JP7285117B2 - Materials for Forming Substrates of Solid Oxide Fuel Cells and Their Applications - Google Patents

Description

TECHNICAL FIELD The present invention relates to a solid oxide fuel cell in which a fuel electrode, a solid electrolyte layer and an air electrode are laminated on an insulating support.

A solid oxide fuel cell (SOFC) comprises a solid electrolyte layer made of an oxide ion conductor, an air electrode (cathode), and a fuel electrode (anode). In such an SOFC, oxygen in the air supplied to the air electrode is electrochemically reduced to oxygen ions, and the oxygen ions reach the fuel electrode via the solid electrolyte layer. Then, the fuel gas (hydrogen or the like) supplied to the fuel electrode is oxidized by the oxygen ions from the air electrode, electrons are emitted to the external load, and electrical energy is generated. Such SOFCs are considered next-generation power generation equipment because of their high power generation efficiency, their low environmental impact due to their low emissions of substances that cause air pollution, and their ability to use a variety of fuels. is being developed as

For example, an SOFC may employ a structure in which a laminate including a fuel electrode, a solid electrolyte layer, and an air electrode is formed on an insulating support (hereinafter referred to as "insulating support"). Such an insulating support has a role of supplying and diffusing the fuel gas to the fuel electrode in addition to the role of retaining the shape of the battery. Therefore, the insulating support is required to have a predetermined strength and a structure that allows a large amount of fuel gas to permeate. Prior arts related to such SOFC supports include those described in Patent Documents 1 and 2. These patent documents 1 and 2 disclose the use of metal oxides such as NiO, Y ₂ O ₃ , MgO, MgAl ₂ O ₄ and TiO ₂ as materials for the support substrate.

JP 2012-94323 A JP 2017-174498 A

By the way, as a method for manufacturing an SOFC, there is a method in which an insulating support, a fuel electrode, a solid electrolyte layer, and an air electrode are sequentially laminated and fired one by one, and a precursor material (green sheet) for each layer is laminated and then summarized. and firing method (co-firing). Among these, co-firing has the advantage of being able to reduce manufacturing steps and reduce costs.

However, when an SOFC is manufactured using co-firing, cracks may occur at the boundary between the fuel electrode and the solid electrolyte layer after firing. Such cracks occur because the solid electrolyte layer, which is a dense layer, and the insulating support, which is a porous body, have different shrinkage rates (firing shrinkage rates) during firing. It is thought that this occurs when stress is applied to the boundary between

Therefore, when manufacturing an SOFC using co-firing, it has been considered to increase the firing shrinkage rate of the insulating support so that the solid electrolyte layer and the insulating support have similar firing shrinkage rates. However, if the firing shrinkage rate of the green sheet of the insulating support is increased, the insulating support after firing becomes denser and the gas permeability is lowered, thereby lowering the power generation performance.

The present invention has been made in view of such circumstances, and its object is to provide a technique capable of preventing the occurrence of cracks during co-firing and forming an insulating support having excellent gas permeability. be.

The present inventors conducted various experiments and studies in order to achieve the above object. As a result, it was found that cracks in co-firing can occur not only when the firing shrinkage rate differs as described above, but also when the shrinkage start temperature differs. For example, even if the firing shrinkage rate of the solid electrolyte layer and the firing shrinkage rate of the insulating support are approximated, if the solid electrolyte layer begins to shrink at a lower temperature than the insulating support, the Stress is applied to the interface with the electrolyte layer and cracks occur. Based on this discovery, the present inventors have found that if the heat shrinkage start temperature of the insulating support can be lowered to the same level as that of the solid electrolyte layer, cracks will occur even if the firing shrinkage rate of the insulating support is not increased more than necessary. can be prevented from occurring, it is thought that the decrease in gas permeability of the insulating support after firing can be suppressed. The support-forming material disclosed herein was made based on the above findings.

The present invention provides a support-forming material having the following constitution. In this specification, the term "support-forming material" refers to a powder material for forming the insulating support of the SOFC. More specifically, the "support-forming material" in this specification is the main component of the green sheet, which is the precursor of the insulating support.
The support-forming material disclosed herein is a mixed powder containing at least coarse-grained zirconia powder having an average particle diameter of 1 μm or more and 4 μm or less and fine-grained zirconia powder having an average particle diameter of 0.1 μm or more and 0.5 μm or less. and a sintering aid comprising transition metal oxide particles. In the support-forming material disclosed herein, the weight of the fine zirconia powder is 20 wt % or more and 80 wt % or less when the total weight of the mixed powder is 100 wt %, and the total weight of the mixed powder is 100 wt %. %, the content of the sintering aid is 0.1 wt % or more and 1.2 wt % or less.

