JP2022119219A - Fuel electrode-solid electrolyte layer composite, fuel electrode-solid electrolyte layer composite member, fuel cell, and fuel cell manufacturing method - Google Patents

Abstract

To easily provide a large-sized fuel cell having a large facing area between a fuel electrode and a solid electrolyte layer.SOLUTION: A fuel electrode-solid electrolyte layer composite 5 includes a porous fuel electrode 3, a first solid electrolyte layer 4a formed on the fuel electrode, and a second solid electrolyte layer 4b having a porosity smaller than that of the fuel electrode, which is laminated on the opposite side of the first solid electrolyte layer to the fuel electrode. The first solid electrolyte layer 4a includes a first solid electrolyte material, and a composite oxide containing nickel and a metal element constituting the first solid electrolyte material. The second solid electrolyte layer 4b contains a second solid electrolyte material and does not substantially contain nickel element. The fuel electrode 3a contains a third solid electrolyte material and metallic nickel.SELECTED DRAWING: Figure 1

Description

The present invention relates to a fuel electrode-solid electrolyte layer composite, a fuel electrode-solid electrolyte layer composite member, a fuel cell, and a method for manufacturing a fuel cell.

A fuel cell is a device that generates electricity through an electrochemical reaction between a fuel gas such as hydrogen and air (oxygen), and can directly convert chemical energy into electricity, resulting in high power generation efficiency. Among them, a solid oxide fuel cell (hereinafter referred to as SOFC), which has an operating temperature of 700° C. or more, particularly about 800° C. to 1000° C., has a high reaction rate and the constituent elements of the cell structure are all solid. Therefore, it is easy to handle. On the other hand, since the operating temperature is very high, it is mainly used for stationary large-scale power generation equipment or household power generation. In today's demand for energy saving, there is a demand for expanded applications of SOFCs, which have high power generation efficiency, low noise, low emissions of environmentally hazardous substances, and simple cell structures.

Metal oxides having oxygen ion conductivity, such as yttria-stabilized zirconia (YSZ), are used as solid electrolytes. The operating temperature of SOFCs using oxygen-ion-conducting YSZ as the electrolyte is as high as 750°C to 1000°C. From the viewpoint of reducing the energy consumption required for heating and selecting materials with high temperature resistance, development of SOFCs that can operate in the medium temperature range of 400 ° C to 600 ° C that can use inexpensive general-purpose stainless steel is progressing. .

The SOFC has a high operating temperature because it moves oxide ions in a solid electrolyte made of a ceramic material. Therefore, PCFCs (Protonic Ceramic Fuel Cells, proton conductive oxide fuel cells) that use hydrogen ions (protons) that can move even in a medium temperature range (for example, 400° C. to 600° C.) instead of oxide ions as charge carriers. ) are being studied.

As solid electrolyte materials that can be applied to PCFCs, Patent Documents 1 and 2 disclose a metal oxide having a perovskite structure of _ABO3 , which contains Ba at the A site and Zr and a trivalent substitution element at the B site. Disclosed are metal oxides comprising:

For example, perovskite oxides such as BaCe _0.8 Y _0.2 O _2.9 (BCY) and BaZr _0.8 Y _0.2 O _2.9 (BZY) exhibit high proton conductivity in the medium temperature range. , is expected as a solid electrolyte for medium-temperature fuel cells.

In order to improve the power generation characteristics of the SOFC, it is preferable that the solid electrolyte layer be as thin as possible. Therefore, an electrolyte layer-electrode composite (joint) in which a solid electrolyte is formed on an air electrode (cathode) or a fuel electrode (anode) with increased mechanical strength is sometimes used. Such a composite (bonded body) is called a cathode-supported solid electrolyte layer or an anode-supported solid electrolyte layer.

Japanese Patent Application Laid-Open No. 2001-307546 JP 2007-197315 A

In a fuel cell (SOFC) with a solid electrolyte having ionic conductivity, the fuel electrode (anode) contains a nickel (Ni) component as a hydrogen dissociation catalyst and a solid electrolyte (metal oxide). Such fuel electrodes are generally produced by sintering a material containing a solid electrolyte and nickel oxide (NiO). An anode-supported solid electrolyte layer is generally produced by forming a coating film containing a solid electrolyte on the surface of a molded body of a mixture of a nickel component (e.g., NiO) and a solid electrolyte, followed by firing (co-sintering). be done.

The fuel electrode thus produced is initially dense. However, by going through the process of reducing NiO to Ni, the function of Ni as a catalyst is enhanced, and at the same time, the fuel electrode is made porous, allowing permeation of fuel gas. The reduction treatment is often performed in the state of the fuel cell. When used as an SOFC, NiO in the fuel electrode is reduced to Ni by hydrogen supplied to the fuel electrode as a fuel, and becomes porous due to volumetric contraction that occurs simultaneously with this reduction.

