JP2001102068A - Cylindrical solid electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cylindrical solid electrolyte fuel cell which can prohibit cracking in the solid electrolyte by heat stress and enhance a power generation efficiency by reducing a maximum air hole diameter within the solid electrolyte and a thickness scattering. SOLUTION: In a cylindrical solid electrolyte fuel cell constituted by forming a porous of air pole 32 in one surface of the solid electrolyte 31 and a porous of fuel electrode 33 in other surface of it and synchronous burning the solid electrolyte 31 and the air electrode 32, the maximum air hole diameter within the solid electrolyte 31 is less than 15 μm and the thickness scattering of the solid electrolyte 31 is also less than 20 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylindrical solid electrolyte fuel cell, and more particularly, to a solid electrolyte comprising a porous air electrode formed on one side and a porous fuel electrode formed on the other side. The present invention relates to a cylindrical solid oxide fuel cell formed by co-firing a fuel cell and an air electrode.

[0002]

2. Description of the Related Art A solid oxide fuel cell has a high power generation efficiency because its operating temperature is as high as 900 to 1050 ° C., and is expected as a third generation power generation system.

[0003] In general, a cylindrical type and a flat type are known as solid oxide fuel cells. Plate-type solid oxide fuel cells have the feature of high power density per unit volume of power generation, but there are problems with practical use, such as incomplete gas seals and non-uniform temperature distribution in the cell. .
In contrast, a cylindrical solid oxide fuel cell has a low output density but a high mechanical strength of the cell,
Another feature is that uniformity of the temperature inside the cell can be maintained.
Both types of solid oxide fuel cells are being actively researched and developed utilizing their respective characteristics.

As shown in FIG. 2, a cylindrical solid oxide fuel cell has a LaMnO having an open porosity of about 30 to 40%.
_A porous air electrode 2 made of a tertiary material is formed, the surface thereof is coated with a solid electrolyte 3 made of ZrO ₂ containing Y ₂ O ₃ , and a porous Ni-zirconia fuel electrode 4 is further formed on this surface. Provided. In the fuel cell module,
Each single cell is connected via a LaCrO ₃ -based current collector (interconnector) 5. Power generation is performed by flowing air 6 (oxygen) inside the air electrode 2 and fuel 7 (hydrogen) outside,
It is performed at a temperature of 0 to 1050 ° C.

[0005] In recent years, as a method for manufacturing a cylindrical solid oxide fuel cell as described above, in order to simplify the manufacturing process and reduce the manufacturing cost, at least two of the constituent materials are simultaneously used. A so-called co-sintering method for firing has been proposed. In this co-sintering method, for example, a solid electrolyte molded body and a current collector molded body are wound around a cylindrical air electrode molded body in a roll shape and simultaneously fired, and thereafter, a fuel electrode is formed on the solid electrolyte surface. Is the way.

For example, Japanese Patent Application Laid-Open No. 9-129245 discloses that a solid electrolyte sheet-like molded body is wound around the surface of a cylindrical air electrode molded body, and then the end of the solid electrolyte sheet-like molded body is opened. After the portion (notch portion) is polished to a flat shape, a sheet-like formed body of the current collector is laminated and pressed, and baked. Then, a slurry containing a metal is applied to the surface of the solid electrolyte to form a fuel electrode. Discloses a solid oxide fuel cell having a cylindrical shape.

In a solid oxide fuel cell, when power is generated, the solid electrolyte is exposed to an oxidizing atmosphere via a porous air electrode and to a reducing atmosphere such as hydrogen via a porous fuel electrode. Therefore, the solid electrolyte material is required to be chemically stable to both the oxidation and reduction atmospheres and to be dense in order to shut off both atmospheres.

Further, when the thickness of the solid electrolyte is large, the permeability of oxygen ions becomes low. Therefore, it is necessary to form the solid electrolyte thin.

[0009]

As described above, the solid electrolyte needs to be formed thin in order to allow ions to pass efficiently, but it is necessary to completely shut off the reducing atmosphere and the oxidizing atmosphere. . However, the conventional solid oxide fuel cell has a problem that cracks occur in the solid electrolyte during power generation, so that the reducing atmosphere and the oxidizing atmosphere cannot be completely shut off, and the power generation characteristics deteriorate.

