JP2010161030A - Method of activating solid oxide fuel cell, and method of manufacturing solid oxide fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of activating a solid oxide fuel cell capable of efficiently improving the performance of the cell in a further short time, and a method of manufacturing a solid oxide fuel cell. <P>SOLUTION: The method includes operating a solid oxide fuel cell on the early stage of power generation at negative voltage. According to this activation method, current-carrying processing for improving the cell performance can be performed in a short time. In the method of manufacturing a solid oxide fuel cell using this activation method, SOFC excellent in cell performance can be efficiently manufactured. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for activating a solid oxide fuel cell and a method for producing a solid oxide fuel cell.

  In recent years, a solid oxide fuel cell (SOFC) attracts attention among fuel cells because of its particularly high electric conversion efficiency and power density. A solid oxide fuel cell has a laminated structure in which a solid oxide electrolyte is sandwiched between a fuel electrode (anode) and an air electrode (cathode) from both sides. For example, in a flat-plate SOFC, the power generation cell, A fuel electrode current collector disposed outside the electrode, an air electrode current collector disposed outside the air electrode, and a separator disposed outside the fuel electrode current collector and air electrode current collector. A plurality of cells are stacked in the vertical direction.

In such an SOFC, an oxidant gas (oxygen) is supplied to the air electrode side, and a fuel gas (H ₂ , CO, CH _4, etc.) is supplied to the fuel electrode side. The oxidant gas supplied to the air electrode side passes through pores in the air electrode and reaches the vicinity of the interface with the solid oxide electrolyte. At this portion, electrons are received from the air electrode side and oxide ions (O ²⁻ ) Is ionized. The oxide ions diffuse and move in the solid oxide electrolyte toward the fuel electrode side. Oxide ions that have reached the vicinity of the interface with the fuel electrode side react with the fuel gas at this portion to generate a reaction product (H ₂ O, CO _2, etc.) and discharge electrons to the fuel electrode side. Electrons generated by the electrode reaction can be taken out as an electromotive force at an external load on another route.

Conventionally, since the operating temperature of SOFC is as high as 900 to 1000 ° C., all the members are made of ceramic, so it is not easy to reduce the manufacturing cost of the cell stack. For example, in Japanese Patent Application Laid-Open No. 2004-259641 (Patent Document 1), scandia activated zirconia (ScSZ) obtained by activating zirconia (ZrO ₂ ) with scandium oxide (Sc ₂ O ₃ ) is used as an electrolyte, and the B site is used. An SOFC using LaNi (Fe) O ₃ doped with iron (Fe) as an air electrode has been proposed. In Patent Document 1, scandia activated zirconia (SASZ) containing aluminum oxide (Al ₂ O ₃ ) is used as a solid oxide electrolyte, and a cell is manufactured at 900 to 1100 ° C. higher than the operating temperature. The battery performance is improved by performing energization processing (constant current operation) for a predetermined time until the battery becomes stable.

As described above, it is known that the SOFC can significantly improve the battery performance (energization effect) by performing the energization process in the early stage of power generation, and this improvement in battery performance also affects long-term power generation characteristics. However, such improvement in battery performance has a large individual difference depending on the cell, and energization treatment is required in the range of several days to several weeks. In Patent Document 1, for example, the current is gradually increased to 1.0 A / cm ² while observing the cell voltage, and then the current is supplied to 1.0 A / cm ² , 1.4 A / cm ² , and 1.8 A / cm ^2. An example is shown in which the energization process is performed for about 4500 minutes (75 hours) under the condition that the process is terminated when the amount is gradually increased and finally the cell voltage becomes constant at 0.2V. (FIG. 2 of Patent Document 1).

For example, FIG. 3 shows a SOFC using nickel-scandia activated zirconia (Ni—ScSZ) as a fuel electrode, scandia activated zirconia (ScSZ) as a solid oxide electrolyte, and lanthanum strontium manganite (LSM) as an air electrode. Is a graph showing the IV characteristics after conducting an energization treatment of 200 mA / cm ² for 20 hours in the initial stage of power generation, in comparison with the initial state, and the vertical axis indicates the terminal Voltage (V), the horizontal axis is current density (Acm ^-2 ). FIG. 4A is a graph showing the impedance spectrum on the air electrode (cathode) side before and after the same energization treatment, and FIG. 4B is a graph showing the impedance spectrum on the fuel electrode (asode) side. 4 (a) and 4 (b), the vertical axis is Z ″ / Ωcm ² and the horizontal axis is Z ′ / Ωcm ² . The IV characteristics and impedance spectrum are a potentio / galvanostat and frequency response analysis at 800 ° C. using 99.4% H ₂ and 0.6% H ₂ O as anode gas at a total flow rate of 100 ml / min. The result measured using the apparatus is shown, and in any graph, A shows the state after the energization process, and B shows the initial state. As shown in FIGS. 3 and 4, in the experiment conducted by the present inventors, an improvement in power generation characteristics was observed even in the energization process for 20 hours. In general, it is considered that such energization effect is caused by a reduction in the reaction overvoltage on the air electrode side, and the results shown in FIGS. 4A and 4B also support this. It has become.

