Catalyst for hydrogen generation reaction, liquid composition containing catalyst for hydrogen generation reaction, electrode including catalyst for hydrogen generation reaction, and water electrolysis device comprising electrode

Abstract

Provided are: a catalyst for a hydrogen generation reaction, the catalyst having extremely high catalytic ability in a hydrogen generation reaction and not utilizing any rare metal; a liquid composition or an electrode that contains the catalyst for a hydrogen generation reaction; and a water electrolysis device comprising the electrode. Provided are a catalyst for a hydrogen generation reaction containing an electroconductive material and a metal complex having a specific structure, a liquid composition containing the catalyst for a hydrogen generation reaction, an electrode including the catalyst for a hydrogen generation reaction, and a water electrolysis device comprising the electrode.

Description

Catalyst for hydrogen generation reaction, liquid composition containing catalyst for hydrogen generation reaction, electrode containing catalyst for hydrogen generation reaction, and water electrolysis device equipped with electrode

[0001] The present invention relates to a catalyst for a hydrogen generation reaction, a liquid composition containing the catalyst for a hydrogen generation reaction, an electrode containing the catalyst for a hydrogen generation reaction, and a water electrolysis device including the electrode.

[0002] In response to the recent worsening of environmental and energy problems, hydrogen is expected to be utilized as a new renewable energy source. For example, hydrogen engines that run directly on hydrogen as fuel and fuel cells that generate electricity using hydrogen as fuel are being developed and put into practical use. In this context, the hydrogen evolution reaction (HER reaction) has attracted attention as one of the hydrogen production technologies.

[0003] Typical catalysts used in hydrogen generation reactions are mainly rare metals such as platinum and rare metal complex catalysts. However, rare metals such as platinum are expensive and their resources are limited, so attempts have been made to develop catalysts using cheaper, more abundant materials. For example, Patent Document 1 discloses alloy fine particles with transition metals in order to reduce the amount of platinum used. However, the technology disclosed in Patent Document 1 requires the use of platinum, and is therefore not sufficient to solve the resource depletion problem.

[0004] On the other hand, Patent Document 2 discloses chalcogenide fine particles that do not use precious metals. However, the technology disclosed in Patent Document 2 involves a high-temperature calcination process during catalyst production, which requires high energy costs and is therefore unsuitable for mass production.

[0005] Non-Patent Document 1 reports a catalyst production method using catalyst molecules having a cobalt phthalocyanine skeleton and its hydrogen generation ability. However, the technology disclosed in Non-Patent Document 1 destroys the phthalocyanine skeleton through a high-temperature calcination process during the catalyst production process, which still requires high energy costs.

[0006] JP 2019-141792 A JP 2022-133863 A

[0007] International Journal of Hydrogen Energy, Volume 46, Issue 37, 19338-19346, 2021

[0008] The present invention has been made to solve the above-mentioned problems of the conventional art, and aims to provide a catalyst for a hydrogen generation reaction that has extremely high catalytic activity in a hydrogen generation reaction and does not use rare metals, a liquid composition or electrode containing the catalyst for a hydrogen generation reaction, and a water electrolysis device including the electrode.

[0009] As a result of intensive research into the above-mentioned problems, the present inventors unexpectedly found that by using a catalyst comprising a metal complex having a specific chemical structure and a conductive material, the catalyst has excellent catalytic ability for a hydrogen generation reaction, and thus arrived at the present invention. That is, in order to solve the above-mentioned problems, one aspect of the present invention includes the following aspects.

[0010] [1] A catalyst for a hydrogen generation reaction, comprising a metal complex and a conductive material, wherein the metal complex is represented by the following formula (1): (wherein M is a metal atom; A1 to A4 each independently represent a ring structure; at least one of A1 to A4 contains one or more nitrogen atoms as ring-constituting atoms; and each of the ring structures of A1 to A4 may have a substituent bonded thereto).

[0011] [2] The catalyst for hydrogen generation reaction according to [1], wherein M is an iron atom, a cobalt atom, or a nickel atom.

[0012] [3] The catalyst for hydrogen generation reaction according to [1] or [2], wherein A1 to A4 each independently represent a monocyclic structure or a fused ring structure in which two or three rings are fused.

[0013] [4] The metal complex is represented by the following formula: The catalyst for hydrogen generation reaction according to any one of [1] to [3], represented by the formula:

[0014] [5] The catalyst for hydrogen generation reaction according to any one of [1] to [4], wherein the metal complex is contained in an amount of 75 mass% or less relative to 100 mass% of the total amount of the metal complex and the conductive material.

[0015] [6] The catalyst for hydrogen generation reaction according to any one of [1] to [5], wherein the conductive material is a carbon material or a metal oxide.

[0016] [7] A liquid composition comprising the catalyst for hydrogen generation reaction according to any one of [1] to [6].

[0017] [8] An electrode comprising the catalyst for hydrogen generation reaction according to any one of [1] to [6].

[0018] [9] An electrode comprising the catalyst for hydrogen generation reaction according to any one of [1] to [6] supported on a carbon sheet or nickel foam.

[0019]

[10] An electrode comprising a metal complex supported on a carbon sheet or nickel foam, the metal complex having the following formula (1): (wherein M is a metal atom; A1 to A4 each independently represent a ring structure; at least one of A1 to A4 contains one or more nitrogen atoms as ring-constituting atoms; and a substituent may be bonded to each of the ring structures of A1 to A4.)

[0020]

[11] A water electrolysis device comprising the electrode according to any one of [8] to

[10] .

[0021] According to the present invention, the hydrogen generation reaction can be carried out with high efficiency by using a catalyst containing a metal complex having a specific structure and a conductive material.

