JP2000311697A - Solid oxide fuel cell - Google Patents

Abstract

[PROBLEMS] To provide a solid oxide fuel cell capable of suppressing the volume expansion of a LaCrO ₃ -based material in a reducing atmosphere and improving the junction between the current collector and the solid electrolyte. A solid electrolyte 31 made of partially stabilized or stabilized ZrO ₂ and a fuel electrode 33 are sequentially formed on an outer surface of a cylindrical air electrode 32, and cover a cutout portion 36 provided in the solid electrolyte 31. In a solid oxide fuel cell unit in which the current collector 35 is joined to the solid electrolyte 31 and the air electrode 32 exposed from the notch 36, the current collector 35 contains La, Cr and Mg as metal elements. The main crystal is a lobskite-type crystal, and the perovskite-type crystal M
There is a high Mg-substituted crystal region A with a large g-substitution amount.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention, on the outer surface of the cylindrical air electrode, partially stabilized or stabilized ZrO ₂ made of a solid electrolyte, a fuel electrode are sequentially formed, the current collector from the solid electrolyte and notch The present invention relates to a solid oxide fuel cell unit joined to an exposed 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, cylindrical and flat plate types of solid oxide fuel cells are known. Flat solid electrolyte fuel cells have the characteristic of high power density per unit volume of power generation.However, there are problems such as imperfect gas seals and non-uniform temperature distribution in the cells for practical use. is there.
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 1 made of a ternary material is formed, the surface of which is coated with a solid electrolyte _{2 made} of ZrO ₂ containing Y ₂ O ₃ , and a porous Ni-zirconia fuel electrode 3 is formed on this surface. Is provided. In the fuel cell module, each single cell is connected via a LaCrO ₃ -based current collector (interconnector) 4. Power generation is performed by flowing air 6 (oxygen) inside the air electrode 1 and fuel 7 (hydrogen) outside the air electrode 1.
It is performed at a temperature of 00 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.

The air electrode of the cylindrical solid oxide fuel cell comprises 15 to 20 atomic% of La, Ca, S
LaM substituted by alkaline earth metals such as r and Ba
consists nO ₃ based compositions, solid electrolyte with respect to _{ZrO 2 Y 2 O 3, Yb} 2 O 3 a stabilizing material, such as 3 to 15 mol% portion was dissolved in a proportion of stabilizing ZrO ₂ or The collector is made of stabilized ZrO ₂ , and the current collector is made of LaCrO _{3 in} which Ca, Mg, and Sr are dissolved.

The surface of the current collector is exposed to hydrogen supplied to the outside of the cell, and is exposed to oxygen inside the cell.
It will be exposed through a porous air electrode. Therefore, the current collector is required to be chemically stable to both the oxidizing and reducing atmospheres and to be dense in order to shut off both the atmospheres. When a metal is used, a portion exposed to an oxidizing atmosphere is oxidized, and therefore, a conductive ceramic is used.

[0009] Both the oxidizing and reducing atmospheres are shut off by the dense current collector and the solid electrolyte, but it is necessary that the boundary between the current collector and the solid electrolyte be closely adhered without any gap.

However, LaCrO used for current collectors
_{The three-} system perovskite material is difficult to join with Y ₂ O ₃ -containing stabilized or partially stabilized ZrO _2, and therefore La
It has been practiced to substitute a part of Cr of the perovskite-type crystal made of CrO ₃ with Mg to satisfactorily join the current collector and the solid electrolyte. Also, by substitution with Mg,
Sinterability and conductivity are also improved.

[0011]

However, in order to improve the bonding of the current collector to the solid electrolyte, it is necessary to use L
It is desirable that the perovskite-type crystal composed of aCrO ₃ has a larger amount of substitution by Mg, but on the other hand, the larger the amount of substitution by Mg, the greater the volume expansion when exposed to a reducing atmosphere such as hydrogen. When a temperature cycle is applied during fabrication or during power generation, there is a problem that the cell is damaged.

On the other hand, when the perovskite-type crystal composed of LaCrO ₃ is reduced in the amount of substitution with Mg, the volume expansion is reduced even when exposed to a reducing atmosphere, but the substitution amount of Mg in the solid electrolyte side of the current collector is also reduced. As a result, there has been a problem that bonding of the current collector to the solid electrolyte becomes poor.

That is, the LaCrO ₃ -based material has a perovskite-type crystal, has a phase transformation from an orthorhombic system to a rhombohedral system at around 300 ° C., and in a reducing atmosphere, accompanying the desorption of oxygen ions. It is known that an increase in volume occurs due to repulsion of the remaining cations.

This volume expansion shows a small value when the substitution amount of Mg in the perovskite type crystal is in the range of 1 to 9 atomic% with respect to all metals, but in the range of these substitution amounts, from the viewpoint of mass production for practical use. As described above, there is a problem that LaCrO ₃ is difficult to sinter, the joining state of the current collector to the solid electrolyte is not good, and gas leaks from between the current collector and the solid electrolyte. .

