JP4820463B2 - Fuel cell and solid oxide fuel cell - Google Patents

Description

  The present invention relates to a fuel cell, and more specifically to a solid oxide fuel cell.

In recent years, attention has been focused on fuel cells from the viewpoint of environmental problems and effective use of energy resources.

Patent Document 1, NiO, Ni, Y ₂ O _3, and support composed of a Yb ₂ O ₃ or the like and, provided on a support, and Ni and / or NiO powder and a rare earth element is dissolved A fuel cell comprising: a fuel electrode composed of ZrO ₂ powder; a solid electrolyte composed of ZrO ₂ provided on the fuel electrode and having Y ₂ O ₃ dissolved therein; an intermediate film; and an interconnector; Has been.

Further, in Patent Document 1, a laminated molded body having a support, a fuel electrode, a solid electrolyte layer, an intermediate film, and an interconnector is produced, the laminated molded body is degreased, and 1300-1600 in an oxygen-containing atmosphere. It is described that co-firing is performed at 0 ° C. After firing, an oxygen electrode and a current collector film are formed to produce a fuel cell.
In Patent Document 1, a test piece is cut out from a support portion of a fuel cell, and its length L1 is measured. Furthermore, the length L2 when this test piece is heat-treated in a reducing atmosphere and cooled to room temperature is measured. Patent Document 1 discloses that when ΔL = L2−L1 and ΔL / L1 is −0.05 to 0.05%, generation of cracks in the solid electrolyte is prevented, and the solid electrolyte is a fuel. It is described that peeling from the pole is prevented. The change amount ΔL of the length of the test piece is expressed by ΔL = L2−L1.

Claim 1 and paragraphs [0071] to [0074] of JP 2004-234970 A

The fuel cell is used at a high temperature of about 800 ° C. Nevertheless, in Patent Document 1, attention is paid to the difference between the dimension when cooled to room temperature after firing and the dimension when cooled to room temperature after reduction. That is, in the setting of the conventional dimensional change rate, the use environment of high temperature is not considered.
An object of the present invention is to prevent the occurrence of cracks in a solid electrolyte layer at a high temperature, that is, in an environment where a fuel cell is used.

A fuel cell according to a first aspect of the present invention includes a fuel electrode, an air electrode, and a solid electrolyte layer provided between the fuel electrode and the air electrode. The fuel electrode includes nickel oxide, a ceramic material having oxygen ion conductivity, and pores that occupy 10 to 40% of the entire volume of the fuel electrode. Compressive stress remains in the solid electrolyte layer, and tensile stress remains in the fuel electrode. The dimensional change rate ΔL of the fuel cell by the reduction treatment at 800 ° C. for 3 hours satisfies | ΔL | ≦ 0.05%. However, ΔL = (LR−LI) / LI × 100, LI is a dimension of the fuel electrode at 800 ° C. before reduction, and LR is a dimension of the fuel electrode at 800 ° C. after reduction.

  Since ΔL satisfies the above-described condition, the difference between the dimensional change rate of the solid electrolyte layer and the dimensional change rate of the fuel electrode is suppressed to be small, so that generation of cracks in the solid electrolyte layer is suppressed.

It is a perspective view which shows the external appearance of an example of a fuel cell. It is a perspective view which shows the internal structure of the fuel battery cell of FIG. It is sectional drawing of the fuel battery cell of FIG. It is sectional drawing which shows the other example of a fuel cell. It is a perspective view which shows the stack structure of a fuel cell provided with the fuel cell of FIG. FIG. 6 is a cross-sectional view showing a conductive connection portion and a surrounding structure in the fuel cell of FIG. It is a perspective view which shows the manufacturing process of the fuel battery cell of FIG. It is a perspective view which shows the manufacturing process of the fuel battery cell of FIG. It is a perspective view which shows the manufacturing process of the fuel battery cell of FIG. It is a perspective view which shows the manufacturing process of the fuel battery cell of FIG. It is a perspective view which shows the attachment process of the member to the fuel cell of FIG. It is a perspective view which shows the attachment process of the member to the fuel cell of FIG. It is a graph which shows the change of the dimensional change rate of the fuel cell in a baking process. It is a perspective view which shows the external appearance of a horizontal stripe type fuel cell. It is an II arrow directional cross-sectional view of the horizontal stripe type fuel battery cell of FIG.

  An example of a fuel cell is a solid oxide fuel cell (SOFC). In particular, the following description will focus on an SOFC having a cell stack structure in which a plurality of fuel cells are stacked.

