JP2003263996A - Solid oxide fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve durability of a solid oxide fuel cell. <P>SOLUTION: The solid oxide fuel cell includes a power generating cell 1 with a fuel electrode layer 4 and an air electrode layer 2 disposed on both faces of a solid electrolyte layer 3, wherein intermediate layers 5, 5 comprising an oxide ion conductor or an electron - oxide ion mixed conductor are formed on both faces of the solid electrolyte layer 3. Through such a structure of the solid electrolyte layer 3, a uniform compressive stress is applied to both faces of the solid electrolyte layer 3 at baking, by contraction of the intermediate layers 5, 5, by which the solid electrolyte layer 3 is reinforced to prevent cracks of the power generating cell 1, and separation resistance of the solid electrolyte layer 3 and the fuel electrode layer 4 is improved and durability of the solid oxide fuel cell is enhanced. <P>COPYRIGHT: (C)2003,JPO

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 in which a fuel electrode layer and an air electrode layer are arranged on both sides of a solid electrolyte layer, and more particularly, the durability of the solid oxide fuel cell is improved. It is about.

[0002]

2. Description of the Related Art A solid oxide fuel cell having a laminated structure in which a solid electrolyte layer made of an oxide ion conductor is sandwiched between an air electrode layer (oxidant electrode layer) and a fuel electrode layer is a third generation type. Development is progressing as a fuel cell for power generation. In the solid oxide fuel cell, oxygen (air) is supplied to the air electrode side and fuel gas (H ₂ , CO, etc.) is supplied to the fuel electrode side. Both the air electrode and the fuel electrode are made porous so that the gas can reach the interface with the solid electrolyte.

Oxygen supplied to the air electrode reaches the vicinity of the interface with the solid electrolyte layer through the pores in the air electrode layer, and at this portion, electrons are received from the air electrode and an oxide ion (O ^{2 -} ) Is ionized. The oxide ions diffuse and move in the solid electrolyte layer toward the fuel electrode. Oxide ions that have reached the vicinity of the interface with the fuel electrode react with the fuel gas and react with the reaction products (H ₂ O, CO _{2) in} this portion.
Etc.) and emit electrons to the fuel electrode.

The electrode reaction when hydrogen is used as the fuel is as follows. Air electrode: 1/2 O ₂ + 2e ⁻ → O ^{2 −} Fuel electrode: H ₂ + O ² → → H ₂ O + 2e ⁻ Overall: H ₂ + 1/2 O ₂ → H ₂ O

The solid electrolyte layer is a moving medium for oxide ions and at the same time functions as a partition wall for preventing direct contact between the fuel gas and air, so that the solid electrolyte layer has a gas impermeable and dense structure. This solid electrolyte layer must have a high oxide ion conductivity, be chemically stable under conditions from an oxidizing atmosphere on the air electrode side to a reducing atmosphere on the fuel electrode side, and be composed of a material that is resistant to thermal shock. As a material that meets such requirements, stabilized zirconia (YSZ) added with yttria is generally used.

On the other hand, both the air electrode (cathode) layer and the fuel electrode (anode) layer, which are electrodes, must be made of a material having a high electron conductivity. Since the air electrode material must be chemically stable in an oxidizing atmosphere at a high temperature of around 700 ° C., the metal is not suitable, and a perovskite type oxide material having electronic conductivity, specifically, LaMnO _{3 is used.} Alternatively, LaCoO ₃ or a part of these La is S
Solid solutions substituted with r, Ca, etc. are generally used.
The fuel electrode material is a metal such as Ni or Co, or N.
Cermets such as i-YSZ and Co-YSZ are common.

There are two types of solid oxide fuel cells, a high temperature type which operates at a high temperature of around 1000 ° C. and a low temperature type which operates at a low temperature around 700 ° C. A low-temperature operation type solid oxide fuel cell is, for example, a stabilized zirconia (YSZ) added with yttria which is an electrolyte to reduce the thickness of the electrolyte as much as possible, thereby lowering the resistance of the electrolyte and generating a fuel cell at a low temperature. Using a power generation cell that has been improved.

As described above, much research has been made on the material of the solid electrolyte layer and the like, and various improvements have been made to the power generation cell until now.

FIG. 2 shows the internal structure of a power generation cell in a conventional solid oxide fuel cell. In the figure, reference numeral 2 is an air electrode layer, reference numeral 3 is a solid electrolyte layer, and reference numeral 4 is a fuel electrode layer. is there. Conventionally, a power generation cell 1 having a three-layer structure in which an air electrode layer 2 and a fuel electrode layer 4 are directly formed on a solid electrolyte layer 3 as shown in the figure is generally used.

