JP5296516B2 - Solid oxide fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain further improvement of an output voltage, in a solid oxide fuel cell with an air electrode structured by perovskite type oxide. <P>SOLUTION: The solid oxide fuel cell includes an electrolyte 101 consisting of a material of a zirconia system, and a fuel electrode 102 formed on one side of the electrolyte 101. And also, an air electrode 103 is formed on the other side of the electrolyte 101, and consists of a metal oxide (perovskite type oxide) of a perovskite structure equipped with a rare earth, copper or nickel, cobalt and manganese. For example, the air electrode 103 consists of a sintered body of perovskite type oxide expressed in the formula: LnE<SB>(1-y-x)</SB>Co<SB>x</SB>Mn<SB>y</SB>O<SB>3</SB>(Ln is a rare earth, E is copper or nickel). <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a solid oxide fuel cell using an air electrode composed of a perovskite metal oxide.

  In recent years, there has been an increasing interest in solid oxide fuel cells using oxide ion conductors as electrolytes. In particular, from the viewpoint of effective use of energy, solid fuel cells have essentially high energy conversion efficiency because they are not restricted by Carnot efficiency, and have excellent features such as good environmental conservation. have. The air electrode used in the solid oxide fuel cell having such characteristics is a reaction field where oxygen reacts with electrons to become oxide ions (oxygen ions), and thus has high electrical conductivity and electrode activity. Is required.

  By the way, the solid oxide fuel cell initially has an operating temperature as high as 900 to 1000 ° C., and all members are made of ceramic. In a solid oxide fuel cell in which a single cell composed of a fuel electrode, an electrolyte, and an air electrode is stacked with an interconnector (separator) sandwiched between them, the interconnector also has a high operating temperature as described above. It was made of ceramic that was not easy to process, and it was not easy to reduce the manufacturing cost of the cell stack.

  Here, if the operating temperature can be lowered to 800 ° C. or lower, a heat-resistant alloy material such as a ferrite-based Fe—Cr alloy can be used for the interconnector, and the manufacturing cost can be reduced. However, a decrease in the operating temperature causes a decrease in the activity of the air electrode. Along with this, the electrochemical resistance at the air electrode, that is, the overvoltage, suddenly increases, leading to a decrease in the output voltage.

For example, conventionally, LaSrMnO ₃ (LSM) or the like is used as a material having low chemical reactivity of an electrolyte made of a zirconia-based material and high reliability as an air electrode. However, when the operating temperature is lowered, the LSM becomes insufficient because the electrode activity as an air electrode does not satisfy the required characteristics. Therefore, an air electrode material having high electrode performance is desired even in the low-temperature operation as described above.

In order to solve the problem of the air electrode due to such a decrease in operating temperature, La _1-X Sr _X Fe _1-Y Co _Y O ₃ (LSFC: X = 0.1 to 0.5, Y = 0.1 ~0.6, X + Y <0.7) , such as _{La 1-X Sr X CoO 3} (X = 0.1~0.5), perovskite metal having a high electrode activity (performance of the electrochemical reaction) There is a technique using an oxide (perovskite oxide).

Here, the perovskite oxide is based on the structure of AMO ₃ , and the A site is composed of a rare earth element and the M site is composed of a transition metal element. The perovskite oxide can be composed of a plurality of elements at both the A site and the M site. For example, in LSM, the A site is composed of lanthanum (La) and strontium (Sr). In the LSCF, the A site is composed of La and Sr, and the M site is composed of cobalt (Co) and manganese (Mn).

T. Komatsu, et al., "Cr Poisoning Suppression in Solid Oxide Fuel Cells Using LaNi (Fe) O3 Electrodes", Electrochem. Solid-State Lett., Vol. 9, pp. A9-A12, 2006. SPJiang, et al., "Deposition of Cr Spices at (La, Sr) (Co, Fe) O3 Cathodes of Solid Oxide Fuel Cells", J. Electrochem. Soc., Vol.153, pp.A127-A134, 2006 . A. Petirc, et al., "Evolution of La-Sr-Co-Fe-O perovskites for solid oxide fuel cells and gas separation membranes", Solid State Ionics, Vol, 135, pp. 719-725, 2000. Y. Matsuzaki, et al., "Electrochemical properties of reduced-temperature SOFCs with mixed ionic-electronic conductors in electrodes and / or referrings", Solid State Ionics 152-153, pp.463-468, 2002.

  As described above, by forming the air electrode from the perovskite oxide, the problem of the air electrode due to a decrease in operating temperature, such as a decrease in output voltage due to an increase in electrochemical resistance in the air electrode, is solved. However, further improvement in output voltage (characteristic) at the air electrode has been demanded.

  The present invention has been made to solve the above-described problems, and a further improvement in output voltage can be obtained in a solid oxide fuel cell in which an air electrode is composed of a perovskite oxide. The purpose is to.

  The solid oxide fuel cell according to the present invention is a solid oxide fuel cell including a fuel electrode, an electrolyte, and an air electrode. The air electrode includes a rare earth element, a transition metal (copper or nickel), cobalt, and manganese. It is made of a metal oxide having a perovskite structure.

In the solid oxide fuel cell, metal _{oxides, LnE (1-yx) Co} x Mn y O 3 (Ln is a rare earth, E is copper or nickel, 0.6 ≦ x + y ≦ 0.8 , x ≦ y ) Ru der. In particular, the metal oxide may be LnE _1/3 Co _1/3 Mn _1/3 O ₃ (Ln is a rare earth, E is copper or nickel). The rare earth is at least one of lanthanum, praseodymium, neodymium, samarium, europium, and gadolinium. Note that the air electrode may include a layer containing cerium oxide disposed on the electrolyte side.

  As described above, according to the present invention, the air electrode is composed of a metal oxide having a perovskite structure including rare earth, transition metal (copper or nickel), cobalt, and manganese. In the solid oxide fuel cell in which the electrode is configured, further improvement in output voltage can be obtained.

