JP2010192288A - Electrolyte, electrode assembly, and their manufacturing method - Google Patents

Abstract

An object of the present invention is to provide a compact electrolyte / electrode assembly that has excellent durability and electrical characteristics.
For example, the thickness of an intermediate layer 20 is set corresponding to the average pore diameter of an anode side electrode 12. That is, the thickness of the intermediate layer 20 is set to be equal to or larger than the average pore diameter of the anode side electrode 12, and the difference obtained by subtracting the value of the average pore diameter of the anode side electrode 12 from the thickness value of the intermediate layer 20 is in the range of 0 to 17 μm. The intermediate layer 20 is formed so as to be inside.
[Selection] Figure 2

Description

  In the present invention, a solid electrolyte is interposed between a first electrode that functions as either the anode-side electrode or the cathode-side electrode and a second electrode that functions as the remaining one of the cathode-side electrode or the anode-side electrode. It is related with the electrolyte-electrode assembly comprised and its manufacturing method.

  The fuel cell has an electrolyte / electrode assembly in which an electrolyte is interposed between an anode side electrode and a cathode side electrode. As the electrolyte, for example, a solid electrolyte such as a solid oxide is employed. In this case, the fuel cell is also referred to as a solid oxide fuel cell.

  As is well known, when power is generated in a fuel cell, fuel gas (for example, hydrogen gas) is supplied to the anode side electrode, while oxidant gas (for example, air) is supplied to the cathode side electrode. The fuel gas diffuses in the anode side electrode and reaches the electrolyte. Similarly, the oxidant gas also diffuses in the cathode side electrode and reaches the electrolyte. As can be understood from this, the anode-side electrode and the cathode-side electrode are formed with pores where fuel gas or oxidant gas can easily diffuse. Examples of this type of object include a porous body.

  In the solid oxide fuel cell thus configured, hydrogen contained in the fuel gas is ionized at the anode side electrode, and protons and electrons are generated. The electrons are taken out to the outside and used as electric energy for energizing a load (for example, a motor) electrically connected to the solid oxide fuel cell, and then reach the cathode side electrode.

On the other hand, in the cathode side electrode, oxygen contained in the oxidant gas is combined with electrons to generate oxide ions (O ²⁻ ). The oxide ions move through the electrolyte, reach the anode side electrode, and bond to the protons at the anode side electrode. This bond produces water (H ₂ O). Thus, the reactions at both electrodes may be collectively referred to as electrode reactions.

  In particular, in a solid oxide fuel cell, during the progress of this electrode reaction, for example, the constituent material of the cathode side electrode and the constituent material of the solid electrolyte may react with each other to generate a high-resistance reaction phase. When such a situation occurs, the electrolyte / electrode assembly has a large internal resistance. In order to avoid this kind of inconvenience, as shown in Patent Document 1, it has been proposed to interpose an intermediate layer as a reaction preventing layer between at least one electrode and an electrolyte.

Apart from this, in the solid oxide fuel cell, the contact resistance between the electrolyte and the anode-side electrode is relatively high, and therefore, it is not easy to reduce the internal resistance. Therefore, in the prior art described in Patent Document 2, a mixed conductive material having both ionic conductivity and electronic conductivity, for example, an oxide such as TiO ₂ or CeO ₂ is interposed between the electrolyte and the anode side electrode. Attempts have been made to intervene. According to Patent Document 2, by interposing this kind of mixed conductive layer, the electrolyte and the anode side electrode are in good contact with each other, and the contact resistance is reduced.

  Furthermore, in Patent Document 3, the anode side electrode has a two-layer structure, and the upper layer portion on the side close to the electrolyte is composed of a mixture of nickel (Ni) and yttria-stabilized zirconia (YSZ). Techniques for improving and reducing internal resistance are described.

JP 2003-173802 A Japanese Patent Laid-Open No. 11-73982 JP-A-6-295730

  In each of the conventional techniques described above, an intermediate layer is interposed between the electrode and the electrolyte, but the intermediate layer has a larger resistance than each electrode, and therefore the intermediate layer itself is interposed, This will increase the internal resistance of the electrolyte / electrode assembly.

  Further, as described above, gas diffuses in each electrode. For this reason, it is necessary to form an intermediate | middle layer so that diffusion of gas may not be prevented.

  That is, the intermediate layer is required to have a resistance as low as possible and to allow gas to diffuse easily, and to be firmly bonded to both the electrolyte and the electrode. There is no known prior art that comprehensively examines this point.

  In particular, the present invention is made by associating various characteristics of the electrolyte / electrode assembly with the physical property values of the intermediate layer, and has a low resistance and can be made compact, and its manufacture. It aims to provide a method.

In order to achieve the above object, the present invention is configured by interposing a solid electrolyte between a first electrode and a second electrode, and the first electrode serves as either an anode side electrode or a cathode side electrode. In the electrolyte / electrode assembly in which the second electrode functions as one of the cathode side electrode or the remainder of the anode side electrode,
The first electrode is a porous body having pores through which gas flows and having a concave portion and a convex portion on an end surface facing the solid electrolyte,
Between the first electrode and the solid electrolyte, an intermediate layer that fills the concave portion and buryes the convex portion,
The thickness of the intermediate layer is set to be equal to or greater than the average pore diameter of the first electrode, and the difference obtained by subtracting the value of the average pore diameter of the first electrode from the thickness value of the intermediate layer is within a range of 0 to 17 μm. It is characterized by being.

  That is, in the present invention, the thickness of the intermediate layer is set to an extent that is equal to or slightly larger than the average pore diameter of the first electrode. For this reason, since the thickness of the intermediate layer does not become excessively large, the internal resistance of the electrolyte / electrode assembly increases with the provision of the intermediate layer, in other words, prevents the IR loss from increasing. It becomes possible to do.