[0022] Furthermore, the present invention can provide an excellent catalytic ability for the hydrogen generation reaction without using rare metals such as platinum, and therefore can provide a catalyst for the hydrogen generation reaction in a water electrolysis device at a relatively low cost.

[0023] Graph showing an example of the results of LSV measurement using RRDE. Graph showing an example of the results of overvoltage measurement using a water electrolysis cell.

[0024] Hereinafter, a mode for carrying out the present invention (hereinafter also simply referred to as "embodiment") will be described in detail. The embodiment is an example for explaining the present invention, and the present invention is not limited to only the embodiment. In other words, the present invention can be modified in various ways without departing from the gist of the present invention.

[0025] [Catalytic ability for hydrogen generation reaction] The catalyst for hydrogen generation reaction of the present invention contains a metal complex and a conductive material. Only one type of metal complex can be used, or two or more types of metal complexes can be used in combination. The metal complex is represented by the following formula (1): (wherein M is a metal atom; A1 to A4 each independently represent a ring structure; at least one of A1 to A4 contains one or more nitrogen atoms as ring-constituting atoms; and a substituent may be bonded to each of the ring structures of A1 to A4).

[0026] The bond between a nitrogen atom and M means that the nitrogen atom is coordinated to M. A halogen atom, a hydroxyl group, or a hydrocarbon group having 1 to 8 carbon atoms may further be bonded to M as a ligand. In addition, an anionic counter ion may be present to make M electrically neutral.

[0027] The valence of M is not particularly limited. A halogen atom, a hydroxyl group, or an alkyloxy group having 1 to 8 carbon atoms may be bonded as a ligand (e.g., an axial ligand) so that the metal complex is electrically neutral, and an anionic counter ion may be present. Examples of the anionic counter ion include a halide ion, a hydroxide ion, a nitrate ion, and a sulfate ion. The structure of the alkyl group in the alkyloxy group having 1 to 8 carbon atoms may be linear, branched, or cyclic.

[0028] Examples of M include a scandium atom, a titanium atom, a vanadium atom, a chromium atom, a manganese atom, an iron atom, a cobalt atom, a nickel atom, a copper atom, a zinc atom, a yttrium atom, a zirconium atom, a niobium atom, a ruthenium atom, a rhodium atom, a palladium atom, a lanthanum atom, a cerium atom, a praseodymium atom, a neodymium atom, a promethium atom, a samarium atom, a europium atom, a gadolinium atom, a terbium atom, a dysprosium atom, a holmium atom, an erbium atom, a thulium atom, a ytterbium atom, a lutetium atom, an actinium atom, a thorium atom, a protactinium atom, a uranium atom, a neptunium atom, a plutonium atom, americium atom, a curium atom, a berkelium atom, a californium atom, an einsteinium atom, a fermium atom, a mendelevium atom, a nobelium atom, and a lawrencium atom. Among these, M is preferably a scandium atom, a titanium atom, a vanadium atom, a chromium atom, a manganese atom, an iron atom, a cobalt atom, a nickel atom, a copper atom, or a zinc atom, more preferably an iron atom, a cobalt atom, or a nickel atom, and particularly preferably a cobalt atom.

[0029] A1 to A4 each independently represent a ring structure. The ring structures represented by A1 to A4 may each independently be a monocyclic structure or a fused ring structure. When the ring structure is a fused ring structure, it is preferably a fused ring structure in which 2 to 5 rings are fused, more preferably a fused ring structure in which 2 to 4 rings are fused, even more preferably a fused ring structure in which 2 or 3 rings are fused, and particularly preferably a fused ring structure in which 2 rings are fused.

[0030] The ring structures represented by A1 to A4 may each independently be a saturated ring or an unsaturated ring. The ring structures represented by A1 to A4 are preferably unsaturated rings, more preferably unsaturated monocyclic structures or fused ring structures in which two to four unsaturated rings are fused, even more preferably fused ring structures in which two or three unsaturated rings are fused, and particularly preferably fused ring structures in which two unsaturated rings are fused.

[0031] At least one of A1 to A4 contains one or more nitrogen atoms as ring-constituting atoms. At least one of A1 to A4 preferably contains 1 to 4 nitrogen atoms as ring-constituting atoms, more preferably 1 to 3 nitrogen atoms, even more preferably 1 or 2 nitrogen atoms, and particularly preferably 1 nitrogen atom. Also, at least two of A1 to A4 preferably contain one or more nitrogen atoms as ring-constituting atoms, more preferably at least three of A1 to A4 contain one or more nitrogen atoms as ring-constituting atoms, and even more preferably all of A1 to A4 contain one or more nitrogen atoms as ring-constituting atoms.

[0032] In each of A1 to A4, when the ring structure is a monocyclic structure, the number of atoms forming the ring structure is preferably independently 4 or more, more preferably 4 to 7, and even more preferably 5 or 6. Examples of the monocyclic structure in the present invention include a benzene ring, a thiophene ring, a triazine ring, a furan ring, a pyrazine ring, and a pyridine ring, and is preferably selected from the group consisting of a pyrazine ring and a pyridine ring.

[0033] In each of A1 to A4, when the ring structure is a fused ring structure, the number of atoms forming the ring structure is preferably each independently 8 or more, more preferably 8 to 20, even more preferably 8 to 18, still more preferably 9 to 14, and particularly preferably 10. Examples of the fused ring structure in the present invention include a naphthalene ring, an anthracene ring, a thieno[3,2-b]thiophene ring, a phenanthrene ring, a fluorene ring, a furo[3,2-b]furan, an acridine ring, a quinoline ring, an isoquinoline ring, an indole ring, a carbazole ring, a carboline ring, a dibenzofuran ring, a cinnoline ring, a thionaphthene ring, a 1,10-phenanthroline ring, a phenothiazine ring, a purine ring, and a benzofuran ring, and is preferably selected from the group consisting of an acridine ring, a quinoline ring, an isoquinoline ring, an indole ring, a carbazole ring, a carboline ring, a cinnoline ring, a phenanthroline ring, and a purine ring, and more preferably selected from the group consisting of a quinoline ring and an isoquinoline ring.

