JPH0272560A - Fuel cell - Google Patents

Abstract

PURPOSE:To make the diffusion of gas produced in an electrode catalyst layer and reaction gases smooth by forming a gas passage having larger pore size than the mean pore size of a porous part in an electrolyte catalyst layer. CONSTITUTION:A gas passage having larger pore size than the mean pore size of a porous part is formed in an electrode catalyst layer 20. Fuel and an oxidizing agent gas are separately supplied to gas passages perpendicularly intersecting each other, and each gas is supplied to the whole area of the electrode catalyst layer 20 and reacts in an electrolyte suction part in the electrode catalyst layer 20 to generate electric power. Steam which is a reaction product is exhausted outside through the gas passage and a gas passing route. Gas produced in the electrode catalyst layer 20 and reaction gases are diffused smoothly.

Description

[Detailed Description of the Invention] r Industrial Application Field] The present invention relates to a fuel cell in which a porous portion is attached to an electrode catalyst layer disposed facing each other with an electrolyte matrix sandwiched therebetween in order to supplement the electrolyte. It is related to.

[Prior art] Figure 4 shows the patent application for Japanese Patent Application Laid-Open No. 1983-24, which the present applicant has already filed.
561 is a cross-sectional view of the fuel cell shown in Publication No. 561, in which 1 is an electrolyte matrix, 2 and 3 are electrode catalyst layers, 4 and 5 are mutually orthogonal gas flow paths for fuel and oxidant gas, and 6 is a gas separation plate. It is integrally constituted by the dense layer 7 and the porous portions 8.9 formed in the shape of ribs on both sides of the dense layer 7.

Next, the operation of the above configuration will be explained. Fuel and acid and arsenic gas are respectively supplied to the mutually orthogonal gas passages 4.5. At this time, the dense portion 7 of the gas separation plate 6 prevents the fuel gas and the oxidizer residue from mixing with each other, and both gases reach the electrode catalyst layer 2.3. The gas that has reached the electrode catalyst layer 2.3 is ionized and reacts through the electrolyte matrix 1 to generate electricity. Here, excess gas not used in the reaction and water vapor gas which is a reaction product are removed from the gas flow path 4.
5 and is discharged to the outside. This exhaust gas contains the electrolyte made of phosphoric acid contained in the electrolyte matrix 1 and the electrode catalyst layer 2.3 in the form of vapor, and therefore, in the case of long-term operation, the electrolyte contained in the electrolyte matrix 1 and the electrode catalyst layer N2. However, the electrolyte impregnated in the porous portions 8.9 moves to the electrolyte matrix 1 and the electrode catalyst layer 2.3 to make up for the shortage.

In Figure 5, the electrode catalyst layer 2.3 is
It is a schematic cross-sectional view when manufactured by the method shown in the publication, and 10 is catalyst-supported carbon supporting an active substance such as platinum that promotes the electrochemical reaction in the electrode;
11 is a binder made of Bolite I to Lafluoroethylene (hereinafter abbreviated as PTFE) particles, 12 is a hole through which a reaction gas or reaction product passes, and 13 is a reaction gas and an electrode necessary for the electrochemical reaction. This is a group of large-diameter hydrophobic particles consisting of carbon particles and PTFE particles that serve as a passage through which the reaction products produced by the Ti chemical reaction pass in gaseous form.

In the electrode of the fuel cell described above, a large-diameter water-repellent particle group 13 is created using carbon particles and PTFE particles, and then the water-repellent particle group 13 and catalyst-supported carbon 10 are mixed by adding a binder 11. It is made by

[Problems to be Solved by the Invention] In the electrode catalyst layer 2.3 of the fuel cell described above, since the catalyst-supported carbon 10 is mixed with the water-repellent particle group 13 in the form of fine particles, the catalyst-supported carbon is formed in the pores 12. 1o is clogged, the pore diameter of the electrode catalyst layers 2 and 3 becomes smaller than the pore diameter of the porous portion 8.9, and the entire area of the electrode catalyst layers 2 and 3 is filled with electrolyte from the porous portion 8.9 due to capillary suction force. This poses a problem in that diffusion of the reaction gas and generated gas in the electrode catalyst layers 2 and 3 is hindered.

This invention was made in order to solve the above-mentioned problems, and it is possible to smoothly diffuse the generated gas and reaction gas in the electrode catalyst layer, and to ensure that the electrolyte from the porous portions is sufficiently absorbed into the electrode catalyst layer. The aim is to obtain fuel cells that will be supplied to

[Means for Solving the Problems] The fuel cell according to the present invention is one in which the electrode catalyst layer is provided with a gas passage portion having a pore diameter larger than the average pore diameter of the porous portion and serving as a gas passage. be.

[For iF] In this invention, gas is smoothly supplied to the entire area of the electrode catalyst layer through the gas passage section.

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

FIG. 1 is a schematic cross-sectional view of an electrode catalyst 120 showing an embodiment of the present invention, and the same or corresponding parts as in FIGS. 4 and 5 are given the same reference numerals, and the explanation thereof will be omitted.

In the figure, 21 is catalyst-supported carbon supporting an active substance such as platinum that promotes electrochemical reactions in the electrode;
22 is a binder made of polytetrafluoroethylene (hereinafter abbreviated as PTFE) particles, and 23 is a hole through which a reaction gas or a reaction product passes.

