JP7782385B2 - catalyst - Google Patents

Description

This disclosure relates to catalysts.

Various studies have been conducted 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 containing the melamine compound or the thiocyanuric acid compound as a monomer.

International Publication No. 2019/221156

Even when an organic nitrogen compound is added as an additive to a catalyst with oxygen reduction activity to improve catalytic performance, the additive may not be adsorbed onto the metal particles, and the additive's catalytic performance improvement effect may not be realized.

The present disclosure was made in consideration of the above-mentioned circumstances, and its primary objective is to provide a catalyst that contains an organic nitrogen compound and can improve catalytic performance.

In the present disclosure, there is provided a catalyst comprising metal particles having oxygen reduction activity, a support, and an additive,
the metal particles are supported on the support,
the additive is at least one organic nitrogen compound;
The catalyst is characterized in that the BET specific surface area of the support is 641 m ² g ⁻¹ _support or less.

The present disclosure provides a catalyst that contains an organic nitrogen compound and can improve catalytic performance.

FIG. 1 is a graph showing the relationship between the average pore diameter of the carriers used in Examples 1 to 4 and Comparative Example 1 and the catalyst mass activity improvement ratio. FIG. 2 is a graph showing the relationship between the BET specific surface area of the carriers used in Examples 1 to 4 and Comparative Example 1 and the catalyst mass activity improvement ratio. FIG. 3 is a graph showing the relationship between the total pore volume of 2-30 nm of the carriers used in Examples 1 to 4 and Comparative Example 1 and the catalyst mass activity improvement ratio.

Hereinafter, embodiments of the present disclosure will be described. It should be noted that matters other than those specifically mentioned in this specification that are necessary for implementing the present disclosure (for example, the general configuration and manufacturing process of the catalyst that do not characterize the present disclosure) can be understood as design matters for those skilled in the art based on prior art in the relevant field. The present disclosure can be implemented based on the contents disclosed in this specification and common general technical knowledge in the relevant field.
In this specification, the use of "to" to indicate a range of values means that the values before and after it are included as the lower and upper limits.
Any combination of upper and lower limits in the numerical range can be adopted.

1. Catalyst In the present disclosure, a catalyst is provided which comprises metal particles having oxygen reduction activity, a support, and an additive,
the metal particles are supported on the support,
the additive is at least one organic nitrogen compound;
The catalyst is characterized in that the BET specific surface area of the support is 641 m ² g ⁻¹ _support or less.

In this disclosure, the catalytic performance-enhancing effect of additives is more easily realized by preferentially supporting metal particles, which are reaction active sites, on the outer surface of the support. To achieve this, we have discovered that by using a support with a large average pore diameter, a small BET specific surface area, and a small pore volume, the catalytic performance-enhancing effect of additives can be confirmed.

The catalyst disclosed herein comprises metal particles having oxygen reduction activity, a support, and an additive.

The additive is at least one organic nitrogen compound.
The organic nitrogen compound may be a compound having a nitrogen equivalent, which represents the dry weight per mole of nitrogen, of 20 to 270 g·eq ⁻¹ , or may be a compound having a nitrogen equivalent of 20 to 70 g·eq ⁻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 ⁻¹ ) = molecular weight (g/mol) ÷ amount of nitrogen substance in molecule (mol _N /mol)
The organic nitrogen compound may be a compound having an amine functional group, a compound having pyridine-type nitrogen, or a compound containing a triazine ring. The organic nitrogen compound may be a monomer represented by the following general formula (1), or a polymer at least partially containing the monomer:

[In general formula (1), R ₁ , R ₂ , and R ₃ each represent a hydrogen atom, a halogen atom, or 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 phosphate 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, or an alkenyl group having 1 to 10 carbon atoms. It is one functional group selected from the group consisting of an amino group, an alkenylsulfonic acid group having 1 to 10 carbon atoms, a perfluoroalkenyl group having 1 to 10 carbon atoms, and an alkenyl group having 1 to 10 carbon atoms, and the functional group may have, in the molecular chain, at least one functional group selected from the group consisting of the above functional groups, an aromatic ring, a heterocycle, an oxygen atom, a sulfur atom, a nitrogen atom, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, and at least one atom selected from the group consisting of a hydrogen atom.]