Specifically, for example, when yttrium-doped barium cerate (BCY) is used as the solid electrolyte and NiO is used as the nickel component, a fuel electrode containing a mixed powder of BCY powder and NiO powder is formed, and the fuel electrode is Then, BCY powder, which is the material of the solid electrolyte layer, is applied thinly, and then co-sintered at a temperature at which both are densified. As a result, a fuel electrode-solid electrolyte layer composite member including a layer containing BCY and a layer containing BCY and NiO is obtained. Next, the fuel electrode-solid electrolyte layer composite member is incorporated into a fuel cell and subjected to reduction treatment in a reducing gas atmosphere such as hydrogen to obtain an anode-supported solid electrolyte layer.

However, Ni in the fuel electrode may diffuse toward the solid electrolyte layer during co-sintering. Ni that has diffused to the solid electrolyte side may form a conductive path in the solid electrolyte and increase leakage current. Also, when a metal oxide is used for the solid electrolyte layer, Ni in the fuel electrode may diffuse into the metal oxide, resulting in a decrease in ion conductivity. Therefore, the power generation performance of the fuel cell (or the electrolysis performance in the steam electrolysis cell) tends to deteriorate. In particular, when a proton-conducting metal oxide having a perovskite structure doped with yttrium or the like, such as BCY or BZY described above, is used for the solid electrolyte layer, considering its low sinterability, it is usually heated at a high temperature of 1400° C. or higher. Co-sintering takes place. Therefore, Ni easily diffuses into the solid electrolyte layer, and the proton conductivity tends to decrease. In addition, when Ni is dissolved in these materials, hole conduction is likely to occur in an oxygen atmosphere, resulting in an increase in leakage current.

In order to suppress the diffusion of Ni, it is conceivable to form a solid electrolyte layer on the fuel electrode after sintering by a low-temperature process such as applying paste. However, in this case, the bonding strength between the fuel electrode and the solid electrolyte layer tends to be weak. In the reduction treatment step, the solid electrolyte layer cannot follow the volume change (shrinkage) of the fuel electrode, and cracks may occur in the solid electrolyte layer, or part of the solid electrolyte layer may peel off from the anode. .

As the contact area (opposing area) between the solid electrolyte layer and the fuel electrode increases, the amount of contraction of the fuel electrode increases, and the solid electrolyte layer is more likely to crack or peel off. For this reason, it is difficult to increase the facing area between the solid electrolyte layer and the fuel electrode, making it difficult to obtain large fuel cells and steam electrolysis cells. That is, there has been a problem in realizing a high output (high output current) fuel cell or steam electrolysis cell.

One aspect of the present disclosure is a porous fuel electrode, a first solid electrolyte layer formed on the fuel electrode, and a layer of the fuel electrode laminated on the opposite side of the first solid electrolyte layer from the fuel electrode. a second solid electrolyte layer having a small porosity, wherein the first solid electrolyte layer is a composite oxide containing a first solid electrolyte material, a nickel element, and a metal element constituting the first solid electrolyte material; and wherein the second solid electrolyte layer includes a second solid electrolyte material and is substantially free of nickel elements, and the fuel electrode includes a third solid electrolyte material and metallic nickel; It relates to a fuel electrode-solid electrolyte layer composite.

Another aspect of the present disclosure is a cell structure including the fuel electrode-solid electrolyte layer composite and an air electrode, wherein the second solid electrolyte layer is interposed between the fuel electrode and the air electrode; The present invention relates to a fuel cell comprising an oxidant channel for supplying an oxidant to an air electrode and a fuel channel for supplying fuel to the fuel electrode.

Still another aspect of the present disclosure is a fuel electrode, a first solid electrolyte layer, and a second solid electrolyte stacked on the first solid electrolyte layer side of a stack of the fuel electrode and the first solid electrolyte layer. a layer, wherein the first solid electrolyte layer includes a first solid electrolyte material and a composite oxide containing a nickel element and a metal element that constitutes the first solid electrolyte material; The solid electrolyte layer contains a second solid electrolyte material and substantially does not contain nickel element, and the fuel electrode contains a third solid electrolyte material and nickel oxide. .

Still another aspect of the present disclosure is a first solid electrolyte material containing a fuel electrode containing nickel oxide (NiO), a first solid electrolyte material, and a composite oxide of nickel and a metal element constituting the first solid electrolyte material. a solid electrolyte layer, and a second solid electrolyte layer containing a second solid electrolyte material and substantially free of nickel element on the first solid electrolyte layer side of the laminate, 850 ° C. or less to obtain a fuel electrode-solid electrolyte layer composite member, and a step of forming an air electrode on the second solid electrolyte layer side of the fuel electrode-solid electrolyte layer composite member to obtain a cell structure. , and relates to a method for manufacturing a fuel cell.

A large-sized fuel cell or steam electrolysis cell can be easily obtained using the fuel electrode-solid electrolyte layer composite or the fuel electrode-solid electrolyte layer composite member according to the present disclosure.

1 is a cross-sectional view schematically showing the configuration of a fuel cell according to one embodiment of the present invention; FIG. 2 is a cross-sectional view schematically showing a cell structure having a fuel electrode-solid electrolyte layer composite included in the fuel cell of FIG. 1. FIG. 2 is a cross-sectional view schematically showing a cell structure having a fuel electrode-solid electrolyte layer composite member used for manufacturing the fuel cell of FIG. 1. FIG.

