JPH1125999A - Solid electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell small in the electric resistance of an electro- conductive member, and excellent in electric conductivity between the conductive member and a fuel electrode. SOLUTION: This fuel cell is equipped with plural fuel cells 1 formed by an air electrode 2 on one side face of a cylindrical solid electrolyte 3 and a fuel electrode 4 on the other side face having an inter-connector 5 electrically connected to the air electrode 2 or the fuel electrode 4, and an electrical- conductive member 10 electrically connecting the inter-connector 5 of the fuel cell 1 and the air electrode 2 or the fuel electrode 4 of the other fuel cell 1 to each other. The electrical-conductive member 10 is formed by folding an electrical-conductive sheet made of the metal fiber aggregate containing Ni as the main component several times.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid oxide fuel cell, and more particularly, to a solid oxide fuel cell having an improved conductive member for electrically connecting a plurality of fuel cells.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional cylindrical solid electrolyte fuel cell. A cylindrical fuel cell 1 has a surface on a cylindrical air electrode 2 made of, for example, a LaMnO ₃ material. _A solid electrolyte ₃ made of ₂ O ₃ stabilized ZrO ₂ is coated, and a surface of the solid electrolyte 3 is coated with a Ni-zirconia fuel electrode 4, and a dense film of an interconnector 5 made of LaCrO ₃ is Is connected to the cathode 2,
It is exposed to the outside.

[0005] As shown in FIG. 5, the fuel cells 1 are vertically connected to each other in a horizontal direction.
0 is electrically connected. That is, the fuel electrodes 4 of the fuel cells 1 adjacent to each other in the left-right direction are
Are electrically connected to each other.

[0005] In addition, the fuel cells 1 in the vertical direction in FIG. 5 are connected between the fuel electrode 4 of one fuel cell 1 and the interconnector 5 of the other fuel cell 1 by Ni.
A conductive member 10 composed of a single conductive sheet made of an aggregate of metal fibers mainly composed of
Thereby, the fuel electrode 4 of one fuel cell 1 and the interconnector 5 of the other fuel cell 1 are electrically connected. Although not shown, the current collector-interconnector and the current collector-fuel electrode are also connected by the conductive member 10 made of Ni metal fiber.

The reason why the conductive member 10 is provided is that electrical conduction between the fuel cells 1 and relaxation of mechanical stress between the fuel cells 1 occur. For this reason, the conductive member 10 is a gas-permeable and resilient aggregate of metal fibers. As a material of the metal fiber of the conductive member 10, Ni metal is used because the atmosphere is stable from a hydrogen atmosphere to an atmosphere containing water vapor generated by power generation.

As for the fuel cell, a stack in which the fuel cells 1 are electrically connected as shown in FIG. 5 is produced, a plurality of these are combined, and both ends (a positive electrode side and a negative electrode side) of the assembly are assembled. And a current collecting member.

As shown in FIG. 4, in the fuel cell, a gas containing oxygen, for example, air 6 flows on the air electrode 2 side of the fuel cell 1 and a fuel, for example, hydrogen 7 flows on the fuel electrode 4 side. And power generation at a temperature near 1000 ° C.

[0008]

Since one of the roles of the conductive member 10 made of Ni metal fiber is to provide electrical conduction between the cells 1, the smaller the loss due to the electric resistance of the conductive member 10, the better. Well, it is originally desired to be dense. On the other hand, at the time of power generation, a sufficient amount of hydrogen gas must be efficiently supplied to the fuel electrode 4, and the conductive member 10 is desired to be porous so that the hydrogen gas can sufficiently pass therethrough. Due to such conflicting requirements, there is a problem that when stacked, the performance of the cell 1 cannot be sufficiently exhibited.

The conductive member 10 comes into contact with the interconnector 5, the fuel electrode 4, and the current collector, but only presses at the interface between them, and the conductive member 10 is formed from a single conductive sheet. The electric conduction at the contact interface is weak, so that the performance of the cell 1 cannot be sufficiently exerted when the cells are stacked, and when a mechanical force acts between the cells 1, the cell 1 The cushioning property for stress relaxation during the period of 1 was insufficient.

According to the present invention, the electric resistance of the conductive member is small,
It is an object of the present invention to provide a solid oxide fuel cell that has good electrical conduction between a conductive member and a fuel electrode or the like and can sufficiently impart cushioning properties for relaxing stress between cells.

[0011]

The solid electrolyte fuel cell of the present invention comprises an air electrode formed on one side and a fuel electrode formed on the other side of a cylindrical solid electrolyte. A plurality of fuel cells having interconnectors electrically connected to each other; and a conductive member electrically connecting the interconnector of the fuel cell and the air electrode or the fuel electrode of another fuel cell. The conductive member is formed by folding a plurality of conductive sheets each made of an aggregate of metal fibers containing Ni as a main component.

