JPH0837018A - Power generation method in solid oxide fuel cell - Google Patents

Abstract

(57) [Summary] [Purpose] The purpose is to prevent the deterioration of power generation characteristics due to repeated stoppage of operation of fuel cells. [Structure] LaMnO ₃ system or La on one side of the solid electrolyte
A solid oxide fuel cell having a CoO ₃ -based material or an air electrode formed by substituting a part of La in these materials with Ca, Sr, Ba or the like, and a fuel electrode on the other side is used at high temperature. In a power generation method in a solid oxide fuel cell in which a cell operating temperature is maintained, an oxygen-containing gas is supplied to the air electrode side, and a fuel gas is supplied to the fuel electrode side to generate an electric current, the temperature rises to the cell operating temperature. An inert gas such as nitrogen, argon, or helium is supplied to the air electrode side at the time of warming or when the temperature is lowered from the battery operating temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolyte fuel cell which maintains a solid electrolyte fuel cell at a high temperature, supplies an oxygen-containing gas to the air electrode side, and supplies a fuel gas to the fuel electrode side to generate electric power. The present invention relates to a power generation method in a fuel cell.

[0002]

2. Description of the Related Art Generally, as a solid oxide fuel cell, for example, a flat type fuel cell shown in FIG. 1 is generally used. This flat plate type fuel cell is Y ₂
LaMnO ₃ or LaCoO _{3 in} which a part of La is replaced with Ca, Sr or the like is formed as the air electrode 2 on one surface of the solid electrolyte 1 made of ZrO ₂ stabilized with O ₃ , and Ni- on the other surface. Fuel electrode 3 made of ZrO ₂ (containing Y ₂ O ₃ )
Are formed to form a single cell. Further, the single cells are electrically connected by a LaCrO ₃ system material called a separator 4.

On the other hand, in addition to the flat plate type fuel cell, a cylindrical type fuel cell is also known. The cylindrical fuel cell is C
An aO-stabilized ZrO ₂ is used as a support tube, and an air electrode, an electrolyte, and a fuel electrode are formed thereon by using the same material as that of the flat-plate fuel cell.

When generating power with cells of any shape, air (oxygen) is supplied to the air electrode side, and reformed gas (fuel gas) of hydrogen gas or methane gas is supplied to the fuel electrode side. Electricity is generated between the fuel electrode and the fuel electrode.

[0005]

However, there is no problem in steady-state power generation in a state where the fuel cell is maintained at a high cell operating temperature, for example, around 1000 ° C., but the first fuel in June 1994 As shown in P314 of the proceedings of the presentation of the battery symposium, there is a problem that the power generation characteristics of the fuel cell are likely to deteriorate when the operation of the fuel cell is repeatedly stopped. As a result, there is a problem that the fuel cell lacks long-term stability.

An object of the present invention is to provide a power generation method in a solid oxide fuel cell, which can surely prevent the deterioration of power generation characteristics due to the repeated thermal shutdown of the fuel cell.

[0007]

As a result of examining the cause of the above problems, the present inventor has found that La, which is an air electrode material, is used.
MnO ₃ , LaCoO ₃ or part of La is Sr, B
LaMnO ₃ -based material or LaC in which a or Ca is substituted
When the crystal structure of the oO ₃ -based material changes around 600 to 800 ° C. and air (oxygen-containing gas) is being supplied to the air electrode side, the operation is repeated across the temperature range of 600 to 800 ° C. It was found that the electrode gradually deteriorates in particle size and the particles forming the air electrode are gradually separated from the solid electrolyte to deteriorate the power generation characteristics.

Further, the inventors of the present invention have found that the change in the crystal structure of the LaMnO ₃ -based and LaCoO ₃ -based materials is caused by absorption of oxygen into the crystal and release of oxygen from the system, resulting in diffusion of component ions within the crystal. It has been clarified that the particle growth of the air electrode occurs by promoting the diffusion of the component ions by the so-called headbar effect.

Therefore, the present inventor introduces an inert gas to suppress the supply of oxygen to the air electrode during the start-up heating process or the stop-cooling process of the fuel cell.
The inventors have found that the grain growth of the air electrode made of aMnO ₃ -based and LaCoO ₃ -based materials is suppressed, and as a result, the peeling of the air electrode is suppressed, and the present invention has been completed.

That is, according to the power generation method in the solid oxide fuel cell of the present invention, an air electrode is formed on one side of the solid electrolyte,
A solid oxide fuel cell having a fuel electrode formed on the other side is maintained at a high cell operating temperature, oxygen-containing gas is supplied to the air electrode side, and fuel gas is supplied to the fuel electrode side to generate electric power. In the method for generating power in a solid oxide fuel cell, the temperature is raised to the cell operating temperature and the temperature is lowered from the cell operating temperature, particularly 300 to 90.
An inert gas is supplied to the air electrode side in a temperature range of 0 ° C., and the air electrode material is a composite oxide containing at least La and Mn and / or Co, or a metal component thereof. Is particularly effective when it is formed by substituting a part of it with an alkaline earth metal.

