JP3111407B1 - Active solid polymer electrolyte membrane in polymer electrolyte fuel cell and method for producing the same - Google Patents

Abstract

An active solid polymer electrolyte membrane capable of improving power generation performance is provided. SOLUTION: An active solid polymer electrolyte membrane 2 in a polymer electrolyte fuel cell is supported on a solid polymer electrolyte membrane 7 and a surface layer 8 thereof by ion exchange, and covers the entire surface layer 8. It comprises a plurality of noble metal catalyst particles 9 that are uniformly dispersed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active polymer electrolyte membrane for a polymer electrolyte fuel cell and a method for producing the same.

[0002]

2. Description of the Related Art Heretofore, as this type of active solid polymer electrolyte membrane, there has been known an active solid polymer electrolyte membrane in which a noble metal catalyst is supported on the surface of a solid polymer electrolyte membrane by a sputtering method.

[0003]

However, since the conventional noble metal catalyst is formed in layers, the conductivity of the generated hydrogen ions to the solid polymer electrolyte membrane and the conductivity from the electrolyte membrane to the air electrode side are reduced. Is relatively low, and the interface between the noble metal catalyst, the solid polymer electrolyte membrane, and the fuel gas (hydrogen and air) in contact with each other, that is, the three-phase interface is small. Despite the large amount, the power generation performance of the fuel cell is low.
There was a problem.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an active solid polymer electrolyte membrane capable of improving the power generation performance of a fuel cell with a small amount of noble metal carried.

[0005] To achieve the above object, according to the present invention,
A solid polymer electrolyte membrane; and a plurality of noble metal catalyst particles supported by ion exchange in a surface layer inside the surface of the solid polymer electrolyte membrane and uniformly dispersed throughout the surface layer. T ₂ is t ₂ ≦ 10 μm ,
An active solid polymer electrolyte membrane in a polymer electrolyte fuel cell is provided.

With the above-mentioned structure, the noble metal catalyst particles are scattered in the surface layer of the electrolyte membrane.
The conductivity of the generated hydrogen ions to the electrolyte membrane and the conductivity from the electrolyte membrane to the air electrode side are high, respectively.
Also, the association between hydrogen ions and oxygen is improved. In addition, there are many three-phase interfaces where the three members of the noble metal catalyst particles, the solid polymer electrolyte membrane, and the fuel gas come into contact. This makes it possible to reduce the amount of noble metal carried in the electrolyte membrane and to improve the power generation performance of the fuel cell.

Another object of the present invention is to provide the above-mentioned production method capable of mass-producing the active solid polymer electrolyte membrane.

[0008] To achieve the above object, according to the present invention,
A step of causing the ion exchange by immersing the solid polymer electrolyte membrane noble metal complex soluble liquid, the solid polymer electrolyte membrane
A step of washing, a step of performing reduction processing on the solid polymer electrolyte membrane, a step of washing the solid polymer electrolyte membrane, and drying the solid polymer electrolyte membrane, successively <br /> in the manufacturing method of the row inadvertent solid polymer electrolyte membrane, wherein
In performing the ion exchange, a mixed solution obtained by mixing at least one additive selected from a water-soluble organic solvent, a nonionic surfactant and a nonmetallic base with the noble metal complex solution is used.
A method for producing an active solid polymer electrolyte membrane is provided.

[0009] Currently known solid polymer electrolyte membranes are polymer ion exchange membranes. Therefore, when ion exchange is performed under the action of the above-described additive, noble metal complex ions are adsorbed at a plurality of ion exchange points in the surface layer of the electrolyte membrane, which are uniformly dispersed throughout the entire surface. In the first cleaning step, free noble metal complex ions and additives existing in the electrolyte membrane are removed. In the reduction step, the atomic group bonded to the noble metal atom of the noble metal complex ion is removed. In the second washing step, the reducing components are removed from the electrolyte membrane, and the active solid polymer electrolyte membrane is obtained through the subsequent drying step.

[0010]

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIGS. 1 and 2, a cell 1 constituting a polymer electrolyte fuel cell comprises an active polymer electrolyte membrane (hereinafter referred to as an active electrolyte membrane in this section) 2 and both sides thereof. Air electrode 3 and fuel electrode 4 that are in close contact with the surface
And a pair of separators 5 and 6 that are in close contact with the electrodes 3 and 4 respectively.

