JP4819568B2 - Solid oxide fuel cell and method for producing the same - Google Patents

Description

  The present invention relates to a solid oxide fuel cell composed of an electrolyte layer made of an oxide such as ceramics and a method for producing the same.

  Solid oxide fuel cells have higher electrical conversion efficiency and power density than other types of fuel cells. For this reason, solid oxide fuel cells are being actively developed as distributed power sources, which are relatively small and medium-sized power generation facilities that are arranged and used in areas where power sources are demanded or in the vicinity thereof. Solid oxide fuel cells generally have an electrolyte composed of zirconia stabilized by scandia or yttria, and an air electrode composed of lanthanum manganite to which a rare earth is added. Nickel oxide (NiO) The fuel electrode is composed of a mixture of and stabilized zirconia, and all the constituent parts are ceramic materials, and have a laminated structure of different materials. Thus, since solid oxide fuel cells use oxide oxide ceramics as an electrolyte, the operating temperature is higher than that of other fuel cells in order to ensure sufficiently high ion conductivity.

  The solid oxide fuel cell having such characteristics is often used as a stack structure in which a plurality of single cells are combined, and the cell structure is large and can be divided into a cylindrical type and a flat plate type. From the viewpoint of cell performance, there are many electrode-supported flat plate cells using an air electrode or a fuel electrode as a support. The advantage of the electrode-supported cell is that the electrolyte layer having the highest resistance among the constituent materials of the cell can be made as thin as several μm to several tens of μm. As the electrolyte layer becomes thinner, the internal resistance of the cell is reduced, so that an improvement in output can be expected. In an electrode-supported cell, either an air electrode or a fuel electrode can be applied as a support electrode. However, the resistance of a fuel electrode containing metallic nickel as the electrode material is smaller, and the IR resistance when applied to a substrate is suppressed. Therefore, more and more fuel electrode-supported cells are being developed.

  FIG. 5 is a cross-sectional view showing the structure of a conventional fuel electrode-supported flat plate fuel cell. As shown in FIG. 5, an electrolyte layer 502 and an air electrode 503 are laminated on a fuel electrode 501 serving as a support substrate. Thus, in the fuel electrode supporting cell, since the fuel electrode 501 bears the strength of the cell, the thickness of the fuel electrode 501 is usually required to be about 0.5 to 1 mm, and occupies most of the volume of the cell. For this reason, in the fuel electrode support type cell, the power generation characteristics are greatly affected by the performance of the fuel electrode.

  FIG. 6 is an explanatory diagram for explaining a power generation reaction in a solid oxide fuel cell. FIG. 6 schematically shows an enlarged partial cross section of the fuel cell. As shown in FIG. 6, in the solid oxide fuel cell, a porous fuel electrode 601 and a porous air electrode 603 are arranged on one side of a dense electrolyte layer 602. The fuel electrode 601 and the air electrode 603 are sintered bodies, are composed of a plurality of sintered body fine particles, and are in a state in which spaces (holes) are formed between the sintered body fine particles.

  When hydrogen gas is supplied as a fuel gas to the fuel electrode 601 having such a structure and oxygen is supplied as an oxidant gas to the air electrode 603, each of the supplied gases diffuses in the holes in the electrodes, It reaches the electrode / electrolyte interface and the power generation reaction proceeds. In addition, in the power generation reaction, electrons flow in addition to these gas flows. Electrons move through the part of the particles (bulk) that make up the electrode. In this way, the electrons move in the part of the particles that are continuously connected to each electrode, the gas moves in the part of the pores between the particles, and at the three-layer interface (reaction field) between the electrode, electrolyte, and gas. The power generation reaction proceeds.

  The power generation reaction is performed at the three-layer interface, and in order for the power generation reaction to proceed efficiently, a structure in which more three-layer interfaces exist is desirable. It can be said that the electrode is highly active. For example, a powder having a finer average particle diameter is sintered to form an electrode, and a structure in which finer sintered particles and fine pores between them are densely formed is used. It is possible to increase the layer interface.