[0015]

Means for Solving the Problems To solve the above problems, the present inventors have improved the sinterability of the LaCrO ₃ -based material, and further suppressed the increase in the volume of the LaCrO ₃ -based material in a reducing atmosphere. As a result of repeated studies on a method for improving and stabilizing the conductivity and improving the bondability with the solid electrolyte, the current collector was replaced with a small amount of Mg to enhance the sinterability of the LaCrO ₃ material. By using a LaCrO ₃ crystal as a main crystal and replacing the Mg in the perovskite-type crystal in the vicinity of a portion in contact with the solid electrolyte of the current collector with a larger amount than in other portions, La in a reducing atmosphere is reduced.
The present inventors have found that the volume expansion of the CrO ₃ -based material can be suppressed and that the current collector can be favorably joined to the solid electrolyte, and the present invention has been accomplished.

That is, according to the present invention, a solid electrolyte composed of partially stabilized or stabilized ZrO ₂ and a fuel electrode are sequentially formed on the outer surface of a cylindrical air electrode, and a notch provided in the solid electrolyte is covered. In a solid oxide fuel cell unit in which a current collector is joined to the solid electrolyte and the air electrode exposed from the notch, the current collector contains La, Cr and Mg as metal elements. The perovskite-type crystal is a main crystal, and a high Mg-substituted crystal region in which the perovskite-type crystal has a higher Mg substitution amount than other regions exists on the solid electrolyte side of the current collector.

Here, it is desirable that the perovskite-type crystal in the high Mg-substituted crystal region has an Mg substitution amount of at least 10 atomic% of all metal elements of the perovskite-type crystal. Further, the current collector preferably contains MgO crystals.

[0018]

According to the solid oxide fuel cell of the present invention, at least a solid electrolyte composed of an air electrode, a partially stabilized or stabilized ZrO ₂ , and a current collector is simultaneously fired with La, La as a metal element. A high Mg-substituted crystal region in which the perovskite-type crystal has a larger amount of Mg substitution than other regions was present in a portion of the current collector having a perovskite-type crystal containing Cr and Mg as a main crystal in contact with the solid electrolyte. Therefore, in the portion of the current collector in contact with the solid electrolyte, the perovskite-type crystal has a large amount of Mg substitution,
The bonding state of the current collector to the solid electrolyte becomes good,
Other parts, for example, in the current collector on the opposite side of the solid electrolyte, since the amount of Mg substitution in the perovskite-type crystal is small,
Even when the current collector is exposed to a reducing atmosphere, the volume expansion is reduced.

Further, in the solid oxide fuel cell of the present invention, the perovskite-type crystal in the high Mg-substituted crystal region has a Mg substitution amount of at least 10 atomic% of all metal elements of the perovskite-type crystal. In addition, the bonding state of the current collector to the solid electrolyte can be further improved.

Further, in the solid oxide fuel cell unit of the present invention, by including MgO crystals in the current collector, the thermal expansion coefficient of the current collector can be increased, and the current expansion coefficient of the current collector matches that of the solid electrolyte or the air electrode. Can be done.

That is, when used as a current collector of a solid oxide fuel cell, the coefficient of thermal expansion of the material other than the current collector, ie, the solid electrolyte or the air electrode, is reduced to prevent damage during cell production or power generation. Need to match. For this purpose, the MgO crystal having a larger thermal expansion coefficient than LaCrO ₃ is present together with the LaCrO ₃ crystal to increase the thermal expansion coefficient of the current collector, which is originally lower than the solid electrolyte or the air electrode. Can be made to match the thermal expansion coefficient of the solid electrolyte or the air electrode.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A solid oxide 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 (containing Y ₂ O ₃ ) cermet containing ８０80 wt% Ni is 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. The coefficient of thermal expansion of the solid electrolyte 31 made of the above material is approximately 10.5 × 10 ⁻⁶ / ° C.

In the solid oxide fuel cell unit according to the present invention, a portion of the current collector 35 which is in contact with the solid electrolyte 31 is:
The present invention is characterized in that a high Mg-substituted crystal region A in which the perovskite-type crystal has a larger amount of Mg substitution than the other region B exists.

Here, the other region B refers to, for example, a portion of the current collector near the cutout portion 36 and a portion near the surface of the current collector exposed to the outside. The perovskite-type crystal of the perovskite-type crystal is La _1.0 Mg _2x Cr _1.0-2x
This is the value of x when expressed as O ₃ .

