JP2008081804A - Heat resistant alloy member, current collecting member for fuel cell, fuel cell stack, and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide: a heat resistant alloy member which has Cr-diffusion preventing effect and can effectively prevent exfoliation even in the case that a member having a thermal expansion coefficient largely different from a Cr-diffusion preventing layer to the heat resistant alloy member; a current collecting member for a fuel cell; a fuel cell stack; and the fuel cell. <P>SOLUTION: In the current collecting member, the surface of a current collecting base material 201 containing Cr is covered with a dense Cr-diffusion preventing layer 202a composed of an oxide and a porous layer 202b composed of an oxide is formed on the surface of the Cr-diffusion preventing layer 202a. It is preferable that the porous layer 202b contains the same components as those of the Cr-diffusion preventing layer 202a. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a heat-resistant alloy member formed by coating the surface of an alloy containing Cr with a Cr diffusion preventing layer, a current collecting member for a fuel cell, a fuel cell stack, and a fuel cell.

  In recent years, for example, various fuel cells in which a stack of fuel cells is accommodated in a storage container have been proposed as next-generation energy. A solid oxide fuel cell is configured by storing a fuel cell stack in which a plurality of fuel cells are electrically connected in a storage container, and flowing fuel gas (hydrogen) to the fuel electrode side of the fuel cell, Electric power is generated at a high temperature of 600 to 900 ° C. by flowing air (oxygen) to the side (also referred to as an oxygen electrode). In order to electrically connect the fuel cells, a felt-shaped or plate-shaped current collecting member for a fuel cell (hereinafter also referred to as a current collecting member unless otherwise specified) has been used.

  As such a current collecting member, an alloy having a high conductivity is adopted, and since it is used at a high temperature, a heat-resistant alloy is preferably adopted. As such a heat-resistant alloy having a high conductivity, 10% of Cr is used. An alloy containing -30% by mass is generally used. However, when a current collecting member made of an alloy containing Cr is interposed between the fuel cells and a plurality of fuel cells are electrically connected, if the fuel cell generates power for a long time, Cr in the current collecting member Diffuses to the outside of the current collector, and the diffused Cr reaches the interface between the air electrode and the solid electrolyte and degrades the activity. This phenomenon is referred to as so-called Cr poisoning and leads to a decrease in the power generation capacity of the fuel cell.

In order to prevent such Cr poisoning, conventionally, the surface of an alloy containing Cr is coated with Mn, Fe, Co, and Ni (see Patent Document 1).
Japanese National Patent Publication No. 11-501764

  However, in order to prevent the diffusion of Cr, when the current collecting member is configured by coating the surface of the Cr-containing alloy with Mn, Fe, Co, Ni as described in Patent Document 1, the Cr-containing alloy contains Although the diffusion of Cr to the outside can be suppressed to some extent, these coating layers are formed as dense layers in order to prevent the Cr from diffusing to the outside.

  Accordingly, when such a current collecting member is disposed between the fuel cells and the current collecting member and the fuel cells are joined by the conductive adhesive, a dense coating layer and a conductive adhesive for diffusing Cr are provided. When the difference in thermal expansion between the current collector and the fuel cell is large, there is a possibility that the current collecting member and the fuel cell are peeled off due to the stress generated by the difference in thermal expansion, and the electrical connection between the fuel cells is not possible.

  Therefore, the present invention has a heat resistance which can effectively prevent peeling even when a member having a Cr diffusion preventing effect and having a coefficient of thermal expansion greatly different from that of the Cr diffusion preventing layer is joined to a heat resistant alloy member. An object is to provide an alloy member, a current collecting member for a fuel cell, a fuel cell stack, and a fuel cell.

  The heat-resistant alloy member of the present invention is obtained by coating the surface of an alloy containing Cr with a dense Cr diffusion preventing layer made of an oxide, and providing a porous layer made of an oxide on the surface of the Cr diffusion preventing layer. It is characterized by becoming.

  In the heat resistant alloy member of the present invention, by covering the surface of the alloy containing Cr with a dense Cr diffusion preventing layer made of oxide, it is possible to prevent the diffusion of Cr and the surface of the Cr diffusion preventing layer. Since a porous layer made of oxide is formed, even if a conductive adhesive such as a conductive ceramic having a significantly different coefficient of thermal expansion is joined to the porous layer, the difference in thermal expansion Can relieve the stress caused by

  That is, when a member having a coefficient of thermal expansion significantly different from that of the Cr diffusion prevention layer is directly bonded to the surface of the Cr diffusion prevention layer of the heat resistant alloy member, peeling based on the difference in thermal expansion coefficient occurs due to temperature history such as temperature rise and fall. There is a case. In the present invention, by forming a porous layer made of an oxide on the surface of a dense Cr diffusion preventing layer made of an oxide, a conductive adhesive such as a conductive ceramic having a significantly different coefficient of thermal expansion. Even if bonded, etc., the stress caused by the difference in thermal expansion in the porous layer can be relieved, and even when a member having a thermal expansion coefficient significantly different from that of the Cr diffusion prevention layer is bonded to the surface of the heat resistant alloy member, peeling is effectively performed. Can be prevented.

  Furthermore, since the porous layer is formed on the surface of the heat-resistant alloy member, the contact area with the conductive adhesive such as a conductive ceramic increases, and the porous layer and the conductive adhesive such as the conductive ceramic increase. The joint strength of the material can be improved.

