JP2012074307A - Power generation cell for solid oxide fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power generation cell for a solid oxide fuel cell which exhibits good power generation performance and high reliability even when the operation temperature is low (e.g. 600°C or lower).SOLUTION: The power generation cell for a solid oxide fuel cell comprises a solid electrolyte (2), an air electrode (3) and a fuel electrode (4). The solid electrolyte has a dense first solid electrolyte (21) composed of (LaSr)(TiFe)O, and a dense second solid electrolyte (22) composed of a Zr oxide and having an oxide ion transport number of 0.96 or higher. The air electrode has a porous air electrode side reaction acceleration layer (32), the reaction acceleration layer is formed on one main surface of the first solid electrolyte, and the second solid electrolyte is formed between the other main surface of the first solid electrolyte and the fuel electrode. The reaction acceleration layer has a dense three-dimensional skeletal structure (34) composed of (LaSr)(TiFe)O, and the surface of the skeletal structure is impregnated with (LaSr)(TiFe)O.

Description

  The present invention relates to a power generation cell for a solid oxide fuel cell. More specifically, the power generation cell for a solid oxide fuel cell exhibits excellent power generation performance and high reliability even when the operating temperature is low. About.

  A solid oxide fuel cell is a device that uses oxide ceramics with high ion conductivity as an electrolyte and takes out electric power by utilizing an electrochemical reaction generated in the device. Among fuel cells, solid oxide fuel cells have high power generation efficiency and do not require expensive catalysts, and are therefore being developed as energy creation devices that contribute to greenhouse gas reduction.

  Conventional solid oxide fuel cells have high operating temperatures (for example, 800 to 1000 ° C.), so that there are problems such as limited materials that can be used or material deterioration due to thermal cycling. Therefore, attempts have been made to lower the operating temperature.

  For example, Patent Document 1 describes a fuel cell in which an active layer is disposed between a solid electrolyte and a fuel electrode so that the average pore diameter of the pores of the fuel electrode is larger than the average pore diameter of the pores of the active layer. Has been. However, in Patent Document 1, since only a material such as YSZ is described as the solid electrolyte, there is a problem that the oxide ion conductivity of the electrolyte is low and the performance at low temperature is lowered. Moreover, there was no description about the reliability when the power generation cell was operated for a long time.

  Patent Document 2 describes a single cell structure of a fuel cell in which a porous ceramic material layer (electrode) contains the same ceramic material as that contained in a dense ceramic material layer (solid electrolyte). Yes. However, since only a material such as YSZ is described as the solid electrolyte, there is a problem in that the oxide ion conductivity of the electrolyte is low and the performance at low temperature is lowered. Moreover, there was no description about the reliability when the power generation cell was operated for a long time.

  Although the thickness of the solid electrolyte can be reduced, the oxide ion conductivity can be improved even if the operating temperature is lowered, but the strength of the solid electrolyte is reduced, and the reliability of the power generation cell is reduced. There was a problem that would decrease.

JP 2007-165143 A JP 2009-230874 A

  The present invention has been made in view of such a situation, and even when the operating temperature is low (for example, 600 ° C. or lower), the power generation cell for a solid oxide fuel cell exhibits good power generation performance and has high reliability. The purpose is to provide.

In order to achieve the above object, a power generation cell for a solid oxide fuel cell according to the present invention comprises:
A power generation cell for a solid oxide fuel cell, comprising: a solid electrolyte; an air electrode formed on one main surface of the solid electrolyte; and a fuel electrode formed on the other main surface of the solid electrolyte. ,
The solid electrolyte is a dense first solid electrolyte made of (La, Sr) (Ti, Fe) O ₃ and a dense first made of Zr oxide having an oxide ion transport number of 0.96 or more. 2 solid electrolytes,
The air electrode has a porous air electrode side reaction promoting layer formed so that a plurality of pores communicate with each other;
The air electrode side reaction promoting layer is formed on one main surface of the first solid electrolyte, and the second solid electrolyte is formed between the other main surface of the first solid electrolyte and the fuel electrode. ,
The air electrode side reaction promoting layer has a dense three-dimensional skeleton structure made of (La, Sr) (Ti, Fe) O ₃ , and (La, Sr) (Co, Fe) O ₃ is impregnated.

In the present invention, a complex oxide ((La, Sr) (Ti, Fe) O ₃ ) having extremely high oxide ion conductivity is used as a solid electrolyte even at a low temperature (for example, 600 ° C. or lower). However, since this composite oxide has a very low oxide ion transport number, that is, extremely high electron conductivity, when the composite oxide and the fuel electrode are in direct contact, the electrons generated at the fuel electrode are mixed with the composite oxide. Move to the side. As a result, a short circuit occurs in the composite oxide, and power cannot be extracted to an external circuit.

  Therefore, in the present invention, as a solid electrolyte, an oxide having a high oxide ion transport number is disposed between the composite oxide and the fuel electrode, so that the movement of electrons to the solid electrolyte side can be performed. Is blocking. By doing so, even if the operating temperature is low, the movement (short circuit) of electrons to the solid electrolyte is prevented, and the oxide ions generated at the air electrode can quickly reach the fuel electrode, thereby reducing the power. Can be taken out to an external circuit.

