JP2008277094A - Diffusion layer for fuel cell and method for producing the same, membrane-electrode assembly, and fuel cell - Google Patents

Abstract

[Objective] To provide a diffusion layer for a fuel cell that can highly prevent the membrane-electrode assembly from drying, a membrane-electrode assembly, and a fuel cell using the same.
[Structure] The fuel cell diffusion layer 1 of the present invention has porous microporous layers 11a and 11b containing carbon and a water repellent resin on both surfaces of a diffusion layer substrate 10 having conductivity and gas permeability. Further, a reaction layer 12 is formed on the microporous layer 11a. The carbon contained in the microporous layers 11a and 11b includes a step S1 for obtaining an organic wet gelled product, a pulverizing step S2 for crushing the organic wet gelled product to obtain a gel powder, and the gel powder as a water-soluble organic solvent. A solvent replacement step S3 in which the solvent replacement is performed by contacting the gel, a supercritical drying step S4 in which the solvent-substituted gel powder is supercritically dried to obtain a gel dry powder, and the gel aerogel is obtained by pyrolyzing the gel dry powder. It is the carbon airgel powder obtained through thermal decomposition process S5 made into powder.
[Selection] Figure 1

Description

  The present invention relates to a diffusion layer for a fuel cell, a production method thereof, a membrane-electrode assembly, and a fuel cell, and is suitable for use in a solid polymer fuel cell.

  A polymer electrolyte fuel cell includes a membrane-electrode assembly in which a membrane made of a polymer electrolyte is sandwiched between catalyst layers, and the outside of the catalyst layer is sandwiched between diffusion layers that play a role of current collection and gas diffusion. ing. The catalyst layer is a mixture of carbon particles carrying a catalyst such as platinum and a solid polymer electrolyte such as Nafion (registered trademark, Nafion (manufactured by Dupont), hereinafter the same). The both surfaces of the membrane-electrode assembly are sandwiched by separators having air or hydrogen gas flow paths to form unit cells, and a stack in which a plurality of unit cells are stacked is formed.

In this polymer electrolyte fuel cell, the following electrochemical reaction is performed.
Anode side: H ₂ → 2H ⁺ + 2e ⁻
Cathode side: 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O
Total reaction: H ₂ + 1 / 2O ₂ → H ₂ O
That is, hydrogen is supplied to the gas flow path of the separator on the anode side, and supplied to the catalyst layer through the diffusion layer. Then, hydrogen is oxidized by the electrochemical reaction in the catalyst layer to generate protons and electrons. The protons thus generated move in the catalyst layer and the polymer solid electrolyte while drawing water in the form of oxonium ions, and reach the cathode side.
On the other hand, oxygen supplied to the cathode side combines with oxonium ions to generate water.

  As described above, in the polymer electrolyte fuel cell, since water moves from the anode side toward the cathode side, the membrane-electrode assembly is easily dried on the anode side, and the internal resistance of the fuel cell increases. This will cause a decrease in the output of the fuel cell. On the other hand, water is supplied from the anode side on the cathode side, but the vapor pressure of water is increased due to the heat generation of the fuel cell itself, and a large amount of water evaporated by the oxidizing gas flowing through the gas flow path of the separator is taken away. Even on the cathode side, the membrane-electrode assembly may be in a dry state.

  When the solid polymer electrolyte membrane constituting the membrane-electrode assembly is dried, proton conductivity is lowered and the internal resistance of the fuel cell is increased. Moreover, since water is required for the electrode reaction, the electrode reaction becomes difficult when the reaction layer is dried. For this reason, the membrane-electrode assembly is cooled to reduce the vapor pressure of water, or the reaction gas is humidified to prevent the membrane-electrode assembly from drying. However, this requires a cooling device and a humidifying device, which has the problem that the structure becomes complicated and large, and the manufacturing cost increases. Further, since the cooling device and the humidifying device are operated by a part of the electric power generated by the fuel cell, there is a problem that the energy efficiency is deteriorated.