  In the heat resistant alloy member of the present invention, the porous layer contains the same component as the Cr diffusion preventing layer. In such a heat resistant alloy member, the bonding strength between the Cr diffusion preventing layer and the porous layer can be improved, and the thermal expansion coefficient can be approximated. From the viewpoint of approximating the thermal expansion coefficient, the porous layer is preferably composed mainly of the same component as the Cr diffusion preventing layer.

  In the heat resistant alloy member of the present invention, the Cr diffusion preventing layer is made of an oxide containing Zn. In the heat-resistant alloy member of the present invention, for example, a Zn-containing slurry is applied to the surface of an alloy containing Cr and heat-treated, thereby forming a Cr diffusion prevention layer made of an oxide. Thereby, the diffusion of Cr from the alloy is suppressed, and so-called Cr poisoning can be suppressed. The reason is not clear, but it is considered that Cr is difficult to dissolve in the surface layer of the alloy due to thermodynamic stability.

  Furthermore, the heat resistant alloy member of the present invention is characterized in that the porous layer is made of an oxide containing Zn. By containing Zn in the porous layer, the Cr diffusion preventing layer containing Zn and the porous layer are chemically bonded, and the bonding becomes stronger.

  Furthermore, the heat resistant alloy member of the present invention is characterized in that the porous layer is conductive. In the heat-resistant alloy member having conductivity, in order to improve the conductivity, a member having a significantly different coefficient of thermal expansion is joined to the surface of the porous layer of the heat-resistant alloy member, so that the present invention is effectively used. Can do. In addition, since a conductive porous layer is formed on the surface of the heat resistant alloy member, for example, the contact area with a conductive adhesive such as a conductive ceramic increases, and the porous layer and the conductive ceramic The contact area with the conductive adhesive increases, and the conductivity can be improved.

  The current collecting member for a fuel cell according to the present invention is characterized in that the heat resistant alloy member is used as a current collecting member for a fuel cell.

  The fuel cell stack of the present invention is characterized in that the fuel cell current collecting member is interposed between a plurality of fuel cells, and the plurality of fuel cells are electrically connected. . In such a fuel cell stack, a plurality of fuel cells can be electrically connected by a current collecting member for a fuel cell having conductivity.

  The current collecting member for a fuel cell and the fuel cell are joined via a conductive adhesive such as a conductive ceramic as described later. However, the dense Cr diffusion prevention layer made of oxide has a larger interatomic bonding force than air electrode materials and conductive adhesives made of a composite perovskite structure containing La, Fe, Mn, etc. used in fuel cells. Since many of them have a small coefficient of thermal expansion, there is a large difference in thermal expansion between the dense Cr diffusion prevention layer covering the surface of the alloy constituting the current collector for fuel cells and the conductive adhesive such as conductive ceramic. In some cases, peeling may occur between the current collecting member for fuel cell and the fuel cell due to temperature history such as temperature rise / fall. In the present invention, the surface of the dense Cr diffusion preventing layer made of oxide is oxidized. By forming a porous layer made of a material, even if a conductive adhesive such as a conductive ceramic having a large thermal expansion is bonded to the porous layer, the stress caused by the thermal expansion difference in the porous layer can be relieved, and the fuel cell Current collector It is possible to prevent the separation of the wood and the fuel cell more effectively.

  Further, the fuel cell stack of the present invention is characterized in that the fuel cell and the fuel cell current collecting member are joined by a conductive adhesive. In such a fuel cell stack, the electrical continuity between the fuel cell and the fuel cell current collector can be further improved.

  In the fuel cell stack of the present invention, the porous layer of the fuel cell current collecting member is provided only on the surface of the Cr diffusion preventing layer in a portion joined to the fuel cell. Features. In such a fuel cell stack, a porous layer is provided only on the surface of the Cr diffusion prevention layer bonded to the fuel cell, and a porous layer is formed on the surface of the Cr diffusion prevention layer in a region not bonded to the fuel cell. Therefore, for example, the porous layer may be formed only on one side surface of the plate-shaped fuel cell current collecting member. Therefore, a part of the manufacturing process of the fuel cell current collecting member can be omitted, the manufacturing of the fuel cell current collecting member of the present invention is facilitated, and the adhesive material can be reduced, thereby reducing the manufacturing cost. it can. Another layer, for example, an insulating material layer having a Cr diffusion preventing function, can be formed on the surface of the Cr diffusion preventing layer on which the porous layer is not formed.

  Furthermore, the fuel cell stack of the present invention is an intermediate in which a component constituting the porous layer and a component constituting the conductive adhesive are mixed between the porous layer and the conductive adhesive. A layer is provided. The intermediate layer includes an oxide containing Zn and a perovskite complex oxide containing La and Fe, or La and Mn. For example, such a fuel cell stack is formed by applying a slurry containing a component constituting the porous layer and a component constituting the conductive adhesive on the surface of the porous layer, and heat-treating the intermediate layer. Is formed. Since the intermediate layer contains the component constituting the porous layer and the component constituting the conductive adhesive, the coefficient of thermal expansion becomes a value between the porous layer and the conductive adhesive, and the porous layer and the conductive adhesive The difference in thermal expansion from the material is reduced, thereby improving the connection reliability between the porous layer and the conductive adhesive. In addition, even if the porous layer and the conductive adhesive are directly joined, the formation of the intermediate layer may be omitted if sufficient connection reliability is ensured.

  The fuel cell of the present invention is characterized in that the fuel cell stack is stored in a storage container. In such a fuel cell, the fuel cell current collector and the fuel cell can be firmly connected, the electrical connection reliability between them can be improved, the voltage drop can be reduced, and the long-term reliability can be improved.