<1. Fuel cell>
<< 1-1. Thin cell with double-sided air electrode >>
Hereinafter, a fuel electrode support type fuel battery cell will be described as an example of the fuel battery cell. The “fuel electrode supported fuel cell” refers to a fuel cell having the largest thickness of the fuel electrode among various layers provided in the fuel cell.
As shown in FIG. 1, the fuel battery cell (simply called “cell”) 1 has a rectangular flat plate shape. As shown in FIGS. 1 to 3, the cell 1 includes a fuel electrode 11, a flow path portion 12, an electrolyte layer 13, an air electrode 14, and a current collector 16.
However, the “cell” may include a fuel electrode, an electrolyte layer, and an air electrode, and other configurations are not essential. The cell is sometimes referred to as a “power generation unit”.
The fuel electrode 11 is a porous fired body formed by compacting, for example. The fuel electrode 11 preferably contains nickel oxide (NiO) and a ceramic material having oxygen ion conductivity. The proportion of the volume occupied by the pores in the volume of the entire fuel electrode 11 may be 10 to 40%. It is preferable that the proportion of the volume occupied by nickel oxide in the entire volume of the fuel electrode 11 including the pores is 6 to 45%. Moreover, it is preferable that the ratio of the volume which the ceramic material which has oxygen ion conductivity accounts for 30 to 80% among the volume of the fuel electrode 11 whole containing a pore.
Examples of ceramic materials having oxygen ion conductivity include YSZ (Yttria Stabilized Zirconia), ScSZ (Scandia Stabilized Zirconia), (Gd, Ce) O ₂ , GDC (Gadolinia Doped Ceria: Gadolinia doped Ceria), (Sm, Ce) O _2, that is, SDC (samarium doped ceria), lanthanum gallate and the like. The ceramic material contained in the fuel electrode 11 may be one type or two or more types.

  The fuel electrode 11 functions as an anode and also functions as a substrate that supports other layers included in the cell 1. That is, the thickness of the fuel electrode 11 is larger than the thickness of the electrolyte layer 13. The substrate may be rephrased as a support. The ratio (T2 / T1) × 100 of the thickness T2 of the electrolyte layer 13 to the thickness T1 of the fuel electrode 11 is preferably set to 0.05 to 5%. Specifically, the thickness of the fuel electrode 11 is about 0.5 to 5 mm.

The fuel electrode 11 may have two or more layers. For example, the fuel electrode 11 may include a substrate having a thickness of about 0.5 to 5 mm and a fuel electrode active layer (fuel side electrode) having a thickness of about 5 to 50 μm formed thereon.
The substrate and the anode active layer may have the same composition as the anode 11.

The fuel electrode 11 acquires conductivity by being subjected to a reduction process. That is, when the fuel electrode 11 is subjected to the reduction process, the cell 1 is in a state where power generation is possible. The material contained in the fuel electrode 11 is converted from an insulating material to a conductive material by reduction treatment. The conversion from the insulating material to the conductive material is realized, for example, by reduction from NiO to Ni.
The reduction treatment is performed after the co-firing of the fuel electrode 11 and the electrolyte layer 13, and the timing may be before or after the formation of the stack structure, or before or after the formation of the air electrode, the current collecting film, or the like. Usually, after the air electrode is formed, the reduction process is performed after the gas flow path is secured. That is, after the stack structure is formed, the reduction treatment may be performed by passing a reducing gas (specifically, a gas containing hydrogen) through a fuel cell 10 described later at a high temperature.

The dimensional change rate ΔL of the cell 1 due to the reduction treatment at 800 ° C. satisfies | ΔL | ≦ 0.05%. However, ΔL = (LR−LI) / LI × 100, LI is a dimension of the fuel electrode at 800 ° C. before reduction, and LR is a dimension of the fuel electrode at 800 ° C. after reduction. That is, this parameter is applied to the cell 1 before reduction.
When ΔL satisfies the above-described condition, the difference between the dimensional change rate of the electrolyte layer 13 and the dimensional change rate of the fuel electrode is suppressed to be small, and therefore, occurrence of cracks in the electrolyte layer 13 is suppressed.
Note that “the dimensional change rate ΔL of the cell 1” may refer to the dimensional change rate of one cell 1 as a whole, or the fuel electrode 11, the electrolyte layer 13, and the like cut out from one cell 1. It may be a dimensional change rate of a portion including the air electrode 14.

  As shown in FIGS. 2 and 3, the flow path portion 12 is provided inside the fuel electrode 11. The cell 1 has a rectangular shape as a whole. As shown in FIG. 2, the flow path portion 12 continues from the first opening 121 of the first short side of the cell 1 to the second opening 122 of the second short side. In addition, the shape of the flow path part 12 can be changed as appropriate.

  The electrolyte layer 13 is also called a solid electrolyte layer. As shown in FIGS. 1 and 3, the electrolyte layer 13 is provided on both surfaces of the fuel electrode 11. Examples of the electrolyte material contained in the electrolyte layer 13 include zirconia-based materials such as yttria stabilized zirconia such as 3YSZ and 8YSZ; and ScSZ (scandia stabilized zirconia). The thickness of the electrolyte layer 13 is, for example, 3 to 30 μm. The electrolyte layer 13 and the fuel electrode 11 are co-fired.

Compressive stress remains in the electrolyte layer 13. Therefore, the residual strain S of the electrolyte layer 13 shows a negative value. Conversely, tensile stress remains in the fuel electrode 11 described above. This compressive stress and tensile stress may occur as a result of co-firing.
The residual strain S of the electrolyte layer 13 preferably satisfies −2% ≦ S ≦ −0.3%. When the residual strain S is within this range, the occurrence of cracks in the electrolyte layer 13 and the separation of the electrolyte layer 13 from the fuel electrode 11 are further suppressed. The residual strain S is represented by the following formula (1).