  In this regard, in the case of an air-cooled non-humidified solid polymer fuel cell, cooling is also performed with air supplied as an oxidizing gas, so that a cooling device is not necessary. However, in the air-cooled polymer electrolyte fuel cell, the membrane-electrode assembly is cooled by increasing the flow rate of the oxidizing gas, so that the amount of water carried away by the oxidizing gas increases, and the membrane-electrode assembly is Easily dry.

  In addition, as a method for preventing the membrane-electrode assembly from drying in a polymer electrolyte fuel cell, it has also been proposed to provide a conductive water-repellent layer on the side of the diffusion layer that contacts the reaction layer or on both sides of the diffusion layer. (Patent Document 1). In the fuel cell using the diffusion layer with the conductive water-repellent layer, the water present in the reaction layer is repelled by the conductive water-repellent layer, making it difficult for the water to pass through. However, it is said that the power generation efficiency does not decrease so much.

On the other hand, as a background art related to the present invention, a carbon aerogel produced using a polymer of dihydroxybenzene and formaldehyde as a starting material is known (Patent Document 2). This carbon aerogel is manufactured by the process shown in FIG. That is, as 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. Next, as a solvent replacement step S92, the gelled product is washed with a water-soluble organic solvent such as methanol or acetone, and the water contained in the gelled product is replaced with a water-soluble solvent. Furthermore, as a supercritical drying step S93, the solvent-substituted gelled product is put into a stainless steel pressure vessel, CO ₂ is introduced, the pressure and temperature are adjusted so as to be in a supercritical state, and then CO ₂ is slowly discharged. In this way, CO ₂ is transferred to gas phase conditions to perform supercritical drying. The gelled product thus dried is composed of particles whose primary particles forming a network structure have a particle size of 0.1 μm or less, and the bulk density is as extremely low as 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. 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. Finally, in the pulverization step S95, the above-mentioned carbide mass is pulverized by a pulverizer to obtain a carbon airgel powder.

  Since the carbon airgel powder thus obtained can have a very small particle size, 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. For this reason, it has also been proposed to use carbon aerogel as an electrode of a polymer electrolyte fuel cell (Patent Document 3).

Furthermore, as a method for producing a carbon airgel powder, a technique relating to a method for producing a carbon airgel powder characterized by pulverizing and drying the organic wet gelled product obtained in the polymerization step S91 (Patent Document) 4). The carbon airgel powder produced by this method has a characteristic that the pore distribution of the carbon airgel is maintained.
JP-A-9-245800 U. S. patent No. 4873218 claim14, 15 Japanese National Patent Publication No. 11-503267 JP 2006-265091 A

  The fuel cell described in Patent Document 1 is not required to have a humidifier, but is required to have a methanol reformer. Since hydrogen obtained from the methanol reformer contains a large amount of water vapor, even if the reaction gas is not humidified by the humidifier, water is supplied to the membrane-electrode assembly by the water vapor supplied together with hydrogen. Is supplied.

  However, in order to provide a methanol reformer, the apparatus becomes complicated and large, and the manufacturing cost increases. For this reason, there has been a demand for a diffusion layer that can be driven without a humidifier, a cooling device, or a methanol reformer and can highly prevent drying of the membrane-electrode assembly.

  The present invention has been made in view of the above-described conventional circumstances, and is a fuel cell diffusion layer capable of highly preventing the drying of the membrane-electrode assembly, the membrane-electrode assembly, and a fuel using the same. Providing a battery is an issue to be solved.

  The inventors have intensively studied to solve the above problems. As a result, in the diffusion layer for a fuel cell in which a porous microporous layer containing carbon and a water-repellent resin is formed on both surfaces of a diffusion layer base material having conductivity and gas permeability, the pore structure of the carbon airgel is The present inventors have found that the above problems can be solved by using a carbon airgel powder kept as it is (see Patent Document 4), and have completed the present invention.