[0010] This is due to the fact that in the manufacturing process of the solid oxide fuel cell, organic substances such as fibers are mixed in the solid electrolyte molded article, and large pores are formed in the solid electrolyte after firing. Thermal stress due to power generation or the like acts on the solid electrolyte in which large pores have been generated, causing a phenomenon in which cracks are generated. Therefore, in order to prevent the occurrence of cracks due to thermal stress, the thickness is set to 200 to
The thickness must be as thick as 300 μm. As a result, there is a problem that oxygen ion permeability is deteriorated and power generation characteristics are deteriorated.

When the thickness of the solid electrolyte is non-uniform, not only the stress is concentrated on the non-uniform portion, causing cracks, but also the amount of ions passing through the solid electrolyte varies depending on the location. Therefore, there is a problem that power generation performance is reduced.

Conventionally, CVD has been used to form a solid electrolyte.
Although methods such as the slurry method and the slurry dipping method have been used, the CVD method has the disadvantage that it is easy to make the layer thinner, but conversely the cost is very high in order to form a thickness with sufficient atmosphere blocking ability. there were. Further, although the slurry dipping method is low cost, it is difficult to form a dense and uniform solid electrolyte without cracks. In particular, in the case of a cylindrical solid oxide fuel cell, there is a problem that the thickness becomes uneven and thermal stress is easily generated.

The present invention reduces the maximum pore diameter in the solid electrolyte and reduces the variation in the thickness of the solid electrolyte, thereby preventing the occurrence of cracks due to thermal stress or the like in the solid electrolyte and improving the power generation efficiency. It is an object of the present invention to provide a solid electrolyte fuel cell.

[0014]

According to the present invention, there is provided a cylindrical solid oxide fuel cell comprising a solid electrolyte having a porous air electrode formed on one surface and a porous fuel electrode formed on the other surface. In a cylindrical solid oxide fuel cell formed by simultaneously firing an electrolyte and the air electrode, the maximum pore size in the solid electrolyte is 15 μm or less, and the thickness variation of the solid electrolyte is 20 μm or less. Things.

By adopting such a configuration, it is possible to prevent the occurrence of cracks due to thermal stress caused by pores, and to reduce the thickness of the solid electrolyte because thermal stress is unlikely to occur. In addition, oxygen ion permeability can be improved, and power generation characteristics can be improved. In addition, since the thickness of the solid electrolyte becomes uniform, stress concentration hardly occurs, the amount of ions passing through the solid electrolyte becomes uniform, and power generation performance can be improved.

In the solid oxide fuel cell of the present invention, it is desirable that the average thickness of the solid electrolyte is 80 to 120 μm. This is because, as described above, cracks and the like do not occur even if the thickness of the solid electrolyte is reduced, so that the average thickness of the solid electrolyte can be set to 80 to 120 μm, and by thus reducing the thickness, The conductivity of oxygen ions can be further improved, and the power generation characteristics can be improved.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A cylindrical solid electrolyte fuel cell according to the present invention has a cylindrical solid electrolyte 3 as shown in FIG.
A cell body 34 is formed by forming an air electrode 32 on the inner surface and a fuel electrode 33 on the outer surface. A current collector 35 electrically connected to the air electrode 32 is formed on the outer surface of the cell body 34. ing.

That is, the notch 36 is formed in a part of the solid electrolyte 31.
Is formed, and a part of the air electrode 32 formed on the inner surface of the solid electrolyte 31 is exposed, and both ends of the solid electrolyte 31 near the exposed surface 37 and the notch 36 are covered with the current collector 35. The current collector 35 is joined to the surfaces of both ends of the solid electrolyte 31 and the surface of the air electrode 32 exposed from the notch 36 of the solid electrolyte 31.

