JP5320497B1 - Fuel cell - Google Patents

Abstract

A fuel battery cell capable of suppressing a decrease in output of the fuel battery cell is provided.
A fuel electrode includes a fuel electrode current collecting layer containing a transition metal and an oxygen ion insulating material, and a fuel electrode active layer. In the fuel electrode current collecting layer 111 in the reduced state, the average value of the junction length between the transition metal particles and the oxygen ion insulating material particles is 0.4 μm or more and 1.8 μm or less.
[Selection] Figure 2

Description

  The present invention relates to a solid oxide fuel cell.

  A solid oxide fuel cell generally includes a fuel electrode, an air electrode, and a solid electrolyte layer disposed between the fuel electrode and the air electrode.

Here, a support containing a transition metal (for example, Ni) and a substance having no oxygen ion conductivity (for example, Y ₂ O ₃ or CaZrO ₃ (CZO)), a transition metal and oxygen ion conductivity A method of forming a fuel electrode with a fuel electrode active layer containing a substance (for example, YSZ) is known (see Patent Document 1). The support functions as an anode current collecting layer.

JP 2004-234970 A

  However, the fuel cell described in Patent Document 1 has a problem that, when operated continuously for a long period of time, the output of the fuel cell decreases because the conductivity of the anode current collecting layer decreases.

  As a result of intensive studies, the present inventors have found that the above-described problem occurs when the anode current collecting layer is reduced and the bonding between the transition metal particles and the particles having no oxygen ion conductivity. We obtained the knowledge that it is caused by insufficientness. That is, since the coupling between the two is insufficient, the Ni particle morphological change occurs during the operation of the fuel cell, so that the coupling between the Ni particles is broken. As a result, the conductivity of the anode current collecting layer is lowered.

  The present invention has been made in view of the above-described situation, and an object thereof is to provide a fuel cell that can suppress a decrease in the output of the fuel cell.

  A fuel cell according to the present invention includes a fuel electrode having an anode current collecting layer containing a transition metal and an oxygen ion insulating material, an anode active layer formed on the anode current collecting layer, and an air And a solid electrolyte layer disposed between the anode active layer and the air electrode. In the fuel electrode current collecting layer in the reduced state, the average value of the junction length between the transition metal particles and the oxygen ion insulating material particles is 0.4 μm or more and 1.8 μm or less.

  ADVANTAGE OF THE INVENTION According to this invention, the fuel battery cell which can suppress the output fall of a fuel battery cell can be provided.

Sectional view showing the configuration of the fuel cell SEM image of cross section of anode current collecting layer The figure which shows the analysis result of the SEM image shown in FIG. Distribution graph showing the distribution of junction length between transition metal and oxygen ion insulating material

  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 so-called vertical stripe fuel cell will be described as an example of a solid oxide fuel cell (SOFC).

<< 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 is formed by connecting a plurality of cells 10 in series with an interconnector.

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

1. Configuration of Fuel Electrode 11 The fuel electrode 11 functions as an anode of the cell 10. As shown in FIG. 1, the fuel electrode 11 includes a fuel electrode current collecting layer 111 and a fuel electrode active layer 112. In the present embodiment, it is assumed that the fuel electrode 11 has been subjected to a known reduction process (for example, a process of reducing NiO to Ni in a hydrogen atmosphere at 800 ° C.).

1-1. Fuel electrode current collecting layer 111
The anode current collecting layer 111 is a porous plate-like fired body. 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. The conductivity at 750 ° C. of the anode current collecting layer 111 subjected to the above reduction treatment is about 500 to 1500 S / cm.

  The anode current collecting layer 111 contains a transition metal and a substance having no oxygen ion conductivity (hereinafter referred to as “oxygen ion insulating substance”). In the anode current collecting layer 111 subjected to the reduction treatment described above, the volume ratio of the oxygen ion insulating material can be 35% by volume to 70% by volume. In other words, in the anode current collecting layer 111 subjected to the reduction treatment, the volume ratio of the transition metal can be set to 30% by volume to 65% by volume. Note that the volume ratio of the oxygen ion insulating substance means the volume ratio of the oxygen ion insulating substance itself, and excludes the volume of pores in the oxygen ion insulating substance.