In general formula (1), R ₁ , R ₂ and R ₃ may each be a primary amine, a secondary amine, a tertiary amine or a quaternary ammonium cation.

Examples of organic nitrogen compounds include melamine compounds (nitrogen equivalent: 21 g·eq ⁻¹ ), thiocyanuric acid compounds (nitrogen equivalent: 59 g·eq ⁻¹ ), cyanuric acid compounds (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(methoxymethyl)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 containing these as monomers, and
Poly(melamine-co-formaldehyde) methylated (nitrogen equivalent: 20 to 40 g·eq ⁻¹ ), and
Poly(melamine-co-formaldehyde) isobutylated (nitrogen equivalent: 20 to 40 g·eq ⁻¹ ), etc. Also, two or more of the above-mentioned additives may be contained.
The melamine compound may be melamine, a derivative of melamine, etc. The thiocyanuric acid compound may be thiocyanuric acid, a derivative of thiocyanuric acid, etc. The cyanuric acid compound may be cyanuric acid, a derivative of cyanuric acid, etc.
Examples of polymers containing a melamine compound, a thiocyanuric acid compound, or a cyanuric acid compound as a monomer include melamine resins, thiocyanuric acid resins, and cyanuric acid resins having the above-mentioned melamine compound, thiocyanuric acid compound, or cyanuric acid compound in the main chain of repeating units.
Among the additives listed above, melamine (1,3,5-triazine-2,4,6-triamine) or a polymer of the melamine may be used. The polymer is more difficult to desorb after adsorption onto metal particles than the monomer, improving adsorption stability. The polymer may have a degree of polymerization in the range of 1 to 10,000.

The metal particles may be any metal having oxygen reduction activity (oxygen reduction catalytic activity), such as platinum, ruthenium, iridium, rhodium, palladium, osnium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, and yttrium, and two or more of these metals may be used. Furthermore, the metal may be an oxide, nitride, sulfide, phosphide, or the like.
Among the above, the metal particles may be at least one type selected from the group consisting of platinum particles, platinum alloy particles, and composite particles containing platinum.
Examples of metals other than platinum contained in the platinum alloy and the platinum-containing composite particles include ruthenium, iridium, rhodium, palladium, osnium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, and yttrium, and the particles may contain two or more of these metals.
The element ratio of metals other than platinum in the platinum alloy is not particularly limited, and may be 0.11 to 50 atm %.
The particle size (particle diameter) of the metal particles is not particularly limited and may be 1 to 100 nm.

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

The catalyst of the present disclosure includes a support (carrier) such as carbon and an oxide.
The metal particles are supported on a carrier.
The method for supporting the metal particles on the carrier is not particularly limited, and any conventionally known method can be appropriately adopted.
The carrier may be either a primary particle or a secondary particle.
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 loaded on the carrier is not particularly limited, and may be 1 to 60%, or may be 18 to 48%.
The support may be a 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, disc black, oil furnace black, gas furnace black, lamp black, thermal black, VULCAN (registered trademark) type carbon, etc.), activated carbon, graphite, glassy carbon, graphene, carbon fiber, carbon nanotubes, carbon nitride, carbon sulfide, carbon phosphide, or a mixture containing at least two of these.
The oxide may be titanium oxide, niobium oxide, tin oxide, tungsten oxide, molybdenum oxide, or a mixture containing at least two of these.

The catalyst of the present disclosure may also include a binder.
The binder is a polyelectrolyte having ion exchange groups.
A polymer electrolyte having an ion exchange group may be referred to as an electrolyte, ionomer, or binder. Hereinafter, the binder will be referred to as a binder. The binder may be any polymer that exchanges ions, and may have ion exchange groups such as sulfonic acid, phosphoric acid, and quaternary ammonium cations. The binder may be a perfluorocarbon sulfonic acid polymer, an anion exchange polymer, or a polymer primarily composed of polyether ether ketone, polybenzimidazole, or the like.

[BET specific surface area of support (m ² g ⁻¹ _support )]
In the catalyst of the present disclosure, the BET specific surface area of the support may be 641 m ² g ⁻¹ _support or less, and may be 224 m ² g ⁻¹ _support or more.