The Mg content of the perovskite-type crystal in the high Mg-substituted crystal region A is at least 10 atomic%, particularly 10 to 13 atomic% (0.1 ≦ x ≦ 0%) of all metal elements of the perovskite crystal. .13). This is because when the content is 10 atomic% or more, the bonding state of the current collector 35 to the solid electrolyte 31 can be further improved while suppressing the volume expansion when exposed to a reducing atmosphere. On the other hand, if it exceeds 13 atomic%, the volume expansion in a reducing atmosphere increases, and the current collector 35 and the solid electrolyte 31
In another region B, the amount of Mg substitution in the perovskite-type crystal is 1 to 1 of all metal elements in the perovskite-type crystal.
It is desirable that the content be 9 atomic% from the viewpoint that volume expansion when exposed to a reducing atmosphere can be suppressed.

Further, the high Mg-substituted crystal region A is preferably 50 μm from the solid electrolyte side surface of the current collector.
It is desirable from the viewpoint of relaxing the internal stress caused by the substitution crystal region A and the other region B.

In the solid oxide fuel cell according to the present invention,
On the solid electrolyte 31 side of the current collector 35, there is a high Mg-substituted crystal region A having a larger amount of Mg substitution of the lobskite-type crystal than in the other region B. Therefore, on the solid electrolyte 31 side of the current collector 35, Since the substitution amount of Mg in the lobskite-type crystal is large, the bonding state of the current collector 35 with the solid electrolyte 31 is improved. On the other hand, in other portions, the substitution amount of Mg in the perovskite-type crystal is small, so Even when the body 35 is exposed to a reducing atmosphere, the volume expansion is reduced, and leakage of gas from between the current collector 35 and the solid electrolyte 31 can be prevented.
Cell breakage due to volume expansion of the current collector can be prevented.

In the solid oxide fuel cell of the present invention, for example, a solid electrolyte sheet produced by a doctor blade method is provided on the outer surface of a cylindrical air electrode molded body (or calcined air electrode body). After sticking so that they are separated (to form an opening) and calcining, polished until both ends of the solid electrolyte sheet are flush with each other. A fuel electrode sheet is attached to the surface of the electrolyte sheet, and thereafter, 1400 to 1600
It is produced by baking in air at a temperature of 2 to 10 hours.
In this case, the fuel electrode may be formed by applying a slurry and firing during co-sintering, or firing after co-sintering. The slurry may be simply applied. In this case, firing is performed during power generation.

A method for manufacturing the current collector sheet will be described. First, LaCO ₃ , Cr ₂ O _3, and MgO powder are mixed using a zirconia ball or the like by a known method such as a rotary mill, and then mixed at a temperature of 1000 to 1500 ° C. and a temperature of 1 to 1 ° C.
After heat treatment for 0 hour, for example, the perovskite crystal M
g substitution amount of La of 10 to 13 atomic% of all metal elements
CrO ₃ -based perovskite raw material powder A and LaCrO ₃ -based perovskite raw material powder B having an Mg substitution amount of 1 to 9 atomic% of the total metal elements are produced, and these powders are pulverized to 0%. 0.5 to 5 μm.

Thereafter, a sheet is formed from the raw material powders A and B by a well-known method such as a doctor blade to produce sheets A and B.

Then, a solid electrolyte sheet is attached to the outer surface of the air electrode molded body so that both ends thereof are separated from each other, calcined, and polished until both ends of the solid electrolyte sheet are flush with each other. Thereafter, the sheet A is attached to both ends of the solid electrolyte sheet, a sheet B is attached so as to cover the sheet A, and the sheet is fired.

The sheets A are arranged at intervals between both ends of the solid electrolyte, that is, at intervals corresponding to the notch width, and the sheets B are arranged on these sheets A, which are press-formed. A current collector sheet may be prepared, and the current collector sheet may be attached and baked so that sheet A of the current collector sheet abuts on both ends of the solid electrolyte sheet.

[0038]

EXAMPLES Commercially available purity of 99.9% or more, average crystal grain size of 1
２2 μm of La ₂ CO ₃ , Cr ₂ O ₃ , and MgO powders were prepared, mixed for 10 hours in a rotary mill using zirconia balls, and then calcined at 1200 ° C. for 2 hours to obtain two types of LaM.
A gCrO ₃ -based perovskite crystal powder was prepared, and MgO powder was added to 100 parts by weight of the calcined powder in amounts shown in Table 1 to obtain raw material powders A and B.

After that, an organic binder is mixed with the raw material powders A and B, and the thickness is 75 μm by a doctor blade method.
m of green sheets A and B were prepared.

[0040] as a powder for forming the air electrode, using the La _0.8 Sr _{0. 2} MnO ₃ powder of commercial average crystal grain size 8 [mu] m, a pore-forming agent to control the shrinkage during sintering Avicel (trade ) Was added and the outer diameter was 18
mm, a hollow cylindrical air electrode molded body having an inner diameter of 12 mm was produced.

