JP2015064948A - Fuel cell and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the strength of fuel electrode while ensuring ventilation of the fuel gas.SOLUTION: In a fuel cell including a solid oxide electrolyte, and a fuel electrode supporting the electrolyte and composed of a composite of a metal and an oxygen ion conductive ceramics, the following structure is employed as the structure of the fuel electrode. In the fuel electrode, multiple first pores 31 are formed while being distributed, a second pore 33 is formed in a partition wall 32 between adjoining first pores, and the adjoining first pores 31 are communicating through the second pore 33. The mean diameter d1 of the first pores 31 is larger than the average thickness t1 of the partition wall 32, and the mean diameter d2 of the second pores 33 is smaller than the average thickness t1 of the partition wall 32. Since the first pores 31 are communicating through the second pore 33, ventilation of the fuel gas can be ensured even if the partition wall 32 between the adjoining first pores 31 is made thick in order to enhance the strength of the fuel electrode.

Description

  The present invention relates to a solid oxide fuel cell and a method for manufacturing the same.

  As this type of fuel cell, there is a fuel cell having a structure in which a solid oxide electrolyte is supported by a fuel electrode. Further, as the fuel electrode, a porous electrode is employed in order to provide fuel gas permeability. The porous fuel electrode is manufactured by firing an unfired sheet formed using raw material powder and a pore former. By this sintering, the raw material powder is sintered to form a sintered body, and the pore former disappears, whereby pores are formed in the sintered body (see, for example, Patent Document 1).

JP 2012-99497 A

  In the structure in which the fuel electrode supports the electrolyte, the fuel electrode is required to have high strength. However, the porous fuel electrode has a problem that the strength is low because the partition walls between the pores formed by the pore former are thin. Therefore, if an attempt is made to thicken the partition walls between the pores in order to improve the strength of the fuel electrode, the pores are likely to become independent, and the air permeability of the fuel gas cannot be ensured.

  The present invention has been made in view of the above points, and an object of the present invention is to improve the strength of a fuel electrode while ensuring air permeability of fuel gas.

In order to achieve the above object, in the invention described in claim 1,
A solid oxide electrolyte (2);
A fuel electrode (3) that supports the electrolyte and is composed of a composite of metal and oxygen ion conductive ceramics;
The fuel electrode has a plurality of first pores (31) dispersedly formed, and second pores (33) are formed inside the partition walls (32) between the adjacent first pores.
The average diameter (d1) of the first pores is larger than the average thickness (t1) of the partition walls, the average diameter (d2) of the second pores is smaller than the average thickness of the partition walls,
Adjacent first pores communicate with each other through second pores.

  According to this, even if the partition between the first pores is thickened, the first pores can be communicated with each other by the second pore provided in the partition. Therefore, according to the present invention, the strength of the fuel electrode can be improved while ensuring the gas gas permeability.

  In addition, the code | symbol in the bracket | parenthesis of each means described in this column and the claim is an example which shows a corresponding relationship with the specific means as described in embodiment mentioned later.

It is sectional drawing of the fuel battery cell in one Embodiment of this invention. It is an enlarged view of area | region A1 of FIG. It is a flowchart which shows the manufacturing process of the fuel cell in one Embodiment of this invention. It is a figure for demonstrating the manufacturing method of the fuel cell in one Embodiment of this invention, Comprising: It is a schematic diagram which shows the structure of the partition before a reduction process. It is a figure for demonstrating the manufacturing method of the fuel cell in one Embodiment of this invention, Comprising: It is a schematic diagram which shows the structure of the partition after a reduction | restoration process.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. A plurality of fuel cells of the present embodiment are stacked to constitute a fuel cell stack. For example, a flat plate fuel cell stack is configured by stacking a plurality of flat plate fuel cells 1.

  As shown in FIG. 1, the fuel cell 1 includes a solid oxide electrolyte 2, a fuel electrode 3, an active layer 4, and an air electrode 5.

  The electrolyte 2 is made of a solid oxide having oxygen ion conductivity, that is, ceramics. Examples of the ceramic include stabilized zirconia in which a rare earth oxide typified by yttria stabilized zirconia (hereinafter referred to as YSZ) is dissolved, ceria-based solid solution, perovskite oxide, and the like.

