JP2002367625A - Electrode structure for solid polymer fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode structure for solid polymer furl cell having a polymer electrolyte film with excellent flexibility, with excellent power generation property, which can be easily manufactured. SOLUTION: The electrode structure comprises a pair of electrode catalysis layers containing carbon grains to which, platinum grains are adhered, and a polymer electrolyte film laid between both electrode catalysis layers. The polymer electrolyte film is composed of a sulfonated compound which is a co-polymer of a first repeating unit expressed by the formula 1, and a second repeating unit expressed by the formula 2. The electrode catalysis layer contains platinum by 0.01-0.8 mg/cm<2> , and the range of the average diameter of the carbon grain is 10-100 nm. The co-polymer is composed of the first repeating unit of 10-80 mol%, and the second repeating unit of 90-20 mol%. The co-polymer contains sulfonic acid group within a range of 0.5-0.3 milliequivalent/g. In the formulas, A represents an electron attractive radical, B represents an electron donating radical, n is 0 or 1, Y is -C(CF3 )2 - or -SO2 -, and the benzene ring includes its derivative.

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, there is a problem that all of the ion conductive materials are inferior in ionic conductivity and mechanical strength.

On the other hand, US Pat. No. 5,403,675 proposes, as the inexpensive ion conductive material, a material obtained by sulfonating rigid polyphenylene. The sulfonated product of rigid polyphenylene described in the above specification is obtained by sulfonating a polymer obtained by polymerizing an aromatic compound having a phenylene chain as a main component, and has excellent ionic conductivity.

However, it is difficult to control the amount of sulfonic acid groups introduced into the sulphonated product of the rigid polyphenylene, and when the sulfonic acid group content is excessive, the toughness is reduced, and the sulphonated product of the rigid polyphenylene is increased. When the electrode structure is configured as a molecular electrolyte membrane, there is a disadvantage that the polymer electrolyte membrane is easily broken.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances and provides an electrode for a polymer electrolyte fuel cell having a polymer electrolyte membrane having excellent toughness, being easy to manufacture, and having excellent power generation performance. It is intended to provide a structure.

[0011]

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 comprises a sulfonated copolymer of a first repeating unit represented by the general formula (1) and a second repeating unit represented by the general formula (2). 0.01 to 0.8 mg / cm ^{2, and} the carbon particles have an average diameter of 10 to 100 mg / cm ^2.
nm.

[0012]

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The sulfonate constituting the polymer electrolyte membrane is a copolymer of a first repeating unit represented by the general formula (1) and a second repeating unit represented by the general formula (2) Is obtained by sulfonation. In the present specification, the electron-withdrawing group means -CO-, -CONH-,-(CF
_{2) p} - _(p is an integer of from 1 to _{10), - C (CF 3)} 2 -, -
COO -, - SO -, - SO 2 - Hammett substituent constant of 0.06 or more is in the meta position of the phenyl group such as in the para position of the phenyl group means a divalent group of 0.01 or more values.
In the present specification, the electron donating group is -O
-, -S-, -CH = CH-, -C≡C- and the like divalent groups.

Here, the sulfonation occurs on a benzene ring to which an electron-withdrawing group is not bonded, in other words, a benzene ring to which only an electron-donating group is bonded. Therefore, when a copolymer of the first repeating unit represented by the general formula (1) and the second repeating unit represented by the general formula (2) is sulfonated, the main chain of the first repeating unit is A sulfonic acid group is not introduced into the benzene ring of the formula (1) and each benzene ring of the second repeating unit, but a sulfonic acid group is introduced into the benzene ring of the side chain of the first repeating unit. Therefore, in the copolymer, by controlling the molar ratio of the first repeating unit and the second repeating unit, the amount of the sulfonic acid group introduced is controlled, and the ion conductivity and the toughness are improved. An excellent polymer electrolyte membrane can be obtained.

Specific examples of the monomer used for the first repeating unit include 2,5-dichloro-4 '-(4-phenoxyphenoxy) benzophenone represented by the following formula (3).

[0016]

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Further, as the monomer used for the first repeating unit, specifically, 2,2 represented by the following formula (4):
-Bis [4- {4- (4-chlorobenzoyl) phenoxy} phenyl] -1,1,1,3,3,3-hexafluoropropane; 2,2-bis [4 represented by the following formula (5):
-{4- (4-chlorobenzoyl) phenoxy} phenyl] sulfone;

[0018]

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The electrode structure of the present invention can be easily manufactured by using a sulfonated product of the copolymer as the polymer electrolyte membrane, and can obtain excellent power generation performance. In the electrode structure of the present invention, the electrode catalyst layer sandwiching the polymer electrolyte membrane contains platinum in the range of 0.01 to 0.8 mg / cm ² as a catalyst, and the platinum catalyst carrier When the average diameter of the resulting carbon particles is in the range of 10 to 100 nm, more excellent power generation performance can be obtained.

The platinum content is 0.01 mg / cm ²
If it is less than 0, sufficient power generation performance may not be obtained.
If it exceeds 8 mg / cm ² , the platinum acts as a negative catalyst, and the deterioration of the copolymer constituting the polymer electrolyte membrane may be 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 may not be obtained.