In addition, since the skeleton structure of the porous air electrode side reaction promoting layer is made of the same material as that of the first solid electrolyte, problems such as interface peeling and element diffusion do not occur. Furthermore, by impregnating the surface of the skeletal structure of the air electrode side reaction promoting layer with (La, Sr) (Co, Fe) O ₃ , the production rate of oxide ions at the three-phase interface on the air electrode side is increased, The power generation performance of the power generation cell can be improved.

Preferably, the power generation cell for a solid oxide fuel cell has a fuel electrode support membrane structure,
The fuel electrode has a porous fuel electrode side reaction promoting layer formed so that a plurality of pores communicate with each other, and a porous support layer formed so that a plurality of pores communicate with each other. ,
The fuel electrode side reaction promoting layer is formed on one main surface of the second solid electrolyte,
The diameter of the pores formed in the fuel electrode side reaction promoting layer is smaller than the diameter of the pores formed in the support layer.

Preferably, the (La, Sr) (Ti, Fe) O ₃ is represented by the general formula (La _1-x Sr _x ) (Ti _1-y Fe _y ) O _3-δ , Satisfies the relationship of 0.1 to 0.5 and y of 0.1 to 0.9. The composite oxide represented by the above general formula is obtained by substituting Sr for the La site of LaTiO ₃ which is the base material and Fe for the Ti site. To express. When x and y are within the above ranges, there is no change in oxide ion conductivity that affects the performance of the power generation cell in the present invention.

  Preferably, the thickness of the first solid electrolyte is 3 to 20 μm.

  Preferably, the thickness of the second solid electrolyte is 3 to 10 μm.

  By controlling the thickness of the first solid electrolyte and the second solid electrolyte, the effect of the present invention can be further enhanced.

  Preferably, the oxide of Zr is yttria stabilized zirconia or scandia stabilized zirconia.

  The thickness of the air electrode side reaction promoting layer is preferably 3 to 20 μm. Preferably, the pores formed in the layer have a diameter of 0.5 to 10 μm. Moreover, Preferably, the porosity is 20 to 90%.

  Regarding the fuel electrode side reaction promoting layer, the thickness is preferably 3 to 20 μm. Preferably, the pores formed in the layer have a diameter of 0.5 to 10 μm. Moreover, Preferably, the porosity is 20 to 90%.

  The thickness of the support layer is preferably 100 to 2000 μm. Preferably, the pores formed in the layer have a diameter of 5 to 50 μm. Moreover, Preferably, the porosity is 30 to 70%.

FIG. 1 is a schematic cross-sectional view of a power generation cell for a solid oxide fuel cell according to an embodiment of the present invention. FIG. 2 is a schematic enlarged sectional view of a portion II shown in FIG.

  Hereinafter, the present invention will be described based on embodiments shown in the drawings.

<Power generation cell 1 for solid oxide fuel cell>
A power generation cell 1 for a solid oxide fuel cell according to this embodiment is shown in FIG. The power generation cell 1 includes a solid electrolyte 2, an air electrode 3 formed so as to be in contact with one main surface of the solid electrolyte 2, and a fuel electrode formed so as to be in contact with the other main surface of the solid electrolyte 2. 4 and.

  The power generation cell 1 is a minimum unit for generating electricity by an electrochemical reaction. By connecting a plurality of power generation cells 1 in series via an interconnector, a stack can be obtained and high output can be obtained. it can.

  The shape of the power generation cell 1 is not particularly limited, and may be determined according to the application. For example, it may be flat or cylindrical. Further, the shape of the flat plate is not limited, and may be a circular shape or an elliptical shape, or may be a polygonal shape of a triangle or more. The dimensions of the power generation cell 1 are not particularly limited, and may be determined according to usage.

  The structure for securing the strength of the power generation cell 1 may be an electrolyte support membrane type or an electrode (air electrode or fuel electrode) support membrane type. In this embodiment, it is a fuel electrode support membrane type.

<Solid electrolyte 2>
In the present embodiment, as shown in FIG. 1, the solid electrolyte 2 has a configuration in which a first solid electrolyte 21 and a second solid electrolyte 22 are laminated. The air electrode 3 is formed on one main surface side of the first solid electrolyte 21, and the second solid electrolyte 22 is disposed between the other main surface of the first solid electrolyte 21 and the fuel electrode 4. That is, the first solid electrolyte 21 is in contact with the air electrode 3, but not in contact with the fuel electrode 4, and the second solid electrolyte 22 is in contact with the fuel electrode 4, but is in contact with the air electrode 3. Absent.

<First solid electrolyte 21>
The first solid electrolyte 21 is made of (La, Sr) (Ti, Fe) O _3. Specifically, the first solid electrolyte 21 has a general formula (La _1-x Sr _x ) (Ti _1-y Fe _y ) O _3-δ ( (Hereinafter also referred to as LSTF). δ represents oxygen deficiency.

