JP2011150813A - Electrolyte-electrode assembly and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte-electrode assembly (MEA) composed of an electrolyte pinched by an anode side electrode and a cathode side electrode, in which occurrence of inter-layer peeling and generation of cracks on a surface of the cathode side electrode are prevented. <P>SOLUTION: The cathode side electrode 14 composing an MEA 10 is formed on an intermediate layer 18 laminated on a solid electrolyte 16. The cathode side electrode 14 is a laminated body having a first layer 20a facing the intermediate layer 18 through an n-th layer 20n of the uppermost layer. In the MEA 10, a linear thermal expansion coefficient becomes larger in an order of the solid electrolyte 16, the intermediate layer 18, and the first layer 20a through the n-th layer 20n. Further, the first layer 20a is formed of one having a difference of 6×10<SP>-6</SP>/K or less of the thermal expansion coefficient against the solid electrolyte 16, and the n-th layer 20n is formed of one having a difference of 5×10<SP>-6</SP>/K or less of the thermal expansion coefficient against the first layer 20a. It is desirable that conductivity of each of the layer becomes higher as it goes from the first layer 20n through the n-th layer 20n. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrolyte / electrode assembly and a manufacturing method thereof, and more specifically, an electrolyte / electrode assembly suitable for constituting a unit cell of a fuel cell interposed between a pair of separators and a manufacturing method thereof. About.

A solid oxide fuel cell (hereinafter also referred to as SOFC) has an electrolyte / electrode assembly (hereinafter also referred to as MEA) constituted by sandwiching a solid electrolyte between an anode side electrode and a cathode side electrode. A unit cell of SOFC is configured by interposing an MEA between a pair of separators. As the material of the solid electrolyte, a material having high oxide ion (O ²⁻ ) conductivity is adopted, and Y ₂ O ₃ stabilized ZrO ₂ (hereinafter also referred to as YSZ) is particularly preferably selected.

In addition, the cathode side electrode has both high ionic conductivity and electron conductivity, has a catalytic activity with respect to the electrode reaction that occurs at the cathode side electrode of oxygen, that is, the oxygen dissociation reaction, and thermodynamically. It is stable and does not easily react with other substances (oxidant gas, solid electrolyte, etc.), is porous to allow sufficient circulation of oxidant gas, is difficult to sinter during power generation, and has mechanical strength. High is required. From this point of view, a perovskite compound represented by LaMO ₃ (M = Mn, Co, Fe) may be selected as the material for the cathode side electrode.

Among the perovskite compounds of this type, LaCoO ₃ or a part of La is substituted with Sr (La, Sr) CoO ₃ (hereinafter also referred to as LSC), and a part of Co is substituted with Fe (La, When the cathode electrode is formed using Sr) (Co, Fe) O ₃ (hereinafter also referred to as LSCF), the SOFC overvoltage can be reduced. However, there is a concern that LSC and LSCF react with YSZ, which is a solid electrolyte, and as a result, a high-resistance reaction product layer may be formed, leading to a decrease in conductivity and an increase in overvoltage. In addition, in this case, the mismatch in the linear thermal expansion coefficient between the solid electrolyte and the cathode-side electrode is increased, so that cracks and peeling may occur at the interface between the solid electrolyte and the cathode-side electrode.

In order to prevent the formation of a reaction product, an intermediate layer as a reaction preventing layer is also interposed. In this case, a CeO ₂ oxide (for example, CeO ₂ doped with Sm ₂ O ₃ ) is generally selected as the material for the intermediate layer.

By interposing such an intermediate layer, it is possible to avoid the reaction between the solid electrolyte and the cathode side electrode. However, although the linear thermal expansion coefficient of CeO ₂ -based oxide generally matches YSZ (solid electrolyte), it does not match so much with LSC and LSCF (cathode side electrode). For this reason, there is a concern that cracks and peeling occur at the interface between the intermediate layer and the cathode side electrode.

  From this point of view, attempts have been made to match the linear thermal expansion coefficients of the solid electrolyte and the cathode side electrode. For example, Patent Document 1 discloses that a first intermediate layer whose linear thermal expansion coefficient approximates that of a solid electrolyte and a second intermediate layer whose linear thermal expansion coefficient approximates that of a cathode side electrode are provided between the solid electrolyte and the cathode side electrode. In this order, it is proposed that the composition be changed in a gradient from the solid electrolyte toward the cathode side electrode. Patent Document 3 proposes that both the solid electrolyte and the intermediate layer be made of lanthanum gallate oxide.

  Here, the MEA is inevitably warped during the manufacturing process. In particular, when the anode side electrode is used as a substrate and the solid electrolyte, intermediate layer, and cathode side electrode are sequentially laminated, the thickness of the cathode side electrode is significantly smaller than that of the anode side electrode, so the anode side electrode is oriented toward the cathode side electrode. Bend. As a result, a tensile load is applied to the cathode side electrode. When an attempt is made to form a stack by stacking and tightening a plurality of unit cells using such an MEA, excessive external stress is applied to the cathode side electrode, so that a crack occurs on the surface of the cathode side electrode. This defect is difficult to avoid only by employing the techniques described in Patent Documents 1 to 3.

  Thus, in order to remove the warp, it is conceived that a weight is placed on the MEA before forming the stack and heat treatment is performed, but even in this case, a crack is generated on the surface of the cathode side electrode.

  Further, as described in Patent Documents 4 and 5, it is conceivable to configure the cathode side electrode as a divided electrode group. In this case, a groove exists between the electrode groups. Accordingly, since the external stress acting on the MEA acts only on the electrode group, deformation of the cathode side electrode (electrode group) is avoided. This is because it is expected that a crack can be generated on the surface of the cathode side electrode.

