JP2008198436A - Electrode for polymer electrolyte fuel cell, its manufacturing method, and polymer electrolyte fuel cell equipped with it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of an electrode for a polymer electrolyte fuel cell with small deterioration of performance even if air is used in place of oxygen as an oxidizer gas, and superior in practical use. <P>SOLUTION: The manufacturing method of the electrode for the polymer electrolyte fuel cell comprises (i) a process to produce a fibril-like polymer by electrolytic oxidation polymerization of a compound having an aromatic ring on a conductive porous support body, (ii) a process to calcine the fibril-like polymer and produce a carbon fiber on the conductive porous support body, (iii) a process to make carry a metal catalyst on the carbon fiber, and (iv) a process to coat a solution dissolving an ion conductive polymer in a solvent and having water over 50 wt.% of the solvent and the remainder being isopropanol and/or n-propanol on the carbon fiber carrying the metal catalyst. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrode for a polymer electrolyte fuel cell, a method for producing the same, and a polymer electrolyte fuel cell provided with the electrode for a polymer electrolyte fuel cell, and particularly uses air instead of oxygen as an oxidant gas. However, the present invention relates to a method for producing an electrode for a polymer electrolyte fuel cell having a small decrease in performance and excellent practicality.

  In recent years, fuel cells have attracted attention as a battery with high power generation efficiency and a low environmental load, and extensive research and development has been conducted. Among fuel cells, polymer electrolyte fuel cells with high output density and low operating temperature are easier to reduce in size and cost than other types of fuel cells. It is expected to spread widely as a household cogeneration system.

  In general, in a polymer electrolyte fuel cell, a pair of electrodes are arranged with a polymer electrolyte membrane sandwiched between them, a fuel gas such as hydrogen is brought into contact with the surface of one electrode, and oxygen is applied to the surface of the other electrode. The contained gas is brought into contact, and electric energy is taken out from between the electrodes by utilizing an electrochemical reaction that occurs at this time (see Non-Patent Documents 1 and 2). A catalyst layer is disposed on the electrode in contact with the polymer electrolyte membrane, and an electrochemical reaction occurs at the three-phase interface between the polymer electrolyte membrane, the catalyst layer, and the gas. Therefore, in order to improve the power generation efficiency of the polymer electrolyte fuel cell, it is necessary to increase the reaction field of the electrochemical reaction.

  In the polymer electrolyte fuel cell, in order to facilitate transmission of protons generated in the catalyst layer on the fuel electrode side to the air electrode (oxygen electrode) side through the polymer electrolyte membrane, the catalyst layer It is also necessary to contain an ion conductive polymer. Therefore, in order to increase the reaction field of the electrochemical reaction and to ensure a sufficient proton conduction path, the catalyst layer has been conventionally produced by supporting a noble metal catalyst such as platinum on granular carbon such as carbon black. It has been formed by applying a paste or slurry obtained by mixing a catalyst powder and an ion conductive polymer onto a conductive porous support such as carbon paper. However, the polymer electrolyte fuel cell including the catalyst layer formed by this method has low power generation efficiency.

  On the other hand, the present inventors prepared carbon fibers by a specific method on a conductive porous support such as carbon paper, supported noble metals on the carbon fibers by electroplating, and further added the noble metals. It has been found that the power generation efficiency of a polymer electrolyte fuel cell can be improved by using an electrode prepared by applying a solution of an ion conductive polymer to a carbon fiber carrying carbon in a polymer electrolyte fuel cell. (See Patent Document 1).

The Chemical Society of Japan, “Chemical Review No. 49, Material Chemistry of New Batteries”, Academic Publishing Center, 2001, p. 180-182 “Polymer fuel cell <2001 edition>”, Technical Information Association, 2001, p. 14-15 International Publication No. 2004/063438 Pamphlet

  However, as a result of further investigations by the present inventors, the polymer electrolyte fuel cell using the electrode produced as described in Patent Document 1 is compared with the case where oxygen is used as the oxidant gas. In addition, it was found that there was a problem in terms of practicality because the performance was greatly reduced when air was used as the oxidant gas.

  Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and the degradation of performance is small even when air is used instead of oxygen as an oxidant gas, and a solid polymer fuel cell electrode excellent in practicality is provided. It is to provide a manufacturing method. Another object of the present invention is to provide a solid polymer fuel cell having such a polymer electrolyte fuel cell electrode and excellent in practicality.