[0034] A substituent may be bonded to each of the ring structures of A1 to A4. Examples of the substituent that may be bonded to the ring structures of A1 to A4 include a halogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, an aryl group, an alkylsulfonyl group, an alkoxy group, an alkylthio group, a carboxyl group, a sulfo group, a cyano group, a nitro group, and an amino group. When a plurality of substituents are present, the plurality of substituents may be the same or different. In one embodiment, adjacent substituents may form a ring structure. Furthermore, the substituent may coordinate a metal ion.

[0035] In the present invention, halogen atoms include fluorine, chlorine, bromine, and iodine.

[0036] In the present invention, the alkyl group refers to a linear or branched monovalent hydrocarbon group. The number of carbon atoms in the alkyl group is preferably 1 to 20, more preferably 1 to 12, and even more preferably 1 to 6. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a sec-pentyl group, a tert-pentyl group, and an n-hexyl group.

[0037] In the present invention, the cycloalkyl group refers to a cyclic monovalent hydrocarbon group. The cycloalkyl group preferably has 3 to 20 carbon atoms, more preferably 3 to 12 carbon atoms, and even more preferably 3 to 6 carbon atoms. Examples of the cycloalkyl group include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a 1-methylcyclopropyl group, a 2-methylcyclopropyl group, and a 2,2-dimethylcyclopropyl group.

[0038] In the present invention, the term "alkenyl group" refers to a linear or branched monovalent hydrocarbon group containing a double bond. The alkenyl group preferably has 2 to 20 carbon atoms, more preferably 2 to 12 carbon atoms, and even more preferably 2 to 6 carbon atoms. Examples of the alkenyl group include vinyl, 1-propenyl, 2-propenyl, 1-butenyl, 2-butenyl, 3-butenyl, 1-methyl-2-propenyl, 2-methyl-2-propenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl, 1-methyl-2-butenyl, 2-methyl-2-butenyl, 1-hexenyl, 2-hexenyl, 3-hexenyl, 4-hexenyl, and 5-hexenyl.

[0039] In the present invention, the term "alkynyl group" refers to a linear or branched monovalent hydrocarbon group containing a triple bond. The number of carbon atoms in the alkynyl group is preferably 2 to 20, more preferably 2 to 12, and even more preferably 2 to 6. Examples of the alkynyl group include an ethynyl group, a 1-propynyl group, a 2-propynyl group, a 1-butynyl group, a 2-butynyl group, a 3-butynyl group, a 1-methyl-2-propynyl group, a 2-methyl-3-butynyl group, a 1-pentynyl group, a 2-pentynyl group, a 3-pentynyl group, a 4-pentynyl group, a 1-methyl-2-butynyl group, a 2-methyl-3-pentynyl group, a 1-hexynyl group, and a 1,1-dimethyl-2-butynyl group.

[0040] In the present invention, the term "aryl group" refers to a monovalent aromatic hydrocarbon group. The number of carbon atoms in the aryl group is preferably 6 to 40, and more preferably 6 to 30. Examples of the aryl group include a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthryl group, an anthracenyl group, a benzophenanthryl group, a benzanthracenyl group, a chrysenyl group, a pyrenyl group, a fluoranthenyl group, a triphenylenyl group, a benzofluoranthenyl group, a dibenzanthracenyl group, a perylenyl group, and a helicenyl group.

[0041] In the present invention, the term "alkylsulfonyl group" refers to a monovalent group in which an alkyl group is bonded to a sulfonyl group. The alkyl group in the alkylsulfonyl group can be any of the groups described above as "alkyl group." The number of carbon atoms in the alkylsulfonyl group is preferably 1 to 20, more preferably 1 to 12, and even more preferably 1 to 6. Examples of alkylsulfonyl groups include methylsulfonyl, ethylsulfonyl, normal propylsulfonyl, isopropylsulfonyl, n-butylsulfonyl, sec-butylsulfonyl, tert-butylsulfonyl, n-pentylsulfonyl, isopentylsulfonyl, tert-pentylsulfonyl, neopentylsulfonyl, 2,3-dimethylpropylsulfonyl, 1-ethylpropylsulfonyl, 1-methylbutylsulfonyl, n-hexylsulfonyl, isohexylsulfonyl, and 1,1,2-trimethylpropylsulfonyl.

[0042] In the present invention, an alkoxy group refers to a monovalent group to which a hydrocarbon group is bonded via an ether bond. The number of carbon atoms in the alkoxy group is preferably 1 to 20, more preferably 1 to 12, and even more preferably 1 to 6. Examples of the alkoxy group include a methoxy group, an ethoxy group, an n-propoxy group, an n-butoxy group, an n-pentyloxy group, an n-hexyloxy group, an isopropoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, and an isohexyloxy group.

[0043] In the present invention, the alkylthio group refers to a group in which the oxygen atom in the ether bond of an alkoxy group is substituted with a sulfur atom. The number of carbon atoms in the alkylthio group is preferably 1 to 20, more preferably 1 to 16, and even more preferably 1 to 12. Examples of the alkylthio group include a methylthio group, an ethylthio group, an n-propylthio group, an n-butylthio group, an n-pentylthio group, an n-hexylthio group, and an isopropylthio group.

