JP2005019268A - Stack structure of solid oxide fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stack structure of a solid oxide fuel cell in which fuel and oxidant gas supplied to cells are separated excellently and the cells can be laminated sturdily and mechanically for a metal separators having different coefficients of thermal expansion. <P>SOLUTION: This solid oxide fuel cell is composed of flat type fuel battery unit cells each constructed of an electrolyte, a fuel electrode, and an air electrode, of interconnectors for electrically connecting the unit cells, and of gas passages for supplying fuel and oxidant gas to each cell. Cell holders which are made of electrically insulating materials having relatively near coefficients of thermal expansion as the unit cells are provided, and perform the separation of the fuel gas and oxidant gas supplied to the cell, and allow sideslip due to thermal expansion between the interconnectors to be laminated by keeping flat the surface of the cell holders which is not the contacting surface with the cell. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for constructing a solid oxide fuel cell, and more particularly to a cell stack structure of a flat plate solid oxide fuel cell.
[0002]
[Prior art]
A fuel electrode and an oxidant electrode are arranged via a ceramic electrolyte, and finally hydrogen is supplied as a fuel and oxygen or air is supplied as an oxidant to generate electricity using the reverse reaction of water electrolysis. In the solid oxide fuel cell, in order to obtain a practically sufficient power generation amount of the fuel cell, a plurality of unit components (single cells) of the above-described solid oxide fuel cell are electrically connected in series and in parallel. It is necessary to connect to (stack).
[0003]
During the operation of the fuel cell, the negative electrode side (fuel electrode side) of the battery is exposed to a reducing atmosphere, and the positive electrode side (oxidant electrode side) is exposed to an oxidizing atmosphere. Therefore, it is necessary to keep the fuel cell main body at a high temperature of 600 ° C. or higher so that the ionic conductivity is ensured. Therefore, in a solid oxide fuel cell, the positive electrode and negative electrode exposed to different atmospheres are electrically connected by a component (interconnector) made of ceramic material or metal material that is impermeable to gas and electrically conductive. There is a need to.
[0004]
5 and 6 show a flat plate fuel cell, the fuel cell of FIG. 5 has a structure in which an electrolyte 51 and an air electrode 53 having an area smaller than that of the electrolyte 51 are provided on a fuel electrode substrate 52. On the other hand, in FIG. 6, the fuel electrode 62 and the air electrode 63 having an area smaller than that of the electrolyte substrate 61 are provided on both surfaces of the electrolyte substrate 61.
[0005]
In the case where the above-described connection is made to the flat-type fuel cell shown in FIGS. 5 and 6, there are roughly two methods. A method in which all parts that stack with only materials with similar coefficients of thermal expansion are configured to firmly connect and seal between cells (rigid structure stack) and a method in which materials with different thermal expansion are stacked and bonded only by load ( Flexible structure stack).
[0006]
The flexible stack has a lot of merits, such as the structure of the cell stack becomes simple and the thermal expansion coefficient is not constrained, so the choice of materials including metal materials is widened and the reliability is relatively high. In general, it is difficult to seal the fuel gas, and it is difficult to apply to the fuel electrode cell of the fuel electrode support type (FIG. 5).
[0007]
In addition, when such stacks are stacked in the vertical direction, an excessive force is applied to the cells located at the bottom of the stack, which may restrict system design. On the other hand, if a rigid stack is taken, the fuel gas can be sealed, and there is a degree of freedom in system design, such as a pressurization system and a fuel gas recovery mechanism, but a slight difference in the coefficient of thermal expansion causes the stack to break. The stack design is more difficult than the flexible stack, and the reliability is poor.
[0008]
[Non-Patent Document 1]
SOLID OXIDE FUEL CELLS VII (SOFCVII) (Proceedings of the 7th International Symposium; 2001-16; edited by H. Yokokawa, SC Singhal)
[0009]
[Problems to be solved by the invention]
The object of the present invention is to solve the above-mentioned problems of the prior art, and can form a stack regardless of whether the cell is an electrolyte-supported type or a fuel-electrode-supported type. Is to construct a stack equivalent to a rigid structure stack. Further, according to the present invention, the cell body has a structure in which a load due to lamination is not applied, so that the stack can be designed independently of the mechanical characteristics of the cell.
[0010]
[Means for Solving the Problems]
To achieve the above object, the structure of a solid oxide fuel cell stack according to the present invention includes a solid oxide fuel cell (SOFC) unit cell electrically connected via an interconnector. A battery stack structure, at least one of which is provided with a cell holder made of a material having a thermal expansion coefficient close to that of the single cell so as to sandwich the single cell from above and below, and a cell made of a material having a thermal expansion coefficient close to that of the single cell The holder performs gas sealing on the electrolyte surface side of the single cell, and also keeps the contact surface with the interconnector side of the cell holder smooth, providing a mechanism that is immune from stress generation and breakage due to thermal expansion differences. Have.
