JP2017091736A - Laminate and method for producing the same, membrane-electrode assembly for fuel cell, polymer electrolyte fuel cell, and direct methanol fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a laminate including a catalyst layer which exhibits high power generation performance, and a method of industrially producing the same; a membrane-electrode assembly for a fuel cell; a polymer electrolyte fuel cell; and a direct methanol fuel cell.SOLUTION: A laminate includes a base material and a catalyst layer including a carbon catalyst, and the catalyst layer has a pore shape index I of 0-0.4, the index being represented by the following expression (1). (pore shape index I)=(volume V[cc/g] of pores with a pore size (diameter) of 0.1-1 μm obtained by a mercury pressing method)/(volume of pores with a pore size (diameter) of 0.01-0.1 μm obtained by a mercury pressing method)SELECTED DRAWING: Figure 1

Description

  The present invention relates to a laminate and a method for producing the same, a membrane electrode assembly for a fuel cell, a solid polymer fuel cell, and a direct methanol fuel cell.

  The polymer electrolyte fuel cell has advantages such as high power generation efficiency, high output density, rapid start / stop, small size and light weight. Portable power source, mobile power source, small stationary device Application to generators is expected.

  In a polymer electrolyte fuel cell, platinum or a platinum alloy is generally used as a catalyst in order to promote the oxygen reduction reaction occurring at the positive electrode. However, since the amount of platinum resources is extremely small and expensive, it is put to practical use. It has become a big barrier.

  Therefore, carbon catalysts that have developed oxygen reduction activity by containing nitrogen and / or transition metals have attracted attention as electrode catalysts for fuel cells that do not require noble metals such as platinum. For example, a carbon catalyst obtained by carbonizing a raw material containing an organic substance containing nitrogen atoms, iron and / or cobalt, and copper has been proposed (see, for example, Patent Document 1).

In a polymer electrolyte fuel cell, the catalyst layer is mainly composed of catalyst particles and a polymer electrolyte, and includes pores. However, in order to cause a reaction efficiently, the structure of the catalyst layer, particularly the pore shape, is required. Design becomes important. For example, in Patent Document 2, a platinum catalyst is used, and pores are controlled by adding carbon whiskers as a pore-forming agent to the catalyst layer, so that the pore volume with a diameter of 60 to 1000 nm is 0.15 to 0.25 cm. It has been proposed to have a catalyst layer of ³ / g.

JP2012-101155A JP 2003-151564 A

  However, the power generation performance of the carbon catalyst is still low, and one reason for this is thought to be that the preferred pore shape of the catalyst layer is not known. The direct methanol fuel cell is considered to have the same problems as those of the solid polymer fuel cell.

  Therefore, the present invention has been made in view of the above circumstances, a laminate including a catalyst layer exhibiting high power generation performance, an industrial production method thereof, a membrane electrode assembly for a fuel cell, a polymer electrolyte fuel cell, It is another object of the present invention to provide a direct methanol fuel cell.

In order to solve the above-mentioned problems, the present inventors have made extensive studies focusing on the pore shape of a catalyst layer having a carbon catalyst. As a result, the pore diameter (diameter) of 0.1 to 1 μm by a mercury intrusion method has been obtained. Adjusting the ratio between the pore volume V ₁ [cc / g] in the range and the pore volume V ₂ [cc / g] in the pore diameter (diameter) range of 0.01 to 0.1 μm by mercury porosimetry As a result, the present inventors have found that the above problems can be solved, and have completed the present invention.

That is, the present invention is as follows.
[1]
Including a catalyst layer having a carbon catalyst, and a substrate,
The pore shape index I represented by the following formula (1) of the catalyst layer is 0 to 0.4,
Laminated body.
(Indicator I of pore shape) = (pore diameter (diameter) by mercury intrusion method 0.1 to 1 μm pore volume V ₁ [cc / g]) / (pore diameter (diameter) 0.01 by mercury intrusion method) ~ 0.1 μm pore volume V ₂ [cc / g]) Formula (1)
[2]
The laminate according to [1], wherein an atomic ratio (N / C) between a nitrogen atom and a carbon atom of the carbon catalyst is 0.005 to 0.3.
[3]
The laminate according to [1] or [2], wherein the carbon catalyst further contains a transition metal.
[4]
The laminate according to [3], wherein the transition metal includes iron and / or cobalt.
[5]
The laminate according to [3] or [4], wherein the content of the transition metal is 0.1 to 20% by mass with respect to 100% by mass of the carbon catalyst.
[6]
[1] to [5] A fuel cell membrane electrode assembly comprising an electrode body comprising a laminate comprising the laminate according to any one of [1] to [5], and an electrode body in which a negative electrode is laminated in this order.
[7]
An ink preparation step of preparing a catalyst ink by mixing a slurry containing a carbon catalyst, an ionomer, and a solvent in a bead mill;
An application step of applying the catalyst ink to a substrate;
Drying the catalyst ink applied to the substrate to form the catalyst layer having the carbon catalyst, thereby obtaining a laminate including the catalyst layer and the substrate, and
A manufacturing method of a layered product.
[8]
The method for producing a laminate according to [7], wherein the material of the beads used in the bead mill is at least one selected from the group consisting of zirconia, yttria stabilized zirconia, and yttria partially stabilized zirconia.
[9]
The method for producing a laminate according to [7] or [8], wherein an average diameter of beads used in the bead mill is 0.1 to 5 mm.
[10]
The manufacturing method of the laminated body of any one of [7]-[9] which has an application | coating process which apply | coats the said catalyst ink to the said base material with a screen printer.
[11]
A solid polymer fuel cell comprising the laminate according to any one of [1] to [5] and / or the membrane electrode assembly for a fuel cell according to claim 6.
[12]
A direct methanol fuel cell comprising the laminate according to any one of [1] to [5] and / or the membrane electrode assembly for a fuel cell according to claim 6.

  ADVANTAGE OF THE INVENTION According to this invention, the laminated body containing the catalyst layer which shows high power generation performance, its industrial manufacturing method, the membrane electrode assembly for fuel cells, a polymer electrolyte fuel cell, and a direct methanol fuel cell are provided. be able to.

It is a cross-sectional schematic diagram of an example of the laminated body of this embodiment. It is a cross-sectional schematic diagram of an example of the membrane electrode assembly for fuel cells of this embodiment. FIG. 3 is a diagram illustrating a pore shape distribution of a catalyst layer of a laminate of Example 1 and Comparative Example 1.

