JP5097867B1 - Fuel cell - Google Patents

Abstract

A fuel battery cell capable of improving output is provided.
A fuel cell includes a fuel electrode containing nickel and an oxygen ion conductive material, an air electrode, and a solid electrolyte layer disposed between the fuel electrode and the air electrode. In the cross section, the fuel electrode has a region in which the average value of the joining length between the nickel particles and the oxygen ion conductive material particles is 0.4 μm or more and 0.9 μm or less.
[Selection] Figure 3

Description

  The present invention relates to a solid oxide fuel 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.

  Further, it is widely known that, for example, nickel oxide (NiO) and yttria-stabilized zirconia (YSZ) are used as the raw material powder of the fuel electrode (see, for example, Patent Document 1).

JP 2006-32132 A

However, when the fuel electrode contains, for example, Ni and YSZ after reduction, if NiO and YSZ, or if YSZ are not sufficiently joined together during firing, Ni will grow excessively in the state after reduction. This reduces the reaction field inside the fuel electrode. As a result, there is a problem that the resistance value of the fuel electrode increases and the output of the cell decreases.
Such a problem is not limited to the case where the fuel electrode contains Ni and YSZ after reduction, and similarly when Fe or Cu is contained in addition to Ni or when ScSZ, GDC or SDC is contained instead of YSZ. It will occur.

  The present invention has been made in view of the above-described situation, and an object thereof is to provide a fuel battery cell capable of improving output.

  The fuel cell according to the present invention includes a fuel electrode, an air electrode, and a solid electrolyte layer disposed between the fuel electrode and the air electrode. The fuel electrode includes nickel and an oxygen ion conductive material. In the cross section of the fuel electrode, the average value of the junction length between the nickel particles and the oxygen ion conductive material particles is 0.4 μm or more and 0.9 μm or less.

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

Sectional view showing the configuration of the fuel cell SEM image of cross section of anode active layer The figure which shows the analysis result of the SEM image shown in FIG. Distribution graph showing distribution of joint length between Ni particles and 8YSZ particles Analysis results of continuous Ni particles and isolated Ni particles (FE-SEM using in-lens secondary electron detector)

  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.

<< 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. In the present embodiment, the reduced fuel electrode 11 is assumed, but the concentration (mol ratio) of the composition constituting the fuel electrode 11 is substantially constant before and after the reduction.

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 contains nickel oxide (NiO) and / or nickel (Ni) as a transition metal. The anode current collecting layer 111 includes, as an oxygen ion conductive substance, zirconia-based materials such as yttria stabilized zirconia (8YSZ, 10YSZ, etc.) and scandia stabilized zirconia (ScSZ), and gadolinium doped ceria (GDC: (Ce, Gd). ) O ₂ ) or ceria-based materials such as samarium-doped ceria (SDC: (Ce, Sm) O ₂ ), or yttria (Y ₂ O ₃ ). 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 the oxygen ion conductive material can be 35 to 65% by volume. .

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 contains at least NiO and / or Ni as a transition metal. The anode active layer 112 may contain, in addition to NiO and / or Ni, Fe ₂ O ₃ (or FeO) and / or Fe, or CuO and / or Cu as a transition metal. The anode active layer 112 is made of, 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, Gd)). Ceria-based materials such as O ₂ ) and samarium-doped ceria (SDC: (Ce, Sm) O ₂ ) are included. 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 the oxygen ion conductive material can be 50 to 75% by volume. Thus, the anode active layer 112 may have a higher content of oxygen ion conductive material than the anode current collecting layer 111.

  The anode active layer 112 preferably contains 200 ppm or less of Si, 50 ppm or less of P, 100 ppm or less of Cr, 100 ppm or less of B, and 100 ppm or less of S. In this case, the anode active layer 112 further 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. Thereby, the durability of the fuel electrode 11 can be improved.

