JP5333724B2 - Manufacturing method of electrolyte membrane for fuel cell - Google Patents

Description

  The present invention relates to a method for producing an electrolyte membrane for a fuel cell. More specifically, an electrolyte membrane for a fuel cell including a hydrolysis step of converting an F-type electrolyte membrane (a membrane of an electrolyte precursor not showing proton conductivity) into an H-type electrolyte membrane (an electrolyte membrane showing proton conductivity). It relates to a manufacturing method.

When manufacturing an electrolyte membrane for a fuel cell, there is a step of activating the F-type electrolyte membrane before using it as a proton conductive material. In that process, it is necessary to convert the precursor group -SO ₂ F (sulfone fluorine group) of the F-type electrolyte membrane into the ionic group -SO ₃ H (sulfonic acid group) of the H-type electrolyte membrane material. The activation of the type electrolyte membrane has been performed by first reacting the F type electrolyte membrane with an alkaline aqueous solution composed of a mixture of a strong alkaline agent and water, and then reacting with an acidic solution.

For example, Patent Document 1 proposes a conventional manufacturing method for converting an F-type electrolyte membrane into an H-type electrolyte membrane. Hereinafter, in particular, a hydrolysis process will be described in the conventional manufacturing method according to the flow of FIG. As shown in FIG. 5, in this manufacturing method, the —SO ₂ F group of the electrolyte polymer forming the F-type electrolyte membrane precursor 1 is first converted into —SO ₃ Na group by hydrolysis. Therefore, the sodium hydroxide aqueous solution (strong alkali aqueous solution) 2A and 2K are apply | coated to the F type electrolyte membrane 1 ((1-b) of the flow of (1)). Alternatively, sodium hydroxide powder (strong alkali powder) 2A ′ and 2K ′ are applied to the F-type electrolyte membrane 1 ((2-b) in the flow (2)).
JP 2008-78091 A

However, the F-type electrolyte membrane contains fluorine and therefore exhibits water repellency. Therefore, in the flow (1) shown in FIG. 1 (1-c), the sodium hydroxide solutions 2A and 2K are repelled on the surface of the F-type electrolyte membrane and become droplets 3A and 3K. Alternatively, in the flow (2) shown in FIGS. 2 (2-c) and (2-d), the sodium hydroxide powder deliquated and dropped 2a and 2k are repelled on the surface of the F-type electrolyte membrane and 3A '3K'. These droplets 3A, 3K and 3A ′, 3K ′ are difficult to react with the surface of the F-type electrolyte membrane, or even when reacted, unevenness occurs and the reaction becomes non-uniform. After this, even if sodium hydroxide is exposed to the F-type electrolyte membrane, for example, when sodium hydroxide is exposed to the F-type electrolyte membrane, the sodium hydroxide penetrates into the F-type electrolyte membrane without being uniform. As a result, the F-type electrolyte membrane becomes a non-uniform H-type electrolyte membrane throughout, and a homogeneous H-type electrolyte membrane is not produced.
In view of such circumstances, an object of the present invention is to produce a uniform (homogeneous) H-type electrolyte membrane from the F-type electrolyte membrane.

(Aspect of the Invention)
Hereinafter, embodiments of the invention will be shown and described.
(1) Hydrolysis in which at least a surface layer portion of the F-type electrolyte membrane is hydrolyzed by adding an alcohol to the F-type electrolyte membrane and adding alcohol to a strong alkaline agent and water, and further applying or impregnating a mixed solution containing the F-type electrolyte resin. A vapor exposure step in which the F-type electrolyte membrane after the hydrolysis step is exposed to water vapor and uniformly hydrolyzed toward the inside of the F-type electrolyte membrane; and the F-type electrolyte membrane after the vapor exposure step An acid treatment step of converting the acid to an H-type electrolyte membrane, and a method for producing an electrolyte membrane for a fuel cell.

