JPH0381966A - Solid electrolyte fuel cell - Google Patents

Abstract

PURPOSE:To obtain a unit cell structure whose voltage drop is small by stacking a pinhole-free solid electrolyte thin film on the surface of a conductive porous base plate having fine, uniform pores, and stacking an electrode thin film thereon. CONSTITUTION:A pinhole-free solid electrolyte thin film 3 is stacked on the surface of a conductive porous base plate 1 having fine, uniform pores on its surface, and an electrode thin film 4 is stacked on the surface of the solid electrolyte 3 to form a unit cell. The solid electrolyte thin film is formed so that the pores of the conductive porous base plate are blocked. Pinholes caused by the breakage of the solid electrolyte thin film on the large pores are not produced and adverse effect on electromotive force is avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application This invention relates to a fuel cell in which a single cell is constructed by laminating a solid electrolyte thin film on a conductive porous substrate.

B1 Summary of the Invention The present invention is a solid electrolyte fuel cell having a stack of single cells, in which a pinhole-free solid electrolyte thin film is laminated on the surface of a conductive porous substrate having fine and uniform pores. However, by laminating a thin electrode film on the surface to form a single battery cell, a good fuel cell can be constructed.

C1 Conventional technology Fuel cells are conventionally applied products using porous substrates.

One type of fuel cell is a flat plate type fuel cell.

In general, a fuel cell main body consists of a unit cell structure (hereinafter referred to as a unit cell structure) by arranging an anode and a cathode electrode plate on both sides of a solid electrolyte. A plurality of them are arranged in series so that they face each other. Hydrogen gas (hydrogen) is supplied as a fuel to the cathode side of the fuel cell body configured in this way, and air (oxygen) is supplied as an oxidizing agent to the anode side, causing the hydrogen and oxygen to react to generate an electromotive force. is occurring. Note that water is produced during this reaction. Next, a conventional fuel cell will be described with reference to FIG.

That is, the fuel cell main body 30, as shown in FIG.
A plurality of single cell structures S and a holding plate 31a for stacking and fixing these single cell structures S in series.

31b, a hydrogen gas supply manifold 32 that supplies hydrogen gas H2 to the cathode plate side of each single cell structure S of the stacked and fixed battery body 3o, and an air supply manifold 32 that supplies air (oxygen) to the anode plate side. 33, and current collecting leads 34 and 35 that take out electricity from the anode plate and cathode plate of each single cell structure S, respectively.

In the stacked fuel cell configured in this manner, the gas supply manifolds 32 and 33 are attached to the outside of the cell main body 30. In addition, water and electrical energy are generated by the reaction between the supplied hydrogen gas and air via the electrolyte, and the current collector leads (busbars) 34 and 35 that extract this generated electrical energy to the outside have a single cell structure. attached to the outside of the body.

Problems that the D1 invention attempts to solve The conventional fuel cell shown in Figure 2 uses a solid electrolyte.

Although it is constructed by combining an oxygen electrode and a hydrogen electrode, it has a drawback in strength. However, although strength can be ensured by a current collector plate provided outside the picture electrode after the unit cell structure is assembled, there is a risk of damage during assembly. Furthermore, in order to ensure a certain degree of strength, it was necessary to form the solid electrolyte layer thickly.

When the solid electrolyte layer is formed thickly, the voltage drop V due to the resistance of the solid electrolyte itself is V=ir−tXIO−′ (f is the current flowing through the solid electrolyte, R is the resistance of the solid electrolyte, and t is the From the relationship expressed by (thickness), it can be seen that the thinner the solid electrolyte is, the better the voltage drop will be. However, in the conventional structure, the thickness of the solid electrolyte must be made thick to a certain extent due to strength, which causes a problem in that the voltage drop becomes large.

In view of the above points, the present invention forms a solid electrolyte into a thin film,
An object of the present invention is to provide a solid oxide fuel cell in which a single cell structure of a fuel cell with a small voltage drop can be obtained.

