JPH1079258A - Current collecting method for flat type solid electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To establish a current collecting method in which contacting of an air electrode with a separator is well kept to allow continued effect of current collection even if a nickel felt or nickel mesh on the fuel electrode side is compressed during the fuel cell being in operation, which does not require a structure involving a load application from the fuel electrode to air electrode, and can prevent cracking of the electrolyte resulting from difference in the coefficient of thermal expansion caused by joining of the fuel electrode with a current collecting material to be installed between the fuel electrode and separator by using a substance having a small modulus of elasticity to the current collecting material. SOLUTION: The current collecting method according to the invention applies to a flat plate type solid electrolyte fuel cell on internal manifold system of such a structure that flat plate unit cells each formed by installing an air electrode 3 and fuel electrode 2 on the surfaces of a flat plate solid electrolyte layer and separators 4, in which adjoining unit cells are connected in series electrically and the fuel and oxidator gas are distributed to the unit cells, are laminated one over another, wherein it is arranged so that the electrolyte layer is bent convex toward the fuel electrode 2 with the load at the time of laminating and the air electrode 3 keeps the contacting condition with the separator 4, and a current collecting member 6 having a small modulus of elasticity is inserted to the side with the fuel electrode 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current collecting method for a flat solid electrolyte fuel cell.

[0002]

2. Description of the Related Art Recently, fuel cells which directly convert chemical energy inherent in fuel into electric energy by using, for example, air and hydrogen as oxidizing gas and fuel gas, respectively, have attracted attention from the viewpoint of resource saving and environmental protection. Research and development are progressing because solid electrolyte fuel cells have many advantages such as high power generation efficiency and effective use of waste heat.

In order to supply a fuel gas and an oxidizing gas to a solid electrolyte fuel cell, gas supply / exhaust holes are provided in a separator and a solid electrolyte layer of the solid electrolyte fuel cell, and each electrode of each unit cell is formed through this hole. The one that supplies and exhausts each gas to and from the surface is called an internal manifold type. A flat solid electrolyte fuel cell of the internal manifold type is made of a zirconia sintered body (Y
SZ), a flat cell having an air electrode of (La, Sr) MnO ₃ and a fuel electrode of Ni / YSZ cermet on both surfaces thereof, and adjacent cells. Are electrically connected in series, and separators for distributing fuel gas and oxidizing gas are alternately stacked on each cell, and a metal mesh is interposed between the fuel electrode and the fuel gas flow path side of the separator. Are stacked in a stack with a sealant or spacer interposed between the solid electrolyte layer and the separator of the unit cell, respectively, by contacting a fuel gas and an oxidizing gas with each electrode surface of each unit cell. Generates electromotive force.

[0004]

Conventionally, during operation of a flat solid electrolyte fuel cell of the internal manifold type,
In order to reduce the contact resistance between the electrode and the separator, and to prevent leakage of fuel gas and oxidizing gas, apply a load to the stack vertically using a weight type, screw type, hydraulic type, etc. I have.

In this case, current collection between the air electrode and the separator is performed by packing a flexible material such as nickel felt or nickel mesh as a current collector between the fuel electrode and the separator facing the fuel electrode. By applying a laminating load from above, the air electrode is pressed against the separator and brought into contact therewith.

[0006] However, when the above-mentioned nickel felt or nickel mesh on the fuel electrode side is compressed and reduced during operation of the fuel cell, the contact between the air electrode and the separator is weakened, so that the contact resistance is increased, and finally the contact resistance is increased. Since the air electrode and the separator are insulated from each other, current collection becomes impossible.

Therefore, when a load is applied from the fuel electrode side as in the prior art, a rigid current collector having a large elastic modulus must be used. When such a material is joined to the fuel electrode, the solid electrolyte layer is cracked by thermal stress caused by a difference in thermal expansion coefficient.

[0008] The present invention has been made in view of the above points, and even if the nickel felt or nickel mesh on the fuel electrode side is compressed during the operation of the flat solid electrolyte fuel cell, the distance between the air electrode and the separator is reduced. The present invention provides a current collecting method that can continue the current collecting operation while maintaining contact with the fuel cell, and prevents a crack in the electrolyte by using a current collecting material having a large porosity and a small elastic modulus between the fuel electrode and the separator. The purpose is to:

[0009]

In order to achieve the above object, the present invention provides a flat cell having an air electrode and a fuel electrode disposed on both surfaces of a flat solid electrolyte layer, and a cell having adjacent cells. Are electrically connected in series and separators for distributing fuel and oxidizing gas to each unit cell are alternately stacked. In the current collector method of the internal manifold type flat solid electrolyte fuel cell, Thus, the solid electrolyte layer is curved so as to protrude toward the fuel electrode side, the air electrode keeps contact with the separator, and a current collector having a small elastic modulus is inserted on the fuel electrode side. .

