JP2007172887A - Carried catalyst for fuel cell, reaction layer for fuel cell, fuel cell, and manufacturing method of carried catalyst for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a supported catalyst for fuel cell capable of lowering polarization resistance, obtaining a high output, and having a high utilization rate of catalyst, a reaction layer for fuel cell, a fuel cell, and a manufacturing method of the supported catalyst for fuel cell. <P>SOLUTION: Catalyst is supported by carbon aerogel powder in which a proton conductive path made of sulfonic acid group and glass phosphate or the like is formed. As a manufacturing method of the carbon aerogel powder, firstly, resorcinol and formaldehyde aqueous solution and sodium carbonate aqueous solution are mixed, agitated, and an organic wet gelation object is obtained. Next, the organic wet gelation object is pulverized and made into a gel powder slurry. Then, the gel powder slurry is solvent substituted by acetone. Then, the gel powder is super-critically dried by CO<SB>2</SB>, and a gel dry powder is obtained. Lastly, the gel dry powder is heated under a nitrogen atmosphere to obtain the carbon aerogel powder. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a supported catalyst for a fuel cell, a reaction layer for a fuel cell, a fuel cell, and a method for producing a supported catalyst for a fuel cell.

A solid polymer electrolyte fuel cell (PEFC) is attracting attention as a new energy source to replace an internal combustion engine because it has a high power density, operates at a low temperature, and does not emit harmful exhaust gas.
This PEFC is constructed by bonding an anode to one surface of a proton conductive polymer membrane and a cathode to the other surface. Then, hydrogen gas is supplied to the anode and oxygen gas is supplied to the cathode. The hydrogen gas is oxidized into protons at the anode, and oxygen is reduced to water at the cathode to generate power. For the anode and the cathode, a supported catalyst for a fuel cell made of fine powder in which catalyst particles made of a noble metal such as Pt are supported on a carrier such as carbon is used.

The theoretical voltage of PEFC is calculated as 1.23 V from the value of the free energy change in the chemical reaction between hydrogen and oxygen, but actually, only an output voltage smaller than this is obtained due to various polarization resistances. Lowering the voltage at the output terminal means lowering the efficiency of PEFC, and there is a need for a supported catalyst for fuel cells that is less prone to polarization.
Moreover, noble metals such as platinum are used as the catalyst used for the fuel cell supported catalyst, and the catalyst cost accounts for several tens of percent of the total battery. For this reason, in order to make fuel cell technology popular, it is essential to reduce the amount of catalyst used.

  In order to meet these requirements, fuel cell supported catalysts using activated carbon powder as a carbon support have been proposed. This is because activated carbon has a very large specific surface area, so that the area of the electrode reaction is widened, thereby reducing the polarization resistance and increasing the utilization of the catalyst.

It has also been proposed to use carbon aerogel as a supported catalyst for fuel cells (Patent Document 1). Carbon airgel can be made extremely small in particle size by being pulverized. Therefore, when used as an electrode in a polymer electrolyte fuel cell, the thickness of the electrode can be reduced. Further, since the carbide obtained by pyrolysis of the dried gelled product has a pore structure, the carbon aerogel obtained by pulverizing the carbide is expected to have excellent gas permeability.
Furthermore, since it has pores larger than micro pores such as activated carbon, the catalyst and the proton conductive polymer easily enter the pores. For this reason, it is considered that in the electrode reaction, it is easy to form a structure (three-phase interface) in which a path of reactants, protons, and electrons exists around the catalyst, and the electrode reaction can be promoted.
Similar effects can be expected even when carbon having mesoporous pores other than carbon aerogel is used. Here, the mesoporous pore means a pore having an intermediate size between micropores and macropores, and specifically refers to pores in the order of 2 nanometers to 50 nanometers (that is, mesopores).

  As a method for producing carbon aerogel, the following production method using dihydroxybenzene and formaldehyde as starting materials is known (Patent Document 2).

(Polymerization step S91)
That is, as shown in FIG. 1, first, as a polymerization step S91, dihydroxybenzene such as resorcinol and catechol and formaldehyde are polymerized in the presence of sodium carbonate to obtain an organic wet gelled product.

(Solvent replacement step S92)
Next, as a solvent replacement step S92, the organic wet gelled product is washed with a water-soluble organic solvent such as methanol or acetone, and the water contained in the organic wet gelled product is replaced with the water-soluble solvent.

