Ionomers

Abstract

One embodiment of the present invention pertains to an ionomer having an acidic functional group, a fluorine-containing cyclic group containing 3-16 ring-forming atoms, and a modification layer for modifying the acidic functional group, the modification layer containing a nitrogen-containing cyclic organic compound, a polymer thereof, or a cation of the nitrogen-containing cyclic organic compound or the polymer thereof. Another embodiment of the present invention relates to a fuel cell having at least an electrode catalyst layer for a cathode, an electrode catalyst layer for an anode, and an electrolyte membrane disposed between the electrode catalyst layer for the cathode and the electrode catalyst layer for the anode, the electrode catalyst layer containing an electrochemical oxygen reduction catalyst and the ionomer according to one embodiment of the present invention. Another embodiment of the present invention relates to a method for producing an ionomer, which comprises a modification step for modifying an acidic functional group by mixing an ionomer material having an acidic functional group and a fluorine-containing cyclic group with a modifier containing a nitrogen-containing cyclic organic compound, a polymer thereof, or a cation thereof.

Description

TECHNICAL FIELD

[0001] The present application relates to an ionomer. BACKGROUND

[0002] A fuel cell generates electric power by electrochemically reacting hydrogen and oxygen. The product generated along with the power generation of the fuel cell is only water in principle. Therefore, the fuel cell is attracting attention as a clean power generation system that has little load on the global environment. The fuel cell is configured with a membrane electrode assembly (hereinafter also referred to as "MEA") as a basic unit, in which an electrode catalyst layer is provided on both sides of an electrolyte membrane, and further a gas diffusion layer is provided on the outer side of each electrode catalyst layer. When the fuel cell operates, an electromotive force is obtained by supplying a fuel gas containing hydrogen to the electrode catalyst layer on the anode (fuel electrode) side and supplying an oxidizing gas containing oxygen to the electrode catalyst layer on the cathode (air electrode) side. An oxidation reaction of hydrogen is performed at the anode, and a reduction reaction of oxygen is performed at the cathode, and an electromotive force is supplied to an external circuit. Therefore, the electrode catalyst layer of the cathode uses an oxygen reduction catalyst having an oxygen reduction ability. The binder of the electrode catalyst layer and the electrolyte membrane generally use a high molecular electrolyte (hereinafter also referred to as "ionomer" or "ionomer") having an ion exchange group.

[0003] For example, Patent Literature 1 describes an ionomer containing a polymer containing an acidic group and a metal complex containing a basic group.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent Application Laid-Open No. 2021-161154 SUMMARY

[0007] As described above, various ionomers that can be used for the electrode catalyst layer of a fuel cell have been developed. In the electrode catalyst layer of a fuel cell, particularly the electrode catalyst layer of the cathode, it is necessary to smoothly supply protons and oxygen to the electrode catalyst. The ionomer generally has an acidic ion exchange group, and can contribute to the proton transport property, but can inhibit the oxygen transport property. In view of such a problem, for example, Patent Literature 1 describes an ionomer containing a polymer containing an acidic group and a metal complex containing a basic group, which exhibits high oxygen solubility even in an acidic state. In addition, Patent Literature 1 describes that the ionomer containing the polymer containing an acidic group exhibits high oxygen permeability, by virtue of the fact that the polymer containing an acidic group has an aliphatic ether ring structure as a cyclic group containing fluorine. However, such an ionomer of the related art has room for improvement in terms of the binder performance and the surface activity performance of the electrode catalyst.

[0008] Therefore, an object of the present application is to provide an ionomer having high binder performance and surface activity performance.

[0009] The present inventors have studied various methods for solving the above-described problem. The present inventors have found that, by using a modification layer containing a nitrogen-containing cyclic organic compound or a polymer thereof or a cation thereof as a modification layer for modifying an acidic functional group of an ionomer having a fluorine-containing cyclic group, the adhesion performance and the surface activity performance of the ionomer are improved. The present inventors have completed the present application based on the above-described insight.

[0010] That is, the present application includes the following aspects and embodiments. (Embodiment 1) An ionomer having an acidic functional group, a fluorine-containing cyclic group having a ring-forming atom number in the range of 3 to 16, and a modification layer modifying the acidic functional group, the modification layer containing a nitrogen-containing cyclic organic compound or a polymer thereof or a cation thereof. (Embodiment 2) The ionomer according to 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 according to Embodiment 1 or 2, wherein the modification layer contains 1,3,5-triazine, cyanuric acid monoamide, or melamine. (Embodiment 4) A fuel cell having at least: an electrode catalyst layer of a cathode having an electrochemical oxygen reduction catalyst and the ionomer according to any one of Embodiments 1 to 3, 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. (Embodiment 5) A method for producing the ionomer according to any one of Embodiments 1 to 3, including a modification step of mixing an ionomer material having an acidic functional group and a fluorine-containing cyclic group with a modifier containing a nitrogen-containing cyclic organic compound or a polymer thereof or a cation thereof to modify the acidic functional group.

