JPH09283160A - Manufacture of solid electrolyte for solid electrolyte type fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance mechanical strength by reducing the porosity of solid electrolyte so as not to allow the permeation of fuel gas. SOLUTION: Sm is doped into CeO2 so as to produce electrolyte material composed of (CQO2 )0.8 (SmO1.5 )0.2 . The electrolyte material is formed into solid electrolyte by a hot press method. In the hot press method the electrolyte material is filled into a material filling room 6. Next, pressure is applied to a water pressure press 10 so as to mold the same. In that case, a furnace, which is surrounded by a fire resistant lining 11 and is formed, is heated so as to complete the solid electrolyte.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a solid electrolyte mainly used in a solid oxide fuel cell.

[0002]

2. Description of the Related Art FIG. 4 shows a schematic configuration diagram of a conventionally known solid oxide fuel cell. In FIG. 4, a porous oxygen electrode (cathode) 42 made of perovskite and a porous hydrogen electrode (anode) 43 made of Ni cermet are mounted on both sides of a solid electrolyte 41 having oxygen ion conductivity. Oxygen pole 4
On the second side, when oxygen gas O ₂ or air is flown into the space 47, the reaction shown by the following equation occurs.

1 / 2O ₂ + 2e ⁻ → O ²⁻ (1) The reduced oxygen ion O ²⁻ reaches the hydrogen electrode 43 through the solid electrolyte 41 having oxygen ion conductivity. On the side of the hydrogen electrode 43, a fuel gas such as hydrogen gas H ₂ or natural gas is caused to flow into the space 48, and the reaction represented by the following formula occurs with the oxygen ion O ^2- which has passed through the solid electrolyte 41.

H ₂ + O ^{2 −} → H ₂ O + 2e ⁻ (2) As shown in FIG. 4, load 44 is applied to oxygen electrode 42 and hydrogen electrode 43.
, The oxygen electrode 42 side is the anode, and the hydrogen electrode 43
A voltage whose side is the cathode is generated across the load 44 by 2e ^{− on} the right side of the equation (2).

The solid electrolyte 41 and the hydrogen electrode 4 are prevented from being reduced by the hydrogen electrode atmosphere or the like.
The first protective film 45 and the second protective film 46 are interposed between the first protective film 45 and the third protective film 45. The first protective film 45 is fixed to the solid electrolyte 41 side, and the material thereof is mainly a member obtained by mixing CeO ₂ and YSZ. The second protective film 46 is fixed to the hydrogen electrode 43 side,
As the material, a member mainly made of 100% YSZ is used.

The above is the operation of the well-known solid oxide fuel cell. Solid electrolyte 4 used in the fuel cell
The electrolyte material of No. 1 is stabilized zirconia (YSZ) produced by solid-dissolving an oxide such as yttrium in zirconia.
Many used.

Since the operating temperature of a fuel cell using YSZ as the electrolyte material is as high as about 1000 ° C., there is a disadvantage that a heat resistant material must be used as a constituent material of the solid oxide fuel cell. Therefore, attempts have been made to lower the operating temperature of the fuel cell to lower the heat resistance of the cell constituent materials.

As a means therefor, electrolyte materials such as
_{(CeO 2) O · 8 (} SmO 1 · 5) using the _{O · 2} to form a solid electrolyte, that the operating temperature of the fuel cell 700 to 800 ° C. has been studied. The solid electrolyte formed using the electrolyte material has a problem of being reduced in a hydrogen electrode atmosphere or the like, but it can lower the operating temperature of the fuel cell as compared with the case where YSZ is used as the electrolyte material. There are advantages. Therefore, in the electrolyte material,
Alternate materials YSZ recently _{(CeO 2) O · 8 (} SmO 1 · 5)
Fuel cells are being manufactured using _{O · 2} .

[0009]

[SUMMARY OF THE INVENTION Usually, as the electrolyte material of the solid electrolyte when using _{(CeO 2) 0 · 8 (} SmO 1 · 5) 0 · 2, so that the solid electrolyte formed becomes dense layer It is necessary to sinter the electrolyte material. Generally, the way to the solid electrolyte is a dense layer, for example by atmospheric pressure sintering particulate state _{(CeO 2) 0 · 8 (} SmO 1 · 5) 0 · 2 to a desired shape After pressure forming, a means of sintering at high temperature is adopted.