  Although this LSTF has very high oxide ion conductivity, the oxide ion transport number indicating the proportion of oxide ions in electrical conductivity is very low, so it should be used alone as a solid electrolyte. Not suitable for. However, as will be described later, it can be applied as a solid electrolyte having good oxide ion conductivity by being used in combination with the second solid electrolyte.

In the above formula, x is preferably 0.1 to 0.5, more preferably 0.2 to 0.4. x indicates the proportion of Sr atoms, and when x is in the above range, the La ³⁺ site is occupied by the Sr ²⁺ site, so that oxygen defects occur and good oxide ion conductivity can be expressed. There are advantages.

  In the above formula, y is preferably 0.1 to 0.9, more preferably 0.6 to 0.9. y indicates the proportion of Fe atoms, and by setting y to the above range, there is an advantage that the electrical conductivity can be improved.

  When the length of the first solid electrolyte 21 in the direction in which the solid electrolyte 2, the air electrode 3 and the fuel electrode 4 are laminated is the thickness of the first solid electrolyte 21, the thickness is preferably 3 to 20 μm, more preferably 3 10 μm. By setting the thickness within the above range, there is an advantage that strength as a solid electrolyte can be secured and power generation performance can be kept high.

<Second solid electrolyte 22>
The second solid electrolyte 22 is made of a dense Zr oxide having an oxide ion transport number of 0.96 (96%) or more. In this embodiment, the oxide is preferably yttria stabilized zirconia (hereinafter also referred to as YSZ) or scandia stabilized zirconia (hereinafter also referred to as ScSZ).

  Such an oxide is preferable because of its high oxide ion transport number and high oxide ion conductivity. In addition, the difference in shrinkage behavior from LSTF can be reduced during the integral firing of the power generation cell. The upper limit of the oxide ion transport number is 1, that is, it is preferable that the oxide ion bears all of the electrical conduction, but it is about 0.995 in the current technology.

YSZ is preferably a solution in which ₃ to 15 mol% of yttria (Y ₂ O ₃ ) is dissolved in zirconia (ZrO ₂ ). As ScSZ, scandia (Sc ₂ O ₃ ) is preferably dissolved in zirconia in 5 to 10 mol%.

  When the length of the second solid electrolyte 22 in the direction in which the solid electrolyte 2, the air electrode 3 and the fuel electrode 4 are laminated is the thickness of the second solid electrolyte 22, the thickness is preferably 3 to 10 μm, more preferably 3 ~ 5 μm. By setting the thickness within the above range, there is an advantage that strength as a solid electrolyte can be secured and power generation performance can be kept high.

  In this embodiment, although the oxide ion conductivity is very high, the first solid electrolyte 21 having a very low oxide ion transport number and the second solid electrolyte 22 having a very high oxide ion transport number are combined. A solid electrolyte 2 is formed.

  The LSTF constituting the first solid electrolyte has very high oxide ion conductivity, but the oxide ion transport number is about 0.01 (1%). Therefore, when the LSTF (first solid electrolyte 21) and the fuel electrode 4 are in contact with each other, electrons generated at the interface between the LSTF (first solid electrolyte 21) and the fuel electrode 4 easily move to the LSTF, and a circuit is formed inside the LSTF. Is formed, and electric power cannot be taken out to the outside.

  Therefore, in this embodiment, an oxide (second solid electrolyte 22) having a very high oxide ion transport number is disposed between the LSTF (first solid electrolyte 21) and the fuel electrode 4. By doing so, it becomes extremely difficult for electrons to permeate the second solid electrolyte 22, so that most of the electrons generated at the fuel electrode move to the air electrode side through the external circuit. On the other hand, the oxide ions generated at the interface between the first solid electrolyte 21 and the air electrode 3 are favorably conducted through the first solid electrolyte 21 and the second solid electrolyte 22 and reach the fuel electrode 4.

  That is, while utilizing the good oxide ion conductivity of the first solid electrolyte 21, electrons can be blocked by the second solid electrolyte 22 and electric power can be taken out to the outside.

  In other words, when configuring a solid electrolyte that is a resistance component for oxide ions, a component having a relatively high resistance (second solid electrolyte) is converted into a component having a very low resistance (to the extent that electron conductivity does not occur) The first solid electrolyte) is substituted.

<Air electrode 3>
The air electrode 3 is made of a porous material in order to improve gas permeability and reactivity at the three-phase interface, and acts as a cathode in the power generation cell 1. In the present embodiment, as shown in FIG. 1, the air electrode 3 includes a surface layer 31 and an air electrode side reaction promoting layer 32 formed on the main surface of the first solid electrolyte 21. You may be comprised only from the air electrode side reaction promotion layer 32. FIG. In the cross section of FIG. 1, it seems that there are few pores 37 communicating with the air electrode side reaction promoting layer 32, but there are cases where the pores 37 exist in other cross sections and communicate with each other. Therefore, the pores 37 in the air electrode side reaction promoting layer 32 are formed so as to communicate sufficiently.

