Catalyst

Abstract

To provide a catalyst containing an organic nitrogen compound and capable of improving catalytic performance.SOLUTION: There is provided a catalyst containing metal particles having oxygen reduction activity, a carrier, an additive, and a binder, wherein the metal particles are supported on the carrier, the additive is at least one organic nitrogen compound, the binder is a polymer electrolyte having an ion exchange group and the ratio of the weight of the binder to the weight of metal particles is 2.45 or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a catalyst.

Background Art

[0002] Various studies have been made on catalysts for electrochemical oxygen reduction. Patent Document 1 discloses an electrochemical oxygen reduction catalyst containing platinum-containing nanoparticles and at least one selected from the group consisting of a melamine compound, a thiocyanuric acid compound, and a polymer having the melamine compound or the thiocyanuric acid compound as a monomer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Even when an organic nitrogen compound is added as an additive to a catalyst having oxygen reduction activity to improve the catalyst performance, in the prior art, the effect of improving the catalyst performance may not be sufficiently exhibited. In a region where the amount of the binder in the catalyst is large, the additive is incorporated into the binder, and the effect of improving the catalyst performance by the additive is not exhibited.

[0005] In view of the above circumstances, the present disclosure has been made, and the main object thereof is to provide a catalyst containing an organic nitrogen compound and capable of improving the catalyst performance.

Means for Solving the Problems

[0006] In the present disclosure, it has metal particles having oxygen reduction activity, a carrier, an additive, and a binder, the metal particles are supported on the carrier, The additive is at least one organic nitrogen compound, The binder is a polyelectrolyte having an ion exchange group, Provided is a catalyst, characterized in that the weight of the binder relative to the weight of the metal particles is 2.45 or less.

Effect of the Invention

[0007] The present disclosure can provide a catalyst that contains an organic nitrogen compound and can improve catalytic performance.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0009] Hereinafter, embodiments according to the present disclosure will be described. In addition, matters other than those specifically mentioned in this specification and necessary for the implementation of the present disclosure (for example, general configurations and manufacturing processes of catalysts that do not characterize the present disclosure) can be grasped as design matters of those skilled in the art based on the prior art in the relevant field. The present disclosure can be implemented based on the content disclosed in this specification and common general knowledge in the relevant field. In this specification, “~” indicating a numerical range is used to mean including the numerical values described before and after it as the lower limit value and the upper limit value. In addition, the upper limit value and the lower limit value in the numerical range can adopt any combination.

[0010] 1. Catalyst In the present disclosure, it has metal particles having oxygen reduction activity, a support, an additive, and a binder, The metal particles are supported on the carrier, The additive is at least one organic nitrogen compound, The binder is a polyelectrolyte having an ion-exchange group, Provided is a catalyst characterized in that the weight of the binder relative to the weight of the metal particles is 2.45 or less.

[0011] The catalyst of the present disclosure has metal particles having oxygen reduction activity, a carrier, an additive, and a binder. The catalyst of the present disclosure improves the catalytic activity by containing an appropriate amount of the binder relative to the weight of the metal particles.

[0012] The additive is at least one organic nitrogen compound. As the organic nitrogen compound, a compound having a nitrogen equivalent of 20 to 270 g·eq per mole of nitrogen, which represents the dry weight, may be used, or a compound having a nitrogen equivalent of 20 to 70 g·eq -1 may be used. -1 The nitrogen equivalent can be calculated from the following formula. In the case of a polymer, the nitrogen equivalent of the monomer is regarded as the nitrogen equivalent of the polymer. Nitrogen equivalent (g·eq ) = molecular weight (g / mol) ÷ amount of nitrogen substance in the molecule (mol -1 / mol) N As the organic nitrogen compound, a compound having an amine functional group may be used, a compound having pyridine-type nitrogen may be used, or a compound containing a triazine ring may be used. As the organic nitrogen compound, a monomer represented by the following general formula (1), or a polymer containing at least a part of the monomer may be used.

