Oxygen reduction catalyst, method for selecting the same, liquid composition or electrode containing the oxygen reduction catalyst, air battery or fuel cell equipped with the electrode

Abstract

To provide an oxygen reduction catalyst having excellent oxygen reduction catalytic activity, a selection method therefor, a liquid composition or an electrode containing the oxygen reduction catalyst, and an air battery or fuel cell provided with the electrode.SOLUTION: Provided are an oxygen reduction catalyst that contains a metal complex and a conductive material and that has an ionization potential of less than or equal to 5.80 eV, a selection method therefor, a liquid composition or an electrode containing the oxygen reduction catalyst, and an air battery or fuel cell provided with the electrode.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a catalyst for oxygen reduction and a method for selecting the same, a liquid composition or an electrode containing the catalyst for oxygen reduction, an air battery or a fuel cell including the electrode.

Background Art

[0002] Fuel cells and air batteries are known as devices that convert chemical energy into electrical energy by utilizing oxidation-reduction reactions in electrodes. In the air electrodes of these batteries, an oxygen reduction reaction occurs, and a catalyst is used to promote the reduction reaction. As a typical catalyst, in the case of a fuel cell, a carbon material supporting platinum is known, and in the case of an air battery, a carbon material supporting manganese dioxide is known.

[0003] However, since rare metals such as platinum are expensive and their resource amounts are limited, the development of catalysts using materials that are cheaper and have abundant resource amounts has been attempted. For example, Patent Document 1 discloses a catalyst for an air electrode containing iron phthalocyanine and a carbon material as a co-catalyst. However, since iron phthalocyanine is difficult to adsorb on the surface of the carbon material, its oxygen reduction ability was not sufficient.

[0004] On the other hand, Patent Document 2 discloses using graphene oxide in combination with iron phthalocyanine as a co-catalyst carbon material. However, in the method for producing the oxygen reduction catalyst disclosed in Patent Document 2, after forming a composite of iron phthalocyanine and graphene oxide once, it is necessary to reduce graphene oxide to obtain a composite of iron phthalocyanine and graphene, so there is a problem that the manufacturing process becomes complicated.

[0005] Patent Document 3 discloses a redox electrode containing a cobalt tetrapyradinoporphyrazine derivative represented by a specific structural formula as a catalyst component. However, since the cobalt tetrapyradinoporphyrazine derivative described in Patent Document 4 has a trifluoromethyl group bonded to pyrazine, there is a risk that the oxygen reduction catalytic ability may decrease.

[0006] In addition, when using the metal complexes described in Patent Documents 1 to 3 in combination with a co-catalyst as an oxygen reduction catalyst, it was unclear how to combine the metal complex and the co-catalyst until the oxygen reduction ability was actually examined, and an oxygen reduction catalyst could not be efficiently selected.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] Therefore, there has been a demand to develop a catalyst having excellent oxygen reduction catalytic ability without using rare metals such as platinum. In addition, there has been a demand for a simple method for selecting a catalyst having excellent oxygen reduction ability without examining the oxygen reduction ability.

[0009] The present invention has been made to solve the above problems of the prior art, and an object thereof is to provide an oxygen reduction catalyst having excellent oxygen reduction catalytic ability and a method for selecting the same, a liquid composition or an electrode containing the oxygen reduction catalyst, and an air battery or a fuel cell including the electrode.

Means for Solving the Problems

[0010] As a result of intensive studies on the above problems, the inventors of the present invention unexpectedly found that by using a catalyst having an ionization potential of a specific value, the catalyst has excellent oxygen reduction catalytic ability and reached the present invention. In particular, when using a metal complex as a catalyst, it was found that the ionization potential when combined with a conductive material or the like as a catalyst, rather than measuring the ionization potential of the metal complex, is very well correlated with the oxygen reduction catalytic ability, and the present invention was completed.

[0011] The object of the present invention is achieved by a catalyst for oxygen reduction, which contains a metal complex and a conductive material and has an ionization potential of 5.80 eV or less. Preferably, the catalyst for oxygen reduction of the present invention has an ionization potential of 4.80 eV or more.