Further, according to the present invention, the projection of the oxidizing gas flow channel on the side facing the cathode of the separator is projected from the gas sealing surface between the separator and the spacer on the air electrode side, and the total thickness of the air electrode and the projection is obtained. Is larger than the thickness of the spacer. Further, the separator is characterized in that the oxidant gas flow channel convex portion on the side facing the cathode of the separator projects from the gas seal surface between the electrolyte and the spacer on the air electrode side. At this time, the projection is made of a cathode component, a separator component or a conductive ceramic. Further, the thickness of the cathode is made larger than the thickness of the spacer.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view of a flat solid electrolyte fuel cell of an internal manifold type in which a current collecting method according to the present invention is implemented.

The flat solid electrolyte fuel cell shown in FIG.
(La, Sr) MnO ₃ air electrode 3 and Ni / Y
A flat cell having an SZ cermet fuel electrode 2 disposed therein, and a separator which electrically connects adjacent cells in series and distributes fuel gas and air (oxidant gas) to each cell. 4 are alternately stacked, and stacked in a stack with a spacer 5 interposed between the solid electrolyte layer 1 and the separator 4 of the unit cell. In addition, the flat plate-type solid electrolyte fuel cell of the internal manifold type is an integrated structure in which cell materials such as a unit cell, a separator 4 and a spacer 5 have functions of supplying and exhausting, distributing, and collecting current of each gas of air and fuel. The gas flow grooves 11 are formed in the separator 4 to evenly distribute air to the corners of the electrode surface of the air electrode 3, and gas between the grooves 11 is used to connect adjacent cells in series. It is a flow passage convex portion 12. The surface of the spacer 5 that contacts the solid electrolyte layer 1 is a gas seal surface 10.
a, the surface in contact with the separator is the gas seal surface 10
b.

According to the current collecting method of the present invention, during operation, the solid electrolyte layer 1 is curved so as to project toward the fuel electrode 2,
In addition, even when no load is applied from the fuel electrode side, the air electrode 3 is kept in contact with the separator 4, and the current collector 6 having a small elastic modulus is mounted on the fuel electrode 2 side (in other words, the fuel electrode 2
(The current collector 6 is inserted between the current collector 6 and the upper separator 4). The current is collected so that a large load is not applied to the electrolyte. The current collector 6 is a nickel felt or a nickel mesh having a high elasticity.

This structure of the present invention is different from a structure in which a large load is applied from the fuel electrode side to nickel felt or nickel mesh to press the air electrode against the separator as in a conventional flat solid electrolyte fuel cell. It is different (the cathode is not pressed against the separator). Therefore, even if nickel felt or nickel mesh is compressed and reduced during operation of the fuel cell, the contact between the air electrode and the separator is weakened, the contact resistance is increased, and finally the air electrode and the separator are insulated. No disadvantages occur. Furthermore, since a current collecting material having a small elastic modulus is used for current collection between the anode and the separator, even when the current collecting material and the anode are joined, the electrolyte does not crack due to a difference in thermal expansion coefficient.

An embodiment of the present invention is as follows. (1) The oxidant gas flow path projection 12 of the separator 4 is projected from the gas sealing surface 10b between the air electrode side separator 4 and the spacer 5, and the total thickness A of the projection 13 and the air electrode is obtained.
Is larger than the thickness of the spacer 5, and the solid electrolyte layer is curved so as to project toward the fuel electrode by the difference. (2) The oxidant gas flow path convex portion 12 on the side of the separator 4 facing the cathode 3 is connected to the gas seal surface 10 of the separator 4.
Projection is made B above a (see FIG. 2). As a result, the solid electrolyte layer 1 is curved by the load at the time of lamination so as to protrude toward the fuel electrode 2 by the thickness of the air electrode and the thickness of B. (3) The projection 13 or 15 is a cathode component. (4) The protrusion is a separator component. (5) The projection is made of a conductive ceramic. (6) The oxidant gas flow path projection 12 on the side of the separator 4 facing the air electrode 3 is connected to the gas seal surface 10a of the separator 4.
The thickness of the air electrode 3 is made larger than the thickness of the spacer 5 without protruding further (see FIG. 3).

[0017]

EXAMPLES The current collecting method of the present invention was applied to a flat plate type solid electrolyte fuel cell as follows.

Lanthanum manganate was applied to the convex portion 12 of the oxidant channel of the lanthanum chromite separator 4 by a screen printing method to a thickness of 50 μm and fired at 1150 ° C.

