JPH0888013A - Thin film electrolyte for normal temperature fuel cell and normal temperature fuel cell using it - Google Patents

Abstract

PURPOSE: To prevent increase in electrolyte ohmic loss even if a film is thick, and make temperature control of a cell easy by impregnating void pores of a polymer porous film with an electrolyte solution containing phosphoric acid and an organic solvent in and conducting moisture control. CONSTITUTION: A thin film electrolyte 3 is produced by impregnating void pores 2 of a polymer porous film 1 with an electrolyte solution 4 containing phosphoric acid and a solvent. The thin film electrolyte 3 is interposed between a pair of electrodes 5, and current collectors 6 surrounded by a Teflon gasket 7 are arranged on both side of the thin film electrolyte 3. The current collectors 6 are sealed between a sealing member 15 having a hydrogen supply port 10 and a hydrogen exhaust gas port 11 and a sealing member 16 having an oxygen supply port 12 and an oxygen exhaust gas port 13, and a supporting member 14 which supports the current collector 6 is arranged inside each sealing member. When hydrogen fuel and oxygen fuel are supplied from the supply ports 10, 12, the reaction takes place on the anode side and the cathode side, and electromotive force is generated between an anode terminal 8 and a cathode terminal 9. Since water is produced by reaction, moisture control is made unnecessary.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film electrolyte for a room temperature fuel cell, and more particularly to a novel polymer thin film electrolyte for a solid polymer fuel cell and a room temperature fuel cell using the same.

[0002]

2. Description of the Related Art As a solid polymer electrolyte for room temperature fuel cells, a fluororesin ion exchange membrane represented by Nafion (registered trademark) manufactured by DuPont is known. A fuel cell using such an ion-exchange membrane is H ₂ → 2H ⁺ + 2e ^{− at} the fuel electrode and at the air electrode at a low temperature of 100 ° C. or lower.
^{_{O 2 + 4H + + 4e -}} → 2H 2 O in the reaction is activated by proceeding. Such a polymer electrolyte fuel cell that operates at a low temperature (normal temperature type) generally has high output density, is easy to manufacture, and can be made compact and lightweight. It is expected to be applied to cogeneration.

[0003]

However, the fluororesin ion-exchange membrane represented by Nafion (registered trademark) has an essential drawback of large gas cross-leakage. It is necessary to set the thickness to 180 μm. The thicker the film, the more the power density increases and the more heat is generated due to the ohmic loss of the electrolyte, which makes it difficult to control the temperature of the cell and increases the energy loss.

Further, there is a drawback that the manufacturing cost is very high because a multi-step process is required to manufacture the fluororesin ion exchange membrane. Further, since the fluororesin ion exchange membrane does not function as an ionic conductor unless water is contained in the membrane, it needs to be humidified by water vapor (water management).

[0005]

In order to solve the above problems, the present invention comprises (1) impregnating the pores of a polymer porous membrane with an electrolyte solution containing phosphoric acid and an organic solvent. Provide a thin film electrolyte for room temperature fuel cells. Further, the present invention also provides an ambient temperature fuel cell using the thin film electrolyte according to (2) and (1).

The preferred embodiments of the present invention are listed below item by item. (3) The thickness of the porous film is 0.1 μm to 50 μm, the porosity is 40% to 90%, the breaking strength is 200 kg / cm ² or more, and the average through pore diameter is 0.001 μm to 0.7 μm. A thin film electrolyte for a room temperature fuel cell according to item (1). (4) The organic solvent is benzonitrile, benzyl cyanide, 1-phenyl-1-cyclopropanecarbonitrile, DL-2-phenylbutyronitrile, 4-phenylbutyronitrile, 2,2-diphenylpropionitrile, It is selected from polyethylene glycol dimethyl ether, polypropylene glycol dimethyl ether, 2-phenylethanol and 2-phenoxyethanol, and a mixture of two or more thereof in combination, which is a room temperature type according to item (1) or (3). Thin film electrolyte for fuel cells. (5) The weight of the organic solvent is 10 to 30 relative to the total weight of the phosphoric acid containing water as the phosphoric acid aqueous solution and the organic solvent.
The thin film electrolyte for a room temperature fuel cell according to item (1), (3) or (4), characterized in that the content is% by weight. (6) An ambient temperature fuel cell using the thin film electrolyte according to any one of (3) to (5).