Here, a concave portion is formed on one end surface of the conductive member that contacts the air electrode or the fuel electrode, the concave portion conforming to the outer surface shape of the air electrode or the fuel electrode, and the other end surface of the conductive member that contacts the interconnector. In addition, it is desirable to form a concave portion that matches the outer surface shape of the interconnector. Further, it is desirable that the thickness of the conductive member is 1 to 8 mm. Further, the thickness of the conductive sheet is desirably 3 mm or less.

[0013]

The most important factor in stacking fuel cells is to join the cells without electrical loss. For this purpose, the joining member is required to have low resistance of itself and low contact resistance at the interface of joining. In order for its own resistance to be low, a dense member having low resistivity should be used. However, in a fuel cell, the fuel gas greatly affects its performance, so that the gas must not be shut off. In addition, it must have sufficient cushioning properties to relieve stress between cells.

In the solid oxide fuel cell according to the present invention, since the conductive member is formed by folding a single conductive sheet, it is possible to have a sufficient cushioning property for alleviating stress between cells, and to provide a cell-to-cell connection. Even if a mechanical stress acts between them, the stress can be relieved. Further, since the conductive member is formed from one conductive sheet, electrical loss between the conductive members can be suppressed. Furthermore, since it has a sufficient cushioning property as described above, on the surface that comes into contact with the fuel electrode and the interconnector, the fuel electrode and the interconnector press against the conductive member, and the contact area can be increased. Continuity can be improved.

Furthermore, since the conductive member is formed by folding a single conductive sheet, a concave portion is formed on the end face that comes into contact with the fuel electrode or the interconnector according to the shape of the outer surface, thereby providing more contact. The area is increased, which allows a reduction in contact resistance.

By setting the thickness of the conductive member to 1 to 8 mm, it is possible to have a cushioning property for sufficiently absorbing mechanical and thermal stresses such as cell warpage and thermal stress.

Further, by setting the thickness of the conductive sheet to 3 mm or less, the contact between the folded conductive sheets can be improved, and the contact resistance can be reduced.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 5, a solid oxide fuel cell according to the present invention comprises a plurality of fuel cells 1 electrically connected. The fuel cell 1 is shown in FIG.
As shown in FIG. 3, the air electrode 2 is formed on the inner surface of the cylindrical solid electrolyte 3 and the fuel electrode 4 is formed on the outer surface. The interconnector 5 electrically connected to the air electrode 2 is connected to the fuel electrode 4. It is exposed outside without conducting.

Then, the fuel electrodes 4 of the fuel cells 1 adjacent to each other in the left-right direction in FIG.

On the other hand, as shown in FIG. 1, the fuel cells 1 in the vertical direction in FIG.
Between the fuel electrode 4 and the interconnector 5 of the lower fuel cell 1, there is provided a conductive member 10 formed by folding a plurality of conductive sheets made of an aggregate of metal fibers containing Ni as a main component. The fuel electrode 4 of the upper fuel cell 1 and the interconnector 5 of the lower fuel cell 1 are electrically connected by the conductive member 10. The conductive member 10 has a bulk density of 0.44 to 2.21 g / cm ^3.
It has been.

As described above, the conductive member 10 made of an aggregate of metal fibers containing Ni as a main component has a bulk density of 0.44 to 0.44.
The reason for setting to 2.21 g / cm ³ is that the bulk density is 0.44 g / cm ^3.
If it is smaller than cm ^3, the electric resistance of the conductive member 10 is large, and sufficient output cannot be obtained when the fuel cells are stacked. If the bulk density exceeds 2.21 g / cm ³ , the permeability of the fuel gas becomes poor, so that the fuel gas cannot be supplied to the contacting fuel electrode, and sufficient power generation performance cannot be obtained.
In addition, the elasticity is reduced, and the stress between the cells cannot be absorbed. The bulk density of the conductive member 10
From the viewpoint of reducing the electric resistance of the conductive member 10 and improving the permeability of the fuel gas, the bulk density of the conductive member 10 is particularly 0.44 to
It is desirably 1.33 g / cm ³ .

