JP4864171B1 - Solid oxide fuel cell - Google Patents

Abstract

A solid oxide fuel cell capable of suppressing the generation of cracks in the vicinity of an interface between a support substrate and a power generation unit is provided.
A solid oxide fuel cell is formed on a support substrate having a fuel gas flow path therein and containing a main composition containing at least MgO and Y ₂ O ₃ ; A power generation unit including a fuel electrode, an air electrode, and a solid electrolyte layer disposed between the fuel electrode and the air electrode. The main composition is composed of 84.5 mol% to 95.5 mol% MgO, 4.5 mol% to 9.5 mol% Y ₂ O ₃ , and 0 mol% to 11.0 mol% NiO.
[Selection] Figure 3

Description

  The present invention relates to a solid oxide fuel cell including a support substrate.

  In recent years, attention has been focused on fuel cells from the viewpoint of environmental problems and effective use of energy resources, and various proposals have been made for materials and structures of fuel cells.

Patent Document 1 discloses a solid oxide fuel cell including a support substrate containing NiO, Y ₂ O ₃ and MgO, and a power generation unit formed on the support substrate. The power generation unit includes a fuel electrode, a solid electrolyte layer, and an air electrode sequentially stacked on the support substrate, and the fuel electrode and a part of the solid electrolyte layer are in contact with the support substrate.

JP 2007-095566 A

  However, when the high-temperature power generation operation is repeated using the solid oxide fuel cell of Patent Document 1, a crack may occur near the interface between the support substrate and the power generation unit. The present inventors have newly found that this phenomenon is due to the volume of the support substrate expanding by reducing NiO to Ni in a reducing atmosphere created by supplying fuel gas.

  Specifically, NiO solid-dissolved in MgO is gradually reduced, so that Ni precipitates as fine particles not only on the surface of MgO but also on the crystal grain boundaries of MgO. In response to this, the volume of the support substrate expands, and stress is generated at the interface between the support substrate and the power generation unit, so that a crack is generated near the interface between the support substrate and the power generation unit. The precipitation of Ni by reduction of NiO dissolved in MgO is as described in "Journal of the Ceramic Society of Japan_117_ (2) _2009_p166-170".

  The present invention has been made based on such new findings, and an object thereof is to provide a solid oxide fuel cell that can suppress the occurrence of cracks in the vicinity of the interface between the support substrate and the power generation unit. .

The solid oxide fuel cell disclosed herein is formed on a support substrate having a fuel gas flow path therein and containing a main composition containing at least MgO and Y ₂ O _3. And a power generation unit including a fuel electrode, an air electrode, and a solid electrolyte layer disposed between the fuel electrode and the air electrode. The main composition is composed of 84.5 mol% to 95.5 mol% MgO, 4.5 mol% to 9.5 mol% Y ₂ O ₃ , and 0 mol% to 11.0 mol% NiO.

  ADVANTAGE OF THE INVENTION According to this invention, the solid oxide fuel cell which can suppress generation | occurrence | production of the crack near the interface of a support substrate and an electric power generation part can be provided.

The perspective view which shows the structure of a horizontal stripe type fuel cell Sectional drawing which shows the structure of a horizontal stripe type fuel cell It is a ternary composition diagram of MgO—Y ₂ O ₃ —NiO as the main composition contained in the support substrate. It is a ternary composition diagram of MgO—Y ₂ O ₃ —NiO of the support substrate according to the example.

  A horizontal stripe fuel cell 100 will be described as an example of a solid oxide fuel cell (SOFC).

1. Configuration of Horizontally Striped Fuel Cell 100 FIG. 1 is a perspective view showing an outline of a horizontally striped fuel cell (hereinafter simply referred to as “cell”) 100. 2 is a cross-sectional view taken along the line II of FIG.

  As shown in FIGS. 1 and 2, the cell 100 includes a support substrate 10, a plurality of power generation units 20, a plurality of interconnectors 30, and a current collection unit 40. In FIG. 1, the current collector 40 is omitted for convenience of explanation.