[0011] According to the present application, it is possible to provide an ionomer having high adhesion performance and surface activity performance. DETAILED DESCRIPTION

[0012] Hereinafter, a preferred embodiment of the present application will be described in detail.

[0013] <1: Ionomer> One aspect of the present application relates to an ionomer. The ionomer of this aspect has an acidic functional group, a fluorine-containing cyclic group, and a modification layer modifying the acidic functional group.

[0014] As the polymer constituting the ionomer of this aspect, for example, a polymer in which perfluorocarbon, polyether ether ketone, and polybenzimidazole, etc. are main components can be cited. The polymer constituting the ionomer of this aspect is preferably perfluorocarbon. By being constituted by the above-described exemplified polymer, the ionomer of this aspect can exhibit high proton conductivity.

[0015] As the acidic functional group in the ionomer of the present embodiment, for example, a sulfonic acid group and a phosphoric acid group, etc. can be given. The acidic functional group is preferably a sulfonic acid group. By having the above-mentioned example of the acidic functional group, the ionomer of the present embodiment is able to exhibit high proton conductivity.

[0016] In each of the embodiments of the present application, the fluorine-containing cyclic group refers to a cyclic group that is a single ring or a multiple ring, and has one or more fluorine atoms as a ring-bonding group and / or a substituent of the ring-bonding group. In the ionomer of the present embodiment, the fluorine-containing cyclic group generally contains 3 to 16 ring-forming atoms. The number of ring-forming atoms of the fluorine-containing cyclic group is preferably in the range of 3 to 6. The cyclic group constituting the fluorine-containing cyclic group can contain one or more heteroatoms such as an oxygen atom, a nitrogen atom, or a sulfur atom, in addition to carbon atoms, as ring-forming atoms. As the cyclic group constituting the fluorine-containing cyclic group, for example, a cyclic group derived from cyclopropane, cyclobutane, cyclopentane, cyclohexane, oxacyclopropane, furan, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, pyrrolidine, pyrrole, imidazole, pyridine, piperidine, piperazine, morpholine, or thiophene, etc. can be given. The above-mentioned example of the cyclic group can have one or more fluorine atoms as a ring-bonding group and / or a substituent of the ring-bonding group. As the substituent having one or more fluorine atoms, for example, a linear or branched perfluoroalkyl group, a perfluoroalkylene group, and a perfluoroalkoxy group having a carbon atom number in the range of 1 to 10 can be given. The above-mentioned example of the substituent can have one or more heteroatoms such as an oxygen atom, a nitrogen atom, or a sulfur atom. In the case where the fluorine-containing cyclic group has a dissociable group, the fluorine-containing cyclic group can be in the form of a free acid or a free base, or in the form of a salt with an arbitrary counter ion. In each of the embodiments of the present application, the fluorine-containing cyclic group is preferably a 1,3-dioxolane-4,5-diyl group substituted with one or more perfluoroalkyl groups. By having the above-mentioned example of the fluorine-containing cyclic group, the ionomer of the present embodiment is able to exhibit high adhesive properties and surface activity properties. A sulfonamide group or a phosphonamide group. The above-mentioned example of the cyclic group can have one or more fluorine atoms as a ring-bonding group and / or a substituent of the ring-bonding group. As the substituent having one or more fluorine atoms, for example, a linear or branched perfluoroalkyl group, a perfluoroalkylene group, and a perfluoroalkoxy group having a carbon atom number in the range of 1 to 10 can be given. The above-mentioned example of the substituent can have one or more heteroatoms such as an oxygen atom, a nitrogen atom, or a sulfur atom. In the case where the fluorine-containing cyclic group has a dissociable group, the fluorine-containing cyclic group can be in the form of a free acid or a free base, or in the form of a salt with an arbitrary counter ion. In each of the embodiments of the present application, the fluorine-containing cyclic group is preferably a 1,3-dioxolane-4,5-diyl group substituted with one or more perfluoroalkyl groups. By having the above-mentioned example of the fluorine-containing cyclic group, the ionomer of the present embodiment is able to exhibit high adhesive properties and surface activity properties.

[0017] In the ionomer of the present embodiment, the structure of the polymer, the acidic functional group, and the fluorine-containing cyclic group as constituent elements can be determined, for example, by analyzing the ionomer of the present embodiment using elemental analysis, various chromatography, ultraviolet-visible spectroscopy (UV-Vis), infrared spectroscopy (IR), or nuclear magnetic resonance spectroscopy (NMR).