In the electrode structure of the present invention, the copolymer constituting the polymer electrolyte membrane is used in order to control the amount of sulfonic acid groups to be introduced so that the ion conductivity and the toughness are in the preferred ranges. It is preferable that the first repeating unit comprises 10 to 80 mol% and the second repeating unit has 90 to 20 mol%. 10 mol% of the first repeating unit
When the content of the second repeating unit is less than 90 mol%, the amount of the sulfonic acid group introduced into the copolymer may be small, and sufficient ion conductivity may not be obtained. When the amount of the first repeating unit exceeds 80 mol% and the amount of the second repeating unit is less than 20 mol%, the amount of sulfonic acid groups introduced into the copolymer increases, and sufficient toughness is obtained. May not be obtained.

In the electrode structure of the present invention, the sulfonated copolymer of the polymer electrolyte membrane may be
In order to set the ion conductivity and the toughness in a preferable range, the sulfonic acid group is preferably contained in a range of 0.5 to 3.0 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 the amount exceeds 3.0 milligram equivalent / g, sufficient toughness is obtained. May not be obtained.

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

[0025]

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 and 1, a polymer electrolyte membrane 2 sandwiched between the two electrode catalyst layers 1 and 1, and each electrode catalyst layer. And diffusion layers 3 and 3 laminated on the layers 1 and 1.

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

First, 2,5-dichloro-4 '-(4-phenoxyphenoxy) benzophenone represented by the following formula (3) and 2,2-bis [4- {4
-(4-chlorobenzoyl) phenoxydiphenyl]-
1,1,1,3,3,3-hexafluoropropane was polymerized at a polymerization ratio of 50:50 to obtain a copolymer represented by the following formula (6).

[0029]

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The copolymer preferably has a polymer molecular weight in the range of 10,000 to 1,000,000 in terms of polystyrene equivalent weight average molecular weight. If the polymer molecular weight is less than 10,000, a suitable mechanical strength as a polymer electrolyte membrane may not be obtained, and if it exceeds 1,000,000, the solubility is low when dissolving in a solvent for film formation as described below. Or the viscosity of the solution increases, making handling difficult.

Next, concentrated sulfuric acid was added to the copolymer to sulfonate it, and a sulfonated product having an ion exchange capacity of 2.1 meq / g was obtained. Next, the sulfonated product of the copolymer is
The polymer electrolyte solution 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.

Next, platinum particles were carried 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 at a weight ratio of carbon black: PTFE particles = 4: 6, and the resulting mixture is uniformly dispersed in ethylene glycol Is applied to 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 electrode catalyst layer 1 side, and hot pressed to obtain an 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 polymer electrolyte membrane 2 used in this embodiment is
It exhibited excellent toughness, and could be easily sandwiched by the pair of electrodes and hot-pressed.

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 the present 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 0.62 V. The results are shown in FIG.

Next, as another embodiment, the above formula (4)
2,2-bis [4- {4- (4-chlorobenzoyl) phenoxy} phenyl] -1,1,1,3,
Except that 3,3-hexafluoropropane was changed to 2,2-bis [4- {4- (4-chlorobenzoyl) phenoxy} phenyl] sulfone represented by the following formula (5),
The electrode structure shown in FIG. 1 was manufactured in exactly the same manner as in the above embodiment, and the electrode structure (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 Example 2 was 0.6.
3V. The results are shown in FIG.

[0041]

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Next, for comparison, the electrode shown in FIG. 1 was made exactly the same as the above embodiment except that a polymer electrolyte membrane 2 made of polyetheretherketone represented by the following formula (7) was used. A structure was manufactured, and the electrode structure (Comparative Example 1) was manufactured.
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 1 was 0.52 V. The results are shown in FIG.

[0043]

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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) 5H018 AA06 AS02 AS03 BB03 BB06 BB08 BB12 BB16 DD08 EE03 EE08 HH01 HH05 5H026 AA06 CC03 CX05 EE02 EE05 HH01 HH05

Claims (4)

[Claims] 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 comprises a sulfonated copolymer of a first repeating unit represented by the general formula (1) and a second repeating unit represented by the general formula (2), The electrode catalyst layer contains platinum in the range of 0.01 to 0.8 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 2. The copolymer according to claim 1, wherein the first repeating unit 1
The electrode structure for a polymer electrolyte fuel cell according to claim 1, comprising 0 to 80 mol% and 90 to 20 mol% of the second repeating unit. 3. The solid polymer according to claim 1, wherein the sulfonated product of the copolymer contains a sulfonic acid group in the range of 0.5 to 3.0 milligram equivalent / g. Electrode structure for molecular fuel cells. 4. 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 ( A first repeating unit represented by 1) and a general formula (2)
Wherein the electrode catalyst layer comprises a sulfonated product of a copolymer with a second repeating unit represented by the following formula:
an electrode structure that contains platinum of ² cm ² and has an average diameter of the carbon particles in the range of 10 to 100 nm, and supplies an oxidizing gas to one surface and supplies a reducing gas to the other surface. A polymer electrolyte fuel cell characterized in that it generates electric power by performing the above steps. Embedded image