JPS59181462A - Fuel battery - Google Patents

Abstract

PURPOSE:To attain high sustaining force of electrolyte and obtain gas diffusion electrode having a small diffusion resistance to reaction gas by using a porous material formed by a fabric substance having holes in difference diameters in the thickness direction as an electrode material. CONSTITUTION:A 3-part of fabric metal consisting of Ni(80)-Cr(20) alloy in average diameter of 25mum is put into a molding device and then a part of fabric metal consisting of Ni(80)-Cr(20) alloy in average diameter of 4mum is stacked thereon. These are then molded into a flat plate. Thereafter, it is sintered for an hour at 850 deg.C in the H2(20)-N2(80) gas ambient. Thereby, a porous material where diameter of hole is changing step by step in the direction of thickness can be obtained. With such porous material used as the fuel pole 2 and Ni porous as oxidizing agent pole 3 respectively in both sides of electrolyte layer 1 of a fuel battery to be formed. In this case, it is apparent from the figure that a current- voltage characteristic (solid line) of such fuel battery is very excellent as compared with a current-voltage characteristic (broken line) of a fuel battery where an existing porous material having uniform diameter of holes is used as the gas diffusion electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to fuel cells, and particularly to improvements in the structure of gas diffusion electrodes thereof.

[Technical background of the invention and its problems]

A fuel cell uses a gas that is easily oxidized, such as hydrogen, and
Direct current power is obtained by reacting with a gas that has oxidizing power such as oxygen through a complete electrochemical reaction process. For example, as shown in FIG. 1, this fuel cell has a pair of gas diffusion electrodes (a fuel electrode and an oxidation electrode) on both sides of an electrolyte layer 1 in which carbonate is held as an electrolyte in a matrix body.
2 and 3 are provided, and these are configured as a unit battery. Then, fuel gas and oxidant gas are completely supplied through the gas diffusion 1 poles 2 and 3 fc, and an electrochemical reaction is caused to occur in the electrolyte layer 1, and the resulting DC electromotive force is extracted.

Therefore, the gas diffusion electrodes 2 and 3 are made of a porous material,
This provides all the locations where the electrogenic reaction described above occurs. For this reason, in order for the electromotive reaction to proceed efficiently, the gas diffusion electrodes 2 and 3 must not be attacked by molten carbonate at a temperature of, for example, 600 to 700°C, which is the operating condition of a molten carbonate fuel cell. In addition to the need for chemical stability without oxidation, it is also necessary to satisfy the following conditions.

That is, (1) fuel gas and oxidant gas can be supplied in a sufficiently stable manner, (ii) carbonate as an electrolyte can always be present at the reaction site, and (Ill) the electrolyte can be supplied for a long period of time. Among other things, it can be stably supplied to the reaction site.

Therefore, conventionally, assuming that these conditions are satisfied,
A porous material obtained by sintering nickel-based alloy powder or its fibers is used as the gas diffusion electrode 2.3. Note that this porous body is usually formed so that the average pore diameter is 2 to 20 μm and 8 degrees, and the pore distribution is as close as possible to p shear 7''.

However, the gas diffusion electrodes 2 and 3, which are made of porous bodies that are homogeneous and have a peak in the distribution of pores, have the following problems. That is, when the average pore diameter is large, for example, 20 μm or more, the gas diffusion electrodes 2 and 3 configured with this have a good supply performance of the reaction gas (fuel gas, oxidant gas), but on the other hand, the electrolyte As the holding force decreases, the characteristics of the battery deteriorate. Moreover, it causes loss of electrolytes,
Since this causes a significant deterioration of its characteristics, it is impossible to extend the life of the battery.

On the other hand, when the average pore diameter is small, for example, 10 μm or less, the gas diffusion electrodes 2 and 3 configured with this can sufficiently secure the holding power of the electrolyte, but the capillary action of the pores causes the electrolyte to The problem is that the gas penetrates into the pores and blocks them, increasing gas diffusion resistance. Therefore, there was a problem in that the supply of the reaction gas was obstructed and the battery characteristics deteriorated. However, because of these contradictory problems, it has been extremely difficult to satisfactorily satisfy all of the conditions required of the gas diffusion electrodes 2 and 3 described above.

