JPH06231782A - Improved solid high polymer electrolytic type fuel cell - Google Patents

Abstract

PURPOSE:To provide a high performance solid high polymer type electrolytic fuel cell by providing a positive ion exchange film having low electric resistance serving as a solid high polymer electrolyte. CONSTITUTION:A fuel cell is formed by providing a positive ion exchange film of parfluorocarbon polymer containing sulfonic acid group, as a solid high polymer electrolyte. For the positive ion exchange film, a film consisting of the layered body of no fewer than two parfluorocarbon polymer films having different contents, is used. The film facing the positive electrode has the highest content.

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.

[0002]

2. Description of the Related Art Recently, a fuel cell using a proton-conducting polymer membrane as an electrolyte (solid polymer electrolyte fuel cell)
Research is progressing. The solid polymer electrolyte fuel cell is
It operates at low temperature, has a high output density, and can be downsized, and is regarded as a promising candidate for applications such as in-vehicle power supplies.

[0003]

As the polymer membrane used for this purpose, a proton conductive ion exchange membrane having a thickness of 100 to 200 μm is usually used, and in particular, a cation composed of a perfluorocarbon polymer having a sulfonic acid group. Exchange membranes have been widely studied because of their excellent basic properties. However, the electrical resistance of currently proposed cation exchange membranes is not necessarily sufficiently low from the viewpoint of obtaining batteries with higher power density.

Methods for reducing the electrical resistance of cation exchange membranes include increasing the concentration of sulfonic acid groups and reducing the film thickness, but a significant increase in the concentration of sulfonic acid groups reduces the mechanical strength of the membrane, During operation, the film easily creeps, which causes problems such as deterioration of durability. On the other hand, the reduction of the film thickness causes problems such as deterioration of the mechanical strength of the film and further deterioration of workability and handleability such as bonding with the gas diffusion electrode. Thus, it has been desired to develop a cation exchange membrane having low electric resistance and high mechanical strength.

[0005]

The present invention has been made to solve the above-mentioned problems, and is a fuel using a cation exchange membrane made of a perfluorocarbon polymer containing a sulfonic acid group as a solid polymer electrolyte. In the battery, the cation exchange membrane is composed of at least two layers of perfluorocarbon polymers having different water contents, and the film facing the positive electrode has the highest water content. I will provide a.

In the present invention, the cation exchange membrane needs to have the polymer film having the highest water content positioned on the side facing the positive electrode of the fuel cell. The water content of the polymer film on the positive electrode side is preferably 5 to 50% by weight, more preferably 10 to 30% by weight, higher than the water content of the polymer film facing the negative electrode. on the other hand,
The water content of each polymer film is controlled to 30 to 110% by weight, particularly 35 to 95% by weight.

In the present invention, the water content (ΔW) of the polymer film (acid type) is defined as follows. ΔW = (W ₁ / W ₂ −1) × 100 (wt%) W ₁ : 90 ° C., film weight after immersion in pure water for 24 hours. W ₂ : The film weight after vacuum-drying at 100 ° C. for 16 hours after measuring W ₁ . When the water content of the perfluorocarbon polymer film is smaller than the lower limit of the above range, the membrane resistance is extremely increased, and when it is larger than the above range, the membrane strength and the membrane handleability in electrode bonding and the like are remarkably lowered, which is not preferable.

The cation exchange membrane laminated with the perfluorocarbon polymer film preferably has a thickness of 30 to 300 μm, more preferably 50 to 250 μm. If it is smaller than the lower limit of the above range, the film strength and the handleability of the film at the time of joining with the electrode are deteriorated, while if it is larger than the upper limit, the film resistance is increased and the output is decreased, which is not preferable.

The perfluorocarbon polymer having a sulfonic acid group used in the present invention includes tetrafluoroethylene and CF ₂ ═CF— (OCF ₂ CFX) _m —O.
_{q - (CF 2) n -A} ( wherein m = 0~3, n = 0~1
A copolymer with a fluorovinyl compound represented by 2, q = 0 or 1, X = F or CF ₃ , A = sulfonic acid type functional group) can be preferably used.

Preferred examples of the fluorovinyl compound include CF ₂ ═CFO (CF ₂ ) _1-8 SO ₂ F CF ₂ ═CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) _1-8 SO ₂ F CF _{2 = CF (CF 2) 0-8 SO} 2 F CF 2 = CF (OCF 2 CF (CF 3)) , such as _{1-5 O (CF 2) 2 SO} 2 F and the like.

It is also possible to use perfluoroolefins such as hexafluoropropylene, chlorotrifluoroethylene, and perfluoroalkoxy vinyl ethers in place of the above tetrafluoroethylene constituting the perfluorocarbon polymer.

In the present invention, the cation exchange membrane may be reinforced with a fibril-like, woven-like or non-woven-like perfluorocarbon polymer. In the present invention, the cation exchange membrane is assembled as a fuel cell by adhering a gas diffusion electrode to the surface of the cation exchange membrane according to a commonly known method and then attaching a current collector.

The gas diffusion electrode is usually composed of a sheet of a porous body in which conductive carbon black powder carrying fine platinum catalyst particles is held by a hydrophobic resin binder such as polytetrafluoroethylene. The body may contain a sulfonic acid type perfluorocarbon polymer or fine particles coated with the polymer. The gas diffusion electrode and the sulfonic acid type perfluorocarbon polymer are adhered to each other by a hot pressing method or the like.

As the current collector, a conductive carbon plate or the like in which a groove serving as a passage for fuel gas or oxidant gas is formed is used.