In the support-forming materials disclosed herein, a sintering aid containing transition metal oxide particles is added. As a result, the shrinkage start temperature in co-firing can be lowered, and the occurrence of cracks in the initial stage of firing can be prevented. Further, the support-forming material disclosed herein uses a mixed powder containing coarse-grained zirconia powder and fine-grained zirconia powder. Such a mixed powder can improve the firing shrinkage rate of the insulating support, and thus can prevent the occurrence of cracks due to the difference in the amount of shrinkage after the middle stage of firing. In the support-forming material disclosed herein, from the viewpoint of preventing the occurrence of cracks during co-firing and forming an insulating support having excellent gas permeability, fine particles with respect to the total weight of the mixed powder The weight of the zirconia powder and the content of the sintering aid with respect to the mixed powder are specified.

In the present specification, the "average particle size" means a particle size corresponding to a cumulative 50% from the fine particle side in a volume-based particle size distribution measured by particle size distribution measurement based on a general laser diffraction/light scattering method. ( _D50 particle size, also referred to as median diameter).

In one preferred aspect of the support-forming material disclosed herein, the sintering aid has an average particle size of 0.02 μm or more and 30 μm or less. As a result, the sintering aid can be appropriately dispersed in the support-forming material, and the insulating support can be shrunk uniformly with a suitable amount of shrinkage at the initial stage of firing. It can be suitably prevented.

In one preferred aspect of _the support-forming material disclosed herein, the sintering aid is one or more particles selected from the group consisting of _Mn3O4 , NiO, CuO, _{Fe2O3 ,} ZnO, and CoO. including. Among transition metal oxides, these have a particularly low melting point and can suitably lower the shrinkage start temperature of the insulating support, thereby more suitably preventing the occurrence of cracks at the initial stage of firing.

Also, as another aspect of the present invention, a solid oxide fuel cell (SOFC) is provided. The SOFC disclosed herein is a porous body permeable to fuel gas, comprising an insulating support containing a zirconia-based component, a fuel electrode formed on the insulating support, and a solid material formed on the fuel electrode. It has an electrolyte layer and an air electrode formed on the solid electrolyte layer. The SOFC insulating support disclosed herein contains a transition metal oxide, and the total weight of the transition metal oxide is 0.1 wt % or more when the total weight of the zirconia-based components is 100 wt %. .2 wt% or less, and the porosity is 5% or more.

The SOFC is an SOFC manufactured using the support-forming material disclosed herein. The insulating support of such SOFCs contains a transition metal oxide derived from the sintering aid contained in the support-forming material. That is, in the SOFC insulating support disclosed herein, the total weight of the transition metal oxides is 0.1 wt % or more and 1.2 wt % when the total weight of the zirconia-based components derived from the mixed powder is 100 wt %. % or less. In the support-forming material described above, since various configurations are defined from the viewpoint of forming an insulating support having excellent gas permeability, the porosity of the insulating support after firing is 5%. That's it. An insulating support having such a porosity exhibits high gas permeability, and thus can contribute to improving the power generation performance of the SOFC.

1 is a diagram schematically showing the layer structure of an SOFC according to one embodiment of the present invention; FIG. It is a top view which shows typically the half cell produced in the test example. 4 is an image (magnification: 400 times) of the boundary between the fuel electrode and the solid electrolyte layer of Sample 1 observed with a laser microscope. 4 is an image (magnification: 400 times) of the boundary between the fuel electrode and the solid electrolyte layer of Sample 4 observed with a laser microscope. 4 is a surface SEM observation image of sample 6 (magnification: 10000 times). 4 is a surface SEM observation image of sample 10 (magnification: 10000 times). It is a surface SEM observation image of sample 14 (magnification: 10000 times).

Preferred embodiments of the present invention will now be described with reference to the drawings as appropriate. Matters other than those specifically mentioned in the present specification and necessary for the implementation of the present invention (for example, detailed components of each layer except for the insulating support, manufacturing methods, etc.) are known in the art. It can be grasped as a design matter of a person skilled in the art based on the conventional technology. The present invention can be implemented based on the contents disclosed in this specification and common general technical knowledge in the field. Further, in the drawings below, members and portions having the same function are denoted by the same reference numerals, and redundant description may be omitted or simplified. In this specification, the notation "X to Y (where X and Y are arbitrary values)" indicating a numerical range means "X or more and Y or less".

<Support forming material>
The support-forming materials disclosed herein are used to form the insulating support that supports the anode of the SOFC. Specifically, the insulating support of the SOFC can be formed by firing a green sheet containing the support-forming material disclosed herein as a main component.
The support-forming material disclosed herein contains a mixed powder and a sintering aid. Each component will be described below.

1. Mixed Powder The mixed powder in the support-forming material disclosed herein is a powder material containing zirconia-based oxide particles as a main component. Such a zirconia-based oxide is not particularly limited as long as it can be used for the insulating support of this type of SOFC, and various components can be used. As an example of such a zirconia-based oxide, stabilized zirconia obtained by adding a stabilizer to zirconia (ZrO ₂ ) is preferably used. A given metal oxide (M ₂ O ₃ or MO) can be used as a stabilizer in such stabilized zirconia. Here, the metal element (M) contained in the stabilizer includes one or more of Y, Sc, Ca, Yb, Gd and Mg. Preferred examples of the stabilized zirconia include yttria-stabilized zirconia (YSZ) stabilized with yttria (Y ₂ O ₃ ) and calcia-stabilized zirconia (CSZ) stabilized with calcia (CaO). . Among these, YSZ is preferable, and YSZ in which yttria is dissolved in an amount of 1 mol % or more and 15 mol % or less (preferably 1 mol % or more and 10 mol % or less) of the whole can be particularly preferably used.