  According to this section, an F-type electrolyte membrane (a precursor membrane of an H-type electrolyte membrane; the same applies hereinafter) and a mixed solution obtained by adding an alcohol to an aqueous solution of a strong alkali agent are reacted by coating or impregnation. At least the surface layer of the type electrolyte membrane is hydrophilized and hydrolyzed. This hydrophilization mainly utilizes the property that the —OH group of the alcohol exhibits hydrophilicity. Therefore, an aqueous solution of a strong alkali agent or sodium hydroxide powder liquefied by deliquescence on the surface layer portion of the hydrophilized F-type electrolyte membrane is not repelled as in the prior art. Thereafter, when the F-type electrolyte membrane is dried in order to remove alcohol from the F-type electrolyte membrane by natural drying and the surface layer portion is exposed to water vapor, the entire surface layer portion is uniformly wetted. Water vapor spreads uniformly toward the inside.

  As a result, even in the next vapor exposure step, the strong alkaline aqueous solution easily penetrates uniformly without being unevenly distributed to the inside of the F-type electrolyte membrane, and further, water is uniformly added toward the inside of the F-type electrolyte membrane. Decomposition takes place. Thereafter, by subjecting the F-type electrolyte membrane to acid treatment, it is possible to finally produce an H-type electrolyte membrane in which the entire membrane has homogeneous proton conductivity.

  Thus, a fuel cell including an H-type electrolyte membrane obtained by the production method according to the present invention, such as a polymer electrolyte fuel cell (hereinafter abbreviated as “PEFC”), has proton conductivity. However, it is improved compared to the conventional one, and more stable power generation performance is demonstrated.

The “F-type electrolyte membrane” is a membrane of a fluorine-based solid polymer electrolyte membrane precursor made of a perfluorosulfonic acid precursor polymer. For example, Nafion (trade name) manufactured by DuPont, Dow Chemical (trade name) by Dow Chemical, Flemion (trade name) by Asahi Glass Co., and Aciplex (trade name) by Asahi Kasei Co., Ltd. are “F-type electrolyte membranes”. Applicable.
As the “F-type electrolyte membrane”, a reinforced F-type electrolyte membrane obtained by impregnating an electrolyte resin into a porous reinforcing membrane made porous by stretching in the surface direction can also be used. By using a reinforced electrolyte membrane, the strength of the electrolyte membrane is inherently fragile because it is a thin film, but the strength can be pre-applied to the electrolyte membrane, and manufacturing of an electrolyte membrane with improved durability Is also possible.

(2) the mixed solution, method for manufacturing a fuel cell electrolyte membrane according to further comprising the F-type electrolyte resin (1) (claim 1).
According to this section, an F-type electrolyte resin is further added to the mixed solution of (1), and the mixed solution obtained by dissolving it is applied or impregnated to the F-type electrolyte membrane or the F-transfer MEA described later. After the reaction by, for example, the whole is dried, for example, a resin layer containing a strong alkali component of sodium hydroxide is formed. Next, by exposing the F-type electrolyte membrane on which the resin layer is formed or the F-transfer MEA to vapor, the sodium hydroxide in the electrolyte resin layer penetrates into the inside of the membrane, and the hydrolysis is uniformly performed inside the membrane. To be At this time, sodium hydroxide not only penetrates into the inside of the membrane but also elutes into the resin layer on the surface layer of the membrane, so that many fine pores are formed in the resin layer.
Furthermore, in this section, by utilizing this phenomenon, for example, by changing the concentration of sodium hydroxide mixed with the F-type electrolyte resin , the size and number of pores of the surface resin layer can be controlled. it can. In addition, the electrolyte membrane in which many fine pores are formed has a higher moisture content than the conventional one. This is because a large number of fine pores serve as capillaries to provide a capillary phenomenon. As a result, it is possible to prevent the electrolyte membrane from losing proton conductivity due to dry-up, so that the fuel cell including the electrolyte membrane stably exhibits power generation performance and also improves its durability. It becomes like this.

(3) the F-type electrolyte membrane is characterized by an electrolyte membrane for a F-type transfer membrane electrode assembly method for manufacturing a fuel cell electrolyte membrane according to (2) (Claim 2).

  In this section, “F-type electrolyte membrane” of the present invention includes not only a literal F-type electrolyte membrane, but also a so-called F-transfer membrane electrode joint in which a catalyst layer is formed into a sheet and transferred to the F-type electrolyte membrane by hot pressing. The body (hereinafter referred to as "F transfer MEA" ("MEA" stands for Membrane Electrode Assembly)). The catalyst layer of the F transfer MEA is a layer that three-dimensionally includes a large number of catalyst-carrying particles (for example, platinum-carrying carbon particles) in the F-type electrolyte membrane, and there are many voids (voids) between the particles. Therefore, the above mixed solution, water vapor, and acid solution easily pass through and permeate the layer through these voids, so that they can easily come into contact with the F-type electrolyte membrane.