That is, the fuel cell diffusion layer according to the first aspect of the present invention comprises:
A diffusion layer for a fuel cell in which a porous microporous layer containing carbon and a water repellent resin is formed on both surfaces of a diffusion layer base material having conductivity and gas permeability,
The carbon 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;
It is a carbon aerogel powder obtained through a pyrolysis step in which the gel dry powder is pyrolyzed to obtain a carbon aerogel powder.

カーボンエアロゲル粉末は極めて小さな孔径を有するため、マイクロポーラス層の孔径も小さくなり、水圧ΔＰはきわめて大きくなる。このため、本発明の燃料電池用拡散層の両面に形成されたマイクロポーラス層は、水が透過し難く、ガスはすみやかに透過することができる。したがって、本発明の燃料電池用拡散層は、膜−電極接合体の乾燥を高度に防ぐことができる。 Such carbon airgel powder is subjected to solvent replacement after pulverizing the organic wet gelled product in the pulverization step. For this reason, it will grind | pulverize in the state in which water was contained in the pore of the gelled material, and as compared with the grinding | pulverization in a dry state, a pore will be protected by the cushion effect of water, and it will become difficult to destroy. For this reason, the carbon airgel powder obtained in this way maintains the pore structure reflecting the pore structure of the gelled product, and has excellent gas permeability. Therefore, when a porous microporous layer is formed by mixing the carbon airgel powder and water repellent resin on both sides of the diffusion layer base material to form a diffusion layer for fuel cells, the microporous layer is an excellent gas. It has permeability.
On the other hand, this microporous layer is difficult to permeate water for the following reasons. That is, the water pressure ΔP required when water passes through the microporous layer is expressed by the following equation (1).

Since the carbon airgel powder has a very small pore size, the pore size of the microporous layer also becomes small, and the water pressure ΔP becomes extremely large. For this reason, the microporous layer formed on both surfaces of the diffusion layer for a fuel cell of the present invention hardly permeates water and allows gas to permeate quickly. Therefore, the fuel cell diffusion layer of the present invention can highly prevent the membrane-electrode assembly from drying.

According to the invention of the second aspect, the organic wet gelled product is obtained by polymerizing polyhydroxybenzene and formaldehyde in the presence of a base catalyst.
Here, polyhydroxybenzene means a compound having two or more hydroxyl groups in the benzene ring. Such a compound can be easily polymerized with formaldehyde to form a network structure and form a pore structure.

According to the invention of the third aspect, dihydroxybenzene and / or a dihydroxybenzene derivative is employed as the polyhydroxybenzene.
Among polyhydroxybenzenes, dihydroxybenzene and dihydroxybenzene derivatives are relatively stable compounds, and are therefore easy to handle and suitable.
Particularly preferred as dihydroxybenzene is resorcinol. Therefore, as the invention of the fourth aspect, resorcinol was adopted as dihydroxybenzene.

According to the fifth aspect of the invention, the water-soluble organic solvent used in the solvent replacement step employs one or more mixed solvents of methanol, acetone, and amyl acetate.
The water-soluble organic solvent used in the solvent replacement step is preferably a mixed solvent of one or more of methanol, acetone and amyl acetate. In this case, water contained in the gelled product can be easily replaced with a solvent.

According to the invention of the sixth aspect, the pulverization of the organic wet gelled product in the pulverization step is performed by a pulverization method using a medium.
According to the test results of the present inventors, when the organic wet gelled material is pulverized using a medium, the particle diameter of the carbon aerogel is controlled by appropriately selecting the pulverization conditions such as the diameter of the medium and the pulverization time. , The pore structure can be retained. For this reason, the carbon airgel of the desired characteristic according to a use can be obtained.
Of course, other pulverization methods that do not use media in advance (for example, a pulverization method using a rotary pulverizer that does not use a homogenizer or media) can be performed before performing the pulverization step using media. This is because if the pulverization process is performed using media at the final stage of the pulverization process, the particle size of the carbon airgel can be controlled and the pore structure can be maintained.
Moreover, there is no limitation in particular about the material of media, Stabilized zirconia, an alumina, agate, quartz etc. can be used. Since the fine powder of media may enter the carbon airgel powder as an impurity, it is preferable to appropriately select a media material that does not have an adverse effect depending on the use of the carbon airgel powder.