  The heat-resistant alloy member of the present invention is obtained by coating the surface of an alloy containing Cr with a dense Cr diffusion preventing layer made of an oxide, and providing a porous layer made of an oxide on the surface of the Cr diffusion preventing layer. Therefore, it is possible to prevent the diffusion of Cr, and even when a conductive adhesive such as a conductive ceramic having a significantly different thermal expansion coefficient is joined to the heat-resistant alloy member, the stress caused by the thermal expansion difference in the porous layer can be prevented. Even when a member having a thermal expansion coefficient significantly different from that of the Cr diffusion preventing layer can be bonded to the surface of the heat resistant alloy member, peeling can be effectively prevented.

  FIG. 1 is a perspective view showing an embodiment of a current collecting member for a fuel cell according to the present invention, and FIGS. 2 and 3 are Cr diffusion preventing layers 202a and porous layers 202b of the current collecting member 20 for a fuel cell shown in FIG. It is sectional drawing which shows the covering state of the intermediate | middle layer 202c. 2 is a cross-sectional view taken along line AA shown in FIG. 1, and FIG. 3 is a cross-sectional view taken along line BB shown in FIG. As shown in FIG. 1, the fuel cell current collecting member 20 is formed, for example, by processing a plate-like heat-resistant alloy into a comb blade shape and alternately bending adjacent blades to the opposite side.

  In the current collecting member 20, a dense Cr diffusion prevention layer 202a made of an oxide (such as ceramics, the same applies hereinafter) is coated on the surface of a heat-resistant alloy (hereinafter referred to as a current collecting base material) 201 containing Cr. Further, a conductive porous layer 202b made of, for example, conductive ceramics is formed on the surface thereof. Here, in the present invention, the Cr diffusion preventing layer 202a covers the entire circumferential surface of the current collecting base material 201 without any gaps. The fuel cell current collecting member 20 of the present invention is not limited to the shape shown in FIG. 1, and may be, for example, a cylindrical shape or a mesh shape.

  Here, as a material of the current collecting base material 201, an alloy containing 10 to 30% by mass of Cr having high conductivity and heat resistance, for example, Fe—Cr alloy, Ni—Cr alloy, or the like can be used.

  Then, the surface of the current collecting base material 201 is covered with a dense Cr diffusion preventing layer 202a made of an oxide, and further a porous layer 202b and an intermediate layer 202c are formed on the surface of the Cr diffusion preventing layer 202a, A current collecting member 20 for a fuel cell of the present invention is configured. The porous layer 202b is formed on the entire circumferential surface of the Cr diffusion preventing layer 202a, and the intermediate layer 202 is formed on the entire circumferential surface of the porous layer 202b.

  As an oxide constituting the Cr diffusion preventing layer 202a, for example, a metal oxide such as Zn, Mn, Fe, Co, and Ni can be appropriately selected and used. Here, the dense Cr diffusion preventing layer 202a made of an oxide preferably has a relative density of 93% or more, particularly 95% or more from the viewpoint of preventing the diffusion of Cr.

  The porous layer 202b may be more porous than the Cr diffusion preventing layer 202a. In particular, the porosity obtained by image analysis of a cross-sectional SEM (scanning electron microscope) photograph is 5 to 60%. It is preferable to set so as to be, and more preferably 10 to 40%. Note that image analysis software such as Scion Image for Windows (Windows is a registered trademark) manufactured by Scion Image Corporation is used for image analysis. In order to increase the conductivity of the current collecting member 20, the porous layer 202b preferably has a low porosity.

  The intermediate layer 202c constitutes the conductive adhesive 25 with the components constituting the porous layer 202b on the surface of the porous layer 202b so as to be formed between the porous layer 202b and the conductive adhesive 25. It is formed by mixing ingredients. Such an intermediate layer 202c is formed by applying a slurry containing a component constituting the porous layer 202b and a component constituting the conductive adhesive 25 on the surface of the porous layer 202b, followed by heat treatment. Is formed. Since the intermediate layer 202c contains a component constituting the porous layer 202b and a component constituting the conductive adhesive 25, the coefficient of thermal expansion becomes a value between the porous layer 202b and the conductive adhesive 25, and the porous layer 202b is porous. The difference in thermal expansion between the layer 202b and the conductive adhesive 25 is reduced, whereby the connection reliability between the porous layer 202b and the conductive adhesive 25 can be improved. In particular, the intermediate layer 202c is configured to contain an oxide containing Zn and a perovskite complex oxide containing La and Fe, or La and Mn. Such an intermediate layer 202c is formed by applying a slurry containing, for example, an oxide containing Zn, La, and a perovskite complex oxide containing Fe or Mn to the surface of the porous layer 202b, and performing a heat treatment. By such an intermediate layer 202c, the difference in thermal expansion between the porous layer 202b and the conductive adhesive 25 can be further reduced, and the conductivity can be improved.

  Even if the porous layer 202b and the conductive adhesive 25 are directly joined, the formation of the intermediate layer 202c may be omitted if sufficient connection reliability is ensured.

  The Cr diffusion preventing layer 202a is formed as a dense layer so as to cover the entire circumferential surface of the current collecting base material 201 in order to effectively prevent Cr contained in the current collecting base material 201 from diffusing. Here, as the Cr diffusion preventing layer 202a, for example, by using a metal oxide containing Zn having at least one of a spinel structure, a corundum structure, a wurtzite structure and a rock salt structure, or a similar structure thereto. A dense Cr diffusion preventing layer 202a can be formed. Furthermore, since the Cr diffusion preventing layer 202a is formed as a dense layer, it is possible to effectively prevent Cr diffusion from the current collecting base material 201 and to effectively prevent a decrease in power generation capacity of the fuel cell.