[0018] In the ionomer of the present embodiment, the modification layer contains a nitrogen-containing cyclic organic compound or a polymer thereof or a cation thereof. The above component can interact with the acidic functional group and / or the polymer constituting the ionomer. For example, the above component generally forms a complex, particularly an ionic bond, with the acidic functional group modified by the modification layer. In the ionomer of the related art not having the modification layer, the crystallinity of the polymer constituting the ionomer is generally high, and thus the oxygen transport property in the interior of the ionomer is low. In addition, in the ionomer of the related art, the adsorption property of the polymer constituting the ionomer to the electrode catalyst is generally high, and thus the oxygen transport property at the interface between the ionomer and the electrode catalyst is low. Furthermore, the ionomer of the related art having a modification layer of an organic compound containing an acidic group having an aliphatic ether ring structure corresponding to a fluorine-containing cyclic group and a metal complex containing a basic group (for example, Patent Document 1) can cause aggregation of particles of the electrode catalyst and / or generation of cracks in the electrode catalyst layer and the like when used as a binder for the electrode catalyst, and thus the binder performance and / or the surface activity performance are low. In contrast, in the ionomer of the present embodiment, the nitrogen-containing cyclic organic compound or the polymer thereof or the cation thereof contained in the modification layer interacts with the acidic functional group, the fluorine-containing cyclic group, and / or the polymer constituting the ionomer, and thus the crystallinity and / or the adsorption property to the electrode catalyst of the polymer are optimized, and not only the oxygen transport property can be improved, but also aggregation of particles of the electrode catalyst when used as a binder for the electrode catalyst can be substantially suppressed. Therefore, by having a catalyst layer containing the above exemplified component, the ionomer of the present embodiment can exhibit high binder performance and surface activity performance in addition to high oxygen transport property.

[0019] In each of the embodiments of the present application, the nitrogen-containing cyclic organic compound or the polymer thereof or the cation thereof refers to a compound or a polymer thereof or a cation thereof in which a nitrogen atom is contained in a ring member and / or a ring bonding group of a cyclic organic compound having a single ring or multiple rings. The nitrogen equivalent of the nitrogen-containing cyclic organic compound is generally in the range of 20 to 270 g / eq, and particularly in the range of 20 to 70 g / eq. The nitrogen equivalent of the nitrogen-containing cyclic organic compound is defined by the following formula: nitrogen equivalent (g / eq) = molecular weight (g / mol) of the nitrogen-containing organic compound / amount of substance (molN / mol) of the nitrogen atom contained in 1 molecule of the nitrogen-containing organic compound. In the case of a polymer of the nitrogen-containing cyclic organic compound, the nitrogen equivalent of the monomer contained in the polymer can be in the above exemplified range.

[0020] The number of nitrogen atoms of the nitrogen-containing cyclic organic compound is not particularly limited. For example, the number of nitrogen atoms of the nitrogen-containing cyclic organic compound is preferably 3 or more, and more preferably in the range of 3 to 6, in terms of the total number of basic nitrogen atoms. In addition, the number of nitrogen atoms of the nitrogen-containing cyclic organic compound is preferably 3 or less, and more preferably in the range of 0 to 3, in terms of the total number of nitrogen atoms of the ring bonding group.

[0021] Examples of nitrogen-containing cyclic organic compounds include pyridine, pyrrole, thiazole, and isothiazole. azole, isotonic azole, imidazole, imidazoline, pyrazole, 1,3,5-triazine, pyrimidine, pyridazine, pyrazine, indole, quinoline, isoquinoline, purine, benzimidazole, benzo[a] Zyrazoles, benzothiazoles, tetrazolium, tetrazines, triazoles, carbazoles, acridines, quinoxalines, and quinazolines. The nitrogen-containing cyclic organic compounds exemplified above may have one or more substituted or unsubstituted amines or amino groups (e.g., primary, secondary, tertiary, or quaternary ammonium cations), hydroxyl groups, halogens (e.g., fluorine, chlorine, bromine, or iodine), nitriles, amides, imides, thiols, sulfonyl groups, carboxyl groups, phosphonyl groups, ketones, aldehydes, esters, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted alkynyl groups, substituted or unsubstituted cycloalkyl groups, substituted or unsubstituted cycloalkenyl groups, substituted or unsubstituted cycloalkynyl groups, substituted or unsubstituted heterocyclic alkyl groups, substituted or unsubstituted... The cyclic bonding group may consist of cycloalkylalkyl, substituted or unsubstituted heterocycloalkylalkyl, substituted or unsubstituted aryl, substituted or unsubstituted aralkyl, substituted or unsubstituted heteroaryl, substituted or unsubstituted heteroarylalkyl, substituted or unsubstituted alkoxy, substituted or unsubstituted cycloalkoxy, substituted or unsubstituted heterocycloalkoxy, substituted or unsubstituted aryloxy, substituted or unsubstituted arylalkoxy, substituted or unsubstituted arylolefin, substituted or unsubstituted heteroaryloxy, substituted or unsubstituted heteroarylalkoxy, or substituted or unsubstituted acyloxy. The number of carbon atoms in the groups exemplified above is typically in the range of 1 to 10 in the chain form and typically in the range of 3 to 16 in the cyclic form. When the groups exemplified above are substituted, the substituents are preferably selected from one or more of the groups exemplified above.

