JP2007157637A - Reinforcement type solid polymer electrolyte membrane and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reinforcement type solid polymer electrolyte membrane B allowing a large quantity of electrolyte resin 4 to be filled in pores even for a porous reinforcing membrane 1 having a further small pore diameter, and thereby capable of securing large mechanical strength while securing desired proton conductivity and gas impermeability, and to provide its manufacturing method. <P>SOLUTION: An electrolyte solution 5 obtained by dissolving the electrolyte resin 4 in an aprotic polarity solvent 3a is impregnated into the porous reinforcement membrane 1. This reinforcement type solid polymer electrolyte membrane B is prepared by evaporating the aprotic polarity solvent 3a by drying it after the impregnation. Even if the porous reinforcing membrane has a pore diameter not greater than 0.45 μm, sufficient impregnation into the pores of the electrolyte resin becomes possible. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a reinforced solid polymer electrolyte membrane used in a solid polymer fuel cell and a method for producing the same.

  A polymer electrolyte fuel cell (PEFC) is known as one of the fuel cells. As shown in FIG. 3, the polymer electrolyte fuel cell includes a membrane electrode assembly (MEA) 15 as a main component, and a separator 14 having a fuel (hydrogen) gas flow path and an air gas flow path, 14, one fuel cell 20 called a single cell is formed. The membrane electrode assembly 15 has an anode side electrode catalyst layer 12a and a diffusion layer 13a laminated on one side of an electrolyte membrane 11 which is an ion exchange membrane, and a cathode side electrode catalyst layer 12b and a diffusion layer 13b on the other side. It has a laminated structure.

  The electrolyte membrane 11 constituting the membrane electrode assembly 15 is required to have high proton conductivity, high mechanical strength, and gas impermeability. On the other hand, an electrolyte membrane used in a polymer electrolyte fuel cell is usually about 10 μm to 200 μm in thickness and does not have sufficient strength. Therefore, as described in Patent Document 1, a porous PTFE membrane is used. A porous reinforcing membrane having pores is used and impregnated with an electrolyte solution. As an electrolyte solution, as described in Patent Document 2, a solution obtained by dissolving an electrolyte in water and 1-propanol or ethanol alcohol solvent, which is a protonic polar solvent, is usually used.

In Patent Document 3, as an electrolyte solution, a polymer electrolyte solution in which perfluorocarbon sulfonic acid resin as an electrolyte is dissolved in a solvent containing a polar solvent having a hydrophilic property and a high boiling point property, and a porous membrane are impregnated with the polymer electrolyte solution The gas diffusion electrode is described.
JP-A-8-329962 JP 2003-249244 A JP 2004-164854 A

  Improvement of the durability of the solid polymer electrolyte membrane in a fuel cell is an issue, and it is required to further increase the mechanical strength as one of means for improving the durability. In a reinforced solid polymer electrolyte membrane in which a porous reinforcing membrane is impregnated with an electrolyte resin, in order to obtain high strength, it is better that the porosity (porosity) is small when the materials are the same. On the other hand, the proton conductivity and gas impermeability of the reinforced solid polymer electrolyte membrane depend on the amount of electrolyte resin impregnated in the pores of the porous reinforced membrane. Therefore, when trying to obtain a reinforced solid polymer electrolyte membrane having equivalent proton conductivity and gas impermeability, if more electrolyte resin is filled in pores with a small diameter, The electrolyte membrane has a higher mechanical strength and the durability is improved.

  In a conventional reinforced solid polymer electrolyte membrane having, for example, a porous PTFE membrane as a reinforcing layer, the electrolyte solution to be impregnated generally contains water and an alcohol such as 1-propanol or ethanol as described above. A solvent using a system solvent (protic polar solvent) is used. Alcohol-based solvents have the advantage of being easily wetted by porous reinforcing membranes such as PTFE. However, since the boiling point is as low as 100 ° C. or less and volatilizes easily, there is a difference in the substitution rate of the electrolyte resin within the pores of the porous reinforcing membrane. Arise. Therefore, when the pore diameter is small, the electrolyte resin cannot be sufficiently impregnated in the pores. Therefore, as long as an alcohol-based solvent is used, it is necessary to increase the pore size in order to obtain the required proton conductivity (currently, porous PTFE membranes having a pore size exceeding 0.45 μm are porous reinforcing membranes). As a result, it was not sufficient in terms of improving the mechanical strength. It was also difficult to obtain sufficient gas impermeability.

