JP2005085520A - Solid oxide fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance power generating efficiency by preventing useless exhaust of gas in the peripheral part of a fuel electrode current collector and an opposite diffusion phenomenon of gas to a fuel electrode side. <P>SOLUTION: A solid oxide fuel cell has a seal-less structure in which a fuel electrode layer and an oxidizing agent electrode layer are arranged on each side of a solid electrolyte layer, a fuel electrode current collector 6 and an oxidizing agent electrode current collector each made of a porous metallic material 23 are arranged on the outside of the fuel electrode layer and the oxidizing agent electrode layer respectively, a separator is arranged on the outside of the fuel electrode current collector 6 and the oxidizing agent electrode current collector, and fuel gas and oxidizing agent gas are supplied to the fuel electrode layer and the oxidizing agent electrode layer through the fuel electrode current collector and the oxidizing agent electrode current collector from the separator. A cover 20 in which a gas exhaust hole is installed is arranged so as to cover the peripheral part of the fuel electrode current collector 6, and exhausting portions of excess gas exhausted from the peripheral part are regulated. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a solid oxide fuel cell, and more particularly to a solid oxide fuel cell having a gas sealless structure in which a gas back diffusion phenomenon in a fuel electrode current collector is prevented to improve power generation efficiency.

A solid oxide fuel cell having a laminated structure in which a solid electrolyte layer made of an oxide ion conductor is sandwiched between an air electrode layer (oxidant electrode layer) and a fuel electrode layer is a third generation fuel cell for power generation. Development is progressing. In a solid oxide fuel cell, oxygen (air) is supplied to the air electrode side, and fuel gas (H ₂ , CO, etc.) is supplied to the fuel electrode side. The air electrode and the fuel electrode are both porous so that the gas can reach the interface with the solid electrolyte.

Oxygen supplied to the air electrode side passes through the pores in the air electrode layer and reaches the vicinity of the interface with the solid electrolyte layer. At this part, it receives electrons from the air electrode and converts them into oxide ions (O ²⁻ ). Ionized. The oxide ions diffuse and move in the solid electrolyte layer toward the fuel electrode. Oxide ions that have reached the vicinity of the interface with the fuel electrode react with the fuel gas at this portion to generate reaction products (H ₂ O, CO _2, etc.), and emit electrons to the fuel electrode.

Incidentally, the electrode reaction when hydrogen is used as the fuel is as follows.
Air electrode: 1/2 O ₂ + 2e ⁻ → O ²⁻
Fuel electrode: H ₂ + O ²⁻ → H ₂ O + 2e ⁻
Overall: H ₂ +1/2 O ₂ → H ₂ O

  The solid electrolyte layer is a moving medium for oxide ions and also functions as a partition wall for preventing direct contact between the fuel gas and air, and thus has a dense structure that is impermeable to gas. This solid electrolyte layer should have a high oxide ion conductivity, be chemically stable under conditions from the oxidizing atmosphere on the air electrode side to the reducing atmosphere on the fuel electrode side, and be made of a material that is resistant to thermal shock. There is generally used stabilized zirconia (YSZ) to which yttria is added as a material satisfying such requirements.

On the other hand, both the air electrode (cathode) layer and the fuel electrode (anode) layer, which are electrodes, must be made of a material having high electron conductivity. Since the air electrode material must be chemically stable in a high-temperature oxidizing atmosphere around 700 ° C., the metal is inappropriate, and a perovskite-type oxide material having electron conductivity, specifically LaMnO ₃ Alternatively, LaCoO ₃ or a solid solution in which a part of these La is substituted with Sr, Ca or the like is generally used. The fuel electrode material is generally a metal such as Ni or Co, or a cermet such as Ni—YSZ or Co—YSZ.

  Solid oxide fuel cells include a high-temperature operation type that operates at a high temperature of about 1000 ° C. and a low-temperature operation type that operates at a low temperature of about 700 ° C. A low temperature operation type solid oxide fuel cell, for example, stabilizes the thickness of stabilized zirconia (YSZ) added with yttria as an electrolyte to a thickness of about 10 μm to reduce the resistance of the electrolyte, and generates electricity as a fuel cell even at low temperatures. So that the improved power generation cell is used.

In a high-temperature solid oxide fuel cell, ceramics having electronic conductivity such as lanthanum chromite (LaCrO ₃ ) is used as a separator. In a low-temperature operation type solid oxide fuel cell, a metal such as stainless steel is used. Material can be used.

  Three types of solid oxide fuel cell structures have been proposed: a cylindrical type, a monolith type, and a flat plate type. Among these structures, since a metal separator can be used for a low temperature operation type solid oxide fuel cell, a flat plate type structure that is easy to give a shape to the metal separator is suitable.

