JPH06231773A - Fuel cell - Google Patents

Abstract

PURPOSE:To improve an output characteristic by forming a porous surface of a separator having a groove for passing humidified reaction gas, and thereby holding moisture in the holes to maintain the wet condition of an ion exchange film. CONSTITUTION:An ion exchange film used as an electrolyte is a film having an H<+> conductivity, or, for example, a compound primarily consisting of high polymer containing fluorine and having sulfonic group and/or carboxyl group, is used. A known gas diffusion electrode is used for an electrode, while a separator is formed of a non-porous portion and a porous part on the side of the gas diffusion electrode, and the preferred vacancy of the porous part is 0.1-0.7. When the vacancy is too small, water retentivity is reduced, and when the vacancy is too large, current collecting function is reduced. Preferred thickness of the porous part is 100mum-5mm, and when it is no more than 100mum, water retentivity is reduced. The material of the porous part is inactivated against reaction gas, and titanium, copper and the like is used to give the porous part conductivity. The width of the open head upper surface of the groove is 0.5-10mm and the depth is 0.2-5mm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid polymer electrolyte fuel cell (hereinafter referred to as PEFC).

[0002]

2. Description of the Related Art Due to the characteristics of low pollution and high efficiency,
Fuel cells are receiving attention. A fuel cell electrochemically oxidizes a fuel such as hydrogen or methanol using oxygen or air to take out the chemical energy of the fuel as electric energy. Phosphoric acid type, depending on the type of electrolyte used
It is classified into molten carbonate type and solid oxide type. Among them, PEFC has been particularly attracting attention in recent years because of its characteristics of low temperature operation and high power density.

The basic structure of PEFC will be described with reference to FIG. As shown in FIG. 2, the battery body is configured by joining gas diffusion electrodes 2 on both sides of a solid polymer electrolyte membrane 1. A catalyst is supported on the gas diffusion electrode 2, and a cell reaction occurs at the bonding interface between the solid polymer electrolyte membrane 1 and the gas diffusion electrode 2. For example, when hydrogen gas is flown through the gas diffusion electrode 2, 2H ₂ → 4H ⁺ +4 at the bonding interface with the film.
e ^- reaction occurs of. H ⁺ moves through the solid polymer electrolyte membrane 1 to the gas diffusion electrode 2 of the counter electrode. When oxygen gas is supplied to the gas diffusion electrode 2, O ₂ → 4H ⁺ + 4e ⁻ → 2H
The reaction of ₂ O occurs at the interface between the membrane and the electrode, and at the same time water is produced, electric energy is obtained.

Since the H ⁺ conductivity of the ion exchange membrane is first expressed in a wet state of the membrane, it is devised to supply water in addition to the humidified reaction gas (JP-A-3-102774, JP (Kaihei 3-269958). However, such a contrivance alone is not sufficient to maintain the wet state of the membrane, which causes a reduction in output as a fuel cell.

[0005]

An object of the present invention is to provide a fuel cell having excellent output performance.

[0006]

Means for Solving the Problems The inventors of the present invention have made earnest studies as to maintaining the wet state of an ion exchange membrane, and as a result, the surface of a separator having a groove for a humidified reaction gas passage is made porous, so that The present invention has been completed by finding that water is retained therein, and as a result, the wet state of the ion exchange membrane is maintained and the output characteristics of the fuel cell are improved.

That is, the present invention provides a fuel cell using an ion exchange membrane as an electrolyte, wherein the separator surface on the gas diffusion electrode side is made of a porous conductive material. In the present invention, the ion exchange membrane used as the electrolyte may have H ⁺ conductivity, and for example, there is one having the fluorinated polymer as a skeleton and having a sulfonic acid group and / or a carboxyl group as shown in the following chemical formula 1. .

[0008]

[Chemical 1]

The electrode may be any known gas diffusion electrode,
For example, it is composed of carbon carrying platinum, Teflon as a binder / water repellent, and, for example, an ion exchange resin component as a proton conducting material. The separator separates a single cell of a fuel cell, and has a reaction gas collecting function by forming a groove for a reaction gas passage in addition to the reaction gas impermeability and current collecting property. In the present invention,
Furthermore, it has a new function of water retention and enhances the H ⁺ conductivity of the ion exchange membrane, which is essential for PEFC. In order to provide water retention, it is effective to make the portion through which the humidified reaction gas passes and the portion in contact with the gas diffusion electrode porous. That is, the separator of the present invention needs to be composed of a non-porous portion and a porous portion on the gas diffusion electrode side. The porosity of the porous portion does not need to be particularly limited, but is preferably 0.1 to 0.7.
Here, the porosity represents the volume occupied by the pores with respect to the total volume of the porous portion. If the porosity is too small, the water retention effect will decrease,
On the other hand, if it is too large, the current collecting function will be reduced.