[0022] The nitrogen-containing cyclic organic compound or the polymer thereof or the cation thereof is preferably melamine (1,3,5-triazine-2,4,6-triamine), ammelide, ammeline, cyanuric acid or triazine (1,2,3-triazine, 1,2,4-triazine or 1,3,5-triazine) or a derivative thereof, or a polymer thereof, or a cation thereof, more preferably melamine or a derivative thereof (nitrogen equivalent 21 g / eq.), ammeline, ammeline, 1,3,5-triazine or a derivative thereof (nitrogen equivalent 27 g / eq.), thiocyanuric acid or a derivative thereof (nitrogen equivalent 59 g / eq.), cyanuric acid or a derivative thereof (nitrogen equivalent 34 g / eq.), oleylamine or a derivative thereof (nitrogen equivalent 267 g / eq.), tetradecylamine or a derivative thereof (nitrogen equivalent 213 g / eq.), 2,4,6-tris[bis(methoxymethyl)amino]-1,3,5-triazine (nitrogen equivalent 65 g / eq.), 6-(dibutylamino)-1,3,5-triazine-2,4-dithiol (nitrogen equivalent 68 g / eq.), 2,4-diamino-6-butylamino-1,3,5-triazine (nitrogen equivalent 30 g / eq.), or 2,4,6-tris(pentafluoroethyl)-1,3,5-triazine (nitrogen equivalent 145 g / eq.), or a polymer having them as monomers, or a melamine-formaldehyde copolymer such as methylated poly(melamine-co-formaldehyde) (nitrogen equivalent 20 to 40 g / eq.) or isobutylated poly(melamine-co-formaldehyde) (nitrogen equivalent 20 to 40 g / eq), or a cation thereof, further preferably 1,3,5-triazine, ammeline or melamine, or a cation thereof.

[0023] As the polymer of the nitrogen-containing cyclic organic compound, for example, a homopolymer or a copolymer containing the above-described exemplified nitrogen-containing cyclic organic compound as at least one monomer can be exemplified. 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.

[0024] The content of the nitrogen-containing cyclic organic compound or the polymer thereof or the cation thereof is preferably in the range of 1 to 120 mol% and more preferably in the range of 10 to 60 mol% relative to the total amount of the acidic functional groups. In addition, the content of the nitrogen-containing cyclic organic compound or the polymer thereof or the cation thereof is preferably 10 mass% or less and more preferably in the range of 0.1 to 10 mass% relative to the total mass of the ionomer of the present embodiment. In the case where the content of the nitrogen-containing cyclic organic compound or the polymer thereof or the cation thereof is less than the above lower limit, the desired effects can not be exerted. In the case where the content of the nitrogen-containing cyclic organic compound or the polymer thereof or the cation thereof exceeds the above upper limit, the adhesive properties and / or the surface activity properties can be reduced. Thus, by the catalyst layer containing the nitrogen-containing cyclic organic compound or the polymer thereof or the cation thereof in the content exemplified above, the ionomer of the present embodiment can exert high adhesive properties and surface activity properties.

[0025] The composition and content of the nitrogen-containing cyclic organic compound or the polymer thereof or the cation thereof contained in the modification layer can be determined, for example, by dissolving and extracting the modification layer contained in the ionomer of the present embodiment and analyzing the components contained in the extract by elemental analysis, various chromatography, ultraviolet-visible spectroscopy (UV-Vis), infrared spectroscopy (IR), or nuclear magnetic resonance (NMR).

[0026] By having the features described above, the ionomer of the present embodiment can exert high adhesive properties and surface activity properties.

[0027] The adhesive properties and surface activity properties of the ionomer of the present embodiment can be evaluated, for example, by preparing a catalyst ink of an electrochemical oxygen reduction catalyst using the ionomer as an adhesive and measuring the particle size distribution (e.g., D50 and D90 values and their variation amounts) of the electrode catalyst particles in the catalyst ink. Alternatively, the adhesive properties and surface activity properties can be evaluated by preparing an MEA in which the electrochemical oxygen reduction catalyst is used for a cathode using the prepared catalyst ink and confirming the occurrence of cracks in the electrode catalyst layer of the cathode.

[0028] The oxygen transport property of the ionomer of the present embodiment can be evaluated, for example, by preparing an electrochemical oxygen reduction catalyst using the ionomer as an adhesive, preparing an MEA in which the electrochemical oxygen reduction catalyst is used for a cathode, and measuring the oxygen diffusion resistance in the electrode catalyst layer of the MEA.

[0029] The proton conductivity of the ionomer of the present embodiment can be evaluated, for example, by preparing an electrochemical oxygen reduction catalyst using the ionomer as a binder, producing an MEA in which the electrochemical oxygen reduction catalyst is used for a cathode, and measuring the current / voltage characteristics (for example, the proton transport resistance in the electrode catalyst layer or the cell voltage at a prescribed current density) of the MEA under low humidification conditions (for example, 30% RH) and high humidification conditions (for example, 80% RH).

