JP5922434B2 - Solid oxide fuel cell - Google Patents

Description

  The present invention relates to a cylindrical solid oxide fuel cell in which a plurality of cells are formed on a base tube.

  A cylindrical solid oxide fuel cell (SOFC) houses a plurality of cell stacks therein. The cell stack is composed of a power generation unit at the center of the base tube and non-power generation units at both ends. In the power generation unit, a cell in which a fuel electrode, a solid electrolyte membrane, and an air electrode are stacked is formed in the circumferential direction of the base tube. A plurality of cells are arranged in the axial direction of the base tube, and adjacent cells are electrically connected in series with an interconnector.

  During the operation of the solid oxide fuel cell, a temperature distribution is generated in the axial direction of the cell stack (base tube). The cell located at the center of the cell stack is as high as 800 ° C. to 950 ° C., but the temperature decreases as the end of the cell stack is approached, and the cell on the end side is about 600 ° C.

  The amount of power generated in one cell depends on the operating temperature. The power generation amount of the cell located in the low temperature part is lower than the power generation amount of the cell located in the high temperature part. For this reason, in order to improve the output of the solid oxide fuel cell, it is essential to increase the power generation amount of the cell located in the low temperature part.

In order to improve the power generation amount of the cell located in the low temperature part, attempts have been made to reduce the bulk resistance value of the solid electrolyte membrane by thinning the solid electrolyte membrane.
On the other hand, for example, when fuel gas or replacement gas cannot be supplied during an abnormal stop, oxygen enters the solid electrolyte membrane from the air electrode side and reaches the fuel electrode. In general, Ni is used for the fuel electrode, but when Ni is oxidized, large volume expansion is accompanied. As a result, cracks occur in the base tube and the solid oxide fuel cell is damaged. The higher the temperature, the larger the diffusion constant of oxygen that has entered the solid electrolyte membrane.

  In Patent Document 1, in a flat solid oxide fuel cell, the thickness of the solid electrolyte layer is formed so as to gradually decrease from the center to the periphery of the surface, and the current density is increased in the surface. It is disclosed to make it uniform. Patent Document 2 and Patent Document 3 disclose that the thickness of the solid electrolyte layer on the fuel gas introduction side is reduced and the thickness of the solid electrolyte layer on the fuel gas discharge side is increased.

JP 2010-238437 A (claims, paragraph [0018], paragraphs [0022] to [0036], FIGS. 1 and 2) JP 2006-127773 A (claim 1, paragraph [0006], paragraphs [0035] to [0043], FIG. 3) JP-A-11-86886 (Claim 1, paragraph [0009], paragraphs [0021] to [0022], FIG. 1)

  As described above, there is a problem of achieving both high output and ensuring the soundness of the cell during an abnormal stop. However, there has been a limit to trying to achieve both improved output and secure cell integrity with only the thickness of the solid electrolyte membrane.

  An object of the present invention is to provide a structure of a solid oxide fuel cell capable of obtaining a high output even when a temperature distribution is generated in a cell stack.

In order to solve the above problems, the present invention provides a cell including a fuel electrode, a solid electrolyte membrane, and an air electrode formed on a base tube in a circumferential direction of the base tube, and a plurality of the cells are formed on the base tube. A cell stack arranged along the axial direction, wherein the area of the cell is from the cell located at the axially central portion of the base tube toward the cell located at the axial end of the base tube The thickness of the solid electrolyte membrane is increased step by step from the cell located at the axial end of the base tube toward the cell located at the center in the axial direction of the base tube. Thus, a solid oxide fuel cell is provided which becomes thicker stepwise for each cell .