  In addition, since the thickness of the intermediate layer is small, it is possible to avoid an increase in the size of the electrolyte / electrode assembly, and thus the fuel cell.

  In addition, pores opened on the end surface of the first electrode facing the solid electrolyte, in other words, the recess is filled with the intermediate layer, and the bulge on the end surface, that is, the protrusion is buried in the intermediate layer. For this reason, even when a solid electrolyte having a small thickness is provided on the intermediate layer, it is possible to avoid the depression or protrusion of the first electrode from being transferred to the solid electrolyte. As a result, the portion where stress concentrates on the solid electrolyte is remarkably reduced, so that the occurrence of cracks in the solid electrolyte can be avoided as much as possible. For this reason, since the thickness of the solid electrolyte can be reduced, ions can move quickly in the solid electrolyte, and eventually the internal resistance of the solid electrolyte is reduced.

  In addition, the contact area between the first electrode and the intermediate layer and the contact area between the intermediate layer and the solid electrolyte are both increased. For this reason, both the contact resistance at the interface between the first electrode and the intermediate layer and the contact resistance at the interface between the intermediate layer and the solid electrolyte are reduced. This also reduces the internal resistance of the electrolyte / electrode assembly. In addition, since the contact area is large, the bonding strength between the first electrode and the intermediate layer and between the intermediate layer and the solid electrolyte is also ensured.

  In addition, since the thickness of the intermediate layer is small, the gas supplied to the first electrode easily diffuses in the intermediate layer. For this reason, since an electrode reaction is prevented from being inhibited, non-IR loss is also reduced.

  Ultimately, according to the present invention, an electrolyte / electrode assembly having excellent durability and low IR loss and non-IR loss and excellent electrical characteristics can be obtained.

  In addition, the suitable average pore diameter of a 1st electrode is 3-20 micrometers. In this case, what is necessary is just to set the thickness of an intermediate | middle layer to 3-20 micrometers according to the average pore diameter of a 1st electrode.

  It is preferable that the porosity of the intermediate layer is smaller than the porosity of the first electrode. In this case, it is possible to reliably fill the recesses (pores opened at the end face) in the first electrode with the intermediate layer.

  For example, when the porosity of the first electrode before being reduced is 10 to 40% by volume, it is preferable to set the thickness of the intermediate layer to 3 to 20 μm.

  In the above configuration, it is preferable that the material of the first electrode and the material of the intermediate layer are the same. In this case, the interfacial resistance between the first electrode and the intermediate layer is reduced, and the first electrode and the intermediate layer are intermediate from the first electrode due to shrinkage rate mismatch at the time of manufacturing the electrolyte / electrode assembly. It is because it can avoid that a layer peels or a crack generate | occur | produces in an intermediate | middle layer. Of course, even when the first electrode and the intermediate layer expand when the fuel cell is operated, the expansion rates of the both match, so the intermediate layer peels off from the first electrode or cracks occur in the intermediate layer. Is avoided.

  For example, a fuel cell including a solid oxide as an electrolyte needs to be set to a high temperature during operation, and therefore is required to be excellent in durability and electrical characteristics even at a high temperature. According to the present invention, as described above, an electrolyte / electrode assembly having excellent durability and excellent electrical characteristics can be obtained. Therefore, sufficient durability and electrical characteristics are exhibited even at high temperatures. That is, in the present invention, a solid oxide can be employed as the solid electrolyte in order to cope with high temperature operation.

In the present invention, a solid electrolyte is interposed between the first electrode and the second electrode, and the first electrode functions as either an anode-side electrode or a cathode-side electrode, and the second electrode In the method for producing an electrolyte / electrode assembly in which the electrode functions as one of the cathode side electrode or the remainder of the anode side electrode,
Forming the first electrode by sheet molding;
Forming an intermediate layer on the first electrode by sheet molding and crimping the intermediate layer to the first electrode;
Forming the solid electrolyte on the intermediate layer by sheet molding and pressing the solid electrolyte to the intermediate layer;
At least a step of subjecting the first electrode, the intermediate layer and the solid electrolyte to a firing treatment;
Have
The first electrode is obtained as a porous body having pores through which gas can flow and having concave portions and convex portions on the end surface facing the solid electrolyte, while the intermediate layer is filled with the concave portions. While burying the convex part, the thickness after sintering is set to be equal to or larger than the average pore diameter of the first electrode, and the difference obtained by subtracting the value of the average pore diameter of the first electrode from the value of the thickness is 0 to It is characterized by being obtained as being within a range of 17 μm.

The first electrode, the intermediate layer, and the solid electrolyte may be obtained by screen printing. That is, according to the present invention, a solid electrolyte is interposed between the first electrode and the second electrode, and the first electrode functions as either the anode side electrode or the cathode side electrode, and the second electrode In the method for producing an electrolyte / electrode assembly in which the electrode functions as one of the cathode side electrode or the remainder of the anode side electrode,
Forming the first electrode by screen printing;
Forming an intermediate layer on the first electrode by screen printing;
Forming the solid electrolyte on the intermediate layer by screen printing;
At least a step of subjecting the first electrode, the intermediate layer and the solid electrolyte to a firing treatment;
Have
The first electrode is obtained as a porous body having pores through which gas can flow and having concave portions and convex portions on the end surface facing the solid electrolyte, while the intermediate layer is filled with the concave portions. While burying the convex part, the thickness after sintering is set to be equal to or larger than the average pore diameter of the first electrode, and the difference obtained by subtracting the value of the average pore diameter of the first electrode from the value of the thickness is 0 to It is characterized by being obtained as being within a range of 17 μm.

