JP2013065518A - Metal support-type electrolyte-electrode assembly and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the internal resistance of a metal support-type electrolyte-electrode assembly while improving its durability, and also to avoid short-circuiting.SOLUTION: An electrode made of a first layer 16a and a second layer 16b is formed on a metal substrate 12 made of a porous body. The unevenness on an upper end face of the metal substrate 12 is buried under the first layer 16a. The unevenness is slightly copied onto an upper end face of the first layer 16a, and the first layer 16a may be removed because of its low binder content. However, the unevenness and removal are buried under the second layer 16b. Thus, an upper end face of the second layer 16b becomes substantially flat so that an intermediate layer 18 and a solid electrolyte 20, which are formed on the second layer 16b, also become substantially flat. Therefore, even if the thickness of the solid electrolyte 20 is reduced, it is possible to avoid the generation of unevenness on the solid electrolyte 20 or the formation of cracks due to the concentration of stress on the unevenness. It should be noted that the electrode is a cathode-side electrode 16, for example.

Description

  The present invention relates to a metal-supported electrolyte / electrode assembly in which an electrolyte / electrode assembly configured by sandwiching an electrolyte between an anode side electrode and a cathode side electrode is supported by a metal substrate, and a method for manufacturing the same.

  A unit cell of a solid oxide fuel cell is generally configured by sandwiching an electrolyte / electrode assembly in which a solid electrolyte is sandwiched between an anode side electrode and a cathode side electrode with a pair of separators. However, recently, a metal-supported electrolyte / electrode assembly in which an electrolyte / electrode assembly is laminated on a metal substrate has been proposed (see, for example, Patent Document 1). In the following, the metal-supported electrolyte / electrode assembly may be referred to as “MSC”.

  Here, the metal substrate is configured as a porous body so that a reaction gas for causing an electrode reaction with respect to an electrode (usually an anode electrode) formed on the metal substrate can flow. That is, the reactive gas flows through the pores formed inside the metal substrate and reaches the electrode on the metal substrate.

  The more the pores exist, in other words, the higher the porosity, the easier it is for a larger amount of reaction gas to flow. Therefore, since the concentration loss of the reaction gas is suppressed, it is possible to obtain a high voltage even in a high current density operation such as when dealing with a sudden load fluctuation or when increasing the power generation efficiency of the unit cell. Become. Of course, if the porosity is excessively increased, the strength of the metal substrate is reduced, so that the MSC is easily broken. For this reason, the porosity and thickness of the metal substrate are set so that the reaction gas can be sufficiently circulated and the rigidity can be secured.

  By the way, since the metal substrate is a porous body, open pores exist on the end surface of the metal substrate facing the electrode. In order to reduce the internal resistance of the MSC, it is effective to reduce the thickness of the electrode and the solid electrolyte as described in Patent Document 2, but when the thickness of the electrode on the metal substrate is extremely reduced, Since the electrode enters the open pores, the upper end surface of the electrode may be undulated or it may be difficult to fill the pores of the electrode. When a solid electrolyte is formed directly on an electrode having such undulations or pores or via an intermediate layer, the solid electrolyte may crack because the thickness of the intermediate layer and the solid electrolyte is small.

  For this reason, there exists a possibility that durability of MSC may fall. Moreover, since the crack exists, there is a concern that the anode side electrode and the cathode side electrode are short-circuited.

  Patent Document 3 proposes that after a protective layer and a solid electrolyte are provided in this order on a metal substrate, the protective layer and the solid electrolyte are simultaneously fired in an oxidizing atmosphere. In this case, the metal substrate is prevented from being oxidized by the protective layer, and the cathode side electrode is obtained from the protective layer.

  However, even in the technique described in Patent Document 3, when the thickness of the protective layer (cathode side electrode) and the solid electrolyte is reduced, the undulations due to the open pores on the upper end surface of the metal substrate are transferred to the solid electrolyte. Therefore, it is not possible to wipe out the concern that cracks will occur in the solid electrolyte.

  Patent Document 4 describes a technique of covering a metal substrate with a coating film, obtaining an anode side electrode or a cathode side electrode from the coating film, and further laminating a solid electrolyte having a thickness of 1 to 20 μm. Yes. When the thickness of the solid electrolyte is set to be large in this way, the solid electrolyte fills up the undulations on the upper end surface of the electrode, and the upper end surface of the solid electrolyte becomes flat. That is, according to this technique, it is assumed that the occurrence of cracks can be avoided by increasing the thickness of the solid electrolyte. However, in this case, since the thickness of the solid electrolyte is increased, problems such as an increase in internal resistance are caused.

Special table 2010-510635 gazette JP-T-2006-505897 JP 2009-187847 A JP 2003-317740 A

  The present invention has been made in order to solve the above-described problem. Even when the thickness of the solid electrolyte is small, the metal-supported electrolyte / electrode assembly capable of avoiding the occurrence of cracks in the solid electrolyte and a method for producing the same The purpose is to provide.

In order to achieve the above-described object, the present invention provides at least a first electrode functioning as either an anode-side electrode or a cathode-side electrode, an electrolyte, a cathode-side electrode, or an anode-side electrode on a metal substrate. A second electrode that functions as one of the remaining layers, and the electrolyte is a metal-supported electrolyte / electrode assembly that exists between the first electrode and the second electrode,
The metal substrate is made of a porous body having open pores on an end surface facing the first electrode side,
The first electrode has a first layer facing the metal substrate and a second layer facing the electrolyte,
The first layer fills the open pores of the metal substrate, the second layer covers the undulations present on the upper end surface of the first layer, and the surface of the upper end surface facing the electrolyte of the second layer Roughness is small as compared with the upper end surface of the first layer.

  In this configuration, the first layer buryes the undulations on the upper end surface of the metal substrate. That is, if there is a depression, it is filled, and if there is a bump, it is filled. Therefore, the surface roughness of the upper end surface of the first layer is smaller than that of the upper end surface of the metal substrate.

