Oxygen reduction catalysts and their applications

Abstract

This technology contributes to improving the radical resistance of organic nitrogen compounds added to oxygen reduction catalysts. [Solution] The oxygen reduction catalyst is provided with a modified layer containing a catalytic metal having oxygen reduction reaction activity, one or more organic nitrogen compounds selected from the group consisting of nitrogen organic compounds having a triazine ring, polymers containing a portion thereof, and cations thereof, and a radical quenching agent containing one or more structural parts selected from the group consisting of a hydroxyphenyltriazine skeleton and a hindered amine skeleton.

Description

[Technical Field]

[0001] This specification relates to oxygen reduction catalysts and their applications. [Background technology]

[0002] Organic nitrogen compounds added to catalyst metals used in fuel cells and metal-air batteries are known to improve the activity of the oxygen reduction reaction in the catalyst, thereby increasing the power generation efficiency of fuel cells. Examples of such organic nitrogen compounds include melamine-formaldehyde polymers obtained by polymerizing monomers having aldehyde groups (Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2024-11754 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, hydrogen peroxide is generated in the catalyst layer to which organic nitrogen compounds, such as melamine-formaldehyde polymers, are added. It has been found that hydrogen peroxide is converted into radicals by coexisting Fe ions, and these radicals can decompose the organic nitrogen compounds in the catalyst layer.

[0005] This specification provides a technology that contributes to improving the radical resistance of organic nitrogen compounds added to oxygen reduction catalysts. [Means for solving the problem]

[0006] This disclosure relates to an oxygen reduction catalyst. The oxygen reduction catalyst comprises a modified layer containing a catalytic metal having oxygen reduction reaction activity, one or more organic nitrogen compounds selected from the group consisting of nitrogen organic compounds having a triazine ring, polymers containing part thereof, and cations thereof, and a radical quenching agent containing one or more structural parts selected from the group consisting of a hydroxyphenyltriazine skeleton and a hindered amine skeleton, It is equipped with.

[0007] This oxygen reduction catalyst contains the organic nitrogen compound and a radical quenching agent in its modified layer. The radical quenching agent coexists with the organic nitrogen compound in the modified layer and remains in the modified layer regardless of fuel cell operation. Therefore, even if hydrogen peroxide radicals are generated in the modified layer, they are stably captured. As a result, the decomposition of the organic nitrogen compound is avoided or suppressed. Consequently, a decrease in the efficiency of the oxygen reduction reaction is avoided or suppressed. [Modes for carrying out the invention]

[0008] The oxygen reduction catalysts disclosed herein may further include the following embodiments. In another embodiment of the oxygen reduction catalyst, the radical quenching agent may include the hydroxyphenyltriazine skeleton and the hindered amine skeleton. This can further contribute to maintaining the power generation efficiency of the fuel cell.

[0009] Another embodiment of the oxygen reduction catalyst includes a hindered amine skeleton in which a hydroxyl group or an alkoxy group containing an alkyl group having 1 to 12 carbon atoms or a cycloalkyl group having 1 to 12 carbon atoms is bonded to the nitrogen atom on the hindered amine skeleton. This further contributes to maintaining the efficiency of fuel cell power generation.

[0010] Furthermore, the disclosure of the present specification may be a cathode for a fuel cell that contains the oxygen reduction catalyst, or may be a fuel cell provided with this cathode. Furthermore, it may be an anode for a water electrolysis system that contains the oxygen reduction catalyst, or may be a water electrolysis system provided with this anode.

[0011] Hereinafter, various embodiments of the oxygen reduction catalyst (hereinafter also simply referred to as catalyst) disclosed in the present specification will be described in detail.

[0012] The oxygen reduction catalyst disclosed in the present specification may be for fuel cells, or may be for metal-air batteries. The catalyst of the present disclosure may be used for a cathode of a fuel cell, may be used for an anode of a fuel cell, or may be used for an air electrode of a metal-air battery. Furthermore, the catalyst of the present disclosure may be used for an anode for water electrolysis which is a reverse reaction of a fuel cell, may be used for a cathode for water electrolysis, may be used for an anode for CO₂ reduction, or may be used for a cathode for CO₂ reduction.