  Thus, by setting the thickness of the intermediate layer corresponding to the average pore diameter of the first electrode, as described above, both the IR loss and the non-IR loss are reduced, and the gas passes through the intermediate layer. An electrolyte / electrode assembly that can be easily diffused can be obtained. The electrolyte / electrode assembly thus configured has excellent electrical characteristics and good bonding strength between the first electrode and the intermediate layer.

  Further, by filling the concave portion of the first electrode with the intermediate layer and burying the convex portion, and providing the solid electrolyte on the intermediate layer, a flat solid electrolyte is obtained even when the thickness of the solid electrolyte is extremely small. be able to. When such a solid electrolyte is sintered, since there are few parts where stress concentrates, cracks are hardly generated in the solid electrolyte. That is, since it can suppress that a crack arises, the outstanding durability expresses.

  In addition, when forming a 1st electrode, an intermediate | middle layer, and a solid electrolyte by screen printing, you may make it perform a calcination process, after forming at least any one. That is, after the step of forming the first electrode, the step of forming the intermediate layer, or the step of forming the solid electrolyte, a step of performing a pre-baking process may be performed.

  Further, when the inorganic component in the raw material of the first electrode is 100% by weight, 10 to 30% by weight of the inorganic component is used as a pore former, and the temperature during the baking treatment is baked at 1200 to 1500 ° C. As a result, it becomes easy to adjust the porosity of the first electrode before the reduction within the range of 10 to 40% by volume. Here, when the first electrode is an anode side electrode, examples of the inorganic component include YSZ and NiO.

  In order to reduce the porosity of the intermediate layer compared to the porosity of the first electrode, for example, the inorganic layer contained in the raw material of the intermediate layer was added to the inorganic component in the raw material of the first electrode. What is necessary is just to add a pore former in a ratio lower than the ratio of a pore former. This includes the case where no pore former is added to the raw material of the intermediate layer.

  In the above manufacturing method, by making the material of the first electrode and the material of the intermediate layer the same, it is possible to avoid the intermediate layer from being peeled off from the first electrode or cracking in the intermediate layer.

  Furthermore, by forming the solid electrolyte from a solid oxide, it is possible to obtain an electrolyte / electrode assembly that can cope with high temperature operation.

  According to the present invention, since the thickness of the intermediate layer is set corresponding to the average pore diameter of the first electrode, first, it is avoided that the thickness of the intermediate layer becomes excessively large, and the first The contact area between the electrode and the intermediate layer is increased and the electrodes are in good contact with each other. As a result, the internal resistance of the electrolyte / electrode assembly is reduced, so that the IR loss can be prevented from increasing.

  Moreover, since the thickness of the intermediate layer is small, the gas supplied to the first electrode can easily diffuse in the intermediate layer. For this reason, it is avoided that an electrode reaction is inhibited, and as a result, non-IR loss is also reduced.

  Furthermore, since the pores opened in the end surface facing the solid electrolyte in the first electrode are filled with the intermediate layer, and the bulges in the end surface are buried in the intermediate layer, the thin solid electrolyte is formed on the intermediate layer. Even if it is provided, it is possible to avoid the depression or bulge of the first electrode being transferred to the solid electrolyte. For this reason, since the site | part where stress concentrates on this solid electrolyte decreases remarkably, it can avoid that a crack generate | occur | produces in a solid electrolyte as much as possible. That is, an electrolyte / electrode assembly excellent in durability can be formed.

  In addition, since the thickness of the intermediate layer does not become excessively large, it is possible to configure the electrolyte / electrode assembly as a small one.

It is a schematic longitudinal cross-sectional view of the electric power generation cell of the fuel cell which has the electrolyte and electrode assembly which concerns on this Embodiment. FIG. 2 is an enlarged explanatory view of a main part of FIG. 1. It is a schematic plane explanatory drawing explaining the definition of the pore diameter used as the basis of an average pore diameter. It is a graph which shows the relationship between the thickness of an intermediate | middle layer, and the loss including both IR loss and non-IR loss. It is a graph which shows the relationship between the ratio of the pore making material added to the inorganic component in the raw material of an anode side electrode, and the porosity in the anode side electrode before a reduction | restoration. It is a schematic flowchart of the manufacturing method of the electrolyte electrode assembly which concerns on this Embodiment. It is a schematic flowchart of the 1st manufacturing method which obtains the anode side electrode as a 1st electrode, an intermediate | middle layer, and a solid electrolyte from a sheet-like molded object. It is a schematic flowchart of the 2nd manufacturing method which obtains the anode side electrode as a 1st electrode, an intermediate | middle layer, and a solid electrolyte from screen printing.

  Hereinafter, preferred embodiments of the electrolyte / electrode assembly and the manufacturing method thereof according to the present invention will be described in detail with reference to the accompanying drawings. In the following, all the numerical values of the porosity were obtained by the Archimedes method or the mercury intrusion method before reducing the inorganic component of the anode side electrode, for example, before reducing nickel oxide (NiO) to nickel (Ni). Indicates the value.

  FIG. 1 is a schematic longitudinal sectional view of a power generation cell of a fuel cell having an electrolyte / electrode assembly according to the present embodiment. The power generation cell 10 includes an electrolyte / electrode assembly 18 in which a solid electrolyte 16 is interposed between an anode side electrode 12 and a cathode side electrode 14 and these are joined to each other. An intermediate layer 20 is provided between the anode side electrode 12 and the solid electrolyte 16.

  The anode side electrode 12 is made of, for example, Ni and YSZ, Ni and scandia stabilized zirconia (ScSZ), Ni and samarium doped ceria (SDC), Ni and gadolinium doped ceria (GDC), etc. It consists of a cermet (sintered body), and the ratio between Ni and the oxide ion conductor is preferably 1: 1 by weight. The thickness of the anode-side electrode 12 is generally 300 μm to 1 mm when the electrolyte / electrode assembly 18 is a so-called anode-side electrode support type produced using the anode-side electrode 12 as a support substrate, Typically, it is about 500 μm.