According to the seventh aspect of the invention, the diameter of the media is 5 mm or less.
According to the test results of the present inventors, when the diameter of the media is 5 mm or less, a gel powder having a small particle diameter can be obtained, and the pore structure is not easily destroyed. For this reason, the particle diameter of the carbon airgel powder finally obtained can be small, and the pore structure of the organic wet gelled product can be maintained. More preferable is a medium having a diameter of 0.65 mm or less.

According to the invention of the eighth aspect, the pulverization step is performed by controlling at least the diameter of the media and the pulverization time.
According to the test results of the present inventors, it has been found that the particle diameter and pore distribution of the carbon airgel powder obtained by the present invention are closely related to the diameter of the media and the grinding time. For this reason, if the grinding | pulverization process is performed by controlling the diameter and grinding | pulverization time of a medium, the carbon airgel of the desired characteristic according to a use can be obtained with sufficient reproducibility.

  According to the ninth aspect of the invention, the microporous layer has a pore diameter of 2 to 30 nm. If the pore diameter is 2 to 30 nm, the water pressure ΔP required when water passes through the microporous layer becomes very large, making it very difficult to pass water through the microporous layer, and drying the membrane-electrode assembly. Can be reliably prevented.

  According to the invention of the tenth aspect, the microporous layer contains 5 to 95% by weight of the carbon airgel powder. If the content of the carbon airgel powder is less than 5%, the conductivity of the microporous layer is lowered, the internal resistance of the fuel cell is increased, and wasted energy due to heat generation is consumed. On the other hand, when the carbon airgel powder is 95% by weight or more, the role as a binder of the water repellent resin becomes insufficient, and it becomes difficult to form a microporous layer.

According to the eleventh aspect of the invention, the microporous layer contains 5 to 95% by weight of the water-repellent resin.
If the content of the water repellent resin is less than 5%, the role of the water repellent resin as a binder becomes insufficient, and it becomes difficult to form a microporous layer. If the water-repellent resin is 95% by weight or more, the content of the carbon airgel powder is less than 5%, the conductivity of the microporous layer is lowered, the internal resistance of the fuel cell is increased, and wasted energy is consumed. Will be.

  A membrane-electrode assembly can be obtained by providing a reaction layer in the fuel cell diffusion layer of the present invention and sandwiching the solid polymer electrolyte membrane. Furthermore, by providing gas flow paths on both sides of the membrane-electrode assembly and providing means for supplying fuel gas and means for supplying oxidizing gas to these gas flow paths, a fuel cell can be obtained. As described above, the fuel cell configured as described above has a membrane-electrode assembly that is highly difficult to dry, and therefore can generate power with good energy efficiency even without a humidifier, a cooling device, or a methanol reformer. it can.

Example 1
As shown in FIG. 1, the diffusion layer 1 of Example 1 has a carbon airgel powder and polytetrafluoroethylene on both surfaces of a diffusion layer substrate 10 made of carbon woven fabric, carbon paper or the like capable of gas diffusion. Porous microporous layers 11a and 11b containing (PTFE) are formed, and a reaction layer 12 containing carbon carrying a platinum catalyst and Nafion (registered trademark) is formed on one side thereof. Yes. This diffusion layer 1 was manufactured by the method shown below.

<Preparation of carbon airgel powder>
The carbon airgel powder contained in the microporous layers 11a and 11b was prepared as follows according to the process diagram shown in FIG.
・ Polymerization process S1
As 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, and then room temperature −24 h, 50 ° C. −24 h, 90 °. A gelled product was obtained by aging C-72h.

