JP2007335193A - Ceria layer for air electrode of solid oxide fuel cell, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve adhesiveness of an air electrode with an electrolyte membrane, and improve electrode characteristics of the air electrode in a solid oxide fuel cell in which a zirconia based electrolyte is used as the electrolyte membrane. <P>SOLUTION: Between the electrolyte substrate 1 that is the electrolyte membrane and the air electrode 2, the ceria layer 4 composed of the ceria based electrolyte material is arranged. A mixed powder in which a high specific surface area powder which is the ceria based electrolyte material powder having a specific surface area of 15 m<SP>2</SP>/g or more and a low specific surface area powder having a specific surface area of 10 m<SP>2</SP>/g or less are mixed at the weight ratio of 15:85 to 80:20 is prepared, and by developing this mixed powder into development liquid, a slurry is produced, and after this slurry is applied to the electrolyte substrate 1, the ceria layer 4 is formed by calcining it. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solid oxide fuel cell (SOFC) (also referred to as a solid oxide fuel cell), and in particular, is disposed between an electrolyte membrane and an air electrode in a solid oxide fuel cell. The present invention relates to a ceria layer and a manufacturing method thereof.

  In recent years, as a fuel cell, there has been an interest in a solid oxide fuel cell using an oxygen ion conductor, which is a solid oxide, as an electrolyte membrane. A solid oxide fuel cell has a configuration in which an electrolyte membrane that is an oxygen ion conductor is sandwiched between a fuel electrode that serves as a negative electrode and is supplied with fuel, and an air electrode that serves as a positive electrode and is supplied with air (or oxygen). In many cases, a dense zirconia solid electrolyte is used as the electrolyte membrane. Both the fuel electrode and the air electrode are made of a porous material, and are typically formed by firing a ceramic material. From the viewpoint of effective use of energy, the solid oxide fuel cell has essentially high energy conversion efficiency because it is not limited by Carnot efficiency, which is a constraint in heat engines, It has excellent features such as good environmental protection. In a solid oxide fuel cell, since an electromotive force generated by a unit cell is small, it is general to configure a cell stack by connecting a plurality of cells in series so that a desired voltage output can be obtained.

  Such a solid oxide fuel cell has an operating temperature as high as 900 ° C. to 1000 ° C. in the initial stage of development, and all the members must be made of ceramic. was difficult. Here, if the operating temperature can be lowered to about 800 ° C., it becomes possible to configure an interconnect used for electrical connection between cells and power extraction from the cell with a heat-resistant alloy material. Cost can be reduced. However, as the operating temperature decreases, the electrochemical resistance at the air electrode, that is, the overvoltage, increases rapidly, resulting in a decrease in the output voltage from the cell stack.

  With regard to such a decrease in output voltage, by reducing the particle size of the material constituting the air electrode when forming the air electrode by firing, the low temperature characteristics of the air electrode are improved, that is, the electrochemical resistance is reduced. It is known that a reduction can be achieved. This is the length of the three-phase interface that is responsible for the electrochemical reaction at the electrode, that is, the portion where the three phases of the oxygen ion conductive electrolyte membrane, air electrode constituent particles, and air contact (three-phase interface length). It is because it can enlarge.

Conventionally, lanthanum (La) -based perovskite-based oxidations such as La (Sr) MnO ₃ and La (Sr) Fe (Ni) O _3, which have high electron conductivity and are stable even in a high-temperature oxidizing atmosphere, have been used for air electrodes. The porous body which baked the powder of the thing is used. However, when a lanthanum-based perovskite material is used for the air electrode, the zirconia-based electrolyte material used as the electrolyte membrane and the air electrode material react slightly to react with La ₂ Zr ₂ O ₇ during firing of the air electrode. A non-conductive layer (insulator layer) is formed. As a result, the characteristics of the air electrode deteriorate. In order to prevent such deterioration of the characteristics of the air electrode, some buffer that prevents the reaction between the electrolyte film made of the zirconia-based electrolyte material and the air electrode made of the lanthanum-based perovskite oxide is used. It is conceivable to provide a layer. The buffer layer is required to have oxygen ion conductivity, and the use of a ceria-based electrolyte material as a material constituting such a buffer layer has been studied.