[Average pore diameter of carrier]
In the catalyst of the present disclosure, the average pore diameter of the support may be 7.7 nm or more and 11.5 nm or less.

[Total pore volume of the support in the 2.0-30 nm range (mL g ⁻¹ _support )]
In the catalyst of the present disclosure, the total pore volume of the support in the 2.0-30 nm range may be 2.62 mL g ⁻¹ _support or more, and may be 6.50 mL g ⁻¹ _support or less.

[BET specific surface area of catalyst (m ² g ⁻¹ _catalyst )]
In the catalyst of the present disclosure, the BET specific surface area of the catalyst may be 458 m ² g ⁻¹ _catalyst or less, or 151 m ² g ⁻¹ _catalyst or more.

[Total pore volume of catalyst in the 2.0-30 nm range (mL g ⁻¹ _catalyst )]
In the catalyst of the present disclosure, the total pore volume of the catalyst in the 2.0-30 nm range may be 1.86 mL g ⁻¹ _catalyst or more, and may be 5.10 mL g ⁻¹ _catalyst or less.

[Binder weight relative to carrier weight]
In the catalyst of the present disclosure, the weight ratio of the binder to the weight of the carrier may be 0.1 or more and 2.0 or less, or may be 0.5 or more and 1.0 or less.
The binder weight relative to the carrier weight is defined as (binder weight)/(carrier weight).

[Weight of additive relative to weight of carrier]
In the catalyst of the present disclosure, the weight ratio of the additive to the weight of the support may be greater than 0 and not greater than 0.20, or may be 0.01 or greater and 0.10 or less.
The weight of the additive relative to the weight of the carrier is defined as (weight of the additive)/(weight of the carrier).

[Weight of additive relative to weight of metal particles]
In the catalyst of the present disclosure, the ratio of the weight of the additive to the weight of the metal particles may be 0.01 or more and 0.20 or less.
The ratio of the weight of the additive to the weight of the metal particles is defined as (weight of the additive)/(weight of the metal particles).

[Additive weight evaluation method]
Methods for evaluating the weight of the additive contained in the catalyst of the present disclosure include a method for measuring the nitrogen content by CHN elemental analysis, and a method for extracting the additive from the catalyst and measuring the additive directly.
The method of measuring nitrogen content using CHN elemental analysis involves burning a sample with oxygen for a certain period of time, then quantifying the amounts of carbon, hydrogen, and nitrogen atoms contained in the sample by quantifying the amounts of carbon dioxide, water, and nitrogen oxides produced. By comparing the amount of nitrogen in the sample before and after adding the additive, it is possible to evaluate the amount of the additive.
The method of extracting additives from oxygen reduction catalysts and measuring them directly involves extracting the additives contained in the catalyst using a solvent that dissolves the additives, and then qualitatively and quantitatively analyzing the additives.
Analytical techniques include chromatography, ultraviolet-visible spectroscopy (UV-vis), infrared spectroscopy (IR), and nuclear magnetic resonance (NMR).

[Method for evaluating metal particle weight, carrier weight, and binder weight]
Methods for evaluating the weight of the metal particles, the weight of the carrier, and the weight of the binder contained in the catalyst of the present disclosure include thermogravimetric analysis (TG), inductively coupled plasma emission spectroscopy (ICP), and the like.
Thermogravimetric analysis (TG) is a method for measuring weight when the gas atmosphere, temperature, etc. are changed. After heating and burning off moisture, conductive carriers, polymers with ion exchange groups, and impurities, the remaining weight is taken as the weight of the metal particles.
Inductively coupled plasma optical emission spectroscopy (ICP) is a technique for qualitatively and quantitatively determining the elements contained in a substance based on the wavelength and intensity of the emission lines emitted by atoms excited by plasma. By controlling the measurement temperature and gas atmosphere, it is possible to calculate the weight of any substance.
It is possible to directly quantify the weight of metal particles, carrier, and binder contained in the catalyst.