(4) The method for producing an electrolyte membrane for a fuel cell according to any one of (2) and (3), wherein the water vapor is superheated water vapor (Claim 3) .

  This section illustrates that the water vapor of (1) is superheated water vapor. According to the superheated steam, the F-type electrolyte membrane and the F-transfer MEA can be rapidly heated with high-temperature steam at or above the saturated water-containing state of the atmosphere in the processing chamber. In this high-temperature steam state, it is possible to create an oxygen-free or low-oxygen state at normal pressure by expelling air from the atmosphere, so that the metal electrode catalyst represented by platinum deteriorates due to oxidation. Can be prevented. In addition, superheated water vapor facilitates more rapid and uniform water penetration into the F-type electrolyte membrane and F-transfer MEA while facilitating quicker and more uniform water penetration from the fine pores.

(5) the strong alkali agent is characterized by a sodium hydroxide method for manufacturing a fuel cell electrolyte membrane according to any one of (2) (4) (Claim 4).
This section exemplifies the material of the strong alkali agent. In this section, sodium hydroxide is exemplified, but the present invention is not limited to this. For example, potassium hydroxide can also be used. However, sodium hydroxide is industrially suitable because it is advantageous in terms of cost.

  According to the present invention, the F-type electrolyte membrane can be converted into a homogeneous H-type electrolyte membrane throughout. Furthermore, according to the present invention, it is possible to uniformly hydrolyze not only the surface of the F-type electrolyte membrane but also the inside of the F-type electrolyte membrane. Therefore, the proton conductivity (ion exchange performance) of the obtained H-type electrolyte membrane is improved. Especially when superheated steam is applied during the hydrolysis inside, when electrolyte resin is included in the mixed solution, it can be hydrolyzed near the porous glass transition temperature, and the physical properties of the electrolyte resin change, so that the electrolyte membrane Drying up can be prevented.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 and FIG. 2 are examples of embodiments for carrying out the invention, and in the drawings, the same reference numerals denote the same components.

<First Embodiment>
FIG. 1 is a conceptual diagram for explaining a flow of a manufacturing method of an electrolyte membrane for a fuel cell according to the first embodiment.
The first embodiment will be described below with reference to FIG.

Hydrolysis step: This step is a step of hydrolyzing the F-type electrolyte membrane by reacting the F-type electrolyte membrane with a mixed solution obtained by adding an alcohol to a strong alkali agent and water.
The F-type electrolyte membrane is preferably made of a fluorine-based polymer having a —SO ₂ F group represented by the aforementioned Nafion (trade name) manufactured by DuPont. Similarly, as described above, it may be an F-transfer MEA, or a reinforced electrolyte membrane in which a F-type electrolyte membrane is stretched in the surface direction to form a pore, and a reinforcing material is buried in the hole. Also good.
In this step, first, as shown in FIG. 1 (a), sodium hydroxide, water for application to both sides (anode side 4A and cathode side 4K) of a long F-type electrolyte membrane. Add a strong alkaline agent such as potassium oxide to water (preferably pure water), alcohol such as ethanol, methanol, 1-propanol, 2-propanol, 1-butanol, 1-pentanol, 1,1-dimethylpropanol. First, a mixed solution is prepared. At this time, for example, sodium hydroxide is adjusted from 7 mol to 11 mol per liter of the mixed solution.

Then, the mixed solution is put into a tank (not shown) of an application unit equipped with nozzles 20A and 20K, and as indicated by arrows, the nozzles 20A and 20K are applied to both sides of the F-type electrolyte membrane 1. The coating films 4A and 4K are formed in a uniform and thin film while being driven substantially parallel to the surface. At this time, for example, the mixed solution is cast from the nozzles 20 </ b> A and 20 </ b> K at room temperature and is naturally dried.
In this step, the anode-side coating film 4A is formed (including natural drying), then the F-type electrolyte film 1 is turned over, and the same treatment is performed to form the cathode-side coating film 4K ( Natural drying) (or vice versa).