The ceria-based electrolyte material includes ceria (CeO ₂ ) added with rare earth such as gadria (Gd ₂ O ₃ ), samaria (Sm ₂ O ₃ ), and yttria (Y ₂ O ₃ ), and has the general formula Ce _{1- xM x} O _2-d (M = Gd, Sm, Y; X = 0.1 to 0.2; d is the amount of oxygen defects), etc., and these have almost the same properties. The ceria-based electrolyte material is suitable for a buffer layer provided between the electrolyte membrane and the air electrode because it has excellent oxygen ion conductivity and low reactivity with the perovskite-based air electrode material. In the following description, when describing the composition of the ceria-based electrolyte material, the oxygen defect amount d is ignored and described as Ce _1-x M _x O _2-d (M = Gd, Sm, Y). However, this does not mean that the oxygen deficiency d is 0, that is, a stoichiometric composition.

  However, the ceria-based electrolyte material has low sinterability, and a layer having relatively strongly bonded crystal grains can be finally obtained by performing high-temperature firing at 1250 ° C. or higher. In particular, when a buffer layer made of a ceria-based electrolyte material is formed using a simple coating method such as a screen printing (screen printing) method, a film with insufficient mechanical strength tends to be formed, and as a result, the electrolyte membrane or air electrode Adhesiveness at the interface with the substrate becomes insufficient, and the characteristics of the cell itself are deteriorated.

  In addition, the ceria-based electrolyte material is easily dissolved in a zirconia-based electrolyte material used as an electrolyte membrane that separates the fuel electrode and the air electrode, so high-temperature firing is performed to form a buffer layer made of the ceria-based electrolyte material. Doing so tends to produce components of low electrical conductivity. Furthermore, since zirconium (Zr) atoms diffuse from the zirconia-based electrolyte material at a high concentration in the buffer layer, the effect as the buffer layer is greatly impaired. Furthermore, there is also a problem that the grain growth of the air electrode proceeds by firing at a high temperature, and the area of the three-phase interface that is an electrochemical reaction field is reduced. In addition, the higher the firing temperature, the more expensive the furnace (firing furnace) becomes necessary, which is disadvantageous in terms of production cost. For these reasons, there is a need to reduce the firing temperature for forming a buffer layer made of a ceria-based electrolyte material.

  A method for producing a buffer layer made of a ceria-based electrolyte material is a slurry in which a powder of ceria-based electrolyte material is developed in a developing solution made of an organic material, and this is applied onto the electrolyte membrane by a screen printing method or the like. It is common to perform firing. By the way, in general, when firing is performed, it is known that by increasing the specific surface area of the raw material powder, the sinterability is improved even when the firing temperature is low. This is because the powder having a large specific surface area has a fine microstructure in the powder particles themselves, and sintering proceeds in the process of disappearance of the microstructure by firing. However, when forming a slurry using a powder particle having a large specific surface area, applying and firing the slurry, and forming a buffer layer made of a ceria-based electrolyte material, in order to produce a slurry of the same viscosity, the specific surface area is more The larger the powder used, the more developing solution needs to be mixed. This is because, due to the fine structure of the powder, the larger the specific surface area, the larger the surface area on which the solution (developing liquid) can be adsorbed, and more developing liquid is adsorbed on the surface inside the fine structure. In this way, when a slurry with a large amount of solution (developing solution) adsorbed inside the microstructure is applied and baked, the film after coating and drying becomes more porous, so the buffer layer after baking is more porous. Become. When the buffer layer is porous, the mechanical strength and the adhesive strength are reduced.

