Ionomer

Abstract

To provide an ionomer having high binder performance and surface active performance.SOLUTION: One embodiment of the present invention relates to an ionomer which has an acidic functional group, a fluorine-containing cyclic group, and a modifying layer that modifies the acidic functional group, the fluorine-containing cyclic group containing 3 to 16 ring member atoms, the modifying layer containing a nitrogen-containing cyclic organic compound or a polymer thereof,or a cation of the nitrogen-containing cyclic organic compound or the polymer. Another embodiment of the present invention relates to a fuel cell which includes at least: an electrode catalyst layer of a cathode containing an electrochemical oxygen reduction catalyst and the ionomer of the one embodiment of the present invention; an electrode catalyst layer of an anode; and an electrolyte membrane disposed between the electrode catalyst layer of the cathode and the electrode catalyst layer of the anode. A still another embodiment of the present invention relates to a method of producing the ionomer of the one embodiment of the present invention, the method including a modification step of mixing an ionomer material having an acidic functional group and a fluorine-containing cyclic group with a modifying agent containing a nitrogen-containing cyclic organic compound or a polymer thereof, or a cation of the nitrogen-containing cyclic organic compound or the polymer, and modifying the acidic functional group.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to ionomers. [Background technology]

[0002] Fuel cells generate electricity through the electrochemical reaction of hydrogen and oxygen. In principle, the only product produced during fuel cell power generation is water. Therefore, fuel cells have attracted attention as a clean power generation system with minimal environmental impact. Fuel cells are constructed using a membrane electrode assembly (MEA) as a basic unit. This assembly consists of electrode catalyst layers on both sides of an electrolyte membrane, with gas diffusion layers on the outer surface of each electrode catalyst layer. During fuel cell operation, electromotive force is generated by supplying a hydrogen-containing fuel gas to the electrode catalyst layer on the anode (fuel electrode) side and an oxygen-containing oxidizing gas to the electrode catalyst layer on the cathode (air electrode) side. The hydrogen oxidation reaction occurs at the anode, and the oxygen reduction reaction occurs at the cathode, supplying electromotive force to an external circuit. For this reason, an oxygen reduction catalyst with oxygen reduction ability is used in the cathode electrode catalyst layer. Polymer electrolytes with ion exchange groups (also referred to as "ionomers" below) are typically used for the binders in the electrode catalyst layers and the electrolyte membrane.

[0003] For example, Patent Document 1 describes an ionomer comprising an acidic group-containing polymer and a basic group-containing metal complex. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-161154 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, various ionomers have been developed that can be used in fuel cell electrode catalyst layers. In fuel cell electrode catalyst layers, particularly cathode electrode catalyst layers, it is necessary to smoothly supply protons and oxygen to the electrode catalyst. Ionomers typically contain acidic ion-exchange groups, which can contribute to proton transport but can also inhibit oxygen transport. To address this issue, for example, Patent Document 1 describes that an ionomer containing an acidic group-containing polymer and a basic group-containing metal complex exhibits high oxygen solubility even under acidic conditions. Patent Document 1 also describes that an ionomer containing the acidic group-containing polymer exhibits high oxygen permeability when the acidic group-containing polymer has an aliphatic ether ring structure, which is a fluorine-containing cyclic group. However, such prior art ionomers have room for improvement in their binder performance and surfactant performance for electrode catalysts.

[0006] Therefore, an object of the present invention is to provide an ionomer having high binder and surfactant properties. [Means for solving the problem]

[0007] The present inventors have investigated various means for solving the above-mentioned problems. They have found that the binder performance and surfactant performance of an ionomer can be improved by using a modifying layer containing a nitrogen-containing cyclic organic compound, a polymer thereof, or a cation of either of them as a modifying layer for modifying the acidic functional group of an ionomer having a fluorine-containing cyclic group. Based on this finding, the present inventors have completed the present invention.

[0008] That is, the present invention includes the following aspects and embodiments. (Embodiment 1) An ionomer having an acidic functional group, a fluorine-containing cyclic group, and a modifying layer that modifies the acidic functional group, wherein the fluorine-containing cyclic group contains 3 to 16 ring atoms, and the modifying layer comprises a nitrogen-containing cyclic organic compound or a polymer thereof, or a cation thereof. Embodiment 2: The ionomer of embodiment 1, wherein the fluorine-containing cyclic group is 1,3-dioxolane-4,5-diyl substituted with one or more perfluoroalkyl groups. (Embodiment 3) The ionomer of embodiment 1 or 2, wherein the modification layer comprises 1,3,5-triazine, ammelide, or melamine. (Embodiment 4) A fuel cell comprising at least a cathode electrode catalyst layer comprising an electrochemical oxygen reduction catalyst and the ionomer described in any one of embodiments 1 to 3, an anode electrode catalyst layer, and an electrolyte membrane disposed between the cathode electrode catalyst layer and the anode electrode catalyst layer. (Embodiment 5) A modification step in which an ionomer material having an acidic functional group and a fluorine-containing cyclic group is mixed with a modifying agent containing a nitrogen-containing cyclic organic compound, a polymer thereof, or a cation thereof to modify the acidic functional group. 4. A method for producing the ionomer of any one of claims 1 to 3, comprising: [Effects of the Invention]

[0009] The present invention makes it possible to provide an ionomer having high binder performance and surfactant performance. DETAILED DESCRIPTION OF THE INVENTION

[0010] Preferred embodiments of the present invention will now be described in detail.

