JP2020167092A - Material for formation of support body of solid oxide fuel cell, and utilization thereof - Google Patents

Abstract

To provide a technique which can prevent the occurrence of a crack in co-firing and which enables the formation of an insulative support body superior in gas permeability.SOLUTION: A material for support body formation herein disclosed comprises: a powder mixture containing at least fine particles of zirconia powder having an average particle diameter of 1-4 μm and fine particles of zirconia powder having an average particle diameter of 0.1-0.5 μm; and a sintering assistant containing transition metal oxide particles. In the material for support body formation, the weight of the fine particles of zirconia powder when the total weight of powder mixture is 100 wt.% is 20-80 wt.%, and the content of the sintering assistant when the total weight of the powder mixture is 100 wt.% is 0.1-1.2 wt.%. According to this embodiment, the occurrence of a crack in co-firing can be prevented, and an insulative support body superior in gas permeability can be formed.SELECTED DRAWING: None

Description

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) includes a solid electrolyte layer made of an oxide ion conductor, an air electrode (cathode), and a fuel electrode (anode). In such 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, etc.) supplied to the fuel electrode is oxidized by oxygen ions from the air electrode, so that electrons are released to the external load and electric energy is generated. Such SOFCs are next-generation power generation devices because of their high power generation efficiency, low emissions of substances that cause air pollution, low environmental impact, and the ability to use a variety of fuels. Development is underway.

For example, in SOFC, a structure in which a laminate having a fuel electrode, a solid electrolyte layer, and an air electrode is formed on an insulating support (hereinafter, referred to as “insulating support”) can be adopted. In addition to maintaining the shape of the battery, the insulating support also has a role of supplying and diffusing fuel gas to the fuel electrode. Therefore, the insulating support is required to have a predetermined strength and a structure capable of transmitting a large amount of fuel gas. As a conventional technique relating to such a support for SOFC, the techniques described in Patent Documents 1 and 2 can be mentioned. These Patent Documents 1 and _{2, NiO, Y 2 O 3,} MgO, may use the MgAl ₂ O _4, TiO _2, etc. of a metal oxide material of the supporting substrate is disclosed.

Japanese Unexamined Patent Publication No. 2012-94323 Japanese Unexamined Patent Publication No. 2017-174498

By the way, as a method of manufacturing SOFC, a method of laminating and firing an insulating support, a fuel electrode, a solid electrolyte layer, and an air electrode one by one in order, and a method of laminating a precursor (green sheet) of each layer are summarized. A method of firing (co-firing) can be mentioned. Of these, co-firing has the advantage of reducing the manufacturing process and reducing costs.

However, when SOFC is produced by using co-firing, cracks may occur at the boundary between the fuel electrode and the solid electrolyte layer after firing. Since such cracks have different shrinkage rates (fired shrinkage rates) during firing between the solid electrolyte layer, which is a dense layer, and the insulating support, which is a porous body, the fuel electrode and the solid electrolyte layer during co-firing are different. It is thought that it is generated by applying stress to the boundary with.

Therefore, when SOFC is produced by using co-firing, it has been considered to increase the firing shrinkage rate of the insulating support and approximate the firing shrinkage rate of the solid electrolyte layer and the insulating support. However, if the firing shrinkage rate of the green sheet of the insulating support is increased, as a trade-off, the insulating support after firing becomes dense and the gas permeability is lowered, so that the power generation performance is lowered.

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

The present inventors have conducted various experiments and studies in order to achieve the above-mentioned object. As a result, it was found that cracks in co-firing can occur not only when the above-mentioned difference in firing shrinkage rate occurs but also when a difference in shrinkage start temperature occurs. For example, even if the firing shrinkage of the solid electrolyte layer and the firing shrinkage of the insulating support are approximated, if the solid electrolyte layer starts shrinking at a lower temperature than the insulating support, the fuel electrode and the solid will be formed at the initial stage of firing. Stress is applied to the boundary with the electrolyte layer and cracks occur. Based on this discovery, we found that if the thermal shrinkage start temperature of the insulating support could be lowered to the same level as the solid electrolyte layer, the insulating support would crack without increasing the firing shrinkage rate more than necessary. It was thought that the decrease in gas permeability of the insulating support after firing could be suppressed because the occurrence of The support forming material disclosed herein is based on the above findings.

