JPH06325787A - Solid oxide fuel cell - Google Patents

Abstract

(57) [Summary] [Objective] The present invention has a difficulty in multilayer stacking, which is a problem of conventional flat plate SOFCs, and there is little hope of enlarging cells.
Further, it is an object to realize an SOFC that solves the problem that it is difficult to reduce the internal resistance because it is difficult to secure electrical contact between the cells and the power generation characteristics are poor. According to the present invention, two kinds of SOFC single cells are formed by using an oxygen ion conductive material and a proton conductive material as electrolytes, and when assembling an SOFC module having a predetermined output, the above two kinds of SOFC modules are assembled. The cells formed by using the electrolyte were alternately arranged, and at this time, the electrode surfaces having the same function were arranged so as to face each other, and the cell itself had a power generation function and a separation function of two kinds of gas. It is characterized by that.

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 power generating cell and a method for assembling the same.

[0002]

2. Description of the Related Art Solid oxide fuel cells (hereinafter referred to as SOF)
C) is a fuel cell that literally uses a solid substance as an electrolyte material. The charge transfer carrier in the electrolyte is either an oxygen ion or a proton depending on the substance, but the ease of ion movement in such a solid substance is small at low temperatures, so at high temperatures of 800 ° C to 1000 ° C. Be driven. Therefore, high temperature resistance is inevitably required for the two electrode materials, and in SOFC, all the constituent materials of the fuel cell are
It is made of a material that can be used at such a high temperature.
On the other hand, the easiness of ion migration in the electrolyte used here increases when the temperature is raised, but this is not enough, and the electrolyte is made thinner to obtain practical power generation characteristics. The voltage drop must be reduced.

FIG. 5 schematically shows the structure of a so-called flat plate type SOFC which has been conventionally manufactured.

FIG. 5 (a) is a self-supporting type in which the electrolyte has mechanical strength, and FIG. 5 (b) is a self-supporting type in which one electrode has strength to form a cell. In the figure, 1 is a unit power generation cell, 2 is a solid electrolyte, 3 is an oxidizer electrode, 4 is a fuel electrode, 5 is an interconnector, 6 is an oxidizer electrode substrate, 7 is a fuel electrode substrate, 8 is a fuel passage, and 9 is It is an oxidant passage. Conventionally, an oxygen ion conductor is often used as a solid electrolyte material. In this case, the solid electrolyte 2 is yttria-stabilized zirconia (YSZ), and the oxidizer electrode 3 is La _{1 -X.}
Materials such as Sr _X MnO ₃ and nickel zirconia cermet are used for the fuel electrode 4.

Further, the interconnector of 5 is required to be a dense body having electronic conductivity, have no gas permeability, and have stable physical properties in both an oxidizing atmosphere and a reducing atmosphere. As a suitable material, LaCr (C
a) O ₃ based substances are used. In this way, the conventional S
The OFC is composed of a sintered body of different kinds of materials, and since the electrolyte is formed as an extremely thin layer in the structure of the power generation section, the unit power generation cell 1 in the conventional example (a) has a thin plate shape. This is obvious considering the resistance value of YSZ, and the resistance of YSZ is about 10 even at 1000 ° C.
Since it is Ωcm, if the thickness of YSZ is 1 mm, it is 1c.
A voltage drop of 1 V occurs at a current of 1 A per m ² , and this alone causes a voltage drop corresponding to the electromotive force (about 1 V). Therefore, in order to suppress the voltage drop and secure a predetermined output voltage, YSZ needs to be a very thin film of 1 mm or less.

As described above, the output of the SOFC has an open circuit voltage of less than 1 V per cell, and the current during power generation is
Since it is 500 to 1000 mA / cm ² , in order to obtain a predetermined output voltage and current, it is necessary to expand the reaction area and stack the unit power generation cells. Therefore, FIG.
In the method of (a), it is necessary to stack the required number of cells having a predetermined electrode area. However, as mentioned earlier, all the materials that form the SOFC are ceramic materials, and there is a risk of damage when a load is applied to the thin cells described above. Will be restricted. Therefore, even if the layers can be laminated without damage under such conditions, the condition of the contact portion between the cells is not necessarily good from the viewpoint of reducing the electrical resistance (solid surfaces are not Micro contact is a set of point contacts.) That is, the unit power generation cell 1 is configured as thin as possible in order to improve the performance, and does not necessarily have sufficient mechanical strength to withstand such pressure contact. Difficult to press. Such difficulty in stacking increases as the cell size increases.