The anode current collecting layer 111 contains nickel (Ni), iron (Fe), copper (Cu), or the like as a transition metal. The anode current collecting layer 111 preferably contains mainly Ni as a transition metal. The anode current collecting layer 111 may contain an oxide of a transition metal. Examples of the transition metal oxide include NiO, Fe ₂ O ₃ , FeO, and CuO.

The anode current collecting layer 111 contains yttrium oxide (Y ₂ O ₃ ), calcium zirconate (CaZrO ₃ ), or the like as an oxygen ion insulating material. In the present embodiment, “not having oxygen ion conductivity” means that the oxygen ion conductivity at 700 ° C. to 800 ° C. is 1.0 × 10 ⁻⁴ S / cm or less.

  Here, the anode current collecting layer 111 is composed of 200 ppm or less of silicon (Si), 50 ppm or less of phosphorus (P), 100 ppm or less of chromium (Cr), 100 ppm or less of boron (B), and 100 ppm or less of It is preferable to contain sulfur (S). In particular, the anode current collecting layer 111 preferably contains 100 ppm or less of Si, 30 ppm or less of P, 50 ppm or less of Cr, 50 ppm or less of B, and 30 ppm or less of S. In the anode current collecting layer 111, the content of each of Si, P, Cr, B, and S is more preferably at least 1 ppm or more.

  The internal microstructure of the anode current collecting layer 111 will be described later.

1-2. Fuel electrode active layer 112
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. The thickness of the anode active layer 112 can be 5.0 μm to 30 μm.

  The anode active layer 112 contains a transition metal and a substance having oxygen ion conductivity (hereinafter referred to as “oxygen ion conductive substance”). In the fuel electrode active layer 112 that has been subjected to the reduction treatment described above, the volume ratio of the oxygen ion conductive material can be 35% by volume to 70% by volume. In other words, in the anode active layer 112 that has been subjected to the reduction treatment, the volume ratio of the transition metal can be 30% to 65% by volume. Note that the volume ratio of the oxygen ion conductive material means the volume ratio of the oxygen ion conductive material itself, and excludes the volume of pores in the oxygen ion conductive material.

  In the anode active layer 112, examples of the transition metal include nickel (Ni), iron (Fe), and copper (Cu). The anode active layer 112 may contain a transition metal oxide.

In addition, the anode active layer 112 includes, as an oxygen ion conductive substance, zirconia-based materials such as yttria stabilized zirconia (8YSZ, 10YSZ, etc.) and scandia stabilized zirconia (ScSZ), gadolinium doped ceria (GDC: (Ce, Cd-based materials such as Gd) O ₂ ) and samarium-doped ceria (SDC: (Ce, Sm) O ₂ ). In the present embodiment, “having oxygen ion conductivity” means that the oxygen ion conductivity at 700 ° C. to 800 ° C. is 5.0 × 10 ⁻³ S / cm or more.

2. Configuration of Solid Electrolyte Layer 12 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.

3. Configuration of Barrier Layer 13 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 ceria (CeO ₂ ) and a ceria-based material containing a rare earth metal oxide dissolved in CeO ₂ . Specifically, examples of the ceria-based material include GDC and SDC. The thickness of the barrier layer 13 can be 3 μm to 20 μm.

4). Configuration of Air Electrode 14 The air electrode 14 is disposed on the barrier layer 13. The air electrode 14 functions as a cathode of the cell 10. The air electrode 14 may contain, for example, a lanthanum-containing perovskite complex oxide as a main component. Examples of the lanthanum-containing perovskite complex oxide include LSCF (lanthanum strontium cobalt ferrite), lanthanum manganite, lanthanum cobaltite, and lanthanum ferrite. The lanthanum-containing perovskite complex oxide may be doped with strontium, calcium, chromium, cobalt, iron, nickel, aluminum, or the like. The thickness of the air electrode 14 can be 10 μm to 100 μm.