  Hereinafter, a mode for carrying out the present invention (hereinafter, simply referred to as “the present embodiment”) will be described in detail. However, the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention. Deformation is possible.

[Laminate]
The laminate of this embodiment includes a catalyst layer having a carbon catalyst and a base material, and the pore-shaped index I represented by the following formula (1) of the catalyst layer is 0 to 0.4. is there. The laminated body of this embodiment can be preferably used as a member for producing a membrane electrode assembly for fuel cells (hereinafter also referred to as “MEA”).
(Indicator I of pore shape) = (pore diameter (diameter) by mercury intrusion method 0.1 to 1 μm pore volume V ₁ [cc / g]) / (pore diameter (diameter) 0.01 by mercury intrusion method) ~ 0.1 μm pore volume V ₂ [cc / g]) Formula (1)

(Catalyst layer)
The catalyst layer has a carbon catalyst, and the pore diameter (diameter) by the mercury intrusion method with respect to the pore volume V ₂ [cc / g] in the range of 0.01 to 0.1 μm pore diameter (diameter) by the mercury intrusion method. ) The ratio of pore volume V ₁ [cc / g] in the range of 0.1 to ₁ μm (pore shape index I: V ₁ / V ₂ ) is 0 to 0.4, preferably 0. It is 01-0.3, More preferably, it is 0.05-0.3. When the pore shape index I is within the above range, the power generation performance of the catalyst layer is further improved. The reason why the power generation performance of the catalyst layer is improved by controlling the index I of the pore shape to the above range is not clear, but is considered as follows. In the membrane electrode assembly for a fuel cell, the pores in the catalyst layer serve as a diffusion path for oxygen as a reactant, water generated by the reaction, and water vapor. From this viewpoint, the pore diameter is preferably large. On the other hand, when the pore diameter increases, the amount of catalyst per unit volume decreases. Therefore, it is considered that when the hole shape index I is within the above range, both are balanced and show high power generation performance.

The hole shape index I can be prepared by controlling the volume V ₁ and the volume V ₂ , respectively. The method for controlling the volume V ₁ is not particularly limited, and examples thereof include changing the mixing conditions in the ink preparation step in the laminate manufacturing method described later. Further, the method for controlling the volume V ₂ is not particularly limited, and examples thereof include changing the particle diameter of the carbon catalyst to be used.

In the case of a laminate, the pore shape index I is measured by removing the catalyst layer from the substrate and other layers and measuring the pore size distribution. In the case of a membrane electrode assembly for fuel cells (hereinafter also referred to as MEA) to be described later, the catalyst layer is cut out and the pore size distribution is measured. The volume V ₁ and the volume V ₂ can be measured by the method described in the examples.

Volume V ₁ was, preferably 0.010~0.500cc / g, more preferably 0.015~0.250cc / g, more preferably from 0.020~0.100cc / g. When the volume V ₁ is within the above range, the power generation performance tends to be further improved.

Further, the volume V ₂ is preferably 0.100 to 1.000 cc / g, more preferably 0.150 to 0.750 cc / g, and further preferably 0.200 to 0.500 cc / g. . When the volume V ₂ is within the above range, the power generation performance tends to be further improved.

(Carbon catalyst)
Although it does not specifically limit as a carbon catalyst, For example, the carbon material containing nitrogen and / or a transition metal is preferable. Moreover, it is preferable that the oxygen reduction activity of a carbon catalyst is high from a viewpoint of the electric power generation performance of a fuel cell catalyst layer.

(Atomic ratio (N / C))
The atomic ratio (N / C) of nitrogen atoms to carbon atoms in the carbon catalyst is preferably 0.005 to 0.3, more preferably 0.01 to 0.2, and still more preferably 0.00. 02 to 0.15. The carbon catalyst has a tendency that the oxygen reduction activity is further improved when the atomic ratio (N / C) is within the above range. The atomic ratio (N / C) can be controlled by adjusting the ratio of the carbon raw material and the nitrogen raw material in the carbon catalyst production method described later. Moreover, atomic ratio (N / C) can be measured by the method as described in the Example mentioned later.

(Transition metal)
The carbon catalyst preferably further contains a transition metal. A carbon catalyst can exhibit higher oxygen reduction activity by including nitrogen and a transition metal. In the carbon catalyst, the content of the transition metal atom is preferably 0.1 to 20% by mass, more preferably 0.3 to 15% by mass, and further preferably 0 to 100% by mass of the carbon catalyst. 5 to 10% by mass. When the content of the transition metal atom is within the above range, the oxygen reduction activity tends to be further improved.

  Although it does not specifically limit as a transition metal atom, For example, Fe, Co, Ni, Cu, Mn, and / or Cr are preferable, Fe, Co, and / or Cu are more preferable, Fe and / or Co are further preferable. By including such a transition metal, the oxygen reduction activity of the carbon catalyst tends to be further improved. In addition, in this embodiment, content of a transition metal atom can be measured by the method as described in the below-mentioned Example.

〔Base material〕
Although it does not specifically limit as a base material, A base material can be selected according to the structure of MEA mentioned later and the manufacturing method of MEA.

  In the first embodiment, the catalyst layer is laminated on the first base material, and the laminate composed of the first base material and the catalyst layer becomes the constituent member of the MEA as it is. For example, a positive electrode gas diffusion layer with a positive microporous layer can be used as the first substrate. In addition, a polymer electrolyte membrane can be used as the first substrate.

  In the second embodiment, a catalyst layer is laminated on the first substrate, and further a second substrate is laminated on the catalyst layer, and then the first substrate is removed from the catalyst layer, A laminate composed of the second base material and the catalyst layer is a constituent member of the MEA. For example, a film such as polytetrafluoroethylene can be used as the first substrate, and a polymer electrolyte membrane can be used as the second substrate.

[Method for producing laminate]
The method for producing the laminate is not particularly limited as long as it is a method for forming a catalyst layer on a substrate. For example, an ink preparation step in which a carbon catalyst and an ionomer are mixed in a solvent to form an ink, Examples thereof include a method including an application step of applying to a material and a drying step of drying the applied ink to form a catalyst layer. More specifically, an ink preparation step of preparing a catalyst ink by mixing a slurry containing a carbon catalyst, an ionomer, and a solvent by a bead mill, a coating step of applying the catalyst ink to a substrate, The manufacturing method which has a drying process which obtains the laminated body containing the said catalyst layer and the said base material by drying the said applied catalyst ink and forming the said catalyst layer which has the said carbon catalyst is preferable.

