JP2005294152A - Solid oxide fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid oxide fuel cell provided with an inside reforming mechanism in which a gas flow passage of superior circulation is secured, and in which excellent reforming performance is obtained in a fuel cell stack without being affected by a supported amount of a reforming catalyst. <P>SOLUTION: A fuel electrode layer 3 and an air electrode layer 4 are arranged on both faces of a solid electrolyte layer 2, a fuel electrode current collector 6 and an air electrode current collector 7 composed of a porous metal are respectively arranged on the outside of the fuel electrode layer 2 and the air electrode layer 4, and a separator 8 is arranged outside these current collectors 6, 7. A reforming catalyst layer 20 is arranged between the separator 8 and the fuel electrode current collector 6. The reforming catalyst layer 20 is constituted by supporting hydrocarbon reforming catalyst grains on the porous metal. By this constitution, the gas flow passage of superior circulation can always be secured in the fuel cell stack 1 without being affected by a filling amount of the hydrocarbon reforming catalyst. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an internal reforming mechanism of a solid oxide fuel cell having a structure in which a current collector made of a porous metal is interposed between a separator and an electrode layer.

  The solid oxide fuel cell is being developed as a third generation fuel cell for power generation. Currently, three types of solid oxide fuel cells of this type have been proposed: a cylindrical type, a monolith type, and a flat plate type, each of which has a solid electrolyte made of an oxide ion conductor on both sides of the air electrode layer ( It has a laminated structure sandwiched between a cathode) and a fuel electrode layer (anode). A high-power fuel cell stack can be configured by stacking a plurality of power generation cells made of this laminate alternately with separators with a fuel electrode current collector and an air electrode current collector interposed therebetween.

In a solid oxide fuel cell, an oxidant gas (oxygen) is supplied to the air electrode layer side and a fuel gas (H ₂ , CO, CH _4, etc.) is supplied to the fuel electrode layer side as a reaction gas. The air electrode layer and the fuel electrode layer are both porous layers so that the reaction gas can reach the interface with the solid electrolyte layer.

The electrode reaction of the solid oxide fuel cell when hydrogen is used as the fuel is as follows.
Oxygen supplied to the air electrode layer passes through the pores in the air electrode layer and reaches the vicinity of the interface with the solid electrolyte layer, and receives electrons from the air electrode layer at this portion to receive oxide ions (O ²⁻ ). Is ionized. The oxide ions diffuse and move in the solid electrolyte layer toward the fuel electrode layer. Oxide ions that have reached the vicinity of the interface with the fuel electrode layer react with the fuel gas at this portion to generate reaction products (H ₂ O, CO _2, etc.), and discharge electrons to the fuel electrode layer. This electron is taken out as an electromotive force by an external load of another route.

  By the way, normally, as a fuel gas of a solid oxide fuel cell, a hydrocarbon compound such as city gas (this is referred to as raw fuel) is used. Therefore, it is actually necessary to use this raw fuel after reforming it into a fuel gas containing hydrogen as a main component. As a reforming method, when the raw fuel is a hydrocarbon-based gas fuel or liquid fuel, a steam reforming method is usually used.

For example, a reforming reaction using methane gas as a raw fuel is as follows.
The desulfurized methane gas is added with water vapor in the reformer to become hydrogen and carbon monoxide. Since this reforming reaction is an endothermic reaction, a high temperature of about 650 to 800 ° C. is required to perform a stable reforming reaction.
CH ₄ + H ₂ O → 3H ₂ + CO
At this time, the generated carbon monoxide further reacts with water vapor and changes into hydrogen and carbon dioxide.
CO + H ₂ O → H ₂ + CO ₂

  Conventionally, as a fuel gas reforming method for a solid oxide fuel cell, an external reforming method in which an external reformer is installed, and an internal reforming method in which a reforming mechanism is incorporated inside a high-temperature fuel cell module. Is known.