Japanese Patent No. 3344883 Japanese Patent Laid-Open No. 9-266000 Japanese Patent No. 3777903 JP 2006-310132 A Japanese Utility Model Publication No. 6-70162

  Patent Documents 4 and 5 do not describe anything about eliminating the mismatch of linear thermal expansion coefficients. Therefore, even if the techniques described in Patent Documents 4 and 5 are adopted, it is difficult to avoid the cathode side electrode from peeling off from the solid electrolyte. Further, Patent Documents 4 and 5 do not describe prevention of the interaction between the cathode side electrode and the solid electrolyte.

  As described above, an attempt was made to simultaneously prevent the cathode side electrode from peeling from the solid electrolyte, the interaction between the cathode side electrode and the solid electrolyte, and the occurrence of cracks on the surface of the cathode side electrode. There is no prior art.

  The present invention has been made to solve the above-described problems, and can prevent the cathode side electrode from peeling from the solid electrolyte and the cathode side electrode and the solid electrolyte from interacting with each other. An object of the present invention is to provide an electrolyte / electrode assembly and a method for producing the same, which can also prevent the occurrence of cracks on the surface.

To achieve the above object, the present invention provides an electrolyte / electrode assembly formed by sandwiching a solid electrolyte between an anode side electrode and a cathode side electrode,
The cathode side electrode is a laminate formed by laminating a plurality of layers,
The difference in coefficient of linear thermal expansion between the lowest layer closest to the solid electrolyte in the laminate and the solid electrolyte is within 6 × 10 ⁻⁶ / K;
And the difference in coefficient of linear thermal expansion between the lowermost layer and the uppermost layer located at the top of the laminate is within 5 × 10 ⁻⁶ / K,
The uppermost layer is composed of a plurality of electrode groups formed apart from each other.

  That is, in the present invention, the linear thermal expansion coefficient of the cathode side electrode is approximated to the solid electrolyte on the side close to the solid electrolyte to achieve matching. For this reason, it is possible to avoid delamination between the cathode side electrode and the solid electrolyte due to mismatch of the linear thermal expansion coefficients of the solid electrolyte and the cathode side electrode.

  In addition, since the linear thermal expansion coefficient between the respective layers of the cathode side electrode is also matched, it is possible to avoid delamination in the cathode side electrode.

  Further, since the uppermost layer of the cathode side electrode is divided, even if the electrolyte / electrode assembly bends and, as a result, stress acts on the cathode side electrode, the stress is alleviated by the dividing groove. Therefore, even when stress is applied to the cathode side electrode when assembling the SOFC using the electrolyte / electrode assembly that has warped, it is possible to avoid the occurrence of cracks on the surface of the cathode side electrode. it can.

  In addition, it is preferable that the electrical conductivity of the layer which comprises a cathode side electrode becomes large as it goes to the uppermost layer from the lowest layer. Thus, charge transfer between the cathode side electrode and the separator in contact with the cathode side electrode is not hindered. This is because the conductivity of the uppermost layer is maximum in this case as described above.

  Therefore, the electrode reaction proceeds easily. For this reason, the electrochemical characteristics of SOFC can be ensured.

  A suitable example of the material of the solid electrolyte is stabilized zirconia. Each layer of the cathode side electrode can be composed of, for example, a LaSrCo-based perovskite-type composite oxide or a LaSrCoFe-based perovskite-type composite oxide having different composition ratios of constituent elements.

  It is preferable to interpose an intermediate layer between the cathode side electrode and the solid electrolyte, more specifically, between the lowermost layer constituting the cathode side electrode and the solid electrolyte. Thereby, it is possible to avoid the mutual reaction between the cathode side electrode and the solid electrolyte.

  In this case, the linear thermal expansion coefficient of the intermediate layer is between the linear thermal expansion coefficient of the solid electrolyte and the linear thermal expansion coefficient of the lowermost layer. That is, the linear thermal expansion coefficients are made different in the order of the solid electrolyte, the intermediate layer, and the lowermost layer. As a result, the linear thermal expansion coefficients can be matched between these layers, and eventually, delamination can be avoided.

  An example of a suitable material for the intermediate layer is cerium-based oxide.

  The electrolyte / electrode assembly configured as described above warps so that, for example, when heat is applied, the anode side electrode is curved toward the cathode side electrode.

Further, the present invention is a method for producing an electrolyte / electrode assembly formed by sandwiching a solid electrolyte between an anode side electrode and a cathode side electrode,
After providing one of the anode side electrode or the cathode side electrode directly on one end face of the solid electrolyte or via an intermediate layer, the cathode side electrode or directly on the remaining other end face of the solid electrolyte or via the intermediate layer The step of providing the remaining one of the anode side electrode is performed, or after providing the solid electrolyte directly on one end surface of the anode side electrode or via the intermediate layer, the intermediate layer is directly or on the solid electrolyte. Providing a cathode side electrode via,
The cathode side electrode is formed as a laminate in which a plurality of layers are laminated,
A lowermost layer closest to the solid electrolyte is provided so that a difference in coefficient of linear thermal expansion from the solid electrolyte is within 6 × 10 ⁻⁶ / K;
And the uppermost layer located in the uppermost layer in the laminate is provided with a difference in coefficient of linear thermal expansion from the lowermost layer within 5 × 10 ⁻⁶ / K,
Further, the uppermost layer is formed as a plurality of electrode groups separated from each other.

  Through such a process, the linear thermal expansion coefficient from the solid electrolyte to the uppermost layer of the cathode electrode can be matched, and as a result, delamination of the electrolyte / electrode assembly can be avoided. be able to.

  In addition, since the cathode side electrode is divided, it is possible to avoid the occurrence of cracks on the surface of the cathode side electrode even if stress acts on the cathode side electrode.

  And it is preferable to form each layer so that the electric conductivity of the layer which comprises a cathode side electrode may become large as it goes to the uppermost layer from the lowest layer. This is because the electrode reaction proceeds sufficiently as described above.