[0011]

In the present invention, the supply of oxygen to the air electrode is suppressed by supplying an inert gas to the air electrode side when increasing the temperature to the battery operating temperature and decreasing the temperature from the battery operating temperature.
It suppresses the absorption of oxygen into the crystal and the release to the outside of the system, whereby even in the case where the operation stop across the temperature range of 600 to 800 ° C. is repeated, those of LaMnO ₃ , LaCoO ₃ or their composite oxides can be reduced. LaMnO ₃ based material in which La is replaced with Sr, Ba or Ca and LaCo
It is possible to suppress the change in the crystal structure of the O ₃ -based material, and as a result, it is possible to prevent the air electrode from peeling off from the solid electrolyte, and to maintain the power generation characteristics stably for a long period of time even during repeated start-stop operations.

[0012]

EXAMPLES The power generation method in the solid oxide fuel cell of the present invention will be described in detail below. The solid oxide fuel cell used in the power generation method of the present invention is composed of, for example, a flat plate fuel cell as shown in FIG. This solid electrolyte 1 is composed of zirconia-stabilized electrolyte such as Y ₂ O ₃ on one surface of which La is Sr or Ba.
Alternatively, it has a structure in which an air electrode 2 made of LaMnO ₃ -based material or LaCoO ₃ -based material partially substituted with Ca is formed, and a fuel electrode 3 made of Ni-zirconia cermet is formed on the other surface.

Then, the fuel cell uses this unit cell as L
It is configured to be electrically connected in series via a separator 4 made of an aCrO ₃ system material. The fuel cell has a basic structure and is laminated with several tens to 100 layers to form a module. In the vicinity of the fuel cell, a heating device that heats the fuel cell to a cell operating temperature that effectively generates electric power, an oxygen supply device that supplies an oxygen-containing gas (eg, air) to the air electrode side, and a fuel electrode. A fuel gas supply device for supplying a fuel gas (for example, hydrogen) to the side and an inert gas supply device for supplying an inert gas to the air electrode side when the temperature rises to the cell operating temperature and when the temperature decreases from the cell operating temperature. The fuel cell power generation device is arranged.

The generation of electric power by such a solid oxide fuel cell is performed by applying an oxygen supply device to the air electrode side while maintaining the solid oxide fuel cell at a cell operating temperature of, for example, about 1000.degree. This is performed by supplying an oxygen-containing gas (for example, air) and at the same time supplying a fuel gas (for example, hydrogen) to the fuel electrode side by the fuel gas supply device to generate electric power between the air electrode and the fuel electrode.

Further, in the present invention, when the temperature is raised to the battery operating temperature (starting heating process) and when the temperature is lowered from the battery operating temperature (stop cooling process), the inert gas is supplied to the air electrode side by the inert gas supply device. It is characterized by supplying gas. That is, the oxygen-containing gas is supplied to the air electrode side at the battery operating temperature at which electric power is effectively generated, but the inert gas is supplied to the air electrode side at the time of heating to the battery operating temperature and at the temperature decrease from the battery operating temperature. It Examples of the inert gas include argon gas, nitrogen gas, helium gas and neon gas, or a mixed gas thereof, and in particular, a high-purity gas having a low oxygen partial pressure of 10 ⁻³ atm or less at 1000 ° C. Is desirable.

According to the power generation method as described above, oxygen is supplied to the air electrode by supplying the inert gas to the air electrode side when the temperature is raised to the battery operating temperature and when the temperature is lowered from the battery operating temperature. To suppress the absorption of oxygen into the crystal and the release of oxygen to the outside of the system, and thereby LaMnO ₃ , L
The temperature range of 600 to 800 ° C., which is the temperature at which the crystal structure of LaMnO ₃ -based material and LaCoO ₃ -based material in which a part of La of aCoO ₃ or a composite oxide thereof is partially replaced by Sr, Ba or Ca, is changed. Even if the crossing out is repeated, it is possible to suppress the change in the crystal structure of those materials. Therefore, the diffusion of the component ions due to the change of the crystal structure can be reduced, and the grain growth of the air electrode can be suppressed, so that the deterioration of the power generation characteristics of the fuel cell can be reliably prevented.

The present invention can also be applied to a cylindrical fuel cell, and can further suppress peeling of the electrolyte and the current collecting material (interconnector) from the air electrode of the cylindrical fuel cell.