The present invention provides a support forming material having the following constitution. In the present specification, the “support forming material” refers to a powder material for forming an insulating support of SOFC. More specifically, the "support forming material" in the present specification is the main component of the green sheet which is a 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 size of 1 μm or more and 4 μm or less, and fine-grained zirconia powder having an average particle size of 0.1 μm or more and 0.5 μm or less. And a sintering aid containing particles of transition metal oxide. 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 when% is 0.1 wt% or more and 1.2 wt% or less.

In the support forming material disclosed herein, a sintering aid containing particles of transition metal oxide 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, in the support forming material disclosed herein, a mixed powder containing coarse-grained zirconia powder and fine-grained zirconia powder is used. Since such a mixed powder can improve the firing shrinkage rate of the insulating support, it is possible to prevent cracks from occurring due to the difference in the amount of shrinkage after the middle stage of firing. The support forming material disclosed herein is fine particles with respect to the total weight of the mixed powder from the viewpoint of preventing the occurrence of cracks during co-firing and forming an insulating support having excellent gas permeability. Each of the weight of the zirconia powder and the content of the sintering aid with respect to the mixed powder is specified.

In the present specification, the "average particle size" is a particle size corresponding to a cumulative 50% from the fine particle side in a volume-based particle size distribution measured by a particle size distribution measurement based on a general laser diffraction / light scattering method. _{(D 50} particle size, also called median diameter.) refers to.

In a preferred embodiment of the support forming material disclosed herein, the average particle size of the sintering aid is 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 uniformly shrunk at a suitable shrinkage amount at the initial stage of firing, so that cracks at the initial stage of firing are more likely to occur. It can be preferably prevented.

In a preferred embodiment of the support forming material disclosed herein, the sintering aid is one or more particles selected from the group consisting of Mn ₃ O ₄ , NiO, CuO, Fe ₂ O ₃ , ZnO, CoO. including. Among the transition metal oxides, these have a particularly low melting point, and the shrinkage start temperature of the insulating support can be suitably lowered, so that the occurrence of cracks at the initial stage of firing can be more preferably prevented.

Further, as another aspect of the present invention, a solid oxide fuel cell (SOFC) is provided. The SOFC disclosed herein is a porous body that allows fuel gas to permeate, and is an insulating support containing a zirconia-based component, a fuel electrode formed on the insulating support, and a solid formed on the fuel electrode. It includes 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 porosity of 5% or more.

The SOFC is an SOFC manufactured by using the support forming material disclosed herein. Such an insulating support of SOFC contains a transition metal oxide derived from a sintering aid contained in the support forming material. That is, in the SOFC insulating support disclosed herein, the total weight of the transition metal oxide 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. Since various configurations of the above-mentioned support forming material 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 is all. Since the insulating support having such a porosity exhibits high gas permeability, it can contribute to the improvement of the power generation performance of the SOFC.

It is a figure which shows typically the layer structure of SOFC which concerns on one Embodiment of this invention. It is a top view which shows typically the half cell prepared in the test example. It is an image (magnification: 400 times) when the boundary between the fuel electrode and the solid electrolyte layer of sample 1 was observed with a laser microscope. It is an image (magnification: 400 times) when the boundary between the fuel electrode and the solid electrolyte layer of sample 4 was observed with a laser microscope. It is a surface SEM observation image (magnification: 10000 times) of sample 6. It is a surface SEM observation image (magnification: 10000 times) of sample 10. It is a surface SEM observation image (magnification: 10000 times) of sample 14.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings as appropriate. It should be noted that matters other than those specifically mentioned in the present specification and necessary for carrying out the present invention (for example, detailed components of each layer excluding the insulating support, manufacturing method, etc.) are in the art. It can be grasped as a design matter of a person skilled in the art based on the prior art. The present invention can be carried out based on the contents disclosed in the present specification and common general technical knowledge in the art. Further, in the following drawings, members / parts having the same function may be described with the same reference numerals, and duplicate 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 material disclosed herein is used to form an insulating support that supports the fuel electrode of the SOFC. Specifically, an insulating support of 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. Hereinafter, each component will be described.