On the other hand, 10 mol% of a commercially available having an average particle size of 0.6μm as the solid electrolyte Y ₂ O _3/90 mole% ZrO ₂
An organic binder was mixed with the powder having the composition, and a green sheet having a thickness of 130 μm was prepared by a doctor blade method.

Thereafter, a solid electrolyte sheet is wound around the surface of the cylindrical molded body made of the air electrode material, green sheets A are attached to both ends of the solid electrolyte sheet, and the green sheets are coated so as to cover the green sheets A. The sheet B was attached to the green sheet A and the exposed surface of the air electrode, and fired at 1500 ° C. for 3 hours.

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.

The manufactured solid oxide fuel cell has an air electrode having an outer diameter of 18 mm, an inner diameter of 12 mm, a thickness of the solid electrolyte of 100 μm, and a thickness of the current collector of 100 μm (the thickness of the high Mg substitution crystal region is 50 μm). Was.

Regarding the obtained solid oxide fuel cell, a point 20 μm from the side of the solid electrolyte of the current collector (high Mg)
The substitution amount of Mg in the perovskite type crystal was determined by EPMA analysis for the substituted crystal region) and the 70 μm point (other region).

Next, a pressure of 1 kgf / cm ² was applied to the inside of the cell, the cell was immersed in water, and the presence or absence of gas leak in the initial state was examined.

Thereafter, the temperature was raised from room temperature to 1000 ° C. for 5 hours while flowing air inside the cell and hydrogen outside the cell.
After being kept at 1000 ° C. for 1 hour, it was cooled to room temperature in 5 hours. This heat cycle was repeated 20 times, and the presence or absence of gas leak in the cell at that time was examined. After holding at 1000 ° C. for 1 hour, the output density was measured. The results are shown in Table 2.

[0048]

[Table 1]

[0049]

[Table 2]

From these Tables 1 and 2, it can be seen that the sample of the present invention in which the high Mg-substituted crystal region exists in the portion of the current collector in contact with the solid electrolyte has an output density of 0.32 W / cm ² or more, There was no gas leak and no gas leak after the thermal cycle.

On the other hand, in Sample No. 1 in which the high Mg-substituted crystal region does not exist, the Mg substitution amount in the perovskite-type crystal is constant at 5 atomic%, so the Mg substitution amount is small, and the solid electrolyte and the solid electrolyte are collected at the time of fabrication. The connection with the conductor becomes poor,
It can be seen that a gas leak has occurred in the initial state. Also,
In Sample No. 10 in which the high Mg-substituted crystal region does not exist, the amount of Mg substitution in the perovskite-type crystal is constant at 12 atomic%, so that the junction between the solid electrolyte and the current collector during the production is good. It can be seen that the volume expansion due to the current collector being exposed to the reducing atmosphere is large, an internal stress is generated, and a gas leak occurs after the thermal cycle test.

[0052]

According to the solid oxide fuel cell of the present invention, a portion of the current collector mainly composed of perovskite crystals containing La, Cr and Mg as metal elements in contact with the solid electrolyte is formed in another region. Since there is a high Mg-substituted crystal region in which the perovskite-type crystal has a larger amount of Mg substitution than the perovskite-type crystal, the amount of Mg substitution in the perovskite-type crystal increases in the solid electrolyte side of the current collector, and In the other part, for example, the part of the current collector opposite to the solid electrolyte, the amount of Mg substitution in the perovskite-type crystal is reduced, and the current collector is exposed to the reducing atmosphere. Even when the volume expansion is small, the current collector and the solid electrolyte are integrated, and the volume change of the porcelain between the atmosphere and the reducing atmosphere is suppressed, and the generation of stress between the members is suppressed,
Damage can be prevented.

[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 cylindrical solid oxide fuel cell.

[Explanation of symbols]

 32 ... air electrode 31 ... solid electrolyte 33 ... fuel electrode 35 ... current collector 36 ... notch A ... high Mg substitution crystal area B ... other area

Claims (2)

[Claims] 1. A current collector in which a solid electrolyte made of partially stabilized or stabilized ZrO ₂ and a fuel electrode are sequentially formed on the outer surface of a cylindrical air electrode, and a cutout provided in the solid electrolyte is covered. Is bonded to the solid electrolyte and the air electrode exposed from the notch, wherein the current collector has La, C as a metal element.
a perovskite-type crystal containing r and Mg as a main crystal, and a high M content, on the solid electrolyte side of the current collector, in which the perovskite-type crystal has a larger amount of Mg substitution than other regions.
A solid oxide fuel cell comprising a g-substituted crystal region. 2. The solid electrolyte according to claim 1, wherein the Mg content of the perovskite-type crystal in the high Mg-substituted crystal region is at least 10 atomic% of all metal elements of the perovskite-type crystal. Type fuel cell.