JPH09231987A - Seal structure of solid electrolyte fuel cell and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a seal structure in which the cross leak of fuel gas and oxidizing agent gas can be prevented by reducing or completely eliminating a gap between ceramics which are constituting material for a flat solid electrolyte fuel cell. SOLUTION: In a fuel cell, flat unit cells and separators are alternately laminated, a metal mesh is interposed between a fuel electrode and the fuel gas passage side of the separator, and seal agents or gaskets are respectively interposed between solid electrolytes and the separators so as to laminate a stack. Lid members 14 are abutting or jointing arranged on the sleeve portions Y of the separators, the sleeve portions Y and the lid members 14 cooperating supply and exhaust oxidizing agent gas or fuel gas to and from a power generation portion X, and simultaneously prevent the leak of both gases. Thereby, at a gas lead-out part to the cell of a manifold and at a gas introduction part from the cell, the cross leak of the oxidizing agent gas and the fuel gas is prevented, the utilization factor of the fuel cell is enhanced, and the deterioration of a cell characteristic resulting from concentration polarization can be suppressed.

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 seal structure and a method for manufacturing the same.

[0002]

2. Description of the Related Art Recently, a fuel cell which directly converts chemical energy originally possessed by a fuel into electric energy by using, for example, air and hydrogen as an oxidant gas and a fuel gas respectively, has attracted attention from the viewpoint of resource saving and environmental protection. In particular, flat-plate solid electrolyte fuel cells have many advantages such as high power generation efficiency and effective utilization of waste heat, and thus research and development are proceeding.

In order to supply the fuel gas and the oxidant gas to the flat plate type solid electrolyte fuel cell, supply and exhaust holes for the respective gases are provided in the separator and the solid electrolyte layer, and from these holes to the electrode surface of each unit cell. The one in which each gas is supplied and exhausted is called an internal manifold type. The flat plate type solid electrolyte fuel cell of the internal manifold type has (La, Sr) on both sides of a flat plate type solid electrolyte layer made of zirconia sintered body (YSZ) doped with yttria or the like.
A plate-shaped unit cell in which an air electrode of MnO ₃ and a fuel electrode of Ni / YSZ cermet are arranged, adjacent unit cells are electrically connected in series, and a fuel gas and an oxidizer are connected to each unit cell. Gas and gas separators are laminated alternately, a metal mesh is interposed between the fuel electrode and the fuel gas flow passage side of the separator, and a sealant or spacer or gasket is provided between the solid electrolyte layer of the unit cell and the separator. And a load is applied to stack them in a stack, and an electromotive force is generated by bringing the fuel gas and the oxidant gas into contact with each electrode surface of each unit cell.

The separator has a function of separating the fuel gas and the oxidant gas supplied to the fuel electrode and the air electrode, respectively, to prevent their cross leak, and a function of electrically connecting the unit cells to each other in series. Is to have. When the fuel gas and the oxidant gas leaking inside the stack are mixed, not only the fuel utilization rate is lowered and the efficiency of the fuel cell is lowered, but also the mixture of both gases causes combustion to cause a local temperature rise, The thermal stress distribution becomes non-uniform, causing cracks and distortions, which shortens the stack life. A typical separator currently used is strontium-doped conductive oxide plate ceramics such as lanthanum chromite. As described above, at present, many kinds of ceramic materials are used for almost all the constituent materials of the solid oxide fuel cell, and in particular, the sealing property and the mechanical strength are important properties required for these materials. .

FIG. 3 is a perspective view of a separator used in a conventional internal manifold type flat plate type solid electrolyte fuel cell.