[0011]
According to the present invention, a flat plate fuel cell unit cell composed of an electrolyte, a fuel electrode, and an air electrode, an interconnector that electrically connects the unit cell, and a gas that supplies fuel and oxidant gas to each cell In a solid oxide fuel cell comprising a flow path, a fuel gas supplied to a cell by providing a cell holder made of an electrically insulating material having a relatively close thermal expansion coefficient to that of the single cell. And oxidant gas are separated, and at the same time, the load on the cell is reduced and the reliability is improved. And when laminating parts made of materials with different coefficients of thermal expansion by allowing the sides that are not cell contact surfaces of the cell holder to be smooth and allowing side slip due to thermal expansion between the stacked interconnectors. Thus, a highly reliable SOFC stack can be obtained.
[0012]
The present invention will be described in more detail. As shown in FIG. 1, when stacking flat plate type solid oxide fuel cells, cell holders 12 and 13 are provided so as to sandwich the single cell 11. Among the cell holders of the present invention, 12 electrolyte surface side cell holders are in contact with the electrolyte surface 111 of the single cell 11, and a sealing material 121 for sealing the oxidant gas is disposed on the contact surface. The substrate surface side cell holder 13 is in contact with the substrate surface (fuel electrode substrate) 112 of the single cell 1 via the buffer material 131.
[0013]
At this time, an insulating material having a thermal expansion coefficient close to that of the constituent material of the single cell 11 is used for the cell holders 12 and 13. As a result, when the cell holders 12 and 13 are brought into close contact with each other, the cell 11 can be disposed between the cell holders 12 and 13 with the electrolyte surface 111 sealed. Only the force due to the buffer material 131 being pressed and crushed is applied to the cell 11. Further, the surface of the cell holders 12 and 13 that does not contact the cell 11 (interconnector side) is made as smooth as possible, and can slide sideways with the contact surface with the interconnector 14 to be laminated. Yes.
[0014]
Depending on the stress due to thermal expansion, it is possible to use, among the above-mentioned cell holders, the substrate surface side cell holder 13 having a thermal expansion coefficient different from that of the cell 11, for example, the same material as the interconnector 14. can do. In this case, the substrate surface side cell holder 13 and the interconnector 14 can be the same component.
[0015]
[Action]
By providing the cell holder and stacking in the order of interconnector 14-substrate surface side cell holder 13-single cell 11-electrolyte surface side cell holder 12, substrate surface side cell holder 13-single cell 11 The gas seal between the cell and the cell holder can be at the same level as that of the rigid stack in the portion of the cell holder 12 on the electrolyte surface side. The gas seal between the cell holders 12 and 13 and the interconnector 14 can be secured only by a load by ensuring sufficient flatness of each component.
[0016]
In actual lamination, the load is applied only to the cell holders 12 and 13 and the interconnector 14 by adjusting the height of the current collecting surface 15 of the interconnector 14, so that an excessive load is prevented from being applied to the cell. Can do.
[0017]
Furthermore, the flat surfaces between the cell holders 12 and 13 and the interconnector 14 on the joint surface are merely overlapped, and the difference in thermal expansion coefficient between the cell holders 12 and 13 and the interconnector 14 is reduced by sliding. Therefore, the material used for the interconnector can be selected regardless of the thermal expansion characteristics of the single cell or the cell holder.
[0018]
【Example】
Hereinafter, the present invention will be described with reference to the drawings.
[0019]
FIG. 2 is a view showing an example of a laminated structure when the present invention is applied to a circular plate type fuel electrode supported fuel cell. 21 is a single cell. As a constituent material of a single cell, it can be applied to all material systems that are generally developed.
[0020]
For example, a zirconia material such as Sc ₂ O ₃ and Al ₂ O ₃ stabilized zirconia (SASZ) or yttria stabilized zirconia (YSZ) is used for the electrolyte 211, and these zirconia materials and nickel oxide are used as the fuel electrode substrate 212. A mixed cermet can be used. In this case, the average coefficient of thermal expansion of the cell from 800 ° C. to 1000 ° C. is about 10 to 11 × 10 ⁻⁶ / K.
[0021]
For such a material cell, macerite, which is a kind of engineering ceramics, can be used to produce the cell holders 22 and 23. The average thermal expansion coefficient of macerite is 10.3 × 10 ⁻⁶ / K, which is very close to the thermal expansion coefficient of a cell using a zirconia-based material, and functions as a good cell holder.
[0022]
As is clear from this figure, the unit cell 21 has the electrolyte 211 surface through the electrolyte surface side cell holder 22 via the sealing material 221, and the fuel electrode substrate 212 surface through the substrate surface side cell holder 23 through the buffer material 231. It is pinched. That is, in this case, the stacking of the electrolyte surface cell holder 22 -the single cell 21 -the substrate surface cell holder 23 can be fixed and sealed by sandwiching the sealing material 221 and the buffer material 231 as shown in FIG. it can.
[0023]
As the sealing material in this case, a glass material such as borosilicate glass or barium silicate glass, a mixture of glass wool and the glass material, a mixture of an alumina adhesive and a glass material, or the like can be used. The glass material to be used is selected from those having an appropriate softening point and working point in accordance with the operating temperature of the fuel cell. As the buffer material, almost any material that can be deformed, such as glass wool, foam metal, and metal net, can be used.
