JP6134085B1 - Electrochemical cell - Google Patents

Abstract

An electrochemical cell capable of suppressing cracks in a seal film is provided. A fuel cell includes an insulating and porous support substrate, a power generation unit disposed on the support substrate, and a dense seal film covering an outer surface of the support substrate. . The support substrate 2 has an outer peripheral region 21 within 10 μm from the interface with the seal film 3 and an inner region 22 exceeding 10 μm from the interface. The average porosity P1 of the outer peripheral region 21 is larger than the average porosity P2 of the inner region 22. The average porosity P2 of the inner region 22 is larger than the average porosity P3 of the seal film 3. [Selection] Figure 3

Description

  The present invention relates to an electrochemical cell.

  Conventionally, as a kind of electrochemical cell, a fuel cell including an insulating and porous support substrate, a power generation unit disposed on the support substrate, and a dense seal film covering the outer surface of the support substrate is known. (For example, refer to Patent Document 1).

Japanese Patent Laying-Open No. 2015-230845

  By the way, when the fuel cell is in operation, a crack may occur in the seal film. As a result of intensive studies by the present inventors, it was found that cracks are generated in the sealing film because thermal stress caused by the difference in thermal expansion coefficient between the sealing film and the support substrate is generated in the sealing film. .

  This invention is made | formed in view of the above-mentioned situation, and it aims at providing the electrochemical cell which can suppress the crack of a sealing film.

  The electrochemical cell includes a porous support substrate, a power generation unit disposed on the support substrate, and a dense seal film that covers the outer surface of the support substrate. The support substrate has an outer peripheral region within 10 μm from the interface with the seal film and an internal region exceeding 10 μm from the interface. The average porosity of the outer peripheral region is larger than the average porosity of the inner region. The average porosity of the inner region is larger than the average porosity of the seal film.

  ADVANTAGE OF THE INVENTION According to this invention, the electrochemical cell which can suppress the crack of a sealing film can be provided.

Perspective view of fuel cell AA sectional view of FIG. BB sectional view of FIG.

(Configuration of fuel cell 1)
The configuration of the fuel cell 1 according to the present embodiment will be described with reference to the drawings. FIG. 1 is a perspective view of the fuel cell 1.

  The fuel cell 1 is a solid oxide fuel cell (SOFC). The fuel cell 1 includes a support substrate 2, a seal film 3, six power generation units 10, and an interconnector 20.

(1) Support substrate 2
The support substrate 2 is formed in a flat plate shape extending in the longitudinal direction. The support substrate 2 has a first main surface S1, a second main surface S2, a first side surface S3, and a second side surface S4.

  The first main surface S1 is provided on the opposite side of the second main surface S2. Each of the first main surface S1 and the second main surface S2 is a plate surface that extends in the longitudinal direction and the short-side direction of the support substrate 2. The short side direction is a direction perpendicular to the long side direction. The first side surface S3 is continuous with the first main surface S1 and the second main surface S2. The second side surface S4 is continuous with the first main surface S1 and the second main surface S2. The second side surface S4 is provided on the opposite side of the first side surface S3. In the present embodiment, each of the first side surface S3 and the second side surface S4 is formed in a curved surface shape.

  The first main surface S1, the second main surface S2, the first side surface S3, and the second side surface S4 are the outer surfaces of the support substrate 2. However, in this embodiment, the area | region where six electric power generation parts are arrange | positioned among 1st main surface S1 and 2nd main surface S2 shall not be contained in the outer surface of the support substrate 2. FIG.

  Although the thickness in the thickness direction of the support substrate 2 is not particularly limited, it can be 1 mm to 10 mm. The thickness direction is a direction perpendicular to the longitudinal direction and the short direction. Six gas flow paths 2 a are formed inside the support substrate 2. Each gas flow path 2 a extends along the longitudinal direction of the support substrate 2. In the present embodiment, fuel gas is caused to flow through each gas flow path 2a during power generation. The number of gas flow paths 2a is not limited to six.

The support substrate 2 contains an electrically insulating porous material as a main component. As a material constituting the support substrate 2, MgO (magnesium oxide), a mixture of MgAl ₂ O ₄ (magnesia alumina spinel) and MgO (magnesium oxide), CSZ (calcia stabilized zirconia), 8YSZ (yttria stabilized zirconia), Insulating ceramics such as Y ₂ O ₃ (yttria) and CZO (calcium zirconate) can be used. In this specification, “containing as a main component” means that the target component is contained in an amount of 80% by weight or more.