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

[Embodiment 1]
First, Embodiment 1 of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view schematically showing a partial configuration example of the solid oxide fuel cell according to Embodiment 1 of the present invention. This solid oxide fuel cell includes an electrolyte 101 made of a zirconia-based material and a fuel electrode 102 formed on one surface of the electrolyte 101. The solid oxide fuel cell according to the present embodiment is formed of a metal oxide (perovskite oxide) having a perovskite structure, which is formed on the other side of the electrolyte 101 and includes rare earth, transition metal, cobalt, and manganese. The air electrode 103 is provided. The transition metal is copper or nickel.

For example, the air electrode 103 is composed of _{LnE (1-yx) Co x} Mn y O 3 (Ln is a rare earth, E is copper or nickel) sintered body of the perovskite type oxide represented by (porous sintered body) ing. Here, oxygen in _{LnE (1-yx) Co x} Mn y O 3 is intended to include a range of slightly deviated value from the stoichiometric composition. The rare earth is at least one of lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), and gadolinium (Gd). For example, these two are included. It may be.

The electrolyte 101 may be, for example, scandium oxide (Sc ₂ O ₃ ) and aluminum oxide (Al ₂ O ₃ ) stabilized ZrO ₂ (SASZ), yttria stabilized zirconia (YSZ), scandia stabilized zirconia (ScSZ), Samaria. What is necessary is just to be comprised from the sintered compact of the powder of zirconia materials, such as stabilized zirconia (SSZ). The fuel electrode 102 is made of, for example, nickel-yttria stabilized zirconia cermet (Ni-YSZ), nickel-scandia stabilized zirconia (Ni-ScSZ), and the like, in which metal nickel is mixed with an oxide material constituting the electrolyte 101. It is only necessary to be composed of a sintered body (porous sintered body) of a powder of a metal-oxide mixture (cermet) having electron conductivity.

  In addition, as is well known, each of these layers produces a slurry of powder or mixed powder, and forms a slurry film (layer) by molding by a doctor blade method or application by a screen printing method, This can be produced by firing at 1000 to 1200 ° C.

  According to the solid oxide fuel cell of the present embodiment configured as described above, the air electrode 103 is composed of a perovskite oxide made of rare earth, Ni or Cu, Co, and Mn. Compared with the case where the perovskite type oxide is used, the air electrode characteristics can be improved at a low operating temperature of about 800 ° C., and the output voltage can be further improved.

  In the above-described embodiment, the basic configuration (single cell) of the solid oxide fuel cell is described. Actually, as is well known, a plurality of single cells are used in a state of being stacked via an interconnector, and obtained by reforming hydrocarbon gas such as city gas in each single cell. A fuel gas containing hydrogen is supplied to the fuel electrode 102 side, and air containing oxygen as an oxidant gas is supplied to the air electrode 103 side, whereby a power generation operation is performed.

  Next, the characteristic measurement result in the single cell of the actually produced solid oxide fuel cell will be described below.

[Measurement method 1]
First, a method for measuring characteristics will be described. In this measurement, as will be described later, the interfacial resistance, which is an index of electrode performance, is measured by an AC impedance method in each sample cell produced. At the time of measurement, it is performed under the condition of an open voltage, and a minute AC signal (current) is applied (flowed) so that an AC voltage of about 5 mV is applied between the air electrode and the fuel electrode. A minute potential change (response) appearing between the electrode and the reference electrode is measured with an impedance measuring instrument, and the impedance (interface resistance) is obtained from the measurement result (frequency response). In the measurement, humidified hydrogen gas at room temperature (about 23 ° C.) is supplied as fuel gas to the fuel electrode, and oxygen is supplied to the air electrode. Moreover, as an open electromotive force, the value of 1.09V or more is obtained at 800 degreeC.

[Cell production 1]
Next, taking a solid oxide fuel cell (comparative sample cell: # 1-0-0) as a comparative sample as an example, production of a single cell will be described. First, well known Sc ₂ O ₃ obtained by firing molded into a sheet by a doctor blade method, Al ₂ O ₃ doped zirconia _{(0.89ZrO 2 -0.10Sc 2 O 3 -0.01Al} 2 O 3: SASZ An electrolyte substrate is prepared. The electrolyte substrate is formed to a thickness of 0.2 mm. Next, a mixed powder in which NiO powder (60 wt%) having an average particle diameter of 0.2 μm is mixed with zirconia powder (40 wt%) having an average particle diameter of about 0.6 μm to which 10 mol% Y ₂ O ₃ has been added ( A slurry of (fuel electrode material powder) is prepared, and this slurry is applied to one surface of the above-described electrolyte substrate by a well-known screen printing method to form a fuel electrode coating film. In addition, a current collector made of platinum mesh is disposed on the fuel electrode coating film, and these are fired in air under a heat treatment condition of 1300 ° C. for 8 hours. A fuel electrode having a thickness of 60 μm is formed.

Next, a slurry of La _0.8 Sr _0.2 MnO ₃ (LSM) powder having an average particle size of 1.0 μm is prepared, and this slurry is applied to the other surface of the electrolyte substrate by the screen printing method and applied with an air electrode. A film is formed. In addition, a current collector made of platinum mesh is disposed on the air electrode coating film, and the electrolyte substrate on which the air electrode coating film is formed is fired under heat treatment conditions of 1100 ° C. for 2 hours, An air electrode having a thickness of 60 μm made of the sintered body is formed.

  As shown in the perspective view of FIG. 3, the unit cell formed in this way is formed on a disk having a diameter of 10 mm on an electrolyte substrate 301 formed in a square plate shape with a side of 30 mm. Has been placed. In FIG. 3, the fuel electrode and the current collector disposed below the electrolyte substrate 301 are not shown and are omitted. In addition, this single cell includes the reference electrode 303 made of platinum around the electrolyte substrate 301, and performs the above-described measurement in a state where it is connected thereto.