In addition, as a general review regarding the solid oxide fuel cell (SOFC), there is one described in Non-Patent Document 1. Non-patent document 2 describes providing a buffer layer made of a ceria-based electrolyte material.
NQ Minh; J. Am. Ceram. Soc., 76, 563 (1993) M. Shiono, K. Kobayashi, TL Nguyen, K. Hosoda, T. Kato, K. Ota and M. Dokiya; Solid State Ionics, 170 (2004) 1

  As described above, in the solid oxide fuel cell, in order to prevent the reaction deterioration between the air electrode and the electrolyte membrane and to improve the electrical characteristics, the air electrode and the electrolyte membrane having oxygen ion conductivity are disposed between the air electrode and the electrolyte membrane. It is effective to provide a buffer layer, and the ceria-based electrolyte material is a promising material for the buffer layer. However, when a powder having a large specific surface area is used as a raw material powder for the ceria-based electrolyte material used for firing, the buffer layer formed by firing becomes porous, and the electrolyte membrane or air The subject that the adhesive force with respect to a pole falls arises.

  In the following description, a buffer layer that is disposed between an electrolyte membrane and an air electrode and is made of a ceria-based electrolyte material is referred to as a ceria layer.

  Accordingly, an object of the present invention is to provide a ceria layer that is dense and has high adhesion even when firing at low temperatures.

  Therefore, another object of the present invention is to provide a raw material powder used for the production of a ceria layer that is dense and has high adhesion even when firing at a low temperature, and a method for producing such a ceria layer. is there.

The air electrode ceria layer of the present invention is an air electrode ceria layer disposed between an air electrode and an electrolyte membrane of a solid oxide fuel cell.
[1] A ceria-based electrolyte material powder having a specific surface area of 15 m ² / g or more, and a ceria-based electrolyte material powder having a specific surface area of 10 m ² / g or less. The powder is mixed so that the mixing ratio of the first powder is 15% or more and 80% or less by weight with respect to the total amount of powder of the ceria-based electrolyte material, or [2] A first powder having an average particle diameter of 0.3 μm or less, and a second powder having a specific surface area of 15 m ² / g or more and an average particle diameter exceeding 0.3 μm, the powder being a ceria-based electrolyte material And a third powder having a specific surface area of 10 m ² / g or less and an average particle size exceeding 0.3 μm, based on the total amount of the ceria-based electrolyte material powder. The mixing ratio of the powder is 5% to 70% by weight and the second So that the mixing ratio of the powder is 15% to 80% by weight,
Then, the mixed powder is developed into a developing solution to produce a slurry, and the slurry is obtained by firing.

The raw material powder of the present invention is a raw material powder used to form a slurry by spreading in a developing solution, and is a first powder having a specific surface area of 15 m ² / g or more, which is a powder of a ceria-based electrolyte material. And a ^second powder having a specific surface area of 10 m ² / g or less, wherein the mixing ratio of the first powder is in a weight ratio with respect to the total amount of the ceria electrolyte material powder. It is mixed so as to be 15% or more and 80% or less.

Another raw material powder of the present invention is a raw material powder used to form a slurry by spreading in a developing solution, and is a ceria-based electrolyte material powder having an average particle size of 0.3 μm or less. A ceria-based electrolyte material powder having a specific surface area of 15 m ² / g or more and an average particle size exceeding 0.3 μm, and a ceria-based electrolyte material powder having a specific surface area of The third powder having an average particle size of 10 m ² / g or less and an average particle size exceeding 0.3 μm is mixed at a weight ratio of 5% to 70% of the first powder with respect to the total amount of the ceria-based electrolyte material powder. The second powder is mixed so that the mixing ratio of the second powder is 15% or more and 80% or less by weight.

  The method for producing a ceria layer according to the present invention is a method for producing a ceria layer for an air electrode disposed between an air electrode and an electrolyte membrane of a solid oxide fuel cell. The slurry is developed to produce a slurry, the slurry is applied on the electrolyte membrane, and then fired. As a method for applying the slurry onto the electrolyte membrane, for example, a wet coating method such as a screen printing method, a dip coating method, or a doctor blade method can be used.