[Purpose of the invention]

The present invention was made in consideration of the above circumstances, and its purpose is to provide a gas diffusion electrode with good characteristics, which has high electrolyte retention and low diffusion resistance to reaction gases. Our goal is to provide fuel cells.

[Summary of the invention]

The present invention relates to a fuel cell having a structure in which a pair of gas diffusion electrodes are provided on both sides of an electrolyte layer, and the structure of the gas diffusion electrode is
It is a porous body made of a fibrous material with pores of different sizes formed in the thickness direction.In particular, the pores are made smaller on the electrolyte layer side, and the gas supply surface is made smaller. It is enlarged on the side.

That is, for example, the size of the pores on the electrolyte layer side, which is about 1/3 of the thickness of the gas diffusion electrode, is about 1 to 20 μm, and the remaining 2/3
The size of the pores on the gas supply side, which is the thickness of 20 to 50
P) classified according to the size of the pores, on the order of μm
It has a so-called multilayer structure.

5- [Effects of the Invention] Thus, according to the present invention, the porous body constituting the NOF diffusion electrode has small pores on the electrolyte layer side and large pores on the gas supply side. The diffusion resistance to the reactant gas is small in the area where it is a dog, and the supply of the reactant gas is stable.
And it's done smoothly. Therefore, it is possible to improve the characteristics of the battery. On the other hand, in the portions of the porous body with small pores, the electrolyte is sufficiently and reliably retained. As a result, the electrolyte is not significantly lost even during long-term operation, and battery performance is therefore ensured over a long period of time. In other words, the gas diffusion electrode that comes from the porous body with the above structure can stably supply and retain all of the electrolyte from the electrolyte layer to the reaction site, and small diffusion from the gas supply surface side. The resistance makes it possible to supply the reaction gas sufficiently stably and efficiently. Therefore, in a fuel cell configured using such a gas diffusion electrode, it is possible to stably generate an electromotive effect by the reactant gas over a long period of time without causing loss of electrolyte. , it becomes possible to exhibit sufficient characteristics as a battery.

Therefore, its practical advantages are extremely great, and effects that could not be expected in the past can be produced.

Furthermore, according to the gas diffusion electrode made of such a porous material, the cell bubble pressure, which is a guideline for preventing cross-mixing of fuel gas and oxidant gas, is approximately 50% lower than that of the conventional structure. The degree of increase in the whole picture is obtained, and the effect is great. Furthermore, even if so-called cracks occur in the electrolyte layer when the temperature of the fuel cell is lowered, gas permeation is blocked because the pores on the electrolyte layer side of the gas diffusion electrode are small, and the fuel gas and oxidizer are prevented from passing through during the next temperature rise. Effects such as cross-mixing with gas can be completely prevented can also be achieved.

[Embodiments of the invention]

Examples of the present invention will be described below.

φ First, N1-Cr alloy with an average diameter of 25 μm (80
) (20) Prepare 3 parts of fibrous metal and put it into a molding machine. After that, N1(8o)Cr(
2o) Prepare a portion of a fibrous metal made of an alloy, place it on top of the large-diameter fibrous metal, place it in the molding machine, and mold it into a flat plate. After that, we convert this to N2(2o)-N2(
80) Place in a gas atmosphere and sinter at 850°C for 1 hour. As a result, a porous body made entirely of Nl(go)''(20) is obtained.This porous body has an average diameter of 4μ.
The gas diffusion electrode 2 has the surface on the side where the fibrous metal of m is placed as the surface on the electrolyte layer side.

When the cross section of the porous body in the thickness direction was observed using an electron microscope, the size of the pores was 22 to 30 μm at the portion where the fibrous metal with a diameter of 25 μmφ was used.
It was confirmed that the size of the pores was approximately 2 to 5 μm at the portion where the fibrous metal with a diameter of 4 μmφ was used. It was confirmed that the size of the pores in the porous material changed stepwise in the thickness direction.

It was confirmed through mechanical tests that the tensile strength, flexibility, and flatness of this porous body were sufficient to allow it to be used as a gas diffusion electrode for a fuel cell.