There are three methods for producing the above electrode catalyst yIzo: (1) tablet method, (2) direct FF granulation method, and (2) spray drying method.

Among these methods, when PTFE is used as a binder in the tablet method and direct granulation method, the PTFE becomes fibrous and a predetermined particle size cannot be obtained, so the spray drying method is used.

In the spray drying method, catalyst-supported carbon 21 is floated in a nitrogen stream at 150°C, and a 30-fold diluted solution of PTFE dispersion heated at 80°C is sprayed onto it.
TFEG, 1m long, size 1-1001J
I11<7) Particles are granulated. The granulated catalyst-supported carbon fine particles are sieved and classified into particles of about 50 μm.

The classified powder is hot-pressed at 50 kg/cm2 at a temperature of 300°C to form an electrode catalyst layer 20 having a predetermined thickness and having pores 23 as shown in FIG.

FIG. 2 is a diagram comparing the pore distribution of this electrode catalyst layer 20 and the porous portions 8 and 9, and shows that pores larger than the average pore diameter of the porous portions 8.9 are provided in the electrode catalyst layer 2o. I know that there is.

FIG. 3 is a distribution diagram showing the distribution of pore diameters in the electrode catalyst layer 20 and the porous portions 8 and 9, and the electrode catalyst layer 2G has a pore diameter larger than that of the porous portions 8. The gas passage part 24 serves as a passage for the gas passage part 24, and the porous part 8.9 has a pore diameter smaller than that of the porous part 8.9.
and an electrolyte suction section 25 that suctions the electrolyte No. 9.

The gas passage portion 24 of the electrode catalyst layer 20 has a smaller capillary suction force than the porous portions 8 and 9, and has a weaker ability to draw in the electrolyte.
As long as the porous portions 8 and 9 are not filled with electrolyte, pores 23 will exist as gas diffusion holes. Furthermore, if the occupancy rate of the electrolyte made of phosphoric acid in the pores of the electrode catalyst layer 20 is less than 20%, there is less electrolyte in contact with the catalyst and a sufficient reaction area cannot be obtained, resulting in poor battery characteristics. In the above case, the gas passage section 24 is occupied by the electrolyte, and the supply of gas to the electrode catalyst layer 20 and the electrolyte matrix 1 is reduced, resulting in poor battery characteristics and the electrode catalyst layer 24.
The occupancy rate of electrolyte consisting of phosphoric acid in the pores of is 20%.
It is desirable to keep it at -80%. Therefore, it is desirable that the gas passage portion 24 occupy 20-80% of the pores of the electrode catalyst layer 20.

Next, to describe in detail the 1st layer of the above configuration, the amount of electrolyte held in the electrode catalyst JIF20 is
is determined by the capillary suction force that p =
46cosθ/d P・capillary attraction force, 6・surface tension, θ・contact angle, d・pore diameter, d/cosθ・equivalent diameter, the smaller the pore diameter and contact angle, that is, the smaller the equivalent diameter. It can be seen that the capillary suction force becomes larger, that is, the force that draws the electrolyte into the electrode catalyst layer 20 becomes larger.

In the fuel cell configured as described above, when fuel and oxidant gas are supplied to the mutually orthogonal gas passages 4 and 5, respectively, these gases are supplied to the entire area of the electrode catalyst layer 20 through the gas passage section 24. . And the electrode catalyst N
The gas that has reached 20° reacts in the electrolyte suction section 25 to generate electricity. Here, water vapor gas, which is a reaction product, is discharged to the outside through the gas passage section 24 and the gas channels 4 and 5.

Note that by imparting water repellency to the electrode catalyst layer 20, the contact angle can be reduced, and the capillary suction force of the electrode catalyst layer can also be reduced. That is, the distribution shown in FIG. 3 can be created by increasing the equivalent diameter.

[Effects of the Invention] As explained above, the fuel cell of the present invention has the following advantages: Produced gas and reaction gas diffuse smoothly in the electrode catalyst layer, and electrolyte is sufficiently supplied from the porous portion to the electrode catalyst layer, making it possible to maintain stable battery characteristics over a long period of time. There is an effect.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of an electrode catalyst layer showing an example of the present invention, and FIGS. 2 and 3 are distribution diagrams showing the pore size distribution of the electrode catalyst layer and porous portion shown in FIG. FIG. 4 is a sectional view showing an example of a conventional fuel cell, and FIG. 5 is a schematic sectional view of an electrode catalyst layer of the conventional fuel cell. 1: Electrolyte matrix, 8.9: Porous section, 20: Electrode catalyst layer, 24: Gas passage section, 25: Electrolyte suction section. In each figure, the same reference numerals indicate the same or corresponding parts. Chi 1 Figure 20: Q German exposure Δ1 Form 2 Figure kJ Rise diameter m] 25: Electrolyte 51 Pressure 4 Figure 5

Claims (1)

[Claims] Comprising an electrode catalyst layer disposed facing each other with an electrolyte matrix in between, and a porous portion attached to the electrode catalyst layer and impregnated with an electrolyte, the electrolyte in the porous portion is smaller than the pore diameter of the porous portion. In a fuel cell in which an electrolyte matrix and an electrode catalyst layer are replenished by an electrolyte suction part of the electrode catalyst layer having a pore diameter and sucked by capillary suction force, the electrode catalyst layer has a pore size larger than the average pore diameter of the porous part. A fuel cell characterized in that a gas passage portion having a large pore diameter and serving as a gas passage is provided.