As described above, the solid electrolyte can be formed using, for example, stabilized ZrO ₂ . On the other hand, each layer constituting the cathode side electrode may be formed using, for example, a LaSrCo-based perovskite-type composite oxide or a LaSrCoFe-based perovskite-type composite oxide having different composition ratios of constituent elements.

  Furthermore, when an intermediate layer is interposed between the lowermost layer and the solid electrolyte, the linear thermal expansion coefficient of the intermediate layer is between the linear thermal expansion coefficient of the solid electrolyte and the lowermost layer. Thus, it is preferable to form the intermediate layer. This is because the linear thermal expansion coefficient of each layer can be matched from the solid electrolyte through the intermediate layer to the uppermost layer of the cathode side electrode.

The intermediate layer can be formed using, for example, a CeO ₂ oxide.

  According to the present invention, the cathode-side electrode is a laminate, and the linear thermal expansion coefficient of the lowest layer closest to the solid electrolyte in the laminate is approximated to that of the solid electrolyte. For this reason, since the linear thermal expansion coefficients of the solid electrolyte and the cathode side electrode are matched, it is possible to avoid delamination between the cathode side electrode and the solid electrolyte.

  In addition, since the uppermost layer of the cathode side electrode is divided, even if a stress acts on the cathode side electrode, the stress is relieved by the dividing groove. When an SOFC is assembled using a warped electrolyte / electrode assembly, stress acts on the cathode side electrode. Since this stress is relaxed as described above, the stress is applied to the surface of the cathode side electrode. The occurrence of cracks can be avoided.

1 is a schematic entire cross-sectional explanatory view of an electrolyte / electrode assembly (MEA) according to an embodiment of the present invention. It is a top view of the cathode side electrode which comprises MEA of FIG. It is a general whole sectional view showing the state where MEA bent. It is a general | schematic whole cross-section explanatory drawing of MEA which concerns on another embodiment. It is a top view which shows another specific example of an electrode group. It is a top view which shows another specific example of an electrode group. It is a top view which shows another specific example of an electrode group. It is the graph which showed the relationship between the linear thermal expansion coefficient of each layer from the solid electrolyte in MEA of Example 1, 2 to the uppermost layer of a cathode side electrode, electrical conductivity, and the presence or absence of delamination and a crack. 3 is a graph showing the linear thermal expansion coefficient of each layer from the solid electrolyte to the uppermost layer of the cathode side electrode in the MEA of Example 1. FIG. 6 is a graph showing the linear thermal expansion coefficient of each layer from the solid electrolyte to the uppermost layer of the cathode side electrode in the MEA of Example 2. FIG. It is the graph which showed the relationship between the linear thermal expansion coefficient of each layer from the solid electrolyte in MEA of Comparative Examples 1-4 to the uppermost layer of a cathode side electrode, electrical conductivity, and the presence or absence of delamination and a crack.

  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.

  FIG. 1 is a schematic overall cross-sectional explanatory view of an electrolyte / electrode assembly (MEA) 10 according to the present embodiment. This MEA 10 is configured by interposing a solid electrolyte 16 between an anode side electrode 12 and a cathode side electrode 14, and an anode side electrode support type (hereinafter also referred to as ASC) in which the thickness of the anode side electrode 12 is maximum. Notation). An intermediate layer 18 is interposed between the cathode side electrode 14 and the solid electrolyte 16.

As the material of the anode side electrode 12, cermet of Ni and Y ₂ O ₃ stabilized ZrO ₂ (YSZ) is preferably selected. Or cermet of Ni and Sc ₂ O ₃ stabilized ZrO ₂ (SSZ), cermet of Ni and Y ₂ O ₃ doped CeO ₂ (YDC), cermet of Ni and Sm ₂ O ₃ doped CeO ₂ (SDC) A cermet of Ni and Gd ₂ O ₃ doped CeO ₂ (GDC) may be used.

  The thickness of the anode side electrode 12 of the ASC made of such a material is set to about 200 to 800 μm, preferably about 600 μm.

The solid electrolyte 16 is made of, for example, Y ₂ O ₃ stabilized ZrO ₂ (8YSZ) to which 8 mol% of Y ₂ O ₃ is added.

  The intermediate layer 18 serves to prevent the elements contained in the cathode side electrode 14 from diffusing into the solid electrolyte 16, in other words, preventing the cathode side electrode 14 and the solid electrolyte 16 from interacting with each other. That is, the intermediate layer 18 functions as a reaction preventing layer. The thickness of the intermediate layer 18 only needs to be sufficient to perform this reaction prevention function, and specifically, about 0.2 to 10 μm is sufficient.

The material of the intermediate layer 18 is not particularly limited as long as it has such a function, but specific examples thereof include Sm ₂ O ₃ doped CeO ₂ (SDC), Y ₂ O ₃ doped CeO _2. Examples include CeO ₂ -based oxides such as (YDC), Gd ₂ O ₃ -doped CeO ₂ (GDC), and La ₂ O ₃ -doped CeO ₂ (LDC).

  On the intermediate layer 18, the cathode side electrode 14 is laminated. Here, the cathode side electrode 14 is formed of a laminate in which the first layer 20a, the second layer 20b,..., The nth layer 20n are laminated in this order from the solid electrolyte 16 side. Of course, the first layer 20a corresponds to the lowermost layer, and the nth layer 20n corresponds to the uppermost layer. It should be noted that the number of layers of the cathode-side electrode 14 may be three or four, but it may be only two layers, the lowermost layer and the uppermost layer. That is, the cathode side electrode 14 may be two or more layers.

  The thickness of the cathode-side electrode 14, that is, the distance from the interface of the intermediate layer 18 in the first layer 20a to the upper end surface in the n-th layer 20n is preferably set to 15 to 50 μm. The thickness of each layer may be obtained, for example, by dividing this total thickness by the number of layers (n), but it is not particularly necessary to equalize the thickness of each layer.

