JP6239719B2 - Fuel cell - Google Patents

Description

  The present invention relates to a fuel cell.

  Conventionally, a fuel cell including a fuel electrode, an air electrode, and a solid electrolyte layer disposed between the fuel electrode and the air electrode is known.

  Here, in order to suppress the formation of a high resistance layer between the air electrode and the solid electrolyte layer, a technique of interposing a barrier layer between the air electrode and the solid electrolyte layer has been proposed (Patent Document). 1).

JP 2004-303455 A

  However, since the thermal expansion coefficients of the solid electrolyte layer and the barrier layer are different, cracks may occur in the barrier layer due to the stress caused by the expansion and contraction during the manufacture of the fuel cell.

  This invention is made | formed in view of such a condition, and it aims at provision of the fuel cell which can suppress that a crack generate | occur | produces in a barrier layer.

  The fuel cell according to the present invention includes a fuel electrode, an air electrode, a solid electrolyte layer, a barrier layer, and an intermediate layer. The solid electrolyte layer contains Zr and is disposed between the fuel layer and the air electrode. The barrier layer includes Ce and is disposed between the air electrode and the solid electrolyte layer. The intermediate layer contains Zr and a rare earth element, and is disposed between the solid electrolyte layer and the barrier layer. The Sr coverage in the intermediate layer is less than 20%.

  ADVANTAGE OF THE INVENTION According to this invention, the fuel cell which can suppress that a crack generate | occur | produces in a barrier layer can be provided.

Sectional view showing the configuration of the fuel cell Cross section of the intermediate layer

  Next, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, the drawings are schematic, and the ratio of each dimension may be different from the actual one. Accordingly, specific dimensions and the like should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

(Configuration of fuel cell 10)
The configuration of the fuel cell 10 will be described with reference to the drawings. The fuel cell 10 is a so-called SOFC (Solid Oxide Fuel Cell). The fuel cell 10 can take various forms such as a vertical stripe type, a horizontal stripe type, a flat plate type, a fuel electrode support type, or a cylindrical type.

  FIG. 1 is a cross-sectional view showing the configuration of the fuel cell 10. The fuel cell 10 includes a fuel electrode 20, a solid electrolyte layer 30, an intermediate layer 40, a barrier layer 50, and an air electrode 60.

  The fuel electrode 20 functions as an anode of the fuel cell 10. During operation of the fuel cell 10, fuel gas (for example, hydrogen gas) is supplied to the fuel electrode 20. The fuel electrode 20 may have a fuel electrode current collecting layer 21 and a fuel electrode active layer 22 as shown in FIG.

The anode current collecting layer 21 is a porous body excellent in gas permeability. As a material constituting the anode current collecting layer 21, materials conventionally used for SOFC anode current collecting layers can be used. For example, NiO (nickel oxide) -8YSZ (8 mol% yttria is stabilized). Zirconia) or NiO—Y ₂ O ₃ (yttria) can be used. When the anode current collecting layer 21 contains NiO, at least a part of NiO may be reduced to Ni during operation of the fuel cell 10. The thickness of the anode current collecting layer 21 can be set to 0.1 mm to 5.0 mm, for example.

  The anode active layer 22 is disposed on the anode current collecting layer 21. The anode active layer 22 is a denser porous body than the anode current collecting layer 21. As a material constituting the anode active layer 22, materials conventionally used for the anode active layer of SOFC can be used, for example, NiO-8YSZ can be used. When the anode active layer 22 contains NiO, at least a part of NiO may be reduced to Ni during operation of the fuel cell 10. The thickness of the anode active layer 22 can be set to, for example, 5.0 μm to 30 μm.

  The solid electrolyte layer 30 is disposed between the fuel electrode 20 and the air electrode 60. In the present embodiment, the solid electrolyte layer 30 is sandwiched between the fuel electrode 20 and the intermediate layer 40. The solid electrolyte layer 30 allows oxygen ions generated at the air electrode 60 to pass therethrough. The thickness of the solid electrolyte layer 30 can be 3 μm to 20 μm.

