JP2010003623A - Solid oxide fuel cell stack, and bonding material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid oxide fuel cell stack that can resist deformation and mechanical impact owing to the junction of metallic members via a flexible and electrically insulating bonding layer, and to provide a bonding material that can implement such a bonding layer. <P>SOLUTION: The bonding material of, for example, a brazing metal surface-coated with insulating ceramics is used to bond the metallic members 2 constituting generation units 1 via the bonding layer 11 having the metal interposed between insulating ceramics layers. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an adhesion technique between units in a solid oxide fuel cell stack. More specifically, the present invention relates to an adhesion layer structure that combines electrical insulation and flexibility in addition to sealing performance, and to such adhesion. The present invention relates to a suitably used adhesive material.

A solid oxide fuel cell (SOFC) has a structure in which a solid electrolyte having oxide ion conductivity such as yttria-stabilized zirconia is used as an electrolyte, and gas permeable electrodes are arranged on both sides thereof. Known as a battery that operates at nearby high temperatures.
However, in recent years, with the improvement in cell performance due to improvements in electrolyte characteristics, etc., the operating temperature has been decreasing, and operation (power generation) at 600 to 800 ° C. is becoming possible.

When the operation at such a temperature becomes possible, it becomes possible to use a heat-resistant metal material instead of a conventional ceramic material for a fuel cell component such as a separator.
The heat-resistant metal material mentioned here is an alloy containing chromium and means stainless steel or nickel-based alloy. Specifically, ferritic stainless steel, Inconel (registered trademark), Hastelloy (registered trademark). ) And the like.

  In the case of such a low temperature operation solid oxide fuel cell, the stack structure has a separator function and a power generation unit (cassette) in which a ceramic cell as a power generation element is included in a case made of a heat-resistant metal that forms a gas flow path. These are also stacked to form a stack.

As the bonding structure in such a cell or power generation unit, various performances are required depending on the part. For bonding between metal members in a single cell, considering gas sealing properties, Ag, It is known to use a brazing material containing one or more metals of Cu, Ti, Ni, Au, and Al (see, for example, Patent Document 1).
JP 2003-86225 A

However, the joining of adjacent power generation units in the power generation stack, that is, the joining between metal cases, requires not only gas sealing properties but also electrical insulation properties. I can't.
Therefore, for such joining, usually a glass material is used as a sealing material, and by matching the thermal expansion coefficient of the glass material with the refractory metal used in the case, cracking of the adhesive layer is prevented, Excellent gas sealing and electrical insulation properties are being achieved.

  However, the glass material is essentially a brittle material and lacks flexibility, so it cannot withstand deformation of the metal case or mechanical shock, while ensuring electrical insulation and gas sealing properties, In order to avoid the vulnerability, there was a problem that a complicated joint structure had to be taken.

  The present invention relates to the above-mentioned problem relating to gas-sealing adhesion between power generation units in a solid oxide fuel cell in which power generation units in which cells are housed in metal cases are stacked and the metal cases are bonded to form a stack. It was made in view of the above. The object is to provide a solid oxide fuel cell stack in which metal members are bonded to each other via a flexible and electrically insulating adhesive layer, and an adhesive layer that can provide such an adhesive layer. To provide materials.

  As a result of intensive studies to achieve the above object, the present inventors have used, for example, an adhesive material made of a powdery or sheet-like metal having an electrically insulating film on the surface, thereby providing an insulating layer. An adhesive layer with a metal intervening therebetween was obtained, and it was found that the above object could be achieved, and the present invention was completed.

  That is, the solid oxide fuel cell stack of the present invention is characterized in that metal members constituting the power generation unit are bonded to each other via an adhesive layer in which a metal is interposed between insulating ceramic layers. .

  The adhesive material of the present invention is typically characterized by applying an insulating ceramic film or a metal film containing at least one of Al and Si on a sheet-like or granular metal surface. . In addition, the adhesive material of the present invention is made of a metal containing at least one of Al and Si, and is characterized by being in the form of a sheet or particles. Furthermore, it is also possible to mix insulating ceramic particles with the above-mentioned adhesive material in the form of particles to form an adhesive material.

