JP3576246B2 - Operating method of fuel cell - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a method for operating a high-temperature solid-electrolyte electrochemical cell such as a solid-electrolyte fuel cell or a solid-electrolyte-type steam electrolyzer operating at a high temperature. The present invention relates to a cell repair method.
[0002]
[Prior art]
Hereinafter, the prior art will be described with reference to FIG. 2 taking a solid oxide fuel cell as an example. A solid oxide fuel cell supplies a fuel such as hydrogen and an oxidizing agent such as air to both sides of the solid electrolyte to generate power. The configuration is as shown in FIG. In FIG. 2, 1 is a solid electrolyte, 2 is a fuel electrode, 3 is an oxygen electrode, 8 is an oxidizing gas such as air, and 9 is a fuel gas such as hydrogen. It is general that such a solid oxide fuel cell is put into operation immediately after assembly as shown in FIG.
[0003]
[Problems to be solved by the invention]
In the case of a solid oxide fuel cell having a configuration as shown in FIG. 2, a fuel gas 9 such as hydrogen and an oxidizing gas 8 such as air are separated and supplied via the solid electrolyte 1. If there is a defect such as a crack, the fuel gas 9 and the oxidizing gas 8 may be mixedly burned to form the combustion zone 10. In this case, since the temperature rises to nearly 2000 ° C., there is a possibility that the members may be damaged, and once the leak combustion phenomenon occurs, it may propagate and eventually become inoperable.
[0004]
The present invention has been made in view of the above-mentioned state of the art, and provides an easy and reliable method of safely operating a solid electrolyte type electrochemical cell by eliminating the above-mentioned problems, and a method of repairing the solid electrolyte of the electrochemical cell when the solid electrolyte is damaged. It is assumed that.
[0005]
[Means for Solving the Problems]
The present invention relates to (1) an element which forms an oxide serving as a solid electrolyte stabilizer on the fuel electrode side at a temperature of 600 to 1000 ° C. before the operation of a solid oxide electrochemical cell operated at 600 ° C. or higher A method for safely operating a solid electrolyte type electrochemical cell, characterized by introducing a mixed gas comprising chloride, ZrCl ₄ and an inert gas into the air electrode side by introducing at least one of air, oxygen and water vapor. And (2) stabilizing ZrO _{2 in} the fuel gas flowing to the fuel electrode side when an abnormal rise in the outlet gas temperature of the battery is observed during the operation of the solid electrolyte electrochemical cell operated at 600 ° C. or higher. A method for repairing a solid electrolyte of a solid electrolyte type electrochemical cell, characterized by adding a chloride of an element forming an oxide serving as an agent and ZrCl ₄ .
[0006]
As the solid electrolyte of the solid electrolyte type electrochemical cell of the present invention, Y ₂ O ₃ stabilized ZrO ₂ (YSZ) or Y ₂ O ₃ stabilized ceria セ (CeO ₂ ) _0.8 (Y ₂ O ₃ ) _0.2 {, Cd ₂ O ₃ stabilized ceria {(CeO ₂ ) _0.8 (Cd ₂ O ₃ ) _0.2 }. Examples of chlorides of elements forming an oxide serving as a stabilizer for the solid electrolyte introduced to the fuel electrode include YCl ₃ , CaCl ₂ , MgCl ₂ , and MgCl ₂ . Examples of the inert gas introduced at the same time include Ar, He, N ₂ , Ne, Kr, and Xc.
[0007]
[Action]
When there is a defect in the solid electrolyte, for example, YCl ₃ and ZrCl ₄ introduced on the fuel electrode side react with oxygen introduced on the oxygen electrode side as shown in the following formula, and Y ₂ O _{3 is} stabilized at the defective portion. Form ZrO ₂ .
[0008]
Embedded image
_{2YCl 3 +1.50 2 = Y 2 O} 3 + 3Cl 2
ZrCl ₄ + O ₂ = ZrO ₂ + 2Cl ₂
[0009]
If water vapor is present in the gas introduced to the oxygen electrode side, it reacts as shown in the following formula, and similarly forms Y ₂ O ₃ stabilized ZrO ₂ at the defect.
[0010]
Embedded image
2YCl ₃ + 3H ₂₀ = Y ₂ O ₃ + 6HCl
ZrCl ₄ + 2H ₂ O = ZrO ₂ + 4HCl
[0011]
Since oxygen or water vapor is supplied from the oxygen electrode side, this means that the above reaction occurs at a leaking portion (defect portion). Here, the inert gas in the mixed gas acts as a carrier gas, but if such a carrier gas is not used, the reaction gas becomes too high in concentration, and a uniform dense film cannot be formed. The defect cannot be completely closed.
[0012]
In this way, the reaction takes place where the gas of both electrodes meets, the leaked part is sealed by the generated components, and when all the parts are sealed, the oxygen stops being supplied from the oxygen electrode side, so the reaction stops. Therefore, after assembling the solid electrolyte type electrochemical cell, if the above reaction is performed, the safe operation of the solid electrolyte type electrochemical cell becomes possible, and a defect occurs during the operation of the solid electrolyte type electrochemical cell. By performing the above-mentioned reaction, it is possible to completely repair the defective portion.
[0013]
【Example】
Hereinafter, specific examples of the present invention will be described to clarify the effects of the present invention.
[0014]
(Example 1)
An embodiment according to the present invention will be described with reference to FIG. Figure 1 is immediately after assembling the solid oxide fuel cell is an explanatory diagram in the case of repairing defective portions existing solid electrolyte of the same cell (the cracking unit) beforehand, YCl ₃ gas to the fuel electrode 2 side of the crack portions 4 5 shows a diagram in which a ZrCl ₄ gas 6 and an inert gas 7 are flowing air 8 to the oxygen electrode 3 side.
[0015]
