing a metal is formed on a resin member such as polypropylene or polyethylene. In this case, the surface layer containing a metal can be an electroplated film or a sputtering 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.

[0038] The conductive substrate 10 contains, for example, a metal M that reacts with chloride ions and elutes in the solution S. The metal M contains, for example, a second transition metal. The second transition metal is a different type of transition metal from the first transition metal described above. That is, the conductive substrate 10 may contain a second transition metal that reacts with chloride ions and elutes in the solution S. In this case, for example, a water electrolysis electrode having advantageous characteristics from the viewpoint of achieving both corrosion resistance and conductivity in alkaline water electrolysis is easily manufactured.

[0039] The surface of the conductive substrate 10 is desirably made of nickel. In this case, the conductive substrate 10 is likely to have excellent alkali resistance. When the surface of the conductive substrate 10 is made of nickel, the entire conductive substrate 10 may be constituted by nickel, or the conductive substrate 10 may have a surface layer made of nickel. The surface layer made of nickel is a sputtering film or a plating film. When the surface of the conductive substrate 10 is made of nickel, for example, an electrode for electrolysis of water having advantageous characteristics from the viewpoint of achieving both corrosion resistance and conductivity in alkaline electrolysis of water is easily manufactured.

[0040] Examples of the method for forming the joint portion 13 include methods such as welding, sintering, and adhesion using a conductive paste material. The horizontal line 11 and the vertical line 12 may be welded using a filler metal containing at least one metal of the same type selected from the group consisting of the metals contained in the horizontal line 11 and the metals contained in the vertical line 12. The conductive paste material may contain at least one metal of the same type selected from the group consisting of the metals contained in the horizontal line 11 and the metals contained in the vertical line 12.

[0041] The conductive substrate 10 may join the horizontal line 11 and the vertical line 12 to each other by sintering. That is, the joint portion 13 may be formed by sintering. According to such a configuration, even when the horizontal line 11 and the vertical line 12 are etched in the solution S, the joining of the metal wires at the intersection is likely to be maintained. That is, even when the horizontal line 11 and the vertical line 12 are etched, a gap is less likely to occur between the horizontal line 11 and the vertical line 12, and the contact resistance between the intersecting metal wires is less likely to increase. Thereby, it is possible to suppress the conduction between the horizontal line 11 and the vertical line 12 from being impaired, and an electrode for electrolysis of water having excellent electrode activity can be obtained.

[0042] In the conductive substrate 10, not all intersections of the horizontal line 11 and the vertical line 12 need to be joined. In the conductive substrate 10, it is sufficient that at least one or more intersections of the horizontal line 11 and the vertical line 12 are joined.

[0043] The thickness of the conductive substrate 10 is not limited to a specific value. The thickness of the conductive substrate 10 is, for example, 0.02 mm or more. In this case, it is easier to handle the conductive substrate 10. The thickness of the conductive substrate 10 is, for example, 10 mm or less, preferably 1 mm or less.

[0044] FIG. 3 is a cross-sectional view schematically showing the conductive substrate 10A after etching. As described above, when the conductive substrate 10 is immersed in the solution S, the horizontal lines 11 and the vertical lines 12 are etched. When the conductive substrate 10 is immersed in the solution S, the metal contained in the horizontal lines 11 and the metal contained in the vertical lines 12 are eluted into the solution S. As a result, in the conductive substrate 10A after etching, the wire diameters of the horizontal lines 11a and the vertical lines 12a are each smaller than the wire diameters of the horizontal lines 11 and the vertical lines 12 in the conductive substrate 10 before etching. In the present embodiment, at the intersection 3 where the horizontal line 11 and the vertical line 12 intersect, the horizontal line 11 and the vertical line 12 are joined to each other by the joint portion 13. For this reason, even when the horizontal line 11 and the vertical line 12 are etched, the conductive substrate 10A has the joint portion 13a. As a result, even when the conductive substrate 10 is etched, the connection between the horizontal line 11a and the vertical line 12a is maintained. Thereby, it is difficult for a gap to occur between the horizontal line 11a and the vertical line 12a, and it is difficult for the contact resistance between the intersecting metal wires to increase. In addition, the conduction between the horizontal line 11a and the vertical line 12a is suppressed from being impaired, and the mechanical strength of the conductive substrate 10A is further improved.

[0045] Next, in step S12, the mixing of the solution S is promoted. In step S12, an LDH layer is formed on the conductive substrate to obtain an electrode for electrolysis of water.