(Supercritical drying step S93)
Further, as the supercritical drying step S93, the solvent-substituted gelled product is put into a stainless steel pressure vessel, CO2 is introduced, the pressure and temperature are adjusted so as to be in a supercritical state, and then CO2 is slowly discharged. To shift the CO2 to the gas phase condition and perform supercritical drying. The gelled product thus dried is composed of primary particles forming a network structure having a particle size of 0.1 microns or less, and the bulk density is extremely small at 100 mg / ml. This is because in supercritical drying, unlike normal drying, drying does not involve shrinkage due to capillary force, so that the pore structure formed by crosslinking with formaldehyde in the polymerization step S1 remains intact without being destroyed. It is thought that it remains.

(Pyrolysis step S94)
Then, as the pyrolysis step S94, the dried gelled product is heated to a high temperature under a nitrogen atmosphere to obtain a carbide lump. The carbide thus obtained maintains the pore structure before carbonization.

(Crushing step S95)
Finally, in the pulverization step S95, the above-mentioned carbide mass is pulverized by a pulverizer to obtain a carbon airgel powder.

Japanese National Patent Publication No. 11-503267 U. S. patent No. 4873218 claim14, 15

  However, the supported catalyst for fuel cells in which the catalyst is supported on the activated carbon does not exhibit the effect of reducing polarization as expected in practice, and the utilization factor of the catalyst is not so high. The cause of this is explained as follows.

  In the PEFC electrode catalyst layer, oxygen that has diffused through the pores in the fuel cell-supported catalyst on the cathode side sorbs and diffuses into the proton-conductive polymer and reaches the catalyst. On the other hand, protons and electrons diffuse through the proton conducting polymer / carbon carrier, reach the catalyst, and react with oxygen to produce water. Therefore, in the electrode reaction, a structure (three-phase interface) in which each path of the reactant, proton and electron exists around the catalyst is indispensable. In order to obtain a supported catalyst for a fuel cell with a limited amount of catalyst and a small decrease in performance, it is necessary to form as many three-phase interfaces as possible around the catalyst introduced into the carrier.

On the other hand, in the fuel cell supported catalyst in which the catalyst is supported on the activated carbon, since the pores existing in the activated carbon are very small micropores, the activated carbon supporting the catalyst has protons such as Nafion (registered trademark). In the macro method of applying and drying the catalyst paste prepared by mixing the conductive polymer, the proton conductive polymer is larger than the primary pore diameter of the activated carbon and cannot enter the pores during mixing. No proton conductive polymer is present in the pores (primary pores), and the catalyst present in the primary pores is not effectively utilized (see FIG. 2).
For this reason, even if the activated carbon powder is simply used as a catalyst carrier, sufficient catalytic activity cannot be obtained, and the polarization resistance cannot be lowered as expected. In addition, the catalyst that has entered the pores is not involved in the electrode reaction and is wasted, and the utilization rate of the catalyst metal is also reduced.

  Further, when the inventors conducted a detailed test on the carbon aerogel described in Patent Document 2, the carbide obtained in the pyrolysis step S94 in FIG. 1 has a pore structure, but this is pulverized. The carbon airgel obtained in this way was found to have almost destroyed its pore structure. For this reason, even when a fuel cell is constructed using a supported catalyst in which a catalyst is supported on the carbon aerogel, a high output as expected cannot be obtained.

  The present invention has been made in view of the above-described conventional circumstances, and can reduce polarization resistance, obtain a high output, and have a high catalyst utilization rate. It is an object to be solved to provide a method for producing a layer, a fuel cell, and a supported catalyst for a fuel cell.

  The inventors focused on the problem that the supported catalyst for a fuel cell using the above-described conventional carbon airgel powder cannot improve the expected characteristics because the pore structure of the carbon airgel is destroyed. First of all, intensive research was conducted on how to produce a carbon airgel powder having a maintained pore structure. As a result, the organic wet gelled product obtained in the polymerization step is pulverized in water before solvent substitution, and then subjected to a solvent substitution step, a supercritical drying step, and a thermal decomposition step, thereby once in the production process. It has been found that a carbon airgel powder can be obtained in which the formed pore structure is maintained as it is.

Furthermore, in order to actively form a structure (three-phase interface) in which each path of reactants, protons and electrons exists around the catalyst, as in the conventional case, the catalyst is simply loaded with carbon. In addition to mechanical mixing with the proton conducting polymer, an attempt was made to form a proton conducting path in the pores of the carbon powder.
And it discovered that if the proton conduction path was formed in the carbon airgel powder with the pore structure maintained as described above, the above problems could be solved, and the present invention was completed.