  The external reforming method is a method in which a reformer having a hydrocarbon reforming catalyst is installed outside the fuel cell to reform the raw fuel, and this reformed gas is introduced into the fuel cell. Since the reaction is an endothermic reaction, it is necessary to supply high heat for the reforming reaction into the external reformer, and wasteful energy is required to obtain this high heat, and the efficiency of the power generation system is increased accordingly. There was a problem of lowering.

  On the other hand, the internal reforming method is an extremely rational method that uses a part of the Joule heat generated by the power generation reaction of the fuel cell as the endothermic reaction of the reforming reaction, and can potentially realize a highly efficient system. have. In addition, since it has a cooling effect of absorbing high-temperature exhaust heat generated during power generation by this endothermic reaction, it has recently been attracting attention as a fuel reforming method for solid oxide fuel cells.

However, on the other hand, research and development of solid oxide fuel cells has progressed, and instead of the high temperature operation type with an operating temperature of around 1000 ° C., a low temperature operation type solid oxide fuel cell with an operating temperature of around 700 ° C. has been developed. Has been proposed.
In the case of the high-temperature operation type, a high temperature required for reforming can be easily obtained. However, in such a low-temperature operation type, the temperature inside the fuel cell module is 600 ° C. or lower and is lower than the optimum reforming temperature. A sufficient reforming ability cannot be obtained in the reformer. When an insufficiently reformed fuel gas containing a large amount of the methane component is introduced into the fuel cell stack and reaches the fuel electrode layer, carbon deposition from methane occurs, resulting in a problem that the cell performance rapidly decreases.

In view of such a situation, the reforming catalyst is disposed inside the fuel cell stack at a high temperature so that the reformed fuel gas can be reformed at a suitable reaction temperature before reaching the fuel electrode layer. A solid oxide fuel cell is proposed, and Patent Document 1 and Patent Document 2 are disclosed as examples.
Patent Literature 1 discloses a reforming catalyst carried on a fuel electrode current collector, and Patent Literature 2 discloses a reforming catalyst filled in a fuel supply passage of a separator.
JP 7-45293 A JP 2002-203588 A

However, in the above reforming mechanism, the gas flow resistance of the separator and the current collector is increased by interposing the reforming catalyst, and the flow of the fuel gas becomes non-uniform, so that it is supplied to the fuel electrode layer. There is a risk that the amount of fuel gas to be produced will be insufficient and the power generation performance will be reduced, or that the temperature distribution will be generated inside the power generation cell and the power generation cell will be deteriorated or damaged.
Such a phenomenon becomes more prominent as the amount of the reforming catalyst supported increases, and has become a major problem to be solved in the internal reforming mechanism.

  In view of such problems, the present invention can ensure a gas flow path that is always in good circulation in the fuel cell stack without being affected by the amount of the reforming catalyst supported, and is excellent in reforming. An object of the present invention is to provide a solid oxide fuel cell having an internal reforming mechanism capable of obtaining performance.

  That is, the present invention according to claim 1 is a fuel electrode current collector comprising a fuel electrode layer and an air electrode layer on both sides of a solid electrolyte layer, and a porous metal on the outside of the fuel electrode layer and the air electrode layer, respectively. A solid oxide fuel cell in which a separator is disposed outside the current collector, and a reaction gas is supplied from the separator to the fuel electrode layer and the air electrode layer through each current collector. A hydrocarbon reforming catalyst is disposed between the separator and the fuel electrode current collector.

  According to a second aspect of the present invention, in the solid oxide fuel cell according to the first aspect, the hydrocarbon reforming catalyst is supported on a porous metal body.

  The present invention described in claim 3 is the solid oxide fuel cell according to claim 2 or 3, wherein the porous metal body for supporting the hydrocarbon reforming catalyst is: It is characterized by comprising Ni.