  The present invention has been made in view of the above circumstances, and allows a large amount of electrolyte resin to be filled in pores even for a porous reinforcing membrane having a smaller pore diameter. Accordingly, it is an object of the present invention to provide a reinforced solid polymer electrolyte membrane and a method for producing the same, which can ensure high mechanical strength while ensuring required proton conductivity and gas impermeability.

  The present inventors have conducted many experiments and studies to solve the above-mentioned problems, and are described in Patent Document 3 instead of an alcohol solvent (protic polar solvent) as a solvent for dissolving the electrolyte resin. When an electrolyte solution is made using an aprotic polar solvent having a high boiling point and impregnated in a porous reinforcing membrane such as a porous PTFE membrane, even if the pore diameter is sufficiently small, It has been found that the electrolytic resin can be almost completely filled in the pores, and a reinforced solid polymer electrolyte membrane having a large mechanical strength can be obtained.

  The present invention is based on the above knowledge, and a method for producing a reinforced solid polymer electrolyte membrane having a porous reinforcing membrane according to the present invention is obtained by dissolving an electrolyte resin in an aprotic polar solvent, A porous reinforcing membrane is impregnated with an electrolyte solution in which a resin is dissolved.

  In the method according to the present invention, an aprotic polar solvent is used, and the dispersibility of the electrolyte resin in the electrolyte solution is improved. The boiling point of the aprotic polar solvent is generally higher than that of the alcohol solvent. For this reason, when the porous reinforcing membrane is impregnated with the electrolyte solution, the volatilization rate of the solvent is suppressed, so that substitution and impregnation of the electrolyte resin into the pores of the porous reinforcing membrane proceeds smoothly. Therefore, even when the pore diameter is small, a desired amount of electrolyte resin can be filled therein. As a result, a reinforced solid polymer electrolyte membrane having high mechanical strength while having predetermined proton conductivity and gas non-diffusibility can be obtained.

  According to the method of the present invention, as shown in the following examples, even a porous reinforcing membrane having a pore diameter of 0.45 μm or less, for example, 0.1 to 0.2 μm, can sufficiently withstand practical use. A reinforced solid polymer electrolyte membrane having proton conductivity can be produced.

  In the present invention, the porous reinforcing membrane may be a polyethylene porous membrane, a polypropylene porous membrane, a polyimide porous membrane, a polytetrafluoroethylene (PTFE) porous membrane, etc. Porous PTFE membranes are particularly preferred for reasons of high and greater mechanical strength.

In the present invention, examples of the aprotic polar solvent include dimethyl sulfoxide (CH ₃ —S (═O) —CH ₃ : DMSO), dimethylformamide (HC—═O) N (CH ₃ ) ₂ having a high boiling point: DMF), among others, a porous reinforcing layer having a boiling point as high as 189 ° C. and pores with smaller diameters (pore diameters of 0.1 to 0.2 μm as shown in the following examples) On the other hand, dimethyl sulfoxide (DMSO) is particularly preferable because it can be filled with a desired electrolyte resin.

  In the present invention, as the electrolyte resin, a conventionally known polymer electrolyte having an ion exchange group and soluble in a solvent can be appropriately used. An example is Nafion solution manufactured by DuPont, USA. In use, an electrolyte solution having an appropriate solid content by adding the above-mentioned aprotic polar solvent to a solution obtained by evaporating the solution from a commercially available electrolyte solution and increasing the solid content to, for example, about 70 to 90%. And

  According to the present invention, as a reinforced solid polymer electrolyte membrane suitably manufactured by the above-described manufacturing method, a porous reinforcing membrane having a pore diameter of 0.45 μm or less (excluding 0) is impregnated with an electrolyte resin. A featured reinforced solid polymer electrolyte membrane is also disclosed. Preferably, the porous reinforcing membrane is a porous PTFE membrane. In this reinforced solid polymer electrolyte membrane, the porous reinforcing membrane is impregnated with an electrolyte solution in which an electrolyte resin is dissolved in an aprotic polar solvent as described above, and then dried to drive off the aprotic polar solvent. Can be obtained.