<Surface layer 31>
The surface layer 31 is a layer in which air supplied from the outside comes into contact with the power generation cell 1, and has a role as a current path of an external circuit as well as a reaction at the air electrode. In the present embodiment, the surface layer 31 is preferably made of a porous material and has (La, Sr) (Co, Fe) O ₃ (hereinafter also referred to as LSCF).

<Air electrode side reaction promoting layer 32>
The air electrode side reaction promoting layer 32 is a layer for promoting the generation of oxide ions, and in this embodiment, is a porous material having a three-dimensional skeleton structure made of LSTF. That is, it has a configuration in which a plurality of pores 37 communicate with the same material as the first solid electrolyte.

In the air electrode side reaction promoting layer 32, when oxygen in the air reaches the interface (three-phase interface) with the first solid electrolyte, electrons and oxygen moving from the fuel electrode side are expressed by the following equation (1). react.
1 / 2O ₂ + 2e ⁻ → O ²⁻ … Formula 1
The oxide ions generated by the reaction shown in the above formula 1 move in the solid electrolyte 2 described above.

  When the length of the air electrode side reaction promoting layer 32 in the direction in which the solid electrolyte 2, the air electrode 3 and the fuel electrode 4 are laminated is the thickness of the air electrode side reaction promoting layer 32, the thickness is preferably 3 to 20 μm. More preferably, it is 5-10 micrometers. By setting the thickness of the air electrode side reaction promoting layer 32 in the above range, both high power generation performance and reliability can be achieved.

  The diameter (pore diameter) of the pores 37 formed in the air electrode side reaction promoting layer 32 is preferably 0.5 to 10 μm, more preferably 1 to 5 μm. Further, the porosity of the air electrode side reaction promoting layer 32 is preferably 20 to 90%, more preferably 40 to 70%. The shape of the pores 37 is not particularly limited, but is preferably spherical. By setting the pore diameter and the porosity of the air electrode side reaction promoting layer 32 within the above ranges, both high power generation performance and reliability can be achieved.

  As described above, since LSTF has very high electron conductivity, electrons moving from the fuel electrode side can quickly reach the interface with the first solid electrolyte, which is suitable as a material constituting the air electrode. It is.

  Moreover, since it is composed of the same material as the first solid electrolyte, for example, it is not necessary to consider the difference in shrinkage behavior even when the power generation cell 1 is integrally fired, and interface separation between the solid electrolyte and the air electrode hardly occurs. Also, diffusion of elements such as mutual diffusion does not occur.

  In FIG. 1, although the air electrode side reaction promoting layer 32 and the first solid electrolyte 21 are described as different layers, the fired power generation cell 1 is indistinguishable except for the presence or absence of pores. In other words, by introducing pores on one main surface side of the dense first solid electrolyte 21 to form a porous air electrode, the solid electrolyte having different functions and the air electrode are integrated. It can be said that there is.

  In the present embodiment, as shown in FIG. 2, the LSCF 35 is impregnated on the surface of the LSTF as the three-dimensional skeleton structure 34 of the air electrode side reaction promoting layer 32. That is, the LSCF 35 is impregnated in a portion that forms the outline of the pores 37 existing in the air electrode side reaction promoting layer 32.

  LSCF, like LSTF, has high electron conductivity and is suitable as a material constituting the air electrode 3, and has a higher ability as a catalyst for promoting the reaction of Formula 1 than LSTF. However, since it is a different material from the first solid electrolyte 21 (LSTF), if the air electrode side reaction promoting layer 32 is made of LSCF, problems such as interfacial delamination and element diffusion occur and reliability as a power generation cell ( Durability).

  Therefore, the skeletal structure 34 is composed of LSTF, and the presence of LSCF 35 on the surface of the skeletal structure in contact with permeating oxygen promotes the reaction of Formula 1 without causing problems such as interface peeling and element diffusion. Thus, the production rate of oxide ions can be improved.

<Fuel electrode 4>
The fuel electrode 4 is made of a porous material in order to improve gas permeability and reactivity at the three-phase interface, and acts as an anode in the power generation cell 1. In the present embodiment, as shown in FIG. 1, the fuel electrode 4 includes a fuel electrode side reaction promoting layer 41 formed on the main surface of the second solid electrolyte 22 and a support layer formed on the reaction promoting layer 32. 42.

<Fuel electrode side reaction promoting layer 41>
In the fuel electrode side reaction promoting layer 41, at the interface with the second solid electrolyte 22, the fuel (hydrogen) supplied from the outside undergoes the following reaction with the oxide ions that have permeated the solid electrolyte, generating electrons. It is a layer to do.
H ₂ + 1 / 2O ₂ ²⁻ → H ₂ O + 2e ⁻ Formula 2
In the present embodiment, the fuel electrode side reaction promoting layer 41 is a porous material formed so that a plurality of pores 47 communicate with each other in order to make hydrogen reach the three-phase interface and promote the reaction shown in the above formula 2. Made of material.