  Further, the second layer buryes the undulations on the upper end surface of the first layer. The surface roughness of the upper end surface of the second layer is smaller than that of the upper end surface of the first layer. That is, the upper end surface of the second layer can approximate a flat surface.

  For this reason, even when an electrolyte with a small thickness is provided directly on the second layer or indirectly through an intermediate layer, the thickness of the electrolyte is substantially constant and the upper end surface is flat. Therefore, the formation of undulations (depressions or bumps) in the electrolyte is avoided. Although stress tends to concentrate on the undulations, since the undulations are extremely small in the electrolyte, the occurrence of cracks can be avoided.

  That is, even when the thickness of the electrolyte is reduced, it is difficult for the electrolyte to crack. Therefore, the durability of the metal-supported electrolyte / electrode assembly can be improved, and the concern that a short circuit will occur is eliminated.

  In addition, since the thickness of the electrolyte can be reduced, oxide ions can quickly move through the electrolyte, and eventually the internal resistance of the electrolyte is reduced. Accordingly, the IR loss is reduced as the metal-supported electrolyte / electrode assembly.

  For these reasons, a metal-supported electrolyte / electrode assembly with a small voltage drop can be obtained, so that, for example, even when discharging at a large current density, a fuel cell exhibiting a large discharge voltage can be configured.

  In the above configuration, the thickness of the first layer and the center line average roughness (Ra), which is a surface roughness parameter, are set to, for example, 20 to 100 μm and 7 to 15 μm. In this case, the thickness of the second layer and the center line average roughness may be set to 5 to 30 μm and 3 to 7 μm.

  On the other hand, the thickness of the electrolyte can be set to, for example, 50 to 500 nm. This thickness is significantly smaller than the thickness of the electrolyte in a general metal-supported electrolyte / electrode assembly. Accordingly, it is possible to set the dimension in the thickness direction of the metal-supported electrolyte / electrode assembly small. As a result, cracks are less likely to occur when thermal expansion or thermal contraction occurs during operation or shutdown.

  Further, the porosity of the metal substrate is preferably 20 to 50%. When the porosity is excessively small, it is not easy for the reaction gas supplied to the electrode formed on the metal substrate to circulate. On the other hand, when the porosity is excessively large, it is difficult to form electrodes on the metal substrate, and the strength of the metal substrate is reduced.

  In addition, the two-dimensional opening diameter of the pores contained in the metal substrate is preferably 20 to 30 μm. The two-dimensional aperture diameter here refers to the longest diameter of pores appearing in the visual field when observed with a scanning electron microscope.

  The pores smaller than 20 μm have a higher ratio of becoming independent closed pores. That is, the number of pores connected in a three-dimensional network for the reaction gas supplied to the metal substrate to flow is reduced, so that it is not easy for the reaction gas to flow. On the other hand, if it is larger than 30 μm, the opening diameter of the pores opened at the upper end surface of the metal substrate becomes large, so that it becomes difficult to fill the pores with the first layer. Furthermore, the oxidation resistance is reduced.

  The first electrode formed on the metal substrate may be a cathode side electrode, for example.

  On the other hand, as a preferred example of the electrolyte, a single crystal of an apatite-type composite oxide can be given. In the apatite complex oxide, excellent oxide ion conductivity is exhibited along the c-axis direction of the unit cell. Therefore, in this case, the c-axis direction is preferably oriented in the thickness direction (stacking direction).

  A polycrystalline body of apatite-type complex oxide may be used as the electrolyte. In this case, the c-axis direction of the unit cell of each crystal grain may be oriented in the thickness direction (stacking direction).

  In any case, an intermediate layer may be formed between the first electrode and the electrolyte. When this intermediate layer becomes a barrier, it is possible to avoid diffusion of elements from the first electrode to the electrolyte or from the electrolyte to the first electrode during operation of the fuel cell. The intermediate layer may be provided between the electrolyte and the second electrode.

Further, the present invention provides a first electrode that functions as at least one of an anode side electrode and a cathode side electrode, an electrolyte, and the remaining one of the cathode side electrode and the anode side electrode on the metal substrate. A method for producing a metal-supported electrolyte / electrode assembly, in which a metal-supported electrolyte / electrode assembly is obtained in which two electrodes are laminated and the electrolyte is present between the first electrode and the second electrode,
A step of filling the open pores in one end face of the metal substrate made of a porous body with the open pores and laminating a tape-shaped molded body forming the first layer;
On the first layer, a second layer that covers the undulations present on the upper end surface of the first layer and has a lower end surface than the upper end surface of the first layer is laminated, and Obtaining a first electrode comprising a first layer and the second layer;
Forming an electrolyte directly or indirectly on the second layer of the first electrode;
Forming a second electrode directly or indirectly on the electrolyte;
It is characterized by having.

  By passing through such a process, it is possible to obtain a metal-supported electrolyte / electrode assembly that is excellent in durability and has sufficient rigidity, and in which the fear of occurrence of a short circuit is eliminated. As described above, since the first layer embeds the undulations on the upper end surface of the metal substrate and the second layer embeds the undulations on the upper end surface of the first layer, even when the thickness of the solid electrolyte is reduced. This is because the occurrence of cracks in the solid electrolyte is avoided. In addition, the thickness of electrolyte can be set to 50-500 nm, for example.

  It is preferable to use a metal substrate having a porosity of 20 to 50% and a two-dimensional opening diameter of pores contained in the metal substrate of 20 to 30 μm. Thereby, it becomes a metal substrate which is easy for the reaction gas to flow and exhibits sufficient strength and oxidation resistance.

  When the tape-shaped molded body forming the first layer is sintered, the first layer is accommodated in the heating means together with the metal substrate, and at least 700 ° C., preferably 1000 ° C. at a temperature rising rate of 15 to 100 ° C./second. It is preferable to hold for 40 seconds to 30 minutes after raising the temperature to the extent. Note that the tape-shaped formed body (first layer) is selectively heated during temperature rise and sintering.

  In this case, the heating time by the heating means and the holding time for sintering the first layer are sufficiently short. Moreover, the first layer is selectively heated. For this reason, it is possible to avoid warping, diffusion of the element of the first layer into the metal substrate, or conversely, diffusion of the element of the metal substrate into the first layer.

