JPH02155171A - Fuel cell - Google Patents

Abstract

PURPOSE:To increase gas diffusion capability and to enhance current-voltage performance at high current density by arranging projections in an electrode substrate so as to well strike against gas. CONSTITUTION:An electrode substrate has gas supply passages 13 which are formed by spaces between projections 12 arranged in array and in which gas flows through the spaces with strike of gas against projections repeated. Diffusion gas is forced to supply to the inside near a catalyst layer in each projection 12, and gas diffusion capability in the projection 12 where an obstruction is easy to occur is increased. Gas supply to the electrode catalyst layer is made uniform and current-voltage performance at high current density is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gas supply path for a fuel cell, and particularly to a gas supply path for an electrode base material and a separate plate.

[Conventional technology]

In the fuel cell, electrodes 6 as shown in FIG. 12 are arranged with an electrolyte layer 8 made of, for example, phosphoric acid sandwiched therebetween, and fuel gas and oxidant gas are supplied to each electrode from an external gas supply system. It is a type of power generation device that electrochemically reacts fuel gas and oxidant gas on the electrode catalyst of each electrode, and extracts the resulting electrical energy outside the system.

The electrode 6 is constructed by adhering an electrode catalyst layer 5 onto a porous carbon base material (electrode base material) 4. The electrode catalyst layer 5 is formed by bonding fine catalyst particles 7 with noble metal fine particles 1 supported on the surface of a catalyst carrier 2 by fine particles 3 of fluororesin. Inside this electrode catalyst layer 5, a porous carbon base material 4
The gas from the side contacts the electrolyte from the electrolyte layer 8, a three-phase interface is formed, and an electrochemical reaction proceeds.

In order to carry out this electrochemical reaction efficiently, it is necessary to maintain as many three-phase interfaces as possible, where the catalyst fine particles 7 in the IT electrode medium layer 5, the electrolyte, and the gas come into contact with each other, as well as stably. In order to ensure smooth movement of ions, it is necessary to maintain sufficient electrolyte in the electrolyte layer 8. To this end, the degree of wetting of the electrode catalyst layer 5 with the electrolyte is controlled by, for example, using a highly water-repellent fluororesin, and the electrolyte layer 8 is coated with the electrolyte by using silicon carbide fine particles 9. Wet 5 comb.

On the other hand, for the carbon base material or electrode base material, the catalyst layer 5
It is necessary to efficiently supply the reactant gas to the three-phase interface. For this purpose, a porous body with good gas diffusivity is used. Carbon base materials include base materials with ribs and base materials without ribs; in the former, a gas supply path is formed by the rib portion of the base material and a separator, and in the latter, a gas supply path is formed by the rib portion of the ribbed separator and the base material. Regarding the ribbed base material, there is also one in which discontinuous protruding ribs are arranged in a chain row in consideration of equal distribution of gas in the lateral direction.

[Problem to be solved by the invention]

Conventionally, a ribbed base material as shown in FIG. 10 has been used, but in cells using such a base material, the rib portion 10 of the base material does not serve as a gas passage, and this Since the rib part has a longer distance to the electrode catalyst layer 5 than other parts, gas cannot sufficiently diffuse into the catalyst layer covered by the rib part 10, resulting in concentration polarization and high current density. There was a problem that the characteristics deteriorated. A similar problem also occurred with a ribbed base material in which the aforementioned discontinuous protruding ribs were arranged in a chain array to ensure equal distribution of gas in the lateral direction.

Further, as the ribbed separate plate, the separate plate t7ii11 shown in FIG. 11 was used, but in the cell using such a separate plate, the rib portion 1 of the separate plate
It is difficult for gas to diffuse inside the porous carbon base material 4a that is in contact with 0a, and therefore gas cannot be sufficiently diffused to the catalyst layer 5a covered with the rib portion 10a.
There was a problem that the characteristics in terms of flow density were insufficient.

This invention was made in view of the above points, and its purpose is to improve the ribs of the ribbed electrode base material and the ribbed separate plate so that the gas supply to the electrode catalyst layer is uniform and the current-voltage characteristics at high current density are improved. The objective is to provide a fuel cell with excellent performance.

[Means to solve the problem]

According to the present invention, the above-mentioned objects are as follows: 1) In a fuel cell comprising an electrode base material having an electrode catalyst layer arranged on one main surface and a gas supply path provided on the other main surface, convexes arranged in an array are provided. 2) an electrode base material provided on one main surface with a gas supply path 13 that is formed by a gap between the arrays and causes gas to flow through the gap of the array while repeatedly colliding with a convex part; In a fuel cell in which a flat porous base material and an electrode catalyst layer are sequentially laminated on the surface of a separate plate provided with a gas supply path, on which the gas supply path exists, the array is formed by gaps between convex portions arranged in an array. This is achieved by providing a separate plate with a gas supply path 13 provided on one main surface that causes gas to flow through the gap while repeatedly colliding with convex portions.

The cross-sectional shape of the convex portion (in the direction parallel to the main surface of the electrode base material or the separate plate) may be a rhombus, a square, a rectangle, a triangle, an ellipse, or a combination thereof.