  The fuel electrode 3 is provided on one surface side of the electrolyte 2 and supports the electrolyte 2. The fuel electrode 3 is composed of a mixture of a metal typified by Ni and ceramics having oxygen ion conductivity. Examples of the ceramic include stabilized zirconia in which a rare earth oxide is solid-solved, ceria-based solid solution, and the like, similar to the ceramic that constitutes the electrolyte 2.

  The active layer 4 is disposed between the fuel electrode 3 and the electrolyte 2. Similar to the fuel electrode 3, the active layer 4 is made of metal and ceramics having oxygen ion conductivity. The active layer 4 is higher in oxygen ion conductivity than the fuel electrode 3, that is, the oxygen ion conductive ceramic content is higher than that of the fuel electrode 3 in order to increase the activity.

  The air electrode 5 is provided on the other surface side opposite to the one surface side of the electrolyte 2. The air electrode 5 is made of metal or metal oxide. Examples of the metal include Pt and Au. Examples of the metal oxide include lanthanum-cobalt oxide and lanthanum-nickel oxide.

  As shown in FIG. 2, the fuel electrode 3 includes first pores 31 that are formed in a distributed manner, and second pores 33 that are formed inside a partition wall 32 between adjacent first pores 31. .

  As will be described later, the first pores 31 are large pores formed by a pore former. The partition wall 32 is a structural portion that exists between the adjacent first pores 31 when the cut surface of the fuel electrode 3 is viewed. The adjacent first pores 31 refer to the first pores 31 that are not directly connected to each other on the cut surface of the fuel electrode 3 and are separated from each other. The interval between the adjacent first pores 31 is the thickness t1 of the partition wall 32. As will be described later, the second pores 33 are minute pores formed by volume contraction due to reduction of the metal oxide in the partition walls.

  The average diameter d1 of the first pores 31 is larger than the average thickness t1 of the partition walls 32, and the average diameter d2 of the second pores 33 is smaller than the average thickness t1 of the partition walls 32. The average diameter d2 of the second pores 33 is 1/5 or more and 1/10 or less of the average diameter d1 of the first pores 31. Illustrating these specific sizes, the average diameter d1 of the first pores 31 is not less than 1 μm and not more than 10 μm, the average diameter d2 of the second pores 33 is not less than 0.1 μm and less than 1 μm, and the average thickness of the partition walls 32 The length t1 is not less than 1 μm and not more than 10 μm.

  A plurality of the second pores 33 are continuous inside the partition wall 32. Adjacent first pores 31 communicate with each other through a plurality of second pores 33. For this reason, when the fuel gas is supplied to the fuel electrode 3, the fuel gas flows from the first pore 31 into the adjacent first pore 31 via the second pore 33. In this way, the fuel gas diffuses inside the fuel electrode 3.

  FIG. 2 shows a state in which a plurality of second pores 33 are continuous in the two-dimensional direction, but actually, a plurality of second pores 33 are continuous in the three-dimensional direction. When the actual cut surface is observed, the second pores 33 can be confirmed one by one, and the diameter of the second pores 33 can be measured. Incidentally, as shown in FIG. 2, in the continuous second pores 33, the length in the direction orthogonal to the longitudinal direction is the diameter d <b> 2 of the second pores 33.

  In the fuel cell 1 having the above-described configuration, when a fuel gas such as hydrogen is supplied to the fuel electrode 3 and an oxidant gas such as air is supplied to the air electrode 5, hydrogen and oxygen via the electrolyte 2 are Electric energy is generated by the electrochemical reaction. At this time, oxygen ions move in the electrolyte 2 from the air electrode 5 toward the fuel electrode 3.

  Next, a method for manufacturing the fuel cell 1 having the above-described configuration will be described.

  As shown in FIG. 3, the fuel cell 1 having the above-described configuration is manufactured by sequentially performing the sheet forming step S1, the firing step S2, and the reduction step S3.

  In the sheet forming step S <b> 1, an unfired sheet that forms the electrolyte 2, the fuel electrode 3, the active layer 4, and the air electrode 5 is formed.

