JP3342726B2 - Solid polymer electrolyte fuel cell and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates, related to the solid polymer electrolyte fuel cell and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, a fuel cell using a proton conductive polymer membrane as an electrolyte (solid polymer electrolyte fuel cell)
Research is progressing. Solid polymer electrolyte fuel cells
It has the feature that it operates at low temperature and has a high output density and can be miniaturized, and is expected to be used for applications such as power supplies for vehicles.

[0003]

The polymer membrane used for the solid polymer electrolyte fuel cell usually has a thickness of 100 to 20.
A proton conductive ion exchange membrane of 0 μm is used, and a cation exchange membrane made of a perfluorocarbon polymer having a sulfonic acid group has been widely studied because of its excellent basic characteristics. However, the electric resistance of the currently proposed cation exchange membrane is not necessarily sufficiently low from the viewpoint of obtaining a battery with a higher output density.

As a method for reducing the electric resistance of the cation exchange membrane, there is an increase in the sulfonic acid group concentration and a decrease in the film thickness. However, a remarkable increase in the sulfonic acid group concentration causes a decrease in the mechanical strength of the membrane or a long term. problems such as film reduces the ease no longer durability creep in operation occurs. On the other hand, reducing the film thickness causes problems such as lowering the mechanical strength of the film and further lowering the workability and handling properties such as bonding with the gas diffusion electrode.

As a method for solving the above problems, a composite cation exchange membrane comprising a film of a perfluorocarbon polymer containing a sulfonic acid group and a porous material of polytetrafluoroethylene (PTFE) has been proposed (Mark. W.
Barbrudge et al., AIChE Journal, 1992, 3
8,93. Hereinafter, this is referred to as Document 1. However, it has been found that although the film thickness can be reduced, the electrical resistance of the film is not sufficiently reduced with the porous PTFE.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has been developed to solve the above-mentioned problems and to provide a sulfonic acid group-containing resin reinforced with a fibril- like fluorocarbon polymer reinforcing material. A cation exchange membrane made of a fluorocarbon polymer is used as a solid polymer electrolyte, and the surface of the cation exchange membrane is
The gas diffusion electrode is disposed in close contact that provides a fuel cell of a solid polymer electrolyte type, wherein the. Also,
A perfluorocarbon polymer containing a sulfonic acid group;
After mixing with PTFE fine powder, extrusion molding
Membrane and reinforced with fibril-like PTFE reinforcement
Cation exchange membrane, and the cation exchange membrane
Gas diffusion electrode is placed in close contact with the surface as a proton electrolyte
Of a polymer electrolyte fuel cell
A manufacturing method is provided.

In the present invention, the fluorocarbon polymer which is a constituent material of the reinforcing material may be a homopolymer or a copolymer such as perfluoroolefin such as tetrafluoroethylene and hexafluoropropylene, chlorotrifluoroethylene and perfluoro (alkyl vinyl ether). Polymers are exemplified. Specific examples thereof include PTFE, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoro (propyl vinyl ether) copolymer (PFA), polychlorotrifluoroethylene, and tetrafluoroethylene-perfluoro. Examples thereof include (2,2-dimethyl-1,3-dioxole) copolymer and polyperfluoro (butenyl vinyl ether), and a perfluorocarbon polymer such as PTFE, FEP or PFA is particularly preferable in terms of characteristics.

[0008] Such polymers are in the form of fibrils ,
It is used as a reinforcing material for a cation exchange membrane made of a perfluorocarbon polymer containing a sulfonic acid group (hereinafter referred to as a sulfonic acid type). Fibrillar forms that increase the及beauty electrical resistance is small can be compared to the PTFE porous body in document 1 can be arbitrarily selected percentage of incorporation of the cation exchange membrane, further excellent dimensional stability It has advantages such as that you are.

The method of applying the reinforcing material to the cation exchange membrane is not particularly limited. For example , a sulfonic acid-type perfluorocarbon polymer constituting the cation exchange membrane and PTFE fine powder are mixed and then extruded to form a film. The method is adopted.