1-1. Support substrate 10
The support substrate 10 is a plate-like member that is flat and extends in one direction (hereinafter referred to as “longitudinal direction”). The support substrate 10 is made of an insulating porous material. A flow path 10 a extending along the longitudinal direction of the support substrate 10 is formed inside the support substrate 10. At the time of power generation, a fuel gas containing hydrogen or the like is caused to flow through the flow path 10a, whereby the fuel gas is supplied to the plurality of power generation units 20 via the support substrate 10. At this time, the support substrate 10 itself is exposed to a reducing atmosphere.

The support substrate 10 contains a main composition containing at least MgO and Y ₂ O ₃ . Further, the support substrate 10 may contain at least one of Fe ₂ O ₃ , SiO ₂ , B ₂ O ₃ , and Al ₂ O ₃ as a sub-composition.

The main composition contained in the support substrate 10 is 84.5 mol% or more and 95.5 mol% or less of MgO, 4.5 mol% or more and 9.5 mol% or less of Y ₂ O ₃ , 0.0 mol% or more and 11.0 mol% or less of NiO, Consists of. When the support substrate material contains NiO, NiO is dissolved in MgO and can precipitate as Ni in a reducing atmosphere. NiO may be completely dissolved in MgO. Y ₂ O ₃ is added as a substitute for reducing the solid solution amount of NiO in order to suppress precipitation of Ni. However, since the thermal expansion coefficient of the Y ₂ O ₃ is lower than the thermal expansion coefficient of NiO, Y addition amount of ₂ O ₃ is too large, or small too if, in the thermal expansion coefficient and the power generation portion 20 of the support substrate 10 heat The difference from the expansion coefficient becomes too large. Therefore, the amount of Y ₂ O ₃ added to the support substrate material is regulated within an appropriate range of 4.5 mol% or more and 9.5 mol% or less.

Here, FIG. 3 is a ternary composition diagram of MgO—Y ₂ O ₃ —NiO as the main composition. As shown in FIG. 3, in the main composition according to this embodiment, (x, y, z) is a point in which MgO is x mol%, Y ₂ O ₃ is y mol%, and NiO is z mol%. Occasionally, the composition in the region X surrounded by a rectangle having vertices at (90.5, 9.5, 0.0), (84.5, 9.5, 6.0), (84.5, 4.5, 11.0) and (95.5, 4.5, 0.0) is doing. The region X includes a first line L1 indicating 4.5 mol% Y ₂ O ₃ , a second line L2 indicating 9.5 mol% Y ₂ O ₃ , a third line L3 indicating 84.5 mol% MgO, and MgO. This is an area surrounded by the axis.

The third line L3 is, MgO is x mol%, Y ₂ O ₃ is y mol%, NiO is a point which is z mol% (x, y, z) when the (84.5,0.0,15.5 ) And (84.5, 15.5, 0.0). The triangular region formed on the left side of the third line L3 is a region where the amount of Ni reduced and precipitated is sufficiently suppressed when NiO is regulated to 15.5 mol% or less. That is, the third line L3 is set to correspond to a region where the reduction precipitation amount of Ni can be suppressed.

1-2. Power generation unit 20
As shown in FIG. 2, the power generation unit 20 is formed on the support substrate 10. The power generation unit 20 includes a fuel electrode 21, a solid electrolyte layer 22, a reaction prevention layer 23, and an air electrode 24.

The fuel electrode 21 is formed on the support substrate 10 and functions as an anode. As the material of the fuel electrode 21, a material for forming a fuel electrode of a known fuel cell can be used. For example, NiO-YSZ (nickel oxide-yttria stabilized zirconia) and / or NiO-Y ₂ O can be used. ₃ (nickel oxide-yttria). The fuel electrode 21 may contain Fe ₂ O ₃ or SiO ₂ in addition to these materials. The thickness of the fuel electrode 21 may be 50 μm to 500 μm.

  The fuel electrode 21 may be divided into two layers, a dense fuel electrode active layer made of fine particles of NiO and YSZ, and a porous fuel electrode current collecting layer excellent in gas permeability. The anode active layer is provided between the solid electrolyte layer 22 and the anode current collecting layer. The fuel electrode active layer has a function of promoting electrode reaction on the fuel electrode 21 side and suppressing electrode reaction resistance to a low level. The thickness of the anode active layer is preferably 5 μm to 30 μm.