  As a result of intensive studies to achieve the above object, the inventors of the present invention have produced a fibril-like polymer on a conductive porous support and calcined the fibril-like polymer into a three-dimensional continuous carbon fiber. By applying a metal catalyst on the carbon fiber, and further applying a solution containing an ion conductive polymer on the carbon fiber on which the metal catalyst is supported, and more than 50% by mass of the solvent is water, An electrode for a polymer electrolyte fuel cell having a high proportion of ion conductive polymer in the vicinity of the surface of the carbon fiber is obtained. By incorporating the electrode into the polymer electrolyte fuel cell, air is used instead of oxygen as an oxidant gas. Even when used, it has been found that a solid polymer fuel cell having a small decrease in performance and excellent practicality can be obtained, and the present invention has been completed.

That is, the method for producing an electrode for a polymer electrolyte fuel cell of the present invention comprises a conductive porous support, a carbon fiber disposed on the conductive porous support, and a carbon fiber supported on the carbon fiber. A method for producing an electrode for a polymer electrolyte fuel cell comprising a metal catalyst and an ion conductive polymer impregnated in the carbon fiber,
(i) on the conductive porous support, a step of electrolytic oxidation polymerization of a compound having an aromatic ring to form a fibril polymer;
(ii) firing the fibrillated polymer to form carbon fibers on the conductive porous support;
(iii) supporting a metal catalyst on the carbon fiber;
(iv) A solution obtained by dissolving an ion conductive polymer in a solvent on a carbon fiber supporting the metal catalyst, wherein more than 50% by mass of the solvent is water and the balance is isopropanol and / or n-propanol. And a step of applying a solution.

  In a preferred embodiment of the method for producing an electrode for a polymer electrolyte fuel cell of the present invention, the solution of the ion conductive polymer contains 60 to 80% by mass of the solvent.

  In the method for producing a polymer electrolyte fuel cell electrode according to the present invention, the ion conductive polymer solution preferably has a content of the ion conductive polymer of less than 5% by mass, and 2 to 4% by mass. More preferably it is.

  In the method for producing an electrode for a polymer electrolyte fuel cell of the present invention, the ion conductive polymer has at least one ion exchange group selected from the group consisting of sulfonic acid, carboxylic acid, phosphonic acid and phosphonous acid. Of these, a perfluorocarbon sulfonic acid polymer is particularly preferable.

  In addition, the polymer electrolyte fuel cell electrode of the present invention is manufactured by the above-described method, and the polymer electrolyte fuel cell of the present invention includes the electrode.

  According to the present invention, it is possible to provide an electrode for a polymer electrolyte fuel cell and a method for producing the same, in which performance deterioration is small even when air is used instead of oxygen as an oxidant gas, and performance is small. Also, a polymer electrolyte fuel cell having such an electrode and excellent in practicality can be provided.

<Electrode for polymer electrolyte fuel cell and method for producing the same>
Below, the electrode for solid polymer type fuel cells of the present invention and its manufacturing method are explained in detail. The method for producing a polymer electrolyte fuel cell electrode of the present invention comprises (i) a step of producing a fibrillated polymer by electrolytic oxidation polymerization of a compound having an aromatic ring on a conductive porous support; and (ii) ) Firing the fibrillated polymer to form carbon fibers on the conductive porous support; (iii) supporting the metal catalyst on the carbon fiber; and (iv) supporting the metal catalyst. And applying a solution obtained by dissolving an ion conductive polymer in a solvent to a carbon fiber, wherein the solvent is more than 50% by mass of water and the balance is isopropanol and / or n-propanol. According to the method, the conductive porous support, the carbon fiber disposed on the conductive porous support, the metal catalyst supported on the carbon fiber, and the carbon An ion conductive polymer impregnated in the fiber and It is possible to manufacture an electrode for a polymer electrolyte fuel cell comprising

  In the method for producing a polymer electrolyte fuel cell electrode of the present invention, carbon fibers carrying a metal catalyst are formed in steps (i), (ii) and (iii), and further, in step (iv), a metal is formed. By applying an ion conductive polymer-containing solution in which more than 50% by mass of the solvent is water to the carbon fiber on which the catalyst is supported, the ion conductive polymer-containing solution is prevented from penetrating deep into the carbon fiber, The ratio of the ion conductive polymer in the vicinity of the surface of the carbon fiber can be improved.