[0015]

The mechanism by which the good effect of the present invention is achieved is not clear, but it is considered as follows. In a hydrogen gas fuel cell, chemical energy is converted into electric energy according to the following reaction. Negative electrode: H ₂ → 2H ⁺ + 2e ⁻ Positive electrode: 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O The mobility of protons in a cation exchange membrane in a fuel cell is greatly related to the water content of the membrane, and The higher the ratio, the higher the proton mobility and the lower the membrane resistance.

Since the positive electrode side of the cation exchange membrane generates water according to the above reaction, it has a high water content state and the mobility of protons is also kept high, while the negative electrode side of the membrane has a relatively high water content. It becomes lower, and it is estimated that the rate of proton transfer in the film becomes rate-determining at the negative electrode. By the way, the water molecules generated in the positive electrode diffuse into the negative electrode side in the film, but it is considered that the diffusion of the water molecule in the film is accelerated by installing a layer having high water-containing property on the positive electrode side of the film. . As a result, a low water content state on the negative electrode side of the film is relaxed to obtain a film having low resistance.

[0017]

【Example】

Example 1 CF ₂ ═CF ₂ and CF ₂ ═CFO (CF ₂ CFC) based on the method described in JP-A-2-88645.
F ₃ ) O (CF ₂ ) ₂ SO ₂ F and ion exchange capacity of 1.0 meq / g dry resin, and 1.1
Two types of copolymer of milliequivalent / g dry resin were obtained. The former copolymer was extruded at 220 ° C to form a film, and the thickness was 80 μm.
I got a film of. Next, the latter copolymer was extruded at 220 ° C. to form a film, to obtain a film having a thickness of 20 μm.

The above two kinds of copolymer films are heated at 220 ° C.
After being laminated by using a roll, the mixture was hydrolyzed in a mixed aqueous solution of 30% by weight of dimethylsulfoxide and 15% by weight of caustic potash, washed with water and then immersed in 1N hydrochloric acid. Next, after washing the membrane with water and restraining the four sides of the membrane with special jigs, 60
It was dried at ℃ for 1 hour to produce a cation exchange membrane.

Ion exchange capacity of 1.0 meq / g dry resin, and 1.1 meq / g dry resin copolymer 90
The water contents in pure water at 0 ° C were 50% by weight and 70% by weight, respectively.

The fuel cell characteristics using this cation exchange membrane were evaluated. Polytetrafluoroethylene was mixed in carbon black powder supporting platinum catalyst fine particles, and a 250 μm thick sheet-shaped gas diffusion electrode was produced by using a roll press. A membrane electrode assembly was produced by inserting the cation exchange membrane between the two gas diffusion electrodes and stacking them using a flat plate heat press. The amount of platinum catalyst in the membrane electrode assembly was 1 mg per 1 cm ² of membrane area.

Next, the membrane electrode assembly is used as a titanium current collector,
A gas supply chamber made of PTFE and a heater were sandwiched in this order from both sides, and a fuel cell having an effective membrane area of 9 cm ² was assembled. At this time, 1.1 meq of the cation exchange membrane / polymer film of dry resin on the negative electrode side, 1.0 meq / g of the positive electrode
The fuel cell was assembled with the polymer film of the dry resin facing. When the cell temperature was maintained at 80 ° C. and oxygen was supplied to the positive electrode and hydrogen was supplied to the negative electrode at 5 atm, respectively, the terminal voltage with respect to the current density was measured. The current density was 1 A / cm ²
The cell voltage was 0.62V.

Comparative Example 1 A copolymer of the same ion exchange capacity of 1.0 meq / g dry resin as used in Example 1 was extruded at 220 ° C. to form a film having a thickness of 100 μm. This was treated in the same manner as in Example 1 to produce a cation exchange membrane. After assembling the fuel cell by the same method as in Example 1, the terminal voltage with respect to the current density was measured under the same conditions and the cell density was 0.60 V at a current density of 1 A / cm ² .

As can be seen from the above results, the cation exchange membrane of Example 1 has a smaller energy loss when the fuel cell is assembled than the membrane of Comparative Example 1.

[0024]

EFFECTS OF THE INVENTION By using a cation exchange membrane having a low electric resistance, which is not available in conventional membranes, as a solid polymer electrolyte, a high performance solid polymer electrolyte fuel cell can be obtained.

Front page continuation (72) Inventor Haruhisa Miyake 1150 Hazawa-machi, Kanagawa-ku, Yokohama-shi, Kanagawa Asahi Glass Co., Ltd. Central Research Laboratory

Claims (4)

[Claims] 1. A fuel cell comprising a cation exchange membrane made of a perfluorocarbon polymer having a sulfonic acid group as a solid polymer electrolyte, wherein the cation exchange membrane has at least two layers having different water contents. A polymer electrolyte fuel cell, comprising a laminate of fluorocarbon polymer films, wherein the film on the side facing the positive electrode has the highest water content. 2. A solid polymer electrolyte fuel cell according to claim 1, wherein the water content of the perfluorocarbon polymer film facing the positive electrode is higher by 5 to 50% by weight than that of the perfluorocarbon polymer film facing the negative electrode. . 3. The solid polymer electrolyte fuel cell according to claim 1, wherein the water content of the perfluorocarbon polymer film is 30 to 110% by weight. 4. The perfluorocarbon polymer is CF ₂ ═C.
F ₂ and _{CF 2 = CF- (OCF 2 CFX} ) m -O q -
(CF _{2) n} -A (wherein m = 0~3, n = 0~12, q
= 0 or 1, X = F or CF ₃ , A = sulfonic acid type functional group), The solid polymer electrolyte fuel cell according to claim 1, 2 or 3.