JP2015032494A - Solid electrolyte fuel cell and solid electrolyte fuel cell stack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a solid electrolyte fuel cell good in bondability between an electrode and a solid electrolyte in a high temperature operation, improved in output, and suppressed in breakage; and a fuel cell stack.SOLUTION: A solid electrolyte fuel cell comprises a support 1, an intermediate layer 2, an air electrode layer 3 and a solid electrolyte layer 4 which are laminated in the order. A cell having a structure where a fuel electrode layer is laminated on the electrolyte layer 4 and the electrolyte layer 4 is sandwiched with the air electrode layer 3 and the fuel electrode layer is constituted. The cell has the intermediate layer 2 between the support 1 and the electrode layer 3. The temperature change of the thermal expansion coefficient of the intermediate layer 2 is similar or same to the temperature change of the thermal expansion coefficient of the solid electrolyte layer 4. A fuel cell stack is obtained by stacking the solid electrolyte fuel cells.

Description

  The present invention relates to a solid oxide fuel cell and a solid oxide fuel cell stack formed by laminating the same, and more particularly, the electrode and the solid electrolyte have good bondability during high-temperature operation, and the output is improved. The present invention relates to a solid oxide fuel cell and a fuel cell stack that can prevent damage during operation.

Conventionally, it is known that a fuel cell is a device that converts chemical energy into electrical energy through an electrochemical reaction.
In a solid oxide fuel cell that is one type of such fuel cell, each layer of a fuel electrode, a solid electrolyte, and an air electrode is laminated, and this is used as a power generation part of the fuel cell to supply fuel gas such as hydrogen or hydrocarbon from the outside. The fuel electrode is supplied, and the air electrode is supplied with an oxidant gas such as air to generate electricity.

  In such a solid oxide fuel cell (SOFC), in order to increase the output per unit volume by reducing the thickness of the battery (cell), it is necessary to improve the mechanical strength of the cell. A so-called support cell structure in which one electrode (for example, a fuel electrode) is formed, a solid electrolyte is formed on the upper surface of the electrode, and the other electrode (for example, an air electrode) is further formed on the upper surface of the solid electrolyte is generally used. (For example, refer to Patent Document 1).

In Patent Document 1, a process for forming a dense fuel electrode containing a metal oxide on a dense metal substrate is disclosed.
The steps include a step of forming a plurality of through holes communicating with the fuel electrode on the metal substrate, a step of forming a dense electrolyte on the fuel electrode, and a step of forming a porous air electrode on the electrolyte. The support cell structure is formed through these steps.

JP 2008-226478 A

However, in such a conventional support cell structure, the cell expansion due to the difference in thermal expansion occurs particularly during high temperature operation, because the coefficient of thermal expansion of the joined electrode and the solid electrolyte are different. In the worst case, the distortion may cause cell breakage, which may reduce the output of the fuel cell.
That is, since the electrode generally has a larger coefficient of thermal expansion than the solid electrolyte, the cell bends so that the solid electrolyte side is recessed during high-temperature operation, resulting in poor bonding and increased IR resistance. The cell output is reduced, and in the worst case, the cell may be damaged.

  The present invention has been made in view of such problems of the prior art, and the object of the present invention is that the electrode and the solid electrolyte have good bondability during high temperature operation, the output is improved, and damage is suppressed. Another object of the present invention is to provide a solid oxide fuel cell and a fuel cell stack.

  As a result of intensive studies to achieve the above object, the present inventor has found that the above object can be achieved by appropriately arranging a predetermined intermediate layer, and has completed the present invention.

That is, the solid oxide fuel cell of the present invention has a structure in which a solid electrolyte layer is sandwiched between a fuel electrode layer and an air electrode layer, and one of the fuel electrode layer and the air electrode layer has gas permeability and conductivity. A solid oxide fuel cell which is an electrode layer with a support formed on a support having the support.
A gas-permeable intermediate layer made of a nonmetallic material having a temperature dependency of a thermal expansion coefficient equivalent to that of the solid electrolyte layer is provided between the support of the electrode layer with the support and the electrode layer. To do.