  In addition, the power generation efficiency of the fuel cell is simply expressed as “power generation efficiency = operating voltage / theoretical voltage × fuel utilization rate”, and is expressed by the product of the fuel cell voltage efficiency and the fuel utilization rate. It is important to generate electricity with voltage and higher fuel utilization. Of these, in order to achieve higher operating voltage, it is important to reduce the internal resistance (IR, reaction resistance, etc.) of the fuel cell (cell). It is important to realize an electrode structure with many phase interfaces. In addition, in order to generate power at a higher fuel utilization rate, it is important to supply a good gas to the electrode reaction field (three-layer interface).

Kazuhiko Nozawa, et al., "FABRICATION AND CHARACTERIZATION OF SOFC CELLS WITH ScSZ ELECTROLYTE AND LaNi1-xFexO3 CATHODE FOR REDUCED TEMPERATURE OPERATION", Electrochemical Society Proceedings, Vol.2001-16, pp.983-988,2001.

  By the way, in the fuel electrode-supported cell, the fuel electrode is formed thick, so that the diffusion distance of the reaction gas in the fuel electrode is large, and gas diffusion inside the fuel electrode is necessary for good gas supply to the reaction field. It is important to improve performance. Usually, from the viewpoint of gas diffusion, it is desirable that the electrode has a high porosity and a large average pore diameter. However, from the viewpoint of the electrode reaction activity described above, there is a problem that if large pores are present at the interface portion between the electrode and the electrolyte, the three-phase interface as a reaction field is reduced and the electrode performance is deteriorated.

  In addition, the fuel electrode support cell is characterized by the thinning of the electrolyte layer, and the advantage of thinning the electrolyte layer is that the warpage of the cell can be suppressed in addition to the reduction of the internal resistance of the cell. In the flat cell, the warp of the cell greatly affects the strength in stacking and the state of current collection. In a fuel electrode-supported cell, a paste layer made of a material that serves as a fuel electrode and a paste layer made of a material that serves as an electrolyte are laminated and then sintered to form an electrolyte layer on the fuel electrode. Yes. In the solid oxide fuel cell formed in this way, in general, the electrolyte tends to have higher sinterability and higher shrinkage than the anode, but the thickness of the electrolyte is larger than the thickness of the anode substrate. It has been confirmed that cell warpage is suppressed as the thickness is reduced.

  However, as the electrolyte layer becomes thinner, the strength of the electrolyte layer becomes smaller, so that damage such as generation of cracks is likely to occur during the sintering process, and the frequency of occurrence of leakage tends to increase. In particular, damage is likely to occur due to the presence of the pore former added from the viewpoint of ensuring the porosity of the fuel electrode. In general, the pore former is often an organic material such as a polymer or carbon and burns in a temperature range of 200 to 700 ° C. to vaporize, thereby forming a hole at a position where the pore former was present. Is. For this reason, the electrolyte layer is easily damaged by the gas pressure when the pore former is vaporized. When the electrolyte layer is damaged in this manner and a leak path is present, a short circuit of the fuel cell, mixing of gas, etc. occur, leading to a decrease in power generation efficiency and a decrease in cell performance. As described above, in the fuel electrode support type solid oxide fuel cell, the damage generated in the electrolyte layer is a serious problem in the production of the fuel cell.

  The present invention has been made to solve the above-described problems, and in the anode-supported solid oxide fuel cell, the configuration capable of generating power with higher efficiency suppresses damage to the electrolyte layer. It is intended to be able to be manufactured in the state where it is made.