[0013] The oxygen reduction catalyst disclosed in the present specification can take the form of, for example, a catalyst ink, and can also take a layered form. If necessary, a binder described later can be used.

[0014] (Oxygen Reduction Catalyst) The oxygen reduction catalyst disclosed in the present specification includes a catalyst metal, and a modification layer containing an organic nitrogen compound and a radical quenching agent.

[0015] (Catalyst Metal) The catalyst metal contained in the catalyst is not particularly limited as long as it has oxygen reduction activity. Examples thereof include metals such as platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, and yttrium, and two or more of these metals may be used. Furthermore, the metal may be an oxide, nitride, sulfide, phosphide, or the like.

[0016] The catalyst metal may preferably be one or more selected from platinum, platinum alloys, and platinum-containing composites. Examples of metals other than platinum included in platinum alloys and platinum-containing composites include ruthenium, iridium, rhodium, palladium, osnium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, and yttrium, and two or more of these metals may be included. The elemental ratio of metals other than platinum in the platinum alloy is not particularly limited and may be 0.11 to 50 atm%.

[0017] Such catalytic metals typically exist in the form of metal particles, and their average particle size is not particularly limited, for example, between 1 nm and 100 nm.

[0018] The catalyst metal may be supported on a carrier. Examples of carriers include carbon and oxides. Examples of carriers include conductive carbon and oxides, or mixtures containing at least two of these. Examples of carbon include carbon black (acetylene black, Ketjen black, channel black, roller black, disc black, oil furnace black, gas furnace black, lamp black, thermal black, and VULCAN® carbon), activated carbon, graphite, glassy carbon, graphite, graphene, carbon fiber, carbon nanotubes, carbon nitride, carbon sulfide, and carbon phosphide, or mixtures containing at least two of these. Examples of oxides include titanium oxide, niobium oxide, tin oxide, tungsten oxide, and molybdenum oxide, or mixtures containing at least two of these.

[0019] The carrier may be primary particles or secondary particles. The average particle diameter of the primary particles is not particularly limited, but for example, it is between 5 nm and 500 nm.

[0020] (modification layer) A modification layer is provided on the surface of the catalyst metal to accelerate its oxygen reduction activity. The modification layer contains an organic nitrogen compound and a radical quenching agent.

[0021] (Organic nitrogen compounds) The organic nitrogen compound included in the catalyst is not particularly limited, as long as it has oxygen reduction activity by the catalytic metal. Examples of such organic nitrogen compounds include organic nitrogen compounds having a triazine ring as a basic functional group, polymers containing such compounds in part, and cations thereof. This also includes cases where a cation is formed by the dissociation of the basic functional group of the organic nitrogen compound with the cation itself, or where the cation forms a salt with an organic acid or an inorganic acid.

[0022] Examples of triazine skeletons include the following structures.

[0023] [ka]

[0024] In formula (1), R 19 , R 20 , R 21These are, respectively, hydrogen atoms, halogen atoms, or nitrile groups, amide groups, imine groups, amino groups, thiol groups, hydroxyl groups, sulfo groups, carboxylic acid groups, phosphoric acid groups, ketone groups, aldehyde groups, ester groups, alkoxy groups, phenol groups, cyclopentyl groups, cyclohexyl groups, alkylamino groups with 1 to 10 carbon atoms, alkylsulfonic acid groups with 1 to 10 carbon atoms, perfluoroalkyl groups with 1 to 10 carbon atoms, alkyl groups with 1 to 10 carbon atoms, and alkeate groups with 1 to 10 carbon atoms. The functional group is selected from the group of functional groups consisting of a nylamino group, an alkenylsulfonic acid group having 1 to 10 carbon atoms, a perfluoroalkenyl group having 1 to 10 carbon atoms, and an alkenyl group having 1 to 10 carbon atoms. Each of these functional groups may have at least one selected from the group consisting of at least one functional group selected from the aforementioned group of functional groups, an aromatic ring, a heterocycle, an oxygen atom, a sulfur atom, a nitrogen atom, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, and a hydrogen atom in its molecular chain.

[0025] In formula (1), R 19 , R 20 , R 21 These may each be a primary amine, a secondary amine, a tertiary amine, or a quaternary ammonium cation.