On the other hand, FIG. 5 (b) shows a substrate 7 made of, for example, the material of the fuel electrode, and cells formed therein. An SOFC module having a predetermined output is formed by stacking such unit power generation cells 1 via the oxidant electrode substrate 6 having a groove in which the interconnector layer 5 is formed. In the method of (b), since the unitary power generation cell 1 is formed on the fuel electrode substrate 7, the strength of the cell itself is larger than that of the method of (a), and the mechanical strength against stacking is improved. However, it is the same in that it is necessary to make sufficient electrical contact between the components when stacking, and from this point of view, too, there is a limit to the precision contact of solid components made of ceramic materials. However, the performance was not always good even if the layers could be formed.

Such a problem is that the direction of current flow is the same as the stacking direction of cells, and gas-impermeable and electron-conductive only interconnectors are arranged between cells to form two cells between each cell. It is common to the flat plate type cell that it must be completely divided to form two kinds of gas flow paths. And, this problem is accompanied and cannot be solved as long as the direction in which the current flows is the same as the cell stacking direction.

The above description has been made with reference to the example of the oxygen ion conductive YSZ electrolyte, but this is an essential problem even if a proton conductive substance is used as the material of the electrolyte.

[0010]

SUMMARY OF THE INVENTION According to the present invention, the conventional flat plate type SOFC has difficulty in multi-layer stacking, there is little hope of making the cells larger, and moreover, electrical contact between the cells can be ensured. The purpose is to realize an SOFC that solves the problems that it is difficult to reduce the internal resistance and the power generation characteristics are poor.

[0011]

The feature of the present invention is to provide an SOFC module having two types of SOFC unit cells, each of which has an oxygen ion conductive substance and a proton conductive substance as an electrolyte and which has a predetermined output. Upon assembly, cells formed by using the above-mentioned two types of electrolytes are alternately arranged, and at this time, the electrode surfaces having the same function are arranged so as to face each other, and two types of cells are generated together with power generation in the cell itself. It is characterized by having a gas separation function.

[0012]

In the conventional SOFC, either the oxygen ion conductive material or the proton conductive material is selected as the electrolyte material for the charge transfer carrier, and the cells thus formed are stacked to produce a power generation module. However, there is no example of using two types of cells in which charge transfer carriers are formed of different electrolyte materials as in the present invention and arranging each cell as in the present invention.

[0013]

EXAMPLES FIG. 1 schematically shows the structure of an SOFC single cell used in the present invention. FIG. 1A shows a single cell 27 using an oxygen ion conductor as an electrolyte material,
FIG. 1 (b) schematically shows the structure of a single cell 27 'in which a proton conductor is used as an electrolyte material. In FIG. 1, 20 and 23 are solid electrolytes, 21 and 24 are fuel electrodes, and 22 and 25 are oxidizer electrodes. In this figure,
Keeping the cell at a given temperature, fuel (eg hydrogen) on each electrode
When an oxidant (for example, air) is supplied, oxygen ions move in (a) and hydrogen ions move in (b) in each electrolyte, whereby an electric current can be taken out to the outside. It should be noted that in both the directions of flow of the respective ions are opposite because of different charge carriers, but the direction of current flowing to the outside is the same in any cell.

Next, when forming a power generation module having a predetermined output by using such two types of unit cells,
The arrangement of each cell is shown below. FIG. 2 is a cell arrangement in the power generation module of the present invention. In FIG. 2, the unit cells 27 and the unit cells 27 'are arranged alternately, and at this time, the fuel electrodes 21 and 24 and the oxidant electrodes 22 and 25 of each cell face each other. By adopting such an arrangement method, the space formed by each cell 27, 27 'and the cell holder can be used as it is as a gas supply path,
By assembling each single cell, two kinds of gas flow paths can be formed. In this single cell arrangement,
The electrical connection status of each cell after the current collectors are arranged between the cells is also shown in FIG. 2, but it is assumed that two cells in parallel due to the use of the current collector are connected in series. Can be used.

Next, concrete examples for forming the cell module of the present invention will be described.