  As shown in FIGS. 1 and 3, the air electrode 14 is provided above the electrolyte layer 13 (on the side opposite to the fuel electrode 11). That is, the electrolyte layer 13 is disposed between the fuel electrode 11 and the air electrode 14. Examples of the material contained in the air electrode 14 include lanthanum-containing perovskite complex oxides such as LSCF (lanthanum strontium cobalt ferrite), lanthanum manganite, lanthanum cobaltite, and lanthanum ferrite. The lanthanum-containing perovskite complex oxide may be doped with strontium, calcium, chromium, cobalt, iron, nickel, aluminum or the like. Other examples include palladium, platinum, ruthenium, platinum-zirconia cermet, palladium-zirconia cermet, ruthenium-zirconia cermet, platinum-cerium oxide cermet, palladium-cerium oxide cermet, ruthenium-cerium oxide cermet. The air electrode 14 can contain the exemplified material as a main component. The air electrode 14 is rectangular in FIG. 1, but its shape can be changed. The thickness of the air electrode 14 is specifically about 5 to 50 μm.

  The thickness of the current collector 16 is specifically about 5 to 200 μm. The current collector 16 preferably contains lanthanum chromite, which is a conductive ceramic that is stable in an oxidizing atmosphere and a reducing atmosphere, as a main component. In FIG. 1, two current collecting layers 16 are provided on one side of the cell 1, two on the short side of the cell 1 with respect to the air electrode 14, and the current collecting unit 16 is rectangular. However, the number and shape of the current collectors can be changed.

  Although not shown, a reaction preventing layer may be provided between the electrolyte layer 13 and the air electrode 14. The reaction preventing layer preferably contains gadolinium-doped ceria (GDC) which is a ceria-based oxide. The thickness of the reaction preventing layer is specifically less than 20 μm.

<< 1-2. Single-sided air electrode type >>
The air electrode may be provided only on one side of the cell. An example of such a cell is shown in FIG. Members having the same functions as those already described are given the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 4, in the cell 2, the air electrode 14 is provided only on one side (first surface) of the cell 2. The current collector 16 is provided on the second surface of the cell 2. The electrolyte layer 13 is provided between the fuel electrode 11 and the air electrode 14 on the first surface, but is not provided on the second surface. That is, the current collector 16 is provided directly on the fuel electrode 11 or is provided between the fuel electrode 11 and an intermediate layer (bonding layer).

<< 1-3. Other forms >>
The cell only needs to have a fuel electrode, an electrolyte layer, and an air electrode, and the presence / absence of other components, the shape, material, dimensions, and the like of each component can be changed. For example, the configuration of the fuel cell may be changed as follows.
(1) The shape of the cell may be a fuel electrode support type, a flat plate shape, a cylindrical shape, a vertical stripe type, a horizontal stripe type, a single-end holding type stack, a double-end holding type stack, or the like. Moreover, the cross section of the cell may be elliptical.
(2) Contrary to the cells 1 and 2 described above, the fuel electrode may be provided outside the cell, and the air electrode may be provided inside.
(3) The flow path is not an essential component for the cell. That is, there may be a flat plate type cell that does not include a flow path portion. In this case, the fuel electrode is provided to be exposed in the cell. Further, the cross section of the flow path is not limited to a rectangle, and may be other shapes such as a circle and an ellipse.
(4) The flow path unit 12 may have a plurality of first openings 121 and a plurality of second openings 122.
(5) The configurations mentioned as different forms can be combined with each other.

<2. Fuel cell>
<< 2-1. Both ends holding type >>
As shown in FIG. 5, the fuel cell 10 including the cells 1 has a stack structure in which the cells 1 are stacked. Specifically, the connecting component 3 is attached to the openings 121 and 122 of the flow path portion of the cell 1, respectively. The interconnector 4 is disposed between the cells 1.

The connecting part 3 is provided with a gas hole 31, and the connecting part 3 is attached to the cell 1 so that the gas hole 31 is connected to the opening 121 or 122.
The interconnector 4 is provided with a conductive connecting portion 41 and a current collecting hole 42. The interconnector 4 is provided with a plurality of conductive connection portions 41.

  As shown in FIG. 6, the conductive connection portion 41 is a concave portion provided in the interconnector 4, and the bottom portion thereof is connected to the air electrode via the conductive adhesive 411. Further, as shown in FIG. 6, in the interconnector 4, a discontinuous portion is provided between the conductive connection portion 41 and the periphery thereof. That is, a gap is provided that communicates from the back surface of the interconnector 4 (the surface facing the cell 1) to the front surface (the surface facing another stacked interconnector 4).

As shown in FIG. 5, the current collection holes 42 are arranged so as to expose the current collection unit 16 from the interconnector 4.
During power generation, fuel gas is supplied from the gas hole 31 of the connecting part 3 fixed to the first opening 121. As shown by a dotted line in FIG. 2, the fuel gas flows into the flow path portion 12 from the first opening 121, and the exhaust gas is discharged from the second opening 122. The exhaust gas is discharged through the gas hole 31 of the connecting part 3 fixed to the second opening 122.

  Air is supplied to the air electrode 14 by blowing air from the side surface side of the cell stack structure (for example, the front side in FIG. 5).

Although not shown, the fuel cell 10 further includes members such as a lead that sends current generated in the cell stack to an external device, a gas reforming unit that includes a catalyst that reforms the fuel gas, and the like.

<< 2-2. Horizontal stripe fuel cell »
The fuel cell 10 described above includes a plurality of stacked cells 1 and an interconnector 4 that electrically connects the cells 1. That is, the fuel cell 10 is a vertically striped fuel cell. However, the present invention is also applicable to a horizontal stripe fuel cell. The horizontal stripe fuel cell will be described below.