  In addition, since it is not necessary to impregnate the metal substrate with the precursor that becomes the barrier layer, an increase in the number of steps is avoided. For this reason, the process becomes simple and a metal-supported electrolyte / electrode assembly can be obtained efficiently.

  In order to selectively heat the metal substrate, for example, a heat shield plate may be provided on the other end surface side where the first layer of the metal substrate is not laminated.

  The electrolyte is preferably formed of a single crystal of an apatite complex oxide. Of course, a polycrystal may be sufficient. An oxide ion excellent in electrolyte by orienting the c-axis direction of a single crystal in the thickness direction (stacking direction) or by orienting the c-axis direction of a unit cell of each crystal grain in the thickness direction (stacking direction) Conductivity develops.

  This type of electrolyte can be formed by any one of atomic layer deposition, ion plating, sputtering, and pulsed laser deposition. According to such a method, since it is possible to form an electrolyte film at a relatively low temperature, it is possible to avoid peeling of the first electrode.

  Furthermore, the second electrode can be formed by sputtering.

  When an intermediate layer is interposed between the first electrode and the electrolyte, a step of forming the intermediate layer after forming the first electrode may be performed. Further, when an intermediate layer is interposed between the electrolyte and the second electrode, a step of forming the intermediate layer after forming the electrolyte may be performed. Of course, both steps may be performed to provide two intermediate layers.

  In the above, when forming a 2nd layer, what is necessary is just to laminate | stack a tape-shaped molded object with a large thermal contraction rate compared with the said 1st layer, for example. In this case, the tape-shaped molded body and the tape-shaped molded body forming the first layer may be sintered simultaneously. The shrinkage stress generated when the second layer is thermally contracted is relieved by the first layer having a smaller thermal contraction rate than the second layer.

  In addition, what is necessary is just to make the quantity of the organic binder added to the slurry for obtaining a tape-shaped molded object different in order to make a thermal contraction rate different.

  The second layer may be laminated on the first layer by screen printing. In this case, it is easy to obtain a second layer in which the undulations of the first layer are buried and the upper end surface is flat. This is because the paste easily flows, so that it is easy to enter the depression of the first layer and to cover the ridges and to be applied so as to be flat.

  According to the present invention, the first electrode formed on the metal substrate has a two-layer structure, the undulation of the upper end surface of the metal substrate is buried in the first layer, and the upper end surface of the first layer is buried in the second layer. Therefore, even when the thickness of the solid electrolyte formed directly on the first electrode or indirectly through the intermediate layer is reduced, the undulation of the solid electrolyte is reduced. Transfer becomes difficult. Therefore, the solid electrolyte becomes substantially flat. In other words, it is possible to avoid the formation of undulations that are the starting points of cracks.

  For this reason, even if it is a case where the thickness of a solid electrolyte is set small, the concern which is excellent in durability and a short circuit generate | occur | produces is wiped out. Moreover, since the thickness of the solid electrolyte can be set small, the internal resistance is reduced. That is, the IR loss is small as the metal-supported electrolyte / electrode assembly. For this reason, it becomes possible to improve the power generation characteristics of the fuel cell.

  In addition, the dimension in the thickness direction of the metal-supported electrolyte / electrode assembly can be set small, and the fuel cell can be downsized.

It is a schematic whole longitudinal cross-sectional explanatory drawing of the metal support type electrolyte electrode assembly which concerns on embodiment of this invention. It is a principal part expanded sectional view of FIG. It is a typical block diagram of the unit cell of an apatite type complex oxide. It is a principal part schematic front view which shows the state which is performing the baking process in an infrared heating furnace provided with an infrared lamp.

  Preferred embodiments of a metal-supported electrolyte / electrode assembly and a method for producing the same according to the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic overall longitudinal cross-sectional explanatory view of a metal-supported electrolyte / electrode assembly (MSC) 10 according to the present embodiment. The MSC 10 is configured by laminating an electrolyte / electrode assembly 14 on a metal substrate 12. In the present embodiment, the electrolyte / electrode assembly 14 is a laminate in which a cathode side electrode 16, an intermediate layer 18, a solid electrolyte 20, and an anode side electrode 22 are formed in this order from the metal substrate 12 side. It is.

  The metal substrate 12 is made of a porous body having pores continuous in a three-dimensional network. For this reason, inside the metal substrate 12, an oxidant gas, which is a reactive gas, can flow through the pores.

  The porosity of the metal substrate 12 is preferably 20 to 50%. If the porosity is less than 20%, it is not easy for the oxidant gas to diffuse. Moreover, when the porosity exceeds 50%, it is not easy to obtain sufficient strength.

  The pores preferably have a two-dimensional opening diameter of 20 to 30 μm that can be confirmed in a visual field when observed with a scanning electron microscope (SEM). If it is less than 20 μm, the pores become independent closed pores, and it is not easy to form a mesh. Further, if it exceeds 30 μm, the porosity tends to increase, and the undulation generated by the open pores 24 (see FIG. 2) on the upper end surface increases, so that the thickness of the cathode-side electrode 16 is increased to bury the undulation. Need arises.

  The metal substrate 12 as the porous body can be made of, for example, a so-called sintered metal. In addition, it is preferable to select a metal having excellent oxidation resistance and a high melting point. Specifically, SUS430 and SUS316 which are 1 type of stainless steel, and Hastelloy X which is 1 type of a nickel base alloy are mentioned.

  Since the metal substrate 12 is a porous body, as shown in FIG. 2, open pores 24 exist on the end surface (upper end surface) facing the cathode side electrode 16. The open pores 24 form undulations on the upper end surface. That is, the upper end surface of the metal substrate 12 is not flat and has a large surface roughness.

  Therefore, in the present embodiment, the cathode-side electrode 16 is formed by two layers of the first layer 16a and the second layer 16b, and the undulation of the upper end surface of the metal substrate 12 is buried by the first layer 16a. Flatten as much as possible. That is, the first layer 16a functions as a planarization layer.