First, the inert gas 7 is caused to flow to the fuel electrode 2 side, and when it reaches a steady state, the YCl ₃ gas 5 and the ZrCl ₄ gas 6 are mixed with each other so that the ratio (molar ratio) of Y to Zr is Y / (Zr + Y) = 8 to 10 %, Gradually increasing the concentrations of YCl ₃ and ZrCl ₄ , and finally eliminating the inert gas 7 and leaving only the YCl ₃ gas 5 and the ZrCl ₄ gas 6. As a result, a reaction product 11 is formed in the cracked portion 4. The reaction conditions for the reaction product 11 may be 600 to 1000 ° C., the time must be at least 30 minutes, and the film formation rate of the reaction product 11 is 1 to 10 μm / Hr. Therefore, if the crack is large, it takes about 10 hours. In the case where steam is used instead of air, the outlet may be suctioned and exhausted by a vacuum pump or the like in order to remove generated hydrogen chloride gas or the like.
[0016]
The gas generated in the present invention is chlorine gas or hydrogen chloride gas when water vapor is used. Since hydrogen chloride gas has a strong corrosive property, it is not desirable to remain. Therefore, forced ventilation or scavenging with a carrier gas as described above is desirable.
[0017]
(Example 2)
Hereinafter, examples of repair during operation will be described. Two sets of unit power generation elements are stacked by sandwiching a power generation membrane having a fuel electrode and an air electrode on both sides of a 75 mm solid electrolyte with an interconnector (current connector) made of lanthanum chromite (LaCrO ₃ ). A fuel cell having a fuel and air inlet / outlet pipe at the lower part of the fuel cell was manufactured.
[0018]
The effective area of this battery is 25 cm ² per set and 50 cm ² for two sets. The battery was set in an electric furnace and heated up to 1000 ° C. at a rate of 100 ° C./hr. Thereafter, 0.25 l / min of hydrogen and 0.5 l / min of air were sent to each cell as fuel, and a voltage of 2.0 V (1.0 V per cell) was obtained. When the current was taken out, 7.5 A was taken out at 0.7 V per cell.
[0019]
Next, the electric furnace of the fuel cell was turned off to rapidly lower the temperature. When the temperature reached room temperature, the temperature was raised again to 1000 ° C. at a rate of 100 ° C./hr. When fuel (hydrogen) and air were supplied again to this fuel cell, the voltage dropped to 1.8 V, and only 4 A at 0.7 V could be taken out. The thermocouple installed in the fuel outlet pipe showed 1100 ° C., which was about 80 ° C. higher than normal 1020 ° C. The most likely cause was cracking of the power generation membrane, so the following measures were taken. First, both the fuel side and the air side were evacuated to discharge gas. Next, 50 cc / min of nitrogen was flown to the fuel side, and air was flown to the air side at the same flow rate. Thereafter, the gas on the fuel side was replaced with a mixed gas of YCl ₃ and ZrCl ₄ gas (Y molar ratio: 10%) and kept for 5 hours. Thereafter, when fuel (hydrogen) and air were supplied again, the voltage increased to 1.95 V, and the current at 0.7 V recovered to 5.5 A. It is considered that part of the electrode did not recover completely due to the deterioration of the electrode due to the burning due to cracking, but the effect was sufficient, and the temperature at the outlet dropped to 1020 ° C, and the cracked part was sealed. It could be confirmed.
[0020]
【The invention's effect】
The following effects are produced by the present invention. That is, (1) the sealing performance is improved. According to the present invention, the leaking portion is selectively sealed, so that the sealing performance is improved as compared with the related art. (2) The repair method of the fuel cell becomes easy. That is, in the case of a conventional fuel cell, when local combustion or the like occurs and the temperature rises, it is necessary to constantly lower the temperature and repair it. Cooling down not only results in time loss, but also results in repairs at room temperature are not guaranteed under cooling, so it was necessary to repeat heating and cooling. If the temperature is slightly lowered (in the range of 600 ° C. to 1000 ° C.), repair becomes possible, and the reliability is improved.
(3) The durability of the fuel cell is improved.
[0021]
By the effects of the above (1) and (2), if the operation of the present invention is performed before the operation of the fuel cell, the sealing properties of the fuel gas and the oxidizing gas can be made perfect, so that there is no fear of deterioration due to local combustion. . Therefore, the durability of the battery is increased.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a method of operating a fuel cell stack according to one embodiment of the present invention.
FIG.
FIG. 2 is an explanatory diagram of one embodiment of a conventional fuel cell operation method.

Claims (2)

Prior to the operation of the solid electrolyte type electrochemical cell operating at 600 ° C. or higher, at a temperature of 600 to 1000 ° C., chloride and ZrCl _{4 of} an element forming an oxide serving as a solid electrolyte stabilizer on the fuel electrode side A method for safely operating a solid electrolyte type electrochemical cell, characterized in that a mixed gas of an inert gas is introduced into the air electrode side with at least one of air, oxygen and water vapor. During the operation of the solid electrolyte type electrochemical cell operated at 600 ° C. or higher, when an abnormal rise in the outlet gas temperature of the battery is observed, the oxidation of the fuel gas flowing to the fuel electrode side as a stabilizer for ZrO ₂ becomes A method for repairing a solid electrolyte of a solid electrolyte type electrochemical cell, characterized by adding a chloride of an element forming a substance and ZrCl ₄ .

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