  Here, the current collecting member 20 is joined to the fuel cell 1 via a conductive adhesive 25 such as a conductive ceramic, as shown in FIG. 7 described later. However, as described above, the Cr diffusion preventing layer 202a made of a dense oxide is formed on the surface of the current collecting base material 201. When the conductive adhesive 25 such as conductive ceramic is bonded to the Cr diffusion preventing layer 202a made of a dense oxide, the difference in thermal expansion coefficient between the Cr diffusion preventing layer 202a and the conductive adhesive 25 such as conductive ceramic. In some cases, stress due to a difference in thermal expansion coefficient occurs due to a temperature history such as temperature rise and fall, and the current collecting member 20 and the fuel battery cell 1 may be separated.

  In the present invention, since the conductive porous layer 202b is formed on the surface of the Cr diffusion prevention layer 202a made of oxide, the porous conductivity used for joining the Cr diffusion prevention layer 202a and the fuel cell. The stress caused by the difference in thermal expansion from the conductive adhesive 25 such as ceramic can be relieved, and the porous layer 202b and the conductive adhesive 25 such as conductive ceramic are firmly bonded.

  Therefore, according to the current collecting member 20 of the present invention, the current collecting member 20 and the fuel battery cell 1 can be firmly joined, and separation between the current collecting member 20 and the fuel battery cell can be more effectively prevented.

  Further, by providing the intermediate layer 202c composed of the components of the porous layer 202b and the conductive adhesive 25 on the surface of the porous layer 202b, the conductive adhesive 25 such as the porous layer 202b and the conductive ceramic has high conductivity. Therefore, it is considered that the conductivity between the fuel cell and the current collecting member 20 can be increased.

  4 and 5 show another embodiment of the current collecting member 20 for a fuel cell of the present invention. In FIGS. 4 and 5, the surface of the Cr diffusion preventing layer 202a joined to the fuel cell is shown. Only the porous layer 202b and the intermediate layer 202c are provided.

  Since it is necessary to reliably prevent Cr contained in the fuel cell current collecting member 20 from diffusing, the Cr diffusion preventing layer 202 a needs to be formed so as to cover the entire surface of the current collecting base material 201. However, since the porous layer 202b and the intermediate layer 202c strengthen the bonding with the fuel cell, it is only necessary to be provided on the surface of the Cr diffusion preventing layer 202a bonded to the fuel cell. In some cases, a part of the manufacturing process of the current collecting member 20 for a fuel cell of the present invention can be omitted, and the porous layer 202b need not be formed on the surface that is not joined to the fuel cell. This leads to cost reduction.

  In the present embodiment, the porous layer 202b is provided only on the surface of the Cr diffusion preventing layer 202a joined to the fuel battery cell. For example, the current collecting member 20 has a comb blade as shown in FIG. In this case, the porous layer 202b and the intermediate layer 202c may be formed only on one side surface (joint surface) of the current collecting member 20 joined to the fuel cell. In this case, the porous layer 202b and the intermediate layer 202c are also formed in the part that is not partly joined to the fuel cell. Accordingly, since one side surface of the current collecting member 20 has the porous layer 202b and the intermediate layer 202c, the porous layer 202b and the intermediate layer 202c can be manufactured without performing a complicated masking process. The manufacturing process of 202b and the intermediate | middle layer 202c can be simplified. Furthermore, since the porous layer 202b and the intermediate layer 202c are formed on the entire one side surface of the current collecting member 20 to be joined to the fuel battery cell, misalignment or the like may occur during joining with the fuel battery cell. The fuel cell and the current collecting member 20 can be firmly joined.

  Therefore, since the current collecting member 20 and the fuel cell can be firmly joined, it is possible to more effectively prevent the current collecting member 20 and the fuel cell from being separated.

  The Cr diffusion preventing layer 202a is preferably made of an oxide containing Zn.

As described above, the Cr diffusion preventing layer 202a is formed of, for example, a metal oxide having a spinel structure in order to effectively prevent Cr contained in the current collector base material 201 from diffusing. Here, in order to prevent Cr from diffusing, the Cr diffusion preventing layer 202a is particularly preferably made of Zn-based spinel, and more preferably made of, for example, Zn-Mn spinel. The Zn—Mn spinel may contain elements such as Fe and Cr. Specifically, a metal oxide containing Zn and Mn composed of a Zn—Mn spinel, for example, (Zn, Fe) Mn ₂ O ₄ , suppresses Cr diffusion because it is difficult to dissolve Cr. Has an effect.

In the present invention, for example, when Mn is contained in the current collecting base material 201, when providing the Cr diffusion prevention layer 202a made of oxide, as the Cr diffusion prevention layer 202a and the porous layer 202b, An oxide containing Zn but not Mn can also be used. In this case, the porous layer contains ZnO, and pure ZnO is an insulator, but Zn _{1 + δ} O becomes a cation-rich n-type semiconductor, and an impurity element having a high valence is added. As a result, an n-type impurity semiconductor is formed. Here, since Zn in ZnO is a +2 valent ion, conductivity is imparted by dissolving a metal element that becomes +3 or higher ion. As the metal element that becomes +3 or more ions, Al and Fe are particularly desirable. The conductive layer made of zinc oxide in which Al and Fe are solid-solved preferably has a conductivity of ¹ S · cm ⁻¹ or more at 550 ° C. to 900 ° C. near the power generation temperature in the atmosphere.