3Y-Y having a thickness of 100 μm and a square of 120 mm
On one surface of the SZ electrolyte layer 1, 100 μm of lanthanum manganate is formed as an air electrode 3 and on the other surface, a thickness of 30 μm is formed.
Ni / YSZ fuel electrode 2 was formed (effective electrode area was 1
00 × 100 mm).

A heat-resistant metal gasket (spacer) 5 having a thickness of 100 μm was inserted between the separator 4 and the gas sealing surface of the electrolyte layer 1.

For collecting current between the fuel electrode 2 and the separator 4, a nickel felt 6 having a density of 0.67 g / cm ³ was used.

The electrode portion (compared with) the gas seal surface of the separator 4 and the electrolyte layer 1 was formed so as to protrude 50 μm toward the fuel electrode 2 side.

At 1000 ° C., a power generation test was performed by applying a load of 0.03 kg / cm ² from above the fuel cell and using air as the oxidant and hydrogen as the fuel.

The results of the power generation test are as follows.

When the internal resistance per layer in the stack at the time of the power generation test was set to 1.00 after 1 hour and the value after 10 and 100 hours was measured, the results are as follows. is there.

After 1 hour After 10 hours After 100 hours 1.00 1.00 1.01 From this result, the contact between the fuel electrode 2, the air electrode 3 and the separator 4 can be taken well even after the lapse of time. You can see that there is.

After the power generation test, the temperature of the fuel cell was lowered to room temperature, and the electrolyte layer was taken out and examined. As a result, no crack was found.

[0028]

As described above, according to the present invention, a flat cell having an air electrode and a fuel electrode disposed on both surfaces of a flat solid electrolyte layer and an adjacent cell are electrically connected to each other. In a current collecting method in a flat solid electrolyte fuel cell of an internal manifold type in which separators connected in series and alternately distributing a fuel and an oxidizing gas to each unit cell are stacked, the solid is charged by the load at the time of stacking. The electrolyte layer is curved so as to protrude toward the fuel electrode side, the air electrode keeps contact with the separator, and a current collector with a small elastic modulus is inserted on the fuel electrode side. The effect is obtained. (1) Even if the current collector such as nickel felt or nickel mesh is compressed and reduced during the operation of the fuel cell, the contact between the air electrode and the separator can be maintained, and the contact does not decrease or disappear. . (2) When a load is applied from the fuel electrode side as in the past,
A rigid current collector with a high modulus of elasticity had to be used. When such a material is bonded to the fuel electrode, the solid electrolyte layer is cracked by thermal stress. However, in the case of the present invention, since no load is applied from the fuel electrode side, a flexible current collector material having a small elastic modulus can be used, and cracking of the solid electrolyte layer can be prevented.

[Brief description of the drawings]

FIG. 1 is a sectional view of a flat solid electrolyte fuel cell of an internal manifold type according to the present invention.

FIG. 2 is a cross-sectional view of an internal manifold type flat solid electrolyte fuel cell according to the present invention.

FIG. 3 is a cross-sectional view of a flat solid electrolyte fuel cell of the internal manifold type according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solid electrolyte layer 2 Fuel electrode 3 Air electrode 4 Separator 5 Spacer 6 Current collector 10a Gas seal surface 10b Gas seal surface 11 Gas flow channel 12 Gas flow channel protrusion 13 Projection 15 Projection

Claims (7)

[Claims] 1. A flat cell in which an air electrode and a fuel electrode are respectively disposed on both surfaces of a flat solid electrolyte layer, an adjacent cell is electrically connected in series, and a fuel cell is connected to each cell. And a separator for distributing the oxidizing gas and the separator, the internal manifold type flat solid electrolyte fuel cell in which the solid electrolyte layer is convex toward the fuel electrode side by the load at the time of stacking. A current collecting method for a flat solid electrolyte fuel cell, characterized in that a current collector having a low elasticity is inserted on the fuel electrode side so that the air electrode keeps contact with the separator. 2. An oxidizing gas passage convex portion of a separator is projected from a gas sealing surface of a separator or a sealing agent on an air electrode side, and the total thickness of the projecting portion and the air electrode is equal to that of a spacer or a sealing agent. The method of claim 1, wherein the thickness is larger than the thickness. 3. The separator according to claim 1, wherein the oxidant gas flow path convex portion on the side facing the cathode of the separator projects from the gas sealing surface between the electrolyte on the air electrode side and the spacer or the sealant. A current collecting method for a flat solid electrolyte fuel cell. 4. The method according to claim 2, wherein the projections are made of a cathode component. 5. The current collection method for a flat solid electrolyte fuel cell according to claim 2, wherein the projections are made of a separator component. 6. The method according to claim 2, wherein the projections are made of a conductive ceramic. 7. The method according to claim 1, wherein the thickness of the cathode is greater than the thickness of the spacer or the sealant.