[0044] The alkyl group, cycloalkyl group, alkenyl group, alkynyl group, aryl group, alkylsulfonyl group, alkoxy group, alkylthio group, carboxyl group, sulfo group, cyano group, nitro group, and amino group may be unsubstituted, or may be substituted with one or more substituents such as halogen, alkyl group, alkenyl group, alkynyl group, aryl group, alkoxy group, alkylthio group, cyano group, carbonyl group, carboxyl group, amino group, nitro group, silyl group, and sulfo group.

[0045] Preferably, the metal complex is a compound represented by the following formula:

[0046]

[0047] In the hydrogen generation reaction catalyst of the present invention, the metal complex of formula (1) is preferably contained in an amount of 75 mass% or less, more preferably 60 mass% or less, even more preferably 50 mass% or less, still more preferably 40 mass% or less, particularly preferably 35 mass% or less, and most preferably 30 mass% or less, relative to the total amount of the metal complex and the conductive material (100 mass%). By containing the metal complex of formula (1) in the above-mentioned range, the hydrogen generation reaction catalyst of the present invention can have extremely high catalytic ability in the hydrogen generation reaction.

[0048] The method for producing the metal complex is not particularly limited, but an example thereof is a method in which a dicyano compound such as 2,3-dicyanopyridine and a metal atom are heated in an alcohol solvent in the presence of a basic substance, where examples of the basic substance include inorganic bases such as potassium carbonate, sodium carbonate, calcium carbonate, sodium bicarbonate, and sodium acetate, and organic bases such as triethylamine, tributylamine, and diazabicycloundecene.

[0049] The conductive material is not particularly limited as long as it has conductivity, and examples thereof include carbon materials, metal materials, and metal oxide materials. As the conductive material, carbon materials or metal oxide materials are preferred, and carbon materials are more preferred. One type of conductive material may be used alone, or two or more types may be used in combination.

[0050] The carbon material is preferably derived from conductive carbon. Specific examples of the carbon material include graphite, amorphous carbon, activated carbon, graphene, carbon black, carbon fiber, mesocarbon microbeads, microcapsule carbon, fullerene, carbon nanofoam, carbon nanotube, and carbon nanohorn. Among these, the carbon material is preferably graphite, amorphous carbon, activated carbon, graphene, carbon black, carbon fiber, fullerene, or carbon nanotube, and more preferably carbon nanotube, carbon black, or graphene.

[0051] Examples of metal materials include titanium and tin. Examples of metal oxide materials include titanium oxide and tin oxide (SnO ２ , ITO, ATO) and the like.

[0052] In the hydrogen generation reaction catalyst of the present invention, it is desirable that the metal complex serving as the catalyst molecule is supported at the molecular level on the surface of a conductive material serving as a support. For example, a metal complex-supported material can be obtained by mixing the metal complex and the conductive material in a solvent in which the metal complex is soluble, irradiating with ultrasonic waves, and then filtering, washing, and drying. Here, the weight ratio of the metal complex to the conductive material in the solvent is preferably 5:5 to 0.5:9.5, more preferably 4:6 to 1:9, and particularly preferably 3.5:6.5 to 2:8. Preferred solvents include dimethyl sulfoxide, dimethylformamide, dimethylacetamide, and hexafluoro-2-propanol. If the metal complex is adsorbed in a monomolecular state, no other manufacturing process can match it. By supporting the metal complex serving as the catalyst molecule at the molecular level on the surface of a conductive material serving as a support, the metal complex can be used more effectively and catalytic performance can be improved compared to when the metal complex is composited in a crystalline state.

[0053] The catalyst for hydrogen generation reaction of the present invention can be obtained by a production method that does not include a high-temperature calcination process, and therefore energy costs can be reduced.

[0054] The use of the catalyst for hydrogen generation reaction of the present invention is not particularly limited, but since it has excellent catalytic ability for hydrogen generation reaction, it can be used for electrodes of water electrolysis devices.

[0055] [Liquid Composition] In one embodiment, the present invention relates to a liquid composition containing the catalyst for hydrogen generation reaction of the present invention. The liquid composition may contain a solvent.

[0056] The solvent is not particularly limited, and may be an inorganic solvent such as water, or may be an organic solvent. Specific examples of organic solvents include alcohols such as methanol, ethanol, propanol, isopropanol (2-propanol), and 1-hexanol; dimethyl sulfoxide; tetrahydrofuran; aprotic polar solvents such as N-methylpyrrolidone, dimethylformamide, and acetone; and nonpolar solvents such as chloroform, dichloromethane, 1,4-dioxane, benzene, and toluene. One type of solvent may be used alone, or two or more types may be used in combination.

[0057] The liquid composition may optionally contain conductive agents, binders, and other additives. It may also contain a perfluorocarbon material containing a polytetrafluoroethylene-based structural unit and a perfluoro side chain having a sulfonic acid group. A specific example of a perfluorocarbon material is Nafion (product name: manufactured by Chemours).

[0058] The liquid composition can be produced by mixing or kneading the catalyst for the hydrogen generation reaction, a solvent, and, if necessary, a perfluorocarbon material. For mixing or kneading, ultrasonic treatment, a mixer, a blender, a kneader, a homogenizer, a bead mill, a ball mill, or the like may be used. Before or after the kneading operation, the average particle size of the particles may be adjusted using a sieve, or the like. Furthermore, when preparing a liquid composition containing a perfluorocarbon material, the catalyst for the hydrogen generation reaction, the perfluorocarbon material, and, if necessary, water and alcohol may be mixed and stirred until homogeneous.