  Note that the nth layer 20n, which is the uppermost layer, is formed as a divided electrode. That is, the nth layer 20n is provided as a pattern in which a plurality of electrode groups 22 are patterned.

  As shown in FIG. 2, each of the electrode groups 22 has a substantially regular hexagonal shape, and the separation distance between the adjacent electrode groups 22, 22, that is, the width dimension D <b> 1 of the dividing groove 24 is substantially equal. Also, the height (thickness) direction dimension T of the electrode group 22 shown in FIG. 1 is substantially the same, and is preferably set to about 10 μm.

  When the dividing groove 24 is filled with the electrode material constituting the nth layer 20n, the nth layer 20n becomes a single layer. When the end face area of the cathode side electrode 14 at this time is 100, the sum of the end face areas of the electrode group 22 is 75 to 95. In other words, the dividing groove 24 is formed in an amount that reduces the end surface area of the single n-th layer 20n by 5 to 25%.

  When the ratio of the end face area of the electrode group 22 to the end face area of the single-layer n-th layer 20n is less than 75, it is not easy to improve the power generation characteristics because the effective area of the n-th layer 20n is reduced. Absent. If it exceeds 95, it is not easy to avoid the occurrence of cracks.

  In the MEA 10 configured as described above, the linear thermal expansion coefficient gradually increases in the order from the solid electrolyte 16 to the intermediate layer 18 and the first layer 20a to the nth layer 20n.

For example, the linear thermal expansion coefficient of the solid electrolyte 16 made of 8YSZ is 10.3 × 10 ⁻⁶ / K in the temperature range of 50 to 1000 ° C. In this case, first, as a suitable example of the material of the intermediate layer 18, CeO ₂ (10GDC) doped with 10 mol% of Gd ₂ O ₃ in the CeO ₂ -based oxide described above can be cited. The linear thermal expansion coefficient of 10GDC is 12 × 10 ⁻⁶ / K in the temperature range of 25 to 900 ° C.

Each layer from the first layer 20a to the nth layer 20n in the cathode side electrode 14 can be composed of, for example, LSCFs having different compositions. For _{example, (La 1-a Sr a} ) (Co 0.2 Fe 0.8) when employing O _x, it is sufficient to differences the values of a as the first layer 20a toward the n-th layer 20n. Similarly, when (La _0.6 Sr _0.4 ) (Co _1-b Fe _b ) O _x is employed, the value of b may be made different from the first layer 20a toward the n-th layer 20n. Of course, you may make it laminate | stack the layer which consists of LSC on the layer which consists of LSCF.

Here, in the present embodiment, the linear thermal expansion coefficient of the first layer 20a is set so that the difference from the linear thermal expansion coefficient of the solid electrolyte 16 is within 6 × 10 ⁻⁶ / K. Further, the difference between the expansion rates of the first layer 20a and the n-th layer 20n is within 5 × 10 ⁻⁶ / K. Further, the conductivity of each layer increases from the first layer 20a to the nth layer 20n.

In the case where the cathode side electrode 14 has a two-layer structure and the first layer 20a which is the lowermost layer and the second layer 20b which is the uppermost layer are both formed of LSCF, the first layer 20a a _{(La 0.7 Sr 0.3) (Co} 0.2 Fe 0.8) O x, the second layer 20b (La _0.6 Sr _0.4) with (Co _0.2 Fe _0.8) O _x may be formed respectively. In this case, first layer 20a, the thermal expansion coefficient of the second layer 20b, respectively, a ^{14.6 × 10 -6 /K,15.3×10 -6 / K} , the conductivity, respectively, 230S / cm, 320 S / cm.

Further, when the cathode side electrode 14 has a three-layer structure, and the first layer 20a that is the lowermost layer, the second layer 20b that is an intermediate layer is formed by LSCF, and the third layer that is the uppermost layer is formed by LSC, The first layer 20a and the second layer 20b may be as described above, and the third layer may be (La _0.8 Sr _0.2 ) CoO _x . In this case, first layer 20a, second layer 20b, the thermal expansion coefficient of the third layer, ^{respectively, 14.6 × 10 -6 /K,15.3×10 -6 /K,19.6×10} - ⁶ / K, and the electrical conductivity is 230 S / cm, 320 S / cm, and 1320 S / cm, respectively.

Of course, the combination of materials of the solid electrolyte 16, the intermediate layer 18 and the cathode side electrode 14 is not particularly limited to this, and the linear thermal expansion coefficient increases in the order of the solid electrolyte 16, the intermediate layer 18 and the cathode side electrode 14. And a combination in which the difference between the linear thermal expansion coefficients of the solid electrolyte 16 and the cathode electrode 14 is within 6 × 10 ⁻⁶ / K.

Further, the material of the cathode electrode 14 is not particularly limited to the above, and the difference in expansion coefficient between the first layer 20a as the lowermost layer and the nth layer 20n as the uppermost layer is 5 × 10. ^-6 / K, and any combination that increases the conductivity of each layer from the first layer 20a to the nth layer 20n may be used.

  The MEA 10 according to the present embodiment is basically configured as described above. Next, the operation and effect will be described in relation to the method of manufacturing the MEA 10.

  The MEA 10 can be manufactured as follows. That is, first, the anode side electrode 12 is formed. In this case, for example, a mixed particle in which NiO particles and YSZ particles are mixed at a volume ratio of 1: 1, a binder such as polyvinyl butyral or acrylic, and a pore former such as PMMA resin or carbon. A paste is prepared by adding. In this preparation, NiO particles and YSZ particles have a predetermined particle size and a BET specific surface area so that the shrinkage rate associated with the firing treatment of the anode-side electrode 12 formed as a sheet-like molded body is within a predetermined range. Are selected, and the amount of binder added is set.