[0046] By promoting the mixing of the solution S, in the solution S, the conductive substrate 10 is etched and an LDH layer is formed on the conductive substrate.

[0047] As a method for promoting the mixing of solution S, there may be mentioned vibrating the conductive substrate 10, shaking the container in which the solution S and the conductive substrate 10 are enclosed, stirring the solution S using a stirrer piece and a stirrer, and the like. According to such a method, forced convection of the solution S occurs, and the mixing of the solution S is promoted. The promotion of the mixing of the solution S may be performed in a state where the container containing the solution S and the conductive substrate 10 is sealed, or may be performed in an inert gas atmosphere.

[0048] "Promote the mixing of solution S" means promoting the diffusion of the ions of metal M eluted from the conductive substrate 10 into the solution S by the method described above.

[0049] The solution S preferably contains Fe ions as ions of the first transition metal. The conductive substrate 10 preferably contains nickel as the metal M. In this case, in step S12, the reaction represented by formula (1) occurs. As a result, the conductive substrate 10 is etched and an LDH layer is formed on the etched conductive substrate 10A. As a result, the electrode for water electrolysis tends to have excellent durability.

[0050] 4Ni 2+ Cl - 2+ 2Fe 3+ Cl - 3+ 2Ni→5Ni 2+ Cl - 2+ 2Fe 2+ Cl - 2+ Ni Formula (1)

[0051] In step S12, the temperature of the solution S is not limited to a specific temperature. The temperature of the solution S is, for example, 20°C ± 15°C. In this case, an electrode for water electrolysis having excellent electrode activity can be obtained.

[0052] FIG. 4 is a cross-sectional view schematically showing the electrode 2 for water electrolysis. The electrode 2 for water electrolysis includes the conductive substrate 10A after etching and the LDH layer 16. Specifically, the electrode 2 for water electrolysis includes the horizontal line 11a and the vertical line 12a, and the LDH layer 16. The LDH layer 16 is formed on the surface of the conductive substrate 10A. Specifically, the LDH layer 16 is formed on the horizontal line 11a and the vertical line 12a. The LDH layer 16 contains a layered double hydroxide (LDH) as a catalyst for water electrolysis. The horizontal line 11a and the vertical line 12a are joined to each other by the joint portion 13a at the intersection 3a. According to such a configuration, even when the LDH layer 16 is formed on the metal wire, the conduction between the horizontal line 11a and the vertical line 12a is hardly impaired. That is, the contact resistance between the horizontal line 11a and the vertical line 12a hardly increases. As a result, the electrode activity of the electrode 2 for water electrolysis is likely to be improved, and the electrode 2 for water electrolysis is likely to exhibit excellent performance.

[0053] The LDH layer 16 can function as a catalyst for the anodic reaction or cathodic reaction of water electrolysis. The LDH layer 16 is, for example, joined to the conductive substrate 10A. For example, an adhesive layer containing an organic material such as a polymer is not disposed between the LDH layer 16 and the conductive substrate 10A, and the LDH layer 16 is directly joined to the surface of the conductive substrate 10A.

[0054] FIG. 5 is a diagram schematically showing an example of the crystal structure of a layered double hydroxide. The layered double hydroxide (LDH) 20 is active with respect to the gas generation reaction such as hydrogen and oxygen in the anode or cathode of a water electrolysis cell. For example, in alkaline water electrolysis, the LDH 20 can be changed to a hydroxide by a water electrolysis reaction.

[0055] The LDH 20 has, for example, a composition represented by the following formula (2). In formula (2), M1 2+ is a divalent transition metal ion. M2 3+ is a trivalent transition metal ion. A n- is an interlayer anion. x is a rational number satisfying the condition 0 <x <1. y is a number corresponding to the required amount of charge balance. n is an integer. m is an appropriate rational number.

[0056] [M1 2+ 1-x M2 3+ x (OH)2][yA n- ·mH2O] of formula (2)

[0057] LDH20 has two or more transition metals. The two or more transition metals in LDH20 are not limited to specific transition metals. In other words, M1 and M2 in the composition shown in formula (2) 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 electrode 2 for water electrolysis is more likely to have excellent electrode activity.

[0058] The two or more transition metals in LDH20 preferably include at least one selected from the group consisting of Ni and Fe. In this case, the electrode for water electrolysis is more likely to have excellent electrode activity. In addition, the manufacturing cost of the electrode for water electrolysis is likely to be low.

