JP2013030470A - Ink, electrode catalyst layer formed using ink and use of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide ink for forming an electrode catalyst layer, capable of inexpensively and efficiently forming a high performance electrode catalyst layer.SOLUTION: Ink for forming an electrode catalyst layer of the present invention includes an electrode catalyst, an electron conductive material, a proton conductive material and a solvent. The electrode catalyst includes a transition metal element, carbon, nitrogen and oxygen, as constituent elements, and, when the atomicity ratio of each of the elements is represented as 1:x:y:z, 0.5<x≤7, 0.01<y≤2 and 0.1<z≤3 are satisfied. A mass ratio (A/B) between a content A of the electrode catalyst and a content B of the electron conductive material is 1 or more and 6 or less, and a mass ratio (D/C) between a content D of the proton conductive material and the total content C of the electrode catalyst and the electron conductive material is 0.1 or more and 0.9 or less.

Description

  The present invention relates to an ink, an electrode catalyst layer formed using the ink, and use thereof.

  A polymer electrolyte fuel cell is a type of fuel in which a solid polymer electrolyte is sandwiched between an anode and a cathode, fuel is supplied to the anode, oxygen or air is supplied to the cathode, and oxygen is reduced at the cathode to extract electricity. It is a battery. Hydrogen or methanol is mainly used as the fuel.

  Conventionally, in order to increase the reaction rate of the fuel cell and increase the energy conversion efficiency of the fuel cell, a layer containing a catalyst has been provided on the cathode (air electrode) surface and the anode (fuel electrode) surface of the fuel cell.

  As this catalyst, a noble metal is generally used, and noble metals such as platinum and palladium which are stable at a high potential and have high activity among the noble metals have been mainly used. However, since these noble metals are expensive and have limited resources, development of alternative catalysts has been required.

  In addition, the noble metal used for the cathode surface may be dissolved in an acidic atmosphere, and there is a problem that it is not suitable for applications that require long-term durability. Therefore, there has been a strong demand for the development of a catalyst that does not corrode in an acidic atmosphere, has excellent durability, and has a high oxygen reducing ability.

  Base metal carbides, base metal oxides, base metal carbonitrides, chalcogen compounds, carbon catalysts and the like that do not use any precious metal have been reported as noble metal substitute catalysts (see, for example, Patent Documents 1 to 4). These materials are cheaper and have abundant resources than noble metal materials such as platinum.

However, these catalysts including the base metal materials described in Patent Document 1 and Patent Document 2 have a problem that a practically sufficient oxygen reducing ability is not obtained.
Moreover, although the catalyst described in patent document 3 and patent document 4 shows high oxygen reduction catalyst activity, it is a problem that stability under fuel cell operation conditions is very low.

As such a precious metal substitute catalyst, Nb and Ti oxycarbonitrides in Patent Document 5 and Patent Document 6 are attracting particular attention because they can effectively exhibit the above performance.
The catalysts described in Patent Document 5 and Patent Document 6 have extremely high performance compared to conventional noble metal substitute catalysts, but heat treatment at a high temperature of 1600 ° C. to 1800 ° C. is necessary in part of the production process. (For example, Patent Document 5 Example 1 or Patent Document 6 Example 1).

  Although such high-temperature heat treatment is not impossible industrially, it is difficult, and it causes a rise in equipment costs and difficulty in operation management, which in turn increases production costs. It was desired.

Patent Document 7 reports a technique relating to the production of a carbon-containing titanium oxynitride containing carbon, nitrogen and oxygen.
However, in the production method described in Patent Document 7, in order to produce a carbon-containing titanium oxynitride, production of titanium oxynitride by reaction of a nitrogen-containing organic compound and a titanium precursor, and phenol resin and titanium oxynitride. A two-step synthesis of producing carbon-containing titanium oxynitride by reaction with a nitride precursor is required and the process is complicated. In particular, the production of the titanium oxynitride precursor requires a complicated process such as stirring at 80 ° C., heating, refluxing, cooling, and concentration under reduced pressure, and thus the production cost is high.

  Moreover, since the phenol resin is a thermosetting resin having a three-dimensional network structure, it is difficult to uniformly mix and react with the metal oxide. In particular, since the thermal decomposition temperature of the phenol resin is 400 ° C. to 900 ° C., there is a problem that a carbonization reaction due to complete decomposition of the phenol resin hardly occurs at a temperature of 1000 ° C. or less.

  Furthermore, Patent Document 7 and Non-Patent Document 1 merely describe applications as a thin film for a solar heat collector and a photocatalyst as their uses, and shapes such as granular or fibrous shapes that are highly useful as electrode catalysts. The method for producing a metal oxycarbonitride and its use has not been disclosed or studied.

  Patent Document 8 discloses a method for producing an electrode catalyst characterized by firing a mixed material of an oxide and a carbon material precursor, but an electrode catalyst having sufficient catalytic performance has not been obtained. .

  Further, Patent Document 9 discloses a fuel cell electrode catalyst using a polynuclear complex such as cobalt. However, there is a problem in that the raw material has high toxicity, is expensive, and does not have sufficient catalytic activity. there were.

  Non-Patent Document 2 discloses a method for producing an electrode catalyst characterized by firing a mixed material of titanium alkoxide and a carbon material precursor, but in the production process, an organic substance containing nitrogen is used. No electrode catalyst having sufficient catalytic performance has been obtained.

JP 2004-303664 A International Publication No. 07/072665 Pamphlet US Patent Application Publication No. 2004/0096728 JP 2005-19332 A International Publication No. 2009/031383 Pamphlet International Publication No. 2009/107518 Pamphlet JP 2009-23887 A JP 2009-255053 A JP 2008-258150 A

Journal of Inorganic Materials (Chinese) 20, 4, P785 Electrochemistry Communications Volume 12, Issue 9, September 2010, Pages 1177-1179.

  An object of the present invention is to solve problems in the prior art. An object of the present invention is to provide an ink for forming an electrode catalyst layer which is mainly useful for a fuel cell, and which can efficiently form an inexpensive and high-performance electrode catalyst layer.

  As a result of intensive studies to solve the above-described problems of the prior art, the present inventors have included a specific electrode catalyst, and the contents of the electrode catalyst, the electron conductive material, and the proton conductive material are within a specific range. It has been found that by using a controlled ink, an inexpensive and high-performance electrode catalyst layer can be efficiently formed, and the power generation characteristics of a fuel cell provided with the catalyst layer can be improved. It came to complete.