  The present invention according to claim 4 is the solid oxide fuel cell according to any one of claim 2 or claim 3, wherein the porous metal body for supporting the hydrocarbon reforming catalyst is: It is characterized by having a through-hole penetrating from the reaction gas discharge portion of the separator to the anode current collector side.

In this configuration, the fuel gas is introduced into the anode current collector through the separator, and in contact with the adjacent reforming catalyst layer in the process of diffusing and moving through the current collector, the reforming reaction of the fuel gas at the contact site. Is done.
As the carrier for the hydrocarbon reforming catalyst, a porous metal body excellent in electrical conductivity and thermal conductivity is desirable. In this configuration, the anode current collector functions as a fuel gas flow path, and the porous metal body functions as a carrier for the hydrocarbon reforming catalyst.

In this way, since there is no reforming catalyst that hinders the flow of fuel gas in the fuel gas flow section, a gas flow path that is always good in flow can be secured in the fuel cell stack, and an efficient and stable interior Reform power generation can be performed.
In addition, the reforming catalyst layer is disposed between the separator, which is the hottest point in the fuel cell stack, and the anode current collector. An excellent reforming ability can be obtained by securing the temperature. As a result, the reforming reaction is activated, a hydrogen-rich fuel gas is obtained in the reforming catalyst layer, and the problem of carbon deposition due to the unreformed gas can be avoided.
Furthermore, in the reforming catalyst layer, a temperature difference occurs due to an endothermic reaction. However, by providing a gas flow path between the cell and the catalyst layer, it is possible to avoid damage to the cell due to the temperature difference of the reforming catalyst layer.

  In addition, as the porous metal body for supporting the reforming catalyst, foam metal, mesh, felt or the like can be used, and any of them can be made of Ni having a high catalytic activity, thereby forming the surface of the porous metal body. Since the reforming is performed in step 1, a more excellent reforming ability can be obtained.

  As described above, according to the present invention, since the reforming catalyst layer is disposed between the separator and the fuel electrode current collector, the inside of the fuel cell stack is not affected by the filling amount of the hydrocarbon reforming catalyst. In this case, it is possible to always ensure a gas flow path with good circulation, and as a result, it is possible to perform efficient and stable internal reforming power generation.

  In addition, since the hydrocarbon reforming catalyst is disposed between the separator at the highest temperature in the fuel cell stack and the anode current collector, the ambient temperature is reduced even in a low temperature operation type fuel cell. It is possible to efficiently absorb and always ensure the optimum reforming temperature, and thus to obtain an excellent reforming ability.

Hereinafter, a flat plate type solid oxide fuel cell according to the present embodiment will be described with reference to FIGS.
1 is a diagram showing a schematic configuration of a fuel cell module, FIG. 2 is a sectional view showing an internal structure of a single cell, and FIG. 3 is a sectional view of a porous metal body carrying a hydrocarbon reforming catalyst.

  As shown in FIGS. 1 and 2, the fuel cell stack 1 includes a power generation cell 5 in which a fuel electrode layer 3 and an air electrode layer 4 are disposed on both surfaces of a solid electrolyte layer 2, and a fuel disposed on the outside of the fuel electrode layer 3. A single cell is constituted by the electrode current collector 6, the air electrode current collector 7 disposed outside the air electrode layer 4, and the separator 8 disposed outside each current collector 6, 7. A large number of layers are stacked to form a cylinder.

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

  The separator 8 has a function of electrically connecting the power generation cells 5 and a function of supplying a reaction gas to the power generation cells 5, and a fuel gas is introduced from the outer peripheral surface of the separator 8 to provide fuel for the separator 8. A fuel passage 11 that is discharged from a substantially central portion of a surface that faces the electrode current collector 6, and a surface that faces the air electrode current collector 7 of the separator 8 by introducing an oxidant gas (air) from the outer peripheral surface of the separator 8. And an oxidant passage 12 to be discharged from each.

