Metal complex or adduct thereof, catalyst comprising metal complex or adduct thereof and method for producing the same, liquid composition or electrode containing catalyst, and air battery or fuel cell equipped with electrode

Abstract

To provide: a metal complex having excellent oxygen reduction catalyst performance, or an adduct of the metal complex; a catalyst comprising the metal complex or the adduct thereof; a method for producing the catalyst; a liquid composition or an electrode, which contains a catalyst; and an air battery or a fuel cell, which is equipped with the electrode.SOLUTION: Provided are: a metal complex represented by formula (1) or (2), or an adduct of the metal complex; a catalyst comprising the metal complex or the adduct thereof; a method for producing the catalyst; a liquid composition or an electrode, which contains a catalyst; and an air battery or a fuel cell, which is equipped with an electrode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a metal complex or an adduct thereof, a catalyst containing the metal complex or an adduct thereof and a method for producing the same, a liquid composition or electrode containing the catalyst, and an air battery or fuel cell equipped with the electrode. [Background technology]

[0002] Fuel cells and air cells are known as devices that convert chemical energy into electrical energy by utilizing an oxidation-reduction reaction at an electrode. An oxygen reduction reaction occurs at the air electrode of these cells, and a catalyst is used to promote this reduction reaction. Typical catalysts for fuel cells include platinum-supported carbon materials, and for air cells, manganese dioxide-supported carbon materials.

[0003] However, because rare metals such as platinum are expensive and their resources are limited, attempts have been made to develop catalysts using less expensive and more abundant materials. For example, Patent Document 1 discloses an air electrode catalyst containing iron phthalocyanine and a carbon material as a co-catalyst. However, because iron phthalocyanine is difficult to adsorb to the surface of the carbon material, its oxygen reduction ability was insufficient.

[0004] On the other hand, Patent Document 2 discloses the use of graphene oxide in combination with iron phthalocyanine as a carbon material co-catalyst. However, the method for producing an oxygen reduction catalyst disclosed in Patent Document 2 requires first forming a composite of iron phthalocyanine and graphene oxide, and then reducing the graphene oxide to obtain a composite of iron phthalocyanine and graphene, which results in a problem of a complicated production process.

[0005] Patent Document 3 discloses an electrode for oxidation-reduction containing a cobalt tetrapyrazinoporphyrazine derivative represented by a specific structural formula as a catalytic component. However, the cobalt tetrapyrazinoporphyrazine derivative described in Patent Document 3 has a trifluoromethyl group bonded to the pyrazine, which may result in a decrease in oxygen reduction catalytic activity. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-85925 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-91061 [Patent Document 3] International Publication No. 2007 / 023964 Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, there is a need to develop catalytic materials and catalysts that have excellent oxygen reduction catalytic activity without using rare metals such as platinum, and a method for producing catalysts that can be easily adsorbed onto conductive materials (co-catalysts) using a simple process.

[0008] The present invention has been made to solve the above-mentioned problems of the conventional art, and aims to provide a metal complex or an adduct thereof having excellent oxygen reduction catalytic activity, a catalyst containing the metal complex or the adduct thereof and a method for producing the same, a liquid composition or electrode containing the catalyst, and an air battery or fuel cell equipped with the electrode. [Means for solving the problem]

[0009] As a result of extensive research into the above-mentioned problems, the present inventors unexpectedly discovered that a metal complex or an adduct thereof having a specific chemical structure has excellent oxygen reduction catalytic activity, and arrived at the present invention.

[0010] The object of the present invention is to provide a compound having the following formula (1) or (2): [ka] (In the formula, M is an iron atom or a cobalt atom, D 1 From D 28 are each independently a nitrogen atom, a sulfur atom, or a carbon atom, D 1 From D 28 is a carbon atom, each of the carbon atoms may independently be bonded to a hydrogen atom, a halogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, an aryl group, an alkylsulfonyl group, an alkoxy group, or an alkylthio group. A metal complex or an adduct thereof represented by However, in equation (1), D 1 From D 16 If there are 8 or fewer carbon atoms in At least one of the carbon atoms has a halogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, an aryl group, an alkylsulfonyl group, an alkoxy group, or an alkylthio group bonded to it; or The metal complex of formula (1) forms an adduct, and this is achieved by the metal complex or its adduct.

[0011] D 1 From D 16 is preferably a nitrogen atom or a carbon atom, and D 17 From D 28 is preferably a sulfur atom or a carbon atom.

[0012] The metal complex or adduct thereof has the following formula: [ka] [ka] [ka] [ka] It is preferable that the formula be represented by the following formula:

[0013] The present invention also relates to a catalyst comprising a metal complex of the present invention or an adduct thereof and a conductive material.

[0014] The metal complex or its adduct is preferably contained in an amount of 75% by mass or less relative to 100% by mass of the total amount of the metal complex or its adduct and the conductive material.

[0015] The conductive material preferably contains a carboxyl group.

[0016] The carboxyl group is preferably contained in an amount of 20% by mass or less relative to 100% by mass of the conductive material.

[0017] The catalyst of the present invention is preferably for oxygen reduction.

[0018] The present invention also relates to a liquid composition comprising the catalyst of the present invention and a solvent.

[0019] The present invention also relates to an electrode comprising the catalyst of the present invention.

[0020] The present invention also relates to an air battery or fuel cell comprising an electrode of the present invention.

[0021] Furthermore, the present invention provides (a) a step of dissolving the metal complex or an adduct thereof in a solvent to prepare a solution; (b) dispersing the conductive material in the solution to prepare a dispersion; and (c) removing the solvent from the dispersion The present invention also relates to a method for producing the catalyst of the present invention, comprising:

[0022] The steps (a) and (b) are preferably carried out at a temperature equal to or lower than the boiling point of the solvent.

[0023] The solubility of the metal complex or its adduct in the solvent is preferably 0.1 g / L or more. [Effects of the Invention]

[0024] According to the present invention, by using the metal complex of the present invention or an adduct thereof, a catalyst having excellent oxygen reduction catalytic activity can be provided. Furthermore, since the metal complex of the present invention or an adduct thereof is easily adsorbed onto a conductive material, the catalyst can be produced without undergoing a complicated production process.

[0025] Furthermore, the present invention can provide an excellent oxygen reduction catalytic function without using rare metals such as platinum, and therefore can provide a catalyst for an air cell or a fuel cell at a relatively low cost. [Brief explanation of the drawings]

[0026] [Figure 1] An example of the results of LSV measurement using RRDE is shown below. DETAILED DESCRIPTION OF THE INVENTION

[0027] [Metal complexes or their adducts] The metal complex or adduct thereof of the present invention is represented by the following formula (1) or (2): [ka] (In the formula, M is an iron atom or a cobalt atom, D 1 From D 28 are each independently a nitrogen atom, a sulfur atom, or a carbon atom, D 1 From D 28 is a carbon atom, each of the carbon atoms may independently be bonded to a hydrogen atom, a halogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, an aryl group, an alkylsulfonyl group, an alkoxy group, or an alkylthio group. is expressed as However, in equation (1), D 1 From D 16 If there are 8 or fewer carbon atoms in At least one of the carbon atoms has a halogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, an aryl group, an alkylsulfonyl group, an alkoxy group, or an alkylthio group bonded to it; or The metal complex of formula (1) forms an adduct.

[0028] 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. An anionic counter ion may also be present to make M electrically neutral. Furthermore, M may exist as an adduct to which an electrically neutral molecule is added.

