JP2002367629A - Electrode structure for solid polymer furl cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode structure for solid polymer furl cell having a cheap polymer electrolyte film made of ion conductive material, with excellent power generating property. SOLUTION: For the electrode structure for solid polymer furl cell, a polymer electrolyte film has repeating units expressed by the formula 1 or the formula 2, and composed of a sulfonated compound of polyether group of which, the range of molecular weight is 10,000-1,000,000. An electrode catalyst layer contains platinum within a range of 0.01-0.6 mg/cm<2> , and the range of average diameter of carbon grain is 10-100 nm. In the formulae, X represents an electron attractive radical, R1 and R2 represent H or hydrocarbon radical with one valence, R3 -R6 represent H, halogen atom, or cyanic radical, a and b represent integers of 0-4, C is 0 or 1, d is 1 or 2. As for Y, 2,5-dihydroxybiphenyl, 4,4'- dichlorobenzophenone, 4,4'-(9H-fluorene-9-ylidene)bisphenol and the like are shown as examples.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode structure used for a polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art While petroleum resources are being depleted, environmental problems such as global warming due to consumption of fossil fuels are becoming more serious.
Fuel cells have attracted attention as a clean power source for electric motors without the generation of carbon dioxide, and have been widely developed.
Some have begun to be commercialized. When the fuel cell is mounted on an automobile or the like, a solid polymer fuel cell using a polymer electrolyte membrane is preferably used because a high voltage and a large current are easily obtained.

As an electrode structure used in the polymer electrolyte fuel cell, a pair of catalysts such as platinum is formed by carrying a catalyst such as platinum on a catalyst carrier such as carbon black and integrated with an ion-conductive polymer binder. There is known an electrode catalyst layer in which an ion-conductive polymer electrolyte membrane is sandwiched between both electrode catalyst layers, and a diffusion layer is laminated on each electrode catalyst layer. The electrode structure further constitutes a polymer electrolyte fuel cell by stacking a separator also serving as a gas passage on each electrode catalyst layer.

In the polymer electrolyte fuel cell, a reducing gas such as hydrogen or methanol is introduced through the diffusion layer using one electrode catalyst layer as a fuel electrode, and the other electrode catalyst layer is used as an oxygen electrode. An oxidizing gas such as air or oxygen is introduced through the diffusion layer. With this configuration, on the fuel electrode side, protons are generated from the reducing gas by the action of the catalyst contained in the electrode catalyst layer, and the protons pass through the polymer electrolyte membrane to the electrode on the oxygen electrode side. Move to the catalyst layer. Then, the protons react with the oxidizing gas introduced into the oxygen electrode in the electrode catalyst layer on the oxygen electrode side by the action of a catalyst contained in the electrode catalyst layer to generate water. Therefore, a current can be taken out by connecting the fuel electrode and the oxygen electrode with a conducting wire.

Conventionally, in the above electrode structure, a perfluoroalkylenesulfonic acid polymer compound (for example, Nafion (trade name) manufactured by DuPont) is used as the polymer electrolyte membrane.
Is widely used. The perfluoroalkylenesulfonic acid polymer compound has excellent proton conductivity due to being sulfonated, and also has chemical resistance as a fluororesin, but is very expensive. There's a problem.

Therefore, it has been studied to construct an electrode structure for a polymer electrolyte fuel cell using an inexpensive ion conductive material instead of a perfluoroalkylenesulfonic acid polymer compound.

As the inexpensive ion conductive material, there is, for example, a material obtained by sulfonating polyether ketone or polybenzimidazole. However, the above-mentioned ion-conductive materials are all inferior in ionic conductivity, and there is a disadvantage that sufficient power generation performance cannot be obtained with an electrode structure provided with a polymer electrolyte membrane made of the ion-conductive material.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned disadvantages, and provides a polymer electrolyte membrane made of an inexpensive ion-conductive material and a solid polymer fuel cell having excellent power generation performance. An object is to provide an electrode structure.