A method for producing a solid oxide fuel cell according to the present invention includes a fuel electrode substrate that is formed of a sintered body and serves as a support substrate, and an electrolyte layer that is formed of a sintered body provided on the fuel electrode substrate. And a method for producing a solid oxide fuel cell comprising an air electrode provided on the electrolyte layer, and a mixed powder obtained by mixing a metal oxide powder with a zirconia oxide powder. A first step in which an unsintered fuel electrode substrate is formed from a first slurry formed by adding a pore material, and a mixed powder is formed on the unsintered fuel electrode substrate. A second step in which an unsintered fuel electrode intermediate layer is formed from the second slurry; and a third slurry formed of zirconia-based oxide powder on the unsintered fuel electrode intermediate layer A third step in which a more unsintered electrolyte layer is formed, an unsintered fuel electrode substrate, The sintered fuel electrode intermediate layer and the unsintered electrolyte layer are heated to form a sintered fuel electrode substrate, a sintered fuel electrode intermediate layer, and a sintered electrolyte layer. A fourth step and a fifth step in which an air electrode is formed on the electrolyte layer, wherein the pore former is composed of powder that is vaporized by heating , and the fuel electrode is connected to the fuel electrode substrate. consist of a fuel electrode intermediate layer, towards the fuel electrode substrate as compared to the fuel electrode the intermediate layer, it formed a higher porosity.

In the method for producing a solid oxide fuel cell, the second slurry has a smaller amount of pore former having a particle size smaller than that of the pore former added to the first slurry than the pore former added to the first slurry. in so that is added. In addition, 10-18 wt% of a pore former having an average particle diameter of 8-12 μm is added to the first slurry, and 8 wt% of a pore former having an average particle diameter of 2-5 μm is added to the second slurry. you like is added.

  In the method for manufacturing a solid oxide fuel cell, the particle size of the metal oxide powder mixed in the second slurry is smaller than the particle size of the metal oxide powder mixed in the first slurry. You may be made to do. Further, it is better to form the fuel electrode intermediate layer thicker as the amount of the pore former added to the first slurry is larger. The pore former may be carbon powder, and the metal oxide may be nickel oxide. In this case, nickel oxide powder having an average particle diameter of 3 to 5 μm is mixed in the first slurry, and nickel oxide powder having an average particle diameter of 1 to 2 μm is mixed in the second slurry. What should I do?

  The solid oxide fuel cell according to the present invention is manufactured by the above-described manufacturing method.

  As described above, in the present invention, the unsintered fuel from the first slurry formed by adding the pore former to the mixed powder obtained by mixing the metal oxide powder with the zirconia oxide powder. An electrode substrate is formed, and an unsintered fuel electrode intermediate layer is formed from the second slurry formed from the mixed powder, and a zirconia-based oxide powder is formed thereon. An unsintered electrolyte layer was formed from the three slurries, and thereafter, these were sintered. As a result, according to the present invention, the anode substrate is formed to have a higher porosity than the anode intermediate layer, and in the anode-supported solid oxide fuel cell, A structure capable of generating power with high efficiency can be manufactured in a state where damage to the electrolyte layer is suppressed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a process diagram showing an example of a method for producing a solid oxide fuel cell according to an embodiment of the present invention. Hereinafter, the single cell portion of the solid oxide fuel cell will be described. First, as shown in FIG. 1A, a plurality of fuel electrode green sheets 121a having a film thickness of 300 to 600 μm are stacked to form an unfired fuel electrode substrate sheet 121 having a film thickness of about 1.2 mm. And FIG. 1A shows a state in which three fuel electrode green sheets 121a having a film thickness of 400 μm are stacked to form a fuel electrode substrate sheet 121 having a film thickness of 1.2 mm.

For example, zirconia (alumina-added scandium-stabilized zirconia: SASZ) powder (average particle size: 0.5 to 0.6 μm) to which Sc ₂ O ₃ and Al ₂ O ₃ are added, and nickel oxide powder A body (average particle size 3 to 5 μm, specific surface area 0.8 to 1.5 m ² / g) is added, and a pore former made of carbon powder having an average particle size 8 to 12 μm is added. A binder and a surfactant are added, and a slurry in which these are dispersed in a dispersion medium composed of an organic solvent such as 2-propanol is prepared. The added amount of the pore former is 10 to 18 w%. Since the added carbon powder burns and vaporizes during sintering, voids are formed at the locations where the carbon particles were present. The pore former is not limited to carbon powder, and any other material may be used as long as it is a material that can be vaporized and form pores during sintering.

