JPH11283643A - Solid-electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-electrolyte fuel cell whose generation characteristic is good as the current collection characteristic of a current collector can be enhanced. SOLUTION: The solid-electrolyte fuel cell has an air electrode 32 formed on one side of a solid electrolyte 31 and a fuel electrode 33 on the other and has a current collector 35 electrically connected to the air electrode 32 or the fuel electrode 33 and exposed to the outer surface thereof. In this case, a cover layer which is made from a cermet with either ZrO2 or CeO2 containing at least one kind selected from among Ni, Co, Mn, and W and at least one kind selected from among Ca, Mg, Y, and rare earth elements, or CeO2 alone, and which has a film thickness of 0.3 to 30 μm, is formed on the exposed surface of the current collector 35, the crystal particle diameters of the Ni, Co, Mn, and W ranging from 0.5 to 5 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid oxide fuel cell, and more particularly to a solid oxide fuel cell having improved current collection characteristics of a current collector.

[0002]

2. Description of the Related Art Conventionally, solid oxide fuel cells have been
Since the operating temperature is as high as about 1000 to 1050 ° C., the power generation efficiency is high and it is expected as a third-generation fuel cell. 2. Description of the Related Art In general, two types of solid oxide fuel cells are known: cylindrical and flat.

[0003] The flat fuel cell has the feature that the output density per unit volume of power generation is high, but when put into practical use, there are problems such as imperfect gas sealing and non-uniform temperature distribution in the cell. On the other hand, the cylindrical fuel cell has the features that the output density is low, but the mechanical strength of the cell is high and the temperature uniformity in the cell can be maintained. Both types of solid electrolyte fuel cells are being actively researched and developed utilizing their respective features.

As shown in FIG. 2, a cylindrical solid oxide fuel cell is, for example, a stabilized ZrO ₂ containing Y ₂ O _3.
A porous air electrode layer 2 made of a LaMnO ₃ -based material is formed on the inner surface of a solid electrolyte layer 3 made of 2 and a fuel electrode layer 4 made of a porous Ni-zirconia is formed on the surface of the solid electrolyte 3. It is configured. A current collector 5 (interconnector) made of a LaCrO ₃ -based material or the like for connecting the cells penetrates the solid electrolyte layer 1 and is electrically connected to the air electrode layer 2. 4 is exposed on the surface of the cell in a non-contact state.

[0005] In the fuel cell module, a plurality of single cells having the above-described configuration are connected via a current collector 5 and a Ni felt (or Ni plate), and power is generated inside the air electrode layer 2 by air (oxygen). And the fuel (hydrogen)
It is performed at a temperature of 00 to 1050 ° C.

[0006] Conventionally, in a solid oxide fuel cell, a Ni plating layer is formed on an exposed surface of a current collector so as to improve a contact area with Ni felt and improve current collection characteristics. Have been.

[0007]

However, in the solid oxide fuel cell described above, the Ni plating layer uniformly formed on the exposed surface of the current collector burns during power generation at a high temperature of 1000 to 1050 ° C. Condensed and condensed to form a state where a Ni plating layer is formed only on a part of the exposed surface of the current collector,
There is a problem that the contact area between the Ni felt and the current collector due to the plating layer is reduced, and the current collecting capability of the current collector is reduced.

[0008] It is an object of the present invention to provide a solid oxide fuel cell capable of improving the current collection characteristics of a current collector.

[0009]

Means for Solving the Problems The present inventors have studied the above problems, and as a result, from the viewpoint of preventing sintering on the exposed surface of the current collector, a predetermined crystal having a predetermined crystal grain system The present inventors have found that sintering and agglomeration of a metal in a cermet can be suppressed by forming a coating layer having a predetermined thickness made of a cermet in which a metal having a particle diameter is mixed with a ceramic.

That is, the solid oxide fuel cell of the present invention comprises an air electrode formed on one surface of a solid electrolyte and a fuel electrode formed on the other surface, and is electrically connected to the air electrode or the fuel electrode. And a current collector that is exposed to the outside.
i, Co, Mn, W and at least one of Ca, M
g, Y and ZrO ₂ or CeO ₂ containing at least one of rare earth elements, or a cermet with CeO ₂ alone, and the Ni, Co, Mn,
W has a crystal grain size of 0.5 to 5 μm and a film thickness of 0.
It is formed by forming a coating layer of 3 to 30 μm. Here, it is desirable that the exposed surface of the current collector is polished.