[0029] The valence of M is not particularly limited. A halogen atom, a hydroxyl group, or an (alkyloxy)alkoxy group having 1 to 8 carbon atoms may be bonded as a ligand (for example, an axial ligand) so that the metal complex or its adduct is electrically neutral, and an anionic counter ion may be present. Examples of anionic counter ions include halide ions, hydroxide ions, nitrate ions, and sulfate ions. The alkyl group in the (alkyloxy)alkoxy group having 1 to 8 carbon atoms may have a linear, branched, or cyclic structure.

[0030] In the present invention, halogen atoms include fluorine, chlorine, bromine, and iodine.

[0031] 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.

[0032] 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.

[0033] In the present invention, the 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.

[0034] 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) 1-butyn-1-yl group, a (2-butynyl group) 2-butyn-1-yl group, a (3-butynyl group) 3-butyn-1-yl group, a (1-methyl-2-propynyl group) 1-methyl-2-propyn-1-yl group, a (2-methyl-3-butynyl group) 2-methyl-3-butyn-2yl group, a (1-pentynyl group) 1-pentyn-1-yl group, a (2-pentynyl group) Examples include (1-pentynyl) 2-pentyn-1-yl, (3-pentynyl) 3-pentyn-2-yl, (4-pentynyl) 4-pentyn-1-yl, 1-methyl-2-butynyl (1-methyl-2-butyn-1-yl), (2-methyl-3-pentynyl) 2-methyl-3-pentyn-1-yl, (1-hexynyl) 1-hexyn-1-yl, and (1,1-dimethyl-2-butynyl) 1,1-dimethyl-2-butyn-1-yl.

[0035] 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.

[0036] 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, n-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.

[0037] 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.

[0038] 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.

[0039] The alkyl group, cycloalkyl group, alkenyl group, alkynyl group, aryl group, alkylsulfonyl group, alkoxy group, and alkylthio 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.

[0040] D 1 From D 16 is preferably a nitrogen atom or a carbon atom, and D 17 From D 28 is preferably a sulfur atom or a carbon atom. 1 From D 16 The number of nitrogen atoms in the group is preferably 2 to 12, and more preferably 4 to 8. 17 From D 28 The number of sulfur atoms is preferably 2 to 10, and more preferably 4 to 8.

[0041] Preferably, the metal complex or adduct thereof of the present invention is a compound represented by the following formula:

[0042] [ka] [ka] [ka] [ka]

[0043] The method for producing the metal complex or its adduct is not particularly limited, but an example thereof is a method in which a dicyano compound such as pyridine-2,3-dicarbonitrile and a metal atom are heated in an alcohol solvent in the presence of a basic substance, examples of which 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.

[0044] [catalyst] In one embodiment, the present invention relates to a catalyst comprising the metal complex or adduct thereof of the present invention and a conductive material. Only one type of metal complex or adduct thereof can be used, or two or more types of metal complexes or adducts thereof can be used in combination.

[0045] 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. Carbon materials are preferred as the conductive material. One type of conductive material may be used alone, or two or more types may be used in combination.

[0046] 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.

[0047] Examples of carbon nanotubes include single-walled carbon nanotubes (hereinafter referred to as "SWCNT"), double-walled carbon nanotubes (hereinafter referred to as "DWCNT"), and multi-walled carbon nanotubes (hereinafter referred to as "MWCNT").

[0048] The carbon material may contain a heteroatom. Examples of the heteroatom include an oxygen atom, a nitrogen atom, a phosphorus atom, a sulfur atom, and a silicon atom. When the carbon material contains a heteroatom, the carbon material may contain one type of heteroatom alone or two or more types of heteroatoms. The carbon material may be oxidized, hydroxided, nitrided, phosphide, sulfide, or silicided.

[0049] Metallic materials include titanium and tin, and metallic oxide materials include titanium oxide and tin oxide (SnO2, ITO, ATO).

[0050] The conductive material may have a functional group such as a hydroxyl group, a carboxyl group, a nitrogen-containing group, a silicon-containing group, a phosphorus-containing group such as a phosphate group, or a sulfur-containing group such as a sulfonic acid group. In particular, the carbon material preferably has a carboxyl group. When the conductive material has a carboxyl group, the metal complex or an adduct thereof is more easily adsorbed onto the surface of the conductive material, improving the durability of the catalyst and further enhancing the oxygen reduction catalytic activity.

[0051] The conductive material may be surface-treated by oxidation. In particular, oxidation of carbon materials such as carbon black can improve the interaction with the metal complex by adding hydrophilic functional groups such as carboxyl groups and hydroxyl groups, thereby making it possible to control the ionization potential within an optimal range. Known oxidation methods can be used, including wet treatments in which the material is stirred and mixed in an aqueous solution of an oxidizing agent such as nitric acid, sulfuric acid, or chloric acid, and gas-phase treatments such as plasma treatment and ozone treatment.

[0052] When the conductive material contains carboxyl groups, the content of the carboxyl groups is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less, relative to 100% by mass of the conductive material. Having a carboxyl group content equal to or less than the upper limit is advantageous because it reduces the production cost of the catalyst. Furthermore, the carboxyl group content is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 8% by mass or more. Having a carboxyl group content equal to or greater than the lower limit can further enhance the durability and oxygen reduction catalytic activity of the catalyst. The carboxyl group content can be measured by elemental analysis, X-ray photoelectron spectroscopy, or the like.

[0053] The specific surface area of ​​the conductive material is 0.8m 2 / g or more is preferable, and 10m 2 / g or more is more preferable, and 50m 2 / g or more is more preferable, and 100m 2 / g or more is particularly preferred, and 500m 2 / g or more is most preferable. 2 When the specific surface area is 1 / g or more, it becomes easier to increase the amount of catalyst supported, and the oxygen reduction catalytic activity of the catalyst can be further improved. 2 The specific surface area can be measured by a nitrogen adsorption BET method using a specific surface area measuring device.

[0054] The average particle size of the conductive material is not particularly limited, but is preferably 5 nm to 1000 μm, more preferably 10 nm to 100 μm, and even more preferably 50 nm to 10 μm. Examples of methods for adjusting the average particle size of the conductive material to fall within the above numerical range include the following (A1) to (A3). (A1): A method in which particles are pulverized using a ball mill or the like, and the resulting coarse particles are dispersed in a dispersant to obtain the desired particle size, and then dried and solidified. (A2): A method in which particles are pulverized using a ball mill or the like, and the resulting coarse particles are sieved or the like to select particle size. (A3): A method for optimizing the manufacturing conditions and adjusting the particle size when manufacturing conductive materials. The average particle size can be measured using a particle size distribution measuring device or an electron microscope.

[0055] In the catalyst of the present invention, the content of the metal complex or adduct thereof is preferably 75% by mass or less, more preferably 50% by mass or less, and even more preferably 30% by mass or less, relative to 100% by mass of the total amount of the metal complex or adduct thereof and the conductive material. When the content of the metal complex or adduct thereof is equal to or less than the above-mentioned upper limit, the conductivity of the catalyst is excellent. Furthermore, the content of the metal complex or adduct thereof is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, relative to 100% by mass of the total amount of the metal complex or adduct thereof and the conductive material. When the proportion of the metal complex or adduct thereof is equal to or more than the above-mentioned lower limit, the oxygen reduction catalytic activity of the catalyst can be further improved.