  That is, the fuel cell supported catalyst of the first invention is a fuel cell supported catalyst in which a catalyst is supported on carbon powder. The carbon powder is obtained by pulverizing the organic wet gelled product and a step of obtaining an organic wet gelled product. A pulverizing step to obtain a gel powder, a solvent replacement step in which the gel powder is contacted with a water-soluble organic solvent to perform solvent replacement, and supercritical drying of the solvent-substituted gel powder to obtain a gel dry powder. A carbon airgel powder obtained through a drying step and a pyrolysis step in which the gel dry powder is pyrolyzed to form a carbon airgel powder, wherein a proton conduction path is formed in the carbon powder. To do.

  Unlike the carbon airgel powder described in Patent Document 2, the carbon powder used as a carrier for the fuel cell supported catalyst of the first invention is different from the carbon airgel powder described in Patent Document 2 in water before solvent replacement of the organic wet gelled product obtained in the polymerization step. And then, the solvent is replaced, the supercritical drying step, and the thermal decomposition step are performed. In such a method for producing a carbon airgel powder, the organic wet gelled product is pulverized in the pulverization step, and then the solvent is replaced. Compared with pulverization, the pores are protected by the cushioning effect of water and are not easily destroyed. In addition, since the organic wet gelled product is pulverized in advance, the solvent replacement time is also shortened. For this reason, the carbon airgel powder obtained in this way maintains the pore structure reflecting the pore structure of the gelled product. For this reason, the specific surface area is large, the area contributing to the electrode reaction is widened, and since it has excellent gas permeability, the polarization resistance due to mass transfer is also reduced, and it can be suitably used as a supported catalyst in polymer electrolyte fuel cells. it can.

  Further, the carbon powder used as a carrier in the fuel cell supported catalyst of the first invention has a proton conduction path, and therefore is essential for promoting the electrode reaction. A structure (three-phase interface) in which an electron path exists around the catalyst is formed in a wide range. Examples of the method for forming the proton conduction path include synthesizing a proton conducting polymer or proton conducting glass in the pores of the carbon powder, or modifying a functional group having proton conductivity.

  Therefore, in the fuel cell-supported catalyst of the first invention, the polarization resistance is reduced and a high output can be obtained, and the catalyst supported in the pores of the carbon powder also effectively contributes to the electrode reaction. The utilization rate of the catalyst is also increased.

  In the second aspect of the first invention, the proton conduction path is formed by including a proton conductor in the pores of the carbon powder. As a result, a structure (three-phase interface) in which a path of reactants, protons, and electrons exists around the catalyst in the pores of the carbon powder can be reliably formed.

In a third aspect of the first invention, the proton conductor is a vitreous proton conductor. Such a proton conduction path can be formed relatively easily. For example, a wet gel made of organic matter (hereinafter referred to as an organic wet gel product), such as resorcinol and formaldehyde polymerized in an alkaline aqueous solution, and tetraethyl orthosilicate and trimethyl phosphate are hydrolyzed and copolymerized. After mixing with the phosphate glass precursor sol,
Examples thereof include a method of condensing a phosphate glass precursor sol in the pores of an organic wet gelled product to form a proton conductive phosphate glass.

  Furthermore, in the invention of the fourth aspect, a functional group that imparts proton conductivity is modified in the pores of the carbon airgel powder. Such a functional group can also form a proton conductive path. Here, the modification of the functional group means that a functional group such as a sulfonic acid group is chemically bonded or physically adsorbed on the carbon surface. Examples of the functional group imparting proton conductivity include a sulfonic acid group, a methylsulfonic acid group, and a phosphoric acid group.

  In the fifth aspect of the invention, the catalyst supported on the carbon airgel powder is a magnetic catalyst having both catalytic action and magnetic action. Oxygen supplied as an oxidant to the fuel cell has paramagnetism, and water generated by the electrode reaction of the fuel cell has diamagnetism. Therefore, if a magnetic catalyst having both catalytic action and magnetic action is used as the catalyst for the fuel cell supported catalyst, oxygen is attracted to the magnetic catalyst by the magnetic action of the magnetic catalyst supported on the air electrode, and the generated water is discharged. (See FIG. 3). For this reason, the mass transfer of oxygen to the catalyst is promoted, and the flooding phenomenon that prevents the mass transfer due to water adhering to the electrode is more reliably suppressed, and the output of the fuel cell system can be improved more reliably.

