JP2015201419A - Fuel battery cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel battery cell capable of improving durability.SOLUTION: An air electrode material used in an air electrode 14 of a fuel battery cell 10 contains (Co,Fe)Oand a perovskite oxide represented by general formula ABOwith A sites containing at least one of La and Sr. The (Co,Fe)Ocontent in the air electrode material is from 0.23 wt.% to 8.6 wt.% inclusive.

Description

  The present invention relates to a fuel battery cell.

  In recent years, attention has been focused on fuel cells from the viewpoint of environmental problems and effective use of energy resources. The fuel cell includes a fuel cell and an interconnector. In general, the fuel battery cell includes a fuel electrode, an air electrode, and a solid electrolyte layer disposed between the fuel electrode and the air electrode.

  Here, it is widely known to use a perovskite oxide such as LSCF as the raw material powder of the air electrode (see, for example, Patent Document 1).

JP 2006-32132 A

However, as power generation using the fuel cell is repeated, the obtained output may decrease. The present inventors have newly stated that one of the causes of the decrease in output is due to the deterioration of the air electrode, and this deterioration of the air electrode is related to the ratio of (Co, Fe) ₃ O ₄ introduced into the inside. I found it.

  The present invention is based on such new knowledge, and an object thereof is to provide a fuel battery cell capable of improving durability.

The fuel cell according to the present invention includes a fuel electrode, an air electrode containing a main phase composed of a perovskite oxide, and a second phase composed of (Co, Fe) ₃ O ₄ , a fuel A solid electrolyte layer disposed between the electrode and the air electrode. The area occupation ratio of the second phase in the cross section of the air electrode is 9.5% or less.

  ADVANTAGE OF THE INVENTION According to this invention, the fuel battery cell which can improve durability can be provided.

Sectional view showing the configuration of the fuel cell SEM image of cross section of anode active layer Histogram in which luminance distribution in SEM image is classified into 256 gradations The figure which shows the image analysis result of the SEM image shown in FIG. Sectional view showing the configuration of the fuel cell Example of TEM image of air electrode cross section Graph showing an example of EDX spectrum in the second phase Example of SAED image in the second phase

  Next, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, the drawings are schematic, and the ratio of each dimension may be different from the actual one. Accordingly, specific dimensions and the like should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  In the following embodiments, a solid oxide fuel cell (SOFC) will be described as an example of a fuel cell. In the following, a so-called vertical stripe fuel cell will be described, but the present invention is not limited to this, and can also be applied to a so-called horizontal stripe fuel cell.

(First embodiment)
<< Configuration of Fuel Cell 10 >>
The configuration of the fuel cell (hereinafter abbreviated as “cell”) 10 will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the configuration of the cell 10.

  The cell 10 is a thin plate body made of a ceramic material. The thickness of the cell 10 is, for example, 300 μm to 3 mm, and the diameter of the cell 10 is, for example, 5 mm to 50 mm. A fuel cell can be formed by connecting a plurality of cells 10 in series by an interconnector.

  The cell 10 includes a fuel electrode 11, a solid electrolyte layer 12, a barrier layer 13, and an air electrode 14.

  The fuel electrode 11 functions as an anode of the cell 10. As illustrated in FIG. 1, the fuel electrode 11 includes a fuel electrode current collecting layer 111 and a fuel electrode active layer 112.

The anode current collecting layer 111 may be a porous plate-like fired body containing a transition metal and an oxygen ion conductive material. The anode current collecting layer 111 may include, for example, nickel oxide (NiO) and / or nickel (Ni) and yttria stabilized zirconia (3YSZ, 8YSZ, 10YSZ, etc.). The thickness of the anode current collecting layer 111 can be set to 0.2 mm to 5.0 mm. The thickness of the anode current collecting layer 111 may be the largest among the constituent members of the cell 10 when it functions as a substrate. In the anode current collecting layer 111, the volume ratio of Ni and / or NiO can be 35 to 65% by volume in terms of Ni, and the volume ratio of YSZ can be 35 to 65% by volume. The anode current collecting layer 111 may include yttria (Y ₂ O ₃ ) instead of YSZ.