[Description of Embodiments of the Invention]
First, the contents of the embodiments of the present disclosure will be listed and described.
(1) An embodiment of the present disclosure includes a porous fuel electrode, a first solid electrolyte layer formed on the fuel electrode, and the first solid electrolyte layer laminated on the opposite side of the fuel electrode from the fuel electrode. and a second solid electrolyte layer having a small porosity. Here, the first solid electrolyte layer includes a first solid electrolyte material and a composite oxide containing a nickel element and a metal element that constitutes the first solid electrolyte material. The second solid electrolyte layer contains a second solid electrolyte material and does not substantially contain nickel element. The fuel electrode includes a third solid electrolyte material and metallic nickel. By using this fuel electrode-solid electrolyte layer composite, it is possible to easily increase the size and realize a fuel cell and a steam electrolysis cell with high output.

The fuel electrode is also called a hydrogen electrode and corresponds to an anode in a fuel cell. In contrast, the cathode in a fuel cell is also called an air electrode or an oxygen electrode. The anode-solid electrolyte layer composite is also called an anode-solid electrolyte layer assembly, an anode-solid electrolyte layer assembly, or an anode-supported solid electrolyte layer.

A first solid electrolyte layer is interposed between the fuel electrode and the second solid electrolyte layer. The second solid electrolyte layer corresponds to the solid electrolyte layer in the conventional anode-supported solid electrolyte layer. While the fuel electrode is porous, the second solid electrolyte layer is usually a dense layer with almost no voids. The porosities of the first and second solid electrolyte layers can be determined based on cross-sectional images of the anode-solid electrolyte layer composite taken by electron micrographs. In the cross-sectional image, the porosity is defined as the ratio of the area of the region where the solid electrolyte layer does not exist to the total area of the region where the solid electrolyte layer is formed. Usually, the porosity of the fuel electrode and the porosity of the second solid electrolyte layer are significantly different, and the difference can be clearly confirmed by visually checking the cross-sectional image.

The first solid electrolyte layer has the role of relieving the stress (shrinkage force) applied to the solid electrolyte layer due to shrinkage of the fuel electrode after the reduction treatment step, and suppressing cracking and peeling of the second solid electrolyte layer.

Like the fuel electrode, the first solid electrolyte layer contains a nickel element, but in the first solid electrolyte layer, at least part of the nickel is in the form of a composite oxide containing a metal element that constitutes the first solid electrolyte material. exists in 60% or more or 85% or more of the nickel atoms contained in the first solid electrolyte layer may exist in the form of a composite oxide. More preferably, 95% or more of the nickel atoms contained in the first solid electrolyte layer are present in the form of a composite oxide.

The composite oxide is a stable oxide that is more difficult to reduce than nickel oxide (NiO). is easily maintained in the state of a composite oxide. Therefore, containing the composite oxide suppresses the volume shrinkage associated with the reduction treatment of the first solid electrolyte layer. Therefore, the stress generated by the contraction of the fuel electrode in the reduction treatment process is applied to the first solid electrolyte layer containing the composite oxide, while the stress transmitted to the second solid electrolyte layer is reduced. Therefore, cracking and peeling of the second solid electrolyte layer are suppressed. This makes it possible to secure a large facing area between the fuel electrode and the second solid electrolyte layer, and easily realize a large-sized fuel cell with a high output current.

Further, since the second solid electrolyte layer does not substantially contain nickel element, an increase in leak current in the second solid electrolyte layer is suppressed. Moreover, when a metal oxide is used for the second solid electrolyte layer, a decrease in ionic conductivity can be suppressed. In particular, when a proton-conducting oxide having a perovskite structure, which will be described later, is used, the decrease in proton conductivity is remarkably suppressed, and high power generation performance is obtained. Note that the fact that the second solid electrolyte layer does not substantially contain the nickel element means that the ratio C2 of Ni atoms contained in the _second solid electrolyte layer is below the detection limit (for example, 0.01% or less in terms of atomic fraction). ). The Ni atom proportion _C2 is determined by an Electron Probe Micro Analyzer (EPMA). _C2 may be obtained at a plurality of locations (for example, 10 points or more) in the second solid electrolyte layer, and the average value of the plurality of locations may be obtained.

In the conventional fuel electrode-solid electrolyte layer composite, the first solid electrolyte layer is not provided between the fuel electrode and the second solid electrolyte layer, and the second solid electrolyte layer is directly laminated on the fuel electrode. . The fuel electrode and the second solid electrolyte layer are usually formed by co-sintering. In this case, nickel contained in the fuel electrode diffuses into the second solid electrolyte layer, easily increasing leakage current, and easily deteriorating the performance (for example, OCV) of the fuel cell. For example, when a fuel electrode containing a nickel component and a second solid electrolyte layer formed without intentionally containing a nickel element are co-sintered, nickel in the fuel electrode diffuses at high temperatures during sintering, Nickel can be uniformly distributed within the two solid electrolyte layers. In this case, the second solid electrolyte layer may contain, for example, about 2% nickel at a depth of 5 μm from the boundary with the fuel electrode.