[0059] The liquid composition can be applied to the surface of various substrates. For example, by applying the liquid composition to the surface of a substrate and removing the solvent, a layer containing a catalyst for the hydrogen generation reaction (hereinafter referred to as a "catalyst layer") can be provided on the surface of various substrates. That is, the liquid composition can be used as a coating liquid to be applied to a substrate when manufacturing an electrode, for example. The liquid composition may be used as a coating liquid as is, or may be used as a coating liquid after adjusting the content or solids concentration of the catalyst for the hydrogen generation reaction. The substrate is not particularly limited, and examples thereof include aluminum alloys such as aluminum foil, electrolytic aluminum foil, aluminum mesh (expanded metal), foamed aluminum, punched aluminum, and duralumin; copper alloys such as copper foil, electrolytic copper foil, copper mesh (expanded metal), foamed copper, punched copper, and brass; brass foil, brass mesh (expanded metal), foamed brass, punched brass, nickel foil, nickel mesh, corrosion-resistant nickel, nickel mesh (expanded metal), punched nickel, nickel foam, sponge nickel, metallic zinc, corrosion-resistant metallic zinc, zinc foil, zinc mesh (expanded metal), steel plate, punched steel plate, and silver. Substrates such as silicon substrates, metal substrates such as gold, iron, stainless steel, copper, aluminum, and lithium, alloy substrates containing any combination of these metals, oxide substrates such as indium tin oxide (ITO), indium zinc oxide (IZO), and antimony tin oxide (ATO), and carbon substrates such as carbon sheets, glassy carbon, pyrolytic graphite, and carbon felt can also be used. Preferably, it may be applied to a substrate selected from nickel foam, sponge nickel, carbon sheet, glassy carbon or carbon felt.

[0060] [Electrode] In one embodiment, the present invention relates to an electrode comprising the catalyst for the hydrogen generation reaction of the present invention. The electrode can be used as a catalyst for the hydrogen generation reaction by supporting the catalyst for the hydrogen generation reaction of the present invention on the above-mentioned substrate. In one embodiment, the electrode more preferably comprises the catalyst for the hydrogen generation reaction of the present invention supported on a substrate, and even more preferably comprises the catalyst for the hydrogen generation reaction of the present invention supported on a substrate selected from a carbon sheet or nickel foam.

[0061] The method for producing the electrode is not particularly limited, and the electrode may be produced, for example, by applying a liquid composition to the surface of a substrate and removing components other than the catalyst for the hydrogen generation reaction. When removing components other than the catalyst for the hydrogen generation reaction, heat drying may be performed, or pressing may be performed after drying. Alternatively, a catalyst layer (a layer containing the catalyst for the hydrogen generation reaction of the present invention) may be provided on the surface of the substrate by vacuum deposition or the like. The electrode may have a catalyst layer on only one side of the substrate, or on both sides of the substrate.

[0062] The electrode functions as a catalyst for the hydrogen generation reaction, and functions as a catalyst for the reaction shown below: ＋ +2e － →H ２

[0063] [Water Electrolysis Apparatus] In one embodiment, the present invention relates to a water electrolysis apparatus comprising the electrode of the present invention. The water electrolysis apparatus may comprise an anode, a cathode, an anion exchange membrane disposed between the anode and the cathode, a power source connected to the anode and the cathode, and a water supply unit that supplies water or an alkaline aqueous solution. The electrode of the present invention may be used as the cathode of the water electrolysis apparatus.

[0064] The present invention will be described in more detail below using examples and comparative examples, but the scope of the present invention is not limited to the examples.

[0065] Synthesis Examples Synthesis Example 1 Synthesis of Compound (1) 1.0 g of 2,3-dicyanopyridine, 482 mg of cobalt acetate tetrahydrate, 59 mg of diazabicycloundecene, and 20 ml of ethoxyethanol were mixed and refluxed for 12 hours. After cooling to room temperature, water was added and the mixture was filtered under reduced pressure, followed by washing with methanol, acetone, and water. The solid was dried in vacuo at 80°C to obtain the target product. Yield: 90.4%.

[0066] Synthesis Example 2 Synthesis of Compound (2) Synthesis was carried out in the same manner as in Synthesis Example 1, except that 2,3-dicyanopyridine, the raw material of Synthesis Example 1, was replaced by a mixture of 2,3-dicyanopyridine and 2,3-dicyano-5,6-dimethylpyrazine in a molar ratio of 3:1. Yield: 92.1%.

[0067] Synthesis Example 3 Synthesis of Compound (3) Synthesis was carried out in the same manner as in Synthesis Example 1, except that 2,3-dicyanopyridine, the raw material of Synthesis Example 1, was replaced by a mixture of 2,3-dicyanopyridine and 2,3-dicyano-5,6-dimethylpyrazine in a molar ratio of 1:1. Yield: 72.3%.

[0068] Synthesis Example 4 Synthesis of Compound (4) Synthesis was carried out in the same manner as in Synthesis Example 1, except that 2,3-dicyanopyridine, the raw material of Synthesis Example 1, was replaced by a mixture of 2,3-dicyanopyridine and 2,3-dicyano-5,6-dimethylpyrazine in a molar ratio of 1:3. Yield: 88.6%.

[0069] Synthesis Example 5 Synthesis of Compound (5) Synthesis was carried out in the same manner as in Synthesis Example 1, except that 2,3-dicyanopyridine, the raw material in Synthesis Example 1, was replaced with 2,3-dicyano-5,6-dimethylpyrazine and mixed. Yield: 87.3%.

[0070] Synthesis Example 6 Synthesis of Compound (6) Synthesis was carried out in the same manner as in Synthesis Example 1, except that 2,3-dicyanopyridine, the raw material of Synthesis Example 1, was mixed with 2,3-dicyanopyridine and 2,3-dicyanopyrazine in a molar ratio of 3:1. Yield: 86.4%.