[0030] The electrochemical oxygen reduction catalyst of the present embodiment has a catalyst metal having oxygen reduction activity, and a binder containing the ionomer of one embodiment of the present invention.

[0031] The catalyst metal in the electrochemical oxygen reduction catalyst of the present embodiment can be any metal having oxygen reduction activity (oxygen reduction catalytic ability). Examples of the catalyst 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 catalyst metal can contain two or more of the above-mentioned metals alone or in the form of an alloy. The catalyst metal can be an oxide, a nitride, a sulfide, or a phosphide of the above-mentioned metals. The catalyst metal is preferably platinum, a platinum alloy, or a composite containing platinum. In the case of a platinum alloy or a composite containing platinum, examples of the metal 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. The platinum alloy or the composite containing platinum can contain two or more of the above-mentioned metals. By containing the above-mentioned catalyst metal, the electrochemical oxygen reduction catalyst of the present embodiment can exhibit high oxygen transportability and / or proton conductivity.

[0032] The content of the catalyst metal is usually in the range of 1 to 70% by mass, for example, in the range of 48 to 50% by mass, and particularly in the range of 18 to 48% by mass, relative to the total mass of the electrochemical oxygen reduction catalyst of the present embodiment. In the case where the catalyst metal is a platinum alloy or a composite containing platinum, the content of the metal other than platinum is usually in the range of 0.11 to 60% by atom, relative to the total mass of the catalyst metal. By containing the catalyst metal in the above-mentioned range, the electrochemical oxygen reduction catalyst of the present embodiment can exhibit high oxygen transportability and / or proton conductivity.

[0033] The particle diameter of the catalyst metal is usually in the range of 1 to 100 nm.

[0034] In the electrochemical oxygen reduction catalyst of the present embodiment, the composition and content of the catalyst metal can be determined, for example, by dissolving and extracting the catalyst metal contained in the electrochemical oxygen reduction catalyst of the present embodiment and analyzing the metal elements contained in the extract by thermogravimetric analysis (TG) or high-frequency inductively coupled plasma emission spectroscopy (ICP).

[0035] In the electrochemical oxygen reduction catalyst of the present embodiment, the particle diameter of the catalyst metal can be determined, for example, by determining the crystallite diameter using X-ray diffraction and calculating the average crystallite diameter. Alternatively, the particle diameter of the catalyst metal can be determined by measuring the particle diameters of 100 to 1000 catalyst metal particles using an electron microscope and calculating the average thereof (average particle diameter).

[0036] The electrochemical oxygen reduction catalyst of the present embodiment generally has a support that supports the catalyst metal. As the support, for example, carbon and oxides having electrical conductivity and the like, and a mixture of one or more of them can be given. The carbon is preferably carbon black (acetylene black, ketjen black, and furnace black, etc.), activated carbon, graphite, glassy carbon, graphite, graphene, carbon fiber, carbon nanotube, carbon nitride, carbon sulfide, carbon phosphide, channel black, drum black, pan black, oil furnace black, gas furnace black, lamp black, pyrolytic carbon black, or Vulcan carbon, or a mixture of one or more of them. The oxide is preferably titanium oxide, niobium oxide, tin oxide, tungsten oxide, or molybdenum oxide, or a mixture of one or more of them. The support is preferably carbon, and more preferably carbon black.

[0037] The support can be either primary particles or secondary particles. The particle diameter of the primary particles of the support is generally in the range of 5 to 5000 nm.

[0038] In the electrochemical oxygen reduction catalyst of the present embodiment, the composition, content, and particle diameter of the support can be determined, for example, by the same methods as those described above for the determination of the composition, content, and particle diameter of the catalyst metal.

[0039] By having the features described above, the electrochemical oxygen reduction catalyst of the present embodiment can exhibit high oxygen transportability and / or proton conductivity without substantially causing the aggregation of particles and / or the generation of cracks in the electrode catalyst layer, and the like.

[0040] The oxygen transportability and proton conductivity of the electrochemical oxygen reduction catalyst of the present embodiment can be evaluated by the same methods as those for the evaluation of the oxygen transportability and proton conductivity of the ionomer of one embodiment of the present invention.

[0041] <3: Use of ionomer> Another aspect of the present application relates to a fuel cell. The fuel cell of this aspect has at least an electrode catalyst layer of a cathode, 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, the electrode catalyst layer of the cathode containing an electrochemical oxygen reduction catalyst and the ionomer of one aspect of the present application.

[0042] Still another aspect of the present application relates to a water electrolysis system. The water electrolysis system of this aspect has at least an electrode catalyst layer of a cathode, an electrode catalyst layer of an anode, an electrolyte membrane disposed between the electrode catalyst layer of the cathode and the electrode catalyst layer of the anode, and a water supply portion, the electrode catalyst layer of the anode containing an electrochemical oxygen reduction catalyst and the ionomer of one aspect of the present application.