The porous film used in the thin film electrolyte of the present invention has a film thickness of 0.1 μm to 50 μm and a porosity of 40% to 90%.
%, A breaking strength of 200 kg / cm ² or more and an average through hole diameter of 0.001 μm to 0.7 μm are preferably used.

The thickness of the porous film is generally 0.1 μm to 50 μm.
μm, and preferably 1 μm to 25 μm. When the thickness is less than 0.1 μm, it is difficult to put it into practical use from the viewpoints of a decrease in mechanical strength as a support and handleability. on the other hand,
When it exceeds 50 μm, it is not preferable from the viewpoint of suppressing the effective resistance. Porosity of porous film is 40% ~ 90%
It is good to be, and it is preferably in the range of 60% to 90%. When the porosity is less than 40%, the ionic conductivity as a thin film electrolyte becomes insufficient, while when it exceeds 90%, the mechanical strength as a support becomes small and it is difficult to put it into practical use.

The average through-pore diameter of the porous membrane should be such that the electrolyte solution can be fixed in the pores, but it is generally 0.001 μm.
Is about 0.7 μm. The preferable average through-hole diameter depends on the material of the porous membrane and the shape of the holes. The breaking strength of the porous membrane is generally 200 kg / cm ² or more, more preferably 500 kg.
It is suitable for practical use as a support by having a ratio of / cm ² or more.

The porous membrane used in the present invention has a function as a support for an electrolyte solution and is made of a polymer material having excellent mechanical strength. From the viewpoint of chemical and electrochemical stability,
For example, polyolefin, polytetrafluoroethylene, polyvinylidene fluoride can be used, but an example of a suitable polymer material from the viewpoint of the compatibility of the design and thinning of the porous structure and mechanical strength of the present invention, Particularly, it is a polyolefin having a weight average molecular weight of 5 × 10 ⁵ or more. Examples of other suitable polymer materials include polycarbonate,
Polyester, polymethacrylate, polyacetal,
Examples thereof include polyvinylidene chloride and polytetrafluoroethylene.

Phosphoric acid is used in the electrolyte solution for the thin film electrolyte of the present invention. The use of phosphoric acid enables a room temperature fuel cell. If the phosphoric acid contains a large amount of water, the ionic conductivity of the electrolyte solution will decrease, so it is desirable that the water content be as low as possible, but usually a phosphoric acid aqueous solution having a high concentration of 85% or more is not available. However, it is preferable that the water content is low (usually, an 85% phosphoric acid aqueous solution is used), but the case where more water is contained is not excluded.

The organic solvent used as a component of the electrolyte solution is necessary for impregnating the pores of the porous polymer membrane with phosphoric acid, is compatible with phosphoric acid (aqueous solution), and is highly porous. It is selected from those that are wettable to the membrane. Further, the operating temperature of the room temperature fuel cell according to the present invention (about 8
Those exhibiting a low vapor pressure at 0 to 150 ° C. are preferable.
Examples of usable organic solvents are benzonitrile, benzyl cyanide, 1-phenyl-1-cyclopropanecarbonitrile, DL-2-phenylbutyronitrile, 4-
Phenylbutyronitrile, 2,2-diphenylpropionitrile, polyethylene glycol dimethyl ether,
Examples thereof include, but are not limited to, polypropylene glycol dimethyl ether, 2-phenylethanol and 2-phenoxyethanol, and a mixture of two or more thereof. The boiling point of the organic solvent is about 20
It is preferably 0 ° C. or higher.