Preparation Example of Single Cell Using Oxygen Ion Conductor as Electrolyte Material As described above, the ion conductivity of the electrolyte material is 90
Even at 0 to 1000 ° C, it is not always sufficient. Therefore, in order not to impair the power generation characteristics of the cell, it is desirable that the electrolyte layer be formed as thin as possible. However, if the film is thinned, it is difficult to form a so-called self-standing cell in which the electrolyte itself supports the two electrodes. Therefore, here, the electrodes are formed by a self-supporting method in which the electrodes serve as a support for the cells. In addition, specifically, a cell support was prepared from a fuel electrode material, and the preparation was carried out by a sheet forming method by a doctor blade method. Nickel zirconia cermet is used as the fuel electrode material, and the amount of nickel added is 30 to
40% by volume, and as zirconia, yttria is 8
Zirconia added at -10 mol% was used. In addition,
A doctor blade slurry was prepared by adding the following additives in a weight ratio to the powder.

Raw material powder 100 Binding agent 10-15 Plasticizer 5-10 Solvent 200 Polyvinyl butyral was used as the binder, butyl phthalate was used as the plasticizer, and isopropyl alcohol was used as the solvent. The solvent can be isopropyl alcohol alone, but toluene was also added if necessary. The amount of binder and plasticizer was ranged to properly control the properties of the slurry. In addition to this, a small amount of a dispersant and an antifoaming agent was also added depending on the properties of the slurry.
Such a mixture was stirred with a ball mill for about 24 to 48 hours, degassed under reduced pressure to remove the solvent, and then a sheet molded body was obtained with a doctor blade device.

In the same manner, a sheet to be an electrolyte was also formed. The material used was zirconia containing 8 to 10 mol% of yttria, which was used to prepare a cermet, and a slurry was prepared and molded with the same composition as above.

Such a sheet molded body was cut into a predetermined size and then heated and pressed to produce a fused sheet. The thickness of the fusion-bonded body can be set arbitrarily by changing the number of sheets to be used, and a large number of fuel electrode sheets were laminated so as to have a thickness of about 3 mm. On the other hand, as the electrolyte sheet, one green sheet having a thickness of 50 to 100 μm was used. The fusion-bonded body of the two types of sheets thus produced was degreased and then sintered to obtain a co-sintered body. Co-sintering is 1300
It was carried out under the conditions of -1400 ° C and 2-10 hours.

Next, the oxidizer electrode powder slurry was applied to the electrolyte surface of such a sintered body and sintered. La _0.8 Sr _0.2 MnO ₃ was used as the powder, and turpentine oil was added to this to make a slurry, and after screen printing, 1100 to 100
Baked at a temperature of 300 ° C.

Here, an example in which a self-supporting type of fuel electrode material was used and an electrolyte layer was formed on this surface by co-sintering was arranged. The reason is that according to this method, 10 to 20 μm is used.
This is because a dense film can be economically formed,
In addition to this, the electrolyte layer can be formed by an EVD method, a thermal spraying method, or the like. Further, also in forming the oxidant electrode, not only the slurry application / sintering but also the co-sintering of three layers including this electrode or the thermal spraying method can be naturally prepared.

Further, although the electrode serving as the self-supporting member was made of the fuel electrode material in the examples, it is also possible to use an oxidizer electrode material instead of the fuel electrode material. It can be performed by molding, EVD, thermal spraying, or the like.

Production Example of Single Cell Using Proton Conductor as Electrolyte Material Also in this cell, in order not to impair the power generation characteristics of the cell, thinning of the electrolyte is essential. Therefore, a self-supporting cell structure is used here as well, and an oxidizer electrode material that has a proven track record as an electrode is used for the support.

Specifically, La _0.8 Sr _0.2 MnO ₃ was used, a slurry was prepared with the same compounding ratio as in the above example, and a sheet was formed. This sheet is heated by a specified number
Pressurized and sintered at a temperature of 1100 to 1300 ° C. to prepare a sintered body having a porosity of 20 to 30%. This sintered body was used as a support for the cell to form an electrolyte and a fuel electrode. The formation of these two layers was performed by a thermal spraying method. Specifically, for electrolytes,
SrCe _0.95 Yb _0.05 O ₃ prepared to have an average particle size of 20 μm
Powder of 100 to 2 by plasma spraying
It was formed into a film having a thickness of 00 μm. Regarding the fuel electrode, nickel was used as the active substance of the electrode, but it was formed as a cermet with the electrolyte in order to reduce the difference in coefficient of thermal expansion from the electrolyte and the oxidizer electrode and to increase the surface area by making it porous. did.