  Further, on the side of the fuel cell stack 1, a fuel manifold 15 into which fuel gas is introduced / distributed and an oxidant manifold 16 into which air is introduced / distributed are arranged along the stacking direction of the power generation cells 5, A reformer 17 having a hydrocarbon catalyst therein is connected to the upstream side of the fuel manifold 15. The fuel manifold 15 is connected to the fuel passage 11 of each separator 8 by a connection pipe 13, and the oxidant manifold 16 is connected to the oxidant passage 12 of each separator 8 by a connection pipe 14.

  The fuel cell stack 1, the manifolds 15 and 16, the reformer 17, and the like described above are collectively stored in a heat-insulating cylindrical can body to constitute the fuel cell module 10.

  By the way, in the fuel cell stack 1 of the present embodiment, the reforming catalyst layer 20 is disposed between the separator 8 and the anode current collector 6 to form a reforming mechanism in the fuel cell stack 1. .

As shown in FIG. 3, the reforming catalyst layer 20 is a thin plate member in which hydrocarbon reforming catalyst particles 22 are supported in a disk-shaped porous metal body 21, and the thin plate member is a separator 8. And is laminated together with the power generation cell 5 so as to cover the upper surface of the electrode, and both surfaces thereof are in close contact with the separator 8 and the fuel electrode current collector 6, respectively. Yes.
The reforming catalyst layer 20 includes a through hole 20a that communicates with the fuel gas discharge port 11a of the separator 8 facing almost the center of the reforming catalyst layer 20 and opens in the surface of the anode current collector 6. The fuel gas introduced into the passage 11 is supplied from the discharge hole 11a to the anode current collector 6 side through the through hole 20a.

As the porous metal body 21, Ni foam metal can be used. As shown in FIG. 3, the hydrocarbon reforming catalyst particles 22 are uniformly dispersed inside the numerous holes 21 a of the Ni foam metal 21. It is attached in a state.
As the hydrocarbon reforming catalyst 22, a composite material in which a Ni catalyst is supported on a ceramic carrier is used, but Pd, Ru, or the like can be used instead of Ni.

Further, as the porous metal body 21, in addition to the above-mentioned foam metal, mesh, felt or the like can be used. In any case, the granular hydrocarbon reforming catalyst 22 is dispersed in the pores or the surface of the fiber metal. It is supported evenly.
When these porous metal bodies are made of Ni having a high catalytic activity like the foam metal, the reforming reaction is also performed on the surface of the porous metal body 21, and the reforming catalyst layer 20 has an excellent reforming ability. can get. In addition, the porous metal body 21 made of Ni is excellent in electrical conductivity, has an excellent current collecting function together with the fuel electrode current collector 6, and has an advantage of excellent workability. Yes.

  In the fuel cell stack 1 in which the reforming mechanism having the above-described configuration is mounted, air supplied from the outside is distributed by the plurality of connecting pipes 14 via the oxidant manifold 16 and is supplied to the oxidant passages 12 of the separators 8. In addition to being introduced, it is discharged from the oxidant gas discharge hole 12a at the end of the passage and supplied to the facing air electrode current collector 7, and further diffuses in the air electrode current collector 7 from the center toward the periphery. In the process of moving, the air electrode layer 4 of the power generation cell 5 is reached.

On the other hand, the fuel gas (mixed gas of CH ₄ and high-temperature steam) supplied from the outside is once reformed by the reformer 17 in the fuel cell module 10, and then the reformed gas passes through the fuel manifold 15. It is distributed by a plurality of connecting pipes 13 and introduced into the fuel passages 11 of the separators 8 and discharged from the fuel gas discharge holes 11a at the end of the passages. The discharged fuel gas is supplied to the facing fuel electrode current collector 6 through the through hole 20a of the reforming catalyst layer 20.
In the process of diffusion and movement of the fuel gas in the anode current collector 6 from the central portion toward the peripheral portion, the reforming reaction is performed while repeatedly contacting the reforming catalyst layer 20 adjacent to the lower portion of the fuel gas.