A suitable ratio of the organic solvent in the electrolyte solution is about 10 to 30% by weight, more preferably 10 to 15% by weight, based on the total weight of phosphoric acid (including water as an aqueous solution) and the organic solvent. is there. If the amount of organic solvent is small, it is difficult to impregnate the pores of the polymer porous membrane with phosphoric acid. On the other hand, when the amount of the organic solvent is too much, the ionic conductivity of the thin film electrolyte is lowered.

The thin film electrolyte of the present invention is produced by impregnating the above-mentioned polymer porous membrane with an electrolyte solution containing phosphoric acid and an organic solvent. The method of impregnating the pores of the polymer porous membrane with the electrolyte solution has already been disclosed by the present applicant in Japanese Patent Laid-Open Nos. 1-158051 and 2-291607, and so on. Please refer. When the surface tension of the electrolyte solution is high, the solution may be impregnated by vacuuming the porous membrane to 10 ⁴ pascals or less, if necessary. Although it depends on the physical properties of the surface of the porous membrane, generally, in the case of an electrolyte solution having a surface tension of 50 dynes / cm or more, it is easier to impregnate it by vacuuming.

The thin film electrolyte of the present invention can be handled as a solid as a whole, there is no fear of liquid leakage, and since the impregnated electrolyte solution is used, it has excellent ionic conductivity,
Further, it has a feature that it can be thinned.

The present invention also provides an ambient temperature fuel cell using the above-mentioned thin film electrolyte. For the electrodes and other structures other than the electrolyte, those known in conventional room temperature fuel cells using a fluororesin ion exchange membrane as the electrolyte can be adopted. The room temperature fuel cell according to the present invention has about 80
It suitably operates at temperatures of ℃ to 150 ℃. Operating temperature is about 8
When the temperature is lower than 0 ° C, the ionic conductivity as an electrolyte is low and it is difficult to put it into practical use. On the other hand, when the temperature is higher than about 150 ° C, the acidity of phosphoric acid increases and the membrane is corroded. The preferred operating temperature range is about 80 ° C to 100 ° C.

With reference to FIGS. 1 to 3, a typical configuration example of the room temperature fuel cell main body of the present invention will be described.

FIG. 1 schematically shows an example of the porous membrane 1 used in the thin film electrolyte of the present invention. The porous membrane 1 is generally produced by a biaxial stretching method and has pores 2 inside. Although the holes 2 are schematically shown in FIG. 1, the holes 2 do not actually need to have a regular arrangement or shape.

FIG. 2 schematically shows an example of the thin film electrolyte 3 produced by impregnating the pores 2 of the porous membrane 1 with the electrolyte solution 4 as shown in FIG. Since the electrolyte solution 4 is fixed inside the pores 2, the thin film electrolyte 3 can be handled as a solid as a whole. Also in FIG. 2, it is not necessary for the cross section of the holes 2 to have a regular arrangement or shape.

FIG. 3 shows an example of a room temperature fuel cell body using the thin film electrolyte 3 as shown in FIG. A thin film electrolyte 3 composed of one or more polymer porous membranes impregnated with an electrolyte solution is sandwiched between a pair of electrodes 5, and a current collector 6 surrounded by a Teflon gasket 7 is arranged on both sides thereof. . This assembly is provided with a hydrogen supply port 10 and a hydrogen exhaust gas port 1
It is sealed between the sealing member 15 having No. 1 and the sealing member 16 having the oxygen supply port 12 and the oxygen exhaust gas port 13. A support member 14 for supporting the current collector 6 is provided inside the enclosing members 15 and 16. For the current collector 6, for example, a titanium base material coated with platinum is used. Encapsulation member 1
For example, stainless steel is used for 5 and 16. The encapsulating member 15 is provided with an anode terminal 8 (hydrogen supply side) and the encapsulating member 16 is provided with a cathode terminal 9 (oxygen supply side) in order to extract a current obtained by an electromotive force between the electrodes.