[Method for evaluating the average pore diameter, pore volume, and BET specific surface area of the carrier]
The physical properties of the carrier may be measured directly. Alternatively, the catalyst in which the carrier and metal particles are combined may be measured and converted into the weight of the carrier. The average pore diameter, pore volume, and specific surface area can all be measured by _N2 adsorption/desorption.
The above three parameters may be obtained from the relative pressure dependence of the amount of N ₂ adsorbed onto the sample.
The specific surface area is calculated using the BET theory.
The evaluation method is not limited to the above, and may be evaluated by Hg porosimetry, H ₂ O adsorption, DBP oil supply amount using dibutyl phthalate, etc. Microscopic observation may also be used.

[Metal particle surface area evaluation method]
Methods for evaluating the surface area of metal particles include, for example, a gas phase gas adsorption method and an electrochemical substance adsorption method.
The gas-phase gas adsorption method is a technique for measuring the surface area of metal particles by introducing a gas that adsorbs onto the metal particles into a sample and measuring the amount of adsorbed gas. Typical examples of adsorbed gases include carbon monoxide, carbon dioxide, nitrogen, and water.
The electrochemical adsorption method is a technique in which a substance that adsorbs to metal particles is introduced into a sample, and the surface area of the metal particles is measured from the amount of adsorbed substance.The amount of adsorbed substance is measured from the amount of electricity that flows when the substance is adsorbed and desorbed from the metal particle surface, and the surface area of the metal particles is then measured.Typical examples of adsorbed substances include carbon monoxide, hydrogen, and copper.

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 in a cathode of a fuel cell, an anode of a fuel cell, or an air electrode of a metal-air battery. Furthermore, the catalyst of the present disclosure may be used in an anode for water electrolysis, which is the reverse reaction of a fuel cell, or in a cathode for water electrolysis, or in an anode for _CO2 reduction, or in a cathode for _CO2 reduction.

The catalyst of the present disclosure may be in the form of a layer, i.e., the catalyst of the present disclosure may be a catalyst layer.
Examples of the method for forming the catalyst layer include the following methods.

[Catalyst ink preparation process]
First, a predetermined amount of a carrier carrying metal particles (metal particle-carrying carrier), a binder, an additive, and a solvent are placed in 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, and may be water, alcohol, or a mixed solution of at least one type of alcohol and water.
Examples of the alcohol include methanol, diacetone alcohol, ethanol, 1-propanol, 2-propanol (isopropanol), tert-butyl alcohol, ethylene glycol, and propylene glycol.
Examples of the stirrer include an ultrasonic homogenizer, a jet mill, a ball mill such as a bead mill, a high shear mill, a film mix, etc. The stirring conditions such as the stirring speed, stirring time, and rotation speed are not particularly limited and can be set appropriately.
Thereafter, a vacuum degassing treatment may be performed. There is no limit to the time for leaving the mixture to stand, and it may be left to stand for one day. It is also possible to use the mixture without leaving it to stand. It is also possible to perform a vacuum degassing treatment again.

[Catalyst ink coating process]
The prepared catalyst ink is applied to a substrate, and the solvent is removed after application. For example, the catalyst ink is applied to a substrate, and the applied 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) made of carbon fiber or metal fiber, and a gas diffusion layer made of carbon fiber or metal fiber having a microporous layer (MPL).
The coating method may be any method that can uniformly coat the catalyst ink on the substrate, and examples thereof include die coating, spin coating, screen printing, doctor blade, squeegee, spray coating, and applicator methods. The heating rate and heating time can be appropriately set depending on the type of solvent, etc. The removal rate may also be increased by degassing simultaneously with heating.
The coating thickness and the metal particle content can be changed.
The coating thickness may be 5 to 30 μm, and the coating may be carried out so that the platinum amount satisfies 0.1 to 0.6 mg cm ⁻² .

2. Air Electrode The present disclosure provides an air electrode for a fuel cell or a metal-air battery, which includes the catalyst.
The cathode of the present disclosure includes the catalyst of the present disclosure. The cathode of the present disclosure may also include the catalyst layer of the present disclosure.
The cathode of the present disclosure may be for use in a fuel cell or a metal-air battery.

3. Fuel Cell The present disclosure provides a fuel cell having the air electrode as a cathode.

The fuel cell of the present disclosure has the air electrode of the present disclosure as the cathode (cathode catalyst layer).
The fuel cell of the present disclosure can appropriately adopt the configuration of a conventionally known fuel cell, except that it has the air electrode of the present disclosure as a cathode. 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).
The fuel cell of the present disclosure uses an air electrode containing the catalyst of the present disclosure as a cathode, and therefore the power generation performance of the fuel cell can be improved.