  The support substrate 2 may contain a transition metal or an oxide of the transition metal that functions as a catalyst for promoting a reforming reaction of the fuel gas. Ni (nickel) is preferred as the transition metal.

  The internal configuration of the support substrate 2 will be described later.

(2) Seal film 3
The seal film 3 covers the outer surface of the support substrate 2. That is, the seal film 3 is formed on the first main surface S1 other than the three power generation units, on the second main surface S2 other than the three power generation units, on the entire first side surface S3 and on the entire second side surface S4. Covering.

The seal film 3 is made of a dense material having no electronic conductivity. The seal film 3 can contain zirconia, magnesia, and alumina as main components. Examples of the material constituting the sealing film 3 include 3YSZ (yttria stabilized zirconia), 8YSZ, ScSZ (scandia stabilized zirconia), Y ₂ O ₃ (yttria), MgO (magnesia), and Al ₂ O ₃ (alumina). MgAl ₂ O ₃ (magnesia alumina spinel) or the like can be used.

  Although the thickness in particular of the sealing film 3 is not restrict | limited, For example, it can be 3 micrometers-50 micrometers. In the present embodiment, the sealing film 3 is formed integrally with a solid electrolyte layer 5 described later. The seal film 3 may have a single layer structure or a multilayer structure. The sealing film 3 may be made of the same material as the solid electrolyte layer 5 or may be made of a material different from that of the solid electrolyte layer 5. When the sealing film 3 has a multilayer structure, each layer may be composed of different materials.

(3) Power generation unit 10
The six power generation units 10 are arranged on the support substrate 2. Each power generation unit has a similar configuration.

  Here, FIG. 2 is an AA cross-sectional view of FIG. Each power generation unit 10 includes a fuel electrode 4, a solid electrolyte layer 5, a reaction preventing layer 6, an air electrode 7, and an air electrode current collecting layer 8.

  The fuel electrode 4 is disposed on the support substrate 2. The fuel electrode 4 functions as an anode. The anode 4 has an anode current collecting layer 41 and an anode active layer 42.

The anode current collecting layer 41 is disposed on the support substrate 2. The anode current collecting layer 41 is made of a material containing NiO and having electron conductivity. The anode current collecting layer 41 may contain a substance having oxygen ion conductivity. The anode current collecting layer 41 can be made of, for example, NiO-8YSZ, NiO—Y ₂ O ₃ , NiO—CSZ, or the like. The thickness of the anode current collecting layer 41 is not particularly limited, but can be 50 μm to 500 μm. The anode current collecting layer 41 may be porous, and the porosity is not particularly limited, but may be 25% to 50%.

  The anode active layer 42 is disposed on the anode current collecting layer 41. The anode active layer 42 is composed of a substance having electron conductivity and a substance having oxygen ion conductivity. The anode active layer 42 can be made of, for example, NiO-8YSZ, NiO-GDC (gadolinium-doped ceria), or the like. The volume ratio of the substance having oxygen ion conductivity in the anode active layer 42 is preferably larger than the volume ratio of the substance having oxygen ion conductivity in the anode current collecting layer 41. The thickness of the anode active layer 42 is not particularly limited, but can be 5 μm to 30 μm. The porosity of the anode active layer 42 is not particularly limited, but can be 25% to 50%.

  The solid electrolyte layer 5 is disposed on the fuel electrode 4. In the present embodiment, the solid electrolyte layer 5 is formed integrally with the seal film 3 (see FIG. 1). The solid electrolyte layer 5 is made of a dense material that has ionic conductivity and does not have electronic conductivity. The solid electrolyte layer 5 can contain zirconia as a main component. As a material constituting the solid electrolyte layer 5, for example, 3YSZ, 8YSZ, ScSZ, or the like can be used. The porosity of the solid electrolyte layer 5 is lower than the porosity of the support substrate 2 and the fuel electrode 4. The porosity of the solid electrolyte layer 5 can be 20% or less, and is preferably 10% or less. The thickness of the solid electrolyte layer 5 is not particularly limited, but can be 3 μm to 50 μm.