The separator shown in FIG. 3 is a composite separator composed of a main body 11 and a current collector 12 made of a conductive oxide. A recessed pocket portion 13 is formed on the surface of the main body portion 11, and the current collecting portion 12 is fitted therein as shown by an arrow in the figure.
A plurality of rows of gas flow grooves 12a and protrusions 12b are alternately provided on the surface of the current collector 12 in order to evenly distribute an oxidant gas, such as air. The separator body 11 has a rectangular shape, and gas supply / exhaust holes 1a, 1b are formed at four corners, the diagonal gas supply / exhaust holes 1a, 1a are used for air, and the other diagonal gas supply / exhaust hole is formed. 1b and 1b are for fuel gas. Although not shown, a fuel gas flow groove and a protrusion are similarly formed on the back surface of the main body 11.
On the surface of FIG. 3, air flows from the left gas supply / exhaust hole 1a to the recess 1d on the left side of the separator body 11 and the current collector 12
Flowing through the gas flow groove 12a and the dent 1d on the opposite side (right side) and flowing into the right air supply / exhaust hole 1a. Similarly, on the back surface of FIG. 3, the fuel gas flows between the gas supply / exhaust holes 1b, 1b in different diagonal directions, and passes through the fuel gas flow groove on the back surface of the main body 11 in the middle thereof.

[0007]

In the solid oxide fuel cell using the separator as shown in FIG. 3, the place where the cross leak between the fuel gas and the oxidant gas is most likely to occur, that is, the place where the sealing property is bad is The surface 1c of the separator in which the fuel gas and the oxidant gas flow closest to each other
Is a gap between the constituent materials in the area A (FIG. 3) and the area of the back surface of the separator body 11 corresponding thereto.
Sealing agents and gaskets are used to improve the sealing performance here, but these are not perfect.In order to further improve the sealing performance, the load applied to the stack at the time of battery assembly should be increased and the gap should be minimized. Make it smaller or
Or you need to get rid of it all. However, there are limits to this.

The present invention has been made in view of the above points, and reduces the gap between ceramics, which is a constituent material of a flat-plate solid electrolyte fuel cell, as much as possible, or eliminates the gap altogether to oxidize fuel gas and oxidation. It is an object of the present invention to provide a seal structure capable of preventing cross leak with agent gas.

[0009]

A solid oxide fuel cell has a high operating temperature of about 1000 ° C., and its constituent material is to maintain high strength and good sealing property continuously from room temperature to this high temperature. , It has been desired to develop a technique for joining the ceramic materials, which are the constituent materials, to each other so that the ceramic materials are firmly bonded to each other and the sealing property is good, but it is easy and easy to simply bond various ceramic materials together. However, it has been difficult to join so as to improve the sealing property of the joint. In order to solve this, the inventor repeated various experiments on bonding of ceramics, and as a result, a metal foil (or a metal plate) inserted in contact with ceramics was used as a skin layer of the metal foil, that is, ceramics. When heated and melted at a temperature of 700 ° C. or higher under the condition that oxidation proceeds only at the interface between the metal foil and the metal foil, only the interface between the skin layer of the metal foil, that is, the ceramic, is oxidized, and the intermediate portion of the metal foil is the original metal. Since the material of the foil is left as it is, it is possible to firmly bond the ceramic materials together,
In addition, the material of the original metal foil remains as it is in the middle part, and since this part has ductility and malleability, it is possible to relieve the stress generated between the ceramics of the objects to be joined, and the sealing property. It has been found that a ceramics bonded body which is most suitable for the constituent members of the solid oxide fuel cell can be obtained because the extremely excellent bonding can be achieved. Therefore, the inventor has applied for a patent for the technique of "ceramic bonding method and bonded body" as Japanese Patent Application No. 8-10284.

The present invention also utilizes the technique of Japanese Patent Application No. 8-10284.

In order to achieve the above object, the seal structure for a solid oxide fuel cell according to the present invention is adjacent to a flat plate type single cell in which an air electrode and a fuel electrode are arranged on both sides of a flat plate type solid electrolyte layer. The cells are electrically connected in series to each other and the separators that distribute the oxidant gas and the fuel gas are alternately laminated to each cell, and a metal is provided between the fuel electrode and the fuel gas flow passage side of the separator. In the seal structure of the flat plate type solid electrolyte fuel cell, wherein the mesh is interposed, and the solid electrolyte layer and the separator of the unit cell are laminated in a stack with a sealant or gasket interposed therebetween,
A power generation portion in which the separator faces the air electrode or the fuel electrode and is alternately engraved with a plurality of rows of gas flow grooves and projections for distributing the oxidant gas or the fuel gas, respectively, and on both sides of the power generation portion. A sleeve part connected to the sleeve part and a lid member arranged to overlap the sleeve part are provided, and the sleeve part and the lid member cooperate to supply and discharge an oxidant gas or a fuel gas to the power generation part. At the same time, it is characterized that leakage of both gases is prevented.

