JPH0660888A - Flat type solid electrolyte fuel cell - Google Patents

Abstract

PURPOSE:To provide high efficiency and reliability by improving the degree of power generation efficiency drop due to the improper seal of fuel and oxygen gases, and the degree of thermal strain due to a crossing type cell module in the conventional structure of a flat type solid electrolyte fuel cell. CONSTITUTION:An oxygen electrode 1 is made of a bottomed rectangular parallelopiped having many holes, and the film of a solid electrolyte 2 as a film resistant against gas permeation is formed on one side of the parellelopiped. The other side thereof is covered with the film of an interconnector 4 as a film against gas permeation as well, thereby forming a single cell 5. With the application of this construction, a mixing process is prevented from taking place between oxygen gas supplied to the inside of the electrode 1, and fuel gas supplied to the outside of the bottomed parellelopiped, without any sealing treatment. A drop in power generation efficiency is thereby prevented. Also, oxygen gas feed tubes 7 are inserted in the upper opening sections 6 of the holes, and an identical flow direction is maintained for oxygen gas on the electrode 1 and fuel gas on a fuel electrode 3 formed on the solid electrolyte 2. As a result, thermal strain distribution over a cell power generation section is made uniform and thermal strain is restrained, thereby improving the reliability of a battery.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a flat plate type solid electrolyte fuel cell, which has a gas sealless structure, a gas supply pipe-containing cell structure, and a fuel gas recycling structure and has a high power generation efficiency. It is about.

[0002]

2. Description of the Related Art A plate type solid electrolyte fuel cell (hereinafter referred to as SOFC) using an oxide solid electrolyte such as zirconia.
Has high power generation efficiency because its operating temperature is as high as 800-1000 ° C, there is no liquid leakage trouble because the constituent material is solid, and it has an internal resistance smaller than the cylindrical SOFC, which is effective for high output. It has features such as Such a flat plate type SOFC has a fuel electrode, an electrolyte,
It is composed of a stack in which single cells consisting of oxygen electrodes and interconnectors or separate plates that connect the single cells are alternately laminated, and grooves that intersect at right angles in three dimensions are formed as gas channels on both sides of the interconnector. Then, different reaction gases (fuel gas on the fuel electrode side and oxygen gas on the oxygen electrode side) respectively flow. Further, the fuel electrode and the oxygen electrode are porous electrodes so that the reaction gas can be easily diffused. Generally, a zirconia fired body is used as the electrolyte and a LaCrO ₃ fired body is used as the interconnector, and these are both gas impermeable dense fired bodies. The unit cell made of such materials and the interconnector are impermeable to gas, but it is difficult to sinter the joint surface, which causes gas leakage from the joint surface and reduces the power generation efficiency. Becomes In order to solve this problem, for example, Japanese Patent Laid-Open Nos. 2-215052 and 2-16
There is a method of glass sealing the inner peripheral surface or the outer peripheral surface of a single cell as disclosed in No. 8568.

[0003]

[Problems to be Solved by the Invention] However, 100
The conventional SOFC described above is operated at a high temperature of 0 ° C. and under the condition that the gas flow rate is increased and the cell internal pressure is increased to obtain a high output.
However, there was a problem that the viscosity of the molten glass of the sealing material was reduced and the sealing property was deteriorated when the operation was performed.

Further, since the fuel flow and the air flow in the conventional flat-plate type cell power generation section are cross-type cells which are orthogonal to each other, a remarkable odor is generated in the current density and temperature distribution of the power generation section, and the inside of the cell There was a problem of long-term reliability due to stress strain (Proceeding of 2nd In
ternary Symposium on So
lid Oxide Fuel Cell, P.M. 305
-312, July 1991). Further, when the cell is made larger, the current density at the gas supply port of the cell becomes remarkably large, and uniform power generation is not performed over the entire surface of the cell, so that there is a problem that the output density of the cell is lowered.

The present invention has been made to solve the above problems, and an object thereof is to solve the problem of the gas sealing between the fuel gas and the oxygen gas, which the conventional flat plate type SOFC has, and the cross type cell module. Flat type SOF with high reliability, high efficiency and high output by improving the problem of thermal strain caused by
To provide C.

[0006]

In order to achieve the above object, in the invention of claim 1 according to the present invention, in a flat plate type solid electrolyte fuel cell comprising a fuel electrode, a solid electrolyte and an oxygen electrode, the oxygen electrode is on the upper surface. A bottomed rectangular parallelepiped in which hollow holes having a large number of openings are formed. A solid electrolyte and a fuel electrode are formed on one surface of the rectangular parallelepiped, and the other surface and the bottom surface and the side surface opposite to the solid electrolyte are formed. The structure is a single cell structure in which a dense film of an interconnector is formed.