[Example 1]
Next, as Example 1, the production of solid oxide fuel cells (sample cells: # 1-1-1 to # 1-1-6) to be samples will be described. The sample cell in place of the LSM used in the air electrode of the comparative sample cell as described above, as shown in Table 1 below, LaNi _(1-xy) powder _{Co x Mn y O 3 (#} 1-1- 1 # 1-1-8) and LACU _{(using 1-xy) Co x Mn y} O 3 powder (# 1-2-1～ # 1-2-8) in addition, like the comparative sample cell To make. In Table 1, in the _{LaNi (1-xy) Co x} Mn y O 3, is changed Ni, Co, the composition of Mn, the sample cell (# 1-1-1～ # 1-1-8 ). Similarly, in _{LaCu (1-xy) Co x} Mn y O 3, Cu, Co, varying the composition of Mn, has a respective sample cell (# 1-2-1～ # 1-2-8). In addition, although the number of atoms is described in the lower right of the element symbol, in the following tables, the number of atoms is greatly described on the right side of the element symbol for easy viewing.

  When the measurement described above is performed in each sample cell shown in Table 1, the sample cells (# 1-1-3 to # 1-1-8 and # 1-2-3 to # 1-2-8) are compared. Compared to the sample cell (# 1-0-0), the interfacial resistance or interfacial resistance is comparable and good results are obtained. Among these, sample cells with relatively small manganese composition ratios (# 1-1-6 to # 1-1-8 and # 1-2-6 to # 1-2-8) operate longer. When energized, the interface resistance tends to be lower than that of the comparative sample cell (# 1-0-0). On the other hand, sample cells (# 1-1-1, # 1-1-2, # 1-2-1, # 1-2-2) with a small amount of Ni or Cu added are comparative sample cells (# Compared with 1-0-0), the initial electrode characteristics are higher in interfacial resistance. However, if the sample cells (# 1-1-1, # 1-1-2, # 1-2-1, # 1-2-2) are operated longer, the comparative sample cells (# 1-0 Compared to -0), there is a tendency that the amount of decrease in interfacial resistance is large.

When the results shown in Table 1 are examined, in the comparative sample cell and any of the sample cells, the longer the energization time, the lower the interfacial resistance. It is considered that a highly resistant substance such as La ₂ Zr ₂ O ₇ formed between the electrolyte and the electrolyte decreases with the passage of energization time. In addition, it is considered that the difference in initial characteristics between different sample cells corresponds to, for example, the difference in the stoichiometric equilibrium of oxygen in the whole compound due to the composition ratio of Ni and Cu. From the results of Table 1, in LaE as the material of the air electrode _{(1-yx) Co x Mn} y O 3 (E copper or nickel), it is in the range of 0 <x and x + y ≦ 0.8, initial It can be seen that the same characteristics as those of LSM are obtained. If 0.1 ≦ x ≦ 0.3 and 0.4 ≦ y ≦ 0.6, better characteristics are obtained after 72 hours.

[Embodiment 2]
Next, Embodiment 2 of the present invention will be described with reference to FIG. FIG. 2 is a cross-sectional view schematically showing a partial configuration example of the solid oxide fuel cell according to Embodiment 2 of the present invention. This solid oxide fuel cell includes an electrolyte 101, a fuel electrode 102 formed on one surface of the electrolyte 101, and an air electrode 203 formed on the other side of the electrolyte 101. In the present embodiment, the air electrode 203, like the air electrode 103 of the first embodiment, includes a first layer 203a made of a perovskite oxide including rare earth, copper, nickel, cobalt, and manganese, and an electrolyte. And a second layer 203b containing cerium oxide in addition to the perovskite oxide arranged on the 101 side.

Here, since the air electrode is manufactured by firing in contact with an electrolyte containing zirconia, a highly resistant substance such as La ₂ Zr ₂ O ₇ is generated in a portion in contact with the electrolyte. The product is one of the causes for deteriorating the characteristics of the air electrode during initial operation. In some cases, La constituting the air electrode and zirconia constituting the electrolyte react with the electrolyte in contact with the air electrode to generate a highly resistant substance such as La ₂ Zr ₂ O _7. It has been reported that this product is one of the causes for deteriorating the characteristics of the air electrode.

On the other hand, a mixture of perovskite oxide particles and cerium oxide (ceria compound) particles added with rare earth such as Gd _0.1 Ce _0.9 O ₂ and Sm _0.2 Ce _0.8 O ₂ is provided in the vicinity of the electrolyte. Thus, there is a technique for solving the above problem in the air electrode (see Non-Patent Document 4). By forming the air electrode in a state where the perovskite oxide powder (powder) and the fine powder of the ceria compound are mixed, the active area of the electrode generated at the junction between the electrolyte and the air electrode is increased, and the electrode It is possible to reduce the interface resistance. In addition, the ceria compound is suitable as a material to be mixed with the air electrode because the reaction deterioration with the air electrode material made of a perovskite oxide hardly occurs.

In the air electrode 203 in the present embodiment, the second layer 203b containing cerium oxide in addition to the perovskite oxide is provided on the electrolyte 101 side. Therefore, the second layer 203b has a perovskite oxidation. The particles of the product are covered with ceria compound particles, and the direct contact between the zirconia-based material portion constituting the electrolyte 101 and the perovskite oxide material is suppressed, and La ₂ Zr ₂ O having high resistance is provided. Generation of ₇ etc. will be suppressed.

  In the embodiment described above, the basic configuration (single cell) of the solid oxide fuel cell is described. Actually, as is well known, a plurality of single cells are used in a state of being stacked via an interconnector, and obtained by reforming hydrocarbon gas such as city gas in each single cell. A fuel gas containing hydrogen is supplied to the fuel electrode 102 side, and air containing oxygen as an oxidant gas is supplied to the air electrode 203 side, whereby a power generation operation is performed.

  Next, the characteristic measurement result in the single cell of the actually produced solid oxide fuel cell will be described below.

[Example 2]
First, production of a solid oxide fuel cell (single cell) as a sample will be described. First, well known Sc ₂ O ₃ obtained by firing molded into a sheet by a doctor blade method, Al ₂ O ₃ doped zirconia _{(0.89ZrO 2 -0.10Sc 2 O 3 -0.01Al} 2 O 3: SASZ An electrolyte substrate is prepared. The electrolyte substrate is formed to a thickness of 0.2 mm. Next, a mixed powder in which NiO powder (60 wt%) having an average particle diameter of 0.2 μm is mixed with zirconia powder (40 wt%) having an average particle diameter of about 0.6 μm to which 10 mol% Y ₂ O ₃ has been added. A slurry is prepared, and this slurry is applied to one surface of the above-described electrolyte substrate by a well-known screen printing method to form a fuel electrode coating film. In addition, a current collector made of platinum mesh is disposed on the fuel electrode coating film, and these are fired in air under a heat treatment condition of 1300 ° C. for 8 hours. A fuel electrode having a thickness of 60 μm is formed.