  The thickness of the first layer 16a is set to about 20 to 100 μm because the opening diameter of the open pores 24 is in the range of about 20 to 30 μm. As described above, by setting the thickness of the first layer 16 a according to the opening diameter of the open pores 24, it is possible to avoid the electrolyte / electrode assembly 14 from becoming thick. In other words, the electrolyte / electrode assembly 14 and thus the MSC 10 do not increase in size with the provision of the first layer 16a.

  As shown in FIG. 2, the thickness of the first layer 16a is a distance D1 from a relatively flat portion on the upper end surface of the metal substrate 12 to the end surface of the first layer 16a facing the second layer 16b. Defined.

  The depth of the open pores 24 opened at the upper end surface of the metal substrate 12 is smaller than the aperture diameter, and the thickness of the first layer 16a is larger than the aperture diameter of the open pores 24, so the first layer 16a. Is filled on the upper end surface by filling the open pores 24 opened at the upper end surface of the metal substrate 12. Thereby, the undulation of the upper end surface of the metal substrate 12 is buried and flattened.

  The upper end surface of the first layer 16 a facing the second layer 16 b is formed as a surface having a smaller surface roughness than the upper end surface of the metal substrate 12. That is, although the undulation of the upper end surface of the metal substrate 12 is transferred to the upper end surface, the surface roughness due to the undulation is smaller than that of the upper end surface of the metal substrate 12. When the center line average roughness, which is one of the surface roughness parameters, is measured for the first layer 16a, it is approximately in the range of 7 to 15 μm.

  The thickness of the second layer 16b formed on the first layer 16a may be set to such an extent that the undulation of the first layer 16a can be sufficiently buried and the upper end surface can be approximated to a flat surface. It can be in the range of ˜30 μm. Here, the thickness of the second layer 16b is defined as a distance D2 from a relatively flat portion on the upper end surface of the first layer 16a to the upper end surface facing the intermediate layer 18.

  As can be understood from this, the upper end surface of the second layer 16b facing the intermediate layer 18 has a smaller surface roughness than the upper end surface of the first layer 16a and is substantially flat. When the center line average roughness is measured for the second layer 16b, it is approximately in the range of 3 to 7 μm.

The first layer 16 a and the second layer 16 b described above are made of a material that can generate oxide ions from oxygen in the oxidant gas supplied through the metal substrate 12. Specific preferred examples of such materials include La—Co—O perovskite oxide, La—Sr—Co—O (LSC) perovskite oxide, La—Sr—Co—Fe—O ( LSCF) type perovskite type oxide, Ba—Sr—Co—Fe—O type perovskite type oxide, or any one of these perovskite type oxides. The mixture etc. which mixed the ionic conductor can be mentioned. As the oxide ion conductor, _Sm 2 _{O 3} doped _{CeO 2 (SDC), Y 2} O 3 doped _{CeO 2 (YDC), Gd 2} O 3 doped _{CeO 2 (GDC), La 2} O 3 doped CeO ₂ A ceria-based oxide such as (LDC) is exemplified.

  As will be described later, the first layer 16a and the second layer 16b can be formed from tape-shaped molded bodies having different shrinkage rates. Alternatively, after obtaining the first layer 16a from the tape-shaped molded body, the paste is applied on the first layer 16a by screen printing, and the second layer 16b is obtained by performing a baking treatment on the paste. Also good.

  The solid electrolyte 20 may be directly laminated on the cathode side electrode 16 having the first layer 16 a and the second layer 16 b configured as described above. However, mutual diffusion between the cathode side electrode 16 and the solid electrolyte 20 is possible. When this occurs, a high-resistance reaction product layer is formed. In order to avoid such a problem, in the present embodiment, an intermediate layer 18 that functions as a diffusion preventing layer is interposed between the cathode side electrode 16 and the solid electrolyte 20.

  Preferable specific examples of the material of the intermediate layer 18 having such a function include the ceria-based oxides as described above, that is, SDC, YDC, GDC, LDC and the like. In order to make the intermediate layer 18 function as a diffusion prevention layer, a thickness of about 0.1 to 2 μm is sufficient.

  Since the thickness of the intermediate layer 18 is relatively small, the shape of the upper end surface of the intermediate layer 18 follows the shape of the upper end surface of the second layer 16b immediately below. As described above, since the upper end surface of the second layer 16b is substantially flat, the upper end surface of the intermediate layer 18 is also substantially flat.

The solid electrolyte 20 formed on the intermediate layer 18 plays a role of conducting oxide ions (O ²⁻ ) generated by the cathode side electrode 16 to the anode side electrode 22. Accordingly, examples of the material of the solid electrolyte 20 include materials capable of conducting oxide ions, such as yttria stabilized zirconia (YSZ) and scandia stabilized zirconia (SSZ). Oxides are more preferred. In this case, it is because excellent oxide ion conductivity is exhibited by aligning the c-axis direction in the thickness direction (the direction of arrow C in FIG. 1).

The apatite-type composite oxide will be described in detail with reference to a composite oxide of lanthanum and silicon whose composition is represented by La _X Si ₆ O _{1.5X + 12} (8 ≦ X ≦ 10, hereinafter the same).

FIG. 3 shows the structure of a unit cell of La _X Si ₆ O _{1.5X + 12} with the viewpoint as the c-axis direction. This unit cell 30 has an apatite type structure including six SiO ₄ tetrahedrons 32, O ²⁻³⁴ occupying 2a sites, and La ³⁺ 36a and 36b occupying 4f sites or 6h sites, respectively. Note that Si ⁴⁺ and O ²⁻ in the SiO ₄ tetrahedron 32 are not shown.

  This unit cell 30 belongs to the hexagonal system. That is, in FIG. 3, the angle α at which the side AB in the a-axis direction and the side BF in the c-axis direction intersect with each other, the angle β at which the side BC in the b-axis direction intersects with the side BF, and the side AB and the side The angles γ at which BC intersects are 90 °, 90 °, and 120 °, respectively. The side AB and the side BC have the same length, and the lengths of the sides AB and BC are different from the side BF.