  Further, the solid oxide fuel cell stack of the present invention is configured by stacking the above solid oxide fuel cells.

  According to the present invention, since the predetermined intermediate layer is appropriately arranged, the solid electrolyte fuel cell and the fuel cell in which the electrode and the solid electrolyte are well bonded during high temperature operation, the output is improved, and the damage is suppressed. A stack can be provided.

It is a fragmentary sectional view showing an example of the solid oxide fuel cell of the present invention. 4 is a partial cross-sectional view showing a joined body of a support 1, an intermediate layer 2, and an electrode layer 3 in another example of the solid oxide fuel cell of the present invention. FIG. It is a fragmentary sectional view showing other examples of a solid oxide fuel cell of the present invention. It is a microscope picture which shows a support body and an intermediate | middle layer. It is a microscope picture which shows the cross section of an intermediate | middle layer. It is a graph which shows the evaluation result of a flatness improvement degree. It is a graph which shows the temperature change of the thermal expansion coefficient of a metal material and a ceramic material.

Hereinafter, the solid oxide fuel cell of the present invention will be described.
FIG. 1 is a partial cross-sectional view showing an example of a solid oxide fuel cell of the present invention.
In this figure, in this solid oxide fuel cell, a support 1, an intermediate layer 2, an electrode layer (air electrode layer) 3, and a solid electrolyte layer 4 are laminated in this order (see FIG. 1A).
An electrode layer (fuel electrode layer) (not shown) is laminated on the solid electrolyte layer 4, and thereby a structure in which the solid electrolyte layer 4 is sandwiched between the air electrode layer 3 and the fuel electrode layer (not shown). The solid oxide fuel cell is configured.

In the solid oxide fuel cell of this example, the electrode layer 3 can be referred to as a support-equipped electrode layer having the support 1, and this solid oxide fuel cell can be said to be a kind of battery having a so-called support cell structure. .
In this solid oxide fuel cell, the intermediate layer 2 is provided between the support 1 and the electrode layer 3, and the temperature dependence of the thermal expansion coefficient of the intermediate layer 2, in other words, the thermal expansion coefficient. This temperature change is similar to or the same as the temperature change of the thermal expansion coefficient of the solid electrolyte layer 4.

Therefore, in the solid oxide fuel cell of this example, as shown in FIG. 1B, the thermal expansion of the electrode layer 3 is regulated by the solid electrolyte layer 4 and the intermediate layer 2 sandwiching the electrode layer 3 during high temperature operation. Will be.
Specifically, since the thermal expansion coefficient of the solid electrolyte layer 4 is generally larger than that of the electrode layer 3, the electrode layer 3 is compressed and held while being sandwiched between the solid electrolyte layer 4 and the intermediate layer 2. Will be.

Thus, in the solid oxide fuel cell of this example, the thermal expansion of the electrode layer 3 is suppressed by the solid electrolyte layer 4 and the intermediate layer 2, so that distortion of the entire battery (entire cell) is suppressed. .
Therefore, the solid oxide fuel cell of this example can maintain good bonding properties between the solid electrolyte 4 and the electrode layer 3 even during high temperature operation, and the IR resistance is difficult to increase, so that the output is difficult to reduce, and thermal distortion Can effectively prevent cell damage.

  The temperature dependence of the thermal expansion coefficient specifically means a change in the thermal expansion coefficient at 550 ° C. to 1250 ° C., and the change in the thermal expansion coefficient between the solid electrolyte layer and the intermediate layer in this temperature range is almost the same. It is desirable to be.

FIG. 2 is a partial cross-sectional view showing a joined body of the support 1, the intermediate layer 2, and the electrode layer 3 in another example of the solid oxide fuel cell of the present invention.
In the figure, a part of the support 1 penetrates through the intermediate layer 2 and enters the electrode layer 3 to form an entry portion 1a.

In a solid oxide fuel cell having a support cell structure, the support 1 needs to be electrically conductive, and usually a conductive metal is used. In this example, the entry portion 1 a of the support 1 is formed on the electrode layer 3. While entering and ensuring electrical connection, even when the intermediate layer 3 is thermally expanded and deformed, the support 1 (and the entry portion 1a) follows and deforms.
Therefore, if the configuration as in this example is adopted, the support 1 is prevented from being cut off as the intermediate layer 3 is deformed, and a reliable electrical connection is ensured. Can fully function as a body.