[0026] The organic nitrogen compound may, for example, contain a melamine compound. Examples of melamine compounds include melamine and derivatives of melamine. Furthermore, it may also contain a thiocyanuric acid compound. Examples of thiocyanuric acid compounds include thiocyanuric acid and derivatives of thiocyanuric acid. Examples of cyanuric acid compounds include cyanuric acid and derivatives of cyanuric acid. Polymers using melamine compounds, thiocyanuric acid compounds, or cyanuric acid compounds as monomers include melamine resins, thiocyanuric acid resins, or cyanuric acid resins having the above-mentioned melamine compounds, thiocyanuric acid compounds, or cyanuric acid compounds in a main chain of repeating units.

[0027] More specifically, examples of organic nitrogen compounds include melamine compounds (nitrogen equivalent 21 g·eq). -1) in addition, a thiocyanuric acid compound (nitrogen equivalent 59g·eq -1 ), a cyanuric acid compound (nitrogen equivalent 34g·eq -1 ), 2,4,6-Tris[bis(methoxymetyl)amino]-1,3,5-triazine (nitrogen equivalent 65g·eq -1 ), 6-(Dibutylamino)-1,3,5-triazine-2,4-dithiol (nitrogen equivalent 68g·eq -1 ), 2,4-Diamino-6-butylamino-1,3,5-triazine (nitrogen equivalent 30g·eq -1 ), 2,4,6-Tris(pentafluoroethyl)-1,3,5-triazne (nitrogen equivalent 145g·eq -1 ), and polymers using these as monomers, as well as methylated Poly(melamine-co-formaldehyde) (nitrogen equivalent 20~40g·eq -1 ), and isobutylated Poly(melamine-co-formaldehyde) (nitrogen equivalent 20~40g·eq -1 ), may be mentioned.

[0028] The organic nitrogen compound may further include oleylamine (nitrogen equivalent 267g·eq -1 ) and tetradecylamine (nitrogen equivalent 213g·eq -1 ).

[0029] Among the above, the organic nitrogen compound may preferably be melamine (1,3,5-triazine-2,4,6-triamine) or a polymer thereof in some cases. In the case of a polymer, it is less likely to desorb after being adsorbed on metal particles than in the case of a monomer, so the adsorption stability is improved. The polymer may have a degree of polymerization in the range of 1 to 10000.

[0030] The organic nitrogen compound may be a compound that satisfies a nitrogen equivalent representing the dry weight per 1 mole of nitrogen of 20~270g·eq -1 , and may be a compound that satisfies 20~70g·eq -1The compound may also satisfy the following conditions. The nitrogen equivalent can be calculated from the following formula. In the case of a polymer, the nitrogen equivalent of the monomer is considered to be the nitrogen equivalent of the polymer. Nitrogen equivalent (g·eq) -1 ) = Molecular weight (g / mol) ÷ Amount of nitrogen in the molecule (mol) N / mol)

[0031] The content of organic nitrogen compounds in the catalyst is not particularly limited. For example, the content of organic nitrogen compounds relative to the mass of the catalyst metal-supported carrier alone can be 1.0% by mass or more and 15% by mass or less.

[0032] Here, the mass of the organic nitrogen compound is determined by extracting the organic nitrogen compound from the catalyst and measuring it by chromatography such as HPLC or GC. The mass of the support can be determined by the following method: After removing organic compounds such as the organic nitrogen compound, radical quenching agent, and binder from the catalyst by solvent separation, a support carrying the remaining catalyst metal is obtained. Furthermore, the remaining portion after burning off the support from the catalyst metal-supported support is used as the catalyst metal, and its mass can be measured. Mass spectroscopy, NMR, IR, UV, etc., can be used as appropriate for identifying the organic nitrogen compound and the support.

[0033] (Radical quenching agent) Radical quenching agents may contain one or more structural components selected from the group consisting of hydroxyphenyltriazine skeletons and hindered amine skeletons. By using radical quenching agents that have these skeletons as structural components, they can coexist with organic nitrogen compounds in the modified layer, thereby avoiding or suppressing a decrease in the radical resistance of the organic nitrogen compounds.

[0034] Radical quenching agents having a hydroxyphenyltriazine skeleton include, for example, compounds represented by the following formula (I). Having a hydroxyphenyltriazine skeleton, that is, having a triazine skeleton, increases compatibility with organic nitrogen compounds and facilitates the promotion of oxygen reduction reactions by catalytic metals.

