JPS59169069A - Electrode for fuel cell - Google Patents

Abstract

PURPOSE:To provide an electrode for a fuel cell having high performance, good mechanical strength, and long life by mixing a catalyst carrier comprising catalyst, carrier for catalyst, and binder with graphite powder and carbon black having a specified particle size in a specified ratio. CONSTITUTION:At least one electrode of positive and negative electrodes consists of an electrode substrate and a catalyst layer comprising catalyst, carrier for catalyst, and binder. The carrier for catalyst comprises a mixture of natural graphite powder having a particle size of 0.1-5mum and furnace carbon black having a particle size of 0.01-0.1mum. The mixing ratio of graphite powder to the total mixed powder is specified to 25-75wt%. Thereby, an electrode for fuel cell having high performance and long life is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an electrode for a fuel cell, and specifically to the composition of a catalyst support layer of the electrode.

[Prior art]

Many inventions have been made regarding electrodes for fuel cells. Most of them concern gas diffusion electrodes. Looking at the details of the inventions of gas diffusion electrodes, there are those that use a porous sintered body of metal or carbon as the electrode base, or those that use metal powder or a plastic binder.
There are two types: catalysts and those that bind and hold conductive powder to form electrodes. However, in recent years, in order to increase the activation of fuel cell catalysts and to reduce costs when putting fuel cells into practical use, technology in which catalyst precious metals are highly dispersed and supported on conductive powders such as carbon powder has attracted attention. has been done. Applying this technique means forming the catalyst-supported powder, which is mostly carbon powder, into an electrode. As the carbon powder for the catalyst carrier, a carbon black type Ii powder having a large specific surface peak and a small average particle diameter is generally used, which has a small bulk density and a large amount of water absorption. In order to make electrodes by binding and coating such bulky powder, a large amount of plastic binder (about 30 to 70%) must be used to make an electrode that is uniform, strong enough, and crack-free. .

However, using such a large amount of binder may cause the binder to cover the active sites of the catalyst supported on the carbon powder, resulting in a decrease in the performance of the glue electrode. Garu. It also prevents the penetration of soluble reactants (for example, reactants into the methanopart), making it even more undesirable.

[Purpose of the invention]

An object of the present invention is to provide an electrode coating layer having a uniform composition in order to solve the problems of the prior art described above. As a result, a fuel cell electrode with high performance and long life can be obtained.

[Summary of the invention]

In the prior art, the use of large amounts of binders has been problematic. However, as long as a carbon black carrier is used, the above problems cannot be avoided. This is because carbon black has a large amount of water absorption and is a bulky powder, so it cannot be applied to an electrode with sufficient strength without using a large amount of a binder. Therefore, the inventors devised the use of a mixed powder of carbon black and graphite powder in order to solve the above problems while maintaining the advantages of carbon black, such as having a large specific surface area and making it easy to form porous electrodes. Graphite powder has high conductivity due to its crystalline cylindrical shape, which is desirable as an electrode material. However, on the other hand, due to its high crystallinity, there are few functional groups on the surface, making it difficult to provide an active field for electrode reactions.
However, since the specific surface area is small and the density is high, it is difficult to fabricate porous electrodes. However, these drawbacks are the advantages of carbon black, and carbon black and graphite are in a complementary relationship, and a preferable electrode can only be obtained by using a mixture of the two. Conceivable. The carbon black used is
Any of acetylene black, thermal black, furnace black, lamp black, and channel black can be used, and the particle size is 0. Preferably, the thickness is 01 to 0.1 μm. As the graphite powder, both natural graphite and artificial graphite can be used, but in order to obtain a sufficient mixing state with carbon black, a relatively coarse and small particle size of 0.1 to 5 μm is preferable.

[Embodiments of the invention]

The present invention will be explained in more detail below with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of a fuel cell that is the object of the present invention. In the figure, numerals 1 and 6 are a fuel electrode and an oxidizer electrode, respectively, and the present invention relates to these two electrodes. There is an electrolyte chamber 5 between the fuel electrode 1 and the oxidizer electrode 6, which is filled with a highly conductive aqueous solution such as a strong alkali or a strong acid as an electrolyte. 1.6 also face the fuel chamber 2 and oxidizer chamber 7, respectively, and have respective inlets 4, 8, outlets 3,
9. Reactants are supplied and discharged. FIG. 2 shows enlarged cross sections of Nos. 1 and 6 according to the present invention. In the figure, 12 is a conductive electrode base made of a porous material such as a metal wire mesh, metal, and carbon, and is generally arranged on the side facing the reactant chamber 2.7.

Reference numeral 13 denotes a coating layer, whose composition is the main part of the present invention, and generally includes a catalyst, a conductive powder such as metal or carbon, and a plastic binder such as polytetrafluoroethylene, polystyrene, or polyvinyl chloride. It is formed by such methods. Since the electrode reaction of a fuel cell occurs in this coating layer, it is the part that greatly affects the overall performance and performance of the fuel cell, so improvements in this part are extremely significant.

The present invention will be specifically explained below using Examples.