The present invention relates to the following (1) to (8), for example.
(1) An ink for forming an electrode catalyst layer, comprising an electrode catalyst, an electron conductive material, a proton conductive material and a solvent,
The electrode catalyst includes a transition metal element, carbon, nitrogen and oxygen as constituent elements, and the ratio of the number of atoms of each element is defined as transition metal element: carbon: nitrogen: oxygen = 1: x: y: z (provided that The number of atoms of the transition metal element is 0.5 <x ≦ 7, 0.01 <y ≦ 2, 0.1 when a plurality of transition metal elements are used.) <Z ≦ 3,
The mass ratio (A / B) of the content A of the electrode catalyst and the content B of the electron conductive material is 1 to 6,
The mass ratio (D / C) of the total content C of the electrode catalyst and the electron conductive material and the content D of the proton conductive material is 0.1 to 0.9. ink.

(2) The ink according to (1), wherein a part or all of the transition metal element is at least one selected from titanium, iron, zirconium, copper, and niobium.
(3) The ink according to (1) or (2), wherein the transition metal element comprises at least one selected from titanium, zirconium, copper, and niobium and iron.

(4) An electrode catalyst layer formed using the ink according to any one of (1) to (3).
(5) An electrode having the electrode catalyst layer according to (4) and a gas diffusion layer.

(6) A membrane electrode assembly having an anode, a cathode which is the electrode according to (5), and an electrolyte membrane disposed between the anode and the cathode.
(7) A fuel cell comprising the membrane electrode assembly according to (6).

  (8) A polymer electrolyte fuel cell comprising the membrane electrode assembly according to (6).

  According to the ink of the present invention, an inexpensive and high-performance electrode catalyst layer can be efficiently formed. Moreover, the fuel cell provided with the electrode catalyst layer of the present invention has extremely excellent power generation characteristics.

≪Ink≫
The ink of the present invention is an ink for forming an electrode catalyst layer, and includes an electrode catalyst, an electron conductive material, a proton conductive material, and a solvent.

The mass ratio (A / B) of the content A of the electrode catalyst and the content B of the electron conductive material is 1 to 6, preferably 1.5 to 5.5, and preferably 2 to 5 It is more preferable that
An electrode catalyst layer formed using an ink having the mass ratio within the above range tends to have a high catalytic ability.

  The mass ratio (D / C) of the total content C of the electrode catalyst and the electron conductive material and the content D of the proton conductive material is 0.1 to 0.9, and It is preferable that it is 15-0.8, and it is more preferable that it is 0.2-0.7. An electrode catalyst layer formed using an ink having the mass ratio within the above range tends to have a high catalytic ability.

A fuel cell or the like including an electrode catalyst layer formed using an ink having the mass ratio (A / B) and the mass ratio (D / C) within the above ranges has extremely excellent power generation characteristics.
Hereinafter, the electrode catalyst, electron conductive material, proton conductive material and solvent used in the present invention will be described.

<Electrode catalyst>
The electrode catalyst used in the present invention contains transition metal elements, carbon, nitrogen, and oxygen as constituent elements.

  It is preferable that part or all of the transition metal element is at least one transition metal element selected from titanium, iron, zirconium, copper, and niobium, and at least one selected from titanium, zirconium, copper, and niobium. More preferably, it consists of a seed transition metal element and iron.

  When the ratio of the number of atoms of each element is transition metal element: carbon: nitrogen: oxygen = 1: x: y: z, 0.5 <x ≦ 7, 0.01 <y ≦ 2, 0. 1 <z ≦ 3. However, the number of atoms of the transition metal element is the total number of atoms when there are a plurality of types of transition metal elements.

  The ratio of the number of atoms is more preferably 0.75 ≦ x ≦ 6.75, 0.02 ≦ y ≦ 1.5, 0.15 ≦ z ≦ 2.8, and 1 ≦ x ≦ 6.5. 0.03 ≦ y ≦ 1.3 and 0.2 ≦ z ≦ 2.6 are more preferable.

The electrode catalyst used in the present invention is preferably an electrode catalyst having a large specific surface area. Specifically, the specific surface area calculated by the BET method is preferably 100 m ² / g or more, more preferably 200 m ² / g or more. More preferably, it is 300 m ² / g or more.

Such an electrode catalyst tends to have a high catalytic ability. Furthermore, it is more preferable that the upper limit of each range of the specific surface area is about 1000 m ² / g for easy handling of the electrode catalyst powder.

Although the method of obtaining the said electrode catalyst is not specifically limited, For example, the method mentioned later is mentioned.
The method for producing an electrode catalyst that can be applied to the present invention includes a step 1 in which at least a transition metal-containing compound, a nitrogen-containing organic compound, and a solvent are mixed to obtain a solution (also referred to herein as “catalyst precursor solution”), The process 2 which removes a solvent from a catalyst precursor solution, and the process 3 which heat-processes the solid residue obtained at the process 2 at the temperature of 500-1100 degreeC, and obtains an electrode catalyst are included. In the present specification, unless otherwise specified, atoms and ions are described as “atoms” without strictly distinguishing them.

(Process 1)
In step 1, at least a transition metal-containing compound, a nitrogen-containing organic compound, and a solvent are mixed to obtain a catalyst precursor solution. Here, it is preferable to further mix at least one element selected from the group consisting of boron, phosphorus and sulfur, and a compound containing fluorine. Specific examples include boric acid derivatives containing fluorine, phosphoric acid derivatives containing fluorine, and sulfonic acid derivatives containing fluorine.

  Examples of the mixing procedure include, for example, procedure (i): a solvent is prepared in one container, the transition metal-containing compound and the nitrogen-containing organic compound are added thereto, dissolved, and these are mixed. (Ii): preparing a solution of the transition metal-containing compound and a solution of the nitrogen-containing organic compound and mixing them.

  When the solvent having high solubility for each component is different, the procedure (ii) is preferable. Further, when the transition metal-containing compound is, for example, a metal halide described later, the procedure (i) is preferable, and when the transition metal-containing compound is, for example, a metal alkoxide or a metal complex described later, the procedure is performed. (Ii) is preferred.

  As a preferred procedure in the procedure (ii) when using a first transition metal-containing compound and a second transition metal-containing compound described later as the transition metal-containing compound, the procedure (ii ′): the first transition A solution of a metal-containing compound, and a solution of the second transition metal-containing compound and the nitrogen-containing organic compound are prepared and mixed.

  The catalyst precursor solution is considered to contain a reaction product of a transition metal-containing compound and a nitrogen-containing organic compound. The solubility of the reaction product in the solvent varies depending on the combination of the transition metal-containing compound, the nitrogen-containing organic compound, the solvent, and the like.