[0011] <1: Ionomer> One aspect of the present invention relates to an ionomer. The ionomer of this aspect has an acidic functional group, a fluorine-containing cyclic group, and a modifying layer that modifies the acidic functional group.

[0012] Examples of the polymer constituting the ionomer of this embodiment include polymers mainly composed of perfluorocarbon, polyether ether ketone, polybenzimidazole, etc. The polymer constituting the ionomer of this embodiment is preferably perfluorocarbon. By being composed of the polymers exemplified above, the ionomer of this embodiment can exhibit high proton conductivity.

[0013] In the ionomer of this embodiment, examples of the acidic functional group include a sulfonic acid group and a phosphoric acid group. The acidic functional group is preferably a sulfonic acid group. By having the acidic functional group exemplified above, the ionomer of this embodiment can exhibit high proton conductivity.

[0014] In each embodiment of the present invention, the fluorine-containing cyclic group refers to a monocyclic or polycyclic group having one or more fluorine atoms as ring-bonding groups and / or as substituents of the ring-bonding groups. In the ionomer of this embodiment, the fluorine-containing cyclic group typically contains 3 to 16 ring atoms. The number of ring atoms in the fluorine-containing cyclic group is preferably 3 to 6. The cyclic group constituting the fluorine-containing cyclic group may contain, in addition to carbon atoms, one or more heteroatoms such as oxygen atoms, nitrogen atoms, or sulfur atoms as ring-bonding atoms. Examples of cyclic groups constituting the fluorine-containing cyclic group include monovalent or polyvalent groups derived from cyclopropane, cyclobutane, cyclopentane, cyclohexane, oxirane, furan, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, or propanedisulfonimide. The cyclic groups exemplified above may have one or more fluorine atoms as ring-bonding groups and / or as substituents of the ring-bonding groups. Examples of substituents having one or more fluorine atoms include linear or branched perfluoroalkyl, perfluoroalkylene, and perfluoroalkoxy groups having 1 to 10 carbon atoms. The above-exemplified substituents may be interrupted by one or more heteroatoms such as oxygen, nitrogen, or sulfur atoms. When the fluorine-containing cyclic group has a dissociable group, the fluorine-containing cyclic group may be in the form of a free acid or free base, or in the form of a salt with any counterion. In each aspect of the present invention, the fluorine-containing cyclic group is preferably 1,3-dioxolane-4,5-diyl substituted with one or more perfluoroalkyl groups. By containing the fluorine-containing cyclic group exemplified above, the ionomer of this aspect can exhibit high binder performance and surfactant performance.

[0015] In the ionomer of this embodiment, the structures of the constituent polymers, acidic functional groups, and fluorine-containing cyclic groups can be determined by analyzing the ionomer of this embodiment, for example, by elemental analysis, various types of chromatography, ultraviolet-visible spectroscopy (UV-Vis), infrared spectroscopy (IR), or nuclear magnetic resonance (NMR).

[0016] In the ionomer of this embodiment, the modifying layer contains a nitrogen-containing cyclic organic compound, a polymer thereof, or a cation thereof. The component can interact with the acidic functional group and / or the polymer constituting the ionomer. For example, the component typically forms a complex, particularly an ionic bond, with the acidic functional group modified by the modifying layer. Conventional ionomers without a modifying layer typically have low oxygen transport properties within the ionomer due to the high crystallinity of the polymer constituting the ionomer. Furthermore, conventional ionomers typically have low oxygen transport properties at the interface between the ionomer and the electrode catalyst due to the high adsorption of the polymer constituting the ionomer to the electrode catalyst. Furthermore, conventional ionomers (e.g., Patent Document 1) that have a modifying layer containing an acidic group-containing polymer having an aliphatic ether ring structure corresponding to a fluorine-containing cyclic group and an organic compound such as a basic group-containing metal complex have poor binder and / or surfactant properties when used as a binder for an electrode catalyst, possibly resulting in aggregation of electrode catalyst particles and / or cracking of the electrode catalyst layer. In contrast, in the ionomer of this embodiment, the nitrogen-containing cyclic organic compound or its polymer, or their cations contained in the modification layer interact with the acidic functional group, the fluorine-containing cyclic group, and / or the polymer constituting the ionomer, thereby optimizing the crystallinity and / or adsorption to the electrode catalyst of the polymer, thereby not only improving the oxygen transport property but also substantially suppressing the aggregation of electrode catalyst particles when used as a binder for the electrode catalyst. Therefore, by having a catalyst layer containing the components exemplified above, the ionomer of this embodiment can exhibit high binder performance and surfactant performance in addition to high oxygen transport property.