・ Crushing step S2
The gelled product was decanted with ion-exchanged water, and then pulverized for 2 hours 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, in the supercritical drying step S4, the solvent-substituted gel powder is put into a stainless steel pressure vessel, CO ₂ is introduced, the pressure and temperature are adjusted so as to be in a supercritical state, and then CO ₂ is slowly discharged. As a result, CO ₂ was transferred to gas phase conditions and supercritical drying was performed to obtain a gel dry powder.

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

・ Microporous layer forming step S6
A fine powder of polytetrafluoroethylene is mixed at 35 parts by weight with respect to the carbon airgel powder, and water added with a surfactant is added to obtain a dispersion. The dispersion is subjected to suction filtration, pressed with a press machine to form a self-supporting film, and further heated and welded in an inert gas at 300 ° C. for 2 hours. Then, a plain weave carbon cloth is prepared, and is sandwiched between the two self-supported films that have been welded together and thermocompression bonded at 345 ° C. to be integrated.
Next, 2 g to 200 g of Nafion (registered trademark) solution (5 wt% water / isopropanol solution) is added to 1 g of commercially available platinum-supported carbon (platinum content 60 wt%), and stirred with a hybrid mixer to obtain a catalyst paste. The surface of the film integrated by the method is printed so that the amount of Pt supported is 0.01 to ² mg / cm ² and dried. Thus, the diffusion layer 1 of Example 1 was obtained.
Instead of printing on the diffusion layer to form the reaction layer, the catalyst paste is printed on a polytetrafluoroethylene sheet, dried, and peeled to produce a self-supporting reaction layer film. The reaction layer may be formed by thermocompression bonding with a diffusion layer.

<Fabrication of fuel cell single layer cell>
Using the diffusion layer 1 prepared as described above, the fuel cell single-layer cell shown in FIG. 3 was prepared. That is, two diffusion layers 1 are prepared, and the reaction layer 12 side is sandwiched between both sides of a polymer electrolyte membrane 13 made of Nafion (registered trademark), and pressure bonded by hot pressing. Further, separators 14a and 14b serving as oxygen and hydrogen gas supply passages are pressed against the outside by a mounting jig (not shown). In this way, the fuel cell single-layer cell 20 is manufactured, and the fuel cell single-layer cell 20 is further laminated to complete the fuel cell stack.

(Comparative Example 1)
In Comparative Example 1, as the carbon used in the microporous layer, the pulverization step S2 in Example 1 was not performed, and the pyrolysis step S5 was performed. Then, the obtained bulk carbon airgel was revolved at 300 rpm and rotated at 300 rpm by a planetary rotating ball mill. The carbon powder obtained by grinding for 2 hours was used.
The characteristics of the obtained carbon airgel powder are as follows.
BET specific surface area: 105 m ² / g
Pore volume: 0.25 cm ³ / g
About others, it is the same as that of Example 1, and description is abbreviate | omitted.

(Comparative Example 2)
In Comparative Example 2, carbon black having a pore diameter of 0.15 μm was used as the carbon used for the microporous layer. About others, it is the same as that of Example 1, and description is abbreviate | omitted.

(Comparative Example 3)
In Comparative Example 3, carbon black having a pore size of 0.07 μm was used as the carbon used for the microporous layer. About others, it is the same as that of Example 1, and description is abbreviate | omitted.

(Comparative Example 4)
In Comparative Example 4, carbon black having a pore diameter of 0.015 μm was used as the carbon used for the microporous layer. About others, it is the same as that of Example 1, and abbreviate | omits description.

(Comparative Example 5)
In Comparative Example 5, carbon black having a pore diameter of 0.15 μm was used as the carbon used for the microporous layer, and the microporous layer was formed only on one side of the plain weave carbon cloth. And it pinched | interposed from both sides so that the microporous layer side might closely_contact | adhere to a Nafion (trademark) film | membrane. About others, it is the same as that of Example 1, and abbreviate | omits description.

  FIG. 4 shows pore distribution curves (by the nitrogen adsorption measurement method) of the microporous layers used in Example 1, Comparative Example 2 and Comparative Example 5. FIG. 5 shows the pore distribution curve (by mercury porosimeter method) of the microporous layer used in Comparative Examples 2-5.