  If the Cr diffusion preventing layer 202a is 5 μm or less, particularly 2 μm or less, the conductivity as the current collecting member 20 is not affected even if it is insulating to some extent. Further, the porous layer 202b is preferably formed to have a thickness of 10 to 100 μm, preferably 10 to 50 μm, together with the Cr diffusion preventing layer 202a, although it depends on the lifetime of the current collecting base material 201. By setting the thickness to 10 μm or more, it is possible to prevent the generation of voids due to air entrainment. Moreover, by making thickness 50 micrometers or less, while being able to suppress the internal stress by the thermal expansion difference with the current collection base material 201 to the minimum, a conductive fall can be suppressed and formation can be made easy.

  For example, when the Cr diffusion preventing layer 202a of the present invention is formed by spraying, the slurry containing Zn or ZnO is sprayed on the current collecting base material 201 containing Mn and heat-treated. it can. In the case of the dip coating method (dipping), the current collecting substrate 201 containing Mn is immersed in a paste containing Zn or ZnO, and can be formed by heat treatment or heating during power generation.

  Here, when the Cr diffusion preventing layer 202a of the present invention is produced by spraying, it can be produced as follows.

That is, for example, Zn or ZnO, Fe ₂ O ₃ or Al ₂ O ₃ , a solvent, a binder, a dispersant, and the like are mixed at a predetermined ratio to produce a slurry. In this case, it is preferable to use a quick-drying organic solvent such as toluene, for example, and the binder needs to be thermally decomposed at a heat treatment temperature of 500 ° C. or lower. For example, an acrylic resin is used. Is preferred.

  Subsequently, the prepared slurry is sprayed on the surface of the current collecting base material containing Mn and Cr. The spray nozzle used here is not particularly limited as long as fine droplets can be formed on the surface of the current collecting base 201. For example, a two-fluid nozzle that mixes and sprays with compressed air, A one-fluid type nozzle using a high pressure of 2 MPa or more is preferable.

  And in order to form a coating film uniformly on the surface of the current collection base material 201, application | coating of a slurry is completed by shaking the current collection base material 201 and a nozzle moderately, and spraying for a predetermined time. At this time, the slurry filled in the spray is sprayed on the current collecting base material 201. In order to form a uniform coating film without unevenness on the surface of the current collecting base material 201, droplets sprayed from the spray as much as possible. It is preferable to spray at a high spray pressure so as to form fine droplets. By this method, a layer to be the Cr diffusion preventing layer 202a is formed.

  The Cr diffusion preventing layer 202a formed in this manner is obtained by reacting Mn contained in the current collecting base material 201 with Zn contained in the slurry for producing the Cr diffusion preventing layer 202a. Since it is formed as a -Mn-based spinel, diffusion of Cr contained in the current collecting base material 201 can be effectively prevented.

  In addition, a porous layer 202b containing Zn can be provided on the surface of the Cr diffusion preventing layer 202a.

  In providing the porous layer 202b, the amount of Zn applied to the current collecting base material 201 is adjusted to be larger than the amount of Mn contained in the current collecting base material 201. By applying, the porous layer 202b containing Zn can be provided on the surface of the Cr diffusion preventing layer 202a made of Zn—Mn spinel.

  Therefore, for example, when the Cr diffusion prevention layer 202a is produced by a spray method, the Cr diffusion prevention layer 202a is produced at the same time as the production of the Cr diffusion prevention layer 202a by increasing the spray amount or increasing the amount of Zn contained in the slurry. A quality layer 202b can be formed.

  In order to further increase the conductivity of the porous layer 202b, it is possible to include a conductive component such as Fe or Al in the slurry for producing the Cr diffusion preventing layer 202a, and in many cases, this is the case. More preferred.

  The porosity of the porous layer 202b is adjusted according to the size of droplets sprayed from the spray. That is, it is preferable to spray by adjusting the spray pressure so that the droplets are relatively large. By this method, the porosity of the porous layer 202b is adjusted.

  As shown in FIGS. 4 and 5, when the porous layer 202b is provided on the surface of the Cr diffusion prevention layer joined to the fuel cell 1, for example, the fuel cell of the Cr diffusion prevention layer 202a. Masking is performed using a plate-like member or the like in addition to the portion joined to the cell 1. Thereafter, the porous layer 202b can be formed only on the surface of the Cr diffusion preventing layer bonded to the fuel cell 1 by spraying with a spray for a predetermined time. In this case, the slurry adhered to the plate-like member used for masking can be recovered and reused. In this case, the amount of slurry used can be reduced, and the cost can be reduced.

  And after apply | coating as mentioned above, for example, the solvent is dried at a temperature of 100 ° C. for 1 hour, and heat treatment is performed in a furnace at a temperature of 800 ° C. to 1100 ° C. for 2 hours. A Cr diffusion prevention layer 202a made of Zn—Mn spinel is formed on the surface, and a porous layer 202b is formed on the surface.

  On the other hand, when the Cr diffusion preventing layer 202a is produced by a dip coating method (dipping), it can be produced by the following method.

  The current collecting base material 201 is immersed in a slurry containing the same components as those in the case where the Cr diffusion preventing layer 202a is produced by the spray method, and after lifting it, it is dried and solidified, and Cr is applied to the surface of the current collecting base material. A coating film to be the diffusion preventing layer 202a is formed.

  In this case, when forming the porous layer 202b, for example, a pore forming agent such as a spherical acrylic resin is added to the slurry, and the current collecting base material 201 containing Cr and Mn is mixed in the mixed slurry. After dipping and pulling it up, it is dried and solidified.