  The anode active layer 112 is disposed between the anode current collecting layer 111 and the solid electrolyte layer 12. The anode active layer 112 is a porous plate-like fired body containing a transition metal and an oxygen ion conductive material. The anode active layer 112 may contain NiO and / or Ni and yttria-stabilized zirconia, like the anode current collecting layer 111. The thickness of the anode active layer 112 can be 5.0 μm to 30 μm. In the anode active layer 112, the volume ratio of Ni and / or NiO can be 25 to 50% by volume in terms of Ni, and the volume ratio of YSZ can be 50 to 75% by volume. Thus, the anode active layer 112 may have a higher YSZ content than the anode current collecting layer 111. The anode active layer 112 may contain a zirconia-based material such as scandia-stabilized zirconia (ScSZ) instead of YSZ.

The solid electrolyte layer 12 is disposed between the fuel electrode 11 and the barrier layer 13. The solid electrolyte layer 12 has a function of transmitting oxygen ions generated at the air electrode 14. The solid electrolyte layer 12 contains zirconium (Zr). The solid electrolyte layer 12 may contain Zr as zirconia (ZrO ₂ ). The solid electrolyte layer 12 may contain ZrO ₂ as a main component. The solid electrolyte layer 12 may contain additives such as Y ₂ O ₃ and / or Sc ₂ O ₃ in addition to ZrO ₂ . These additives function as stabilizers. In the solid electrolyte layer 12, mol compositional ratio of ZrO ₂ stabilizer (stabilizer: ZrO ₂₎ is 3: 97 to 20: may be about 80. That is, examples of the material for the solid electrolyte layer 12 include yttria-stabilized zirconia such as 3YSZ, 8YSZ, and 10YSZ, and zirconia-based materials such as ScSZ. The thickness of the solid electrolyte layer 12 can be 3 μm to 30 μm.

The barrier layer 13 is disposed between the solid electrolyte layer 12 and the air electrode 14. The barrier layer 13 has a function of suppressing the formation of a high resistance layer between the solid electrolyte layer 12 and the air electrode 14. Examples of the material of the barrier layer 13 include cerium (Ce) and a ceria-based material containing a rare earth metal oxide dissolved in Ce. Specifically, examples of the ceria-based material include GDC ((Ce, Gd) O ₂ : Gadolinium doped ceria), SDC ((Ce, Sm) O ₂ : samarium doped ceria) and the like. The thickness of the barrier layer 13 can be 3 μm to 20 μm.

  The air electrode 14 is disposed on the barrier layer 13. The air electrode 14 functions as a cathode of the cell 10. The thickness of the air electrode 14 can be 2 μm to 100 μm.

The air electrode 14 is represented by the general formula ABO ₃ and contains, as a main phase, a perovskite oxide containing at least one of La and Sr at the A site. As the perovskite type oxide, for example, lanthanum-containing perovskite type composite oxide or SSC (Samarium Strontium Cobaltite: (Sm, Sr) CoO ₃ ) containing no lanthanum is preferably used, but is not limited thereto. Absent. Examples of the lanthanum-containing perovskite complex oxide include LSCF (lanthanum strontium cobalt ferrite: (La, Sr) CoO ₃ ), LSF (lanthanum strontium ferrite: (La, Sr) FeO ₃ ), LSC (lanthanum strontium cobaltite: (La , Sr) CoO ₃ ) and LNF (lanthanum nickel ferrite: La (Ni, Fe) O ₃ ). However, the air electrode 14 may not contain Co (cobalt). Density of constructed main phase by perovskite oxide ^can be ^{5.5g / cm 3 ~8.5g / cm 3} .

  The area occupation ratio of the main phase in the cross section of the air electrode 14 can be 87.5% or more and 99.75% or less. A method for calculating the area occupancy will be described later.

The air electrode 14 contains a second phase composed of (Co, Fe) ₃ O ₄ having a spinel crystal structure. (Co, Fe) ₃ O ₄ includes Co ₂ FeO ₄ , Co _1.5 Fe _1.5 O _4, CoFe ₂ O _{4, and the} like. Density of the second phase ^can be ^{5.2g / cm 3 ~6.2g / cm 3} . The density of the second phase may be smaller than the density of the main phase.

  The area occupation ratio of the second phase in the cross section of the air electrode 14 is preferably 9.5% or less. Thereby, since the inactive part inside the air electrode is reduced, it is possible to suppress a decrease in initial output, and it is possible to suppress the progress of deterioration of the air electrode during energization by the reaction between the second phase and the main phase. As a result, the durability of the air electrode 14 can be further improved.