[0059] The two or more transition metals in LDH20 include Ni and Fe. For example, in the composition shown in formula (2), M1 may be Ni and M2 may be Fe. In this case, the electrode for water electrolysis is more likely to have excellent electrode activity.

[0060] Anion A between layers n- may be an inorganic ion or an organic ion. Examples of inorganic ions are CO3 2- NO3 - Cl - SO4 2- Br - OH - F - I - Si2O5 2- B4O5(OH)4 2- and PO4 3- is. Examples of organic ions are CH3(CH2) n SO4 - CH3(CH2) nCOO - 、 CH3(CH2) n PO4 2- 、 and CH3(CH2) n NO3 - is. A n- can be inserted between the layers of the metal hydroxide together with water molecules. A n- The charge and size of the ions are not limited to specific values. LDH20 may contain one type of A n- or may contain multiple types of A n- .

[0061] As shown in FIG. 5, LDH20 has OH 2+ or M2 3+ ions at each vertex of the octahedron centered on. In LDH20, [M1 - 2+ 1-x M2 3+ x (OH)2] x+ contains the metal hydroxide represented by. This metal hydroxide has a layered structure in which the octahedrons of the hydroxide share edges and are connected two-dimensionally. Between the layers of the metal hydroxide, there are anions A n- and water molecules. The layer of the metal hydroxide functions as the host layer 21, and the guest layer 22 containing the anion A n- and water molecules is arranged between the host layers 21. In other words, LDH20 as a whole has a sheet-like structure in which the host layer 21 of the metal hydroxide and the guest layer 22 of the anion A n- and water molecules are alternately stacked. LDH20 has a structure in which a part of M1 2+ contained in the layer of the metal hydroxide is replaced by M2 3+ .

[0062] ​The LDH layer 16 may contain a chelating agent. The chelating agent is, for example, the chelating agent contained in the solution S. The chelating agent may coordinate with the transition metal ions contained in the LDH 20. Thereby, the LDH 20 is stably present in the LDH layer 16. In addition, the LDH 20 is easily synthesized to have a small particle size. In addition, the LDH 20 nucleated on the conductive substrate easily grows slowly in crystal. For this reason, the dense LDH layer 16 with few voids containing the LDH 20 is likely to have a desired thickness with respect to the conductive substrate and be firmly fixed. Thereby, the LDH layer 16 is likely to effectively contribute to the anodic reaction or the cathodic reaction, and the electrode for water electrolysis is likely to have excellent electrode activity.

[0063] FIG. 6 is a flowchart showing another example of a method for manufacturing an electrode for water electrolysis.

[0064] The method for manufacturing an electrode for water electrolysis may include step S13. Step S13 is a step of adjusting the solution S to be alkaline. In step S13, an LDH layer is formed on the conductive substrate to obtain an electrode for water electrolysis. Step S13 is carried out after step S12.

[0065] By step S13, an LDH layer containing a layered double hydroxide is formed. The LDH layer containing the layered double hydroxide is formed on the conductive substrate.

[0066] The method for adjusting the solution S to be alkaline is not limited to a specific method. For example, the solution may be adjusted to be alkaline by mixing the above solution S and an alkaline solution. Alternatively, a pH increasing agent may be added to the above solution to adjust the solution to be alkaline. In this case, the pH increasing agent is not limited to a specific compound. The pH increasing agent is, for example, a compound having an epoxy group. Examples of the pH increasing agent are propylene oxide, ethylene oxide, and butylene oxide.

[0067] When a pH increasing 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, hydrogen ions present in the solution S can be captured by the pH increasing agent along with the ring-opening reaction of the epoxy group. As a result, the pH of the solution S increases and the solution S becomes alkaline. The pH of the solution S is, for example, 1. When the pH increasing agent is added to this solution S, the pH of the solution S gradually increases from, for example, 1, and finally the solution S becomes alkaline. The final pH of the solution S is, for example, 8 or more and 12 or less. By adding the pH increasing agent to the solution, the reaction in which hydrogen ions in the solution S are supplemented proceeds. As a result, the pH of the solution S gradually increases. The time from the addition of the pH increasing agent to the solution S until the pH of the solution S reaches a steady state is not limited to a specific time. That time is, for example, 24 hours or more and can be several days.