(Ink preparation process)
In the ink preparation step, a catalyst ink is prepared by mixing a slurry containing a carbon catalyst, an ionomer (polymer electrolyte), and a solvent with a bead mill. In addition, the manufacturing method of a carbon catalyst is mentioned later.

  Although it does not specifically limit as an ionomer, For example, a Nafion (product name) dispersion liquid can be used. Although it does not specifically limit as a solvent, From a viewpoint of the dispersibility of a carbon catalyst and an ionomer, water, lower alcohol (methanol, ethanol, 1-propanol, 2-propanol, etc.) and its mixture can be used preferably.

  Since the carbon catalyst powder is generally agglomerated in a dry state, in order to control the pore shape index I of the catalyst layer within the range of 0 to 0.4, the agglomerate is crushed and the ink is removed. It is necessary to disperse it uniformly. For this purpose, a bead mill having a strong crushing power is used.

  The material of the beads to be used is not particularly limited, but a material with less wear is preferable from the viewpoint of crushing force and impurity mixing suppression, and one kind selected from the group consisting of zirconia, yttria stabilized zirconia, and yttria partially stabilized zirconia. The above can be preferably used.

  Moreover, from a viewpoint of disperse | distributing a carbon catalyst uniformly, the average diameter of a bead becomes like this. Preferably it is 0.1-5 mm, More preferably, it is 0.2-4 mm, More preferably, it is 0.3-3 mm.

(Coating process and drying process)
The catalyst ink obtained in the ink preparation step is applied to the substrate in the application step, and the solvent in the catalyst ink is removed in the drying step to form a catalyst layer having a carbon catalyst on the substrate. The substrate is selected according to the structure of MEA and the MEA manufacturing method described later.

  As a coating apparatus used in the coating process, a screen printer, a bar coater, a spray coater, or the like can be used, but a screen printer is preferably used from the viewpoint of controlling the pore shape index I in the range of 0 to 0.4. be able to.

  It does not specifically limit as a drying apparatus used at a drying process, A heat dryer, a hot air dryer, a vacuum dryer etc. can be used.

[Method for producing carbon catalyst]
Although it does not specifically limit as a manufacturing method of a carbon catalyst, For example, the precursor preparation process which prepares the precursor containing a carbon raw material and a nitrogen raw material, The 1st heat treatment process of baking the said precursor and obtaining a carbon catalyst A method having a particle diameter adjusting step for adjusting the particle diameter of the carbon catalyst obtained in the first heat treatment step and a second heat treatment step for further heat treating the carbon catalyst is preferable.

[Precursor preparation step]
The precursor preparation step is a step of preparing a precursor by combining a carbon raw material and a nitrogen raw material, or a carbon raw material, a nitrogen raw material, and a transition metal raw material.

(precursor)
The precursor may be a composite of a carbon raw material and a nitrogen raw material, or a composite of a carbon raw material, a nitrogen raw material, and a transition metal raw material. The precursor can also contain other components as required. Although it does not specifically limit as another component, For example, the compound etc. which contain boron and / or phosphorus are mentioned.

  The carbon raw material, the nitrogen raw material, and the transition metal raw material are not particularly limited as long as they each contain a carbon atom, a nitrogen atom, and a transition metal atom, and one kind of compound may be used as a raw material for a plurality of atoms. A plurality of compounds may be used as a raw material for a certain atom. For example, only a metal phthalocyanine containing a carbon atom, a nitrogen atom and a transition metal atom may be used as a precursor, or a composite of carbon black containing a carbon atom and polyaniline containing a carbon atom and a nitrogen atom is used as a precursor. It may be a body.

  Here, “composite” may be a state in which a carbon raw material and a nitrogen raw material, or a carbon raw material, a nitrogen raw material and a transition metal raw material are physically mixed, a carbon raw material and a nitrogen raw material, or The carbon raw material, the nitrogen raw material, and the transition metal raw material may be in a state in which a chemical bond is formed, but it is preferable that they are uniformly dispersed.

(Carbon raw material)
Although it does not specifically limit as a carbon raw material, For example, the organic compound and carbon material itself with a high carbonization yield are mentioned. Here, “high carbonization yield” means that the yield of the carbon material obtained by heat treatment at 1000 ° C. for 1 hour under nitrogen gas flow is 1% by mass or more.

  The organic compound having a high carbonization yield is not particularly limited. For example, phenol resin, polyfurfuryl alcohol, furan, furan resin, phenol formaldehyde resin, epoxy resin, polyvinylidene chloride, polythiophene, polysulfone, polyvinyl alcohol, polyvinyl butyral. , Polyester, polylactic acid, polyether, polyetheretherketone, cellulose, carboxymethylcellulose, lignin, pitch, polycarbazole, polyacrylic acid, polyacrylic acid ester, polymethacrylic acid ester and polymethacrylic acid.

  The carbon material itself having a high carbonization yield is not particularly limited, and examples thereof include graphite, activated carbon, amorphous carbon, carbon black, coal, charcoal, coke, carbon nanotube, fullerene, and graphene. These are used singly or in combination of two or more.

(Nitrogen raw material)
Although it does not specifically limit as a nitrogen raw material, For example, the low molecular organic compound which has a nitrogen atom, the high molecular organic compound which has a nitrogen atom can be used, and those 2 or more types of mixtures may be sufficient.

  Although it does not specifically limit as a low molecular organic compound which has a nitrogen atom, For example, the organic compound with a number average molecular weight less than 1000 which has a nitrogen atom is mentioned. Such an organic compound is not particularly limited, and specifically, for example, diaminomaleonitrile, phthalocyanine, porphyrin, phenanthroline, melamine, acrylonitrile, pyrrole, pyridine, vinylpyridine, aniline, imidazole, 1-methylimidazole, Examples include 2-methylimidazole, benzimidazole, pyridazine, pyrimidine, piperazine, quinoxaline, pyrazole, morpholine, hydrazine, hydrazide, urea, salen, triazine and cyanuric acid.