  Thereafter, for example, by performing heat treatment in a furnace at a temperature of 800 ° C. to 1100 ° C. for 2 hours, a Cr diffusion preventing layer 202a made of Zn—Mn spinel and its surface are formed on the surface of the current collecting base material 201. A porous layer 202b is formed.

  According to these production methods, a dense Cr diffusion preventing layer 202a made of an oxide is coated on the surface of an alloy containing Cr, and a porous layer 202b is formed on the surface of the Cr diffusion preventing layer 202a. The current collecting member 20 can be manufactured.

  When using the current collecting base material 201 that does not contain Mn, a slurry containing Mn in the above-described slurry may be used as the slurry of the Cr diffusion preventing layer 202a. At that time, in order to efficiently produce a Zn—Mn spinel, it is preferable to produce a slurry so that the amounts of Zn and Mn have the same number of moles.

  In this case, since the slurry is prepared with the same amount of Zn and Mn as the number of moles, the porous layer 202b is not formed.

  Therefore, in order to provide the porous layer 202b in this case, for example, a Cr diffusion preventing layer 202a is formed on the surface of the current collecting base material 201, and a slurry containing Zn is sprayed on the surface of the Cr diffusion preventing layer 202a. The porous layer 202b is formed by applying and heat-treating using a method or a dip coating method.

  FIG. 6 is a perspective view of the fuel cell, and FIG. 7 is a cross-sectional view showing a cell stack in which the fuel cells are electrically connected by a current collecting member. In the cell stack according to the present invention, as shown in FIG. 7, a fuel cell current collecting member 20 is disposed between the hollow flat plate fuel cells 1 shown in FIG. It has a configuration to connect.

  As shown in FIG. 6, the fuel battery cell 1 includes a flat support substrate 10, a porous fuel electrode layer 2 provided around the flat support substrate 10, a dense solid electrolyte layer 3, a porous The oxygen electrode layer 4, the dense interconnector 5, and the oxygen electrode material layer 14, and the support substrate 10 further extends in the direction intersecting with the stacking direction of the fuel cells 1 (cell length direction). A plurality of fuel gas passages 16 are provided.

The support substrate 10 is made of, for example, a porous and conductive material, and has a flat section and arc-shaped portions at both ends of the flat portion as shown in FIG. A porous fuel electrode layer 2 is provided so as to cover one of the opposing surfaces of the flat portion and arc-shaped portions at both ends thereof, and a dense solid electrolyte layer 3 is laminated so as to cover the fuel electrode layer 2. Further, an oxygen electrode layer 4 made of a porous conductive ceramic is laminated on the solid electrolyte layer 3 so as to face the fuel electrode layer 2. A dense interconnector 5 is formed on the surface of the support substrate 10 that faces the surface on which the electrode layers 2 and 4 are provided. An oxygen electrode material layer 14 made of an oxygen electrode material is formed on the surface of the interconnector 5. Here, the oxygen electrode material is an oxide (for example, La (Fe, Mn) O ₃ , (La, Sr) (Co, Fe) O _3, etc.) having a perovskite structure such as LaFeO ₃ or LaMnO _3. Conductive ceramic). However, the oxygen electrode material layer 14 is not necessarily formed. As shown in FIG. 6, the fuel electrode layer 2 and the solid electrolyte layer 3 extend to both sides of the interconnector 5 and are configured so that the surface of the support substrate 10 is not exposed to the outside.

  In the fuel cell 1 having such a structure, the portion of the fuel electrode layer 2 facing the oxygen electrode layer 4 operates as a fuel electrode to generate electric power. That is, an oxygen-containing gas such as air is allowed to flow outside the oxygen electrode layer 4 and a fuel gas (hydrogen) is supplied to the gas passage 16 in the support substrate 10 and heated to a predetermined operating temperature. Then, an electrode reaction of the following formula (1) occurs, and power is generated by, for example, an electrode reaction of the following formula (2) occurring in the portion that becomes the fuel electrode of the fuel electrode layer 2.

Oxygen electrode: 1 / 2O ₂ + 2e ⁻ → O ₂ ⁻ (solid electrolyte) (1)
Fuel electrode: O ₂ ⁻ (solid electrolyte) + H ₂ → H ₂ O + 2e ⁻ (2)
The current generated by the electrode reaction is collected through the interconnector 5 attached to the support substrate 10.

  As shown in FIG. 7, a current collecting member 20 is interposed and electrically connected between the plurality of fuel cells as described above, thereby constituting a cell stack. That is, the current collecting member 20 is joined to the oxygen electrode layer 4 of one fuel battery cell 1 by a conductive adhesive 25 such as a porous conductive ceramic, and the oxygen of the other fuel battery cell 1 adjacent thereto is joined. The electrode material layer 14 is joined by a conductive adhesive 25, whereby the plurality of fuel cells 1 are electrically connected in series to form a cell stack.

  The cell stack is manufactured by alternately stacking the fuel cells 1 and the current collecting members 20.

  First, the conductive adhesive 25 is applied to the electrode portions (the oxygen electrode layer 4 and the oxygen electrode material layer 14) of the fuel cell 1 by screen printing. Next, the fuel cell current collecting member 20 is placed on the electrode portion of the fuel cell 1, and the next fuel cell 1 is placed thereon. This is repeated as many times as necessary to produce a laminate of the fuel cell 1 and the fuel cell current collecting member 20.

  Next, the laminated body is heated to a temperature of 900 ° C. to 1100 ° C., and the conductive adhesive 25 is baked on the electrode part of the fuel cell 1 and the current collecting member 20 to produce a cell stack.