  The area occupation ratio of the second phase is more preferably 0.25% or more. Thereby, since the second phase is appropriately introduced and the sinterability of the air electrode 14 is improved, the skeleton of the porous structure can be strengthened. As a result, changes in the microstructure of the air electrode 14 during energization are suppressed, and the durability of the air electrode 14 can be further improved.

  Moreover, it is preferable that the circle | round | yen equivalent average diameter of the particle | grains which comprise a 2nd phase is 0.05 to 0.5 micrometer. By controlling the equivalent-circle average diameter of the second phase within such a range, the deterioration rate of the air electrode 14 can be further reduced. The circle equivalent average diameter is an arithmetic average of the diameters of circles having the same area as the particles constituting the second phase.

The air electrode 14 may also contain a third phase composed of _Co 3 _{O 4} (tricobalt tetroxide) or CoO (cobalt oxide). However, the area occupation ratio of the third phase in the cross section of the air electrode 14 is preferably less than 3.0%. Further, the air electrode 14 may contain an oxide of a constituent element of the main phase in addition to the second phase and the third layer.

<< Calculation method of area occupancy ratio of second phase >>
Next, a method for calculating the area occupancy of the second phase will be described with reference to FIGS.

(1) SEM image FIG. 2 is a cross section of the air electrode 14 magnified by a magnification of 10,000 times by an FE-SEM (Field Emission Scanning Electron Microscope) using an in-lens secondary electron detector. It is a SEM image which shows. FIG. 2 shows a cross section of the air electrode 14 containing LSCF ((La _0.6 Sr _0.4 ) (Co _0.2 Fe _0.8 ) O ₃ ) as a main component. Note that the cross section of the air electrode 14 is preliminarily subjected to ion milling processing by IM4000 of Hitachi High-Technologies Corporation after precision mechanical polishing. Moreover, the SEM image of FIG. 2 was obtained by FE-SEM (model: ULTRA55) made by Zeiss (Germany) set to acceleration voltage: 1 kV and working distance: 3 mm.

In the SEM image of FIG. 2, the main phase (LSCF) and the second phase ((Co, Fe) ₃ O ₄ ) are different in the brightness difference between the pores, the main phase is “light gray”, and the second phase is “dark”. Gray and pores are displayed in black. Such ternarization by light and dark difference can be realized by classifying the luminance of an image into 256 gradations. Here, FIG. 3 is a histogram in which the luminance distribution of the SEM image shown in FIG. 2 is classified into 256 gradations. As shown in FIG. 3, the luminance of the second phase is detected at a low frequency from the low luminance side of the main phase to the high luminance side of the pores. Therefore, in FIG. 2, the second phase is displayed with a darker contrast than the main phase and a brighter contrast than the pores.

  However, the method for discriminating the main phase, the second phase, and the pores is not limited to using the light / dark difference in the SEM image. For example, after acquiring element mapping by SEM-EDS in the same field of view, it is also possible to identify each particle in the image by comparing it with a previously obtained FE-SEM image using an in-lens secondary electron detector. It can be ternized well.

(2) Analysis of SEM Image FIG. 4 is a diagram showing a result of image analysis of the SEM image shown in FIG. 2 by image analysis software HALCON manufactured by MVTec (Germany). In FIG. 4, the second phase is surrounded by a white solid line. Based on the analysis image shown in FIG. 4, the area occupancy of the main phase and the second phase can be calculated.

  First, the total area of the second phase surrounded by the solid line in the analysis image is calculated. Next, the ratio of the total area of the second phase to the total area of the analysis image is calculated. The ratio of the total area of the second phase thus calculated is the area occupancy of the second phase.

<Air electrode material>
As an air electrode material constituting the air electrode 14, a mixed material of a perovskite oxide represented by the general formula ABO ₃ and (Co, Fe) ₃ O ₄ can be preferably used.

Examples of the perovskite complex oxide include LSCF, LSF, LSC, LNF, and SSC. Examples of (Co, Fe) ₃ O ₄ include Co ₂ FeO ₄ , Co _1.5 Fe _1.5 O _4, and CoFe ₂ O ₄ .