  In addition, in this example, although the entrance part 1a is based also on the material of the intermediate | middle layer 3 to be used, it is preferable that the constituent material of the support body 1 is exposed in the one part or all part. And good electrical conductivity between the electrode layer 3 and the current collecting characteristics of the support 1 can be improved.

FIG. 3 is a partial cross-sectional view showing still another example of the solid oxide fuel cell of the present invention, and shows the same state as FIG.
As in the example shown in FIG. 2, a part of the support 1 penetrates the intermediate layer 2 and enters the electrode layer 3 to form the entry portion 1 b. In this example, the entry portion 1 b is electrically conductive. It is formed by particles.
Further, similarly to the example shown in FIG. 2, in this example as well, it is desirable that the whole or a part of the entry portion 1 b is formed of the support constituent material.

  Next, materials such as an air electrode that are constituent elements of the solid oxide fuel cell described above will be described.

First, metal powder particles such as silver (Ag) and platinum (Pt) may be used as the air electrode, but in general, a perovskite structure typified by LaSrMnO (LSM) or LaSrCoO (LSC) is used. The oxide powder particles are used.
The necessary characteristics of this air electrode are that it is resistant to oxidation, permeates oxidant gas (typically air or oxygen), has high electrical conductivity, and excels in its catalytic action to convert oxygen molecules into oxygen ions. Can be mentioned.

On the other hand, noble metals such as nickel (Ni), cobalt (Co) and Pt, cermet of Ni and solid electrolyte, etc. are generally used for the fuel electrode.
The characteristics required for this fuel electrode include that it is strong in a reducing atmosphere, permeates the fuel gas, has high electrical conductivity, and has an excellent catalytic action for converting hydrogen molecules into protons.

  At the air electrode, oxygen gas molecules decompose into oxygen ions and electrons at the three-phase interface that becomes the active point, and the oxygen ions pass through the solid electrolyte layer to the fuel electrode, and at the fuel electrode, the three-phase also becomes the active point. At the interface, it reacts with oxygen ions, fuel gas molecules, and electrons conducted from the solid electrolyte layer.

As the solid electrolyte, in general, stabilized zirconia in which Y ₂ O ₃ , Nd ₂ O ₃ , Sm ₂ O ₃ , Gd ₂ O _3, Sc ₂ O _3, or the like is used as a solid solution is used, and a CeO ₂ solid solution is used. Inorganic oxides such as Bi ₂ O ₃ and LaGaO ₃ are used.
What is particularly important in the solid electrolyte layer is that it has the ability to pass ions without passing electrons, and when oxygen ions are power generation conductors, it is desirable that oxygen ions have a high conduction characteristic. It is also required to be gas impermeable.

Next, as the constituent material of the intermediate layer, any non-metallic material having a temperature dependence of the coefficient of thermal expansion equivalent to that of the solid electrolyte as described above is sufficient. The same kind of material may be selected.
For example, when a predetermined stabilized zirconia is used as the solid electrolyte, the predetermined stabilized zirconia may be selected as the intermediate layer. However, even in this case, it is important that the temperature dependence of the thermal expansion coefficient is the same, and there is no problem even if the concentration of the stabilizer doped in zirconia is slightly different.

The support is formed of a conductive material that also serves as an electrode current collector for the purpose of improving the output per unit volume of the battery. However, in order to supply fuel gas or oxidant gas to the electrode, the support is also gas permeable. Required.
Therefore, a nonwoven fabric made of a conductive material or a porous structure can be used as the support. Moreover, as a material of a support body, a single metal, an alloy, a ceramics-metal mixed material, etc. are mentioned.

Next, the manufacturing method of the solid oxide fuel cell of this invention is demonstrated.
This solid oxide fuel cell can be manufactured by a conventionally known method using the constituent materials of the constituent elements described above.
However, in the present invention, it is preferable to use a film forming method in which particles of the electrode constituent material collide with a solid electrolyte substrate or the like.