Current collector 35 electrically connected to air electrode 32
Is formed on the outer surface of the cell body 34 so as to cover the continuous same surface 39 having almost no level difference, and is not electrically connected to the fuel electrode 33. When connecting the cells, the current collector 35 is electrically connected to the fuel electrode of another cell via Ni felt, thereby forming a fuel cell module. The continuous same surface 39 is formed by polishing between both ends of the solid electrolyte molded body until both end portions of the solid electrolyte molded body and a part of the air electrode molded body become substantially the same continuous surface.

The solid electrolyte 31 is, for example, 3 to 20 mol%
A partially stabilized or stabilized ZrO ₂ containing Y ₂ O ₃ or Yb ₂ O ₃ is used, and the air electrode 32 is made of a perovskite-type composite oxide containing La and Mn as a main component. , Ca is 8 to 1 in terms of oxide.
0% by weight and at least one of the rare earth elements may be contained in an amount of 10 to 20% by weight in terms of oxide. Rare earth elements include Y, Nd, Dy, Er, Yb and the like, and among them, Y is desirable. As the fuel electrode 33, for example, 50
ZrO ₂ (Y ₂ O ₃ content) containing 80 wt% Ni are used.

The current collector 35 is composed of La and Cr as metal elements.
And a perovskite-type crystal containing Mg as a main crystal, and may contain a rare earth element or an alkaline earth metal element. It is desirable that the current collector 35 further contain MgO crystals since the thermal expansion coefficient of the current collector 35 can be increased to match that of the solid electrolyte 31 and the air electrode 32.

Solid electrolyte 31, air electrode 32, fuel electrode 33
Is not limited to the above example, and a known material may be used.

In the cylindrical solid oxide fuel cell according to the present invention, the maximum pore diameter present in the solid electrolyte is 1
The thickness is 5 μm or less, and the thickness variation of the solid electrolyte is 20 μm or less. The reason why the maximum pore diameter generated inside the solid electrolyte is set to 15 μm or less is that if the maximum pore diameter is larger than 15 μm, the pores serve as starting points to cause cracks. It is particularly desirable that the maximum pore diameter is 10 μm or less.

The thickness variation of the solid electrolyte is 20 μm.
When it is larger than 20 μm, the stress is concentrated on a portion having a non-uniform thickness to cause cracks, and the amount of ions passing through the solid electrolyte becomes non-uniform. This is because the power generation performance is reduced. It is particularly desirable that the thickness variation of the solid electrolyte is 15 μm or less.

Further, the thickness of the solid electrolyte is 80 to 120.
μm is desirable. By thus reducing the thickness of the solid electrolyte, ionic conductivity is improved, and power generation characteristics can be improved. On the other hand, when the thickness of the solid electrolyte is less than 80 μm, cracks are easily generated due to thermal stress, and when the thickness is more than 120 μm, oxygen ion permeability tends to decrease.

The solid oxide fuel cell constructed as described above can be manufactured as follows. For example, a solid electrolyte sheet produced by a doctor blade method is placed on the outer surface of a cylindrical air electrode molded body (or calcined air electrode body) so that both ends thereof are separated (so that an opening is formed). After sticking and calcining, the solid electrolyte calcined body is polished until both ends are flush with each other, a current collector sheet is attached to this portion, and a fuel electrode sheet is further attached to the surface of the solid electrolyte sheet, Thereafter, it is fired in the air at a temperature of 1400 to 1600 ° C. for 2 to 10 hours to produce. In this case, the fuel electrode may be formed by applying a slurry and firing at the time of co-sintering, or firing after co-sintering the air electrode, the solid electrolyte, and the current collector. The slurry may be simply applied. In this case, firing is performed during power generation.

In order to reduce the maximum pore size in the solid electrolyte to 15 μm or less, it is necessary to adopt the following production method.

Preventing generation of coarse pores in the solid electrolyte layer,
In order to manufacture a solid oxide fuel cell having stable power generation performance, it is necessary to remove foreign matter, a non-uniform mixture portion, coarse particles, and the like, which are sources of pores, in the solid electrolyte sheet.