On the other hand, in the conventional structure, when the second solid electrolyte layer is formed on the fuel electrode by a low-temperature process such as paste coating or sputtering, although the diffusion of nickel is suppressed, Low adhesion. Therefore, when the stress associated with shrinkage of the fuel electrode is directly transmitted to the second solid electrolyte layer in the reduction treatment step, the second solid electrolyte layer breaks or cracks occur, or the second solid electrolyte layer peels off from the fuel electrode. Sometimes.

On the other hand, in the fuel electrode-solid electrolyte layer composite of the present disclosure, the first solid electrolyte layer is interposed between the fuel electrode and the second solid electrolyte layer, so that the stress associated with reduction shrinkage of the fuel electrode is The first solid electrolyte layer absorbs and the contraction force is suppressed from being transmitted to the second solid electrolyte layer. Therefore, cracking and peeling of the second solid electrolyte layer are suppressed. Also, the second solid electrolyte layer can be formed on the first solid electrolyte layer by a low-temperature process such as sputtering. As a result, diffusion of nickel existing in the fuel electrode or the first solid electrolyte layer into the second solid electrolyte layer is suppressed, so that high power generation performance or electrolysis performance can be obtained.

The anode-solid electrolyte layer composite having the first and second solid electrolyte layers is, for example, a precursor of the anode (first precursor) and a precursor of the first solid electrolyte layer (second precursor). and co-sintering the laminate at a high temperature of 1400° C. or higher, and then forming a second solid electrolyte layer substantially free of nickel on the first solid electrolyte layer by a low-temperature process of, for example, 850° C. or lower. can be manufactured by A specific manufacturing method will be described later.

(2) The nickel content in the first solid electrolyte layer may be lower than the nickel content in the fuel electrode. The nickel content ratio in the fuel electrode means the ratio (atomic fraction) _CA of Ni atoms contained in the fuel electrode. The nickel content ratio in the first solid electrolyte layer means the ratio (atomic fraction) C1 of Ni atoms contained in the _first solid electrolyte layer. C _A and C ₁ , like C ₂ , are determined by EPMA. C _A and/or C ₁ may be obtained at a plurality of locations (for example, 10 points or more) in the solid electrolyte layer, and an average value may be obtained. In this case, the shrinkage rate of the first solid electrolyte layer in the reduction treatment process tends to be smaller than the shrinkage rate of the fuel electrode. Therefore, the stress generated by the contraction of the fuel electrode is easily relieved in the first solid electrolyte layer and is less likely to be transmitted to the second solid electrolyte layer.

(3) The first solid electrolyte layer may be substantially free of metallic nickel. At least part of the nickel oxide in the solid electrolyte layer can be converted to metallic nickel by the reduction treatment. Therefore, the fact that the first solid electrolyte layer does not substantially contain metallic nickel means that the nickel oxide content in the first solid electrolyte layer before reduction is extremely low and the volume change is small.
Most of the nickel in the first solid electrolyte layer may be contained in the form of a nickel compound (for example, the composite oxide described above) that is difficult to reduce so as not to be converted into metallic nickel by reduction treatment. In this case, since the first solid electrolyte layer undergoes little change in volume even in the reduction treatment step, the stress accompanying contraction of the fuel electrode is absorbed by the first solid electrolyte layer, and most of the stress is transmitted to the second solid electrolyte layer. There is no Therefore, cracking and peeling of the second solid electrolyte layer are effectively suppressed.

Here, the fact that the first solid electrolyte layer does not substantially contain metallic nickel means that the proportion _C1M of Ni atoms present in the metallic nickel state in the first solid electrolyte layer is below the detection limit (for example, the atomic fraction 0.01% or less). The ratio C _1M is the ratio of the number of Ni atoms existing in a metallic nickel state to the total number of Ni atoms contained in the first solid electrolyte layer to the ratio (atomic fraction) C ₁ of Ni atoms contained in the first solid electrolyte layer. It is calculated by multiplying by _rM . The ratio _rM is determined by, for example, X-ray photoelectron spectroscopy (XPS). r _M may be an average value of measured values at a plurality of locations (for example, 10 or more points) in the first solid electrolyte layer.
In addition, the ratio _C1M can be calculated by comparing the EPMA analysis result with the SEM photo image. The X-ray diffraction (XRD) spectrum may be analyzed by the RIR (Reference Intensity Ratio) method to determine the ratio C _1M .

(4) The first solid electrolyte layer may be substantially free of nickel oxide. In this case, the volume change of the first solid electrolyte layer in the reduction treatment step is suppressed. Therefore, the stress accompanying contraction of the fuel electrode is absorbed by the first solid electrolyte layer, and the stress transmitted to the second solid electrolyte layer is significantly reduced. As a result, cracking and peeling of the second solid electrolyte layer are effectively suppressed.