Japanese Patent Laid-Open No. 2004-259641

  The SOFC is desired to improve the battery performance by performing the above-described energization process. However, since this energization process requires a lot of time, there is a problem that the production efficiency of the SOFC decreases. For this reason, development of a method capable of improving the SOFC battery performance in a shorter time than before is desired.

  The present invention has been made to solve the above-described problems, and the object of the present invention is to provide an SOFC activation method capable of improving battery performance more efficiently in a shorter time than conventional methods, and SOFC. It is to provide a manufacturing method.

  The SOFC activation method of the present invention is characterized in that the SOFC in the initial stage of power generation is operated with a negative voltage.

  In the SOFC activation method of the present invention, the negative voltage is preferably in the range of not less than −1.5 V and less than 0 V.

  In the SOFC activation method of the present invention, it is preferable to provide a zirconia-based solid oxide electrolyte.

Moreover, according to this invention, it is preferable to operate | move by a negative voltage for 1-4 hours.
The present invention also provides a method for manufacturing an SOFC, including a step of operating the SOFC in the initial stage of power generation with a negative voltage.

  According to the present invention, the energization process that has conventionally been required for several days to several weeks for improving SOFC performance can converge the activation of battery performance in a short time of about several hours.

It is a graph which shows the result about a preferable example of the activation method of SOFC of this invention. The current-voltage at the time of operating at 850 ° C. at 0 hour, 1 hour, 3.5 hours, 6.5 hours, 9.5 hours, and a negative voltage for a single cell of SOFC similar to the case of FIG. It is a graph which shows a characteristic, a vertical axis | shaft is terminal voltage (V) and a horizontal axis is a current density (A / cm < ² >). The present inventors prepared an SOFC using nickel-scandia activated zirconia (Ni-ScSZ) as a fuel electrode, scandia activated zirconia (ScSZ) as a solid electrolyte, and lanthanum strontium manganite (LSM) as an air electrode. It is a graph which shows the IV characteristic after carrying out the energization process of 200 mA / cm < ² > for 20 hours in the early stage of electric power generation compared with an initial state, a vertical axis | shaft is terminal voltage (V) and a horizontal axis is current density. (Acm ^-2 ). FIG. 4A is a graph showing the impedance spectrum on the air electrode (cathode) side before and after the energization process, and FIG. 4B is a graph showing the impedance spectrum on the fuel electrode (asode) side. In both a) and (b), the vertical axis represents Z ″ / Ωcm ² , and the horizontal axis represents Z ′ / Ωcm ² .

The solid oxide fuel cell (SOFC) activation method of the present invention is characterized by operating a solid oxide fuel cell in the early stage of power generation with a negative voltage (that is, operating as an oxygen pump). Here, FIG. 1 is a graph showing the results of a preferred example of the SOFC activation method of the present invention. FIG. 1 shows a single-cell fuel cell using, for example, nickel-yttria activated zirconia (Ni-YSZ) for the fuel electrode, YSZ for the solid electrolyte, and LSM for the air electrode, with 1% H on the fuel electrode side. ₂ O + 99% H ₂ was supplied to the _{21% O 2 + 79% N} 2 to the air electrode side is supplied to the air electrode at 850 ° C., the terminal voltage is a current of 1.2A / cm ² was applied to a 0V (A in the figure), then, a current of 1.5 A / cm ² was applied until the terminal voltage became 0 V (B in the figure), and a current of 2.0 A / cm ^{2 was} further applied for a certain period of time (FIG. Middle, after C), the result of conducting the energization treatment is shown as applying a current of 3.0 A / cm ² (D in the figure), the vertical axis is the terminal voltage (V), the horizontal axis Is time. From FIG. 1, if the current to be applied is increased stepwise while looking at the terminal voltage so that the terminal voltage becomes 0 V or less, the terminal voltage once decreases when the current is increased. It can be seen that the terminal voltage increases with time during the process, and eventually stabilizes at a constant level.

FIG. 2 shows a SOFC single cell similar to that in FIG. 1 operated at 850 ° C. at 0 hour, 1 hour, 3.5 hours, 6.5 hours, 9.5 hours, and a negative voltage. It is a graph which shows the current-voltage characteristic in a time point, a vertical axis | shaft is terminal voltage (V) and a horizontal axis is a current density (A / cm < ² >). In FIG. 2, curve a is the result of 3.5 hours, 6.5 hours, and 9.5 hours, which are almost overlapping. Curve b is the result for 1 hour, and curve c is the result for 0 hour. From the results shown in FIG. 2, it can be seen that the battery performance of the SOFC is significantly improved by operating at a negative voltage for 1 hour or more.