The mixed powder disclosed herein contains two types of zirconia powders with different average particle diameters. Specifically, the mixed powder disclosed herein contains coarse-grained zirconia powder having a large average particle size and fine-grained zirconia powder having a small average particle size. By using a mixed powder in which two kinds of zirconia powders having different average particle diameters are mixed in an appropriate ratio, it is possible to prevent the occurrence of cracks after the middle stage of firing. A specific description will be given below.

Coarse-grained zirconia powder is zirconia powder having an average particle diameter of 1 μm or more and 4 μm or less. When the content of such relatively large zirconia particles increases, there is a tendency for the shrinkage rate (firing shrinkage rate) of the green sheet in cofiring to decrease. The average particle diameter of the coarse-grained zirconia powder may be 1.2 μm or more, or may be 1.4 μm or more. On the other hand, the upper limit of the average particle size of the coarse-grained zirconia powder may be 3 μm or less, or may be 2 μm or less. An example of the average particle size of such coarse-grained zirconia powder is 1.5 μm.

Fine zirconia powder is zirconia powder having an average particle size of 0.1 μm or more and 0.5 μm or less. When the content of such zirconia particles with a relatively small particle size increases, the firing shrinkage tends to increase. Incidentally, the average particle size of the fine zirconia powder may be 0.15 μm or more, or may be 0.2 μm or more. On the other hand, the upper limit of the average particle diameter of fine zirconia powder may be 0.45 μm or less, 0.4 μm or less, or 0.3 μm or less. An example of the average particle size of such fine-grained zirconia powder is 0.25 μm.

In the mixed powder disclosed herein, the weight of the fine zirconia powder is specified to be 20 wt % or more and 80 wt % or less when the total weight of the mixed powder is 100 wt %. If the weight of the fine zirconia powder is less than 20 wt %, the firing shrinkage rate of the insulating support becomes too small relative to the other layers, and cracks tend to occur after the middle stage of co-firing. On the other hand, when the weight of the fine zirconia powder exceeds 80 wt %, the insulating support after firing tends to be too dense and the porosity tends to decrease. Based on these points, in the support forming material disclosed herein, the weight of fine zirconia powder is adjusted to 20 wt % or more and 80 wt % or less to prevent cracks after the middle stage of sintering and provide an insulating support after sintering. It is compatible with the gas permeability of
From the viewpoint of more preferably preventing cracks after the middle stage of firing, the weight of the fine zirconia powder is preferably 25 wt% or more, more preferably 27 wt% or more, still more preferably 30 wt% or more, and particularly 35 wt% or more. preferable. On the other hand, from the viewpoint of forming an insulating support having excellent gas permeability after firing, the upper limit of the weight of the fine zirconia powder is preferably 75 wt% or less, more preferably 70 wt% or less, and 65 wt% or less. More preferably, 60 wt % or less is particularly preferable.

The coarse-grained zirconia powder and the fine-grained zirconia powder may be composed of the same kind of zirconia particles, or may be composed of different kinds of zirconia particles. For example, YSZ with a yttria solid-solution amount of 5 mol % (5YSZ) can be used for the coarse-grain zirconia powder, and YSZ with an yttria solid-solution amount of 8 mol % (8YSZ) can be used for the fine-grain zirconia powder.

A zirconia powder having an average particle size different from that of the coarse-grained zirconia powder and the fine-grained zirconia powder (hereinafter referred to as "another zirconia powder") is mixed powder as long as it does not impair the effects of the present invention. may be contained in the body. Such other zirconia powders include ultra-small zirconia powder with an average particle size of less than 0.1 μm, intermediate zirconia powder with an average particle size of more than 0.5 μm and less than 1 μm, and extra-large zirconia powder with an average particle size of more than 4 μm. etc. However, from the viewpoint of suitably preventing breakage of other layers during co-firing, it is preferable not to substantially contain the other zirconia powder. The phrase "substantially does not contain other zirconia powders" as used herein means that no other zirconia powders are intentionally added. Therefore, in the case where the components that can be interpreted as other zirconia powder are contained in trace amounts due to raw materials, manufacturing processes, etc., the term "substantially does not contain other zirconia powder" in the present specification is used. subsumed in the concept. For example, when the total weight of the mixed powder is 100 wt%, the content of the other zirconia powder is 1 wt% or less (preferably 0.1 wt% or less, more preferably 0.01 wt% or less, still more preferably 0 wt%). .001 wt% or less, particularly preferably 0.0001 wt% or less), it can be said that "substantially no other zirconia powder is contained".