Here, the fact that the first solid electrolyte layer does not substantially contain nickel oxide means that the ratio _C1O of Ni atoms present in the state of nickel oxide (NiO) in the first solid electrolyte layer is below the detection limit (for example, , 0.01% or less in atomic fraction). The ratio _C1O is the ratio of the number of Ni atoms present in the nickel oxide state to the total number of Ni atoms contained in the _first solid electrolyte layer to the ratio (atomic fraction) C1 of Ni atoms contained in the first solid electrolyte layer. It is a value multiplied by _rO . The ratio _C1O is determined in the same manner as the ratio _C1M .

(5) The thickness of the second solid electrolyte layer may be 0.2 μm to 20 μm. Thereby, the resistance of the ion conduction of the solid electrolyte layer can be kept low.

When using a conventional fuel electrode-solid electrolyte layer composite in which the second solid electrolyte layer is formed on the fuel electrode without interposing the first solid electrolyte layer, the second solid electrolyte is The thickness of the second solid electrolyte layer must be thicker than a certain value so that cracks and peeling of the layer do not occur. However, as a result, the resistance of ion conduction increases, and the power generation efficiency tends to decrease.

In contrast, in the fuel electrode-solid electrolyte layer composite according to the embodiment of the present disclosure, cracking and peeling of the second solid electrolyte layer are suppressed due to the interposition of the first solid electrolyte layer. Thickness does not need to be increased. The thickness of the second solid electrolyte layer can be reduced to 10 μm or less, or 5 μm or less. Therefore, a fuel cell with high power generation efficiency can be easily realized.

(6) At least one of the first solid electrolyte material, the second solid electrolyte material, and the third solid electrolyte material has a perovskite structure, and satisfies the following formula (1): A _x B _{1- y My} A metal oxide represented by O _3-δ may also be included. Here, element A is at least one selected from the group consisting of Ba, Ca and Sr. Element B is at least one selected from the group consisting of Ce and Zr. Element M is at least one selected from the group consisting of Y, Yb, Er, Ho, Tm, Gd, In and Sc. δ is the amount of oxygen deficiency and satisfies 0.95≦x≦1 and 0<y≦0.5.

Metal oxides satisfying the above conditions have high proton conductivity even in the temperature range of 400°C to 600°C. Therefore, by configuring a fuel cell using this metal oxide for the solid electrolyte layer, high power generation performance can be exhibited. Further, by using this metal oxide for the second solid electrolyte layer to configure a steam electrolysis cell, high steam electrolysis performance can be exhibited. At least the second solid electrolyte material among the first to third solid electrolyte materials preferably contains the metal oxide represented by the above formula (1).

Element A may contain Ba, element B may contain Zr, and element M may contain Y. This can improve the durability of the fuel electrode-solid electrolyte layer composite.

(7) Another embodiment of the present disclosure is a cell structure including the above fuel electrode-solid electrolyte layer composite and an air electrode, wherein a second solid electrolyte layer is interposed between the fuel electrode and the air electrode, The present invention relates to a fuel cell comprising an oxidant channel for supplying an oxidant to an air electrode and a fuel channel for supplying fuel to a fuel electrode. This fuel cell has excellent power generation performance and can be easily increased in size.

(8) Still another embodiment of the present disclosure is a fuel electrode, a first solid electrolyte layer, and a second solid layer stacked on the first solid electrolyte layer side of a stack of the fuel electrode and the first solid electrolyte layer. and an anode-solid electrolyte layer composite member having an electrolyte layer. Here, the first solid electrolyte layer includes a first solid electrolyte material and a composite oxide containing a nickel element and a metal element that constitutes the first solid electrolyte material. The second solid electrolyte layer contains a second solid electrolyte material and does not substantially contain nickel element. The fuel electrode includes a third solid electrolyte material and nickel oxide. By subjecting such a fuel electrode-solid electrolyte layer composite member to a reduction treatment, the above fuel electrode-solid electrolyte layer composite can be obtained.

(9) In the fuel electrode-solid electrolyte layer composite member of (8) above, the first solid electrolyte layer does not substantially contain nickel oxide, or the content of nickel oxide in the first solid electrolyte layer is may be smaller than the content of nickel oxide in When the first solid electrolyte layer contains nickel oxide, the nickel oxide contained in the fuel electrode and the first solid electrolyte layer is reduced and changed to metallic nickel in the reduction treatment step, and accordingly the fuel electrode and the first solid electrolyte layer. shrinks. However, when the content of nickel oxide in the first solid electrolyte layer is smaller than that in the fuel electrode, the contraction rate of the first solid electrolyte layer tends to be smaller than that of the fuel electrode. Therefore, the interposition of the first solid electrolyte layer facilitates suppressing the contraction force generated in the fuel electrode from being transmitted to the second solid electrolyte layer.

(10) In the fuel electrode-solid electrolyte layer composite member of (8) above, the first solid electrolyte layer may be substantially free of nickel oxide. In this case, since the first solid electrolyte layer hardly shrinks even in the reduction treatment step, the first solid electrolyte layer absorbs the stress accompanying the contraction of the fuel electrode, and the stress is hardly transmitted to the second solid electrolyte layer. Therefore, cracking and peeling of the second solid electrolyte layer are effectively suppressed.