The reason why La _X Si ₆ O _{1.5X + 12} having such an apatite structure is an oxide ion conductor is that O ²⁻ 34 occupying the 2a site is bonded to the SiO ₄ tetrahedron 32 or La ³⁺ 36a. This is probably because they are not involved. This is because the force acting on O ²⁻³⁴ is not strong, and therefore O ²⁻³⁴ can move relatively freely along the c-axis direction without being bound to the 2a site.

  That is, in this unit cell, oxide ions move along the c-axis direction, in other words, the [001] direction. Therefore, the oxide ion conductivity increases in the direction along the c axis and decreases in the direction along the a axis and the b axis. In other words, anisotropy occurs in oxide ion conduction.

  Therefore, as indicated by an arrow C in FIG. 1, when the c-axis direction is matched with the thickness direction of the solid electrolyte 20, the cathode side electrode 16 and the anode side electrode 22 have the highest oxide ion conductivity in the solid electrolyte 20. Therefore, the oxide ions can move quickly from the cathode side electrode 16 toward the anode side electrode 22.

The most preferred composition is La _9.33 Si ₆ O ₂₆ . This is because the oxide ion conduction along the c-axis shows the maximum value.

  The apatite-type composite oxide may be a single crystal or a polycrystalline body oriented such that the c-axis direction of each crystal grain is in the direction of arrow C. The single crystal can be obtained, for example, by a known single crystal production method such as the Czochralski method. On the other hand, a polycrystal can be obtained by atomic layer deposition or sputtering. Alternatively, the powder of the apatite-type composite oxide is added to a solvent to form a slurry, and then the slurry is solidified in the presence of a strong magnetic field of about 10 T (Tesla), and the compact is further sintered. By doing so, a polycrystalline body is obtained in which the c-axis direction of each crystal grain is oriented in the direction of arrow C.

  The upper end surface of the intermediate layer 18 located immediately below the solid electrolyte 20 that performs such a function is substantially flat. Therefore, it is not necessary to provide a marginal part for burying the relief of the intermediate layer 18 at the lower end of the solid electrolyte 20. That is, the thickness of the solid electrolyte 20 can be made sufficiently small.

  Even if the thickness of the solid electrolyte 20 is small, the solid electrolyte 20 has substantially the same thickness throughout. This is because the upper end surfaces of the second layer 16b and the intermediate layer 18 are substantially flat as described above. For this reason, it is possible to avoid the occurrence of undulations in the solid electrolyte 20 or the occurrence of cracks due to stress concentration on the undulations.

  The thickness of the solid electrolyte 20 can be in the range of 50 to 500 nm, for example. As described above, in a general MSC, the thickness of the solid electrolyte exceeds 10 μm, whereas in the present embodiment, the thickness of the solid electrolyte 20 is 500 nm at the maximum.

  By setting the thickness of the solid electrolyte 20 as small as described above, the internal resistance of the entire MSC 10 can be reduced. In other words, the MSC 10 having a small IR loss can be obtained.

  What is necessary is just to select what is generally employ | adopted as the material of the anode side electrode 22 laminated | stacked on the solid electrolyte 20 in a solid oxide fuel cell. Typical examples thereof include Ni-YSZ cermet and Ni-SSZ cermet. Alternatively, a cermet of Ni and yttrium doped ceria (YDC), a cermet of Ni and samarium doped ceria (SDC), a cermet of Ni and gadolinium doped ceria (GDC), and the like may be used.

  The thickness of the anode side electrode 22 is not particularly limited, but can be set to about 0.1 to 30 μm.

  As described above, in the MSC 10 according to the present embodiment, the thickness of the cathode side electrode 16, the intermediate layer 18, the solid electrolyte 20, and the anode side electrode 22 constituting the electrolyte / electrode assembly 14 can be reduced. Therefore, the IR loss of the electrolyte / electrode assembly 14 can be reduced, and the occurrence of cracks due to expansion / contraction associated with oxidation / reduction during operation of the fuel cell can be avoided.

  Moreover, according to the present embodiment, the occurrence of cracks in the solid electrolyte 20 as described above is avoided. In addition, the concern that a short circuit occurs between the cathode side electrode 16 and the anode side electrode 22 is also eliminated.

  The MSC 10 can be manufactured as follows.

  First, the metal substrate 12 is prepared. A substrate made of sintered metal having a porosity of 20 to 50% and a two-dimensional opening diameter of pores of 20 to 30 μm is commercially available, for example, made of SUS430, SUS316 or Hastelloy X. Is available. In addition, the thermal expansion coefficients in 30-700 degreeC of SUS430, SUS316, and Hastelloy X are 12.4 ppm / K, 20.0 ppm / K, and 15.8 ppm / K, respectively.

  On the other hand, the slurry is prepared by adding the starting material which becomes the first layer 16a and the second layer 16b of the cathode side electrode 16, for example, particles of perovskite oxide such as LSC, to the solvent. In order to obtain the cathode-side electrode 16 containing an oxide ion conductor (SDC or the like), particles such as SDC may be added together with the perovskite oxide particles.

  An organic binder is further added to each solvent. Here, the amount of the organic binder added is less in the slurry that becomes the first layer 16a. For example, in the slurry that becomes the first layer 16a, the organic binder is 30% by volume, and in the slurry that becomes the second layer 16b, the organic binder is 40% by volume.

  Each slurry is formed into a tape-like molded body by a doctor blade method, an extrusion molding method, a roll coating method, or the like. Thereafter, on one end surface of the metal substrate 12, a tape-shaped molded body (one with a small amount of organic binder added) to be the first layer 16a, and a tape-shaped molded body (the organic binder added in a large amount) to be the second layer 16b. Are stacked in this order.

  Furthermore, the metal substrate 12, the first layer 16a, and the second layer 16b are laminated in this order by thermocompression bonding each layer by hot pressing or the like, and the undulation of the upper end surface of the metal substrate 12 is caused by the first layer 16a. A laminate 44 (see FIG. 4) is obtained that is buried and the undulation of the upper end surface of the first layer 16a is buried by the second layer 16b.