[0012] The metal complex is represented by the following formula (1) or (2): [Chemical formula] (In the formula, M is a metal atom, D 1 to D 28 are each independently a nitrogen atom, a sulfur atom or a carbon atom, D 1 to D 28 When it is a carbon atom, the carbon atom may be independently 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) and is preferably represented by

[0013] It is preferable that the M is a manganese atom, an iron atom, a cobalt atom, a nickel atom, a copper atom or a zinc atom.

[0014] D 1 to D 16 are preferably a nitrogen atom or a carbon atom, and D 17 to D 28is preferably a sulfur atom or a carbon atom.

[0015] The metal complex has the following formula:

Chemical formula

Chemical formula

[0016] The metal complex is preferably contained in an amount of 75% by mass or less based on 100% by mass of the total amount of the metal complex and the conductive material.

[0017] The conductive material is preferably a carbon material.

[0018] The conductive material preferably contains a carboxyl group.

[0019] The carboxyl group is preferably contained in an amount of 20% by mass or less based on 100% by mass of the conductive material.

[0020] The present invention also relates to a liquid composition containing the oxygen reduction catalyst and a solvent of the present invention.

[0021] The present invention also relates to an electrode containing the oxygen reduction catalyst of the present invention.

[0022] The present invention also relates to an air battery or a fuel cell including the electrode of the present invention.

[0023] Furthermore, the present invention relates to a method for designing an oxygen reduction catalyst, including a step of selecting a catalyst containing a metal complex and a conductive material and having an ionization potential of 5.80 eV or less by measuring the ionization potential of the oxygen reduction catalyst.

Advantages of the Invention

[0024] According to the present invention, by using the oxygen reduction catalyst of the present invention, excellent oxygen reduction catalytic ability can be provided. In addition, since the oxygen reduction catalyst of the present invention can appropriately select an excellent catalyst by examining the ionization potential, a catalyst suitable for oxygen reduction can be easily selected.

[0025] Further, since the present invention can obtain excellent oxygen reduction catalytic ability without using rare metals such as platinum, an oxygen reduction catalyst for an air battery or a fuel cell can be provided at a relatively low cost.

Brief Description of the Drawings

[0026]

Figure 1

Modes for Carrying Out the Invention

[0027] [Oxygen Reduction Catalyst] The oxygen reduction catalyst of the present invention includes a metal complex and a conductive material, and is characterized by having an ionization potential of 5.80 eV or less. The ionization potential of the oxygen reduction catalyst is preferably 4.50 eV or more, more preferably 4.70 or more, and even more preferably 4.80 eV or more. Further, the ionization potential of the oxygen reduction catalyst is preferably 5.40 eV or less, and more preferably 5.20 eV or less. When the ionization potential is within the above range, the catalyst has high redox ability.

[0028] The method for measuring the ionization potential is not particularly limited, but it can be measured by irradiating the catalyst with ultraviolet light and measuring the emitted photoelectrons accompanying ionization. The measurement of the ionization potential can be carried out in a vacuum or in the atmosphere. For example, it can be measured using an atmospheric photoelectron spectrometer (AC-1 to AC-5, manufactured by Riken Keiki Co., Ltd.). It is also possible to determine the oxidation potential by electrochemical measurement such as cyclic voltammetry in a solution and calculate it by conversion using a material with a known ionization potential.

[0029] The oxygen reduction catalyst 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 preferably has an azaphthalocyanine skeleton, and the following formula (1) or (2):

Chemical formula

[0030] The bond between the nitrogen atom and M means the coordination of the nitrogen atom 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. Also, an anionic counter ion may be present so as to be electrically neutral.

[0031] 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 (for example, 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. Further, the structure of the alkyl group of the alkyloxy group having 1 to 8 carbon atoms may be linear, branched, or cyclic.

[0032] 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, an ytterbium atom, a lutetium, an actinium atom, a thorium atom, a protoactinium atom, a uranium atom, a neptunium atom, a plutonium atom, an 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 manganese atom, an iron atom, a cobalt atom, a nickel atom, a copper atom, or a zinc atom, and more preferably an iron atom, a cobalt atom, a nickel atom, or a copper atom.

