JP2010061829A - Operation method of solid oxide fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide sufficient electric conductivity for a fuel electrode of using a cermet of nickel oxide and zirconia, when operating a solid oxide fuel cell. <P>SOLUTION: First of all, the fuel electrode is put in an atmosphere of the atmosphere or inert gas, by starting supply of the atmosphere or the inert gas to the fuel electrode for constituting the solid oxide fuel cell in a cell starting stage of the initial state of power generation (Step S101). Next, a temperature rise in the fuel electrode (the solid oxide fuel cell) put in an atmosphere of the atmosphere or the inert gas is started (Step S102). After the fuel electrode (the solid oxide fuel cell) reaches the reduction temperature by this heating temperature rise (Step S103), supply of the atmosphere or the inert gas to the fuel electrode is stopped (Step S104). Afterwards, reduction processing of the fuel electrode is performed by supplying fuel gas to the fuel electrode in a state of the reduction temperature. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for operating a solid oxide fuel cell, and more particularly to an operation method at startup.

  Solid oxide fuel cells have higher electrical conversion efficiency and power density than other fuel cells, and are therefore actively being developed as distributed power sources. A single cell of a fuel cell has a structure in which an electrolyte is sandwiched between an air electrode and a fuel electrode. An oxidant gas (generally air) is supplied to the air electrode, and a fuel containing hydrogen as a main component (generally a fuel electrode) Supplies the reformed gas of methane).

  Since solid oxide fuel cells use solid oxide ceramics as an electrolyte, the operating temperature is higher than that of other fuel cells in order to ensure sufficiently high ion conductivity. As a general constituent material, stabilized zirconia is used for the electrolyte, lanthanum manganite added with rare earth is used for the air electrode, and cermet mixed with nickel and zirconia is used for the fuel electrode.

  By the way, the operating temperature of the initial solid oxide fuel cell is as high as about 1000 ° C., and it was necessary to use an expensive ceramic material for cell connection in order to cope with this temperature. On the other hand, in recent years, development of solid oxide fuel cells that generate electricity at a temperature of about 600 to 800 ° C., in which an inexpensive alloy can be used as a material for connecting cells, has been actively performed ( Non-patent document 1).

  The decrease in the operating temperature is desirable because the deterioration of the cell itself is suppressed even from the viewpoint of the connection material, so that the battery life can be extended. However, a decrease in operating temperature leads to a decrease in the conductivity of the constituent materials, leading to a decrease in battery performance. For this reason, in order to lower the operating temperature, it is important to apply a material having high conductivity even at a low operating temperature.

  In addition, examples of the cell structure of a solid oxide fuel cell include a cylindrical type and a flat plate type. From the viewpoint of cell performance, the development of a flat plate cell in which a thin film electrolyte is formed by using a fuel electrode as a support has been vigorous. (See Non-Patent Document 2). In the fuel electrode support type cell, the thickness of the layers constituting the cell is about several tens of μm for the electrolyte and the air electrode, whereas the fuel electrode substrate serving as the support is about 1 to 2 μm. Will occupy the majority. For this reason, the characteristics of the fuel electrode greatly affect the cell characteristics.

  In order to obtain a sufficient output in a single cell, the cell size may be increased. However, in the case where power is generated as a stack in which flat plate-type large area cells are stacked in series with the connection portion interposed therebetween, In addition to the current, an in-plane current is also generated, so that the electrode itself is also required to have a current collecting function. For this reason, it is important to apply a material exhibiting high conductivity even in an operating state to the fuel electrode substrate of the fuel electrode supporting cell.

M. Shibata, et al., "Development of Intermediate-Temperature SOFC Module and Systems", ECS Transactions, Vol. 7, No. 1, pp. 77-83, 2007 D. Ghosh, et al., "STATUS OF DEVELOPMENTS AT GLOBAL THERMOELECTRIC", Electrochemical Society Proceedings, Vol. 2001-16, pp.100-110, 2001. Shuzo Murakami, et al., "Studies on solid oxide fuel cells (I) Effect of zirconia content in nickel anode on electrode performance", Electrochemistry, Vol.59, No.4, pp.320-324, 1990.

  Here, in a solid oxide fuel cell using cermet of nickel oxide and zirconia as a fuel electrode, nickel oxide contained in the fuel electrode functions as an electrode by being reduced to nickel prior to power generation. For this reason, if the nickel dispersed in the cermet is insufficiently bonded after the reduction treatment of the fuel electrode, sufficient conductivity as an electrode may not be obtained.