  A horizontal stripe fuel cell (hereinafter simply referred to as “fuel cell”) 100 includes a support substrate 102, a fuel electrode 103, an electrolyte layer 104, a reaction preventing layer 105, an air electrode 106, an interconnector 107, and a current collector 108. . The fuel cell 100 includes a cell 110. In FIG. 10, the current collector 108 is not shown for convenience of explanation.

  The fuel cell 100 includes a plurality of cells 110 disposed on a support substrate 102 and an interconnector 7 that electrically connects the cells 110. The cell 110 is a part that includes a fuel electrode 103 and an air electrode 106 corresponding to the fuel electrode 103. Specifically, the cell 110 includes a fuel electrode 103, an electrolyte layer 104, and an air electrode 106 that are stacked in the thickness direction (y-axis direction) of the support substrate 102. In the present embodiment, the cell 110 further includes the reaction preventing layer 105, but the present invention is not limited to this configuration.

The support substrate 102 is flat and has a shape that is long in one direction (z-axis direction). The support substrate 102 is a porous body having insulating properties. The support substrate 102 may contain nickel. More specifically, the support substrate 102 may contain Ni—Y ₂ O ₃ (nickel-yttria) as a main component. Nickel may be contained as an oxide (NiO). During power generation, NiO may be reduced to Ni by hydrogen gas.

  As shown in FIGS. 10 and 11, a flow path 123 is provided inside the support substrate 102. The flow path 123 extends along the longitudinal direction (z-axis direction) of the support substrate 102. At the time of power generation, the fuel gas is caused to flow through the flow path 123, and the fuel gas is supplied to the fuel electrode 103, which will be described later, through the holes of the support substrate 102.

  The fuel electrode 103 is provided on the support substrate 102. On one support substrate 102, a plurality of fuel electrodes 103 are arranged in the longitudinal direction (z-axis direction) of the support substrate 102. That is, a gap is provided between adjacent fuel electrodes 103 in the longitudinal direction (z-axis direction) of the support substrate 102.

As the composition of the fuel electrode 103, the same composition as that of the fuel electrode 11 can be applied.
The fuel electrode 103 may have a fuel electrode current collecting layer and a fuel electrode active layer. The anode current collecting layer is provided on the support substrate 102, and the anode active layer is provided on the anode current collecting layer so as not to overlap the interconnector 107.

  The fuel electrode 103 may have a fuel electrode current collecting layer and a fuel electrode active layer. The anode current collecting layer is provided on the support substrate 102, and the anode active layer is provided on the anode current collecting layer. The composition of the anode current collecting layer and the anode active layer is as described above.

  The electrolyte layer 104 is also referred to as a solid electrolyte layer. As shown in FIG. 11, the electrolyte layer 104 is provided on the fuel electrode 103. In a region where the fuel electrode 103 is not provided on the support substrate 102, the electrolyte layer 104 may be provided on the support substrate 102.

  The electrolyte layer 104 has discontinuous portions in the longitudinal direction (z-axis direction) of the support substrate 102. That is, the plurality of electrolyte layers 104 are arranged at intervals in the z-axis direction. The electrolyte layers 104 adjacent in the z-axis direction are connected by an interconnector 107. In other words, the electrolyte layer 104 is provided continuously from a certain interconnector 107 to the interconnector 107 adjacent to the interconnector 107 in the longitudinal direction (z-axis direction) of the support substrate 102. The interconnector 107 and the electrolyte layer 104 have a dense structure as compared with the support substrate 102 and the fuel electrode 103. Therefore, the interconnector 107 and the electrolyte layer 104 have a structure that is continuous in the z-axis direction in the fuel cell 100, and thus function as a seal portion that separates air and fuel gas.

  As for the composition of the electrolyte layer 104, the same composition as the electrolyte layer 13 described above can be applied.

  The reaction preventing layer 105 is provided on the electrolyte layer 104. In FIG. 2, the reaction preventing layer 105 is not provided at a location where the electrolyte layer 104 is not provided. That is, one reaction preventing layer 105 is provided so as to correspond to one fuel electrode 103. Accordingly, a single support substrate 102 is provided with a plurality of electrolyte layers 104 along the longitudinal direction (z-axis direction) of the support substrate 102.

The reaction preventing layer 105 may contain ceria (cerium oxide) as a main component. Specifically, as the material of the reaction preventing layer 105, ceria and a ceria-based material containing a rare earth metal oxide dissolved in ceria can be given. Specific 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 air electrode 106 is disposed on the reaction preventing layer 105 so as not to exceed the outer edge of the reaction preventing layer 105. One air electrode 106 is laminated on one fuel electrode 103. In other words, one support substrate 102 is provided with a plurality of air electrodes 106 along the longitudinal direction (z-axis direction) of the support substrate 102.

  As the composition of the air electrode 106, the same composition as that of the air electrode 14 described above can be applied.

  The interconnector 107 may be disposed so as to electrically connect the cells 110 as described above. In FIG. 11, the interconnector 107 is stacked on the fuel electrode 103. The interconnector 107 may be provided directly on the fuel electrode 103. An intermediate layer, which will be described later, may be disposed between the fuel electrode 103 and the interconnector 107.

  In this specification, “lamination” includes a case where two elements are arranged so as to be in contact with each other and a case where they are arranged so as not to be in contact but overlap in the y-axis direction.