  In conventional ionic conductive polymer-containing solutions, 50% by mass of the solvent is water, so the affinity between the ionic conductive polymer-containing solution and the carbon fiber is high, and the ionic conductive polymer-containing solution penetrates deep into the carbon fiber. However, the ratio of the ion conductive polymer in the vicinity of the surface of the carbon fiber (that is, the portion of the carbon fiber on the solid polymer electrolyte membrane side) that is largely involved in proton conduction was low. On the other hand, by controlling the affinity between the ion conductive polymer-containing solution and the carbon fiber by increasing the ratio of water in the solvent of the ion conductive polymer-containing solution to more than 50% by mass, the ion conductive polymer is controlled. The penetration of the containing solution to the deep part of the carbon fiber is suppressed, and the proportion of the ion conductive polymer in the vicinity of the surface of the carbon fiber can be increased to facilitate proton conduction. Therefore, a polymer electrolyte fuel cell including an electrode manufactured by the method of the present invention has a small deterioration in performance even when air is used instead of oxygen as an oxidant gas, and is excellent in practicality.

  In the method for producing an electrode for a polymer electrolyte fuel cell of the present invention, in step (i), a compound having an aromatic ring is subjected to electrolytic oxidation polymerization on a conductive porous support to produce a fibril polymer. Here, as the conductive porous support to be used, any porous and conductive material may be used, and specific examples include carbon paper, porous carbon cloth, and the like. Among these, Carbon paper is preferred.

  Examples of the compound having an aromatic ring include a compound having a benzene ring and a compound having an aromatic heterocyclic ring. Here, as the compound having a benzene ring, aniline and aniline derivatives are preferable, and as the compound having an aromatic heterocyclic ring, pyrrole, thiophene and derivatives thereof are preferable. These compounds having an aromatic ring may be used singly or as a mixture of two or more.

In the electrolytic oxidation polymerization, it is preferable to mix an acid together with a raw material compound having an aromatic ring. In this case, the negative ion of the acid is taken into the fibril polymer synthesized as a dopant to obtain a fibril polymer excellent in conductivity. By using this fibril polymer, the conductivity of the carbon fiber is finally improved. Further improvement can be achieved. Here, examples of the acid mixed in the electrolytic oxidation polymerization include HBF ₄ , H ₂ SO ₄ , HCl, HClO _{4 and the} like. The acid concentration is preferably in the range of 0.1 to 3 mol / L, more preferably in the range of 0.5 to 2.5 mol / L.

In the step (i), in the solution containing the compound having an aromatic ring, the conductive porous support is immersed as a working electrode, the counter electrode is further immersed, and the oxidation potential of the compound having an aromatic ring between both electrodes Or an electric current having a condition sufficient to secure a voltage sufficient to polymerize the compound having an aromatic ring may be applied, and thereby the conductive porous support (working electrode) may be energized. A fibrillar polymer is formed. Here, as the counter electrode, a plate made of a highly conductive material such as stainless steel, platinum, or carbon, a porous support, or the like can be used. An example of a method for synthesizing a fibrillated polymer by this electrolytic oxidative polymerization method is as follows. A working electrode composed of a conductive porous support in an electrolytic solution containing a compound having an acid such as HCl and H ₂ SO ₄ and an aromatic ring, and A method of polymerizing and depositing a fibril-like polymer on the side of the working electrode comprising a conductive porous support by immersing a counter electrode and passing a current of 0.1 to 1000 mA / cm ² , preferably 0.2 to 100 mA / cm ² between both electrodes Etc. are exemplified. The fibrillar polymer is mainly generated on the surface facing the counter electrode of the working electrode made of a conductive porous support. Here, the concentration of the compound having an aromatic ring in the electrolytic solution is preferably 0.05 to 3 mol / L, and more preferably 0.25 to 1.5 mol / L. Moreover, in addition to the said component, you may add a soluble salt etc. to an electrolyte solution suitably in order to adjust pH.

  The fibril-like polymer obtained by electrolytic oxidation polymerization of the compound having an aromatic ring usually has a three-dimensional continuous structure, has a diameter of 30 to several hundred nm, preferably 40 to 500 nm, and has a length of 0.5. It is μm to 100 mm, preferably 1 μm to 10 mm.