  For this reason, the catalyst precursor solution may contain precipitates and dispersoids. However, these precipitates and dispersoids are preferably as few as possible, and it is more preferable that the catalyst precursor solution is clear.

  The temperature at the time of mixing a transition metal containing compound, a nitrogen containing organic compound, and a solvent is 0-60 degreeC, for example. Assuming that a complex is formed from the transition metal-containing compound and the nitrogen-containing organic compound, when this temperature is excessively high, the complex is hydrolyzed when the solvent contains water, resulting in the precipitation of hydroxide. It is considered that an excellent catalyst cannot be obtained. If this temperature is excessively low, the transition metal-containing compound is precipitated before the complex is formed, and it is considered that an excellent catalyst cannot be obtained.

<Transition metal-containing compound>
The transition metal-containing compound is preferably a compound containing at least one transition metal element selected from titanium, iron, zirconium, copper, and niobium. The said transition metal containing compound may be used individually by 1 type, and may use 2 or more types together.

  The transition metal-containing compound is preferably a compound having at least one selected from an oxygen atom and a halogen atom, and may be used alone or in combination of two or more.

The transition metal-containing compound having an oxygen atom is preferably an organometallic complex, for example, a transition metal complex such as alkoxide or acetylacetone.
Specific examples of the transition metal-containing compound include titanium tetraethoxide, titanium tetraisopropoxide, titanium tetraacetylacetonate, niobium pentaethoxide, niobium pentaisopropoxide, zirconium tetraethoxide, zirconium tetraisopropoxide, Zirconium tetraacetylacetonate, copper (II) methoxide, copper (II) isopropoxide, and copper (II) acetylacetonate.

Further, together with the transition metal-containing compound not containing iron (hereinafter also referred to as “first transition metal-containing compound”), a transition metal-containing compound containing iron (hereinafter also referred to as “second transition metal-containing compound”). May be used in combination. Use of the second transition metal-containing compound improves the performance of the resulting catalyst.
Specific examples of the second transition metal-containing compound include iron compounds such as ferrocene, iron (II) acetate, iron (II) lactate, and iron (III) citrate.

<Nitrogen-containing organic compound>
The nitrogen-containing organic compound is preferably a compound (preferably a compound capable of forming a mononuclear complex) that can be a ligand capable of coordinating to a metal atom in the transition metal-containing compound. More preferred are compounds that can be (preferably bidentate or tridentate) (can form chelates).

The said nitrogen containing organic compound may be used individually by 1 type, and may use 2 or more types together.
The nitrogen-containing organic compound is preferably an amino group, a nitrile group, an imide group, an imine group, a nitro group, an amide group, an azido group, an aziridine group, an azo group, an isocyanate group, an isothiocyanate group, an oxime group, a diazo group, It has a functional group such as a nitroso group, or a ring such as a pyrrole ring, a porphyrin ring, an imidazole ring, a pyridine ring, a pyrimidine ring, or a pyrazine ring (these functional groups and rings are also collectively referred to as “nitrogen-containing molecular groups”). More preferably a compound having at least one nitrogen-containing molecular group selected from an amino group, an imine group, a pyrrole ring and a pyrazine ring, particularly preferably at least selected from an amino group and a pyrazine ring. It is a compound having a kind of nitrogen-containing molecular group. With these compounds, the activity of the resulting catalyst is particularly high.

  The nitrogen-containing organic compound is preferably a hydroxyl group, a carboxyl group, an aldehyde group, an acid halide group, a sulfo group, a phosphoric acid group, a ketone group, an ether group or an ester group (these are collectively referred to as “oxygen-containing molecular group”). .)

Among the oxygen-containing molecular groups, a carboxyl group and an aldehyde group are particularly preferable because the activity of the resulting catalyst is particularly high.
As the compound having the nitrogen-containing molecular group and the oxygen-containing molecular group, amino acids and derivatives thereof are preferable. Examples of the amino acids include protein-constituting amino acids and isomers thereof, and the activity of the resulting catalyst is high, so alanine, glycine, lysine, methionine, and tyrosine are preferable, and the resulting catalyst exhibits extremely high activity. Alanine, glycine and lysine are particularly preferred.

  Specific examples of the nitrogen-containing organic compound containing an oxygen atom in the molecule include acyl pyrroles such as acetyl pyrrole, acyl imidazoles such as pyrrole carboxylic acid and acetyl imidazole, carbonyldiimidazole, in addition to the above amino acids and the like. , Imidazole carboxylic acid, pyrazole, acetanilide, pyrazine carboxylic acid, piperidine carboxylic acid, piperazine carboxylic acid, morpholine, pyrimidine carboxylic acid, nicotinic acid, 2-pyridine carboxylic acid, 2,4-pyridine dicarboxylic acid, 8-quinolinol, and polyvinyl Pyrrolidone is exemplified, and the resulting catalyst has high activity, so that it can be a bidentate ligand, specifically pyrrole-2-carboxylic acid, imidazole-4-carboxylic acid, 2-pyrazinecarboxylic acid, 2- Piperidine Bon acid, 2-piperazine carboxylic acid, nicotinic acid, 2-pyridinecarboxylic acid, 2,4-pyridinedicarboxylic acid, and 8-quinolinol are preferable, and 2- pyrazine carboxylic acid, and 2-pyridine carboxylic acid is more preferable.

<Solvent>
Examples of the solvent used in the production of the electrode catalyst include water, acetic acid, and alcohols. As alcohols, ethanol, methanol, butanol, propanol and ethoxyethanol are preferable, and ethanol and methanol are more preferable. In order to increase the solubility, the solvent preferably contains an acid. As the acid, acetic acid, nitric acid, hydrochloric acid, phosphoric acid and citric acid are preferable, and acetic acid and nitric acid are more preferable. These may be used alone or in combination of two or more.

<Precipitation inhibitor>
When the transition metal-containing compound is a metal complex and water is used alone or water and another compound are used as the solvent, it is preferable to use a precipitation inhibitor. In this case, the precipitation inhibitor is preferably a compound having a diketone structure, more preferably diacetyl, acetylacetone, 2,5-hexanedione and dimedone, and further preferably acetylacetone and 2,5-hexanedione.

  These precipitation inhibitors may be added in an amount that can sufficiently reduce the precipitation of the transition metal-containing compound solution. The precipitation inhibitor may be added at any stage in step 1. For example, it may be added in advance to the solvent used in Step 1.

(Process 2)
In step 2, the solvent is removed from the catalyst precursor solution obtained in step 1.
The removal of the solvent may be performed in the atmosphere, or may be performed in an inert gas (for example, argon, helium) atmosphere.