[0017] In each embodiment of the present invention, the nitrogen-containing cyclic organic compound or its polymer, or their cation means a compound containing nitrogen atoms in the ring members and / or ring-bonding groups of a monocyclic or polycyclic organic compound, or its polymer, or their cation. The nitrogen equivalent of the nitrogen-containing cyclic organic compound is usually in the range of 20 to 270 g / equivalent, particularly in the range of 20 to 70 g / equivalent. The nitrogen equivalent of the nitrogen-containing cyclic organic compound can be calculated by the following formula: Nitrogen equivalent (g / equivalent) = molecular weight of nitrogen-containing organic compound (g / mol) / amount of nitrogen atoms contained in one molecule of nitrogen-containing organic compound (mol N / mol) In the case of a polymer of a nitrogen-containing cyclic organic compound, the nitrogen equivalent of the monomer contained in the polymer may be within the range exemplified above.

[0018] The number of nitrogen atoms in the nitrogen-containing cyclic organic compound is not particularly limited. For example, the number of nitrogen atoms in the nitrogen-containing cyclic organic compound is preferably 3 or more, more preferably 3 to 6, as the total number of basic nitrogen atoms. In addition, the number of nitrogen atoms in the nitrogen-containing cyclic organic compound is preferably 3 or less, more preferably 0 to 3, as the total number of nitrogen atoms in the ring-bonding groups.

[0019] Examples of nitrogen-containing cyclic organic compounds include pyridine, pyrrole, thiazole, isothiazole, oxazole, isoxazole, imidazole, imidazoline, pyrazole, 1,3,5-triazine, pyrimidine, pyritazine, pyrazine, indole, quinoline, isoquinoline, purine, benzimidazole, benzoxazole, benzthiazole, tetrazole, tetrazine, triazole, carbazole, acridine, quinoxaline, and quinazoline. The nitrogen-containing cyclic organic compounds exemplified above may include one or more substituted or unsubstituted amines or aminos (e.g., primary amines, secondary amines, tertiary amines, or quaternary ammonium cations), hydroxyls, halogens (e.g., fluorine, chlorine, bromine, or iodine), nitriles, amides, imides, thiols, sulfonyls, carboxyls, phosphonyls, ketones, aldehydes, esters, substituted or unsubstituted alkyls, substituted or unsubstituted alkenyls, substituted or unsubstituted alkynyls, substituted or unsubstituted cycloalkyls, substituted or unsubstituted cycloalkenyls, substituted or unsubstituted cycloalkynyls, substituted or unsubstituted heterocycloalkyls, substituted or unsubstituted cycloalkyl ... The ring may have an alkylalkyl, a substituted or unsubstituted heterocycloalkylalkyl, a substituted or unsubstituted aryl, a substituted or unsubstituted arylalkyl, a substituted or unsubstituted heteroaryl, a substituted or unsubstituted heteroarylalkyl, a substituted or unsubstituted alkoxy, a substituted or unsubstituted cycloalkoxy, a substituted or unsubstituted heterocycloalkoxy, a substituted or unsubstituted aryloxy, a substituted or unsubstituted arylalkyloxy, a substituted or unsubstituted arylalkenyloxy, a substituted or unsubstituted heteroaryloxy, a substituted or unsubstituted heteroarylalkyloxy, or a substituted or unsubstituted acyloxy as a ring-linking group. The number of carbon atoms in the above-exemplified groups is usually 1 to 10 in the case of a linear structure, and usually 3 to 16 in the case of a cyclic structure. When the above-exemplified groups are substituted, the substituents are preferably one or more groups selected from the above-exemplified groups.