  The bonding method of the present invention is characterized by heating in an oxidizing atmosphere with the bonding material of the present invention interposed between the members to be bonded.

  According to the present invention, since the metal members are bonded to each other through the adhesive layer in which the metal is interposed between the insulating ceramic layers, the insulating ceramic layer in contact with the metal member that is the bonded member has electrical insulation properties. It is ensured and flexibility is ensured by the metal interposed between the insulating ceramic layers.

  Hereinafter, the solid oxide fuel cell stack of the present invention will be described more specifically and in detail together with the bonding material and bonding method used therefor. In the present specification, “%” means mass percentage unless otherwise specified.

FIGS. 1 and 2 are explanatory views showing an embodiment of a solid oxide fuel cell stack according to the present invention. FIGS. 1 (a) and 1 (b) show a power generation unit including cells as power generation elements. It is a perspective view and sectional drawing.
FIGS. 2A and 2B are a perspective view and a sectional view, respectively, showing the structure of a stack formed by stacking the power generation units.

The power generation unit 1 shown in FIG. 1 is formed of, for example, ferritic stainless steel, and includes a cell support plate 2a made of a porous metal having gas permeability and a separator plate 2b, and forms air and fuel gas flow paths. A cell 3 having a case 2 and having a solid electrolyte sandwiched between both electrodes is formed on the cell support plate 2a.
A felt-shaped fuel electrode side current collector 4 made of a fibrous metal is disposed between the cell support plate 2a and the separator plate 2b, and a felt-shaped current collector 4 is also formed on the lower side of the separator plate 2b in the figure. An air electrode side current collector 5 is disposed. The air electrode side current collector 5 is in contact with the air electrode of the adjacent lower power generation unit 1 in the stacked state, as shown in FIG.

  The cell 3 as a power generation element basically has a three-layer structure in which a fuel electrode and an air electrode are formed on both sides of a solid electrolyte. Examples of the electrolyte material include YSZ (yttria stabilized zirconia), SDC. (Samaria doped ceria), SSZ (scandia stabilized zirconia), LSGM (lanthanum is a rate) and the like. Further, as the fuel electrode material, for example, Ni-YSZ, Ni-SDC, Ni-SSZ, etc., and as the air electrode material, electrons such as LSM (LaSrMnO), SSC (SrSmCoO), LSC (LaSrCoO), LSCF (LaSrCoFeO), etc. An oxygen ion conductive oxide or a metal material such as Pt or Ag can be mentioned, but is not particularly limited thereto.

The metal case 2 further includes an air hole 2c through which air and fuel gas are exhausted and a fuel hole 2d, respectively, and an air flow path 6 and a fuel gas flow path 7 separated by a separator plate 2b are formed.
In the power generation unit 1, electrical insulation is not particularly required for joining between the cell support plate 2 a and the metal case 2, but there is no problem even if the adhesive material of the present invention described later is used. There is no.

FIG. 2 shows the structure of a solid oxide fuel cell stack composed of the power generation unit 1, and the fuel cell stack 10 shown in the figure has a plurality of power generation units 1 shown in FIG. 1 (three in the illustrated example). Laminated.
Here, the cases 2 (metal members) in each power generation unit 1 are bonded to each other in an electrically insulated state and a gas sealed state through an adhesive layer 11 in which a metal is interposed between insulating ceramic layers. The air flow path 6 and the fuel gas flow path 7 communicate with each other.

The adhesive layer 11 can be formed by using, for example, an adhesive material of the present invention described later, and since a metal is interposed between the insulating ceramic layers, between the metal cases 2 of each power generation unit 1. Is ensured by the ceramic layer.
On the other hand, the ductility and flexibility of the adhesive layer 11 are ensured by the intermediate metal, and even if the metal case 2 is subjected to deformation or mechanical impact, the adhesive layer 11 can be prevented from cracking or breaking. .