[0071] Synthesis Example 7 Synthesis of Compound (7) Synthesis was carried out in the same manner as in Synthesis Example 1, except that 2,3-dicyanopyridine, the raw material of Synthesis Example 1, was mixed with 2,3-dicyanopyridine and 2,3-dicyanopyrazine in a molar ratio of 1:1. Yield: 74.1%.

[0072] Synthesis Example 8 Synthesis of Compound (8) Synthesis was carried out in the same manner as in Synthesis Example 1, except that 2,3-dicyanopyridine, the raw material of Synthesis Example 1, was mixed with 2,3-dicyanopyridine and 2,3-dicyanopyrazine in a molar ratio of 1:3. Yield: 88.4%.

[0073] Synthesis Example 9 Synthesis of Compound (9) Synthesis was carried out in the same manner as in Synthesis Example 1, except that iron acetate was used instead of cobalt acetate tetrahydrate, which was the raw material in Synthesis Example 1. Yield: 72.9%.

[0074] Synthesis Example 10 Synthesis of Compound (10) Synthesis was carried out in the same manner as in Synthesis Example 2, except that iron acetate was used instead of cobalt acetate tetrahydrate, which was the raw material in Synthesis Example 2. Yield: 59.2%.

[0075] Synthesis Example 11 Synthesis of Compound (11) Synthesis was carried out in the same manner as in Synthesis Example 3, except that iron acetate was used instead of cobalt acetate tetrahydrate, which was the raw material in Synthesis Example 3. Yield: 64.2%.

[0076] Synthesis Example 12 Synthesis of Compound (12) Synthesis was carried out in the same manner as in Synthesis Example 4, except that iron acetate was used instead of cobalt acetate tetrahydrate, which was the raw material in Synthesis Example 4. Yield: 76.7%.

[0077] Synthesis Example 13 Synthesis of Compound (13) Synthesis was carried out in the same manner as in Synthesis Example 5, except that iron acetate was used instead of cobalt acetate tetrahydrate, which was the raw material in Synthesis Example 5. Yield: 75.9%.

[0078] Synthesis Example 14 Synthesis of Compound (14) Synthesis was carried out in the same manner as in Synthesis Example 6, except that iron acetate was used instead of cobalt acetate tetrahydrate, which was the raw material in Synthesis Example 6. Yield: 59.5%.

[0079] Synthesis Example 15 Synthesis of Compound (15) Synthesis was carried out in the same manner as in Synthesis Example 7, except that iron acetate was used instead of cobalt acetate tetrahydrate, which was the raw material in Synthesis Example 7. Yield: 67.8%.

[0080] Synthesis Example 16 Synthesis of Compound (16) Synthesis was carried out in the same manner as in Synthesis Example 8, except that iron acetate was used instead of cobalt acetate tetrahydrate, which was the raw material in Synthesis Example 8. Yield: 63.1%.

[0081] Synthesis Example 17 Synthesis of Compound (17) 5.0 g of quinoline-2,3-dicarboxylic acid, 1.4 g of cobalt acetate tetrahydrate, 11.1 g of urea, 175 mg of diazabicycloundecene, 28 mg of hexaammonium heptamolybdate tetrahydrate, and 25.6 ml of 1,3-dimethyl-2-imidazolidinone were mixed and refluxed for 12 hours under a nitrogen flow. After cooling to 140°C, the mixture was subjected to hot filtration under reduced pressure and then washed with hot water and methanol. The solid was dried under vacuum at 80°C to obtain the target product. Yield: 38.2%.

[0082] Synthesis Example 18 Synthesis of Compound (18) Synthesis was carried out in the same manner as in Synthesis Example 17, except that iron acetate was used instead of cobalt acetate tetrahydrate, which was the raw material in Synthesis Example 17. Yield: 40.1%.

[0083] Synthesis Example 19 Synthesis of Compound (19) Synthesis was carried out in the same manner as in Synthesis Example 17, except that nickel acetate tetrahydrate was used instead of cobalt acetate tetrahydrate, the raw material of Synthesis Example 17. Yield: 37.9%.

[0084] Synthesis Example 20 Synthesis of Compound (20) 5.0 g of diaminomaleonitrile was dissolved in 100 ml of trifluoroacetic acid. 21.0 g of 2,3-dichloro-5,6-dicyano-p-benzoquinone was added in small portions and refluxed for 12 hours. The reaction solution was cooled to room temperature and then filtered under reduced pressure. The crude product was dispersed in toluene and filtered again, after which it was washed with toluene and a mixture of methanol and water. The resulting solid was dried under vacuum at 80°C to obtain a white solid. 2.0 g of the aforementioned product, 483 mg of iron acetate, 85 mg of diazabicycloundecene, and 20 ml of ethoxyethanol were mixed and refluxed for 12 hours. After cooling to room temperature, water was added and the mixture was filtered under reduced pressure, followed by washing with methanol, acetone, and water. The solid was dried under vacuum at 80°C to obtain the target product. Yield: 42.2%.