  In the method for producing an electrode for a polymer electrolyte fuel cell of the present invention, in the step (ii), the fibrillated polymer is baked and carbonized to generate carbon fibers on the conductive porous support. In addition, before the step (ii), it is preferable that the fibrillated polymer is washed with a solvent such as water or an organic solvent and dried. Here, the drying method is not particularly limited, and examples thereof include a method using a fluidized bed drying device, an air dryer, a spray dryer, etc., in addition to air drying and vacuum drying.

  The firing conditions in the above step (ii) are not particularly limited, and may be set as appropriate so as to obtain optimum conductivity. Particularly, when high conductivity is required, the temperature is 500 to 3000 ° C., Preferably, baking is performed at 600 to 2800 ° C. for 0.5 to 6 hours. In the production method of the present invention, the firing step is preferably performed in a non-oxidizing atmosphere, and examples of the non-oxidizing atmosphere include a nitrogen atmosphere, an argon atmosphere, and a helium atmosphere. It can also be.

The carbon fiber usually has a three-dimensional continuous structure, has a diameter of 30 to several hundred nm, preferably 40 to 500 nm, has a length of 0.5 μm to 100 mm, preferably 1 μm to 10 mm, and has a surface resistance. 10 ⁶ to 10 ⁻² Ω, preferably 10 ⁴ to 10 ⁻² Ω. The carbon fiber has a residual carbon ratio of 90 to 20%, preferably 80 to 25%. Since the carbon fiber has a structure in which the entire carbon is three-dimensionally continuous, the carbon fiber has higher conductivity than the granular carbon.

  In the method for producing an electrode for a polymer electrolyte fuel cell of the present invention, a metal catalyst is supported on the carbon fiber in the step (iii). Here, as the metal catalyst supported on the carbon fiber, a noble metal is preferable, and Pt is particularly preferable. In the present invention, Pt may be used alone or as an alloy with another metal such as Ru. By using Pt as the noble metal, hydrogen can be oxidized with high efficiency even at a low temperature of 100 ° C. or lower. In addition, by using an alloy such as Pt and Ru, it is possible to prevent poisoning of Pt by CO and prevent a decrease in the activity of the catalyst. The particle size of the metal catalyst supported on the carbon fiber is preferably in the range of 0.5 to 20 nm, and the support rate of the metal catalyst is preferably in the range of 0.05 to 5 g with respect to 1 g of the carbon fiber. Here, the method for supporting the metal catalyst on the carbon fiber is not particularly limited, and examples thereof include an impregnation method, an electroplating method (electrolytic reduction method), an electroless plating method, and a sputtering method. .

In the method of the present invention, it is preferable to carry the metal catalyst on the carbon fiber by an electroplating method in which a current is applied in a pulsed manner. Here, the current application condition is the following formula (I):
Duty ratio = t ₁ / (t ₁ + t ₂ ) × 100 (I)
It is preferable that the duty ratio represented by [where t ₁ represents current application time (seconds) and t ₂ represents rest time (seconds)] be 2 to 20%. If the duty ratio in the pulse current is less than 2%, it takes a long time to satisfy the predetermined energized charge amount, which is not suitable for practical use, and the effect of improving the surface area of the metal catalyst is insufficient, while the duty ratio is 20 If it exceeds%, the effect of applying current in a pulsed manner is small, and the surface area of the supported metal catalyst cannot be sufficiently improved.

Dwell time in the electroplating (t ₂₎ is preferably set to 0.05 to 0.5 seconds. When the pause time (t ₂ ) is less than 0.05 seconds, the effect of applying the current in a pulsed manner is small, and the surface area of the supported metal catalyst cannot be sufficiently improved, while the pause time (t ₂ ) is 0.5. If it exceeds 2 seconds, it takes a total time to satisfy the predetermined energized charge amount, which is not suitable for practical use, and the effect of improving the surface area of the metal catalyst is insufficient.

In the electroplating, the current density is preferably in the range of 10 to 500 mA / cm ² , and the energization charge amount is preferably in the range of 0.1 to 5C. The application time (t ₁ ) is preferably selected so that the rest time (t ₂ ) is in the range of 0.05 to 0.5 seconds while the duty ratio is 2 to 20%. Furthermore, the number of pulses (number of cycles) in pulse plating is preferably selected as appropriate so as to be in the above-described range of the preferred energized charge amount.