The sulfonic acid type perfluorocarbon polymer used in the present invention includes tetrafluoroethylene and CF ₂ ＣＦCF— (OCF ₂ CFX) _m —O _q — (CF ₂ ) _n
-A (m is 0 to 3, n is 0 to 12, q is 0 or 1,
X is F or CF ₃ , A is a sulfonic acid group. A copolymer with a fluorovinyl compound represented by the formula (1) can be preferably employed.

Preferred examples of the above fluorovinyl compound include CF ₂ ＣＦCFO (CF ₂ ) _r SO ₃ H and CF ₂ ＣC.
FOCF ₂ CF (CF ₃ ) O (CF ₂ ) _s SO ₃ H , CF ₂ =
CF (CF ₂ ) _t SO ₃ H , CF ₂ = CF (OCF ₂ CF
(CF ₃ )) _uO (CF ₂ ) ₂ SO ₃ H , and the like. Where r is 1 to 8, s is 1 to 8, and t is
Is 0-8 and u is 1-5. The concentration of the sulfonic acid group in the sulfonic acid type perfluorocarbon polymer, that is, the ion exchange capacity is 0.5 to 2.0 meq / g dry resin, and further 0.7 to 1.6 meq / g dry. The range of the resin is preferred. When the ion exchange capacity is lower than this range, the electric resistance of the membrane increases, while when the ion exchange capacity is high, the mechanical strength of the membrane is hardly sufficient.

In the cation exchange membrane, the ratio of the fluorocarbon polymer used as a reinforcing material to the sulfonic acid type perfluorocarbon polymer is 0.1 / 99.9 to 50 /.
50 (weight ratio), more preferably 0.5 / 99.5 to 40/60
(Weight ratio) is preferable. When the proportion of the reinforcing material is larger than this range, the membrane resistance increases, while when the proportion is small, the reinforcing effect is hard to appear.

A cation exchange membrane made of a reinforced sulfonic acid type perfluorocarbon polymer is assembled with a gas diffusion electrode on the surface thereof according to a commonly known method, and then a current collector is attached to the membrane to form a fuel cell.

The gas diffusion electrode is usually made of a porous sheet in which conductive carbon black powder carrying platinum catalyst fine particles is held by a hydrophobic resin binder such as PTFE. It may contain an acid-type perfluorocarbon polymer or fine particles whose surface is coated with the polymer. The gas diffusion electrode and the cation exchange membrane are brought into close contact with each other by a hot press method or the like.

As the current collector, a conductive carbon plate having a groove serving as a passage for the fuel gas or the oxidizing gas is used.

[0016] is supplied hydrogen gas to the negative hydrogen gas fuel cells to the positive electrode side is supplied oxygen or air, chemical energy is converted into electrical energy by the following reaction. ^{_{Anode: H 2 → 2H + + 2e}} - ^{_{cathode: 1 / 2O 2 + 2H +}} + 2e - → H 2 O

[0017]

EXAMPLES Example 1 According to the method described in JP-A-2-88645, an ion exchange capacity of 1.1 meq / g of dry resin C
F ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ SO ₂ F and a copolymer of tetrafluoroethylene and 1% by weight of the copolymer were mixed with fine powder made of PTFE, and then mixed with 220 extruded film formation at ° C., reinforced by fibrin Le
A film having a thickness of 100 μm was obtained. Next, the film was hydrolyzed in an aqueous solution containing 30% by weight of dimethyl sulfoxide and 15% by weight of potassium hydroxide, washed with water, and then immersed in 1N hydrochloric acid at 25 ° C. for 24 hours. About the obtained cation exchange membrane, using the Mullen-type tear strength tester, tear strength (when parallel to the extrusion direction)
Was measured, the tear strength was 65 g.

The PTFE-made file on the same copolymer as used in Comparative Example 1 Example 1
After extruding the film at 220 ° C. without mixing the powder and obtaining a film having a thickness of 100 μm, the tear strength of the cation exchange membrane obtained by performing the same treatment as in Example 1 was measured. there were.