The amount of (Co, Fe) ₃ O ₄ added to the air electrode material is preferably 8.6% by weight or less. Thus, the area occupancy of the second phase ((Co, Fe) ₃ O ₄ ) in the cross section of the air electrode 14 can be controlled to 9.5% or less. The amount of (Co, Fe) ₃ O ₄ added to the air electrode material is more preferably 0.23% by weight or more. Thereby, the area occupation ratio of the second phase in the cross section of the air electrode 14 can be controlled to 0.25% or more.

Note that the area occupancy of the second phase can also be finely adjusted by adjusting the state of the (Co, Fe) ₃ O ₄ raw material (whether it is an oxide or a chloride) and the particle size.

Moreover, the density of the second phase in the air electrode 14 can be made smaller than the density of the main phase by making the density of the (Co, Fe) ₃ O ₄ raw material smaller than that of the perovskite oxide.

Further, by adjusting the particle size of the (Co, Fe) ₃ O ₄ raw material, the equivalent circle diameter of the particles constituting the second phase in the air electrode 14 can be adjusted. In the particle size adjustment of the raw material (Co, Fe) ₃ O _4, precise classification including an upper limit value and a lower limit value is possible by using an airflow classifier.

<< Manufacturing Method of Cell 10 >>
Next, an example of a method for manufacturing the cell 10 will be described. However, various conditions such as the material, particle size, temperature, and coating method described below can be changed as appropriate. Hereinafter, the “molded body” refers to a member before firing.

  First, a slurry is prepared by adding polyvinyl alcohol (PVA) as a binder to a mixture of NiO powder, YSZ powder, and a pore-forming agent (for example, PMMA (polymethyl methacrylate resin)). Next, this slurry is dried and granulated with a spray dryer to obtain a fuel electrode current collecting layer powder. Next, a molded body of the fuel electrode current collecting layer 111 is formed by molding the fuel electrode powder by a die press molding method.

  Next, a slurry is prepared by adding polyvinyl alcohol as a binder to a mixture of NiO powder, YSZ powder, and a pore-forming agent (for example, PMMA). Next, this slurry is printed on the molded body of the anode current collecting layer 111 by a printing method to form a molded body of the anode active layer 112. Thereby, a molded body of the fuel electrode 11 is formed.

  Next, a slurry is prepared by mixing the YSZ powder with a mixture of water and a binder in a ball mill for 24 hours. Next, the slurry is applied on the molded body of the fuel electrode 11 and dried to form a molded body of the solid electrolyte layer 12. Note that a tape lamination method or a printing method may be used instead of the coating method.

  Next, a slurry is prepared by mixing a mixture of water and a binder with the GDC powder in a ball mill for 24 hours. Next, the molded body of the barrier layer 13 is formed by applying and drying the slurry on the molded body of the solid electrolyte layer 12. Note that a tape lamination method or a printing method may be used instead of the coating method.

  From the above, a laminate of the molded body of the fuel electrode 11, the molded body of the solid electrolyte layer 12, and the molded body of the barrier layer 13 is formed.

  Next, the laminated body is co-sintered at 1300 to 1600 ° C. for 2 to 20 hours, so that the fuel electrode current collector layer 111 and the fuel electrode active layer 112 are composed of the fuel electrode 11, the solid electrolyte layer 12, and the dense barrier. A co-fired body of layer 13 is formed.

  Next, a slurry is prepared by mixing the air electrode material, water, and binder described above with a ball mill for 24 hours.

  Next, after applying the slurry onto the co-fired barrier layer 13 and drying, the porous air electrode 14 is formed on the barrier layer 13 by firing in an electric furnace (oxygen-containing atmosphere, 1000 ° C.) for 1 hour. Form. Thus, the cell 10 is completed.

(Second Embodiment)
<< Configuration of Fuel Cell 20 >>
Next, the configuration of the fuel battery cell 20 according to the second embodiment will be described with reference to the drawings. FIG. 5 is a cross-sectional view showing the configuration of the cell 20. The difference between the cell 10 according to the first embodiment and the cell 20 according to the second embodiment is that the area occupancy of the second phase is managed only in the region on the solid electrolyte layer side of the air electrode 14. is there. In the following, the difference will be mainly described.

  As shown in FIG. 5, the air electrode 14 ′ includes a first region 141 and a second region 142.