  Incidentally, the reforming reaction inside the anode current collector 6 is as described in the section of the prior art, and the explanation is omitted here. However, due to this reforming reaction, the methane in the fuel gas is oxidized with hydrogen. Modified to carbon. This hydrogen-rich reformed gas reaches the fuel electrode layer 3 of the power generation cell 5 from the fuel electrode current collector 6, reacts with Ni and Co on the fuel electrode layer, and the reforming reaction is performed again.

As described above, the reforming catalyst layer 20 of the porous metal body 21 of the present embodiment functions not only as a fuel gas flow path but as a carrier for the hydrocarbon reforming catalyst particles 22 and is located in the upper layer. The anode current collector 6 composed of a porous sintered metal plate that functions as a gas flow path.
Therefore, since the hydrocarbon reforming catalyst particles 22 that prevent the flow of the fuel gas are not arranged at all in the fuel gas circulation portion, the fuel cell stack 1 is not affected by the filling amount of the hydrocarbon reforming catalyst particles 22. Inside, a gas flow path with good circulation is always secured. In other words, in this configuration, a sufficient amount of the hydrocarbon catalyst particles 22 can be disposed in the fuel cell stack.

  In addition, the hydrocarbon reforming catalyst 22 includes the separator 8 and the fuel electrode current collector 6 that are the highest temperature locations in the fuel cell stack 1 while being supported on the porous metal body 21 made of Ni having excellent heat conductivity. Therefore, even if the present invention is applied to the low temperature operation type fuel cell module 10 whose operating temperature is around 700 ° C., the porous metal body 21 efficiently absorbs the temperature in the stack and is optimally modified. The temperature range (650 to 800 ° C.) can be ensured reliably, so that the equilibrium shifts according to the amount of power generation (fuel gas consumption), and the reforming catalyst layer 20 always has excellent reforming ability. Can be obtained.

As a result, even if an insufficiently reformed fuel gas containing a large amount of methane is supplied to the fuel cell stack 1 from the reformer 17 installed in an atmosphere where the temperature in the fuel cell module 10 is approximately 600 ° C. The unreformed fuel gas is reformed into a hydrogen-rich fuel gas before reaching the fuel electrode layer 3 by the in-stack reforming mechanism.
As a result, carbon deposition due to unreformed gas can be avoided, and efficient and stable internal reforming power generation becomes possible.

The figure which shows schematic structure inside a fuel cell module. Sectional drawing which shows the internal structure of a single cell. Sectional drawing of the porous metal body which carry | supported the hydrocarbon reforming catalyst.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell stack 2 Solid electrolyte layer 3 Fuel electrode layer 4 Air electrode layer 6 Fuel electrode current collector 7 Air electrode current collector 10 Solid oxide fuel cell (fuel cell module)
20 Hydrocarbon reforming catalyst 20a Through hole 21 Porous metal body

Claims (4)

A fuel electrode layer and an air electrode layer are arranged on both sides of the solid electrolyte layer, and a fuel electrode current collector and an air electrode current collector made of porous metal are arranged outside the fuel electrode layer and the air electrode layer, respectively. In a solid oxide fuel cell in which a separator is disposed outside the electric body, and a reaction gas is supplied from the separator to each of the fuel electrode layer and the air electrode layer through each current collector.
A solid oxide fuel cell, wherein a hydrocarbon reforming catalyst is disposed between the separator and the fuel electrode current collector. 2. The solid oxide fuel cell according to claim 1, wherein the hydrocarbon reforming catalyst is supported on a porous metal body. The solid oxide fuel cell according to claim 2, wherein the porous metal body for supporting the hydrocarbon reforming catalyst is made of Ni. The porous metal body for supporting the hydrocarbon reforming catalyst includes a through hole penetrating from the reaction gas discharge portion of the separator to the fuel electrode current collector side. Any one of the solid oxide fuel cells.

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