[0033] Examples of the halogen atom in the present invention include fluorine, chlorine, bromine, and iodine.

[0034] In the present invention, the alkyl group represents a linear or branched monovalent hydrocarbon group. The number of carbon atoms in the alkyl group is preferably from 1 to 20, more preferably from 1 to 12, and even more preferably from 1 to 6. Examples of the alkyl group include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, sec-pentyl group, tert-pentyl group, and n-hexyl group.

[0035] In the present invention, the cycloalkyl group represents a cyclic monovalent hydrocarbon group. The number of carbon atoms in the cycloalkyl group is preferably from 3 to 20, more preferably from 3 to 12, and even more preferably from 3 to 6. Examples of the cycloalkyl group include cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, 1-methylcyclopropyl group, 2-methylcyclopropyl group, and 2,2-dimethylcyclopropyl group.

[0036] In the present invention, the alkenyl group represents a linear or branched monovalent hydrocarbon group containing a double bond. The number of carbon atoms in the alkenyl group is preferably from 2 to 20, more preferably from 2 to 12, and even more preferably from 2 to 6. Examples of the alkenyl group include vinyl group, 1-propenyl group, 2-propenyl group, 1-butenyl group, 2-butenyl group, 3-butenyl group, 1-methyl-2-propenyl group, 2-methyl-2-propenyl group, 1-pentenyl group, 2-pentenyl group, 3-pentenyl group, 4-pentenyl group, 1-methyl-2-butenyl group, 2-methyl-2-butenyl group, 1-hexenyl group, 2-hexenyl group, 3-hexenyl group, 4-hexenyl group, and 5-hexenyl group.

[0037] In the present invention, the alkynyl group represents 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 ethynyl group, 1-propynyl group, 2-propynyl group, 1-butynyl group, 2-butynyl group, 3-butynyl group, 1-methyl-2-propynyl group, 2-methyl-3-butynyl group, 1-pentynyl group, 2-pentynyl group, 3-pentynyl group, 4-pentynyl group, 1-methyl-2-butynyl group, 2-methyl-3-pentynyl group, 1-hexynyl group, and 1,1-dimethyl-2-butynyl group.

[0038] In the present invention, the aryl group represents 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 phenyl group, biphenyl group, terphenyl group, naphthyl group, fluorenyl group, benzofluorenyl group, dibenzofluorenyl group, phenanthryl group, anthracenyl group, benzophenanthryl group, benzoanthracenyl group, chrysenyl group, pyrenyl group, fluoranthenyl group, triphenylenyl group, benzofluoranthenyl group, dibenzoanthracenyl group, perylenyl group, and helicenyl group.

[0039] In the present invention, the alkylsulfonyl group represents a monovalent group in which an alkyl group is bonded to a sulfonyl group. The alkyl group in the alkylsulfonyl group can be the group described as the above "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 thereof include methylsulfonyl group, ethylsulfonyl group, normal propylsulfonyl group, isopropylsulfonyl group, n-butylsulfonyl group, sec-butylsulfonyl group, tert-butylsulfonyl group, n-pentylsulfonyl group, isopentylsulfonyl group, tert-pentylsulfonyl group, neopentylsulfonyl group, 2,3-dimethylpropylsulfonyl group, 1-ethylpropylsulfonyl group, 1-methylbutylsulfonyl group, n-hexylsulfonyl group, isohexylsulfonyl group, and 1,1,2-trimethylpropylsulfonyl group.

[0040] In the present invention, the alkoxy group represents a monovalent group in 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 methoxy group, ethoxy group, n-propoxy group, n-butoxy group, n-pentyloxy group, n-hexyloxy group, isopropoxy group, isobutoxy group, sec-butoxy group, tert-butoxy group, and isohexyloxy group.

[0041] In the present invention, the alkylthio group represents a group in which the oxygen atom in the ether bond of the 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 methylthio group, ethylthio group, n-propylthio group, n-butylthio group, n-pentylthio group, n-hexylthio group, and isopropylthio group.