[0056] Although the use of the catalyst of the present invention is not particularly limited, it is preferably used for oxygen reduction because of its excellent oxygen reduction catalytic activity. Specifically, the catalyst of the present invention can be used in oxygen reduction electrodes for air batteries, fuel cells, electrochemical sensors, and the like.

[0057] [Liquid composition] In one embodiment, the present invention relates to a liquid composition comprising the catalyst of the present invention and a solvent. The solvent may be a solvent that easily dissolves the catalyst (i.e., has a high solubility), or a solvent that does not easily dissolve the catalyst (i.e., has a low solubility). If the solvent easily dissolves the catalyst, the liquid composition is in the form of a solution. If the solvent does not easily dissolve the catalyst, the liquid composition is in the form of a dispersion.

[0058] 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.

[0059] 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 DuPont).

[0060] The liquid composition can be produced by mixing or kneading a catalyst, a solvent, and, if necessary, a perfluorocarbon material. Mixing or kneading may be performed using ultrasonic treatment, a mixer, a blender, a kneader, a homogenizer, a bead mill, a ball mill, or the like. 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, the perfluorocarbon material, and, if necessary, water and alcohol may be mixed and stirred until homogeneous.

[0061] 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 (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 the surface of 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 catalyst content or solids concentration.

[0062] The substrate is not particularly limited, and examples 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, foamed nickel, sponge nickel, metallic zinc, corrosion-resistant metallic zinc, zinc foil, zinc mesh (expanded metal), steel plate, punched steel plate, and silver. Substrates that can also be used include 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 glassy carbon, pyrolytic graphite, and carbon felt.

[0063] [electrode] In one embodiment, the present invention relates to an electrode comprising the catalyst of the present invention. The electrode can have a layer (i.e., a catalyst layer) comprising the catalyst of the present invention on the above-mentioned substrate, and can be used as a catalyst for reduction reactions, particularly oxygen reduction reactions. The catalyst layer can be in direct contact with the substrate, or other layers can be present between the substrate and the catalyst layer.

[0064] 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 conductive substrate and removing components other than the catalyst. When removing components other than the catalyst, heat drying may be performed, or pressing may be performed after drying. Alternatively, a catalyst layer 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.

[0065] The thickness of the catalyst layer is not particularly limited, but can be, for example, 0.01 to 100 μm. When the thickness is equal to or greater than the lower limit, the electrode has excellent durability. When the thickness is equal to or less than the upper limit, the electrode performance is less likely to deteriorate.

[0066] The electrode can function as a catalyst for any electrochemical reaction such as a reduction reaction or an oxidation reaction, and for example, can function as a catalyst for the reduction reaction shown below. O2+4H + +4e - →2H2O O2+2H2O+4e - →4OH -

[0067] [Air battery] In one embodiment, the present invention relates to an air battery including the electrode of the present invention. The electrode of the present invention can be used as an oxygen electrode of the air battery. The air battery can include an oxygen electrode, a metal electrode, an electrolyte, and a separator. In the present invention, the oxygen electrode is an electrode that uses gaseous oxygen as the electrode active material, and is also called an air electrode.

[0068] The metal electrode is not particularly limited, but examples thereof include simple metals such as aluminum, magnesium, calcium, lithium, and zinc, and oxides of these metals.

[0069] The electrolyte is preferably an aqueous electrolyte, and is not particularly limited, but examples thereof include alkaline aqueous solutions such as potassium hydroxide aqueous solution and sodium hydroxide aqueous solution, and acidic aqueous solutions such as sulfuric acid aqueous solution. One type of electrolyte may be used alone, or two or more types may be used in combination. Inorganic solid electrolytes may also be used.

[0070] The separator is a component that separates the oxygen electrode and the metal electrode, retains an electrolyte, and ensures ionic conductivity between the oxygen electrode and the metal electrode. The separator is not particularly limited, but examples include polymers having micropores such as polyethylene, polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, cellulose, cellulose acetate, hydroxyalkyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, cellophane, polystyrene, polyacrylonitrile, polyacrylamide, polyvinyl chloride, polyimide, polyamide, vinylon, poly(meth)acrylic acid, gel compounds, ion exchange membranes, cyclized polymers, poly(meth)acrylate-containing polymers, sulfonate-containing polymers, quaternary ammonium salt-containing polymers, and quaternary phosphonium salt-containing polymers. The separator may be a non-porous or porous membrane, and in the case of a porous membrane, the pore size is preferably 10 μm or less.

[0071] [Fuel cell] In one embodiment, the present invention relates to a fuel cell comprising the electrode of the present invention. The electrode of the present invention can be used as an oxygen electrode of the fuel cell. The fuel cell can comprise an oxygen electrode, a fuel electrode, an electrolyte, and a separator.

[0072] As the fuel electrode, electrolyte, and separator used in the fuel cell, the same metal electrode, electrolyte, and separator as those used in the air battery can be used.

[0073] The fuel cell may be a primary cell or a secondary cell. Examples of the fuel cell form include a metal-air cell, a molten carbonate fuel cell (MCFC), a phosphoric acid fuel cell (PAFC), a solid oxide fuel cell (SOFC), a polymer electrolyte fuel cell (PEFC), an enzymatic (bio) fuel cell, a microbial fuel cell, a hydrazine fuel cell, and a direct methanol oxidation fuel cell (DMFC). The fuel cell form is not limited to these examples, but a PEFC, an enzymatic (bio) fuel cell, a microbial fuel cell, a hydrazine fuel cell, or a DMFC is preferred. Examples of the secondary cell include a hydrogen-air secondary cell using a hydrogen storage alloy for the anode.

[0074] [Catalyst manufacturing method] In one embodiment, the present invention relates to a method for preparing the catalyst of the present invention, the method comprising: (a) a step of dissolving the metal complex or an adduct thereof in a solvent to prepare a solution; (b) dispersing the conductive material in the solution to prepare a dispersion; and (c) removing the solvent from the dispersion Includes:

[0075] Step (a) is a step of preparing a solution by dissolving a metal complex or an adduct thereof in a solvent. The solution contains the metal complex or an adduct thereof dissolved in the solvent and the solvent. The conditions, such as temperature and pressure, when preparing the solution are not particularly limited as long as the conditions are such that the metal complex or the adduct thereof can be dissolved in the solvent. For example, the temperature when preparing the solution is preferably a temperature below the boiling point of the solvent, more preferably 5 to 80°C, and even more preferably 10 to 50°C. The solution is most preferably prepared at room temperature (25°C). The pressure can be, for example, atmospheric pressure.

[0076] The solvent is not particularly limited as long as it can dissolve the metal complex or its adduct. The solubility of the metal complex or its adduct in the solvent is preferably 0.1 g / L or more, more preferably 0.4 g / L or more, even more preferably 2.0 g / L or more, and particularly preferably 10 g / L or more. The upper limit of the solubility of the metal complex or its adduct is not particularly limited, but may be, for example, 20 g / L or less, preferably 50 g / L or less, and more preferably 100 g / L or less. When the solubility of the metal complex or its adduct is equal to or greater than the lower limit, the metal complex or its adduct is more easily dissolved in the solvent, and the metal complex or its adduct is more easily adsorbed uniformly on the surface of the conductive material. As a result, the oxygen reduction catalytic activity of the catalyst is improved, and the durability when used as an electrode for an air battery or a fuel cell is further improved.