  The first layer 16a and the second layer 16b cause thermal contraction as a part of the organic binder is vaporized during thermocompression bonding. The first layer 16a has a smaller amount of heat shrinkage than the second layer 16b because the amount of organic binder added is small. Accordingly, the first layer 16a relieves the shrinkage stress generated with the thermal contraction of the second layer 16b. As a result, the occurrence of cracks in the second layer 16b is avoided.

  On the other hand, the second layer 16b is strongly bonded to the first layer 16a because the amount of the organic binder added is large. In other words, peeling is unlikely to occur.

  For the reasons as described above, it is possible to obtain the cathode-side electrode 16 whose upper end surface is substantially flat and that cracks are avoided and which is difficult to peel off from the metal substrate 12.

  Before forming the intermediate layer 18, it is preferable to degrease the laminated body to remove the remaining organic binder. In the degreasing treatment, for example, the first layer 16a and the second layer 16b may be heated together with the metal substrate 12 to about 600 ° C. and held for about 2 hours. At this temperature, the perovskite oxide particles and ceria oxide particles contained in the first layer 16a and the second layer 16b are not sintered.

  Thereafter, the perovskite oxide particles and the ceria oxide particles contained in the first layer 16a and the second layer 16b are sintered. At this time, as shown in FIG. 4, rapid heating is performed using an infrared heating furnace 42 (manufacturing apparatus) having an infrared lamp 40.

  The infrared heating furnace 42 will be described briefly. Inside the infrared heating furnace 42, a laminate 44 of the metal substrate 12 and the cathode side electrode 16 (first layer 16a and second layer 16b) is surrounded by a plurality of infrared lamps 40 arranged in an annular shape. Has been.

  Here, the laminate 44 is placed on the heat shield plate 48 on the pedestal 46 so that the metal substrate 12 faces downward. The pedestal 46 is preferably made of quartz. Further, a thermocouple 50 is disposed inside the pedestal 46, and the temperature inside the infrared heating furnace 42 is measured by the thermocouple 50.

  The heat shield plate 48 is for shielding heat from the lower infrared lamp 40 in FIG. In order to fulfill such a role, as the heat shield plate 48, one made of a material having low thermal conductivity, for example, one made of ceramics is selected. Specific examples of ceramics include cordierite, mullite, zirconia, alumina, silicon carbide and the like.

  That is, the heat shield plate 48 suppresses heating of the lower end surface of the metal substrate 12 where the cathode-side electrode 16 is not thermocompression bonded. For this reason, the cathode side electrode 16 is selectively heated together with the upper end surface of the metal substrate 12 only on the upper end surface side.

  In the heating by the infrared lamp 40, the rate of temperature rise from room temperature to a predetermined temperature can be increased. In the present embodiment, the rate of temperature rise is in the range of 15 to 100 ° C./second. Even if the temperature is raised relatively rapidly in this way, the difference between the thermal expansion coefficients of the cathode side electrode 16 and the metal substrate 12 is small. It is possible to avoid peeling from the metal substrate 12 due to a mismatch with the thermal expansion coefficient of the substrate 12.

  During heating, the first layer 16a and the second layer 16b undergo thermal expansion after contracting slightly as the perovskite oxide and ceria-based oxide, which are electrode components, are sintered. On the other hand, since heat from the infrared lamp 40 is prevented from being transmitted to the metal substrate 12 by the heat shield plate 48, the metal substrate 12 does not cause thermal expansion so much and is warped or deformed by heat. hard. This, combined with the fact that the thermal expansion coefficients of the cathode side electrode 16 and the metal substrate 12 are matched as described above, prevents the cathode side electrode 16 from being peeled off from the metal substrate 12. Therefore, good bonding strength is ensured between the metal substrate 12 and the cathode side electrode 16. Further, since the amount of heat reaching the metal substrate 12 is small, it is possible to avoid the metal substrate 12 from being oxidized.

  Here, when the rate of temperature increase is less than 15 ° C./second, the temperature increase time until reaching the predetermined temperature becomes long, so there is a concern that the metal substrate 12 may be oxidized, warped or deformed. . On the other hand, when the temperature exceeds 100 ° C./second, uneven temperature rise may easily occur in the paste, and the cathode side electrode 16 and the metal substrate 12 are different in thermal expansion amount. There is a concern of peeling from 12. A suitable heating rate is, for example, 50 ° C./second.

  In addition, if the ultimate temperature is excessively low, the electrode components of the first layer 16a and the second layer 16b are not sufficiently sintered. On the other hand, if it is too high, the metal substrate 12 will melt. In order to avoid the above inconvenience, the ultimate temperature is set in a range of 700 ° C. to less than the melting point of the metal substrate 12. When the metal substrate 12 is made of stainless steel or the like as described above, the ultimate temperature can be set to, for example, 700 to 1300 ° C, more preferably 1000 ° C.

  For example, when the temperature is raised from room temperature to 1000 ° C. at 50 ° C./second, the temperature reaches 1000 ° C. in about 20 seconds. Even if the subsequent holding is within the range of 40 seconds to 30 minutes, the cathode-side electrode 16 sintered substantially the same as when held in an electric furnace at 1000 ° C. for 2 hours is obtained.

  Thus, according to the present embodiment, the time to reach a predetermined sintering temperature and the holding time at the sintering temperature can be significantly shortened. For this reason, generation | occurrence | production of curvature is avoided. Further, it is possible to avoid the element of the metal substrate 12 from diffusing into the cathode side electrode 16 and conversely, the element of the cathode side electrode 16 from diffusing into the metal substrate 12.

  The first layer 16a is baked on the upper end surface of the metal substrate 12 and the second layer 16b is baked on the upper end surface of the first layer 16a by the above heating, and the first layer 16a and the second layer 16b Sintering of electrode components proceeds. As a result, the cathode side electrode 16 having a thickness of about 25 to 130 μm is formed.

  After the above operation is completed, the laminate 44 is taken out from the infrared heating furnace 42. Next, an intermediate layer 18 is formed on the upper end surface of the cathode side electrode 16.