[0020] The nitrogen-containing cyclic organic compound or its polymer, or its cation is preferably melamine (1,3,5-triazine-2,4,6-triamine), ammeline, ammelide, cyanuric acid, or triazine (1,2,3-triazine, 1,2,4-triazine, or 1,3,5-triazine), or its derivative, or its polymer, or its cation, and examples thereof include melamine or its derivative (nitrogen equivalent: 21 g / equivalent), ammeline, ammelide, 1,3,5-triazine or its derivative (nitrogen equivalent: 27 g / equivalent), thiocyanuric acid or its derivative (nitrogen equivalent: 59 g / equivalent), cyanuric acid or its derivative (nitrogen equivalent: 34 g / equivalent), oleylamine or its derivative (nitrogen equivalent: 267 g / equivalent), tetradecylamine or its derivative (nitrogen equivalent: 213 g / equivalent), g / equivalent), 2,4,6-tris[bis(methoxymethyl)amino]-1,3,5-triazine (nitrogen equivalent 65 g / equivalent), 6-(dibutylamino)-1,3,5-triazine-2,4-dithiol (nitrogen equivalent 68 g / equivalent), 2,4-diamino-6-butylamino-1,3,5-triazine (nitrogen equivalent 30 g / equivalent), or 2,4,6-tris(pentafluoroethyl)-1,3,5-triazine (nitrogen equivalent 145 g / equivalent), or polymers of these monomers, or methylated poly(melamine-co-formaldehyde) (nitrogen equivalent 20 to 40 g / equivalent), or isobutylated poly(melamine-co-formaldehyde) (nitrogen equivalent 20 to 40 g / equivalent). More preferably, the copolymer is a copolymer such as a melamine-formaldehyde copolymer such as a melamine-formaldehyde copolymer (g / equivalent), or a cation thereof, and even more preferably, 1,3,5-triazine, ammelide, or melamine, or a cation thereof.

[0021] Examples of the polymer of the nitrogen-containing cyclic organic compound include a homopolymer or copolymer containing at least one of the above-mentioned nitrogen-containing cyclic organic compounds as a monomer. In the case of the polymer of the nitrogen-containing cyclic organic compound, the degree of polymerization is preferably in the range of 1 to 10,000, more preferably in the range of 10 to 10,000.

[0022] The content of the nitrogen-containing cyclic organic compound, its polymer, or its cation is preferably in the range of 1 to 120 mol%, more preferably 10 to 60 mol%, based on the total amount of acidic functional groups. Furthermore, the content of the nitrogen-containing cyclic organic compound, its polymer, or its cation is preferably 10 mass% or less, more preferably 0.1 to 10 mass%, based on the total mass of the ionomer of this embodiment. If the content of the nitrogen-containing cyclic organic compound, its polymer, or its cation is less than the above-mentioned lower limit, the desired effects may not be achieved. If the content of the nitrogen-containing cyclic organic compound, its polymer, or its cation exceeds the above-mentioned upper limit, the binder performance and / or surfactant performance may be reduced. Therefore, by having a catalyst layer containing the nitrogen-containing cyclic organic compound, its polymer, or its cation in the above-mentioned content, the ionomer of this embodiment can exhibit high binder performance and surfactant performance.

[0023] The composition and content of the nitrogen-containing cyclic organic compound or its polymer, or their cations contained in the modified layer can be determined, for example, by dissolving and extracting the modified layer contained in the ionomer of this embodiment, and analyzing the components contained in the extract by elemental analysis, various types of chromatography, ultraviolet-visible spectroscopy (UV-Vis), infrared spectroscopy (IR), or nuclear magnetic resonance (NMR).

[0024] By having the above-described characteristics, the ionomer of this embodiment can exhibit high binder performance and surfactant performance.

[0025] The binder performance and surface activity performance of the ionomer of this embodiment can be evaluated, for example, by preparing a catalyst ink for an electrochemical oxygen reduction catalyst using the ionomer as a binder and measuring the particle size distribution of the electrode catalyst particles in the catalyst ink (e.g., the D50 and D90 values ​​and the amount of change therein). Alternatively, the binder performance and surface activity performance can be evaluated by fabricating an MEA using the prepared catalyst ink and employing the electrochemical oxygen reduction catalyst as the cathode, and checking for the occurrence of cracks in the electrode catalyst layer of the cathode.

[0026] The oxygen transport property of the ionomer of this embodiment can be evaluated, for example, by preparing an electrochemical oxygen reduction catalyst using the ionomer as a binder, fabricating an MEA using the electrochemical oxygen reduction catalyst as the cathode, and measuring the oxygen diffusion resistance in the electrode catalyst layer of the MEA.

[0027] The proton conductivity of the ionomer of this embodiment can be evaluated, for example, by preparing an electrochemical oxygen reduction catalyst using the ionomer as a binder, fabricating an MEA using the electrochemical oxygen reduction catalyst as a cathode, and measuring the current-voltage characteristics (e.g., proton transport resistance in the electrode catalyst layer or cell voltage at a predetermined current density) of the MEA under low humidification conditions (e.g., 30% RH) and high humidification conditions (e.g., 80% RH).

[0028] <2: Electrochemical oxygen reduction catalyst> Another aspect of the present invention relates to an electrochemical oxygen reduction catalyst, which comprises a catalytic metal having oxygen reduction activity and a binder containing the ionomer of one aspect of the present invention.