<< Fine structure of anode current collecting layer 111 >>
In the following, the microstructure of the anode current collecting layer 111 will be described with reference to FIGS. In the present embodiment, as described above, a state in which the fuel electrode 11 is reduced is assumed. In the following description, Ni is an example of a transition metal, and Y ₂ O ₃ is an example of an oxygen ion insulating material. Therefore, in the following description, Ni may be replaced with other transition metals (Fe, Cu, etc.), and Y ₂ O ₃ may be replaced with other oxygen ion insulating substances (CaZrO _3, etc.).

1. SEM image FIG. 2 is a cross-sectional view of the fuel electrode current collecting layer 111 magnified by 3000 times by an FE-SEM (Field Emission Scanning Electron Microscope) using an in-lens secondary electron detector. It is a SEM image. FIG. 2 shows a cross section of the anode current collecting layer 111 made of Ni—Y ₂ O _{3. The} anode current collecting layer 111 is cross-sectioned by IM4000 of Hitachi High-Technologies Corporation after precision mechanical polishing. Ion milling processing is applied.

  FIG. 2 is an SEM image obtained by an FE-SEM (model: ULTRA55) manufactured by Zeiss (Germany) set at an acceleration voltage of 1 kV and a working distance of 2 mm. The size of one visual field shown in FIG. 2 is 7 μm long × 34 μm wide.

In the SEM image shown in FIG. 2, particles of Ni (an example of a transition metal), particles of Y ₂ O ₃ (an example of an oxygen ion insulating material), and pores are individually displayed depending on the difference in brightness. In FIG. 2, Ni particles are displayed as “white”, Y ₂ O ₃ particles as “gray”, and pores as “black”. However, in FIG. 2, a part of the outline of the pore is displayed as if it is whiteout.

In addition, the method of discriminating Ni particles, Y ₂ O ₃ particles, and pores is not limited to using the light / dark difference in the SEM image. For example, after obtaining element mapping by SEM-EDS in the same field of view, in comparison with a previously obtained FE-SEM image (including in-lens image and out-lens image) using an in-lens secondary electron detector, By identifying each particle in the SEM image, the Ni particles, the Y ₂ O ₃ particles, and the pores can be ternarized. At this time, each particle is identified by determining the low luminance region on the out-lens image as a pore, then determining the high luminance region in the region other than the pore on the in-lens image as a Ni particle, and setting the low luminance region as Y _2. O ₃ can be easily performed by determining the particle.

2. Analysis of SEM Image FIG. 3 is a diagram showing a result of image analysis of the SEM image shown in FIG. 2 using image analysis software HALCON manufactured by MVTec (Germany). In FIG. 3, a joining line between Ni particles and Y ₂ O ₃ particles, a boundary line between Ni particles and pores (hereinafter referred to as “first boundary line”), Y ₂ O ₃ particles and pores, The boundary line (hereinafter referred to as “second boundary line”) is highlighted with a solid line. As shown in FIG. 3, Ni particles and Y ₂ O ₃ particles are bonded to each other inside the anode current collecting layer 111. In addition, Ni particles and pores are adjacent at a plurality of locations, and Y ₂ O ₃ particles and pores are adjacent at a plurality of locations.

3. Average value of junction length between Ni particles and Y ₂ O ₃ particles FIG. 4 is a distribution graph showing a distribution of junction lengths between Ni particles and Y ₂ O ₃ particles. This distribution graph is created based on the analysis result of the image of one field of view shown in FIG. However, in the present embodiment, in the calculation of the average value of the bonding length, which will be described later, and the calculation of the standard deviation of the average value of the bonding length, the bonding portion of 0.2 μm or less recognized by the above-described image analysis software is used. Data is not used. According to the observation result at a higher magnification, the existence itself of the joint portion of 0.2 μm or less recognized by the above-described image analysis software is uncertain, and as a factor governing output performance and deterioration of the fuel electrode. This is because it is judged that it is better not to consider.

Here, the average value of the junction length between the Ni particles and the Y ₂ O ₃ particles (hereinafter referred to as “average value of the junction length”) is preferably 0.4 μm or more and 1.8 μm or less. The average value of the junction length is a value obtained by dividing the sum of the junction lengths of the Ni particles and the Y ₂ O ₃ particles by the number of junctions, and is 0.59 μm in the example shown in FIG. The average value of the joining length may be calculated from the analysis result in one visual field or a plurality of visual fields.