  In the present embodiment, the fuel electrode side reaction promoting layer 41 is made of a composite material of NiO and YSZ (hereinafter also referred to as NiO / YSZ). This material can disperse NiO having good electron conductivity in YSZ, thereby preventing aggregation of NiO during firing, increasing the three-phase interface, and enhancing the reactivity. In addition, since the Zr oxide composing the second solid electrolyte and the base material are common, interface peeling and element diffusion with the second solid electrolyte are unlikely to occur.

  When the length of the fuel electrode side reaction promoting layer 41 in the direction in which the solid electrolyte 2, the air electrode 3 and the fuel electrode 4 are laminated is the thickness of the fuel electrode side reaction promoting layer 41, the thickness is preferably 3 to 20 μm. More preferably, it is 5-10 micrometers. By setting the thickness of the fuel electrode side reaction promoting layer 41 in the above range, both high power generation performance and reliability can be achieved.

  The diameter (pore diameter) of the pores 47 formed in the fuel electrode side reaction promoting layer 41 is preferably 0.5 to 10 μm, more preferably 1 to 5 μm. Further, the porosity of the fuel electrode side reaction promoting layer 41 is preferably 20 to 90%, more preferably 40 to 70%. The shape of the pores 47 is not particularly limited, but is preferably spherical. By setting the pore diameter and the porosity of the fuel electrode side reaction promoting layer 41 in the above ranges, both high power generation performance and reliability can be achieved.

<Support layer 42>
The support layer 42 is a layer that bears the strength of the power generation cell 1 in the fuel electrode support membrane structure, and also allows the fuel (hydrogen) supplied from the outside to quickly reach the fuel electrode side reaction promoting layer 41. Of layers.

  In this embodiment, the support layer 42 is made of a composite material of NiO and YSZ (hereinafter also referred to as NiO / YSZ), like the fuel electrode side reaction promoting layer 41. By using the same material as the fuel electrode side reaction promoting layer 41, the same effect as the reaction promoting layer 41 can be obtained.

  When the length of the support layer 42 in the direction in which the solid electrolyte 2, the air electrode 3 and the fuel electrode 4 are laminated is the thickness of the support layer 42, the thickness is preferably 100 to 2000 μm, more preferably 200 to 500 μm. is there. By setting the thickness of the support layer 42 in the above range, the strength of the power generation cell 1 can be secured, and furthermore, high power generation performance and reliability can be achieved at the same time.

  The diameter of the pores 48 formed in the support layer 42 may be larger than the diameter of the pores 47 formed in the fuel electrode side reaction promoting layer 41, but is preferably 5 to 50 μm, more preferably 10 to 30 μm. . Further, the porosity of the support layer 42 is preferably 30 to 70%, more preferably 40 to 70%. The shape of the pores 48 is not particularly limited, but is preferably spherical.

  By setting the pore diameter and the porosity of the support layer 42 within the above ranges, it is possible to ensure the strength of the power generation cell 1 and achieve both high power generation performance and reliability. Moreover, since the reaction rate of Formula 1 is slower than the reaction rate of Formula 2, the electrochemical reaction in the power generation cell 1 is limited to Formula 1. Therefore, it becomes easy to make the reaction rate of Formula 2 close to the reaction rate of Formula 1 by making the support structure of the power generation cell 1 a fuel electrode support membrane structure and increasing the thickness of the fuel electrode.

<Method for Producing Power Generation Cell 1 for Solid Oxide Fuel Cell>
The method for producing the power generation cell 1 for the solid oxide fuel cell according to the present embodiment is not particularly limited, and a known method may be adopted. However, in the following, the sheet method is used for the solid electrolyte and the fuel electrode. The method of manufacturing the power generation cell 1 using screen printing will be specifically described for the air electrode used.

  First, raw materials for forming a solid electrolyte, an air electrode, and a fuel electrode are prepared, and this is made into a paint to prepare each paste.

  As the raw materials, oxides of the above-described components, mixtures thereof, and composite oxides can be used. In addition, various compounds that become the above-described oxides or composite oxides by firing, such as carbonates and oxalates. , Nitrates, hydroxides, organometallic compounds, and the like may be selected as appropriate and used as a mixture.

  In addition, as the raw material, a conductive material made of a conductive metal such as Ni or an alloy, or various oxides, organometallic compounds, resinates, or the like that become the conductive material described above after firing may be used.

  Each paste is usually an organic paint obtained by kneading the above raw material, binder resin, and organic solvent, but may be an aqueous paint using water as a solvent. Each paste may contain additives such as a plasticizer as necessary.

  Further, in order to make the air electrode (surface layer + reaction promoting layer) and the fuel electrode (reaction promoting layer + support layer) porous, a pore forming agent is added to the air electrode paste and the fuel electrode paste. . The pore-forming agent is not particularly limited, but in the present embodiment, resin beads that decompose and vaporize at a temperature lower than the holding temperature during firing are used.

  Using each paste, a green sheet of a first solid electrolyte, a green sheet of a second solid electrolyte, a fuel electrode side reaction promoting layer, and a green sheet of a support layer are formed by, for example, a doctor blade method.

  Subsequently, the formed green sheets are laminated and pressure-bonded in the order of the first solid electrolyte, the second solid electrolyte, the fuel electrode side reaction promoting layer, and the support layer to obtain a green sheet laminate.