[0029] In the electrochemical oxygen reduction catalyst of this embodiment, the catalytic metal may be any metal having oxygen reduction activity (oxygen reduction catalytic ability). Examples of the catalytic metal include 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. The catalytic metal may contain the above-exemplified metals alone or as an alloy of two or more of them. The catalytic metal may also be an oxide, nitride, sulfide, or phosphide of the above-exemplified metal. The catalytic metal is preferably platinum, a platinum alloy, or a platinum-containing composite. In the case of platinum alloys and platinum-containing composites, examples of metals other than platinum include ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, and yttrium. Platinum alloys and platinum-containing composites may contain two or more of the metals exemplified above. By containing the catalytic metals exemplified above, the electrochemical oxygen reduction catalyst of this embodiment can exhibit high oxygen transport properties and / or proton conductivity.

[0030] The content of the catalytic metal is typically in the range of 1 to 70 mass%, for example, 48 to 50 mass%, and particularly 18 to 48 mass%, relative to the total mass of the electrochemical oxygen reduction catalyst of this embodiment. Furthermore, when the catalytic metal is a platinum alloy or a platinum-containing composite, the content of metals other than platinum is typically in the range of 0.11 to 60 atomic % relative to the total mass of the catalytic metal. By containing the catalytic metal in an amount within this range, the electrochemical oxygen reduction catalyst of this embodiment can exhibit high oxygen transportability and / or proton conductivity.

[0031] The particle size of the catalyst metal is usually in the range of 1 to 100 nm.

[0032] In the electrochemical oxygen reduction catalyst of this embodiment, the composition and content of the catalytic metal can be determined, for example, by dissolving and extracting the catalytic metal contained in the electrochemical oxygen reduction catalyst of this embodiment, and analyzing the metal elements contained in the extract by thermogravimetric analysis (IG) or inductively coupled plasma optical emission spectroscopy (ICP).

[0033] In the electrochemical oxygen reduction catalyst of this embodiment, the particle size of the catalytic metal can be determined, for example, by measuring the crystallite size by X-ray diffraction and calculating the average crystallite size. Alternatively, the particle size of the catalytic metal may be determined by measuring the particle sizes of 100 to 1,000 catalytic metal particles using an electron microscope and calculating the average value (average particle size) of these.

[0034] The electrochemical oxygen reduction catalyst of this embodiment typically has a support that supports the catalytic metal. Examples of the support include electrically conductive carbon and oxides, as well as mixtures of one or more thereof. The carbon is preferably carbon black (such as acetylene black, ketjen black, and furnace black), activated carbon, graphite, glassy carbon, graphite, graphene, carbon fiber, carbon nanotubes, carbon nitride, sulfurized carbon, carbon phosphide, channel black, roller black, disc black, oil furnace black, gas furnace black, lamp black, thermal black, or vulcanized carbon, or a mixture of one or more thereof. The oxide is preferably titanium oxide, niobium oxide, tin oxide, tungsten oxide, or molybdenum oxide, or a mixture of one or more thereof. The support is preferably carbon, and more preferably carbon black.

[0035] The carrier may be either primary particles or secondary particles. The particle size of the primary particles of the carrier is usually in the range of 5 to 5000 nm.

[0036] In the electrochemical oxygen reduction catalyst of this embodiment, the composition, content and particle size of the support can be determined, for example, by the same means as those for determining the composition, content and particle size of the catalytic metal described above.

[0037] By having the above-described characteristics, the electrochemical oxygen reduction catalyst of this embodiment can exhibit high oxygen transportability and / or proton conductivity without substantially causing particle aggregation and / or cracks in the electrode catalyst layer.

[0038] The oxygen transport property and proton conductivity of the electrochemical oxygen reduction catalyst of this embodiment can be evaluated by the same method as used to evaluate the oxygen transport property and proton conductivity of the ionomer of one embodiment of the present invention.

[0039] <3: Uses of ionomers> Another aspect of the present invention relates to a fuel cell, which includes at least a cathode electrode catalyst layer, an anode electrode catalyst layer, and an electrolyte membrane disposed between the cathode electrode catalyst layer and the anode electrode catalyst layer, and the cathode electrode catalyst layer contains an electrochemical oxygen reduction catalyst and the ionomer according to one aspect of the present invention.

[0040] Yet another aspect of the present invention relates to a water electrolysis system, comprising at least a cathode electrode catalyst layer, an anode electrode catalyst layer, an electrolyte membrane disposed between the cathode electrode catalyst layer and the anode electrode catalyst layer, and a water supply unit, wherein the anode electrode catalyst layer contains an electrochemical oxygen reduction catalyst and the ionomer according to one aspect of the present invention.

[0041] Yet another aspect of the present invention relates to a metal-air battery, which includes at least a cathode electrode catalyst layer, an anode metal layer, and an electrolyte membrane disposed between the cathode electrode catalyst layer and the anode metal layer, and the cathode electrode catalyst layer contains an electrochemical oxygen reduction catalyst and the ionomer according to one aspect of the present invention.