Next, a slurry of a mixed powder of the same material as the above-described air electrode and Gd _0.2 Ce _0.8 O ₂ (GDC) as a ceria compound is prepared, and this slurry is screen-printed on the other surface of the above-described electrolyte substrate. The second layer coating film of the air electrode is formed by coating by the method. In addition, the slurry in which the powder of the air electrode material is dispersed is thickly applied on the second layer coating film, so that the first layer coating film is formed. In addition, a current collector made of platinum mesh is placed on the first layer coating film, and these are fired under heat treatment conditions of 1100 ° C. for 2 hours, and the thickness of the powder sintered body is 3 μm. It is assumed that an air electrode composed of the second layer and the first layer having a thickness of 60 μm is formed.

  As shown in the perspective view of FIG. 3, the unit cell formed in this way is formed on a disk having a diameter of 10 mm on an electrolyte substrate 301 formed in a square plate shape with a side of 30 mm. Has been placed. In FIG. 3, the fuel electrode disposed below the electrolyte substrate 301 is omitted from illustration. In addition, this single cell includes the reference electrode 303 made of platinum around the electrolyte substrate 301, and performs the measurement of [Measuring method 1] described above while being connected to the reference electrode 303.

In Example 2, solid oxide fuel cells (# 2-0-0 to # 2-0-3) serving as reference samples use La _0.8 Sr _0.2 MnO ₃ as an air electrode material, and serve as samples. The solid oxide fuel cells (# 2-1-1 to # 2-1-4) use LaNi _0.3 Co _0.3 Mn _0.4 O ₃ as the air electrode material, and the sample is a solid oxide fuel cell ( # 2-2-1 to # 2-2-4) use LaCu _0.3 Co _0.3 Mn _0.4 O ₃ as the air electrode material. As shown in Table 2 below, the mixing ratio of the air electrode material and the ceria compound is 9: 1, 8: 2, 6: 4, and 4: 6, respectively.

As shown in Table 2, in both cases, the initial interface resistance is low. This is considered to indicate that formation of a highly resistant substance such as La ₂ Zr ₂ O ₇ between the air electrode and the electrolyte is suppressed in the cell production stage. Also in this example, in the sample cells (# 2-1-1 to # 2-1-4 and # 2-2-1 to # 2-2-4), the longer the energization time, the higher the interface resistance. There is a tendency to decrease.

[Example 3]
Next, another embodiment will be described. In Example 1 and Example 2 described above, a so-called electrolyte-supported single cell was produced and measurement was performed between the air electrode and the reference electrode. The case where it is produced will be described.

[Measurement method 2]
First, measurement is performed by applying (flowing) a minute AC signal (current) so that an AC voltage of about 5 mV is applied between the fuel electrode and the air electrode. A small potential change appearing between them is measured with an impedance measuring instrument, and the impedance is obtained from the measurement result. In this measurement, humidified hydrogen gas at room temperature (about 23 ° C.) is supplied as fuel gas to the fuel electrode, and oxygen is supplied to the air electrode.

[Cell production 2]
Next, taking a solid oxide fuel cell (comparative sample cell: # 3-0-0) as a comparative sample as an example, production of a single cell will be described. First, an electrolyte sheet made of SASZ formed into a sheet shape by a doctor blade method is bonded to a fuel electrode sheet made of a fuel electrode material formed into a sheet shape by a doctor blade method, and these are fired under heating conditions of 1300 ° C., A fuel electrode-supported half cell is manufactured.

Next, a slurry in which La _0.8 Sr _0.2 MnO ₃ (LSM) powder having an average particle diameter of 1.0 μm is dispersed in ethylene glycol is prepared, and this slurry is applied on the above-described half-cell electrolyte layer by a screen printing method. Thus, an air electrode coating film is formed. In addition, a current collector made of platinum mesh is disposed on the air electrode coating film, and the electrolyte substrate on which the air electrode coating film is formed is fired under heat treatment conditions of 1100 ° C. for 2 hours, An air electrode having a thickness of 60 μm made of the sintered body is formed.

  As shown in the cross-sectional view of FIG. 4, the unit cell thus formed has a state in which a solid electrolyte 402 is laminated on a fuel electrode substrate 401 and an air electrode 403 is formed on the solid electrolyte 402. Has been. In addition, current lines 411 and 431 for applying the current for performing the above-described measurement are connected to the fuel electrode substrate 401 and the air electrode 403, and the voltage lines 412 and 432 for measuring the potential change are connected to the single cell. It is connected. In FIG. 4, the current collector is omitted and not shown. The power line and the voltage line are connected via a current collector.

Next, the solid oxide fuel cells (sample cells: # 3-1-1 to # 3-1-3, # 3-2-1 to # 3-2-3) which are samples in Example 3 The creation will be described. The sample cell in place of the LSM used in the air electrode of the comparative sample cell as described above, as shown in Table 3 below, LaNi _(1-xy) powder _{Co x Mn y O 3 (#} 3-1- 1 # 3-1-3) and LACU _{(using 1-xy)} powder _{Co x Mn y O 3 (#} 3-2-1~ # 3-2-3), the other comparative sample cell (# Prepare in the same manner as 3-0-0). In Table 3, in the _{LaNi (1-xy) Co x} Mn y O 3, by changing the composition of Co and Mn, as the sample cell (# 3-1-1～ # 3-1-3) Yes. Similarly, in _{LaCu (1-xy) Co x} Mn y O 3, by changing the composition of Co and Mn, are each sample cell (# 3-2-1～ # 3-2-3).