1. 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. The zirconia-based oxide is not particularly limited as long as it can be used for the insulating support of this kind of SOFC, and various components can be used. As an example of such a zirconia-based oxide, stabilized zirconia in which a stabilizer is added to zirconia (ZrO ₂ ) is preferably used. The stabilizer in accordance stabilized zirconia, predetermined metal oxide (M ₂ O ₃ or MO) can be used. Here, examples of the metal element (M) contained in the stabilizer include one or more elements of Y, Sc, Ca, Yb, Gd and Mg. Preferred examples of the stabilized zirconia, and yttria (Y 2 _{O 3)} stabilized with yttria-stabilized zirconia (YSZ) and, stabilized calcia-stabilized zirconia (CSZ) or the like with calcia (CaO) is .. 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 having different average particle sizes. Specifically, the mixed powder disclosed herein includes 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 types of zirconia powders having different average particle sizes are mixed at an appropriate ratio, the occurrence of cracks after the middle stage of firing can be prevented. Hereinafter, a specific description will be given.

The coarse-grained zirconia powder is a zirconia powder having an average particle size of 1 μm or more and 4 μm or less. When the content of such relatively large particle size zirconia particles increases, the shrinkage rate (fired shrinkage rate) of the green sheet in co-firing tends to decrease. The average particle size of the coarse-grained zirconia powder may be 1.2 μm or more, or 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 2 μm or less. An example of the average particle size of such coarse-grained zirconia powder is 1.5 μm.

The fine zirconia powder is a zirconia powder having an average particle size of 0.1 μm or more and 0.5 μm or less. When the content of such relatively small particle size zirconia particles increases, the firing shrinkage rate tends to increase. The average particle size of the fine zirconia powder may be 0.15 μm or more, or 0.2 μm or more. On the other hand, the upper limit of the average particle size of the 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 zirconia powder is 0.25 μm.

In the mixed powder disclosed herein, the weight of the fine zirconia powder is defined as 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 with respect to the other layers, and cracks are likely 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 the fine zirconia powder is adjusted to 20 wt% or more and 80 wt% or less to prevent cracks after the middle stage of firing and to provide an insulating support after firing. It has both gas permeability and gas permeability.
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, further preferably 30 wt% or more, and particularly preferably 35 wt% or more. preferable. On the other hand, from the viewpoint of forming an insulating support having better 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 type of zirconia particles or may be composed of different types of zirconia particles. For example, YSZ (5YSZ) having a yttria solid solubility of 5 mol% can be used for coarse zirconia powder, and YSZ (8YSZ) having an yttria solid solubility of 8 mol% can be used for fine zirconia powder.

A zirconia powder having an average particle size different from that of the above-mentioned coarse-grained zirconia powder and fine-grained zirconia powder (hereinafter referred to as "other zirconia powder") is a mixed powder as long as the effect of the present invention is not impaired. It may be contained in the body. Examples of such other zirconia powders include extremely small zirconia powders having an average particle size of less than 0.1 μm, intermediate zirconia powders having an average particle size of more than 0.5 μm and less than 1 μm, and maximum zirconia powders having an average particle size of more than 4 μm. And so on. However, from the viewpoint of preferably preventing damage to other layers during co-firing, it is preferable that the other zirconia powder is not substantially contained. The term "substantially free of other zirconia powder" as used herein means that no other zirconia powder is intentionally added. Therefore, when a component that can be interpreted as the other zirconia powder is contained in a trace amount due to the raw material, the manufacturing process, or the like, "substantially does not contain the other zirconia powder" in the present specification. Included 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). When it is .001 wt% or less, particularly preferably 0.0001 wt% or less), it can be said that "it does not substantially contain other zirconia powder".

2. Sintering aid Sintering aid is a powder material containing particles of transition metal oxide as the main component. By adding a sintering aid containing such a transition metal oxide to the support forming material, the shrinkage start temperature can be lowered and the occurrence of cracks at the initial stage of co-firing can be suppressed. Although there is no intention of limiting the present invention, the reason why such an effect can be obtained is presumed as follows. Since the sintering aid containing the transition metal oxide has a lower melting point than the zirconia powder (for example, 2000 ° C. or lower), it melts before the 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, so that the shrinkage start temperature drops. 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 the transition metal oxide having such a melting point include Mn ₃ O ₄ , NiO, CuO, Fe ₂ O ₃ , ZnO, and CoO. By using the particles of these transition metal oxides as a sintering aid, the shrinkage start temperature can be suitably lowered.