[0043] Still another aspect of the present application relates to a metal-air battery. The metal-air battery of this aspect has at least an electrode catalyst layer of a cathode, a metal layer of an anode, and an electrolyte membrane disposed between the electrode catalyst layer of the cathode and the metal layer of the anode, the electrode catalyst layer of the cathode containing an electrochemical oxygen reduction catalyst and the ionomer of one aspect of the present application.

[0044] The fuel cell, the water electrolysis system, and the metal-air battery of this aspect are able to exhibit high oxygen transportability and / or proton conductivity without substantially causing generation of cracks and the like in the electrode catalyst layer of the cathode or the anode by containing the ionomer of one aspect of the present application in the electrode catalyst layer of the cathode or the anode. Therefore, the fuel cell of this aspect can be applied to, for example, a fuel cell for an automobile, a ship, or a railway vehicle.

[0045] <4: Method for producing ionomer> Another aspect of the present application relates to a method for producing the ionomer of one aspect of the present application. The method of this aspect includes a modification step. As necessary, the method of this aspect can also include a preparation step, an electrode catalyst preparation step, and an electrode catalyst layer production step.

[0046] [4-1: Preparation step] This step includes a step of preparing an ionomer material having an acidic functional group and a fluorine-containing cyclic group (hereinafter also simply referred to as "ionomer material") and a modifier. This step also typically includes a step of preparing a catalyst metal, a support, and a binder. Furthermore, as necessary, this step can also include a step of preparing a solvent and further materials such as a substrate.

[0047] The ionomer material, the catalyst metal, the support, and the binder prepared in this step are only required to be materials having the features described above. For example, the catalyst metal prepared in this step can be in a form supported on the support described above.

[0048] The modifier prepared in this step contains at least a cation of a nitrogen-containing cyclic organic compound or a polymer thereof. The cation of a nitrogen-containing cyclic organic compound or a polymer thereof contained in the modifier is only required to be a material having the features described above.

[0049] In this step, each material can be prepared by preparing a material having a prescribed feature by oneself, or can be prepared by purchasing a commercial product or the like. For example, the ionomer material can be prepared based on a known document (for example, Japanese Patent Application Publication No. 2013-216811).

[0050] [4-2: Modification Step] This step includes a step of modifying the acid functional group of the ionomer material having an acid functional group and a fluorine-containing cyclic group by mixing the ionomer material with a modifier.

[0051] In this step, the ionomer material having an acid functional group and a fluorine-containing cyclic group and the modifier are usually mixed together with a solvent. As the solvent, there is no particular limitation, and any liquid can be used. As the solvent, for example, water and alcohol, and a mixture of one or more kinds thereof can be cited. As the alcohol, for example, methanol, ethanol, 1-propanol, 2-propanol, 2-methyl-2-propanol (tert-butanol), diacetone alcohol, ethylene glycol, propylene glycol, and the like can be cited.

[0052] In this step, the method of mixing the materials is not particularly limited. As the method of mixing, for example, an ultrasonic homogenizer, a jet mill, a bead mill, a ball mill, a high shear machine, a high-speed stirrer (Filmix), and the like can be cited. The specific conditions (for example, stirring speed, stirring time, rotation speed, and the like) of the above-described example of the method of mixing are not particularly limited, and can be appropriately set within any range.

[0053] As needed, this step can also include a vacuum defoaming treatment of defoaming the obtained mixture under vacuum. In this case, the specific conditions (for example, pressure and treatment time) of the vacuum defoaming treatment are not particularly limited, and can be appropriately set within any range. The vacuum defoaming treatment can be performed a plurality of times.

[0054] In this step, an electrochemical oxygen reduction catalyst containing the ionomer of one aspect of the present application can be obtained by removing the solvent from the obtained mixture. The removal of the solvent is not particularly limited, and can be performed by any method such as heating and drying or filtration.

[0055] By performing this step, the acid functional group of the ionomer material can be modified with a modification layer containing a nitrogen-containing cyclic organic compound or a polymer thereof or a cation thereof.

[0056] [4-3: Electrode Catalyst Preparation Step] This step includes a step of preparing an electrode catalyst by mixing a catalyst metal with a binder. The binder used in this step contains the ionomer having a modification layer prepared in the above-described step.

[0057] In this process, the catalyst metal and the binder are usually mixed together with a solvent. As the solvent, the same solvent as that used in the modification process described above can be used. In addition, as the method of mixing the materials, the same method as that used in the modification process described above can be used.

[0058] If necessary, this process can include a vacuum degassing treatment in which the obtained mixture is degassed under vacuum. In this case, the specific conditions (e.g., pressure and treatment time, etc.) of the vacuum degassing treatment are not particularly limited and can be appropriately set within any range. The vacuum degassing treatment can be performed a plurality of times.