  As the magnetic catalyst, a Pt alloy having an fct structure as a main phase can be adopted. Since the Pt alloy having the fct structure as the main phase has a high coercive force, the output of the fuel cell can be further increased. More specifically, a Pt—Fe alloy can be adopted as the magnetic catalyst. According to the phase diagram of the Pt—Fe alloy, when the heat treatment temperature is 900 ° C., the main phase is a Pt / Fe = 35 / 65-54 / 46 (at%) fct structure that exhibits a magnetic action. -Fe alloy is obtained. Further, by setting the heat treatment temperature to 1300 ° C., a P t—Fe alloy having a main phase of an fct structure exhibiting a magnetic action in a range of Pt / Fe = 41/59 to 74/26 (at%) can be obtained. It was. From the magnetization curve of a Pt-Fe alloy having a main phase of an fct structure obtained by heat-treating a Pt-Fe alloy of Pt / Fe = 38.5 / 61.5 (at%) at 1046 ° C. for 100 hours and quenching with water, It has been confirmed that a Pt—Fe alloy having this fct structure as a main phase has a high coercive force of −3.8 to 3.8 kOe. According to the inventors' estimation, it is preferable to employ a Pt—Fe alloy having a composition of Pt / Fe = 40/60 to 75/25 (at%). Moreover, it is preferable to employ a Pt—Fe alloy having a coercive force of 2 kOe or more in absolute value. Furthermore, it is preferable to employ a Pt—Fe alloy having a particle size of 1 to 10 nm. This type of Pt—Fe alloy can be obtained by a reverse micelle method based on an aqueous solution reaction, a synthesis method using an organic metal, or the like.

  Further, a Pt—Co alloy can be adopted as the magnetic catalyst. According to the phase diagram of the Pt—Co alloy, a Pt—Co alloy whose main phase is an fct structure that exhibits magnetic action in the range of Pt / Co = 40/60 to 73/27 (at%) can be obtained. According to the inventors' estimation, it is preferable to employ a Pt—Co alloy having a composition of Pt / Co = 40/60 to 75/25 (at%). Moreover, it is preferable to employ a Pt—Co alloy having a coercive force of 2 kOe or more in absolute value. Furthermore, it is preferable to employ a Pt—Co alloy having a particle size of 1 to 10 nm. This type of Pt—Co alloy is also obtained by a reverse micelle method based on an aqueous solution reaction, a synthesis method using an organic metal, or the like.

  The supported catalyst for a fuel cell of the second invention is that the catalyst is supported on porous carbon having mesoporous pores into which proton conductive polymer cannot enter, and that a proton conduction path is formed in the mesoporous pores. Features.

In the fuel cell supported catalyst of the second invention, the proton conducting path is formed in the mesoporous pores of the porous carbon. Therefore, the fuel cell supported catalyst of the second invention and the proton conducting polymer are mixed to form a fuel cell. In the case where the reaction layer is formed, the proton conducting polymer itself does not enter the mesoporous pores of the porous carbon, but the proton is porous via the proton conducting path formed in the mesoporous pores. It can move into the carbon pores. For this reason, a structure (three-phase interface) is also formed inside the mesoporous pores of porous carbon so that the reactants, proton and electron paths essential for promoting the electrode reaction exist around the catalyst. The
Therefore, the fuel cell supported catalyst of the second invention has a low polarization resistance and can obtain a high output, and the catalyst supported in the pores of the carbon powder also contributes effectively to the electrode reaction. The utilization rate of the catalyst is also increased.

  In the second aspect of the second invention, the proton conduction path is formed by including a proton conductor in the mesoporous hole. As a result, a structure (three-phase interface) in which a path of reactants, protons, and electrons exists around the catalyst in the pores of the carbon powder can be reliably formed.

  According to a third aspect of the second invention, the proton conductor is a vitreous proton conductor. Such a proton conduction path can be formed relatively easily as in the case of the third aspect of the first invention.

  Furthermore, in the invention of the fourth aspect, a functional group imparting proton conductivity is modified in the mesoporous pore. Such a functional group can also form a proton conductive path. Examples of the functional group imparting proton conductivity include a methylsulfonic acid group.

  In the fifth aspect of the invention, the catalyst supported on the porous carbon is a magnetic catalyst having both catalytic action and magnetic action. If this is the case, as described in the fifth aspect of the first invention, the mass transfer of oxygen to the catalyst is promoted from the nature of oxygen as paramagnetism and the nature of water as diamagnetism, The flooding phenomenon that prevents water from adhering to the electrode and preventing mass transfer is more reliably suppressed, and the output of the fuel cell system can be improved more reliably.

  Further, as described in the fifth aspect of the first invention, the magnetic catalyst may employ a Pt alloy such as a Pt—Fe alloy or a Pt—Co alloy having a fct structure as a main phase.

  As described above, if a fuel cell reaction layer or a fuel cell is produced using the fuel cell supported catalyst of the first and second inventions, the polarization resistance can be reduced and a high output can be obtained. Thus, the utilization rate of the catalyst is also high.