  The first region 141 is a region within 3 μm from the surface 14S on the solid electrolyte layer 12 side. The first region 141 is an example of a “solid electrolyte layer side region”. In the cell 20 according to the present embodiment, since the barrier layer 13 is interposed between the solid electrolyte layer 12 and the air electrode 14 ′, the first region 141 is in contact with the barrier layer 13. However, when the cell 20 does not include the barrier layer 13, the first region 141 is in contact with the solid electrolyte layer 12.

The first region 141 is represented by the general formula ABO ₃ and contains a perovskite oxide containing at least one of La and Sr at the A site as a main phase. The area occupation ratio of the main phase in the cross section of the first region 141 can be 87.5% or more and 99.75% or less.

The first region 141 contains a second phase composed of (Co, Fe) ₃ O ₄ having a spinel crystal structure. The area occupation ratio of the second phase in the cross section of the first region 141 is preferably 9.5% or less. Thus, (Co, _Fe) 3 is possible to improve the film strength of the first region 141 by the addition of _{O 4,} (Co, _Fe) thermal expansion of the solid electrolyte layer 12 and the barrier layer 13 in the excessive addition of 3 _{O 4} An increase in the difference can be suppressed. As a result, separation of the air electrode 14 ′ can be suppressed. The area occupation ratio of the second phase in the cross section of the first region 141 is more preferably 0.25% or more. Thereby, since the film strength of the first region 141 can be sufficiently improved by the addition of (Co, Fe) ₃ O ₄ , peeling of the air electrode 14 ′ can be further suppressed. The method for calculating the area occupancy of the second phase is as described in the first embodiment.

In addition, in the cross section of the first region 141, the circle-equivalent average diameter of the particles constituting the second phase is preferably 0.05 μm or more and 0.5 μm or less. In the first region 141, the density of the second phase may be smaller than the density of the main phase. The first region 141 may contain a third phase composed of Co ₃ O ₄ (tricobalt tetroxide) or CoO (cobalt oxide). However, the area occupation ratio of the third phase in the cross section of the first region 141 is preferably less than 3.0%. Furthermore, the first region 141 may contain an oxide of a constituent element of the main phase in addition to the second phase and the third layer.

  As the material of the first region 141 as described above, the air electrode material described in the first embodiment can be suitably used.

The second region 142 is a region separated by 3 μm or more from the surface 14S on the solid electrolyte layer 12 side. The second area 142 is disposed on the first area 141. The second region 142 is represented by the general formula ABO ₃ and contains a perovskite oxide containing at least one of La and Sr at the A site. The second region 142 may not contain (Co, Fe) ₃ O ₄ having a spinel crystal structure.

  The surface 14S of the air electrode 14 ′ on the solid electrolyte layer 12 side can be defined as a line whose concentration distribution changes abruptly when the component concentration is mapped in the cross section of the air electrode 14 ′ and the solid electrolyte layer 12. . Further, the surface 14S of the air electrode 14 'on the solid electrolyte layer 12 side may be defined as a line in which the porosity rapidly changes in the cross section of the air electrode 14' and the solid electrolyte layer 12.

<< Method for Manufacturing Fuel Cell 20 >>
Next, a method for manufacturing the fuel battery cell 20 according to the second embodiment will be described. Since the manufacturing method of the fuel electrode 11, the solid electrolyte layer 12, and the barrier layer 13 is as described in the first embodiment, the manufacturing method of the air electrode 14 'will be mainly described below.

  First, a co-fired body of the fuel electrode 11, the solid electrolyte layer 12, and the barrier layer 13 is prepared.

  Next, a slurry for the first region is prepared by mixing the air electrode material for the first region 141 (including the main phase and the second phase described above), water, and a binder with a ball mill for 24 hours.

  Next, the molded body of the first region 141 is formed by applying and drying the first region slurry on the co-fired barrier layer 13.

  Next, a slurry for the second region is prepared by mixing a general air electrode material (for example, LSCF), water, and a binder with a ball mill for 24 hours.

  Next, the molded body of the second region 142 is formed by applying and drying the slurry for the second region onto the molded body of the first region 141.

  Next, the air electrode 14 ′ is formed on the barrier layer 13 by firing the formed body of the first region 141 and the formed body of the second region 142 in an electric furnace (oxygen-containing atmosphere, 1000 ° C.) for 1 hour.

<< Other Embodiments >>
The present invention is not limited to the embodiment described above, and various modifications or changes can be made without departing from the scope of the present invention.