The thickness of the porous portion is 100 μm to 5 mm
Is preferred. If it is smaller than 100 μm, the water retention effect is lowered, while if it is larger than 5 mm, the water retention effect is not changed, but the compactness when assembled as a cell is deteriorated. The material of the porous part is inert to the reaction gas,
In addition, any material that is a conductor may be used, and examples thereof include titanium, niobium, copper, nickel, carbon, alloys thereof, or those structures plated with a noble metal such as platinum, silver, palladium, or rhodium. . To form a porous structure, for example, a method of burning powder of the above material, a molding method,
There are a method of including a hole forming material and removing the hole forming material after molding, and a sputtering method for a structure composed of a non-porous portion. The porous portion has a groove through which the humidified reaction gas passes.

The width of the open upper surface of the groove is 0.5 to 10 mm, preferably 1 to 5 mm. If it is less than 0.5 mm, the pressure loss becomes large when the reaction gas flows, and the reaction gas must flow at a high pressure, and at the same time, partial separation of the electrode and the separator is likely to occur. While 10
If it is larger than mm, a one-way flow of the reaction gas occurs in one groove, which causes deterioration of performance. The width of the bottom surface of the groove is preferably less than or equal to the width of the open upper surface of the groove. One end of the groove is connected to the reaction gas inlet and the other end is connected to the reaction gas outlet.

The depth of the groove is 0.2 to 5 mm, preferably 1 to 3 mm. If it is less than 0.2 mm, the groove tends to be closed when the gas diffusion electrode and the separator are overlapped and tightened, while if it is more than 5 mm, the separator becomes thick and the unused portion of the reaction gas increases, which is not preferable. The non-porous portion of the separator may be any material that is inert to the reaction gas, has no gas permeability, and is an electric conductor, such as titanium, niobium, copper, nickel, carbon, or a structure thereof. Thing plated with platinum, silver, palladium, rhodium, or polytetrafluoroethylene, tetrafluoroethylene-
A mixture of a fluororesin such as a perfluoroalkyl vinyl ether copolymer and a tetrofluoroethylene-hexafluoropropylene copolymer and the above metal is preferable.

An example of a single cell fuel cell using the separator of the present invention is shown in FIG. In addition to this, there is, for example, one in which a porous portion is thinly formed by sputtering on a non-porous portion having a reaction gas passage groove.

[0014]

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples.

[0015]

Example 1 A gas diffusion electrode having an area of 10 cm ² (US E
-TEK Co., Ltd.) Two pieces of platinum loading 0.38 mg / cm ² were prepared, while a perfluorocarbon ion exchange membrane A
ciplex [Asahi Kasei Co., Ltd. trademark 1000g /
Equivalent weight] was dissolved in a mixed solvent of 50:50 by weight of ethanol and water to give a 5% by weight solution. The prepared gas diffusion electrode was impregnated with 0.15 ml of this Aciplex solution, and dried under reduced pressure at 70 ° C. for 2 hours. From the weight measurement of the obtained electrode, the impregnated Aciplex component amount was 0.6 mg.
Was / cm ² .

An Aciplex film having a thickness of 4 mils was sandwiched between these electrodes, and a hot press machine was used to perform a bonding treatment at 140 ° C. for 90 seconds. In the separator shown in FIG. 3,
Titanium material (TB-made by Daido Steel Sheet Co., Ltd.)
35) and graphite (IG-11 porosity 15%, manufactured by Toyo Tanso Co., Ltd.) was used in the porous portion. The depth of the reaction gas passage groove in the porous portion was 1 mm, and the thickness of the porous portion at the bottom of the groove was 4 mm.

Using the evaluation device shown in FIG.
Cell temperature is 55 ° C, humidification temperature is 70 ° C, oxygen and hydrogen are used as reaction gases, and flow rates are 50 ml / min and 100 ml / min, respectively.
The output of the fuel cell was evaluated at min. The obtained current density vs. voltage curve is shown in FIG.

[0018]

[Comparative Example 1] Using a joined body prepared by the same operation as that of the example, a titanium material (TB manufactured by Daido Steel Co., Ltd.) was used as a separator shown in Fig. 3 for both the non-porous portion and the porous portion.
The output was evaluated under the same conditions with the same apparatus as in the example, which was created in -35). The result is shown in FIG.

[0019]

The output performance of the fuel cell of the present invention is greatly improved.

[Brief description of drawings]

FIG. 1 is a graph showing current density vs. voltage as an evaluation result of an example and a comparative example.

FIG. 2 is a schematic cross-sectional view showing a single cell structure for evaluation.

FIG. 3 is a schematic sectional view showing a single cell structure using a separator which is an example of the present invention.

FIG. 4 is an explanatory diagram showing a bonded body evaluation apparatus used in Examples and Comparative Examples.

[Explanation of symbols]

 1 Ion Exchange Membrane 2 Gas Diffusion Electrode 3 Separator 4 Gas Collection Groove 5 Reactor Gas Channel Groove Opening 6 Reaction Gas Inlet / Outlet 7 Fuel Cell Single Cell 8 Humidifier 9 Pure Water 10 Porous Part 11 Non-Porous Part

Claims (1)

[Claims] 1. A fuel cell using an ion exchange membrane as an electrolyte, characterized in that the separator surface on the gas diffusion electrode side is made of a porous conductive material.