<Evaluation>
For the fuel cell single-layer cells of Example 1 and Comparative Examples 1 to 5, the cell temperature was set to 60 ° C. under non-humidifying conditions, and the relationship between the dew point of the introduced air and the cell voltage was examined. The measurement result when the current is 2A is shown in FIG. 6, and the measurement result when the current is 6A is shown in FIG. From FIG.6 and FIG.7, in the fuel cell single layer cell of Example 1, although it was under non-humidified conditions, the high cell voltage was shown. On the other hand, in the fuel cell single-layer cell of Comparative Example 1, as in Example 1, although the carbon airgel powder was used, the cell voltage was low, particularly when the current was as large as 6A, The cell voltage drop was particularly significant when the dew point was low. This is due to the difference in the manufacturing method of the carbon airgel powder. As will be described later, the carbon airgel powder of Example 1 retains pores in the pulverization step S2, whereas in Comparative Example 1, This is probably because the pores were destroyed and it was difficult for gas to pass through the microporous layer. Moreover, also in Comparative Examples 2 to 5, the cell voltage was lower than that of Example 1, and among them, the larger the pore diameter, the lower. This is considered to be because when the pore diameter is large, water as a liquid easily moves through the microporous layer, and water is taken away to the gas flow path side, so that the membrane-electrode assembly is easily dried. In Comparative Example 5, the cell voltage was low, and the cell voltage was 0 in the measurement at 6A. This is because the microporous layer is not formed on the gas flow path side of the diffusion layer of Comparative Example 5 and the carbon cloth is exposed, so that the water contained in the carbon cloth flows in the air flowing through the gas flow path. It was because it was evaporated and quickly taken away.

<Changes in carbon airgel powder characteristics due to differences in manufacturing conditions>
Changes in the characteristics of the carbon airgel powder were investigated by changing the production conditions.
(Test Example 1)
In Test Example 1, the grinding time in the grinding step S2 was 4 hours. Other conditions are the same as those in the first embodiment, and a description thereof will be 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

(Test Example 2)
In Test Example 2, the pulverization step S2 in 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 the first embodiment, and a description thereof will be 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

<Evaluation>
For the carbon aerogels of Example 1 and Test Example 2, the pore distribution was measured by the BET adsorption method. As a result, as shown in FIG. 8, the carbon airgel of Example 1 has almost no difference in pore distribution even when compared with Test Example 2 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 Comparative Example 1, as shown in FIG. 9, it can be seen that the pores are reduced and the pore structure is almost destroyed.

  Moreover, the particle size distribution of the gel dry powder immediately after performing supercritical drying and the carbon aerogel immediately after pyrolysis in Example 1 and Test Example 1 was measured. As a result, as shown in FIGS. 10 and 11, it was found that the particle size 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.

  Furthermore, the pore distribution of the carbon airgel powders of Example 1 and Test Example 1 was measured by the BET adsorption method. As a result, as shown in FIG. 12, there is a difference in the pore distribution between Example 1 and Test Example 1, and the pore distribution of the carbon airgel can be controlled by controlling the pulverization time in the pulverization step S2. Further confirmed.

(Test Example 4 to Test Example 15)
In Test Example 4 to Test Example 15, the relationship between the pulverization condition of the gelled product and the characteristics of the obtained carbon airgel powder was examined. The grinding process was performed in three stages as shown in FIG. That is, as a first pulverization step, the gelled product obtained in the polymerization step S1 in Example 1 is pulverized with a homogenizer (rotation speed 2000 rpm, pulverization time 15 minutes). Next, as a second pulverization step, the pulverized material obtained in the first pulverization step is placed in a container of a planetary rotating ball mill, and further, a 5 mm diameter stabilized zirconia-made medium is pulverized (revolution 255 rpm, rotation 550 rpm). , Grinding time 2 hours). Further, as a third pulverization step, crushed by a planetary rotating ball mill was performed using stabilized zirconia media having various diameters to obtain gel powder slurry. Table 1 shows the grinding conditions of Test Example 4 to Test Example 15 in the third grinding process. Thus, after performing the 1st-3rd grinding | pulverization process, the solvent substitution process S2, the supercritical drying process S3, and the thermal decomposition process S4 similar to Example 1 and Test Example 1 were performed, and carbon airgel powder was obtained.