[0059] In this process, by removing the solvent from the obtained mixture, an electrochemical oxygen reduction catalyst including the ionomer of one aspect of the present application can be obtained. The removal of the solvent is not particularly limited and can be performed by any method such as heating and drying or filtration.

[0060] Alternatively, in the case where the electrode catalyst layer production process described below is performed, the mixture obtained in this process can be used as a catalyst ink containing an electrochemical oxygen reduction catalyst including the ionomer of one aspect of the present application in the electrode catalyst layer production process. In this case, the mixture obtained in this process can be used as it is or can be used further by adding the solvent exemplified above.

[0061] By performing this process, an electrochemical oxygen reduction catalyst including the ionomer of one aspect of the present application can be obtained.

[0062] [4-4: Electrode Catalyst Layer Production Process] This process includes a step of coating a catalyst ink containing the electrochemical oxygen reduction catalyst obtained in the electrode catalyst preparation process on the surface of a substrate.

[0063] As the substrate used in this process, any material can be used without particular limitation, such as polytetrafluoroethylene (PTFE), an electrolyte membrane having an ion exchange group, carbon fibers, and metal fibers.

[0064] In this process, the method of coating the catalyst ink is not particularly limited. As the coating method, for example, die coating, spin coating, screen printing, doctor blade, blade coating, spray coating, and applicator methods, etc. can be given. The specific conditions of the coating methods exemplified above are not particularly limited and can be appropriately set within any range.

[0065] In this process, the solvent is usually removed from the coated catalyst ink. The removal of the solvent is not particularly limited and can be performed by any method such as heating and drying. The specific conditions (e.g., temperature, pressure, and treatment time, etc.) of the removal of the solvent are not particularly limited and can be appropriately set within any range.

[0066] By carrying out the present procedure, an electrochemical oxygen reduction catalyst comprising the ionomer of one aspect of the present application can be obtained in the form of an electrode catalyst layer configured on the surface of a substrate. In this case, the film thickness of the electrode catalyst layer is usually in the range of 5 to 30 μm. In addition, the content of the catalyst metal in the electrode catalyst layer is usually in the range of 0.1 to 0.6 mg / cm 2 of the total area of the electrode catalyst layer, in terms of mass.

[0067] As described above, by carrying out the method of the present aspect, the ionomer of one aspect of the present application and the electrochemical oxygen reduction catalyst comprising the same can be manufactured.

[0068] As shown in detail in the present specification, the ionomer of one aspect of the present application and the electrochemical oxygen reduction catalyst comprising the same have high oxygen transportability, binder properties, and / or surface activity properties. In addition, the manufacturing method of one aspect of the present application can effectively provide the ionomer of one aspect of the present application and the electrochemical oxygen reduction catalyst comprising the same, which have high oxygen transportability, binder properties, and / or surface activity properties. Therefore, by applying the electrochemical oxygen reduction catalyst comprising the ionomer of one aspect of the present application to, for example, the cathode of a fuel cell, a fuel cell having high oxygen transportability and / or proton conductivity without substantially causing the generation of cracks in the electrode catalyst layer, and the like can be provided. Such a fuel cell can be used, for example, as a fuel cell for a vehicle, a ship, or a railway vehicle.

[0069] Examples

[0070] Hereinafter, the present application will be further specifically described using examples. However, the technical scope of the present application is not limited to these examples.

[0071] <I: Manufacture of ionomer> [I-1: Preparation of ionomer] Based on a known document (Japanese Patent Application Publication No. 2013-216811), a perfluorocarbon sulfonic acid polymer (EW: 900) having 1,3-dioxolane-4,5-diyl substituted with one or more perfluoroalkyl groups as a fluorine-containing cyclic group was prepared as an ionomer material. A modifier comprising a prescribed nitrogen-containing cyclic organic compound or a polymer thereof or a cation thereof was prepared in such a manner that the total amount (mol) of the acidic functional groups of the ionomer material having the acidic functional groups was 10 mol%. The ionomer material, the modifier, and a solvent (water) were put into a container in prescribed amounts. Using an ultrasonic homogenizer and a stirrer, these materials were stirred and mixed for 15 minutes or more, and an ionomer having a modification layer was prepared (modification step).

[0072] As Comparative Example 1, a non-cyclic ionomer not having a modification layer was prepared in the same procedure as described above, using an ionomer material not having a 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 not having a modification layer were prepared in the same procedure as described above, using ionomer materials having a fluorine-containing cyclic group prepared in the same procedure as described above, and without adding a modifier.

[0073] [II-1: Preparation of catalyst ink] A catalyst metal particle support carrier (primary particle diameter: 10 to 100 nm) in which platinum particles (particle diameter: 3 to 4 nm) were supported on a support (acetylene black), a binder containing the ionomer prepared in the above procedure, and a solvent (water) were put into a container in prescribed amounts. These materials were mixed and stirred using a blender (homogenizer and high-speed stirrer) 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 mass% relative to the total mass of the catalyst.

