Ionomer

Abstract

To provide an ionomer having high oxygen transportability.SOLUTION: One embodiment of the present invention relates to an ionomer which has an acidic functional group, and a modifying layer that modifies the acidic functional group, 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, the content of the nitrogen-containing cyclic organic compound or the polymer thereof, or the cation of the nitrogen-containing cyclic organic compound or the polymer being 120 mol% or less in relation to the total substance amount of the acidic functional group. 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 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.

[0004] Patent Document 2 describes a membrane-electrode assembly for a solid polymer electrolyte fuel cell, which comprises a solid polymer electrolyte membrane and a pair of electrodes disposed on either side of the solid polymer electrolyte membrane, wherein at least one of the electrodes is composed of a catalyst layer made of a mixture containing a catalyst body made of a noble metal catalyst and carbon powder, a polymer electrolyte, and a polyfunctional basic compound, and a gas diffusion layer. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-161154 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-246041 Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, various ionomers have been developed that can be used in the electrode catalyst layer of a fuel cell. The electrode catalyst layer of a fuel cell, particularly the cathode electrode catalyst layer, must smoothly supply protons and oxygen to the electrode catalyst. Ionomers typically have acidic ion-exchange groups, which can contribute to proton transport but can also inhibit oxygen transport. Therefore, the oxygen transport performance of conventional ionomers remains to be improved.

[0007] Therefore, an object of the present invention is to provide an ionomer having high oxygen transport properties. [Means for solving the problem]

[0008] The present inventors have investigated various means for solving the above problems. They have found that the oxygen diffusibility of an ionomer can be improved by using a modifying layer containing a nitrogen-containing cyclic organic compound, a polymer thereof, or a cation thereof in a predetermined content as a modifying layer for modifying the acidic functional groups of the ionomer. Based on this finding, the present inventors have completed the present invention.

[0009] That is, the present invention includes the following aspects and embodiments. (Embodiment 1) An ionomer having an acidic functional group and a modifying layer that modifies the acidic functional group, wherein the modifying layer contains a nitrogen-containing cyclic organic compound or a polymer thereof, or a cation thereof, and the content of the nitrogen-containing cyclic organic compound or the polymer thereof, or the cation thereof is 120 mol% or less relative to the total amount of substance of the acidic functional group. (Embodiment 2) The ionomer according to embodiment 1, wherein the content of the nitrogen-containing cyclic organic compound or its polymer, or their cation is in the range of 10 to 80 mol% based on the total amount of the acidic functional groups. (Embodiment 3) The ionomer according to embodiment 1 or 2, wherein a cation of the nitrogen-containing cyclic organic compound or a polymer thereof contained in the modification layer forms an ionic bond with the acidic functional group. (Embodiment 4) The ionomer according to any one of embodiments 1 to 3, wherein the nitrogen-containing cyclic organic compound or its polymer, or their cation is melamine, ammeline, ammelide, cyanuric acid, triazine, or its derivative, or its polymer, or their cation. (Embodiment 5) The ionomer of any one of embodiments 1 to 4, wherein the modification layer comprises 1,3,5-triazine, ammeline, ammelide, melamine, or a melamine-formaldehyde copolymer. (Embodiment 6) 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 5, an anode electrode catalyst layer, and an electrolyte membrane disposed between the cathode electrode catalyst layer and the anode electrode catalyst layer. (Embodiment 7) A modification step in which an ionomer material having an acidic functional 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. 6. A method for producing the ionomer of any one of embodiments 1 to 5, comprising: [Effects of the Invention]

[0010] The present invention makes it possible to provide an ionomer having high oxygen transport properties. DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments of the present invention will now be described in detail.

[0012] <1: Ionomer> One aspect of the present invention relates to an ionomer. The ionomer of this aspect has an acidic functional group and a modifying layer that modifies the acidic functional group.

[0013] 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.

[0014] 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.

[0015] In the ionomer of this embodiment, the modifying layer contains a nitrogen-containing cyclic organic compound or its polymer, or a cation thereof. This 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. In conventional ionomers without a modifying layer, the polymer constituting the ionomer typically has high crystallinity, resulting in low oxygen transport within the ionomer. Furthermore, in conventional ionomers, the polymer constituting the ionomer typically has high adsorption to the electrode catalyst, resulting in low oxygen transport at the interface between the ionomer and the electrode catalyst. In contrast, in the ionomer of this embodiment, the nitrogen-containing cyclic organic compound or its polymer, or a cation thereof, contained in the modifying layer interacts with the acidic functional group and / or the polymer constituting the ionomer, thereby optimizing the crystallinity and / or adsorption to the electrode catalyst of the polymer, thereby improving oxygen transport. Therefore, by having a catalyst layer containing the components exemplified above, the ionomer of this embodiment can exhibit high oxygen transport.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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 (e.g., 1,3,5-triazine, ammeline, ammelide, melamine, or a melamine-formaldehyde copolymer, or a cation thereof, and even more preferably, the copolymer is a melamine-formaldehyde copolymer (e.g., 1,3,5-triazine, ammeline, ammelide, melamine, or a cation thereof).