[0042] The alkyl group, cycloalkyl group, alkenyl group, alkynyl group, aryl group, alkylsulfonyl group, alkoxy group, and alkylthio group may be unsubstituted substituents, but each 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.

[0043] 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. D 1 from D 16 Among them, the number of nitrogen atoms is preferably 2 to 12, more preferably 4 to 8. D 17 from D 28 Among them, the number of sulfur atoms is preferably 2 to 10, more preferably 4 to 8.

[0044] Preferably, the metal complex is a compound represented by the following formula.

[0045]

Chemical formula

Chemical formula

[0046] The method for producing the metal complex is not particularly limited. For example, a method of heating a dicyano compound such as pyridine-2,3-dicarbonitrile and a metal atom in an alcohol solvent in the presence of a basic substance is exemplified. Here, examples of the basic substance include inorganic bases such as potassium carbonate, sodium carbonate, calcium carbonate, sodium hydrogen carbonate, and sodium acetate; and organic bases such as triethylamine, tributylamine, and diazabicycloundecene.

[0047] The conductive material is not particularly limited as long as it has conductivity. Examples thereof include carbon materials, metal materials, and metal oxide materials. As the conductive material, a carbon material is preferable. The conductive material may be used alone or in combination of two or more kinds.

[0048] 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.

[0049] Examples of the carbon nanotube include single-walled carbon nanotube (hereinafter referred to as "SWCNT"), double-walled carbon nanotube (hereinafter referred to as "DWCNT"), and multi-walled carbon nanotube (hereinafter referred to as "MWCNT").

[0050] The carbon material may have 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 has a heteroatom, the carbon material may contain one kind of heteroatom alone or two or more kinds of heteroatoms. Note that the carbon material may be oxidized, hydroxylated, nitrided, phosphated, sulfided, or silicided.

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

[0052] The conductive material may have functional groups such as hydroxyl groups, carboxyl groups, nitrogen-containing groups, silicon-containing groups, phosphorus-containing groups such as phosphate groups, and sulfur-containing groups such as sulfonic acid groups. In particular, the carbon material preferably has a carboxyl group. When the conductive material has a carboxyl group, metal complexes are likely to adsorb on the surface of the conductive material, improving the durability of the catalyst and further enhancing the oxygen reduction catalytic ability.

[0053] The conductive material may be surface-treated by oxidation treatment. In particular, carbon materials such as carbon black can be improved in their interaction with metal complexes by imparting hydrophilic functional groups such as carboxyl groups and hydroxyl groups through oxidation treatment, and it becomes possible to control the ionization potential within an optimal range. As the oxidation treatment method, known methods can be adopted, such as wet treatment by stirring and mixing in an aqueous solution of an oxidizing agent such as nitric acid, sulfuric acid, and chloric acid, or gas-phase treatment such as plasma treatment and ozone treatment.

[0054] When the conductive material contains a carboxyl group, the content of the carboxyl group is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less with respect to 100% by mass of the conductive material. When the content of the carboxyl group is below the above upper limit value, it is advantageous because the manufacturing cost of the catalyst is reduced. Also, the content of the carboxyl group is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 8% by mass or more. When the content of the carboxyl group is above the above lower limit value, the durability of the catalyst and the oxygen reduction catalytic ability can be further enhanced. The content of the carboxyl group can be measured by elemental analysis or X-ray photoelectron spectroscopy, etc.

[0055] The specific surface area of the conductive material is preferably 0.8 m 2 / g or more, more preferably 10 m 2 / g or more, even more preferably 50 m 2 / g or more, particularly preferably 100 m 2 / g or more, and most preferably 500 m 2 / g or more. When the specific surface area is 0.8 m 2If it is / g or more, it becomes easier to increase the supported amount of the catalyst, and the oxygen reduction catalytic ability of the catalyst can be further enhanced. The upper limit value of the specific surface area is not particularly limited. For example, it can be 2000 m 2 / g. The specific surface area can be measured by a specific surface area measuring device using the nitrogen adsorption BET method.