2. Sintering Aid The sintering aid is a powder material containing transition metal oxide particles as a main component. By adding a sintering aid containing such a transition metal oxide to the support-forming material, the shrinkage initiation temperature can be lowered, and the occurrence of cracks at the initial stage of co-firing can be suppressed. Although not intending to limit the present invention, the reason why such an effect is obtained is presumed as follows. A sintering aid containing a transition metal oxide has a lower melting point (for example, 2000° C. or lower) than zirconia powder, and therefore melts earlier than zirconia powder at the initial stage of co-firing. Then, the molten sintering aid flows into the voids between the zirconia particles, causing the insulating support to shrink, thereby lowering the shrinkage start temperature. The sintering aid can be appropriately changed to one having an appropriate melting point according to the firing temperature. For example, the melting point of the sintering aid may be 1700° C. or lower, 1500° C. or lower, or 1200° C. or lower. Examples of transition metal oxides having such melting points include Mn ₃ O ₄ , NiO, CuO, Fe ₂ O ₃ , ZnO and CoO. By using these transition metal oxide particles as a sintering aid, the shrinkage initiation temperature can be suitably lowered.

Further, in the support-forming material disclosed herein, the content of the sintering aid is 0.1 wt % or more and 1.2 wt % or less with respect to the total weight (100 wt %) of the mixed powder. Specifically, in the support-forming material disclosed herein, the lower limit of the content of the sintering aid is set to It is specified to be 0.1 wt% or more. On the other hand, since the sintering aid fills the voids between the zirconia particles at the initial stage of sintering, it can also be a factor in reducing the porosity of the insulating support after sintering. Therefore, in the support-forming material disclosed herein, the upper limit of the content of the sintering aid is set to 1.2 wt% in order to ensure the porosity of the insulating support after firing. . From the viewpoint of more preferably preventing the occurrence of cracks at the initial stage of firing, the lower limit of the content of the sintering aid is preferably 0.2 wt% or more, more preferably 0.4 wt% or more, and 0.6 wt% or more. is more preferable, and 0.8 wt% or more is particularly preferable. Moreover, from the viewpoint of securing the porosity of the insulating support after firing, the upper limit of the content of the sintering aid is more preferably 1.1 wt % or less. A suitable example of the content of such a sintering aid is 1 wt %.

As described above, in the support-forming material disclosed herein, a predetermined amount of sintering aid is added to lower the shrinkage start temperature, so cracks can be prevented from occurring in the initial stage of firing. Further, since the mixed particles containing a predetermined amount of fine zirconia powder are used to increase the firing shrinkage rate, cracks can be prevented from occurring after the middle stage of firing. In addition, cracks can be appropriately prevented from occurring at each stage of co-firing, so there is no need to increase the thermal shrinkage rate more than necessary. Therefore, the content of each of the sintering aid and the fine-grained zirconia powder can be defined so that a suitable porosity can be obtained in the insulating support after firing. Therefore, according to the support-forming material disclosed herein, it is possible to prevent the occurrence of cracks during co-firing and to form an insulating support excellent in gas permeability.

Incidentally, as the average particle size of the sintering aid increases, there is a tendency that the amount of shrinkage of the insulating support at the initial stage of firing increases. From this point of view, the average particle size of the sintering aid is preferably 0.02 μm or more, more preferably 0.1 μm or more, still more preferably 0.5 μm or more, and particularly preferably 1 μm or more. On the other hand, the upper limit of the average particle size of the sintering aid is preferably 30 μm or less, more preferably 20 μm or less, from the viewpoint of uniformly shrinking the support-forming material at the initial stage of sintering and more preferably preventing the occurrence of cracks. , is more preferably 15 μm or less, and particularly preferably 10 μm or less.

3. Other components The support-forming material disclosed herein may optionally contain other components (for example, a binder, a pore-forming material, etc.) that can be optionally added, as long as they do not impair the effects of the present invention. may contain. Other components that can be added to the support-forming material are not particularly limited, and can be appropriately selected from conventionally known components for use in forming the insulating support. For example, cellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, carboxyethylcellulose, carboxyethylmethylcellulose, ethylcellulose, methylcellulose, ethylhydroxyethylcellulose, butyral and salts thereof can be used as the binder. Although the content of the binder is not particularly limited, it is preferably 1 wt % or more and 10 wt % or less (for example, 6.5 wt %) when the total amount of the mixed powder is 100 wt %. Thereby, a green sheet having a suitable shape can be formed.

The pore-forming material is selected from the group consisting of acrylic resin, methacrylic resin, polystyrene resin, cellulose resin, polyvinyl acetal resin, polyester resin, polyurethane resin, epoxy resin, phenol resin, polyvinyl acetate resin, and polyvinyl alcohol resin. Resin beads containing one or more resins, or particles made of carbon, starch, or the like may be added. These materials are suitable for use as pore formers. Among these materials, resin beads made of acrylic resin or methacrylic resin can be particularly suitably used as the pore-forming material because of their low burnout temperature. From the viewpoint of further improving the gas permeability of the insulating support by forming a plurality of open pores in which a plurality of pores communicate with each other, the average particle size of the pore-forming material is 1 μm or more, and the mixed powder It is preferable that the amount of the pore-forming material added to the total weight is 5 wt % or more. Considering the strength of the insulating support after firing, it is preferable that the average particle diameter of the pore-forming material is 10 μm or less and the amount of the pore-forming material added is 25 wt % or less.