  The temperature at the time of solvent removal may be room temperature when the vapor pressure of the solvent is high, but from the viewpoint of mass production of the catalyst, it is preferably 30 ° C or higher, more preferably 40 ° C or higher, and still more preferably. From the viewpoint of not decomposing the catalyst precursor that is estimated to be a metal complex such as a chelate, which is contained in the solution obtained in Step 1 at 50 ° C or higher, preferably 250 ° C or lower, more preferably 150 ° C. Below, it is 110 degrees C or less more preferably.

  The removal of the solvent may be performed under atmospheric pressure when the vapor pressure of the solvent is high, but in order to remove the solvent in a shorter time, it is performed under reduced pressure (for example, 0.1 Pa to 0.1 MPa). Also good.

The solvent may be removed while the mixture obtained in Step 1 is allowed to stand, but in order to obtain a more uniform solid residue, it is preferable to remove the solvent while stirring the mixture.
Depending on the method of removing the solvent or the properties of the transition metal-containing compound or the nitrogen-containing organic compound, the composition or aggregation state of the solid residue obtained in Step 2 may be non-uniform. In such a case, a catalyst having a more uniform particle size can be obtained by mixing and crushing the solid residue and using a more uniform and fine powder in Step 3.

(Process 3)
In Step 3, the solid residue obtained in Step 2 is heat-treated to obtain an electrode catalyst.
The temperature at the time of this heat treatment is 500 to 1100 ° C, preferably 600 to 1050 ° C, more preferably 700 to 950 ° C.

  If the temperature of the heat treatment is too higher than the above range, sintering and grain growth occur between the particles of the obtained electrode catalyst, resulting in a decrease in the specific surface area of the electrode catalyst. As a result, the processability during processing into a catalyst layer is poor. On the other hand, if the temperature of the heat treatment is too lower than the above range, an electrode catalyst having high activity cannot be obtained.

  Examples of the heat treatment method include a stationary method, a stirring method, a dropping method, and a powder trapping method. When it is desired to obtain an electrode catalyst having a particularly high catalytic activity, it is desirable to use an electric furnace capable of strict temperature control.

As an atmosphere at the time of performing the heat treatment, the main component is preferably an inert gas atmosphere from the viewpoint of enhancing the activity of the obtained electrode catalyst.
However, when the reactive gas mentioned later exists in the atmosphere of the said heat processing, the electrode catalyst obtained may express a higher catalyst performance.

  Examples of the reactive gas include nitrogen gas, a mixed gas of nitrogen gas and argon gas, a mixed gas of nitrogen gas and hydrogen gas, a mixed gas of argon gas and hydrogen gas, and a mixture of ammonia gas and oxygen gas. Gas.

  The heat-treated product obtained by the heat treatment may be used as an electrode catalyst as it is, or may be used after being further crushed as an electrode catalyst. In the present specification, operations for making the heat-treated product fine, such as crushing and crushing, are referred to as “crushing” without any particular distinction. When pulverization is performed, it may be possible to improve the workability in producing an electrode using the obtained electrode catalyst and the characteristics of the obtained electrode. For this crushing, for example, a roll rolling mill, a ball mill, a small-diameter ball mill (bead mill), a medium stirring mill, an airflow grinder, a mortar, an automatic kneading mortar, a tank disintegrator, or a jet mill can be used.

<Electronic conductive material>
The electron conductive material used for this invention will not be specifically limited if it is generally used in order to form an electrode catalyst layer.

  Specific examples of the electron conductive material include carbon, a conductive polymer, a conductive ceramic, a metal, or a conductive inorganic oxide such as tungsten oxide or iridium oxide. These electron conductive materials may be used alone or in combination of two or more. In particular, conductive particles made of carbon are preferable because they have a large specific surface area, are easily available at low cost and have excellent chemical resistance and high potential resistance. When using conductive particles made of carbon, carbon alone or a mixture of carbon and other conductive particles is preferable.

Examples of the carbon include carbon black, graphite, graphite, activated carbon, carbon nanotube, carbon nanofiber, carbon nanohorn, fullerene, and graphene. The particle diameter or fiber diameter of carbon is preferably in the range of 10 to 1000 nm, and more preferably in the range of 10 to 100 nm, as a measurement value measured by TEM observation. When the carbon particle diameter is less than 10 nm, it is difficult to form an electron conduction path. When the carbon particle diameter exceeds the upper limit, the gas diffusibility of the electrode catalyst layer to be formed is decreased, or the utilization factor of the electrode catalyst is decreased. Tend to. Further, BET specific surface area value of the electron conductive particles composed of carbon is preferably ^{50m 2 / g~3000m 2 / g,} 100m 2 / g~3000m 2 / g is more preferable.

  The conductive polymer is not particularly limited. For example, polyacetylene, poly-p-phenylene, polyaniline, polyalkylaniline, polypyrrole, polythiophene, polyindole, poly-1,5-diaminoanthraquinone, polyaminodiphenyl, poly (o -Phenylenediamine), poly (quinolinium) salt, polypyridine, polyquinoxaline, polyphenylquinoxaline, and derivatives thereof. These may contain a dopant for obtaining high conductivity.

<Proton conductive material>
The proton conductive material used in the present invention is not particularly limited as long as it is generally used for forming an electrode catalyst layer.

  Specific examples of the proton conductive material include a perfluorocarbon polymer having a sulfonic acid group (for example, NAFION (registered trademark)), a hydrocarbon polymer compound having a sulfonic acid group, and an inorganic acid such as phosphoric acid. And an organic / inorganic hybrid polymer partially substituted with a proton conductive functional group, and a proton conductor obtained by impregnating a polymer matrix with a phosphoric acid solution or a sulfuric acid solution. Among these, NAFION (registered trademark) is preferable. Further, when a “Flemion” membrane manufactured by Asahi Glass Co., Ltd. or an “Aciplex” membrane manufactured by Asahi Kasei Co., Ltd. is used as the proton conductive material, the reaction in the fuel cell tends to proceed even under conditions of high temperature and low humidity.

<solvent>
The solvent used in the present invention is not particularly limited as long as it is generally used for forming an electrode catalyst layer, and examples thereof include a volatile organic solvent or water.

  Specific examples of the solvent include alcohol solvents, ether solvents, aromatic solvents, aprotic polar solvents, water and the like. Among these, water, acetonitrile, and alcohol having 1 to 4 carbon atoms are preferable, and specifically, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, and t-butanol are preferable. . In particular, water, acetonitrile, 1-propanol and 2-propanol are preferable. These solvents may be used alone or in combination of two or more.