[0085] Synthesis Example 21 Synthesis of Compound (21) 10 g of 5,6-dichloro-2,3-pyrazinodicarbonitrile, 5.8 g of N,N'-diethylethylenediamine, and 17 g of potassium carbonate were mixed in acetonitrile and stirred overnight at room temperature. Water and a small amount of ethanol were added, and the mixture was filtered under reduced pressure and washed with water and methanol to obtain a white solid (yield: 10.6 g, 87.6%). 5.0 g of the aforementioned product and 4.72 g of a 10% solution of lithium methoxide in methanol were stirred in 50 ml of 1-pentanol at 120°C for 5 hours. After cooling to room temperature, the mixture was filtered under reduced pressure and washed with methanol to obtain a purple solid (yield: 3.35 g, 65.9%). Furthermore, 300 mg of the aforementioned purple solid and 152 mg of cobalt acetate tetrahydrate were stirred in 5 ml of dimethyl sulfoxide at 120°C for 1 hour. Methanol was added to the mixture, which was then filtered under reduced pressure, and the solid was dried in vacuo at 80° C. to obtain the target product in a yield of 90.0%.

[0086] Synthesis Example 22 Synthesis of Compound (22) 6.74 g of diaminomaleonitrile, 16.0 g of 1,3-diphenyl-1,3-propanedione, and 3.0 g of diphosphorus pentoxide were mixed in ethanol and refluxed for 12 hours. The mixture was concentrated using an evaporator, and the resulting precipitate was collected by filtration under reduced pressure and then heated under vacuum at 80°C to obtain a white solid. 5.93 g of the aforementioned white solid and 4.62 g of a 10% lithium methoxide methanol solution were heated under reflux in 1-pentanol for 3 hours. The reaction solution was concentrated under reduced pressure, and the resulting precipitate was filtered under reduced pressure and washed with methanol. This solid was dried under vacuum at 80°C to obtain a black powder. Furthermore, 1.5 g of the aforementioned black powder and 0.47 g of cobalt acetate tetrahydrate were stirred in dimethylformamide at 120°C for 12 hours, and methanol was added to cause precipitation. The mixture was then filtered under reduced pressure, washed with methanol, and dried under vacuum at 80°C to obtain a black powder. Yield: 80.4%.

[0087] Synthesis Example 23 Synthesis of Compound (23) 5.0 g of 5,6-dichloro-2,3-pyrazinodicarbonitrile, 5.3 g of methanesulfonamide, and 10.3 g of potassium carbonate were stirred in acetonitrile at room temperature for 12 hours. Water and ethyl acetate were added for extraction, and the organic layer was concentrated to obtain a white solid. 0.5 g of the above product, 0.2 g of iron chloride tetrahydrate, and 2.0 g of urea were mixed and heated to reflux at 190°C for 12 hours. The solid was collected by filtration and then washed with an aqueous potassium hydroxide solution, hydrochloric acid, water, methanol, and acetone. The solid was dried under vacuum at 80°C to obtain the target product. Yield: 52.7%.

[0088] Synthesis Example 24 Synthesis of Compound (24) The synthesis was carried out in the same manner as in Synthesis Example 18, except that 3-ethyl-2,3-dicyanopyridine was used instead of quinoline-2,3-dicarboxylic acid, the raw material of Synthesis Example 18. Yield: 25.3%.

[0089] Example 1 20 mg of compound (1) and 100 mg of carbon black (Carbon ECP, manufactured by Lion Specialty Chemicals Co., Ltd.) were dispersed in 20 mL of dimethyl sulfoxide. The dispersion was irradiated with ultrasound for 3 minutes, filtered under reduced pressure, and then washed with methanol and acetone. The filtered product was dried under reduced pressure at room temperature to obtain the catalyst of Example 1.

[0090] Next, 0.82 mg of the obtained catalyst of Example 1, 84 μL of pure water, 336 μL of isopropyl alcohol, and 6 μL of a 0.5 mass % Nafion aqueous solution were mixed and subjected to ultrasonic irradiation. Then, the dispersion was applied to a GC (glassy carbon) electrode to obtain the electrode of Example 1.

[0091] Examples 2 to 24 Electrodes of Examples 2 to 24 were obtained under the same conditions as in Example 1, except that the metal complex (compound (1)) in Example 1 was changed to metal complexes (2) to (24), respectively.

[0092] Comparative Example 1 In Comparative Example 1, an electrode of Comparative Example 1 was obtained under the same conditions as in Example 1, except that no metal complex serving as a catalyst molecule was added and only carbon black was used.

[0093] (LSV measurement by RRDE)

[0094] LSV measurements were performed by RRDE on the electrodes of Examples 1 to 24 and Comparative Example 1. LSV measurements by RRDE were performed using a rotating ring-disk electrode (RRDE-3A, manufactured by BAS Corporation) with an oxygen-saturated 1 M potassium hydroxide aqueous solution as the electrolyte, at a sweep rate of 5 mV / s. The rotating disk rotation speed was set to 1600 rpm, and LSV was measured. Pt was used as the counter electrode, and Hg / HgO was used as the reference electrode.

[0095] An example of the results of LSV measurement by RRDE is shown in Figure 1. In the graph of Figure 1, when the applied voltage shown on the horizontal axis is the same, a higher current value indicates a more excellent hydrogen generation catalytic ability.

[0096] For the electrodes of Examples 1 to 24 and Comparative Example 1, the current density [A / cm 2 ] when −1.0 V (vs. RHE) was applied ２ ] are shown in Table 1.

[0097] (Evaluation of coated sheet activity) Example 25 3 g of compound (5) and 7 g of carbon black (Carbon ECP, manufactured by Lion Specialty Chemicals Co., Ltd.) were dispersed in 500 mL of dimethyl sulfoxide. The dispersion was irradiated with ultrasound for 1 hour, filtered under reduced pressure, and then washed with methanol and acetone. The filtered product was dried under reduced pressure at room temperature to obtain the catalyst of Example 25.