[0035] This compound R1~R 15 Of these, for example, it is preferable to have at least one hydroxyl group. Having a hydroxyl group can facilitate coexistence with organic nitrogen compounds. For example, the hydroxyl group site can be the ortho position relative to the linkage site to the triazine skeleton. Note that R1~R 15 Each of these represents an independent functional group, but since there is a wide variety of radical quenching agents of this type, the type of individual functional group is not particularly limited. For example, the ortho position relative to the linking site of the phenyl group may have an alkyl group with 1 to 4 carbon atoms, such as a hydroxyl group or a methyl group. In addition, the para position relative to the linking site of the phenyl group may have a cycloalkyl group with 1 to 15 carbon atoms or a phenyl group, as well as a hydroxyl group in which the hydrogen atoms may be substituted with an alkyl group with 1 to 15 carbon atoms and / or an alkylene glycol alkyl ether with 1 to 10 carbon atoms.

[0036] [ka]

[0037] This type of radical quenching agent can be commercially available, for example, as so-called triazine-based light stabilizers (UV absorbers). Examples of triazine-based radical quenching agents include Tinuvin (a registered trademark of BASF; the same applies hereinafter) 400, Tinuvin 405, Tinuvin 477, Tinuvin 479, Tinuvin 1600 (all manufactured by BASF), D4527 (2-(2,4-Dihydroxyphenyl)-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine), D4819 (2-(2,4-Dihydroxyphenyl)-4,6-diphenyl-1,3,5-triazine), and E1312 (Ethylhexyl T3240(N,N',N''-Tri(m-tolyl)-1,3,5-triazine-2, 4,6-triamine), T3869(2,4,6-Tris(2,4-dihydroxyphenyl)-1,3,5-triazine), T3870(2,4,6-Tris(4-butoxy-2-hydroxyphenyl)-1,3,5-tria Examples include B4399 (2,4-Bis(2,4-dimethylphenyl)-6-(2-hydroxy-4-n-octyloxyphenyl)-1,3,5-triazine), B6145 (Bemotrizinol), and B6601 (2-[4,6-Bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl]-5-[3-[(2-ethylhexyl)oxy]-2-hydroxypropoxy]phenol) (all manufactured by Tokyo Chemical Industry Co., Ltd. (TCI)).

[0038] Examples of radical quenching agents having a hindered amine skeleton include compounds represented by the following formula (II): R 16 ~R 18Examples of these include, independently, a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group, an alkyl group having 1 to 12 carbon atoms, and an alkoxy group of a cycloalkyl group. For example, R 16 and R 17 R is a hydrogen atom, a carbonyloxy group having an alkyl group or alkenyl group with 1 to 12 carbon atoms, 18 It is preferable that the group is an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 1 to 12 carbon atoms, an alkyloxy group comprising an alkyl group or cycloalkyl group having 1 to 12 carbon atoms, or a hydroxyl group. 18 However, with these substituents, the radical quenching agent can maintain its ability to effectively promote the catalytic reaction of the catalytic metal in the modified layer. In particular, hydroxyl groups and alkoxy groups linked to the nitrogen atom on the hindered amine skeleton can sometimes promote the catalytic reaction. 18 The hydrogen atoms of the alkyl groups, cycloalkyl groups, and various alkyloxy groups may be substituted with halogen atoms, hydroxyl groups, aldehyde groups, or carboxyl groups.

[0039] R 16 ~R 18 In some cases, two hindered amine skeleton-containing compounds may be linked via one substituent to form a radical quenching agent having two hindered amine skeletons. For example, R 16 and R 17 The radical quenching agent may have two hindered amine skeletons via a linking group having a triazine skeleton, through one of the two. Having a triazine skeleton allows for good compatibility with organic nitrogen compounds, making it easier for the radical quenching agent to coexist in the modified layer and promoting the oxygen reduction reaction by the catalytic metal. In this case, R 18 However, it is even more preferable that each is an alkoxy group having a cycloalkyl group with 1 to 12 carbon atoms, such as a cyclohexyl group, an alkoxy group having an alkyl group with 1 to 12 carbon atoms, or a hydroxyl group.