<Ink production method>
The ink of the present invention is produced, for example, by mixing the above-described electrode catalyst, electron conductive material, proton conductive material, and solvent. The mixing order of the electrode catalyst, the electron conductive material, the proton conductive material and the solvent is not particularly limited. For example, an ink can be prepared by mixing an electrode catalyst, an electron conductive material, a proton conductive material and a solvent sequentially or simultaneously and dispersing the electrode catalyst or the like in the solvent. In addition, after preparing a solution in which a solid proton conductive material is premixed in water and / or an alcohol solvent such as methanol, ethanol, propanol, etc., the premixed solution is prepared as an electrode catalyst, an electron conductive material, and a solvent. May be mixed with.

The mixing time can be appropriately determined according to the dispersibility of the mixing means, the electrode catalyst, etc., the volatility of the solvent, and the like.
As the mixing means, a stirring device such as a homogenizer may be used, a ball mill, a bead mill, a jet mill, an ultrasonic dispersion device, a kneading defoaming device, or the like may be used, or these means may be combined. Among these, a mixing means using an ultrasonic dispersion device, a homogenizer, a ball mill, and a kneading defoaming device is preferable. Further, if necessary, mixing may be performed using a mechanism or device that maintains the temperature of the ink within a certain range.
What is necessary is just to adjust the solid content concentration in an ink suitably according to a coating method etc., and it exists in the range of 0.1 mass%-25 mass% normally.

≪Electrocatalyst layer≫
The electrode catalyst layer of the present invention is formed using the ink described above. A fuel cell or the like having an electrode catalyst layer formed using the ink described above has extremely excellent power generation characteristics. Moreover, the electrode catalyst layer of the present invention tends to be excellent in durability.

  The method for forming the electrode catalyst layer is not particularly limited, and examples thereof include a method in which the above-described ink is applied to an electrolyte membrane and / or gas diffusion layer described later and then dried. A method of forming an electrode catalyst layer on an electrolyte membrane and / or a gas diffusion layer by a transfer method after forming the electrode catalyst layer on the transfer substrate by applying the ink described above to the transfer substrate and drying it. Is mentioned.

Examples of the application method include a dipping method, a screen printing method, a roll coating method, a spray method, a bar coater method, and a doctor blade method.
The drying method is not particularly limited, and examples thereof include natural drying and a method of heating with a heater.

In the case of heating, the drying temperature is preferably 30 to 120 ° C, more preferably 40 to 110 ° C, and further preferably 45 to 100 ° C.
The application and the drying may be performed simultaneously. In this case, it is preferable that the drying is completed immediately after coating by adjusting the coating amount and the drying temperature.

≪Usage≫
The electrode catalyst layer of the present invention can be effectively used as a catalyst layer that replaces part or all of the platinum catalyst layer, particularly as a fuel cell electrode catalyst layer.

  The electrode catalyst layer of the present invention can be used for either the anode catalyst layer or the cathode catalyst layer, but is preferably used for the cathode catalyst layer because of its high oxygen reducing ability. In particular, it is useful for a cathode catalyst layer of a membrane electrode assembly provided in a polymer electrolyte fuel cell.

The electrode of the present invention is characterized by having the above-described electrode catalyst layer and gas diffusion layer.
The electrode of the present invention can be used as either a cathode or an anode. Since the electrode of the present invention has a large oxygen reducing ability, it is more industrially superior when used as a cathode.

  The gas diffusion layer is a layer that diffuses gas, and is not particularly limited as long as it has electron conductivity, high gas diffusibility, and high corrosion resistance. As the gas diffusion layer, generally used are carbon-based porous materials such as carbon paper and carbon cloth, and aluminum foil coated with stainless steel and corrosion-resistant material for weight reduction.

  The membrane electrode assembly of the present invention is a membrane electrode assembly comprising a cathode, an anode, and an electrolyte membrane disposed between the cathode and the anode, wherein the cathode is the electrode described above. Yes.

  The membrane / electrode assembly can be obtained by forming the electrode catalyst layer on the electrolyte membrane and / or the gas diffusion layer, then sandwiching both surfaces of the electrolyte membrane with the gas diffusion layer with the catalyst layer inside, and hot pressing. .

  The temperature at the time of hot pressing is appropriately selected depending on the components in the electrolyte membrane and / or catalyst layer to be used, but is preferably 100 to 160 ° C, more preferably 120 to 160 ° C, and 120 to 140 More preferably, the temperature is C. If the temperature during hot pressing is less than the lower limit, bonding may be insufficient, and if it exceeds the upper limit, components in the electrolyte membrane and / or the catalyst layer may be deteriorated.

  The pressure during hot pressing is appropriately selected depending on the components in the electrolyte membrane and / or the catalyst layer and the type of the gas diffusion layer, but is preferably 1 to 10 MPa, more preferably 1 to 6 MPa. More preferably, it is ˜5 MPa. If the pressure during hot pressing is less than the lower limit, bonding may be insufficient, and if the pressure exceeds the upper limit, the porosity of the catalyst layer and the gas diffusion layer may be reduced and performance may be deteriorated. .

  The hot pressing time is appropriately selected depending on the temperature and pressure during hot pressing, but is preferably 1 to 20 minutes, more preferably 3 to 20 minutes, and further preferably 5 to 20 minutes. preferable.

The catalytic ability of the membrane electrode assembly can be evaluated by, for example, the maximum power density calculated as follows.
First, the membrane electrode assembly is fixed with a bolt with a sealing material (gasket), a separator with a gas flow path, and a current collector plate, and tightened to a predetermined surface pressure (4N). Create a single cell of the fuel cell.

Hydrogen was supplied to the anode side as a fuel at a flow rate of 1 liter / minute, oxygen was supplied to the cathode side as an oxidant at a flow rate of 2 liters / minute, and a back pressure of 300 kPa was applied on both sides while the single cell temperature was 90 ° C. Measure current-voltage characteristics. The maximum power density is calculated from the obtained current-voltage characteristic curve. The larger the maximum power density, the higher the catalytic ability of the membrane electrode assembly. The maximum power density is preferably 100 mW / cm ² or more, more preferably 200 mW / cm ² or more, and further preferably 300 mW / cm ² or more.

  As the electrolyte membrane, for example, a perfluorosulfonic acid-based electrolyte membrane or a hydrocarbon-based electrolyte membrane is generally used, but a membrane or porous body in which a polymer microporous membrane is impregnated with a liquid electrolyte. A membrane filled with a polymer electrolyte may be used.

