The present invention relates to a solid oxide type fuel cell having a structure in which power generation cells and separators are alternately laminated and, in particular, to a solid oxide type fuel cell capable of ensuring uniform temperature in the lamination direction of a stack.
In recent years, the solid oxide type fuel cell, which converts chemical energy of fuel directly into electric energy, has received widespread attention as a highly efficient and clean generator. The solid oxide type fuel cell has a laminated structure in which a solid electrolyte layer made of an oxide ion conductor is sandwiched between an air electrode layer (a cathode) and a fuel electrode layer (an anode) from both sides.
In the process of electric power generation, oxidant gas (oxygen) is supplied to the air electrode layer side, and fuel gas (H2, CO, CH4 or the like) is supplied to the fuel electrode side, respectively, as reaction gases. The air electrode layer and the fuel electrode layer are both made to be porous so that reaction gases can reach interfaces in contact with the solid electrolyte layer.
Oxygen supplied to the air electrode side passes through pores in the air electrode layer and reaches near the interface in contact with the solid electrolyte layer, and in that portion, the oxygen receives electrons from the air electrode layer to be ionized into oxide ions (O2−). These generated oxide ions diffuse and move in the solid electrolyte layer toward the fuel electrode layer. The oxide ions having reached near the interface in contact with the fuel electrode layer react with fuel gas in that portion to produce reaction products (H2O, CO2 and the like), and release electrons to the fuel electrode layer. The electrodes generated by the electrode reaction (power generation reaction) can be taken out as an electromotive force by an external load of another route.
A flat plate type solid oxide fuel cell is constructed by alternately laminating a plurality of power generation cells, current collectors and separators to form a stacked body (hereinafter referred to as a “fuel cell stack”) and by applying a load in the lamination direction to the fuel cell stack to bring the above respective components into close pressure contact with each other.
The flat plate type fuel cell stack has a tendency for the cell temperature (separator temperature) of a middle stack portion to become extremely higher than that of an end stack portion, as shown by a temperature distribution curve (a) in
When a temperature difference occurs in the lamination direction of the fuel cell stack, a hot portion thereof has low concentration of flowing gas and breaks uniform distribution of reaction gas to respective power generation cells, so that cell voltages become uneven.
A fuel cell stack constructed by connecting a number of power generation cells in series has the following problem: when such uneven voltages occur in the respective power generation cells, a total output of fuel cells is restricted by a part of low-voltage cells, resulting in inefficient electric power generation.
As a technique for uniformalizing the temperature of a fuel cell stack, a fuel cell the radiation of which is controlled by attaching radiators to respective separators has been disclosed in Japanese Patent Laid-Open No. 2004-273140. The Japanese Patent Laid-Open No. 2004-273140 has proposed the fuel cell that is set so as to make the cross-sectional area of the heat dissipating fins variable in accordance with positions of the separators in respect to the layer direction in which power generating parts and the separators are layered.
The purpose of the present invention is to provide a fuel cell capable of attaining high power generation efficiency and high durability by uniformalizing temperature distribution of a fuel cell stack in a lamination direction.
According to the present invention, there is provided a solid oxide type fuel cell, having a fuel cell stack constructed by alternately laminating power generation cells and separators and generating an electric power generation reaction by supplying reaction gas to the respective power generation cells, the solid oxide type fuel cell comprising: a radiator disposed between the separators at a middle portion of the fuel cell stack in the lamination direction, the radiator including a columnar support portion mainly serving as a path for cell currents and supporting a load in the lamination direction, flange portions provided on both ends of the support portion and providing a contact with the adjacent separators, and a radiation member.
Preferably, the support portion of the solid oxide type fuel cell is positioned at the central portion of the fuel cell stack in a plane direction thereof.
Moreover, the plurality of radiation members of the solid oxide type fuel cell are projected in a radial condition from a peripheral side surface of the support portion.
Furthermore, according to the present invention, there is provided a solid oxide type fuel cell, having a fuel cell stack constructed by alternately laminating power generation cells and separators and generating an electric power generation reaction by supplying reaction gas to the respective power generation cells, the solid oxide type fuel cell comprising: a radiator disposed between the separators at a middle portion of the fuel cell stack in the lamination direction, the radiator including a plurality of radiation members erected in the lamination direction and arranged side by side in a line, serving as a path for cell currents and supporting a load in the lamination direction, and flange portions positioned on both ends of the radiation member and providing a contact with adjacent separators.
According to the present invention, since a radiator is disposed at a middle portion of the stack which becomes hot at the time of the power generation, it becomes possible to radiate Joule heat generated by a power generation reaction from the radiator through adjacent separators, thus suppressing an excessive temperature rise at the middle portion of the stack and uniformalizing a temperature distribution in the lamination direction of the stack. This enables high efficiency of electric power generation as the whole stack and prevention of breakage to the power generating cells, such as peeling of an electrode layer, which is apt to occur under a high temperature, thus enhancing the durability of the fuel cell.