(11) In the fuel electrode-solid electrolyte layer composite member of (8) above, at least one of the first solid electrolyte material, the second solid electrolyte material, and the third solid electrolyte material has a perovskite structure, It may also contain a metal oxide represented by the following formula (2): A _x B _{1- y My} O _3-δ . Here, element A is at least one selected from the group consisting of Ba, Ca and Sr. Element B is at least one selected from the group consisting of Ce and Zr. Element M is at least one selected from the group consisting of Y, Yb, Er, Ho, Tm, Gd, In and Sc. δ is the amount of oxygen deficiency and satisfies 0.95≦x≦1 and 0<y≦0.5. As a result, in the temperature range of 400° C. to 600° C., a fuel cell with high power generation performance or a steam electrolysis cell with high electrolysis performance can be realized. At least the second solid electrolyte material among the first to third solid electrolyte materials preferably contains the metal oxide represented by the above formula (2).

(12) Still another embodiment of the present disclosure is a first solid electrolyte material containing a fuel electrode containing nickel oxide, a first solid electrolyte material, and a composite oxide of nickel and a metal element constituting the first solid electrolyte material. a step of obtaining a laminate of a solid electrolyte layer; and a second solid electrolyte layer containing a second solid electrolyte material and substantially free of nickel element on the first solid electrolyte layer side of the laminate at 850°C. a step of forming an anode-solid electrolyte layer composite member by forming below, and a step of forming an air electrode on the second solid electrolyte layer side of the anode-solid electrolyte layer composite member to obtain a cell structure. , to a method for manufacturing a fuel cell. A large-sized fuel cell can be easily obtained by this manufacturing method.

The second solid electrolyte layer can be formed using a second solid electrolyte material that does not intentionally contain nickel element. Since the second solid electrolyte layer is formed at a low temperature of 850° C. or lower, nickel contained in the fuel electrode or the first solid electrolyte layer is suppressed from diffusing into the second solid electrolyte layer. Therefore, the second solid electrolyte layer is maintained substantially free of nickel. As a result, in the manufactured fuel cell, leakage current due to nickel present in the second solid electrolyte layer is suppressed. Also, the ion conductivity of the second solid electrolyte layer can be kept high.

(13) The fuel cell manufacturing method may further include a reduction treatment step of reducing nickel oxide contained in the fuel electrode to metal nickel. As a result, the fuel electrode becomes porous, and the solid electrolyte composite member changes into a fuel electrode-solid electrolyte layer composite. The reduction treatment step may be performed after obtaining the cell structure (after forming the air electrode), or by subjecting the fuel electrode-solid electrolyte layer composite member to heat treatment in a hydrogen atmosphere, for example, before forming the air electrode. you can go

At this time, if the first solid electrolyte layer contains nickel oxide, the nickel oxide contained in the first solid electrolyte layer may be reduced and changed to metallic nickel. On the other hand, the composite oxide contained in the first solid electrolyte layer is difficult to be reduced and remains in the state of composite oxide even after the reduction treatment step. In this case, the shrinkage rate of the first solid electrolyte layer in the reduction treatment can be smaller than the shrinkage rate of the fuel electrode.

Therefore, since the first solid electrolyte layer contains the composite oxide, the stress generated by the shrinkage of the fuel electrode due to the reduction of nickel oxide is relieved by the first solid electrolyte layer, and the second solid electrolyte layer cracks and Peeling is suppressed.

(14) In the step of obtaining the laminate, the first solid electrolyte layer may be substantially free of nickel oxide, or may contain less nickel oxide than the fuel electrode. The fuel electrode and the first solid electrolyte layer may shrink in volume due to reduction of nickel oxide. However, when the content of nickel oxide in the first solid electrolyte layer is smaller than that in the fuel electrode, the contraction rate of the first solid electrolyte layer tends to be smaller than that of the fuel electrode. On the other hand, since the second solid electrolyte layer does not substantially contain nickel oxide, it hardly shrinks. Therefore, since the contraction rate of the first solid electrolyte layer is smaller than the contraction rate of the fuel electrode, the stress generated by the contraction of the fuel electrode is relieved by the first solid electrolyte layer, and the contraction force is transmitted to the second solid electrolyte layer. is reduced.

In particular, when the first solid electrolyte layer does not substantially contain nickel oxide, the stress associated with contraction of the fuel electrode is absorbed by the first solid electrolyte layer and is hardly transferred to the second solid electrolyte layer. Therefore, cracking and peeling of the second solid electrolyte layer can be effectively suppressed.

(15) The step of obtaining the laminate includes forming a second precursor layer containing the first solid electrolyte material on the first precursor layer containing the third solid electrolyte material and nickel oxide; A step of heat-treating the layer and the second precursor layer at 1400° C. or higher to obtain a fuel electrode corresponding to the first precursor layer and a first solid electrolyte layer corresponding to the second precursor layer may be included.