[0042] By including the ionomer according to one aspect of the present invention in the cathode or anode electrode catalyst layer, the fuel cell, water electrolysis system, and metal-air battery of this aspect can exhibit high oxygen transportability and / or proton conductivity without substantially causing cracks in the electrode catalyst layer, etc. Therefore, the fuel cell of this aspect can be applied to fuel cells for automobiles, ships, or railway vehicles, for example.

[0043] <4: Ionomer manufacturing method> Another aspect of the present invention relates to a method for producing the ionomer of the aspect of the present invention. The method of this aspect includes a modification step. The method of this aspect may optionally include a preparation step, an electrode catalyst preparation step, and an electrode catalyst layer formation step.

[0044] [4-1: Preparation process] This process includes preparing an ionomer material having an acidic functional group and a fluorine-containing cyclic group (hereinafter also referred to simply as "ionomer material") and a modifier. This process also typically includes preparing a catalyst metal, a support, and a binder. Furthermore, this process may include preparing additional materials such as a solvent and a substrate, if desired.

[0045] The ionomer material, catalytic metal, support, and binder prepared in this step may be materials having the characteristics described above. For example, the catalytic metal prepared in this step may be in a form supported on the support described above.

[0046] The modifying agent prepared in this step contains at least a cation of a nitrogen-containing cyclic organic compound or a polymer thereof. The cation of the nitrogen-containing cyclic organic compound or a polymer thereof contained in the modifying agent may be any material having the characteristics described above.

[0047] In this step, each material may be prepared by self-preparing one having predetermined characteristics, or may be prepared by purchasing a commercially available product, etc. For example, an ionomer material may be prepared based on known literature (e.g., JP 2013-216811 A).

[0048] [4-2: Modification process] This process involves mixing an ionomer material having an acidic functional group and a fluorine-containing cyclic group with a modifying agent to modify the acidic functional group.

[0049] In this process, the ionomer material having an acidic functional group and a fluorine-containing cyclic group and the modifier are typically mixed together with a solvent. The solvent is not particularly limited, and any liquid can be used. Examples of the solvent include water and alcohol, as well as mixtures of one or more of these. Examples of the alcohol include methanol, ethanol, 1-propanol, 2-propanol, 2-methyl-2-propanol (tert-butyl alcohol), diacetone alcohol, ethylene glycol, and propylene glycol.

[0050] In this step, the means for mixing the materials is not particularly limited. Examples of mixing means include an ultrasonic homogenizer, a jet mill, a bead mill, a ball mill, a high-shear mill, and a Filmix. The specific conditions for the above-mentioned mixing means (e.g., stirring speed, stirring time, rotation speed, etc.) are not particularly limited and can be set appropriately within any range.

[0051] This step may optionally include a vacuum degassing treatment in which the resulting mixture is degassed under vacuum conditions. In this case, the specific conditions for the vacuum degassing treatment (e.g., pressure, treatment time, etc.) are not particularly limited and can be set appropriately within any range. The vacuum degassing treatment may be performed multiple times.

[0052] In this step, the solvent is removed from the mixture obtained, thereby obtaining an electrochemical oxygen reduction catalyst containing the ionomer of one embodiment of the present invention. The method for removing the solvent is not particularly limited, and can be carried out by any means such as heating and drying or filtration.

[0053] By carrying out this step, the acidic functional groups of the ionomer material can be modified with a modifying layer containing a nitrogen-containing cyclic organic compound, a polymer thereof, or a cation thereof.

[0054] [4-3: Electrode catalyst preparation process] This step involves preparing an electrocatalyst by mixing a catalytic metal with a binder, the binder used in this step comprising the ionomer having the modified layer prepared in the previous step.

[0055] In this step, the catalyst metal and the binder are usually mixed together with a solvent. The solvent may be the same as that used in the modification step described above. Furthermore, the means for mixing the materials may be the same as that used in the modification step described above.

[0056] This step may optionally include a vacuum degassing treatment in which the resulting mixture is degassed under vacuum conditions. In this case, the specific conditions for the vacuum degassing treatment (e.g., pressure, treatment time, etc.) are not particularly limited and can be set appropriately within any range. The vacuum degassing treatment may be performed multiple times.

[0057] In this step, the solvent is removed from the mixture obtained, thereby obtaining an electrochemical oxygen reduction catalyst containing the ionomer of one embodiment of the present invention. The method for removing the solvent is not particularly limited, and can be carried out by any means such as heating and drying or filtration.

[0058] Alternatively, when the electrode catalyst layer preparation step described below is carried out, the mixture obtained in this step can be used in the electrode catalyst layer preparation step as a catalyst ink containing an electrochemical oxygen reduction catalyst including an ionomer of one embodiment of the present invention. In this case, the mixture obtained in this step may be used as is, or may be used after further adding the solvent exemplified above.