[0098] Next, 0.5 g of the catalyst obtained in Example 25, 9.5 mL of pure water, 37.9 mL of isopropyl alcohol, and 0.51 mL of a 20% by mass aqueous Nafion solution were mixed and stirred in a ball mill. This dispersion was then sprayed onto a carbon sheet (Toray Paper TGP-H-120) using a spray coater (SimCoat, manufactured by Sono-Tek Corporation) at a basis weight of 1 mg / cm. ２ A catalyst electrode sheet of Example 25 was obtained.

[0099] Example 26 A catalyst electrode sheet of Example 26 was obtained under the same conditions as in Example 25, except that the metal complex (compound (5)) in Example 25 was changed to a metal complex of compound (17).

[0100] Comparative Example 2 In Comparative Example 2, a catalyst electrode sheet of Comparative Example 2 was obtained under the same conditions as in Example 25, except that a platinum carbon catalyst (manufactured by Sigma-Aldrich, platinum supported on graphitized carbon 40% Pt / Vulcan) was used instead of the catalyst of Example 25.

[0101] The catalyst electrode sheet was placed in a dedicated electrode holder (AE9-1, manufactured by EC Frontier) that allows the electrode area to be defined, and the hydrogen generation catalytic activity of the catalyst-coated sheet was evaluated. The catalyst-coated electrode was punched out with a Φ9 mm punch and then set in the holder. A 1 M KOH solution was used as the electrolyte, with Pt used as the counter electrode and Hg / HgO used as the reference electrode. The LSV measurement results for various catalyst electrode sheets are shown in Table 2. A higher potential at a given current density indicates better hydrogen generation catalytic activity.

[0102]

[0103] 1 A / cm of the catalyst electrode sheets of Examples 25 and 26 and Comparative Example 2 ２ When the potentials at 1000 kJ / cm 3 were compared, it was found that the potential was higher than that of the platinum-carbon catalyst, and that the catalyst of the present invention exhibited better hydrogen generation catalytic performance than platinum.

[0104] (Evaluation of Water Electrolysis Cell) Example 27 A water electrolysis test was carried out using an AEM-type water electrolysis cell (Dioxide Materials). The catalyst electrode sheet prepared in Example 25 was cut into a 2.24 cm square and used as the cathode. Fumasep (FAA-3-50, manufactured by Fumatech) was used as the anion exchange membrane, and Ni foam was used as the anode. The temperature of the water electrolysis cell was kept at 30°C, and a 1.0 M potassium hydroxide aqueous solution was flowed at a flow rate of 3 mL / min, and the current was 1 A / cm. ２ The current value was swept up to 1000 kJ / s, and the overvoltage value was measured.

[0105] An example of the results of overvoltage measurement using a water electrolysis cell is shown in Figure 2. In the graph of Figure 2, when the applied current value shown on the horizontal axis is the same, the smaller the overvoltage value, the more excellent the hydrogen generation catalytic ability.

[0106] Example 28 An electrolytic cell was measured under the same conditions as in Example 27, except that the catalyst electrode sheet in Example 27 was changed to a catalyst electrode sheet using compound (17) used in Example 26.

[0107] Comparative Example 3 An electrolytic cell was measured under the same conditions as in Example 27, except that the catalyst electrode sheet in Example 27 was changed to an uncoated carbon sheet (Toray Paper TGP-H-120) that was not coated with a catalyst.

[0108] Table 3 shows a comparison of the overvoltage values ​​in water electrolysis for Examples 27 and 28 and Comparative Example 3. A lower overvoltage indicates higher catalytic performance, and it was confirmed that the catalyst electrode sheets of Examples 27 and 28 exhibited higher electrolytic cell performance than the carbon sheet of Comparative Example 3 that was not coated with a catalyst.

[0109]

[0110] The catalyst for hydrogen generation reaction of the present invention is useful because it has excellent catalytic activity for hydrogen generation reaction when used as a catalyst for electrodes in water electrolysis devices. Furthermore, since it does not use rare metals, production costs can be reduced and a production process suitable for mass production can be designed.

Claims

1. A catalyst for a hydrogen generation reaction comprising a metal complex and a conductive material, wherein the metal complex is represented by the following formula (1): (wherein M is a metal atom; A1 to A4 each independently represent a ring structure; at least one of A1 to A4 contains one or more nitrogen atoms as ring-constituting atoms; and each of the ring structures of A1 to A4 may have a substituent bonded thereto).

2. The catalyst for hydrogen generation reaction according to claim 1, wherein M is an iron atom, a cobalt atom, or a nickel atom.

3. The catalyst for hydrogen generation reaction according to claim 1, wherein A1 to A4 each independently represent a monocyclic structure or a fused ring structure in which two or three rings are fused.

4. The metal complex has the formula: The catalyst for hydrogen generation reaction according to claim 1, represented by the formula:

5. The catalyst for hydrogen generation reaction according to claim 1, wherein the metal complex is contained in an amount of 75 mass % or less relative to 100 mass % of the total amount of the metal complex and the conductive material.

6. The catalyst for hydrogen generation reaction according to claim 1, wherein the conductive material is a carbon material or a metal oxide.

7. A liquid composition comprising the catalyst for hydrogen generation reaction according to any one of claims 1 to 6.

8. An electrode comprising the catalyst of claim 1.

9. An electrode comprising the catalyst of claim 1 supported on a carbon sheet or nickel foam.

10. An electrode comprising a metal complex supported on a carbon sheet or nickel foam, the metal complex being represented by the following formula (1): (wherein M is a metal atom; A1 to A4 each independently represent a ring structure; at least one of A1 to A4 contains one or more nitrogen atoms as ring-constituting atoms; and a substituent may be bonded to each of the ring structures of A1 to A4.) 11. A water electrolysis device comprising an electrode according to any one of claims 8 to 10.

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