  The method for producing a supported catalyst for a fuel cell according to the present invention is characterized in that a proton conductor is synthesized in the pores of catalyst-supporting porous carbon having mesoporous pores into which proton-conducting polymers cannot enter. Thereby, it is possible to reliably form a structure (three-phase interface) in which the paths of the reactants, protons and electrons exist around the catalyst in the pores of the porous carbon.

  Furthermore, in the second aspect of the method for producing a supported catalyst for a fuel cell of the present invention, the catalyst-supporting porous carbon having mesoporous pores comprises a step of obtaining an organic wet gelled product, and a step of pulverizing the organic wet gelled product. A pulverizing step to obtain a gel powder, a solvent replacement step in which the gel powder is contacted with a water-soluble organic solvent to perform solvent replacement, and supercritical drying of the solvent-substituted gel powder to obtain a gel dry powder. A catalyst is supported on a carbon airgel powder obtained through a drying step and a pyrolysis step in which the gel dry powder is pyrolyzed to obtain a carbon airgel powder.

  The fuel cell supported catalyst thus obtained has excellent gas permeability because the pore structure reflecting the pore structure of the gelled product is maintained as described in the first invention. Gas mass transfer is facilitated, and polarization resistance due to mass transfer can be reduced. Moreover, since the particle diameter can be made extremely small, when used as an electrode in a polymer electrolyte fuel cell, the thickness of the electrode can be reduced.

Examples 1 to 4 embodying the present invention will be described below.
<Preparation of carbon airgel powder>
The carbon airgel powder used for the fuel cell supported catalysts of Examples 1 to 4 was prepared as follows.
(Preparation Example 1)
Polymerization step S1
As shown in FIG. 4, as the polymerization step S1, 4 g of resorcinol, 5.5 ml of 37% formaldehyde aqueous solution, and 0.019 g of sodium carbonate 99.5% powder were mixed and stirred for 3 hours. An organic wet gelled product was obtained by aging at a temperature of -24C for 90C.

Grinding step S2
The organic wet gelled product was decanted with ion-exchanged water, and then pulverized for 2 hours with a ball mill in the presence of water to obtain a gel powder slurry.

Solvent replacement step S3
And as solvent substitution process S3, after wash | cleaning the said gel powder slurry 5 times with acetone by the suction filtration method, the slurry was made into the cake layer type | mold.

Supercritical drying process S4
Furthermore, as the supercritical drying step S4, the solvent-substituted gel powder is put into a stainless steel pressure vessel, CO2 is introduced, the pressure and temperature are adjusted so as to be in a supercritical state, and then CO2 is slowly discharged. Thus, CO2 was transferred to gas phase conditions and supercritical drying was performed to obtain a gel dry powder.

Thermal decomposition process S5
Finally, as the pyrolysis step S5, the gel dry powder is placed in an electric furnace, heated in a nitrogen atmosphere at 1000 ° C. for 4 hours, and then cooled to obtain the carbon airgel powder of Preparation Example 1. It was.
The characteristics of the obtained carbon airgel powder are as follows.
BET specific surface area: 629 m ² / g
Pore volume: 2.00cm ³ / g

(Preparation Example 2)
In Preparation Example 2, the grinding time in the grinding step S2 was 4 hours. Other conditions are the same as those in Preparation Example 1, and a description thereof is omitted.
The characteristics of the obtained carbon airgel powder are as follows.
BET specific surface area: 632 m ² / g
Pore volume: 1.83 cm ³ / g

(Comparative Example 1)
In Comparative Example 1 and Comparative Example 2, the pulverization step S2 in Preparation Example 1 was not performed, and the pyrolysis step S5 was performed, and then the obtained bulk carbon airgel was used as a measurement sample. Other conditions are the same as those in Preparation Example 1, and a description thereof is omitted.
The characteristics of the obtained carbon airgel powder are as follows.
BET specific surface area: 670 m ² / g
Pore volume: 2.17 cm ³ / g

(Comparative Example 2)
In Comparative Example 2, a powder obtained by pulverizing the massive carbon aerogel obtained in Comparative Example 1 with a pulverizer for 2 hours was used as a measurement sample.
The characteristics of the obtained carbon airgel powder are as follows.
BET specific surface area: 105 m ² / g
Pore volume: 0.25cm ³ / g

<Evaluation>
With respect to the carbon aerogels of Preparation Example 1 and Comparative Example 1, the pore distribution was measured by the BET adsorption method. As a result, as shown in FIG. 5, the carbon airgel of Preparation Example 1 has almost no difference in pore distribution compared to Comparative Example 1 in which no pulverization is performed, and the pore structure is not broken. I found out that I was leaning.