For example, when the particle diameter of the NiO particles and the BET specific surface area are 1 to ² μm and 6 to 9 m ² / g, and the particle diameter of the YSZ particles and the BET specific surface area are 0.5 to 3 μm and 4 to 8 m ² / g The binder addition ratio is preferably 40 to 65% by volume. In this case, the shrinkage rate of the anode side electrode 12 accompanying the firing process can be controlled to 8 to 30%.

  Next, the anode side electrode 12 as a sheet-like molded body is formed by the doctor blade method using the paste prepared as described above. The thickness of the sheet-like molded body is set so that the thickness of the anode-side electrode 12 after being subjected to pressure bonding by a hot press or the like and baking treatment is preferably 200 to 800 μm. When the thickness after the baking treatment is smaller than 200 μm, the strength as the support substrate is not sufficient, and the fuel gas supplied to the anode side electrode 12 is not easily diffused. On the other hand, if it is larger than 800 μm, the dimension of the MEA 10 in the stacking direction (thickness direction) becomes large, and the SOFC becomes large for this reason. Further, since the fuel gas flow distance along the thickness direction of the anode-side electrode 12 becomes longer during the operation of the SOFC, there is a concern that the amount of fuel gas leakage along the thickness direction increases.

  Thereafter, a degreasing process is performed on the anode side electrode 12 as necessary. By this degreasing treatment, the pore former disappears, and closed pores and open pores having a diameter corresponding to the average particle diameter of the pore former are formed in the disappearance trace. In addition, when not performing a degreasing process, a pore making material lose | disappears at the time of a baking process.

  At this point, the anode side electrode 12 is made of NiO—YSZ.

  Meanwhile, a paste that is a starting material for the solid electrolyte 16 and the intermediate layer 18 is prepared. The solid electrolyte 16 paste can be prepared by adding 8YSZ powder to a solvent together with the binder as described above, and the intermediate layer 18 paste can be prepared by adding 10 GDC powder together with the binder as described above to the solvent. Can be prepared.

  Thereafter, for example, a sheet-like formed body of the solid electrolyte 16 and a sheet-like formed body of the intermediate layer 18 are each formed by a doctor blade method. In addition, it can replace with a doctor blade method and can form each sheet-like molded object of desired thickness also by performing an extrusion molding method, a roll coating method, etc.

  Next, these sheet-like molded bodies, that is, the solid electrolyte 16 and the intermediate layer 18 are sequentially laminated on the anode side electrode 12 in this order. Thereafter, each layer is pressure-bonded by hot pressing or the like to obtain a laminate including the anode-side electrode 12, the solid electrolyte 16 and the intermediate layer 18.

  Next, a firing treatment is performed on the laminate. What is necessary is just to set the temperature in this case to 1100-1450 degreeC, for example. By this firing treatment, the anode side electrode 12, the solid electrolyte 16 and the intermediate layer 18 undergo thermal contraction.

  In this Embodiment, after laminating | stacking a sheet-like molded object, it is trying to crimp | bond by applying temperature and pressure with respect to each layer. As a result, the adjacent layers firmly adhere to each other, so that the layers are hardly separated during the firing process.

  Next, the cathode-side electrode 14 is laminated on the intermediate layer 18 of the laminate thus obtained.

That is, pastes are prepared as starting materials for the first layer 20a, the second layer 20b,..., The n-th layer 20n. When the cathode side electrode 14 has a three-layer structure, for example, the pastes of the first layer 20a, the second layer 20b, and the third layer are (La _0.8 Sr _0.2 ) (Co _0.2 Fe _0.8 ) O _x , (La _0.4 Sr). A powder of _0.6 ) (Co _0.2 Fe _0.8 ) O _x , (La _0.8 Sr _0.2 ) CoO _x can be prepared by adding it to a solvent together with a binder as described above.

  And the paste used as the 1st layer 20a is printed on the intermediate | middle layer 18 with a screen printing method. Here, the thickness of the first layer 20a corresponds to the thickness of the screen mesh plate. That is, as the screen mesh plate, one having a thickness capable of obtaining the first layer 20a having a desired thickness is selected.

  Thereafter, the paste is left at room temperature to level the paste. Although the standing time is set depending on how flattened the paste is, the paste is substantially flattened in about 1 to 2 hours.

  Furthermore, the substantially flat first layer 20a is formed by drying the paste at an appropriate temperature, for example, 90 to 120 ° C.

  The above operations are repeated until the (n-1) th layer, which is directly below the uppermost layer (nth layer 20n), is formed. Then, a baking process is performed. In this firing treatment, the temperature may be increased at a temperature increase rate of 100 to 200 ° C./hour and then held at 800 to 1100 ° C. for 1 to 4 hours. After that, it is allowed to cool naturally until it reaches room temperature.

  Next, the paste of the uppermost layer, that is, the nth layer 20n is printed on the (n-1) th layer in a state of being patterned by, for example, screen printing. Here, in order to form the n-th layer 20n as the electrode group 22, a screen on which a pattern is formed in advance is used. Thereby, for example, the electrode group 22 is formed in a pattern as shown in FIG.

  Thereafter, drying and baking are performed under the same conditions as described above. Thereby, the n-th layer 20n obtained by solidifying and sintering the paste is formed on the top of the laminate, and the MEA 10 is formed.

  The anode side electrode 12, the solid electrolyte 16 and the intermediate layer 18 are fired at the same time, and then the cathode side electrode 14 is formed by screen printing or the like and then dried and fired. The electrode 12 and the solid electrolyte 16 are fired at the same time, then the intermediate layer 18 is formed by screen printing or the like, and then fired. Further, the cathode side electrode 14 is formed by screen printing or the like, followed by drying and firing treatment. You may make it give.