  As shown in FIG. 2, the anode side electrode 12 has a small diameter pore 22 and a large diameter pore 24. Among these, the small diameter pores 22 are generated by causing volume shrinkage as the NiO particles that are the raw material of the anode-side electrode 12 are reduced to Ni, while the large diameter pores 24 are, for example, pore forming described later. It is caused by the disappearance of the material.

  The pore diameters of the small-diameter pores 22 to the large-diameter pores 24 are defined as the longest dimension a between both ends in the longitudinal direction in the opening of the two-dimensional cross section, as shown in FIG. The pore diameter of the small pores 22 is approximately in the range of 0.5 to 1 μm, and the pore diameter of the large pores 24 is approximately in the range of 3 to 20 μm.

  In the present embodiment, the pore diameter of the small pores 22 is not included in the calculation when determining the average pore diameter of the pores. That is, in the present embodiment, the “average pore diameter” is the sum of the pore diameters of the large pores 24 whose longest dimension a shown in FIG. 3 exceeds 1 μm, and this is the number of the large pores 24. It is calculated by dividing by. The actual calculation is performed with reference to an arbitrary cross section visually recognized by a scanning electron microscope (SEM).

  As described above, when the pore-forming material is eliminated and the large-diameter pores 24 are formed, the average pore diameter of the large-diameter pores 24 can be controlled, for example, by setting the average particle diameter of the pore-forming material. is there. In addition, the pore size distribution of the large pores 24 can be narrowed by narrowing the particle size distribution of the pore former. For example, when pore formers having an average particle diameter of 8 μm and 20 μm are used, the average pore diameter of the large pores 24 in the anode-side electrode 12 is approximately 4 to 6 μm and approximately 12 to 14 μm, respectively. Become.

  On the other hand, the porosity can be controlled, for example, by setting the amount of pore former used. The porosity is determined by a mercury intrusion method in which all pores including the small diameter pores 22 and the large diameter pores 24 are filled with mercury.

  As will be described later, when 10 to 30% by weight of the pore former is added to the inorganic component in the raw material of the anode side electrode 12, the porosity of the anode side electrode 12 is approximately 10 to 40% by volume.

  In this case, the intermediate layer 20 (see FIG. 2) provided adjacent to the anode-side electrode 12 is made of cermet in which Ni and YSZ are in a weight ratio of 1: 1, similar to the anode-side electrode 12. . Here, in the present embodiment, the porosity of the intermediate layer 20 is set smaller than the porosity of the anode-side electrode 12. Specifically, it is 0 to 35% by volume, and typically 0 to 30% by volume. As can be understood from this, the anode-side electrode 12 and the intermediate layer 20 are composed of the same material and the same composition ratio, but have different porosities.

  The thickness of the intermediate layer 20 defined as a distance D (see FIG. 2) from the bottom of the large-diameter pore 24 opened at the end surface of the anode side electrode 12 to the end surface of the intermediate layer 20 facing the cathode side electrode 14. Is set to be equal to or larger than the average pore diameter of the large pores 24. That is, for example, when the average pore diameter of the large pore 24 is approximately 3 μm, it is set to 3 μm or more, and when it is approximately 12 μm, it is set to 12 μm or more. Thus, by setting the thickness of the intermediate layer 20 to be equal to or larger than the average pore diameter of the large-diameter pores 24, the large-diameter pores 24 opened in the end face facing the solid electrolyte 16 in the anode-side electrode 12, in other words, the concave portions Fills reliably.

  On the other hand, the intermediate layer 20 covers the convex portion 26 protruding from the end face and buryes the convex portion 26. As described above, as the intermediate layer 20 is formed, the concave portion in the end face is filled, while the convex portion 26 is buried, so that the end face facing the solid electrolyte 16 side of the anode side electrode 12 is flat. It becomes.

  As a result, the anode-side electrode 12 is in close contact with the solid electrolyte 16 via the intermediate layer 20. Therefore, the contact resistance at the interface between the anode side electrode 12 and the intermediate layer 20 and the interface between the intermediate layer 20 and the solid electrolyte 16 is reduced, and as a result, the IR loss from the anode side electrode 12 to the solid electrolyte 16 is reduced. Therefore, an electrolyte / electrode assembly having a low internal resistance can be formed. In addition, since the contact areas of the anode side electrode 12 and the intermediate layer 20 and between the intermediate layer 20 and the solid electrolyte 16 are large, the bonding strength between the anode side electrode 12 and the intermediate layer 20 and between the intermediate layer 20 and the solid electrolyte 16 is also ensured. .

  Further, since the thickness of the intermediate layer 20 is reduced, when the fuel gas is supplied to the anode side electrode 12, the fuel gas can easily diffuse through the intermediate layer 20. Therefore, the electrode reaction proceeds easily. For this reason, non-IR loss is also reduced.

  FIG. 4 is a graph showing the relationship between the thickness of the intermediate layer and the loss including both IR loss and non-IR loss. It can be seen from FIG. 4 that the loss can be suppressed to 0.33 V or less by optimizing the thickness of the intermediate layer.

  As can be seen from the above, the intermediate layer 20 need only be thick enough to fill the open large-diameter pores 24 (concave portions) and bury the convex portions 26, and When the value of the thickness of the intermediate layer 20 is excessively increased with respect to the value of the average pore diameter, there is a concern that the internal resistance of the electrolyte / electrode assembly 18 as a whole increases. For this reason, it is preferable to set the thickness of the intermediate layer 20 corresponding to the average pore size of the large pores 24 in the anode side electrode 12.