  The intermediate layer 18 may be formed as a tape-shaped molded body by a doctor blade method using slurry as in the cathode side electrode 16, or may be formed by screen printing using a paste, It is preferable to employ sputtering. In this case, since it is not necessary to heat the laminate 44, it is possible to prevent the cathode side electrode 16 from being peeled off from the metal substrate 12 in the process of forming the intermediate layer 18.

  When the intermediate layer 18 is formed by sputtering, a target made of a constituent material of the intermediate layer 18 is used. This target can be obtained, for example, by compacting a powder such as SDC or GDC by press molding.

  Next, a glow discharge is generated by applying a negative voltage to the target in the vacuum chamber, and inert gas atoms are ionized to collide with the surface of the target at a high speed. Thereby, particles of the material constituting the target are sputtered and adhere to the laminate 44. As a result, the intermediate layer 18 is formed on the upper end surface of the cathode side electrode 16.

  Sputtering has an advantage that a thin film having a thickness of less than 10 μm can be obtained as a dense film. That is, the dense intermediate layer 18 having a thickness of about 0.1 to 2 μm can be easily formed by performing sputtering.

  After forming the intermediate layer 18 as described above, the solid electrolyte 20 is formed on the intermediate layer 18.

When a single crystal of an apatite-type composite oxide such as La _X Si ₆ O _{1.5X + 12} is used as the solid electrolyte 20, this single crystal is prepared separately. For example, by adopting the method described in JP-A-11-130595, a single crystal having a crystal growth direction oriented in the c-axis direction can be obtained.

  Next, the single crystal of the apatite complex oxide is bonded to the upper end surface side of the cathode side electrode 16. In this bonding, for example, room temperature bonding in which the bonding surface is irradiated with plasma, diffusion bonding by heating, or anodic bonding in which a voltage is applied may be performed.

  Next, the single crystal is polished to a predetermined thickness, for example, 10 μm to 50 μm. As a result, a solid electrolyte 20 made of a single crystal of an apatite-type composite oxide and having the c-axis direction aligned with the stacking direction (thickness direction) is obtained.

  When the apatite-type complex oxide polycrystal is used as the solid electrolyte 20, the c-axis direction of each crystal grain is oriented so as to coincide with the stacking direction (thickness direction). Such a polycrystalline body can be obtained, for example, by atomic layer deposition (ALD), ion plating, sputtering, or pulsed laser deposition (PLD). In this case, by controlling the film forming conditions, the solid electrolyte 20 having a very small thickness of 50 to 500 nm can be easily formed as described above. In addition, according to atomic layer deposition, it is also possible to obtain the solid electrolyte 20 made of a single crystal of an apatite type complex oxide and having a thickness of 50 to 500 nm.

  Moreover, in this case, film formation can be performed at a relatively low temperature in the process of forming the solid electrolyte 20. Therefore, peeling of the intermediate layer 18 and the cathode side electrode 16 can be avoided.

  Alternatively, the powder of the apatite-type composite oxide is added to a solvent to form a slurry, and then the slurry is solidified in the presence of a strong magnetic field of about 10 T (Tesla), and the compact is further sintered. You may make it do.

  Next, the anode side electrode 22 is formed on the solid electrolyte 20.

  The anode side electrode 22 can also be formed by screen printing, a doctor blade method, or ion plating, but sputtering can also be employed. Even in this case, since it is not necessary to heat the laminate 44, it is possible to avoid the cathode-side electrode 16, the intermediate layer 18, and the solid electrolyte 20 from being separated.

  When sputtering is performed, argon ions or the like collide against a constituent material of the anode-side electrode 22, for example, a target made of Ni or YSZ. Thereby, the element sputtered from the target is deposited on the upper end surface of the intermediate layer 18 until the thickness becomes about 0.1 to 1 μm. When ion plating is performed, deposition may be performed until the thickness is about 0.2 to 8 μm, and when screen printing is performed, the thickness may be applied to about 8 to 30 μm.

  The anode side electrode 22 can also be formed by a chemical vapor deposition (CVD) method. In this case, it may be deposited until the thickness becomes about 2 to 8 μm.

  By forming the anode side electrode 22 as described above, the electrolyte / electrode assembly 14 is obtained.

  Note that the second layer 16b may be formed by screen printing. In this case, a paste containing particles of perovskite oxide such as LSC and, if necessary, particles of oxide ion conductor may be prepared and used.

  The paste flows easily. Therefore, the paste applied on the first layer 16a embeds the undulations on the upper end surface of the first layer 16a, thereby flattening the upper end surface of the first layer 16a. In addition, when screen printing is performed, the upper end surface of the paste becomes relatively flat. This is because the paste easily flows as described above. For this reason, the undulation of the first layer 16a is hardly transferred to the upper end surface of the paste.

  Next, a binder removal process is performed as necessary. At this time, the holding may be performed at about 600 ° C. for about 2 hours in an air atmosphere. Thereby, the solvent in the paste is volatilized, and the second layer 16b as a solid phase is obtained. At this point, the sintering of the electrode components contained in the paste does not proceed.

  Thereafter, similarly to the above, for example, the first layer 16a and the second layer 16b may be sintered using the infrared heating furnace 42 shown in FIG.

  The present invention is not particularly limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention.

  For example, when heating is performed using the infrared heating furnace 42, the paste is selectively heated without using the heat shield plate 48 by turning off the infrared lamp 40 on the lower end surface side of the metal substrate 12. Good. As can be appreciated from this, it is not essential to use the heat shield plate 48.

  The electrode formed on the metal substrate 12 may be the anode side electrode 22. In this case, the cathode side electrode 16 may be formed as the uppermost layer.

  In either case, an intermediate layer may be interposed between the anode side electrode 22 and the solid electrolyte 20. On the other hand, the intermediate layer 18 between the cathode side electrode 16 and the solid electrolyte 20 may be omitted.