The performance (power generation amount) in one cell depends on the cell temperature and the cell area during operation. The higher the cell temperature during operation, the greater the amount of power generated in one cell. Moreover, the larger the cell area, the greater the amount of power generated in one cell.
In a solid oxide fuel cell, a temperature distribution is generated in the power generation chamber. Therefore, a temperature distribution is generated in the axial direction of the cell stack in the power generation section (the portion where the cells are formed) of the cell stack during operation. Generally, the cell located at the center of the cell stack is located in a region where the temperature becomes high during operation, and the temperature during operation becomes lower as the both ends of the cell stack are reached.
Therefore, in the solid oxide fuel cell of the present invention, the cell area is changed according to the temperature distribution in the axial direction of the cell stack. The cell in the region where the temperature during operation is low is provided so as to have a larger area than the cell in the region where the temperature is high. Specifically, the cell area is increased stepwise from the center of the cell stack having a high temperature toward both ends. By doing so, even if a temperature distribution occurs in the cell stack during power generation, the power generation amount can be made substantially uniform among the cells. As a result, a high output solid oxide fuel cell can be obtained.

  The diffusion of oxygen in the solid electrolyte depends on the temperature and the thickness of the solid electrolyte membrane. If the solid electrolyte membrane in the cell that becomes high temperature during operation is thickened as described above, oxygen can hardly reach the fuel electrode particularly in a region where the temperature becomes high during an abnormal stop. As a result, the oxidation resistance of the cell stack at the time of abnormal stop can be improved.

In order to solve the above problems, the present invention provides a cell including a fuel electrode, a solid electrolyte membrane, and an air electrode formed on a substrate tube in a circumferential direction of the substrate tube, and a plurality of the cells are formed on the substrate. The cell has a cell stack arranged along the tube axis direction, and the air electrode of the cell located in the high temperature part is formed in the air electrode of a different material according to the temperature distribution in the axial direction of the cell stack during operation. The electrode is a perovskite oxide represented by (La, Sr) MnO ₃ or (La, Sr, Ca) MnO ₃ , and the air electrode of the cell located in the low temperature part is (La, Sr, Co) Provided is a solid oxide fuel cell having a perovskite oxide represented by any of FeO ₃ , (Sm, Sr) CoO ₃ and (La, Sr) CoO ₃ .

  Thus, by using an air electrode made of a different material corresponding to the temperature distribution in the cell stack during operation, it is possible to ensure good power generation performance in the low temperature part.

  By changing the area of the cell according to the temperature distribution, and increasing the size of the low temperature cell located at both ends of the cell stack, it is possible to make the output uniform among the cells. In order to change the area of the cell, it is only necessary to change the region where the fuel electrode and the solid oxide film are formed.

It is the cross-sectional schematic of the electric power generation part of the cell stack in a cylindrical solid oxide fuel cell. It is the schematic explaining the formation condition of each cell of the cell stack in the solid oxide fuel cell which concerns on 1st Embodiment. It is the schematic explaining the formation condition of each cell of the cell stack in the solid oxide fuel cell which concerns on 2nd Embodiment.

<First Embodiment>
FIG. 1 is a schematic cross-sectional view of a power generation section of a cell stack in a cylindrical solid oxide fuel cell. FIG. 1 shows a cross section along the axial direction of the substrate tube. In the cell stack 10 of FIG. 1, a cell 12 in which a fuel electrode 13, a solid electrolyte membrane 14, and an air electrode 15 are stacked in this order from the substrate tube 11 side is formed on the outer peripheral surface of a cylindrical substrate tube 11. In the cell stack 10, fuel (hydrogen gas or the like) flows inside the base tube 11, and air flows outside the base tube 11.

  One cell 12 is formed in the circumferential direction of the base tube 11, and a plurality of cells 12 are arranged in stripes in the axial direction of the base tube 11. A part of the solid electrolyte membrane 14 contacts the base tube 11 at one end of the cell 12 in the axial direction of the base tube 11. However, the solid electrolyte membrane 14 of one cell 12 is not in contact with the fuel electrode 13 of the adjacent cell 12. An interconnector 16 that connects adjacent cells is formed between each of the plurality of cells 12. The interconnector 16 is in contact with the base tube 11 between the solid electrolyte membrane 14 of one cell 12 and the fuel electrode 13 of the adjacent cell 12. The air electrode 15 is provided in contact with the solid electrolyte membrane 14 and the interconnector 16.