  A stack of flat plate type solid oxide fuel cells has a structure in which power generation cells, current collectors, and separators are alternately stacked. A pair of separators sandwich the power generation cell from both sides, one being in contact with the air electrode via the air electrode current collector and the other being in contact with the fuel electrode via the fuel electrode current collector. A sponge-like porous body such as a Ni-based alloy can be used for the fuel electrode current collector, and a sponge-like porous body such as an Ag-based alloy can be used for the air electrode current collector. Can do. A sponge-like porous body has a current collecting function, a gas permeation function, a uniform gas diffusion function, a cushion function, a thermal expansion difference absorption function, and the like, and is therefore suitable as a multifunctional current collector material.

  The separator has a function of electrically connecting the power generation cells and supplying gas to the power generation cells. The fuel is introduced from the outer peripheral surface of the separator and discharged from the surface facing the separator fuel electrode layer. A gas passage and an oxidant gas passage for introducing an oxidant gas from the outer peripheral surface of the separator and discharging the gas from a surface facing the oxidant electrode layer of the separator are provided.

By the way, in this type of solid oxide fuel cell, there is a solid oxide fuel cell having a sealless structure that does not include a gas seal mechanism at the outer peripheral portion of the power generation cell (conventionally, a gas seal is provided at the outer peripheral portion of the power generation cell. The structure which gave the mechanism is common, and patent documents 1 are indicated as the gas seal mechanism).
A solid oxide fuel cell with a sealless structure simplifies the structure by eliminating the sealing mechanism at the outer periphery of the power generation cell, improving productivity, and eliminating troubles due to differences in thermal expansion between components. It has the merit of being able to.
JP-A-9-115530

  However, the solid oxide fuel cell having the sealless structure has problems due to the sealless structure in addition to the above-described advantages.

That is, in the sealless structure, fuel gas and oxidant gas are supplied into the power generation cell during operation to cause a power generation reaction, and residual gas (exhaust gas) that has not been used for the power generation reaction is discharged from the outer periphery of the power generation cell. It discharges outside the cell.
Therefore, because of the difference in the linear velocity between the gas flowing in the peripheral part of the power generation cell and the air flowing in the outer peripheral part, the so-called reverse diffusion phenomenon, in which the air outside the power generation cell is entrapped in the reverse direction, is likely to occur. The problem is that this back-diffused air and the fuel gas in the power generation cell undergo a combustion reaction and consumes a fuel gas that can be used for the electrode reaction, resulting in a decrease in power generation performance and a local temperature rise due to this combustion reaction. There is a problem that the thermal stress distribution in the inside becomes uneven and the life of the fuel cell stack is extremely shortened.

  In view of such problems inherent to the sealless structure, the present invention provides a solid oxide fuel cell that prevents the gas back-diffusion phenomenon in the outer peripheral portion of the anode current collector and improves the power generation efficiency. It is intended to provide.

  That is, according to the present invention, the fuel electrode layer and the oxidant electrode layer are disposed on both sides of the solid electrolyte layer, and the fuel is composed of a porous metal body on the outside of the fuel electrode layer and the oxidant electrode layer. An electrode current collector and an oxidant electrode current collector are disposed, a separator is disposed outside the fuel electrode current collector and the oxidant electrode current collector, and the fuel electrode current collector and the oxidant electrode current collector are disposed from the separator. In a solid oxide fuel cell having a sealless structure for supplying fuel gas and oxidant gas to the fuel electrode layer and oxidant electrode layer through an electric body, gas is discharged so as to cover the outer periphery of the fuel electrode current collector A cover having a hole is provided, and the exhaust gas exhausted from the outer periphery is restricted.

The present invention according to claim 2 is the solid oxide fuel cell according to claim 1, wherein the cover includes a plurality of locking claws at an edge portion, and the porous claw is formed by the locking claws. It was set as the structure which supports the both surfaces or single side | surface of a solid metal body.
According to a third aspect of the present invention, in the solid oxide fuel cell according to the first or second aspect, the cover is made of a heat-resistant metal. As the heat-resistant metal material, Kanthal, Inconel, Nichrome or the like can be used.

  According to the configuration of claim 1 to claim 3, it is possible to prevent wasteful discharge of the fuel gas from the outer peripheral portion of the anode current collector and the reverse diffusion phenomenon of the gas to the anode side, The power generation efficiency can be improved and the output density of the fuel cell can be increased.