[0040] [ka]

[0041] Examples of this type of radical quenching agent include, for example, Tinuvin 123 (Decanedioic acid, bis(2,2,6,6-tetramethyl-1-(octyloxy)-4-piperidinyl)ester, reaction products with 1,1-dimethylethylhydroperoxide and octane), Tinuvin 152, Tinuvin 144 (Bis(1,2,2,6,6-pentamethyl-4-piperidinyl)-[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butylmalonate), Tinuvin 292 (Bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate Methyl(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate), Tinuvin770DF (Bis(2,2,6,6-tetramethyl-4-piperidyl)Sebacate) (all manufactured by BASF), and B5642 (Bis(2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) Sebacate), B6267 (Bis(1,2,2,6,6-pentamethyl-4-piperidyl) Butyl(3,5-di-tert-butyl-4-hydroxybenzyl)malonate), S0448 (Bis(2,2,6,6-tetramethyl-4-piperidyl) Sebacate), T2324 (2,2,6,6-Tetramethyl-4-piperidyl Methacrylate), P1513 (1,2,2,6,6-Pentamethyl-4-piperidyl Methacrylate (stabilized with MEHQ), B6154(N 1 ,N 3Examples include Bis(2,2,6,6-tetramethylpiperidin-4-yl)isophthalamide) (manufactured by TCI Corporation).

[0042] Furthermore, it is preferable that the radical quenching agent having a hindered amine skeleton has a pkb of 7.0 or higher. Such basicity may make it easier to retain in the modified layer.

[0043] The structural formulas for Tinuvin 400, 405, and 152, as shown in the examples above, are as follows.

[0044] [ka]

[0045] The amount of radical quenching agent is not particularly limited, but it is sufficient if it is an amount that can avoid or suppress the decomposition of the organic nitrogen compound by radicals. For example, an equivalent amount of radical quenching agent can be used relative to the mass of the organic nitrogen compound. For example, the amount of radical quenching agent can be used such that it is 70% to 130%, 80% to 120%, or 90% to 110% relative to the mass of the support and the content of the organic nitrogen compound (mass%). The mass of the radical quenching agent is measured by extracting the radical quenching agent from the catalyst and measuring the radical quenching agent by chromatography such as HPLC or GC. The mass of the support can be measured by the following method: After removing the organic nitrogen compound and other organic compounds such as binders from the catalyst by solvent separation, a support carrying the remaining catalyst metal can be obtained, and the mass of the support can be measured from the remaining portion after the support has been burned off by calcination. Mass spectroscopy, NMR, IR, UV, etc. can be used as appropriate for identifying the quenching agent, etc.

[0046] (Binder) The catalyst may also contain a binder. The binder is a polymer electrolyte, for example, an ion exchange group such as an acidic functional group or a basic functional group. Polymer electrolytes are sometimes called electrolytes, ionsomers, or ionsomers. Examples of acidic functional groups include sulfonic acid and phosphoric acid. Examples of basic functional groups include quaternary ammonium cations. The binder may be a perfluorocarbon sulfonic acid polymer, an anion exchange polymer, or a polymer mainly composed of polyether ether ketone and polybenzimidazole.

[0047] The binder content in the catalyst is not particularly limited; it is sufficient as long as it can form a modification layer on the catalyst metal. For example, the ratio of binder mass to support mass can be between 70% and 115% by mass. The support mass is as previously explained. The binder mass is determined by extracting the binder from the catalyst and measuring its mass. For binder identification, mass spectrometry, NMR, IR, UV, etc., can be used as appropriate.

[0048] As previously described, the catalyst can take the form of a catalyst ink, and after the application of the catalyst ink, it can take the form of a catalyst layer. The formation of the catalyst ink and catalyst layer will be described below.

[0049] (Catalyst ink preparation) First, predetermined amounts of a catalyst metal-supported carrier (catalyst metal-supported carrier), an organic nitrogen compound, a radical quenching agent, a binder, and a solvent are added to a container, and these are stirred using a stirrer to prepare the catalyst ink. The type of solvent is not particularly limited, and any liquid can be used. For example, alcohol or a mixed solution of at least one alcohol and water can be used. Examples of alcohols include methanol, diacetone alcohol, ethanol, 1-propanol, 2-propanol, tert-butyl alcohol, ethylene glycol, and propylene glycol.