In other words, it is preferable to use a film forming method in which the powdery constituent material particles are given an optimum flow velocity with a carrier gas such as helium (He) or nitrogen (N ₂ ), and this powder flow collides with a solid electrolyte or the like. .
At this time, the size of the constituent material particles is preferably in the range of submicron to 5 μm. When the thickness exceeds 5 μm, it may be difficult to form an appropriate thin film.
Thus, if the intermediate layer is formed by the method of spraying the constituent material, it is not necessary to apply a high temperature sintering process, and the manufacturing cost of the cell can be reduced.

Examples of the film formation method by collision include a powder jet deposition method, a worm spray method, a thermal spray method, an aerosol deposition method, and a cold spray method.
In particular, the intermediate layer is preferably formed by the film forming method as described above, in which the nonmetallic material powder constituting the intermediate layer is sprayed on the support.
The structure shown in FIG. 3 is formed when a metal material, for example, a SUS non-woven fabric is used as the support 1 and the intermediate layer constituting material is formed into a film by the above method.

  The solid oxide fuel cell stack of the present invention is obtained by stacking the solid oxide fuel cells described above using an interconnector or the like, and has excellent durability and output due to the solid oxide fuel cell. Demonstrate the characteristics.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these Examples.

Example 1
The electrode layer was sandwiched between YSZ intermediate layers, in which the temperature change in the coefficient of thermal expansion was similar to or the same as that of the YSZ solid electrolyte layer.
A metal nonwoven fabric made of SUS (wire diameter φ5 μm, minimum opening diameter 10 μm) was used for the support. The YSZ particles were placed on a high-speed He gas by a supersonic nozzle and sprayed onto the support to produce an intermediate layer on the support (see FIG. 4A).

When the cross section was observed after the formation of the intermediate layer, an intermediate layer composed of a YSZ layer was formed on the support, and some metal fibers of the support penetrated the intermediate layer and entered the intermediate layer (FIG. 4). (See (B)). Moreover, it was confirmed that the YSZ particle | grains did not adhere to the metal fiber which entered the intermediate | middle layer, and the metal was exposed (refer FIG. 4 (B)).
In addition, when the cross section of the intermediate | middle layer (YSZ part) was observed, it turned out that the porous structure is taken (refer FIG. 5).

Next, an LSCF (LaSrCoFe) paste was applied by screen printing on the metal nonwoven fabric support on which the YSZ intermediate layer was formed as described above, and then dried at 100 ° C. or higher to form an air electrode.
Further, a YSZ paste as a solid electrolyte was applied on the air electrode by screen printing and baked at 900 ° C. or higher, and the support, the intermediate layer, the air electrode and the solid electrolyte were laminated in this order. A single electrode cell having a layer structure was obtained.
When the obtained one-electrode cell of this example was observed in cross section, the thickness of the intermediate layer, the electrode, and the solid electrolyte layer were all 15 μm.
In addition, when the air electrode was printed and the electrical conductivity between the air electrode and the support was confirmed by a tester, it was found that the air electrode and the support were electrically connected.

(Comparative Example 1)
A single electrode cell of this example was obtained by repeating the same operation as in Example 1 except that the intermediate layer was not formed.

(Comparative Example 2)
As a comparative example, the same operation as in Example 1 was repeated except that SUS430, which is the same metal species as the metallic nonwoven fabric, has a temperature change in the coefficient of thermal expansion different from that of the YSZ solid electrolyte layer. A single electrode cell was obtained.
The same conduction check as described above was performed, and the conduction between the air electrode and the support was confirmed.

<Performance evaluation>
(Flatness change)
The single electrode cell was exposed to a temperature of 750 ° C. in the atmosphere for 1 hour, and the warpage of the cell surface before and after this thermal history was measured and evaluated as a flatness change value. Note that the single electrode cell having the above-described configuration warps upward after the thermal history. That is, the support is curved so that it protrudes (the solid electrolyte layer is recessed).
As a result, the flatness change value of the single electrode cell of Example 1 was 0.009 μm on average, whereas the flatness change value of the single electrode cell of Comparative Example 1 having no intermediate layer was 0 on average. .19 μm, and according to the single electrode cell of Example 1, the thermal expansion of the electrode layer is regulated by the YSZ solid electrolyte and the YSZ intermediate layer sandwiching the electrode layer, so that the warp due to the thermal history is effectively suppressed. I understand that.