  The present invention will be further described with reference to the drawings. FIG. 1a schematically illustrates a production process of a reinforced solid polymer electrolyte membrane A according to a conventional production method, and FIG. 1b illustrates a reinforced solid polymer electrolyte membrane B produced by the production method according to the present invention. The process is schematically explained. In FIG. 1 a, 1 is a porous reinforcing membrane such as a porous PTFE membrane, and has a large number of pores 2 having an average diameter of about 0.45 μm or less, for example. When the porosity is the same, the porous membrane having smaller diameter pores has higher mechanical strength than the porous membrane having larger diameter pores. 5 is an electrolyte solution in which an electrolyte resin is dissolved in a protic polar solvent 3 such as water + alcohol solvent.

  The porous reinforcing membrane 1 is impregnated with the electrolyte solution 5 and the electrolyte resin 4 is filled in the pores 2. However, as described above, the alcohol solvent has a boiling point as low as 100 ° C. or less and easily volatilizes. In addition, since there is a difference in the substitution rate of the electrolyte resin 4 in the pores 2 of the porous reinforcing membrane 1, in the case of the porous reinforcing membrane 1 in which the diameter of the pores 2 is about 0.45 μm or smaller, The pores 2 cannot be sufficiently impregnated with the electrolyte resin 4.

  The reinforced solid polymer electrolyte membrane A is formed by drying and drying the solvent 3, but the filling amount of the electrolyte resin 4 in the pores 2 is insufficient and the mechanical strength is satisfactory. However, satisfactory proton conductivity and gas impermeability cannot be obtained.

  In the production method according to the present invention shown in FIG. 1b, an aprotic polar solvent 3a (for example, DMSO, DMF) having a high boiling point of, for example, 150 ° C. or higher is used, and the electrolyte resin 4 in the electrolyte solution 5a is used. The dispersibility of is improved. In the experiments by the present inventors, swelling of the reinforcing film 1 itself was also observed. Therefore, when the porous reinforcing membrane 1 is impregnated in the electrolyte solution 5a, the volatilization rate of the solvent 3a is suppressed, so that substitution and impregnation of the electrolyte resin 4 into the pores 2 proceed smoothly.

  The reinforced solid polymer electrolyte membrane B is formed by drying and evaporating the solvent 3a. However, the electrolyte resin 4 is sufficiently filled in the pores 2 and maintains a desired mechanical strength. However, satisfactory proton conductivity and gas impermeability can be obtained.

Hereinafter, the present invention will be described by way of examples.
[Example 1]
Nafion DE2020 (trade name) solution (side chain terminal H type) EW value 1100, solid content 20% is evaporated to water and alcohol as a solvent by an evaporator and the solid content is increased to 70% to 90%. This is because if the solvent is completely volatilized, it cannot be re-solutionized.

  Dimethyl sulfoxide (hereinafter abbreviated as DMSO), which is an aprotic polar solvent, was added to the Nafion solution having a solid content of about 80%, and adjusted to a solid content of 15% to obtain an electrolyte solution.

  As the porous PTFE reinforcing membrane, a PTFE porous membrane manufactured by Sumitomo Electric Industries, a pore diameter of 0.1 μm, a porosity of 60%, and a membrane pressure of 30 μm was used. After 2 ml of the electrolyte solution was poured into a glass petri dish and uniformly spread, a porous PTFE reinforcing membrane cut to 5 cm × 5 cm was placed thereon, and further 2 ml of the same electrolyte solution was poured onto the glass petri dish to uniformly extend. It was dried in a dryer at a temperature of 140 ° C. for 1 hour to obtain a reinforced fixed polymer electrolyte membrane.

[Example 2]
The same electrolyte solution was prepared by adding DMSO to a Nafion DE2020 solution (side chain terminal H type) EW value of 1100, solid content of 20%, and solid content of 20%, and mixing to a solid content of 15%. Thereafter, in the same manner as in Example 1, a reinforced fixed polymer electrolyte membrane was obtained.

[Example 3]
The same electrolyte solution was prepared by adding DMSO to a Nafion DE2020 solution (side chain terminal H type) EW value of 1100, solid content of 20%, and solid content of 20%, and mixing to a solid content of 15%.