  In the method for producing an electrode for a polymer electrolyte fuel cell of the present invention, in the step (iv), a solution obtained by dissolving an ion conductive polymer in a solvent on a carbon fiber carrying the metal catalyst, A solution is applied in which more than 50% by weight of water is water, preferably 60-80% by weight is water and the balance is isopropanol and / or n-propanol. When the proportion of water in the solvent of the ion conductive polymer-containing solution is 50% by mass or less, the affinity between the ion conductive polymer-containing solution and the carbon fiber is high, and the ion conductive polymer-containing solution penetrates deep into the carbon fiber, The proportion of the ion conductive polymer in the vicinity of the surface of the carbon fiber that is largely involved in proton conduction is reduced. In addition, from the viewpoint of further improving the ratio of the ion conductive polymer in the vicinity of the surface of the carbon fiber, the ion conductive polymer solution preferably contains 60% by mass or more of the solvent as water. From the viewpoint of solubility, the proportion of water in the solvent is preferably 80% by mass or less.

  In the ion conductive polymer solution, the content of the ion conductive polymer is preferably less than 5% by mass, and more preferably in the range of 2 to 4% by mass. If the content of the ion conductive polymer in the solution of the ion conductive polymer is 5% by mass or more, it tends to be difficult to control the weight and plane distribution of the applied ion conductive polymer. If the content is less than 2% by mass, the viscosity of the solution is low and it becomes difficult to control the weight and distribution of the ion conductive polymer to be applied.

In the step (iv), for example, a solution is prepared by dissolving an ion conductive polymer in a solvent composed of water and isopropanol and / or n-propanol, and the solution of the ion conductive polymer is supported on a metal catalyst. This can be carried out by applying it to carbon fiber. The coating amount of the ion-conducting polymer is preferably in the range of ^{0.01mg / cm 2 ~4.0mg / cm 2} , the coating amount is less than 0.01 mg / cm ² of ion-conductive polymers, proton conductivity decreases On the other hand, if it exceeds 4.0 mg / cm ² , the gas permeability decreases and flooding is likely to occur.

  In addition, after the application of the ion conductive polymer-containing solution, it is preferable to dry to remove the solvent. The drying method is not particularly limited, but is not limited to air drying, vacuum drying, fluid bed drying. Examples thereof include a method using an apparatus, an air dryer, a spray dryer and the like. Examples of the ion conductive polymer include polymers having an ion exchange group such as sulfonic acid, carboxylic acid, phosphonic acid, and phosphonous acid. The polymer may or may not contain fluorine. Examples of the ion conductive polymer include perfluorocarbon sulfonic acid polymers such as Nafion (registered trademark).

The electrode for a polymer electrolyte fuel cell of the present invention produced by the above-described method includes a conductive porous support, a carbon fiber disposed on the conductive porous support, and a carbon fiber on the carbon fiber. It comprises a supported metal catalyst and an ion conductive polymer impregnated in the carbon fiber, and can be used as a fuel electrode or an air electrode (oxygen electrode). Here, in the polymer electrolyte fuel cell electrode, the carbon fiber supported with the metal catalyst and impregnated with the ion conductive polymer functions as a catalyst layer, and the conductive porous support is supplied to the catalyst layer with hydrogen. It functions as a gas diffusion layer for supplying a fuel such as gas or an oxygen-containing gas such as oxygen or air, and as a current collector for transferring generated electrons. The thickness of the catalyst layer is not particularly limited, but is preferably in the range of 0.1 to 100 μm. The amount of the metal catalyst supported on the catalyst layer is determined by the loading rate and the thickness of the catalyst layer, and is preferably in the range of 0.001 to 0.8 mg / cm ² .