  The obtained green sheet laminate is cut into a predetermined shape to obtain a solid electrolyte / fuel electrode laminate green body.

  The green body is fired to obtain a sintered body. A binder removal treatment may be performed before firing. As firing conditions, the holding temperature is preferably 1300 to 1500 ° C., and the holding time is preferably 1 to 6 hours. The atmosphere during firing is preferably in the air.

  Next, an air electrode side reaction promoting layer is formed by screen printing on the solid electrolyte on the surface of the solid electrolyte / fuel electrode laminated sintered body facing the fuel electrode.

  After forming the air electrode side reaction promoting layer, baking is performed in order to maintain adhesion with the solid electrolyte to obtain a sintered body. As firing conditions, the holding temperature is preferably 1000 to 1200 ° C., and the holding time is preferably 1 to 6 hours. The atmosphere during firing is preferably in the air.

  In the air electrode side reaction promoting layer and the fuel electrode (reaction promoting layer + support layer) of the obtained sintered body, pores formed by vaporizing the pore forming agent are communicated with each other. In the present embodiment, a paste containing an LSCF raw material is further applied on the air electrode side reaction promoting layer of the sintered body, and vacuuming is performed before the paste is dried. Then, the LSCF contained in the paste is impregnated on the surface of the LSTF constituting the skeleton structure of the air electrode side reaction promoting layer through the pores. In order to fix the impregnated LSCF, baking is performed at a holding temperature of 1000 to 1200 ° C., and the power generation cell 1 having the configuration shown in FIG. 1 is obtained.

  The power generation cells of this embodiment manufactured in this way are connected in series via an interconnector so as to obtain a desired output, form a stack, and are used for a solid oxide fuel cell.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the embodiment mentioned above at all, and can be variously modified within the range which does not deviate from the summary of this invention.

  For example, in the above-described embodiment, the means for forming the air electrode by the screen printing method is shown. However, the green sheet of the air electrode side reaction promoting layer is formed by the sheet method to obtain the solid electrolyte / fuel electrode laminated sintered body. After that, an air electrode side reaction promoting layer green sheet may be laminated and baked on the solid electrolyte.

  At this time, a green sheet for forming the first solid electrolyte 21 and a green sheet for forming the air electrode side reaction promoting layer 31 may be separately prepared, but the first solid electrolyte 21 is formed. Only a green sheet is produced, and a pore-forming agent or pores are introduced into the green sheet so that after firing, one main surface of the dense first solid electrolyte 21 becomes a porous air electrode side reaction promoting layer. Also good.

  Hereinafter, although this invention is demonstrated based on a more detailed Example, this invention is not limited to these Examples.

  First, the raw material for manufacturing a power generation cell was prepared.

La _0.6 Sr _0.4 Ti _0.3 Fe _0.7 O ₃ (hereinafter referred to as LSTF) powder was prepared as a raw material for the material constituting the first solid electrolyte. LSTF powder: 100 parts by weight, butyral resin as binder resin: 15 parts by weight, dioctyl phthalate (DOP) as plasticizer: 4 parts by weight, alcohol as solvent: 80 parts by weight To obtain a first solid electrolyte paste. Using the obtained paste, a green sheet was formed by a doctor blade method so that the thickness after firing would be the thickness shown in Tables 1 and 2. For Sample No. 1, zirconia stabilized with 8 mol% yttria (hereinafter referred to as 8YSZ) was used as the solid electrolyte.

  Next, 8YSZ powder was prepared as a raw material for the second solid electrolyte. 8YSZ powder: 100 parts by weight, butyral resin as binder resin: 15 parts by weight, dioctyl phthalate (DOP) as plasticizer: 4 parts by weight, alcohol as solvent: 80 parts by weight To obtain a second solid electrolyte paste. Using the obtained paste, a green sheet was formed by a doctor blade method so that the thickness after firing would be the thickness shown in Tables 1 and 2. For sample numbers 11 and 12, the second solid electrolyte was made of the material shown in Table 1 instead of 8YSZ.

  Next, LSTF powder was prepared as a raw material for the material constituting the air electrode side reaction promoting layer. LSTF powder: 100 parts by weight, acrylic beads as pore forming agent: 25 parts by weight, butyral resin as binder resin: 15 parts by weight, dioctyl phthalate (DOP) as plasticizer: 4 parts by weight, as solvent 80 parts by weight of alcohol was mixed and dispersed with a ball mill to obtain a paste, and a paste for an air electrode side reaction promoting layer was obtained. Further, the pore forming agent having a pore size shown in Tables 1 and 2 was used. For sample numbers 1 and 2, the air electrode was made of the material shown in Table 1 instead of LSTF.