Such an average value of the joining length is an index indicating the neck thickness between the Ni particles and the Y ₂ O ₃ particles. That is, a neck having a necessary and sufficient thickness can be formed between the Ni particles and the Y ₂ O ₃ particles by controlling the average value of the joining length within a predetermined range. Therefore, it is possible to prevent the Ni particles from being changed in shape during the operation of the cell 10, so that the bond between the Ni particles can be prevented from being broken. As a result, it is possible to suppress a decrease in the output of the cell 10 by suppressing a decrease in the conductivity of the anode current collecting layer 111.

In order to adjust the average value of the joining length, for example, it is effective to control the particle size distribution of the NiO raw material powder and the Y ₂ O ₃ raw material powder. Further, the average value of the joining length can be finely adjusted by the average particle diameter and the addition amount of the pore former and the firing conditions. Hereinafter, an example of manufacturing conditions for controlling the average value of the junction length in the above-described range of 0.4 μm to 1.8 μm is shown.

-The average particle size of the NiO raw material powder is 0.3 to 2.8 µm and fine particles having a particle size of 0.1 µm or less are removed by classification treatment. · The average particle size of the Y ₂ O ₃ raw material powder is 0. 0.7 μm or more and 5.5 μm or less and removing fine particles having a particle size of 0.2 μm or less by classification treatment ・ The average particle size of the pore former should be 0.8 μm or more and 15 μm or less. _3. Addition amount is 25% by volume or less with respect to the ceramic raw material (NiO + Y ₂ O ₃ ). • The co-firing temperature is 1350 ° C. or more and 1500 ° C. or less, and the treatment time is 1 hour or more and 20 hours or less. Percentage of joints having a joint length greater than the average value Ratio of joints having a joint length greater than the average value among all joints of Ni particles and Y ₂ O ₃ particles (hereinafter referred to as “joint over average value”) It is preferable that it is 22.2% or more and 51.2% or less. In the distribution graph shown in FIG. 4, the joint location ratio equal to or higher than the average value corresponds to the ratio of the sum of the average frequency equal to or higher than 0.59 μm with respect to the total frequency, and is 32.1%. The joint portion ratio equal to or higher than the average value is an index indicating the difficulty of changing the shape of the Ni particles. That is, by controlling the joint portion ratio equal to or higher than the average value within a predetermined range, the change in the shape of the Ni particles is further suppressed, and the decrease in the conductivity of the anode current collecting layer 111 can be further suppressed.

In order to adjust the proportion of the joints that are equal to or greater than the average value, it is effective to control the particle size distribution of the NiO raw material powder and the Y ₂ O ₃ raw material powder as in the adjustment of the average value of the joint length. Moreover, the ratio of the joint location more than the average value can be finely adjusted depending on the material mixing method and firing conditions. Below, an example of the production conditions for controlling the joint location ratio of the average value or more to the range of 22.2% or more and 51.2% or less is shown.

The average particle size of the NiO raw material powder and the Y ₂ O ₃ raw material powder is set to 0.4 μm to 4.0 μm, and fine particles having a particle size of 0.2 μm or less and coarse particles of 10 μm or more are removed by classification treatment. Mix NiO raw material powder and Y ₂ O ₃ raw material powder (printing paste when formed by printing method) uniformly ・ Appropriate when making printing paste containing NiO raw material powder and Y ₂ O ₃ raw material powder After preparing a slurry with good dispersibility to which a suitable dispersant is added, the slurry is uniformly mixed by sufficient pot mill mixing and triroll mill mixing. The firing temperature is 1400 ° C. or higher and 1450 ° C. or lower, and the treatment time is 5 hours or longer 10 4. Less than time Variation in bonding length In an SEM image of 10 fields of view (3000 times magnification) arbitrarily acquired, the standard deviation of the average value of the bonding length between the transition metal particles and the oxygen ion insulating material particles is 0.52 or less. Preferably there is.