DESCRIPTION OF SYMBOLS 10 ... Metal support type electrolyte and electrode assembly 12 ... Metal substrate 14 ... Electrolyte / electrode assembly 16 ... Cathode side electrode 16a ... First layer 16b ... Second layer 18 ... Intermediate layer 20 ... Solid electrolyte 22 ... Anode side electrode 24 ... open pores 30 ... unit cell 32 ... SiO ₄ tetrahedron 34 ... oxide ion (O ²⁻ )
36a, 36b ... Lanthanum ion (La ³⁺ )
40 ... Infrared lamp 42 ... Infrared heating furnace 44 ... Laminate 48 ... Heat shield

Claims (18)

On the metal substrate, at least a first electrode that functions as one of an anode side electrode and a cathode side electrode, an electrolyte, and a second electrode that functions as one of the remainder of the cathode side electrode or the anode side electrode are laminated. And the electrolyte is a metal-supported electrolyte / electrode assembly present between the first electrode and the second electrode,
The metal substrate is made of a porous body having open pores on an end surface facing the first electrode side,
The first electrode has a first layer facing the metal substrate and a second layer facing the electrolyte,
The first layer fills the open pores of the metal substrate, the second layer covers the undulations present on the upper end surface of the first layer, and the surface of the upper end surface facing the electrolyte of the second layer A metal-supported electrolyte / electrode assembly, wherein the roughness is smaller than that of the upper end surface of the first layer.   2. The joined body according to claim 1, wherein the thickness of the first layer is 20 to 100 μm, the center line average roughness (Ra) as a surface roughness parameter is 7 to 15 μm, and the thickness of the second layer is 5. A metal-supported electrolyte / electrode assembly, wherein the metal-supported electrolyte / electrode assembly has a center line average roughness (Ra) of 3 to 7 μm.   3. The metal-supported electrolyte / electrode assembly according to claim 1, wherein the electrolyte has a thickness of 50 to 500 nm.   The joined body according to any one of claims 1 to 3, wherein the porosity of the metal substrate is 20 to 50%, and the two-dimensional opening diameter of the pores included in the metal substrate is 20 to 30 µm. A metal-supported electrolyte / electrode assembly characterized by   5. The metal-supported electrolyte / electrode assembly according to claim 1, wherein the first electrode is a cathode-side electrode.   The joined body according to any one of claims 1 to 5, wherein the electrolyte is a single crystal of an apatite-type composite oxide in which the c-axis direction is oriented in the thickness direction, or the c-axis direction of each crystal grain is a thickness. A metal-supported electrolyte / electrode assembly comprising a polycrystal of an apatite-type complex oxide oriented in a direction.   The joined body according to any one of claims 1 to 6, wherein an intermediate layer is interposed between at least one of the first electrode and the electrolyte or between the electrolyte and the second electrode. A metal-supported electrolyte / electrode assembly characterized by being mounted. On the metal substrate, at least a first electrode that functions as one of an anode side electrode and a cathode side electrode, an electrolyte, and a second electrode that functions as one of the remainder of the cathode side electrode or the anode side electrode are laminated. And a method for producing a metal-supported electrolyte / electrode assembly to obtain a metal-supported electrolyte / electrode assembly in which the electrolyte is present between the first electrode and the second electrode,
A step of filling the open pores in one end face of the metal substrate made of a porous body with the open pores and laminating a tape-shaped molded body forming the first layer;
On the first layer, a second layer that covers the undulations present on the upper end surface of the first layer and has a lower end surface than the upper end surface of the first layer is laminated, and Obtaining a first electrode comprising a first layer and the second layer;
Forming an electrolyte directly or indirectly on the second layer of the first electrode;
Forming a second electrode directly or indirectly on the electrolyte;
A method for producing a metal-supported electrolyte / electrode assembly, comprising:   9. The method of manufacturing a metal-supported electrolyte / electrode assembly according to claim 8, wherein the electrolyte has a thickness of 50 to 500 nm.   10. The manufacturing method according to claim 8 or 9, wherein the metal substrate has a porosity of 20 to 50% and a two-dimensional opening diameter of the pores contained in the metal substrate is 20 to 30 [mu] m. A method for producing a metal-supported electrolyte / electrode assembly, which is characterized.   In the manufacturing method of any one of Claims 8-10, the said tape-shaped molded object which makes the said 1st layer is accommodated in a heating means with the said metal substrate, and it is a temperature increase rate of 15-100 degrees C / sec. After the temperature is raised to at least 700 ° C., the metal is sintered by holding for 40 seconds to 30 minutes, and the tape-shaped molded body is selectively heated during the temperature rise and the sintering. A method for producing a supported electrolyte / electrode assembly.   The manufacturing method according to claim 11, wherein the first layer is selectively heated by disposing a heat shield on the other end surface side of the metal substrate on which the first layer is not laminated. To produce a metal-supported electrolyte / electrode assembly.   13. The manufacturing method according to claim 8, wherein the electrolyte is a single crystal of an apatite-type composite oxide in which the c-axis direction is oriented in the thickness direction, or the c-axis direction of each crystal grain is a thickness. A method for producing a metal-supported electrolyte / electrode assembly, comprising forming a polycrystalline body of an apatite-type complex oxide oriented in a direction.   14. The metal-supported electrolyte according to claim 8, wherein the electrolyte is formed by any one of atomic layer deposition, ion plating, sputtering, and pulsed laser deposition. -Manufacturing method of electrode assembly.   15. The method for manufacturing a metal-supported electrolyte / electrode assembly according to claim 8, wherein the second electrode formed above the electrolyte is obtained by sputtering.   16. The manufacturing method according to claim 8, wherein an intermediate layer is formed between at least one of the first electrode and the electrolyte, or between the electrolyte and the second electrode. A method for producing a metal-supported electrolyte / electrode assembly, further comprising a step.   The manufacturing method according to any one of claims 8 to 16, wherein the second layer is laminated on the first layer as a tape-like molded body having a larger thermal shrinkage rate than the first layer. A method for producing a metal-supported electrolyte / electrode assembly, characterized by:   17. The method for manufacturing a metal-supported electrolyte / electrode assembly according to claim 8, wherein the second layer is laminated on the first layer by screen printing.

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