  The anode active layer 112 has a plurality of pores. The porosity in the anode active layer 112 is preferably 10% or more and 40% or less in a state after a known reduction process (for example, a process of reducing NiO to Ni in a hydrogen atmosphere at 800 ° C.). The porosity is, for example, the area occupation ratio of all the pores exposed in the cross section with respect to the cross sectional area of the fuel electrode active layer 112. However, the porosity may be a volume occupation ratio of all pores with respect to the volume of the fuel electrode active layer 112. The microstructure of the anode active layer 112 will be described later.

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 ceria (Ce) and a ceria-based material containing a rare earth metal oxide dissolved in Ce. 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.

  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.

<< Micro structure of anode active layer 112 >>
Hereinafter, the microstructure of the anode active layer 112 will be described with reference to FIGS. In the present embodiment, description will be made on the assumption that the fuel electrode 11 is in a reduced state.

(1) SEM image FIG. 2 shows a fuel electrode active layer 112 enlarged by a magnification of 3000 times by a field emission scanning electron microscope (FE-SEM) using an in-lens secondary electron detector. It is a cross-sectional SEM image. FIG. 2 shows a cross section of the fuel electrode active layer 112 made of Ni-8YSZ. The cross section of the fuel electrode active layer 112 is subjected to ion milling processing by IM4000 of Hitachi High-Technologies Corporation after precision mechanical polishing. It has been subjected. 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. One field of view shown in FIG. The size is 7 μm long × 34 μm wide.

  In this SEM image, Ni particles, 8YSZ particles, and pores are individually displayed according to the difference in brightness. In FIG. 2, Ni particles are displayed as “white”, 8YSZ particles are displayed as “black”, and pores are displayed as “grey”. Yes. 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, 8YSZ 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, Ni particles, 8YSZ particles, and pores can be ternized. 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 Ni particles, and defining the low-luminance region as 8YSZ particles. It can carry out simply by determining.

  In this embodiment, the Ni particles are an example of “transition metal particles”, and the 8YSZ particles are an example of “oxygen ion conductive substance particles”.

(2) Analysis of SEM Image FIG. 3 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. 3, the joining line between the Ni particles and the 8YSZ particles is indicated by a solid line, the boundary line between Ni particles and pores (hereinafter referred to as “first boundary line”) is indicated by a broken line, A boundary line with the pores (hereinafter referred to as “second boundary line”) is indicated by a one-dot chain line. As shown in FIG. 3, inside the anode active layer 112, Ni particles and 8YSZ particles are joined at a plurality of locations. Further, Ni particles and pores are adjacent at a plurality of locations, and 8YSZ particles and pores are adjacent at a plurality of locations.

(3) Joint Length Distribution Graph FIG. 4 is a distribution graph showing the joint length distribution of Ni particles and 8YSZ particles. This distribution graph is created based on the image analysis result of one visual field 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. The reason for this is that, according to the observation result at a higher magnification, the presence of the joint portion of 0.2 μm or less recognized by the above image analysis software is uncertain, and as a factor governing the output performance and the deterioration of the fuel electrode. It is because it was judged that it was not suitable to take into consideration.

  Here, it is preferable that the average value of the joining length of the Ni particles and the 8YSZ particles (hereinafter referred to as “average value of the joining length”) is 0.4 μm or more and 0.9 μm or less. The average value of the bonding length is a value obtained by dividing the sum of the bonding lengths of the Ni particles and the 8YSZ particles by the number of bonding points, and is 0.63 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, and the magnification of the SEM image is not limited to 3000 times.

  Such an average value of the joining length is an index indicating the neck thickness between the Ni particles and the 8YSZ particles. That is, by controlling the average value of the joining length within a predetermined range, a neck having a necessary and sufficient thickness can be formed between the Ni particles and the 8YSZ particles. Thereby, since the network of Ni particle and 8YSZ which is an aggregate can be joined firmly, the form change of Ni particle is suppressed and the reaction field in the fuel electrode active layer 112 can be ensured. As a result, the resistance value of the anode active layer 112 is reduced and the output of the cell 10 is improved.