By heat-treating the first precursor layer and the second precursor layer at 900° C. or higher, a laminate of the fuel electrode and the first solid electrolyte layer is obtained. If the heat treatment temperature is 900° C. or higher, nickel in the first precursor layer can diffuse into the second precursor layer to form a composite oxide. More preferably, by heat-treating the first precursor layer and the second precursor layer at 1400° C. or higher, the first precursor layer and the second precursor layer can be integrated while being strongly bonded. On the other hand, heat treatment at 900° C. or higher facilitates diffusion of nickel in nickel oxide contained in the first precursor layer. The diffused nickel can combine with the elements that make up the first solid electrolyte material within the second precursor layer to form various complex compounds. In the first solid electrolyte layer after the heat treatment, at least part of the diffused nickel can exist in the form of a composite oxide containing nickel and the metal element that constitutes the first solid electrolyte material.

(16) In (15) above, the second precursor layer may be substantially free of nickel element. That is, when the second precursor layer is formed by a coating method, the raw material of the second precursor layer only needs to contain the first solid electrolyte material, and does not need to contain nickel. Alternatively, when the second precursor layer is formed by a vapor phase method (for example, a sputtering method), only the target containing the elements constituting the first solid electrolyte material may be used, and the target containing nickel may not be used. The heat treatment may cause some of the nickel contained in the first precursor layer to diffuse and form a complex oxide within the second precursor layer. As a result, a first solid electrolyte layer containing the first solid electrolyte material and the composite oxide is formed.

Although the upper limit of the heat treatment temperature of the laminate is not particularly limited, it may be 1800° C. or lower.

For example, when the first solid electrolyte material is BZY, in the first solid electrolyte layer after heat treatment, nickel may exist in a state of replacing Ba or Zr in BZY. It can also exist in the form of complex oxides such as BaY ₂ NiO ₅ and BaNiO ₂ .

In the above (12), the step of obtaining the laminate may be performed, for example, by coating the raw material of the second precursor layer on the first precursor layer and then heating and co-sintering the first precursor layer. A second precursor layer may be grown on the body by a vapor phase method. The first precursor layer contains a third solid electrolyte material and nickel oxide as essential components. The raw material of the second precursor layer contains the first solid electrolyte material as an essential component. The raw material of the second precursor layer may be a mixture of the first solid electrolyte material and the composite oxide powder mixed in advance. The first precursor layer and/or the second precursor layer may optionally contain additives such as binders, surfactants, and/or peptizers.

When forming the second precursor layer by coating, screen printing, spray coating, spin coating, dip coating, or the like can be used. A paste obtained by dispersing the raw material of the second precursor layer in a dispersion medium such as water or an organic solvent may be applied. By drying the coating film and heat-treating it, the dispersion medium and the additive are removed, the first precursor layer changes to the fuel electrode, the second precursor layer changes to the first solid electrolyte layer, and the fuel electrode and the first solid electrolyte layer is obtained.

When the second precursor layer is formed by a vapor phase method, the vapor phase method may be a sputtering method, a PVD method, a CVD method, or the like. For example, when the sputtering method is used, a target containing elements constituting the first solid electrolyte material and a target containing nickel can be used. The substrate temperature during film formation may be, for example, 400.degree. C. to 700.degree. A complex oxide can be formed in the first solid electrolyte layer by performing heat treatment after film formation.

At least one of the first precursor layer and the second precursor layer may be formed by pressure molding. For example, a pellet-like first precursor layer may be obtained by filling a mold with a powder obtained by mixing the third solid electrolyte material and nickel oxide, and pressing the powder of the first solid electrolyte material into the mold. A second precursor layer in pellet form may be obtained by pressing. More preferably, after the mixed powder of the third solid electrolyte material and nickel oxide is packed in a mold, the powder of the first solid electrolyte material is packed in the same mold, and the second precursor layer is formed on the first precursor layer. may be stacked, and the first precursor layer and the second precursor layer may be pressurized at the same time to obtain a laminate.
Since the first precursor layer constitutes the fuel electrode, it is usually formed thicker than the second precursor layer. Therefore, the first precursor layer may be formed into pellets by pressure molding, and the second precursor layer may be formed on the first precursor layer by applying a paste.

Further, in (12) above, the formation of the second solid electrolyte layer after obtaining the laminate may be performed by coating a raw material for the second solid electrolyte layer that does not contain nickel element, or may be performed in a gas phase. It may be grown by law. When forming the second solid electrolyte layer by coating, screen printing, spray coating, spin coating, dip coating, or the like can be used. The raw material of the second solid electrolyte layer includes powder of the second solid electrolyte material. Additives such as binders, surfactants, and/or peptizers may be included, as desired. A paste obtained by dispersing the second solid electrolyte material in a dispersion medium such as water or an organic solvent may be applied. The coating film is dried and heat-treated to remove the dispersion medium and the additive, thereby forming the second solid electrolyte layer.
When the second solid electrolyte layer is formed by a vapor phase method, the vapor phase method may be a sputtering method, a PVD method, a CVD method, or the like.

[Details of the embodiment of the invention]
Specific examples of embodiments of the present invention will be described below with reference to the drawings as appropriate. The present invention is not limited to these examples, but is indicated by the scope of the attached claims, and is intended to include all modifications within the scope and meaning equivalent to the scope of the claims. .