[0056] The average particle size of the conductive material is not particularly limited. For example, 5 nm to 1000 μm is preferable, 10 nm to 100 μm is more preferable, and 50 nm to 10 μm is even more preferable. Examples of the method for adjusting the average particle size of the conductive material to the above numerical range include the following (A1) to (A3). (A1): A method in which particles are pulverized by a ball mill or the like, the obtained coarse particles are dispersed in a dispersant to a desired particle size, and then dried. (A2): A method in which particles are pulverized by a ball mill or the like, and the obtained coarse particles are sieved or the like to select the particle size. (A3): A method in which, when producing the conductive material, the production conditions are optimized to adjust the particle size of the particles. The average particle size can be measured by a particle size distribution measuring device, an electron microscope, or the like.

[0057] In the oxygen reduction catalyst of the present invention, the content of the metal complex is preferably 75% by mass or less, more preferably 50% by mass or less, and even more preferably 30% by mass or less with respect to 100% by mass of the total amount of the metal complex and the conductive material. When the content of the metal complex is below the above upper limit value, the conductivity of the catalyst is excellent. Also, the content of the metal complex 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 with respect to 100% by mass of the total amount of the metal complex and the conductive material. When the ratio of the metal complex is above the above lower limit value, the oxygen reduction catalytic ability of the catalyst can be further enhanced. If the content of the metal complex is too high, the ionization potential deviates from the preferable range and approaches the value of the metal complex alone, resulting in a decrease in the oxygen reduction performance of the catalyst. Conversely, if the content of the metal complex is too low, the ionization potential approaches the value of the conductive material, resulting in a decrease in the oxygen reduction performance of the catalyst. An optimal metal complex content can be selected based on the ionization potential values of the conductive material and the metal complex composite.

[0058] The use of the oxygen reduction catalyst of the present invention is not particularly limited. However, since it has excellent oxygen reduction catalytic ability, it can be used for oxygen reduction electrodes such as air batteries, fuel cells, and electrochemical sensors.

[0059] [Liquid composition] In one embodiment, the present invention relates to a liquid composition containing the oxygen reduction catalyst of the present invention and a solvent. The solvent may be a solvent that easily dissolves the oxygen reduction catalyst (i.e., has a high solubility), or a solvent that hardly dissolves the oxygen reduction catalyst (i.e., has a low solubility). When the solvent easily dissolves the oxygen reduction catalyst, the liquid composition is in the form of a solution. When the solvent hardly dissolves the oxygen reduction catalyst, the liquid composition is in the form of a dispersion.

[0060] The solvent is not particularly limited and may be an inorganic solvent such as water or an organic solvent. Specific examples of the organic solvent 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. The solvent may be used alone or in combination of two or more.

[0061] The liquid composition can contain, as optional components, any conductive agent, binder, and other additives. Further, it may contain a perfluorocarbon material containing a structural unit based on polytetrafluoroethylene and a perfluorinated side chain having a sulfonic acid group. Specific examples of the perfluorocarbon material include Nafion (product name: manufactured by DuPont).

[0062] The liquid composition can be produced by mixing or kneading a catalyst for oxygen reduction, a solvent, and, if necessary, a perfluorocarbon material. The mixing or kneading may be carried out using, for example, ultrasonic treatment, a mixer, a blender, a kneader, a homogenizer, a bead mill, a ball mill, or the like. Before and after the kneading operation, a sieve or the like may be used to adjust the average particle diameter of the particles. Further, when preparing a liquid composition containing a perfluorocarbon material, the catalyst for oxygen reduction, the perfluorocarbon material, and, if necessary, water and alcohol may be mixed and stirred until homogeneous.

[0063] The liquid composition can be applied to the surfaces 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 oxygen reduction (hereinafter referred to as "catalyst layer") can be provided on the surfaces of various substrates. That is, the liquid composition can be used, for example, as a coating liquid to be applied to the surface of a substrate when manufacturing an electrode. The liquid composition may be used as the coating liquid as it is, or may be used as the coating liquid after adjusting the content of the catalyst for oxygen reduction or the solid content concentration.