  As the conductive adhesive 25, an oxygen electrode material or a material containing the oxygen electrode material and the Cr diffusion preventing layer 202a is usually used. When the oxygen electrode material layer 14 is not formed, it is joined to the interconnector.

  Since the porous layer 202b is formed on the surface of the Cr diffusion preventing layer 202c on the surface of the current collecting member 20 for the fuel cell, the conductive adhesive 25 containing the oxygen electrode material is formed on the surface of the porous layer 202b. The oxygen electrode layer 4 is joined to the projections and depressions. Therefore, since the conductive adhesive 25, the porous layer 202b, and the oxygen electrode layer 4 are firmly bonded by the anchor effect, the current collecting member 20 and the fuel cell 1 can be strongly bonded. Separation from the fuel cell 1 can be more effectively prevented.

  Here, in FIG. 6, the fuel cell 1 is a hollow plate type fuel cell 1, but a cylindrical fuel cell can also be used, for example. However, in the present invention, in order to prevent the fuel cell 1 and the fuel cell current collecting member 20 from being peeled off, it is preferable to join both of them face to face. In addition, joining with a surface means the state by which the surfaces where the fuel cell 1 and the current collecting member 20 for fuel cells oppose are joined by a conductive adhesive or the like. Thereby, the fuel cell 1 and the fuel cell current collecting member 20 are joined with a sufficient joining area.

  Therefore, it is preferable to use a hollow plate type fuel cell as the fuel cell 1. Thereby, the fuel cell 1 and the plate-shaped fuel cell current collecting member 20 can be firmly bonded, and separation of both of them can be effectively prevented.

Here, the thermal expansion coefficient of each member will be described. At 750 ° C., the thermal expansion coefficient of the LaFeO ₃ system generally used as the oxygen electrode material of the fuel cell is 15 to 17 × 10 ⁻⁶ / ° C., and the LaMnO ₃ system is 10 to 11 × 10 ⁻⁶ / ° C., LaCrO ₃ system used as an interconnector is about 14 × 10 ⁻⁶ / ° C., and for the current collecting member 20, the current collecting substrate 201 is 11 × 10 ^−6. The porous layer 202b containing Fe or Al in ZnO formed on the surface layer of the Cr diffusion preventing layer 202a and the Cr diffusion preventing layer 202a made of Zn / Mn spinel is about 6-8 × 10 ⁻⁶ / ° C.

  Accordingly, when the fuel cell 1 and the current collecting member 20 are joined, some stress is generated at the interface based on the difference in thermal expansion. However, the porous layer 202b relieves the stress, so that the current collecting member The bonding between the fuel cell 20 and the fuel battery cell can be strengthened, and peeling of these can be prevented.

  In addition, a cell stack in which fuel cells are joined via a current collecting member 20 is erected on a manifold to which fuel gas is supplied (not shown), and the fuel gas supplied in the manifold is the fuel cell 1. It passes through the gas passage 16.

  A fuel cell is configured by housing the cell stack in a storage container, and disposing a fuel gas introduction pipe for supplying a fuel gas such as city gas and an air introduction pipe for supplying air to the storage container. Is done.

First, 2 mol% of Fe ₂ O ₃ powder with an average particle diameter of 1.5 μm was mixed with ZnO powder with an average particle diameter of 1.0 μm in terms of Fe, a solvent, a binder, and a dispersant by a ball mill for about 24 hours. A slurry was prepared.

  The slurry thus prepared is supplied to a spray nozzle, and the spray pressure is adjusted to form fine droplets of about 5 to 50 μm in which powders such as ZnO are aggregated, and the surface of the current collecting base material containing Mn Sprayed on. At this time, spraying was performed at a pressure of 0.5 MPa to form a Cr diffusion preventing layer, and then spraying was performed at a pressure of 0.1 MPa to form a porous layer. Further, the current collecting base material and the nozzle were appropriately shaken and sprayed for a predetermined time to form a uniform coating film on the surface of the current collecting base material.

  After applying the slurry, the slurry was dried at 100 ° C. for 1 hour, and then baked in a furnace at a temperature of 1000 ° C. for 2 hours to form a Cr diffusion preventing layer 202a and a porous layer 202b. A cross-sectional SEM (scanning electron microscope) photograph of the current collecting member is shown in FIG. The bar shown at the lower right indicates 10 μm, and both the photographs (a) and (b) were taken at a magnification of 1000 times.

  (A) is a cross-sectional photograph of the current collecting member produced by the above method, and the surface of the current collecting base material 201 is covered with a dense Cr diffusion preventing layer 202a made of oxide, and the surface is porous. A quality layer 202b is formed. As shown in FIG. 9, the porosity of the porous layer 202b was calculated by image analysis of a cross-sectional SEM (scanning electron microscope) photograph and found to be 5%.

FIG. 8B shows a case where a conductive adhesive 25 made of (La, Sr) (Co, Fe) O ₃ is printed on the surface of the current collecting member produced by the above method, and the temperature is 1000 ° C. for 2 hours. It is the cross-sectional photograph which baked in the furnace. From this cross-sectional photograph, it is clear that the conductive adhesive 25 and the porous layer 202b can be firmly joined by the anchor effect.

Since the porous layer 202b is porous, the stress caused by the difference in thermal expansion between the current collecting member 25 and the conductive adhesive ((La, Sr) (Co, Fe) O ₃ ) made of conductive ceramic. It is clear that the joint reliability between the current collecting member and the fuel cell can be improved.