  As described above, according to the present invention, a cover provided with a gas discharge hole is provided so as to cover the outer peripheral portion of the anode current collector, and the discharge location of excess gas discharged from the outer peripheral portion is limited. Thus, it is possible to prevent the unnecessary gas from being discharged from the outer peripheral portion of the fuel electrode current collector and the reverse diffusion phenomenon of the gas from the outside to the fuel electrode side. As a result, the power generation efficiency is improved, the fuel cell can have a high output density, and the life of the fuel cell can be extended.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

First, the overall configuration of a solid oxide fuel cell to which the present invention is applied will be described with reference to FIGS. FIG. 2 is an exploded cross-sectional view showing the main part of the solid oxide fuel cell, and FIG. 3 is an exploded perspective view of the main part.
In the figure, reference numeral 1 denotes a fuel cell stack. The fuel cell stack 1 includes a power generation cell 5 in which a fuel electrode layer 3 and an air electrode layer (oxidant electrode layer) 4 are arranged on both surfaces of a solid electrolyte layer 2, and a fuel electrode current collector 6 outside the fuel electrode layer 3. And an air electrode current collector (oxidant electrode current collector) 7 outside the air electrode layer 4 and a separator 8 outside the current collectors 6 and 7 are sequentially stacked.

Here, the solid electrolyte layer 2 is made of stabilized zirconia (YSZ) or the like to which yttria is added, and the fuel electrode layer 3 is made of a metal such as Ni or Co or a cermet such as Ni—YSZ or Co—YSZ. The air electrode layer 4 is made of LaMnO ₃ , LaCoO ³ or the like, the fuel electrode current collector 6 is made of a sponge-like porous sintered metal plate such as a Ni-based alloy, and the air electrode current collector 7 is made of The separator 8 is made of stainless steel or the like, and is made of a sponge-like porous sintered metal plate such as an Ag-based alloy.

  The separator 8 has a function of electrically connecting the power generation cells 5 and supplying gas to the power generation cells 5. The fuel gas is introduced into the separator 8 from the outer peripheral surface thereof to collect the fuel electrode of the separator 8. A fuel gas passage 11 that is discharged from the substantially central portion of the surface facing the electric body 6 and an oxidation gas that is introduced from the outer peripheral surface of the separator 8 and discharged from the surface of the separator 8 that faces the air electrode current collector 7. An agent gas passage 12 is provided. However, the separators 8 (8A, 8B) at both ends have only one of the gas passages 11, 12.

  Further, on the side of the fuel cell stack 1, as shown in FIG. 2, a fuel manifold 15 for supplying fuel gas to the fuel gas passage 11 of each separator 8 through the connection pipe 13, and an oxidant gas for each separator 8. An oxidant manifold 16 for supplying an oxidant gas (air) to the passage 12 through the connection pipe 14 extends in the stacking direction of the power generation cells 5.

  In addition, this solid oxide fuel cell has a sealless structure in which a gas leakage prevention seal is not provided on the outer peripheral portion of the power generation cell 5, and during operation, as shown in FIG. The fuel electrode layer 3 and the air electrode layer 4 are diffused while the fuel gas and the oxidant gas (air) supplied from the substantially central portion of the separator 8 through the gas passage 12 toward the power generation cell 5 are diffused toward the outer periphery of the power generation cell 5. The power generation reaction is caused to spread over the entire surface, and the remaining high-temperature gas that has not been consumed in the power generation reaction is freely discharged from the outer peripheral portion of the power generation cell 5 to the outside. Further, since the outer peripheral portions of the current collectors 6 and 7 are also opened to the outside, a part of the gas diffusing in the current collectors 6 and 7 passes through the holes of the current collectors 6 and 7 and is thus It is discharged from the whole surface.

  In such a sealless structure, in this embodiment, particularly in the anode current collector 6, as shown in FIG. 1, the outer peripheral portion of the circular porous metal body 23 constituting the current collector is provided. A ring-shaped metal cover 20 is disposed so as to cover it. The cover 20 is preferably disposed so as to be in close contact with the outer peripheral surface of the porous metal body 23. Further, the cover 20 is made of a conductive and heat-resistant metal such as Kanthal, Inconel, Nichrome, etc., and a large number of gas discharge holes 21 are formed over the entire circumference of the peripheral side portion. It is formed at intervals. The number of the gas discharge holes 21 may be as small as 4 to 8, for example, but it is preferable that the gas discharge holes 21 are provided uniformly over the entire circumference of the peripheral side portion.