[0009]

In order to achieve the above object, an electrode structure for a polymer electrolyte fuel cell according to the present invention is provided.
An electrode structure for a polymer electrolyte fuel cell, comprising: a pair of electrode catalyst layers containing carbon particles carrying platinum particles as a catalyst; and a polymer electrolyte membrane sandwiched between both electrode catalyst layers. The electrolyte membrane includes a repeating unit represented by the general formula (1) or (2), and is formed of a sulfonated polyether-based polymer having a weight average molecular weight in the range of 10,000 to 1,000,000. The catalyst layer is 0.01 ~
It is characterized in that it contains platinum in the range of 0.6 mg / cm ^{2 and} the carbon particles have an average diameter of 10 to 100 nm.

[0010]

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[0011]

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The polyether polymer comprising a repeating unit represented by the above general formula (1) or (2) is inexpensive because it does not contain fluorine in its molecular structure, and constitutes the polymer electrolyte membrane. Is obtained by sulfonating the polyether-based polymer. In the present specification, the electron-withdrawing group is -CO-, -C
_{ONH -, - (CF 2)} p - (p is an integer of from 1 to 10), -
The Hammett's substituent constant such as C (CF ₃ ) _2- , -COO-, -SO-, -SO _2- is 0.0 at the meta position of the phenyl group.
A divalent group having a value of 6 or more and a value of 0.01 or more in the para position of the phenyl group.

The polyether polymer needs to have a weight average molecular weight in the range of 10,000 to 1,000,000 in order to form the polymer electrolyte membrane by forming a film after sulfonation. If the weight average molecular weight of the polyether polymer is less than 10,000, the mechanical strength as a film is insufficient,
If it exceeds 1,000,000, the solubility in a solvent becomes insufficient and the film formation itself becomes difficult.

In the electrode structure of the present invention, the polyether polymer sulfonate is used as the polymer electrolyte membrane, and the electrode catalyst layer sandwiching the polymer electrolyte membrane has a catalyst of 0.01 to 0 as a catalyst. Excellent power generation performance can be obtained by containing platinum in the range of 0.6 mg / cm ² and the average diameter of the carbon particles serving as the platinum catalyst carrier being in the range of 10 to 100 nm.

The platinum content is 0.01 mg / cm ²
If the amount is less than 0.6 mg / cm, sufficient power generation performance cannot be obtained.
^If it exceeds ² , the platinum acts as a negative catalyst, and the deterioration of the copolymer constituting the polymer electrolyte membrane is promoted.

When the average diameter of the carbon particles is less than 10 nm, the dispersibility of the platinum is reduced. When the average diameter exceeds 100 nm, the activation overpotential becomes large, and sufficient power generation performance cannot be obtained.

Further, in the electrode structure of the present invention, the sulfonated product of the polyether polymer constituting the polymer electrolyte membrane has a sulfonic acid group in order to keep ion conductivity and toughness in a preferable range. Is preferably contained in the range of 1.5 to 3.5 milligram equivalent / g. If the amount of the sulfonic acid group contained in the copolymer is less than 0.5 milligram equivalent / g, sufficient ion conductivity may not be obtained, and if it exceeds 3.5 milligram equivalent / g, sufficient durability may be obtained. May not be obtained.

The polyether polymer can be obtained, for example, as a copolymer by polymerization of an aromatic active dihalide compound and a dihydric phenol compound. As the aromatic active dihalide compound, the compound represented by the general formula (1)
And 4,4'-dichlorobenzophenone.

Further, as the dihydric phenol compound, monomers corresponding to the general formula (3) include 2,2.
5-dihydroxybiphenyl, 2,5-dihydroxy-
Examples of the monomer corresponding to the general formula (4) such as methylbiphenyl include the general formula (4) such as 5,5 ′-(1-methylethylidene) bis [1,1 ′-(biphenyl) -2-ol]. As monomers corresponding to 4,4'-dichlorobenzophenone, 4,4 '-(9H-fluorene-9-ylidene) bisphenol, 4,4'-dichlorobenzophenone, and 4,4'-(9H-fluorene- 9
-Ylidene) bis [1-methylphenol] and the like.

The electrode structure of the present invention can constitute a polymer electrolyte fuel cell which generates electricity by supplying an oxidizing gas to one surface and a reducing gas to the other surface.

[0021]

Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. FIG. 1 is an explanatory cross-sectional view showing the configuration of the electrode structure of the present embodiment, and FIG. 2 is a graph showing the power generation performance of the electrode structure of the present embodiment.