The solid electrolyte layer 30 contains Zr (zirconium). The solid electrolyte layer 30 may contain a zirconia-based material containing ZrO ₂ (zirconia) as a main component. Examples of the zirconia-based material include YSZ (yttria stabilized zirconia), ScSZ (scandia stabilized zirconia), and CaSZ (calcia stabilized zirconia), and YSZ is particularly preferable. In the present embodiment, the phrase “the composition X contains the substance Y as a main component” means that the substance Y accounts for 70% by weight or more in the entire composition X, and is 90% by weight or more. It is more preferable.

  The solid electrolyte layer 30 is preferably dense. The porosity of the solid electrolyte layer 30 is preferably lower than the porosity of the intermediate layer 40 and the barrier layer 50. Specifically, the porosity of the solid electrolyte layer 30 can be 7% or less, and preferably 5% or less. The porosity of the solid electrolyte layer 30 can be calculated by dividing the sum of the pore areas by the total area of the solid electrolyte layer 30 on an electron microscope (SEM) image of a cross section in the thickness direction of the solid electrolyte layer 30. it can.

The intermediate layer 40 is disposed between the solid electrolyte layer 30 and the barrier layer 50. The intermediate layer 40 includes Zr and Ce. The intermediate layer 40 may contain Zr as ZrO ₂ . The intermediate layer 40 may contain Ce as CeO ₂ . In particular, the intermediate layer 40 preferably includes YSZ and GDC (gadolinium-doped ceria) as main components. In this case, it is preferable that ZrO ₂ and CeO ₂ form a solid solution. As a result, the bonding strength between the solid electrolyte layer 30 and the barrier layer 50 can be improved. Furthermore, the intermediate layer 40 more preferably contains a solid solution of ZrO ₂ and CeO ₂ as main components.

  When the intermediate layer 40 includes cerium and zirconium, the cerium concentration D1 and the zirconium concentration D2 may satisfy one or more of the following conditions (a) to (h).

  (A) The ratio D2 / D1 of the zirconium concentration D2 to the cerium concentration D1 satisfies 0.1 ≦ D2 / D1.

  (B) The ratio D2 / D1 of the concentration D2 of zirconium to the concentration D1 of cerium satisfies D2 / D1 ≦ 1.

  (C) The concentration D1 of cerium satisfies D1 ≦ 80 mol%.

  (D) The cerium concentration D1 satisfies 40 mol% ≦ D1.

  (E) The concentration D2 of zirconium satisfies D2 ≦ 50 mol%.

  (F) The zirconium concentration D2 satisfies 10 mol% ≦ D2.

  (G) The ratio of the cerium concentration D1 in the intermediate layer 40 to the cerium concentration D3 in the barrier layer 50 satisfies D1 / D3 ≦ 0.9.

  (H) The ratio of the zirconium concentration D2 in the intermediate layer 40 to the zirconium concentration D4 in the solid electrolyte layer 30 satisfies D2 / D4 ≦ 0.5.

  In the present embodiment, the “concentration” of the component contained in each layer is the concentration in the entire layer (that is, the average content in each layer) unless otherwise specified. The “concentration” is obtained by line analysis based on an atomic concentration profile in the thickness direction, that is, comparison of characteristic X-ray intensities by EPMA (Electron Probe Micro Analyzer).

The intermediate layer 40 includes Sr (strontium). The intermediate layer 40 may contain Sr as SrZrO ₃ . If the intermediate layer 40 comprises SrZrO _3, the SrZrO ₃ is preferably a rare earth element (Y, at least one of Gd and Ce) is not a solid solution. As a result, the bonding strength between the solid electrolyte layer 30 and the barrier layer 50 can be improved.