Three parts of a fibrous metal made of N1 with an average diameter of 30μ...φ and one part of a fibrous metal made of Ni with an average diameter of 8μm0 were put into a molding machine in layers, and this was molded into a flat plate. However, this was sintered in a FI2 (20) N2 (80) gas atmosphere at a temperature of 820° C. for 1 hour to form a porous body made of N1. This Ni porous body has a diameter of 8
．． The side into which the fibrous metal amφ is placed is the gas diffusion electrode 3 with the electrolyte layer side.

When the cross-sectional structure of the Ni porous body in the thickness direction was observed using an electron microscope, the following results were obtained. That is, the size of the pores in a part using a fibrous metal with an average diameter of 30 μmφ is about 25 to 35 μm, and the size of the pores in a part using a fibrous metal with an average surface diameter of 8 μmφ is about 25 to 35 μm. The size was 8 to 12 μm. Then, the thickness of the fibrous metal layer with a diameter of 30 μm7 and the diameter of 8 μmφ
The ratio of the thickness of the fibrous metal layer is approximately (32) to (1,
0).

Afterwards) Upper RQ Nt (go) Cr (20
) The porous body is used as the fuel electrode 2, and the Ni porous body is used as the oxidizer electrode 3.
A fuel cell was assembled by providing each of the electrolyte layers on both sides of the electrolyte layer I. The electrolytic layer I is formed by hot-pressing a mixture of a 60i carbonate and a 40-layer ceramic for holding the carbonate at 450° C. and molding the mixture.

Figure 2 shows the current-voltage characteristics (solid line) of the fuel cell fabricated in this way, and the current-voltage characteristics (solid line) of a fuel cell using a porous body with a conventional structure with uniform pore size 7 as a gas diffusion electrode. Broken line)'f: Shown for comparison. This second
As is clear from the characteristics shown in the figure, it can be seen that the fuel cell having the structure according to the present invention has better characteristics than that of the conventional structure. This also indicates that the reactant gas is being supplied satisfactorily because the pores in the electrode on the gas supply side are large in size.

Furthermore, Figure 3 shows changes in battery characteristics during long-term operation as changes in output voltage.The characteristics shown by the solid line are for the structure of the present invention, and the characteristics shown by the broken line are for the conventional structure. .

As shown in FIG. 3, it can be seen that the fuel cell 10-' having the structure of the present invention exhibits a stable electromotive action over a long period of time. This fact indicates that the electrolyte is sufficiently stably retained at the diffusion 'flt electrode.
This proves that the small pores in the front porous body are working effectively.

As described above, the present invention can greatly improve the performance characteristics of a fuel cell with a simple structure, and its effects are extremely remarkable.

Note that the present invention is not limited only to the above embodiments. For example, the fibrous material used to form the porous body forming the gas diffusion electrode is not limited to metals or alloys. Nickel oxide and ceria (CeO
2), and also many perovskite-type oxides, such as SrxLal-xMn03 HLaXK1-, MnO3
+Laxzr 1-x Co -05+ LaxSr
It is possible to use a fibrous material such as 1''-x Co-03.Other car inventions can be carried out by modifying the glaze without departing from the gist of the invention.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the basic structure of a fuel cell, and FIGS. 2 and 3 are diagrams showing a comparison between the characteristics of a fuel cell according to an embodiment of the present invention and the characteristics of a conventional SEIZO fuel cell. 1... Electrolyte layer, 2, 3... Gas diffusion electrode.

Claims (3)

[Claims] (1) It comprises an electrolyte layer formed in a flat plate shape and a pair of gas diffusion electrodes provided on both sides of the electrolyte layer, and the gas diffusion electrodes have pores of different sizes in the thickness direction. A fuel cell characterized in that it is constituted by a porous body made of a fibrous material. (2) Fibrous material forming pores, diameter 1 to 50 μm
The fuel cell according to claim 1, which is made of a fibrous gold ingot of approximately φ. (3) The porous body forming the gas diffusion electrode has two layers with different pore sizes in the thickness direction, and the pore size in the layer on the electrolyte layer side is 1. ~20μm
and the size of the pores in the layer on the gas supply side is 20 to 5.
The fuel cell according to claim 1, wherein the fuel cell has a diameter of 0 μm.