[0064] The base material is not particularly limited, and examples thereof include aluminum foil, electrolytic aluminum foil, aluminum mesh (expanded metal), foamed aluminum, punched aluminum, aluminum alloys such as duralumin, copper foil, electrolytic copper foil, copper mesh (expanded metal), foamed copper, punched copper, copper alloys such as 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, silver, etc. Further, a silicon substrate; a metal substrate such as gold, iron, stainless steel, copper, aluminum, and lithium; an alloy substrate containing any combination of these metals; an oxide substrate such as indium tin oxide (ITO), indium zinc oxide (IZO), and antimony tin oxide (ATO); and a substrate-like base material such as a glassy carbon, pyrolytic graphite, and carbon felt can also be used.

[0065] [Electrode] In one embodiment, the present invention relates to an electrode containing the oxygen reduction catalyst of the present invention. The electrode can be provided with a layer containing the oxygen reduction catalyst of the present invention (i.e., a catalyst layer) on the above-mentioned base material and can be used as a catalyst for the oxygen reduction reaction. The catalyst layer may be in direct contact with the base material, or another layer may be present between the base material and the catalyst layer.

[0066] The method for manufacturing the electrode is not particularly limited. For example, it may be manufactured by applying a liquid composition to the surface of a conductive base material and removing components other than the oxygen reduction catalyst. When removing components other than the oxygen reduction catalyst, heat drying may be performed, or pressing may be performed after drying. Further, the catalyst layer may be provided on the surface of the base material by vacuum deposition or the like. The electrode may have the catalyst layer on only one side of the base material, or may have it on both sides of the base material.

[0067] The thickness of the catalyst layer is not particularly limited, and can be, for example, 0.01 to 100 μm. When the thickness is equal to or greater than the lower limit value, the durability of the electrode is excellent. When the thickness is equal to or less than the upper limit value, the performance of the electrode is less likely to deteriorate.

[0068] The electrode has a function as a catalyst for the oxygen reduction reaction and has the function as a catalyst for the reduction reaction shown below. O 2 +4H + +4e - →2H 2 O O 2 +2H 2 O+4e - →4OH -

[0069] [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 the oxygen electrode of an 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 using gaseous oxygen as an electrode active material and is also called an air electrode.

[0070] The metal electrode is not particularly limited, and examples thereof include simple metals such as aluminum, magnesium, calcium, lithium, and zinc, and metal oxides thereof.

[0071] The electrolyte is preferably an aqueous electrolyte and is not particularly limited, and examples thereof include alkaline aqueous solutions such as aqueous potassium hydroxide solution and aqueous sodium hydroxide solution, and acidic aqueous solutions such as aqueous sulfuric acid solution. The electrolyte may be used alone or in combination of two or more. Further, an inorganic solid electrolyte can also be used.

[0072] The separator is a member that separates the oxygen electrode and the metal electrode, holds the 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, polymers containing poly(meth)acrylate, polymers containing sulfonate, polymers containing quaternary ammonium salts, and polymers containing quaternary phosphonium salts. The separator may be a non-porous membrane or a porous membrane. In the case of a porous membrane, the pore diameter is preferably 10 μm or less.

[0073] [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 the oxygen electrode of a fuel cell. The fuel cell can comprise an oxygen electrode, a fuel electrode, an electrolyte, and a separator.

[0074] As the fuel electrode, electrolyte, and separator used in the fuel cell, those exemplified for the metal electrode, electrolyte, and separator used in the air cell can be used respectively.

[0075] The fuel cell may be a primary battery or a secondary battery. Examples of the form of the fuel cell include metal-air batteries, molten carbonate fuel cells (MCFC), phosphoric acid fuel cells (PAFC), solid oxide fuel cells (SOFC), polymer electrolyte fuel cells (PEFC), enzyme (bio) fuel cells, microbial fuel cells, hydrazine fuel cells, and direct methanol oxidation fuel cells (DMFC). The form of the fuel cell is not limited to these examples, but PEFC, enzyme (bio) fuel cells, microbial fuel cells, hydrazine fuel cells, or DMFC are preferred. Examples of the secondary battery include hydrogen-air secondary batteries using a hydrogen storage alloy for the negative electrode.