The ceramic layer constituting the adhesive layer 11 is not particularly limited as long as it is electrically insulating, such as glass, oxide, nitride, or silicide.
On the other hand, as the metal interposed in the ceramic layer in the adhesive layer 11, for example, a metal brazing material typified by silver brazing can be suitably used. Depending on the form in the adhesive material, Interspersed in layers or grains.

  The adhesive layer 11 having the above-described structure, that is, the adhesive layer 11 in which a metal is interposed between the insulating ceramic layers is electrically insulating on the surface of, for example, a powdery (granular) or sheet-like metal brazing material. It can be formed by using an adhesive material on which a ceramic film is formed.

As the first method, an adhesive material in which an insulating ceramic film such as glass is formed in advance on the surface of a metal braze powder or a metal braze sheet by a sol-gel method or the like is used between metal members as members to be joined. And a method of performing heat treatment in the air (oxidizing atmosphere).
The insulating film on the surface of the metal brazing forms an insulating ceramic layer between the metal member and the brazing metal during the heat treatment. At this time, the metal brazing powder is intercalated between the ceramic layers in the form of particles, or softened and melted as it is depending on the heating temperature.

Moreover, it is also possible to use a material provided with a metal film containing Al or Si, which is a metal that is more easily oxidized than the brazing metal and forms a dense insulating film, on the surface of the metal brazing powder or the metal brazing sheet. Is possible.
Al and Si in the film are oxidized by heat treatment in an oxidizing atmosphere, and similarly, an insulating ceramic layer is spontaneously formed between the metal member which is a bonded member and the metal brazing material. The metal film can be formed on the surface of the metal brazing material by plating, thermal spraying, coating, or the like. It is also possible to cover or paste an aluminum foil.

Further, as a third method, Al or Si, which is a metal that is more easily oxidized than the brazing metal and forms a dense insulating film, can be added in advance to the brazing metal.
These metal elements in the brazing material are similarly oxidized by heat treatment in an oxidizing atmosphere, and an insulating ceramic layer is formed on the surface of the brazing material. Similarly, an insulating ceramic layer is spontaneously formed between the metal member and the metal brazing material, and the adhesive layer 11 having the above structure is obtained.

  Furthermore, the above-mentioned structure, that is, a metal brazing material particle provided with an insulating film or a metal film containing Al or Si, or a metal brazing material particle containing Al or Si and insulating ceramic particles such as glass powder. It is possible to obtain the adhesive layer 11 having a similar structure also by using a mixed material.

In addition, as the heat-resistant metal constituting the case 2 (metal member) of the power generation unit 1 in the solid oxide fuel cell stack of the present invention, it is desirable to use, for example, ferritic stainless steel. It is desirable to use steel to which at least one of Si is added.
That is, by using a steel material to which such a metal element is added, an insulating film made of alumina or silica is formed on the surface of the metal member during the joining process by heating in an oxidizing atmosphere, and the film side is coated with the insulating film. Since the insulating ceramic components contained in the adhesive material are collected, it becomes easier to form the adhesive layer 11 having the above structure.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, it cannot be overemphasized that this invention is not limited at all by such an Example.

[Example 1]
(1) Adhesive material As a ceramic for an electrical insulating film, a BCAS (BaO—Ca0—SiO ₂ —Al ₂ O ₃ ) -based glass (softening point: 750 ° C., thermal expansion coefficient: 10 × 10 − 6 [1 / K]) powder was used.
This glass powder and ethyl cellulose as a binder were mixed at a mass ratio of 1: 1, and a glass slurry was prepared using butyl acetate as a solvent.

  The glass slurry is spray-coated on both front and back surfaces of an Ag-8 mol% Cu alloy sheet having a thickness of 100 μm, and then heat-treated at 850 ° C. for 15 minutes in the atmosphere to form a glass film having a thickness of 50 μm on the metal brazing sheet. Formed.

(2) Bonding method Metal formed by forming a glass film on the surface as described above at the bonding portion between the metal cases 2 between the power generation units in the solid oxide fuel cell stack 10 shown in FIGS. 2 (a) and (b). The adhesive sheet 11 was formed by installing a brazing sheet and heat-treating at 950 ° C. for 30 minutes in the atmosphere, and the power generation units were bonded. The metal case is made of ferritic stainless steel having a component composition of Fe-20Cr-5Al.