  The present invention has been made in order to solve the above-described problems. When a solid oxide fuel cell is operated, the fuel electrode using nickel oxide and zirconia cermet has sufficient conductivity. Is intended to be obtained.

  An operation method of a solid oxide fuel cell according to the present invention is a solid oxide fuel cell operation method including a fuel electrode manufactured using a cermet of nickel oxide and zirconia. A first step of raising the temperature of the fuel electrode to at least one of an atmosphere and an inert gas to a reduction temperature; and supplying the fuel gas to the fuel electrode after the reduction temperature is reached, and reducing the fuel electrode at the reduction temperature At least a second step to be performed, and the reduction temperature is a temperature higher by 200 ° C. or more than the temperature at which the weight starts to decrease when the cermet is heated in a reducing atmosphere.

  In the solid oxide fuel cell operation method, the zirconia may be zirconium oxide stabilized with yttrium oxide. In this case, the reduction temperature may be 600 ° C. or higher. The zirconia may be scandia-stabilized zirconia. In this case, the reduction temperature may be 700 ° C. or higher.

  In the operation method of the solid oxide fuel cell, when the zirconia is scandia-stabilized zirconia, the second step is followed by a third step of performing the power generation operation of the solid oxide fuel cell at the operation temperature. The reduction temperature is preferably higher than the operating temperature. In this case, the operating temperature can be 600 to 800 ° C. The scandia-stabilized zirconia only needs to be added with one selected from aluminum oxide, cerium oxide, and yttrium oxide.

  As described above, according to the present invention, after the temperature of the fuel electrode produced using nickel oxide and zirconia cermet is raised to the reduction temperature as the atmosphere of at least one of air and inert gas, Since the reduction process is performed by supplying the fuel gas, when the solid oxide fuel cell is operated, sufficient conductivity can be obtained in the fuel electrode using nickel oxide and zirconia cermet. .

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Embodiment 1]
First, a method for operating the solid oxide fuel cell according to Embodiment 1 of the present invention will be described. As shown in the flowchart of FIG. 1, in the operation method of the solid oxide fuel cell according to the present embodiment, first, at the cell starting stage of power generation, the fuel electrode constituting the solid oxide fuel cell is connected to the atmosphere or The supply of the inert gas is started, and the fuel electrode is set to the atmosphere or the atmosphere of the inert gas (step S101).

  Next, the temperature of the fuel electrode (solid oxide fuel cell) set to the atmosphere or the atmosphere of an inert gas is started (step S102). When the fuel electrode (solid oxide fuel cell) reaches the reduction temperature due to this heating temperature rise (step S103), the supply of air or inert gas to the fuel electrode is stopped (step S104). The reduction temperature is at least 200 ° C. higher than the temperature at which the weight begins to decrease when the cermet is heated in a reducing atmosphere. Thereafter, fuel gas is supplied to the fuel electrode in the reduction temperature state, and the fuel electrode is reduced (step S105). In this reduction process, nickel oxide (NiO) constituting the fuel electrode is reduced.

  According to the operation method of the solid oxide fuel cell in the present embodiment described above, in the solid oxide fuel cell including the fuel electrode manufactured using NiO and zirconia cermet, as described later, the fuel electrode Sufficient conductivity can be obtained.

  Here, the structure of the single cell of the above-described solid oxide fuel cell will be described with reference to a cross-sectional view showing a portion of FIG. The solid oxide fuel cell includes a fuel electrode 201 serving as a support substrate, an electrolyte 202 formed on the fuel electrode 201, and an air electrode 203 formed on the electrolyte 202.

  The fuel electrode 201 is produced as shown below. First, a nickel oxide (NiO) powder having a flat particle size of 2 to 4 μm and a zirconia powder having a flat particle size of 0.3 to 0.6 μm are mixed at a weight ratio of 6: 4, and a binder, a plasticizer, Add a dispersing agent to make a slurry.

The zirconia powder may be ZrO ₂ (YSZ) stabilized with 8 mol% yttrium oxide (Y ₂ O ₃ ). The zirconia powder may be scandia-stabilized zirconia (Zr (Sc, Al ₂ O ₃ ) O ₂ : SASZ) to which a small amount of Al ₂ O ₃ is added. Hereinafter, it is described that the fuel electrode using YSZ for zirconia is made of Ni-YSZ, and the fuel electrode using SASZ for zirconia is made of Ni-SASZ.