The fuel cell of the present invention is characterized by including the membrane electrode assembly described above.
The electrode reaction of the fuel cell occurs at a so-called three-phase interface (electrolyte-electrode catalyst-reaction gas). Fuel cells are classified into several types depending on the electrolyte used, etc., and include molten carbonate type (MCFC), phosphoric acid type (PAFC), solid oxide type (SOFC), and solid polymer type (PEFC). . Especially, it is preferable to use the membrane electrode assembly of this invention for a polymer electrolyte fuel cell.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
In addition, various measurements in Examples and Comparative Examples were performed by the following methods.

[Analysis method]
1. Elemental analysis Carbon: About 0.01 g of a sample was weighed and measured with a carbon sulfur analyzer (EMIA-920V manufactured by Horiba, Ltd.).

Nitrogen / oxygen: About 0.01 g of a sample was weighed, and the sample was sealed in a Ni capsule, and measurement was performed with an oxygen-nitrogen analyzer (TC600 manufactured by LECO).
Metal (niobium, titanium, iron, lanthanum, copper, zirconium): About 0.1 g of a sample is weighed into a quartz beaker, and the sample is completely thermally decomposed using sulfuric acid, nitric acid and hydrofluoric acid. After cooling, the solution is made up to 100 ml. This solution was appropriately diluted and quantified using ICP-OES (VISA-PRO manufactured by SII) or ICP-MS (HP7500 manufactured by Agilent).

2. BET specific surface area measurement BET specific surface area was measured using Micromeritics Gemini 2360 manufactured by Shimadzu Corporation.

[Reference Example 1]
1. Preparation of anode ink Pt-supported carbon (TEC10E60E, Tanaka Kikinzoku Kogyo) 0.6 g was added to 50 ml of pure water, and further an aqueous solution (Nafion 5% aqueous solution) containing a proton conductive material (NAFION (registered trademark); 0.25 g). Ink for the anode (1) was prepared by adding 5 g of Wako Pure Chemical Industries, Ltd.) and mixing with an ultrasonic disperser (UT-106H type Sharp Manufacturing System) for 1 hour.

2. Preparation of electrode having anode catalyst layer A gas diffusion layer (carbon paper TGP-H-060, manufactured by Toray Industries, Inc.) was immersed in acetone for 30 seconds to perform degreasing. After drying, it was immersed in a 10% polytetrafluoroethylene (hereinafter also referred to as “PTFE”) aqueous solution for 30 seconds. After drying at room temperature, heating was performed at 350 ° C. for 1 hour to disperse PTFE inside the carbon paper to obtain a gas diffusion layer (hereinafter also referred to as “GDL”) having water repellency.

Next, the anode ink (1) prepared in 1 above was applied to the surface of the GDL having a size of 5 cm × 5 cm at 80 ° C. by an automatic spray coating apparatus (manufactured by Saneitec Co., Ltd.). By repeatedly spraying, an electrode having an anode catalyst layer (1) having a Pt amount of 1 mg / cm ² per unit area was produced.

[Manufacture of catalyst]
1. Production of catalyst (1) 5 mL of titanium tetraisopropoxide (manufactured by Junsei Chemical Co., Ltd.) and 5 mL of acetylacetone (manufactured by Junsei Chemical Co., Ltd.) and 15 mL of ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) and acetic acid (Wako Pure Chemical Industries, Ltd.) In addition to 5 mL solution, a titanium-containing mixture solution was prepared while stirring at room temperature.

In addition, 2.507 g of glycine (manufactured by Wako Pure Chemical Industries, Ltd.) and 0.306 g of iron acetate (manufactured by Aldrich) were added to 20 mL of pure water and stirred at room temperature to completely dissolve to prepare a glycine-containing mixture solution. . The titanium-containing mixture solution was slowly added to the glycine-containing mixture solution to obtain a clear solution. Using a rotary evaporator, the temperature of the hot stirrer was set to about 100 ° C. under reduced pressure in a nitrogen atmosphere, and the solvent was slowly evaporated while heating and stirring the solution. The solid residue obtained by completely evaporating the solvent was finely and uniformly crushed in a mortar to obtain a powder. This powder is put into a tubular furnace, heated to 900 ° C. at a heating rate of 10 ° C./min in an argon gas atmosphere, held at 900 ° C. for 1 hour, and naturally cooled to form a powder (hereinafter referred to as “catalyst (1)”). I wrote.)
Table 1 shows the results of elemental analysis of the catalyst (1). The BET specific surface area of the catalyst (1) was 181 m ² / g.

2. Preparation of catalyst (2) 2.60 g (25.94 mmol) of acetylacetone was placed in a beaker, and 5 ml (17.59 mmol) of titanium tetraisopropoxide was added while stirring this, and 28 ml (490.0 mmol) of acetic acid was further added. The solution was added dropwise over a period of minutes to prepare a titanium solution. In a beaker, 60 ml of water, 50 ml of ethanol, and 60 ml of acetic acid were added, and 8.74 g (70.36 mmol) of pyrazinecarboxylic acid was added and completely dissolved. While stirring this, 10 ml of 5% NAFION (registered trademark) dispersion (DE521, DuPont) was added to the resulting solution, and 290 mg (1.67 mmol) of iron acetate was added in small portions to dissolve. I let you. Next, while maintaining the temperature at room temperature and stirring, the above titanium solution was added dropwise over 10 minutes, and after the addition, the mixture was further stirred for 30 minutes to obtain a catalyst precursor solution.

Using a rotary evaporator, the temperature of the hot stirrer was set to about 100 ° C. under reduced pressure in a nitrogen atmosphere, and the solvent was slowly evaporated while heating and stirring the catalyst precursor solution. The solid residue obtained by completely evaporating the solvent was ground in an automatic mortar to obtain 11.3 g of powder for firing (2). A rate of 20 ml / min of 1.2 g of the powder for firing (2), nitrogen gas containing 4% by volume of hydrogen gas in a rotary kiln furnace (that is, hydrogen gas: nitrogen gas = 4% by volume: 96% by volume of mixed gas) The mixture was heated to 890 ° C. at a rate of temperature increase of 10 ° C./min., Baked at 890 ° C. for 0.5 hours, and naturally cooled to obtain 208 mg of powdered catalyst (2). The weight of the powder for firing obtained in this process was 11.7 g.
Table 1 shows the results of elemental analysis of the catalyst (2). Further, the BET specific surface area of the catalyst (2) was 296.6 m ² / g.

3. Production of catalyst (3) 2.60 g (25.94 mmol) of acetylacetone was placed in a beaker, and 4.80 g (17.59 mmol) of niobium ethoxide was added thereto while stirring to prepare a niobium solution.