In order to form the solid electrolyte sheet into a uniform structure, it is necessary to increase the mixing property of the slurry. In order to improve the mixing property of the slurry, only a part of the total amount of the binder is added in the initial stage of slurry preparation, and the slurry is mixed in a low viscosity state. Thereby, a sufficient mixing state between the powder components can be obtained. Thereafter, the binder is added stepwise. Thereby, a higher mixing state between the powder and the binder can be obtained. In addition, by ensuring a sufficient time for the initial mixing, a sufficiently high mixing state of the whole can be obtained.

Further, before mixing the slurry, the powder is baked at a temperature at which the ceramic powder does not sinter to remove organic foreign substances such as fibers, and before the slurry is formed into green sheets. By passing through the metal mesh and the resin fiber filter, foreign substances such as fibers that can be a source of aggregated particles and pores after sintering can be removed. Thereby, the maximum pore diameter can be set to 15 μm or less, and occurrence of defects such as cracks in the solid electrolyte can be prevented.

The thickness variation of the solid electrolyte is reduced by 20 μm.
m or less, by sintering the solid electrolyte sheet between smooth resin sheets and isostatic pressing before sintering,
A solid electrolyte sheet having a uniform thickness can be obtained, and by using such a solid electrolyte sheet, the thickness variation of the solid electrolyte can be reduced to 20 μm or less.
By laminating a plurality of such sheets, a solid electrolyte sheet having a more uniform thickness can be obtained.

In the solid oxide fuel cell configured as described above, the maximum pore size existing in the solid
μm or less, and the thickness variation of the solid electrolyte is set to 20 μm or less, so that cracks due to pores can be prevented, and thermal stress does not easily occur, so that the thickness of the solid electrolyte can be reduced, and Oxygen ion permeability can be improved, and power generation characteristics can be improved. In addition, since the thickness of the solid electrolyte becomes uniform, stress concentration hardly occurs, the amount of ions passing through the solid electrolyte becomes uniform, and the power generation performance can be further improved.

Since the occurrence of cracks due to pores can be prevented, the thickness of the solid electrolyte can be reduced.
The thickness of the solid electrolyte can be set to 80 to 120 μm, whereby the amount of ions passing through the solid electrolyte increases, and the power generation performance can be further improved.

[0034]

EXAMPLE As a powder for forming an air electrode, a commercially available La _0.8 Sr _0.2 MnO ₃ powder having an average crystal grain size of 8 μm was used.
Avicel (trade name) as a pore-forming agent was added to control the shrinkage during sintering, and the outer diameter was 18 m by extrusion molding.
m, a hollow cylindrical air electrode molded body having an inner diameter of 12 mm was produced.

A commercially available La ₂ CO ₃ , Cr ₂ O ₃ , MgO having a purity of 99.9% or more and an average crystal grain size of 1 to ₂ μm.
Were mixed in a rotary mill using zirconia balls for 10 hours, and then calcined at 1200 ° C. for 2 hours to obtain La.
A calcined powder having a composition of (Mg _0.3 Cr _0.7 ) _0.97 O ₃ +10 wt% MgO was prepared, and a current collector sheet having a thickness of 130 μm was prepared using the powder by a doctor blade method.

Further, a commercially available partially stabilized ZrO ₂ powder having a solid solution of 8 mol% of Y ₂ O ₃ having a purity of 99.9% or more and an average crystal grain size of 0.5 to 0.8 μm was prepared.

The powder was calcined in air at 500 ° C. for 1 hour. 5% by weight of a binder was added to the powder and mixed for 2 days. In addition, 20
The slurry was prepared by adding 2 wt% of the binder and mixing for 2 days. This slurry was passed through a # 400 stainless steel mesh, and further passed through a filter having a filtering ability of 20 μm. This slurry was formed into a green sheet for a solid electrolyte having a thickness of 40 to 100 μm by a doctor blade method.

Further, a green sheet for a solid electrolyte was prepared using a slurry which was passed through a stainless steel mesh of # 400 but was not passed through a filter having a filtering ability of 20 μm. Further, a green sheet for a solid electrolyte was prepared using a slurry which was passed through a stainless steel mesh of # 200 but was not passed through a filter having a filtering ability of 20 μm with a stainless steel mesh of # 400. In addition, a green sheet for a solid electrolyte was prepared using a slurry in which neither the stainless mesh nor the filter was passed.