In order to adjust the average value of the joining length, for example, it is effective to control the particle size distribution of the 8YSZ raw material powder and the NiO 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 or more and 0.9 μm or less is shown.
・ The average particle diameter of the raw material powder is 0.5 μm or more and 1.3 μm or less, and fine particles having a particle diameter of 0.2 μm or less are removed by classification treatment. ・ The average particle diameter of the pore former is 0.8 μm or more and 10 μm. The amount of pore forming material added is 20% by volume or less with respect to the ceramic raw material (8YSZ + NiO). 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. In addition, the ratio of joint portions having a joint length greater than or equal to the average value among all joint portions of Ni particles and 8YSZ particles (hereinafter referred to as “joint portion ratio greater than or equal to the average value”) is 25.9. % Or more and 48.9% or less is preferable. In the distribution graph shown in FIG. 4, the joint portion ratio equal to or higher than the average value corresponds to the ratio of the sum of frequencies equal to or higher than the average value of 0.63 μm with respect to the total frequency, and is 34.0%. 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. In other words, by controlling the ratio of the joining points that are equal to or higher than the average value within a predetermined range, the shape change of the Ni particles is further suppressed, and the durability of the anode active layer 112 can be improved.

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 8YSZ raw material powder and the NiO 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 manufacturing conditions for controlling the joint location ratio more than an average value to the above-mentioned range of 25.9% or more and 48.9% or less is shown.
・ The average particle size of the raw material (8YSZ, NiO) powder is 0.5 μm to 1.3 μm, and fine particles having a particle size of 0.3 μm or less and coarse particles of 2 μm or more are removed by classification treatment. Mix the material for forming the layer (print paste if it is formed by the printing method) ・ When preparing the print paste as the material for forming the anode active layer, dispersibility with appropriate dispersant 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 and 10 hours or shorter. The average value of the first boundary length (broken line) between the particles and the pores is preferably 0.2 μm or more and 0.7 μm or less. Moreover, it is preferable that the average value of the second boundary length (one-dot chain line) between the YSZ particles and the pores is 0.5 μm or more and 1.2 μm or less.

(4) Variation in bonding length In an SEM image of 10 fields of view (magnification 3000 times) arbitrarily acquired, the standard deviation of the average value of the bonding length of Ni particles and 8YSZ particles should be 0.48 or less. Is preferred. The standard deviation of the average value of the junction length is an index indicating the variation in the neck thickness between the Ni particles and the 8YSZ particles in the anode active layer 112. That is, by reducing the standard deviation of the average value of the junction length, the conductivity inside the anode active layer 112 becomes uniform, and current is prevented from concentrating and flowing in part of the anode active layer 112. it can. Therefore, it is possible to suppress a part of the anode active layer 112 from being acceleratedly deteriorated, so that the durability of the cell 10 can be further improved.

  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 8YSZ particles. Therefore, in order to control the standard deviation of the average value, it is particularly effective to suppress the variation in the junction length by controlling the mixing of impurities. Specifically, mixing of Si, B, Cr, P, S and the like may be controlled to about 200 ppm or less.

  In the SEM image of 10 fields of view (magnification 3000 times) arbitrarily acquired, the standard deviation of the average value of the first boundary length between the Ni particles and the pores is 0.2 or more and 0.6 or less. Is preferred. In addition, in an SEM image with 10 fields of view (magnification 3000 times) arbitrarily acquired, the standard deviation of the average value of the second boundary length between the YSZ particles and the pores is 0.6 or more and 1.0 or less. Is preferred.

(5) Ratio of Isolated Ni Particles FIG. 5 is an FE-SEM image using an in-lens secondary electron detector and shows the analysis results of continuous Ni particles and isolated Ni particles.

  Here, by using the in-lens secondary electron detector, the difference in conductivity of each Ni particle can be output as an 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").