As shown in FIG. 1, the electrode structure of the present embodiment comprises a pair of electrode catalyst layers 1, 1; a polymer electrolyte membrane 2 sandwiched between the two electrode catalyst layers 1, 1; And diffusion layers 3 and 3 laminated on the layers 1 and 1.

In this embodiment, the electrode structure was manufactured as follows.

First, 4,4'-dichlorobenzophenone represented by the following formula (6) and 4,4'-dichlorobenzophenone represented by the following formula (7)
4 ′-(9H-fluorene-9-ylidene) bisphenol is polymerized at a polymerization ratio of 50:50 to obtain the following formula (8)
Was obtained.

[0025]

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Next, concentrated sulfuric acid was added to the polyether copolymer to sulfonate it, and the ion exchange capacity was 2.1 me.
q / g of the sulfonate was obtained. Next, the sulfonated product of the polyether copolymer was dissolved in N-methylpyrrolidone to prepare a polymer electrolyte solution, and a polymer electrolyte membrane 2 having a dry film thickness of 50 μm was formed from the polymer electrolyte solution by a casting method. did.

Next, platinum particles were supported on carbon black (furnace black) having an average diameter of 50 nm at a weight ratio of carbon black: platinum = 1: 1 to prepare catalyst particles. Next, the catalyst particles were added to a solution of a perfluoroalkylenesulfonic acid polymer compound (Nafion (trade name) manufactured by DuPont) as an ion conductive binder, and the weight of the ion conductive binder: catalyst particles = 8: 5. The catalyst paste was prepared by uniformly dispersing the catalyst paste in the same ratio.

Next, a slurry in which carbon black and polytetrafluoroethylene (PTFE) particles are mixed in a weight ratio of carbon black: PTFE particles = 4: 6, and the resulting mixture is uniformly dispersed in ethylene glycol Is applied on one side of carbon paper and dried to form an underlayer, and a diffusion layer 3 comprising the underlayer and carbon paper is formed.
Were created.

Next, on each of the diffusion layers 3, the catalyst paste
With a platinum content of 0.5 mg / cm ^TwoSo that
The electrode catalyst layer 1 is formed by lean printing and drying.
Then, a pair of electrodes composed of the electrode catalyst layer 1 and the diffusion layer 3 is formed.
Done. The drying was performed at 60 ° C. for 10 minutes.
Thereafter, vacuum drying was performed at 120 ° C. for 60 minutes.

Next, the polymer electrolyte membrane 2 was sandwiched between the electrodes on the side of the electrode catalyst layer 1 and hot pressed to obtain the electrode structure shown in FIG. The hot press is 80 ° C, 5MP
After primary hot pressing for 2 minutes at 160 ° C, 4MP
The secondary hot pressing was performed for 1 minute at a.

The electrode structure obtained in this embodiment can constitute a polymer electrolyte fuel cell by further laminating a separator also serving as a gas passage on the diffusion layers 3 and 3.

Next, the electrode structure obtained in this embodiment (Example 1) was used as a single cell to test the power generation performance. In the power generation performance test, power was generated by supplying air using the one diffusion layer 3 side as an oxygen electrode and supplying pure hydrogen using the other diffusion layer 3 side as a fuel electrode to generate a current density of 1 A / cm ^2.
After generating power for 200 hours, the measurement was performed by measuring the cell potential at a current density of 1 A / cm ² . The power generation conditions were a temperature of 85 ° C., a relative humidity of 40% on the fuel electrode side, and a relative humidity of 75% on the oxygen electrode side.

As a result, the cell potential of the electrode structure of Example 1 was 0.60 V. The results are shown in FIG.

Next, as another embodiment, the above equation (7)
In place of the 4,4 ′-(9H-fluorene-9-ylidene) bisphenol represented by
4 '-(9H-fluoren-9-ylidene) bis [2-
1 was manufactured in exactly the same manner as in the above embodiment except that methyl phenol was used, and the electrode structure (Example 2) was made the same as the above embodiment as a single cell. Then, the power generation performance was tested. As a result, Example 2
The cell potential of the electrode structure was 0.61 V. The results are shown in FIG.