  The reaction preventing layer 6 is disposed on the solid electrolyte layer 5. As a material constituting the reaction preventing layer 7, for example, a ceria-based material containing ceria and a rare earth metal oxide dissolved in ceria can be used. Examples of such ceria-based materials include GDC and SDC (samarium-doped ceria). The thickness of the reaction preventing film 6 is not particularly limited, but can be 3 μm to 50 μm.

The air electrode 7 is disposed on the reaction preventing layer 6. The air electrode 7 is made of a porous material having mixed conductivity. Examples of the material constituting the air electrode 7 include (La, Sr) (Co, Fe) O ₃ (LSCF, lanthanum strontium cobalt ferrite), (La, Sr) FeO ₃ (LSF, lanthanum strontium ferrite), La ( Ni, Fe) O ₃ (LNF, lanthanum nickel ferrite), (La, Sr) CoO ₃ (LSC, lanthanum strontium cobaltite), and the like. The thickness of the air electrode 7 is not particularly limited, but can be 10 to 100 μm.

  The air electrode current collecting layer 8 is disposed on the air electrode 7. The air electrode current collecting layer 8 is made of a porous material having electronic conductivity. The air electrode current collecting layer 8 can be made of, for example, LSCF, LSC, Ag (silver), Ag—Pd (silver palladium alloy), or the like. Further, the air electrode current collecting layer 8 may be made of the same material as that of the connection member 30 described above. The thickness of the air electrode current collecting layer 8 is not particularly limited, but can be 50 μm to 500 μm.

(4) Interconnector 20
The interconnector 20 is disposed on the fuel electrode 4. The interconnector 20 electrically connects two adjacent power generation units 10. The interconnector 20 is interposed between the fuel electrode 4 of one power generation unit 10 and the air electrode current collecting layer 7 of the other power generation unit 10.

The interconnector 20 is a dense layer compared to the support substrate 2 and the fuel electrode 4. The interconnector 20 can be made of, for example, LaCrO ₃ (lanthanum chromite), (Sr, La) TiO ₃ (strontium titanate), or the like. The interconnector 20 only needs to be denser than the fuel electrode 4, and the porosity is not particularly limited, but is preferably 20% or less, and more preferably 10% or less. The thickness of the interconnector 20 is not particularly limited, but can be 10 μm to 100 μm.

(Internal structure of support substrate 2)
3 is a cross-sectional view taken along line BB in FIG. The support substrate 2 has an outer peripheral region 21 and an inner region 22.

  The outer peripheral region 21 surrounds the inner region 22. The outer peripheral region 21 is formed in a cylindrical shape as a whole. The outer peripheral region 21 is a region within 10 μm from the interface with the seal film 3 in the support substrate 2. The interface between the support substrate 2 and the seal film 3 is the first main surface S1, the second main surface S2, the first side surface S3, and the second side surface S4 of the support substrate 2.

  The inner region 22 is disposed inside the outer peripheral region 21. The internal region 22 is formed in a plate shape. Six gas flow paths 2 a are formed inside the internal region 22. The internal region 22 is a region exceeding 10 μm from the interface with the seal film 3 in the support substrate 2. That is, the internal region 22 is separated from the interface between the support substrate 2 and the seal film 3 by more than 10 μm.

  The average porosity P1 of the outer peripheral region 21 is larger than the average porosity P2 of the inner region 22. The average porosity P2 of the inner region 22 is larger than the average porosity P3 of the seal film 3. Since the average porosity P1 of the outer peripheral region 21 is larger than the average porosity P2 of the inner region 22, the Young's modulus of the outer peripheral region 21 is smaller than the Young's modulus of the inner region 22. In this way, by inserting the outer peripheral region 21 having a relatively low Young's modulus between the seal film 3 and the inner region 22, the difference in thermal expansion coefficient between the seal film 3 and the support substrate 2 during operation of the fuel cell 1. It can suppress that the thermal stress resulting from this arises in the sealing film 3. FIG. As a result, generation of cracks in the seal film 3 can be suppressed.

  The average porosity P1 of the outer peripheral region 21 is preferably 5 points or more larger than the average porosity P2 of the inner region 22. The average porosity P1 of the outer peripheral region can be 25 to 70%. The average porosity P2 of the inner region 22 can be 20 to 50%. The average porosity of the seal layer 3 can be 10% or less, preferably 7% or less, and more preferably 5% or less. The average porosity P3 of the seal film 3 can be made equal to the porosity of the solid electrolyte layer 5 described above.