According to the present invention, the contact surface of the lid member with the separator sleeve portion is smoothly polished, the lid member and the separator sleeve portion are joined with an inorganic glass material, and the lid member is The separator sleeve part is joined with a metal foil or metal plate in which only the skin layer is oxidized, and the metal foil or metal plate is aluminum or Al
-A Mg-based alloy.

In the method for manufacturing the seal structure for a solid oxide fuel cell according to the present invention, a metal foil or a metal plate is inserted between the lid member and the sleeve part of the separator in a contact state. Is characterized in that it is heated to a temperature of 700 ° C. or higher and bonded under the condition that only the skin layer of the ceramics is oxidized.
l is vapor-deposited or sputtered.

[0014]

1 is a perspective view of a separator of a flat plate type solid oxide fuel cell having a sealing structure according to the present invention.

The flat plate type solid electrolyte fuel cell comprises a flat plate type single cell in which an air electrode and a fuel electrode are arranged on both sides of a flat plate type solid electrolyte layer, and adjacent single cells are electrically connected in series. An oxidant gas and a separator that distributes a fuel gas are alternately stacked in each cell, a metal mesh is interposed between the fuel electrode and the fuel gas flow passage side of the separator, and a solid electrolyte layer of the cell. A sealant or a gasket is interposed between the separator and the separator to form a stack.

The separator shown in FIG. 1 is roughly classified into a main body 1
1 is a composite separator including a current collector 12, and a lid member 14. The main body 11 has a rectangular shape, the central portion thereof serves as a power generation portion X, and a recessed pocket portion 13 is formed on the surface thereof, and the current collecting portion 12 is fitted therein as shown by an arrow A in the figure. A plurality of rows of gas flow grooves 12a and projections 12b are alternately formed on the surface of the current collector 12 in order to evenly distribute an oxidant gas such as air. Although not shown, a fuel gas flow groove and a protrusion are similarly formed on the back surface of the main body 11.

A sleeve portion Y is connected to both sides of the power generation portion X, and the sleeve portion Y supplies and discharges an oxidant gas or a fuel gas to the power generation portion X. That is, gas supply / exhaust holes 11a, 11b are formed at four corners, the diagonal gas supply / exhaust holes 11a, 11a are for air, and the other diagonal gas supply / exhaust holes 11b, 11b are for fuel gas. Become. The lid member 14 is placed in contact with the sleeve portion Y so as to be in contact with each other, and the sleeve portion Y and the lid member 14 cooperate to supply and discharge the oxidant gas or the fuel gas to the air electrode or the fuel electrode, and the lid member 14 is sleeved. By overlapping on the portion Y, cross leak of both gases can be prevented. The lid member 14 is an essential part of the present invention. As shown in FIG. 1, a total of four lid members 14 are arranged on the front surface 11c and the back surface of the sleeve portion Y, four in total, as shown by an arrow B (FIG. 1). This is the sleeve portion Y of the lid member 14.
The notch groove 14d is provided on the side surface that contacts the front surface 11c or the back surface (not shown) of the above and abuts on the current collector 12. Further, the lid member 14 has a gas supply / exhaust hole 11a in the sleeve portion Y,
Corresponding to 11b, gas supply / exhaust holes 11a and 11b having the same size and the same arrangement are opened.