(3) Bonding result FIG. 3 shows the bonding structure between the power generation units obtained in this manner.
As shown in the figure, a chromia layer is formed on the case (metal member) side of the power generation unit by an adhesion process, and an alumina layer is formed on the surface layer side, and a metal layer is formed between the glass layer, which is an insulating ceramic, in the adhesion layer. A layer of wax was formed.

After heating the stack thus bonded to 700 ° C. at a heating rate of 50 ° C./min, and carrying out a thermal cycle test to cool down to room temperature, the adhesive layer did not crack even after 50 cycles, and it was good It was confirmed that it showed excellent durability.
Moreover, the electrical conductivity between the power generation units showed a specific resistance of 10 × 10 ⁵ [Ωcm] or more, and it was confirmed that the electrical conductivity was excellent.

[Example 2]
(1) Adhesive material A thickness of 2 in an inert gas atmosphere at 300 ° C. with an aluminum foil having a thickness of 10 μm adhered to both front and back surfaces of an Ag-8 mol% Cu alloy sheet having a thickness of 200 μm. The material for bonding was prepared by rolling to a fraction of 1 and having a 5 μm thick Al layer on the surface of the metal brazing sheet having a thickness of 100 μm.

(2) Bonding method The above-mentioned rolled metal brazing sheet is installed at the bonding portion between the metal cases 2 between the power generation units in the solid oxide fuel cell stack 10 shown in FIGS. The adhesive layer 11 was formed by heat treatment at 30 ° C. for 30 minutes, and the power generation units were similarly bonded together.

(3) Bonding result FIG. 4 shows the bonding structure between the power generation units obtained as described above.
As shown in the figure, on the case (metal member) side of the power generation unit, a chromia layer and an alumina layer are formed on the surface layer side by an adhesion process, and an aluminum foil is formed on the adhesion layer, as in the above embodiment. A layer made of metal brazing was formed between the oxidized alumina layer (insulating ceramics) layer.

When a similar thermal cycle test was performed in which the stack thus bonded was heated to 700 ° C. at a heating rate of 50 ° C./min and then cooled to room temperature, no crack was observed in the adhesive layer even after 50 cycles. It was found to show good durability.
Moreover, the electrical conductivity between the power generation units showed a specific resistance of 10 × 10 ⁶ [Ωcm] or more, and it was confirmed that the electrical conductivity was good.

Example 3
(1) Adhesive material A metal brazing powder having a composition of Ag-4 mol% Cu-4 mol% Al and a particle diameter of 10 μm is prepared, and this metal powder and ethyl cellulose as a binder are mixed at a mass ratio of 1: 1. A metal braze paste was prepared using butyl acetate as a solvent.

(2) Bonding method The metal brazing paste is applied to the bonding portion between the metal cases 2 between the power generation units in the solid oxide fuel cell stack 10 shown in FIGS. Then, the adhesive layer 11 was formed by heat treatment for 30 minutes to bond the power generation units.

(3) Bonding result FIG. 5 shows the bonding structure between the power generation units obtained as described above, and the case (metal member) side of the power generation unit is subjected to chromia by the bonding treatment in the same manner as in the above embodiment. A layer and an alumina layer are formed. In the adhesive layer, the brazing metal particles covered with the alumina layer formed by oxidizing Al added in the particles are interposed in a deformed state.

A similar thermal cycle test was performed in which the stack thus bonded was heated to 700 ° C. at a heating rate of 50 ° C./min and then cooled to room temperature, and no cracks occurred in the adhesive layer after 50 cycles. It was found to show good durability.
Moreover, the electrical conductivity between the power generation units showed a specific resistance of 10 × 10 ⁵ [Ωcm] or more, and good electrical insulation was confirmed.