[0013]

Chemical formula

[0014] ​In general formula (1), R1, R2, and R3 are each a hydrogen atom, a halogen atom, or a functional group selected from the group consisting of a nitrile group, an amide group, an imine group, an amino group, a thiol group, a hydroxyl group, a sulfo group, a carboxylic acid group, a phosphoric acid group, a ketone group, an aldehyde group, an ester group, an alkoxy group, a phenol group, a cyclopentyl group, a cyclohexyl group, an alkylamino group having 1 to 10 carbon atoms, an alkylsulfonic acid group having 1 to 10 carbon atoms, a perfluoroalkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms, an alkenylamino group having 1 to 10 carbon atoms, an alkenylsulfonic acid group having 1 to 10 carbon atoms, a perfluoroalkenyl group having 1 to 10 carbon atoms, and an alkenyl group having 1 to 10 carbon atoms, and each of the functional groups may have at least one selected from the group consisting of at least one functional group selected from the above functional group group, an aromatic ring, a heterocyclic ring, an oxygen atom, a sulfur atom, a nitrogen atom, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, and a hydrogen atom in the molecular chain.

[0015] In general formula (1), R1, R2, and R3 may each be a primary amine, a secondary amine, a tertiary amine, or a quaternary ammonium cation.

[0016] Examples of the organic nitrogen compound include a melamine compound (nitrogen equivalent: 21 g·eq -1 ), a thiocyanuric acid compound (nitrogen equivalent: 59 g·eq -1 ), a cyanuric acid compound (nitrogen equivalent: 34 g·eq -1 ), oleylamine (nitrogen equivalent: 267 g·eq -1 ), tetradecylamine (nitrogen equivalent: 213 g·eq -1 ), 2,4,6-Tris[bis(methoxymetyl)amino]-1,3,5-triazine (nitrogen equivalent: 65 g·eq -1 ), 6-(Dibutylamino)-1,3,5-triazine-2,4-dithiol (nitrogen equivalent: 68 g·eq -1 ), 2,4-Diamino-6-butylamino-1,3,5-triazine (nitrogen equivalent: 30 g eq-1 ) 2,4,6-Tris(pentafluoroethyl)-1,3,5-triazine (nitrogen equivalent 145 g·eq -1 ), and polymers using these as monomers, and Poly(melamine-co-formaldehyde)methylated (nitrogen equivalent 20~40 g·eq -1 ), and Poly(melamine-co-formaldehyde)isobutylated (nitrogen equivalent 20~40 g·eq -1 ) etc. may be used. Also, two or more of the above-mentioned additives may be included. As the melamine compound, melamine, derivatives of melamine, etc. may be used. As the thiocyanuric acid compound, thiocyanuric acid, derivatives of thiocyanuric acid, etc. may be used. As the cyanuric acid compound, cyanuric acid, derivatives of cyanuric acid, etc. may be used. As the polymer using a melamine compound, a thiocyanuric acid compound, or a cyanuric acid compound as a monomer, examples include a melamine resin, a thiocyanuric acid resin, or a cyanuric acid resin having the above-mentioned melamine compound, thiocyanuric acid compound, or cyanuric acid compound in the main chain of the repeating unit. Among the above, as the additive, melamine (1,3,5-triazine-2,4,6-triamine), or a polymer of the melamine may be used. In the case of a polymer, after adsorption to metal particles, it becomes more difficult to desorb than in the case of a monomer, so the adsorption stability is improved. The degree of polymerization of the polymer may be in the range of 1 to 10,000.

[0017] The metal particles may be any metal having oxygen reduction activity (oxygen reduction catalytic ability), such as platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, and yttrium, etc. Two or more of these metals may be used. Also, the metal may be an oxide, nitride, sulfide, phosphide, etc. Among the above, the metal particles may be at least one selected from the group consisting of platinum particles, platinum alloy particles, and composite particles containing platinum. The metals other than platinum contained in the platinum alloy and the composite particles containing platinum are, for example, metals such as ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, and yttrium, etc. Two or more of these metals may be contained. The elemental ratio of the metal other than platinum in the platinum alloy is not particularly limited and may be 0.11 to 50 atm%. The particle diameter (particle size) of the metal particles is not particularly limited and may be 1 to 100 nm.