  In FIG. 11, the interconnector 107 is disposed so as to connect the electrolyte layers 104 in the longitudinal direction (z-axis direction) of the support substrate 102. Thereby, the cells 110 adjacent in the longitudinal direction (z-axis direction) of the support substrate 102 are electrically connected.

  The interconnector 107 is a dense layer as compared with the support substrate 102 and the fuel electrode 103. The interconnector 107 contains a perovskite complex oxide as a main component. In particular, chromite-based materials can be used as the perovskite complex oxide.

  The current collector 108 is arranged to electrically connect the interconnector 107 and the cell 110. Specifically, the current collector 108 is provided so as to continue from the air electrode 106 to the interconnector 107 included in the cell 110 adjacent to the cell 110 including the air electrode 106. The current collector 108 only needs to have conductivity, and may be made of the same material as the interconnector 107, for example.

An intermediate layer may be disposed between the fuel electrode 103 and the interconnector 107.
The intermediate layer preferably contains at least one element among the elements constituting the fuel electrode 103 and at least one element among the elements that constitute the interconnector 107.

  The air electrode 106 included in the cell 110 is electrically connected to the fuel electrode 103 of the adjacent cell 110 by the current collector 108 and the interconnector 107. In other words, not only the interconnector 107 but also the current collector 108 contributes to the connection between the cells 110. Such a form is also included in the form of “the interconnector electrically connects the cells”. .

Specifically, the dimensions of each part of the fuel cell 100 can be set as follows.
Width D1 of support substrate 102: 1 to 10 cm
Support substrate 102 thickness D2: 1 to 10 mm
Support substrate 102 length D3: 5 to 50 cm
Distance D4 from outer surface of support substrate 102 (interface between support substrate 102 and fuel electrode) to flow path 123: 0.1 to 4 mm
The thickness of the fuel electrode 103: 50 to 500 μm
(When the anode 103 has an anode current collecting layer and an anode active layer:
The thickness of the anode current collecting layer: 50 to 500 μm
(The thickness of the anode active layer: 5 to 30 μm)
The thickness of the electrolyte layer 104: 3 to 50 μm
Reaction prevention layer 105 thickness: 3 to 50 μm
The thickness of the air electrode 106: 10 to 100 μm
The thickness of the interconnector 107: 10 to 100 μm
Current collector 108 thickness: 50-500 μm
Needless to say, the present invention is not limited to these values.

<< 2-3. Other forms >>
(1) In addition to the both-end holding type described above, the fuel cell can be applied to a one-end holding type fuel cell. In the one-end holding type fuel cell, one end of the stacked fuel cells is fixed to the gas manifold. The stacked cells are connected by an interconnector. Power generation is started by the gas manifold sending fuel gas into the flow path in the cell.

  (2) Either a single-sided air electrode or a double-sided air electrode can be applied to either the both-end holding type or the one-end holding type.

<3. Manufacturing method of fuel cell>
The following manufacturing methods can be applied regardless of the shape of the cell such as the fuel electrode support type, flat plate type, cylindrical type, vertical stripe type, horizontal stripe type, one end holding type stack, and both end holding type stack.

[Outline of manufacturing method]
The manufacturing method described below is only one form of the manufacturing method of a fuel cell.

<< 3-1. Co-firing >>
The method for manufacturing a fuel cell includes co-firing (co-sintering) of the fuel electrode 11 and the electrolyte layer 13. The firing temperature and time are set according to the cell material and the like.

  By baking (if degreasing described below is performed, degreasing), the cellulose sheet and pore-forming agent described later are burned away, and the flow path portion 12 and the pores are formed.

Distortion occurs between the fuel electrode 11 and the electrolyte layer 13 due to a difference in contraction timing and a contraction amount in the co-firing. Specifically, tensile stress remains in the fuel electrode 11 and compressive stress remains in the electrolyte layer 13. The residual strain S generated in the electrolyte layer preferably satisfies −2% ≦ S ≦ −0.3%. When the residual strain S is within this range, the occurrence of cracks in the electrolyte layer 13 and the separation of the electrolyte layer 13 from the fuel electrode 11 are further suppressed.
The residual strain S is represented by the above formula (1).

The residual strain S is a strain generated in the electrolyte layer 13 at the interface between the fuel electrode 11 and the electrolyte layer 13. Due to the firing, a firing strain difference occurs between these two materials (between the fuel electrode 11 and the electrolyte layer 13). Assuming that the firing strain of the fuel electrode 11 is ε ₁ and the firing strain of the electrolyte layer 13 is ε ₂ , ε ₁ and ε ₂ are expressed by the following equations (2) and (3).

これら２材料の焼成歪差によって、燃料極１１及び電解質層１３のそれぞれに、残留歪が生じる。これらの残留歪のうち、電解質層１３における歪が、残留歪Ｓである。すなわち、以下の通りに上記式（１）が導き出される。

Residual strain occurs in each of the fuel electrode 11 and the electrolyte layer 13 due to the difference in firing strain between these two materials. Among these residual strains, the strain in the electrolyte layer 13 is the residual strain S. That is, the above formula (1) is derived as follows.

なお、残留歪Ｓが負の値であるということは、電解質層１３に圧縮応力が残留することを示す。

The fact that the residual strain S is a negative value indicates that compressive stress remains in the electrolyte layer 13.

<< 3-2. Formation of fuel electrode >>
In the fuel cell manufacturing method, the fuel electrode may be formed by compacting. That is, the manufacturing method may include forming a green compact by putting powder mixed with the fuel electrode material into a mold and compressing the powder.