[0059] By carrying out this step, an electrochemical oxygen reduction catalyst containing the ionomer of one embodiment of the present invention can be obtained.

[0060] [4-4: Electrode catalyst layer production process] This step involves applying a catalyst ink containing the electrochemical oxygen reduction catalyst obtained in the electrode catalyst preparation step onto the surface of a substrate.

[0061] The substrate used in this step is not particularly limited, and any material such as polytetrafluoroethylene (PTFE), an electrolyte membrane having an ion exchange group, carbon fiber, and metal fiber can be used.

[0062] In this step, the means for applying the catalyst ink is not particularly limited. Examples of application methods include die coating, spin coating, screen printing, doctor blade, squeegee, spray coating, and applicator. The specific conditions for the application methods exemplified above are not particularly limited and can be set appropriately within any range.

[0063] In this step, the solvent is usually removed from the catalyst ink after application. The method for removing the solvent is not particularly limited and can be carried out by any means, such as heat drying. The specific conditions for removing the solvent (e.g., temperature, pressure, treatment time, etc.) are not particularly limited and can be set appropriately within any range.

[0064] By carrying out this step, an electrochemical oxygen reduction catalyst containing an ionomer according to one embodiment of the present invention can be obtained in a form (electrocatalytic layer) arranged on the surface of a substrate. In this case, the thickness of the electrocatalytic layer is usually in the range of 5 to 30 μm. The content of the catalytic metal in the electrocatalytic layer, expressed as the mass relative to the total area of ​​the electrocatalytic layer, is usually 0.1 to 0.6 mg / cm. 2 The range is.

[0065] As described above, by implementing the method of this aspect, an ionomer of one aspect of the present invention and an electrochemical oxygen reduction catalyst containing the ionomer can be produced.

[0066] In this specification, as described in detail, the ionomer of one aspect of the present invention and the electrochemical oxygen reduction catalyst containing the ionomer have high oxygen transportability, binder performance, and / or surfactant performance. Further, the production method of one aspect of the present invention can efficiently provide the ionomer of one aspect of the present invention and the electrochemical oxygen reduction catalyst containing the ionomer, which have high oxygen transportability, binder performance, and / or surfactant performance. Therefore, by applying the electrochemical oxygen reduction catalyst containing the ionomer of one aspect of the present invention, for example, to the cathode of a fuel cell, a fuel cell having high oxygen transportability and / or proton conductivity can be provided without substantially causing the occurrence of cracks in the electrode catalyst layer. Such a fuel cell can be suitably used, for example, as a fuel cell for automobiles, ships, or railway vehicles.

Examples

[0067] Hereinafter, the present invention will be described more specifically using examples. However, the technical scope of the present invention is not limited to these examples.

[0068] <I: Production of ionomer> [I-1: Preparation of ionomer] Based on the known document (Japanese Patent Application Laid-Open No. 2013-216811), as an ionomer material, a perfluorocarbon sulfonic acid polymer (EW: 900) having 1,3-dioxolane-4,5-diyl substituted with one or more perfluoroalkyls as a fluorine-containing cyclic group was prepared. A predetermined nitrogen-containing cyclic organic compound or its polymer, or a modifier containing their cations was prepared so as to be 10 mol% with respect to the total amount of substances (mol) of the acidic functional groups of the ionomer material having acidic functional groups. A predetermined amount of the ionomer material, the modifier, and a solvent (water) were put into a container. Using an ultrasonic homogenizer and a stirrer, these materials were stirred and mixed for 15 minutes or more to prepare an ionomer having a modified layer (modification step).

[0069] As Comparative Example 1, an acyclic ionomer having no modified layer was prepared in the same procedure as above, using an ionomer material having no fluorine-containing cyclic group (perfluorocarbon sulfonic acid polymer, Nafion, manufactured by Chemours, EW: 1100) and without adding a modifier. As Comparative Examples 2 and 3, fluorine-containing cyclic ionomers having no modified layer were prepared in the same procedure as above, using ionomer materials having fluorine-containing cyclic groups prepared in the same procedure as above and without adding a modifier.

[0070] <II: Production of Electrochemical Oxygen Reduction Catalyst> [II-1: Preparation of Catalyst Ink] A catalyst metal particle-supported carrier (primary particle size: 10 to 100 nm) having platinum particles (particle size: 3 to 4 nm) supported on a carrier (acetylene black), a binder containing the ionomer prepared by the above procedure, and a solvent (water) were put into a container in a predetermined amount. Using a stirrer (homogenizer and filmix), these materials were mixed and stirred to prepare a catalyst ink containing an electrochemical oxygen reduction catalyst (modification step). The content of platinum particles in the electrochemical oxygen reduction catalyst was 48 to 50% by mass with respect to the total mass of the catalyst.