[Action]
When it is intended to obtain a ceria layer having a desired thickness by applying and baking the slurry, it is important to control the viscosity of the applied slurry. In particular, when a thin ceria layer is formed, it is necessary to reduce the layer thickness of the slurry to be applied, and it is necessary to reduce the viscosity of the slurry. Here, as the ceria-based electrolyte material powder for forming the ceria layer, a high specific surface area powder having a specific surface area of 15 m ² / g or more and a relatively large specific surface area, and a relative surface area of 10 m ² / g or less Consider a case where a low specific surface area powder having a small specific surface area is mixed and developed into a developing solution to produce a slurry. In order to obtain a slurry having the same viscosity, an amount of a developing solution corresponding to the ratio of the high specific surface area powder and the low specific surface area powder is required. Therefore, by reducing the amount of powder having a relatively large specific surface area, the amount of the developing solution made of organic matter can be kept low.

  On the other hand, regarding the sinterability, if the slurry contains a powder having a large specific surface area to some extent, the sinterability can be kept high. This is because powder particles with high sinterability (high specific surface area powder) adhere powder particles with low sinterability (low specific surface area powder). Specifically, the mixing amount of the high specific surface area powder is 15% or more and 80% or less in a weight ratio with respect to the total weight of the ceria-based electrolyte material, but this may be 20% or more and 80% or less. Preferably, it is more preferably 30% or more and 70% or less. By setting the mixing amount of the high specific surface area powder to the value as described here, high sinterability is exhibited even when firing at a relatively low temperature, and since the porosity during drying is low, it is dense. A ceria layer having high adhesion can be obtained.

  Furthermore, the porosity when the slurry is dried can be obtained by adding a powder of a ceria-based electrolyte material having an average particle size of 0.3 μm or less (fine particle powder) as a third powder to the slurry. And a better layer is obtained. Further, the slurry containing powder having an average particle size of about 0.3 μm becomes smooth and easy to apply. As a result, the amount of the developing solution can be further reduced, and a denser and highly adherent ceria layer can be obtained. Specifically, the mixing amount of the fine-grained powder is preferably 5% or more and 70% or less by weight ratio with respect to the total weight of the ceria-based electrolyte material, and more preferably 10% or more and 50% or less. preferable. In addition, although the average particle diameter of the powder of a commercially available ceria type | system | group electrolyte material is about 0.5 micrometer-1 micrometer, the powder whose average particle diameter is 0.3 micrometer or less is also marketed.

In the present invention, a solid oxide fuel cell has a relatively large specific surface area of 15 m ² / g or more when forming a ceria layer provided between an electrolyte membrane having oxygen ion conductivity and an air electrode. By mixing a powder particle having a high sinterability (high specific surface area powder) and a powder particle having a relatively small specific surface area (low specific surface area powder) of 10 m ² / g or less to produce a slurry, In such a mixture, powder particles (fine particle powder) with an average particle size of 0.3 μm or less are further mixed to minimize the amount of developing liquid composed of organic matter without increasing the viscosity of the slurry. Can do. As a result, the porosity of the ceria layer forming slurry is reduced when applied and dried, and then the sinterability is increased when sintering is performed, improving the mechanical strength and interfacial adhesion of the ceria layer. Can be made.

  Thus, a highly reliable air electrode for a solid oxide fuel cell can be obtained. The present invention greatly contributes to improving the reliability of a solid oxide fuel cell.

  Next, the present invention will be described using examples. As a matter of course, the present invention is not limited to the following examples.

[Example 1, Comparative Examples 1 and 2]
First, a solid consisting of 0.2mm thick by _{Sc 2 O 3, Al 2 O} 3 doped zirconia fired at a doctor blade method _{(SASZ) (0.89ZrO 2 -0.10Sc 2} O 3 -0.01Al 2 O 3) 40 masses of NiO—YSZ (0.92ZrO ₂ −0.08Y ₂ O ₃ ) slurry (10 mol% Y ₂ O ₃ added zirconia (YSZ) powder having an average particle size of about 0.3 μm) on one surface of the electrolyte substrate And a platinum (Pt) mesh current collector was placed thereon by applying a screen printing method, and a platinum (Pt) mesh current collector 1400. Firing was performed in air at 4 ° C. for 4 hours, and a fuel electrode having a thickness of 60 μm was provided. In the description of the examples and comparative examples of the present specification, the average particle diameter of the powder is measured by a laser diffraction method, and the laser diffraction / scattering type particle size distribution measuring apparatus manufactured by HORIBA, Ltd. is used for the measurement. HORIBA LA-920 was used. The specific surface area of the powder was measured by the BET 1-point method, and Flow Sorb 2000 manufactured by Shimadzu Corporation was used for the measurement.