[0011]

In the solid oxide fuel cell of the present invention, the exposed surface of the current collector contains at least one of Ni, Co, Mn, and W and at least one of Ca, Mg, Y, and a rare earth element. It is made of cermet with ZrO ₂ or CeO ₂ or CeO ₂ alone, and has a thickness of 0.3 to 3
A coating layer of 0 μm is formed. Thereby, since the ceramics are dispersed in the metal, the metal (Ni, C
sintering of at least one of o, Mn, and W), thereby suppressing metal aggregation.
The contact area between the i-felt and the current collector can be improved.

Further, by setting the thickness of the coating layer to 0.3 to 30 μm, sintering and aggregation of the metal of the coating layer can be further suppressed. Further, by polishing the exposed surface of the current collector and setting the metal particle diameter to 0.5 to 5 μm, the sintering of the metal is suppressed, and the sintering of the metal is suppressed, and the current collection of the coating layer is performed. The adhesion to the body can be improved, and the contact area between the Ni felt and the current collector by the coating layer can be improved.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a solid oxide fuel cell according to the present invention comprises a cylindrical solid electrolyte 31 having an air electrode 32 formed on the inner surface and a fuel electrode 33 formed on the outer surface. A main body 34 is formed, and a current collector 35 is provided on the outer surface of the fuel cell main body 34, one side of which is electrically connected to the air electrode 32 and the other side is exposed to the outside. That is, a part of the solid electrolyte 31 is cut away, and a part of the air electrode 32 formed on the inner surface of the solid electrolyte 31 is exposed. A body 35 is formed. still,
The cylindrical fuel cell of the present invention may be configured such that a porous support tube is formed, and an air electrode 32, a solid electrolyte 31, and a fuel electrode 33 are sequentially stacked on the outer surface of the porous support tube.

A current collector 35 electrically connected to the air electrode 32
Are formed on the outer surface of the fuel cell main body 34 so as to cover the same continuous surface 39, and are not electrically connected to the fuel electrode 33. The continuous same surface 39 exposes a part of the air electrode 32 formed on the inner surface of the solid electrolyte 31 and makes the end portion of the solid electrolyte 31 and the exposed surface 37 of the air electrode 32 substantially flush with each other (the solid electrolyte 31). Of the air electrode 32 and the exposed surface 37 of the air electrode 32 are in a planar state with few steps. The same surface 39 is formed by polishing the outer peripheral surface of the cell body until a part of the solid electrolyte molded body and a part of the air electrode molded body are substantially flush with each other.

In the cylindrical fuel cell of the present invention, at least one of Ni, Co, Mn, and W and Ca, Mg, Y and rare earth elements are formed on the exposed surface of the current collector 35. ZrO ₂ containing at least one kind
Or CeO ₂ or a coating layer 50 made of cermet is a mixture of ceramic consisting of CeO ₂ alone,
Are formed. As a metal, Ni is used for economic reasons.
ZrO ₂ containing Y ₂ O ₃ is desirable as ceramics from the viewpoint of suppressing the sinterability of metal. Further, the crystal grain size of the metal is preferably 0.5 to 5 μm, particularly preferably 1 to 3 μm from the viewpoint of suppressing the sinterability. If the crystal particle diameter is smaller than 0.5 μm, sintering of the metal cannot be suppressed. On the other hand, if it exceeds 5 μm, it is easy to peel off.

The composition of the coating layer 50 is preferably such that the weight ratio of the ceramic is 0.1 to 30% by weight, and particularly preferably 1 to 10% by weight.

The thickness of the coating layer 50 is 0.3 to 30 μm.
m. This is because if the thickness of the coating layer 50 is less than 0.3 μm, the dispersion of the ceramics is poor, so that the sintering of the metal in the coating layer 50 due to long-time power generation cannot be prevented, and the current collecting capability of the current collector 35 Decrease. On the other hand, if the thickness exceeds 30 μm, the coating layer 50 tends to peel off. The thickness of the coating layer 50 is preferably 1 to 5 μm from the viewpoint of preventing sintering of the metal and preventing peeling. The average particle size of the ceramic to be dispersed is preferably 0.05 to 3 μm, particularly preferably 0.1 to 1 μm from the viewpoint of suppressing sinterability.