[0010]

The power generation cell 1 having the above structure has excellent power generation characteristics (current-voltage-power characteristics) in a short-term power generation test. The cracking resistance (crack) and the deterioration of power generation performance in a long-term power generation test are problems. The crack of the power generation cell is largely due to the thermal stress generated by the temperature distribution in the cell during power generation (at the time of temperature rise), and is caused by using an extremely thin ceramic material with a thickness of about 200 μm as the solid electrolyte layer. It is thought that The main causes of the deterioration of the power generation characteristics are the separation phenomenon between the solid electrolyte layer 3 and the electrode layers (particularly the fuel electrode layer 4), the mutual diffusion of metal elements between the solid electrolyte layer 3 and the electrode layers, and the like. ing.

In the case of a solid oxide fuel cell, a power generation cell for practical use is required to have durability of at least 40,000 to 50,000 hours, but the power generation cell 1 of the conventional structure shown in FIG. In this case, deterioration of power generation characteristics was recognized in a durability test for about 100 hours at the longest, and many problems still remain to be overcome for practical use.

The present invention has been made in view of the above-mentioned conventional problems.
An object of the present invention is to provide a solid oxide fuel cell having high durability, which has improved cracking resistance of a power generation cell and improved peeling resistance between a solid electrolyte layer and a fuel electrode layer.

[0013]

That is, the present invention as set forth in claim 1 is a power generation system in which a fuel electrode layer (4) and an air electrode layer (2) are arranged on both sides of a solid electrolyte layer (3). In a solid oxide fuel cell comprising a cell (1), an intermediate layer (5, 5) made of an oxide ion conductor or an electron-oxide ion mixed conductor is formed on both surfaces of the solid electrolyte layer (3). The structure is characterized in that a compressive stress is applied in advance from both sides of the solid electrolyte layer (3).

The present invention according to claim 2 provides the solid oxide fuel cell according to claim 1, wherein the intermediate layer (5, 5) is made of CeSmO ₂ (samarium-added ceria).
It is characterized by consisting of.

Further, the present invention according to claim 3 is the solid oxide fuel cell according to claim 1 or 2, wherein after forming an intermediate layer on both surfaces of the solid electrolyte layer (3), The air electrode layer (2) and the fuel electrode layer (4) are formed.

In the above structure, the contraction of the intermediate layer (5) during firing of the electrolyte layer uniformly applies compressive stress to both surfaces of the solid electrolyte layer (3), so that the solid electrolyte layer (3) is reinforced and power is generated. The cracking of the cell (1) is prevented, and the presence of the intermediate layer (5) improves the contact between the solid electrolyte layer (3) and each electrode layer, and in particular, the solid electrolyte layer (3) and the fuel electrode layer. The peel resistance with (4) is improved.

[0017]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a sectional view showing the structure of a power generation cell to which the present invention is applied.

As shown in FIG. 1, the power generation cell 1 of this embodiment is composed of an air electrode layer 2, a solid electrolyte layer 3, and a fuel electrode layer 4, and the solid electrolyte layer 3 is sandwiched between the two surfaces. The air electrode layer 2 and the fuel electrode layer 4 are respectively arranged.

Here, the air electrode layer 2 is made of LaMnO ₃ , La.
It is composed of CoO ₃ or the like, the solid electrolyte layer 3 is composed of stabilized zirconia added with yttria (YSZ), etc., the fuel electrode layer 4 is Ni, a metal such as Co or Ni-YSZ,
It is composed of a cermet or the like such as Co-YSZ. Further, the structure of the solid electrolyte layer 4 is different from that of the conventional type shown in FIG. 2, and an intermediate layer 5 having a predetermined thickness is formed on both surfaces thereof, that is, on the air electrode layer side interface and the fuel electrode layer side interface of the solid electrolyte layer 4. 5 are formed. As the material of the intermediate layers 5 and 5, an oxide ion conductor or an electron-oxide ion mixed conductor is suitable, and CeSmO ₂ (samarium-added ceria) is used in this embodiment.

In a so-called fixed electrolyte fuel cell,
It is necessary to raise the temperature inside the battery module to a predetermined temperature at the time of start-up (at the start of power generation). As described above, the operating temperature of the high temperature type is around 1000 ° C, and the operating temperature of the low temperature type is 700.
The temperature is around ℃, and in any case, the power generation cell itself is exposed to a high temperature environment. Therefore, a temperature distribution sometimes occurs in the surface of the power generation cell, and thermal stress at that time causes cracks in the power generation cell (solid electrolyte layer 4).

By the way, generally, a ceramic material has a property that cracks easily occur when a tensile force is applied to the surface. Therefore, in the case of a ceramic member that requires particularly durability, it is possible to improve the strength of the material several times by making a state in which a compressive stress is applied to the surface thereof in advance.