  The average porosity P1 of the outer peripheral region 21 is 10 spots (observation range 12 μm × 9 μm) of the cross section of the outer peripheral region 21 observed by SEM (scanning electron microscope) at 7500 times, and the occupied area ratio of the pores in each SEM image is Obtained by arithmetic averaging. The 10 spots observed with the SEM are set to positions that divide the outer peripheral region 21 into 11 equal parts in the circumferential direction. The average porosity P2 of the inner region 22 and the average porosity P3 of the seal film 3 are obtained by the same method as the average porosity P1 of the outer peripheral region 21. The 10 spots for observing each of the inner region 22S and the sealing film 3 with the SEM are set to positions adjacent to the 10 spots for the outer peripheral region 21 observed with the SEM in the thickness direction.

  The average equivalent circle diameter R1 of the pores in the outer peripheral region 21 is not particularly limited, but may be 0.5 μm to 3 μm, and preferably 0.5 μm or more. The average equivalent circle diameter R2 of the pores in the inner region 22 can be made smaller than the average equivalent circle diameter R1 of the pores in the outer peripheral region 21. The average equivalent circular diameter R2 of the pores in the inner region 22 is not particularly limited, but can be 0.2 μm to 2.5 μm, and preferably 2.5 μm or less. The average equivalent circle diameter R3 of the pores in the seal film 3 can be made smaller than the average equivalent circle diameter R2 of the pores in the inner region 22. The average equivalent circle diameter R3 of the pores in the seal film 3 is not particularly limited, but can be 0.1 μm to 2 μm, and preferably 2 μm or less.

  In the present embodiment, the circle equivalent diameter of the pores is a diameter of a circle having the same area as the cross-sectional area of the pores in the SEM image. The average equivalent circle diameter of pores can be obtained by arithmetically averaging the equivalent circle diameters of 20 pores randomly selected from one SEM image.

  The average equivalent circle diameter D1 of the ceramic particles constituting the outer peripheral region 21 is not particularly limited, but may be 0.2 μm to 2 μm, and preferably 2 μm or less. The average bonding width L1 of the ceramic particles constituting the outer peripheral region 21 can be 0.2 μm to 2 μm, and preferably 2 μm or less. The average equivalent circle diameter D2 of the ceramic particles constituting the internal region 22 is not particularly limited, but may be 0.5 μm to 5 μm, preferably 0.5 μm or more. The average bonding width L2 of the ceramic particles constituting the inner region 22 can be set to 0.2 μm to 5 μm, and is preferably 0.2 μm or more.

  The equivalent circle diameter of the ceramic particles is the diameter of a circle having the same area as the cross-sectional area of the ceramic particles in the SEM image. The average equivalent circle diameter of the ceramic particles can be obtained by arithmetically averaging the equivalent circle diameters of 20 ceramic particles randomly selected from one SEM image.

  The average bonding width of the ceramic particles is an index indicating the neck thickness between the ceramic particles bonded to each other. The average bonding width of the ceramic particles can be obtained by arithmetically averaging the widths of 20 bonding portions randomly selected from one SEM image.

(Manufacturing method of fuel cell 1)
An example of a method for manufacturing the fuel cell 1 will be described.

  First, a molded body of the internal region 22 having six gas flow paths 2a is formed by extruding a clay prepared by adding a pore former and a binder to the support substrate material powder described above. The average particle diameter of the support substrate material used for the molded body of the inner region 22 can be set to 0.5 μm to 3 μm. The average porosity of the inner region 22 can be controlled by adjusting the amount of pore former added.

  Next, tape molding is performed using the slurry for the outer peripheral region prepared by adding the pore former and the binder to the above-described support substrate material. Then, the molded tape is wound around the molded body in the inner region 22. As a result, a molded body of the outer peripheral region 21 is formed. The average particle diameter of the support substrate material used for the molded body in the outer peripheral region 21 can be set to 0.5 μm to 5 μm. The average porosity of the outer peripheral region 21 can be controlled by adjusting the amount of pore former added. The thickness of the outer peripheral region 21 can be adjusted by the tape thickness.