It should be noted that the support-forming material disclosed herein is used to form the insulating support of the SOFC. Here, when the sintering aid containing the transition metal oxide is reduced, it can become a conductive material. However, according to experiments by the present inventors, the transition metal oxide used as a sintering aid is difficult to be reduced, and at least if the content of the sintering aid is 5 wt % or less, the high temperature at which the SOFC operates can be reduced. Since the oxide state is maintained even in a hydrogen atmosphere, it has been confirmed that the insulating properties of the support can be ensured. Therefore, it can be said that the support-forming material disclosed herein does not substantially contain a conductive material having electron conductivity, and can suitably form an insulating support for SOFC.

In addition, as described above, the support-forming material disclosed herein does not substantially contain a conductive material having electronic conductivity in order to ensure the insulating properties of the support after firing. Examples of such conductive materials include nickel (Ni), copper (Cu), gold (Au), platinum (Pt), palladium (Pd), ruthenium (Ru), cobalt (Co), lanthanum (La), strontium ( Sr), titanium (Ti), and the like. The phrase "substantially contains no conductive material" as used herein means that no conductive material is added with the intention of imparting conductivity to the support after firing. Therefore, when a trace amount of a component that can be interpreted as a conductive material is added on the premise that the insulation of the support after firing is ensured, the term "substantially does not contain a conductive material" in the present specification is used. subsumed in the concept. For example, the content of the conductive material with respect to the total weight (100 wt%) of the mixed powder is 5 wt% or less (preferably 1 wt% or less, more preferably 0.1 wt% or less, still more preferably 0.01 wt% or less, particularly (preferably 0.001 wt % or less), the insulating properties of the support after firing can be ensured, so it can be said that "the conductive material is not substantially contained".

<Manufacture of SOFC>
Next, the manufacture of SOFC using the support-forming material described above will be described. The manufacturing method in this embodiment includes a green sheet manufacturing process, a green sheet lamination process, and a firing process. In such a manufacturing method, so-called co-firing is performed in which the green sheets of each layer of the insulating support, fuel electrode, solid electrolyte layer, and air electrode are fired at the same time. Each step will be described below.

1. Green Sheet Production Process In this process, green sheets for each layer (insulating support, fuel electrode, solid electrolyte layer, air electrode) constituting the SOFC are produced. Here, first, a slurry is prepared by dispersing the support-forming material described above in a predetermined dispersion medium (for example, water). Such a slurry is prepared, for example, by putting the support-forming material and the dispersion medium into an arbitrary stirring/mixing device and stirring and mixing them. Various conventionally known devices such as ball mills, mixers, dispersers and kneaders can be used for such stirring and mixing. Additives such as lubricants and release agents may be added in the preparation of the slurry. This makes it possible to easily form the green sheet. As the lubricant and release agent, any material that can be used for molding the green sheet can be used without particular limitation, and detailed description thereof will be omitted since the present invention is not limited.

In this step, the prepared slurry is then molded to produce a green sheet (green sheet for insulating support) having a desired shape. The means for molding the green sheet is not particularly limited, and conventionally known means such as vacuum extrusion molding can be employed. After molding, the green sheet contains the support-forming material disclosed herein as a solid. Specifically, the green sheet after molding is a mixed powder containing at least coarse-grained zirconia powder having an average particle diameter of 1 μm or more and 4 μm or less and fine-grained zirconia powder having an average particle diameter of 0.1 μm or more and 0.5 μm or less. It contains as solids a body and a sintering aid comprising particles of a transition metal oxide. In the green sheet, the weight of the fine zirconia powder is 20 wt% or more and 80 wt% or less when the total weight of the mixed powder is 100 wt%, and the total weight of the mixed powder is 100 wt%. The content of the binder is 0.1 wt % or more and 1.2 wt % or less.

2. Green Sheet Lamination Step In this step, the green sheets of each layer including the green sheet for forming the support are laminated. Specifically, in this step, green sheets of an insulating support, a fuel electrode, a solid electrolyte layer, and an air electrode are laminated in this order to produce a laminate, which is a precursor of the SOFC. In addition, the green sheet of the layers (fuel electrode, solid electrolyte layer, air electrode) other than the insulating support is not particularly limited as long as it can be used in the production of this type of SOFC, and the present invention is limited. Therefore, detailed description is omitted.

3. Firing Step In this step, co-firing for firing the produced laminate is performed. As a result, the green sheets of each layer are fired at the same time to produce an SOFC including an insulating support, a fuel electrode, a solid electrolyte layer, and an air electrode. The firing temperature in this step can be, for example, approximately 1200° C. to 1500° C. (eg, 1400° C.). Also, the firing time can be, for example, about 1 hour to 5 hours.