[0018] In the present disclosure, the particle size of the particles is the average crystallite size measured by the X-ray diffraction method. The particle size of the particles may be measured by an electron microscope for the particle sizes of 100 to 1000 particles, and the average value of these may be used as the average particle size of the particles. In the present disclosure, the particle size was measured by the above two methods.

[0019] The catalyst of the present disclosure includes carriers (supporters) such as carbon and oxides. The metal particles are supported on the carrier. The method for supporting the metal particles on the carrier is not particularly limited, and a conventionally known method can be appropriately adopted. The carrier may be primary particles or secondary particles. The particle size of the primary particles of the carrier may be, for example, 5 to 500 nm. The metal loading ratio of the metal particles supported on the carrier is not particularly limited and may be 1 to 60%, or may be 18 to 48%. The carrier may be conductive carbon, an oxide, or a mixture containing at least two of these. The carbon may be carbon black (acetylene black, ketjen black, channel black, roller black, disk black, oil furnace black, gas furnace black, lamp black, thermal black, and VULCAN (registered trademark) - based carbon, etc.), activated carbon, graphite, glassy carbon, graphite, graphene, carbon fiber, carbon nanotube, carbon nitride, carbon sulfide, and carbon phosphide, or a mixture containing at least two of these. The oxide may be titanium oxide, niobium oxide, tin oxide, tungsten oxide, and molybdenum oxide, or a mixture containing at least two of these.

[0020] The binder is a polyelectrolyte having an ion - exchange group. The polyelectrolyte having an ion - exchange group may be called an electrolyte, an ionomer, or a binder. In the present disclosure, it is hereinafter referred to as a binder. The binder may be a polymer that exchanges ions and may have a sulfonic acid, phosphoric acid, and quaternary ammonium cation, etc. as the ion - exchange group. The binder may be a perfluorocarbon sulfonic acid polymer, an anion - exchange polymer, or a polymer mainly composed of polyether ether ketone, polybenzimidazole, etc.

[0021] [Weight of binder relative to weight of metal particles] In the catalyst of the present disclosure, the weight of the binder relative to the weight of the metal particles may be 2.45 or less, or may be 1.22 or more and 2.45 or less. The weight of the binder relative to the weight of the metal particles is defined as (binder weight) / (metal particle weight).

[0022] [Binder weight relative to carrier weight] In the catalyst of the present disclosure, the weight of the binder relative to the weight of the carrier may be 1.00 or less, or may be 0.50 or more and 1.00 or less. The weight of the binder relative to the carrier weight is defined as (binder weight) / (carrier weight).

[0023] [Additive weight relative to metal particle weight] In the catalyst of the present disclosure, the ratio of the weight of the additive to the weight of the metal particles may be greater than 0 and 0.041 or less. The weight of the additive relative to the metal particle weight is defined as (additive weight) / (metal particle weight).

[0024] [Additive weight evaluation method] Evaluation methods for the weight of the additive contained in the catalyst of the present disclosure include a method of measuring the nitrogen content by CHN elemental analysis, a method of extracting the additive from the catalyst and directly measuring the additive, and the like. The method of measuring the nitrogen content by CHN elemental analysis is a method of quantifying the amounts of carbon, hydrogen, and nitrogen atoms contained in a sample by burning the sample with oxygen for a certain period of time and then quantifying the generated carbon dioxide, water, and nitrogen oxides respectively. It is possible to evaluate the amount of the additive by comparing the nitrogen amounts in the samples before and after introducing the additive. The method of extracting the additive from the oxygen reduction catalyst and directly measuring the additive is a method of qualitatively and quantitatively analyzing the additive after extracting the additive contained in the catalyst with a solvent that dissolves the additive. As analysis methods, there are chromatography, ultraviolet-visible spectroscopy (UV-vis), infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR), and the like.