[0020] 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.

[0021] The content of the nitrogen-containing cyclic organic compound, its polymer, or its cation is typically 120 mol% or less, based on the total amount of acidic functional groups. The content of the nitrogen-containing cyclic organic compound, its polymer, or its cation is preferably in the range of 1 to 120 mol%, and more preferably in the range of 10 to 80 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 in the range of 0.1 to 10 mass%, and even more preferably in the range of 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 lower limit, the desired effect may not be achieved. If the content of the nitrogen-containing cyclic organic compound, its polymer, or its cation exceeds the upper limit, the oxygen transport property and / or proton conductivity may be reduced. Therefore, by having a catalyst layer containing a nitrogen-containing cyclic organic compound or a polymer thereof, or a cation thereof in the amounts exemplified above, the ionomer of this embodiment can exhibit high oxygen transport properties and / or proton conductivity.

[0022] 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).

[0023] By having the above-described characteristics, the ionomer of this embodiment can exhibit high oxygen transport properties and / or proton conductivity.

[0024] 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.

[0025] 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).

[0026] <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.

[0027] 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-mentioned 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-mentioned metals. 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 catalytic activity.

[0028] 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 50 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 a content within this range, the electrochemical oxygen reduction catalyst of this embodiment can exhibit high catalytic activity.

[0029] The particle size of the catalyst metal is usually in the range of 1 to 100 nm.

[0030] 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).

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] By being provided with the above-described characteristics, the electrochemical oxygen reduction catalyst of this embodiment can exhibit high oxygen transportability and / or proton conductivity.

[0036] 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.

[0037] <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.

[0038] 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.

[0039] 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.

[0040] The fuel cell, water electrolysis system, and metal-air battery of this embodiment can exhibit high oxygen transportability and / or proton conductivity by containing the ionomer of one embodiment of the present invention in the electrode catalyst layer of the cathode or anode. Therefore, the fuel cell of this embodiment can be applied to fuel cells for automobiles, ships, and railway vehicles, for example.

[0041] <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.

[0042] [4-1: Preparation process] This process includes preparing an ionomer material having acidic functional groups (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, as desired.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] [4-2: Modification process] This process involves mixing an ionomer material having acidic functional groups with a modifying agent to modify the acidic functional groups.

[0047] In this process, the ionomer material having acidic functional groups 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] [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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] By carrying out this step, an electrochemical oxygen reduction catalyst containing the ionomer of one embodiment of the present invention can be obtained.

[0058] [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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] As described above, by carrying out the method of this embodiment, it is possible to produce the ionomer of one embodiment of the present invention and the electrochemical oxygen reduction catalyst containing the ionomer.

[0064] As described in detail herein, the ionomer of one aspect of the present invention and the electrochemical oxygen reduction catalyst containing the ionomer have high oxygen transportability and / or proton conductivity. 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 and / or proton conductivity. Therefore, by applying the electrochemical oxygen reduction catalyst containing the ionomer of one aspect of the present invention to, for example, the cathode of a fuel cell, a fuel cell having high oxygen transportability and / or proton conductivity can be provided. Such a fuel cell can be suitably used, for example, as a fuel cell for automobiles, ships or railway vehicles.

Examples

[0065] 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.

[0066] <I: Production of ionomer> [I-1: Preparation of ionomer] A predetermined nitrogen-containing cyclic organic compound or its polymer, or a modifier containing their cations was prepared so as to have a predetermined content with respect to the total amount of substance (mol) of the acidic functional groups of the perfluorocarbon sulfonic acid polymer (Nafion, manufactured by Chemours, EW: 1100). A predetermined amount of the perfluorocarbon sulfonic acid polymer, 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).

[0067] <II: Production of electrochemical oxygen reduction catalyst> [II-1: Preparation of catalyst ink] A catalyst metal particle-supported carrier (primary particle diameter: 10 to 100 nm) in which platinum particles (particle diameter: 3 to 4 nm) were supported on a carrier (acetylene black), a binder containing an ionomer with a modified layer prepared by the procedure described above, and a solvent (water) were placed in a container in predetermined amounts. These materials were mixed and stirred using a stirrer (homogenizer and Filmix) to prepare a catalyst ink containing an electrochemical oxygen reduction catalyst (modification step). The platinum particle content in the electrochemical oxygen reduction catalyst was 48 to 50 mass% of the total mass of the catalyst.