As described above, in the technique disclosed herein, the green sheet for forming the insulating support contains 0.1 wt % or more of the sintering aid. As a result, since the shrinkage start temperature of the green sheet for forming the insulating support is lowered, it is possible to prevent cracks from occurring due to the difference in the amount of shrinkage between the insulating support and other layers in the initial stage of firing. Furthermore, the green sheet disclosed herein uses mixed powder containing 20 wt % or more of fine zirconia powder. As a result, since the shrinkage rate of the green sheet is improved, it is possible to prevent the occurrence of cracks due to the difference in the amount of shrinkage between the green sheet and the other layers after the middle stage of firing. Therefore, according to the technology disclosed herein, the occurrence of cracks during co-firing can be suitably prevented.

In the technology disclosed herein, the upper limit of the content of the sintering aid is set at 1.2 wt%, and the upper limit of the content of the fine zirconia powder is set at 80 wt% or less. . As a result, the porosity of the insulating support after sintering can be maintained, so that an insulating support having excellent gas permeability can be formed.

4. SOFCs
Next, an example of SOFC manufactured using the support-forming material disclosed herein will be described. FIG. 1 is a diagram schematically showing the layer structure of an SOFC according to this embodiment. As shown in FIG. 1, the SOFC 10 according to this embodiment includes an insulating support 12, a fuel electrode 14, a solid electrolyte layer 16, and an air electrode 18. As shown in FIG.

(1) Insulating Support The insulating support 12 is formed using the support-forming material disclosed herein. That is, the insulating support 12 does not substantially contain a conductive material, but contains a zirconia-based component (YSZ, etc.) derived from the zirconia powder described above as a main component. The insulating support 12 of the SOFC 10 disclosed herein contains a transition metal oxide derived from the sintering aid. In this insulating support 12, the weight ratio of the zirconia-based component and the transition metal oxide can be approximately the same as the ratio of the mixed particles and the sintering aid in the support-forming material used as the material. That is, in the insulating support 12 of the SOFC 10 disclosed herein, the total weight of the transition metal oxides can be 0.1 wt% or more and 1.2 wt% or less when the total weight of the zirconia-based components is 100 wt%. .

Furthermore, as described above, in the support-forming material disclosed herein, the contents of the fine-grained zirconia powder and the sintering aid are adjusted so that the insulating support 12 after firing maintains a suitable porosity. An upper limit is specified. Therefore, the insulating support 12 has a preferable porosity of 5% or more. Thereby, the fuel gas supplied from the lower surface of the insulating support 12 can be suitably supplied to the fuel electrode 14 . From the viewpoint of further improving the gas permeability of the insulating support 12, the porosity of the insulating support 12 is preferably 7% or more, more preferably 10% or more. % or more is more preferable. In addition, the upper limit of the porosity is not particularly limited as long as a predetermined strength (for example, 29 MPa or more) of the insulating support 12 can be secured, and may be 90% or less, or 80% or less. It may be 70% or less, or 60% or less.

From the viewpoint of appropriately supporting each of the fuel electrode 14, the solid electrolyte layer 16, and the air electrode 18 to maintain the shape of the battery, the strength of the insulating support 12 (three-point bending strength according to JIS R 1601) is suitable as long as it is 29 MPa or more, preferably 50 MPa or more, more preferably 100 MPa or more, still more preferably 120 MPa or more, and particularly preferably 130 MPa or more. Here, since the transition metal oxide obtained by melting and solidifying the sintering aid exists so as to fill the gaps between the zirconia-based components inside the insulating support 12, the strength of the porous structure of the insulating support 12 is improved. can also contribute to Therefore, by increasing the content of the sintering aid in the support-forming material, the insulating support 12 having the strength described above can be easily formed.

(2) Fuel Electrode The fuel electrode 14 is formed on the insulating support 12 . This fuel electrode 14 is, for example, a porous body containing a conductive material (material having catalytic activity). Like the insulating support 12, the fuel electrode 14 has a large number of communicating pores extending from the bottom surface to the top surface. Thereby, the fuel gas can be supplied to the entire area of the fuel electrode 14 . The porosity of the fuel electrode 14 is preferably in the range of 5-20%, for example, about 15%. Although not particularly limited, conductive materials that can be used for the fuel electrode 14 include nickel (Ni), copper (Cu), gold (Au), platinum (Pt), palladium (Pd), and ruthenium (Ru). , cobalt (Co), lanthanum (La), strontium (Sr), titanium (Ti), or metal oxides thereof. Such materials can be used singly or in appropriate combination of two or more. Among them, nickel is particularly suitable because it is less expensive than other metals and exhibits high reaction activity (sufficiently high reactivity with fuel gas). Further, the fuel electrode 14 may contain the same zirconia-based oxide (for example, YSZ) as the insulating support 12 . In this case, the mixing ratio of the conductive material and the zirconia-based oxide is preferably in the range of 3:7 to 7:3, for example, about 6:4 in mass ratio.