[0050] The agitator is not particularly limited, and various known agitators can be used as appropriate. Examples include ultrasonic homogenizers, jet mills, ball mills such as bead mills, high-shear mills, film mixers, etc. The stirring conditions, such as stirring speed, stirring time, and rotation speed, are not particularly limited and can be set as appropriate.

[0051] After stirring, perform vacuum degassing and let it stand for one day. There is no limit to the standing time; it can be set as desired. It is also possible to use the product without standing. Furthermore, vacuum degassing may be performed again.

[0052] (Fabrication of the catalyst layer) The prepared catalyst ink is coated onto a predetermined substrate, and the solvent is removed after coating. For example, the catalyst ink is coated onto the substrate, the coated catalyst ink is heated, and the solvent is dried and removed.

[0053] The substrate is not particularly limited, but examples include polytetrafluoroethylene (PTFE), an electrolyte membrane having ion exchange groups, a gas diffusion layer (GDL) composed of carbon fibers or metal fibers, and a gas diffusion layer composed of carbon fibers or metal fibers having a microporous layer (MPL).

[0054] The coating method can be any method that allows for uniform coating of the catalyst ink onto the substrate, and examples include die coating, spin coating, screen printing, doctor blade coating, squeegee coating, spray coating, and applicator coating. The heating rate and heating time can be appropriately set depending on the type of solvent, etc. The removal rate may also be increased by degassing simultaneously with heating. The coating film thickness may be 5 to 30 μm, and the platinum content may be 0.1 to 0.6 mg / cm². -2 The coating may be applied in such a way that it satisfies the following conditions.

[0055] (catalyst layer) This specification provides an oxygen reduction catalyst layer or an oxygen evolution catalyst layer containing the catalyst. Since the oxygen reduction reaction of the catalyst metal is reversible, a fuel cell is also provided that includes this catalyst layer as a cathode (oxygen reduction catalyst layer). The fuel cell is, for example, a PEFC. In such a fuel cell, a decrease in the power generation efficiency of the fuel cell due to radical generation is avoided or suppressed.

[0056] Furthermore, a water electrolysis device is also provided that includes a catalyst layer containing the catalyst as an anode (oxygen evolution reaction catalyst layer). In such a water electrolysis device, a decrease in the water production efficiency of the water electrolysis device due to radical generation is avoided or suppressed. [Examples]

[0057] The following describes embodiments that embody the disclosures of this specification. These embodiments are illustrative and not intended to limit the scope of the disclosure. [Examples]

[0058] A catalyst metal particle-supported carrier, on which platinum particles (particle size: 3-4 nm) as a catalyst metal are supported, was prepared. A predetermined amount of the following were added to a container: an organic nitrogen compound (a melamine resin), a radical quenching agent, perfluorocarbon sulfonic acid as a binder, and a water-alcohol mixture as a solvent, as shown in the table below. The mass of the organic nitrogen compound and the radical quenching agent were both 3% by mass relative to the carrier mass. These materials were mixed and stirred using a stirrer (homogenizer, film mix) to prepare catalyst inks for Examples 1-4, which contained an oxygen reduction catalyst. Comparative Example 1's catalyst ink was prepared in the same manner as Example 1, except that it did not contain a radical quenching agent. Furthermore, Comparative Example 2's catalyst ink was prepared in the same manner as Example 1, except that it did not contain an organic nitrogen compound or a radical quenching agent.

[0059] [Table 1]

[0060] The radical quenching agents used in Examples 1 to 4 had the following characteristics in addition to those shown in Table 1. Example 1: Two hindered amine skeletons are linked to a carbon atom of one hydroxyphenyltriazine skeleton. Example 2: Two hindered amine skeletons are linked to each other. Example 3: Two hindered amine skeletons are linked to each other. Example 4: It has two hydroxyl groups.

[0061] A catalyst ink, which had undergone degassing treatment as appropriate, was coated onto a substrate. After coating, the catalyst ions were heated to dry and remove the solvent, thereby creating a catalyst layer.