  The standard deviation of the average value of the junction length is an index indicating the variation in the neck thickness between the transition metal particles and the oxygen ion insulating material particles in the anode current collecting layer 111. That is, by reducing the standard deviation of the average value of the junction length, the Ni particles are less likely to change in shape locally, so that the conductivity of the anode current collecting layer 111 can be made uniform. Therefore, a decrease in the output of the cell 10 can be further suppressed.

The standard deviation of the average value can be adjusted by controlling the average particle diameter of the raw material powder, the mixing condition of the material forming the fuel electrode active layer, or the firing condition, in the same manner as the adjustment of the ratio of the joining points above the average value. is there. Furthermore, the standard deviation of the average value can be adjusted by controlling the mixing of impurities in the mixing process. By controlling the mixing of such impurities, it is possible to improve the structure controllability and ensure reproducibility during co-firing, and to improve the uniformity of the sintering progress of NiO particles and Y ₂ O ₃ particles. it can. Specifically, it is preferable to control the mixing of Si, B, Cr, P, S, etc. to about 200 ppm or less.

6). Porosity The anode current collecting layer 111 has a plurality of pores. The porosity of the anode current collecting layer 111 is preferably 20% or more and 50% or less. The porosity is an area occupancy ratio of all pores in the cross section of the anode current collecting layer 111 or a volume occupying ratio of pores with respect to a unit volume of the anode current collecting layer 111.

  The porosity in the anode current collecting layer 111 can be controlled by adjusting the amount of added pore forming agent and the particle size added when the anode current collecting layer 111 is produced.

7). The ratio of the isolated Ni particles The details of the Ni particles in the anode current collecting layer 111 will be described. In the FE-SEM image using the in-lens secondary electron detector, the difference in conductivity of each Ni particle can be output as the image contrast. Particles with high electrical conductivity, that is, high continuity with reliable electrical connection with surrounding Ni particles are displayed brightly, and particles with low electrical conductivity, that is, electrical connection with surrounding Ni particles are dark (See "Solid State lonics 178 (2008) 1984").

  It is also effective to confirm that the brightness of the Ni particles obtained from the FE-SEM image using the in-lens secondary electron detector represents the continuity of the Ni particles, that is, the difference in conductivity. . In order to confirm the continuity of Ni particles, a method of evaluating the resistance of each Ni particle using an atomic force microscope (AFM) in the same field of view by scanning the cross section with a cantilever to which a predetermined voltage is applied. Can be used. Specifically, first, based on the magnitude of the current, the region constituted by the Ni particles is classified into a region having conduction and a region having no conduction. Next, based on the analysis result, a region with continuity is determined as “continuous Ni particles”, and a region without continuity is determined as “isolated Ni particles”. The continuous Ni particles are Ni particles connected to at least one adjacent Ni particle, and the isolated Ni particles are Ni particles that exist independently without being connected to adjacent Ni particles.

  Here, the ratio of the occupied area of isolated Ni particles out of the total occupied area of Ni existing in one field of view (hereinafter referred to as “isolated Ni particle ratio”) is preferably 25% or less. The isolated Ni particle ratio is an index of conductivity of the anode current collecting layer 111. That is, the smaller the ratio of isolated Ni particles, the more the change in the conductivity of the anode current collecting layer 111 before and after the reduction process can be suppressed.

  Such a ratio of isolated Ni particles can be controlled, for example, by adjusting the powder characteristics (particle diameter, specific surface area) of NiO powder mixed in the slurry for the fuel electrode 11. The adjustment of the isolated Ni particle ratio can also be controlled by adjusting the firing time and the firing temperature, or by adjusting the particle size and the amount of the pore former.

In particular, it is important to use a material having high activity of NiO particles. By using a NiO raw material having a high specific surface area, bondability with other NiO or Y ₂ O ₃ is improved during firing, and the ratio of isolated Ni particles can be reduced even after reduction treatment. Specifically, it is preferable to use NiO particles having a specific surface area of 5 m ² / g to ²⁰ m ² / g as a raw material. However, when a raw material having a high specific surface area is used, it is necessary to add an effective dispersant (for example, a wet dispersant “DISPERBYK ^(R) -180” manufactured by Big Chemie Japan Co., Ltd. ⁾ during slurry adjustment. This is because, in a slurry with low dispersibility, the high specific surface area particles become aggregates, and rather the sinterability is hindered, resulting in an increase in the ratio of isolated Ni particles. The firing temperature is preferably from 1400 ° C. to 1450 ° C., and the treatment time is preferably from 5 hours to 10 hours.