  By including Sr in the intermediate layer 40, the thermal expansion coefficient (that is, the linear expansion coefficient) of the intermediate layer 40 can be reduced. In the present embodiment, as will be described later, the thermal expansion coefficient of the intermediate layer 40 is adjusted to a value between the solid electrolyte layer 30 and the barrier layer 50 by controlling the Sr coverage in the intermediate layer 40. When the thermal expansion coefficient of the barrier layer 50 is higher than the thermal expansion coefficient of the solid electrolyte layer 30, the thermal expansion coefficient of the intermediate layer 40 is higher than that of the solid electrolyte layer 30 and lower than that of the barrier layer 50. The Sr coverage in the intermediate layer 40 will be described later.

  The intermediate layer 40 has a first surface 40S and a second surface 40T. The first surface 40 </ b> S is an interface between the solid electrolyte layer 30 and the intermediate layer 40. The second surface 40T is an interface between the intermediate layer 40 and the barrier layer 50. The intermediate layer 40 contacts the solid electrolyte layer 30 on the first surface 40S, and contacts the barrier layer 50 on the second surface 40T. The distance in the thickness direction between the first surface 40S and the second surface 40T corresponds to the thickness of the intermediate layer 40.

  The first surface 40S is defined by a line indicating a concentration of 85% of the maximum zirconium concentration in the solid electrolyte layer 30. The intermediate layer 40 exhibits a maximum zirconium concentration and a minimum cerium concentration on the first surface 40S.

  The second surface 40T is defined by a line indicating a concentration of 85% of the maximum cerium concentration in the barrier layer 50. The intermediate layer 40 exhibits a maximum cerium concentration and a minimum zirconium concentration on the second surface 40T.

  The average thickness of the intermediate layer 40 can be 200 nm or more and 2000 nm or less. The average thickness of the intermediate layer 40 is preferably 1800 nm or less. The average thickness of the intermediate layer 40 is an average interval between the first surface 40S and the second surface 40T in the thickness direction. The average distance between the first surface 40S and the second surface 40T is a value obtained by arithmetically averaging distances measured at five points on the cross section of the intermediate layer 40 in the thickness direction. The five points at which the distance is measured are preferably set at positions where the intermediate layer 40 is equally divided into six in the plane direction perpendicular to the thickness direction.

  The intermediate layer 40 is denser than the fuel electrode 20 and the air electrode 60. The porosity of the intermediate layer 40 may be higher than the porosity of the solid electrolyte layer 30. Thereby, the stress generated at the interface between the intermediate layer 40 and the solid electrolyte layer 30 can be relaxed. The porosity of the intermediate layer 40 is preferably 15% or less.

  The barrier layer 50 is disposed between the solid electrolyte layer 30 and the air electrode 60. In the present embodiment, the barrier layer 50 is sandwiched between the intermediate layer 40 and the air electrode 60. The barrier layer 50 suppresses the formation of a high resistance layer between the solid electrolyte layer 30 and the air electrode 60. The barrier layer 50 is denser than the fuel electrode 20 and the air electrode 60.

The barrier layer 50 contains Ce. The barrier layer 50 may contain Ce as CeO ₂ . The barrier layer 50 can be made of a ceria-based material including CeO ₂ and a rare earth metal oxide solid-dissolved in CeO ₂ . The barrier layer 50 may contain a ceria-based material as a main component. Examples of the ceria-based material include GDC ((Ce, Gd) O ₂ : Gadolinium doped ceria), SDC ((Ce, Sm) O ₂ : samarium doped ceria) and the like. The ratio of rare earth metal oxide: ceria (mol composition ratio) can be 5:95 to 20:80. The barrier layer 50 may contain an additive in addition to the ceria-based material.

  The average thickness of the barrier layer 50 can be 1 μm or more and 30 μm or less, and is preferably 10 μm or less.

  The air electrode 60 is disposed on the barrier layer 50. The air electrode 60 functions as a cathode of the fuel cell 10. The air electrode 60 is a porous body. The thickness of the air electrode 60 can be, for example, 10 μm to 300 μm. During the operation of the fuel cell 10, an oxidant gas (for example, air) is supplied to the air electrode 60. The air electrode 60 allows the oxidant gas to pass therethrough.