Further, in the support forming material disclosed herein, the content of the sintering aid with respect to the total weight (100 wt%) of the mixed powder is 0.1 wt% or more and 1.2 wt% or less. Specifically, in the support forming material disclosed herein, the lower limit of the content of the sintering aid is set from the viewpoint of ensuring the shrinkage amount of the insulating support at the initial stage of firing and appropriately preventing cracks. 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 firing, it can also be a factor of lowering the porosity of the insulating support after firing. 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 secure 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. Further, from the viewpoint of ensuring 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 here, since the shrinkage start temperature is lowered by adding a predetermined amount of the sintering aid, it is possible to prevent the occurrence of cracks at the initial stage of firing. Since the firing shrinkage rate is increased by using mixed particles containing a predetermined amount of fine zirconia powder, it is possible to prevent the occurrence of cracks after the middle stage of firing. Further, since the occurrence of cracks can be appropriately prevented at each stage of co-firing, it is not necessary to increase the heat shrinkage rate more than necessary. Therefore, the contents of each of the sintering aid and the fine zirconia powder can be specified 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 in co-firing and to form an insulating support having excellent gas permeability.

As the average particle size of the sintering aid increases, the amount of shrinkage of the insulating support at the initial stage of firing tends to increase. From this viewpoint, the average particle size of the sintering aid is preferably 0.02 μm or more, more preferably 0.1 μm or more, further preferably 0.5 μm or more, and particularly preferably 1 μm or more. On the other hand, from the viewpoint of uniformly shrinking the support forming material at the initial stage of firing to more preferably prevent the occurrence of cracks, the upper limit of the average particle size of the sintering aid is preferably 30 μm or less, more preferably 20 μm or less. , 15 μm or less is more preferable, and 10 μm or less is particularly preferable.

3. 3. Other components As long as the effects of the present invention are not impaired, the support-forming material disclosed herein may optionally add other components (for example, a binder, a pore-forming material, etc.). It may be included. The other components that can be added to the support forming material are not particularly limited, and can be appropriately selected from conventionally known components in the formation of the insulating support. For example, as the binder, cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, carboxyethyl cellulose, carboxyethyl methyl cellulose, ethyl cellulose, methyl cellulose, ethyl hydroxyethyl cellulose, butyral and salts thereof can be used. The binder content is not particularly limited, but 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%. As a result, a green sheet having a suitable shape can be formed.

The pore forming material was 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 kinds of resins, or particles made of carbon or starch may be added. These materials can be suitably used as a pore forming material. Further, among these materials, resin beads made of acrylic resin and methacrylic resin can be particularly preferably used as a pore-forming material because they have a low burning temperature. From the viewpoint of forming a plurality of open pores in which a plurality of pores are communicated to further improve the gas permeability of the insulating support, the average particle size of the pore forming material is 1 μm or more, and the mixed powder The amount of the pore-forming material added to the total weight is preferably 5 wt% or more. Further, considering the strength of the insulating support after firing, it is preferable that the average particle size of the pore-forming material is 10 μm or less and the amount of the pore-forming material added is 25 wt% or less.

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

Further, as described above, the support forming material disclosed herein does not substantially contain a conductive material having electron conductivity in order to ensure the insulating property of the support after firing. As an example of such a conductive material, nickel (Ni), copper (Cu), gold (Au), platinum (Pt), palladium (Pd), ruthenium (Ru), cobalt (Co), lanthanum (La), strontium ( Sr), titanium (Ti) and the like can be mentioned. The term "substantially free of conductive material" as used herein means that the conductive material is not added with the intention of imparting conductivity to the support after firing. Therefore, when a small amount of a component that can be interpreted as a conductive material is added on the premise that the insulating property of the support after firing is ensured, "substantially contains no conductive material" in the present specification. Included 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 When it is preferably 0.001 wt% or less), it can be said that "substantially no conductive material is contained" because the insulating property of the support after firing can be ensured.