  Specifically, the difference obtained by subtracting the value of the average pore diameter of the anode side electrode 12 from the value of the thickness of the intermediate layer 20 is set in the range of 0 to 17 μm. That is, for example, when the average pore diameter of the large diameter pores 24 of the anode side electrode 12 is approximately 3 μm, it is preferable to set the thickness of the intermediate layer 20 within a range of 3 to 20 μm.

  Thus, by setting the thickness of the intermediate layer 20 in accordance with the average pore diameter of the large pores 24 in the anode-side electrode 12, it is possible to avoid the electrolyte / electrode assembly 18 from becoming excessively thick. In other words, it is possible to prevent an increase in internal resistance of the electrolyte / electrode assembly 18 (an increase in IR loss) due to the provision of the intermediate layer 20, and the power generation cell 10 is increased in size. This can also be avoided.

  The thickness of the intermediate layer 20 may be set according to the porosity of the anode side electrode 12. That is, in this case, the thickness of the intermediate layer 20 is set according to the porosity of the anode side electrode 12.

  As described above, the electrolyte / electrode assembly 18 can be prevented from becoming excessively thick by setting the thickness of the intermediate layer 20 corresponding to the porosity of the anode-side electrode 12. Therefore, in this case as well, it is possible to prevent the internal resistance of the electrolyte / electrode assembly 18 from increasing (IR loss increases) and to avoid the power generation cell 10 from becoming large.

  Although not shown in FIG. 2, the intermediate layer 20 also has pores for diffusing the fuel gas supplied to the anode side electrode 12. In the present embodiment, the porosity of the intermediate layer 20 is set smaller than the porosity of the anode side electrode 12. This is because the large pores 24 opened in the anode side electrode 12 are surely filled by the intermediate layer 20.

  In addition, the suitable porosity of the intermediate | middle layer 20 is 0-35 volume% as above-mentioned. In order to make the porosity of the anode side electrode 12 and the intermediate layer 20 different, for example, the anode side electrode 12 is made after adding a pore former to the raw material, while the intermediate layer 20 is added with a pore former to the raw material. What is necessary is just to produce it. Alternatively, the ratio of the pore former added to the inorganic component of the raw material of the intermediate layer 20 is made smaller than the ratio of the pore former added to the inorganic component of the raw material of the anode side electrode 12. May be.

The solid electrolyte 16 is made of, for example, stabilized zirconia such as YSZ, ScSZ, ceria-based oxides such as SDC, GDC, yttrium-doped ceria (YDC), or lanthanum gallate-based oxides such as LaSrGaMgO ₃ and LaSrGaMgCoO ₃ . The thickness is set to about 3 to 15 μm, generally about 5 μm. The end surface of the solid electrolyte 16 facing the cathode side electrode 14 is flat. In addition, although the thickness of the solid electrolyte 16 is as small as 3 to 15 μm on this end face, the amount of cracks is remarkably small as compared with the electrolyte / electrode assembly according to the prior art that does not include the intermediate layer 20. .

  Between the solid electrolyte 16 and the cathode side electrode 14, a reaction preventing layer 28 made of, for example, SDC, GDC, YDC or the like is interposed. The thickness of the reaction preventing layer 28 is set to about 1 μm at the maximum. Thus, since the thickness of the reaction preventing layer 28 is extremely small, it is possible to avoid an increase in the internal resistance of the electrolyte / electrode assembly 18.

  The remaining cathode electrode 14 is, for example, a La—Sr—Co—Fe composite oxide (LSCF), a La—Sr—Mn composite oxide (LSM), a La—Sr—Co composite acid (LSC), It consists of Ba—Sr—Co—Fe based complex oxide (BSCF), Ba—Sr—Co based complex acid (BSC), Sm—Sr—Co based complex acid (SSC), etc. It is set to 10 μm or more, preferably about 30 μm.

  The electrolyte / electrode assembly 18 thus configured is interposed between a pair of separators 30a and 30b (see FIG. 1). Terminal electrodes 32a and 32b are disposed outside the separators 30a and 30b, respectively, and end plates 34a and 34b are respectively disposed outside the terminal electrodes 32a and 32b. The end plates 34a and 34b are connected to each other by a tie rod or the like (not shown), and the electrolyte / electrode assembly 18, separators 30a and 30b, and terminal electrodes 32a and 32b are sandwiched between the end plates 34a and 34b. Is configured. The separators 30a and 30b are provided with gas flow paths 36a and 36b for supplying fuel gas or oxygen-containing gas to the anode side electrode 12 or the cathode side electrode 14, respectively.

  The electrolyte / electrode assembly 18 according to the present embodiment is basically configured as described above. Next, the function and effect will be described.

  When operating the power generation cell 10 configured as described above, the temperature of the power generation cell 10 is raised to about 500 to 1000 ° C. Thereafter, an oxidant gas containing oxygen is circulated through the gas flow path 36b provided in the separator 30b, while a fuel gas containing hydrogen is circulated through the gas flow path 36a provided in the separator 30a.

Oxygen in the oxygen-containing gas is combined with electrons at the cathode side electrode 14 to generate oxide ions (O ²⁻ ). The generated oxide ions are conducted from the cathode side electrode 14 to the solid electrolyte 16.

  Here, as described above, the end surface of the solid electrolyte 16 facing the cathode side electrode 14 is provided flat. For this reason, since the contact area of the cathode side electrode 14 and the solid electrolyte 16 becomes large, the interface resistance between the cathode side electrode 14 and the solid electrolyte 16 becomes small. Therefore, the voltage drop in the electrolyte / electrode assembly 18 is reduced.