Next, a slurry in which a powder of LNF (LaNi _0.6 Fe _0.4 O ₃ ) having an average particle diameter of 1.0 μm is developed in polyethylene glycol is prepared, and this is applied to the back surface of the electrolyte substrate by a screen printing method. A platinum mesh current collector was placed and baked in air at 1100 ° C. for 2 hours to provide an air electrode having a thickness of 40 μm. As a result, the fuel electrode and the air electrode are provided on both surfaces of the solid electrolyte substrate used as the electrolyte membrane having oxygen ion conductivity, respectively. Both the fuel electrode and the air electrode were provided with a diameter of 10 mm. The fuel cell thus produced is referred to as the fuel cell of Comparative Example 1, and is represented by cell # 1-0-0 in the following description.

  FIG. 1 is a perspective view showing a configuration of a fuel cell (cell # 1-0-0) of Comparative Example 1, and (A) shows a configuration of a single cell when a power generation test is performed as a fuel cell. B) shows the structure of the half cell when the adhesion test is performed. In the single cell shown in (A), an air electrode 2 is formed as a circular region having a diameter of 10 mm at a substantially central portion of the upper surface of the substantially rectangular electrolyte substrate 1. A reference electrode 3 made of platinum mesh or the like is formed on the outer periphery of the electrolyte substrate 1. Although it is a perspective view, the back surface side of the electrolyte substrate 1 is not shown, but a fuel electrode having the same shape as the air electrode 2 is provided on the back surface of the electrolyte substrate 1 at a position corresponding to the air electrode 2. Further, the half cell shown in (B) has a configuration in which only the air electrode 2 is provided on the electrolyte substrate 1. In the half cell, the air electrode 2 is formed as a rectangular area of 10 mm square for convenience of the adhesion test.

Next, a fuel cell having a ceria layer made of a ceria-based electrolyte material was produced as a fuel cell (cell # 1-1-0) of Comparative Example 2. In this fuel cell, after forming up to the fuel electrode on the surface of the electrolyte substrate in the same procedure as the manufacturing process of the cell of Comparative Example 1 (cell # 1-0-0) described above, the specific surface area is formed on the back surface of the electrolyte substrate. There _{^{10m 2 / g, Ce 0.8 Gd}} 0.2 O 2 powder with an average particle size of 0.5 [mu] m; the slurry was developed (powder a low specific surface area powders) polyethylene glycol was coated by screen printing, 2 at 1000 ° C. The ceria layer was provided by firing in air for a period of time. The thickness of the ceria layer after firing was 5 μm. After that, a platinum mesh current collector is placed on the ceria layer by the same procedure as in Comparative Example 1, and an LNF slurry is applied and baked in air at 1100 ° C. for 2 hours to form an air electrode. did.

Next, the fuel cell (cell # 1-1-1 to # 1-1-5) of the example was formed. This fuel cell is a Ce _0.8 Gd _0.2 O ₂ powder having a specific surface area of 10 m ² / g and an average particle size of 0.5 μm as a powder used for forming a ceria layer in the fuel cell of Comparative Example 2. Instead of Ce _0.8 Gd _0.2 O ₂ powder (powder A; low specific surface area powder) having a specific surface area of 10 m ² / g and an average particle diameter of 0.5 μm, a specific surface area of 20 m ² / g and an average particle diameter of Using a mixture of Ce _0.8 Gd _0.2 O ₂ powder (powder B; high specific surface area powder) of 0.5 μm, a slurry of such a mixture was prepared to form a ceria layer under the same conditions as in Comparative Example 2. It is a thing. The electrolyte substrate, fuel electrode, air electrode, and reference electrode are the same as those in Comparative Example 2. Here, in the mixed powder for forming the ceria layer, those in which the weight ratios of the powder A and the powder B are 85:15, 70:30, 50:50, 30:70, and 20:80 are the cell # 1-1. -1 to # 1-1-5.