[0077] The solubility of a metal complex or its adduct in a solvent is usually the maximum amount (g) of the metal complex or its adduct dissolved in 1 L of solvent measured using ultraviolet-visible spectroscopy at 25°C and atmospheric pressure. Note that the conditions for measuring the solubility of a metal complex or its adduct in a solvent are independent of the conditions for preparing the solution.

[0078] Step (b) is a step of dispersing a conductive material in a solution to prepare a dispersion, and in this step, the metal complex or an adduct thereof can be adsorbed onto the surface of the conductive material to form a composite. That is, the dispersion contains a composite in which the metal complex or an adduct thereof is adsorbed onto the surface of the conductive material. The conditions, such as temperature and pressure, used to prepare the dispersion are not particularly limited as long as they allow the conductive material to be dispersed. For example, the temperature used to prepare the dispersion is preferably a temperature below the boiling point of the solvent, more preferably 5 to 80°C, and even more preferably 10 to 50°C. It is most preferable to prepare the dispersion at room temperature (25°C).

[0079] Step (c) is a step of removing the solvent from the dispersion, thereby obtaining a complex in which the metal complex or its adduct is adsorbed on the surface of the conductive material as a catalyst. The method for removing the solvent from the dispersion is not particularly limited, but it can be removed, for example, by solid-liquid separation. Filtration is preferred as a solid-liquid separation method because it reduces the temperature load on the catalyst. In filtration, it is preferable that the absorbance of the filtrate is reduced by 10% or more compared to the solution. This allows us to determine whether the metal complex or its adduct has been effectively adsorbed on the conductive material.

[0080] The catalyst production method of the present invention is useful because it can form a composite of a metal complex or an adduct thereof with a conductive material without high-temperature heat treatment. The catalyst production method of the present invention can be carried out at 200°C or less, preferably 100°C or less, and more preferably 50°C or less. The metal complex or an adduct thereof of the present invention has relatively high solubility in a solvent, allowing it to exist in a high concentration in the solvent. Furthermore, the affinity of the metal complex or an adduct thereof with the conductive material is high, allowing it to be effectively adsorbed onto the surface of the conductive material. For example, the metal complex or an adduct thereof can form a molecular layer of the metal complex or an adduct thereof adsorbed in a monomolecular state on the surface of the conductive material.

[0081] In the catalyst production method of the present invention, each step may be an independent step, or a plurality of steps may be integrated. For example, step (a) and step (b) may be independent steps, or may be performed simultaneously as the same step. [Example]

[0082] 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.

[0083] Synthesis Example 1 Synthesis of Compound (1) To 1.29 g of pyridine-3,4-dicarbonitrile, 410 mg of anhydrous ferric chloride and 5 mL of 1-pentanol were added, followed by 1.52 g of 1,8-diazabicyclo[5.4.0]undec-7-ene, and the mixture was heated in an oil bath set to 160°C. After 3 hours, 20 mL of N,N-dimethylformamide was added and the mixture was heated for an additional hour. After cooling, 20 mL of methanol was added, and the precipitated solid was collected by filtration. The solid was washed with methanol and dried to obtain compound (1). Yield: 920 mg.

[0084] Synthesis Example 2: Synthesis of Compound (2) Synthesis Example (2-1) Synthesis of pyridine-2,3-dicarboxylate diethyl N-oxide 25.0 g of diethyl pyridine-2,3-dicarboxylate was added to 150 mL of methylene chloride and stirred. 100 mg of methyltrioxorhenium was added to this solution, and while monitoring the progress of the reaction by TLC, 3 mL of 30% hydrogen peroxide was added in increments of 3 mL. Stirring was continued for two days. Remaining raw materials were confirmed, so 100 mg of methyltrioxorhenium and hydrogen peroxide were added until the raw materials disappeared.

[0085] After the raw materials had disappeared, 200 mL of water was added and stirred. The organic phase was separated, and the aqueous phase was extracted three times with methylene chloride. The combined organic phases were dehydrated over anhydrous sodium sulfate, concentrated, and then purified by silica gel column chromatography. The target product was obtained as colorless crystals in a yield of 20.2 g.

[0086] Synthesis Example (2-2) Synthesis of diethyl 6-chloropyridine-2,3-dicarboxylate 15 mL of acetonitrile was added to 4.28 g of pyridine-2,3-dicarboxylate diethyl N-oxide and stirred. 5.5 g of phosphorus oxychloride was added to this solution at room temperature and heated under reflux for 5 hours. After cooling, the reaction mixture was poured into ice water and extracted with ethyl acetate. The organic phase was dried over anhydrous sodium sulfate, concentrated, and purified by silica gel column chromatography. Yield: 2.7 g.

[0087] Synthesis (2-3) Synthesis of 6-methoxypyridine-2,3-dicarboxylic acid 20 mL of methanol was added to 2.5 g of diethyl 6-chloropyridine-2,3-dicarboxylate, and 2.0 g of potassium carbonate was added and stirred at room temperature. After 4 hours, the inorganic matter was filtered off, and the solvent was evaporated under reduced pressure. 20 mL of methanol was added to the residue, and the mixture was stirred. 1.63 g of lithium hydroxide monohydrate was added. After 5 hours, the reaction mixture was poured into dilute aqueous hydrochloric acid and extracted with ethyl acetate.

[0088] The organic phase was dried over anhydrous sodium sulfate and concentrated to obtain the target product (yield: 0.62 g).

[0089] Synthesis Example (2-4) Synthesis of Compound (2) 500 mg of 6-methoxypyridine-2,3-dicarboxylic acid, 6 g of urea, 330 mg of ferric chloride hexahydrate, and 22 mg of hexaammonium heptamolybdate tetrahydrate were mixed, stirred, and heated in an oil bath set to 190°C. After reacting for 3 hours, the mixture was cooled to 100°C, water was added, and the mixture was stirred for an additional 10 minutes. After returning to room temperature, the solid was collected by vacuum filtration, washed with water, methanol, and finally acetone, and dried.

[0090] 5 mL of N,N-dimethylformamide was added to the solid and heated under reflux. After cooling, methanol was added little by little with stirring, and the precipitated crystals were collected by filtration, washed with methanol and acetone, and then dried to obtain compound (2). Yield: 230 mg.

[0091] Synthesis Example 3: Synthesis of Compound (3) Synthesis Example (3-1) Synthesis of dibutyl pyridine-3,4-dicarboxylate To 18.0 g of pyridine-3,4-dicarboxylic acid, 100 mL of toluene, 40 mL of n-butanol, and 10 g of p-toluenesulfonic acid monohydrate were added and stirred. Using a Soxhlet apparatus and magnesium sulfate, the mixture was heated under reflux while removing the generated water.

[0092] After 10 hours of reaction, the main product was separated using alumina column chromatography (yield: 26.2 g).

[0093] Synthesis Example (3-2) Synthesis of pyridine-3,4-dicarboxylate dibutyl N-oxide 25.0 g of dibutyl pyridine-3,4-dicarboxylate was mixed with 100 mg of methyltrioxorhenium and 150 mL of methylene chloride and stirred at room temperature. 30% aqueous hydrogen peroxide was added to this mixture in small portions. The progress of the reaction was monitored by TLC. Additional aqueous hydrogen peroxide and methyltrioxorhenium were added until the raw materials were consumed, and the reaction was continued for a total of two days. After the reaction was completed, 100 mL of water was added and the mixture was separated.

[0094] The organic phase was washed with water and then with an aqueous solution of sodium sulfite. After dehydration with anhydrous sodium sulfate, it was concentrated to obtain a crude product as a reddish oil. The yield was approximately 25 g.