  Note that continuous Ni particles and isolated Ni particles can also be determined by detecting in detail the brightness and darkness of Ni particles when an SEM image is analyzed by image analysis software. For example, in FIG. 2, among the areas uniformly classified as “white”, a bright area may be determined as “continuous Ni particles” and a dark area may be determined as “isolated Ni particles”.

  Further, in the above-described various methods relating to determination of continuous Ni particles and isolated Ni particles, a cross section obtained by actually cutting the sample of the cell 10 by machining along the thickness direction (stacking direction) is used. Is done. Therefore, it is considered that among the Ni particles distributed in the vicinity of the cross section, there may exist those that were continuous Ni particles before cutting but changed to isolated Ni particles after cutting (or vice versa). However, the proportion of Ni particles distributed in the vicinity of the cross section that changed from continuous Ni particles to isolated Ni particles (or vice versa) before and after cutting is considered to be very small. Therefore, the isolated Ni particle ratio calculated based on the cross section obtained by cutting the sample of the cell 10 by machining is substantially the same as the true isolated Ni particle ratio before the sample of the cell 10 is cut. Conceivable.

<< 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 state before firing.

First, a transition metal oxide raw material (for example, NiO), an oxygen ion insulating material (for example, Y ₂ O ₃ ), and a pore former (for example, PMMA (polymethyl methacrylate resin)) are mixed. At this time, by adjusting the particle size distribution of the transition metal oxide raw material and the oxygen ion insulating substance raw material, the transition metal particles and the oxygen ion insulating substance particles in the anode current collecting layer 111 after the reduction are reduced. Control is made so that the average value of the junction length is 0.4 μm or more and 1.8 μm or less.

  Next, a slurry is prepared by adding polyvinyl alcohol (PVA) as a binder to a mixture of a transition metal oxide raw material, an oxygen ion insulating material raw material, and a pore former.

  Next, this slurry is dried and granulated with a spray dryer to obtain a fuel electrode current collecting layer powder.

  Next, the anode current collector layer 111 is formed by molding the anode current collector layer powder by a die press molding method.

  Next, a transition metal oxide material (for example, NiO), an oxygen ion conductive material (for example, 8YSZ), and a pore former (for example, PMMA) are mixed.

  Next, a slurry is prepared by adding PVA as a binder to a mixture of a transition metal oxide raw material, an oxygen ion conductive material, and a pore former.

  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. Thus, a molded body of the fuel electrode 11 is formed.

  Next, a molded body of the solid electrolyte layer 12 is formed by applying / drying a slurry prepared by mixing a mixture of water and a binder to 8YSZ powder with a ball mill for 24 hours on the molded body of the fuel electrode 11. . However, a tape lamination method or a printing method may be used instead of the coating method.

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

  From the above, a laminate in which the molded bodies of the fuel electrode 11, the solid electrolyte layer 12, and the barrier layer 13 are sequentially laminated is formed.

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

  Next, a slurry is prepared by mixing a mixture of water and a binder with LSCF powder in 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.

<< 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, 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, the barrier layer 13, and the air electrode 14, and between the fuel electrode 11 and the solid electrolyte layer 12 and between the barrier layer 13 and the air electrode 14. Other 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.

  (B) Although the so-called vertical stripe fuel cell 10 has been described as an example of the solid oxide fuel cell in the above embodiment, the present invention is not limited to this. The fuel cell may be a horizontal stripe type, a fuel electrode support type, a flat plate type, or a cylindrical type. The cross section of the cell 10 may be elliptical.

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

[Production of Sample No. 1 to No. 21]
Samples No. 1 to No. 21 of the fuel electrode supporting cell using the fuel electrode current collecting layer as a supporting substrate were produced as follows.