The fuel cell main body as shown in FIG. 3 is placed in a thermostatic chamber (not shown) for maintaining the operating temperature (80 ° C. to 150 ° C.), and hydrogen fuel is supplied to the hydrogen supply port 10 and oxygen. When oxygen is supplied to the supply port 12, the above H ₂ → 2
H ^{+ +} 2e ^- (anode) and ^{_{O 2 + 4H + + 4e -}} → 2H 2
O (cathode side) reaction occurs, and at that time, electromotive force is generated between the anode terminal 8 and the cathode terminal 9.

[0022]

Example: A polyethylene porous film having a porosity of 41%, an average through-pore diameter of 0.02 μm and a thickness of 25 μm, obtained by biaxial stretching, was coated with dipropylene glycol diethyl ether 10.
A thin film electrolyte was prepared by impregnating with an electrolyte solution containing 90% by weight of phosphoric acid (85% aqueous solution) by weight.

Two thin film electrolytes were stacked (the total thickness of the electrolyte was 50 μm), and a fuel cell body as shown in FIG. 3 was assembled. 0.35 m of platinum is used for the electrode 5 of the fuel cell body.
A carbon powder supported g / cm ² was used in combination with a support material composed of glassy carbon and carbon cloth.

Oxygen gas and hydrogen gas were supplied to the fuel cell body at a pressure of 1 kg / cm ² at a flow rate of 40 ml / min and 40 ml / min, respectively, and power was continuously generated at 80 ° C. for 10 hours.

As a result, an open circuit voltage of 0.80 V and an output density of 0.18 W / cm ² were obtained. In addition, in the fuel cell main body of the above-mentioned embodiment, a thin film electrolyte having a thickness of 25 μm
The same open circuit voltage and power density were obtained when used in a single sheet and similarly generated. As a comparative example, thin film electrolyte 3
An experiment was conducted under the same conditions except that the film was replaced with a 125 μm-thick Nafion (registered trademark) film, and no electromotive force was obtained because it was not humidified.

[0026]

INDUSTRIAL APPLICABILITY The thin film electrolyte for a room temperature fuel cell of the present invention can be handled as a solid electrolyte and exhibits high room temperature power generation performance comparable to that of a conventional fluororesin ion exchange membrane, and further, the thin film is impregnated with a solution. Manufacturing cost is significantly lower than that of a fluororesin ion exchange membrane. Further, since gas permeability can be suppressed, it is possible to make the electrolyte thinner than before. Further, since the films are impregnated with the solution, the contact resistance can be suppressed to be relatively low even when a plurality of films are stacked and used, and heat generation due to ohmic loss can be suppressed. Moreover, the thin film electrolyte of the present invention is
Contribution to downsizing and cost reduction of the entire fuel cell system because there is no need for water management when the fuel cell operates.

[Brief description of drawings]

FIG. 1 is a perspective view schematically showing a porous membrane for a thin film electrolyte of the present invention.

FIG. 2 is a vertical sectional view schematically showing a thin film electrolyte of the present invention.

FIG. 3 is a developed perspective view showing a configuration example of a fuel cell body of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Porous film 2 ... Porosity 3 ... Thin film electrolyte 4 ... Electrolyte solution 5 ... Electrode 6 ... Current collector 7 ... Gasket 8 ... Anode terminal 9 ... Cathode terminal 10 ... Hydrogen supply port 11 ... Hydrogen exhaust port 12 ... Oxygen supply port 13 ... Oxygen exhaust gas port 14 ... Support member 15, 16 ... Sealing member

Claims (2)

[Claims] 1. A thin film electrolyte for a room temperature fuel cell, which is obtained by impregnating pores of a polymer porous membrane with an electrolyte solution containing phosphoric acid and an organic solvent. 2. An ambient temperature fuel cell using the thin film electrolyte according to claim 1.