  As described above, in the present invention, the activation of the battery performance can be converged in a short time by the operation with the negative voltage in a remarkably short time as compared with the conventional one to four hours.

  In the SOFC activation method of the present invention, the negative voltage is preferably in the range of −1.5 V or more and less than 0 V, and more preferably in the range of −1.0 V or more and less than 0 V. This is because when the negative voltage is less than −1.5 V, the battery tends to be irreversibly deteriorated, and when it is 0 V or more, it does not function as an oxygen pump.

  The SOFC in the present invention usually has a power generation cell having a laminated structure in which the above-described solid oxide electrolyte is sandwiched between a fuel electrode (anode) and an air electrode (cathode) from both sides. SOFCs can be broadly divided into two types of structures, flat plate type and cylindrical type. For example, in a flat plate type SOFC, the power generation cell, a fuel electrode current collector disposed outside the fuel electrode, and an outside of the air electrode. And a plurality of single cells composed of separators disposed outside the fuel electrode current collector and the air electrode current collector in the vertical direction.

  In the present invention, as the solid oxide electrolyte used in the SOFC, a conventionally known appropriate solid oxide electrolyte used in a normal SOFC can be used without particular limitation. For example, a zirconia solid oxide electrolyte, a cerium solid Examples thereof include oxide electrolytes and lanthanum-based solid oxide electrolytes. Among these, zirconia-based solid oxide electrolytes are preferable for reasons such as ion conductivity, reliability, compatibility between constituent materials, and cost. Examples of the zirconia-based solid oxide electrolyte include yttria activated zirconia (YSZ) and scandia activated zirconia (ScSZ). Among these, YSZ is preferable among these because of reliability and cost.

  As a material used for forming the fuel electrode, for example, a mixture of an oxide ion conductor such as a ceramic powder material and a metal catalyst can be used. As the oxide ion conductor, one having a fluorite type or perovskite type crystal structure can be preferably used. Examples of those having a fluorite-type crystal structure include ceria-based oxides doped with samarium and gadolinium, and zirconia-based oxides containing scandium and yttrium. Further, examples of those having a perovskite type crystal structure include lanthanum galide oxides doped with strontium and magnesium. As the metal constituting the metal catalyst, a material that is stable in a reducing atmosphere and has hydrogen oxidation activity can be used. For example, nickel, iron, cobalt, noble metals (platinum, ruthenium, palladium, etc.) Etc. can be used. Among the above materials, nickel having high hydrogen oxidation activity is preferable. Specifically, nickel-yttria activated zirconia (Ni-YSZ) is particularly preferably used. Moreover, the oxide ion conductor particle | grains mentioned above may be used individually by 1 type, and may mix and use 2 or more types.

As a material used for forming the air electrode, for example, a metal oxide having a perovskite crystal structure can be used. Specifically, (Sm, Sr) CoO ₃ , (La, Sr) MnO ₃ (LSM), (La, Sr) CoO ₃ , (La, Sr) (Fe, Co) O ₃ , (La, Sr) ( Examples thereof include metal oxides such as Fe, Co, Ni) O ₃ , and (La, Sr) MnO ₃ is preferably used from the viewpoint of stability in an oxidizing atmosphere and compatibility with YSZ. One kind of the metal oxides described above may be used alone, or two or more kinds may be mixed and used. Moreover, noble metals, such as platinum, ruthenium, and palladium, can also be used as a material for forming the air electrode.

  Further, the fuel electrode current collector, the air electrode current collector, and the separator in the SOFC can be configured by using conventionally known appropriate materials, and these are not particularly limited. Specifically, for a fuel electrode current collector, a sponge-like porous sintered metal plate such as an Ni-based alloy, and for an air electrode current collector, a sponge-like porous sintered metal plate such as an Ag-based alloy, a separator Can be suitably made of stainless steel or the like.

  The present invention also provides a method for manufacturing an SOFC, including a step of operating the SOFC in the initial stage of power generation with a negative voltage. According to the SOFC manufacturing method of the present invention, since the energization process for improving the battery performance is completed in a short time, an SOFC having excellent battery performance can be efficiently manufactured. In the SOFC manufacturing method of the present invention, the steps other than the step of operating the SOFC in the initial stage of power generation with a negative voltage are not particularly limited, and each step in a conventionally known appropriate SOFC manufacturing method can be adopted. .

Claims (5)

  A method for activating a solid oxide fuel cell, wherein the solid oxide fuel cell in the initial stage of power generation is operated at a negative voltage.   The method according to claim 1, wherein the negative voltage is within a range of −1.5V or more and less than 0V.   The method according to claim 1, comprising a zirconia-based solid oxide electrolyte.   4. The method according to any of claims 1 to 3, wherein the method is operated with a negative voltage for 1 to 4 hours.   A method for producing a solid oxide fuel cell, comprising a step of operating a solid oxide fuel cell in an initial stage of power generation with a negative voltage.

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