[0095] Synthesis Example (3-3) Synthesis of dibutyl 2-chloropyridine-4,5-dicarboxylate 10.0 g of pyridine-3,4-dicarboxylate dibutyl N-oxide was added in small portions to 25 g of phosphorus oxychloride. After stirring for 10 minutes, the reaction temperature was raised to 110°C and the reaction was continued for 5 hours. After cooling to room temperature, the mixture was carefully poured into a mixture of 150 mL of ethyl acetate and 200 g of ice. After stirring for 1 hour, the layers were separated, and the organic phase was washed with aqueous sodium bicarbonate, dehydrated over anhydrous sodium sulfate, and concentrated. Two major products were observed. These were separated and purified by silica gel column chromatography. Hexane and ethyl acetate were used as eluents. The product that eluted first was the desired 2-chloropyridine-4,5-dicarboxylate. The product that eluted second was 2-chloropyridine-3,4-dicarboxylate dibutyl. The yield of each product was 7 g.

[0096] Synthesis Example (3-4) Synthesis of dimethyl 2-methoxypyridine-4,5-dicarboxylate 2.5 g of dibutyl 2-chloropyridine-4,5-dicarboxylate was dissolved in 40 mL of methanol and stirred at room temperature. 2.0 g of potassium carbonate was added and stirred for 5 hours. The reaction solution was poured into dilute hydrochloric acid, extracted with ethyl acetate, washed with water, washed with aqueous sodium bicarbonate, and dehydrated with anhydrous sodium sulfate. The residue was crystallized from hexane. Yield: 0.9 g.

[0097] Synthesis Example (3-5) Synthesis of 2-methoxypyridine-4,5-dicarboxylic acid 10 mL of methanol was added to 0.9 g of dimethyl 2-methoxypyridine-4,5-dicarboxylate and stirred at room temperature. 670 mg of lithium hydroxide monohydrate was added and the reaction was carried out at room temperature. After 30 minutes, an additional 670 mg of lithium hydroxide monohydrate was added and the reaction was continued for another hour.

[0098] Acidifying the solution with concentrated hydrochloric acid gave a homogeneous solution. Diluting the solution with water resulted in the precipitation of colorless crystals. These crystals were filtered, washed with water, and dried to give the desired 2-methoxypyridine-4,5-dicarboxylic acid. Yield: 0.67 g.

[0099] Synthesis Example (3-6) Synthesis of Compound (3) 250 mg of 2-methoxypyridine-4,5-dicarboxylic acid, 165 mg of ferric chloride hexahydrate, 11 mg of hexaammonium heptamolybdate tetrahydrate, and 3 g of urea were mixed and stirred, and the mixture was immersed in an oil bath at 185°C to carry out the reaction. After reacting for 1 hour, the temperature of the oil bath was increased to 200°C, and the reaction was carried out for an additional 2 hours. 5 mL of N-methylpyrrolidone was added to the mixture, and after reacting for 1 hour, the mixture was cooled to 80°C, methanol was added, and the precipitated solid was collected by filtration.

[0100] This solid was adsorbed onto silica gel using N,N-dimethylformamide. Excess solvent was removed under reduced pressure using a rotary evaporator. The adsorbent was placed on top of silica gel and eluted with N,N-dimethylformamide to obtain the purified target product. Yield: 95 mg.

[0101] Synthesis Example 4 Synthesis of Compound (6) Synthesis Example (4-1) Synthesis of 5,6-dimethoxy-2,3-pyrazinedicarbonitrile 15 mL of methanol was added to 2.0 g of 5,6-dichloro-2,3-pyrazinedicarbonitrile and stirred at room temperature. 3.0 g of potassium carbonate was added to the mixture and the reaction was carried out overnight. 80 mL of water was added to the reaction solution, and the precipitated crystals were collected by filtration. The product was washed with water and methanol and dried to obtain the target product. Yield: 1.90 g.

[0102] Synthesis Example (4-2) Synthesis of Compound (6) 260 mg of anhydrous ferric chloride was added to 1.0 g of 5,6-dimethoxy-2,3-pyrazinedicarbonitrile, followed by 5 mL of 1-pentanol and 1 mL of pyridine, and the mixture was heated in an oil bath at 155°C. After overnight reaction, the mixture was cooled, methanol was added, and the precipitated solid was purified by silica gel column chromatography. A mixed solvent of chloroform and methanol was used as the eluent. The yield was 130 mg.

[0103] Synthesis Example 5 Synthesis of Compound (7) 5 mL of 1-pentanol was added to 1.44 g of 5-methylpyrazine-2,3-dicarbonitrile, 410 mg of anhydrous ferric chloride, and 1 mL of pyridine were added, and the mixture was heated in an oil bath set to 150 °C to carry out the reaction. After 7 hours, the mixture was cooled, and 1 mL of concentrated hydrochloric acid and 2 mL of water were added. 20 mL of methanol was then added, and the precipitated solid was collected by filtration. The resulting solid was purified by silica gel column chromatography to obtain 80 mg of compound (7).

[0104] Synthesis Example 6 Synthesis of Compounds (8) and (9) Synthesis Example (6-1) Synthesis of 5,6-dimethyl-2,3-pyrazinedicarbonitrile 10 mL of acetic acid was added to 3.24 g of diaminomaleonitrile, followed by 2.64 mL of diacetyl, and the mixture was heated for 1 hour. Upon cooling, crystals precipitated. 10 mL of water was added, and the crystals were collected by filtration. After washing with water, the crystals were dried to obtain the target product. Yield: 4.45 g.

[0105] Synthesis Example (6-2) Synthesis of Compound (9) 30 mL of 1-pentanol was added to 6.32 g of 5,6-dimethyl-2,3-pyrazinedicarbonitrile, followed by 1.78 g of anhydrous ferric chloride and 1.9 mL of 4-methylpyridine. The mixture was heated in an oil bath set to 145°C and allowed to react. After 5 hours of reaction, the heating was stopped. When the temperature of the reaction solution reached 100°C, 30 mL of methanol was added dropwise. After cooling to room temperature, the mixture was filtered under reduced pressure, carefully washed with water and methanol, then washed with acetone, and dried. Yield: 6.8 g.

[0106] Synthesis Example (6-3) Synthesis of Compound (8) 1.8 g of compound (9) was taken, 20 mL of concentrated sulfuric acid was added, and the mixture was stirred at room temperature. After 1 hour, the mixture was added dropwise to 200 mL of water. The precipitated solid was separated by centrifugation, and the resulting solid was washed with water and methanol using a centrifuge to obtain compound (8). Yield: 1.0 g.

[0107] Synthesis Example 7 Synthesis of Compound (10) 1.58 g of 5,6-dimethyl-2,3-pyrazinedicarbonitrile (synthesized in Synthesis Example (6-1)) was added to 5 mL of 1-pentanol and 410 mg of anhydrous ferric chloride and stirred. Next, 1.0 mL of 4-tert-butylpyridine was added, and the mixture was heated in an oil bath set to 155 °C. After 1 hour, 10 mL of N,N-dimethylformamide was added, and the mixture was stirred for an additional 30 minutes. After cooling to room temperature, the precipitated solid was collected by filtration and washed with N,N-dimethylformamide and then with methanol to obtain crude compound (10). 15 mL of N,N-methylformamide was added to the crude product, and the mixture was heated to reflux for 30 minutes. After cooling to room temperature, the solid was collected by filtration and washed with N,N-dimethylformamide and then with methanol. This procedure was repeated twice and then dried to obtain compound (10). Yield: 761 mg.