[0068] In Comparative Example 1, a catalyst ink containing an electrochemical oxygen reduction catalyst containing an ionomer having no modifying layer was prepared using the same procedure as above, except that a binder containing an ionomer having no modifying layer was used.In Comparative Examples 2 and 3, catalyst inks containing an electrochemical oxygen reduction catalyst having a catalytic metal modified with a modifying layer were prepared using a binder containing an ionomer having no modifying layer, and using the same procedure as above, except that a modifier containing a specified nitrogen-containing cyclic organic compound or a polymer thereof, or a cation thereof, was mixed and stirred with the above materials.

[0069] [II-2: Preparation of catalyst layer] The prepared catalyst ink was applied to a substrate (a polytetrafluoroethylene (PTFE) plate) using a homogenizer and a Filmix. The applied catalyst ink was heated to dry and remove the solvent (catalyst ink application process). The resulting catalyst layer had a film thickness of 5 to 30 μm and a thickness of 0.1 to 0.6 mg / cm. 2 The platinum loading was 10 ...

[0070] [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 each 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 disposed outside the cathode catalyst layer and the anode catalyst layer to fabricate a membrane electrode assembly (MEA) (electrode portion: 1 × 1 cm).

[0071] <III: Performance Evaluation of Electrochemical Oxygen Reduction Catalysts> [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 are 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.

[0072] [III-2: Evaluation Results] The evaluation results of the composition of the ionomer prepared by the above procedure and the MEA having an electrochemical oxygen reduction catalyst containing the ionomer are shown in Tables 1 and 2. In the tables, the melamine-formaldehyde copolymer shown as a component of the modification layer means methylated poly(melamine-co-formaldehyde) (nitrogen equivalent: 20 to 40 g / equivalent).

[0073]

Table 1

[0074] [Table 2] TIFF2025174564000006.tif169164

[0075] As shown in Tables 1 and 2, MEAs containing the electrochemical oxygen reduction catalysts containing the ionomers of the Examples exhibited improved cell voltages compared to MEAs containing the electrochemical oxygen reduction catalysts of Comparative Example 1, which did not have a modification layer. In contrast, MEAs containing the electrochemical oxygen reduction catalysts of Comparative Examples 4, 5, and 6, in which the content of nitrogen-containing cyclic organic compounds or their polymers or their cations exceeded 120 mol% relative to the total amount of acidic functional groups, exhibited lower cell voltages compared to MEAs containing the electrochemical oxygen reduction catalysts of Comparative Example 1, which did not have a modification layer. All MEAs containing the electrochemical oxygen reduction catalysts containing the ionomers of the Examples exhibited low proton transport resistance and oxygen diffusion resistance in the electrode catalyst layer, whereas MEAs containing the electrochemical oxygen reduction catalysts containing the ionomers of Comparative Examples 4, 5, and 6 exhibited high proton transport resistance and oxygen diffusion resistance in the electrode catalyst layer. These results demonstrate that the ionomers of the present invention have high proton conductivity and oxygen diffusivity.

[0076] 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 and a modifying layer that modifies the acidic functional group, wherein the modifying layer contains a nitrogen-containing cyclic organic compound or a polymer thereof, or a cation thereof, and the content of the nitrogen-containing cyclic organic compound or the polymer thereof, or the cation thereof is 120 mol% or less relative to the total amount of substance of the acidic functional group.

2. 2. The ionomer according to claim 1, wherein the content of the nitrogen-containing cyclic organic compound or its polymer, or their cations is in the range of 10 to 80 mol % based on the total amount of acidic functional groups.

3. 2. The ionomer according to claim 1, wherein a cation of the nitrogen-containing cyclic organic compound or a polymer thereof contained in the modification layer forms an ionic bond with the acidic functional group.

4. 2. The ionomer according to claim 1, wherein the nitrogen-containing cyclic organic compound, a polymer thereof, or a cation thereof is melamine, ammeline, ammelide, cyanuric acid, triazine, a derivative thereof, a polymer thereof, or a cation thereof.

5. 10. The ionomer of claim 1, wherein the modifying layer comprises 1,3,5-triazine, ammeline, ammelide, melamine, or a melamine-formaldehyde copolymer.

6. 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.

7. a modifying step in which the ionomer material having an acidic functional 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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