  As the porous PTFE reinforcing membrane, a PTFE porous membrane manufactured by Sumitomo Electric Industries, a pore diameter of 0.45 μm, a porosity of 80%, and a membrane pressure of 30 μm was used. After 2 ml of the electrolyte solution was poured into a glass petri dish and uniformly spread, a porous PTFE reinforcing membrane cut to 5 cm × 5 cm was placed thereon, and further 2 ml of the same electrolyte solution was poured onto the glass petri dish to uniformly extend. It was dried in a dryer at a temperature of 140 ° C. for 1 hour to obtain a reinforced fixed polymer electrolyte membrane.

[Comparative Example 1]
The same Nafion DE2020 solution (side chain terminal H type) EW value 1100 as in Example 1 was added to a solid content of 20% so that the solid content was 15% with 1-propanol and mixed to prepare an electrolyte solution. Using the solution, a reinforced fixed polymer electrolyte membrane was obtained in the same manner as in Example 1 below.

[Comparison test]
[Test 1] Conductivity test Using each of the reinforced fixed polymer electrolyte membranes in Examples 1 and 2 and Comparative Example 1, the conductivity in a saturated water-containing state was measured. The results are shown in Table 1.

  As shown in Table 1, the reinforced fixed polymer electrolyte membranes of Examples 1 and 2 showed higher conductivity than that of Comparative Example 1 while using the same porous PTFE reinforcing membrane. In the reinforced fixed polymer electrolyte membrane produced by the method of the present invention, it can be seen that the impregnation property of the electrolyte resin into the pores of the reinforced membrane is improved.

[Test 2] Strength test The reinforced fixed polymer electrolyte membrane of Example 2 and the reinforced fixed polymer electrolyte membrane of Example 3 were subjected to a stress-elongation test under the same conditions. The results are shown in FIG. In FIG. 2, the curve P1 is that of the reinforced fixed polymer electrolyte membrane of Example 2, and the curve P2 is that of the reinforced fixed polymer electrolyte membrane of Example 3.

  As shown in FIG. 2, even though the thickness of the reinforcing membrane is the same (30 μm), the reinforced fixed polymer electrolyte membrane of Example 2 having a pore size of 0.1 μm has a pore size of 0.45 μm. The mechanical strength is improved as compared with the reinforced fixed polymer electrolyte membrane of Example 3.

  From this and the result of Test 1, according to the production method according to the present invention that can satisfactorily impregnate the electrolyte resin even in pores with smaller diameters, mechanical strength, proton conductivity, gas impermeability It is shown that a reinforced fixed polymer electrolyte membrane satisfying both of the above can be obtained.

FIG. 1A schematically illustrates a manufacturing process of a reinforced solid polymer electrolyte membrane according to a conventional manufacturing method (FIG. 1a), and schematically illustrates a process of manufacturing a reinforced solid polymer electrolyte membrane according to the manufacturing method of the present invention. FIG. 1B is an explanatory diagram. The stress-elongation curve figure of two reinforcement type | mold fixed polymer electrolyte membranes manufactured by this invention. The figure which shows an example of a polymer electrolyte fuel cell.

Explanation of symbols

  A, B ... reinforced solid polymer electrolyte membrane, 1 ... porous PTFE membrane (reinforced membrane), 2 ... pore, 3 ... protic polar solvent, 3a ... aprotic polar solvent, 4 ... electrolyte resin, 5, 5a ... electrolyte solution

Claims (6)

  A method for producing a solid polymer electrolyte membrane having a porous reinforcing membrane, wherein an electrolyte resin is dissolved in an aprotic polar solvent, and then the porous reinforcing membrane is impregnated with an electrolyte solution in which the electrolyte resin is dissolved A method for producing a reinforced solid polymer electrolyte membrane, comprising:   The method for producing a reinforced solid polymer electrolyte membrane according to claim 1, wherein a porous reinforcing membrane having a pore diameter of 0.45 µm or less is used as the porous reinforcing membrane.   The method for producing a reinforced solid polymer electrolyte membrane according to claim 2, wherein the porous reinforcing membrane is a porous PTFE membrane.   The method for producing a reinforced solid polymer electrolyte membrane according to any one of claims 1 to 3, wherein the aprotic polar solvent is dimethyl sulfoxide (DMSO) or dimethylformamide (DMF).   A reinforced solid polymer electrolyte membrane, wherein a porous reinforcing membrane having a pore diameter of 0.45 μm or less (excluding 0) is impregnated with an electrolyte resin.   6. The reinforced solid polymer electrolyte membrane according to claim 5, wherein the porous reinforcing membrane is a porous PTFE membrane.

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