  The process of forming the solid oxide fuel cell according to the first embodiment will be described below. Note that the materials of the base tube 11, the fuel electrode 13, the solid electrolyte membrane 14, the air electrode 15, and the interconnector 16 listed below are examples, and are not limited to these materials.

  The base tube 11 is made of a porous material mainly composed of calcia-stabilized zirconia (CSZ) or a mixture of CSZ and nickel oxide (NiO). The diameter of the base tube 11 is substantially uniform in the axial direction. The base tube 11 is porous, and hydrogen gas used as fuel can flow from the inside of the base tube 11 to the outside (the fuel electrode 13 side). The base tube 11 is formed by, for example, an extrusion method.

A fuel electrode 13 is formed on the base tube 11. The fuel electrode 13 is made of, for example, a composite material of nickel oxide (NiO) and a zirconia-based electrolyte material. As the composite material, for example, a mixture of NiO and yttria stabilized zirconia (YSZ) is used.
For example, a mixed powder of Ni and YSZ and an aqueous vehicle (water added with a dispersant, a binder, and an antifoaming agent) are mixed to produce a fuel electrode slurry. The mixing ratio of Ni and YSZ is appropriately selected depending on the performance required for the fuel electrode 13. The mixing ratio of the mixed powder and the water-based vehicle is appropriately selected in consideration of the thickness of the fuel electrode 13, the state of the fuel electrode film after slurry application, and the like. In the circumferential direction on the outer peripheral surface of the base tube 11, the fuel electrode slurry is applied by screen printing. The fuel electrode 13 is divided into a plurality of areas corresponding to the number of cells.

  Since temperature distribution is generated in the power generation chamber during operation of the solid oxide fuel cell, temperature distribution is also generated in the cell stack. Specifically, a temperature distribution is generated in which the central portion of the cell stack is hot and the temperature continuously decreases toward the end. The cell located at the center of the cell stack is about 950 ° C., and the cells located at both ends of the power generation unit of the cell stack are about 600 ° C. In the first embodiment, as shown in FIG. 2, the application area of the fuel electrode is changed according to the temperature distribution in the cell stack during operation. FIG. 2 is a schematic cross-sectional view of the power generation unit of the cell stack of the solid oxide fuel cell according to the first embodiment. The fuel electrode 13a is a fuel electrode located in a region where the temperature is highest during operation at the center of the cell stack. The fuel electrode 13b is a fuel electrode located in a region (intermediate region between the central portion and the end portion in the cell stack) where the temperature is lower than that of the fuel electrode 13a during operation. The fuel electrode 13c is a fuel electrode located in a region where the temperature is lower than that of the fuel electrode 13b (region close to the end of the cell stack). In the present embodiment, the width of the fuel electrode 13a located at the center of the cell stack (the axial length of the base tube) is the narrowest. The width is wider as it is located closer to the end of the cell stack, and the width of the fuel electrode 13c is the widest in FIG. Thus, in the first embodiment, the fuel electrodes having different widths are formed in multiple stages so that the width gradually increases from the central part of the cell stack toward both ends. Since the diameter of the base tube 11 is substantially uniform in the axial direction, the area of the fuel electrode increases as the width of the fuel electrode increases as viewed in the cross section of FIG.

  In the first embodiment, the fuel electrodes 13a to 13c have substantially the same film thickness. The film thickness of the fuel electrodes 13a to 13c is specifically set to 100 μm to 300 μm.