<Manufacturing of SOFC>
Next, the production of SOFC using the above-mentioned support forming material will be described. The manufacturing method in the present embodiment includes a green sheet manufacturing step, a green sheet laminating step, and a firing step. In such a manufacturing method, so-called co-firing is performed, in which the green sheets of the insulating support, the fuel electrode, the solid electrolyte layer, and the air electrode are simultaneously fired. Hereinafter, each step will be described.

1. 1. Green sheet manufacturing process In this step, green sheets for each layer (insulating support, fuel electrode, solid electrolyte layer, air electrode) that make up SOFC are produced. Here, first, a slurry in which the above-mentioned support forming material is dispersed in a predetermined dispersion medium (for example, water) is prepared. 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 a ball mill, a mixer, a dispenser, and a kneader can be used for such stirring and mixing. In preparing such a slurry, additives such as a lubricant and a mold release agent may be added. As a result, the green sheet can be easily molded. As the lubricant and the mold release agent, materials that can be used for molding the green sheet can be used without particular limitation, and the present invention is not limited, so detailed description thereof will be omitted.

In this step, next, the prepared slurry is molded to prepare a green sheet (green sheet for an 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 adopted. The molded green sheet contains the support forming material disclosed herein as a solid substance. Specifically, the molded green sheet is a mixed powder containing at least coarse-grained zirconia powder having an average particle size of 1 μm or more and 4 μm or less, and fine-grained zirconia powder having an average particle size of 0.1 μm or more and 0.5 μm or less. It contains the body and a sintering aid containing particles of transition metal oxide as a solid content. 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 baking is performed when the total weight of the mixed powder is 100 wt%. The content of the aid is 0.1 wt% or more and 1.2 wt% or less.

2. Green sheet laminating step In this step, the green sheets of each layer including the above-mentioned green sheet for forming a support are laminated. Specifically, in this step, the green sheets of the insulating support, the fuel electrode, the solid electrolyte layer, and the air electrode are laminated in this order to prepare a laminate which is a precursor of SOFC. 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 limits the present invention. Since it is not, a detailed explanation will be omitted.

3. 3. Firing step In this step, co-firing is performed by calcining the produced laminate. As a result, the green sheets of each layer are fired at the same time to produce an SOFC having 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 (for example, 1400 ° C). 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 an insulating support contains 0.1 wt% or more of a 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 the other layer at the initial stage of firing. Further, in the green sheet disclosed herein, a mixed powder containing 20 wt% or more of fine zirconia powder is used. As a result, since the firing shrinkage rate of the green sheet is improved, it is possible to prevent cracks from occurring due to the difference in shrinkage amount from the other layers after the middle firing stage. Therefore, according to the technique disclosed herein, it is possible to suitably prevent the occurrence of cracks in co-firing.

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

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

(1) Insulating Support The insulating support 12 is formed by 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 or the like) derived from the above-mentioned zirconia powder as a main component. The SOFC 10 insulating support 12 disclosed herein contains a transition metal oxide derived from the sintering aid. Then, in the insulating support 12, the weight ratio of the zirconia-based component and the transition metal oxide can be substantially equal to 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 SOFC10 disclosed herein, the total weight of the transition metal oxide when the total weight of the zirconia-based components is 100 wt% can be 0.1 wt% or more and 1.2 wt% or less. ..

Further, as described above, in the support forming material disclosed herein, the content of the fine zirconia powder and the sintering aid is adjusted so that the insulating support 12 after firing can maintain a suitable porosity. There is an upper limit. Therefore, the insulating support 12 has a suitable porosity of 5% or more. As a result, 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, and 13 It is more preferably% or more. The upper limit of the porosity is not particularly limited as long as the strength of the insulating support 12 can be secured at a predetermined level (for example, 29 MPa or more), and may be 90% or less, or 80% or less. It may be 70% or less, or 60% or less.

The strength of the insulating support 12 (three-point bending strength according to JIS R 1601) 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 battery shape. As described above, 29 MPa or more is suitable, 50 MPa or more is preferable, 100 MPa or more is more preferable, 120 MPa or more is further preferable, and 130 MPa or more is particularly preferable. Here, since the transition metal oxide obtained by melting and solidifying the sintering aid exists inside the insulating support 12 so as to fill the gaps between the zirconia-based components, 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 above-mentioned strength can be easily formed.