Example 2 The fuel cell characteristics of the cation exchange membrane reinforced with fibrils obtained in Example 1 were evaluated. PTFE was mixed with the carbon black powder carrying the platinum catalyst fine particles, and a 250 μm-thick sheet-shaped gas diffusion electrode was prepared using a roll press. The cation exchange membrane was inserted between the two gas diffusion electrodes, and laminated by using a flat plate heat press to produce a membrane electrode assembly. The platinum catalyst amount of the membrane electrode assembly was 1 mg per cm ² of the membrane area.
Next, the membrane electrode assembly is sandwiched between a collector made of titanium, a gas supply chamber made of PTFE, and a heater in this order, and the effective membrane area is 9 cm.
We assembled ² fuel cells. The cell voltage was 0.60 V at a current density of 1 A / cm ² when the cell temperature was maintained at 80 ° C. and the terminal voltage was measured with respect to the current density when oxygen was supplied to the positive electrode and hydrogen was supplied to the negative electrode at 5 atm.

Comparative Example 2 A fuel cell was assembled in the same manner as in Example 2 with the reinforced cation exchange membrane produced in Comparative Example 1, and the terminal voltage with respect to the current density was measured under the same conditions. When measured, the cell voltage was 0.60 V at a current density of 1 A / cm ² .

[0021] As can be seen from the above results, the cation exchange membrane of Example 1, despite having a high tear strength as compared with the film of Comparative Example 1, Ru can hold substantially the same fuel cell characteristics.

[0022]

According to the present invention, a solid polymer electrolyte is used as a reinforced cation exchange membrane having a low electric resistance and a high mechanical strength which cannot be obtained in a conventional membrane, and a high-performance solid polymer electrolyte fuel cell can be obtained.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-53-141187 (JP, A) JP-A-63-37134 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 8 / 02,8 / 10 C08J 5 / 04,5 / 22

Claims (6)

(57) [Claims] A cation exchange membrane comprising a sulfonic acid group-containing perfluorocarbon polymer reinforced with a fibril- like fluorocarbon polymer reinforcing material is used as a solid polymer electrolyte, and gas diffusion is performed on the surface of the cation exchange membrane. Electrodes are dense
A solid polymer electrolyte type fuel cell, wherein the fuel cell is disposed while being worn . 2. The ratio of the fluorocarbon polymer reinforcing material to the sulfonic acid group-containing perfluorocarbon polymer in the cation exchange membrane is 0.1 / 99.9 to 50/50 (weight ratio). 2. The solid polymer electrolyte fuel cell according to 1. 3. The method according to claim 1, wherein the fluorocarbon polymer reinforcing material comprises polytetrafluoroethylene, tetrafluoroethylene-perfluoro (propyl vinyl ether) copolymer, or tetrafluoroethylene-hexafluoropropylene copolymer. The solid polymer electrolyte type fuel cell according to the above. 4. A perfluorocarbon polymer containing a sulfonic acid group, CF ₂ = CF ₂ and CF ₂ = CF- (OCF _{2
CFX) m -O q - (CF} 2) n -A ( wherein m is 0 to 3, n
= 0 to 12, q is 0 or 1, X is F or CF _3, A is a sulfonic acid group. 4. The copolymer of claim 1, 2 or 3, wherein
4. The solid polymer electrolyte fuel cell according to item 1. (5) Perfluorocar containing sulfonic acid group
Bone polymer and polytetrafluoroethylene fine particles
Powder and then extruded to form a fibril
Reinforced with polytetrafluoroethylene reinforcing material
A cation exchange membrane, and the cation exchange membrane is a solid polymer.
A gas diffusion electrode is placed in close contact with the surface as an electrolyte
Of a solid polymer electrolyte fuel cell
Construction method. 6. Reinforcing material and sulfone in the cation exchange membrane
The ratio with the perfluorocarbon polymer containing an acid group is
The ratio is 0.1 / 99.9 to 50/50 (weight ratio).
6. The method for producing a solid polymer electrolyte fuel cell according to 5.