JPH06260184A - Fuel cell with solid highpolymer electrolyte - Google Patents

Abstract

PURPOSE:To provide a high performance fuel cell which uses a solid high- polymer electrolyte having a low electric resistance. CONSTITUTION:The solid electrolyte used consists of a positive ion exchange film which is made from a perfluorocarbon polymeride film having an AC specific resistance value of 5-11OMEGAcm.

Description

Detailed Description of the Invention

[0001]

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 the above-mentioned application, 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 excellent basic characteristics and have been widely studied. However, the electric 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 problems, and is a fuel cell using a cation exchange membrane of a perfluorocarbon polymer containing a sulfonic acid group as a solid polymer electrolyte. In the above, there is provided a solid polymer electrolyte fuel cell, wherein the cation exchange membrane has an AC specific resistance value of 5 to 11 Ωcm.

In the present invention, the AC specific resistance value of the cation exchange membrane is measured on a cation exchange membrane (the ion exchange group is an acid type) immersed in a 1 M aqueous sulfuric acid solution at 25 ° C. for 24 hours. It is calculated as 1.

[0007]

[Equation 1] AC specific resistance value (Ωcm) = resistance (Ω) × film effective area (cm ² ) ÷ film thickness (cm)

In the present invention, when the AC specific resistance value of the cation exchange membrane is larger than the above upper limit value, the membrane resistance is increased and the output of the battery is lowered, while when it is less than the lower limit value, the membrane strength and the membrane handling are improved. It is not preferable because it deteriorates the property. Among them, the AC specific resistance value is particularly preferably 6 to 10 Ωcm.

In the present invention, the method for keeping the AC specific resistance value of the cation exchange membrane within the above range is to adjust the swelling degree of the membrane to 50 to 90% by weight in the hydrolysis treatment in which an ion exchange group is introduced. The cation exchange membrane is boiled in pure water, or pressurized and heated to increase the degree of swelling to 65 to 110.
It can be preferably adopted that the content is set to weight%.

The cation exchange membrane of the perfluorocarbon polymer is preferably a single layer film, and the thickness thereof is preferably 30 to 300 μm, more preferably 50 to 250 μm. When it is smaller than the lower limit, the membrane strength and handleability in electrode bonding and the like are deteriorated. On the other hand, when it is larger than the upper limit, the membrane resistance is increased and the battery output is reduced, which is not preferable.

The perfluorocarbon polymer containing 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 , and A = sulfonic acid type functional group) can be preferably used. Preferred examples of the fluorovinyl compound include the compounds shown in Chemical formula 1 and the like.

[0012]

Embedded image 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 )) _1-5 O (CF ₂ ) ₂ SO ₂ F

Incidentally, perfluoroolefin such as hexafluoropropylene, chlorotrifluoroethylene or perfluoroalkoxy vinyl ether may be used in place of the above tetrafluoroethylene which is a monomer constituting the fluorocarbon polymer.

The cation exchange membrane composed of the perfluorocarbon polymer film may be reinforced with a fibril-like, woven cloth-like or non-woven cloth-like perfluorocarbon polymer.

The cation exchange membrane of the present invention has a gas diffusion electrode adhered to the surface thereof according to a conventional known method,
Then, a current collector is attached and the fuel cell is assembled. The gas diffusion electrode is usually composed of a sheet of a porous body in which conductive carbon black powder carrying platinum catalyst fine particles is held by a hydrophobic resin binder such as polytetrafluoroethylene (PTFE). The substance 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 the fuel gas or the oxidant gas is formed is used.

[0016]

EXAMPLES In accordance with the method described in JP-A-2-88645, CF ₂ ═CF ₂ and CF ₂ ═CFOCF ₂
Ion exchange capacity of 1.1 meq / g dry resin composed of a copolymer with CFCF ₃ O (CF ₂ ) ₂ SO ₂ F
Film extrusion was carried out at 0 ° C. to obtain a film having a thickness of 100 μm.

The above-mentioned copolymer film was hydrolyzed in a mixed aqueous solution of 30% by weight of dimethyl sulfoxide and 15% by weight of caustic potash, washed with water and then immersed in 1N hydrochloric acid. Next, the membrane was washed with water, the four sides of the membrane were restrained with dedicated jigs, and then dried at 60 ° C. for 1 hour to produce a cation exchange membrane. When the AC specific resistance value of this cation exchange membrane was measured, it was 8
It was Ωcm.

The fuel cell characteristics using this cation exchange membrane were evaluated. That is, PTFE was mixed with 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 was replaced with a titanium current collector,
When a gas supply chamber made of PTFE and a heater are sandwiched from both sides in this order, the temperature of the cell in which a fuel cell having an effective membrane area of 9 cm ² is assembled is maintained at 80 ° C, and oxygen is supplied to the positive electrode and hydrogen to the negative electrode at 5 atm, respectively. When the terminal voltage with respect to the current density was measured, the cell voltage was 0.65 V at a current density of 1 A / cm ² .

[0020]

[Comparative Example] CF ₂ ═CF ₂ and CF ₂ ═CFOCF _{2 based on the} method described in JP-A-2-88645.
An ion exchange capacity of 1.0 meq / g dry resin composed of a copolymer with CFCF ₃ O (CF ₂ ) ₂ SO ₂ F is used.
Film extrusion was carried out at 0 ° C. to obtain a film having a thickness of 100 μm. This was subjected to the same treatment as in the example to produce a cation exchange membrane. The AC specific resistance value of this film was 12.6 Ωcm.

After assembling the fuel cell by the same method as in the example, the terminal voltage with respect to the current density was measured under the same conditions. When the current density was 1 A / cm ² , the cell voltage was 0.6
It was 0V.

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

[0023]

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.

Claims (3)

[Claims] 1. A fuel cell in which a cation exchange membrane made of a perfluorocarbon polymer having a sulfonic acid group is a solid polymer electrolyte type, and the cation exchange membrane has 5-1.
A solid polymer electrolyte fuel cell having an AC specific resistance of 1 Ωcm. 2. The thickness of the cation exchange membrane is 30 to 300 μm.
The solid polymer electrolyte fuel cell according to claim 1. 3. 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), and the solid polymer electrolyte fuel cell according to claim 1 or 2.