(3) Solid Electrolyte Layer The solid electrolyte layer 16 is formed on the fuel electrode 14 . This solid electrolyte layer 16 is a dense layer containing a solid electrolyte having ion conductivity. As the solid electrolyte, a zirconia-based oxide (for example, YSZ) similar to that of the insulating support 12 described above can be used. The thickness of the solid electrolyte layer 16 is preferably 1 μm or more and 10 μm or less, for example, about 3 μm. Incidentally, the relative density of the solid electrolyte layer 16 is, for example, about 95 to 100 (%).

(4) Air electrode The air electrode 18 is formed on the solid electrolyte layer 16 . The air electrode 18 is, for example, (La, Sr) CoO ₃ (eg, La _0.6 Sr _0.4 CoO ₃ ; hereinafter referred to as LSC) or (La, Sr) (Co, Fe) O ₃ (eg, , La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ ; hereinafter referred to as LSCF). For these LSC and LSCF, the substitution ratio of both the A and B sites can be determined variously, and suitable substitution ratios can be used according to the desired ionic conductivity, reduction expansion coefficient, and the like. Similarly to the insulating support 12 and the fuel electrode 14, the air electrode 18 is a porous body and has a large number of communicating pores extending from the upper surface to the lower surface. As a result, air (oxygen) can be dispersed and supplied to the entire air electrode 18 .

As described above, the insulating support 12 of the SOFC 10 according to the present embodiment maintains a porosity of 5% or more in spite of the measures taken to prevent cracks. It can exhibit gas permeability.

[Test example]
Some test examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in such test examples.

A. First Test In this test, four types of support-forming materials (Samples 1 to 4) having different compositions were prepared, and green sheets were produced using each of the support-forming materials. Then, it was evaluated whether or not cracks would occur during firing of the green sheet.

1. Sample preparation (1) Sample 1
Mixed powder containing coarse-grained zirconia powder (8YSZ with an average particle size of 1.5 μm) and fine-grained zirconia powder (8YSZ with an average particle size of 0.25 μm), and a sintering aid (average particle size of 1.5 μm). Mn ₃ O ₄ of 69 μm), a pore-forming material (acrylic fine particles), and a methylcellulose binder were mixed with a double-arm kneader to prepare a support-forming material. Table 1 shows the contents of coarse-grained zirconia powder, fine-grained zirconia powder, and sintering aid. 9 wt % of the pore-forming material was added to 100 wt % of the coarse-grained zirconia powder. 7 wt % of the binder was added to 100 wt % of the coarse-grained zirconia powder.

(2) Samples 2-4
A support-forming material was prepared under the same conditions as Sample 1, except that the conditions regarding the sintering aid were changed. Specifically, in sample 2, NiO was used as a sintering aid. Also, in sample 3, MgO was used as a sintering aid. Then, in Sample 4, a support-forming material was prepared without adding a sintering aid.

2. Evaluation Test (1) Production of Insulating Support In the evaluation test, first, an insulating support was produced using the support-forming material of each sample. Specifically, an appropriate amount of dispersion medium (water) was added to the support-forming material described above, and the mixture was kneaded for 25 minutes in a kneader (rotation speed: 25 rpm) to prepare a slurry for forming a green sheet. Next, the prepared slurry was extruded into a disk shape using a vacuum extruder. Then, by drying with a hot air dryer (110° C.) for 10 hours, a green sheet for an insulating support was produced.

Then, a fuel electrode paste (main component: NiO) and a solid electrolyte layer paste (main component: YSZ) are sequentially printed on the surface of the green sheet for the support, and then the firing temperature is set to 1400 ° C. It was sintered by holding it in a furnace for 2 hours to obtain a SOFC half cell for evaluation test. As shown in FIG. 2, such a half cell 100 has a pair of fuel electrodes 140 formed on the upper surface of a disk-shaped insulating support 120 with a gap therebetween. A solid electrolyte layer 160 is formed across the pair of fuel electrodes 140 .

(2) Surface observation The boundary between the fuel electrode 140 and the solid electrolyte layer 160 of the half cell 100 was observed with a laser microscope (magnification: 400x). I checked if there was The evaluation results are shown in Table 1, and laser microscope photographs of samples 1 and 4 are shown in FIGS.

As shown in Table 1 and FIG. 3, in sample 1, the insulating support 120 was not exposed, and cracks at the boundary between the fuel electrode 140 and the solid electrolyte layer 160 were suppressed. Similar results were obtained for sample 2 as well. On the other hand, as shown in Table 1 and FIG. 4, cracks occurred in Sample 4, and the insulating support 120 was exposed. From this, it was found that the addition of a sintering aid to the support-forming material can suppress the occurrence of cracks during co-firing. Furthermore, in sample 3, cracks similar to those in sample 4 occurred despite the addition of metal oxide (MgO). From this, it turned out that it is necessary to use a transition metal oxide as a sintering aid.

B. Second test In this test, 13 types of support forming materials (Samples 5 to 17) with different contents of fine zirconia powder and sintering aid were prepared to prevent cracks and maintain porosity. We investigated compatibility conditions.