[0025] [Evaluation methods for metal particle weight, carrier weight, and binder weight] The evaluation methods for the weight of metal particles, the weight of the support, and the weight of the binder contained in the catalyst of the present disclosure include thermogravimetric analysis (TG), high-frequency inductively coupled plasma optical emission spectroscopy (ICP), and the like. Thermogravimetric analysis (TG) is a method for measuring the weight when the gas atmosphere, temperature, etc. are changed. It is a measurement method in which, after raising the temperature and burning off moisture, a conductive support, a polymer having an ion-exchange group, and impurities, the remaining weight is taken as the weight of the metal particles. High-frequency inductively coupled plasma optical emission spectroscopy (ICP) is a method for qualitatively and quantitatively analyzing the contained elements from the wavelength and intensity of the emission lines emitted by atoms excited by a plasma. It is possible to calculate the weight of any substance by controlling the measurement temperature and gas atmosphere. It is possible to directly quantify the weight of metal particles, the weight of the support, and the weight of the binder contained in the catalyst.

[0026] The catalyst of the present disclosure may be used for a fuel cell or a metal-air battery. The catalyst of the present disclosure may be used for the cathode of a fuel cell, the anode of a fuel cell, or the air electrode of a metal-air battery. Further, the catalyst of the present disclosure may be used for the anode for water electrolysis, which is the reverse reaction of a fuel cell, the cathode for water electrolysis, the anode for CO2 reduction, or the cathode for CO2 reduction.

[0027] The shape of the catalyst of the present disclosure may be layered. That is, the catalyst of the present disclosure may be a catalyst layer. Examples of the catalyst layer formation method include the following methods.

[0028] [Catalyst ink preparation step] First, a predetermined amount of a support carrying metal particles (metal particle-carrying support), a binder, an additive, and a solvent are put into a container, and these are stirred using a stirrer to prepare a catalyst ink. The type of solvent is not particularly limited, and any liquid can be used, such as water, alcohol, or a mixed solution of at least one alcohol and water. Examples of the alcohol include methanol, diacetone alcohol, ethanol, 1-propanol, 2-propanol, tert-butyl alcohol, ethylene glycol, propylene glycol, and the like. Examples of the stirrer include a ball mill such as an ultrasonic homogenizer, a jet mill, and a bead mill, a high shear, a filmix, and the like. Stirring conditions such as the stirring speed, the stirring time, and the rotation speed are not particularly limited and can be set as appropriate. Thereafter, a vacuum degassing treatment may be performed. There is no limitation on the standing time, which can be arbitrarily set, and it may be left standing for one day. It is also possible to use it without standing. Further, the vacuum degassing treatment may be performed again.

[0029] [Catalyst Ink Coating Step] The prepared catalyst ink is coated on a substrate, and the solvent is removed after coating. For example, the catalyst ink is coated on the substrate, and the coated catalyst ink is heated to dry and remove the solvent. Examples of the substrate include polytetrafluoroethylene (PTFE), an electrolyte membrane having an ion exchange group, a gas diffusion layer (GDL) composed of carbon fibers or metal fibers, and a gas diffusion layer composed of carbon fibers or metal fibers having a microporous layer (MPL). The coating method may be any method capable of uniformly coating the catalyst ink on the substrate, and examples thereof include a die coating method, a spin coating method, a screen printing method, a doctor blade method, a squeegee method, a spray coating method, and an applicator method. The heating rate and the heating time can be appropriately set depending on the solvent type and the like. Further, the removal rate may be increased by degassing simultaneously with heating. It is also possible to change the coating film thickness and the metal particle content. The coating film thickness may be 5 to 30 μm, and the coating may be performed so as to satisfy a platinum amount of 0.1 to 0.6 mg cm -2

[0030] 2. Air Electrode In the present disclosure, there is provided an air electrode for a fuel cell or a metal-air battery, which contains the catalyst.​ The air electrode of the present disclosure contains the catalyst of the present disclosure. The air electrode of the present disclosure may be the catalyst layer of the present disclosure. The air electrode of the present disclosure may be for a fuel cell or a metal-air battery.