  When forming an unfired sheet to be the fuel electrode 3, a metal oxide powder such as nickel oxide (NiO), a ceramic powder such as YSZ, and a pore former such as resin or carbon were dispersed in a solvent. Form a slurry. At this time, regarding the size relationship between the metal oxide powder and the ceramic powder, the average particle size of the metal oxide powder is made larger than the average particle size of the ceramic powder. This is because the second pores 33 are formed in the partition wall 32 so that the adjacent first pores 31 are sufficiently communicated with each other. As for the particle diameter and the amount of addition of the pore former, the size of the first pores 31 in the fuel electrode 3 after manufacture, the thickness of the partition walls 32, and the combined porosity of the first and second pores 33 are desired. Set to be the value of. Then, the formed slurry is formed into a sheet and dried to form an unfired sheet.

  Then, the laminated body which laminated | stacked the unbaked sheet | seat is baked by baking process S2. When the unsintered sheet serving as the fuel electrode 3 is fired, the metal oxide powder and the ceramic powder are sintered, and the pore former disappears, whereby the first pores 31 and the partition walls 32 are formed. At this stage, as shown in FIG. 4, the partition wall 32 is composed of a metal oxide 321 and a ceramic 322.

  Thereafter, in the reducing step S3, the fired body after the firing step is heated in a reducing gas atmosphere. Thereby, the metal oxide in the partition wall 32 in the fuel electrode 3 is reduced to become a metal, and the partition wall 32 is formed of a composite of the metal 323 and the ceramic 322 as shown in FIG. At this time, the reduction of the metal oxide 321 causes volume shrinkage, and the second pores 33 are formed in the partition wall 32. For example, when the metal oxide 321 is NiO, when heated in a hydrogen gas atmosphere, the NiO is reduced to Ni as shown in the following formula, resulting in volume shrinkage.

第１気孔３１は、造孔材の形状に応じた形状となる。このため、球状の造孔材を用いた場合、形成される第１気孔３１は、球状もしくは回転楕円体状となる。一方、第２気孔３３は、体積収縮によって形成されるため、不特定な形状となる。

The first pores 31 have a shape corresponding to the shape of the pore former. For this reason, when the spherical pore former is used, the formed first pores 31 are spherical or spheroid. On the other hand, since the 2nd pore 33 is formed by volume contraction, it becomes an unspecified shape.

  As described above, in the present embodiment, as the configuration of the fuel electrode 3, the plurality of first pores 31 are formed in a distributed manner, and the second pores 33 are formed in the partition walls 32 between the adjacent first pores 31. The formed configuration is adopted. In this configuration, the average diameter d1 of the first pores 31 is larger than the average thickness t1 of the partition walls 32, and the average diameter d2 of the second pores 33 is smaller than the average thickness t1 of the partition walls 32. The pores 31 communicate with each other through the second pores 33.

  According to this, even if the partition 32 between the first pores 31 is thickened, the first pores 31 can be communicated with each other by the second pores 33 provided in the partition 32. Therefore, according to the present invention, the strength of the fuel electrode 3 can be improved while ensuring the gas gas permeability.

  Further, since the size of the second pores 33 is very small, a plurality of second pores 33 are formed inside the partition wall 32. The average diameter d2 of the second pores 33 is not less than 1/5 and not more than 1/10 of the average diameter d1 of the first pores 31, and is specifically not less than 0.1 μm and less than 1 μm. As described above, since the second pores 33 formed in the partition wall 32 are very small, the strength is improved by increasing the thickness of the partition wall 32 rather than the strength reduction by forming the second pores 33 in the partition wall 32. Greatly contributes.

  The present invention is not limited to the above embodiment, and can be appropriately changed within the scope described in the claims as follows.

  In the above-described embodiment, the laminate in which the unfired sheets that are the electrolyte 2, the fuel electrode 3, the active layer 4, and the air electrode 5 are laminated is fired, but each unfired sheet is fired separately and joined together. May be. Moreover, in the said embodiment, although the fuel cell 1 was set as the structure by which the electrolyte 2, the fuel electrode 3, the active layer 4, and the air electrode 5 were laminated | stacked, the structure which abbreviate | omitted the active layer 4, and other than these It is good also as a structure containing a layer.