Production Example of Power Generation Module According to the Present Invention Next, a power generation module was constructed using the two types of single cells thus produced. 3 and 4 show specific configurations of the power generation module of the present invention. In this figure,
40 is an intermediate cell holder, 41 is a lower cell holder, 42
Is an upper cell holder, 43 is an end current collector, 43-1 is a slit, 44 is an oxidizer electrode side intermediate part current collector, 45 is a fuel electrode side intermediate part current collector, 46 is a fuel supply port, and 47 is a fuel. It is an outlet. Further, 48 is a collecting line. An insulating layer 44-1 is provided at an intermediate position on the oxidizer electrode side intermediate portion current collector 44 so that both sides of the current collector 44 are electrically insulated. Note that 27 and 27 'are the single cells already shown in FIG.

On the other hand, the appearance of the power generation module constituted by such members is as shown in FIG. 4, and the oxidant gas supply port 48 is arranged orthogonal to the fuel supply port 46. In assembling the module, first, the end current collector 43 is installed in the lower cell holder 41, the single cell 27 is placed on top of this, and then the fuel electrode side intermediate part current collector 45 is overlaid. The single cell 27 ′, the oxidizer electrode side intermediate current collector 44, the intermediate cell holder 40 and the single cell 27 are sequentially arranged on the upper side to perform stacking. At this time, as the oxidizer electrode side intermediate portion current collector 44, the insulating layer 44-l is formed in the central portion.
The thickness of the structure is such that no gap is generated when the two cells are attached to the intermediate portion holder 40 so as to face each other. Then, in the fuel electrode side intermediate portion current collector 45,
Uses a porous material with high elasticity. As a result, when the module is assembled, the fuel electrode side intermediate portion current collector 45, which is highly elastic, acts to spread the two cells between the unit cells 27 and 27 ', and It is possible to securely fix the two cells and make electrical contact with each other.

A wiring material 48 is formed on each of the single cells thus laminated.
It is possible to take out the generated power from each cell to the outside by connecting the. Here, the wiring member 48 was connected in the state as shown in FIG. 2, and the two cells 27 and 27 'were first arranged in parallel (output: 1V), and were further connected in series.

Each unit cell is made of the material as described above, and as a material of the module, the cell holder (40,
41, 42) is alumina, and the end current collector (43) is a sintered body of a pressed body of lanthanum manganite, which is appropriately grooved, and the intermediate collector 44 on the oxidant electrode side is the intermediate layer 44. −
1, an electrically insulating thin plate such as alumina or zirconia is used in the middle part, and lanthanum manganite is arranged on both sides, and the fuel electrode side middle part current collector 45 is a compressible conductor such as nickel felt. It was used.

The power generation of the module thus constructed is
It can be carried out by the same operation as the conventional SOFC, the module is brought to a high temperature of 900 to 1000 ° C., the manifold is connected to the fuel supply port 46 and the oxidant gas supply port 48,
Power generation can be performed by supplying hydrogen humidified at room temperature as a fuel and air as an oxidant. In the module of the present invention, the gas supply port (4
The gas introduced from 6 or 48) is basically a single cell 2
It can react with the electrode surfaces of both 7 and 27 'cells. Here, the power generation characteristics of the unit cells 27 and 27 'are not necessarily the same because the constituent materials and methods of the cells are different. However, even if the power generation characteristics do not match, in the present invention, since two types of cells are used in a parallel connection state, each cell corresponds to the output voltage at the time of power generation according to the power generation characteristics of each cell. Only a fixed constant current flows, and the characteristics of the module are not limited by the characteristics of either one. Rather, the parallel connection makes it possible to expand the entire power generation area and increase the generated current.

On the other hand, in the conventional method, when cells are laminated, electrodes having different polarities are arranged to face each other.
A separator for separating the two kinds of gas supplied to the two electrode surfaces was arranged between the cells. This separator is required to be stable and obtain a predetermined electric conductivity in both oxidizing and reducing atmospheres.
A CrO ₃ based material has been selected. With such a material, a plate-like separator having both sides machined with grooves to be gas passages is manufactured. However, such a separator has a high material cost and a high processing cost, and moreover, the volume occupied by the separator is also required, and the volume of the module becomes large. On the other hand, in the present invention, one of the cells functions not only as a gas separator but also as a power generation section, so that the power generation output of the entire module can be increased.