  Next, the produced slurry was formed by, for example, a well-known doctor blade method to form a slurry layer, and the dispersion medium was removed from the slurry layer and dried to form the fuel electrode green sheet 121a. State. The dispersion medium is not limited to alcohol solvents such as 2-propanol, and other organic solvents such as toluene, xylene, and ketones may be used. In addition to the organic solvent, a slurry in which the mixed powder is dispersed in water may be used. For example, by using a predetermined surfactant, the mixed powder can be dispersed in water.

Next, as shown in FIG. 1B, a fuel electrode intermediate green sheet 122 having a film thickness of 30 to 300 μm is laminated on the fuel electrode substrate sheet 121. For example, first, SASZ powder (average particle size 0.5 to 0.6 μm) and nickel oxide powder (average particle size 1 to ² μm, specific surface area 6 to 8 m ² / g) are mixed and added. Then, a pore former made of carbon powder having an average particle diameter of 2 to 5 μm is added to prepare a slurry in which these are dispersed in the same dispersion medium as described above. The maximum amount of pore former added is 8 w%.

  Next, the produced slurry is formed by a doctor blade method to form a slurry layer, and the dispersion medium is removed from the slurry layer to dry the fuel electrode intermediate green sheet 122. The fuel electrode intermediate green sheet 122 formed in this way is laminated on the fuel electrode substrate sheet 121, and these are hot pressed. The fuel electrode intermediate green sheet 122 may be formed not only by the doctor blade method but also by screen printing.

  Next, as shown in FIG. 1C, an electrolyte layer green body 123 is formed on the fuel electrode intermediate green sheet 122. For example, a SASZ powder (average particle size of 0.5 to 0.6 μm) is dispersed in a predetermined medium to prepare a slurry, and the slurry prepared by screen printing is applied onto the fuel electrode intermediate green sheet 122. The coating film is formed. By performing this application a plurality of times and laminating the coating film, an electrolyte layer green body 123 having a film thickness of 7 to 20 μm is formed.

  Next, after the electrolyte layer green body 123 formed by coating is dried, the laminated structure including the fuel electrode substrate sheet 121, the fuel electrode intermediate green sheet 122, and the electrolyte layer green body 123 is heated, and these are sintered. State. Further, the outer diameter of the sintered body is processed so as to have a predetermined dimension, and as shown in FIG. 1D, the fuel electrode intermediate layer 102 is formed on the fuel electrode substrate 101, and the fuel electrode intermediate layer 102 is formed. An electrolyte layer 103 is formed on the substrate.

  By setting it as a sintered compact, the film thickness of the electrolyte layer 103 will be about 5-16 micrometers, and the film thickness of the fuel electrode intermediate | middle layer 102 will be about 23-240 micrometers. The fuel electrode substrate 101 has a porosity of 28 to 33% and an average pore diameter of 0.62 to 0.75 μm, and the fuel electrode intermediate layer 102 has a porosity of 6 to 20% and an average pore diameter of 0.1. 15 to 0.25 μm. In addition, a porosity and an average pore diameter are the results measured by the mercury intrusion method. As is well known, according to the mercury intrusion method, it is possible to see a wide pore size distribution of 7 nm to 400 μm, such as average pore size, porosity, pore volume, and pore specific surface area. Information on the pore size distribution can be obtained.

Thereafter, as shown in FIG. 1 (e), by setting the air electrode 104 on the electrolyte layer 103, a state in which the cells of the solid oxide fuel cell are formed can be obtained. The air electrode 104 is, for example, a powder sintered body having an average particle diameter of about 1 μm made of LaNi (Fe) O ₃ doped with iron (Fe) at the B site. In addition, each average particle diameter mentioned above is the value measured on the particle size distribution measurement conditions shown next. Measuring device: Laser diffraction / scattering particle size distribution measuring device LA-910 manufactured by HORIBA, Ltd. Measurement mode: Manual flow cell measurement. Measurement range: 0.02 μm to 1000 μm. Dispersion medium: 200 ml of ion exchange water. Dispersion method: Measurement is performed by irradiating the sample with ultrasonic waves for 5 minutes in the measurement apparatus. Refractive index: 1.40-0.00i.