(Flatness improvement)
For the one-side electrode cells of Example 1 and Comparative Examples 1 and 2, the degree of flatness improvement was calculated by the following method.
(1) Measure the expansion coefficient of the SUS430 porous material to be the intermediate layer and calculate the strain.
(2) The distortion of each member, that is, the support, the LSFC electrode layer, and the YSZ electrolyte layer when there is no intermediate layer (YSZ) is calculated from the warpage value of the change in flatness.
In this case, if each member is deformed by thermal expansion, each member strain ε = expansion coefficient × ΔT.
(3) Combining (1) and (2) above, the strain (ε) = warpage of the whole cell when the intermediate layer is a metal, the porous support, the intermediate layer (SUS430) having a thickness of 15 μm, the thickness of 15 μm The calculation is made on the assumption that the layers of the laminate model in which the LSCF electrode layer and the 15 μm-thick YSZ electrolyte layer are laminated in this order are completely joined.
In this case, the internal stress σi in each member is calculated as strain (ε) × Ei (Young's modulus).
Since the force applied to the whole is balanced, the total internal stress Σ in each member is set to ΣσiAi = 0 and is calculated by convergence calculation so as to match the actual measurement value.

The result of the obtained flatness improvement degree is shown in FIG. As shown in the figure, the flatness improvement degree of the one-side electrode cell of Example 1 is improved by 90% with respect to Comparative Example 1 without the intermediate layer and 70% with respect to Comparative Example 2 in which the intermediate layer is SUS430. It is clear that it has excellent effects.
In addition, FIG. 7 also shows that the metal material of SUS430 used for the intermediate layer in Comparative Example 2 changes abruptly at 600 ° C. or more as compared with ceramic materials such as YSZ.
As described above, the intermediate layer having a large change in the coefficient of thermal expansion cannot match the difference in coefficient of thermal expansion between the solid electrolyte layer and the electrode layer, and distortion occurs again, resulting in cell damage and reducing the output of the fuel cell. Needless to say, there is a fear.

  As mentioned above, although this invention was demonstrated with some embodiment and an Example, this invention is not limited to these, A various deformation | transformation is possible within the range of the summary of this invention.

DESCRIPTION OF SYMBOLS 1 Support body 1a, 1b Entrance part 2 Intermediate | middle layer 3 Electrode layer (air electrode)
4 Solid electrolyte layer

Claims (8)

An electrode with a support having a structure in which a solid electrolyte layer is sandwiched between a fuel electrode layer and an air electrode layer, and one of the fuel electrode layer and the air electrode layer is formed on a support having gas permeability and conductivity. In a solid oxide fuel cell that is a layer,
A gas-permeable intermediate layer made of a nonmetallic material having a temperature dependency of a thermal expansion coefficient equivalent to that of the solid electrolyte layer is provided between the support of the electrode layer with the support and the electrode layer. Solid electrolyte fuel cell.   2. The solid oxide fuel cell according to claim 1, wherein the temperature dependence of the coefficient of thermal expansion means a change in coefficient of thermal expansion at 550 to 1250 ° C. 3.   3. The solid oxide fuel cell according to claim 1, wherein a part of the support passes through the intermediate layer and enters the electrode layer. 4.   4. The solid oxide fuel cell according to claim 3, wherein a constituent material of the support is exposed at all or a part of the support portion entering the electrode layer.   The solid oxide fuel cell according to any one of claims 1 to 4, wherein the support is made of a porous structure having conductivity.   6. The solid oxide fuel cell according to claim 5, wherein the support is a conductive nonwoven fabric.   The solid oxide fuel cell according to any one of claims 1 to 6, wherein the intermediate layer is formed by spraying a nonmetallic material powder on the support.   A solid oxide fuel cell stack comprising the solid oxide fuel cells according to any one of claims 1 to 7 stacked.

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