FIGS. 1B and 1C conceptually show a state where the mixed solution is applied to both surfaces of the F-type electrolyte membrane 1 and then naturally dried. As shown in FIG. 1 (b), the F electrolyte membrane 1 is formed so that a mixed solution obtained by adding alcohol to a strong alkali agent and water has a mesh pattern indicated by reference numbers 4A ′ and 4K ′. It is impregnated uniformly over the surface to a certain depth. Furthermore, as shown in FIG. 1 (c), after natural drying (in some cases after heat drying), the hydrolyzed layer is shown at 4a, 4a ′ on the anode side, and at 4k, 4k ′ on the cathode side. Formed to be.
In the solution of only sodium hydroxide and water, the F-type electrolyte membrane 1 exhibits water repellency, so that the F-electrolyte membrane 1 is not impregnated so as to have a mesh pattern indicated by reference numbers 4A ′ and 4K ′. The solution will be repelled.
However, since alcohol is added to the strong alkali agent (sodium hydroxide) and water in this step, the solution (mixed solution) exhibits hydrophilicity to the F-type electrolyte membrane 1 due to the —OH group of the alcohol. Thus, the F-type electrolyte membrane 1 can be preferably uniformly penetrated.

  However, at the stage of this process, the hydrolyzed layer is impregnated with a uniform depth in the surface direction of the F-type electrolyte membrane 1, but is still in the depth direction of the membrane 1. It is not uniformly impregnated (the central layer in FIG. 1 corresponds to an unhydrolyzed layer). Therefore, the following vapor exposure process is required.

Vapor exposure step: This step is a step of exposing both surfaces of the F-type electrolyte membrane after the hydrolysis step to water vapor.
By this step, the hydrolyzed layer formed to some extent in the surface direction of the F-type electrolyte membrane 1 in the previous step can be formed evenly in the depth direction. As a result, the F electrolyte membrane 1 The whole is uniformly hydrolyzed. The water vapor may be pressurized. The water of steam is preferably pure water or distilled water. However, it is necessary to control the temperature below the melting temperature of the F-type electrolyte membrane 1.

  Furthermore, when superheated steam is used as the steam, the hydrolysis treatment in the depth direction of the F-type electrolyte membrane 1 can be performed more suitably. The reason is as described above, and the details are omitted here.

Acid treatment step: This step is a step of converting the F-type electrolyte membrane after the vapor exposure step into an H-type electrolyte membrane by acid treatment.
As shown in FIG. 1E, the F-type electrolyte membrane 10 (FIG. 1D) after the vapor exposure process uses a nitric acid solution having a concentration of about 1 mol / liter to 9 mol / liter, for example. Then, it is acid-treated and converted into a homogeneous H-type electrolyte membrane 11 throughout. Thereafter, the H-type electrolyte membrane 11 can be used as an electrolyte membrane for a fuel cell after being washed with water and dried.
In the first embodiment, an F-type electrolyte membrane is used as a starting material. However, if an F transfer MEA is used instead, an MEA for a fuel cell can be manufactured through the same process.

Second Embodiment
FIG. 2 is a conceptual diagram for explaining a flow of a method for manufacturing an electrolyte membrane for a fuel cell according to a second embodiment.
Hereinafter, the second embodiment will be described with reference to FIG.

Hydrolysis step: This step is a step of hydrolyzing the F-type electrolyte membrane by reacting the F-type electrolyte membrane with a mixed solution obtained by adding an alcohol or further an F-type electrolyte resin to a strong alkali agent and water. .

  As in the first embodiment, the starting material film may be an F-type electrolyte film or an F-transfer MEA, or the F-type electrolyte film is stretched in the surface direction to form a porous material and reinforced in the pores. It may be a reinforced electrolyte membrane filled with a material.

In this step, first, as shown in FIG. 2 (a), a strong alkali such as sodium hydroxide or potassium hydroxide is formed on both sides (anode side and cathode side) of a long F-type electrolyte membrane. First, a mixed solution in which an agent is mixed with water (preferably pure water) by adding an alcohol such as ethanol or methanol and further an F-type electrolyte resin is first prepared. At this time, similarly, sodium hydroxide is adjusted to 7 to 11 mol per liter of the mixed solution.
The electrolyte resin is made of a resin having the same components as the electrolyte membrane, and is preferably in the form of powder or liquid so that it can be easily dissolved in the mixed solution.