Except having replaced the titanium solution in manufacture of the said catalyst (2) with the said niobium solution, operation similar to manufacture of the said catalyst (2) was performed, and 231 mg of powdery catalysts (3) were obtained.
Table 1 shows the result of elemental analysis of the catalyst (3). Further, the BET specific surface area of the catalyst (3) was 220 m ² / g.

4). Production of catalyst (4) 50 ml of methanol was placed in a beaker, and 2.75 g (20.45 mmol) of copper dichloride, 5% NAFION (registered trademark) dispersion (DE521, DuPont) 10 while stirring this. 0.0 ml and 355 mg (2.045 mmol) of iron (II) acetate were sequentially added. After adding 10.15 g (81.80 mmol) of pyrazinecarboxylic acid little by little to the resulting solution, stirring was performed for 3 hours to obtain a catalyst precursor solution (4). Using a rotary evaporator, the temperature of the hot stirrer was set to about 100 ° C. under reduced pressure in a nitrogen atmosphere, the solvent was slowly evaporated while heating and stirring the catalyst precursor solution (4), and further under a nitrogen stream, By heating at 300 ° C. for 1 hour, chloride residues and the like were removed, and 3.56 g of powder for firing (4) was obtained. A rate of 20 ml / min of 1.2 g of powder for firing (4), nitrogen gas containing 4% by volume of hydrogen gas in a rotary kiln furnace (that is, hydrogen gas: nitrogen gas = 4% by volume: 96% by volume of mixed gas) The mixture was heated to 890 ° C. at a rate of temperature increase of 10 ° C./min., Baked at 890 ° C. for 0.5 hours, and naturally cooled to obtain 562 mg of a powdery catalyst (4).
Table 1 shows the results of elemental analysis of the catalyst (4). Further, the BET specific surface area of the catalyst (4) was 213 m ² / g.

5. Production of catalyst (5) The same operation as in the production of the catalyst (3) was carried out except that 7.94 g (17.59 mmol) of zirconium butoxide was used instead of niobium ethoxide, and 341 mg of the powdery catalyst (5) was obtained. Obtained. Table 1 shows the results of elemental analysis of the catalyst (5). Further, the BET specific surface area of the catalyst (5) was 245 m ² / g.

6). Production of catalyst (6) 5.88 g (56 mmol) of niobium carbide (NbC, manufactured by Soekawa Rikagaku Co., Ltd.), 0.87 g (5 mmol) of iron acetate (Fe (CH ₃ CO ₂ ) ₂ , manufactured by ALDRICH) and niobium nitride ( NbN (manufactured by High-Purity Chemical Laboratory Co., Ltd.) 5.14 g (48 mmol) was thoroughly mixed, and this mixed powder was heated in a tube furnace at 1600 ° C. for 3 hours in a nitrogen atmosphere to obtain 10.89 g of a sintered body. Got. The obtained sintered body was pulverized in a mortar, and 1.05 g was circulated with nitrogen gas containing 0.75 volume% oxygen gas and 4 volume% hydrogen gas in a rotary kiln at 900 ° C. for 7 hours. By heating, 1.18 g of a fired product was obtained. This was crushed by a planetary ball mill (Premium 7 manufactured by Fritche, rotation radius: 2.3 cm, revolution radius: 16.3 cm) as follows. In a sealable zirconia mill container (capacity 45 ml, inner diameter 45 mm), 0.9 g of the fired product, 40 g of zirconia balls having a diameter of 0.5 mm (manufactured by Nikkato), and 7 ml of acetonitrile (dispersing solvent) were placed. The zirconia mill container was sealed, and the inside of the container was sufficiently purged with argon. Next, crushing was performed in a rotation speed: 700 rpm, revolution speed: 350 rpm, rotation centrifugal acceleration: 12.6 G, revolution centrifugal acceleration: 22.3 G, crushing time: 5 minutes. After the pulverization, acetonitrile and zirconia balls were separated to obtain a powdery catalyst (6). Table 1 shows the results of elemental analysis of the catalyst (6). Further, the BET specific surface area of the catalyst (6) was 30 m ² / g.

7). Production of Catalyst (7) 4 g (50 mmol) of titanium oxide (TiO ₂ ), 1.5 g (125 mmol) of carbon black (manufactured by Cabot, XC-72) and 0.16 g (0.5 mmol) of lanthanum oxide (La ₂ O ₃ ) ) Was mixed well. This mixture was heated at 1700 ° C. for 3 hours in a nitrogen atmosphere to obtain 2.7 g of a sintered body. This sintered body was pulverized in a mortar, and 1.0 g was heated at 900 ° C. for 4 hours in a tubular furnace while flowing nitrogen gas containing 1% by volume oxygen gas and 1% by volume hydrogen gas. 1.18 g of the fired product was obtained. Thereafter, the same operation as in the production of the catalyst (6) was performed to obtain a powdery catalyst (7).
Table 1 shows the results of elemental analysis of the catalyst (7). Further, the BET specific surface area of the catalyst (7) was 45 m ² / g.

[Examples 1 to 12, Comparative Examples 1 to 4 and 9 to 10]
Production of Fuel Cell Membrane Electrode Assembly and Evaluation of Power Generation Characteristics For each example and each comparative example, the catalyst described in Table 2 was used, the content of the catalyst described in Table 2, the content of the electron conductive material The following operations were performed according to the amount and the content of the proton conductive material.

(1) Preparation of ink To a mixed solvent of 25 ml of 2-propanol (manufactured by Wako Pure Chemical Industries) and 25 ml of ion-exchanged water, carbon black (Ketjen Black EC300J, manufactured by LION) was added as an electron conductive material. Furthermore, Nafion (NAFION (registered trademark)) is added as a 5% aqueous solution (manufactured by Wako Pure Chemical Industries, Ltd.) as a proton conductive material, and mixed for 1 hour with an ultrasonic disperser (UT-106H type Sharp Manufacturing System). Thus, an ink for cathode was prepared.

(2) Preparation of electrode having electrode catalyst layer A gas diffusion layer (carbon paper (TGP-H-060, manufactured by Toray Industries, Inc.)) was immersed in acetone for 30 seconds, degreased, dried, and then 10% PTFE. It was immersed in the aqueous solution for 30 seconds. The immersion material was dried at room temperature and then heated at 350 ° C. for 1 hour to obtain a gas diffusion layer (hereinafter also referred to as “GDL”) having PTFE dispersed in the carbon paper and having water repellency. Next, the cathode ink is applied to the surface of the GDL having a size of 5 cm × 5 cm by an automatic spray coating apparatus (manufactured by Sanei Tech Co., Ltd.) at 80 ° C., and an electrode having a cathode catalyst layer on the GDL surface ( Hereinafter also referred to as “cathode”.