[0068] The temperature of the solution S when adjusting the solution S to be alkaline is not limited to a specific temperature. The temperature of the solution S is, for example, normal temperature 20°C ± 15°C. In this case, it is easy to obtain an electrode for water electrolysis having excellent electrode activity.

[0069] Step S13 desirably includes increasing the pH. Thereby, a layered double hydroxide can be formed on the conductive substrate in a short period of time, and it is easy to obtain an electrode for water electrolysis having excellent electrode activity. In addition, the manufactured electrode for water electrolysis is likely to have excellent durability.

[0070] Next, the mechanism for manufacturing the electrode for water electrolysis in the solution S will be described.

[0071] FIG. 7 is a diagram schematically showing a mechanism for manufacturing an electrode for water electrolysis. As shown in FIG. 7, a conductive substrate 10 is immersed in a solution S containing ions TM1 of a first transition metal and a chelating agent 30. The solution S may contain ions TM2 of a second transition metal. For example, the ions TM1 of the first transition metal are iron ions, and the ions TM2 of the second transition metal are nickel ions. In addition, nickel, for example, is present on the surface of the conductive substrate 10. A part of the ions TM1 of the first transition metal etches and elutes the nickel present on the surface of the conductive substrate 10. In addition, a part of the chelating agent 30 reacts with the conductive substrate 10, and a complex C2 of the ions TM2 of the second transition metal derived from the conductive substrate 10 and the chelating agent 30 is formed. Thereby, a conductive substrate 10A after etching is produced.

[0072] When the solution S is adjusted to be alkaline, in the solution S, a complex C1 of the ions TM1 of the first transition metal derived from the solution S and the chelating agent 30 is formed. In addition, when the ions TM2 of the second transition metal are contained in the solution S, a complex C2 of the ions TM2 of the second transition metal and the chelating agent 30 is also formed. Next, the complexes C1 and C2 react on the surface of the conductive substrate 10A, and LDH20 is synthesized along the surface of the conductive substrate 10A. Since the complexes C1 and C2 contain the chelating agent 30, crystal growth of LDH20 is suppressed. Thereby, an LDH layer containing LDH20 and the chelating agent 30 is formed on the conductive substrate 10A, and an electrode for water electrolysis is obtained.

[0073] The electrode 2 for water electrolysis according to the present embodiment can be used, for example, as an electrode of a water electrolysis cell of an alkaline water electrolysis device or an anion exchange membrane type water electrolysis device. The electrode 2 for water electrolysis is used, for example, in at least one selected from the group consisting of an anode and a cathode in these water electrolysis devices. Thereby, the activity of the anodic reaction or cathodic reaction of water electrolysis is likely to be increased.

[0074] (Supplementary Note) From the above description, the following techniques are disclosed.

[0075] (Technology 1) Promoting the mixing of the solution while immersing a conductive substrate in a solution containing transition metal ions and chloride ions; forming a layered double hydroxide layer having two or more transition metals on the surface of the conductive substrate, including; The conductive substrate has a mesh structure including a plurality of metal wires, and the intersecting metal wires are joined to each other at intersections. A method for manufacturing an electrode for water electrolysis.

[0076] According to Technology 1, a method for manufacturing an electrode for water electrolysis that is advantageous from the viewpoint of exhibiting excellent performance can be provided.

[0077] (Technology 2) The method for manufacturing an electrode for water electrolysis according to Technology 1, wherein the conductive substrate contains a metal that reacts with the chloride ions and elutes from the conductive substrate. According to such a configuration, an electrode for water electrolysis having advantageous characteristics from the viewpoint of achieving both corrosion resistance and conductivity in alkaline water electrolysis can be easily manufactured.

[0078] (Technology 3) The method for manufacturing an electrode for water electrolysis according to Technology 1 or 2, wherein the metal wires are joined to each other at the intersections by sintering. According to such a configuration, even when the conductive substrate is etched, the joining of the metal wires at the intersections is likely to be maintained.

[0079] (Technology 4) The method for manufacturing an electrode for water electrolysis according to any one of Technologies 1 to 3, wherein the plurality of metal wires are woven. According to such a configuration, the strength of the conductive substrate can be improved.

[0080] (Technology 5) The method for manufacturing an electrode for water electrolysis according to any one of Technologies 1 to 4, wherein the transition metal ions contain ions of at least one transition metal selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru.

[0081] (Technology 6) The method for manufacturing an electrode for water electrolysis according to any one of Technologies 1 to 5, wherein the ions of the transition metal include ions of at least one transition metal selected from the group consisting of Ni and Fe.