The material of the fuel electrode is as described in the above description of the configuration of the fuel cell. As the material, for example, nickel oxide, zirconia, and, if necessary, a pore forming agent are used. The pore-forming agent is an additive for providing pores in the fuel electrode. As the pore-forming agent, a material that disappears in a later step is used. An example of such a material is cellulose powder.

The mixing ratio of each material is not particularly limited, and is appropriately set according to characteristics required for the fuel cell.

The pressure applied to the powder during compacting is set so that the fuel electrode has sufficient rigidity. The pressure is set to, for example, 5 to 150 MPa.

In addition, the formation of the fuel electrode may be performed in a state in which a member that disappears in a later process is disposed inside the powder. Thereby, the flow path part 12 is formed in a later process. Examples of the member that disappears include cellulose that is burned off during degreasing or baking described below. Specifically, the cellulose sheet formed in the shape of the flow path portion 12 can be placed in the powder and compacted. Not only the flow path part 12 but the internal space in the fuel electrode can be formed by this method.

<< 3-3. Formation of electrolyte layer >>
The manufacturing method of a fuel cell may include forming an electrolyte layer on a molded body of a fuel electrode formed by compacting.
Examples of the method of forming the electrolyte include CIP (cold isostatic pressing) or thermocompression bonding using an electrolyte material processed into a sheet shape, or a slurry dip method in which a fuel electrode is immersed in an electrolyte material prepared in a slurry shape.

<< 3-4. Degreasing >>
The method for producing a fuel cell may include a degreasing step before the firing step. Degreasing is performed by heating. Conditions such as temperature and time are set according to the material of the cell.

<< 3-5. Formation of air electrode >>
The air electrode is formed, for example, by forming a layer of an air electrode material on a substrate after firing (fuel electrode and electrolyte layer) by a printing method or the like and then firing the layer.

<< 3-6. Preparation of granules >>
The manufacturing method of the fuel cell may include granulating a mixture of materials of the fuel electrode. For granulation, a conventionally known method such as an SD (spray dry) method can be suitably used.

The conditions such as the particle size of the granule and the rigidity of the granule (easiness of collapsing when pressure is applied) are not limited to specific numerical values, but are set to such an extent that the fuel electrode can be formed by compaction. The For example, the average particle size of the granules is preferably set to about 50 to 250 μm. The rigidity of the granules can be set according to the pressure at the time of compacting.

<< 3-7. Other processes >>
Depending on the configuration of the fuel cell, the manufacturing method may further include other steps, and the above-described steps may be changed. For example, the manufacturing method may include a step of providing a reaction preventing layer between the electrolyte layer and the air electrode, or a step of forming the fuel electrode into a two-layer structure of the substrate and the fuel electrode active layer (step of forming the substrate). And a step of forming the anode active layer). The reaction preventing layer and the fuel electrode active layer can be formed by sheet sticking, printing, slurry dip method or the like, and may be co-fired with the fuel electrode and the electrolyte layer.
<< 3-8. Manufacturing method of horizontal stripe fuel cell >>
The horizontal stripe fuel cell 100 can also be manufactured by a manufacturing method substantially similar to the above-described method. For example, the support substrate 102 is formed by compacting, and the other components can be formed by attaching a sheet, slurry dipping, printing, or the like.

[Specific example of manufacturing method]
As a specific example of the manufacturing method, the flow of the manufacturing method of the cell of FIG. 1 will be described below.
The granules 111 of the material of the fuel electrode 11 are compacted with the cellulose sheet 51 inside (FIG. 7A).

The ceramic green sheets 52 of the electrolyte material are pasted on both surfaces of the thin plate-shaped green compact 112 thus formed (FIG. 7B). If the ceramic green sheet 52 is larger than the molded body 112, the side of the molded body 112 can be covered with the electrolyte. Note that the side portion of the molded body 112 can also be coated with an electrolyte by a slurry dipping method, a brush coating method, a stamp method, or the like.

The molded body 112 thus formed with the electrolyte layer is degreased and fired to obtain a fired body 113. Processing such as forming openings 121 and 122 in the fired body 113 is performed (FIG. 7C).

Next, the air electrode 14 and the current collector 16 are formed (FIG. 7D). The air electrode 14 is formed by applying an air electrode material onto the fired body 113 by a printing method and then firing at 1000 ° C. for 2 hours. The cell 1 is completed through the above steps.
Thereafter, the connecting part 3 and the interconnector 4 are attached (FIGS. 8A and 8B) and further stacked, whereby the fuel cell 10 is manufactured.