When the measurement described above is performed in each sample cell shown in Table 3, the sample cells (# 3-1-1 to # 3-1-3 and # 3-2-1 to # 3-2-3) are compared. Compared to the sample cell (# 3-0-0), the interfacial resistance or interfacial resistance is comparable and good results are obtained. In addition, when operated (energized) longer, the interface resistance tends to be lower than that of the comparative sample cell (# 3-0-0). In the sample cell shown in Table 3, in LaE as the material of the air electrode _{(1-yx) Co x Mn} y O 3 (E copper or nickel), 0 <a range of x and x + y ≦ 0.8 It has become.

  By the way, in the solid oxide fuel cell having a stack structure, the air electrode is used in contact with the interconnector. For this reason, when the power generation operation is continued for a long time, a reaction product of chromium oxide contained in the interconnector made of a heat-resistant alloy and strontium (Sr) contained in the air electrode comes to be formed. There exists a problem of causing the performance fall of a solid oxide fuel cell (air electrode) (refer nonpatent literatures 1 and 2). This problem occurs because a material containing Sr is used for the air electrode. If the air electrode is made of a material not containing Sr, the problem can be solved. In general, however, materials that do not contain Sr (perovskite oxide) have extremely low electrical conduction characteristics, and if an air electrode is formed from this, the performance will be greatly reduced compared to an air electrode that contains Sr. (See Non-Patent Document 3).

  On the other hand, in Embodiment 1 and Embodiment 2 of the present invention described above, since the air electrode does not contain strontium (Sr), chromium oxide and Sr contained in the interconnector made of a heat-resistant alloy. No reaction product is formed, and deterioration of the solid oxide fuel cell (air electrode) due to use over time can be suppressed.

[Example 4]
Hereinafter, the characteristic measurement result in the single cell of the solid oxide fuel cell actually produced regarding the connection with the interconnector will be described below.

  The reference sample cell (# 4-0-0) and sample cell (# 4-1-1 to # 4-1-3, # 4-2-1 to # 4-2-3) in Example 4 are As shown in Table 4 below, the materials and fabrications that make up the fuel electrode, electrolyte, and air electrode are the same as in Example 3 described above. In Example 4, a current collector made of an iron-chromium heat-resistant alloy (ZMG232) mesh is disposed on the air electrode coating film, and the electrolyte substrate on which the air electrode coating film is formed is fired. Therefore, in Example 4, it is the structure equivalent to the state which the interconnector which consists of a heat-resistant alloy is contacting the air electrode. As shown in Table 4, in this example, the interface resistance after 1000 hours of energization is measured.

As shown in Table 4, the interfacial resistance increased in the comparative sample cell (# 4-0-0) at 1000 hours energization, but the sample cells (# 4-1-1 to # 4-1-3) , # 4-2-1 to # 4-2-3), the interface resistance is lowered. For these reasons, in the solid oxide fuel cell according to the present embodiment, since the air electrode does not contain Sr, a reaction product of chromium oxide and Sr with the current collector made of a heat-resistant alloy. It is thought that the formation of is suppressed. Also in the sample cell shown in Table 4, in LaE as the material of the air electrode _{(1-yx) Co x Mn} y O 3 (E copper or nickel), 0 <a range of x and x + y ≦ 0.8 It has become.

[Example 5]
Next, the rare earth constituting the air electrode material will be examined. In the above-described embodiments, the case where La is used as the rare earth constituting the air electrode material has been described. However, a single cell manufactured by replacing La with another rare earth will be described below.

In Example 5, as shown in Table 5 below, in addition to La as a rare earth, Pr, Nd, Sm, Eu, Gd, and a powder of an air electrode material in combination of these, the air electrode is used in the same manner as described above. Is made. _{Incidentally, LnE (1-yx) Co} x Mn y O 3 (Ln is a rare earth, E is copper or nickel) in general rare earth position Ln called A-site, Pr, Nd, Sm, Eu, etc. Gd It is changing. The current collector is composed of a platinum mesh. The produced cell is a fuel cell-supported single cell similar to those in Examples 3 and 4 described above. In Example 5, the measurement is performed under the conditions of [Measurement Method 2].

  As shown in Table 5, regardless of which rare earth is used, the same results as in Example 3 are shown. Further, in any sample cell using rare earth, the interface resistance after 72 hours of energization is lower than that in the reference sample cell using LSM. From these results, it is considered that the air electrode is composed of a metal oxide having a perovskite structure including rare earth, transition metal, cobalt, and manganese, and the transition metal may be selected from copper and nickel. It is done.

[Embodiment 3]
Next, a third embodiment of the present invention will be described. FIG. 5 is a cross-sectional view schematically showing a partial configuration example of the solid oxide fuel cell according to Embodiment 3 of the present invention. This solid oxide fuel cell includes an electrolyte 501 made of a zirconia-based material and a fuel electrode 502 formed on one surface of the electrolyte 501. Further, the solid oxide fuel cell of the present embodiment is a metal oxide (perovskite) formed on the other side of the electrolyte 501 and having a rare earth, transition metal E, cobalt (Co), and manganese (Mn). An air electrode 503 made of a type oxide).

  The transition metal is copper or nickel. The rare earth is at least one of lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), and gadolinium (Gd). For example, these two are included. It may be. For example, the air electrode 503 is composed of a sintered body (porous sintered body) of the perovskite oxide.

Here, the present embodiment is characterized in that the perovskite oxide is represented by LnE _1/3 Co _1/3 Mn _1/3 O ₃ (Ln is rare earth, E is copper or nickel). There is. In addition, the number of atoms of each element in LnE _1/3 Co _1/3 Mn _1/3 O ₃ includes a range of values slightly deviating from the stoichiometric composition.

The electrolyte 501 includes, for example, scandium oxide (Sc ₂ O ₃ ) and aluminum oxide (Al ₂ O ₃ ) stabilized ZrO ₂ (SASZ), yttria stabilized zirconia (YSZ), scandia stabilized zirconia (ScSZ), and Samaria. What is necessary is just to be comprised from the sintered compact of the powder of zirconia materials, such as stabilized zirconia (SSZ). The fuel electrode 502 is made of, for example, nickel-yttria stabilized zirconia cermet (Ni-YSZ), nickel alumina-added scandia stabilized zirconia (Ni-SASZ), etc. mixed with metallic nickel in an oxide material constituting the electrolyte 501. What is necessary is just to be comprised from the sintered body (porous sintered body) of the powder of the metal-oxide mixture (cermet) which was made electronic conductivity.