[0082] According to Technologies 5 and 6, an electrode for water electrolysis having more excellent electrode activity can be manufactured.

Examples

[0083] Hereinafter, the present disclosure will be described in more detail 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.

[0084] (Example 1) 4.1880 g of nickel chloride hexahydrate and 2.3813 g of iron chloride hexahydrate were dissolved in 123.175 milliliters (mL) of water to prepare a solution. Nickel chloride hexahydrate and iron chloride hexahydrate were purchased from Fujifilm Wako Pure Chemical Corporation. To this solution, 0.831 mL of acetylacetone (ACAC) was added as a chelating agent to obtain a chelating agent-containing solution. ACAC was purchased from Fujifilm Wako Pure Chemical Corporation. The amount of substance of 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.

[0085] The Ni mesh sintered body manufactured by Fuji Filter Kogyo Co., Ltd. was washed with acetone for 10 minutes and washed with a 0.1 mol / liter (mol / L) aqueous HCl solution for 10 minutes to degrease the Ni mesh and remove impurities. In the Ni mesh according to Example 1, the wire diameter of the Ni mesh was 0.1 mm. The mesh number of the Ni mesh was 30. The steel type of the Ni mesh was Ni200. The Ni mesh was a rectangle having a size of 120 mm × 50 mm in plan view. The total weight of the Ni mesh was 2.1444 g. Next, the Ni mesh was washed with water and dried to complete the washing process of the Ni mesh.

[0086] Figure 8 is a scanning electron microscope (SEM) image of a cross-section of a Ni mesh sintered body before etching according to Example 1. As shown in Figure 8, the Ni mesh sintered body before etching had horizontal lines 11 and vertical lines 12. In addition, in the Ni mesh sintered body, the horizontal line 11 and the vertical line 12 intersected at the intersection 3. Further, at this intersection 3, the horizontal line 11 and the vertical line 12 were joined to each other by the joint portion 13.

[0087] Next, the Ni mesh after the cleaning process was immersed in the above chelating agent-containing solution. In this state, the chelating agent-containing solution containing the Ni mesh was shaken and stirred at about 20 °C for 24 hours. At this time, according to the formula of the above formula (1), the outermost surface of the Ni mesh was etched.

[0088] Next, as a pH increasing agent, 8.957 mL of propylene oxide (POX) was added to the chelating agent-containing solution. The addition amount of POX 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 became 2. The obtained mixed solution was shaken and stirred at about 20 °C for 72 hours. In the shaking and stirring of the mixed solution, it was understood that POX gradually captured the 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, and the Ni mesh was washed with water and dried. In this way, the electrode according to Example 1 was obtained.

[0089] (Comparative Example 1) An electrode according to Comparative Example 1 was produced in the same manner as in Example 1, except that a Ni mesh manufactured by Company X was used. The Ni mesh according to Comparative Example 1 was a non-sintered body. That is, in the Ni mesh according to Comparative Example 1, the intersecting metal wires were not joined to each other at the intersection. In the Ni mesh according to Comparative Example 1, the wire diameter of the Ni mesh was 0.1 mm. The mesh number of the Ni mesh was 30. The steel type of the Ni mesh was Ni200. The Ni mesh was a rectangle having a size of 120 mm × 50 mm in plan view.

[0090] [Evaluation of Electrode] The oxygen evolution (OER) overvoltage of the electrode according to Example 1 and the electrode according to Comparative Example 1 was evaluated. For the measurement, a potentiostat VersaSTAT4 manufactured by Princeton Applied Research, an alkali sample vial (100 mL) manufactured by BAS, and a Teflon cap (for 100 mL) manufactured by BAS were used. A plate electrode AE-2 manufactured by EC Frontier was used as a jig for the working electrode. The material of this plate electrode was Ni. The electrode according to Example 1 and the electrode according to Comparative Example 1, which are working electrodes, were fixed to this jig. A Pt counter electrode 23 cm long manufactured by BAS was used as a counter electrode. The counter electrode was in a coil shape. The current derived from the anode reaction of the water electrolysis cell was measured by the three-electrode method under the following measurement conditions. The anode reaction was an oxygen evolution reaction. In Example 1 and Comparative Example 1, a sample cut into a circular shape with a diameter of 15 mm from the electrode prepared by the above method was used as the working electrode.