(2) Fuel pole The fuel pole 14 is formed on the insulating support 12. The 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 lower surface to the upper surface. As a result, 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 to 20%, for example, about 15%. Although not particularly limited, the 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), Lantern (La), Strontium (Sr), Titanium (Ti) and other metals, or metal oxides thereof. Such materials may be used alone or in combination of two or more. Among them, nickel is particularly suitable because it is cheaper than other metals and exhibits high reactive activity (sufficiently high reactivity with fuel gas). Further, the fuel electrode 14 may contain a zirconia-based oxide (for example, YSZ) of the same type 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, for example, 3: 7 to 7: 3, for example, about 6: 4 in terms of mass ratio.

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

(4) Air pole The air pole 18 is formed on the solid electrolyte layer 16. The air electrode 18 includes, for example, (La, Sr) CoO ₃ (for example, La _0.6 Sr _0.4 CoO ₃ ; hereinafter appropriately referred to as LSC) or (La, Sr) (Co, Fe) O ₃ (for example). , La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ ; hereinafter, as appropriate, LSCF) and the like, it is composed of a perovskite-type oxide containing La, Sr, Co. As these LSC and LSCF, the substitution ratios of both A and B sites can be variously determined, and those having an appropriate substitution ratio can be used according to the desired ionic conductivity, reduction expansion coefficient and the like. Further, the air electrode 18 is a porous body like the insulating support 12 and the fuel electrode 14, 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 over the entire air electrode 18.

As described above, the insulating support 12 of the SOFC 10 according to the present embodiment is sufficient because the porosity of 5% or more is maintained even though measures for preventing the occurrence of cracks are taken. Can exhibit gas permeability.

[Test example]
Hereinafter, some test examples relating to the present invention will be described, 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 a green sheet was prepared using each of the support forming materials. Then, it was evaluated whether or not cracks were generated during the firing of the green sheet.

1. 1. Preparation of sample (1) Sample 1
A mixed powder containing coarse zirconia powder (8YSZ having an average particle size of 1.5 μm) and fine zirconia powder (8YSZ having an average particle size of 0.25 μm), and a sintering aid (average particle size 1. A support forming material was prepared by mixing 69 μm Mn ₃ O ₄ ), a pore-forming material (acrylic fine particles), and a methyl cellulose-based binder with a double-arm kneader. Table 1 shows the contents of the coarse zirconia powder, the fine zirconia powder, and the sintering aid. The pore-forming material was added in an amount of 9 wt% with respect to 100 wt% of the coarse-grained zirconia powder. Further, 7 wt% of the binder was added to 100 wt% of the coarse zirconia powder.

(2) Samples 2-4
A support forming material was prepared under the same conditions as in Sample 1 except that the conditions regarding the sintering aid were changed. Specifically, in Sample 2, NiO was used as the sintering aid. Further, in Sample 3, MgO was used as a sintering aid. Then, in Sample 4, a support forming material to which no sintering aid was added was prepared.

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

Then, a paste for the fuel electrode (main component: NiO) and a paste for the solid electrolyte layer (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 calcined by holding it in a furnace for 2 hours to obtain a SOFC half cell for evaluation test. As shown in FIG. 2, in the half cell 100, a pair of fuel poles 140 are formed at intervals on the upper surface of the disc-shaped insulating support 120. Then, the solid electrolyte layer 160 is formed so as to straddle the pair of fuel poles 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: 400 times), and a crack was generated at the boundary to expose the insulating support 120. I checked whether it was. The evaluation results are shown in Table 1, and the laser micrographs of Samples 1 and 4 are shown in FIGS. 3 and 4.

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 also obtained for Sample 2. On the other hand, as shown in Table 1 and FIG. 4, cracks were generated in the sample 4 and the insulating support 120 was exposed. From this, it was found that the occurrence of cracks in co-firing can be suppressed by adding the sintering aid to the support forming material. Further, in sample 3, cracks similar to those in sample 4 were generated even though the metal oxide (MgO) was added. From this, it was found that it is necessary to use a transition metal oxide as the 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 the conditions that are compatible.