  Next, the above-described slurry is formed into a sheet having a thickness of about 1 mm by, for example, a well-known doctor blade method, and the formed plurality of sheets are stacked and cut into a predetermined shape. Next, an electrolyte coating layer having a film thickness of 10 to 15 μm made of a slurry of the raw material powder constituting the electrolyte (electrolyte slurry) is formed on the molded body to be the fuel electrode thus produced. For example, an electrolyte coating layer can be formed by preparing an electrolyte slurry from a powder of SASZ (average particle size: 0.3 to 0.6 μm) and applying the slurry onto the molded body by a screen printing method.

Next, a half cell in which the electrolyte 202 is formed on the fuel electrode 201 is obtained by heating and firing the laminate in which the molded body and the electrolyte coating layer described above are formed. Thereafter, by forming the air electrode 203 on the electrolyte 202, a single cell of a solid oxide fuel cell can be formed. The air electrode 203 is, for example, a powder sintered body made of LaNi (Fe) O ₃ doped with iron (Fe) at the B site and having an average particle diameter of about 1 μm. As is well known, a stack of solid oxide fuel cells can be obtained by stacking a plurality of single cells thus produced in series with a connection portion such as an interconnector in between.

  Next, it will be described in more detail that the conductivity of the fuel electrode manufactured using NiO and zirconia cermets can be improved by the operation method of the solid oxide fuel cell according to the present embodiment.

  First, in order to confirm the starting temperature of the reduction reaction of NiO, thermogravimetric analysis (TGA) of NiO is performed in a reducing gas atmosphere. NiO is placed in a reducing gas atmosphere, and the temperature is raised from room temperature (25 ° C.). In the reducing gas atmosphere TG, as shown in FIG. 3, a decrease in weight is confirmed at 300 ° C. or higher. This shows that NiO is reduced at a temperature of 300 ° C. or higher in a reducing atmosphere.

  In addition, from FIG. 3, the weight change of NiO due to heating in a reducing atmosphere does not change uniformly after exceeding 300 ° C., but the weight reduction rate decreases after about 420 ° C., from about 500 ° C. There is also a tendency for the rate of weight loss to increase. In other words, there is a tendency that the reduction rate of NiO decreases after about 420 ° C. and increases again from about 500 ° C.

  Next, a Ni-YSZ fuel electrode sample and a Ni-SASZ fuel electrode sample prepared in the same manner as the fuel electrode described above were placed in a reducing gas atmosphere from room temperature to the operating temperature of the solid oxide fuel cell (800 ° C.). The electrical conductivity of each fuel electrode sample at 800 ° C. is measured. Conductivity is measured by the four probe method.

  In this case, considering the above-described analysis results of the reduction characteristics in NiO, in the process of raising the temperature of each fuel electrode sample to 800 ° C., the reduction treatment of the fuel electrode is completed, and when the temperature reaches 800 ° C., the electrode It should be in a state of functioning as (fuel electrode). However, as a result of the measurement, as shown in Table 1 below, the Ni-YSZ fuel electrode sample shows conductivity of 142 S / cm, while the Ni-SASZ fuel electrode sample shows 0.03 S / cm, Almost no conductivity.

  Next, thermogravimetric analysis is performed by raising the temperature of each fuel electrode sample in the reducing gas atmosphere in the same manner as described above. The TG in the reducing gas atmosphere of each fuel electrode sample changes as shown in FIG. As shown by the solid line in FIG. 4, in the Ni-YSZ fuel electrode sample, a decrease in weight is confirmed from 400 ° C., and it can be seen that the reduction of NiO starts from 400 ° C. It can also be seen that the NiO-YSZ fuel electrode sample undergoes a mild reduction reaction of NiO. This result shows the characteristic in the cermet of NiO and YSZ.

  On the other hand, as shown by a line in FIG. 4, in the fuel electrode sample of Ni-SASZ, a decrease in weight is confirmed from about 500 ° C., and it can be seen that the reduction of NiO starts from 500 ° C. It can also be seen that in the Ni-SASZ fuel electrode sample, when the NiO reduction reaction is started, this reaction proceeds rapidly. From these results, it can be seen that Ni in Ni-SASZ is less likely to be reduced than in the case of Ni-YSZ, and it is necessary to heat it to a higher temperature in order to reduce it. This result shows the characteristics in the cermet of NiO and SASZ.