In order to further increase the adhesion of the coating layer 50 to the current collector 35, it is desirable to polish the surface of the current collector 35. In this case, the surface roughness Ra is 0.1 to 5 μm,
In particular, the range of 0.5 to 2 μm is excellent. The surface of the current collector 35 is not only simply roughened, but also
The provision of the irregularities having a size of 30 μm is excellent from the viewpoint of improving the surface area of the current collector 35. Also in this case, it is preferable that at least the convex portion is polished as described above. Polishing may be performed by sanding or sandblasting with a commercially available sandpaper.

Next, the method for forming the coating layer 50 of the present invention will be described by taking the case of ZrO ₂ containing Ni / Y ₂ O ₃ as an example. The coating layer 50 is formed, for example, by dispersing a predetermined Y ₂ O ₃ -containing ZrO ₂ ceramic powder or the like in a commercially available Ni plating solution, and coating the exposed surface of the current collector of the solid oxide fuel cell by electrolytic plating or It can be easily formed by electroless plating.

Alternatively, a commercially available pore-forming material is contained in the Ni plating solution, and a porous plating layer is formed on the exposed surface of the current collector of the solid oxide fuel cell by an electrolytic plating method or an electroless plating method. And Y, Zr in the pore
After impregnating with an aqueous solution containing a metal organic salt containing
Ceramics may be dispersed by thermal decomposition at a temperature of 00 to 1000 ° C. In this case, when the processing temperature exceeds 500 ° C., Ar or N ₂ containing 1% or less of oxygen is used.
The treatment with gas is excellent from the viewpoint of preventing oxidation of the current collector.

In the fuel cell according to the present invention, LaMnO in which La is partially substituted with Sr and Ca is used as an air electrode.
₃ is a solid electrolyte with respect to ZrO _2
2 O _3, Yb ₂ O ₃ stabilized material was dissolved in a proportion of 3 to 15 mol% portion of such stabilized ZrO ₂ or stabilized Z
rO ₂ powder, Y ₂ O ₃ , Yb ₂ O ₃ , Gd ₂ O ₃ etc.
CeO ₂ is used containing 0 to 30 mol%. Also,
Ni / ZrO ₂ (containing Y ₂ O ₃ ) cermet is used as the fuel electrode, and Ca, M is used as the powder forming the current collector.
LaCrO _{3 in} which g and Sr are dissolved is used.

The fuel cell of the present invention is not limited to a cylindrical solid electrolyte fuel cell, but is also applicable to a flat solid electrolyte fuel cell.

[0023]

EXAMPLES Example 1 La ₂ O ₃ , MnO ₂ , C
aCO ₃ powder was weighed and mixed so as to be La _0.85 Ca _0.15 MnO _3, and then calcined at 1500 ° C. (La, C
a) MnO ₃ powder was obtained. Thereafter, this was pulverized to prepare powders each having an average particle diameter of 8 μm. Further, Y ₂ O having an average particle size of 0.5 μm is used as a powder for forming a solid electrolyte.
_A ZrO ₂ powder prepared by coprecipitation containing ₃ at a ratio of 10 mol% was prepared. Further, as a powder for forming the fuel electrode, NiO
Powder and ZrO ₂ (containing Y ₂ O ₃ ) powder in a weight ratio of 80:
A compound powder composed of La _0.8 Ca _0.21 CrO ₃ having an average particle diameter of 1 μm was prepared as a powder for forming a current collector by mixing the mixture at a ratio of 20.

First, the above-mentioned 8 μm (La, Ca) Mn
A slurry was prepared from O ₃ powder using water as a solvent, and the slurry was used to form an inner diameter of 13 mm and an outer diameter of 1 using an extrusion molding apparatus.
A 6 mm cylindrical air electrode molding was obtained. On the other hand, a slurry was prepared by using Y ₂ O ₃ -stabilized ZrO ₂ powder as the solid electrolyte and La _0.8 Ca _0.21 CrO ₃ powder as a current collector, and toluene was used as a solvent. A sheet-like molded body was produced.

Further, the solid electrolyte sheet-like molded body was wound around the surface of the air electrode molded body via an adhesive made of an acrylic resin, and the end portions thereof were polished to form a continuous same surface. Further, the sheet-shaped formed body of the current collector was laminated and pressed, and fired at 1500 ° C. for 5 hours in the air.

For the fuel electrode layer, a slurry is prepared from the above powder using toluene as a solvent, and the slurry is dipped in the slurry.
After drying to form a fuel electrode, a cylindrical fuel cell as shown in FIG. 1 was produced.

