JP3275652B2 - Electrode for polymer electrolyte fuel cell and fuel cell using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell using a reducing agent, such as pure hydrogen or reformed hydrogen from methanol and fossil fuel, and an oxidizing agent, such as air or oxygen, as a fuel. The present invention relates to a polymer fuel cell electrode and a polymer electrolyte fuel cell using the same.

[0002]

2. Description of the Related Art A polymer electrolyte fuel cell (PEFC) uses an ion exchange membrane, which is a solid polymer electrolyte, as an electrolyte. When hydrogen is used as a fuel, a reaction of formula (1) occurs at the negative electrode.

[0003]

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When oxygen is used as an oxidizing agent, a reaction of the formula (2) occurs at the positive electrode, and water is generated.

[0005]

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[0006] PEFC is a high-performance fuel cell capable of obtaining a high output of 1 A / cm ² or more at normal temperature and normal pressure. To achieve this high output, it is important to design an electrode in consideration of an increase in the contact area between Pt particles as an electrode catalyst and the solid polymer electrolyte, that is, a reaction area, and formation of a gas channel for supplying a reaction gas.

A phosphoric acid type fuel cell (PAFC) using a catalyst in which a noble metal similar to PEFC is supported on carbon for an electrode
In the case of an electrode for Electroanal. Che
m. , 195 (1985) 81, an electrolytic solution is held in fine pores having a diameter of 0.1 μm or less, and a diameter of 0.1 μm
The larger pores are said to be a supply path for the reaction gas. In JP-A-6-267545, the pore diameter of the catalyst layer is 0.1 μm or less and the volume of 0.1 to 1.0 μm is 42% or less, respectively, as the positive electrode of the phosphoric acid fuel cell.
A volume of 容積 100 μm is effective at 11% or more.

[0008]

SUMMARY OF THE INVENTION However, PEF
In the case of C, since a polymer having a bulk at the molecular level is used for the electrolyte, the reaction field formed is different from that of the conventional fuel cell using an electrolyte such as phosphoric acid, which is a low molecule. Conceivable. For this reason, Japanese Unexamined Patent Application Publication No.
No. 5 relates to an electrode for a phosphoric acid type fuel cell,
It does not serve as a guideline for designing electrodes. Also, until now, PEF
There has been no study on the pore structure of the electrode suitable for C. Therefore, in order to realize a higher performance PEFC, it is necessary to obtain an optimal pore structure of a PEFC electrode having a large contact area between the Pt catalyst and the solid polymer electrolyte and having a high reaction gas supply capability. Met.

The present invention has been made to solve the above-mentioned problems. The present invention examines the pore distribution of the catalyst layer of a PEFC electrode, and obtains an optimal pore structure of the PEFC electrode to obtain a high-performance PEFC electrode. Electrode and PEF using the same
C is intended to be provided.

[0010]

The electrode for a polymer electrolyte fuel cell of the present invention is an electrode in which a catalyst layer comprising a solid polymer electrolyte and a carbon powder supporting a noble metal catalyst is formed on one surface of a gas diffusion layer. The catalyst layer has a diameter of 0.04 to 1.0 μm.
m, having a specific volume of 0.06 cm.
3 / g or more, and the solid polymer electrolyte is
Are distributed.

Further, there is provided a polymer electrolyte fuel cell using the electrodes on at least one of the electrodes arranged on both sides of the polymer electrolyte membrane.

[0012]

In the electrode for PEFC, it can be said that the solid polymer electrolyte is distributed in pores having a diameter of 0.04 to 1.0 μm. That is, it is considered that the pores function as a reaction field. Further, it is considered that the pores also function as a supply path (gas channel) for a reaction gas of hydrogen and oxygen as in the case of the phosphoric acid type fuel cell. Therefore,
In PEFC, it can be said that the reaction field exists in pores having a diameter of 0.04 to 1.0 μm which also function as gas channels.