  Next, NiO / YSZ mixed powder in which NiO and 8YSZ were mixed at a weight ratio of 60:40 was prepared as a raw material for the materials constituting the fuel electrode side reaction promoting layer and the support layer. NiO / YSZ raw material powder: 100 parts by weight, acrylic beads as pore forming agent: 20 parts by weight, butyral resin as binder resin: 7.5 parts by weight, dioctyl phthalate (DOP) as plasticizer: 4 parts by weight Parts and 70 parts by weight of alcohol as a solvent were mixed and dispersed by a ball mill to obtain a paste, and a fuel electrode side reaction promoting layer paste and a support layer paste were obtained. In these pastes, pastes differing only in the particle size of the pore-forming agent and having pore sizes shown in Tables 1 and 2 were used. Using the obtained paste, a green sheet was formed by a doctor blade method so that the thickness after firing would be the thickness shown in Tables 1 and 2.

  Next, each green sheet produced as described above is laminated in the order of the first solid electrolyte, the second solid electrolyte, the fuel electrode side reaction promoting layer and the support layer, and pressure-bonded to obtain a green sheet laminate. It was. This green sheet laminate was punched out to a diameter of 20 mm after firing to obtain a solid electrolyte / fuel electrode laminate green body.

  The obtained green body was fired under conditions of firing temperature: 1400 ° C., holding time: 5 hours, firing atmosphere: air, and a solid electrolyte / fuel electrode laminated sintered body was obtained.

  Next, an air electrode side reaction promoting layer was formed on the solid electrolyte on the surface facing the fuel electrode of the solid electrolyte / fuel electrode laminated sintered body by screen printing.

  After printing the air electrode side reaction promoting layer, baking temperature: 1200 ° C., holding time: 3 hours, baking atmosphere: atmospheric conditions were baked to obtain a sintered body.

  A paste containing LSCF powder is applied to the surface of the air electrode side reaction promoting layer of the obtained sintered body by screen printing, and vacuuming is performed before the paste is dried. The pores formed in the side reaction promoting layer were filled (vacuum impregnation). The sintered body after vacuum impregnation was fired again under the conditions of firing temperature: 1200 ° C., holding time: 5 hours, firing atmosphere: air, and the surface layer and air in which the LSCF was fixed to the surface of the LSTF having a skeleton structure A sintered body of the power generation cell 1 shown in FIG. 1 having the pole-side reaction promoting layer was obtained.

  With respect to the obtained power generation cell, the open circuit electromotive force and the maximum output density are measured by the following methods as an evaluation of power generation performance, and the voltage after 1000 hours of operation is evaluated as an evaluation of cell reliability (durability). The reduction rate was measured by the method shown below. The pore diameter and porosity were measured by a mercury intrusion method.

<Open circuit electromotive force>
Air is supplied to the air electrode side of the obtained power generation cell at a flow rate of 200 ml / min, hydrogen is supplied to the fuel electrode side at a flow rate of 200 ml / min, and the current applied to the power generation cell at 500 ° C. is 0 A. The voltage at the time was measured and this was taken as the open circuit electromotive force. The open circuit electromotive force is preferably as close as possible to the standard electromotive force of oxygen and hydrogen in the concentration cell. In this example, 0.95 V or more was considered good. The results are shown in Tables 1 and 2.

<Maximum output density>
Under open circuit electromotive force measurement conditions, current is applied to the power generation cell, the output is obtained from the applied current value and the voltage of the power generation cell at that time, and the maximum output when the current is applied is measured in unit area. The value divided was taken as the maximum power density. This maximum power density is preferably as large as possible. In this example, 200 mW / cm ² or more is considered good, and 300 mW / cm ² or more is more preferable. The results are shown in Tables 1 and 2.

<Voltage drop rate>
At 500 ° C., a current is applied until the initial cell voltage becomes 0.7 V, and the rate of change of the cell voltage is measured with the applied current at that time being constant. The cell voltage at the time when the power generation cell was operated for 1000 hours was measured, and the rate of decrease from the cell voltage at the start of operation was calculated by the following equation.
Voltage drop rate (%) = 100 × (initial cell voltage−cell voltage after 1000 hours) / initial cell voltage voltage drop rate was 0.25% or less. The results are shown in Tables 1 and 2.

  From Table 1, sample number 1 provides a sufficient open circuit electromotive force, but because YSZ is used as the solid electrolyte (first solid electrolyte + second solid electrolyte), the maximum output density is inferior, and the power generation performance In addition, it was confirmed that the voltage drop rate was large and the reliability was lacking.

  In Sample No. 2, since the air electrode side reaction promoting layer was not formed, it was confirmed that the maximum output density was slightly low, the voltage drop rate was large, and the reliability was lacking.

  In Sample No. 3, it was considered that the resistance increased because the first solid electrolyte was thick, and the maximum output density tended to decrease. Further, it was confirmed that the voltage decrease rate was large and the reliability was lacking. did it.

  In Sample No. 7, the strength of the first solid electrolyte was lowered and cracks were generated, so that the power generation performance could not be evaluated.

  Moreover, in the sample number 8, since the 2nd solid electrolyte was thick, it has confirmed that resistance became large and the maximum output density fell.

  In Sample No. 10, since the second solid electrolyte was thin, electrons generated at the fuel electrode could not be sufficiently blocked, and it was confirmed that the open circuit electromotive force was reduced.