[0035]

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Next, for comparison, the same as the above embodiment except that a polymer electrolyte membrane 2 made of polyetheretherketone represented by the following formula (10) was used.
The electrode structure shown in FIG. 1 was manufactured, and the electrode structure (Comparative Example 1) was used as a single cell.
The power generation performance was tested. As a result, the cell potential of the electrode structure of Comparative Example 1 was 0.52 V. The results are shown in FIG.

[0037]

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Further, for further comparison, except that the polymer electrolyte membrane 2 made of polybenzimidazole was used,
The electrode structure shown in FIG. 1 was manufactured exactly in the same manner as in the above embodiment, and the electrode structure (Comparative Example 2) was used as a single cell, and the power generation performance was tested in exactly the same manner as in the above embodiment. As a result, the cell potential of the electrode structure of Comparative Example 2 was 0.5
2V. The results are shown in FIG.

As shown in FIG. 2, the electrode structure of the present embodiment is the same as the electrode structure using the polymer electrolyte membrane 2 made of polyetheretherketone (Comparative Example 1) or the polymer electrolyte membrane 2 made of polybenzimidazole. It is clear that the electrode structure has much better power generation performance than the electrode structure used (Comparative Example 2).

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view showing a configuration of an electrode structure of the present invention.

FIG. 2 is a graph showing the power generation performance of the electrode structure of the present invention.

[Explanation of symbols]

 1 ... electrode catalyst layer, 2 ... polymer electrolyte membrane.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Nagayuki Kanaoka 1-4-1 Chuo, Wako-shi, Saitama Pref. Honda Technology Laboratory Co., Ltd. (72) Inventor Hiroshi Soma 1-4-1 Chuo, Wako-shi, Saitama No. F-term in Honda R & D Co., Ltd. (reference) 4J005 AA24 BA00 BD06 5H018 AA06 AS01 CC06 DD08 EE03 EE05 EE17 HH00 HH01 5H026 AA06 CX05 EE02 EE05 EE17 HH00 HH01

Claims (5)

[Claims] 1. An electrode structure for a polymer electrolyte fuel cell, comprising: a pair of electrode catalyst layers containing carbon particles carrying platinum particles as a catalyst; and a polymer electrolyte membrane sandwiched between both electrode catalyst layers. In the above, the polymer electrolyte membrane includes a repeating unit represented by the general formula (1) or (2), and has a weight average molecular weight in the range of 10,000 to 1,000,000, and is a sulfonated product of a polyether polymer. The electrode catalyst layer contains platinum in the range of 0.01 to 0.6 mg / cm ^{2 and} the carbon particles have an average diameter of 10
An electrode structure for a polymer electrolyte fuel cell, wherein the electrode structure is in the range of 100 nm to 100 nm. Embedded image Embedded image 2. The sulfonated product of the polyether polymer has a sulfonic acid group content of 1.5 to 3.5 milligram equivalent / g.
The electrode structure for a polymer electrolyte fuel cell according to claim 1, wherein the electrode structure is contained in the range of: 3. The polyether-based polymer is a copolymer obtained by polymerizing an aromatic active dihalide compound and a dihydric phenol compound.
3. An electrode structure for a polymer electrolyte fuel cell according to claim 2. 4. The polyether-based polymer is 4,4′-
4. A copolymer obtained by polymerizing dichlorobenzophenone and 4,4 '-(9H-fluoren-9-ylidene) bisphenol or a derivative thereof, wherein the copolymer is obtained by polymerization. Item 8. The electrode structure for a polymer electrolyte fuel cell according to Item 1. 5. A catalyst comprising a pair of electrode catalyst layers containing carbon particles carrying platinum particles as a catalyst, and a polymer electrolyte membrane sandwiched between both electrode catalyst layers, wherein the polymer electrolyte membrane has a general formula It comprises a sulfonated polyether polymer having a repeating unit represented by the general formula (1) or (2) and having a weight average molecular weight in the range of 10,000 to 1,000,000.白金 0.6 mg / cm ^{2, and} the carbon particles have an average diameter of 10-100
A polymer electrolyte fuel cell comprising an electrode structure in the range of nm and supplying an oxidizing gas to one surface and supplying a reducing gas to the other surface to generate power. Embedded image Embedded image