The air electrode 60 contains a perovskite complex oxide represented by the general formula ABO ₃ as a main component. Examples of such perovskite complex oxides include LSCF ((La, Sr) (Co, Fe) O ₃ : lanthanum strontium cobalt ferrite), LSF ((La, Sr) FeO ₃ : lanthanum strontium ferrite), LSC (( La, Sr) CoO ₃ : lanthanum strontium cobaltite), LNF (La (Ni, Fe) O ₃ : lanthanum nickel ferrite), LSM ((La, Sr) MnO ₃ : lanthanum strontium manganate), etc. It is not limited to this.

(Sr coverage in the intermediate layer 40)
Next, the Sr coverage in the intermediate layer 40 will be described with reference to the drawings. FIG. 2 is a cross-sectional view of the intermediate layer 40 parallel to the thickness direction.

  The Sr coverage indicates how much Sr is present in the intermediate layer 40. The higher the Sr coverage, the lower the thermal expansion coefficient of the intermediate layer 40, and the lower the Sr coverage, the higher the thermal expansion coefficient of the intermediate layer 40.

  The Sr coverage can be measured by observing a cross section of the intermediate layer 40 with a TEM and performing element mapping of Sr. Specifically, a virtual line L parallel to the first surface 40S of the intermediate layer 40 is drawn in a cross section in the thickness direction of the intermediate layer 40, and the total length A of the solid phase region (that is, the region other than the pores) on the virtual line L. The ratio of the total length B of the Sr existence region to the Sr coverage can be defined as the Sr coverage. What is necessary is just to set the length of the virtual line L in the range of 3 micrometers-30 micrometers.

  In addition, when a plurality of virtual lines L can be drawn from the first surface 40S toward the second surface 40T at intervals of 200 nm, the largest value of the Sr coverage calculated for each of the plurality of virtual lines L is set. The Sr coverage in the intermediate layer 40 is assumed.

  In the example shown in FIG. 2, it is assumed that three virtual lines L1 to L3 are set and no pores exist. On the phantom line L1, the ratio R1 of the total length B1 + B2 of the Sr existence region to the full length A1 of the solid phase region is ((B1 + B2) / A1) × 100. On the imaginary line L2, the ratio R2 of the total length B3 + B4 + B5 + B6 of the Sr existing region to the full length A1 of the solid phase region is ((B3 + B4 + B5 + B6) / A1) × 100. On the phantom line L3, the ratio R3 of the total length B7 + B8 + B9 of the Sr existence region to the full length A1 of the solid phase region is ((B7 + B8 + B9) / A1) × 100. R2 which is the largest value among R1 to R3 is adopted as the Sr coverage in the intermediate layer 40.

  The higher the Sr coverage, the smaller the thermal expansion coefficient of the intermediate layer 40 and the closer to the thermal expansion coefficient of the solid electrolyte layer 30. On the other hand, the smaller the Sr coverage, the greater the thermal expansion coefficient of the intermediate layer 40 and the closer to the thermal expansion coefficient of the barrier layer 50.

  In the present embodiment, the Sr coverage in the intermediate layer 40 is less than 20%. Thereby, the thermal expansion coefficient of the intermediate layer 40 becomes a value between the thermal expansion coefficient of the solid electrolyte layer 30 and the thermal expansion coefficient of the barrier layer 50. By such an intermediate layer 40 being interposed between the solid electrolyte layer 30 and the barrier layer 50, the difference in thermal expansion coefficient between the solid electrolyte layer 30 and the barrier layer 50 is alleviated. Therefore, since it can suppress that a stress arises in barrier layer 50 with expansion and contraction at the time of manufacture of fuel cell 10, it can control that a crack occurs in barrier layer 50. The Sr coverage in the intermediate layer 40 is more preferably 15% or less, and still more preferably 10% or less.

(Manufacturing method of fuel cell 10)
Next, an example of a method for manufacturing the fuel cell 10 will be described.

  First, a molded body of the anode current collecting layer 21 is formed by molding the anode current collecting layer material powder by a die press molding method.