1. 1. Preparation of sample A mixed powder containing coarse zirconia powder (8YSZ with an average particle size of 1.5 μm) and fine zirconia powder (8YSZ with an average particle size of 0.25 μm), and a sintering aid (average grain size). and _Mn 3 _{O 4)} of diameter 1.69Myuemu, was prepared by mixing with the support forming material and a cellulose based binder in a double-arm kneader. At this time, if the content of the fine zirconia powder with respect to the mixed powder (100 wt%) is different in the range of 0 wt% to 100 wt% and the content of the sintering aid is different in the range of 0 wt% to 5 wt%. 13 kinds of support forming materials (samples 5 to 17) were prepared by making the material. The composition of each sample is shown in Table 2. The other conditions were set to the same conditions as in sample 1 of the first test.

2. Evaluation test An SOFC half cell 100 was prepared under the same conditions as in the first test, and the presence or absence of cracks was examined using a laser microscope. The results are shown in Table 2.
In addition, in this test, the surface of the insulating support was observed using SEM. The surface SEM observation image of the sample 6 is shown in FIG. 5, the surface SEM observation image of the sample 10 is shown in FIG. 6, and the surface SEM observation image of the sample 14 is shown in FIG.

Furthermore, in this test, the porosity was measured for the insulating support of each sample based on the Archimedes method. Specifically, first, the dry weight was measured W _air of insulating support of each sample. Next, after immersing each sample in distilled water, the sample was placed in a desiccator equipped with a vacuum pump and evacuated for 45 minutes to measure the underwater weight W _aq and the water content weight _{WA + w} of the insulating support. Then, the porosity (P) was calculated based on the following formula (1). Then, when the porosity was 5% or more, it was evaluated as "possible", and when it was less than 5%, it was evaluated as "impossible". The results are shown in Table 2.
P = (WA _{+ w-} W _Air ) / (WA _{+ w-} W _aq ) (1)

As shown in Table 2, in each sample except samples 9 and 14, cracks were prevented from occurring during co-firing. From this, it was found that the occurrence of cracks in 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, from the measurement results of the porosity, the porosity is remarkable in the samples 5, 8, 15 to 17 containing the sintering aid of 1.5 wt% or more and the sample 10 in which the content of the fine zirconia powder is 100 wt%. A significant decrease was confirmed. From this, in order to maintain the porosity of the insulating support after firing in a suitable state, the upper limit of the content of the sintering aid should be 1.2 wt% or less, and the upper limit of the content of the fine zirconia powder should be set. It turned out that it is necessary to specify 80 wt% or less.

Further, from the surface SEM observation image of each sample, in the sample 10 (see FIG. 6) using only the fine zirconia powder, an insulating support having a smooth surface was formed, and the sample 14 using only the coarse zirconia powder was formed. In (see FIG. 7), an insulating support having a plurality of wavy irregularities was formed on the surface. In sample 6 (see FIG. 5) using the mixed powder containing the fine zirconia powder and the coarse zirconia powder, an insulating support having less wavy irregularities than the sample 14 was formed.

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

10 SOFC
12, 120 Insulating support 14, 140 Fuel pole 16, 160 Solid electrolyte layer 18 Air pole 100 Half cell

Claims (4)

A support forming material for forming an insulating support that supports the fuel electrode of a solid oxide fuel cell.
A mixed powder containing at least a coarse zirconia powder having an average particle size of 1 μm or more and 4 μm or less and a fine zirconia powder having an average particle size of 0.1 μm or more and 0.5 μm or less.
Contains a sintering aid containing particles of transition metal oxides,
When the total weight of the mixed powder is 100 wt%, the weight of the fine zirconia powder is 20 wt% or more and 80 wt% or less.
A material for forming a support 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%. The material for forming a support according to claim 1, wherein the average particle size of the sintering aid is 0.02 μm or more and 30 μm or less. The support forming according to claim 1 or 2, wherein the sintering aid contains one or more particles selected from the group consisting of Mn ₃ O ₄ , NiO, CuO, Fe ₂ O ₃ , ZnO, and CoO. Material for. An insulating support that is a porous body that allows fuel gas to permeate and contains zirconia-based components,
With the fuel electrode formed on the insulating support,
The solid electrolyte layer formed on the fuel electrode and
A solid oxide fuel cell provided with 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 components is 100 wt%. A solid oxide fuel cell having a pore ratio of 5% or more.