After the fuel electrode 13 is formed, solid electrolyte membranes 14 a to 14 c are formed on the base tube 11. The solid electrolyte membranes 14a to 14c are made of, for example, Y ₂ O ₃ stabilized ZrO ₂ (YSZ). A YSZ powder and an aqueous vehicle are mixed to produce a solid electrolyte membrane slurry. The mixing ratio is appropriately selected in consideration of the thickness of the solid electrolyte membranes 14a to 14c and the state and thickness of the solid electrolyte membrane after slurry application.

The solid electrolyte membrane slurry is applied by screen printing in the circumferential direction on the outer peripheral surface of the base tube 11 to form solid electrolyte membranes 14a to 14c. Corresponding to the widths of the fuel electrodes 13a to 13c, the widths of 14a to 14c differ depending on the positions. The solid electrolyte membrane 14a formed on the fuel electrode 13a has the smallest width, and the width becomes wider as it is located on the end side of the cell stack.
In the first embodiment, as shown in FIG. 2, the solid electrolyte membranes 14a to 14c have substantially the same thickness. The film thickness of the solid electrolyte membranes 14a to 14c is set to a film thickness that can ensure oxidation-reduction resistance, and is specifically set to 20 μm to 80 μm.

An interconnector 16 is formed on the base tube 11. The interconnector material is LaCrO ₃ , (La, Sr) CrO ₃ , La (Cr, Mg) O ₃ , (La, Ca) CrO ₃ , (Sr, La) TiO ₃ or the like. The interconnector material powder and an aqueous vehicle are mixed to prepare an interconnector slurry. The composition of the powder is appropriately selected according to the performance required for the interconnector. The mixing ratio of the powder and the water-based vehicle is appropriately selected in consideration of the state of the interconnector after applying the slurry.

  Between the laminated film of the fuel electrode 13 and the solid electrolyte membrane 14, the interconnector slurry is applied by screen printing in the circumferential direction of the outer peripheral surface of the base tube 11 to form the interconnector 16. In FIG. 2, the width of the interconnector is substantially the same in each cell.

  The base tube 11 on which the fuel electrode 13, the solid electrolyte membrane 14, and the interconnector 16 are formed is co-sintered in the atmosphere. The sintering temperature is specifically 1350 ° C. to 1450 ° C.

An air electrode 15 is formed on the base tube 11 after co-sintering. The air electrode 15 is mainly composed of a perovskite oxide represented by LaMnO ₃ , (La, Sr) MnO ₃ , (La, Ca) MnO ₃ , (La, Sr, Ca) MnO ₃ , LaCoO ₃ , for example. . (La, Sr, Ca) MnO ₃ powder and an aqueous vehicle are mixed to prepare an air electrode slurry. The mixing ratio of the powder and the water-based vehicle is appropriately selected in consideration of the state of the air electrode and the film thickness after slurry application.

  The air electrode slurry is applied onto the solid electrolyte membrane 14 and the interconnector 16 along the circumferential direction of the base tube 11 to form the air electrode 15. As a coating method, screen printing, brush coating, film formation with a roller, film formation with a jet dispenser, film formation with an ink jet, or the like can be employed.

  The base tube 11 on which the air electrode 15 is formed is sintered in the atmosphere. The sintering temperature is specifically 1100 ° C. to 1250 ° C. The sintering temperature here is lower than the co-sintering temperature after the base tube 11 to the interconnector 16 are formed.

By the above process, the cell stack 10 in which the cells 12 are formed on the base tube 11 is obtained. The fuel electrode is formed so that the width of the fuel electrode gradually increases from the center to both ends of the cell stack. For this reason, the cell area gradually increases from the center of the cell stack toward both ends.
In the first embodiment, the width of the fuel electrode 13 is changed in order to change the cell area. In the first embodiment, since the cell area is changed by such a simple method, the cell formation process is easy.

  In the above description, the case where the width of the adjacent fuel electrode is changed so that the areas of the adjacent cells are different is illustrated, but cells having the same area may be provided continuously corresponding to the temperature distribution.