[0076] [Method for Designing Catalyst for Oxygen Reduction] In one embodiment, the present invention relates to a method for selecting a catalyst for oxygen reduction, which includes a step of selecting a catalyst containing a metal complex and a conductive material and having an ionization potential of 5.80 eV or less by measuring the ionization potential of the catalyst for oxygen reduction. The catalyst for oxygen reduction of the present invention is particularly useful as a catalyst for oxygen reduction in an air battery or a fuel cell, especially as a catalyst for an electrode. By using an electrode containing the catalyst for oxygen reduction of the present invention as an oxygen electrode, an air battery or a fuel cell having excellent performance can be manufactured. As the catalyst for oxygen reduction, the liquid composition, the electrode, the air battery, and the fuel cell, those described above can be used.

[0077] The method for selecting a catalyst for oxygen reduction of the present invention is characterized by measuring the ionization potential of the entire catalyst for oxygen reduction. Specifically, instead of measuring the ionization potential of only the main component of the catalyst, by measuring it in the form of a composite in combination with a conductive material, a promoter, etc., the usefulness as a catalyst for oxygen reduction can be effectively examined. For example, when using the catalyst for oxygen reduction of the present invention that uses a metal complex, even if the ionization potential of only the metal complex is measured, no significant correlation is observed between the ionization potential and the performance as a catalyst for oxygen reduction. However, the ionization potential of the catalyst formed as a composite with the conductive material highly correlates with the performance as a catalyst for oxygen reduction. Therefore, an appropriate catalyst for oxygen reduction can be selected by measuring the ionization potential of the catalyst without examining the oxygen reduction catalytic ability.

[0078] The catalyst for oxygen reduction selected according to the method for selecting a catalyst for oxygen reduction of the present invention can have excellent oxygen reduction catalytic ability and can satisfy the performance required as a catalyst in the oxygen electrode of an air battery and a fuel cell.

Example

[0079] Hereinafter, the present invention will be described more specifically using examples and comparative examples, but the scope of the present invention is not limited to the examples.

[0080] <Example 1> To 1.29 g of pyridine-3,4-dicarbonitrile, 410 mg of ferric chloride anhydride and 5 mL of 1-pentanol were added, 1.52 g of 1,8-diazabicyclo[5.4.0]undec-7-ene was added, and the mixture was heated in an oil bath set at 160 °C. After 3 hours, 20 mL of N,N-dimethylformamide was added and heating was continued for another 1 hour. After cooling, 20 mL of methanol was added and the precipitated solid was collected by filtration. This solid was washed with methanol and dried to obtain the reaction product having the following formula:

[0081] [Chemical formula] Compound (1) (yield 920 mg) was obtained.

[0082] The reaction product was centrifuged three times with acetone and dried. The precipitate after centrifugation was dissolved in concentrated sulfuric acid, dropped into water, and compound (1) was precipitated. The precipitated compound (1) was recovered by centrifugation and washed with methanol to obtain compound (1). Next, 0.1 mg of the obtained compound (1) was dissolved in 1.0 mL of DMSO (dimethyl sulfoxide) to prepare a solution with a concentration of 0.1 g / L of compound (4). 5 mg of carbon black having a carboxyl group was dispersed in the obtained solution. The dispersion was carried out by ultrasonic treatment (20 kHz) for 15 minutes. The obtained dispersion was subjected to solid-liquid separation and washed with methanol to remove DMSO as the solvent, and dried at room temperature for 24 hours to obtain the catalyst of Example 1.

[0083] 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 0.5 mass% Nafion aqueous solution were kneaded with an ultrasonic stirrer and applied to a GC electrode to obtain the electrode of Example 1.