  The oxide ions then move to the interface of the solid electrolyte 16 facing the anode side electrode 12. As described above, in the solid electrolyte 16, the amount of cracks that hinder the movement of oxide ions is remarkably small. In other words, the oxide ions can easily move inside the solid electrolyte 16. That is, since the thickness of the solid electrolyte 16 can be reduced, the oxide ions can quickly move through the solid electrolyte 16, and eventually the internal resistance of the solid electrolyte 16 is reduced.

  Thus, in the present embodiment, the voltage drop of the electrolyte / electrode assembly 18 is small, and the internal resistance and volume resistance of the solid electrolyte 16 are small. Therefore, even when the power generation cell 10 is discharged at a large current density, a relatively large discharge voltage can be obtained.

  When the intermediate layer 20 is not provided, the voltage drops while the elapsed time from the start of supplying the fuel gas to the anode side electrode 12, that is, the reduction time is relatively short, whereas the intermediate layer 20 When the is provided, a constant voltage can be obtained for a long time. From this, it is clear that a fuel cell excellent in power generation performance can be obtained by providing the intermediate layer 20.

  The oxide ions further conduct inside the anode side electrode 12 through YSZ particles that are constituent particles of the anode side electrode 12 (cermet).

  On the other hand, most of the fuel gas supplied to the anode side electrode 12 diffuses through the large diameter pores 24 and partly diffuses through the small diameter pores 22. In this way, hydrogen contained in the fuel gas that has entered the pores reacts with oxide ions conducted through the YSZ particles that are the constituent particles of the anode-side electrode, and as a result, water vapor and electrons are released.

  The emitted electrons are taken out to an external circuit electrically connected to the terminal electrodes 32a and 32b, used as direct current electric energy for energizing the external circuit, and then to the cathode side electrode 14. Finally, it is combined with oxygen supplied to the cathode side electrode 14.

  Further, the water vapor quickly diffuses to the separator 30a through the large diameter pores 24 to the small diameter pores 22 of the anode side electrode 12, and is discharged from the gas flow path 36a of the separator 30a to the outside of the system.

  Next, a manufacturing method of the electrolyte / electrode assembly 18 configured as described above will be described.

  As shown in FIG. 6, the electrolyte / electrode assembly 18 according to the present embodiment includes a first step of forming the anode side electrode 12 as a porous body, and a step of providing an intermediate layer 20 on the anode side electrode 12. 2 processes, the 3rd process of providing the solid electrolyte 16 in the said intermediate | middle layer 20, and the 4th process of sintering these anode side electrodes 12, the intermediate | middle layer 20, and the solid electrolyte 16 at least. The anode side electrode 12, the intermediate layer 20, and the solid electrolyte 16 can be formed by sheet molding or screen printing.

  First, a first manufacturing method in which the anode side electrode 12, the intermediate layer 20, and the solid electrolyte 16 are obtained by sheet molding will be described.

  In the first manufacturing method, as shown in FIG. 7, the anode side electrode 12, the intermediate layer 20 and the solid electrolyte 16 are laminated, and the anode side electrode 12, the intermediate layer 20 and the solid electrolyte 16 are collectively fired. Is to be applied.

  In this case, first, in the first step, for example, NiO particles and YSZ particles are mixed at a weight ratio of 1: 1. A binder such as polyvinyl alcohol or acrylic and a pore former such as polymethyl methacrylate resin or carbon are added to the mixed particles.

  As the pore former, those having an average particle diameter such that the average pore diameter of the large pores 24 provided in the anode side electrode 12 is within a desired range are selected. For example, when the average pore diameter of the large pores 24 is about 4 to 6 μm, the average particle size is 8 μm, and when the average pore size of the large pores 24 is about 12 to 14 μm, the average particle size Each having a thickness of 20 μm may be selected.

  The addition ratio of the pore former is set so that the porosity of the anode-side electrode 12 is within a desired range. For example, when the porosity is 10 to 40% by volume, the addition ratio of the pore former to the mixed particles (the inorganic component of the raw material of the anode side electrode 12) may be 10 to 30% by weight.

  A slurry is prepared by dispersing the above mixed particles in a solvent, and the anode blade electrode 12 as a sheet-like molded body is formed by performing a doctor blade method using this slurry. The anode side electrode 12 contracts as a fourth process described later is performed. Therefore, what is necessary is just to set the thickness of the anode side electrode 12 (sheet-like molded object) so that the thickness after shrinkage may be about 300 μm to 1 mm.

  Next, in the second step, the intermediate layer 20 is formed. That is, a slurry of NiO and YSZ is prepared in the same manner as described above except that no pore former is added, and the doctor blade method is used to form the intermediate layer 20 as a sheet-like molded body. Form. What is necessary is just to set the thickness of this intermediate | middle layer 20 so that the thickness after shrinking | contracting in connection with performing the 4th process mentioned later may be set to about 3-20 micrometers. Further, the intermediate layer 20 (sheet-like molded body) is pressure-bonded to one end face of the anode side electrode 12.

  Next, in the third step, the solid electrolyte 16 is formed. That is, as described above, by preparing a slurry containing particles such as YSZ, ScSZ, SDC, GDC, YDC, or lanthanum gallate oxide, and performing the doctor blade method using this slurry, as a sheet-like molded body A solid electrolyte 16 is formed. In addition, the thickness of the solid electrolyte 16 is set so that the thickness after a baking process is performed in the 4th process of the next process may be set to about 3-15 micrometers. Further, the solid electrolyte 16 is pressure bonded to one end surface of the intermediate layer 20.

  As described above, a laminated structure in which three sheet-like molded bodies are laminated is obtained. Next, in the fourth step, the laminated structure is subjected to a firing process. As a result, each sheet-like molded body is sintered and contracted to form the anode side electrode 12, the intermediate layer 20, and the solid electrolyte 16 that have the above thickness.