(1) Procedure a. Preparation of test piece <3. The fired body 113 was produced by the method described in [Specific Example of Manufacturing Method] in the> column. Specific production conditions are as follows.
a-1. Formation of fuel electrode A fuel electrode (thickness after firing: 1 mm) was formed by the following procedure.
First, the compacting body 112 was produced by compacting. NiO powder manufactured by Sumitomo Metal Mining Co., Ltd. was used as NiO, YSZ powder manufactured by Tosoh Corporation was used as YSZ, and cellulose powder manufactured by Nippon Paper Industries Co., Ltd. was used as a pore former. First, the quantity ratio of NiO powder and YSZ powder was adjusted so that the Ni volume ratio and the YSZ volume ratio were as shown in Table 1. The amount of cellulose powder added was 10% by weight with respect to the total amount of NiO powder and YSZ powder. These powders were granulated by the SD method. The particle size of the granules was about 80-100 μm. The compacting pressure is preferably about 5 to 150 MPa.
Moreover, the firing activity of the material could be changed by changing the particle diameter and specific surface area of nickel oxide and zirconia in the fuel electrode material; and the particle diameter and specific surface area of zirconia in the electrolyte layer material described later. As a result, even if the volume ratio of the material of each layer was the same, the shrinkage rate at the time of firing could be varied (Tables 1 to 3).
In addition, Table 4 and Table 5 show the volume ratio, the hydrogen concentration of the reducing gas, and the results when ScSZ or GDC is used instead of YSZ.
The volume ratios shown in Tables 1 to 5 were obtained by cutting a fired body and photographing 10 cross sections per fired body with a scanning electron microscope (SEM) -EPMA (Electron Probe Micro Analyzer). The image was obtained by image analysis.

a-2. Formation of electrolyte layer a-1. A ceramic green sheet (thickness after firing: 5 μm) made of 3YSZ on which a fuel electrode active layer (material: a composite of NiO and YSZ) is printed is laminated on the surface of the molded body 112 manufactured in Step 1, and a pressure of 50 to 300 MPa is applied. And bonded to the molded body 112 by the CIP method.

a-3. Degreasing and firing The fired body 113 was produced by degreasing and firing the molded body 112 on which the YSZ sheet and the GDC sheet were laminated. Degreasing was completed by raising the temperature at a rate of 10 to 50 ° C./hr and holding at 600 ° C. for 3 hours. At this time, the cellulose powder as the pore forming agent and the cellulose sheet as the flow path material disappeared, and pores and spaces were formed. Then, after heating up at 200 degreeC / hr, baking was completed by hold | maintaining at 1400 degreeC for 2 hours.

a-4. Formation of Air Electrode An air electrode made of LSCF (thickness after firing: 5 to 50 μm) was formed by a printing method, and the air electrode was formed by firing at 1000 ° C. for 2 hours.

b. Measurement of reduction and dimensional change rate before and after reduction a-4. The sample piece obtained in (1) was placed in a chamber of a heating device, and the temperature in the chamber was raised in an air atmosphere. After the temperature in the chamber reached 800 ° C., the reducing gas was allowed to flow into the chamber. The reduction process was performed by keeping the temperature in the chamber at 800 ° C. for 3 hours after the start of the flow of the reducing gas.
The reducing gas contained hydrogen at a predetermined concentration (4 to 100%). In the reducing gas, the remainder excluding hydrogen was argon gas.

  The dimensional change before and after the reduction was measured with a thermal expansion coefficient measuring device (manufactured by Rigaku Corporation, TMA8310), and the dimensional change rate of the fuel electrode was measured based on the measurement result. The results are shown in Tables 1 to 3.

c. Evaluation of Sample Pieces The electrolyte layer and the air electrode of the sample pieces after reduction were observed to confirm the presence or absence of cracks. The evaluation results are shown in Tables 1 to 3.

d. Measurement of residual strain The fuel electrode material and the electrolyte layer material were separately fired. The dimensional change of the fuel electrode material and the electrolyte layer material due to firing was measured. Further, the residual strain was calculated based on the measurement result. Specifically, it is as described below.
A green compact of the fuel electrode material is used as the a-1. The same as the above a-3. Baked in the same manner.

Moreover, the sample piece which consists of electrolyte layer material is said a-3. Baked in the same manner.
By the above-described coefficient of thermal expansion measurement, the dimensions of the fuel electrode (a green compact) at room temperature (25 ° C.) before firing, the dimensions of the fuel electrode when cooled to room temperature after firing, and the electrolyte layer at room temperature before firing The dimensions and the dimensions of the electrolyte layer when cooled to room temperature after firing were measured, and the residual strain S was calculated based on the above formula (1). The results are shown in Tables 1 to 3.

(2) Results (2-1) Example of dimensional change during firing An example of dimensional change during firing is shown in FIG. As the graph of FIG. 9 shows, the dimensional change rate of each of the fuel electrodes a and b and the electrolyte layer became + (plus) as the temperature increased. This expansion is due to the thermal expansion of the material.
The reason why the inclination differs between the fuel electrode and the electrolyte layer is because the thermal expansion coefficient of the material forming each layer is different.

As firing proceeds further, the dimensional change rate of each material changes in the-(minus) direction. This is because shrinkage (densification of ceramics) by firing has started.
As shown in FIG. 9, the fuel electrode a (two-dot chain line) has earlier contraction timing than the electrolyte layer indicated by the solid line. That is, the shrinkage start temperature is lower. On the other hand, the fuel electrode b (dotted line) is contracted later than the electrolyte layer. That is, the shrinkage start temperature is higher. Also, the dimensional change rate (shrinkage rate) at the completion of firing is different for each of the fuel electrode a, the fuel electrode b, and the electrolyte layer.

  Due to the difference between the shrinkage start temperature due to the firing and the final shrinkage amount, strain is generated between the electrolyte layer and the fuel electrode.