  Although it does not specifically limit as a high molecular organic compound which has a nitrogen atom, For example, the organic compound with a number average molecular weight 1000 or more which has a nitrogen atom is mentioned. Such an organic compound is not particularly limited. Specifically, for example, azulmic acid, diaminomaleonitrile polymer, melamine resin, polyamideimide resin, polyacrylonitrile, polyacrylonitrile-polymethacrylic acid copolymer, polypyrrole. , Polyvinyl pyrrole, polyvinyl pyridine, polyaniline, polybenzimidazole, polyimide, polyamide, chitin, chitosan, polyamino acid, silk, hair, nucleic acid, DNA, RNA, polyurethane, polyamidoamine, polycarbodiimide, polybismaleimide and polyaminobis Maleimide is mentioned. A carbon catalyst can maintain an atomic ratio (N / C) in an appropriate range by manufacturing using such a nitrogen raw material.

  Among these, it is preferable that azurmic acid and / or diaminomaleonitrile is included as a nitrogen raw material and a carbon raw material, and diaminomaleonitrile is more preferable. By including azulmic acid and / or diaminomaleonitrile, the oxygen reduction activity of the carbon catalyst tends to be further improved. Further, by containing diaminomaleonitrile having higher solubility in a solvent, complex formation of the transition metal with the nitrogen raw material and the carbon raw material proceeds favorably, and as a result, a carbon catalyst in which the transition metal is more evenly dispersed is obtained. Therefore, the oxygen reduction activity of the carbon catalyst tends to be further improved.

(Transition metal raw material)
Although it does not specifically limit as a transition metal raw material, For example, a transition metal salt and a transition metal complex can be used, and those 2 or more types of mixtures may be sufficient. Although it does not specifically limit as a transition metal, For example, Fe, Co, Ni, Cu, Mn, and Cr are preferable, Fe, Co, and Cu are more preferable, Fe and Co are further more preferable. The transition metal salt is not particularly limited, and examples thereof include transition metal chlorides, bromides, iodides, nitrates, sulfates, phosphates, acetates, and cyanides. Examples of transition metal complexes include transition metal acetylacetone complexes, cyclopentadienyl complexes, phthalocyanine complexes, porphyrin complexes, and phenanthroline complexes. A carbon catalyst tends to improve oxygen reduction activity by producing using such a transition metal.

  Specific iron salts are not particularly limited. For example, iron (II) chloride, iron (II) chloride tetrahydrate, iron (III) chloride, iron (III) chloride hexahydrate, iron bromide (II), iron (II) bromide hexahydrate, iron (III) bromide, iron (III) bromide hexahydrate, ammonium hexacyanoferrate (II) trihydrate, iron hexacyanoferrate (II) Potassium acid trihydrate, ammonium hexacyanoferrate (III), potassium hexacyanoiron (III), sodium hexacyanoferrate (II) decahydrate, sodium hexacyanoferrate (III) monohydrate, iron nitrate (II ) Hexahydrate, iron (III) nitrate nonahydrate, iron (III) thiocyanate, iron (II) carbonate, iron (II) carbonate monohydrate, methylammonium hexachloroferrate (III), tetrachloro Tetramethy iron (II) acid Ammonium, potassium pentacyanonitrosyl iron (III) dihydrate, potassium iron (III) hexacyanoferrate (II), sodium pentacyanonitrosyl iron (III) dihydrate, ammine pentacyanoiron ( II) Sodium acid trihydrate, aquapentacyanoiron iron (II) sodium heptahydrate, iron (II) thiocyanate trihydrate, iron acetate, iron (III) oxalate pentahydrate, oxalic acid Iron (II) dihydrate, iron (III) citrate trihydrate, iron (II) iodide, iron (II) iodide tetrahydrate, iron (III) sulfate, iron (III) sulfate nine Hydrates, ammonium tetrachloroferrate (II), iron (II) perchlorate hexahydrate, iron (III) perchlorate hexahydrate, potassium aquapentafluoroiron (III), potassium iron sulfate (III) Twelve water Bis (sulfato) iron (II) diammonium hexahydrate, tris (sulfate) iron (III) sodium trihydrate, iron (III) phosphate dihydrate, iron (II) phosphate eight Examples thereof include hydrates, iron (II) sulfate heptahydrate, and the like. Preferable examples include iron (II) chloride, iron (III) chloride, iron (II) bromide, iron (III) bromide, and iron (III) nitrate nonahydrate.

Specific cobalt salts are not particularly limited, and examples thereof include potassium hexacyanocobalt (III), cobalt nitrate (II) hexahydrate, cobalt (II) fluoride, cobalt (II) bromide, and cobalt bromide. (II) hexahydrate, cobalt carbonate (II), cobalt thiocyanate (II) trihydrate, cobalt acetate (II) tetrahydrate, cobalt acetate (III), cobalt chloride (II), cobalt chloride ( II) Hexahydrate, cesium tetrachlorocobalt (II), potassium hexafluorocobalt (III), cobalt (II) iodide, cobalt (II) iodide hexahydrate, hexanitrocobalt (III) acid Examples include potassium, cobalt (II) phosphate, cobalt (II) phosphate octahydrate, cobalt (II) sulfate, cobalt (II) sulfate heptahydrate, etc. It can can be mentioned. Preferred examples include cobalt (II) chloride, cobalt (II) bromide, and cobalt (II) nitrate hexahydrate.
Specific nickel salts are not particularly limited, and examples thereof include nickel chloride (II), nickel chloride (II) hexahydrate, nickel bromide (II), nickel nitrate (II) hexahydrate and the like. It is done.

  Specific copper salts are not particularly limited, and examples include copper (II) chloride, copper (II) chloride dihydrate, copper (II) bromide, copper nitrate (II) dihydrate, and the like. It is done.

  Specific examples of the manganese salt include, but are not limited to, manganese chloride (II), manganese bromide (II), manganese nitrate (II) tetrahydrate, and the like.

  Specific examples of the chromium salt include, but are not limited to, chromium (III) chloride, chromium (III) bromide, and chromium (III) nitrate nonahydrate.

  The content of the transition metal atom in the precursor is preferably 0.01% by mass to 10% by mass, more preferably 0.03% by mass to 5% by mass, and further preferably 0.05% by mass to 3% by mass. When the content of the transition metal atom in the precursor is within the above range, the oxygen reduction activity of the carbon catalyst tends to be further improved.