Here, in the present embodiment, as described above, the linear thermal expansion coefficient is set to increase in the order of the solid electrolyte 16, the intermediate layer 18, the first layer 20a to the nth layer 20n, and the first The difference in thermal expansion coefficient between the layer 20a and the solid electrolyte 16 is set within 6 × 10 ⁻⁶ / K, and the difference between the thermal expansion coefficients between the first layer 20a and the nth layer 20n is set within 5 × 10 ⁻⁶ / K. is doing. That is, the linear thermal expansion coefficient gradually increases from the solid electrolyte 16 toward the nth layer 20n, and there is no significant difference. In other words, the linear thermal expansion coefficient of each layer is matched. Therefore, in the above process, separation between the solid electrolyte 16 and the intermediate layer 18 and between the intermediate layer 18 and the first layer 20a is prevented.

  In addition, since the intermediate layer 18 is interposed between the solid electrolyte 16 and the cathode side electrode 14, the mutual reaction between the solid electrolyte 16 and the cathode side electrode 14 is prevented.

  The MEA 10 thus manufactured has a shape in which the anode side electrode 12 is warped toward the cathode side electrode 14 as shown in FIG. Therefore, a tensile load acts on the cathode side electrode 14.

  When configuring an SOFC, a unit cell may be formed by sandwiching the above-described MEA 10 with a separator, and a predetermined number of unit cells may be stacked to form a stack. After that, the unit cells located at both ends of the stack are sandwiched between a pair of end plates, and these end plates are fastened with tie rods or the like to form an SOFC.

  By this tightening, the end of the anode side electrode 12 is pressed toward the cathode side electrode 14. In other words, the warp is corrected and the state shown in FIG. 1 is obtained.

  As described above, the cathode side electrode 14 is formed as the electrode group 22 in which the nth layer 20n is divided. For this reason, at the time of the tightening, the electrode group 22 is not deformed, and only the dividing groove 24 is reduced. That is, since the n-th layer 20 n in the cathode side electrode 14 is formed as the electrode group 22, it can be deformed by an external stress. Due to this deformation, the occurrence of cracks in the n-th layer 20n can be avoided.

  Prior to the operation of the SOFC, NiO-YSZ constituting the anode side electrode 12 is subjected to an initial reduction process to change NiO to Ni. Accordingly, an anode side electrode 12 made of Ni—YSZ is obtained, and the MEA 10 can generate power.

  When operating the SOFC, after raising the SOFC to a predetermined temperature, a fuel gas containing hydrogen is supplied to the anode side electrode 12 of each unit cell, and an oxidant gas containing oxygen is supplied to the cathode side electrode 14. Supplied. The cathode side electrode 14 undergoes an ionization reaction of oxygen, and oxide ions generated thereby move to the anode side electrode 12 side through the solid electrolyte 16.

  At this time, in the cathode-side electrode 14, the conductivity of each layer increases from the first layer 20a to the n-th layer 20n. Therefore, the contact resistance between the cathode side electrode 14 and the separator in contact with the cathode side electrode 14 is reduced. Therefore, since charges are easily transferred between the cathode side electrode 14 and the separator, an electrode reaction in the cathode side electrode 14 proceeds. That is, the electrochemical characteristics of SOFC are ensured.

  When stopping the SOFC, the temperature of the SOFC is lowered while adjusting the supply amounts of the fuel gas and the oxidant gas.

  In the power generation start / stop described above, the MEA 10 may be subjected to stress due to a redox reaction during power generation or thermal stress due to expansion / contraction caused by a temperature change during start / stop. However, in the present embodiment, as described above, the linear thermal expansion coefficients of the solid electrolyte 16, the intermediate layer 18, and the cathode side electrode 14 are matched. In the meantime, delamination between the intermediate layer 18 and the cathode electrode 14 is avoided.

  Further, since the nth layer 20n in the cathode side electrode 14 can be deformed in accordance with the thermal stress as described above, it is possible to avoid the occurrence of cracks in the nth layer 20n.

  In the above-described embodiment, ASC using the anode-side electrode 12 as a substrate has been described as an example, but an electrolyte support type (ESC) using the solid electrolyte 16 as a substrate may be used. In this case, as shown in FIG. 4, an electrolyte supported MEA 10 having a maximum thickness (about 70 to 100 μm) of the solid electrolyte 16 is configured.

  When the MEA 10 is manufactured, the anode-side electrode 12 is provided on one end face of the solid electrolyte 16, and the intermediate layer 18 and the cathode-side electrode 14 are provided in this order on the remaining end face. Of course, the cathode-side electrode 14 is formed as a stacked body that includes the first layer 20a to the n-th layer 20n and is an electrode group 22 in which the n-th layer 20n is divided. In ESC, the thickness of the anode side electrode 12 is set to about 50 to 100 μm, preferably about 90 μm.

  In the case of the ASC MEA 10 using the anode side electrode 12 as a substrate, an intermediate layer may be interposed between the anode side electrode 12 and the solid electrolyte 16. This intermediate layer plays a role of flattening by filling or burying unevenness on the side facing the solid electrolyte 16 in the anode-side electrode 12 which is a porous body. That is, this intermediate layer functions as a planarization layer.

  Moreover, although the said manufacturing method has illustrated and demonstrated the case where a sheet | seat body is produced, it is not limited to this in particular. For example, after the anode-side electrode 12 or the solid electrolyte 16 is formed by any known method, the remaining layer may be provided by printing, film formation by CVD or PVD, coating by spin coating, dip, or the like. Good.

  Furthermore, the pattern of the electrode group 22 is not limited to that shown in FIG. 2, and may be an electrode group 30 having an annular shape provided concentrically as shown in FIG. 5. 6 may be an electrode group 32 divided into fan-shaped patterns as shown in FIG. Alternatively, as shown in FIG. 7, it may be an electrode group 34 divided into a lattice pattern.

  In accordance with the above, after producing a sheet-like molded body made of NiO-YSZ with a thickness of 100 μm, a sheet-like molded body made of 8YSZ with a thickness of 10 μm, and a sheet-like molded body made of 10 GDC with a thickness of 1 μm, they were laminated in this order. By performing the firing treatment, a laminate of the anode side electrode, the solid electrolyte, and the intermediate layer was obtained.