  Next, an experiment is conducted on the relationship between the reducing gas introduction temperature and the conductivity when the reducing gas is introduced and the reduction treatment is started when each fuel electrode sample reaches a predetermined temperature. In this experiment, after reaching a set temperature (reduction temperature), supply of fuel gas to each fuel electrode sample is started to perform reduction treatment, and the conductivity of the treated fuel electrode sample is measured by the four-terminal method. Until the fuel gas is supplied, the air atmosphere is maintained. In addition, as the set temperature, the Ni-YSZ fuel electrode sample is set to room temperature (25 ° C), 600 ° C, 700 ° C, and 800 ° C. In addition, the Ni-SASZ fuel electrode sample is set to room temperature, 600 ° C., 700 ° C., 800 ° C., and 900 ° C.

  As a result of the above-described experiment, first, as shown in the white square of FIG. 5, in the fuel electrode sample of Ni-YSZ, when the supply of fuel gas is started after exceeding 600 ° C., high conductivity of about 600 S / cm is obtained. can get. Further, as shown by the black squares in FIG. 5, in the Ni-SASZ fuel electrode sample, when the supply of fuel gas is started after exceeding 700 ° C., conductivity of about 200 S / cm is obtained.

  As described above, when the fuel gas is supplied from the beginning, in other words, when heating is performed in a reducing atmosphere, the Ni-YSZ fuel electrode sample is as high as 142 S / cm even when heated to 800 ° C. Conductivity is not obtained. On the other hand, when the heating temperature reaches 600 ° C., the supply of fuel gas is started and the reduction process is performed, so that higher conductivity can be obtained as described above.

  In addition, when heating is performed in a reducing atmosphere, the Ni-SASZ fuel electrode sample exhibits almost no conductivity even when heated to 800 ° C. On the other hand, when the heating temperature reaches 700 ° C., the supply of fuel gas is started and the reduction process is performed, so that conductivity can be obtained as described above.

  Here, both the Ni-YSZ fuel electrode sample and the Ni-SASZ fuel electrode sample reach a temperature 200 ° C. higher than the temperature at which the weight starts to decrease when heated in a reducing atmosphere as shown in FIG. It can be seen that higher conductivity is obtained by starting the supply of fuel gas after that.

  Further, the same effect as described above can be obtained even when the initial temperature raising step is performed in an atmosphere of inert gas instead of air. In other words, it may be performed in a state where there is no reducing gas such as hydrogen in the initial temperature rising stage. Moreover, although the case where Ni-YSZ and Ni-SASZ were used was demonstrated above, it cannot be overemphasized that it is not restricted to this. As described above, the effect of reducing the fuel electrode by supplying the fuel gas after reaching the reduction temperature is due to the characteristics shown in FIG. 3 when NiO contained in the fuel electrode is reduced. Conceivable. Therefore, it is considered that the above-described effects can be obtained in the same manner as long as the solid oxide fuel cell includes a fuel electrode manufactured using a cermet of NiO and zirconia.

[Embodiment 2]
Next, a method for operating the solid oxide fuel cell according to Embodiment 2 of the present invention will be described. In a solid oxide fuel cell having a fuel electrode manufactured using a cermet of NiO and zirconia, actual power generation as a fuel cell is achieved even when sufficient conductivity is obtained at the beginning of power generation operation. However, nickel in the fuel electrode exposed to a high temperature over a long period of time aggregates over time, resulting in a decrease in conductivity, and as a result, there is a problem that the performance of the battery is degraded (see Non-Patent Document 3). In the second embodiment, this problem is solved.

  The operation method of the solid oxide fuel cell in the present embodiment is as shown in the flowchart of FIG. 6 in the early stage of power generation of the solid oxide fuel cell including the fuel electrode manufactured using NiO and zirconia cermet. In the battery starting stage, first, fuel gas is supplied to the fuel electrode, and the temperature is raised to the reduction processing temperature (first temperature) to perform the reduction processing (step S601). This reduction process is performed by supplying fuel gas after reaching the reduction temperature, as in the first embodiment.