4. Metal-Air Battery The present disclosure provides a metal-air battery having the air electrode as a cathode.

The metal-air battery of the present disclosure has 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, except that it has the air electrode of the present disclosure as the cathode.
The metal-air battery of the present disclosure uses an air electrode containing the catalyst of the present disclosure as a cathode, and therefore the power generation performance of the metal-air battery can be improved.

Example 1
Platinum particles were used as the metal particles, 1,3,5-triazine-2,4,6-triamine (melamine, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used as the additive, carbon was used as the carrier, and perfluorocarbon sulfonic acid polymer (DE2020 manufactured by Chemours) was used as the binder. An electrode for evaluation was fabricated using a catalyst containing these as follows.
The platinum particles used as the metal particles had a metal particle diameter of 2 to 3 nm.
The carbon support used was Ketjen black, with a metal loading ratio of 28.5 wt %, an average pore diameter of 9.4 nm, a BET specific surface area of 641 m ² g ⁻¹ _support , and a total pore volume in the 2.0-30 nm range of 6.30 mL g ⁻¹ _support .
The catalyst used had a BET specific surface area of 458 m ² g ⁻¹ _catalyst and a total pore volume of 4.50 mL g ⁻¹ _catalyst in the range of 2.0 to 30 nm.
[Preparation of evaluation electrodes]
The carrier carrying metal particles (metal particle-supported carrier), binder, and additives were dispersed in a mixed solvent of ² -propanol and ultrapure water. The dispersion was added dropwise to a Hokuto Denko glassy carbon rotating electrode (diameter 5 mm) so that the carrier amount was 20 μg/cm2, and then dried to prepare an electrode for evaluation.
The ratio of the binder weight to the carrier weight in the catalyst was set to 0.5.
The weight ratio of the additive to the weight of the carrier in the catalyst was 0.1.

Example 2
An electrode for evaluation was prepared using a catalyst under the same conditions as in Example 1, except that platinum particles with a metal particle diameter of 2 to 3 nm were used as the metal particles, and acetylene black with a metal loading ratio of 17.9 wt%, an average pore diameter of 7.7 nm, a BET specific surface area of 252 m ² g ⁻¹ _support , and a total pore volume in the 2.0-30 nm range of 6.22 mL g ⁻¹ _support was used as the carrier.
The catalyst used had a BET specific surface area of 207 m ² g ⁻¹ _catalyst and a total pore volume of 5.10 mL g ⁻¹ _catalyst in the range of 2.0 to 30 nm.

Example 3
An electrode for evaluation was prepared using a catalyst under the same conditions as in Example 1, except that platinum particles with a metal particle diameter of 4 to 5 nm were used as the metal particles, and acetylene black with a metal loading ratio of 43.9 wt%, an average pore diameter of 9.5 nm, a BET specific surface area of 269 m ² g ⁻¹ _support , and a total pore volume in the 2.0-30 nm range of 6.50 mL g ⁻¹ _support was used as the carrier.
The catalyst used had a BET specific surface area of 151 m ² g ⁻¹ _catalyst and a total pore volume of 3.64 mL g ⁻¹ _catalyst in the range of 2.0-30 nm.

Example 4
An evaluation electrode using a catalyst was prepared under the same conditions as in Example 1, except that platinum particles with a metal particle diameter of ² to ³ nm were used as the metal particles, and VULCAN (registered trademark) XC72 ( _manufactured by Cabot Corporation) with a metal loading ratio of 29 wt%, an average pore diameter of 11.5 nm, a BET specific surface area of 224 m 2 g −1 _support , and a total pore volume in the 2.0-30 nm range of 2.62 mL g ⁻¹ support was used as the carrier.
The catalyst used had a BET specific surface area of 159 m ² g ⁻¹ _catalyst and a total pore volume of 1.86 mL g ⁻¹ _catalyst in the range of 2.0-30 nm.