<Solid polymer fuel cell>
Next, a polymer electrolyte fuel cell using the polymer electrolyte fuel cell electrode of the present invention will be described with reference to FIG. The illustrated polymer electrolyte fuel cell includes a membrane electrode assembly (MEA) 1 and separators 2 located on both sides thereof. The membrane electrode assembly (MEA) 1 includes a solid polymer electrolyte membrane 3, a fuel electrode 4A and an air electrode (oxygen electrode) 4B located on both sides thereof. In the fuel electrode 4A, a reaction represented by 2H ₂ → 4H ⁺ + 4e ⁻ occurs, the generated H ⁺ passes through the solid polymer electrolyte membrane 3 to the air electrode 4B, and the generated e ⁻ is taken out to the outside. Current. On the other hand, in the air electrode 4B, a reaction represented by O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O occurs, and water is generated. The fuel electrode 4 </ b> A and the air electrode 4 </ b> B include a catalyst layer 5 and a gas diffusion layer (conductive porous support) 6, and are disposed so that the catalyst layer 5 is in contact with the solid polymer electrolyte membrane 3.

  In the polymer electrolyte fuel cell of the present invention, an ion conductive polymer can be used as the solid polymer electrolyte membrane 3, and the ion conductive polymer includes a carbon fiber carrying the metal catalyst. What was illustrated as an ion conductive polymer which can be impregnated in can be used. Moreover, as the separator 2, the normal separator with which flow paths (not shown), such as fuel, air, and produced | generated water, were formed in the surface can be used.

  In the solid polymer fuel cell of the present invention, the catalyst layer 5 is formed by supporting a metal catalyst on carbon fibers and further applying an ion conductive polymer-containing solution to the carbon fibers. The catalyst layer 5 has a high proportion of ion conductive polymer on the side in contact with the solid polymer electrolyte membrane 3, and a proton conduction path is sufficiently formed by the ion conductive polymer. For this reason, the polymer electrolyte fuel cell of the present invention having the catalyst layer 5 is excellent in practicality even when air is used instead of oxygen as the oxidant gas, and the performance is small. Further, the solid polymer fuel cell of the present invention has a very large surface area of the metal catalyst in the catalyst layer 5, and the reaction of the electrochemical reaction at the three-phase interface between the solid polymer electrolyte membrane 3, the catalyst layer 5, and the gas. Since the field is very large, the power generation performance is greatly improved compared to the conventional one.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

(Example 1)
<Production of carbon fiber>
In an acidic aqueous solution containing aniline 0.5 mol / L and hydrochloric acid 1.0 mol / L, carbon paper (manufactured by Toray) was installed as the working electrode, carbon felt was installed as the counter electrode, and a constant of 20 mA / cm ² was established at 20 ° C. Electrolytic oxidation polymerization was carried out at a current for 140 seconds to deposit polyaniline on the working electrode. The obtained polyaniline was immersed in a 1.0 mol / L NaOH aqueous solution for 1 hour, washed thoroughly with pure water, and dried at 100 ° C. under reduced pressure. Further, the obtained polyaniline was heated together with carbon paper to 2300 ° C. in an Ar reduced pressure atmosphere over 5 hours, and held at that temperature for 1 hour for firing treatment. Then, it cooled to room temperature and took out the obtained baked material (carbon fiber).

<Platinum support>
Next, the fired product (carbon fiber) obtained above was placed as a working electrode in an aqueous solution obtained by dissolving 10 g of chloroplatinic acid hexahydrate together with carbon paper in 1 L of pure water, and further, white as a counter electrode. A gold-plated titanium plate was installed. Thereafter, a pulse current of 80 mA / cm ² was passed at room temperature, and platinum was supported on the carbon fiber. The pulse conditions were as follows: application time (on time): 0.005 seconds, rest time (off time): 0.1 seconds, and energization amount: 0.4 C / cm ² . Moreover, after energization was completed, it was sufficiently washed and dried. The platinum loading was calculated from the mass change and found to be 0.13 mg / cm ² .

<Production of MEA>
Next, the carbon paper with platinum-supported carbon fibers obtained as described above was punched out to a size of 50 mm square, and on the side where the platinum-supported carbon fibers were disposed, a Nafion (registered trademark) solution (Nafion: 3% by mass) , Isopropyl alcohol: 27% by mass, water: 70% by mass) were applied with a brush so that the whole was uniform. Next, the solvent was removed by drying at 100 ° C. for 10 minutes. Here, the Nafion coating amount after removing the solvent was adjusted to 0.15 mg / cm ² . Next, the two Nafion-coated platinum-supported carbon fibers / carbon paper were sandwiched with a Nafion 112 membrane and integrated by hot pressing to obtain a membrane electrode assembly (MEA).