  Next, after performing the reduction process, the temperature is lowered (decreased) to a steady operating temperature lower than the reduction temperature (step S602). Thereafter, a steady power generation operation is performed in a steady operation temperature state (step S603). The present embodiment is characterized in that the reduction process is performed at a temperature higher than the steady operating temperature. Note that the above-described zirconia is scandia-stabilized zirconia (SASZ) to which aluminum oxide is added. The steady operation temperature is a temperature at which the solid oxide fuel cell is operated to generate electricity, and is, for example, 600 to 800 ° C.

  According to the operation method of the solid oxide fuel cell in the present embodiment described above, in the solid oxide fuel cell including the fuel electrode manufactured using NiO and SASZ cermet, as described later, for example, It is possible to suppress a decrease in electrical conductivity at the fuel electrode due to changes over time, such as suppressing Ni aggregation in the fuel electrode during long-term use.

Here, the structure of the single cell of the solid oxide fuel cell described above will be described with reference to the cross-sectional view shown in FIG. The solid oxide fuel cell includes a fuel electrode 701 serving as a support substrate composed of scandia-stabilized zirconia (SASZ) added with a small amount of NiO and Al ₂ O ₃ , and an electrolyte 202 formed on the fuel electrode 701. And an air electrode 203 formed on the electrolyte 202.

  The fuel electrode 701 is manufactured as shown below. First, a NiO (NiO) powder having a flat particle size of 2 to 4 μm and a SASZ powder having a flat particle size of 0.3 to 0.6 μm are mixed at a weight ratio of 6: 4, and this is mixed with a binder, a plasticizer, and a dispersion. Add an agent to make a slurry.

  Next, the above-described slurry is formed into a sheet having a thickness of about 1 mm by, for example, a well-known doctor blade method, and the formed plurality of sheets are stacked and cut into a predetermined shape. Next, an electrolyte coating layer having a film thickness of 10 to 15 μm made of a slurry of the raw material powder constituting the electrolyte (electrolyte slurry) is formed on the molded body to be the fuel electrode thus produced. For example, an electrolyte coating layer can be formed by preparing an electrolyte slurry from a powder of SASZ (average particle size: 0.3 to 0.6 μm) and applying the slurry onto the molded body by a screen printing method.

Next, a half cell in which the electrolyte 202 is formed on the fuel electrode 701 is obtained by heating and firing the laminate in which the molded body and the electrolyte coating layer described above are formed. Thereafter, by forming the air electrode 203 on the electrolyte 202, a single cell of a solid oxide fuel cell can be formed. The air electrode 203 is, for example, a powder sintered body made of LaNi (Fe) O ₃ doped with iron (Fe) at the B site and having an average particle diameter of about 1 μm. As is well known, a stack of solid oxide fuel cells can be obtained by stacking a plurality of single cells thus produced in series with a connection portion such as an interconnector in between.

  Next, it will be described in detail that the fuel electrode manufactured using NiO and SASZ cermets can be stabilized for a long period of time by the operation method of the solid oxide fuel cell according to the present embodiment. In the following, treatment of each condition is performed on a fuel electrode sample (Ni-YSZ) manufactured using a cermet of Ni and YSZ and a fuel electrode sample (Ni-SASZ) manufactured using a cermet of Ni and SASZ. The result of measuring the conductivity when added by the four probe method is shown.

  First, FIG. 8 shows the change over time in the conductivity at the operating temperature (800 ° C.) of each fuel electrode sample reduced at 800 ° C. As described above, the reduction treatment at 800 ° C. is performed by raising the temperature to 800 ° C. in an atmosphere that does not contain a reducing gas such as fuel gas and then supplying the fuel gas. As shown by the white circles in FIG. 8, the conductivity of Ni-SASZ does not decrease even when the operation time reaches 600 hours. In contrast, the conductivity of Ni—YSZ decreases with time. As described above, when the reduction treatment is performed at 800 ° C., the decrease in conductivity of Ni-SASZ over time is suppressed.

  Moreover, when the cross section of each fuel electrode sample after 600 hours is observed with an electron microscope, the Ni-SASZ confirms a microstructure that is almost the same as the initial state immediately after the reduction treatment. In contrast, Ni-YSZ confirms the presence of Ni aggregates. From this, the above-mentioned decrease in conductivity measured by Ni-YSZ is caused by the fact that Ni in the fuel electrode aggregates over time at high temperatures, and the connections between Ni dispersed in the entire fuel electrode are broken. This is thought to be due to this. Such Ni aggregation is considered to be suppressed in Ni-SASZ.