The solid electrolyte layer 22 is disposed between the fuel electrode 21 and the air electrode 24, and a part of the solid electrolyte layer 22 is formed on the support substrate 10 between the fuel electrodes 21 of the two power generation units 20. The solid electrolyte layer 22 can contain zirconia (ZrO ₂ ) as a main component. The solid electrolyte layer 22 can contain additives such as Y ₂ O ₃ and / or Sc ₂ O ₃ in addition to zirconia. These additives function as stabilizers. The addition amount of the additive in the solid electrolyte layer 22 is about 3 to 20 mol%. That is, examples of the material for the solid electrolyte layer 22 include zirconia-based materials such as yttria-stabilized zirconia such as 3YSZ, 8YSZ, and 10YSZ; and ScSZ (scandia-stabilized zirconia). The thickness of the solid electrolyte layer 22 is preferably 3 μm or more and 50 μm or less.

The reaction preventing layer 23 is formed on the solid electrolyte layer 22. The reaction preventing layer 23 may contain ceria (cerium oxide) as a main component. Specifically, examples of the material for the reaction preventing layer 23 include ceria and a ceria-based material containing a rare earth metal oxide solid-dissolved in ceria. 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 thickness of the reaction preventing layer 23 is preferably 3 μm or more and 50 μm or less.

  The air electrode 24 is disposed on the reaction preventing layer 23 so as not to exceed the outer edge of the reaction preventing layer 23. The air electrode 24 functions as a cathode. The air electrode 24 may be made of, for example, a lanthanum-containing perovskite complex oxide. Examples of the lanthanum-containing perovskite complex oxide include 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. The thickness of the air electrode 24 is preferably 10 μm or more and 100 μm or less.

1-3. Interconnector 30
The interconnector 30 is formed on the fuel electrode 21. The interconnector 30 is connected to a current collector 40 extending from the first power generation unit 20 and a fuel electrode 21 of the second power generation unit 20, whereby the two power generation units 20 are electrically connected. Are connected in series. The interconnector 30 contains a perovskite complex oxide as a main component. In particular, examples of the perovskite complex oxide used for the interconnector 30 include chromite materials such as lanthanum chromite (LaCrO ₃ ) and titanate materials such as SrTiO ₃ . The thickness of the interconnector 30 is preferably 10 μm or more and 100 μm or less.

  Further, a layer may be provided between the interconnector 30 and the current collecting layer 40 for ensuring the connection between the two materials. Similarly, a layer may be provided between the interconnector 30 and the fuel electrode 21 to ensure the connection between both materials.

1-4. Current collector 40
The current collector 40 is formed so as to cover from the air electrode 24 to the interconnector 30 on the power generator 20 adjacent to the power generator 20 including the air electrode 24, and electrically connects the interconnector 30 and the power generator 20. Are connected in series. The current collector 40 only needs to have conductivity, and can be made of the same material as the interconnector 30 and the air electrode 24, for example. The thickness of the current collector 40 is preferably 50 μm or more and 500 μm or less.

2. 2. Manufacturing method of cell 100 2-1. Formation of Support Substrate 10 The support substrate 10 can be formed by compacting. That is, the support substrate 10 includes a step of forming a green compact by putting powder mixed with the material of the support substrate 10 into a mold and compressing the powder.

As described above, the material of the support substrate 10 is 84.5 mol% or more and 95.5 mol% or less of MgO, 4.5 mol% or more and 9.5 mol% or less of Y ₂ O ₃ , and 0 mol% or more and 11.0 mol% or less of NiO. Can be used as a main component. Such a material may contain Fe ₂ O ₃ , SiO ₂ , B ₂ O ₃ , Al ₂ O _{3 and the} like as subcomponents. The pressure applied to the powder at the time of compacting may be set so that the support substrate 10 has sufficient rigidity.

  Moreover, the gas flow path 10a is formed by performing compaction molding in a state where a cellulose sheet or the like that disappears by firing is embedded in the powder, and then performing firing.

2-2. Formation of Fuel Electrode 21 The fuel electrode 21 can be formed by compacting. That is, the fuel electrode 21 may include forming a green compact by putting powder mixed with the material of the fuel electrode 21 into a mold and compressing the powder. The fuel electrode 21 can be formed by a printing method. That is, the fuel electrode 21 may be formed on the support substrate 10 by screen printing using a paste containing the material of the fuel electrode 21. As the material of the fuel electrode 21, as described above, for example, nickel oxide, zirconia, and, if necessary, a pore former are used. The pore former is an additive for providing pores in the fuel electrode. As the pore former, a material that disappears in a later step is used. An example of such a material is cellulose powder.