  On the other hand, in the comparative example 2, as shown in FIG. 6, it turns out that the pore is reducing and the pore structure is almost destroyed.

  Further, the particle size distributions of the gel powder slurry and the carbon aerogel immediately after pyrolysis in Preparation Example 1 and Preparation Example 2 were measured. As a result, as shown in FIGS. 7 and 8, it was found that the pore distribution of the carbon airgel can be controlled by controlling the pulverization time in the pulverization step S2. It was also found that the gel powder slurry and the carbon airgel powder showed almost the same particle size distribution.

  Further, the pore distribution of the carbon airgel powders of Preparation Example 1 and Preparation Example 2 was measured by the BET adsorption method. As a result, as shown in FIG. 9, there is a difference in pore distribution between Preparation Example 1 and Preparation Example 2, and the pore distribution of the carbon airgel can be controlled by controlling the pulverization time in the pulverization step S2. Further confirmed.

  From the above results, it was found that the carbon airgel powders of Preparation Example 1 and Preparation Example 2 maintained the pore structure reflecting the pore structure of the organic wet gelled product and had a large specific surface area. For this reason, since the area which contributes to an electrode reaction becomes large and it is excellent also in gas permeability, it turns out that polarization resistance also becomes low.

Next, using the carbon airgel of Preparation Example 1, fuel cell supported catalysts of Examples 1 to 4 described later were prepared.
<Preparation of Pt-supported carbon aerogel>
Preparation Example 1 Carbon airgel powder added to a dinitrodiamine platinum nitric acid aqueous solution, dispersed by stirring and ultrasonic waves, then reduced by heating in hydrogen, and Pt-supported carbon airgel having Pt supported on carbon airgel powder Got. As shown in the schematic diagram of FIG. 10, the Pt-supported carbon airgel obtained in this way has Pt supported on the pores of the carbon airgel powder in which the pore structure is maintained as it is.

  In addition, it is also possible to use a Pt—Fe alloy having an fct structure as a main phase or a Pt—Fe alloy having an fct structure as a main phase instead of Pt as a catalyst. These magnetic catalysts can be obtained by heat-treating a fine powder of Pt—Fe alloy or Pt—Fe alloy and quenching with water.

<Preparation of fuel cell supported catalyst>
Using the Pt catalyst-supported carbon airgel powder of Preparation Example 1 obtained as described above, fuel cell-supported catalysts of Examples 1 to 4 were prepared by the following procedure.

Example 1
In Example 1, the Pt catalyst-carrying carbon airgel powder of Preparation Example 1 was modified with a methylsulfonic acid group (see the process diagram of FIG. 11).
That is, first, an aqueous formaldehyde solution and sodium sulfite are added to the Pt catalyst-carrying carbon airgel powder of Preparation Example 1 and stirred at 110 ° C. for 24 hours. Thereby, as shown in FIG. 12, a methylol group is introduced and further converted into a methylsulfonic acid group. After the reaction, ion exchange is performed for 15 minutes with 1M sulfuric acid aqueous solution, so that sodium is ion-exchanged with hydrogen, and Soxhlet extraction is carried out in an aqueous system all day and night to remove unreacted substances. Thus, a Pt catalyst-supported carbon airgel powder of Example 1 modified with methylsulfonic acid groups was obtained.
Note that, instead of the method of Example 1, the carbon airgel powder may be modified with methylsulfonic acid groups and then loaded with a Pt catalyst.

  In the fuel cell supported catalyst of Example 1 obtained in this way, since a methylsulfonic acid group having proton conductivity is introduced into the pores, this becomes a proton conduction path inside the pores and is necessary for the electrode reaction. A three-phase interface is formed inside the pores. For this reason, an electrode reaction advances rapidly. Moreover, the pore structure reflecting the pore structure of the organic wet gelled product is maintained, the specific surface area is large, the area contributing to the electrode reaction is widened, and it has excellent gas permeability. Resistance also decreases.

(Example 2)
In Example 2, a proton conductive polymer was introduced into the Pt catalyst-carrying carbon airgel powder of Preparation Example 1 by grafting within the pores (see the process diagram of FIG. 13).
That is, first, the Pt catalyst-carrying carbon airgel powder of Preparation Example 1 was dispersed in water, 30% formaldehyde aqueous solution and sodium hydroxide aqueous solution were added, and ultrasonic dispersion was performed for 5 minutes, and then at 70 ° C. for 24 hours. Stir. And suction filtration is performed and it is made to dry under 100 degrees under nitrogen atmosphere. 0.47 mol / L 2-acrylamido-2-methylpropanesulfonic acid (hereinafter abbreviated as “ATBS”) and 0.2 mol / L ammonium cerium sulfate were added to the powder thus obtained, and graft polymerization was performed inside the pores. Thus, the Pt catalyst-supported carbon airgel powder of Example 2 obtained by graft polymerization of ATBS in the pores was obtained.
Instead of the method of Example 2, the Pt catalyst may be supported after the ATBS is graft polymerized in the pores.