  In addition, since the nitrogen content in the carbon catalyst obtained by the heat treatment step varies greatly depending on the carbon raw material and nitrogen raw material used, the atomic ratio (N / C) of nitrogen atoms to carbon atoms in the carbon catalyst powder is within the above range. It is preferable to adjust the ratio of the carbon raw material and the nitrogen raw material. The atomic ratio (N / C) can be largely controlled by using a nitrogen raw material having a high atomic ratio (N / C) and / or increasing the ratio of the nitrogen raw material in the precursor. ) And / or lowering the ratio of the nitrogen source in the precursor can be controlled to be small.

  The method for compounding the nitrogen material, the carbon material, and the transition metal material is not particularly limited. For example, a method using a material in which each material is compounded in advance as a precursor, evaporating and drying each material in a solvent. Examples thereof include a method of solidifying, a method of physically mixing each raw material with a ball mill or the like. The composite method is not particularly limited. For example, all raw materials may be dissolved in one solvent, but the respective solvents may be mixed after dissolving the respective raw materials in different solvents. “Each raw material is pre-complexed” refers to a case where a single compound such as an iron phthalocyanine complex that becomes a nitrogen raw material, a carbon raw material, and a transition metal raw material is used as a precursor.

  Although what can be used as a solvent is not specifically limited, For example, what has high solubility of each raw material can be used preferably. As the solvent, one type of solution may be used alone, or two or more types of solutions may be used in combination.

[Heat treatment process]
The heat treatment step is a step of obtaining a carbon catalyst by heat-treating a precursor containing a carbon raw material and a nitrogen raw material. The heat treatment step may be a one-step heat treatment, but may be a two-step or more heat treatment. Moreover, when performing a heat processing process in two or more steps, you may incorporate another process in the meantime. The heat treatment step includes a first heat treatment step of heat-treating the precursor in an inert gas atmosphere, and a second heat treatment step of heat-treating the precursor treated in the first heat treatment step in an ammonia-containing gas atmosphere; It is preferable to contain.

  Among these, in the heat treatment step, a first heat treatment step of heat-treating the precursor in an inert gas atmosphere, a particle diameter adjustment step of adjusting the particle size of the carbon catalyst obtained in the first heat treatment step, It is preferable to perform in this order the second heat treatment step in which the carbon catalyst having the adjusted particle diameter is heat-treated in an ammonia-containing gas atmosphere. The first heat treatment step in the inert gas atmosphere is mainly for the purpose of carbonization, and the second heat treatment step in the ammonia-containing gas atmosphere is mainly for the purpose of activation. By performing an appropriate heat treatment step, a carbon catalyst that is superior in oxygen reduction activity tends to be obtained.

(First heat treatment step)
In the first heat treatment step, the precursor is heat-treated in an inert gas atmosphere. Although it does not specifically limit as said inert gas, For example, nitrogen, a noble gas, a vacuum etc. can be used. The heat treatment temperature in an inert gas atmosphere is preferably 400 to 1500 ° C, more preferably 500 to 1400 ° C, and further preferably 550 to 1300 ° C. When the heat treatment temperature is 400 ° C. or higher, the carbonization of the precursor tends to proceed sufficiently. Further, when the heat treatment temperature is 1500 ° C. or less, a sufficient yield tends to be obtained.

  The heat treatment time in an inert gas atmosphere is preferably 5 minutes to 50 hours, more preferably 10 minutes to 20 hours, and further preferably 20 minutes to 10 hours. When the heat treatment time is 5 minutes or longer, carbonization of the precursor tends to proceed sufficiently. Moreover, it exists in the tendency for sufficient yield to be acquired because heat processing time is 50 hours or less.

(Second heat treatment step)
In the second heat treatment step, the precursor treated in the first heat treatment step is heat-treated in an ammonia-containing gas atmosphere. The target of the heat treatment in the second heat treatment step may be the carbon catalyst after performing the particle size adjustment step as described above.

  The ammonia-containing gas is not particularly limited. For example, it is preferable to use only ammonia or a gas obtained by diluting ammonia with nitrogen or a rare gas. The heat treatment temperature in an ammonia-containing gas atmosphere is preferably 600 to 1200 ° C, more preferably 700 to 1100 ° C, and still more preferably 800 to 1050 ° C. When the heat treatment temperature is 600 ° C. or higher, activation of the carbon catalyst having the pores proceeds sufficiently, and a carbon catalyst excellent in oxygen reduction activity tends to be obtained. Moreover, it exists in the tendency for sufficient yield to be acquired because heat processing temperature is 1200 degrees C or less.

  The heat treatment time in an ammonia-containing gas atmosphere is preferably 5 minutes to 5 hours, more preferably 10 minutes to 3 hours, and even more preferably 15 minutes to 2 hours. When the heat treatment time is 5 minutes or more, activation of the carbon catalyst having the pores proceeds sufficiently, and a carbon catalyst excellent in oxygen reduction activity tends to be obtained. Moreover, it exists in the tendency for sufficient yield to be acquired because heat processing time is 5 hours or less.

(Transition metal removal process)
Before and after the first heat treatment step in the inert gas atmosphere and / or the second heat treatment step in the ammonia-containing gas atmosphere, a part of the transition metal may be removed using hydrochloric acid, sulfuric acid, or the like. In particular, when transition metal particles are generated on the surface by heat treatment, it is preferable to remove the transition metal particles after the heat treatment step from the viewpoint of suppressing a decrease in the concentration of nitrogen atoms in the carbon catalyst. The ease with which transition metal particles can be produced varies depending on the type, concentration, dispersibility, or heat treatment temperature of the transition metal. Further, in order to increase the removal rate of the transition metal particles, the first heat treatment step in the inert gas atmosphere and / or the second heat treatment step in the ammonia-containing gas atmosphere is divided into a plurality of sub-steps, and the heat treatment is performed. It is also preferable to repeat the process and the transition metal removing process.

[Particle size adjustment step]
From the viewpoint of oxygen reduction activity, the average particle size of the carbon catalyst (meaning the average particle size of primary particles not containing aggregated particles) is preferably 60 to 800 nm, more preferably 80 to 600 nm, More preferably, it is 100-500 nm.
In the method for adjusting the average particle size, the average particle size of the precursor may be controlled in the precursor preparation step, or the carbon catalyst after the heat treatment step may be pulverized and adjusted.