[Effect]

In fuel cell electrodes, if the ribbed base material and the ribbed separate plate are arranged with convex parts so that they collide well with the gas, the diffused gas will be forced into the base material or the inside of the convex part of the separate plate close to the catalyst layer. Supplied. In this way, gas diffusivity is improved in the convex portions where inhibition occurs.

〔Example〕

(Example 1) Both sides are flat, the thickness is 1.5 to 2 mm, and the porosity is about 70%.
A porous carbon base material with good gas permeability is used as a material, and a convex portion 12 of 2 m x 2 m is provided on one side of the base material as shown in Fig.
'l va and 0.8 m wide so that it is one crane in height.

A groove with a depth of 1fi was machined using a 2.80 inch pinch at an angle of 45'' with respect to the gas supply direction.In order to compare the characteristics of the conventional base material and the base material of the present invention, the protrusions and grooves were The area is now the same as the previous one.

The porous carbon base material 4 thus obtained was made of 5% by weight polytetrafluoroethylene (hereinafter referred to as PTFE).
The base material was immersed in a dispargy run solution, dried at about 100°C, and then fired at 350 to 380°C to impart freeness to the base material.

After forming an electrode catalyst layer 5 on this base material so that the PTFE content is about 5096, it is fired at 350 to 380°C to achieve 1! I got the pole.

The current-voltage characteristics of the battery thus obtained are shown in FIG. Curve A is the characteristic when using the base material according to the example of the present invention, and curve B is the characteristic when using the conventional base material.

The characteristics of the electrode using the base material of this invention are that since the supplied gas collides with the convex part of the base material, gas diffusion into the convex part is improved;
Results showed that the performance improved at high currents of 0 taA/- or more.

The material is a carbonaceous molded plate that is flat on both sides and has a thickness of 6 fins and is impermeable to gases.Both sides of this plate have convex portions of 2 m x 2 I.
A groove with a width of 0.8 m and a depth of 2 fl is machined using a 2.8 fl pinch so that the groove is 2 mo in height at an angle of 45' to the gas supply direction in the same manner as in Fig. 1 to obtain a separate plate. Ta. In order to compare the characteristics of the conventional separate plate and the separate plate of the present invention, the areas of the convex portions and the groove portions were made to be the same as in the conventional separate plate.

The thus obtained separate plate and the sintered porous carbon substrate with a thickness of 0.4 nm were immersed in 5% by weight PTFE dispersion, dried at about 100°C,
It is sintered at 80°C to give it water repellency, and this base material is coated with PTFE.
The t-electrode catalyst layer is formed so that the ratio is about 50%.
An electrode was obtained by sintering at 80°C.

The characteristics of the battery thus obtained are shown in FIG. In the figure, curve 41C is the characteristic curve when the separate plate of the present invention is used.The curve is the characteristic when the conventional separate plate is used.

The characteristics of the battery using the separate plate of this invention are that since the supplied gas collides with the convex part of the separate plate, gas diffusion into the porous base material in contact with the convex part is improved, especially at 300 mA/c.
Improvement is seen at high current densities of i or higher.

(Example 2) As shown in FIGS. 4 to 9, snow shoveling substrates or separate plates with different convex shapes were fabricated so that the convex and groove areas were equal as in Example 1. When the characteristics were tested, it was found that the performance of the fuel cell improved with the same tendency as in Example 1.

〔Effect of the invention〕

By arranging the protrusions on the base material and separate plate of the fuel cell electrode so that they collide well with the gas, the gas diffusivity of the protrusions where gas diffusion is likely to be inhibited can be improved, resulting in an increase of 300 mA/aJ or more. can improve the characteristics of fuel cells at high current densities.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a convex portion and a gas supply path formed by the convex portion according to an embodiment of the present invention, and FIG. 2 is a plan view showing an electrode base material provided with a gas supply path according to an embodiment of the present invention. FIG. 3 is a diagram showing the characteristics of a battery, and FIG. 4 is a diagram showing the characteristics of a battery equipped with a separate plate provided with a gas supply path according to an embodiment of the present invention. FIG. 5, FIG. 6, FIG. 7, FIG. 8, and FIG. 9 are plan views showing convex portions and gas supply paths according to other embodiments of the present invention;
Figure 0 is a perspective view showing the arrangement of the conventional electrode base material and electrode catalyst layer, Figure 11 is a perspective view showing the arrangement of the conventional separate plate, porous carbon base material, and electrode catalyst layer, and Figure 12 is the conventional arrangement. FIG. 3 is a cross-sectional view showing an electrode configuration. 12, 12a, 12b, 12c, 12d, 12
e, 12f: Convex portion, 13: Gas supply path.

Claims (1)

[Claims] 1) In a fuel cell comprising an electrode base material having an electrode catalyst layer arranged on one main surface and a gas supply path provided on the other main surface, a gap between the convex parts arranged in an array 1. A fuel cell comprising: an electrode base member having a gas supply path formed on one main surface thereof, which causes gas to flow through gaps in the array while repeatedly colliding with convex portions. 2) In a fuel cell in which a flat porous base material and an electrode catalyst layer are sequentially laminated on the surface having the gas supply path of a separate plate having a gas supply path on at least one main surface, an array arrangement is performed. 1. A fuel cell comprising a separate plate provided on one main surface with a gas supply path formed by gaps between the protrusions and causing gas to flow through the gaps of the array while repeatedly colliding with the protrusions.