  (A) In the above embodiment, in FIGS. 2 to 4, a cross-sectional view of the air electrode 14 containing LSCF as a main phase is used. As long as it is contained.

  (B) In the above embodiment, the cell 10 includes the fuel electrode 11, the solid electrolyte layer 12, the barrier layer 13, and the air electrode 14. However, the present invention is not limited to this. The cell 10 only needs to include the fuel electrode 11, the solid electrolyte layer 12, and the air electrode 14. Between the fuel electrode 11 and the solid electrolyte layer 12 and between the solid electrolyte layer 12 and the air electrode 14, there are other cells. These layers may be inserted. For example, the cell 10 may include a porous barrier layer between the barrier layer 13 and the air electrode 14 in addition to the barrier layer 13.

  (C) Although not particularly mentioned in the above embodiment, the shape of the cell 10 may be a fuel electrode support type, a flat plate shape, a cylindrical shape, a vertical stripe type, a horizontal stripe type, or the like. The cross section of the cell 10 may be elliptical.

  (D) In the second embodiment, a region within 3 μm from the surface 14S on the solid electrolyte layer 12 side in the air electrode 14 ′ is defined as a “solid electrolyte layer side region”, but the thickness of the air electrode 14 ′ is 3 μm or less. In this case, the entire air electrode 14 ′ becomes the “solid electrolyte layer side region”.

  Examples of the cell according to the present invention will be described below, but the present invention is not limited to the examples described below.

[Sample No. 1-No. Production of 22]
In the following manner, the sample No. of the fuel electrode support type cell having the fuel electrode current collecting layer as the support substrate was used. 1-No. 22 was produced.

  First, a fuel electrode current collecting layer (NiO: 8YSZ = 50: 50 (Ni volume% conversion)) having a thickness of 500 μm is formed by a die press molding method, and a fuel electrode active layer (NiO: 8YSZ = 20 μm thickness) is formed thereon. 45:55 (Ni volume% conversion)) was formed by a printing method.

  Next, an 8YSZ electrolyte having a thickness of 5 μm and a GDC barrier film having a thickness of 5 μm were sequentially formed on the fuel electrode active layer to prepare a laminate.

  Next, the laminate was co-sintered at 1400 ° C. for 2 hours to obtain a co-fired body. Thereafter, an air electrode having a thickness of 30 μm was baked at 1000 ° C. for 2 hours, so that a sample number of a fuel electrode supported coin cell (φ15 mm) was obtained. 1-No. 22 was produced.

Here, as shown in Table 1, LSCF, LSF, and SSC were used as the main components of the air electrode material. As (Co, Fe) ₃ O ₄ added to the air electrode material, sample No. CoFe ₂ O ₄ is used for samples _2, 7, and 13, and sample Nos. Co _1.5 Fe _1.5 O ₄ was used for ₄ , 6, 14, and 20, and Co ₂ FeO ₄ was used for the other samples.

[Measurement of area occupancy]
First, sample no. 1-No. After the 22 air electrodes were subjected to precision mechanical polishing, ion milling was performed by IM4000 of Hitachi High-Technologies Corporation.

  Next, an SEM image showing a cross section of the air electrode magnified by a magnification of 10,000 times by FE-SEM using an in-lens secondary electron detector was acquired (see FIG. 2).

  Next, an analysis image was obtained by analyzing the SEM image of each sample with image analysis software HALCON manufactured by MVTec (Germany) (see FIG. 3).

Next, in the analysis image, the area occupancy of the second phase composed of (Co, Fe) ₃ O ₄ was calculated. The calculation results of the area occupation ratio of the second phase are as shown in Table 1.

[Component analysis of the second phase]
Sample No. 1-No. The component analysis of the 2nd phase was conducted about 22 and the constituent material of the 2nd phase of each sample was identified.

First, a TEM image of an air electrode cross section was obtained by TEM (Transmission Electron Microscope). FIG. 6 is an example of a TEM image of the air electrode cross section, and shows a second phase composed of Co ₂ FeO ₄ . The location of the second phase was confirmed with reference to this TEM image.

Next, the elements of the particles constituting the second phase were analyzed by EDX (Energy Dispersive X-ray Spectroscopy). FIG. 7 is a graph showing an example of an EDX spectrum of the second phase composed of Co ₂ FeO ₄ . The semi-quantitative analysis of this EDX spectrum can be used to infer the constituent material of the second phase. In FIG. 7, Cu is detected, but this is because the component of the sample holder of the analyzer is detected and is not a constituent material of the second phase.