  When controlling the average particle size of the precursor in the precursor preparation step, it is not particularly limited. For example, a method of granulating a solution containing a carbon raw material, a nitrogen raw material and a transition metal raw material with a spray dryer, or fine particles by polymerization Can be used.

  The pulverization method is not particularly limited, and examples thereof include a method of pulverizing the precursor or the carbon catalyst with a dry ball mill, a dry jet mill, a wet bead mill, a wet jet mill or the like. Since the particle diameter that can be charged and the particle diameter after pulverization differ depending on the pulverizing apparatus, it can be atomized stepwise by combining a granulation method and a plurality of pulverizing apparatuses. In the case of dry pulverization, classification may be performed as necessary. In order to efficiently adjust to a preferable average particle diameter range, first, a method of adjusting to a range of 60 to 800 nm with a wet bead mill or a wet jet mill after pulverizing to a few tens of μm or less with a dry ball mill or a dry jet mill. preferable.

  The solvent of the wet bead mill or the wet jet mill is preferably one in which the precursor or the carbon catalyst is easily dispersed, and is not particularly limited, and examples thereof include water, ethanol, isopropyl alcohol, and a mixed solvent thereof. The solvent removal method when the particle size is adjusted by a wet bead mill or a wet jet mill is not particularly limited, but spray drying can be preferably used from the viewpoint of productivity.

[Membrane electrode assembly for fuel cells]
The fuel cell membrane electrode assembly of the present embodiment includes an electrode body in which a positive electrode, a polymer electrolyte membrane, and a negative electrode including the laminate are laminated in this order.

[Polymer electrolyte membrane]
The polymer electrolyte membrane is not particularly limited, and examples thereof include a general polymer electrolyte membrane such as a Nafion (product name) membrane.

[Positive electrode]
The structure of the positive electrode is a single layer or a multilayer structure including a catalyst layer (hereinafter referred to as “positive electrode catalyst layer” when it is necessary to distinguish from the negative electrode catalyst layer). From the viewpoint of power generation performance, a positive electrode having a three-layer structure including the positive electrode catalyst layer, the positive electrode microporous layer, and the positive electrode gas diffusion layer shown in FIG. 2 is preferable. A positive electrode contains the said laminated body, and contains the said catalyst layer contained in the said laminated body.

(Cathode layer)
The positive electrode catalyst layer contains a carbon catalyst, and may further contain an additive such as a polymer electrolyte and a conductive additive such as carbon black. Although it does not specifically limit as a polymer electrolyte, For example, Nafion is mentioned. The weight ratio i / C (positive electrode) = (weight of polymer electrolyte) / (weight of carbon material powder) between the carbon material powder as the electrode catalyst and the polymer electrolyte is preferably 0.2 to 5. More preferably, it is 0.3-3, More preferably, it is 0.4-2.5.

From the viewpoint of oxygen reduction activity and oxygen supply rate, the basis weight per unit area of the carbon material powder is preferably 0.1 to 10 mg / cm ² , more preferably 0.2 to 5 mg / cm ² . More preferably, it is 0.3-3 mg / cm < ² >.

  The film thickness of the positive electrode catalyst layer is preferably 5 to 500 μm, more preferably 10 to 250 μm, and still more preferably 20 to 100 μm.

(Positive electrode microporous layer and positive electrode gas diffusion layer)
The positive electrode microporous layer and the positive electrode gas diffusion layer are layers that play a role of promoting diffusion of the reaction substrate (oxygen) and reaction product (water) and collecting current. As the positive electrode microporous layer and the positive electrode gas diffusion layer, commercially available gas diffusion layers, gas diffusion layers with a microporous layer, and those subjected to water repellency or hydrophilic treatment can be preferably used.

  The positive electrode gas diffusion layer is not particularly limited. For example, carbon paper (for example, TGP-H-030, 060, 090, 120 manufactured by Toray, Sigracet 10AA, 24AA, 25AA, 34AA, 35AA manufactured by SGL), carbon cloth ( For example, NuVant Hydrophilic ELAT), water repellent treated carbon paper (for example, SGL's Sigracet 10BA, 24BA, 25BA, 34BA, 35BA), water repellent treated carbon cloth (obtained by dipping a commercially available carbon cloth in a PTFE solution and drying. Can be preferably used.

  Although it does not specifically limit as a positive electrode gas diffusion layer with a positive electrode microporous layer, For example, what attached the microporous layer to carbon paper (For example, Freudenberg C2, C4, H2415C5 made from FuelCellsEtc), microporous to water-repellent treatment carbon paper It is preferable to use a layer with a layer (for example, SGRACE 10BB, 10BC, 24BC, 25BC, 34BC, 35BC manufactured by SGL), a water repellent carbon cloth with a microporous layer (for example, ELAT LT1400W, 2400W manufactured by NuVant). be able to.

[Negative electrode]
The structure of the negative electrode is a single layer or a multilayer structure including a catalyst layer (hereinafter referred to as “negative electrode catalyst layer” when it is necessary to distinguish from the positive electrode catalyst layer). From the viewpoint of power generation performance, a negative electrode having a three-layer structure composed of the negative electrode catalyst layer, the negative electrode microporous layer, and the negative electrode gas diffusion layer shown in FIG. 2 is preferable.

(Negative electrode catalyst layer)
The negative electrode catalyst layer includes metal fine particles, for example, an electrode catalyst made of platinum or platinum ruthenium supported on a carrier, for example, carbon black, and a polymer electrolyte, and further includes a conductive additive, for example, an additive such as carbon black. Good. Although it does not specifically limit as a polymer electrolyte, For example, Nafion is mentioned. The weight ratio i / C (negative electrode) = (weight of polymer electrolyte) / (weight of negative electrode catalyst) of the negative electrode catalyst to the polymer electrolyte is preferably 0.1 to 3, more preferably. It is 0.2-2, More preferably, it is 0.3-1.5.

  The coating amount of the negative electrode catalyst is preferably 0.01 to 10 mg, more preferably 0.02 to 5 mg, and still more preferably 0.03 to 3 mg.

  The film thickness of the negative electrode catalyst layer is preferably 0.5 to 500 μm, more preferably 1 to 250 μm, and further preferably 2 to 100 μm.