Further, as a powder used for forming the ceria layer, a Ce _0.8 Gd _0.2 O ₂ powder (powder A; low specific surface area powder) having a specific surface area of 10 m ² / g and an average particle size of 0.5 μm and a specific surface area A mixture of 30 m ² / g and Ce _0.8 Gd _0.2 O ₂ powder (powder C; high specific surface area powder) having an average particle size of 0.5 μm was used to prepare a slurry of such a mixture, and a comparative example By forming the ceria layer under the same conditions as in Example 2, fuel cells (cells # 1-2-1 to # 1-2-5) of the example were formed. The electrolyte substrate, fuel electrode, air electrode, and reference electrode are the same as those in Comparative Example 2. Here, in the mixed powder for forming the ceria layer, those in which the weight ratios of the powder A and the powder C are 85:15, 70:30, 50:50, 30:70, and 20:80 are the cell # 1-2. -1 to # 1-2-5.

Similarly, Ce _0.8 Gd _0.2 O ₂ powder (powder A; low specific surface area powder) having a specific surface area of 10 m ² / g and an average particle diameter of 0.5 μm and a specific surface area are used as powders for forming the ceria layer. compared to prepare a slurry with a mixture of a; (high specific surface area powder powder D), such mixtures but 45 m ² / g, an average particle diameter of Ce _0.8 Gd _0.2 O ₂ powder is 0.9μm By forming the ceria layer under the same conditions as in Example 2, the fuel cell of Example (cells # 1-3-1 to # 1-3-5) was formed. The electrolyte substrate, fuel electrode, air electrode, and reference electrode are the same as those in Comparative Example 2. Here, those in which the weight ratio of powder A to powder D in the mixed powder for ceria layer formation is 85:15, 70:30, 50:50, 30:70, and 20:80 are the cell # 1-3. -1 to # 1-3-5.

  FIG. 2 shows the configuration of a single cell of a fuel cell having a ceria layer. An electrolyte substrate 1 made of a dense zirconia solid electrolyte used as an oxygen ion conductor, a fuel electrode 5 provided in a substantially central region of one surface of the electrolyte substrate 1, and an outer peripheral portion of the electrolyte substrate 1 A reference electrode 3, an air electrode 2 provided in a substantially central region of the other surface of the electrolyte substrate 1, and a ceria layer 4 disposed at the interface between the electrolyte substrate 1 and the air electrode 2 are provided.

The cells of Examples and Comparative Examples produced as described above were assembled into a fuel cell, and the electrode characteristics of the air electrode at 800 ° C. were measured by the AC impedance method. Here, 3% humidified hydrogen (H ₂ + H ₂ O) was supplied to the fuel electrode, and oxygen (O ₂ ) was supplied to the air electrode and the reference electrode. Humidification to hydrogen was performed at room temperature. The electrode characteristics were evaluated by the interface resistance under open electromotive force conditions. For any cell, an open electromotive force of 1.14 V or higher was obtained. FIG. 3 is a cross-sectional view showing the configuration of the fuel cell at the time of electrode characteristic evaluation. Although not shown, in the case of the cell of Comparative Example 2 and each example, a ceria layer is formed between the air electrode and the electrolyte substrate. Also, platinum terminals are connected to the platinum mesh current collectors of the fuel electrode and the air electrode, respectively. A platinum terminal is also connected to the reference electrode.