  FIG. 5 is an FE-SEM image using an in-lens secondary electron detector. In order to confirm that the brightness of the obtained Ni particles indicates the continuity of Ni particles, that is, the difference in conductivity. Furthermore, the resistance of each Ni particle was evaluated 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 was applied. At this time, based on the magnitude of the current, the region constituted by the Ni particles was classified into a region having conduction and a region having no conduction. From the analysis result, a region with continuity is determined as “continuous Ni particles”, and a region without continuity is determined as “isolated Ni particles”. That is, continuous Ni particles are Ni particles that are connected to at least one adjacent Ni particle, and isolated Ni particles are Ni particles that exist independently without being connected to adjacent Ni particles. In FIG. 5, isolated Ni particles are surrounded by a solid line, and continuous Ni particles are surrounded by a broken line.

  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 active layer 112. That is, since the reaction resistance of the fuel electrode active layer 112 can be reduced as the ratio of isolated Ni particles is smaller, the output of the cell 10 can be further maintained.

  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 8YSZ 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 1400 ° C. or higher and 1450 ° C. or lower, and the treatment time is preferably 5 hours or longer and 10 hours or shorter.

  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 regions classified uniformly as “gray”, a bright region may be determined as “continuous Ni particles” and a dark region 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, polyvinyl alcohol (PVA) is added as a binder to a mixture of NiO powder (an example of a transition metal), YSZ powder (an example of an oxygen ion conductive material), and a pore former (for example, PMMA (polymethyl methacrylate resin)). To prepare a slurry. 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.

  In this embodiment, by adjusting the particle size distribution of the zirconia-based material and the amount of pore-forming agent added in this step, the average value of the junction length in the anode active layer 112 formed by the subsequent co-firing, the average Control is performed so that each of the proportions of the joining points equal to or greater than the value and the standard deviation of the average value of the joining lengths are within the desired range described above. Further, by adjusting the powder characteristics (particle size, specific surface area) of the NiO powder, the ratio of isolated Ni particles in the fuel electrode active layer 112 is controlled to fall within a desired range.

  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 electrolyte membrane 120. 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 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. Thus, the cell 10 is completed.

<< 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 description has been made with a focus on the fine structure of the anode active layer 112. However, the anode current collecting layer 111 is made of the same material as the anode active layer 112 (for example, Ni-8YSZ). In the case of being configured, the fuel electrode 11 only needs to have a region where the average value of the junction length is 0.4 μm or more and 0.9 μm or less in the vicinity of the interface with the solid electrolyte layer 12. This is because a desired effect can be obtained at least in this region. In this region, as described in the above embodiment, it is preferable that the ratio of the joining points greater than the average value is 25.9% or more and 48.9% or less, and the joining length between the Ni particles and the 8YSZ particles. The standard deviation of the average value is preferably 0.48 or less.

  (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, 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.

(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 above embodiment, the anode active layer 112 includes at least NiO and / or Ni as a transition metal. However, the present invention is not limited to this. The anode active layer 112 may include a transition metal other than Ni and / or an oxide of a transition metal other than Ni instead of NiO and / or Ni. Examples of such transition metals or oxides thereof include Fe ₂ O ₃ (or FeO) and / or Fe, CuO and / or Cu, and the like. The anode active layer 112 may contain a mixture of a plurality of transition metals (or oxides).

  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.

[Production of sample No. 1 to No. 49]
Samples No. 1 to No. 49 of the fuel electrode support type cell using the fuel electrode current collecting layer as a support substrate were produced as follows.