  In addition, as is well known, each of these layers is a slurry of powder or mixed powder, and a sheet is formed by molding by a doctor blade method or application by a screen printing method. It can produce by baking with.

According to the solid oxide fuel cell of the present embodiment configured as described above, the air electrode 503 is composed of a perovskite oxide made of rare earth, Ni or Cu, Co, and Mn. Compared with the case where the perovskite type oxide is used, the air electrode characteristics can be improved at a low operating temperature of about 800 ° C., and the output voltage can be further improved. In addition, according to the present embodiment, the perovskite oxide constituting the air electrode is composed of LnE _1/3 Co _1/3 Mn _1/3 O ₃ (Ln is rare earth, E is copper or nickel), Since the composition ratio of Mn, Co, and element E is approximately 1: 1: 1, the entire crystal of the perovskite oxide can be stabilized and excellent in durability, as will be described later.

  In the above-described embodiment, the basic configuration (single cell) of the solid oxide fuel cell is described. Actually, as is well known, a plurality of single cells are used in a state of being stacked via an interconnector, and obtained by reforming hydrocarbon gas such as city gas in each single cell. A fuel gas containing hydrogen is supplied to the fuel electrode 502 side, and air containing oxygen as an oxidant gas is supplied to the air electrode 503 side, whereby a power generation operation is performed.

Next, the fact that the air electrode 503 is made of LnE _1/3 Co _1/3 Mn _1/3 O ₃ (Ln is rare earth, E is copper or nickel) will be described in more detail. In the oxide having the perovskite structure represented by the composition formula AMO ₃ , the composition ratio of cobalt, manganese, and element E (copper or nickel) constituting M is approximately 1: 1: 1. It is possible to stabilize and improve the durability of the air electrode.

The reason for this will be described below. First, in the perovskite type oxide made of LnE _1/3 Co _1/3 Mn _1/3 O ₃ (Ln is rare earth, E is copper or nickel), as shown in the plan view of FIG. 6A, Co, Mn, And the transition metal layer 601 in which the transition metal of the element E exists equivalently in the same plane. In addition, as shown in the schematic cross-sectional view of FIG. 6B, this perovskite type oxide is laminated in such a manner that transition metal layers 601 alternately exist with layers 602 made of rare earth (Ln) and oxygen. It is in the state.

Alternatively, in the perovskite oxide made of LnE _1/3 Co _1/3 Mn _1/3 O ₃ (Ln is rare earth, E is copper or nickel), Mn is in the same plane as shown in the plan view of FIG. 7A. In addition, an Mn layer 701, Co layer 702, in which Co exists independently in the same plane, and an element E layer 703, in which element E exists independently in the same plane, are provided. In addition, as shown in the schematic cross-sectional view of FIG. 7B, the Mn layer 701, the Co layer 702, and the element E layer 703 are independent every other layer with the layer 704 made of rare earth (Ln) and oxygen interposed therebetween. It exists as a layer and is in a laminated state.

  In the perovskite oxide constituting the air electrode in the present embodiment configured as described above, first, the effects of the respective elements of Co, Mn, and the transition metal of element E appear equally in the transition metal layer 601. . In addition, in the Mn layer 701, the Co layer 702, and the element E layer 703, the effect of each element appears periodically. As described above, these are considered as reasons why the entire crystal can be stabilized and the durability can be improved.

From the above, LnE _1/3 Co _1/3 Mn _1/3 O ₃ (Ln is rare earth, E is copper or nickel), in other words, the composition ratio of Co, Mn, and element E is possible. It is desirable to be close to 1: 1: 1 in the range. If these constituent ratios deviate from 1: 1: 1, excess or deficiency of elements occurs, and the stable arrangement as shown in FIGS. 6A, 6B, 7A, and 7B is not possible. Therefore, it is considered that the entire crystal cannot be stabilized and durability cannot be improved.

In the case of the arrangement of the transition elements shown in FIG. 6A, the distances between Mn, Co, and element E are regularly arranged as 3 ^1/2 of the distance between adjacent elements. A structure is formed. When this regularity is remarkable, a characteristic peak can be observed in the X-ray diffraction measurement or the neutron diffraction measurement. For example, in a perovskite oxide having a hexagonal crystal, when the a-axis length is 0.55 nm and the c-axis length is 1.32 nm, all the X The line diffraction peak is on the higher angle side than the peak at 2θ = 19.8 ° on the (101) plane, and 2θ has no peak on the lower angle side than 19 °.

  On the other hand, in the case of the superlattice structure as described above, it is predicted that the peak of the (1/2 1/2 0) plane appears at 2θ = 18.6 °. However, Co, Mn, and element E, whose atomic scattering factors are close to each other, are difficult to distinguish and the above-described peak detection is not easy. On the other hand, in neutron diffraction, it is possible to distinguish between Co, Mn, and element E, so that the peak detection of the superlattice structure described above is easier than in X-ray diffraction.

In addition, by setting Ln (rare earth) of LnE _1/3 Co _1/3 Mn _1/3 O ₃ to one or more selected from La, Pr, Nd, Sm, Eu, and Gd, air The pole can be stabilized. This is considered to be because, for example, in the case of a rare earth element having a small ion radius such as lutetium, the distance between oxygen and oxygen becomes short, and the perovskite structure becomes unstable.

  Next, the characteristic measurement result in the single cell of the actually produced solid oxide fuel cell will be described below.