  Further, with respect to the cells of these examples and comparative examples, a half cell (see FIG. 1B) that does not include a fuel electrode and a reference electrode is manufactured, and how close the air electrode is to the solid electrolyte substrate. An adhesion test was conducted. In this case, as described above, the shape of the air electrode was a square shape with one side of 1 cm. The test was performed by forming an air electrode on a solid electrolyte substrate by firing in a state where the platinum mesh current collector was not placed, and then attaching an adhesive tape on the air electrode and peeling off the adhesive tape. If the adhesion of the air electrode to the solid electrolyte substrate is weak, when the adhesive tape is peeled off, a part of the air electrode is peeled off and remains attached to the adhesive tape, which increases the mass of the adhesive tape. To do. Therefore, the original mass of the air electrode is obtained separately, and after calculating the amount of the air electrode remaining after applying and peeling the adhesive tape, calculate this. The residual ratio (residual mass ratio) was used. The closer the residual mass ratio is to 1 (ie 100%), the stronger the adhesion. The particle residual rate was similarly evaluated for the ceria layer components. In each of the following examples, the cell shown in FIG. 1A and the cell shown in FIG. 1B are manufactured using a slurry having the same composition, and the cell shown in FIG. 1A is used. The air electrode interface resistance was measured, and an adhesion test was performed using the cell shown in FIG. 1B. For convenience, the cell shown in FIG. 1A and the cell shown in FIG. As the same cell number.

  Examples (cells # 1-1-1 to # 1-1-5, # 1-2-1 to # 1-2-5, # 1-3-1 to # 1-3-5) and comparative examples Table 1 shows the evaluation results of the electrode characteristics and the evaluation results of the particle residual ratio for (cells # 1-0-0 and # 1-1-0).

Cell # 1-1 of Comparative Example 2 in which a ceria layer made of Ce _0.8 Gd _0.2 O ₂ was formed using only a low specific surface area powder, as compared with Cell # 1-0-0 of Comparative Example 1 which originally did not have a ceria layer. −0 indicates a smaller interface resistance, and the electrode characteristics are improved. On the other hand, as for the adhesion, the comparative example 2 is lower than the comparative example 1 (the residual rate is small). The cells of the examples (cells # 1-1-1 to # 1-2-5) exhibit an interface resistance comparable to or lower than that of Comparative Example 2, and have electrode characteristics equivalent to or higher than those of Comparative Example 2. And has improved adhesion. That is, by forming a ceria layer using a slurry in which a high specific surface area powder having a specific surface area of 15 m ² / g or more is mixed with a low specific surface area powder, the ceria that has improved electrical characteristics and adhesion as an electrode. It can be seen that a layer is obtained.

Here, in the case of powder B having a specific surface area of 20 m ² / g, considering the mixing ratio when the particle residual ratio is maximum for each of powder B, powder C, and powder D, which are high specific surface area powders. In the case of powder C having a specific surface area of 30 m ² / g when the mixing amount is 70%, the particle residual rate is maximum when the mixing amount is 50%. In the case of the powder D having a surface area of 45 m ² / g, the particle residual rate is maximized when the mixing amount is 30%. Further, the air electrode interface resistance when the particle residual ratio is maximum is substantially equal to the minimum value of the air electrode interface resistance when the powder is used. From this, it can be seen that by using a ceria-based electrolyte powder having a larger specific surface area as the high specific surface area powder, the optimum mixing amount is reduced (the ratio of the low specific surface area powder can be increased).

[Example 2]
In Example 1, two types of ceria-based electrolyte material powders (Ce _0.8 Gd _0.2 O ₂ powder) having different specific surface areas are mixed. In Example 2, a ceria-based electrolyte material for forming a ceria layer is used. As a powder, a Ce _0.9 Gd _0.1 O ₂ powder (powder E; fine-grained powder) having a specific surface area of 10 m ² / g and an average particle diameter of 0.2 μm, a specific surface area of 10 m ² / g, and an average particle diameter of 0. a 5μm Ce _0.9 Gd _0.1 O ₂ powder (powder F; low specific surface area powders), a specific surface area of _{^{30m 2 / g, Ce 0.9 Gd}} 0.1 O 2 powder with an average particle size of 0.5 [mu] m (powder G; low ratio Surface area powder) at a mass ratio of 5:80:15, 70:15:15, 5:15:80, 10:60:30, 50:20:30, 10:20:70, 20:30:50. A slurry was prepared using mixed powders mixed with each other, and the same conditions as in Comparative Example 2 were obtained. In to produce a fuel cell, and they and the cell # 2-1-1～ # 2-1-7. Then, as in the case of Example 1, the electrode characteristics and the adhesion were evaluated. These results are shown in Table 2.