81 Means for Solving the Problems The solid electrolyte fuel cell of the present invention has a pinhole-free solid electrolyte thin film laminated on the surface of a conductive i+h porous substrate having fine and uniform pores at least on its surface, A feature of the battery is that a thin electrode film is laminated on the surface of the solid electrolyte to constitute a single cell of the battery.

11 Effect By configuring as described above, a thin film of solid electrolyte is formed so as to close the pores of the conductive porous substrate, and the thin film of solid electrolyte is cut on the large pores, causing pinholes. This has the effect of eliminating the negative effect on the electromotive force caused by this.

G. Example Embodiments of the present invention will be described below based on the drawings.

Fig. 1 is a vertical cross-sectional view of a solid oxide fuel cell main body in a stacked configuration.
, the oxygen bridge thin film 4 is laminated to form a single cell structure.

First, this conductive porous substrate can be made not only of stainless steel but also of conductive materials such as platinum or silver (
Note that it may be made of nickel, copper, or the like. ) to form.

Furthermore, since it also serves as a hydrogen electrode, it is better if at least its surface portion has catalytic ability. In addition, a porous substrate made of such a material has a porosity of 40% or more, and has a diameter of 2 to 3 on the surface where the solid electrolyte thin film is to be laminated.
A material with uniform pores of about μm size is used.

Furthermore, this porous substrate itself has a two-layer structure, and the surface side on which the solid electrolyte thin film is to be laminated has pores with a diameter of 2 to 3 μm, and the other surface side has rough pores. Of course, it is possible.

In addition, when using the porous substrate I made of stainless steel which is a metal conductor as described above, this porous substrate I
It has the advantage that it can be used as a current collector for the hydrogen electrode in a single cell, and that it has good heat resistance because it is made of stainless steel.

Further, when a porous substrate 1 made of nickel is used, the hydrogen resistance can be made better than that of stainless steel.

Furthermore, in order to improve the portion of the conductive porous substrate I that will become the electrode surface, platinum (PT) is laminated to a thickness of 200 μm on the surface of the conductive porous substrate 1 by sputtering.

Sputtering was carried out using a high-frequency sputtering device in an atmosphere of argon gas under a pressure of 5×10 mmHg for 1 hour using pt as a target.

When the conductive porous substrate l is coated with Pt in this manner, platinum acts as a catalyst, so the reaction can be accelerated as shown in the following chemical formula, and a large current can be easily extracted.

0”-+Ht-+H, O+ 2 e Next, an example of manufacturing the solid electrolyte thin film 3 will be described.

First, in the first manufacturing example, a thin film of solid electrolyte is formed on the upper surface of a porous substrate I to a thickness of 10 μm. For this purpose, an electron beam evaporation method was used, and a turbo pump was used for the evaporation at a vacuum level of 10 mmHg, and the substrate temperature was kept at room temperature to 580 mmHg.
The temperature was varied up to ℃, and the deposition rate was controlled by a controller.

Note that single crystal L a F s was used as the solid electrolyte, and the conditions for forming the thin film of the solid electrolyte were a substrate temperature of 500° C., a vapor rate of 20 people/5ec1, and an acceleration voltage of −3.0 kV.

When a thin film of solid electrolyte is formed as described above, a film free from pinholes can be obtained.

Next, a second manufacturing example of the solid electrolyte thin film 3 will be described.

The second fabrication example adopted the resistance heating method, the degree of vacuum was set to 1 (I" mmHg) using the same pump as above, and the substrate temperature was set to 400°C. The evaporation rate was 3 to 5 in/s, about 5 A thin film with a thickness of 108 m was obtained in ~6 hours.The thin film obtained by this method also had no pinholes as in the above example.

In addition to L a F 3, solid electrolytes include 1,
a 1-xS r F s-x, in particular, La
As a result of X-ray diffraction of a thin film using o, ssS r o, ssF *, and ss as raw materials, only the L a F s peak was observed. From this, it can be seen that the thin film of this solid electrolyte is L
It can be confirmed that it is not a mixture of a F s and S r F t.