Description will be made below of a first embodiment of the present invention with reference to
As shown in
In the unit cell 10 of the above structure, the solid electrolyte layer 2 is made of stabilized zirconia (YSZ) doped with yttria or the like; the fuel electrode layer 3 of metal such as Ni or Co, or cermet such as Ni-YSZ or Co-YSZ; the air electrode layer of LaMnO3 or LaCoO3; the fuel electrode current collector 6 of spongy porous sintered metal plate such as Ni based alloy; the air electrode current collector 7 of spongy porous sintered metal plate such as Ag based alloy; and the separator 8 of stainless or the like.
The separator 8 has a function of electrically connecting the power generation cells 5 to each other and supplying reaction gas to the power generation cell 5, and further a fuel gas passage 11 and an oxidant gas passage 12. The fuel gas passage 11 introduces fuel gas from an outer peripheral surface of the separator 8 and discharges the gas from the center portion 11a of a surface facing the fuel electrode current collector 6, while the oxidant gas passage 12 introduces oxidant gas from the outer peripheral surface of the separator 8 and discharges the gas from the center portion 12a of a surface facing the air electrode current collector 7.
Inside the fuel cell stack 1, as shown in
The fuel cell stack 1 uses a sealless structure without attaching gas leak prevention seal to an outer peripheral portion of the power generation cell 5, which permits excess gas (exhaust gas) not consumed by a power generation reaction to be freely released from the outer peripheral portion of the power generation cell. Moreover, the Joule heat of the power generation cell portion generated in the process of the power generation reaction is thermally transmitted to the adjacent separator 8 and radiated from the outer peripheral portion of the separator.
In one embodiment of the preset invention, as shown in
The radiator 20 is formed of stainless steel plate with excellent thermal conductivity and, as shown in
The flange portion 21, formed into a rectangular one of the same shape and size as the separator 8, is disposed in a closely contacted state between the separators 8, thus providing a good electric contact with the adjacent separators 8, 8. For better contact with the adjacent separators, for example, a thin sheet of spongy porous sintered metal such as Ni based alloy may be intervened in between the separator 8 and the flange portion 21.
The support portion 22 mainly becomes a path for cell current and supports a load in the lamination direction applied to the top flange portion 21. The support portion 22 is disposed at the central portion of the stack in the plane direction, by which stack currents running in the lamination direction can be relayed to the power generation cell 5 at the next stage with high efficiency, concentrated on the central portion of the power generation cell 5. In
The radiating fins 23 are radially provided around the support portion 22, by which the fluid ability of exhaust gas can be improved at the periphery of the radiating fin 23, thus enhancing a radiation effect by the radiating fins 23.
In this embodiment, the radiator 20 is made of stainless steel plate, however, a radiator made of iron plate with Ag plating on the surface thereof may be used. Otherwise, a radiator of stainless steel plate with aluminum spread and penetrated into surface thereof and with Fe—Ag alloy layer, which is excel in durability and radiation performance, formed thereon may be used. This can be applied to the radiator 20 as well in
As described above, the radiator 20 is disposed at the middle portion of the stack in a closely contacted state between the separators 8, 8. This permits Joule heat from the power generation cell 5 to be thermally transmitted from the whole surface of the adjacent separators 8, 8 for highly efficient radiation from the radiating fins 23, in the middle portion of the stack where the temperature is liable to be high compared with the other portion within the stack. As a result, as shown by a temperature distribution curve (b) in
Thus, the temperature distribution of the stack in the lamination direction is made uniform, which permits a voltage distribution in the respective power generation cells 5 to be suppressed, and the temperature of the whole stack to be maintained within a predetermined temperature range suited to a power generation reaction temperature. Accordingly, highly efficient power generation can be performed without being regulated by some of the low-voltage cells, and breakage to the power generation cells 5, such as peeling of the respective electrode layers 3, 4 due to thermal stress apt to occur under a high temperature, can be prevented, thus improving durability (thermal cycle characteristics) of fuel cells.
In the embodiment shown in
Next, another example of the radiator 20 according to the present invention will be shown in
The radiator 20 shown in
In such a configuration, the structure is simplified compared to the radiator 20 in
Next, further another example of the radiator 20 according to the present invention will be shown in
The radiator 20 shown in
The solid oxide type fuel cell according to the present invention provides highly efficient power generation as the whole stack and prevention of breakage to the power generating cells, such as peeling of an electrode layer, which is apt to occur under a high temperature, thus enhancing the durability of the fuel cell.
Number | Date | Country | Kind |
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2005-007122 | Jan 2005 | JP | national |
2006-000696 | Jan 2006 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2006/300267 | 1/12/2006 | WO | 00 | 7/7/2008 |