Moreover, the cross section was cut out and the semi-quantitative analysis by EPMA of the conductive adhesive was performed. For the EPMA analysis, JXA-8100 manufactured by JEOL Ltd. was used. As measurement conditions, an acceleration voltage of 15 kV, a probe current of 2.0 × 10 ⁻⁷ A, an analysis area of 50 μm × 50 μm, and LIF were used for the spectroscopic crystal. As a result, in the conductive adhesive material outside the Cr diffusion prevention layer, the Cr diffusion amount was 0.5% by mass or less of the detection limit. Therefore, it has been clarified that the Cr diffusion preventing layer 202a covers the current collecting base material 201 and effectively prevents Cr diffusion.

First, 2 mol% of Fe ₂ O ₃ powder with an average particle diameter of 1.5 μm in ZnO powder with an average particle diameter of 1.0 μm in terms of Fe, solvent, binder, dispersant, and 100 parts by mass of the raw material powder A spherical pore former made of 10 parts by mass of an acrylic resin was added, and this was kneaded with a ball mill for about 24 hours to prepare a slurry for dipping.

The current collecting base material containing Mn is immersed in the slurry for immersion thus prepared, dried, and subsequently baked in a furnace at a temperature of 1000 ° C. for 2 hours, and the Cr diffusion preventing layer 202a and A porous layer 202b was formed. Thereafter, a conductive adhesive 25 made of (La, Sr) (Co, Fe) O ₃ was printed and baked in a furnace at a temperature of 1000 ° C. for 2 hours. The cross-sectional photograph and image analysis are shown in FIG. In addition, (a) is the current collector base material immersed in the slurry twice with the drying sandwiched, and the thickness after baking of the porous layer is about 20 μm. (B) is the current collector base material in the slurry. The thickness after baking of the porous layer is about 15 μm. When the porosity of these porous layers was calculated in the same manner as above, (a) was 34% and (b) was 31%.

  In addition, as a comparative example, when a porous adhesive layer was not formed on the Cr diffusion preventing layer 202a, and a conductive adhesive was directly formed, partial peeling occurred between the conductive adhesive and the intermediate layer. It was. An SEM photograph of the cross section is shown in FIG. When the fuel cell was joined to the fuel cell using the current collecting member of this comparative example with a conductive adhesive and a power generation test of the fuel cell was performed at 750 ° C., it had a porous layer as in Examples 1 and 2 above. The output voltage was about 10% lower than when the current collecting member was used to join the fuel cell with a conductive adhesive.

It is a perspective view which shows an example of the current collection member for fuel cells of this invention. It is sectional drawing of the current collection member for fuel cells along the AA line shown in FIG. It is sectional drawing of the current collection member for fuel cells along the BB line shown in FIG. The other form of the current collection member for fuel cells of this invention is shown, and it is sectional drawing along the AA shown in FIG. FIG. 5 is a cross-sectional view of FIG. 4. It is a cross-sectional perspective view of a fuel battery cell. It is a longitudinal cross-sectional view of the fuel cell stack of the present invention. (A) is a cross-sectional SEM photograph of a current collecting member for a fuel cell in which a Cr diffusion preventing layer and a porous layer are provided on the surface of the current collecting substrate, and (b) is an upper surface of the porous layer of (a). It is a cross-sectional SEM photograph which adhered the conductive adhesive. It is a figure which shows the state which performed the SEM photograph of the cross section which formed Cr diffusion prevention layer and the porous layer by the spray method, and formed the electroconductive adhesive material on the upper surface of the porous layer, and the image analysis. It is a figure which shows the SEM photograph of the cross section which formed the Cr diffusion prevention layer and the porous layer by the dip method, and formed the electroconductive adhesive on the upper surface of the porous layer, and the state which image-analyzed. It is a cross-sectional SEM photograph which formed the conductive adhesive directly on the Cr diffusion prevention layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell 20 Current collecting member 25 Conductive adhesive material 201 Current collecting base material 202a Cr diffusion preventing layer 202b Porous layer 202c Intermediate layer

Claims (12)

A heat-resistant alloy characterized in that the surface of an alloy containing Cr is covered with a dense Cr diffusion preventing layer made of an oxide, and a porous layer made of an oxide is provided on the surface of the Cr diffusion preventing layer. Element. The heat resistant alloy member according to claim 1, wherein the porous layer contains the same component as the Cr diffusion preventing layer. The heat resistant alloy member according to claim 1, wherein the Cr diffusion preventing layer is made of an oxide containing Zn. The heat-resistant alloy member according to any one of claims 1 to 3, wherein the porous layer is made of an oxide containing Zn. The heat-resistant alloy member according to any one of claims 1 to 4, wherein the porous layer is conductive. 6. A current collecting member for a fuel cell, wherein the heat resistant alloy member according to claim 5 is used as a current collecting member for a fuel cell. 7. A fuel cell stack comprising a plurality of fuel cell current collectors interposed between the plurality of fuel cells and electrically connecting the plurality of fuel cells. The fuel cell stack according to claim 7, wherein the fuel cell and the current collecting member for the fuel cell are joined by a conductive adhesive. 9. The fuel cell according to claim 8, wherein the porous layer of the current collecting member for the fuel cell is provided only on a surface of the Cr diffusion preventing layer in a portion joined to the fuel cell. Cell stack. An intermediate layer in which a component constituting the porous layer and a component constituting the conductive adhesive are mixed is provided between the porous layer and the conductive adhesive. The fuel cell stack according to claim 8 or 9. The fuel cell stack according to claim 10, wherein the intermediate layer contains an oxide containing Zn and a perovskite complex oxide containing La and Fe, or La and Mn. A fuel cell comprising the fuel cell stack according to any one of claims 7 to 11 stored in a storage container.

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