<Fuel cell performance evaluation 1 (hydrogen / oxygen)>
The obtained membrane electrode assembly was incorporated into a test cell (EFC25-01SP) manufactured by Electrochemical Co., and a fuel cell was produced. The power generation characteristics of the obtained fuel cell were determined with a fuel gas (hydrogen) flow rate of 0.3 L / min, Measurement was performed under the conditions of a fuel gas humidification temperature of 80 ° C., an oxidizing gas (oxygen) flow rate of 0.3 L / min, an oxidizing gas humidification temperature of 80 ° C., and a cell temperature of 80 ° C. Table 1 shows the voltage at each current.

<Fuel cell performance evaluation 2 (hydrogen / air)>
The fuel cell power generation characteristics are as follows: fuel gas (hydrogen) flow rate 0.3L / min, fuel gas humidification temperature 80 ° C, oxidizing gas (air) flow rate 2.0L / min, oxidizing gas humidification temperature 75 ° C, cell temperature 80 ° C Measured with Table 1 shows the voltage at each current.

(Comparative Example 1)
Carbon fibers were produced in the same manner as in Example 1 and supported with platinum. Further, an MEA was produced in the same manner as in Example 1 except that a Nafion solution [DE521CS manufactured by Wako Pure Chemical Industries] consisting of 5% by mass of Nafion, 47.5% by mass of water, and 47.5% by mass of isopropyl alcohol was applied. The Nafion coating amount was 0.15 mg / cm ² . Using the obtained MEA, a fuel cell was assembled, and the power generation performance was evaluated under the same conditions as in Example 1. Table 2 shows the voltage at each current.

  From Table 1, the performance of the fuel cell of Example 1 provided with an electrode prepared by applying a Nafion solution having a water content of 70% by mass is reduced even when air is used instead of oxygen as the oxidant gas. It can be seen that it is small and practical. On the other hand, from Table 2, the fuel cell of Comparative Example 1 having an electrode prepared by applying a Nafion solution having a water content of 42.5% by mass has a large performance degradation when air is used as the oxidant gas. I understand.

It is sectional drawing of an example of the polymer electrolyte fuel cell of this invention.

Explanation of symbols

1 Membrane electrode assembly (MEA)
2 Separator 3 Solid polymer electrolyte membrane 4A Fuel electrode 4B Air electrode (oxygen electrode)
5 Catalyst layer 6 Gas diffusion layer (conductive porous support)

Claims (8)

A conductive porous support, carbon fibers disposed on the conductive porous support, a metal catalyst supported on the carbon fibers, and an ion conductive polymer impregnated in the carbon fibers; A method for producing an electrode for a polymer electrolyte fuel cell comprising:
(i) on the conductive porous support, a step of electrolytic oxidation polymerization of a compound having an aromatic ring to form a fibril polymer;
(ii) firing the fibrillated polymer to form carbon fibers on the conductive porous support;
(iii) supporting a metal catalyst on the carbon fiber;
(iv) A solution obtained by dissolving an ion conductive polymer in a solvent on a carbon fiber supporting the metal catalyst, wherein more than 50% by mass of the solvent is water and the balance is isopropanol and / or n-propanol. And a step of applying a solution. A method for producing an electrode for a polymer electrolyte fuel cell, comprising:   2. The method for producing an electrode for a polymer electrolyte fuel cell according to claim 1, wherein 60 to 80% by mass of the solvent of the ion conductive polymer is water.   The method for producing an electrode for a polymer electrolyte fuel cell according to claim 1, wherein the content of the ion conductive polymer in the solution of the ion conductive polymer is less than 5% by mass.   The method for producing an electrode for a polymer electrolyte fuel cell according to claim 3, wherein the content of the ion conductive polymer in the ion conductive polymer solution is 2 to 4% by mass.   2. The polymer electrolyte fuel according to claim 1, wherein the ion conductive polymer has at least one ion exchange group selected from the group consisting of sulfonic acid, carboxylic acid, phosphonic acid and phosphonous acid. Manufacturing method of battery electrode.   6. The method for producing an electrode for a polymer electrolyte fuel cell according to claim 5, wherein the ion conductive polymer is a perfluorocarbon sulfonic acid polymer.   An electrode for a polymer electrolyte fuel cell produced by the method according to claim 1.   A polymer electrolyte fuel cell comprising the electrode for a polymer electrolyte fuel cell according to claim 7.

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