Next, the crystal structure (lattice constant, lattice type, crystal orientation) of the particles constituting the second phase was analyzed by SAED (Selected Area Electron Diffraction). FIG. 8 is an example of a second phase SAED image composed of Co ₂ FeO ₄ . By analyzing the lattice constant, lattice type, and crystal orientation based on this SAED image, the constituent material of the second phase can be inferred.

As a result of analyzing the second phase of each sample by the above method, sample No. _{2, 7} and 13 were identified as CoFe ₂ O ₄ and sample No. 4, 6, 14, and 20 were identified as Co _1.5 Fe _1.5 O _4, and other samples were identified as Co ₂ FeO ₄ .

[Durability test]
Sample No. 1-No. For No. 22, the temperature was raised to 750 ° C. while supplying nitrogen gas to the fuel electrode side and air to the air electrode side, and when the temperature reached 750 ° C., reduction treatment was performed for 3 hours while supplying hydrogen gas to the fuel electrode.

After this, sample no. 1-No. For No. 22, the voltage drop rate per 1000 hours was measured as the deterioration rate. As the output density, a value at a temperature of 750 ° C. and a rated current density of 0.2 A / cm ² was used. The measurement results are summarized in Table 1. In Table 1, a deterioration rate of 1.5% or less is evaluated as a low deterioration state.

  In addition, after the durability test, the presence or absence of cracks in the air electrode was observed by observing the cross section of the air electrode with an electron microscope. The observation results are summarized in Table 1.

As shown in Table 1, in the sample in which the amount of (Co, Fe) ₃ O ₄ added to the air electrode material is 8.6% by weight or less, the deterioration rate of the air electrode should be reduced to 1.5% or less. I was able to. This is because the area occupancy of the second phase is suppressed to 9.5% or less by limiting the amount of (Co, Fe) ₃ O ₄ added to the air electrode material. Specifically, by appropriately reducing the second phase, the inactive portion inside the air electrode is reduced, and the second phase and the main phase can be prevented from reacting when energized, resulting in deterioration of the air electrode. Was suppressed.

Further, as shown in Table 1, in the sample in which the amount of (Co, Fe) ₃ O ₄ added to the air electrode material was 0.25% by weight or more, generation of cracks inside the air electrode could be suppressed. This is because the area occupation ratio of the second phase can be secured by 0.25% or more by securing the amount of (Co, Fe) ₃ O ₄ added to the air electrode material. Specifically, by appropriately introducing the second phase, the sinterability of the air electrode was improved, and as a result, the skeleton of the porous structure could be strengthened.

  Further, as shown in Table 1, the deterioration rate could be suppressed to 1.2% or less in the sample having the equivalent-circle average diameter of the second phase of 0.05 μm or more and 0.5 μm or less.

[Sample No. 23-No. Production of 44]
Sample no. 23-No. 44 was produced.

  First, a fuel electrode current collecting layer (NiO: 8YSZ = 50: 50 (Ni volume% conversion)) having a thickness of 500 μm is formed by a die press molding method, and a fuel electrode active layer (NiO: 8YSZ = 20 μm thickness) is formed thereon. 45:55 (Ni volume% conversion)) was formed by a printing method.

  Next, an 8YSZ electrolyte having a thickness of 5 μm and a GDC barrier film having a thickness of 5 μm were sequentially formed on the fuel electrode active layer to prepare a laminate.

  Next, the laminate was co-sintered at 1400 ° C. for 2 hours to obtain a co-fired body.

  Next, an air electrode material including the main phase and the second phase shown in Table 2, water, and a binder were mixed by a mill to prepare a first region slurry.

  Next, the first region slurry was applied onto the co-fired body to form a molded body in the first region of the air electrode.

  Next, LSCF, water, and a binder were mixed with a mill to prepare a slurry for the second region.

  Next, the slurry for the second region was applied onto the molded body in the first region to form a molded body in the second region of the air electrode.

  Next, the molded article in the first region and the molded article in the second region were fired at 1000 ° C. for 2 hours, so that a sample number of a fuel electrode supported coin cell (φ15 mm) was obtained. 23-No. 44 was produced.