[0084] (Ionization Potential) The ionization potential was measured for the metal complex alone, which is the main component of the catalyst, and for the catalyst supported on carbon black by the above method, respectively. For the measurement of the ionization potential, an atmospheric photoelectron spectrometer AC-3 manufactured by Riken Keiki Co., Ltd. was used.

[0085] (Half-Wave Potential) In the LSV (Linear Sweep Voltammetry) curve, the potential at which the current value reached half of the current value when the potential was 0.5 (V vs. RHE) was defined as the half-wave potential.

[0086] (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 (RRDE-3A manufactured by BAS Inc.) under the condition of a sweep rate of 5 mV / s. The rotation speed of the rotating disk was 1600 rpm, a Pt wire was used as the counter electrode, and Ag / AgCl was used as the reference electrode.

[0087] (LSV Measurement by RRDE) The LSV measurement by RRDE was performed using an oxygen-saturated 0.1 M potassium hydroxide aqueous solution as the electrolyte with a rotating ring-disk electrode (RRDE-3A manufactured by BAS Inc.) under the condition of a sweep rate of 5 mV / s. The LSV was measured for each case where the rotation speed of the rotating disk was set to 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.

[0088] In the graph showing the results of the LSV measurement by RRDE, the higher the applied potential (starting potential) shown on the horizontal axis when the generation of the current shown on the vertical axis starts, the better the oxygen reduction catalytic ability.

[0089] (Examples 2 to 7, and Comparative Examples 1 and 2) The ionization potential, 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 complexes shown in Table 1 below. The compound of Comparative Example 1 has the following structure.

[0090]

Chemical formula

[0091] The measurement results are shown in Table 1.

[0092]

Table 1

[0093] The graphs of the results of LSV measurements by RRDE for Example 1 and 3, and Comparative Example 1 are shown in Fig. 1. From the results of the graphs shown in Table 1 and Fig. 1 above, it can be seen that the oxygen reduction catalyst of the present invention having an ionization potential of 5.80 eV or less has a high onset potential and excellent oxygen reduction catalytic ability. Also, even if the ionization potential of the metal complex alone exceeds 5.80 eV, it has become clear that a desired redox catalytic ability can be obtained if the ionization potential as an oxygen reduction catalyst has an ionization potential of 5.80 eV or less.

Industrial Applicability

[0094] The oxygen reduction catalyst of the present invention is useful because it has excellent oxygen reduction catalytic ability when used as a catalyst for the oxygen electrode of an air battery or a fuel cell. Also, an excellent oxygen reduction catalyst can be easily selected by examining the ionization potential. Furthermore, since no rare metal is used, the manufacturing cost can be suppressed, and a manufacturing process suitable for mass production can be designed.

Claims

1. A method for selecting an oxygen reduction catalyst, comprising a step of selecting a catalyst having an ionization potential of 4.80 eV or more and 5.80 eV or less, which contains a metal complex and a conductive material, by measuring the ionization potential of the oxygen reduction catalyst, wherein the metal complex has the following formula (1): 【Chemical 1】 (In the formula, M is an iron atom, D １ from D １６ is, independently of one another, a nitrogen atom or a carbon atom, D １ from D １６ When the carbon atom 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) represented by, and the conductive material is a carbon material. A method for selecting an oxygen reduction catalyst.)

2. The method for selecting an oxygen reduction catalyst according to claim 1, wherein the metal complex is represented by the following formula: 【Chemical 2】 【Chemical Formula 3】

3. The method for selecting an oxygen reduction catalyst according to claim 1 or 2, wherein the metal complex is contained in an amount of 75% by mass or less based on 100% by mass of the total amount of the metal complex and the conductive material.

4. The method for selecting an oxygen reduction catalyst according to any one of claims 1 to 3, wherein the conductive material contains a carboxyl group.

5. The method for selecting an oxygen reduction catalyst according to claim 4, wherein the carboxyl group is contained in an amount of 20% by mass or less based on 100% by mass of the conductive material.

6. The method for selecting an oxygen reduction catalyst according to any one of claims 1 to 5, wherein the oxygen reduction catalyst is an oxygen reduction catalyst for an air battery or a fuel cell.

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