First, a fuel electrode current collector 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 having a thickness of 20 μm is formed thereon by a printing method. did. In samples No. 1 to No. 20, Ni as a transition metal and 8YSZ as an oxygen ion conductive material were used as raw materials for the fuel electrode active layer. In samples No. 21 to No. 26, Ni as a transition metal and 10YSZ as an oxygen ion conductive material were used as raw materials for the fuel electrode active layer. In Samples Nos. 27 to 32, Ni as a transition metal and ScSZ as an oxygen ion conductive material were used as raw materials for the fuel electrode active layer. In samples No. 33 to No. 38, Ni and Fe as transition metals and 8YSZ as an oxygen ion conductive material were used as raw materials for the fuel electrode active layer. In samples No. 39 to No. 42, Ni and Cu as transition metals and 8YSZ as an oxygen ion conductive material were used as raw materials for the fuel electrode active layer. In samples No. 43 to No. 47, Ni as a transition metal and GDC as an oxygen ion conductive material were used as raw materials for the fuel electrode active layer. The mixing ratio of the transition metal to the oxygen ion conductive material (transition metal: oxygen ion conductive material) was as shown in Table 1.
In samples No. 48 and No. 49, Ni as a transition metal and 8YSZ as an oxygen ion conductive material were used as raw materials for the fuel electrode active layer. In sample No. 48, the mixing ratio of transition metal and oxygen ion conductive material was 40:60, and in No. 49, the mixing ratio of transition metal and oxygen ion conductive material was 45:55.
In addition, as shown in Tables 1 and 2, by adjusting the particle size distribution of 8YSZ, the amount of pore-forming agent added, and the powder characteristics (particle size, specific surface area) of the NiO powder in the molding process of the fuel electrode active layer, The average value of the junction length in the fuel electrode active layer, the proportion of the junctions above the average value, the standard deviation of the average value of the junction length, and the ratio of isolated Ni particles were varied.

  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 anode active layer to produce 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 to prepare Samples No. 1 to No. 49 of fuel electrode supported coin cells (φ15 mm).

[Observation of cross section of anode active layer]
For samples No. 1 to No. 49, the cross section of the anode active layer was observed.

  Specifically, first, the anode active 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 active layer magnified 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 junctions where the average value was exceeded, 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.

[Output density measurement]
For samples No. 1 to No. 47, the temperature was raised to 750 ° C. while supplying nitrogen gas to the fuel electrode side and air to the air electrode side. When the temperature reached 750 ° C., reduction was performed while supplying hydrogen gas to the fuel electrode. The treatment was performed for 3 hours. Thereafter, the output densities of samples No. 1 to No. 47 were measured. As the output density, a value at a temperature of 750 ° C. and a rated voltage of 0.8 V was used.

The measurement results are summarized in Table 1. In Table 1, an output density of 600 mW / cm ² or higher is evaluated as a high output state. As is apparent from Table 1, it was found that the average value of the joining length is preferably 0.4 μm or more and 0.9 μm or less. This is because when the average value of the junction length is 0.4 μm or more, the neck thickness between the Ni particles and the oxygen ion conductive material can be sufficiently secured, and when it is 0.9 μm or less, sufficient electrochemical This is because the reaction area can be secured.
Further, it has been found that such an effect can be obtained by ensuring a sufficient neck thickness between the Ni particles and the oxygen ion conductive material, and does not depend on the type of the oxygen ion conductive 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.

[Durability test 1]
Regarding the 12 types of samples shown in Table 2, the temperature is raised to 750 ° C. while supplying nitrogen gas to the fuel electrode side and air to the air electrode side, and hydrogen gas is supplied to the fuel electrode when the temperature reaches 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.

  Table 2 summarizes the measurement results. In Table 2, a deterioration rate of 1.5% or less is evaluated as a low deterioration state.

  As can be seen from Table 2, it was found that the proportion of joints above the average value is preferably 25.9% or more and 48.9% or less. This is because the joint portion ratio is 25.9% or more, it is possible to make it difficult to change the shape of the Ni particles, and when it is 48.9% or less, a sufficient electrochemical reaction region can be secured, This is because an excessive increase in overvoltage can be suppressed.

  Further, as can be seen from Table 2, it was found that the isolated Ni particle ratio is preferably 25% or less. This is because the reaction resistance of the fuel electrode active layer is reduced and the output is easily maintained by setting the isolated Ni particle ratio to 25% or less.

  However, the sample numbers shown in Table 2 No. 13, although the isolated Ni particle ratio is an appropriate value of 8.5%, the average value of the junction length was too large at 0.92, so that other samples can obtain better results. could not. From this, it was found that the deterioration rate is more easily rate-controlled by the average value of the junction length than the ratio of isolated Ni particles.

  Further, as apparent from Table 2, it was found that the standard deviation of the average value of the joining length is preferably 0.48 or less. This is because the standard deviation of the average value is 0.48 or less, the conductivity inside the anode active layer becomes uniform, and current can be prevented from concentrating and flowing in part of the anode active layer. This is because.