  Then, the mixed solution is put into a tank of an application means including nozzles 20A and 20K, and the nozzles 20A and 20B are formed at room temperature so that the application films 7A and 4B are formed in a uniform and thin film like the first embodiment. From 20K, the mixed solution is cast and air-dried.

2B and 2C conceptually show a state where a mixed solution is formed on both surfaces of the F-type electrolyte membrane 1 and is naturally dried. As shown in FIG. 2B, a mixed solution obtained by adding an alcohol to a strong alkali agent (for example, sodium hydroxide) and water has a mesh pattern indicated by reference numerals 7A ′ and 7K ′. F electrolyte membrane 1 is impregnated to some extent, and then, as shown in FIG. 2 (c), after natural drying, a hydrolyzed layer containing F type electrolyte resin is formed on the anode side by 7a, 7a ′, cathode It is formed on the side as indicated by 7k and 7k ′. Similarly, in the solution comprising sodium hydroxide, water, and electrolyte resin, the F-type electrolyte membrane 1 exhibits water repellency, so that the F electrolyte membrane is in a mesh pattern indicated by reference numbers 7A ′ and 7K ′. 1 is not impregnated and the solution is repelled. However, in this step, alcohol is added to the strong alkali agent (sodium hydroxide), water, and the F-type electrolyte resin , so that the F-type electrolyte membrane 1 becomes hydrophilic due to the —OH group of the alcohol. .

However, at the stage of this process, the hydrolyzed layer containing the F-type electrolyte resin is impregnated with a uniform depth in the surface direction of the F-type electrolyte membrane 1. It has not been impregnated uniformly in the vertical direction (the central layer 1 in FIG. 2 corresponds to an unhydrolyzed layer that does not contain the F-type electrolyte resin ).

Vapor exposure step: This step is a step of exposing both surfaces of the F-type electrolyte membrane after the hydrolysis step to water vapor.
The action and effect of this process is the first implementation including superheated steam (for example, normal pressure, 100% steam (oxygen-free and nitrogen-free), 100 ° C. to 180 ° C.). Since it is the same as the form, the description thereof is omitted.

However, in the second embodiment, unlike the first embodiment, since an F-type electrolyte resin is further added to the mixed solution, an amorphous electrolyte resin layer (hereinafter, “ 12A and 12B (refer to FIG. 2 (d)) are formed. The porous electrolyte resin layers 12A and 12B are made up of water generated on the cathode side, hydrogen gas containing a certain amount of water supplied to the anode side and the cathode side, and water of air gas (oxygen gas) by capillary action. It serves as a bypass means for absorbing and maintaining the swelling state of the electrolyte membrane (11), and can improve the water retention of the electrolyte membrane.

  Acid treatment step: Since this step is the same as in the first embodiment, the description thereof is omitted, but as shown in FIG. 2 (e), an H-type electrolyte having porous electrolyte resin layers 12A and 12B After being converted into a membrane 15, the H-type electrolyte membrane 15 can be used as an electrolyte membrane for a fuel cell after being washed with water and dried.

<Examples 1 and 2 and Comparative Example>
Example 1: Nafion, which is a F-type electrolyte membrane, is reacted with a mixed solution obtained by adding ethanol to sodium hydroxide, which is a strong alkali agent, and water to hydrolyze Nafion, and Nafion after the hydrolysis step Exposure to superheated steam at 200 ° C. with vapor pressure and 100% steam (oxygen-free and nitrogen-free conditions), and the Nafion after the steam exposure is acid-treated with a nitric acid solution having a concentration of 5 mol / liter to form an H-type electrolyte membrane. Using the electrolyte membrane obtained by the conversion, a single cell according to Example 1 (fuel cell; the same applies hereinafter) was produced by a conventional method.