  The fuel cell supported catalyst of Example 2 obtained in this way has poly ATBS, which is a proton conducting polymer, in the pores as shown in FIG. proceed. Further, by appropriately adjusting the amount of the monomer to be polymerized inside the pores, the pore structure of the organic wet gelled product can be left, the area contributing to the electrode reaction can be widened, and the polarization resistance can be reduced.

(Example 3)
In Example 3, potassium trifluoromethanesulfonate was physically adsorbed to the Pt catalyst-carrying carbon airgel powder of Preparation Example 1 (see the process diagram of FIG. 15).
That is, first, the Pt catalyst-carrying carbon airgel powder of Preparation Example 1 is dispersed in water, potassium trilloromethanesulfonate is added, and ultrasonic dispersion is performed for 5 minutes, followed by solid-liquid separation by suction filtration. Then, a predetermined amount of water is added, and further 5% by mass of Nafion (registered trademark) EW1100 is added to prepare a catalyst paste for the fuel cell reaction layer. The catalyst paste thus obtained is applied to one side of an electrode substrate such as carbon cloth or carbon paper and dried to form a reaction layer. Then, the electrode substrate is immersed in 0.5 mol / L sulfuric acid to perform proton substitution, thereby forming a proton conduction path in the pores. Then, the electrode substrate is taken out, washed several times with pure water, and then dried at 60 ° C. for 10 hours. In this way, two electrode base materials having a reaction layer in which a proton conduction path is formed in the pores are prepared, and hot pressing is performed while sandwiching from both sides so that the reaction layer and the polymer electrolyte membrane are in contact with each other. Produced.
Instead of the method of Example 3, the carbon airgel powder may be modified with trifluoromethanesulfonic acid and then supported with a Pt catalyst.

Example 4
In Example 4, proton conductive phosphate glass was synthesized inside the pores of the organic wet gelled product of Preparation Example 1 (see FIG. 16).
That is, first, the organic wet gelled product of Preparation Example 1 is impregnated with a phosphate glass precursor. This phosphate glass precursor is a sol formed by adding trimethyl phosphate, hydrochloric acid, methanol and formamide to a metal alkoxide such as tetraethyl orthosilicate. Further, the mixture is heated to 90 ° C. to be gelled, and pulverized in a wet state to obtain a gel powder slurry. Furthermore, the gel powder slurry was solvent-substituted with acetone to obtain a gel powder, and a supercritical drying process using CO2 was performed to obtain a gel dry powder. The gel dry powder was pyrolyzed at 800 to 1000 ° C. to form phosphate glass as a vitreous proton conductor in the pores.

  In the fuel cell-supported catalyst of Example 4 obtained in this way, since phosphate glass having proton conductivity is introduced into the pores, this becomes a proton conduction path inside the pores and is necessary for the electrode reaction. A three-phase interface is also formed inside the pores. For this reason, an electrode reaction advances rapidly. Moreover, the pore structure reflecting the pore structure of the organic wet gelled product is maintained, the specific surface area is large, the area contributing to the electrode reaction is widened, and the gas permeability is excellent, so the polarization resistance is also small. Become.

  A fuel cell can be constructed using the fuel cell supported catalysts of Examples 1 to 4 obtained as described above. That is, a Nafion (registered trademark) solution (5% by mass solution) is added to the fuel cell supported catalyst so that the mass ratio of the fuel cell supported catalyst to the Nafion solution is about 0.5. Then, this is thoroughly stirred and mixed to produce an electrode paste. After applying this electrode paste on one side of the carbon cloth, it is dried to form an electrode reaction layer. In this way, two fuel cell electrodes having an electrode reaction layer formed on the carbon cloth are prepared.

  A polymer solid electrolyte layer (thickness: about 50 μm) made of Nafion 112 (registered trademark) is sandwiched between the two fuel cell electrodes thus obtained. Then, thermocompression bonding by hot pressing is performed under conditions of a temperature of 140 to 160 ° C. and a surface pressure of 70 to 100 kg / cm 2. In this way, a membrane electrode assembly is obtained. Furthermore, a fuel cell can be produced by assembling this membrane electrode assembly and a pair of separators.