  According to the solid oxide fuel cell shown in FIG. 1E manufactured as described above, the electrolyte layer 103 is formed in a leak-free state even when the film thickness is as thin as 5 to 16 μm. As described above, since the thin electrolyte layer 103 can be formed in a leak-free state, the internal resistance of the cell can be reduced. In addition, since the fuel electrode substrate 101 has a high porosity and a large pore diameter, high gas diffusibility is ensured. On the other hand, since the fuel electrode intermediate layer 102 has a low porosity and a small pore diameter, a state where more three-layer interfaces exist is obtained, and a high electrode activity is obtained.

  According to the solid oxide fuel cell in the present embodiment described above, the fuel electrode substrate 101 mainly responsible for gas diffusion of the fuel electrode and the fuel electrode intermediate layer 102 in contact with the electrolyte layer 103 are laminated. Thus, both high electrode activity and good gas diffusivity can be achieved. Thereby, high output is realized even under power generation conditions with a high fuel utilization rate, and the power generation efficiency of the fuel cell is improved. In addition, since the fuel electrode intermediate layer 102 adjacent to the electrolyte layer 103 has a structure having a small pore diameter, defects in the electrolyte layer 103 that occur when these are simultaneously sintered are suppressed, and the thickness of the cell can be reduced. The flatness of the is improved. This suppresses cell damage during stacking, thereby improving the reliability of the cell stack.

  Here, the production of a thin electrolyte layer without leakage will be described. Here, two sample cells (first sample cell and second sample cell) having different porosity and pore diameter (average pore diameter) in the fuel electrode were prepared, and the state of the electrolyte layer in these two sample cells was investigated. The results will be described. First, an unfired fuel electrode having a thickness of about 1.2 mm is prepared by stacking a plurality of fuel electrode green sheets having a thickness of 300 to 600 μm in the same manner as described above.

In the first sample cell, SASZ powder (average particle size 0.5 to 0.6 μm) and nickel oxide powder (average particle size 3 to 5 μm, specific surface area 0.8 to 1.5 m ² / g). And a slurry added with carbon powder in an average particle size range of 8 to 12 μm. The addition amount of carbon powder shall be 10-20 w%.

On the other hand, in the second sample cell, SASZ powder (average particle size 0.5 to 0.6 μm) and nickel oxide powder (average particle size 1 to ² μm, specific surface area 6 to 8 m ² / g) And a slurry added with carbon powder in an average particle size range of 2 to 5 μm is used. The amount of carbon powder added is 7 to 10 w%.

  Next, an electrolyte green body is laminated on the laminated structure of each fuel electrode green sheet. First, a SASZ powder (average particle size 0.5 to 0.6 μm) is dispersed in a predetermined medium to prepare a slurry, and the slurry prepared by a screen printing method is applied onto a laminate of fuel electrode green sheets. Then, the coating film is formed. By applying this coating a plurality of times and laminating the coating film, an electrolyte green body is formed in a thickness range of 7 to 16 μm.

  Thus, after laminating | stacking the green body of electrolyte, these are sintered and it is set as the state in which the 1st sample cell and the 2nd sample cell were formed. By sintering, the electrolyte layer has a thickness of 5 to 14 μm. Moreover, in the first sample cell, the fuel electrode has a porosity of 30 to 33% and an average pore diameter of 0.62 to 0.75 μm by sintering. In the second sample cell, the fuel electrode has a porosity of 27 to 30% and an average pore diameter of 0.23 to 0.3 μm.

  In the first sample cell thus fabricated, a large number of leaks were observed in the electrolyte layer formed to a thickness of about 10 μm. On the other hand, in the second sample cell, no leakage was observed in the electrolyte layer until the film thickness was about 10 μm.