On the other _{hand, (La 1-a Sr a} ) (Co 0.2 Fe 0.8) O a in _x paste containing powder is either 0.2,0.3,0.4,0.5, and A paste containing powder in which b in either (La _0.6 Sr _0.4 ) (Co _1-b Fe _b ) O _x is 0.8 or 0.9 was prepared. Moreover, apart from this, to prepare a paste containing a powder a is any of 0.2,0.3,0.4,0.5 in _{(La 1-a Sr a)} CoO x.

Then, either (La _1-a Sr _a ) (Co _0.2 Fe _0.8 ) O _x paste or (La _0.6 Sr _0.4 ) (Co _1-b Fe _b ) O _x paste is applied to the intermediate layer by screen printing. Printed as a single flat layer. This was leveled and then dried to form the first layer.

Next, a paste of (La _1-a Sr _a ) CoO _x was printed on the first layer as a pattern shown in FIG. 2 by screen printing, that is, as a group of electrodes scattered apart from each other. This was leveled and then dried, and further subjected to a baking treatment to obtain a second layer having a divided shape. Thereby, MEA was obtained.

  Of course, in the above, the values of a and b are set so that the linear thermal expansion coefficient of each layer from the solid electrolyte to the second layer increases in this order.

  Changes in the linear thermal expansion coefficient of each layer from the solid electrolyte to the second layer in this case are shown in FIGS. In addition, since the linear thermal expansion coefficients of the first layer and the second layer vary depending on the values of a and b, in FIG. In addition to indicating the width, the average value is indicated by a black circle (●).

  In the MEA that has undergone the above manufacturing process, no delamination or cracks were observed.

  Further, a plurality of unit cells composed of this MEA were stacked to obtain SOFC. When the SOFC was operated for a predetermined time and then the unit cell was disassembled and the MEA was observed, no delamination or cracks were observed at this point.

After obtaining a stack of anode, solid electrolyte and the intermediate layer in conformity with Example _{1, (La 1-a Sr} a) (Co 0.2 Fe 0.8) O x paste, or (La _0.6 Sr _0.4) Any of the (Co _1-b Fe _b ) O _x pastes were printed as a single flat layer on the intermediate layer by screen printing. This was leveled and then dried to form the first layer.

Next, a paste of (La _1-a Sr _a ) (Co _0.2 Fe _0.8 ) O _x or (La _0.6 Sr _0.4 ) (Co _1-b Fe _b ) O _x , which is more than the first layer. A material having a large linear thermal expansion coefficient was selected and printed as a single flat layer on the intermediate layer by screen printing. This was leveled and then dried to form a second layer.

Next, (La _1-a Sr _a ) CoO _x paste was printed on the second layer as an electrode group having the pattern shown in FIG. 2 by screen printing. This was leveled and then dried, and further subjected to a firing treatment to obtain a third layer having a divided shape. Thereby, MEA was obtained.

  Changes in the linear thermal expansion coefficient of each layer from the solid electrolyte to the second layer in this case are shown in FIGS. Also in this case, the linear thermal expansion coefficients of the first layer, the second layer, and the third layer vary depending on the values of a and b. Therefore, in FIG. The range from the value to the maximum value is shown, and the average value is shown by a black circle (●).

  Neither delamination nor cracking was observed in this MEA. Furthermore, as in Example 1, an SOFC composed of this MEA was obtained. Observation of the MEA after the SOFC was operated for a predetermined time was observed, but no delamination or cracking was observed.

Comparative Example 1

An MEA was obtained in accordance with Example 1 except that a cathode side electrode composed of a single layer (no division) of (La _1-a Sr _a ) CoO _x was provided. In this case, even if a was 0.2, 0.3, 0.4, or 0.5, delamination between the intermediate layer and the cathode electrode was observed in many samples. Further, when the MEA was observed after being disassembled after constituting the SOFC, it was found that cracks were generated on the surface of the cathode side electrode.

Comparative Example 2

In accordance with Example 1, a laminate of an anode electrode, a solid electrolyte, and an intermediate layer was obtained. Next, an electrode group patterned in the same shape as in Example 1 was formed on the intermediate layer of this laminate using a paste of (La _1-a Sr _a ) CoO _x . Furthermore, baking process was performed and MEA was obtained.

Also in this case, delamination between the intermediate layer and the cathode electrode was observed in many samples regardless of whether a was 0.2, 0.3, 0.4, or 0.5. This is because, 8YSZ and a solid electrolyte, since the coefficient of linear thermal expansion than the coefficient of linear thermal expansion of 10GDC an intermediate layer _{(La 1-a Sr a)} CoO x is large, i.e., coefficient of linear thermal expansion This is thought to be due to the inconsistency.

Comparative Example 3

  An MEA was obtained in the same manner as in Example 1 except that the second layer was provided without being divided. In this case, no delamination was observed, but when the MEA was confirmed by disassembling after assembling the SOFC, it was confirmed that many samples had cracks on the surface of the cathode side electrode.

Comparative Example 4

  In accordance with Example 1, a laminate of an anode electrode, a solid electrolyte, and an intermediate layer was obtained.

Next, the first layer is formed of (La _1-a Sr _a ) (Co _0.2 Fe _0.8 ) O _{x in} which a is set to 0.6 and 0.7, or b is 0.6, By forming with (La _0.6 Sr _0.4 ) (Co _1-b Fe _b ) O _x set to 0.7, the linear thermal expansion coefficient of the solid electrolyte and the intermediate layer and the linear thermal expansion coefficient of the first layer Increased the difference. Further, the MEA was configured by providing the second layer without dividing it on the first layer.

  In this case, even if a and b were 0.6 and 0.7, delamination between the intermediate layer and the cathode electrode was observed in many samples. Further, when the MEA was observed after being disassembled after constituting the SOFC, it was found that cracks were generated on the surface of the cathode side electrode.