A plurality of the above-mentioned sheets for solid electrolyte are laminated, sandwiched between resin sheets, and pressed by a hydrostatic press.
A solid electrolyte sheet having a thickness of about 130 μm was formed.

Thereafter, the solid electrolyte sheet is wound around the surface of the cylindrical air electrode molded body, then calcined, and the both ends of the calcined solid electrolyte body are polished to polish the air electrode calcined body and the solid electrolyte. A flat portion was formed from the calcined body, a current collector sheet was attached to the flat portion, and baked at 1500 ° C. for 3 hours.
As a result, a cylindrical solid oxide fuel cell having a solid electrolyte having a thickness of 80 to 120 μm as shown in FIG.

Then, 80% by weight NiO / 20% by weight Y
A mixed powder of partially stabilized ZrO ₂ containing ₂ O ₃ was applied to the surface of the solid electrolyte to a thickness of 50 μm, and heat-treated at 1400 ° C. in the air for 1 hour to produce a solid oxide fuel cell shown in FIG. did.

Thereafter, one end of the cell was sealed, and the cell was immersed in water with the inside pressurized to 1 kgf / cm ² with air, and the occurrence of cracks was investigated by confirming the occurrence of gas leak. The occurrence of cracks was calculated by determining the number of cracks generated in the solid electrolyte per 50 cm of the cylindrical solid oxide fuel cell. The cross section of the cell is 5
Scanning Electron Microscope (SE)
M) Observation was performed, the diameter of the largest pore was measured, and the measured diameter was defined as the maximum pore diameter. In addition, the difference between the maximum part and the minimum part of the thickness of the solid electrolyte was measured to determine the thickness variation. Table 1 shows the results.

[0043]

[Table 1]

As shown in Table 1, the samples Nos. 5 to 9 of the present invention in which the maximum pore size in the solid electrolyte is 15 μm or less and the thickness variation of the solid electrolyte is 20 μm or less,
It can be seen that no cracks occurred. On the other hand, in Samples Nos. 1 to 3 which were not subjected to the powder baking, the mesh pass, and the filter pass, it was found that cracks occurred at two or more places.

The inventors of the present invention have found that the current density on the fuel electrode surface of Sample Nos.
A / cm ² was adjusted, and the change over time in the potential drop of the solid electrolyte portion was measured while the power generation state was maintained. Table 2 shows the results.

[0046]

[Table 2]

As can be seen from Table 2, when the sample No. 4 in Table 1 was used, the potential drop was remarkable, and the sample was damaged after 100 hours. On the other hand, when the sample No. 5 of the present invention was used, it was found that the potential drop was small, the conductivity of the solid electrolyte during power generation operation was stabilized, and breakage could be prevented.

[0048]

According to the solid oxide fuel cell of the present invention, the maximum pore diameter in the solid electrolyte is set to 15 μm or less, and the thickness variation of the solid electrolyte is set to 20 μm or less. Since the thermal stress is not easily generated, the thickness of the solid electrolyte can be reduced, and as a result, the permeability of oxygen ions can be improved, the power generation characteristics can be improved, and the thickness of the solid electrolyte becomes uniform. Therefore, stress concentration hardly occurs, the amount of ions passing through the solid electrolyte becomes uniform, and good power generation performance can be maintained for a long time.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a cylindrical solid oxide fuel cell according to the present invention.

FIG. 2 is a perspective view showing a conventional solid oxide fuel cell.

[Explanation of symbols]

 32 ... air electrode 31 ... solid electrolyte 33 ... fuel electrode 35 ... current collector

Claims (2)

[Claims] 1. A cylindrical solid formed by forming a porous air electrode on one side of a solid electrolyte and a porous fuel electrode on the other side, and simultaneously firing the solid electrolyte and the air electrode. A cylindrical solid electrolyte fuel cell, wherein the maximum pore size in the solid electrolyte is 15 μm or less, and the thickness variation of the solid electrolyte is 20 μm or less. 2. The cylindrical solid electrolyte fuel cell according to claim 1, wherein the thickness of the solid electrolyte is 80 to 120 μm.