2-3. Formation of Solid Electrolyte Layer 22 The solid electrolyte layer 22 can be formed by, for example, CIP (cold isostatic pressing), thermocompression bonding, or slurry dip method. Examples of the material of the solid electrolyte layer 22 include zirconia-based materials such as yttria-stabilized zirconia such as 3YSZ, 8YSZ, and 10YSZ; and ScSZ (scandia-stabilized zirconia). In addition, the pressure at the time of pressure bonding of the sheet in the CIP method is preferably 50 to 300 MPa.

2-4. Formation of Reaction Prevention Layer 23 The reaction prevention layer 23 can be formed by a slurry dip method or the like. Examples of the material of the reaction preventing layer 23 include GDC ((Ce, Gd) O ₂ : Gadolinium doped ceria), SDC ((Ce, Sm) O ₂ : Samarium doped ceria) and the like.

2-5. Firing includes co-firing (co-sintering) of the support substrate 10, the fuel electrode 21, the solid electrolyte layer 22, and the reaction prevention layer 23 that have been compacted. The firing temperature and time are set according to the cell material and the like.

2-6. Formation of the air electrode 24 After the air electrode 24 is formed, for example, on the laminate (fired body) of the fuel electrode 21, the electrolyte layer 22, and the reaction prevention layer 23, a material layer of the air electrode 24 is formed by a printing method or the like. It is formed by firing.

2-7. Formation of Current Collector 40 The current collector 40 is made of, for example, a material of the current collector 40 by a printing method or a slurry dip method on a laminate (fired body) of the fuel electrode 21, the electrolyte layer 22, and the reaction preventing layer 23. After the layer is formed, it is formed by firing. The air electrode 24 and the current collecting layer 40 may be formed by firing separately, or may be formed by sequentially stacking and firing together.

3. Actions and Effects When the high temperature power generation operation is repeated using a conventional cell, the inventors have confirmed that NiO in the support substrate is reduced to Ni due to cracks generated near the interface between the support substrate and the power generation unit. It was newly found out that the volume of the support substrate expands accordingly.

Therefore, in the cell 100 according to the present embodiment, the main composition contained in the support substrate 10 is 84.5 mol% to 95.5 mol% MgO, 4.5 mol% to 9.5 mol% Y ₂ O ₃ , and 0 It is supposed that it is comprised by NiO of mol%-11.0 mol%.

  Thus, since the solid solution amount of NiO in MgO is limited, the amount of Ni precipitated as fine particles at the MgO crystal grain boundary can be suppressed. Therefore, it is possible to suppress the occurrence of cracks near the interface between the support substrate 10 and the power generation unit 20.

Moreover, the addition amount of Y ₂ O ₃ added instead of reducing the solid solution amount of NiO is defined in an appropriate range of 4.5 mol% or more and 9.5 mol% or less.

  Therefore, it can be suppressed that the difference between the thermal expansion coefficient of the support substrate 10 and the thermal expansion coefficient of the power generation unit 20 becomes too large.

1. Production of Experimental Examples No. 1 to No. 10 Co-fired bodies according to Experimental Examples No. 1 to No. 10 including a support substrate were produced as follows. In this example, since it is only necessary to confirm the occurrence of cracks at the interface between the support substrate and the power generation unit, a co-fired body of the support substrate and the electrolyte layer was produced.

First, the materials were weighed for each of Experimental Examples No. 1 to No. 10 at the ratios shown in Table 1 below, and mixed in a pot mill for 5 hours. Then, a slurry was prepared by adding polyvinyl alcohol (PVA) as a binder and mixing for another hour. 4 is a ternary composition diagram of MgO—Y ₂ O ₃ —NiO in Experimental Examples No. 1 to No. 10.

  Next, the slurry was dried with a dryer and granulated through a sieve having an opening of 150 μm.

Next, the granulated powder was compressed by a uniaxial press (forming pressure: 0.4 tf / cm ² ) to form a plate-like green compact (supporting substrate) having a length and width of 20 mm × 20 mm and a thickness of 3 mm.