  From these results, it is considered that when the carbon powder having an average particle diameter of 8 to 12 μm is added as the pore former, the electrolyte layer is damaged by the combustion of the carbon powder during sintering. In contrast, by using a carbon powder with a small average particle size of 2 to 5 μm as the pore former and reducing the amount added, the electrolyte layer is not damaged much by the combustion of the carbon powder during sintering. it is conceivable that.

  Accordingly, as shown in FIG. 1, the fuel electrode intermediate layer 102 provided in contact with the electrolyte layer 103 uses a finer pore-forming material than the fuel electrode substrate 101, and the pore-forming material. It can be seen that the damage to the electrolyte layer 103 can be suppressed by reducing the addition amount of. In forming the fuel electrode intermediate layer 102, the pore former may not be used. When comparing the first sample cell and the second sample cell, the first sample cell uses nickel oxide powder having a larger particle size. For this reason, the contraction of the fuel electrode due to sintering is smaller in the first sample cell. For this reason, the shrinkage rate of the fuel electrode and the shrinkage rate of the electrolyte layer in the first sample cell are different, and also in this respect, the fuel electrode and the electrolyte layer are simultaneously sintered (co-sintered). ) In some cases, the contraction rate of the fuel electrode is very small with respect to the electrolyte, which prevents densification of the electrolyte and causes leakage of the electrolyte.

  Incidentally, the fuel electrode intermediate layer 102 has a lower proportion of pores and a smaller pore diameter than the fuel electrode substrate 101. This state is confirmed by observation of a cross section with a scanning electron microscope. For this reason, the fuel electrode intermediate layer 102 does not have a very high gas permeability, and if the fuel electrode intermediate layer 102 is thickened, gas diffusion in the fuel electrode during power generation may be hindered. Therefore, the relationship between the film thickness of the fuel electrode intermediate layer 102 and the gas permeability was investigated, and the film thickness condition of the fuel electrode intermediate layer 102 was calculated.

In the investigation, helium gas was supplied at a differential pressure of 100 to 500 mmH ₂ O from one side of a fuel electrode sample formed in the same manner as the fuel electrode intermediate layer 102 and having a thickness of 1 mm, and from the other side surface of the fuel electrode sample. Gas permeation is measured with a soap film flow meter. Further, using the measured gas permeation amount q, the gas permeation coefficient Q is calculated by the equation of “q = Q × differential pressure on both sides of the membrane × measurement area / film thickness”. Note that 1 mmH ₂ O = 9.80665 Pa, and the above-described differential pressure is 980.7 to 4903.3 Pa. As a result of the investigation, the gas permeability coefficient of the fuel electrode intermediate layer 102 was 3.1 × 10 ⁻⁵ (ml · cm / g · sec).

Further, the upper limit of the film thickness of the fuel electrode intermediate layer 102 can be estimated by the above-described formula. FIG. 2 is a characteristic diagram showing the relationship between the film thickness of the fuel electrode intermediate layer 102 and the gas permeation amount at a differential pressure of 100 mmH ₂ O. When a current of 1 A / cm ² flows during power generation by the fuel cell, the amount of hydrogen necessary for power generation is only 7 ml / min. In the operation of the fuel cell, when an attempt is made to generate 1 A / cm ² at a fuel utilization rate of 70%, the hydrogen supply amount necessary for the generation is calculated as 10 ml / min · cm ² . Therefore, from FIG. 2, the upper limit of the film thickness of the fuel electrode intermediate layer 102 is considered to be 200 μm. However, this 200 μm is the upper limit of the film thickness in the fuel electrode intermediate layer 102, and it is possible to make the film thickness thicker by using a fuel electrode intermediate layer with a higher porosity and increasing the gas permeability coefficient. Become.

  Further, as described above, the anode intermediate layer 102 can be formed by a screen printing method, and according to this method, an anode intermediate green body layer having a film thickness of about 5 to 20 μm can be formed. Become. However, in the formation of the fuel electrode intermediate layer using the screen printing method, when the pore former is added to the slurry for forming the intermediate layer, leakage is observed in the formed electrolyte layer. Also, if the film thickness is less than 10 μm, even if the fuel electrode intermediate sheet is formed without adding the pore former, it is damaged by the burning of the pore former in the fuel electrode substrate sheet 121 during sintering, and the electrolyte layer is damaged. Leaks can be seen. For these reasons, it is preferable that the fuel electrode intermediate layer has a thickness of 10 μm or more.