  In the firing process, the pore former added to the anode side electrode 12 disappears. Large pores 24 having an average pore diameter corresponding to the average particle diameter of the pore former are formed in the disappearance trace.

  Here, the total of the mixed particles and the pore former (both inorganic components) which are the raw materials of the anode side electrode 12 is set to 100% by weight, and the ratio of the pore former in the 100% by weight is changed, The result of investigating how the porosity of the anode-side electrode 12 changes is shown as a graph in FIG. As shown in FIG. 5, by setting the ratio of the pore former contained in the raw material of the anode side electrode 12 to 10 to 30% by weight and setting the firing temperature to 1200 to 1500 ° C., the anode side electrode 12 It becomes easy to adjust the porosity in the range of 10 to 40% by volume.

  On the other hand, since the pore forming material is not added to the raw material of the intermediate layer 20, the large-diameter pores 24 are not generated. For this reason, the porosity of the intermediate layer 20 is smaller than that of the anode electrode 12. That is, it is possible to provide the intermediate layer 20 having the same material and composition as the anode side electrode 12 but having a lower porosity than the anode side electrode 12.

  In addition, when the anode side electrode 12 and the intermediate layer 20 are made of the same material and the same composition, the shrinkage rates of the anode side electrode 12 and the intermediate layer 20 are substantially the same. For this reason, it is possible to avoid the intermediate layer 20 from being peeled off from the anode side electrode 12 due to the mismatch of the shrinkage rate.

  Thereafter, a slurry such as SDC, GDC, or YDC is applied to the exposed end surface of the solid electrolyte 16 by, for example, a screen printing method or the like. The reaction preventing layer 28 is obtained by sintering this slurry by a baking treatment.

Finally, a slurry such as LSCF, LSM, LSC, BSFC, BSC, SSC or the like is applied on the reaction preventing layer 28, and this slurry is sintered by a firing process. Thus, the cathode side electrode 14 is formed, and the electrolyte / electrode assembly 18 in which the anode side electrode 12, the intermediate layer 20, the solid electrolyte 16, the reaction preventing layer 28, and the cathode side electrode 14 are laminated in this order is obtained. .

  Next, a second manufacturing method for obtaining the anode side electrode 12, the intermediate layer 20, and the solid electrolyte 16 by screen printing will be described with reference to FIG.

  As can be seen from FIG. 8, in a preferred example of the second manufacturing method, after each of the anode side electrode 12, the intermediate layer 20, and the solid electrolyte 16 is formed, preliminary firing is performed. The main baking process is performed after the 16 preliminary baking.

  Specifically, first, the anode side electrode 12 is formed by screen printing the slurry for the anode side electrode 12 prepared as described above. Thereafter, provisional firing is performed, whereby the anode side electrode 12 is contracted. At this time, the large-diameter pores 24 may be formed by the pore former.

  Next, the intermediate layer 20 is formed by screen-printing the slurry for the intermediate layer 20 prepared as described above on the anode side electrode 12. Thereafter, the intermediate layer 20 is contracted by performing temporary baking.

  Furthermore, the solid electrolyte 16 is formed by screen-printing the slurry for the solid electrolyte 16 prepared as described above on the intermediate layer 20. Thereafter, provisional firing is performed to shrink the solid electrolyte 16.

  Finally, a main baking process is performed, and sintering of the anode side electrode 12, the intermediate layer 20, and the solid electrolyte 16 is advanced. In this case, since the anode side electrode 12, the intermediate layer 20, and the solid electrolyte 16 are contracted in advance, the shrinkage amount of the anode side electrode 12, the intermediate layer 20, and the solid electrolyte 16 is small in the main firing process. For this reason, even when the mismatch between the thermal expansion coefficients of each other is large, it is possible to effectively prevent the anode side electrode 12, the intermediate layer 20, and the solid electrolyte 16 from being separated from each other.

  Thereafter, in the same manner as described above, by forming the reaction preventing layer 28 and the cathode side electrode 14, the electrolyte / electrode assembly 18 is obtained.

  In addition, you may make it include all or one part of temporary baking of each process in this baking processing. That is, for example, at least any one of temporary baking for the anode side electrode 12, temporary baking for the intermediate layer 20, and temporary baking for the solid electrolyte 16 is omitted, and in the main baking process, these anode side electrode 12 and intermediate layer are omitted. It is conceivable to perform a baking process on the 20 and the solid electrolyte 16 at once.

  In order to constitute the power generation cell 10 (see FIG. 1), separators 30a and 30b, terminal electrodes 32a and 32b, and terminal electrodes 32a and 32b are provided on one end surfaces of the anode side electrode 12 and the cathode side electrode 14 in the electrolyte / electrode assembly 18, respectively. What is necessary is just to arrange | position the end plates 34a and 34b.

  In the above-described embodiment, the intermediate layer 20, the solid electrolyte 16, the reaction preventing layer 28, and the cathode side electrode 14 are provided in this order on the anode side electrode 12. First, the cathode side electrode 14 is provided. The reaction preventing layer 28, the solid electrolyte 16, the intermediate layer 20, and the anode side electrode 12 may be provided in this order on the cathode side electrode 14. In any case, the reaction preventing layer 28 may be omitted.

  Moreover, the anode side electrode 12 or the cathode side electrode 14 provided initially may be formed by obtaining a molded body by subjecting the particles as the raw material to press molding or the like, and firing this.

  Further, the intermediate layer is not particularly limited to the same material and the same composition as the anode side electrode or the cathode side electrode serving as the substrate. For example, the anode side electrode has a 1: 1 weight ratio of YSZ and Ni. In this case, the intermediate layer may be composed of YSZ and Ni having a weight ratio of 3: 7, or a weight ratio of 7: 3.