  Next, the relationship between the reduction treatment temperature and the operating temperature in Ni-SASZ will be described. As shown in FIG. 9, even in Ni-SASZ treated at any reduction temperature, the lower the temperature (operating temperature), the higher the conductivity in the operating temperature range of 600 to 800 ° C. In FIG. 9, the black square is Ni-SASZ that has been reduced at a reduction temperature of 900 ° C., the white square is Ni-SASZ that has been reduced at a reduction temperature of 800 ° C., and the asterisk “*” is the reduction temperature of 700 ° C. The result of Ni-SASZ which carried out the reduction process as is shown.

  Further, as is clear from the results shown in FIGS. 4 and 9, Ni-SASZ can obtain higher conductivity as the reduction treatment temperature is higher. As is clear from these facts, in the solid oxide fuel cell including the fuel electrode manufactured using nickel oxide and SASZ cermet, after the fuel electrode is reduced at a temperature higher than the operating temperature, By performing the power generation operation (operation) at an operation temperature lower than the temperature of the reduction treatment, higher conductivity in the fuel electrode can be obtained. This indicates that it can be operated at a lower temperature. From the result of FIG. 9, it is understood that the operating temperature may be 600 to 800 ° C. In addition, a decrease in conductivity over time is suppressed.

  The same applies not only to SASZ but also to scandia-stabilized zirconia to which cerium oxide or yttrium oxide is added. Alternatively, scandia-stabilized zirconia to which a metal oxide such as aluminum oxide, cerium oxide, or yttrium oxide is not added may be used. It is important that the fuel electrode is produced using a cermet in which NiO and scandia-stabilized zirconia are present simultaneously.

3 is a flowchart for illustrating a method of operating the solid oxide fuel cell according to Embodiment 1 of the present invention. It is sectional drawing which shows the structure of the single cell of a solid oxide fuel cell. It is a characteristic view which shows the result of the thermogravimetric analysis of NiO in a reducing gas atmosphere. It is a characteristic view which shows the result of the thermogravimetric analysis in the reducing gas atmosphere of each fuel electrode sample. It is a characteristic view which shows the supply start temperature of fuel gas, and the state of the electrical conductivity after the reduction process in each fuel electrode sample. 5 is a flowchart for explaining a method of operating a solid oxide fuel cell according to Embodiment 2 of the present invention. It is sectional drawing which shows the structure of the single cell of a solid oxide fuel cell. It is a characteristic figure shown about the time-dependent change of electric conductivity in operation temperature (800 ° C) of each fuel electrode sample reduced at 800 ° C. It is a characteristic view shown about the relationship between the reduction process temperature in Ni-SASZ, and operating temperature.

Explanation of symbols

  201 ... Fuel electrode, 202 ... Electrolyte, 203 ... Air electrode.

Claims (6)

In a method for operating a solid oxide fuel cell including a fuel electrode produced using a cermet of nickel oxide and zirconia,
A first step of raising the temperature of the fuel electrode to a reduction temperature as an atmosphere of at least one of air and inert gas at a battery starting stage in an initial stage of power generation;
A second step of supplying a fuel gas to the fuel electrode after the reduction temperature and performing a reduction treatment of the fuel electrode at the reduction temperature;
The method for operating a solid oxide fuel cell, wherein the reduction temperature is 200 ° C. or more higher than a temperature at which the weight starts to decrease when the cermet is heated in a reducing atmosphere. In the operation method of the solid oxide fuel cell according to claim 1,
The zirconia is zirconium oxide stabilized with yttrium oxide,
The reduction temperature is 600 ° C. or higher. A method for operating a solid oxide fuel cell. In the operation method of the solid oxide fuel cell according to claim 1,
The zirconia is scandia stabilized zirconia,
The reduction temperature is 700 ° C. or higher. A method for operating a solid oxide fuel cell. In the operation method of the solid oxide fuel cell according to claim 3,
After the second step, comprising a third step of performing a power generation operation of the solid oxide fuel cell in an operating temperature state,
The method for operating a solid oxide fuel cell, wherein the reduction temperature is higher than the operation temperature. In the operation method of the solid oxide fuel cell according to claim 4,
The operating temperature is 600 to 800 ° C. A method for operating a solid oxide fuel cell. In the operation method of the solid oxide fuel cell according to any one of claims 3 to 5,
The scandia-stabilized zirconia is added with one selected from aluminum oxide, cerium oxide, and yttrium oxide. A method for operating a solid oxide fuel cell, wherein:

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