  Next, the fuel electrode material is made into a paste and screen-printed on the molded body of the support substrate 2 to form the molded body of the fuel electrode 4.

  Next, the interconnector material is formed into a paste and screen-printed on the molded body of the fuel electrode 4 to form a molded body of the interconnector 20.

  Next, the solid electrolyte material is formed into a paste, and the solid electrolyte material 5 is screen-printed on the molded body of the fuel electrode 4 to form a molded body of the solid electrolyte layer 5. At this time, the molded body of the seal film 3 can be integrally manufactured by screen printing the paste of the solid electrolyte material so as to cover the entire exposed surface of the support substrate 2.

  Next, the reaction preventing layer 6 is formed on the solid electrolyte layer 5 by dip forming the reaction preventing layer material.

  Next, the molded body of the support substrate 2, the sealing film 3, the fuel electrode 4, the interconnector 20, the solid electrolyte layer 5 and the reaction preventing layer 6 is co-fired (1300 to 1600 ° C., 2 to 20 hours).

  Next, the air electrode material is made into a paste and screen-printed on the solid electrolyte layer 5 to form a molded body of the air electrode 7. Subsequently, the air electrode current collecting layer material is made into a paste and screen-printed on the air electrode 7 shaped body to form the air electrode current collecting layer 8 shaped body.

  Next, the molded object of the air electrode 7 and the air electrode current collection layer 8 is baked (900-1100 degreeC, 1 to 20 hours).

(Other embodiments)
The present invention is not limited to the embodiment described above, and various modifications or changes can be made without departing from the scope of the present invention.

  In the above embodiment, the case where the support substrate according to the present invention is applied to a solid oxide fuel cell has been described. However, the support substrate according to the present invention is not only a solid oxide fuel cell but also a solid oxide electrolytic cell. It is applicable to a solid oxide electrochemical cell containing

  In the above embodiment, the outer peripheral region 21 is formed on the entire support substrate 2, but the outer peripheral region 21 may be formed only on a part of the support substrate 2. Even in this case, cracks of the seal film 3 can be suppressed at least in the region where the outer peripheral region 21 is formed.

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

(Sample No. 1-10)
First, an inner part having six gas flow paths is formed by extruding a clay prepared by adding a binder (cellulose) and a pore former (graphite) to MgO powder (average particle diameter 0.5 μm to 3 μm). An area compact was formed. At this time, the average porosity of the internal region was changed for each sample as shown in Table 1 by adjusting the addition amount of the pore former.

  Next, tape molding was performed using a slurry for the outer peripheral region prepared by adding a binder (cellulose) and a pore former (graphite) to MgO powder (average particle size 0.5 μm to 5 μm). At this time, by adjusting the addition amount of the pore former, the average porosity in the outer peripheral region was changed for each sample as shown in Table 1. And the molded object of the outer peripheral area | region was formed by winding the shape | molded tape around the molded object of an internal area | region.

  Next, a slurry obtained by adding a binder (cellulose) to a composite material of NiO powder and YSZ powder (NiO powder: YSZ powder = 50 vol%: 50 vol%) is printed on the molded body of the support substrate, thereby collecting the anode current collector. A layered compact was formed.

  Next, a slurry obtained by adding a binder (cellulose) to a composite material of NiO powder and YSZ powder (NiO powder: YSZ powder = 50 vol%: 50 vol%) is printed on the molded body of the anode current collecting layer, thereby A molded body of the extremely active layer was formed.

Next, a slurry obtained by adding cellulose as a binder to LaCrO ₃ powder was printed on the molded body of the anode current collecting layer, thereby forming an interconnector molded body.

  Next, a solid electrolyte membrane molded body was formed by printing a slurry obtained by adding cellulose as a binder to 8YSZ powder on the molded body of the fuel electrode active layer. At this time, the slurry for the solid electrolyte membrane was printed on the entire outer surface of the molded body in the outer peripheral region of the support substrate, whereby the molded body of the seal film was formed integrally with the molded body of the solid electrolyte membrane.

  Next, a slurry obtained by adding cellulose as a binder to the GDC powder was printed on a solid electrolyte membrane molded body to form a reaction-prevented film molded body.