The active electrolyte membrane 2 has a thickness t ₁ of 5 μm ≦ t.
₁ ≦ 200 μm solid polymer electrolyte membrane (hereinafter referred to as electrolyte membrane in this section) 7 and a surface layer 8 inside the surface thereof supported by ion exchange, and the surface layer A plurality of noble metal catalyst particles 9 uniformly dispersed throughout the entire part 8
It is composed of The supported amount CA of the noble metal catalyst particles is 0.
14 mg / cm ² ≦ CA ≦ 0.35 mg / cm ² . The thickness t ₂ of Table <br/> layer portion 8 is t ₂ ≦ 10 [mu] m. Each noble metal catalyst particle 9 has a crystallite diameter d ₁ by X-ray diffraction d ₁ ≦ 5 nm.
Are secondary particles in which the primary particles are bonded and aggregated, and the particle diameter d ₂ is 10 nm ≦ d ₂ ≦ 200 nm.

As the electrolyte membrane 7, a fluororesin-based ion exchange membrane, for example, Flemio (trade name) manufactured by Asahi Glass Co., Ltd.
n); Nafion (trade name, manufactured by DuPont) or the like is used. The noble metal catalyst particles 9 correspond to, for example, Pt particles.

The air electrode 3 and the fuel electrode 4 each comprise a porous carbon plate 10 and an auxiliary catalyst layer 11 formed on one surface of the porous carbon plate 10, and the auxiliary catalyst layer 11 is provided on both surfaces of the electrolyte membrane 7. Adhere each other. Each auxiliary catalyst layer 11
It is composed of carbon black particles having Pt particles supported on the surface thereof, and a fluororesin-based ion exchanger (trade name Flemion) which is a polymer electrolyte. The porous carbon plates 10 of the poles 3 and 4 are connected to a load 12, for example, a DC motor for a vehicle.

Each of the separators 5 and 6 is made of graphitized carbon so as to have the same form, and air is supplied to a plurality of grooves 13 in the separator 5 on the cathode 3 side, and air is supplied to the separator 6 on the fuel electrode 4 side. Hydrogen is supplied to the plurality of grooves 14 which intersect with the grooves 13.

In producing the active electrolyte membrane 2, a mixture of a noble metal complex solution and at least one additive selected from a water-soluble organic solvent, a nonionic surfactant and a nonmetallic base is used. A step of immersing the electrolyte membrane 7 to perform ion exchange, a step of cleaning the electrolyte membrane 7 with pure water, a step of performing a reduction treatment on the electrolyte membrane 7, and a step of cleaning the electrolyte membrane 7 with pure water. And a step of drying the electrolyte membrane 7 are sequentially performed.

As the noble metal complex solution, for example, a cationic P containing Pt complex ion [Pt (NH ₃ ) ₄ ] ²⁺ is used.
A t-complex solution is used. In the additives, methanol, ethanol, ethylene glycol and the like are used as water-soluble organic solvents, and polyoxyethylene dodecyl ether (for example, trade name Briji 35) and polyoxyethylene octylphenyl are used as nonionic surfactants. Ether and the like are used, and ammonia and the like are used as the nonmetallic base.

When ion exchange is performed under the action of the above-mentioned additives, Pt complex ions are present at a plurality of ion exchange points in the surface layer portion 8 of the electrolyte membrane 7 and uniformly dispersed throughout the entire surface. Adsorb. In the first cleaning step, free Pt complex ions and additives existing in the electrolyte membrane 7 are removed. In the reduction step, the atomic group bonded to the Pt atom of the Pt complex ion is removed. In the second washing step, the reducing components are removed from the electrolyte membrane 7, and the active electrolyte membrane 2 is obtained through the next drying step.

If the reduction treatment is performed without performing the first cleaning, Pt atoms will remain in the electrolyte membrane 7 in a free state .
Wastes expensive Pt because it does not contribute to generation
become. If the second cleaning is not performed,
Power generation performance as hydrogen ionization is hindered by residuals
Decrease.

Hereinafter, a specific example will be described.

Example 1 of the active electrolyte membrane 2 was obtained through the following steps.

(A) The target amount of supported Pt (0.15
mg / cm ² ) cationic Pt containing 3 times the amount of Pt
100 cc of 25% aqueous ammonia (additive) in the complex solution
Was added to prepare a mixed solution.

(B) In order to perform ion exchange, an electrolyte membrane (trade name: Flemion) 7 having a length of 70 mm and a width of 70 mm is immersed in the mixed solution, and then the mixed solution is heated to 60 ° C. and kept at the temperature for 12 hours Stirred.