[0074] [II-2: Production of catalyst layer] The prepared catalyst ink was coated on a substrate (a plate made of polytetrafluoroethylene (PTFE)) using a homogenizer and a high-speed stirrer. The coated catalyst ink was subjected to warming to dry and remove the solvent (catalyst ink coating step). The obtained catalyst layer was a film having a thickness of 5 to 30 μm and a platinum support amount of 0.1 to 0.6 mg / cm 2 .

[0075] [II-3: Production of membrane electrode assembly] Each of the catalyst layers produced in the above procedure was prepared as a cathode catalyst layer, a perfluorocarbon sulfonic acid polymer (Nafion NR211 manufactured by Chemours, EW: 1100) was prepared as an electrolyte membrane, and a platinum-supporting carbon catalyst (TEC10E50E manufactured by Tanaka Kikinzoku) was prepared as an anode catalyst layer. The electrolyte membrane was sandwiched with the cathode catalyst layer and the anode catalyst layer. The cathode catalyst layer, the electrolyte membrane, and the anode catalyst layer were subjected to hot press bonding under heating (130°C) and pressurization (3 MPa). A gas diffusion layer (GDL22BB manufactured by SGL) composed of carbon fibers was arranged on the outer side of the cathode catalyst layer and the anode catalyst layer, and a membrane electrode assembly (MEA) (electrode part: 1 x 1 cm) was produced.

[0076] <III: Evaluation of the performance of the electrochemical oxygen reduction catalyst> [III-1: Evaluation of the electrochemical performance of the MEA] Using the MEA produced according to the above procedure as a single cell, the current / voltage characteristics under low humidification conditions (30% RH) and high humidification conditions (80% RH) were measured. The measurement conditions were as follows. Scan rate: 20 mA / s (anode scan), cell temperature: 80°C, pressure: 150 kPa_abs, cathode gas species: air, cathode gas flow rate: 2.0 L / minute.

[0077] [III-2: Evaluation results] The evaluation results of the compositions of the ionomer prepared according to the above procedure and the MEA having the electrochemical oxygen reduction catalyst containing the ionomer are shown in Tables 1 and 2. In the tables, the melamine-formaldehyde copolymer indicated as the component of the modification layer refers to methylated poly(melamine-co-formaldehyde) (nitrogen equivalent 20 to 40 g / equivalent). In addition, in the tables, the D50 value and the D90 value of the electrode catalyst particles in the catalyst ink in the case of Examples 1 to 4 refer to the change amounts with respect to the D50 value and the D90 value of Comparative Example 2, and in the case of Example 5 refer to the change amounts with respect to the D50 value and the D90 value of Comparative Example 3.

[0078] [Table 1]

[0079]

[0080] [Table 2]

[0081]

[0082] As shown in Tables 1 and 2, the electrochemical oxygen reduction catalyst containing the ionomer of Examples 1 to 5 has smaller particle diameters of the electrode catalyst particles in the catalyst ink than the electrochemical oxygen reduction catalyst containing the ionomer of Comparative Examples 2 and 3 having a fluorine-containing cyclic group but not having a modification layer. In addition, in the MEA having the electrochemical oxygen reduction catalyst containing the ionomer of Comparative Examples 2 and 3, the generation of cracks was confirmed in the electrode catalyst layer of the cathode, whereas, in the MEA having the electrochemical oxygen reduction catalyst containing the ionomer of Examples 1 to 5, the generation of cracks and the like was not confirmed in the electrode catalyst layer of the cathode. These results indicate that the ionomer of the present application has high binder properties and surface activity properties that can inhibit the agglomeration of the electrode catalyst particles and the generation of cracks in the electrode catalyst layer.

[0083] Note that the present application is not limited to the above-described examples, and includes various modifications. For example, the above-described examples are examples that are described in detail in order to easily understand the present application, and are not necessarily limited to having all the configurations described. In addition, to a part of the configuration of each example, other configurations can be added, deleted, and / or replaced.

Claims

1. An ionomer having an acidic functional group, a fluorinated cyclic group, and a modifying layer modifying the acidic functional group, the fluorinated cyclic group containing 3 to 16 cyclic atoms, and the modifying layer comprising a nitrogen-containing cyclic organic compound or a polymer thereof or a cation thereof.

2. The ionomer according to claim 1, wherein, The fluorinated cyclic group is a 1,3-dioxolane-4,5-diyl group substituted with one or more perfluoroalkyl groups.

3. The ionomer according to claim 1, wherein, The modification layer contains 1,3,5-triazine, cyanuric acid monoamide, or melamine.

4. A fuel cell comprising at least: an electrode catalyst layer of a cathode comprising an electrochemical oxygen reduction catalyst and the ionomer of claim 1, 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.

5. A method for manufacturing the ionomer of claim 1, comprising a modification step: modifying the acidic functional group by mixing an ionomer material having acidic functional groups and fluorinated cyclic groups with a modifier containing a nitrogen-containing cyclic organic compound or a polymer thereof or their cations.

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