  On the other hand, from Tables 1 and 2, Sample Nos. 4 to 6, 9, and 11 to 40 provide sufficient open circuit electromotive force and high maximum output density even when the operating temperature is 600 ° C. or lower. The voltage drop rate was also low, and it was confirmed that the power generation performance and reliability were sufficient. In Sample Nos. 13, 16, 22, 23, 26, 32, and 33, although a sufficient open circuit electromotive force was obtained, the maximum output density tended to decrease slightly.

Note that the oxide ion conductivity of YSZ at 600 ° C. is about 3.0 × 10 ⁻² (S / cm), and the oxide ion conductivity of LSTF at 600 ° C. (1.7 × 10 ⁻¹ (S / cm). Therefore, even if the first solid electrolyte is made of YSZ or the like, the effect of the present invention cannot be obtained.

DESCRIPTION OF SYMBOLS 1 ... Power generation cell for solid oxide fuel cells 2 ... Solid electrolyte 21 ... 1st solid electrolyte 22 ... 2nd solid electrolyte 3 ... Air electrode 31 ... Surface layer 32 ... Air electrode side reaction promotion layer 34 ... Skeletal structure 35 ... LSCF
37 ... Pore 4 ... Fuel electrode 41 ... Fuel electrode side reaction promoting layer 47 ... Pore 42 ... Support layer 48 ... Pore

Claims (15)

A power generation cell for a solid oxide fuel cell, comprising: a solid electrolyte; an air electrode formed on one main surface of the solid electrolyte; and a fuel electrode formed on the other main surface of the solid electrolyte. ,
The solid electrolyte is a dense first solid electrolyte made of (La, Sr) (Ti, Fe) O ₃ and a dense first made of Zr oxide having an oxide ion transport number of 0.96 or more. 2 solid electrolytes,
The air electrode has a porous air electrode side reaction promoting layer formed so that a plurality of pores communicate with each other;
The air electrode side reaction promoting layer is formed on one main surface of the first solid electrolyte, and the second solid electrolyte is formed between the other main surface of the first solid electrolyte and the fuel electrode. ,
The air electrode side reaction promoting layer has a dense three-dimensional skeleton structure made of (La, Sr) (Ti, Fe) O ₃ , and (La, Sr) (Co, A power generation cell for a solid oxide fuel cell, which is impregnated with Fe) O ₃ . The solid oxide fuel cell power generation cell has a fuel electrode support membrane structure,
The fuel electrode has a porous fuel electrode side reaction promoting layer formed so that a plurality of pores communicate with each other, and a porous support layer formed so that a plurality of pores communicate with each other. ,
The fuel electrode side reaction promoting layer is formed on one main surface of the second solid electrolyte,
2. The power generation cell for a solid oxide fuel cell according to claim 1, wherein a pore diameter formed in the fuel electrode side reaction promoting layer is smaller than a pore diameter formed in the support layer. The (La, Sr) (Ti, Fe) O ₃ is represented by the general formula (La _1-x Sr _x ) · (Ti _1-y Fe _y ) O ₃ , where x is 0.1 The power generation cell for a solid oxide fuel cell according to claim 1 or 2, which satisfies a relationship of -0.5 and y of 0.1 to 0.9.   4. The power generation cell for a solid oxide fuel cell according to claim 1, wherein the first solid electrolyte has a thickness of 3 to 20 μm.   The power generation cell for a solid oxide fuel cell according to any one of claims 1 to 4, wherein the thickness of the second solid electrolyte is 3 to 10 µm.   The power generation cell for a solid oxide fuel cell according to any one of claims 1 to 5, wherein the Zr oxide is yttria stabilized zirconia or scandia stabilized zirconia.   The power generation cell for a solid oxide fuel cell according to any one of claims 1 to 6, wherein the air electrode side reaction promoting layer has a thickness of 3 to 20 µm.   The power generation cell for a solid oxide fuel cell according to any one of claims 1 to 7, wherein the pores formed in the air electrode side reaction promoting layer have a diameter of 0.5 to 10 µm.   The power generation cell for a solid oxide fuel cell according to any one of claims 1 to 8, wherein the air electrode side reaction promoting layer has a porosity of 20 to 90%.   10. The power generation cell for a solid oxide fuel cell according to claim 2, wherein the fuel electrode side reaction promoting layer has a thickness of 3 to 20 μm.   The power generation cell for a solid oxide fuel cell according to any one of claims 2 to 10, wherein the pores formed in the fuel electrode side reaction promoting layer have a diameter of 0.5 to 10 µm.   The power generation cell for a solid oxide fuel cell according to any one of claims 2 to 11, wherein the fuel electrode side reaction promoting layer has a porosity of 20 to 90%.   13. The power generation cell for a solid oxide fuel cell according to claim 2, wherein the support layer has a thickness of 100 to 2000 μm.   The power generation cell for a solid oxide fuel cell according to any one of claims 2 to 13, wherein a diameter of pores formed in the support layer is 5 to 50 µm.   The power generation cell for a solid oxide fuel cell according to any one of claims 2 to 14, wherein the porosity of the support layer is 30 to 70%.

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