Example 2: A mixed solution of Nafion, which is an F-type electrolyte membrane, sodium hydroxide, which is a strong alkaline agent, and water, and ethanol, and an electrolyte resin having a component equivalent to that of Nafion ( fluorine-based compound having —SO ₂ F groups) A single cell according to Example 2 was produced by a conventional method using an electrolyte membrane obtained by the same formulation as in Example 1 except that a solution in which a polymer F-type electrolyte resin) was dissolved was reacted. .

  Comparative Example: Using an electrolyte membrane obtained by the same formulation as in Example 1, except that Nafion, which is an F-type electrolyte membrane, was reacted with a solution comprising sodium hydroxide, which is a strong alkali agent, and water. A single cell according to a comparative example was produced by a conventional method.

  FIG. 3 compares the IV characteristics of the single-cell electrolyte membrane according to Example 1 and the IV characteristics of the single cell according to the comparative example (conventional method). 4 compares the IV characteristics of the single cell according to Example 2 and the IV characteristics of the electrolyte membrane for a fuel cell according to the same comparative example (conventional method).

  FIG. 3 shows that when the IV characteristics of Example 1 and the comparative example by the conventional method are compared, the fuel cell of Example 1 exhibits an IV characteristic superior to that of the conventional fuel cell. Also, referring to FIG. 4, when comparing the IV characteristics of Example 2 and the comparative example by the conventional method, the fuel cell of Example 2 exhibits the IV characteristics superior to the conventional fuel cell. I understood. Further, when the IV characteristics of Example 1 and Example 2 shown in FIGS. 3 and 4 are compared, the fuel cell of Example 2 exhibits better IV characteristics than the fuel cell of Example 1. I found out that

In summary, according to the production method of the present invention, it is possible to produce an H-type electrolyte membrane having a proton conductivity superior to that of the prior art, and further, an F-type electrolyte membrane with a strong alkali agent and water with alcohol. Furthermore, according to the manufacturing method according to the present invention including the step of hydrolyzing the F-type electrolyte membrane by reacting the mixed solution to which the F-type electrolyte resin is added, the H-type electrolyte membrane having further excellent proton conductivity It was found that can be manufactured.

  In addition, the manufacturing method of the electrolyte membrane for fuel cells of this invention is not limited to above-described embodiment, Of course, various changes can be added within the range which does not deviate from the summary of this invention.

FIG. 1 is a concept of a manufacturing flow for explaining the manufacturing method of the electrolyte membrane according to the first embodiment. FIG. 2 is a concept of a manufacturing flow for explaining the manufacturing method of the electrolyte membrane according to the second embodiment. FIG. 3 is a graph of the same characteristic for comparing the IV characteristics of the electrolyte membrane manufactured by Example 1 according to Embodiment 1 and the electrolyte membrane manufactured by the conventional technique (conventional method). is there. FIG. 4 is a graph of the same characteristic for comparing the IV characteristics of the electrolyte membrane manufactured by Example 2 according to Embodiment 2 and the electrolyte membrane manufactured by the conventional technique (conventional method). is there. FIG. 5 is a conceptual diagram of a manufacturing flow for explaining the prior art.

1: F type electrolyte membrane, 4A, 4K, 7A, 7K: Mixed solution, 9A, 9B: Water vapor, 10: F type electrolyte membrane after vapor exposure, 11, 15: H type electrolyte membrane

Claims (4)

A hydrolysis step of hydrolyzing at least the surface layer portion of the F-type electrolyte membrane by adding alcohol to the F-type electrolyte membrane and applying or impregnating a mixed solution containing the F-type electrolyte resin to the alcohol;
A steam exposure step in which the F-type electrolyte membrane after the hydrolysis step is exposed to water vapor, and the hydrolysis is uniformly performed toward the inside of the F-type electrolyte membrane ;
And an acid treatment step for converting the F-type electrolyte membrane after the vapor exposure step into an H-type electrolyte membrane, and a method for producing an electrolyte membrane for a fuel cell. The method for producing an electrolyte membrane for a fuel cell according to claim 1 , wherein the F-type electrolyte membrane is an electrolyte membrane for an F-type transfer membrane electrode assembly. The method for producing an electrolyte membrane for a fuel cell according to claim 1 or 2 , wherein the water vapor is superheated water vapor. The method for producing an electrolyte membrane for a fuel cell according to any one of claims 1 to 3 , wherein the strong alkali agent is sodium hydroxide.