Next, in order to confirm the effect of suppressing the particle growth of the air electrode by supplying an inert gas to the air electrode side when the temperature is raised to the battery operating temperature and when the temperature is lowered from the battery operating temperature, the present inventor Conducted the following experiment.

Experiment 1 Commercially available La ₂ O ₃ , CoO, CaCO having a purity of 99.9%
₃ , BaCO ₃ , SrCO ₃ , and MnO were mixed so as to have a predetermined material composition, and a solid phase reaction was performed at 1300 ° C. for 10 hours to obtain La _0.9 Ca _0.1 O ₃ and La _0.9 Sr.
_0.1 O ₃ and La _0.9 Sr _0.1 CoO ₃ powders were produced. Then, it was pulverized for 20 hours using zirconia balls to prepare an air electrode powder having an average particle diameter of about 2 μm. In addition, commercially available La _0.8 Ca _0.21 C having a purity of 99.8%
The rO ₃ powder was molded and fired at 1500 ° C. for 5 hours.
Thus, a separator plate having a groove having a width of 100 mm and a thickness of 3 mm and a relative density of 99.8% was prepared.

Commercially available 8 mol% Y ₂ O _{3 having} a purity of 99.9%
A ZrO ₂ powder containing was extruded and sintered at 1450 ° C. for 5 hours to prepare an electrolyte sheet having a width of 100 mm and a thickness of 0.3 mm and a relative density of 99.5%. The above-mentioned air electrode powder was printed on one surface of this electrolyte sheet to a thickness of about 30 μm. Also, 70 wt% Ni on the other surface
A mixed powder of O-30 wt% ZrO ₂ (containing 8 mol% Y ₂ O ₃ ) was similarly printed to a thickness of about 30 μm to form a fuel electrode. Then, this electrolyte sheet was heat-treated at 1200 ° C. for 2 hours to bake the electrode on the electrolyte to form a single cell.

This unit cell is sandwiched between the separators as shown in FIG. 1, and oxygen gas is flown to the air electrode side and hydrogen gas is flown to the fuel electrode side from room temperature to 1000 ° C.
The temperature was raised at a rate of ℃ / h, the power density was measured at 1000 ℃ for 1 hour, and the power density was measured.
The temperature was lowered at a rate of h. This is one cycle, and up to 5
The cycle was repeated. At this time, when the temperature is raised from room temperature to 1000 ° C. and the temperature is lowered from 1000 ° C. to room temperature, N
₂ (1000 ° C. oxygen partial pressure, 8 × 10 ⁻⁴ atm) or Ar gas (1000 ° C. oxygen partial pressure, 3 × 10 ⁻⁴ atm) was introduced. On the other hand, the power generation characteristics of the cell in which oxygen gas was allowed to flow when the temperature was raised and lowered were also examined.

As a result, as shown in Table 1, cell sample no. The output densities of the samples Nos. 1, 3, and 6 gradually decreased, and sample No. In No. 3, the air electrode was completely peeled off after 3 cycles and the output became low. On the other hand, the power density of the sample into which N ₂ and Ar gas were introduced at the time of temperature increase and decrease was always stable regardless of the cycle.

[0023]

[Table 1]

Similarly, when an experiment was conducted in a neon or helium gas having an oxygen partial pressure of 10 ⁻⁴ atm, an excellent grain growth suppressing effect and a stable output were obtained as with N ₂ and Ar.

[0025]

According to the power generation method in the solid oxide fuel cell of the present invention, the LaMnO ₃ -based material in which Sr, Ba, or Ca is substituted, even when the operation stop is repeated across the temperature range of 600 to 800 ° C., It is possible to suppress the change in the crystal structure of the LaCoO ₃ based material and prevent the grain growth of the air electrode. As a result, it is possible to reliably prevent deterioration of the power generation function of the fuel cell unit.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a flat plate type fuel battery cell.

[Explanation of symbols]

 1 solid electrolyte 2 air electrode 3 fuel electrode 4 separator

Claims (2)

[Claims] 1. A solid electrolyte fuel cell comprising an air electrode formed on one side of a solid electrolyte and a fuel electrode formed on the other side of the solid electrolyte is maintained at a high cell operating temperature, and an oxygen-containing gas is supplied to the air electrode side. In the power generation method in a solid oxide fuel cell that supplies fuel gas to the fuel electrode side to generate electric power, the air is supplied when the temperature is raised to the cell operating temperature and when the temperature is lowered from the cell operating temperature. A method of power generation in a solid oxide fuel cell, which comprises supplying an inert gas to the electrode side. 2. The solid according to claim 1, wherein the air electrode is made of a material in which at least La and a composite oxide containing Mn and / or Co or a part of their metal components are replaced with an alkaline earth metal. A power generation method in an electrolyte fuel cell.