In the first embodiment, the cell area is changed in accordance with the temperature distribution of the cell stack during operation. The amount of power generated in one cell depends on the cell temperature during operation and the area of the power generation section of the cell (the area of the portion where the three layers of the fuel electrode, electrolyte, and air electrode overlap). By making the cell area relatively large in the region where the cell temperature during operation is low and relatively small in the region where the cell temperature is high, the power generation amount in each cell is made uniform throughout the cell stack. Can be made. The area of each cell is appropriately set according to the temperature during operation and the amount of power generation.
In FIG. 2, the description is given using cells having different areas in three stages. However, the areas can be changed in more stages depending on the temperature distribution and the number of cells. In the present embodiment, the fuel electrode may be formed so that the cell area continuously increases from the center to the end of the cell stack.

Second Embodiment
FIG. 3 is a schematic diagram illustrating the formation status of each cell in the cell stack in the solid oxide fuel cell according to the second embodiment. FIG. 3 is a cross-sectional view along the axial direction of the cell stack. In the second embodiment, as in the first embodiment, the widths of the fuel electrodes 13a to 13c are changed so that the area of the cell differs according to the temperature distribution of the cell stack during operation.

Furthermore, in the second embodiment, the thickness of the solid electrolyte membrane 14 is changed according to the temperature distribution of the cell stack during operation. In a cell located in a region where the temperature is highest during operation at the center of the cell stack, the resistance of the solid electrolyte is low, and the amount of oxygen that has entered from the air electrode is large. From the viewpoint of preventing oxidation of the fuel electrode by oxygen, the solid electrolyte membrane 14a of the cell located in the region where the temperature becomes highest during operation is formed to be the thickest. On the other hand, in the region where the temperature during operation is low, the resistance of the solid electrolyte is high, but the diffusion amount of oxygen entering from the air electrode is small. For this reason, the solid electrolyte membranes 14b and 14c are formed thinner as the cell is located in a region where the temperature is lower during operation. In FIG. 3 , the solid electrolyte membranes 14a to 14c are formed so as to increase in thickness step by step from both ends of the cell stack toward the center. In FIG. 2, the solid electrolyte membranes 14a to 14c have a substantially uniform thickness in one cell.

  As a method for forming the solid electrolyte membranes 14a to 14c, screen printing, ink-jet film formation, film formation using a jet dispenser, masking CVD method, transfer method, and the like can be applied. When screen printing is applied, the number of times of slurry application is increased in a region where a thick film is formed. In the case of applying film formation by a jet dispenser, the thickness of the solid electrolyte membrane is changed by changing the amount of slurry discharged from the jet dispenser. In the transfer method, a laminated body of a solid electrolyte having a different film thickness is formed on a film or the like, and the laminated body is transferred to the substrate tube by sticking this film to the substrate tube.

When the solid electrolyte membrane 14 is formed thick, the step between the solid electrolyte membrane 14 provided on the base tube 11 and the solid electrolyte membrane 14 provided on the fuel electrode 13 in FIG. Due to the large step, it may be difficult to form the interconnector 16 and the air electrode 15 with a uniform film thickness. Therefore, when a thick solid electrolyte membrane 14a, 14 b as shown in FIG. 3, as the portions indicated by symbol A in FIG. 3, the film thickness at the boundary between the substrate tube 11 and the fuel electrode 13 A gentle slope is formed by changing.

In the method of forming a thick film by laminating a plurality of layers (screen printing, transfer method, etc.), the inclination is formed by shifting the position of the layer end and providing a step. Alternatively, viscosity is low, the wettability of the substrate tube and the fuel electrode is used good slurry becomes gentle inclination of the film edge after coating, the contact angle decreases. In film formation using a jet dispenser or the like, by utilizing this property, the layer end is formed by a continuous gradient rather than a stepwise process.