The optimum sintering temperature of the electrolyte material is 1650.
It is known to be as high as ℃.

However, when the solid electrolyte is formed at the optimum sintering temperature, each crystal grain of the solid electrolyte increases (about 15
[mu] m), pores remain inside the crystal particles, and the relative density of the sintered body decreases, causing a problem that the fuel gas permeates the solid electrolyte.

It is now known that if the fuel gas permeates the solid electrolyte, the electromotive force of the fuel cell is reduced, and the amount of power generation is greatly reduced. In addition, since the mechanical strength of the fuel cell decreases as the porosity of the solid electrolyte increases, it is not desirable to manufacture the fuel cell using the solid electrolyte having pinholes. It is to be noted that an ideal solid electrolyte has a small crystal grain size and is uniform. That is, it is desired that the fuel gas does not pass through the solid electrolyte and that the mechanical strength is high.

The present invention has been made based on the above-mentioned problems, and it forms a dense solid electrolyte to reduce the porosity, prevents the fuel gas from passing through the solid electrolyte, and improves the mechanical strength of the solid electrolyte. It is an object of the present invention to provide a method for producing a solid electrolyte of a solid oxide fuel cell which is increased.

[0014]

In order to solve the above-mentioned problems, the first method of the present invention is to pressure-mold an electrolyte material by a molding machine to obtain a solid electrolyte, and an oxygen electrode and hydrogen are provided on the sides of the solid electrolyte. After mounting the electrode, a protective film is interposed between the solid electrolyte and the hydrogen electrode, in the method for producing a solid electrolyte of a solid oxide fuel cell that operates by fuel gas by providing a load on the oxygen electrode and the hydrogen electrode, It is characterized in that the electrolyte material is pressure-molded by a hot pressing method and simultaneously sintered to form a solid electrolyte.

A second invention is the hot pressing method, wherein the pressing pressure is 1000 kg / cm ² , and the sintering temperature is 16.
It is characterized by forming a solid electrolyte below 50 ° C.

A third aspect of the present invention uses the electrolyte material (CeO ₂ )
_{0 · 8 (SmO 1 · 5} ) , characterized in that the _0-2.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. Obtained by doping CeO ₂ with Sm
_{(CeO 2) 0 · 8 (} SmO 1 · 5) 0 · 2 an electrolyte material made of a hot press method is to form a solid electrolyte and sintered simultaneously when pressure molded into a desired shaped body, by the hot pressing A hot press machine used for forming a solid electrolyte will be described with reference to the schematic configuration diagram of the hot press machine shown in FIG.

In FIG. 1, a mold supporting block 2 is arranged on the upper surface of a heat-resistant block 1 arranged to support the entire molding machine for pressure-molding an electrolyte material. A plug 3 for forming an electrolyte material into a desired molded body is arranged in the center of the upper surface of the mold supporting block 2, and a replaceable inner lining 5 is provided on the side surface of the plug 3 so that a material filling chamber 4 is provided. Place it so that it surrounds it. Further, the replaceable lining 5
The mold 6 is arranged at the upper end of the mold supporting block 2 so as to surround the side surface of the mold 6.

A heat resistant punch 7 for pressure forming an electrolyte material is loaded in the material filling chamber 4, and a high strength heat resistant block 8 is provided on the upper surface of the heat resistant punch 7. A cooling plate 9 is arranged on the upper surface of the high-strength heat-resistant block 8,
A hydraulic press 10 is provided on the cooling plate 9. By applying pressure to the hydraulic press 10, the electrolyte material filled in the material filling chamber is shaped into a desired solid electrolyte.

A hot press machine is constructed by forming a furnace 12 so that the entire molding machine constructed as described above is surrounded by a refractory lining 11. A hole 13 is formed in the center of the upper part of the furnace 12 for penetrating the heat resistant punch 10, and the high temperature part 14 of the furnace is the highest temperature when sintering the electrolyte material.

As described above, the sintering temperature 1500, 1550, 1600, 165 is used by using the sample of the solid electrolyte produced by pressure-forming and simultaneously sintering the electrolyte material.
The relative density (%) of the solid electrolyte with respect to 0 ° C. was observed. In order to compare with the solid electrolyte produced by the method of the present invention, a sample of the solid electrolyte produced by the conventional method by the atmospheric pressure sintering method was used, and the observation results are shown in Table 1 below. The molding conditions and sintering conditions for the solid electrolyte are shown below.