(Comparative Example 1)
An electrode for evaluation was prepared using a catalyst under the same conditions as in Example 1, except that platinum particles with a metal particle diameter of 2 to 3 nm were used as the metal particles, and Ketjen black with a metal loading ratio of 27.3 wt%, an average pore diameter of 5.4 nm, a BET specific surface area of 680 m ² g ⁻¹ _support , and a total pore volume in the 2.0-30 nm range of 15.50 mL g ⁻¹ _support was used as the carrier.
The catalyst used had a BET specific surface area of 494 m ² g ⁻¹ _catalyst and a total pore volume of 10.54 mL g ⁻¹ _catalyst in the range of 2.0 to 30 nm.

[Evaluation of catalyst mass activity]
Electrochemical measurements were carried out in a three-electrode system using each of the evaluation electrodes prepared in Examples 1 to 4 and Comparative Example 1 as a working electrode, a reversible hydrogen electrode as a reference electrode, and a carbon rod as a counter electrode.
As the electrolyte, an aqueous solution of perchloric acid adjusted to 0.1 M with ultrapure water was used.
Cyclic voltammetry was carried out 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, and 3600 rpm, and the linear sweep voltammetry measurement was repeated.
From the obtained potential-current characteristics, a Kouteckey-Levich plot was created, and the catalyst mass activity (A/g) at 0.9 Vvs RHE was calculated.
Catalyst mass activity is the current per unit weight of metal particles. The current represents the reaction rate of an electrochemical reaction, and the larger the current, the higher the catalytic activity.
In addition, the catalytic mass activity of a catalyst containing an additive (catalytic mass activity of the catalyst after the additive was introduced) and the catalytic mass activity of a catalyst having the same configuration except that it did not contain an additive (catalytic mass activity of the catalyst before the additive was introduced) were calculated, and the catalytic mass activity improvement ratio was calculated from these.
The catalyst mass activity improvement factor is defined as (catalyst mass activity of the catalyst after the addition of the additive)/(catalyst mass activity of the catalyst before the addition of the additive).
The surface area of the metal particles was calculated from the hydrogen adsorption current value of the reduction wave in the cyclic voltammogram.
The results are shown in Table 1.

[Evaluation results]
FIG. 1 is a graph showing the relationship between the average pore diameter of the carriers used in Examples 1 to 4 and Comparative Example 1 and the catalyst mass activity improvement ratio.
2 is a graph showing the relationship between the BET specific surface area (m ² g ⁻¹ _carbon ) of the support used in Examples 1 to 4 and Comparative Example 1 and the catalyst mass activity improvement ratio. The BET specific surface area (m ² g ⁻¹ _carbon ) of the support is synonymous with the BET specific surface area (m ² g ⁻¹ _support ) of the support.
3 is a graph showing the relationship between the total pore volume (mL g ⁻¹ _carbon ) of 2-30 nm of the support used in Examples 1 to 4 and Comparative Example 1 and the catalyst mass activity improvement factor. The total pore volume (mL g ⁻¹ _carbon ) of 2-30 nm of the support is synonymous with the total pore volume (mL g ⁻¹ _support ) of the support in the 2.0-30 nm range.
As shown in Figures 1 to 3 and Table 1, it can be seen that the catalyst activity improvement rate is higher when a carrier having a larger average pore diameter, a smaller BET specific surface area, and a smaller pore volume is used.
The above results demonstrate that the performance of the catalyst can be improved by using a support with a large average pore diameter, a small BET specific surface area, and a small pore volume.

Claims (3)

A catalyst for electrochemical oxygen reduction, comprising:
the catalyst comprises metal particles having oxygen reduction activity, a support, and an additive;
the metal particles are supported on the support,
the additive is at least one organic nitrogen compound;
The BET specific surface area of the carrier is 224 m ² g ⁻¹ _support or more and 641 m ² g ⁻¹ _support or less,
The average pore diameter of the carrier is 7.7 nm to 11.5 nm,
The total pore volume of the support in the 2.0-30 nm range is 2.62 mL g ⁻¹ _support or more and 6.50 mL g ⁻¹ _support 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 platinum-containing composite particles;
The catalyst is characterized in that the support is electrically conductive carbon. The catalyst described in claim 1, wherein the organic nitrogen compound is melamine. 2. The catalyst of claim 1, wherein the support has a BET specific surface area of 224 m ² g ⁻¹ _support .