  Next, the molded body of the support substrate, the fuel electrode, the interconnector, the solid electrolyte membrane, and the reaction preventing membrane was fired (atmospheric atmosphere, 1400 ° C., 2 hours). The thickness of the outer peripheral region of the support substrate was 10 μm.

  Next, a slurry in which cellulose was added as a binder to the LSCF powder was printed on the reaction preventing film to form an air electrode molded body.

  Next, the slurry which added the cellulose as a binder to LSCF powder was printed on the molded object of the air electrode, and the molded object of the air electrode current collection layer was formed.

  Next, the compacts of the air electrode and the air electrode current collecting layer were fired (atmospheric atmosphere, 1400 ° C., 2 hours). As described above, sample no. Fuel cells according to 1 to 10 were completed.

(Sample Nos. 11-13)
Sample No. except that no outer peripheral area was provided on the support substrate. In the same process as in No. 1, sample no. Fuel cells according to 11 to 13 were produced.

(Porosity of sealing film and support substrate)
Ten spots on the cross section of the sealing film (observation range: 12 μm × 9 μm) were observed at 7500 times using an SEM (manufactured by JEOL Ltd., model JSM-6610LV), and the area occupied by pores in each SEM image was arithmetically averaged As a result, the porosity of the sealing film was calculated. The 10 spots obtained by observing the outer peripheral area with the SEM were set at positions where the outer peripheral area was equally divided into 11 in the circumferential direction, and the 10 spots obtained by observing the inner area 22S and the seal film 3 with the SEM were observed with the SEM. It was set at a position adjacent to 10 spots in the thickness direction. Moreover, the average porosity of each of the inner region and the outer peripheral region was calculated by the same method. The calculation results of porosity are summarized in Table 1.

(Fuel cell thermal cycle test)
Sample No. 1-No. A heat cycle test was conducted on No. 13.

  Specifically, first, the temperature is raised from room temperature to 750 ° C. over 90 minutes, and then 4% hydrogen gas (4% hydrogen gas with respect to Ar gas) is supplied to the fuel electrode side while maintaining the temperature at 750 ° C. The reduction process was performed.

  Then, the initial output of the fuel cell was measured. Next, the temperature was lowered to 100 ° C. or lower while maintaining the reducing atmosphere by continuing the supply of 4% hydrogen gas. Then, the temperature raising step and the temperature lowering step were set as one cycle and repeated 20 cycles.

  Then, the presence or absence of the crack in a sealing film was confirmed by observing the cross section of a sealing film and a support substrate with a microscope. The confirmation results are summarized in Table 1. In Table 1, a sample having 3 or more cracks of 10 μm or more in 10 fields of view was evaluated as x, a sample having 1 to 2 cracks was ◯, and there was no crack (0). Is rated as ◎.

  As shown in Table 1, a sample No. in which an outer peripheral region having a relatively high porosity was interposed between the seal film and the inner region. In 1-10, it was suppressed that a crack generate | occur | produces in a sealing film. This is because an outer peripheral region having a relatively small Young's modulus is interposed between the seal membrane and the inner region, so that the thermal stress caused by the difference in thermal expansion coefficient between the seal membrane and the support substrate is sealed when the fuel cell is in operation. This is because it can be suppressed from occurring in the film.

  In particular, sample No. 1 in which the average porosity of the outer peripheral region 21 is larger by 5 points or more than the average porosity of the inner region 22. In 1 to 7, the occurrence of cracks could be reduced to zero.

DESCRIPTION OF SYMBOLS 1 Fuel cell 2 Support substrate 21 Internal area | region 22 Outer peripheral area | region 2a Gas flow path S1 1st main surface S2 2nd main surface S3 1st side surface S4 2nd side surface 3 Sealing film 4 Fuel electrode 5 Solid electrolyte layer 6 Reaction prevention layer 7 Air Electrode 8 Air electrode current collector layer 10 Power generation unit 20 Interconnector

Claims (1)

An insulating and porous support substrate;
A power generation unit disposed on the support substrate;
A dense sealing film covering the outer surface of the support substrate;
With
The support substrate has an outer peripheral region within 10 μm from the interface with the seal film, and an internal region more than 10 μm from the interface;
The average porosity of the outer peripheral region is greater than the average porosity of the inner region,
The average porosity of the inner region is larger than the average porosity of the seal film,
Electrochemical cell.

Images