(Negative electrode microporous layer and negative electrode gas diffusion layer)
The negative electrode microporous layer and the negative electrode gas diffusion layer are layers that play a role of promoting diffusion and collecting current of the reaction substrate (hydrogen, methanol) and the reaction product (carbon dioxide). The positive electrode microporous layer and the positive electrode negative electrode gas diffusion layer Similarly, commercially available gas diffusion layers, gas diffusion layers with a microporous layer, and those subjected to water repellency or hydrophilic treatment can be preferably used. The same microporous layer and gas diffusion layer may be used for the positive electrode and the negative electrode, or different ones may be used.

[Method for producing membrane electrode assembly for fuel cell]
The MEA production method is not particularly limited. For example, a catalyst ink in which constituent components of the catalyst layer are dispersed in a solvent is prepared on both the negative electrode side and the positive electrode side, and one main surface and the other of the polymer electrolyte membrane are prepared. Examples thereof include a method in which each of the main surfaces is applied and dried, and a gas diffusion layer with a microporous layer is pressure-bonded to the dried catalyst layer. In this method, a laminate having a polymer electrolyte membrane as a base material is formed. In addition, the catalyst ink is applied to a film such as polytetrafluoroethylene, dried, and thermocompression bonded with the polymer electrolyte membrane sandwiched between the negative electrode side and the positive electrode side, and then the catalyst layer is peeled off on the polymer electrolyte membrane. And a method in which a gas diffusion layer with a microporous layer is pressure-bonded onto the catalyst layer. In this method, a first laminate in which a film of polytetrafluoroethylene or the like is a base material and a second laminate in which a polymer electrolyte membrane is a base material are formed. In addition, a general method such as a method in which the ink is applied to a gas diffusion layer with a microporous layer and dried to form a catalyst layer, and a polymer electrolyte membrane is sandwiched between the negative electrode side and the positive electrode side is used. Can do. In this method, a laminate having a gas diffusion layer with a microporous layer as a base material is formed. As described in the foregoing section, a commercially available gas diffusion layer with a microporous layer can be used.

[Use]
The membrane electrode assembly including the laminate according to this embodiment can be suitably used for a polymer electrolyte fuel cell and a direct methanol fuel cell. The polymer electrolyte fuel cell and the direct methanol fuel cell of this embodiment include the laminate and / or the membrane electrode assembly for a fuel cell and have high power generation performance.

Hereinafter, the present embodiment will be described in more detail with reference to examples and the like. However, these are illustrative, and the present embodiment is not limited to the following examples. A person skilled in the art can implement the present embodiment by making various modifications to the examples described below, and such modifications are included in the scope of the present invention.
The analysis method was as follows.

(Measurement of V ₁ and V ₂₎
The pore size distribution of the catalyst layers obtained in Examples and Comparative Examples was measured in accordance with JIS R1655 “Method for testing pore size distribution of molded ceramics by mercury porosimetry”. Specifically, the catalyst layer was peeled off from the gas diffusion layer with a microporous layer after the production steps of the laminates in Examples and Comparative Examples, and the pore size distribution was measured. Autopore IV9500 manufactured by Shimadzu Corporation is used as the measuring device, and the pore volume in the range of pore diameter (diameter) of 0.1 to 1 μm is integrated to obtain V ₁ [cc / g], in the range of 0.01 to 0.1 μm. The pore volume was integrated to obtain V ₂ [cc / g].

(Indicator I of hole shape)
Based on V ₁ and V ₂ measured as described above, I = V ₁ / V ₂ in the catalyst layers obtained in Examples and Comparative Examples was calculated.

(N / C measurement)
The mass concentrations of carbon and nitrogen in the carbon catalysts obtained in Examples and Comparative Examples were measured according to JIS M8819 “Coal and cokes—elemental analysis method using instrumental analyzer”. N / C was calculated by converting this to an atomic ratio. Note that a CHN coder MT-6 manufactured by Yanaco Technical Science was used as the measuring apparatus.

(Measurement of transition metal content)
The carbon catalysts obtained in the examples and comparative examples were heat-treated at 900 ° C. for 1 hour under air flow to burn off carbon and nitrogen, and the residue was dissolved in aqua regia and analyzed by ICP emission spectroscopic analysis. The transition metal content of was measured. SPS3520UV-DD made by SII Nano Technology was used as the measuring device.

[Example 1]
<Precursor preparation step>
To a 2 L eggplant-shaped flask, 20 g of diaminomaleonitrile, 0.045 g of iron (II) chloride and 500 g of methanol were added and stirred at room temperature for 12 hours. Then, the solvent was removed using a rotary evaporator in a 50 ° C. water bath, and the precursor was obtained by drying at 80 ° C. for 2 hours using a vacuum dryer.

<First heat treatment step>
20 g of the prepared precursor was placed on an alumina boat and accommodated in a box furnace. The inside of the furnace was heated from room temperature to 900 ° C. over 60 minutes under a nitrogen flow of 1 NL / min at atmospheric pressure, and kept at 900 ° C. for 1 hour to obtain 4.1 g of a carbon catalyst.

<Average particle size adjustment step>
The carbon catalyst was dry-ground using a zirconia ball having a diameter of 10 mm in a planetary ball mill (Pulverisete-5 manufactured by Fritsch Japan Co., Ltd.) to adjust the average particle size to 980 nm.

  Next, a slurry comprising 10 g of the dry pulverized carbon catalyst, 300 mL of ion exchange water, and 300 mL of ethanol was pulverized with zirconia beads having a diameter of 0.3 mm to obtain a slurry containing a carbon catalyst having an average particle size of 290 nm. An ultra apex mill manufactured by Kotobuki Industries Co., Ltd. was used as the bead mill, the peripheral speed was 2 m / s, and the operation time was 2 hours.

  The slurry was dried with a spray dryer (using MDL-015MGC manufactured by Fujisaki Electric Co., Ltd.). Specifically, nitrogen heated to 200 ° C. as a drying gas was 350 L / min, nitrogen was sprayed as 36 L / min, and the slurry was sprayed and dried at 15 g / min.

<Second heat treatment step>
The carbon catalyst (2.0 g) having an adjusted average particle diameter was placed on a quartz boat and accommodated in a quartz tube furnace having an inner diameter of 36 mm. The inside of the furnace was heated from room temperature to 975 ° C. over 60 minutes under an atmospheric pressure, 1 NL / min ammonia gas flow, and kept at 975 ° C. for 1 hour.