[Cell preparation 3]
First, taking a solid oxide fuel cell (comparative sample cell: # 6-0-0) as a comparative sample as an example, production of a single cell will be described. First, Sc ₂ O ₃ · Al ₂ O ₃ added zirconia (0.89ZrO ₂ -0.10Sc ₂ O ₃ -0.01Al ₂ O ₃ : SASZ) formed into a sheet by the well-known doctor blade method and fired An electrolyte substrate is prepared. The electrolyte substrate is formed to a thickness of 0.2 mm. Next, mixed powder obtained by mixing zirconia powder (40 wt%) having an average particle diameter of about 0.6 μm to which 10 mol% Y ₂ O ₃ has been added with NiO powder (60 wt%) having an average particle diameter of 0.2 μm. Then, this slurry is applied to one surface of the above-described electrolyte substrate by a screen printing method to form a fuel electrode coating film. In addition, a current collector made of platinum mesh is disposed on the fuel electrode coating film, and these are fired in air under a heat treatment condition of 1300 ° C. for 8 hours. A fuel electrode having a thickness of 60 μm is formed.

Next, a slurry of La _0.8 Sr _0.2 MnO ₃ (LSM) powder having an average particle size of 1.0 μm is prepared, and this slurry is applied to the other surface of the electrolyte substrate by the screen printing method and applied with an air electrode. A film is formed. In addition, a current collector made of platinum mesh is disposed on the air electrode coating film, and the electrolyte substrate on which the air electrode coating film is formed is fired under heat treatment conditions of 1100 ° C. for 2 hours, An air electrode having a thickness of 60 μm made of the sintered body is formed.

  The single cell formed in this way is the same as that of the first embodiment described above, and as shown in the perspective view of FIG. 3, on the electrolyte substrate 301 formed in a square plate shape with a side of 30 mm, An air electrode 302 formed on a disk having a diameter of 10 mm is arranged. In FIG. 3, the fuel electrode and the current collector disposed below the electrolyte substrate 301 are not shown and are omitted. In addition, this single cell includes a reference electrode 303 made of platinum around the electrolyte substrate 301, and performs the measurement according to [Measuring method 1] described above while being connected thereto.

[Example 6]
Next, as Example 6, a solid oxide fuel cell serving as a sample (sample cells: # 6-1-0 to # 6-1-2, # 6-2-0 to # 6-2-2) The creation of will be described. In this sample cell, as shown in Table 6 below, LnNi _1/3 Co _1/3 Mn _1/3 O ₃ powder (# 6- 1-0 to # 6-1-2) and LnCu _1/3 Co _1/3 Mn _1/3 O ₃ powders (# 6-2-1 to # 6-2-8) were used. It is produced in the same manner as the sample cell. In Table 6, in LnNi _1/3 Co _1/3 Mn _1/3 O ₃ , the composition ratio of Ni, Co, and Mn is set to about 1: 1: 1, and the type of Ln is changed to change each sample cell. (# 6-1-0 to # 6-1-2). Similarly, in LnCu _1/3 Co _1/3 Mn _1/3 O ₃ , the composition ratio of Cu, Co, and Mn is approximately 1: 1: 1, and the type of Ln is changed to change each sample cell (# 6- 2-0 to # 6-2-2).

  When the measurement described above is performed in each sample cell shown in Table 6, all of the sample cells (# 6-1-0 to # 6-1-2 and # 6-2-0 to # 6-2-2) Compared with the comparative sample cell (# 6-0-0), the interfacial resistance or the interfacial resistance is about the same, and good results are obtained. Moreover, the tendency for interface resistance to become lower is obtained after 1000 hours.

Examining the results shown in Table 6, in the comparative sample cell and any of the sample cells, the longer the energization time, the lower the interfacial resistance. It is considered that a substance having high resistance such as La ₂ Zr ₂ O ₇ formed between the electrolyte and the electrolyte decreases with the passage of current. In addition, it is considered that the difference in initial characteristics between different sample cells corresponds to, for example, the difference in the stoichiometric equilibrium of oxygen in the whole compound due to the composition ratio of Ni and Cu. From the results of Table 6, the material of the air electrode is LnE _1/3 Co _1/3 Mn _1/3 O ₃ (E is copper or nickel) (Mn, Co, composition ratio of element E is approximately 1: 1: 1), it is considered that the same result as in Table 6 is obtained.

[Embodiment 4]
Next, Embodiment 4 of the present invention will be described with reference to FIG. FIG. 8 is a cross-sectional view schematically showing a partial configuration example of the solid oxide fuel cell according to Embodiment 4 of the present invention. This solid oxide fuel cell includes an electrolyte 801, a fuel electrode 802 formed on one surface of the electrolyte 801, and an air electrode 803 formed on the other side of the electrolyte 801. In this embodiment, the air electrode 203 is a perovskite type of LnE _1/3 Co _1/3 Mn _1/3 O ₃ (Ln is a rare earth, E is copper or nickel) in the same manner as the air electrode 503 of the third embodiment. The first layer 803a is made of an oxide, and the second layer 803b is arranged on the electrolyte 801 side and contains cerium oxide in addition to the perovskite oxide.

In the air electrode 803 in this embodiment, the second layer 803b is provided on the electrolyte 801 side. Therefore, in the second layer 803b, the perovskite oxide particles are covered with ceria compound particles. In addition, the direct contact between the zirconia-based material portion constituting the electrolyte 801 and the perovskite oxide material is suppressed, and the production of highly resistive substances such as La ₂ Zr ₂ O ₇ is suppressed. .

  In the embodiment described above, the basic configuration (single cell) of the solid oxide fuel cell is described. Actually, as is well known, a plurality of single cells are used in a state of being stacked via an interconnector, and obtained by reforming hydrocarbon gas such as city gas in each single cell. A fuel gas containing hydrogen is supplied to the fuel electrode 802 side, and air containing oxygen as an oxidant gas is supplied to the air electrode 803 side, whereby a power generation operation is performed.

  Next, the characteristic measurement result in the single cell of the actually produced solid oxide fuel cell will be described below.