First, a fuel electrode current collecting layer (NiO: Y ₂ O ₃ or CZO = 45: 55 (Ni volume% conversion)) having a thickness of 500 μm is formed by a die press molding method, and a fuel electrode active layer having a thickness of 20 μm is formed thereon. (NiO: 8YSZ = 40: 60 (Ni volume% conversion)) was formed by a printing method.

At this time, in the formation process of the anode current collecting layer, by adjusting the particle size distribution of Y ₂ O ₃ or CZO and the powder characteristics (particle size, specific surface area) of the NiO powder, as shown in Table 1, Adjust the average value of the junction length between transition metal particles and oxygen ion insulating substance particles in the pole current collector layer, the proportion of junctions above the average value, the standard deviation of the average junction length, and the ratio of isolated Ni particles. did. Furthermore, as shown in Table 1, the porosity in the anode current collecting layer was adjusted by adjusting the addition amount and particle size of the pore forming agent.

  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, a LSCF air electrode having a thickness of 30 μm was baked at 1000 ° C. for 2 hours, thereby preparing samples No. 1 to No. 21 of fuel electrode supported coin cells (φ15 mm).

[Observation of cross section of anode current collecting layer]
For samples No. 1 to No. 21, the cross section of the anode current collecting layer was observed.

  Specifically, first, the anode current collecting layer of each sample was subjected to precision mechanical polishing, and then subjected to ion milling processing using IM4000 of Hitachi High-Technologies Corporation.

  Next, an SEM image of a cross section of the anode current collecting layer enlarged by 3000 times was obtained by FE-SEM using an in-lens secondary electron detector (see FIG. 2).

  Next, the cross-sectional photograph shown in FIG. 2 was analyzed with image analysis software HALCON manufactured by MVTec (Germany), thereby detecting a bonding line between the Ni particles and the oxygen ion conductive material (see FIG. 3).

  Next, using the analysis result of the image analysis software, the average value of the junction length in the SEM image of one field of view, the proportion of the joint portion above the average value, and the proportion of isolated Ni particles were calculated. In addition, using the analysis result of the image analysis software, the standard deviation of the average value of the joining length was calculated in SEM images of arbitrary 10 fields of view. The calculation results were as shown in Tables 1 and 2.

[Measurement of change rate of conductivity]
Samples No. 1 to No. 21 were heated to 750 ° C. while supplying nitrogen gas to the fuel electrode side and air to the air electrode side, and reduced while supplying hydrogen gas to the fuel electrode when the temperature reached 750 ° C. The treatment was performed for 3 hours. Thereafter, with respect to Samples No. 1 to No. 21, the change rate (that is, the decrease rate) of the conductivity of the anode current collecting layer per 1000 hours was measured. In Table 1, the case where the rate of change in conductivity was 20% or less was evaluated as ◯, and the case where the rate of change in conductivity was 10% or less was evaluated as ◎.

  As shown in Table 1, it was found that the average value of the joining length is preferably 0.4 μm or more and 1.8 μm or less. This is because when the average value of the junction length is 0.4 μm or more, a sufficient neck thickness between the transition metal particles and the oxygen ion insulating material can be secured, and when the average value is 1.8 μm or less, the Ni particles This is because the ratio of the area to be bonded to other Ni particles on the surface of the surface was secured, and the continuity of the Ni particles could be maintained.

  Further, it has been found that such an effect can be obtained by ensuring a sufficient neck thickness between the transition metal particles and the oxygen ion insulating material, and does not depend on the type of the oxygen ion insulating material. Furthermore, it has been found that the same effect can be obtained even when Fe and Cu are included as transition metals in addition to Ni.

  Moreover, as Table 1 showed, it turned out that the change of electrical conductivity can be suppressed more by making the joint location ratio more than an average value into 22.2% or more and 51.2% or less.

  Further, as shown in Table 1, it was found that the change in conductivity can be further suppressed by setting the isolated Ni particle ratio to 25% or less.

  Further, as shown in Table 1, it was found that the change in conductivity can be further suppressed by setting the standard deviation of the average value of the junction length to 0.52 or less.