(3) Fabrication of membrane electrode assembly for fuel cell A NAFION (registered trademark) membrane (N-212, manufactured by DuPont) as an electrolyte membrane and the above cathode as a cathode) were produced in Reference Example 1 as an anode. Electrodes having an anode catalyst layer (1) (hereinafter also referred to as “anode”) were prepared. A membrane electrode assembly for fuel cells (hereinafter also referred to as “MEA”) in which the electrolyte membrane is disposed between the cathode and the anode was produced as follows.

  The electrolyte membrane is sandwiched between the cathode and the anode, and these are heated for 6 minutes at a temperature of 140 ° C. and a pressure of 3 MPa using a hot press machine so that the cathode catalyst layer and the anode catalyst layer are in close contact with the electrolyte membrane. The MEA was manufactured by pressure bonding.

(4) Manufacture of a single cell The MEA is fixed with bolts by sandwiching it with two sealing materials (gaskets), two separators with gas flow paths, two current collector plates and two rubber heaters. The solid polymer fuel cell single cell (hereinafter also referred to as “single cell”) (cell area: 25 cm ² ) was produced by tightening to a pressure (4N).

(5) Evaluation of power generation characteristics (measurement of catalytic performance)
The temperature of the single cell was adjusted to 90 ° C., the anode humidifier to 90 ° C., and the cathode humidifier to 50 ° C. Supplying hydrogen as fuel to the anode side at a flow rate of 1 liter / min, supplying oxygen as an oxidant to the cathode side at a flow rate of 2 liters / min, and applying a back pressure of 300 kPa on both sides, current-voltage characteristics in a single cell Was measured. The maximum output density was calculated from the obtained current-voltage characteristic curve, and the measurement results are shown in Table 2. It shows that the catalyst ability in MEA is so high that the said maximum output density is large.

[Examples 13 to 20, Comparative Examples 5 to 8]
Production of Fuel Cell Membrane Electrode Assembly and Evaluation of Power Generation Characteristics For each example and each comparative example, the catalyst described in Table 2 was used, the content of the catalyst described in Table 2, the content of the electron conductive material The following operations were performed according to the amount and the content of the proton conductive material.

(1) Preparation of ink A catalyst and carbon black (Ketjen Black EC300J, manufactured by LION) as an electron conductive material are added to 0.87 ml of water, and Nafion (NAFION (registered trademark)) is added as a proton conductive material. In addition, a cathode ink was prepared by defoaming and mixing with a kneading defoaming device (manufactured by Nawataro Awatori, manufactured by Shinky Co., Ltd.) as a% aqueous solution (manufactured by Wako Pure Chemical Industries).

(2) Preparation of an electrode having an electrode catalyst layer The cathode ink was applied to the surface of a gas diffusion layer (carbon paper (GDL24BC, manufactured by SGL Carbon Group)) by a bar coater (manufactured by Techno Supply). Was dried to prepare an electrode having a cathode catalyst layer on the GDL surface (hereinafter also referred to as “cathode”).

(3) Fabrication of fuel cell membrane electrode assembly-(5) Evaluation of power generation characteristics (measurement of catalytic ability)
As in Example 1, (3) Production of membrane electrode assembly for fuel cell, (4) Production of single cell and (5) Evaluation of power generation characteristics (measurement of catalytic ability), current-voltage characteristics in single cell Was measured. The maximum output density was calculated from the obtained current-voltage characteristic curve, and the measurement results are shown in Table 2.

インクに含有される電極触媒として、遷移金属元素、炭素、窒素および酸素を構成元素として含む物を用い、該触媒の各元素の原子数の比を、遷移金属元素：炭素：窒素：酸素＝１：ｘ：ｙ：ｚとした場合に、０．５＜ｘ≦７、 ０．０１＜ｙ≦２、 ０．１＜ｚ≦３とし、前記電極触媒の含有量Ａとインクに含有される電子伝導性材料の含有量Ｂとの質量比（Ａ／Ｂ）を、１〜６とし、前記電極触媒と前記電子伝導性材料との合計含有量Ｃと、インクに含有されるプロトン伝導性材料の含有量Ｄとの質量比（Ｄ／Ｃ）を、０．１〜０．９とするインクを用いると、得られるＭＥＡの触媒能、すなわち最大出力密度が大きくなることがわかった。

As the electrode catalyst contained in the ink, a material containing a transition metal element, carbon, nitrogen and oxygen as constituent elements is used, and the ratio of the number of atoms of each element of the catalyst is defined as transition metal element: carbon: nitrogen: oxygen = 1. : X: y: z, 0.5 <x ≦ 7, 0.01 <y ≦ 2, 0.1 <z ≦ 3, and the content A of the electrode catalyst and the electrons contained in the ink The mass ratio (A / B) to the content B of the conductive material is 1 to 6, the total content C of the electrode catalyst and the electron conductive material, and the proton conductive material contained in the ink It was found that when an ink having a mass ratio (D / C) with respect to the content D of 0.1 to 0.9 is used, the catalytic ability of the obtained MEA, that is, the maximum output density is increased.

Claims (8)

An ink for forming an electrode catalyst layer, comprising an electrode catalyst, an electron conductive material, a proton conductive material and a solvent,
The electrode catalyst includes a transition metal element, carbon, nitrogen and oxygen as constituent elements, and the ratio of the number of atoms of each element is defined as transition metal element: carbon: nitrogen: oxygen = 1: x: y: z (provided that The number of atoms of the transition metal element is 0.5 <x ≦ 7, 0.01 <y ≦ 2, 0.1 when a plurality of transition metal elements are used.) <Z ≦ 3,
The mass ratio (A / B) of the content A of the electrode catalyst and the content B of the electron conductive material is 1 to 6,
The mass ratio (D / C) of the total content C of the electrode catalyst and the electron conductive material and the content D of the proton conductive material is 0.1 to 0.9. ink.   The ink according to claim 1, wherein a part or all of the transition metal element is at least one selected from titanium, iron, zirconium, copper, and niobium.   The ink according to claim 1 or 2, wherein the transition metal element comprises at least one selected from titanium, zirconium, copper, and niobium and iron.   It forms using the ink as described in any one of Claims 1-3, The electrode catalyst layer characterized by the above-mentioned.   An electrode comprising the electrode catalyst layer according to claim 4 and a gas diffusion layer.   A membrane electrode assembly comprising: an anode; a cathode which is an electrode according to claim 5; and an electrolyte membrane disposed between the anode and the cathode.   A fuel cell comprising the membrane electrode assembly according to claim 6.   A polymer electrolyte fuel cell comprising the membrane electrode assembly according to claim 6.