[0031] 3. Fuel Cell In the present disclosure, a fuel cell having the air electrode as a cathode is provided.

[0032] The fuel cell of the present disclosure has the air electrode of the present disclosure as a cathode (cathode catalyst layer). Except for having the air electrode of the present disclosure as a cathode, the fuel cell of the present disclosure can appropriately adopt the configuration of a conventionally known fuel cell. The fuel cell of the present disclosure may have an anode containing the catalyst of the present disclosure. The fuel cell of the present disclosure may have the catalyst layer of the present disclosure as an anode (anode catalyst layer). Since the fuel cell of the present disclosure uses the air electrode containing the catalyst of the present disclosure as a cathode, the power generation performance of the fuel cell can be improved.

[0033] 4. Metal-Air Battery In the present disclosure, a metal-air battery having the air electrode as a cathode is provided.

[0034] The metal-air battery of the present disclosure has the air electrode of the present disclosure as a cathode. Except for having the air electrode of the present disclosure as a cathode, the metal-air battery of the present disclosure can appropriately adopt the configuration of a conventionally known metal-air battery. Since the metal-air battery of the present disclosure uses the air electrode containing the catalyst of the present disclosure as a cathode, the power generation performance of the metal-air battery can be improved.

Examples

[0035] (Example 1) Platinum particles (metal particle diameter 2 - 3 nm) as metal particles, 1,3,5-triazine-2,4,6-triamine (melamine, manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) as an additive, carbon (acetylene black) as a carrier, and a perfluorocarbon sulfonic acid polymer (DE2020 manufactured by Chemours) as a binder were prepared, and an evaluation electrode using a catalyst containing these was fabricated as follows. [Fabrication of Evaluation Electrode] A carrier supporting metal particles (metal particle-supported carrier, metal loading ratio 29 wt%), a binder, and an additive were dispersed in a mixed solvent of 2-propanol and ultrapure water. The dispersion was dropped onto a glassy carbon rotating electrode (diameter 5 mm) manufactured by Hokuto Denko so that the amount of the carrier became 20 μg / cm 2 and dried to fabricate an evaluation electrode. The weight of the binder with respect to the weight of the carrier in the catalyst was set to 0.50. The weight of the binder with respect to the weight of the metal particles in the catalyst was set to 1.22. The weight of the additive with respect to the weight of the metal particles in the catalyst was set to 0.041.

[0036] (Examples 2 - 4, Comparative Example 6) An evaluation electrode using a catalyst was fabricated under the same conditions as in Example 1, except that the weight of the binder with respect to the weight of the carrier and the weight of the binder with respect to the weight of the metal particles were changed as shown in Tables 1 and 3.

[0037] (Comparative Examples 1 - 5) An evaluation electrode using a catalyst was fabricated under the same conditions as in Example 1, except that no additive was used and the weight of the binder with respect to the weight of the carrier and the weight of the binder with respect to the weight of the metal particles were changed as shown in Tables 2 and 3. Since no additive was used, the weight of the additive with respect to the weight of the metal particles in Comparative Examples 1 - 5 was 0.