  Next, using each sample cell described above and the single cell shown in FIG. 1, a solid oxide fuel cell as shown in the cross-sectional view of FIG. 3 is obtained, and the relationship between the power generation output and the hydrogen gas supply amount in each cell is measured. did. First, the solid oxide fuel cell shown in FIG. 3 will be described. An electrolyte layer 302 and an air electrode 303 are provided on a fuel electrode substrate 301, and a current collector layer made of Pt is formed on the back surface of the fuel electrode substrate 301. 304 is provided, and a current collector layer 305 made of Pt is provided on the air electrode 303. Further, the peripheral end portion of the fuel electrode substrate 301 is fixed to the inner side surface of the alumina manifold 307 through a glass seal 306, and is sealed so as to prevent the gas from entering the air electrode 303 side. A platinum terminal wire 308 is connected to the current collector layer 304, and a platinum terminal wire 309 is connected to the current collector layer 305.

  In the solid oxide fuel cell configured as described above, hydrogen gas serving as fuel gas is supplied from the manifold 307 side to the fuel electrode side of the cell, and air is supplied to the air electrode 303 side, so that power generation operation is performed. Made. The solid oxide fuel cell shown in FIG. 3 is arranged in an electric heating furnace, heated with a heater 310 while supplying air to the air electrode 303 and supplying nitrogen gas to the fuel electrode substrate 301. When the heating temperature reaches 800 ° C., the supply of nitrogen gas is stopped and the hydrogen gas is supplied to the fuel electrode substrate 301 to start the power generation operation.

  FIG. 4 is a characteristic diagram showing the results of measuring the relationship between the power generation output and the hydrogen gas supply amount by configuring the solid oxide fuel cell shown in FIG. 3 using each of the sample cells described above and the single cell of FIG. It is. As shown in FIG. 4, in the battery using the second sample cell indicated by the black circle, a higher output is obtained as the supply flow rate of the hydrogen gas serving as the fuel increases. However, in the region where the flow rate is low, the output is larger. It is falling. In addition, in a battery using the first sample cell indicated by a white circle, a very high output cannot be obtained even if the supply flow rate of hydrogen gas is increased, and the output is small compared to the case of the first sample. However, even if the supply flow rate of hydrogen gas decreases, the output does not decrease greatly.

  From these facts, it is considered that the first sample cell has higher gas diffusibility at the fuel electrode, and the second sample cell has higher electrode activity with more three-layer interfaces. Further, in the battery using the single cell of FIG. 1 indicated by the black triangle, a high output is obtained regardless of the hydrogen gas supply flow rate, and even if the hydrogen gas supply flow rate decreases, the output decrease is small. Accordingly, it can be seen that the single cell shown in FIG. 1 has high gas diffusibility in the fuel electrode and high electrode activity.

  In the above description, the fuel electrode is composed of the two layers of the fuel electrode substrate and the fuel electrode intermediate layer. However, the present invention is not limited to this. In the layer in contact with the electrolyte layer, the porosity is lowered and the pore diameter is reduced, so that the three-layer interface is increased.In the layer far from the electrolyte layer, the porosity is increased and the pore diameter is increased. It is important to increase the diffusibility of the supplied fuel gas by increasing the value of. Therefore, the fuel electrode may be composed of not only two layers but also three or more layers. For example, in the first layer in contact with the electrolyte layer, no pore former is added, and in the second layer following the first layer, a pore former having a smaller particle size is added, and the third layer following the second layer is added. In the layer, the fuel electrode and the electrolyte layer may be produced by adding a pore former having a larger particle size and sintering in these states. Alternatively, the particle diameter of the nickel oxide powder in the first layer <the particle diameter of the nickel oxide powder in the second layer <the particle diameter of the nickel oxide powder in the third layer.