Next, a third manufacturing example of the solid electrolyte thin film 3 will be described. The third production example uses magnetron sputtering at a substrate temperature of 400°C and 5.3X in an argon gas atmosphere.
Sputtering was performed for 40 hours using L a F s powder as a target under a pressure of 10-3 mmHg.
A thin film with a thickness of IO μm was obtained.

As a result of X-ray diffraction of this thin film, it was found to be polycrystalline LaF with poor crystallinity.

Note that the raw material for the solid electrolyte thin film is not limited to L a F 3 and the following materials may also be used.

(b) L a o, es S r o, os F z
, ss (b) L ao, ss S r o, +o F
t, s.

(c) L a o, sa B a o, os F v
ts (d) L a o, so B a o, +o
F t,ts Even if the thin film obtained by the magnetron sputtering described above has a complex composition, the obtained thin film has roughly the composition of the raw material, so Lao, esS r o
, osP z, es, etc.

Next, a fourth manufacturing example of the solid electrolyte thin film 3 will be described.

In this fourth production example, La
An organometallic compound containing F and F in its molecules was thermally decomposed to form a thin film of La and Fs. The above organometallic compound is L
It is a compound called anthanun fod.

The structural formula of this compound is as follows.

[CF, -CF, -CF, -C-CH, -C-CI, -
(CH3)t)LaThe film forming conditions are a substrate temperature of 600°C.
The organometallic compound was kept at 230°C, and argon gas (Ar) was used as a carrier gas at a flow rate of 100 m12/m.
A thin film of LaF3 is obtained by moving the organometallic compound vapor to the surface of the porous substrate 1 in the reactor and reacting with it.

Next, a fifth manufacturing example of the solid electrolyte thin film 3 will be described.

This fifth production example is +1! as shown in Figure 5! ! A high-frequency sputtering device was used on the surface of the third nickel layer 13, and the sputtering conditions were a substrate temperature of 800° C., an argon pressure of 5.3×fO-”ax Hy, and zirconia stabilized with ittria as a target. Then, sputtering was performed for 40 hours, and a pinhole-free thin film of solid electrolyte having a thickness of 10 μl was laminated.

In addition, cerium oxide or the like may also be used.

Finally, an example of manufacturing the oxygen electrode thin film 4 will be described.

In the first manufacturing example, an electrode thin film for oxygen is created from a perovskite compound.
, eS ro4coox). This uses cobalt acetate (CH3COO), C0.4)(to, lanthanum acetate (CH3COO) t L a , and strontium acetate (CH3COO> * s r ) as raw materials, and L a o
, sS r 11.4c OO-x, the powders were weighed and mixed, heated at 1000° C. in an oxygen atmosphere, and fired for 5 hours. The electrical resistivity of the perovskite compound thus created was 4.4 ΩCm.

There are three methods for forming an oxygen electrode thin film using the perovskite compound produced as described above.

(1) Dissolve the perovskite compound in propylene glycol, apply it to the surface of the solid electrolyte thin film 3, apply a slight pressure, and heat it in an oxygen atmosphere at a temperature of 300°C.
The electrode thin film 4 is obtained by baking for a period of time.

(2) A perovskite compound and platinum black are mixed in a ratio of 3=1 and dissolved in propylene glycol. Thereafter, this liquid is applied to the surface of the solid electrolyte thin film 3 and fired under the same conditions as above to obtain the electrode thin film 4.

(3) A perovskite compound is formed on the surface of the solid electrolyte thin film 3 using a high frequency sputtering device. This was carried out for about 2 hours at a deposition rate of 0.5 μm/hour under a pressure of I X l O-” mmHg of argon gas, resulting in a deposition of about I μm.
A thick electrode thin film 4 is obtained.

The perovskite compound has performance equivalent to that of platinum, but is much cheaper than platinum.

Next, a second manufacturing example of an electrode thin film for oxygen will be described.

In this second production example, Ag powder is dissolved in propylene glycol, and this solution is applied to the surface of the solid electrolyte thin film 3.
An electrode thin film is obtained by baking in an oxygen atmosphere at a temperature of 300° C. for 8 hours while applying a slight pressure force.