[0038] [Evaluation of Catalyst Mass Activity] Using each of the evaluation electrodes fabricated in Examples 1 - 4 and Comparative Examples 1 - 6 as the working electrode, a reversible hydrogen electrode as the reference electrode, and a carbon rod as the counter electrode, electrochemical measurements were performed in a three-electrode configuration. As the electrolyte, an aqueous perchloric acid solution adjusted to 0.1 M with ultrapure water was used. Cyclic voltammetry was performed under an inert gas atmosphere. Thereafter, the gas atmosphere was changed to oxygen, and linear sweep voltammetry was performed from the low potential side. The electrode rotation speed was changed to 400, 900, 1600, 2000, 2500, 3600 rpm, and the linear sweep voltammetry measurement was repeated. From the obtained potential-current characteristics, a Kouteckey-Levich plot was created, and the catalytic mass activity (A / g) at 0.9 V vs. RHE was calculated. The catalytic mass activity is the current per unit weight of metal particles. The current is a value representing the reaction rate of the electrochemical reaction, and the larger it is, the higher the catalytic activity. Also, the catalytic mass activity of the catalyst containing the additive (the catalytic mass activity of the catalyst after the introduction of the additive) and the catalytic mass activity of the catalyst having the same composition except for not containing the additive (the catalytic mass activity of the catalyst before the introduction of the additive) were calculated respectively, and from these, the magnification of the improvement in catalytic mass activity was calculated. The magnification of the improvement in catalytic mass activity is defined as (the catalytic mass activity of the catalyst after the introduction of the additive) / (the catalytic mass activity of the catalyst before the introduction of the additive). The magnification of the improvement in catalytic mass activity of each catalyst in Examples 1 to 4 was calculated as the ratio of the catalytic mass activity of each catalyst after the introduction of the additive in Examples 1 to 4 to the catalytic mass activity of each catalyst before the introduction of the additive in Comparative Examples 1 to 4, with each catalyst in Comparative Examples 1 to 4 being the catalyst before the introduction of the additive. The magnification of the improvement in catalytic mass activity of the catalyst in Comparative Example 6 was calculated as the ratio of the catalytic mass activity of the catalyst after the introduction of the additive in Comparative Example 6 to the catalytic mass activity of the catalyst before the introduction of the additive in Comparative Example 5, with the catalyst in Comparative Example 5 being the catalyst before the introduction of the additive. These results are shown in Tables 1 to 3.

[0039] [Table 1]

[0040] [Table 2]

[0041] [Table 3]

[0042] [Evaluation Results] Figure 1 is a graph showing the relationship between the binder weight and the catalyst mass activity with respect to the carrier weight in the catalysts of Examples 1 to 4 and Comparative Examples 1 to 6. Figure 2 is a graph showing the relationship between the binder weight and the magnification of improvement in catalyst mass activity with respect to the carrier weight in the catalysts of Examples 1 to 4 and Comparative Example 6. As shown in FIGS. 1 to 2 and Tables 1 to 3, it can be seen that each catalyst of Examples 1 to 4 has a higher catalyst mass activity and a higher magnification of improvement in catalyst mass activity than each corresponding catalyst of Comparative Examples 1 to 4. Also, as shown in Comparative Examples 5 to 6, it can be seen that when the weight of the binder increases, the effect of improving the catalyst mass activity cannot be obtained. From the above results, it was demonstrated that the catalyst performance can be improved by including an organic nitrogen compound and having the weight of the binder be 2.45 or less with respect to the weight of the metal particles.

Claims

Claim 1: A catalyst for electrochemical oxygen reduction, comprising: the catalyst includes metal particles having oxygen reduction activity, a carrier, an additive, and a binder; the metal particles are supported on the carrier; the additive is at least one kind of organic nitrogen compound; the binder is a polymer electrolyte having an ion-exchange group; the weight of the binder relative to the weight of the metal particles is 1.22 or more and 2.45 or less; the organic nitrogen compound is melamine (1,3,5-triazine-2,4,6-triamine) or a polymer of the melamine; the metal particles are at least one selected from the group consisting of platinum particles, platinum alloy particles, and composite particles containing platinum, characterized in that it is a catalyst. Claim 2 The catalyst according to claim 1, wherein the organic nitrogen compound is melamine. Claim 3 The catalyst according to claim 1, wherein the metal particles are platinum particles. Claim 4 The catalyst according to claim 1, wherein the weight of the additive relative to the weight of the metal particles is 0.041.

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