  In the above-described embodiment, it is needless to say that elements constituting the embodiment are not necessarily essential except when clearly stated to be essential and clearly considered essential in principle. .

  As Examples 1-6, the fuel electrode was formed independently by the following method.

A slurry was prepared by dispersing NiO powder, YSZ powder in which 8 mol% of yttria was dissolved, polyvinyl butyral (PVB) as a binder, and pore former in 2-butisoaluminum and ethanol as a mixed solvent. The mass ratio of the NiO powder and the YSZ powder was 60:40. Moreover, in each Example, the addition amount of the pore former was set so that the porosity shown in the following Tables 1 to 3 was obtained. The average particle size of each powder and the material of the pore former used in each example are as follows.
(Examples 1-3)
NiO powder: 0.7 μm
YSZ powder: 0.6 μm
Porous material (acrylic): 10 μm
(Examples 4 to 6)
NiO powder: 0.7 μm
YSZ powder: 0.6 μm
Porous material (acrylic + carbon): 3μm
And the green sheet was formed using the adjusted slurry, and this green sheet was baked at 1325 ° C. Thereafter, the fired sheet was heated at 800 ° C. in an N ₂ gas atmosphere, and NiO was reduced while replacing the N ₂ gas with 100% hydrogen gas, thereby forming a fuel electrode.

  About each formed fuel electrode, the fine structure was observed with the scanning electron microscope (SEM). As a result, it was confirmed that in each of the fuel electrodes of Examples 1 to 6, the second pores having an average diameter of 0.1 μm or more and less than 1 μm were formed in the partition walls.

  Further, the porosity, strength, and average partition wall thickness of each fuel electrode were measured. The porosity was measured by Archimedes method. The strength was measured by a 4-point bending test. The average partition wall thickness was determined from the SEM image. The results are shown in Tables 1-3.

表１の実施例１、４、表２の実施例２、５、表３の実施例３、６に示されるように、気孔率が同じもの同士を比較すると、隔壁が厚い方が、強度が高いことを確認できた。

As shown in Examples 1 and 4 in Table 1, Examples 2 and 5 in Table 2, and Examples 3 and 6 in Table 3, when the same porosity is compared, the thicker the partition, It was confirmed that it was expensive.

2 Electrolyte 3 Fuel electrode 31 1st pore 32 Bulkhead 33 2nd pore

Claims (6)

A solid oxide electrolyte (2);
A fuel electrode (3) configured to support the electrolyte and composed of a composite of metal and oxygen ion conductive ceramics,
The fuel electrode has a plurality of first pores (31) dispersedly formed, and second pores (33) are formed inside the partition walls (32) between the adjacent first pores,
The average diameter (d1) of the first pores is larger than the average thickness (t1) of the partition walls, the average diameter (d2) of the second pores is smaller than the average thickness of the partition walls,
Adjacent first pores communicate with each other through the second pores. A plurality of the second pores are formed in the partition wall;
2. The fuel cell according to claim 1, wherein the adjacent first pores communicate with each other via a plurality of the second pores.   3. The fuel cell according to claim 1, wherein an average diameter of the second pores is 1/5 or more and 1/10 or less of an average diameter of the first pores. The average thickness of the partition walls is 1 μm or more and 10 μm or less,
4. The fuel cell according to claim 1, wherein an average diameter of the second pores is 0.1 μm or more and less than 1 μm. A method for producing a fuel cell according to any one of claims 1 to 4,
A sheet forming step (S1) for forming an unsintered sheet serving as the fuel electrode using a metal oxide powder, an oxygen ion conductive ceramic powder and a pore former
A firing step (S2) of firing the green sheet to sinter the metal oxide powder and the ceramic powder and forming the first pores and the partition walls by disappearance of the pore former. ,
After the firing step, the reduction step (S3) of forming the second pores in the partition by reducing the metal oxide in the partition is sequentially performed. The said sheet | seat formation process uses the said metal oxide powder and the said ceramic powder which have the relationship that the average particle diameter of the said metal oxide powder is larger than the average particle diameter of the said ceramic powder, The ceramic powder is used. The manufacturing method of the fuel cell described in 1.

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