  Next, a fuel electrode active layer slurry is prepared by adding PVA (polyvinyl alcohol) as a binder to a mixture of the fuel electrode active layer material powder and a pore-forming agent (for example, PMMA). And the molded object of the fuel electrode active layer 22 is formed by printing the slurry for fuel electrode active layers on the molded object of the fuel electrode current collecting layer 21 by a printing method or the like. Thus, a molded body of the fuel electrode 20 is formed.

  Next, terpineol and a binder are mixed with the solid electrolyte layer material powder containing Zr to produce a solid electrolyte layer slurry. Then, the solid electrolyte layer 30 molded body is formed by applying the solid electrolyte layer slurry on the molded body of the fuel electrode active layer 22 by a printing method or the like.

  Next, an intermediate layer slurry is prepared by mixing Sr-containing powder, terpineol, and a binder with an intermediate layer material powder containing a Zr powder and a rare earth element. At this time, the mixing amount of the Sr-containing powder is adjusted so that the Sr coverage in the intermediate layer 40 is less than 20%. Then, the intermediate layer 40 formed body is formed by applying the intermediate layer slurry onto the solid electrolyte layer 30 formed body by a printing method or the like.

  Next, a barrier layer slurry is prepared by mixing terpineol and a binder into a barrier layer material powder containing Ce. And the molded object of the barrier layer 50 is formed by apply | coating the slurry for barrier layers on the molded object of the intermediate | middle layer 40 by a printing method.

  Next, the fuel electrode 20, the solid electrolyte layer 30, the intermediate layer 40, and the barrier layer 50 are fired (1350 ° C. to 1450 ° C., 1 hour to 20 hours) to thereby form the fuel electrode 20 and the solid electrolyte layer 30. Then, the intermediate layer 40 and the barrier layer 50 are formed.

  Next, a slurry for the air electrode is prepared by mixing a perovskite type complex oxide material for the air electrode, water and a binder with a ball mill for 24 hours. And the molded object of the air electrode 60 is formed by apply | coating the slurry for air electrodes on the barrier layer 50 by the printing method etc. FIG.

  Next, the air electrode 60 is formed by firing the body of the air electrode 60 (1000 to 1100 ° C., 1 to 10 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 barrier layer 50 has a single layer structure, but may have a multilayer structure in which a dense barrier layer and a porous barrier layer are laminated (in no particular order).

  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.

(Production of sample No. 1 to No. 10)
Sample no. 1-No. 10 was produced.

First, a NiO powder and Y ₂ O ₃ powder and the pore former (PMMA) slurry prepared by mixing blended powder and of IPA to prepare a mixed powder by drying under a nitrogen atmosphere.

  Next, the mixed powder is uniaxially pressed (molding pressure 50 MPa) to form a plate 30 mm long × 30 mm wide and 3 mm thick, and the plate is further consolidated with CIP (molding pressure: 100 MPa) to collect the fuel electrode. A layered compact was prepared.

  Next, a mixture of NiO-8YSZ and PMMA mixed powder and IPA was applied onto the anode current collector layer to produce an anode active layer molded body.

  Next, terpineol and a binder were mixed with the solid electrolyte layer material powder containing Zr shown in Table 1 to prepare a solid electrolyte layer slurry. Then, a solid electrolyte layer molded body was formed by applying the solid electrolyte layer slurry onto the fuel electrode active layer molded body.

  Next, Sr-containing powder, terpineol, and a binder were mixed with the intermediate layer material powder containing Zr and Ce shown in Table 1 to prepare an intermediate layer slurry. Under the present circumstances, in order to change the Sr coverage in the intermediate | middle layer after baking mentioned later for every sample, the addition amount of Sr containing powder was adjusted for every sample.

  Next, the intermediate layer formed body was formed by applying the intermediate layer slurry onto the solid electrolyte layer formed body. Under the present circumstances, in order to change the thickness of the intermediate | middle layer mentioned later for every sample, the application quantity and the frequency | count of application | coating of the slurry for intermediate | middle layers were adjusted for every sample.