[0024]
A cell stack can be configured by stacking the cell 21-cell holders 22 and 23, the fuel gas flow channel 26, and the interconnector 24 provided with the oxidant gas flow channel 27, which are produced in this manner. Various metal materials including a ferritic stainless material such as SUS430 can be used for the interconnector. Of course, you may comprise with the conductive ceramics represented by the lanthanum chromite type | system | group. On one surface of the interconnector 24, a groove (not shown) for allowing the fuel gas to pass is formed from one fuel gas channel 26 to the other fuel gas channel 26 through the current collecting surface 25. Yes. On the other surface of the interconnector 24, a groove 271 for allowing the oxidant gas to pass therethrough is formed from one oxidant gas flow path 27 through the current collecting surface 25 to the other fuel gas flow path 27. .
[0025]
At this time, regardless of which material is used, it is important to adjust the height of the current collecting surface 25 of the interconnector 24 so that the cell is not overloaded. Further, a current collecting material having a buffer function such as foam metal, metal net, or expanded metal may be sandwiched between the cell 21 and the current collecting surface 25. The cell stack configured as described above has good gas seal characteristics and stability, and also shows a strong characteristic against a load due to a stress on a thermal history. Moreover, a metal can also be used for the separator material and can be determined independently of the cell constituent material.
[0026]
The present invention can be applied to all shapes such as a square in addition to the circular cell shown in the example.
[0027]
Further, the present invention can be applied not only to a fuel electrode support type cell but also to an electrolyte support type cell. An example of this configuration is shown in FIG. In this case, there is no distinction between the electrolyte surface side cell holder and the substrate surface side cell holder such as 12, 13 in FIG. 1 and 22, 23 in FIG. That is, in the case of a self-supporting cell, the fuel electrode and the air electrode are formed on both surfaces of the electrolyte substrate 411. Cell holders 42 are stacked on both surfaces of the unit cell 41 with a sealant 421 interposed therebetween. A stack is formed by further stacking an interconnector 43 on the cell holder 42.
[0028]
【The invention's effect】
By using the present invention, it is possible to freely select a material for an interconnector, whether it is a cell of a fuel electrode substrate or a cell of an electrolyte substrate, and has a solid gas oxidation and mechanical robustness. A physical fuel cell stack can be constructed.
[Brief description of the drawings]
FIG. 1 is a diagram showing a stack configuration of the present invention.
FIG. 2 is an overhead view of a configuration of a circular flat plate fuel cell stack.
FIG. 3 is an enlarged view of a cell-cell holder joint.
FIG. 4 is a view showing a stack configuration of an electrolyte supported flat solid oxide fuel cell.
FIG. 5 is a cross-sectional view of a flat electrode type solid oxide fuel cell supported by a fuel electrode.
FIG. 6 is a cross-sectional view of an electrolyte-supported planar solid oxide fuel cell.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Single cell 12 Electrolyte side cell holder 121 Seal material 13 Substrate surface side cell holder 131 Buffer material 14 Interconnector 15 Current collecting surface 16 Fuel gas flow path 17 Oxidant gas flow path 21 Single cell 22 Electrolyte side cell holder 221 Seal Material 23 Substrate surface side cell holder 231 Buffer material 24 Interconnector 25 Current collecting surface 26 Fuel gas flow channel 27 Oxidant gas flow channel 31 Single cell 32 Electrolyte surface side cell holder 33 Substrate surface side cell holder 34 Electrolyte surface 35 Substrate surface 36 Seal material 37 Buffer material 41 Single cell 411 Electrolyte substrate 412 Fuel electrode 42 Cell holder 421 Seal material 44 Interconnector 51 Electrolyte 52 Fuel electrode substrate 53 Air electrode 61 Electrolyte substrate 62 Fuel electrode 63 Air electrode

Claims (5)

A solid oxide fuel cell stack structure in which flat cell solid oxide fuel cell single cells are electrically connected via an interconnector, at least one of which is made of a material having a thermal expansion coefficient close to that of the single cell The cell holder is provided so as to sandwich the single cell from above and below, and the cell holder made of a material having a coefficient of thermal expansion close to that of the single cell performs gas sealing on the electrolyte surface side of the single cell, and the cell holder interconnector A solid oxide fuel cell stack structure characterized by maintaining a smooth contact surface with the side. A cell holder is laminated on the electrolyte surface of a fuel electrode-supported fuel cell single cell in which an electrolyte and an air electrode having an area smaller than the surface of the electrolyte are provided on a fuel electrode substrate, through a sealing material. 2. A stack structure of a solid oxide fuel cell according to 1. 3. The stack structure of a solid oxide fuel cell according to claim 2, wherein a cell holder is laminated on the substrate surface side of the single cell via a buffer material. 2. A cell holder is laminated on the electrolyte substrate of an electrolyte-supporting fuel cell single cell in which a fuel electrode and an air electrode each having an area smaller than the substrate are provided on both surfaces of the electrolyte substrate via a sealing material. A stack structure of the described solid oxide fuel cell. 4. The stack structure of a solid oxide fuel cell according to claim 1, wherein a cell holder on the substrate surface side of the cell holder is made of the same material as that of the interconnector.

Images