Here, the bulk density of the conductive member 10 is 0.44.
In the case of 導電 2.21 g / cm ³ , the specific gravity is 5 to 25% of the specific gravity when the conductive member 10 is made of Ni metal. That is, when the specific gravity when the conductive member 10 is made of a lump of Ni metal is ρ ₁ and the bulk density when the conductive member 10 is an aggregate of metal fibers is ρ ₂ , ρ ₂ / ρ ₁ is 5 to 25. %. The bulk density of the conductive member 10 is 0.44 to
The increase to 2.21 g / cm ³ can be achieved by pressing an aggregate (felt or the like) of Ni metal fibers with a predetermined pressure by a press. Incidentally, the specific gravity in the case of Ni metal is 8.845, the bulk density of ordinary Ni felt is 0.35 g / cm ³ , and the conductive member 1
The bulk density of 0 is about 4% of the specific gravity when the conductive member 10 is made of Ni metal. The metal fiber is mainly composed of Ni,
At least one of Fe, Co and Cr may be contained.

As shown in FIG. 2, the conductive member 10 is formed by folding the conductive sheet 21 six times.
6 are formed in six places. A recess 24 is formed in the upper end surface of the conductive member 10 in contact with the fuel electrode 4 so as to conform to the outer shape of the fuel electrode 4 of the upper cell 1, and the conductive member is in contact with the interconnector 5 of the lower cell 1. The lower end face 10 has a recess 25 which matches the outer shape of the interconnector 5. These recesses 24, 25 allow the conductive member 10, the fuel electrode 4 of the upper cell 1, Of the cell 1 with the interconnector 5 can be reduced.

The thickness t of the conductive member 10 is 1 to 8 mm
It is desirable that The thickness t of the conductive member 10 is 1 mm
If the temperature is less than the above, the cell cannot absorb the warpage and the thermal stress, the cushioning property against the mechanical and thermal stress is insufficient, and the power generation performance is deteriorated. If it does, cell destruction may be caused.
On the other hand, when the thickness is more than 8 mm, the resistance of the conductive member itself increases, and the performance as a stack deteriorates. In particular, the thickness t of the conductive member is desirably 2 to 5 mm. The conductive member 10
In the case of FIG. 1, the thickness t of the fuel cell 4 means the distance between the fuel electrode 4 of the upper cell 1 and the interconnector 5 of the lower cell 1.

Further, the thickness of the conductive sheet is desirably 3 mm or less. This is because the thickness of the conductive sheet is 3m
When the thickness is larger than m, the contact of the folded surface becomes poor. In particular, 1 to 3 mm is desirable.

The conductive member 10 has a folded portion 23 of 2 to 8
It is desirable to fold it from two to eight so that it is formed in several places. If the fold is not made, no effect is exhibited, and if the fold is eight or more, it is difficult to maintain the dimensional accuracy of one conductive member 10, and therefore, it may cause an electrical short. In particular, three to six folds are desirable. FIG. 2 shows the conductive member 10 folded in six.

In the solid oxide fuel cell of the present invention, the conductive member 10 is formed by folding the conductive sheet 21 made of an aggregate of metal fibers containing Ni as the main component six times, so that the conductive member 10 is not folded. Also has high cushioning properties,
Furthermore, since it is formed from one conductive sheet 21, the loss of voltage is small, and the bonding between the fuel cells 1 is good even at a high temperature of 1000 ° C. Also, mechanical between the cells 1,
Thermal stress can also be absorbed. Also, since it is formed from one conductive sheet 21, the recesses 24 and 25 can be formed in accordance with the outer shape of the cell 1 and the interconnector in order to reduce the contact resistance at the interface. And good joining can be performed without increasing the number of layers.

[0028]

EXAMPLE First, on the outer surface of an air electrode made of La _0.9 Sr _0.1 MnO ₃ , the purity was 99.9% or more and the average particle diameter was 0.4 mm.
A paste having 5 μm of ZrO ₂ (containing 10 mol% of Y ₂ O ₃ ) was applied and fired at 1500 ° C. for 3 hours to form a solid electrolyte. The surface of the solid electrolyte was polished to expose the internal air electrode, and the exposed portion was exposed to 0.5 μm La.
After applying a solution composed of _0.9 Sr _0.1 CrO ₃ , the solution was dried and heat-treated at 1800 ° C. in the air for 10 hours to produce an interconnector. Then, a solution composed of 80% by weight of Ni and 20% by weight of ZrO ₂ is applied to the surface of the solid electrolyte by a screen printing method so as not to be electrically connected to the interconnector, and then dried and at 1200 ° C. in the atmosphere for 2 hours. Heat treatment was performed to produce a fuel electrode, and a fuel cell as shown in FIG. 4 was produced.

Power was generated at 1000 ° C. while flowing air to the air electrode side and hydrogen to the fuel electrode side so as to have a fuel utilization of 60% in the fuel cell thus manufactured.
When the output after time was measured, it was 50 W, and the area per unit area of the portion that substantially generates power, that is, the output per unit area of the portion sandwiched between the air electrode and the fuel electrode was 0.3 W / cm ² . .