The method of the present invention: hot press (press pressure ... 10)
00 kg / cm ² , sintering time ... 1 hour) Conventional method: normal pressure sintering (molding pressure ... 1500 kg / cm ² , sintering time ... 15 hours)

[0023]

[Table 1]

From the observation results shown in Table 1, at all sintering temperatures, the solid electrolyte produced by the method of the present invention has a higher relative density than the solid electrolyte produced by the conventional method. It turned out that In particular, there was a large difference in relative density between the solid electrolyte produced by the method of the present invention and the solid electrolyte produced by the conventional method at a sintering temperature of 1500 ° C. Note that, in the above observation results, a relative density characteristic diagram with respect to the sintering temperature is shown in FIG.

FIG. 3 shows a fine structure diagram of the solid electrolytes produced by the method of the present invention and the conventional method used in the above observation.
In FIG. 3, the fine structure of the solid electrolyte produced by the conventional method has a large crystal grain size, and the variation of each crystal grain size is large, whereas the fine structure of the method of the present invention has a small crystal grain size. It was found that the diameters were almost uniform and the variation was small.

From the above, by compacting the electrolyte material simultaneously by hot pressing by the hot pressing method to form a solid electrolyte, the fine structure inside the particles becomes dense and each particle size becomes almost the same, and pinholes are formed. It becomes possible to form a solid electrolyte free of the charge.

Therefore, even if it is used as a solid electrolyte of a fuel cell, the problem of reduction of electromotive force does not occur.

[0028]

As described above, according to the present invention, a solid electrolyte having a dense particle interior and no pinhole is formed by pressure-forming an electrolyte material by hot pressing and simultaneously sintering it to form a solid electrolyte. Can be formed.
By producing a fuel cell using this solid electrolyte, the fuel gas does not pass through the solid electrolyte,
A high open circuit voltage is obtained, and the problem of reduced electromotive force does not occur.

Further, the porosity of the solid electrolyte can be suppressed to a low level, and the respective particle sizes of the solid electrolyte can be reduced, and the solid electrolyte can be machined as compared with the solid electrolyte formed by the conventional pressure sintering method. It was found that the target strength becomes higher.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a hot press device.

FIG. 2 is a relative density characteristic diagram with respect to the sintering temperature in the observation result.

FIG. 3 is a microstructure diagram inside the particles of the solid electrolyte formed by the method of the present invention and the conventional method.

FIG. 4 is a schematic configuration diagram of a conventionally known solid oxide fuel cell.

[Explanation of symbols] 1 ... Heat-resistant block 2 ... Mold support block 3 ... Plug 4 ... Replaceable lining 5 ... Mold 6 ... Material filling chamber 7 ... Heat resistant punch 8 ... High strength heat resistant block 9 ... Cooling plate 10 ... Hydraulic pressure Press 11 ... Fireproof lining 12 ... Furnace 13 ... Hole 14 ... High temperature part of furnace 31a, 31b ... Crystal 41 ... Solid electrolyte 42 ... Oxygen electrode 43 ... Hydrogen electrode 44 ... Load 45 ... First protective film 46 ... Second protective film 47 , 48 ... space

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Chieko Imazawa 2-17 Osaki, Shinagawa-ku, Tokyo Inside the Meidensha Co., Ltd.

Claims (3)

[Claims] 1. A solid electrolyte is obtained by pressure molding an electrolyte material with a molding machine, an oxygen electrode and a hydrogen electrode are attached to the side surfaces of the solid electrolyte, and a protective film is inserted between the solid electrolyte and the hydrogen electrode. A method for producing a solid electrolyte of a solid oxide fuel cell in which a load is placed on the oxygen electrode and the hydrogen electrode to operate with a fuel gas, wherein the electrolyte material is pressure-molded by a hot pressing method and simultaneously sintered to form a solid electrolyte A method for producing a solid electrolyte for a solid oxide fuel cell, comprising: 2. The solid electrolyte for a solid oxide fuel cell according to claim 1, wherein in the hot pressing method, the solid electrolyte is formed at a pressing pressure of 1000 kg / cm ² and a sintering temperature of less than 1650 ° C. Manufacturing method. 3. The electrolyte material is (CeO ₂ ) _0.8 (SmO 2
_1.5 ) _{0.2, The} method for producing a solid electrolyte for a solid oxide fuel cell according to claim 1 or 2, wherein