(C) For cleaning, the electrolyte membrane 7 was immersed in pure water, then heated to 50 ° C. and stirred at that temperature for 2 hours.

(D) In order to perform the reduction treatment, the electrolyte membrane 7
The water after the washing was discarded from the container in which was stored, new pure water was added to the container, and the electrolyte membrane 7 was immersed in the pure water. In addition, a reducing mixed solution having a molar amount of 10 times the target amount of Pt supported,
That is, a mixed solution containing sodium borohydride and sodium carbonate was prepared. Next, the pure water in which the electrolyte membrane 7 was immersed was heated to 50 ° C., and the entire amount of the reducing mixture was dropped into the pure water at that temperature over 30 minutes. Thereafter, the reaction was left for about 1.5 hours, and when the gas (mainly hydrogen) was not generated from the solution, the reaction was regarded as completed.

(E) In order to perform the washing for removing the Na component,
The electrolyte membrane 7 was immersed in pure water, and then heated to 50 ° C. and stirred at that temperature for 2 hours.

(F) The electrolyte membrane 7 was dried in a dryer at 60 ° C. for 4 hours.

Example 2 of the active electrolyte membrane 2 was obtained under the same conditions as in Example 1 except that the addition amount of 25% aqueous ammonia (additive) was 200 cc.

Example 3 of the active electrolyte membrane 2 was obtained under the same conditions as in Example 1 except that 100 cc of ethanol was used as an additive.

The active electrolyte membrane 2 was prepared under the same conditions as in Example 1 except that 5% polyoxyethylene dodecyl ether (trade name: Briji 35) was used as an additive.
Example 4 was obtained.

The target amount of supported Pt (0.15 mg / c
Example 5 of the active electrolyte membrane 2 was obtained under the same conditions as in Example 1 except that the same cationic Pt complex solution containing 1.5 times the amount of Pt with respect to m ² ) was used. Was.

The target amount of supported Pt (0.15 mg / c
Example 6 of the active electrolyte membrane 2 was obtained under the same conditions as in Example 1 except that the same cationic Pt complex solution containing 6 times the amount of Pt with respect to m ² ) was used.

A Pt catalyst layer was formed on the surface of the same electrolyte membrane (Flemion, trade name) as in Example 1 by a sputtering method. This active electrolyte membrane 2 is referred to as Comparative Example 1.

A mixture of carbon black particles having Pt particles supported thereon and a fluororesin ion exchanger (trade name Flemion) which is a polymer electrolyte is applied to one surface of the porous carbon plate 10 to assist. The air electrode 3 and the fuel electrode 4 were manufactured by a method such as forming the catalyst layer 11.
In this case, the weight ratio between the carbon black particles and the Pt particles is 1: 1.

Table 1 shows the structures of Examples 1 to 3 of the auxiliary catalyst layer 11. In the table, C means carbon black particles, and PE means a polymer electrolyte.

[0036]

[Table 1]

Example 3 is a layer made of only carbon black, not the auxiliary catalyst layer 11, but is described for convenience, and PTFE (polytetrafluoroethylene) is used instead of the polymer electrolyte. .

Table 2 shows combinations of the active electrolyte membranes 2 in Examples 1 to 7 and Comparative Examples 1 and 2 with the auxiliary catalyst layer 11 in the fuel cell.

[0039]

[Table 2]

The active electrolyte membrane 2 of Example 7 is the same as that of Example 1, the Pt catalyst of Comparative Example 1 has a laminar shape, and the electrolyte membrane 7 of Comparative Example 2 is subjected to the ion exchange as described above. The film itself has not been done.

Next, each fuel cell was operated, and the relationship between the current density and the terminal voltage was examined. The results shown in Table 3 were obtained. In Table 3, Examples 1 to 7 and Comparative Examples 1 and 2 mean fuel cells using Examples 1 to 7 and Comparative Examples 1 and 2 such as the active electrolyte membrane 2 in Table 2.

[0042]

[Table 3]

FIG. 3 is a graph showing the relationship between the terminal voltage and the current density for each fuel cell using Examples 1 to 4 and Comparative Examples 1 and 2 in Table 3. FIG. 4 shows a fuel cell using Examples 1 to 4 and a fuel cell using Comparative Example 1 based on Tables 2 and 3, and shows the thickness t of the surface layer portion 8.
₂ is a graph showing the relationship between the terminal voltage and the terminal voltage when the current density is 0.6 A / cm ² . 3 and 4, the Pt particles 9
In the case of using Examples 1 to 4 having the surface layer 8 in which
It can be seen that the power generation performance is improved as compared with the case of using Comparative Examples 1 and 2 having no such surface layer. The power generation performance of each fuel cell using Examples 5 and 6 was close to that of the fuel cell using Example 2, and the power generation performance of the fuel cell using Example 7 was that of the fuel cell using Example 4. near.