  The average pore diameter of the large pores 24 is not limited to the above range, and can be changed according to the particle size of the pore former and its particle size distribution.

  Further, pores can be formed without adding a pore former. In this case, for example, the porosity of the anode-side electrode 12 (first electrode) and the porosity may be made different by controlling the sintering temperature and time of the intermediate layer 20.

DESCRIPTION OF SYMBOLS 10 ... Power generation cell 12 ... Anode side electrode 14 ... Cathode side electrode 16 ... Solid electrolyte 18 ... Electrolyte / electrode assembly 20 ... Intermediate layer 22, 24 ... Pore 26 ... Convex part 28 ... Reaction prevention layer 30a, 30b ... Separator 32a, 32b ... Terminal electrodes 36a, 36b ... Gas flow paths

Claims (13)

A solid electrolyte is interposed between the first electrode and the second electrode, the first electrode functions as either an anode side electrode or a cathode side electrode, and the second electrode is a cathode side electrode or In the electrolyte / electrode assembly that functions as one of the remaining anode electrodes,
The first electrode is a porous body having pores through which gas flows and having a concave portion and a convex portion on an end surface facing the solid electrolyte,
Between the first electrode and the solid electrolyte, an intermediate layer that fills the concave portion and buryes the convex portion,
The thickness of the intermediate layer is set to be equal to or greater than the average pore diameter of the first electrode, and the difference obtained by subtracting the value of the average pore diameter of the first electrode from the thickness value of the intermediate layer is within a range of 0 to 17 μm. An electrolyte / electrode assembly characterized by being.   2. The electrolyte / electrode assembly according to claim 1, wherein the average pore diameter of the first electrode is 3 to 20 μm, and the thickness of the intermediate layer is 3 to 20 μm. .   3. The electrolyte / electrode assembly according to claim 1, wherein the porosity of the intermediate layer is smaller than the porosity of the first electrode. 4.   2. The electrolyte / electrode assembly according to claim 1, wherein the porosity of the first electrode before being reduced is 10 to 40% by volume, and the thickness of the intermediate layer is 3 to 20 μm. Electrolyte / electrode assembly.   5. The electrolyte / electrode assembly according to claim 1, wherein a material of the first electrode and a material of the intermediate layer are the same. 6.   The electrolyte / electrode assembly according to any one of claims 1 to 5, wherein the solid electrolyte is made of a solid oxide. A solid electrolyte is interposed between the first electrode and the second electrode, the first electrode functions as either an anode side electrode or a cathode side electrode, and the second electrode is a cathode side electrode or In the method of manufacturing an electrolyte / electrode assembly that functions as one of the remaining anode-side electrodes,
Forming the first electrode by sheet molding;
Forming an intermediate layer on the first electrode by sheet molding and crimping the intermediate layer to the first electrode;
Forming the solid electrolyte on the intermediate layer by sheet molding and pressing the solid electrolyte to the intermediate layer;
At least a step of subjecting the first electrode, the intermediate layer and the solid electrolyte to a firing treatment;
Have
The first electrode is obtained as a porous body having pores through which gas can flow and having concave portions and convex portions on the end surface facing the solid electrolyte, while the intermediate layer is filled with the concave portions. While burying the convex part, the thickness after sintering is set to be equal to or larger than the average pore diameter of the first electrode, and the difference obtained by subtracting the value of the average pore diameter of the first electrode from the value of the thickness is 0 to A method for producing an electrolyte / electrode assembly, which is obtained in a range of 17 μm. A solid electrolyte is interposed between the first electrode and the second electrode, the first electrode functions as either an anode side electrode or a cathode side electrode, and the second electrode is a cathode side electrode or In the method of manufacturing an electrolyte / electrode assembly that functions as one of the remaining anode-side electrodes,
Forming the first electrode by screen printing;
Forming an intermediate layer on the first electrode by screen printing;
Forming the solid electrolyte on the intermediate layer by screen printing;
At least a step of subjecting the first electrode, the intermediate layer and the solid electrolyte to a firing treatment;
Have
The first electrode is obtained as a porous body having pores through which gas can flow and having concave portions and convex portions on the end surface facing the solid electrolyte, while the intermediate layer is filled with the concave portions. While burying the convex part, the thickness after sintering is set to be equal to or larger than the average pore diameter of the first electrode, and the difference obtained by subtracting the value of the average pore diameter of the first electrode from the value of the thickness is 0 to A method for producing an electrolyte / electrode assembly, which is obtained in a range of 17 μm.   9. The manufacturing method according to claim 8, wherein the step of forming a first electrode, the step of forming the intermediate layer, or the step of performing a pre-baking process after at least one of the steps of forming the solid electrolyte. Furthermore, the manufacturing method of the electrolyte electrode assembly characterized by having.   10. The manufacturing method according to claim 7, wherein when the inorganic component in the raw material of the first electrode is 100% by weight, 10 to 30% by weight of the inorganic component is used as a pore former. The pores are formed with the pore former by setting the temperature during the firing treatment to 1200 to 1500 ° C.   The manufacturing method according to any one of claims 7 to 10, wherein the pore former added to the inorganic component in the raw material of the first electrode is added to the inorganic component in the raw material of the intermediate layer. A method for producing an electrolyte / electrode assembly, wherein the pore former is added at a rate lower than the rate.   The manufacturing method according to any one of claims 7 to 11, wherein the material of the first electrode and the material of the intermediate layer are the same.   The method for producing an electrolyte-electrode assembly according to any one of claims 7 to 12, wherein the solid electrolyte is formed of a solid oxide.

Images