The distance between the interconnector and the fuel electrode of an adjacent fuel cell and the distance between the fuel electrodes are set to 5 mm, and the distance between the fuel electrodes is 5 mm. Having a sheet thickness as shown in Table 1 and a bulk density of 0.8
Using a conductive sheet of 8 g / cm ^3, a conductive member having a width of 10 mm, a length of 50 cm, and a thickness of 5 mm, which is formed by folding the conductive sheet so as to form the number of folded portions shown in Table 1, is arranged. As shown in FIG. 3 (a), a stack in which two fuel cells are connected in series (in the table, indicated by 2), and as shown in FIG. 3 (b), four fuel cells are connected in series and in parallel. A connected stack (in the table, described as 2 straight 2 flat) was produced. In addition, as shown in FIGS. 1 and 2, the end surface of the conductive member that contacts the fuel electrode is formed with a concave portion that matches the outer surface shape of the fuel electrode, and the end surface that contacts the interconnector is A recess is formed which conforms to the outer shape of the interconnector.

Next, a Ni metal plate for taking out current and a voltage terminal are attached to the stack, and the stack is put into a furnace at 1000 ° C.
The power generation was performed while flowing air to the inside of the cell and hydrogen to the outside of the cell so as to have a fuel utilization of 60%, and the power generation output of the stack was measured.

Thereafter, the output per unit area of the stack was compared with the output per unit area in the case of one fuel cell, and the performance was evaluated. When the output per unit area of the stack was 80% or more of the output per unit area in the case of one fuel cell, it was judged that there was no performance deterioration in the conductive member. Table 1 shows the results.

[0033]

[Table 1]

From Table 1, the output ratio in the conventional case where the conductive member is a single conductive sheet is 60% (sample No.
In contrast to 1), in the sample of the present invention in which the conductive member is formed by folding a plurality of conductive sheets made of an aggregate of metal fibers containing Ni as a main component, the output ratio is 80% or more,
It can be seen that the performance deterioration due to the conductive member is small.

[0035]

According to the solid oxide fuel cell of the present invention, since the conductive member is formed by folding a plurality of conductive sheets each made of an aggregate of metal fibers containing Ni as a main component, one conductive sheet is folded. By improving the cushioning property, it is possible to reduce the stress generated between the cells, and since it is formed from a single conductive sheet, it is possible to suppress the electric loss, and to further reduce the thickness of the conductive sheet. Since it is a body, it can be joined to the cell at the contact surface according to the shape of the cell, and the contact resistance can be reduced. Therefore, in the solid oxide fuel cell of the present invention, the performance of the fuel cell can be sufficiently exhibited.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a state in which cells of a solid oxide fuel cell of the present invention are connected by a conductive member.

FIG. 2 is an explanatory view showing a conductive member of the solid oxide fuel cell of FIG.

FIG. 3 shows a two-stack fuel cell according to the embodiment (a).
FIG. 4 is a schematic diagram for explaining a two-by-two flat stack (b).

FIG. 4 is a perspective view showing a conventional solid oxide fuel cell.

5 is an explanatory diagram showing a stack in which nine fuel cells of FIG. 4 are connected.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Fuel cell 2 ... Air electrode 3 ... Solid electrolyte 4 ... Fuel electrode 5 ... In-ita connector 10 ... Conductive member

Claims (4)

[Claims] 1. A plurality of fuel cells comprising a cylindrical solid electrolyte having an air electrode formed on one surface and a fuel electrode formed on the other surface, and having an interconnector electrically connected to the air electrode or the fuel electrode. A solid oxide fuel cell comprising: a cell; and a conductive member that electrically connects the interconnector of the fuel cell and the air electrode or the fuel electrode of another fuel cell. A solid oxide fuel cell comprising a plurality of conductive sheets each formed of an aggregate of metal fibers containing Ni as a main component. 2. A conductive member abutting on an air electrode or a fuel electrode has a concave portion formed on one end surface of the conductive member in contact with the outer surface of the air electrode or the fuel electrode, and the other of the conductive members abutting on the interconnector. 2. The solid oxide fuel cell according to claim 1, wherein a concave portion is formed on an end surface of the concave portion, the concave portion corresponding to an outer shape of the interconnector. 3. The solid oxide fuel cell according to claim 1, wherein the thickness of the conductive member is 1 to 8 mm. 4. The solid oxide fuel cell according to claim 1, wherein the thickness of the conductive sheet is 3 mm or less.