  All the cells were smaller than the cell of Comparative Example 1 (Cell # 1-0-0) and exhibited an interface resistance comparable to or lower than that of the cell of Comparative Example 2 (Cell # 1-1-0). . About the adhesive force, it is improving rather than the cell of each comparative example.

  Thus, according to the present invention, the adhesion of the ceria layer can be improved, and the mechanical strength of the ceria layer itself can be improved.

(A) is a perspective view which shows the single cell of a fuel cell, (B) is a perspective view which shows the half cell of a fuel cell. It is sectional drawing of the fuel battery cell which has a ceria layer. It is a schematic cross section which shows the fuel cell structure used in the Example.

Explanation of symbols

1 Electrolyte Substrate 2 Air Electrode 3 Reference Electrode 4 Ceria Layer 5 Fuel Electrode

Claims (5)

In the ceria layer for the air electrode disposed between the air electrode and the electrolyte membrane of the solid oxide fuel cell,
A first powder having a specific surface area of 15 m ² / g or more, and a second powder having a specific surface area of 10 m ² / g or less, which is a powder of ceria-based electrolyte material and having a specific surface area of 15 m ² / g or more. Then, mixing is performed such that the mixing ratio of the first powder is 15% or more and 80% or less by weight with respect to the total amount of powder of the ceria-based electrolyte material, and the mixed powder is developed into a developing solution to prepare a slurry. A ceria layer for an air electrode obtained by firing the slurry. In the ceria layer for the air electrode disposed between the air electrode and the electrolyte membrane of the solid oxide fuel cell,
A first powder having a mean particle size of 0.3 μm or less, which is a powder of ceria-based electrolyte material, and a powder of ceria-based electrolyte material having a specific surface area of 15 m ² / g or more and an average particle size of 0.1. A second powder exceeding 3 μm and a third powder having a specific surface area of 10 m ² / g or less and an average particle size exceeding 0.3 μm are a powder of ceria-based electrolyte material. And mixing so that the mixing ratio of the first powder is 5% to 70% by weight and the mixing ratio of the second powder is 15% to 80% by weight with respect to the total amount of A ceria layer for an air electrode, which is obtained by spreading a powder into a developing solution to produce a slurry, and firing the slurry. A raw material powder used to form a slurry by spreading in a developing solution,
A first powder having a specific surface area of 15 m ² / g or more and a second powder having a specific surface area of 10 m ² / g or less and having a specific surface area of 15 m ² / g or more. Raw material powder obtained by mixing so that the mixing ratio of the first powder is 15% or more and 80% or less by weight with respect to the total amount of powder of the ceria-based electrolyte material. A raw material powder used to form a slurry by spreading in a developing solution,
A first powder having a mean particle size of 0.3 μm or less, which is a powder of ceria-based electrolyte material, and a powder of ceria-based electrolyte material having a specific surface area of 15 m ² / g or more and an average particle size of 0.1. A second powder exceeding 3 μm and a third powder having a specific surface area of 10 m ² / g or less and an average particle size exceeding 0.3 μm are a powder of ceria-based electrolyte material. The mixing ratio is such that the mixing ratio of the first powder is 5% or more and 70% or less by weight and the mixing ratio of the second powder is 15% or more and 80% or less by weight. , Raw powder. In the method for producing a ceria layer for an air electrode disposed between an air electrode and an electrolyte membrane of a solid oxide fuel cell,
The raw material powder according to claim 3 or 4 is developed into a developing solution to produce a slurry,
Applying the slurry on the electrolyte membrane;
Then, baking is performed, The manufacturing method characterized by the above-mentioned.

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