Further, a plurality of trapezoidal trapezoidal locking claws 22 that are hollowed out are formed on the upper and lower peripheral edges of the cover 20, and the base of the locking claws 22 is bent at a right angle as shown in the figure, thereby forming a porous metal. The body 23 is supported on its upper and lower surfaces.
Since the cover 20 is made of metal, the workability is good, and the electrical connection between the separator 8 and the power generation cell 5 is not hindered due to its conductivity.
Further, by providing the engagement claw 22 with the hollow 22a, the engagement claw 22 does not interfere with the flow of the fuel gas supplied from the separator 8 in the stacking direction. Note that the locking claw 22 may be provided only on one side to support any one of the porous metal bodies 23.

  In this way, by forming a structure in which the outer peripheral surface of the porous metal body 23 is covered with the ring-shaped cover 20, the gas discharged from the outer peripheral portion of the fuel electrode current collector 6 can be discharged only at the gas discharge hole 21 portion. As a result, it is avoided that the fuel gas diffusing in the porous metal body 23 is discharged from the entire outer peripheral portion, and the fuel gas that does not contribute to the power generation reaction is discharged from the outer peripheral portion. While suppressing the amount, the fuel gas can be efficiently supplied to the power generation cell 5 side accordingly.

  In addition, the cover 20 prevents a back diffusion phenomenon of air to the fuel electrode side, and a problem that combustion power generated in the power generation cell consumes fuel gas that can be used for the electrode reaction and deteriorates power generation performance. Due to the local temperature rise caused by the above, the thermal stress distribution in the power generation cell becomes non-uniform, and the problem peculiar to the sealless structure that shortens the life of the fuel cell stack 1 can be eliminated as much as possible. As a result, the power generation efficiency can be improved, the output density of the fuel cell can be increased, and the life of the fuel cell stack 1 can be increased.

  In the stacking process of the power generation cell 5, the current collectors 6, 7 and the separator 8, the porous metal body 23 of the anode current collector 6 serves as a guide plate for the load in the stacking direction by the metal cover 20. Therefore, the porous metal body 23 is not excessively crushed by the pressure at the time of stacking, and the porous metal body 23 has a substantially spherical hole after the stacking. A uniform and good gas flow can be ensured in the gas tank 23.

  Incidentally, a porous metal body having a thickness of about 2 mm is usually used, and in the case of the air electrode current collector 7 not having the metal cover 20, the porous metal body is thick due to the pressure at the time of lamination. Although it is crushed to about 0.7 mm, the air electrode current collector 7 is originally supplied with a large amount of air that is about twice as much as the required reaction amount. There is no problem in the performance and the amount of gas supplied to the power generation cell.

  Thus, by covering the outer peripheral surface of the porous metal body 23 with the cover 20, the anode current collector 6 can be made thicker, and if the thickness of the porous metal body 23 increases, the flow rate of the fuel gas increases. can do. A large amount of the fuel gas supplied into the current collector is restricted from being discharged from the outer peripheral portion by the arrangement of the cover 20, so that the gas diffused in the current collector is efficiently disposed on the power generation cell 5 side. Will be supplied to.

The fuel-electrode current collector by embodiment of this invention is shown, (a) is a top view, (b) is a side view, (c) is a bottom view. The exploded sectional view showing the important section of the solid oxide fuel cell to which the present invention was applied. The exploded perspective view of the principal part same as the above. It is a principal part schematic block diagram of a fuel cell stack, and shows the gas flow at the time of operation.

Explanation of symbols

2 Solid electrolyte layer 3 Fuel electrode layer 4 Oxidant electrode layer (air electrode layer)
6 Fuel electrode current collector 7 Oxidant electrode current collector (air electrode current collector)
8 Separator 20 Cover
21 Gas discharge hole 22 Locking claw 23 Porous metal body

Claims (3)

A fuel electrode layer and an oxidant electrode layer are arranged on both sides of the solid electrolyte layer, and a fuel electrode current collector and an oxidant electrode current collector made of a porous metal body are respectively disposed outside the fuel electrode layer and the oxidant electrode layer. A separator is disposed outside the fuel electrode current collector and the oxidant electrode current collector, and the fuel electrode layer and the oxidant electrode layer are passed from the separator through the fuel electrode current collector and the oxidant electrode current collector. In a solid oxide fuel cell having a sealless structure for supplying fuel gas and oxidant gas to
A solid oxide fuel cell characterized in that a cover having a gas discharge hole is provided so as to cover the outer peripheral portion of the fuel electrode current collector, and the exhaust gas exhaust locations discharged from the outer peripheral portion are limited. . 2. The solid oxide fuel according to claim 1, wherein the cover includes a plurality of locking claws at an edge, and supports both or one side of the porous metal body with the locking claws. battery. 3. The solid oxide fuel cell according to claim 1, wherein the cover is made of a heat-resistant metal such as Kanthal, Inconel, or Nichrome.

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