[Durability test]
In order to investigate the relationship between the concentration of the mixture (Si, P, Cr, B, S) in the anode current collecting layer and the deterioration rate, the above-mentioned sample was able to suppress the rate of change in conductivity of the anode current collecting layer Samples Nos. 4-1 to 4-5 were prepared by adjusting the mixing amount of the mixture in the anode current collecting layer as shown in Table 2 on the basis of No. 4. The mixture may be mixed in advance in the raw material for the anode current collecting layer, or may be mixed in the course of production.

Regarding Sample Nos. 4-1 to 4-5, the temperature was raised to 750 ° C. while supplying nitrogen gas to the electrode side and air to the air electrode side, and hydrogen gas was supplied to the fuel electrode when the temperature reached 750 ° C. The reduction treatment was performed for 3 hours. Thereafter, the voltage drop rate per 1000 hours was measured as the deterioration rate for each sample. 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.

  As shown in Table 2, the anode current collecting layer contains Si of 200 ppm or less, P of 50 ppm or less, Cr of 100 ppm or less, B of 100 ppm or less, and S of 100 ppm or less. It was confirmed that the deterioration rate of can be improved.

  Further, as shown in Table 2, the anode current collecting layer contains Si of 100 ppm or less, P of 30 ppm or less, Cr of 50 ppm or less, B of 50 ppm or less, and S of 30 ppm or less. Furthermore, it was confirmed that the deterioration rate of the fuel electrode can be improved. This is because the change in conductivity of the anode current collecting layer can be suppressed by mixing a small amount of Si, P, Cr, B, and S. It has been experimentally confirmed that it is preferable to mix at least 1 ppm of Si, P, Cr, B, and S.

DESCRIPTION OF SYMBOLS 10 Fuel cell 11 Fuel electrode 111 Fuel electrode current collection layer 112 Fuel electrode active layer 12 Solid electrolyte layer 13 Barrier layer 14 Air electrode

Claims (9)

A fuel electrode having a fuel electrode current collecting layer containing a transition metal and an oxygen ion insulating material; and a fuel electrode active layer formed on the fuel electrode current collecting layer;
The air electrode,
A solid electrolyte layer disposed between the fuel electrode active layer and the air electrode;
With
In the fuel electrode current collecting layer in a reduced state, the average value of the junction length between the transition metal particles and the oxygen ion insulating substance particles is 0.4 μm or more and 1.8 μm or less.
Fuel cell. In the anode current collecting layer, the content of silicon is 200 ppm or less, the content of phosphorus is 50 ppm or less, the content of chromium is 100 ppm or less, and the content of boron is 100 ppm or less. Yes, the sulfur content is 100 ppm or less,
The fuel battery cell according to claim 1. The content of each of silicon, phosphorus, chromium, boron and sulfur in the fuel electrode is 1 ppm or more.
The fuel battery cell according to claim 1 or 2. When one field of view of the cross section of the anode current collecting layer is observed by FE-SEM using an in-lens secondary electron detector, all the junctions between the transition metal particles and the oxygen ion insulating material particles are observed. Of these, the proportion of the joints having a joint length equal to or greater than the average value of the joint lengths is 22.2% or more and 51.2% or less.
The fuel cell according to any one of claims 1 to 3. When one field of view of the cross section of the anode current collecting layer is observed by FE-SEM using an in-lens secondary electron detector, it is not connected to the adjacent transition metal particles out of the total occupied area of the transition metal. The ratio of the area occupied by the transition metal present in is 25% or less,
The fuel cell according to any one of claims 1 to 4. When arbitrary 10 visual fields of the cross section of the anode current collecting layer are observed by FE-SEM using an in-lens secondary electron detector, the standard deviation of the average value of the junction length in the 10 visual fields is 0.52. Is
The fuel cell according to any one of claims 1 to 5. When one field of view of the cross section of the anode current collecting layer is observed by FE-SEM using an in-lens secondary electron detector, the proportion of pores is 20% or more and 50% or less.
The fuel cell according to any one of claims 1 to 6. The oxygen ion insulating material is a rare earth oxide or a zirconium composite oxide.
The fuel cell according to any one of claims 1 to 7. The transition metal is nickel;
The fuel cell according to any one of claims 1 to 8.