Next, a third manufacturing example of the oxygen electrode thin film 4 will be described.

In the third production example, an electrode thin film is obtained by dissolving chloroplatinic acid (HzP t CI2 g) in propylene glycol, applying this in the same manner as above, and baking under the same conditions as above.

As mentioned above, generally available porous substrates have pore diameters that vary, for example, from 0.5 to 40 μm, and when hydrogen and oxygen electrodes and solid electrolyte thin films are laminated on the surface of this porous substrate, If the substrate had large holes, pinholes were likely to form in the solid electrolyte above the holes.

However, when hydrogen and oxygen electrodes and solid electrolytes were created as described above, pinholes no longer occurred. Due to the difference in oxygen partial pressure between the solid electrolyte and the fuel cell,
It constitutes a type of oxygen agrochemical battery, in which an electromotive force is generated at both ends of a solid electrolyte. The electromotive force Eo at this time is expressed by the following formula.

Eo-(RT/4F)X12n (P, /P*) From the above equation, the electromotive force Eo increases in proportion to the ratio of oxygen partial pressures. In addition, in the formula, R is the gas constant, T is the absolute temperature, and F
is the Faraday constant, and P+ and Pt are the oxygen partial pressures across the solid electrolyte.

From the above equation, if a pinhole is formed in the solid electrolyte, the ratio of oxygen partial pressure will be small, and the electromotive force Eo will be small. However, by manufacturing a solid electrolyte that does not have pinholes as in the present invention, The electromotive force no longer decreases.

The single cell structure configured as described above is housed in a conductive cell case, and the conductive porous substrate 1 of the single cell structure is
and the cell case 5, and a conductive end separator 7 is attached to the oxygen electrode thin film 4 side to electrically connect the thin film 4 and the end separator 7, The fuel cell main body 20a is constructed by interposing an insulator 6 between the cell case 5 and the end separator 7.

The porous substrate l of the cell case 5 of this fuel cell main body 20a
As shown in FIG. 1, conductive separators 7.8 are electrically connected to the sides. The oxygen electrode thin film 4 of the single cell structure is electrically connected to the separator 8 in the same manner as described above, and the conductive porous substrate l and the cell case 5 are also electrically connected. An insulator 6 is interposed between them to form a fuel cell main body 20b. Similarly, the fuel cell bodies 20c, 20d, . . . are stacked, and the fuel cells can be connected in series by simply stacking the fuel cell bodies 20a, 20b, . . . with a single cell structure. Then, oxygen is supplied from the air inlet 9 of the separator 7.8, and hydrogen is supplied from the air inlet IO of the cell case 5, thereby generating electricity.

H0 Effects of the Invention As described above, according to the present invention, a solid electrolyte thin film in which no pinholes occur on the surface of a conductive porous substrate having fine and uniform pores at least in the surface portion,
Since the single cell structure is formed by forming the electrode thin film, a single cell structure with a small voltage drop can be obtained.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of a main part of a cell stack part of a fuel cell for explaining an embodiment of a solid oxide fuel cell of the present invention, and FIG.
The figure shows the principle of a stacked fuel cell. ! ...-porous substrate, 3... solid electrolyte thin film, 4...
- Oxygen electrode thin film serving as an electrode thin film, 5... Cell case, 6... Insulator, 7° 8... Separator, 20a. 0 b. 20c...Fuel cell main body. Figure 1 Main part longitudinal cross-sectional view 0a 1 Porous substrate 3 Solid electrolyte thin film 4 Oxygen electrode thin film a Cell case 6 Insulator 7.8 Separator 20b Fuel cell main body

Claims (1)

[Claims] (1) Forming a conductive porous substrate having fine and uniform pores at least on its surface, laminating a pinhole-free solid electrolyte thin film on the surface of the porous substrate, and depositing a pinhole-free solid electrolyte thin film on the surface of the solid electrolyte thin film. A solid electrolyte fuel cell characterized in that a single cell of the battery is constructed by laminating thin electrode films.