  When the thickness of the solid electrolyte membrane is changed in the cell stack as in the second embodiment, if the interconnector and the air electrode are provided on the screen by screen printing, the pressure distribution when the squeegee is pressed against the base tube is distributed. Arise. For this reason, an air electrode with a uniform film thickness cannot be formed by screen printing. Therefore, in the second embodiment, when forming the interconnector and the air electrode, it is preferable to employ a film forming method in which the film forming apparatus does not contact the base tube, such as a film formed by a jet dispenser or an ink jet or a CVD method. .

  Although FIG. 3 illustrates the case where the thickness of the solid electrolyte membrane is changed between adjacent cells, solid electrolyte membranes having the same thickness may be provided in successive cells. In this case, the continuous number of cells provided with the solid electrolyte membrane having the same film thickness is determined in accordance with the temperature distribution of the cell stack during operation.

<Third Embodiment>
In the solid oxide fuel cell according to the third embodiment, the width of the fuel electrode is changed so that the cell area varies depending on the temperature distribution of the cell stack during operation, as in the first embodiment. The thickness of the solid electrolyte membrane is substantially the same in one cell stack.

In the third embodiment, the air electrode material is further changed according to the temperature distribution of the cell stack during operation.
Depending on the temperature during operation, the power generation section of the cell stack is classified into a high temperature section and a low temperature section. For example, the high temperature portion is defined as a region that reaches a range of 800 ° C. to 950 ° C. during operation, and the low temperature portion is defined as a region that reaches a range of 600 ° C. to 800 ° C. during operation. The air electrode of the cell located in the high temperature part and the low temperature part is stable in the operating conditions, stable in thermodynamics, has high affinity with oxygen, and conducts electrons in the operating temperature and oxidizing atmosphere. The performance that the rate and the ionic conductivity are large and the thermal expansion coefficient is close to other constituent materials is required. A material that satisfies the above-mentioned required performance is selected in each operating condition of the high temperature part and the low temperature part. Specifically, the air electrode in the high temperature portion is mainly composed of a perovskite oxide represented by (La, Sr) MnO ₃ or (La, Sr, Ca) MnO ₃ . The air electrode in the low temperature portion is mainly composed of a perovskite oxide represented by any one of (La, Sr, Co) FeO ₃ , (Sm, Sr) CoO ₃ and (La, Sr) CoO ₃ . Thus, the favorable power generation performance in a low-temperature part is securable by applying the said material to a low-temperature part.

DESCRIPTION OF SYMBOLS 10 Cell stack 11 Base tube 12 Cell 13, 13a, 13b, 13c Fuel electrode 14, 14a, 14b, 14c Solid electrolyte membrane 15 Air electrode 16, 16a, 16b, 16c Interconnector

Claims (2)

A cell having a fuel electrode, a solid electrolyte membrane, and an air electrode is formed on the base tube in the circumferential direction of the base tube, and a plurality of the cells are arranged along the axial direction of the base tube. ,
The area of the cell gradually increases from the cell located in the axial center of the base tube toward the cell located at the axial end of the base tube for each cell.
The film thickness of the solid electrolyte membrane gradually increases from the cell located at the axial end of the base tube toward the cell located at the axial center of the base tube for each cell. Solid oxide fuel cell.   A cell having a fuel electrode, a solid electrolyte membrane, and an air electrode is formed on the base tube in the circumferential direction of the base tube, and a plurality of the cells are arranged along the axial direction of the base tube. ,
  Depending on the temperature distribution in the axial direction of the cell stack during operation, the air electrode of a different material is formed,
  The air electrode of the cell located in the high temperature part is (La, Sr) MnO. ₃ Or (La, Sr, Ca) MnO ₃ And a perovskite oxide represented by
  The air electrode of the cell located in the low temperature part is (La, Sr, Co) FeO. ₃ , (Sm, Sr) CoO ₃ And (La, Sr) CoO ₃ A solid oxide fuel cell having a perovskite oxide represented by any of the above:

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