[Example 7]
First, production of a solid oxide fuel cell (single cell) as a sample will be described. First, well known Sc ₂ O ₃ obtained by firing molded into a sheet by a doctor blade method, Al ₂ O ₃ doped zirconia _{(0.89ZrO 2 -0.10Sc 2 O 3 -0.01Al} 2 O 3: SASZ An electrolyte substrate is prepared. The electrolyte substrate is formed to a thickness of 0.2 mm. Next, a mixed powder in which NiO powder (60 wt%) having an average particle diameter of 0.2 μm is mixed with zirconia powder (40 wt%) having an average particle diameter of about 0.6 μm to which 10 mol% Y ₂ O ₃ has been added. A slurry is prepared, and this slurry is applied to one surface of the above-described electrolyte substrate by a well-known screen printing method to form a fuel electrode coating film. In addition, a current collector made of platinum mesh is disposed on the fuel electrode coating film, and these are fired in air under a heat treatment condition of 1300 ° C. for 8 hours. A fuel electrode having a thickness of 60 μm is formed.

Next, an air electrode material similar to that of Example 6 described above and Gd _0.2 Ce _0.8 O ₂ (GDC) as a ceria compound are mixed at a weight ratio of 6: 4 to prepare a mixed powder slurry. Then, this slurry is applied to the other surface of the above-described electrolyte substrate by a screen printing method to form a second layer coating film of the air electrode. In addition, the slurry in which the powder of the air electrode material is dispersed is thickly applied on the second layer coating film, so that the first layer coating film is formed. In addition, a current collector made of platinum mesh is placed on the first layer coating film, and these are fired under heat treatment conditions of 1100 ° C. for 2 hours, and the thickness of the powder sintered body is 3 μm. It is assumed that an air electrode composed of the second layer and the first layer having a thickness of 60 μm is formed.

  The single cell formed in this way is the same as that of the second embodiment described above, and as shown in the perspective view of FIG. 3, on the electrolyte substrate 301 formed in a square plate shape with a side of 30 mm, An air electrode 302 formed on a disk having a diameter of 10 mm is arranged. In addition, this single cell includes the reference electrode 303 made of platinum around the electrolyte substrate 301, and performs the measurement of [Measuring method 1] described above while being connected to the reference electrode 303.

In Example 7, a solid oxide fuel cell (# 7-0-0) serving as a reference sample uses La _0.8 Sr _0.2 MnO ₃ as an air electrode material, and serves as a sample. (# 7-1-0 to # 7-1-2) uses LaNi _1/3 Co _1/3 Mn _1/3 O ₃ as an air electrode material, and a solid oxide fuel cell (# 7-2-0 to # 7-2-2) use LaCu _1/3 Co _1/3 Mn _1/3 O ₃ as the air electrode material.

As shown in Table 7, in both cases, the initial interface resistance is low. This is considered to indicate that formation of a highly resistant substance such as La ₂ Zr ₂ O ₇ between the air electrode and the electrolyte is suppressed in the cell production stage. Also in this example, in the sample cells (# 7-1-0 to # 7-1-2 and # 7-2-0 to # 7-2-2), the longer the energization time, the higher the interface resistance. There is a tendency to decrease significantly. Further, from the results of Table 7, the material of the air electrode is LnE _1/3 Co _1/3 Mn _1/3 O ₃ (E is copper or nickel) (Mn, Co, element E composition ratio is approximately 1: It is considered that the same result as in Table 7 can be obtained.

  In addition, the particle diameter mentioned above is an average particle diameter obtained from the measurement of the light intensity distribution pattern by the well-known laser diffraction scattering method. For example, the particle size can be measured by using a laser diffraction / scattering particle size distribution measuring device LA-910 manufactured by HORIBA, Ltd.

  As described above, according to the present invention, even when a current collector made of a heat-resistant alloy is used, deterioration of the characteristics of the air electrode can be suppressed even when used for a long time. Further, although the air electrode is configured without using Sr, desired electrode characteristics can be obtained over a long time by using the perovskite oxide in the present invention. Thus, the present invention is suitable for a solid oxide fuel cell that requires high reliability and high efficiency.

It is sectional drawing which shows typically the structural example of the solid oxide fuel cell in Embodiment 1 of this invention. It is sectional drawing which shows typically the structural example of the solid oxide fuel cell in Embodiment 2 of this invention. It is a perspective view which shows the structure of a sample cell. It is sectional drawing which shows the structure of a sample cell. It is sectional drawing which shows typically the partial structural example of the solid oxide form fuel cell in Embodiment 3 of this invention. It is a top view which shows typically the partial structure of the perovskite type | mold oxide which comprises the air electrode 503 in Embodiment 3 of this invention. It is sectional drawing which shows typically the partial structure of the perovskite type | mold oxide which comprises the air electrode 503 in Embodiment 3 of this invention. It is a top view which shows typically the other partial structure of the perovskite type oxide which comprises the air electrode 503 in Embodiment 3 of this invention. It is sectional drawing which shows typically the other partial structure of the perovskite type oxide which comprises the air electrode 503 in Embodiment 3 of this invention. FIG. 8 is a cross-sectional view schematically showing a partial configuration example of the solid oxide fuel cell according to Embodiment 4 of the present invention.

Explanation of symbols

  101 ... electrolyte, 102 ... fuel electrode, 103, 203 ... air electrode.

Claims (4)

In a solid oxide fuel cell comprising a fuel electrode, an electrolyte, and an air electrode,
The air electrode is
Consists of metal oxides of perovskite structure with rare earths, transition metals, cobalt and manganese,
The transition metal state, and are not selected from copper and nickel,
The metal oxide is characterized by _{LnE (1-yx) Co x} Mn y O 3 ( the Ln rare earth, E is copper or nickel, 0.6 ≦ x + y ≦ 0.8 , x ≦ y) is Solid oxide fuel cell. The solid oxide fuel cell according to claim 1 , wherein
2. The solid oxide fuel cell according to claim ₁ , wherein the metal oxide is LnE _1/3 Co _1/3 Mn _1/3 O ₃ (Ln is a rare earth, E is copper or nickel). The solid oxide fuel cell according to claim 1 or 2 ,
The solid oxide fuel cell, wherein the rare earth is at least one of lanthanum, praseodymium, neodymium, samarium, europium, and gadolinium. The solid oxide fuel cell according to any one of claims 1 to 3 ,
The air electrode includes a layer containing cerium oxide disposed on the electrolyte side. A solid oxide fuel cell, wherein:

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