(Example 1) Natural graphite powder with an average particle size of 0.7 μm and an average particle size of 0.02
Furnace black type carbon black of μm was fractionated at a weight ratio of 1:0, 3:1, 1:1.3゜0:1, transferred to a Raikai machine, and 10jr of carbon powder was mixed with 30mt of water. Add and stir for 1 hour. The resulting mixture, 4i1! *250-350mt of water for 32g, platinum chloride e ()fxPtc74-61 (2015, 4g
Add and mix thoroughly with Magnetic Star 2, process and mix 20ml of 33ml formalin, and add 10ml of hydrium hydroxide aqueous solution somt. Thereafter, stirring was continued for 2 hours, followed by filtration, washing with water, and drying in air at 100 °C to obtain a catalyst-supported carbon powder. To 10 parts by weight of the obtained powder, 40 parts by weight of water, 1 part of polytetrafluoroethylene (PTFEI fine powder, 1 part of fine powder) were thoroughly kneaded, and 80 parts by weight of powder was added.
Apply to mesh platinum wire mesh and let dry. Thereafter, it is fired for 1 to 2 hours at 250 to 350 tons in a nitrogen tank. The obtained electrode was immersed in an aqueous solution containing 2 mol/l sulfuric acid and 1 mot/l methanol, and the current density-potential characteristics of the electrode were measured at 25C. The results obtained are shown in FIG. In FIG. 3, the vertical axis shows the potential at a current density of 40 m<4> with respect to the graphite powder content (weight percent) on the horizontal axis.

As is clear from the figure, when the amount of graphite exceeds 75%, the electrode potential increases and the ti performance decreases. However, when the graphite content is small, the performance is sufficient, but there are problems in terms of strength. This is shown in FIG. Figure 4 shows a 2 m electrode with a graphite content of 01,251,501.
25 containing oA/l sulfuric acid and 1 mot/l methanol
This figure shows the change in potential over time when the sample was immersed in an aqueous solution of C and continuously discharged at a current density of 60 mλ/cm''.

As is clear from the figure, those with zero graphite content have extremely low performance. This was consistent with peeling of the coating layer, which was observed with the naked eye.

As is clear from the above, it was found that the preferable range of graphite content in the coating layer is 25 to 75 parts. An electrode using carbon powder having a composition within this range as a catalyst carrier can provide a high-performance electrode with sufficiently high performance and no problems in terms of strength.

(Example 2) Natural graphite powder with an average particle size of 0.7 μm and an average particle size of 0.04
The weight ratio of μm carbon black is 1:0.3. :
1.1 : 1.1 : 3.0 : 1 weighed, transferred to a Raikai machine, added 30 mt of water to 10 g of carbon powder, and kneaded for 1 hour. PTFE was added to the resulting mixture. Add 1 g of fine powder, mix well, apply to 80 mesh platinum wire mesh and dry.

Thereafter, it is fired in air at 250 to 300 C for 1 to 2 hours. The obtained electrode was impregnated with an ethanol solution of chloroplatinic acid, dried, and then kept in a hydrogen stream at 150 C for 2 hours to reduce the electrode. The performance of the obtained electrode showed the same tendency as shown in FIGS. 3 and 4.

〔Effect of the invention〕

According to the present invention, a fuel cell electrode with high performance, sufficient strength and long life can now be obtained.

In the above embodiments, the invention was applied to the methanol electrode of an acidic electrolyte methanol fuel cell, but the invention is not limited thereto and can be applied to a wide range of fuel cells in general. That is, it is effective for the fuel electrode and oxidizing agent of acidic and alkaline Sa fuel cells, and there is no problem whether the oxidizing agent and fuel are liquid or gas.

[Brief explanation of the drawing]

Fig. 1 is a schematic cross-sectional view of a fuel cell, Fig. 2 is a cross-sectional view of an electrode for a fuel cell, Fig. 3 is a diagram comparing the initiality of electrodes according to the present invention, and Fig. j@4 is a cross-sectional diagram of an electrode according to the present invention. FIG. 2 is a diagram comparing the life characteristics of . 1...Fuel electrode, 2...Fuel outlet, 3...Fuel outlet,
4... Fuel inlet, 5... Electrolytic formation, 6... Oxidizer electrode, 10... Battery container. Agent Patent Attorney Akio Takahashi Daiichi Sencha 2 Figure 1/ r5ゝ-1 ′\Kaya 3
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/θO graphite person Rei Zhu Kanyu+ <7. ) $4 0 2
/ θ # 衾 弼 ＜ h ) 4, ° Black G content θ 7 ° δ: # zs; /. C: 5σ2 Continuation of page 1 - Plastic invention Inventor Omihira Matsuda 3-1-1 Saiwaimachi, Tachi-shi Stock% formula %

Claims (1)

[Claims] 1. In a unit cell of a fuel cell formed by a fuel electrode as a negative electrode, an oxidizer electrode as a positive electrode, and an electrolyte between the two electrodes to electrochemically connect the two electrodes, at least one of the positive and negative electrodes is It is composed of an electrode base and a catalyst layer, and the catalyst layer contains a catalyst, a catalyst carrier, and a binder, and the catalyst carrier is composed of graphite powder with a particle size of 0.1 to 5 μm and a particle size of 0.
．． 01~0.1μm), the mixing ratio of graphite powder is 25~0.1μm to the total mixed powder.
A fuel cell electrode characterized in that it occupies a weight range of 75.