Further, according to the second aspect of the present invention, the oxygen gas supply pipe is inserted from the opening of the oxygen electrode upper surface of the rectangular parallelepiped with a bottom, and the oxygen gas is supplied from the oxygen gas supply pipe into the oxygen electrode. It is assumed to have.

Also, in the third aspect of the invention, the electrical connection between the unit cells is made of nickel felt.

Further, according to the fourth aspect of the invention, the gas discharged from the fuel electrode is guided to a route for recycling the fuel gas of the fuel electrode.

[0010]

According to the flat plate type solid electrolyte fuel cell of the invention of claim 1, the oxygen electrode is a bottomed rectangular parallelepiped having a large number of holes, and a solid electrolyte membrane of a gas impermeable membrane is formed on one surface of the bottomed rectangular parallelepiped. Also, the other surface without the solid electrolyte membrane is covered with the interconnector membrane of the gas impermeable membrane, and the oxygen gas supplied into the oxygen electrode and the outside of the bottomed rectangular parallelepiped are provided without providing a gas seal structure. The mixing with the supplied fuel gas is prevented from occurring and the power generation efficiency is prevented from lowering accordingly.

According to the second aspect of the present invention, in particular, the directions of the air flow of the fuel gas on the fuel electrode surface formed on the solid electrolyte membrane and the oxygen gas on the oxygen electrode surface in contact with the solid electrolyte membrane are mutually different. In the same direction, the heat distribution in the cell power generation section is made more uniform than in the conventional flat plate SOFC in which the gas flows are orthogonal, stress distortion is improved, and reliability is increased.

According to the third aspect of the present invention, in particular, the direction of the current flowing through the cell is set to the direction perpendicular to the plane type SOFC cell surface, so that the current flow in the direction of the electrode surface is greater than that of the cylindrical SOFC. By eliminating it, the internal resistance of the cell is reduced and high efficiency and high output are realized.

Further, according to the invention of claim 4, in particular, a high efficiency SOFC is realized by recycling most of the unused fuel gas discharged from the fuel electrode.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 shows a flat plate type S according to an embodiment of the present invention.
FIG. 2 is a perspective view of a single cell structure of OFC, and FIG.
It is sectional drawing of a module structure. The oxygen electrode 1 is a bottomed rectangular parallelepiped having a plurality of openings 6 on its upper surface. The oxygen electrode 1 is
Using La ₀ .9 Sr ₀ .1 MnO ₃ powder as a material, a bottomed rectangular parallelepiped having an opening 6 was formed by a hydrostatic pressing method,
It is produced by making it a sintered body. The sintered body is a porous body having a porosity of 30%. Oxygen electrode 1 of this sintered body
Of the solid electrolyte 2 is masked, and the other surface is chemically vapor deposited (CVD) -electrochemical vapor deposition (EV).
A lanthanum chromite (LaCr ₀ .95 Mg ₀ .05 O ₃ ) film having a thickness of 20 μm and doped with magnesium is formed as the interconnector 4 by the method D). Next, the mask is removed, and the position is 20 μm thick by the CVD-EVD method.
The zirconia (ZrO ₂ ) film doped with yttria (Y ₂ O ₃ ) of 10 mol% is formed as the solid electrolyte 2. Next, nickel-zirconia powder is applied as a slurry to the surface of the solid electrolyte 2 and sintered to form the fuel electrode 3.

The single cells 5 thus produced are vertically arranged and housed in a heat insulating container 10, and the single cells are electrically connected by nickel felt 8 to form an SOFC module. The oxygen gas is supplied into the oxygen electrode 1 of the unit cell 5 from the lower side to the upper side by the oxygen gas supply pipe 7 inserted from the opening 6 of the oxygen electrode 1. Hydrogen gas as the fuel gas is supplied to the outer surface of the unit cell 5 from the bottom side of the unit cell 5 through the nickel felt 8. Unreacted hydrogen gas that is not used in the cell reaction is taken out from the upper part of the unit cell 5, mixed with fuel gas, and recycled as fuel gas to the fuel electrode 3. Further, a part of the unreacted hydrogen gas enters the combustion chamber 9 through the porous plate 11 and is mixed and burned with the unreacted oxygen gas. The combustion heat generated at that time is used as residual heat of the supplied oxygen gas.

The operation and action of the embodiment configured as described above will be described. In this embodiment, the oxygen electrode 1 has a rectangular parallelepiped shape, and has a bottomed rectangular parallelepiped in which hollow holes having a large number of openings 6 are formed on the upper surface thereof, and the solid electrolyte is formed on one surface of the bottomed rectangular parallelepiped. 2, the fuel electrode 3 is sequentially formed, and a dense film of the interconnector 4 is formed on one surface, a bottom portion, and a side surface opposite to the fuel electrode 3, and oxygen gas is supplied through the opening 6 to the oxygen gas supply pipe 7 Is supplied to the inside of the oxygen electrode 1, and is discharged into the combustion chamber 9 through the gap between the outer wall of the oxygen gas supply pipe 7 and the opening 6. The fuel gas is supplied to the surfaces of the fuel electrode 3 and the interconnector 4 on the outer surface of the bottomed rectangular parallelepiped, and the oxygen flow and the fuel flow are parallel flows in the power generation part, so that the temperature distribution and current density of the power generation part are made uniform, Stress strain is improved and long-term reliability is enhanced. Oxygen gas and fuel gas are completely separated by the solid electrolyte and interconnector, which are dense membranes, and do not mix. Therefore, the conventional flat plate type S
Gas separation can be achieved without the special gas sealing process performed in OFC.