Then, 10 mol% of CaO, MgO, Y ₂ O ₃ , Yb ₂ O ₃ , 10 mol% having an average particle size of about 0.1 μm is added to a commercially available plating solution containing Ni, W, Co, and Mn. Nd ₂
ZrO ₂ powder containing O ₃ , Sm ₂ O ₃ or CeO
₂ powder or CeO ₂ simple powder was dispersed, and a cermet coating layer in which ceramics were dispersed was formed by electroless plating using this solution in an ultrasonic cleaning vessel.
Further, for comparison, a Ni plating layer containing no ceramics was produced by an electrolytic plating method, which was used as a comparative example. At this time, the ratio of metal to ceramic in the coating layer was determined by fluorescent X-ray analysis using a calibration curve method. The thickness of the coating film and the crystal grain size of the metal were determined using a scanning electron microscope. Power generation is performed at 1000 ° C. for 1000 hours by flowing oxygen inside the solid oxide fuel cell and hydrogen outside, and the power density after 100 hours and 100 hours after 100 hours.
Table 1 shows the reduction rate of the output density after 0 hour and the output density after 1000 hours.

[0028]

[Table 1]

From Table 1, it can be seen that the sample No. 1. Sample N whose coating layer thickness is less than 0.3 μm
o. Sample No. 2 having a coating layer thicker than 30 μm. 9
In this case, the rate of decrease in output density is large. Further, in sample No. 1 in which the metal crystal particle diameter was smaller than 0.5 μm. Sample No. 18 and Sample NO. Even at 19, the output density is greatly reduced. In contrast, the samples of the present invention all exhibited stable power densities.

Example 2 The surface roughness of the current collector surface was measured for the cell of Example 1 with and without the current collector surface polished with # 220 sandpaper. Y ₂ O ₃
A coating layer composed of the contained ZrO ₂ powder or CeO ₂ single powder and having the composition shown in Table 2 was formed in the same manner as described above, and power generation was performed for 1000 hours in the same manner as above, and after 100 hours, Power density and 10 hours after 100 hours
The reduction rate of the output density after 00 hours and the output density after 1000 hours were measured. Table 2 shows the results. At this time, the thickness of the metal coating layer and the crystal particle diameter were determined by a scanning electron microscope according to Example 1.

[0031]

[Table 2]

From Table 2, it can be seen that the output of the sample polished on the collector surface is more stable for a long time than that of the unpolished one. This indicates that the coating layer is more firmly adhered when polished. Further, it can be seen that the ratio of ceramics in the range of 0.1 to 30% by weight is excellent from the viewpoint of cell durability.

[0033]

According to the solid oxide fuel cell of the present invention, at least one of Ni, Co, Mn and W and at least one of Ca, Mg, Y and rare earth elements are formed on the exposed surface of the current collector. Containing ZrO ₂ or CeO ₂ ,
Alternatively, it is made of a cermet with CeO ₂ alone, and has a metal crystal particle diameter of 0.5 to 5 μm and a film thickness of 0.1 to 30 μm.
Was formed, the metal (Ni, Co,
Sintering of at least one of Mn and W), thereby suppressing aggregation of the metal, preventing a decrease in the connection area between the Ni felt and the current collector due to the coating layer, and current collection characteristics of the current collector. Can be improved.

[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]

 DESCRIPTION OF SYMBOLS 31 ... Solid electrolyte 32 ... Air electrode 33 ... Fuel electrode 34 ... Fuel cell main body 34 35 ... Current collector 50 ... Coating layer

Claims (2)

[Claims] An air electrode is formed on one surface of a solid electrolyte and a fuel electrode is formed on the other surface, and a current collector electrically connected to the air electrode or the fuel electrode and exposed to the outside is provided. In the solid oxide fuel cell, at least one of Ni, Co, Mn, and W is formed on the exposed surface of the current collector.
a, Mg, Y and ZrO ₂ or CeO ₂ containing at least one of rare earth elements, or a cermet with CeO ₂ alone, and the Ni, Co,
A solid oxide fuel cell comprising a coating layer having a crystal particle diameter of Mn and W of 0.5 to 5 μm and a thickness of 0.3 to 30 μm. 2. The solid oxide fuel cell according to claim 1, wherein the exposed surface of the current collector is polished.