[0013] For this reason, by obtaining the optimum pore distribution for the PEFC in which the contact area between the Pt catalyst and the solid polymer electrolyte, that is, the reaction area is large, and the supply capability of the reaction gas is high, a higher pore distribution is obtained. A high-performance PEFC electrode and PEFC can be provided.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

Example 1 A 5% N solution manufactured by Aldrich Chemical Company as an alcohol solution of a solid polymer electrolyte was used.
afion solution with a solid polymer electrolyte mass of 0.1 to
The resultant was mixed and stirred with n-butyl acetate at a concentration of 1.4 mg / cm ² to produce colloidal dispersions of four types of polymer electrolytes. A Pt catalyst is added to this colloidal dispersion liquid for 20 to 30 minutes.
The carbon powder supported by weight% was added, and the colloid was adsorbed on the surface of the carbon powder supported by the Pt catalyst. This dispersion was made into a paste using an ultrasonic disperser. This paste was applied on carbon paper previously coated with 30 to 60% by weight of a fluororesin to prepare an electrode of the present invention.

In order to clarify the pore structure of the electrode in which the mass of the solid polymer electrolyte was changed, the pore distribution was measured by a mercury intrusion method.

FIG. 1 shows the change in pore distribution when the solid polymer electrolyte mass of the electrode is changed using Pt-supported carbon powder. From the figure, it can be seen that the specific pore volume (differential value) of the portion having a peak of 0.04 to 1.0 μm has a change due to the change in the solid polymer electrolyte mass. Note that 1.0
Although the specific volume of pores of μm or more also changes, this portion is a pore portion caused by carbon paper.

FIG. 2 shows the mass of the solid polymer electrolyte and the diameter of 0.04.
The relationship of the specific pore volume in the range of ~ 1.0 µm is shown. From the figure,
Due to the increase of the solid polymer electrolyte, the diameter is 0.04 to 1.0.
Since the specific volume of pores in μm decreases, it can be said that the solid polymer electrolyte was distributed in these pores.

That is, it is considered that the pores function as a reaction field. In addition, the diameter is 0.04 to 1.0 μm
Is considered to function as a supply channel (gas channel) for a reaction gas of hydrogen and oxygen, as in the case of the phosphoric acid type fuel cell. Therefore, in PEFC, the reaction field has a diameter of 0.04 to 1.0 μm which also functions as a gas channel.
It can be said that it exists in the fine pore portion.

Example 2 An electrode was manufactured in the same manner as in Example 1. At this time, nine types of carbon powders having different specific surface areas and primary particle diameters were used as carbon powders serving as a carrier of the Pt catalyst. The solid polymer electrolyte mass is 1.0 mg / c
It was m ^2.

This electrode was applied to both surfaces of a solid polymer electrolyte membrane Nafion 115 manufactured by DuPont at a temperature of 120 to 200 ° C.
Hot pressing was performed at a pressure of 50 to 100 kg / cm ² to produce a unit cell of the present invention.

The pore distribution of the electrode was measured by a mercury intrusion method. Further, the discharge test of the unit cell was performed at a normal pressure and a cell temperature of 50 ° C. using hydrogen-oxygen as fuel.

FIG. 3 shows the electrode of this embodiment having a diameter of 0.04 to 0.04.
The relationship between the specific pore volume at 1.0 μm and the current density at 850 mV of the cell is shown. As a result, the current density that can be taken out increased as the specific volume of the pores increased. Since the current density at 850 mV, which is the region where activation polarization is dominant, increases, it can be said that the reaction area increases along with the specific pore volume.

Note that the carbon at point A deviates from this straight line. This is because the addition amount of the solid polymer electrolyte in the electrode catalyst layer is constant at 1.0 mg / cm ^2, and the continuity of the solid polymer electrolyte is reduced due to the large pore specific volume, and the reaction area is reduced. is there. The solid polymer electrolyte mass was 1.
If optimized as 5 mg / cm ² , the reaction area increases and the current density increases as the pore specific volume increases,
Ride on a straight line. (Point A ').

FIG. 4 shows the electrode of the present embodiment having a diameter of 0.04 to 0.04.
A pore specific volume of 1.0 μm and a cell of 400 mA / cm ²
Shows the relationship of the voltage values at Pore specific volume is 0.04c
The voltage was high at m ³ / g or more, and the voltage was almost constant at 0.06 cm ³ / g or more.