[0062] Next, each of the fabricated catalyst layers was prepared as a cathode catalyst layer, a perfluorocarbon sulfonic acid polymer (Nafion NR211, EW:1100, manufactured by Chemors) as the electrolyte membrane, and a platinum-supported carbon catalyst (TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo) as the anode catalyst layer. The electrolyte membrane was sandwiched between the cathode catalyst layer and the anode catalyst layer. The cathode catalyst layer, electrolyte membrane, and anode catalyst layer were thermocompressed together under heating (130°C) and pressurizing (3 MPa) conditions. A gas diffusion layer made of carbon fibers (GDL 22BB, manufactured by SGL) was placed outside the cathode catalyst layer and the anode catalyst layer to fabricate a membrane electrode assembly (MEA) (electrode section: 1 cm × 1 cm).

[0063] Next, the current-voltage characteristics were measured using the fabricated MEA as a single cell under low humidity conditions (30%RH) and high humidity conditions (80%RH). The measurement conditions were as follows: Sweep speed: 20mA / s (anode sweep), cell temperature: 80℃, pressure: 150kPa_ABS, cathode gas type: air, cathode gas flow rate: 2.0L / min.

[0064] (Evaluation of radical quenching performance) Using a membrane electrode assembly into which 2 μg of Fe ions were introduced, the temperature was set to 95°C, 40% RH, and 0.05 A / cm². 2The system was held for 72 hours. This prepared a system in which hydrogen peroxide generated within the system was converted into radicals by Fe ions. Subsequently, the current-voltage characteristics were evaluated and the cell voltage maintenance rate was calculated in the same manner as described above. The results are shown in Table 1.

[0065] As shown in Table 1, Example 1, which used a radical quenching agent having a hindered amine skeleton with an alkoxy group having a cycloalkyl group as OR and further containing a triazine skeleton internally, showed the highest cell voltage maintenance rate (94%). Next, Example 2, which used a radical quenching agent having a hindered amine skeleton with an alkoxy group having an alkyl group as OR and further not containing a triazine skeleton internally, showed the next highest maintenance rate (90%). Example 3, which used a radical quenching agent having a hindered amine skeleton with a methyl group as R and not containing a triazine skeleton internally, showed the following maintenance rate (87%).

[0066] From the above, it was found that in radical quenching agents having a hindered amine skeleton, the presence of a triazine skeleton may be preferable for exhibiting radical quenching performance. Furthermore, it was found that having various alkoxy groups linked to the N of the hindered amine may be preferable for exhibiting radical quenching performance than having alkyl groups, and that the alkoxy group of a cycloalkyl group may be preferable for exhibiting radical quenching performance than the alkoxy group of an alkyl group.

[0067] It was found that radical quenching agents having a hydroxyphenyltriazine skeleton can exhibit radical quenching performance by inherently possessing the triazine skeleton.

[0068] The results from Comparative Examples 1 and 2 showed that the inclusion of organic nitrogen compounds is useful, and that the inclusion of radical quenching agents significantly contributes to maintaining the oxygen reduction reaction promoting activity of the catalytic metal of the organic nitrogen compound.

Claims

1. An oxygen reduction catalyst, A catalyst metal having oxygen reduction reaction activity, A modified layer containing one or more organic nitrogen compounds selected from the group consisting of a nitrogen organic compound having a triazine ring, a polymer containing a part thereof, and cations thereof, and a radical quenching agent containing one or more structural parts selected from the group consisting of a hydroxyphenyltriazine skeleton and a hindered amine skeleton, An oxygen reduction catalyst equipped with the following features.

2. The oxygen reduction catalyst according to claim 1, wherein the radical quenching agent comprises the hydroxyphenyltriazine skeleton and the hindered amine skeleton.

3. The oxidation-reduction catalyst according to claim 1, wherein the radical quenching agent has a hydroxyl group or an alkoxy group containing an alkyl group having 1 to 12 carbon atoms or a cycloalkyl group having 1 to 12 carbon atoms bonded to a nitrogen atom on the hindered amine skeleton.

4. A cathode for a fuel cell comprising the oxygen reduction catalyst according to any one of claims 1 to 3.

5. A fuel cell comprising the cathode described in claim 4.

6. An anode for a water electrolysis system comprising the oxygen reduction catalyst according to any one of claims 1 to 3.

7. A water electrolysis system comprising the anode described in claim 6.

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