[0071] [II-2: Preparation of Catalyst Layer] Using a homogenizer and a film mixer, the prepared catalyst ink was applied onto a substrate (a plate made of polytetrafluoroethylene (PTFE)). After application, the catalyst ink was heated to dry and remove the solvent (catalyst ink application process). The obtained catalyst layer had a film thickness of 5 to 30 μm and a platinum loading of 0.1 to 0.6 mg / cm 2 ².

[0072] [II-3: Fabrication of Membrane Electrode Assembly] Using each catalyst layer prepared by the above procedure as a cathode catalyst layer, a perfluorocarbon sulfonic acid polymer (Nafion NR211, EW: 1100, manufactured by Chemours) as an electrolyte membrane, and a platinum-supported carbon catalyst (TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) as an anode catalyst layer, they were respectively prepared. The electrolyte membrane was sandwiched between the cathode catalyst layer and the anode catalyst layer. Under the conditions of heating (130 °C) and pressurization (3 MPa), the cathode catalyst layer, the electrolyte membrane, and the anode catalyst layer were thermocompression bonded. A gas diffusion layer (GDL 22BB, manufactured by SGL) made of carbon fiber was arranged outside the cathode catalyst layer and the anode catalyst layer to fabricate a membrane electrode assembly (MEA) (electrode part: 1×1 cm).

[0073] [III: Performance Evaluation of Electrochemical Oxygen Reduction Catalyst] [III-1: Electrochemical Performance Evaluation of Membrane Electrode Assembly] Using the MEA prepared by the above procedure as a single cell, the current-voltage characteristics under low humidity conditions (30%RH) and high humidity conditions (80%RH) were measured. The measurement conditions were as follows. Sweep rate: 20 mA / s (anode sweep), cell temperature: 80 °C, pressure: 150 kPa_abs, cathode gas species: air, cathode gas flow rate: 2.0 L / min.

[0074] [III-2: Evaluation Results] The compositions of the ionomers prepared by the above procedure and the evaluation results of MEAs having electrochemical oxygen reduction catalysts containing the ionomers are shown in Tables 1 and 2. In the tables, the melamine-formaldehyde copolymer shown as a component of the modification layer refers to methylated poly(melamine-co-formaldehyde) (nitrogen equivalent: 20 to 40 g / equivalent). Furthermore, in the tables, the changes in the D50 and D90 values ​​of the electrode catalyst particles in the catalyst ink refer to the changes relative to the D50 and D90 values ​​of Comparative Example 2 for Examples 1 to 4, and the changes relative to the D50 and D90 values ​​of Comparative Example 3 for Example 5.

[0075] [Table 1]

[0076] [Table 2]

[0077] As shown in Tables 1 and 2, the electrochemical oxygen reduction catalysts containing the ionomers of Examples 1 to 5 had smaller particle sizes of electrode catalyst particles in the catalyst ink than the electrochemical oxygen reduction catalysts containing the ionomers of Comparative Examples 2 and 3, which had a fluorine-containing cyclic group but no modification layer. Furthermore, while cracks were observed in the cathode electrode catalyst layer of the MEAs containing the electrochemical oxygen reduction catalysts containing the ionomers of Comparative Examples 2 and 3, no cracks were observed in the cathode electrode catalyst layer of any of the MEAs containing the electrochemical oxygen reduction catalysts containing the ionomers of Examples 1 to 5. These results demonstrate that the ionomers of the present invention have high binder and surfactant properties that can suppress aggregation of electrode catalyst particles and cracks in the electrode catalyst layer.

[0078] The present invention is not limited to the above-described embodiments, but includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to add, delete, and / or replace part of the configuration of each embodiment with other configurations.

Claims

1. An ionomer having an acidic functional group, a fluorine-containing cyclic group, and a modifying layer that modifies the acidic functional group, wherein the fluorine-containing cyclic group contains 3 to 16 ring atoms, and the modifying layer comprises a nitrogen-containing cyclic organic compound or a polymer thereof, or a cation thereof.

2. 2. The ionomer of claim 1, wherein the fluorine-containing cyclic group is 1,3-dioxolane-4,5-diyl substituted with one or more perfluoroalkyl groups.

3. 10. The ionomer of claim 1, wherein the modification layer comprises 1,3,5-triazine, ammelide, or melamine.

4. 1. A fuel cell comprising at least a cathode electrode catalyst layer comprising an electrochemical oxygen reduction catalyst and the ionomer according to claim 1, an anode electrode catalyst layer, and an electrolyte membrane disposed between the cathode electrode catalyst layer and the anode electrode catalyst layer.

5. a modifying step in which the ionomer material having an acidic functional group and a fluorine-containing cyclic group is mixed with a modifying agent containing a nitrogen-containing cyclic organic compound, a polymer thereof, or a cation thereof to modify the acidic functional group; 2. A method for producing the ionomer of claim 1, comprising:

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