(Relationship between media diameter and arbitrary particle diameter)
About the gel powder slurry which concerns on Test Example 4-Test Example 15 obtained at the 3rd grinding | pulverization process, the particle size distribution measurement by a laser diffraction and a scattering system was performed. The results are shown in FIG. From this figure, it was found that when the diameter of the media used in the third pulverization step was reduced, the arbitrary% particle size was reduced. Further, it was found that the arbitrary% particle size is reduced when the pulverization time of the third pulverization step is increased. From the above results, it was found that a carbon airgel powder having a desired particle size according to the purpose can be obtained by controlling the pulverization time and the media diameter.

(Relationship between media diameter, total pore volume and BET specific surface area)
About the carbon airgel powder obtained by Test Example 4-Example 15, the total pore volume and the BET specific surface area were measured by the nitrogen adsorption method (FIG. 15). As a result, there was little difference due to the difference in the third pulverization process.

(Relationship between average particle size and pore volume fraction of gel powder slurry)
About the gel powder slurry obtained in Test Example 4 to Example 15, the average particle diameter and the pore volume fraction of 10-30 nm (10-30 nm relative to the mesopore volume determined from the desorption side of the nitrogen adsorption isotherm) The ratio of pore volume) was plotted. As a result, as shown in FIGS. 16 and 17, it was found that the pore volume fraction rapidly decreases when the average particle size of the gel powder slurry is less than 1 μm. This shows that it is difficult to damage the pore structure if the pulverization conditions are appropriately controlled so that the particle size of the gel powder slurry does not become less than 1 μm. Further, it can be seen from FIG. 16 that the pore volume fraction decreases according to the pulverization time in the third pulverization step. Furthermore, it can be seen from FIG. 17 that if the diameter of the media is 5 mm or less, the pore volume can be maintained by adjusting the grinding time. It can also be seen that if the media diameter is 0.65 mm or less, it is easier to maintain the pore volume.

(Relationship between average particle size of gel powder slurry and pore volume fraction of carbon airgel powder)
The result of having plotted the diameter of the medium used at the 3rd grinding | pulverization process in Test Example 4-Example 15, and the pore volume fraction of the obtained carbon airgel powder is shown in FIG. From this figure, it can be seen that when the media diameter is 5 mm or less, the pore volume fraction does not change so much and the pore structure is easily maintained. It can also be seen that the pore volume fraction is particularly well maintained when the media diameter is 0.3 mm and 0.65 mm.

  From the above results, it can be seen that the particle size and pore distribution of the carbon airgel powder are closely related to the media diameter and the grinding time. It can be seen that if the pulverization process is performed while controlling the diameter of the media and the pulverization time, a carbon airgel powder having desired characteristics according to the application can be obtained with good reproducibility.

  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.