Comparative Example 5

  In accordance with Example 1, a laminate of an anode electrode, a solid electrolyte, and an intermediate layer was obtained.

Next, the first layer is formed of (La _1-a Sr _a ) (Co _0.2 Fe _0.8 ) O _{x in} which a is set to 0.6 and 0.7, or b is 0.6, By forming with (La _0.6 Sr _0.4 ) (Co _1-b Fe _b ) O _x set to 0.7, the linear thermal expansion coefficient of the solid electrolyte and the intermediate layer and the linear thermal expansion coefficient of the first layer Increased the difference. Further, on this first layer, an MEA was configured by providing an electrode group patterned in the same shape as in Example 1, that is, a divided second layer.

  In this case, even if a and b were 0.6 and 0.7, delamination between the intermediate layer and the cathode electrode was observed in many samples.

  FIG. 11 also shows the relationship between the values of the linear thermal expansion coefficients of the first layer and the second layer in the above Comparative Examples 1 to 5 and the presence or absence of delamination or cracks. 8 and FIG. 11, delamination can be avoided by matching the linear thermal expansion coefficient of the cathode side electrode with the linear thermal expansion coefficient of the solid electrolyte and the intermediate layer, and the uppermost layer of the cathode side electrode It is clear that cracking can avoid the generation of cracks.

DESCRIPTION OF SYMBOLS 10 ... Electrolyte electrode assembly (MEA) 12 ... Anode side electrode 14 ... Cathode side electrode 16 ... Solid electrolyte 18 ... Intermediate | middle layer 20a ... 1st layer (lowermost layer)
20n: n-th layer (uppermost layer) 22, 30, 32, 34 ... electrode group 24 ... dividing groove

Claims (11)

An electrolyte / electrode assembly formed by sandwiching a solid electrolyte between an anode side electrode and a cathode side electrode,
The cathode side electrode is a laminate formed by laminating a plurality of layers,
The difference in coefficient of linear thermal expansion between the lowest layer closest to the solid electrolyte in the laminate and the solid electrolyte is within 6 × 10 ⁻⁶ / K;
And the difference in coefficient of linear thermal expansion between the lowermost layer and the uppermost layer located at the top of the laminate is within 5 × 10 ⁻⁶ / K,
The electrolyte / electrode assembly is characterized in that the uppermost layer is composed of a plurality of electrode groups formed apart from each other.   2. The electrolyte / electrode assembly according to claim 1, wherein the conductivity of the layer constituting the cathode side electrode increases from the lowermost layer toward the uppermost layer. 3.   3. The electrolyte / electrode assembly according to claim 1 or 2, wherein the solid electrolyte is made of stabilized zirconia, and each layer constituting the cathode side electrode is composed of LaSrCo-based perovskite composite oxides having different composition ratios of constituent elements. An electrolyte / electrode assembly comprising an oxide or a LaSrCoFe-based perovskite complex oxide.   The electrolyte / electrode assembly according to any one of claims 1 to 3, wherein an intermediate layer is interposed between the lowermost layer and the solid electrolyte, and a linear thermal expansion coefficient of the intermediate layer is An electrolyte / electrode assembly, which is between the linear thermal expansion coefficient of the solid electrolyte and the linear thermal expansion coefficient of the lowermost layer.   5. The electrolyte / electrode assembly according to claim 4, wherein the intermediate layer is made of a cerium-based oxide.   The electrolyte / electrode assembly according to any one of claims 1 to 5, wherein when the heat is applied, the anode side electrode warps so as to bend toward the cathode side electrode. Electrolyte / electrode assembly. A method for producing an electrolyte / electrode assembly formed by sandwiching a solid electrolyte between an anode side electrode and a cathode side electrode,
After providing one of the anode side electrode or the cathode side electrode directly on one end face of the solid electrolyte or via an intermediate layer, the cathode side electrode or directly on the remaining other end face of the solid electrolyte or via the intermediate layer The step of providing the remaining one of the anode side electrode is performed, or after providing the solid electrolyte directly on one end surface of the anode side electrode or via the intermediate layer, the intermediate layer is directly or on the solid electrolyte. Providing a cathode side electrode via,
The cathode side electrode is formed as a laminate in which a plurality of layers are laminated,
A lowermost layer closest to the solid electrolyte is provided so that a difference in coefficient of linear thermal expansion from the solid electrolyte is within 6 × 10 ⁻⁶ / K;
And the uppermost layer located in the uppermost layer in the laminate is provided with a difference in coefficient of linear thermal expansion from the lowermost layer within 5 × 10 ⁻⁶ / K,
Furthermore, the uppermost layer is formed as a plurality of electrode groups spaced apart from each other, and a method for producing an electrolyte / electrode assembly.   8. The method of manufacturing an electrolyte / electrode assembly according to claim 7, wherein the conductivity of the layer constituting the cathode side electrode is set to increase from the lowermost layer toward the uppermost layer.   9. The manufacturing method according to claim 7, wherein the solid electrolyte is formed of stabilized zirconia and each layer constituting the cathode side electrode is made of LaSrCo-based perovskite complex oxide or LaSrCoFe having different composition ratios of constituent elements. A method for producing an electrolyte / electrode assembly, comprising forming a perovskite complex oxide.   The manufacturing method according to any one of claims 7 to 9, wherein when an intermediate layer is interposed between the lowermost layer and the solid electrolyte, a linear thermal expansion coefficient of the intermediate layer is set to be equal to that of the solid electrolyte. A method for producing an electrolyte / electrode assembly, wherein the coefficient is set between a linear thermal expansion coefficient and a linear thermal expansion coefficient of the lowermost layer.   11. The method for manufacturing an electrolyte / electrode assembly according to claim 10, wherein the intermediate layer is formed of a cerium-based oxide.

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