  Next, terpineol and a binder were mixed with the barrier layer material powder containing Ce shown in Table 1 to prepare a barrier layer slurry. Then, a barrier layer molded body was prepared by applying the barrier layer slurry onto the intermediate layer molded body.

  Next, the molded body of the fuel electrode, solid electrolyte layer, intermediate layer and barrier layer was fired (1450 ° C., 5 hours) to form the fuel electrode, solid electrolyte layer, intermediate layer and barrier layer.

  Next, the slurry for air electrodes was produced by mixing LSCF powder with terpineol and a binder. And the air electrode molded object was produced by apply | coating the slurry for air electrodes on a barrier layer.

  Next, the air electrode compact was fired (1100 ° C., 1 hour) to form an air electrode.

(Sr coverage in the intermediate layer after firing)
First, a 200 kV electron beam was irradiated to the cell cross section using TEM, and a 3.5 μm × 3.5 μm square range including the solid electrolyte layer, the intermediate layer, and the barrier layer was observed at a magnification of 30,000 times. Then, element mapping of Zr and Sr was performed inside the square range.

  Next, within the square range observed by TEM, a line indicating the concentration of 85% of the maximum zirconium concentration in the solid electrolyte layer is defined on the surface of the intermediate layer on the solid electrolyte layer side (first surface), and the maximum cerium in the barrier layer A line showing a concentration of 85% of the concentration was defined on the barrier layer side surface (second surface) of the intermediate layer. And in the square range observed with TEM, the distance of the solid electrolyte layer side surface and the barrier layer side surface was measured in five places, and the average thickness of the intermediate | middle layer was obtained by arithmetically averaging the measured value. The five places where the distance was measured were set at positions where the intermediate layer 40 was equally divided into six in the plane direction.

  Next, a plurality of virtual lines parallel to the solid electrolyte layer side surface were drawn every 200 nm from the solid electrolyte layer side surface of the intermediate layer to the barrier layer side surface. Then, the ratio of the total length of the Sr existing area to the total length of the solid phase area on each imaginary line was calculated, and the ratio with the largest value was defined as the Sr coverage in the intermediate layer. Table 1 shows the Sr coverage in the intermediate layer after firing.

(Cracks in the intermediate layer after firing)
After fabrication of the fuel cell, the presence or absence of cracks in the cross section was confirmed by observing the cross section of the intermediate layer of each sample with a microscope. The observation field of cracks by a microscope was 3 mm × 3 mm. In Table 1, a sample having less than 3 cracks was evaluated as “◯ (good)”, and a sample having 3 or more cracks was evaluated as “x (no)”.

  As shown in Table 1, sample No. 1 with an Sr coverage of less than 20% in the intermediate layer was used. In 1 to 9, the generation of cracks in the intermediate layer could be suppressed. This is because the difference in the thermal expansion coefficient between the solid electrolyte layer and the barrier layer can be alleviated by the intermediate layer, so that the occurrence of stress in the barrier layer due to the expansion and contraction during firing can be suppressed.

DESCRIPTION OF SYMBOLS 10 Fuel cell 20 Fuel electrode 30 Solid electrolyte layer 40 Intermediate | middle layer 50 Barrier layer 60 Air electrode

Claims (2)

An anode,
The air electrode,
A solid electrolyte layer containing Zr and disposed between the fuel layer and the air electrode;
A barrier layer containing Ce and disposed between the air electrode and the solid electrolyte layer;
An intermediate layer comprising Zr and Ce, and disposed between the solid electrolyte layer and the barrier layer;
With
The Sr coverage in the intermediate layer is 0.8% or more and less than 20%,
The intermediate layer, Ce, observed including a SrZrO ₃ at least one is solid-solved of Gd and Y,
The thermal expansion coefficient of the intermediate layer is a value between the thermal expansion coefficient of the solid electrolyte layer and the thermal expansion coefficient of the barrier layer.
Fuel cell. The intermediate layer contains a solid solution of ZrO ₂ and CeO ₂ as main components.
The fuel cell according to claim 1.

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