1. Sample preparation A mixed powder containing coarse-grained zirconia powder (8YSZ with an average particle size of 1.5 μm) and fine-grained zirconia powder (8YSZ with an average particle size of 0.25 μm), and a sintering aid (average particle size Mn ₃ O ₄ having a diameter of 1.69 μm) and a methyl cellulose binder were mixed with a double-arm kneader to prepare a support forming material. At this time, the content of the fine zirconia powder with respect to the mixed powder (100 wt%) is varied within the range of 0 wt% to 100 wt%, and the content of the sintering aid is varied within the range of 0 wt% to 5 wt%. Thirteen kinds of support-forming materials (Samples 5 to 17) were prepared by applying them. Table 2 shows the composition of each sample. Other conditions were set to be the same as those of sample 1 of the first test.

2. Evaluation Test An SOFC half-cell 100 was fabricated under the same conditions as in the first test, and the presence or absence of crack generation was examined using a laser microscope. Table 2 shows the results.
In addition, in this test, SEM was used to observe the surface of the insulating support. A surface SEM observation image of sample 6 is shown in FIG. 5, a surface SEM observation image of sample 10 is shown in FIG. 6, and a surface SEM observation image of sample 14 is shown in FIG.

Furthermore, in this test, porosity measurement based on the Archimedes method was performed on the insulating support of each sample. Specifically, first, the dry weight W _air of the insulating support of each sample was measured. Next, each sample was immersed in distilled water, placed in a desiccator equipped with a vacuum pump, vacuumed for 45 minutes, and measured for the underwater weight W _aq and water content W _A+w of the insulating support. Then, the porosity (P) was calculated based on the following formula (1). A porosity of 5% or more was evaluated as "acceptable", and a porosity of less than 5% was evaluated as "impossible". Table 2 shows the results.
P=(W _A+w −W _Air )/(W _A+w −W _aq ) (1)

As shown in Table 2, in each sample except for samples 9 and 14, the occurrence of cracks during co-firing was prevented. From this, it was found that cracks during co-firing can be prevented by setting the content of the sintering aid to 0.1 wt % or more and the content of the fine zirconia powder to 20 wt % or more. On the other hand, according to the results of porosity measurement, samples 5, 8, 15 to 17 containing 1.5 wt% or more of the sintering aid, and sample 10 containing 100 wt% of fine zirconia powder had a significant porosity. decrease was confirmed. From this, in order to maintain the porosity of the insulating support after sintering in a suitable state, the upper limit of the content of the sintering aid is 1.2 wt% or less, and the upper limit of the content of the fine zirconia powder is 1.2 wt% or less. It turned out that it is necessary to specify 80 wt% or less.

Further, from the surface SEM observation images of each sample, sample 10 (see FIG. 6) using only fine-grained zirconia powder formed an insulating support with a smooth surface, and sample 14 using only coarse-grained zirconia powder was formed. (See FIG. 7), an insulating support having a plurality of wavy irregularities on its surface was formed. Sample 6 (see FIG. 5), which uses a mixed powder containing fine-grained zirconia powder and coarse-grained zirconia powder, formed an insulating support with less wavy unevenness than sample 14.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

10 SOFCs
Reference Signs List 12, 120 insulating support 14, 140 fuel electrode 16, 160 solid electrolyte layer 18 air electrode 100 half cell

Claims (4)

A support-forming material for forming an insulating support that is a porous body that supports a fuel electrode of a solid oxide fuel cell,
mixed powder containing at least coarse zirconia powder with an average particle size of 1 μm or more and 4 μm or less and fine zirconia powder with an average particle size of 0.1 μm or more and 0.5 μm or less;
a sintering aid comprising transition metal oxide particles;
The weight of the fine zirconia powder is 20 wt% or more and 80 wt% or less when the total weight of the mixed powder is 100 wt%,
A support-forming material for a solid oxide fuel cell, wherein the content of the sintering aid is 0.1 wt % or more and 1.2 wt % or less when the total weight of the mixed powder is 100 wt %. 2. The material for forming a support according to claim 1, wherein the sintering aid has an average particle size of 0.02 [mu]m or more and 30 [mu]m or less. Support formation according to claim 1 or 2, wherein the sintering aid comprises _one or more particles selected from the group consisting of _Mn3O4 , _NiO , CuO, _Fe2O3 , ZnO, CoO. material. an insulating support which is a porous body permeable to fuel gas and contains a zirconia-based component;
a fuel electrode formed on the insulating support;
a solid electrolyte layer formed on the fuel electrode;
A solid oxide fuel cell comprising an air electrode formed on the solid electrolyte layer,
The insulating support contains a transition metal oxide, and the total weight of the transition metal oxide is 0.1 wt % or more and 1.2 wt % or less when the total weight of the zirconia-based component is 100 wt %. , and the porosity is 5% or more,
A solid oxide fuel cell , wherein the transition metal oxide is present throughout the insulating support .

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