[0091] (Measurement conditions) Solution: 1mol / L KOH solution Potential vs. reversible hydrogen electrode (RHE): 1.0V to 1.7V Number of cycles: 5 cycles Potential sweep speed: 10mV / sec Temperature: 20℃ Number of measurement samples: 5

[0092] Current density at 5th cycle: 10mA / 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 above. The results are shown in Table 1. In Example 1 and Comparative Example 1, the number of measurement samples was five. The average overpotential and standard deviation shown in Table 1 are the average value and standard deviation of the OER overpotential for the five measurement samples, respectively.

[0093] [Table 1]

[0094] As shown in Table 1, the average overpotential of OER in the electrode according to Example 1 was lower than that in the electrode according to Comparative Example 1. This result indicates that the conductive substrate used in Example 1 is excellent from the viewpoint of electrode activity. In addition, the standard deviation of the average overpotential of OER in the electrode according to Example 1 was lower than that of the average overpotential of OER in the electrode according to Comparative Example 1. This result indicates that the conductive substrate used in Example 1 is excellent from the viewpoint of suppressing the variation in the quality of the electrode.

[0095] Figure 9 is a graph showing the measurement results of the OER overpotential of the electrode according to Example 1 and the electrode according to Comparative Example 1. In Figure 9, the vertical axis represents the current density, and the horizontal axis represents the potential with respect to the reversible hydrogen electrode. As shown in Figure 9, when the current density of the electrode according to Example 1 and the current density of the electrode according to Comparative Example 1 are the same value, the electrode according to Example 1 has a lower overpotential than the electrode according to Comparative Example 1. This result indicates that the electrode activity of the electrode according to Example 1 is higher than that of the electrode according to Comparative Example 1.

[0096] Figure 10A is a photograph of the electrode after measuring the OER overpotential using the electrode according to Example 1. Figure 10B is an enlarged photograph of the X part of Figure 10A. As shown in Figure 10A and Figure 10B, in the electrode according to Example 1, the entire surface of the electrode after measurement had changed color to black. This indicates that Ni-Fe LDH had changed to a hydroxide by the water electrolysis reaction. That is, in Example 1, since the intersecting metal wires were joined to each other at the intersection points in the conductive substrate, even after the electrode was fabricated, the contact resistance between the intersecting metal wires was unlikely to increase, suggesting that conduction was ensured between the intersecting metal wires.

[0097] FIG. 11A is a photograph of an electrode after measuring the OER overvoltage using the electrode according to Comparative Example 1. FIG. 11B is an enlarged photograph of the Y portion of FIG. 11A. As shown in FIGS. 11A and 11B, in the electrode according to Comparative Example 1, a part of the electrode after measurement did not change color to black. This suggests that in the electrode according to Comparative Example 1, in the conductive base material, the intersecting metal wires were not joined to each other at the intersection points, so after manufacturing the electrode, the contact resistance between the intersecting metal wires increased and conduction was not ensured between the intersecting metal wires.

[0098] From the above description, many improvements and other embodiments of the present disclosure will be apparent to those skilled in the art. Therefore, the above description should be construed as illustrative only and provided for the purpose of teaching those skilled in the art the best mode of carrying out the present disclosure. Without departing from the spirit of the present disclosure, its operating conditions, composition, structure, and / or function can be substantially changed.

Industrial Applicability

[0099] The water electrolysis electrode obtained by the method for manufacturing a water electrolysis electrode of the present disclosure can be used as an anode or a cathode for water electrolysis.

Claims

1. promoting the mixing of the solution while immersing a conductive substrate in a solution containing transition metal ions and chloride ions; forming a layered double hydroxide layer having two or more transition metals on the surface of the conductive substrate, wherein the conductive substrate has a mesh structure including a plurality of metal wires, and the intersecting metal wires are joined to each other at intersections, wherein the plurality of metal wires are woven, wherein the conductive substrate contains a metal that reacts with the chloride ions and elutes from the conductive substrate, A method for manufacturing an electrode for water electrolysis.

2. The method for manufacturing an electrode for water electrolysis according to claim 1, wherein the metal wires are joined to each other at the intersections by sintering.

3. The method for manufacturing an electrode for water electrolysis according to claim 1, wherein the transition metal ions include ions of at least one transition metal selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, W, and Ru.

4. The method for manufacturing an electrode for water electrolysis according to claim 1, wherein the transition metal ions include ions of at least one transition metal selected from the group consisting of Ni and Fe.

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