<Production of laminate>
A laminate was produced from the carbon catalyst subjected to the second heat treatment by the following method. First, 50 mg of a carbon catalyst, 390 mg of ethanol, and 1.5 g of zirconia beads having a diameter of 1 mm were placed in a polypropylene microtube, and mixed at 2850 rpm for 10 minutes with a bead mill (manufactured by Scientific Industries, Disruptor Jenny). Next, 313 mg of a 20% Nafion solution (DE2021CS, manufactured by Wako Pure Chemical Industries, Ltd.) was added to the microtube and mixed at 2850 rpm for 10 minutes with the bead mill to prepare an ink. This positive electrode ink was applied to a gas diffusion layer with a microporous layer (SGL, 25BC) with a screen printer (MEC-2400 manufactured by Mitani Micronics Co., Ltd.) and dried at 120 ° C. for 30 minutes to obtain a laminate. It was. The carbon catalyst coating amount (unit weight) per unit area of the substrate was 2.5 mg / cm ² . The pore distribution of the catalyst layer is shown in FIG. 2, and the pore shape index I = 0.13.

<Production of MEA>
On the positive electrode (positive electrode catalyst layer-positive electrode microporous layer-positive electrode gas diffusion layer), a polymer electrolyte membrane (Nafion membrane: manufactured by DuPont, NR211), a negative electrode (platinum-ruthenium-supported gas diffusion layer: (stock) ) Produced an electrode body on which platinum-ruthenium 0.5 mg / cm ² supported by Chemix was mounted, and thermocompression bonded at 150 ° C. and 0.2 MPa to obtain MEA.

<Fuel cell evaluation>
The power generation evaluation of the above MEA was performed with a potentiostat (manufactured by Solartron). Hydrogen that was humidified at 80 ° C. was supplied at 0.1 MPaG to the negative electrode, air that was humidified at 80 ° C. was supplied at 0.1 MPaG, and the cell voltage was 80 ° C., and current-voltage characteristics were measured. The current density at 0.6 V was 150 mA / cm ² . It was determined that the power generation performance was higher as the current density was higher.

[Comparative Example 1]
<Production of laminate>
A laminate was produced from the carbon catalyst obtained after the second heat treatment in Example 1 by the following method. First, 50 mg of a carbon catalyst and 390 mg of ethanol were placed in a glass bottle and stirred for 1 hour with a magnetic stirrer. Next, 313 mg of 20% Nafion solution (manufactured by Wako Pure Chemical Industries, Ltd., DE2021CS) was added to this glass bottle and stirred overnight with a magnetic stirrer to prepare ink. This positive electrode ink was applied to a gas diffusion layer with a microporous layer (manufactured by SGL, 25BC) with a screen printer and dried at 120 ° C. for 30 minutes to obtain a laminate. The coating amount (weight per unit area) of the carbon catalyst per unit substrate area was 2.5 mg / cm ² . The pore distribution of the catalyst layer is shown in FIG. 2, and the pore shape index I = 0.56.

<Production of MEA>
An MEA was produced in the same manner as in Example 1 from the positive electrode (positive electrode catalyst layer-positive electrode microporous layer-positive electrode gas diffusion layer).

<Fuel cell evaluation>
The power generation performance of the MEA was evaluated in the same manner as in Example 1. The current density at 0.6 V was 50 mA / cm ² . The current density was lower in power generation performance than the MEA of Example 1.

FIG. 3 shows the pore shape distribution of the catalyst layers of the fuel cell membrane electrode assemblies of Example 1 and Comparative Example 1. As shown in FIG. 3, it can be seen that the power generation performance is excellent when the ratio between the pore volume V ₁ and the pore volume V ₂ (the pore shape index I) is within a predetermined range.

  The membrane electrode assembly obtained from the laminate of the present invention has industrial applicability as an electrode for solid polymer fuel cells and direct methanol fuel cells.

Claims (12)

Including a catalyst layer having a carbon catalyst, and a substrate,
The pore shape index I represented by the following formula (1) of the catalyst layer is 0 to 0.4,
Laminated body.
(Indicator I of pore shape) = (pore diameter (diameter) by mercury intrusion method 0.1 to 1 μm pore volume V ₁ [cc / g]) / (pore diameter (diameter) 0.01 by mercury intrusion method) ~ 0.1 μm pore volume V ₂ [cc / g]) Formula (1)   The layered product according to claim 1 whose atomic ratio (N / C) of the nitrogen atom of said carbon catalyst and a carbon atom is 0.005-0.3.   The laminate according to claim 1 or 2, wherein the carbon catalyst further contains a transition metal.   The laminate according to claim 3, wherein the transition metal includes iron and / or cobalt.   The laminate according to claim 3 or 4, wherein a content of the transition metal is 0.1 to 20% by mass with respect to 100% by mass of the carbon catalyst.   A membrane electrode assembly for a fuel cell, comprising an electrode body in which a positive electrode, a polymer electrolyte membrane, and a negative electrode comprising the laminate according to any one of claims 1 to 5 are laminated in this order. An ink preparation step of preparing a catalyst ink by mixing a slurry containing a carbon catalyst, an ionomer, and a solvent in a bead mill;
An application step of applying the catalyst ink to a substrate;
Drying the catalyst ink applied to the substrate to form the catalyst layer having the carbon catalyst, thereby obtaining a laminate including the catalyst layer and the substrate, and
A manufacturing method of a layered product.   The manufacturing method of the laminated body of Claim 7 whose material of the bead used with the said bead mill is 1 or more types selected from the group which consists of a zirconia, a yttria stabilized zirconia, and a yttria partially stabilized zirconia.   The manufacturing method of the laminated body of Claim 7 or 8 whose average diameter of the bead used with the said bead mill is 0.1-5 mm.   The manufacturing method of the laminated body of any one of Claims 7-9 which has an application | coating process which apply | coats the said catalyst ink to the said base material with a screen printer.   A polymer electrolyte fuel cell comprising the laminate according to any one of claims 1 to 5 and / or the membrane electrode assembly for a fuel cell according to claim 6.   A direct methanol fuel cell comprising the laminate according to any one of claims 1 to 5 and / or the membrane electrode assembly for a fuel cell according to claim 6.