  Next, polyvinyl butyral (PVB) as a binder and terpineol as a solvent were added to a powder of TZ-8Y (manufactured by Tosoh) to prepare a paste.

  Next, an electrolyte layer having a length and width of 15 mm × 15 mm and a thickness of 20 μm was formed by applying a paste on the support substrate using a screen printing method. As a result, a laminate of the support substrate and the electrolyte layer was formed.

  Next, the laminate was degreased at 800 ° C. for 5 hours, and then subjected to a firing process at 1500 ° C. for 2 hours to obtain a co-fired body of the support substrate and the electrolyte layer.

2. Implementation of Reduction Treatment The co-fired bodies according to Experimental Examples No. 1 to No. 10 were placed in a furnace, and reduction treatment was performed at 800 ° C. for 2000 hours while supplying humidified H ₂ at 30 ° C.

  After the reduction treatment for 2000 hours, the occurrence of cracks on the electrolyte surfaces of Experimental Examples No. 1 to No. 10 was confirmed. The confirmation results are shown in Table 1 below.

3. Next, a thermal cycle test was performed using the co-fired body after the reduction treatment while supplying H ₂ humidified to 4% at 30 ° C. The thermal cycle test was performed 20 cycles, with one cycle consisting of reciprocating from room temperature to 800 ° C at 300 ° C / hr.

  After 2000 hours of reduction treatment and thermal cycle test, the occurrence of cracks on the electrolyte surfaces of Experimental Examples No. 1 to No. 10 was confirmed. The confirmation results are shown in Table 1 below.

4). Results As shown in Table 1 above, after 2000 hours of reduction treatment and thermal cycle test, cracks were confirmed at the interface between the support substrate and the electrolyte in Experimental Examples No. 8 to No. 10.

Therefore, as shown in FIG. 4, the composition of the material of the supporting substrate is MgO—Y ₂ O ₃ —NiO on the ternary composition diagram, MgO is x mol%, Y ₂ O ₃ is y mol%, NiO (X, y, z), (90.5, 9.5, 0.0), (84.5, 9.5, 6.0), (84.5, 4.5, 11.0) and (95.5, 4.5, 0.0) It has been confirmed that it suffices to be within an area surrounded by a rectangle with) as a vertex.

  The solid oxide fuel cell disclosed herein is useful in the field of fuel cells because the occurrence of cracks in the vicinity of the interface between the support substrate and the power generation unit can be suppressed.

DESCRIPTION OF SYMBOLS 100 Horizontal stripe type fuel cell 10 Support substrate 20 Power generation part 21 Fuel electrode 22 Solid electrolyte layer 23 Reaction prevention layer 24 Air electrode 30 Interconnector 40 Current collection part

Claims (4)

A support substrate having a fuel gas flow path therein and containing a main composition containing at least MgO and Y ₂ O ₃ ;
A power generation unit formed on the support substrate and having a fuel electrode, an air electrode, and a solid electrolyte layer disposed between the fuel electrode and the air electrode;
With
The main composition is:
84.5 mol% or more and 95.5 mol% or less of MgO,
4.5 mol% or more and 9.5 mol% or less of Y ₂ O ₃ ,
0 to 11.0 mol% NiO,
Composed of,
Solid oxide fuel cell. When the support substrate material contains NiO, NiO is dissolved in MgO.
The solid oxide fuel cell according to claim 1. The support substrate material contains at least one of Fe ₂ O ₃ , SiO ₂ , B ₂ O ₃ , and Al ₂ O ₃ as a sub-composition.
The solid oxide fuel cell according to claim 1 or 2. A support substrate having a fuel gas flow path therein and containing a main composition containing at least MgO and Y ₂ O ₃ ;
A power generation unit formed on the support substrate and having a fuel electrode, an air electrode, and a solid electrolyte layer disposed between the fuel electrode and the air electrode;
With
On the ternary composition diagram of MgO—Y ₂ O ₃ —NiO, the main composition is such that MgO is x mol%, Y ₂ O ₃ is y mol%, and NiO is z mol% (x, (y, z), a region surrounded by a rectangle with (90.5, 9.5, 0.0), (84.5, 9.5, 6.0), (84.5, 4.5, 11.0) and (95.5, 4.5, 0.0) as vertices Having a composition within,
Solid oxide fuel cell.

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