[Measurement of area occupancy]
First, sample no. 23-No. After precision mechanical polishing of 44 first regions, ion milling was performed by IM4000 manufactured by Hitachi High-Technologies Corporation.

  Next, the SEM image which shows the cross section of the 1st area | region expanded by 10000 times of magnification by FE-SEM using the in-lens secondary electron detector was acquired.

  Next, each SEM image was analyzed with image analysis software HALCON manufactured by MVTec (Germany) to obtain an analysis image.

Next, in the analysis image, the area occupancy of the second phase composed of (Co, Fe) ₃ O ₄ was calculated. The calculation results of the area occupancy ratio of the second phase are as shown in Table 2.

[Component analysis of the second phase]
Sample No. 23-No. The component analysis of the 2nd phase in 44 1st area | regions was performed, and the constituent material of the 2nd phase of each sample was identified.

  First, a TEM image of the air electrode cross section was obtained by TEM.

  Next, the elements of the particles constituting the second phase were analyzed by EDX.

  Next, the crystal structure (lattice constant, lattice type, crystal orientation) of the particles constituting the second phase was analyzed by SAED.

As a result of analyzing the second phase of each sample by the above method, as shown in Table 2, sample No. No. 29 was identified as CoFe ₂ O ₄ and sample no. 26, 28, 36 and 42 were identified as Co _1.5 Fe _1.5 O _4, and other samples were identified as Co ₂ FeO ₄ .

[Thermal cycle test]
While supplying nitrogen gas to the fuel electrode side and supplying air to the air electrode side of each sample, the cycle of raising the temperature from room temperature to 750 ° C. in 2 hours and then lowering to room temperature in 4 hours was repeated 10 times.

  Then, the presence or absence of the peeling in the interface of a barrier layer and an air electrode was confirmed by observing the air electrode cross section of each sample with a microscope. The confirmation results are summarized in Table 2.

  In Table 2, a sample in which peeling that may affect the characteristics of the air electrode is confirmed as “x”, and a sample in which slight peeling that does not affect the characteristics of the air electrode is confirmed is “ A sample was evaluated as “A”, and a sample in which no peeling was confirmed was evaluated as “A”.

As shown in Table 2, by setting the content ratio of (Co, Fe) ₃ O ₄ in the material of the first region to 8.6% by weight or less, the area occupation ratio of the second phase in the first region is 9. In the sample of 5% or less, interfacial peeling could be suppressed. This is because the addition of (Co, Fe) ₃ O ₄ improves the film strength of the first region, while suppressing the increase in thermal expansion difference from the barrier layer due to the excessive addition of (Co, Fe) ₃ O _4. It was because of it.

Further, as shown in Table 2, by setting the content ratio of (Co, Fe) ₃ O ₄ in the material of the first region to 0.23% by weight or more, the area occupation ratio of the second phase in the first region is reduced. In the sample with 0.25% or more, slight interface peeling could be suppressed. This is because the film strength in the first region can be sufficiently improved by securing the amount of (Co, Fe) ₃ O ₄ added.

  The fuel cell according to the present invention is useful in the field of fuel cells because the durability of the air electrode can be improved.

DESCRIPTION OF SYMBOLS 10, 20 Fuel cell 11 Fuel electrode 111 Fuel electrode current collecting layer 112 Fuel electrode active layer 12 Solid electrolyte layer 13 Barrier layer 14, 14 'Air electrode 141 1st area | region 142 2nd area | region

Claims (4)

An anode,
An air electrode containing a perovskite oxide represented by the general formula ABO ₃ and containing at least one of La and Sr at the A site;
A solid electrolyte layer disposed between the fuel electrode and the air electrode;
With
The air electrode includes a solid electrolyte layer side region within 3 μm from the surface of the solid electrolyte layer side,
The solid electrolyte layer side region contains a main phase composed of the perovskite oxide and a second phase composed of (Co, Fe) ₃ O ₄ ,
The area occupancy of the second phase in the cross section of the solid electrolyte layer side region is 9.5% or less,
Fuel cell. The area occupation ratio of the second phase in the cross section of the solid electrolyte layer side region is 0.25% or more.
The fuel battery cell according to claim 1. The density of the second phase is smaller than the density of the main phase,
The fuel battery cell according to claim 1 or 2. The perovskite oxide is LSCF.
The fuel cell according to any one of claims 1 to 3.