2 is a schematic cross-sectional view of a fuel cell diffusion layer of Example 1. FIG. 2 is a process diagram showing a method for producing the carbon airgel powder used in Example 1. FIG. 1 is a schematic cross-sectional view of a fuel cell stack of Example 1. FIG. 4 is a graph showing the pore distribution of Example 1 and Comparative Examples 2 and 4. It is a graph which shows the pore distribution of Comparative Examples 2, 3, 4 and 5. It is a graph which shows the relationship between the dew point of introductory air when a current is 2A, and a cell voltage. It is a graph which shows the relationship between the dew point of the introductory air when a current is 6A, and a cell voltage. 3 is a graph showing the pore distribution of Example 1 and Test Example 2. 6 is a graph showing the pore distribution of Test Example 2 and Test Example 3. It is a graph which shows the particle size distribution of the gel powder slurry after performing the grinding | pulverization process S2 in Example 1 and Test Example 1. FIG. It is a graph which shows the particle size distribution of the carbon airgel powder thermally decomposed after performing supercritical drying in Example 1 and Test Example 1. 2 is a graph showing the pore distribution of carbon airgel powders of Example 1 and Test Example 1. FIG. It is process drawing of the crushing process in Test Examples 4-15. It is a graph which shows the relationship between the media diameter in Test Examples 4-15, and the arbitrary% particle diameter of a gel powder slurry. It is a graph which shows the relationship between the media diameter in Test Examples 4-15, the total pore volume of a carbon airgel powder, and a BET specific surface area. It is a graph which shows the relationship between the average particle diameter of the gel powder slurry in each grinding | pulverization time in Test Examples 4-15, and the pore volume fraction of carbon airgel powder. It is a graph which shows the relationship between the average particle diameter of the gel powder slurry in each media diameter in Test Examples 4-15, and the pore volume fraction of carbon airgel powder. It is a graph which shows the relationship between the media diameter in each grinding | pulverization time in Test Examples 4-15, and the pore volume fraction of carbon airgel powder. It is process drawing which shows the manufacturing method of the conventional carbon airgel powder.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Diffusion layer base material 11a, 11b ... Microporous layer 1 ... Fuel cell diffusion layer S1 ... Polymerization step S2 ... Grinding step S3 ... Solvent replacement step S4 ... Supercritical drying step S5 ... Pyrolysis step

Claims (14)

A diffusion layer for a fuel cell in which a porous microporous layer containing carbon and a water repellent resin is formed on both surfaces of a diffusion layer base material having conductivity and gas permeability,
The carbon 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 diffusion layer for a fuel cell, which is a carbon airgel powder obtained through a thermal decomposition step of thermally decomposing the gel dry powder to obtain a carbon airgel powder.   2. The fuel cell diffusion layer according to claim 1, wherein the organic wet gelled product is obtained by polymerizing polyhydroxybenzene and formaldehyde in the presence of a base catalyst.   The fuel cell diffusion layer according to claim 2, wherein the polyhydroxybenzene is dihydroxybenzene and / or a dihydroxybenzene derivative.   The diffusion layer for a fuel cell according to claim 3, wherein the dihydroxybenzene is resorcinol.   5. The fuel cell diffusion according to claim 1, wherein the water-soluble organic solvent used in the solvent substitution step is one or a mixed solvent of methanol, acetone, and amyl acetate. layer.   The fuel cell diffusion layer according to any one of claims 1 to 5, wherein the pulverization of the organic wet gelled product in the pulverization step is performed using a medium.   The fuel cell diffusion layer according to claim 6, wherein the diameter of the medium is 5 mm or less.   The fuel cell diffusion layer according to any one of claims 1 to 7, wherein the pulverization step is performed by controlling at least the diameter of the media and the pulverization time to retain the pores of the carbon airgel.   The fuel cell diffusion layer according to any one of claims 1 to 8, wherein the microporous layer has a pore diameter of 2 to 30 nm.   10. The fuel cell diffusion layer according to claim 1, wherein the microporous layer contains 5 to 95% by weight of carbon airgel powder. 11.   The diffusion layer for a fuel cell according to any one of claims 1 to 10, wherein the microporous layer contains 5 to 95 wt% of a water-repellent resin.   A membrane-electrode assembly comprising the fuel cell diffusion layer according to claim 1.   A fuel cell comprising the membrane-electrode assembly according to claim 12. 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 pyrolysis step of thermally decomposing the gel dry powder into a carbon aerogel powder;
A microporous layer forming step of forming a porous microporous layer containing the carbon airgel powder and the water repellent resin on both surfaces of a diffusion layer base material having conductivity and gas permeability;
A method for producing a diffusion layer for a fuel cell, comprising:

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