It is process drawing which shows the example of a manufacturing method of the solid oxide fuel cell in embodiment of this invention. It is a characteristic view showing the relationship between the film thickness of the fuel electrode intermediate layer 102 and the gas permeation amount at a differential pressure of 100 mmH ₂ O. It is sectional drawing which shows the structural example of a solid oxide fuel cell. It is a characteristic view which shows the result of having comprised the solid oxide fuel cell shown in FIG. 3 using each sample cell, and measuring the relationship between an electric power generation output and hydrogen gas supply amount. It is sectional drawing which shows the structure of the conventional fuel electrode support type flat fuel cell. It is explanatory drawing for demonstrating the electric power generation reaction in a solid oxide fuel cell.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101 ... Fuel electrode substrate, 102 ... Fuel electrode intermediate layer, 103 ... Electrolyte layer, 104 ... Air electrode, 121 ... Fuel electrode substrate sheet, 121a ... Fuel electrode green sheet, 122 ... Fuel electrode intermediate green sheet, 123 ... Electrolyte layer green body.

Claims (7)

A fuel electrode substrate made of a sintered body and serving as a support substrate, an electrolyte layer formed of a sintered body provided on the fuel electrode substrate, and an air electrode provided on the electrolyte layer In a method for producing a solid oxide fuel cell provided,
A non-sintered fuel electrode substrate is formed from a first slurry formed by adding a pore former to a mixed powder obtained by mixing metal oxide powder with zirconia oxide powder. 1 process,
A second step in which an unsintered fuel electrode intermediate layer is formed from the second slurry formed from the mixed powder on the unsintered fuel electrode substrate;
A third step in which an unsintered electrolyte layer is formed from a third slurry formed of zirconia-based oxide powder on the unsintered fuel electrode intermediate layer;
The unsintered fuel electrode substrate, the unsintered fuel electrode intermediate layer, and the unsintered electrolyte layer are heated to obtain a sintered fuel electrode substrate, a sintered fuel electrode intermediate layer, and a sintered body. A fourth step in which the bound electrolyte layer is formed;
And at least a fifth step in which an air electrode is formed on the electrolyte layer,
In the second slurry, a pore former having a particle size smaller than that of the pore former added to the first slurry is added in a smaller amount than the pore former added to the first slurry,
To the first slurry, 10-18 wt% of a pore former having an average particle size of 8-12 μm is added,
A maximum of 8 wt% of a pore former having an average particle diameter of 2 to 5 μm is added to the second slurry,
The pore-forming material state, and are not constructed from a powder to vaporize by heating,
A method for producing a solid oxide fuel cell, characterized in that the porosity of the fuel electrode intermediate layer is smaller than the porosity of the fuel electrode substrate . In the manufacturing method of the solid oxide fuel cell of Claim 1 ,
The particle size of the metal oxide powder mixed in the second slurry is smaller than the particle size of the metal oxide powder mixed in the first slurry. A method for producing a solid oxide fuel cell. In the manufacturing method of the solid oxide fuel cell of Claim 1 or 2 ,
The method for producing a solid oxide fuel cell, characterized in that the fuel electrode intermediate layer is formed thicker as the amount of pore former added to the first slurry is larger. In the manufacturing method of the solid oxide fuel cell of any one of Claims 1-3 ,
The method for producing a solid oxide fuel cell, wherein the pore former is carbon powder. In the manufacturing method of the solid oxide fuel cell of any one of Claims 1-4 ,
The method for producing a solid oxide fuel cell, wherein the metal oxide is nickel oxide. The method for producing a solid oxide fuel cell according to claim 5 ,
The first slurry is mixed with nickel oxide powder having an average particle size of 3 to 5 μm,
A method for producing a solid oxide fuel cell, wherein the second slurry is mixed with nickel oxide powder having an average particle diameter of 1 to 2 μm. A solid oxide fuel cell produced by the method for producing a solid oxide fuel cell according to any one of claims 1 to 6 .

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