The flow of oxidant gas or fuel gas in the stack is as follows. For example, if the oxidant gas flows from the bottom to the top in the stack, it rises from the left gas supply / exhaust hole 14a (of the lower left lid member 14 in FIG. 1) through the supply / exhaust hole 11a of the left sleeve portion Y. The left sleeve Y
Flowing into the dent 11d, passing through the cutout groove 14d of the lid member 14 (on the left side in FIG. 1), flowing through the gas flow groove 12a of the current collector 12, and moving toward the lid member 14 (on the right side in FIG. 1). Passing through the cutout groove 14d, the opposite side (right side) sleeve part Y
Entering the recess 11d, the right air supply / exhaust hole 11a and the air supply / exhaust hole 14 (of the lid member 14 on the right side in FIG. 1)
outflow to a. The flow of the fuel gas in the stack flows through the gas supply / exhaust holes 14b and 11b, the gas flow groove of the separator facing the fuel electrode, and the like.

As the material for the separator, ceramic alumina or Al-Mg spinel is used, and heat-resistant metal Fe-Ni-Cr base alloy or Ni-Cr base alloy is used. An Al alloyed product and a ceramic coated surface are used.

In some cases, the lid member and the sleeve portion of the separator are simply brought into contact with each other, and face-to-face pressure is applied by the load applied to the stack. In this case, the sealability is improved by polishing the contact surface between the lid member and the sleeve part of the separator as smooth as possible.

Further, the lid member and the sleeve portion of the separator may be joined together. The joining method in this case includes the following methods. (1) The lid member and the sleeve portion of the separator are joined with an inorganic glass material. (2) The lid member and the sleeve part of the separator are joined by a metal foil or a metal plate in which only the skin layer is oxidized. (3) The metal foil or metal plate is aluminum. (4) The metal foil or metal plate is an Al-Mg based alloy. (5) A product obtained by inserting a metal foil or a metal plate in a contact state between the lid member and the sleeve part of the separator is prepared under the condition that the oxidation of only the skin layer of the metal foil or the metal plate proceeds.
Heat to a temperature of ℃ or more to join. (6) In the joining method of (5), Al is previously vapor-deposited or sputtered on the joining surface of the ceramics.

In cases (2) to (6) above, the technique of the above-mentioned Japanese Patent Application No. 8-10284 of the present inventor is used.

[0023]

EXAMPLE A flat plate type solid electrolyte fuel cell having a seal structure according to the present invention was manufactured by the following method.

3Y-YS 60 mm square and 0.1 mm thick
Ni-YSZ is 30 μm as a fuel electrode on one surface of Z, and (La, Sr) MnO ₃ is 100 as an air electrode on the opposite surface.
μm each applied, 1450 ℃, 1150 ℃
The one fired in 1. was used as a single cell. The effective electrode area was 25 cm ² .

An alumina lid member was joined to each of the four sleeve portions of the alumina separator.

The method of joining the lid members is as follows. (1) Thickness between separator sleeve and lid member is 0.1
Insert a mm aluminum foil. (2) Joining by holding at 1000 ° C. for 3 hours in an atmosphere of N ₂ -3% H ₂ . (3) Grinding and lapping are performed so that there is no step between the separator on the fuel electrode side and the lid member. (4) On the air electrode side, grinding and lapping are performed so that the (La, Sr) CrO ₃ separator and the lid member are flat.

A power generation test was carried out using the unit cell and the separator manufactured as described above under a load of 0.3 A / cm ^{2 at} 1000 ° C. Air was used as the oxidant gas, and the utilization rate was 30%. The potential of the single cell stack (between the fuel electrode / electrolyte / air electrode / lanthanum chromite) when hydrogen was used as the fuel gas and the utilization factor was changed was measured. In addition,
The fuel utilization rate was set to 40% for the convenience of the device.

FIG. 2 is a diagram comparing the results of power generation tests of the flat plate type solid electrolyte fuel cell having the seal structure of the present invention and the conventional flat plate type solid electrolyte fuel cell having the seal structure.

In FIG. 2, the horizontal axis represents the fuel utilization rate (unit:
%) And the vertical axis represents voltage (unit: V). The curve indicated by the dotted line in the graph is the case where the separator having the seal structure of the present invention is used, that is, the case where the separator has the lid member, and the curve indicated by the solid line is the case where the conventional separator having no lid member is used.

From FIG. 2, it is proved that the use of the separator having the lid member significantly improves the utilization rate and the power generation performance is good. The reason is that the cross leak at the introduction portion of the oxidant gas and the fuel gas into the cell was suppressed by attaching the lid member.