[0108] Synthesis Example 8 Synthesis of Compound (11) 1.29 g of 2,3-dicyanopyrazine was mixed with 5 mL of 1-pentanol, 410 mg of anhydrous ferric chloride, and 1 mL of 4-methoxypyridine and stirred. The mixture was heated in an oil bath set to 155°C and reacted for 5 hours. After cooling to room temperature, the solid was collected by filtration, washed with N,N-dimethylformamide, then with methanol, and dried to obtain crude compound (11). This crude product was purified by silica gel column chromatography to obtain compound (11). Yield: 110 mg.

[0109] Synthesis Example 9 Synthesis of Compound (13) 1.29 g of 2,3-dicyanopyrazine was mixed with 5 mL of 1-pentanol, 410 mg of anhydrous ferric chloride, and 1 mL of pyridine and stirred. This mixture was heated in an oil bath set to 150°C and reacted overnight. After cooling to room temperature, 3 mL of water and 2 mL of concentrated hydrochloric acid were added, and 30 mL of methanol was added with stirring. The precipitated solid was collected by filtration and purified by silica column chromatography to obtain compound (13). Yield: 405 mg.

[0110] Synthesis Example 10 Synthesis of Compound (14) 410 mg of anhydrous ferric chloride and 5 mL of 1-pentanol were added to 1.3 g of 2,3-dicyanopyrazine and stirred. 1 mL of 4-tert-butylpyridine was added and heated in an oil bath set to 150°C. After reacting for 5 hours, the mixture was allowed to cool to room temperature, and the precipitated solid was collected by filtration. After washing with methanol and acetone, crude compound (14) was obtained. 10 mL of N,N-dimethylformamide was added to the obtained crude compound (14), and the mixture was heated to reflux for 1 hour. After cooling to room temperature, the solid was collected by filtration and washed with methanol and acetone to obtain compound (14). Yield: 760 mg.

[0111] Synthesis Example 11 Synthesis of Compound (15) 1.29 g of 2,3-dicyanopyridine was added to 5 mL of 1-pentanol, 410 mg of anhydrous iron chloride, and 1 mL of 4-methoxypyridine, and the mixture was heated in an oil bath set to 155°C. After 5 hours of reaction, 10 mL of N,N-dimethylformamide was added, and heating was continued for an additional 30 minutes. The mixture was allowed to cool to room temperature, and the precipitated solid was collected by filtration. This solid was washed with N,N-dimethylformamide, then methanol, and acetone, and then dried to obtain compound (15). Yield: 464 mg.

[0112] Synthesis Example 12 Synthesis of Compound (17) 1.67 g of pyridine-2,3-dicarboxylic acid was mixed with 498 mg of ferrous chloride tetrahydrate, 2.4 g of urea, and 30 mg of hexaammonium heptamolybdate tetrahydrate and reacted for 1 hour in an oil bath set to 180°C. After cooling to room temperature, water was added to loosen the solid, which was then filtered under reduced pressure and washed with water, methanol, and acetone to obtain 650 mg of a dark green solid. Next, 7 mL of dimethyl sulfoxide and 5 g of methyl paratoluenesulfonate were added to the solid, and the reaction was carried out at an internal temperature of 75°C for 22 hours. The mixture was then cooled to room temperature, and acetone was added until a solid precipitated. The solid was collected by filtration and dissolved in methanol.

[0113] To this methanol solution was added a methanol solution prepared separately from 3 g of ammonium hexafluorophosphate. A solid precipitated and was collected by filtration. The resulting solid was washed with methanol and then with acetone to obtain approximately 150 mg of a solid.

[0114] 30 mL of methanol was added to this solid, and the mixture was heated to reflux for 15 minutes. After allowing to cool to room temperature, the solid was collected by filtration, washed with methanol, and dried to obtain compound (17). Yield: 110 mg.

[0115] Synthesis Example 13 Synthesis of compound (18) 1.95 g of 5-ethylpyridine-2,3-dicarboxylic acid, 10 g of urea, 87 mg of hexaammonium heptamolybdate tetrahydrate, and 1.35 g of ferric chloride tetrahydrate were mixed and heated in an oil bath set to 190°C for 3 hours. After cooling, water was added to loosen the solid and collect it by filtration. 120 mL of water was added to the solid and heated under reflux for 30 minutes. After cooling, the solid was collected by filtration, purified by silica gel column chromatography, and then dissolved in concentrated sulfuric acid. This concentrated sulfuric acid solution was added dropwise to 500 mL of water, and the precipitated solid was collected by centrifugation. The solid was washed with methanol and dried to obtain the desired product. Yield: 822 mg.

[0116] Synthesis Example 14 Synthesis of compound (19) 10 mL of 1-pentanol was added to 1.29 g of 2,3-dicyanopyridine and 390 mg of anhydrous cobalt chloride, and 0.1 mL of 1,8-diazabicyclo[5.4.0]undec-7-ene was added thereto, followed by heating to 155° C. and reaction overnight.

[0117] 20 mL of N,N-dimethylformamide was added to the reaction mixture, and the mixture was stirred at 155°C for 30 minutes. After cooling to room temperature, the precipitated solid was collected by vacuum filtration, washed with N,N-dimethylformamide, water, methanol, and acetone, and then dried to obtain the target product. Yield: 0.75 g.

[0118] Synthesis Example 15 Synthesis of Compound (20) Synthesis Example (15-1) Synthesis of thiophene-2,3-dicarbaldehyde dioxime 5.2 g of thiophene-2,3-dicarbaldehyde, 50 mL of methanol, and 6.3 g of hydroxylamine hydrochloride were mixed and stirred, 7.4 g of sodium acetate was added, and the mixture was heated under reflux for 6 hours. After adding 0.9 g of hydroxylamine hydrochloride, the mixture was allowed to react overnight.

[0119] After concentration, ethyl acetate and water were added for extraction. The organic phase was dehydrated over anhydrous sodium sulfate, concentrated, and crystallized with hexane and ethyl acetate. The crystals were collected by filtration to obtain thiophene-2,3-dicarbonitrile dioxime. Yield: Approximately 6 g.

[0120] Synthesis Example (15-2) Synthesis of thiophene-2,3-dicarbonitrile Approximately 6 g of the dioxime was dissolved in 60 mL of acetonitrile, and 16 mL of triethylamine and 11.5 g of acetic anhydride were added. The mixture was allowed to react at room temperature for 5 days. After concentration, water and ethyl acetate were added for extraction. The organic phase was dried over anhydrous sodium sulfate and then purified by silica gel column chromatography to obtain thiophene-2,3-dicarbonitrile. Yield: 3.8 g.

[0121] Synthesis Example (15-3) Synthesis of Compound (20) 1 g of a 10% solution of lithium methoxide in methanol was added to 3 mL of 1-octanol and heated in an oil bath set to 230 °C to evaporate the methanol. 360 mg of thiophene-2,3-dicarbonitrile was added to this solution. After 15 minutes of reaction, the mixture was cooled to 100 °C and 272 mg of ferric chloride hexahydrate was added. The reaction was continued for 1 hour, followed by the addition of 15 mL of methanol and the precipitated solid, which was collected by filtration. N,N-dimethylformamide and silica gel were added to the resulting solid, which was then dissolved by heating. The solvent was then removed under reduced pressure. The solid was loaded onto a silica gel column and eluted with N,N-dimethylformamide. The blue component was collected and concentrated to give compound (20). Yield: 30 mg.