(2-2) Results for individual samples Tables 1 to 3 show the test results of each sample piece. Table 1 shows the results when the hydrogen concentration in the reducing gas is 100%, and Tables 2 and 3 show the results when the hydrogen concentrations in the reducing gas are different. Tables 2 and 3 contain the same samples as in Table 1. In Tables 2 and 3, the corresponding sample numbers in Table 1 are written in parentheses.
In all the tables, the symbols x, Δ, and ◯ represent the following evaluations.
X: Defect (crack was seen in both electrolyte layer and air electrode)
○: Good (a crack was observed in either the electrolyte layer or the air electrode)
A: Excellent (no cracks were found in either the electrolyte layer or the air electrode)

表１に示すように、還元前後の寸法変化率が−０．０５〜０．０５％の範囲にあるとき、電解質層において、クラックは見られなかった。また、焼成によって固体電解質に生じる残留歪Ｓは、−２％〜−０．３％の範囲内、特に−２．３％〜−０．３％の範囲内にあることが好ましいことが見出された。

As shown in Table 1, when the dimensional change rate before and after the reduction was in the range of -0.05 to 0.05%, no crack was observed in the electrolyte layer. Further, it is found that the residual strain S generated in the solid electrolyte by firing is preferably in the range of -2% to -0.3%, particularly in the range of -2.3% to -0.3%. It was done.

In addition, for the samples that were evaluated as “x” in Table 1, only the hydrogen concentration of the reducing gas was changed (the conditions other than the hydrogen concentration were the same), and as shown in Tables 2 and 3, before and after the reduction. Changes in the dimensional change rate and evaluation were observed. That is, it has been clarified that the dimensional change rate can be controlled by a combination of materials and reducing conditions.
Further, as shown in Tables 4 and 5, even when ScSZ or GDC is used instead of YSZ, when the rate of dimensional change before and after reduction is in the range of -0.05 to 0.05%, the electrolyte No cracks were seen in the layer. Further, it is found that the residual strain S generated in the solid electrolyte by firing is preferably in the range of -2% to -0.3%, particularly in the range of -2.2% to -0.3%. It was done.

  In the fuel electrode cell supporting the fuel electrode, the fuel electrode is formed relatively thick. Therefore, the electrolyte layer is thinner than the fuel electrode and is easily broken. The electrolyte layer is a ceramic thin film and has a property of being relatively strong against compressive stress and weak against tensile stress. Therefore, it is considered that when the compressive stress remains in the electrolyte layer, cracks are less likely to occur than when the tensile stress remains.

  For example, in the example of FIG. 9, when combined with the fuel electrode a, compressive stress remains in the electrolyte layer of this graph due to firing at 1200 ° C. On the other hand, when combined with the fuel electrode b, a tensile stress remains in the electrolyte layer of this graph by firing at 1200 ° C.

  In addition, when the thickness of the electrolyte layer 13 was changed, when the thickness was less than 3 μm, it was difficult to form the ceramic green sheet. Further, when the thickness of the electrolyte layer 13 was larger than 30 μm, the fired body was warped. It is considered that the cause of the warp is that the strength of the electrolyte layer 13 is large, so that the strain is released not by the crack but by the warp.

1, 2, 110 Fuel cell 11 Fuel electrode 12 Flow path part 121 First opening 122 Second opening 13 Electrolyte layer 14 Air electrode 16 Current collecting part 111 Granule 112 Powder compacting body 113 Firing body 10, 100 Fuel cell 3 connection Component 31 Gas hole 4 Interconnector 41 Conductive connection part 42 Current collecting hole 51 Cellulose sheet 52 Ceramic green sheet 102 Support substrate 103 Fuel electrode 104 Electrolyte layer 106 Air electrode 107 Interconnector 108 Current collecting part

Claims (8)

A fuel cell comprising a fuel electrode, an air electrode, and a solid electrolyte layer provided between the fuel electrode and the air electrode,
The fuel electrode includes nickel oxide, a ceramic material having oxygen ion conductivity, and pores occupying 10 to 40% of the total volume of the fuel electrode,
Compressive stress remains in the solid electrolyte layer,
Tensile stress remains in the fuel electrode,
The dimensional change rate ΔL of the fuel cell by the reduction treatment at 800 ° C. for 3 hours satisfies | ΔL | ≦ 0.05% (where ΔL = (LR−LI) / LI × 100, where LI is (The dimension of the fuel electrode at 800 ° C. before reduction, and LR is the dimension of the fuel electrode at 800 ° C. after reduction)
Fuel cell. The residual strain S generated in the solid electrolyte layer satisfies −2% ≦ S ≦ −0.3%,
The residual strain S is represented by the following formula (1).

The fuel battery cell according to claim 1. The nickel oxide occupies 6 to 45% of the entire volume of the fuel electrode including the pores.
The fuel battery cell according to claim 1 or 2. The ceramic material having oxygen ion conductivity occupies 30 to 80% of the entire volume of the fuel electrode including the pores.
The fuel cell according to any one of claims 1 to 3. The fuel electrode and the solid electrolyte layer are co-fired,
The fuel cell according to any one of claims 1 to 4.   A solid oxide fuel cell comprising: the fuel cell according to any one of claims 1 to 5; and an interconnector that electrically connects the fuel cells. Further comprising a substrate,
Two or more of the fuel cells are provided on a single substrate;
The solid oxide fuel cell according to claim 6, wherein the interconnector is disposed so as to electrically connect two or more of the fuel cells provided on one of the substrates. Two or more of the fuel cells are stacked,
The interconnector is arranged to electrically connect the fuel cells.
The solid oxide fuel cell according to claim 6.

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