The thickness t ₂ of the surface layer 8 due to the additive is 25
% Ammonia water 100cc (Example 1), 25% ammonia water 200cc (Example 2), ethanol 100cc (Example 3), 5% polyoxyethylene dodecyl ether (Example 4). Power generation performance is decreasing. This is due to the permeability of hydrogen gas to the Pt particles 9 existing in the surface layer portion 8.

FIG. 5 is a graph showing the relationship between the current density and the terminal voltage for each of the fuel cells using Examples 1, 5 to 7 and Comparative Examples 1 and 2 in Table 3.

A fuel cell using the embodiment 7 having the active electrolyte membrane 2 but not having the auxiliary catalyst layer 11 and a comparative example 2 having the auxiliary catalyst layer 11 but not having the active electrolyte membrane 2 were used. When compared with the conventional fuel cell, the power generation performance of both fuel cells is substantially the same, although the amount of Pt particles carried in Comparative Example 2 is about 3.1 times that of Example 7. From this fact, it is clear that the Pt particles 9 are dispersed and supported on the surface layer 8 of the electrolyte membrane 7.

[0047]

According to the first and second aspects of the present invention, there is provided an active polymer electrolyte membrane capable of improving the power generation performance of a polymer electrolyte fuel cell by having the above-described structure. be able to.

According to the third and fourth aspects of the present invention, it is possible to provide a production method capable of mass-producing the active solid polymer electrolyte membrane.

[Brief description of the drawings]

FIG. 1 is a schematic side view of a cell constituting a polymer electrolyte fuel cell.

FIG. 2 is a schematic sectional view of an active solid polymer electrolyte membrane, and FIG.
Corresponds to a sectional view taken along line 2-2 of FIG.

FIG. 3 is a graph showing the relationship between terminal voltage and current density in various polymer electrolyte fuel cells.

FIG. 4 is a graph showing the relationship between the surface layer thickness and the terminal voltage in various polymer electrolyte fuel cells.

FIG. 5 is a graph showing the relationship between current density and terminal voltage in various polymer electrolyte fuel cells.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Cell 2 ... Active solid polymer electrolyte membrane 7 ... Solid polymer electrolyte membrane 8 ... Surface layer part 9 ... Noble metal catalyst particles

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-9-87882 (JP, A) JP-A-10-8285 (JP, A) JP-A-10-330979 (JP, A)

Claims (4)

(57) [Claims] 1. A solid polymer electrolyte membrane (7) and a table thereof.
Carried by ion exchange on the surface portion (8) in located on the inner surface, are and further configured its surface portion and a plurality of noble metal catalyst particles uniformly dispersed throughout the (8) (9), the table
An active solid polymer electrolyte membrane in a polymer electrolyte fuel cell, wherein the thickness (t ₂ ) of the layer (8) is t ₂ ≦ 10 μm . 2. The method according to claim 1, wherein the carried amount CA of the noble metal catalyst particles is 0.1.
A ^{14mg / cm 2 ~0.35mg / cm 2} , the active solid polymer electrolyte membrane in a polymer electrolyte fuel cell according to claim 1, wherein. Wherein said solid polymer electrolyte membrane (7) immersed in a noble metal complex soluble liquid comprising the steps of causing the ion exchange, a step of washing the solid polymer electrolyte membrane (7), wherein a step of performing a reduction treatment to the solid polymer electrolyte membrane (7), the solid polymer electrolyte membrane (7) a step of washing, the solid and drying the polymer electrolyte membrane (7), successively rows A method for producing a solid polymer electrolyte membrane , comprising:
When performing the exchange, add a water-soluble organic solvent to the noble metal complex solution.
Selected from detergents, nonionic surfactants and nonmetallic bases
Use a mixture of at least one additive
A method for producing an active solid polymer electrolyte membrane, comprising: 4. The method as claimed in claim 1, wherein the additive comprises a water-soluble organic solvent.
Is methanol, ethanol, ethylene glycol
And non-ionic surfactants include polyoxyethylene
N-decyl ether, polyoxyethylene octylfe
Nyl ethers and non-metallic bases
4. The active solid polymer electrolyte according to claim 3, wherein the near corresponds to
Manufacturing method of membrane.