Most of the unused fuel gas in the power generation section is discharged from the recycling outlet at the top of the bottomed rectangular parallelepiped unit cell 5, mixed with new fuel gas, and the reformer (not shown),
It is re-supplied to the power generation unit via the carbon dioxide removal device, and the power generation efficiency can be increased. Further, a part of the unused fuel gas enters the fuel chamber 9 located on the upper surface of the unit cell 5 having a bottomed rectangular parallelepiped shape. On the other hand, as described above, the unused oxygen gas discharged from the gap between the opening 6 at the upper surface of the unit cell 5 having a bottomed rectangular parallelepiped and the oxygen gas supply pipe 8 also enters the combustion chamber 9. Therefore, the unused fuel gas burns with the oxygen gas, and the combustion heat generated at that time is used as the residual heat of the supplied oxygen gas.

The electrical connection between the unit cells 5 is performed by the fuel electrode 3 on one side of the unit cell 5 and the interconnector 4 on the other side of the unit cell 5.
Via nickel felt 8. The current flow is in a direction perpendicular to each flat plate surface formed by stacking the fuel electrode 3, the solid electrolyte 2, the oxygen electrode 1, and the interconnector 4, and in the direction of the electrode surface generated in the case of a cylindrical SOFC. Since there is no current flow, the internal resistance of the unit cell 5 is reduced, and high efficiency and high output can be realized.

In the above embodiment, hydrogen gas is used as the fuel gas and air is used as the oxygen gas, and the fuel utilization rate is 80%.
%, Oxygen utilization rate 25%, temperature 3 in 5 cm square 3 cells
High power generation efficiency of 50
% (LHV), a high power density of 0.7 w / cm ² was obtained.

[0021]

As is clear from the above description, since the flat plate type solid electrolyte fuel cell of the present invention has the gas sealless structure in the power generation section, it is possible to mix the fuel gas and the oxygen gas due to the gas seal failure. No power generation loss can occur.

According to the second aspect of the invention, in particular, the fuel gas flow and the oxygen gas flow are in the same direction due to the gas supply pipe-containing cell structure, so that the temperature distribution in the cell can be reduced as compared with the cross type SOFC. It is possible to realize a highly reliable flat plate solid oxide fuel cell.

According to the third aspect of the invention, in particular, the direction of the current flowing in the cell is perpendicular to the cell surface,
The internal resistance of the cell is reduced and high efficiency and high output are realized.

Further, according to the invention of claim 4, in particular,
By recycling the fuel gas, waste of fuel can be eliminated and power generation efficiency can be improved.

[Brief description of drawings]

FIG. 1 is a perspective view of a single cell structure of a flat plate type solid electrolyte fuel cell showing an embodiment of the present invention.

FIG. 2 is a sectional view of the flat plate type solid electrolyte fuel cell module of the above embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Oxygen electrode 2 ... Solid electrolyte 3 ... Fuel electrode 4 ... Interconnector 5 ... Single cell 6 ... Opening part 7 ... Oxygen gas supply pipe 8 ... Nickel felt 9 ... Combustion chamber 10 ... Thermal insulation container 11 ... Perforated plate

Claims (4)

[Claims] 1. A flat plate solid electrolyte fuel cell comprising a fuel electrode, a solid electrolyte and an oxygen electrode, wherein the oxygen electrode is a bottomed rectangular parallelepiped having a hollow hole having a large number of openings on the upper surface. The solid electrolyte on one side of the bottomed rectangular parallelepiped,
A flat plate type solid electrolyte fuel cell comprising the fuel electrode, and a single cell structure in which a dense film of an interconnector is formed on one surface, a bottom surface and a side surface opposite to the fuel electrode. 2. An oxygen gas supply pipe is inserted from an opening on the upper surface of the oxygen electrode of a rectangular parallelepiped with a bottom, and oxygen gas is supplied to the inside of the oxygen electrode from the oxygen gas supply pipe. 1. The flat plate solid electrolyte fuel cell described in 1. 3. The flat plate type solid electrolyte fuel cell according to claim 1, wherein the electrical connection between the unit cells is made by nickel felt. 4. The flat plate type solid electrolyte fuel cell according to claim 1, wherein the gas discharged from the fuel electrode is led to a path for recycling as the fuel gas of the fuel electrode.