The present invention focuses on such a reinforced structure of the ceramic material. As described above, the intermediate layers 5 and 5 are formed on both surfaces of the solid electrolyte layer 3, and a compressive stress is applied to the solid electrolyte 3 in advance. The solid electrolyte layer 3 is added in advance.
It is intended to strengthen.

In this embodiment, the manufacturing process of the power generation cell 1 is performed.
In forming the electrolyte layer 3, for example, a doctor
A green sheet formed into a thin plate by the lade method, etc.
CeSmO on both sides by screen printing₂ Applied
After that, firing is performed. Solid electrolysis during this firing
Depending on the difference in heat shrinkage between the quality layer 3 and the intermediate layer 5, it may be
The solid electrolyte layer 3 in a state where compressive stress is evenly applied.
It can be molded, and as a result, the strength of the fixed electrolyte layer 3 is increased.
Of the power generation cell 1 due to temperature rise during power generation, etc.
It becomes possible to prevent cracks. Incidentally, contraction
The rate is CeSmO ₂ > It is used as an electrolyte layer. Of solid electrolyte layer
After firing, apply the fuel electrode material by screen printing, etc.
After the firing process and the coating and firing process of the air electrode material, both
The solid electrolyte layer 3 having the intermediate layers 5 and 5 formed on its surface is sandwiched.
Thus, the air electrode layer 2 and the fuel electrode layer 4 are formed.
It will be.

Further, in the above structure, the strength of the solid electrolyte layer 3 is increased.
In addition to the effect of improving the degree of strength, the dense structure of the intermediate layers 5, 5
Contact between the solid electrolyte layer 3 and the air electrode layer 2 or the fuel electrode layer 4
And the peeling resistance between the solid electrolyte layer 3 and each electrode layer is improved.
To be done. In addition, CeSmO ₂ To the intermediate layer 5 using
By providing child conductivity, the contact resistance at the interface can be increased.
Can be reduced and the power generation efficiency of the power generation cell 1 can be improved.
It

If the intermediate layer 5 is too thin, the compressive stress is reduced and sufficient strength cannot be obtained. On the contrary, if it is too thick, the resistance loss in the intermediate layer increases. Therefore, it is necessary to set the thickness of the intermediate layer 5 in consideration of both strength improvement and resistance loss.

[0026]

As described above, according to the present invention,
Since the intermediate layer is formed on both sides of the solid electrolyte layer, compressive stress is evenly applied to both sides of the solid electrolyte layer, which improves the crack resistance of the power generation cell and improves the solid electrolyte layer and the fuel electrode. The peel resistance of the layers is also improved, thus improving the durability of the solid oxide fuel cell.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a power generation cell to which the present invention is applied.

FIG. 2 is a cross-sectional view showing the structure of a conventional power generation cell.

[Explanation of symbols]

1 power generation cell 2 Air electrode layer 3 Solid electrolyte layer 4 Fuel pole layer 5 Middle class

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Koji Hoshino             1002-14 Mukoyama, Naka-machi, Naka-gun, Ibaraki Prefecture             Terari Co., Ltd.             Inside (72) Inventor Toru Inagaki             3-3-22 Nakanoshima, Kita-ku, Osaka City, Osaka Prefecture             Kansai Electric Power Co., Inc. (72) Inventor Hiroyuki Yoshida             3-3-22 Nakanoshima, Kita-ku, Osaka City, Osaka Prefecture             Kansai Electric Power Co., Inc. (72) Inventor Tsunehisa Sasaki             3-3-22 Nakanoshima, Kita-ku, Osaka City, Osaka Prefecture             Kansai Electric Power Co., Inc. F-term (reference) 5H026 AA06 BB01 BB04 EE13

Claims (3)

[Claims] 1. A solid oxide fuel cell comprising a power generation cell (1) having a fuel electrode layer (4) and an air electrode layer (2) disposed on both sides of a solid electrolyte layer (3). An intermediate layer (5, composed of an oxide ion conductor or an electron-oxide ion mixed conductor) on both surfaces of the electrolyte layer (3).
The solid oxide fuel cell is characterized in that 5) is formed and a compressive stress is applied from both sides of the solid electrolyte layer (3) in advance. 2. The intermediate layer (5, 5) comprises (Ce, S
m) The solid oxide fuel cell according to claim 1, wherein the solid oxide fuel cell comprises O ₂ (samarium-added ceria). 3. The air electrode layer (2) and the fuel electrode layer (4) are formed after forming an intermediate layer on both surfaces of the solid electrolyte layer (3). The solid oxide fuel cell according to claim 2.