FIG. 5 shows the electrode of the present embodiment having a diameter of 0.04 to 0.04.
1.0 μm pore specific volume and 800 mA / cm ^{2 of} cell
Shows the relationship of the voltage values at Pore specific volume is 0.06c
A high battery voltage was exhibited at m ³ / g or more. On the other hand, 0.04
In the range of ０．０0.06 cm ³ / g, the battery voltage with respect to the specific pore volume varied depending on the battery.

At 400 and 800 mA / cm ² , the concentration polarization becomes dominant, so not only the reaction area but also the ability to supply the reaction gas is important. Since the pores having a diameter of 0.04 to 1.0 μm also function as gas channels, it is considered that when the pore specific volume is 0.04 cm ³ / g or less, the gas supply ability is low, and the battery voltage has decreased.

In the high current density region, the ability to supply the gas and the ability to discharge the produced water are also important. For this reason, 800 mA /
It is considered that the variation in the voltage of the battery in the range of 0.04 to 0.06 cm ³ / g in cm ² is due to the difference in the ability of each carbon powder to discharge generated water due to the hydrophilicity / hydrophobicity.
Therefore, in order not to depend on the properties of the carbon powder, a specific pore volume of 0.06 cm ³ / g or more is required in a high current density region.

In this embodiment, a 5% Nafion solution manufactured by Aldrich Chemical Co., USA, was used as a solid polymer electrolyte as a typical example of a polymer composed of a copolymer of tetrafluoroethylene and perfluorovinyl ether. The solid polymer electrolyte having a proton exchange group is not limited to the above examples, but may be a polymer having a different molecular structure, such as perfluorovinyl ethers and polymers having different side chain molecular lengths, or styrene and vinyl. Similar effects were obtained by using a polymer composed of a copolymer with benzene.

Further, the electrode manufacturing method of this embodiment is an example, and the present invention is not limited to this.

Further, in this embodiment, a hydrogen-oxygen fuel cell using a solid polymer electrolyte membrane as an electrolyte is taken up as an example of a fuel cell, but reformed hydrogen using methanol, natural gas, naphtha or the like as a fuel is used. It is also possible to apply the present invention to a conventional fuel cell or a fuel cell using air as an oxidant.

[0032]

As described above, according to the present invention, PEFC
By elucidating the pore structure suitable for Pt, the contact area of the Pt catalyst with the solid polymer electrolyte is large, and the reaction gas supply ability is high. Can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the solid polymer electrolyte mass and pore distribution of an electrode according to an example of the present invention

FIG. 2 is a diagram showing the relationship between the mass of solid polymer electrolyte and the specific volume of pores of an electrode according to an example of the present invention.

FIG. 3 is a diagram showing the relationship between the specific pore volume of the electrode of the embodiment of the present invention and the cell characteristics (part 1).

FIG. 4 is a diagram showing the relationship between the specific pore volume of the electrode of the embodiment of the present invention and the cell characteristics (part 2).

FIG. 5 is a view showing the relationship between the specific volume of pores of an electrode according to an embodiment of the present invention and cell characteristics (part 3).

Continuation of the front page (72) Inventor Nobuo Eda 1006 Kazuma Kadoma, Kazuma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-8-221310 (JP, A) (58) Fields investigated .Cl. ⁷ , DB name) H01M 4/86 H01M 8/10

Claims (2)

(57) [Claims] 1. An electrode in which a catalyst layer composed of a solid polymer electrolyte and a carbon powder supporting a noble metal catalyst is formed on one surface of a gas diffusion layer, wherein the catalyst layer has a diameter of 0.04 to 1.
It has pores of 0 μm, and the specific volume of the pores is 0.06
cm3 / g or more, and the solid polymer
Solid polymer fuel cell characterized by distribution of decomposition
Pond electrode. 2. A solid polymer electrolyte fuel cell comprising electrodes disposed on both sides of a solid polymer electrolyte membrane, wherein at least one of the electrodes comprises a solid polymer electrolyte and a carbon powder carrying a noble metal catalyst. An electrode having a catalyst layer formed on one side of a gas diffusion layer, wherein the catalyst layer has a diameter of 0.04 to 1.
It has pores of 0 μm, and the specific volume of the pores is 0.06
cm3 / g or more, and the solid polymer
Solid polymer fuel cell characterized by distribution of decomposition
pond.