  The present invention is not limited to the description of the embodiments and examples of the invention described above. Various modifications are also included in the present invention as long as those skilled in the art can easily conceive without departing from the scope of the claims.

It is process drawing which shows the manufacturing method of the conventional carbon airgel powder. It is a schematic diagram of the fuel cell electrode using the conventional activated carbon carrying | support catalyst. It is a characteristic conceptual diagram of the carbon airgel which carry | supported the magnetic catalyst. It is process drawing which shows the manufacturing method of the carbon airgel powder of a preparation example. 4 is a graph showing the pore distribution of Preparation Example 1 and Comparative Example 1. 6 is a graph showing the pore distribution of Comparative Example 1 and Comparative Example 2. It is a graph which shows the particle size distribution of the gel dry powder immediately after performing supercritical drying in the preparation examples 1 and 2. It is a graph which shows the pore distribution of the carbon airgel immediately after performing thermal decomposition in the preparation example 1 and the preparation example 2. FIG. It is a graph which shows the pore distribution of the carbon airgel powder of the preparation examples 1 and 2. It is a schematic diagram of Pt carrying | support carbon aerogel. 2 is a process diagram of Example 1. FIG. 1 is a diagram showing a reaction mechanism for introducing a methylsulfonic acid group in Example 1. FIG. 10 is a process diagram of Example 2. FIG. 3 is a schematic enlarged view of a supported catalyst for a fuel cell in Example 2. FIG. 6 is a process diagram of Example 3. FIG. FIG. 6 is a process diagram of Example 4.

Explanation of symbols

S1 ... polymerization step S2 ... grinding step S3 ... solvent replacement step S4 ... supercritical drying step S5 ... pyrolysis step

Claims (14)

In a fuel cell supported catalyst in which a catalyst is supported on carbon powder,
The carbon powder is
Obtaining an organic wet gelled product;
A pulverizing step of pulverizing the organic wet gelled product to form a gel powder;
A solvent replacement step of contacting the gel powder with a water-soluble organic solvent to perform solvent replacement;
A supercritical drying step of obtaining a gel dry powder by supercritical drying the solvent-substituted gel powder;
A thermal decomposition step of thermally decomposing the gel dry powder into a carbon aerogel powder;
Is a carbon airgel powder obtained through
2. The supported catalyst for a fuel cell according to claim 1, wherein a proton conduction path is formed in the carbon powder.   The supported catalyst for a fuel cell according to claim 1, wherein the proton conduction path is formed by including a proton conductor in the pores of the carbon powder.   The supported catalyst for a fuel cell according to claim 2, wherein the proton conductor is a vitreous proton conductor.   The supported catalyst for a fuel cell according to claim 1, wherein the proton conduction path is modified with a functional group imparting proton conductivity in the pores of the carbon powder.   The supported catalyst for a fuel cell according to any one of claims 1 to 4, wherein the catalyst is a magnetic catalyst having both a catalytic action and a magnetic action. A catalyst is supported on porous carbon having mesoporous pores into which proton conductive polymer cannot enter,
A supported catalyst for a fuel cell, wherein a proton conduction path is formed in the mesoporous hole.   The supported catalyst for a fuel cell according to claim 6, wherein the proton conduction path is formed by including a proton conductor in the mesoporous hole.   8. The fuel cell supported catalyst according to claim 7, wherein the proton conductor is a vitreous proton conductor.   7. The supported catalyst for a fuel cell according to claim 6, wherein the proton conduction path is modified with a functional group imparting proton conductivity in the mesoporous pores.   The supported catalyst for a fuel cell according to any one of claims 6 to 9, wherein the catalyst is a magnetic catalyst having both a catalytic action and a magnetic action.   The reaction layer for fuel cells using the supported catalyst for fuel cells of any one of Claims 1 thru | or 10.   A fuel cell using the reaction layer for a fuel cell according to claim 11.   A method for producing a supported catalyst for a fuel cell, comprising synthesizing a proton conductor in a catalyst-supporting porous carbon having a mesoporous pore that supports a catalyst and cannot contain a proton-conducting polymer. The catalyst-supporting porous carbon having the mesoporous pores is
Obtaining an organic wet gelled product;
A pulverizing step of pulverizing the organic wet gelled product to form a gel powder;
A solvent replacement step of contacting the gel powder with a water-soluble organic solvent to perform solvent replacement;
A supercritical drying step of obtaining a gel dry powder by supercritical drying the solvent-substituted gel powder;
A thermal decomposition step of thermally decomposing the gel dry powder into a carbon aerogel powder;
A method for producing a supported catalyst for a fuel cell, wherein the catalyst is supported on a carbon airgel powder obtained through the above process.