[0122] Synthesis Example 16 Synthesis of Compounds (21) and (22) Synthesis Example (16-1) Synthesis of dimethyl 5-bromopyridine-2,3-dicarboxylate 250 mL of methanol was added to 30.0 g of pyridine-2,3-dicarboxylic acid and stirred. 10 mL of concentrated sulfuric acid and 20 mL of trimethyl orthoformate were added dropwise to the reaction mixture. The mixture was heated to reflux for two days, then 20 mL of trimethyl orthoformate was added and refluxed for another day. After cooling to 40°C, 16 mL of bromine was added in small increments while monitoring the progress of the reaction by TLC, maintaining the temperature below 55°C. After one day, 8 mL of bromine was added, and the reaction was continued for another three days at 58°C. The reaction mixture was poured in small increments into a mixture of ethyl acetate, water, and sodium bicarbonate (enough to neutralize the acid component) while stirring. After separation, the organic phase was washed with aqueous sodium sulfite. The organic phase was dehydrated with anhydrous sodium sulfate, concentrated, and crystallized by adding chilled isopropanol. The crystals were collected by filtration. The product was washed with isopropanol, then with hexane, and dried to obtain the target product. Yield: 34.4 g.

[0123] Synthesis Example (16-2) Synthesis of dimethyl 5-(2-ethylhexylthio)pyridine-2,3-dicarboxylate 5.9 g of dimethyl 5-bromopyridine-2,3-dicarboxylate was added to 3.2 g of 2-ethylhexanethiol, and 25 mL of N,N-dimethylformamide was added and stirred. 6.1 g of potassium carbonate was added, and the oil bath temperature was set to 85°C and heated. The reaction was allowed to proceed overnight, and then 120 mL of ethyl acetate was added. The organic phase was washed with an aqueous potassium carbonate solution, concentrated, and purified by silica gel column chromatography to obtain the desired product. Yield: 6.2 g.

[0124] Synthesis Example (16-3) Synthesis of 5-(2-ethylhexylthio)pyridine-2,3-dicarboxylic acid 50 mL of methanol was added to 5.0 g of dimethyl 5-(2-ethylhexylthio)pyridine-2,3-dicarboxylate, and 2.5 g of lithium hydroxide monohydrate was added. After the reaction was completed, the mixture was acidified with dilute hydrochloric acid and extracted with ethyl acetate. The organic phase was washed with water three times and concentrated. Toluene was added to the concentrate, and the process of distilling under reduced pressure was repeated three times to obtain the target product.

[0125] Synthesis Example (16-4) Synthesis of Compound (21) 1.07 g of 5-(2-ethylhexylthio)pyridine-2,3-dicarboxylic acid was added with 3.2 g of urea and 30 mg of hexaammonium heptamolybdate tetrahydrate and heated in an oil bath set to 160°C for 30 minutes. 465 mg of ferric chloride hexahydrate and 3.2 g of urea were added to this reaction mixture, and the oil bath was set to 200°C for 1 hour. 6 mL of N-methylpyrrolidone was added and the mixture was heated for an additional 1 hour. After cooling to room temperature, water was added, and the precipitated solid was collected by filtration, washed with methanol, and purified by silica gel column chromatography to obtain compound (21). Yield: 320 mg.

[0126] Synthesis Example (16-5) Synthesis of dimethyl 5-(2-ethylhexylsulfonyl)pyridine-2,3-dicarboxylate To 6.0 g of dimethyl 5-(2-ethylhexylthio)pyridine-2,3-dicarboxylate, 80 mL of acetic acid and 300 mg of sodium tungstate dihydrate were added and stirred. The mixture was heated to 40°C, and 4.4 mL of 30% aqueous hydrogen peroxide was added dropwise, while monitoring the progress of the reaction by TLC. After the entire amount of aqueous hydrogen peroxide was added, the reaction was continued for 1 hour, and then 150 mL of water was added. After extraction with ethyl acetate, the organic phase was washed twice with aqueous sodium bicarbonate and twice with aqueous sodium sulfite, and then dehydrated with anhydrous sodium sulfite and concentrated. The residue was purified by silica gel column chromatography to obtain the desired product as a colorless oil. Yield: 6.0 g

[0127] Synthesis Example (16-6) Synthesis of 5-(2-ethylhexylsulfonyl)pyridine-2,3-dicarboxylic acid 150 mL of methanol was added to 13.6 g of dimethyl 5-(2-ethylhexylsulfonyl)pyridine-2,3-dicarboxylate and stirred. 6.8 g of lithium hydroxide was added to the mixture and the reaction was carried out at room temperature for 2 hours. After the reaction was completed, the mixture was acidified with dilute hydrochloric acid and extracted with ethyl acetate. The organic phase was washed three times with water and concentrated. Toluene was added to the concentrate and the mixture was evaporated under reduced pressure three times to obtain the target product.

[0128] Synthesis Example (16-7) Synthesis of Compound (22) 1.0 g of 5-(2-ethylhexylsulfonyl)pyridine-2,3-dicarboxylic acid was added with 3.0 g of urea and 25.3 mg of hexaammonium heptamolybdate tetrahydrate and heated in an oil bath set to 160°C for 30 minutes. Then, 400 mg of ferric chloride hexahydrate and 3.0 g of urea were added, and the oil bath was set to 200°C for 3 hours. After cooling to room temperature, water was added, and the precipitated solid was collected by filtration. This solid was purified by silica gel column chromatography to obtain compound (22). Yield: 199 mg.

[0129] Synthesis Example 17 Synthesis of compound (23) Synthesis Example (17-1) Synthesis of dimethyl 4-bromophthalate 100 mL of methanol was added to 10 g of 4-bromophthalic anhydride and refluxed for 1 hour. After cooling to room temperature, 5 g of trimethyl orthoformate was added, and 10 mL of acetyl chloride was slowly added dropwise. The reaction mixture was heated and refluxed for 3 days. After concentration, ethyl acetate and sodium bicarbonate solution were added, and the mixture was separated. The organic phase was dehydrated with anhydrous sodium sulfate and concentrated to obtain the target product. Yield: 10.8 g.

[0130] Synthesis Example (17-2) Synthesis of dimethyl 4-(2-ethylhexylthio)phthalate 8.18 g of dimethyl 4-bromophthalate, 6.3 g of potassium carbonate, and 40 mL of N,N-dimethylformamide were added to 4.38 g of 2-ethylhexanethiol, and the system was purged with nitrogen. The reaction mixture was heated to 100°C and reacted overnight. After cooling, ethyl acetate and water were added, extraction was performed, and the mixture was concentrated and purified by silica gel column chromatography to obtain the target product. Yield: 5.2 g.