Example 4
(1) Adhesive material As ceramic for the electrical insulating film, powder of BCAS glass (softening point: 750 ° C., coefficient of thermal expansion: 10 × 10 −6 [1 / K]) having a particle size of 3 μm is prepared. As the metal powder, a metal brazing powder having a composition of Ag-4 mol% Cu-1 mol% Al and having a particle size of 10 μm was prepared.
And the said metal brazing powder and glass powder are mixed by the volume ratio of 80:20, this mixed powder and ethyl cellulose as a binder are mixed by 1: 1 by mass ratio, and metal brazing-glass using butyl acetate as a solvent. The paste was adjusted.

(2) Bonding method The metal brazing-glass paste is applied to the bonding portion between the metal cases 2 between the power generation units in the solid oxide fuel cell stack 10 shown in FIGS. An adhesive layer 11 was formed by heat treatment at 900 ° C. for 30 minutes, and the power generation units were bonded together.

(3) Bonding result FIG. 6 shows the bonding structure between the power generation units obtained as described above.
As shown in the figure, on the case (metal member) side of the power generation unit, a chromia layer and an alumina layer are formed by an adhesion process, as in the above embodiment. On the other hand, in the adhesive layer, a metal braze powder having a thin alumina layer formed by oxidation of the inner Al on the surface is interposed between the glass layers, which are insulating ceramics, in a granular state. There was found.

A similar thermal cycle test was performed in which the stack thus bonded was heated to 700 ° C. at a heating rate of 50 ° C./min and then cooled to room temperature, and no cracks occurred in the adhesive layer after 50 cycles. Similarly, it was confirmed that good durability was exhibited.
Moreover, the electrical conductivity between the power generation units showed a specific resistance of 10 × 10 ⁶ [Ωcm] or more, and it was confirmed that the electrical conductivity was good.

(A) And (b) is the perspective view and sectional drawing which respectively show the structural example of the electric power generation unit which comprises the solid oxide fuel cell stack of this invention. (A) And (b) is the perspective view and sectional drawing which respectively show the structural example of the solid oxide fuel cell stack of this invention. It is sectional drawing which shows the adhesion structure between the electric power generation units formed by the 1st Example of this invention. It is sectional drawing which shows the adhesion structure between the electric power generation units formed by the 2nd Example of this invention. It is sectional drawing which shows the adhesion structure between the electric power generation units formed by the 3rd Example of this invention. It is sectional drawing which shows the adhesion structure between the electric power generation units formed by the 4th Example of this invention.

Explanation of symbols

1 Power generation unit 2 Case (metal member)
10 Solid Oxide Fuel Cell Stack 11 Adhesive Layer

Claims (14)

  A solid oxide fuel cell stack, wherein metal members constituting a power generation unit are bonded to each other through an adhesive layer in which a metal is interposed between insulating ceramic layers.   2. The solid oxide fuel cell stack according to claim 1, wherein the metal in the adhesive layer is layered.   3. The solid oxide fuel cell stack according to claim 2, wherein a surface of the metal layer is coated with an insulating ceramic.   2. The solid oxide fuel cell stack according to claim 1, wherein the metal in the adhesive layer is granular.   The solid oxide fuel cell stack according to claim 4, wherein the surface of the metal particles is coated with an insulating ceramic.   The solid oxide fuel cell stack according to any one of claims 1 to 5, wherein the metal in the adhesive layer contains Al and / or Si.   The solid oxide fuel cell stack according to any one of claims 1 to 6, wherein the metal member is made of stainless steel containing Al and / or Si.   An adhesive material comprising a metal containing Al and / or Si and having a sheet shape or a granular shape.   An adhesive material comprising an insulating ceramic film on a sheet-like or granular metal surface.   An adhesive material comprising a sheet-like or granular metal surface provided with a metal film containing Al and / or Si.   A bonding material comprising a mixture of metal particles containing Al and / or Si and insulating ceramic particles.   An adhesive material comprising a mixture of metal particles having an insulating ceramic film on the surface and insulating ceramic particles.   A bonding material comprising a mixture of metal particles having a metal film containing Al and / or Si on the surface and insulating ceramic particles.   A bonding method comprising: interposing the bonding material according to any one of claims 8 to 13 between members to be bonded and heating in an oxidizing atmosphere.

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