  However, sample No. shown in Table 1 9, although the standard deviation of the average value of the joint length is 0.45, which is an appropriate value, the average value of the joint length is too small, 0.32, and thus good results can be obtained. could not. From this, it was found that the power density is more easily rate-controlled by the average value of the junction length than the standard deviation of the average value.

[Durability test 2]
In order to investigate the relationship between the concentration of the mixture at the fuel electrode and the deterioration rate, a sample was prepared by adjusting the mixing amount of the mixture as shown in Table 3 on the basis of sample No. 7 where a good power density was obtained. Nos. 7-1 to 7-5 were produced. Here, the mixture is silicon (Si), phosphorus (P), chromium (Cr), boron (B), and sulfur (S). The mixture may be mixed in advance in the raw material of the fuel electrode, or may be mixed during the manufacturing process.

For Sample Nos. 7-1 to 7-5, when the temperature was raised to 750 ° C. while nitrogen gas was supplied to the fuel electrode side and air was supplied to the air electrode side as in the above durability test 1, the temperature reached 750 ° C. Then, reduction treatment was performed for 3 hours while supplying hydrogen gas to the fuel electrode. 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 3, the deterioration rate of the fuel electrode is reduced by containing 200 ppm or less of Si, 50 ppm or less of P, 100 ppm or less of Cr, 100 ppm or less of B, and 100 ppm or less of S. It was confirmed that it could be improved.

  Further, as shown in Table 3, by containing 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, the fuel electrode further It was confirmed that the deterioration rate can be improved.

  Such a result was obtained because the mixed Si, P, Cr, B and S could stabilize the porous structure during firing and reduction. Specifically, by mixing the mixture, the sinterability of the fuel electrode was improved, and the skeleton of the fuel electrode, which is a porous body, could be strengthened. On the other hand, by controlling the mixing amount of the mixture to a very small amount, the sintering of Ni during long-term operation was suppressed, and the reduction of the reaction field in the fuel electrode could be suppressed.

  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 (8)

A fuel electrode containing nickel and an oxygen ion conductive material;
The air electrode,
A solid electrolyte layer disposed between the fuel electrode and the air electrode;
With
The fuel electrode has a region in which the average value of the junction length between the nickel particles and the oxygen ion conductive material particles is 0.4 μm or more and 0.9 μm or less in a cross section.
Fuel cell. The fuel electrode contains silicon, phosphorus, chromium, boron and sulfur,
The silicon content in the fuel electrode is 200 ppm or less,
The phosphorus content in the fuel electrode is 50 ppm or less,
The chromium content in the fuel electrode is 100 ppm or less,
The content of boron in the fuel electrode is 100 ppm or less,
The sulfur content in the fuel electrode is 100 ppm or less.
The fuel battery cell according to claim 1. When one field of view of the cross section of the fuel electrode is observed by FE-SEM using an in-lens secondary electron detector, the junction length among all junctions of nickel particles and oxygen ion conductive material particles The proportion of joints having a joint length equal to or greater than the average value is 25.9% or more and 48.9% or less.
The fuel battery cell according to claim 1 or 2. Of the total occupied area of nickel present in the one field of view, the proportion of the occupied area of nickel alone without being connected to the adjacent nickel particles is 25% or less.
The fuel battery cell according to claim 3. When arbitrary 10 visual fields of the cross section of the fuel electrode 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 0.48 or less. is there,
The fuel cell according to any one of claims 1 to 4. The oxygen ion conductive material is yttria stabilized zirconia,
The fuel cell according to any one of claims 1 to 5.   The fuel cell according to any one of claims 1 to 6, wherein a ratio of pores in the one visual field is 10% or more and 40% or less. The anode is composed of an anode current collecting layer, and an anode active layer disposed between the anode current collecting layer and the solid electrolyte layer,
The region where the average value of the junction length is 0.4 μm or more and 0.9 μm or less is the fuel electrode active layer,
The fuel cell according to any one of claims 1 to 7.