[0131] Synthesis Example (17-3) Synthesis of dimethyl 4-(2-ethylhexylsulfonyl)phthalate 5.0 g of dimethyl 4-(2-ethylhexylthio)phthalate was added to 50 mL of acetic acid and 250 mg of sodium tungstate dihydrate and stirred. The mixture was heated in an oil bath set to 40°C, and 3.7 mL of 30% hydrogen peroxide solution was added dropwise. After reacting for 1 hour, the oil bath was set to 75°C and the reaction was continued for 4 hours. After the reaction was completed, the mixture was returned to room temperature, and water and ethyl acetate were added for extraction. The organic phase was washed with aqueous sodium bicarbonate and then with sodium sulfite solution. Sodium sulfite was added to this organic phase to remove moisture, and the mixture was concentrated. The residue was purified by silica gel column chromatography to obtain the target product. Yield: 4.78 g

[0132] Synthesis Example (17-4) Synthesis of 4-(2-ethylhexylsulfonyl)phthalic acid 30 mL of methanol was added to 4.4 g of dimethyl 4-(2-ethylhexylsulfonyl)phthalate, and 2.2 g of lithium hydroxide monohydrate was added. The mixture was allowed to react overnight at room temperature. The mixture was acidified with concentrated hydrochloric acid and concentrated. Ethyl acetate and water were added for extraction, and the organic phase was washed with saturated brine. After removing water with anhydrous sodium sulfate, the mixture was concentrated. The target product solidified from the oil and was obtained as a colorless solid. Yield: 3.8 g.

[0133] Synthesis Example (17-5) Synthesis of Compound (23) 1.5 g of 5-(2-ethylhexylsulfonyl)phthalic acid was added with 4.5 g of urea and 40 mg of hexaammonium heptamolybdate tetrahydrate, and the mixture was heated in an oil bath set to 165°C for 30 minutes. Then, 600 mg of ferric chloride hexahydrate and 4.5 g of urea were added, and the oil bath was set to 200°C, and the reaction was carried out for 1 hour. After cooling, water was added, and the precipitated solid was collected by filtration and purified by silica gel column chromatography to obtain compound (23). Yield: 250 mg.

[0134] Synthesis Example 18 Synthesis of compound (24) Synthesis Example (18-1) Synthesis of diethyl 2-phenylpyrimidine-4,5-dicarboxylate 21.0 g of sodium diethyl oxaloacetate was dissolved in water, acidified with 10 mL of concentrated hydrochloric acid, extracted with ethyl acetate, and concentrated. 22.2 g of triethyl orthoformate and 31.0 g of acetic anhydride were added to the residue, and the mixture was heated at 120°C for 30 minutes, 140°C for 1 hour, and 150°C for 2 hours while trapping the distillate. The distillate was then removed under reduced pressure while heating to 80°C. Toluene was added to the residue, and the azeotropic removal process was repeated.

[0135] Separately, 50 mL of ethanol was added to 6.24 g of benzamidine hydrochloride and stirred, and 20% sodium ethoxide ethanol solution was added until the mixture became basic. The toluene azeotropic residue was added to this reaction mixture. After stirring at room temperature for 30 minutes, the mixture was reacted at 85°C for 3 hours. After cooling, ethyl acetate and water were added for extraction, and the organic phase was concentrated and purified by silica gel column chromatography. The target product was precipitated as crystals from hexane. Yield: 1.0 g.

[0136] Synthesis Example (18-2) Synthesis of 2-phenylpyrimidine-4,5-dicarboxylic acid 30 mL of methanol was added to 1.7 g of diethyl 2-phenylpyrimidine-4,5-dicarboxylate, and 1.0 g of lithium hydroxide monohydrate was added. After reacting overnight at room temperature, the mixture was concentrated and water was added. When acidified with concentrated hydrochloric acid, crystals precipitated. These were collected by filtration, washed with cold water, and dried to obtain the desired product. Yield: 1.36 g.

[0137] Synthesis Example (18-3) Synthesis of Compound (24) 600 mg of 2-phenylpyrimidine-4,5-dicarboxylic acid was added with 5 g of urea, 22 mg of hexaammonium heptamolybdate tetrahydrate, and 330 mg of ferric chloride hexahydrate, and heated in an oil bath set to 185°C for 2 hours. The oil bath temperature was then set to 205°C, and the reaction was carried out for 2 hours. After this, 3 mL of N-methylpyrrolidone was added, and the mixture was heated at 205°C for 4 hours. After cooling to room temperature, 40 mL of methanol and 40 mL of water were added, and the precipitated solid was collected by filtration.

[0138] This solid was purified by silica gel column chromatography. Impurities were eluted with a mixture of chloroform and methanol, and the target compound was then eluted with N,N-dimethylformamide. The solvent was distilled off, and methanol was added. The product was filtered and dried to obtain compound (24). Yield: 198 mg.

[0139] Example 1 0.1 mg of compound (1) was dissolved in 1.0 mL of DMSO (dimethyl sulfoxide) to prepare a solution with a compound (1) concentration of 0.1 g / L. 5 mg of carbon black having a carboxyl group was dispersed in the resulting solution. During dispersion, ultrasonic treatment (20 kHz) was performed for 15 minutes. The solvent DMSO was removed from the resulting dispersion by solid-liquid separation and washing with methanol, and the resulting mixture was dried at room temperature for 24 hours to obtain the catalyst of Example 1.

[0140] Next, 0.82 mg of the obtained catalyst of Example 1, 84 μL of Milli-Q water, 336 μL of isopropyl alcohol, and 6 μL of a 0.5 mass % Nafion aqueous solution were kneaded using an ultrasonic stirrer and applied to a GC (glassy carbon) electrode to obtain the electrode of Example 1.

[0141] (half-wave potential) In an LSV (Linear Sweep Voltammetry) curve, the potential at which the current value reached half the current value at a potential of 0.5 (V vs. RHE) was defined as the half-wave potential.

[0142] (LSV curve) The LSV curve was obtained using an oxygen-saturated 0.1 M potassium hydroxide aqueous solution as the electrolyte and a rotating ring-disk electrode (BAS Corporation, RRDE-3A) at a sweep rate of 5 mV / s. The rotating disk was rotated at 1600 rpm. A Pt wire was used as the counter electrode, and Ag / AgCl was used as the reference electrode.

[0143] (LSV measurement by RRDE) LSV measurements using the RRDE were performed using a rotating ring-disk electrode (BAS Corporation, RRDE-3A) with an oxygen-saturated 0.1 M potassium hydroxide solution as the electrolyte at a sweep rate of 5 mV / s. The LSV was measured at the following rotational speeds: 0 rpm, 400 rpm, 800 rpm, 1200 rpm, 1600 rpm, 2000 rpm, and 2400 rpm. Pt was used as the counter electrode, and Ag / AgCl was used as the reference electrode.

[0144] An example of the results of LSV measurement by RRDE is shown in Figure 1. In the graph in Figure 1, the higher the applied potential (initiation potential) shown on the horizontal axis when current generation begins, shown on the vertical axis, the more excellent the oxygen reduction catalytic activity.

[0145] The onset potential and half-wave potential were measured under the same conditions as in Example 1, except that the metal complex (compound (1)) in Example 1 was changed to the metal complex shown in Table 1 below. In Comparative Example 1, manganese dioxide was used instead of the metal complex. The respective results are shown in Table 1.

[0146] [Table 1]

[0147] As shown in Table 1, the catalysts of Examples 1 to 5 according to the present invention had higher onset potentials and half-wave potentials than the catalyst of Comparative Example 1, and were found to have superior oxygen reduction catalytic activity. [Industrial Applicability]

[0148] The metal complex or adduct thereof of the present invention is useful because it has excellent oxygen reduction catalytic activity when used as a catalyst. Furthermore, it can be easily adsorbed onto conductive materials and does not require rare metals, which reduces production costs and allows the design of a production process suitable for mass production.

Claims

[Claim 1] The following formula: 【Chemistry 1】 A metal complex or an adduct thereof represented by the following formula:

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