[0031]

As described above, according to the present invention, the lid member is disposed in contact with or joined to the sleeve portion of the separator of the flat plate type solid oxide fuel cell, and the sleeve portion and the lid member cooperate to generate the power generating portion. On the other hand, since the oxidant gas or the fuel gas is supplied and discharged and the leakage of the both gases is prevented, the following extremely excellent effects are obtained. (1) It is possible to prevent cross-leakage of the oxidant gas and the fuel gas at the gas outlet portion of the manifold to the battery and the gas inlet portion of the battery. (2) Since cross leak can be prevented, the utilization rate of the fuel cell can be improved. (3) It is possible to suppress deterioration of battery characteristics due to concentration polarization.

[Brief description of drawings]

FIG. 1 is a perspective view of a separator of a flat plate type solid electrolyte fuel cell having a seal structure according to the present invention.

FIG. 2 is a diagram comparing the results of power generation tests of a flat plate solid electrolyte fuel cell having a seal structure of the present invention and a conventional flat plate solid electrolyte fuel cell having a seal structure.

FIG. 3 is a perspective view of a separator used in a conventional flat plate type solid electrolyte fuel cell of an internal manifold type.

[Explanation of symbols]

 1a Gas supply / exhaust hole 1b Gas supply / exhaust hole 1c Surface 1d Dimple 9 Conductive hole 11 Main body 11a Gas supply / exhaust hole 11b Gas supply / exhaust hole 11c Surface 11d Dimple 11e Conductive hole 12 Current collecting part 12a Gas distribution groove 12b Protrusion 13 Pocket 14 Lid member 14a Gas supply / exhaust hole 14b Gas supply / exhaust hole 14d Notch groove X Power generation part Y Sleeve part

Claims (8)

[Claims] 1. A flat plate-shaped cell in which an air electrode and a fuel electrode are arranged on both sides of a plate-shaped solid electrolyte layer, and adjacent cells are electrically connected in series and oxidized to each cell. The agent gas and the separator for distributing the fuel gas are alternately laminated, a metal mesh is interposed between the fuel electrode and the fuel gas flow passage side of the separator, and between the solid electrolyte layer and the separator of the unit cell. In a seal structure of a flat plate type solid electrolyte fuel cell which is laminated in a stack with a sealant or gasket interposed, the separator faces the air electrode or the fuel electrode and distributes the oxidant gas or the fuel gas, respectively. A plurality of rows of gas flow grooves and protrusions are alternately engraved, sleeve portions connected to both sides of the power generation portion, and a lid member that is arranged to overlap the sleeve portion. A solid oxide fuel cell, wherein the sleeve portion and the lid member cooperate to supply and discharge an oxidant gas or fuel gas to the power generation portion and prevent leakage of both gases. Seal structure. 2. The seal structure for a solid oxide fuel cell according to claim 1, wherein the contact surface of the lid member with the sleeve portion of the separator is polished to be smooth. 3. The sealing structure for a solid oxide fuel cell according to claim 1, wherein the lid member and the sleeve portion of the separator are joined with an inorganic glass material. 4. The seal structure for a solid oxide fuel cell according to claim 1, wherein the lid member and the separator sleeve portion are joined by a metal foil or a metal plate in which only a skin layer is oxidized. . 5. The seal structure for a solid oxide fuel cell according to claim 4, wherein the metal foil or the metal plate is aluminum. 6. The seal structure for a solid oxide fuel cell according to claim 4, wherein the metal foil or the metal plate is an Al—Mg based alloy. 7. A metal foil or a metal plate inserted in a contact state between the lid member and the sleeve portion of the separator is used under conditions such that the oxidation of only the skin layer of the metal foil or the metal plate proceeds 700. The method for producing a seal structure for a solid oxide fuel cell according to claim 1, wherein the sealing structure is heated to a temperature of ℃ or more and bonded. 8. The method for manufacturing a seal structure for a solid oxide fuel cell according to claim 7, wherein Al is previously vapor-deposited or sputtered on the joint surface of the ceramics.