[0031]

As described above, the SOFC of the present invention
Then, two kinds of single cells are formed by using a proton conductive material and an oxygen ion conductive material as electrolytes, and a power generation module is configured by these two kinds of single cells. The electrodes are alternately arranged so that the oxidizer electrodes or the fuel electrodes face each other, a current collector is arranged in the space between the electrodes, and each gas is supplied to this portion. In addition, when electrically connecting two types of cells, the two types of cells are connected in parallel and are connected in series. With such a structure, either one of the electrodes also functions as a gas separator, so that a separator plate is not required as in the conventional case, and it is inevitable to use an expensive LaCrO ₃ system plate having a groove processed. Cost can be reduced. In addition, the portion occupied by this separator can also be directed to power generation, and the power generation current can be increased by expanding the power generation area of the entire module.

In addition, when stacking the cells, a steel body-like unit composed of an intermediate cell holder, an oxidizer electrode side intermediate section current collector and two types of cells is used to form a highly compressible fuel electrode side intermediate section. It is supposed to be connected only with a current collector. At this time, each cell is given mechanical strength by being integrated with the intermediate cell holder. In the present invention, modularization can be realized by simply stacking such units, and simplification of modularization is also a feature.

[Brief description of drawings]

FIG. 1 is a schematic view of a unit power generation cell of the present invention.

FIG. 2 is an arrangement and electrical connection state of each single cell in the power generation module of the present invention.

FIG. 3 is a diagram showing a structure of a power generation module of the present invention, showing a structure taken along a line AA ′ in FIG.

FIG. 4 is a diagram showing the structure of the power generation module of the present invention, showing the appearance of the power generation module of the present invention and the positions of the supply and exhaust ports for each gas.

FIG. 5 is a structural diagram of a conventional flat plate SOFC.

[Explanation of symbols]

1 unit power generation cell, 2 solid electrolyte, 3 oxidizer electrode, 4 fuel electrode, 5 interconnector, 6 oxidizer electrode substrate, 7 fuel electrode substrate, 8 fuel passage, 9 oxidant passage, 20 solid electrolyte (oxygen ion conduction A single cell using the body as an electrolyte material), 21 a fuel electrode, 22 an oxidant electrode 23 a solid electrolyte (a single cell using a proton conductor as an electrolyte material), 24 a fuel electrode, 25 an oxidant electrode, 26 a load, 27 Single cell using oxygen ion conductor as electrolyte material, 27 'Single cell using proton conductor as electrolyte material, 40 Middle cell holder, 41 Lower cell holder, 42 Upper cell holder, 43 End current collector, 43 -1 slit, 44 oxidant electrode side intermediate portion current collector, 44-l insulating layer, 45 fuel electrode side intermediate portion current collector, 46 fuel supply port, 47 fuel discharge port, 48 current collecting line, 9 oxidant gas supply port.

Claims (2)

[Claims] 1. A solid electrolyte fuel in which an oxidant electrode and a fuel electrode are arranged via an electrolyte, and an oxidant gas such as air is supplied to the oxidant electrode and a fuel gas is supplied to the fuel electrode to generate electric power. A battery, a single cell formed by using a proton conductive material as an electrolyte material, and a single cell formed by using an oxygen ion conductive material as an electrolyte material, and these two types of single cells When forming a power generation module using, the two types of single cells are alternately arranged so that the oxidizer electrodes face each other and the fuel electrodes face each other. At this time, the electrodes contact each other between the facing electrodes. A solid oxide fuel cell characterized in that a current collector is arranged as described above. 2. The SrC as the proton conducting material
_{e 1-X M X O 3} (M: scandium, yttrium, ytterbium, X = 0.01 to 0.5) or, BaCe
_1-X M _X O ₃ (M: neodymium, lanthanum, gadolinium,
X = 0.01 to 0.5), as the oxygen ion conductive material, zirconia oxide having yttrium oxide added to stabilize the crystal structure,
Yttria-stabilized zirconia in which the amount of yttrium added is 5 to 10 mol%, and as the electrode material, when the proton-conducting material is an electrolyte, nickel is used as the fuel electrode and the oxidant electrode material is
(La _1-X M (1) _X ) _1-Y M (2) O ₃ (M (1): S
r, Ba, M (2): Mn, Co, X = 0.01 to 0.
5, Y = 0.01 to 0.10), when the oxygen ion conductive material is an electrolyte, a cermet composed of nickel and an electrolyte material as a fuel electrode, and (La _1-X M
(1) _X ) _1-Y M (2) O ₃ (M (1): Sr, Ca, M
(2): Mn, Co, X = 0.01 to 0.5, Y = 0.
01-0.10) is used.
The solid oxide fuel cell described.