(Fuel cell)
FIG. 1 shows a specific example of a fuel cell using the fuel electrode-solid electrolyte layer composite of this embodiment. FIG. 1 is a schematic diagram showing a cross-sectional structure of a fuel cell (solid oxide fuel cell).

A fuel cell 10 includes a cell structure 1 . An example of the cross-sectional structure of the cell structure is schematically shown in FIG. As shown in FIG. 2, the cell structure 1 includes an air electrode (cathode) 2, a fuel electrode (anode) 3, and a solid electrolyte layer 4 interposed therebetween. The fuel electrode 3 and the solid electrolyte layer 4 are integrated to form a composite.

The fuel cell 10 includes, in addition to the cell structure 1 , an oxidant channel 23 for supplying an oxidant to the air electrode 2 and a fuel channel 53 for supplying fuel to the fuel electrode 3 . In the example shown in FIG. 1, the oxidant channel 23 is formed by the air electrode side separator 22, the fuel channel 53 is formed by the fuel electrode side separator 52, and the cell structure 1 is formed by the air electrode side separator 22. , and the fuel electrode side separator 52 . The oxidant channel 23 of the air electrode side separator 22 is arranged to face the air electrode 2 of the cell structure 1, and the fuel channel 53 of the fuel electrode side separator 52 is arranged to face the fuel electrode 3. be done.

(Fuel electrode-solid electrolyte composite)
The fuel electrode 3 is porous. The solid electrolyte layer 4 includes a first solid electrolyte layer 4a formed on the fuel electrode 3, and a densely formed second solid electrolyte layer 4b having a smaller porosity than the fuel electrode 3. The second solid electrolyte layer 4b is laminated on the side opposite to the fuel electrode 3 of the first solid electrolyte layer 4a. The fuel electrode 3, the first solid electrolyte layer 4a, and the second solid electrolyte layer 4b are integrated to form a fuel electrode-solid electrolyte layer composite 5. FIG.

(First solid electrolyte layer)
The first solid electrolyte layer 4a constitutes at least part of the solid electrolyte layer 4 together with the second solid electrolyte layer 4b. The first solid electrolyte layer 4a is interposed between the fuel electrode 3 and the second solid electrolyte layer 4b.

For the first solid electrolyte layer, a metal oxide having a perovskite structure (ABO _three -phase) and having a composition represented by the above formula (1) can be used as the first solid electrolyte material. The A site of the perovskite structure contains the element A, and the B site contains the element B (not indicative of boron). Part of the B site is substituted with the element M from the viewpoint of ensuring high proton conductivity.

The ratio x of element A to the sum of element B and element M is preferably 0.95 ≤ x ≤ 1, and 0.98 ≤ x ≤ 1, from the viewpoint of ensuring high proton conductivity and ion transference number. It is more preferable to have In addition, when x does not exceed 1, precipitation of the element A is suppressed, and corrosion of the proton conductor due to the action of moisture can be suppressed. From the viewpoint of ensuring proton conductivity, y preferably satisfies 0<y≦0.5, more preferably 0.1<y≦0.3.

Element A is at least one selected from the group consisting of Ba (barium), Ca (calcium) and Sr (strontium). Among them, the element A preferably contains Ba in terms of obtaining excellent proton conductivity. The proportion of Ba in the element A is preferably 50 atomic % or more, more preferably 80 atomic % or more. More preferably, the element A consists only of Ba.

Element B is at least one selected from the group consisting of Ce (cerium) and Zr (zirconium). Among them, from the viewpoint of durability, the element B preferably contains Zr. The ratio of Zr to the element B is preferably 50 atomic % or more, more preferably 80 atomic % or more. More preferably, the element B consists only of Zr.

Element M is selected from the group consisting of Y (yttrium), Yb (ytterbium), Er (erbium), Ho (holmium), Tm (thulium), Gd (gadolinium), In (indium) and Sc (scandium) at least one. The element M is a dopant, which causes oxygen defects, and the metal oxide having a perovskite structure develops proton conductivity.

In the formula (1), the oxygen deficiency amount δ can be determined according to the amount of the element M, and for example, 0≦δ≦0.15. The ratio of each element in the metal oxide can be determined by, for example, Wavelength Dispersive X-ray spectroscopy (hereinafter referred to as WDX) using an electron probe microanalyzer.

Specific examples of metal oxides include yttrium-doped barium zirconate [Ba _x Zr _{1-y Y y} O _3-δ (hereinafter referred to as BZY)] and yttrium-doped barium cerate [Bax _Ce1 -yYyO3-[ _delta ] (BCY)], yttrium-doped barium zirconate/barium cerate mixed oxide [ _BaxZr1 - _{y - zCezYyO3-} [ _delta ] ( _BZCY )] and the like. As a specific example of BZY, BaZr _0.8 Y _0.2 O _2.9 (x=1, y=0.2, δ=0.1) may be used. As a specific example of BCY, BaCe _0.8 Y _0.2 O _2.9 (x=1, y=0.2, δ=0.1) may be used. BCY and BZY exhibit high proton conductivity in the medium temperature range of 400°C to 600°C.

The first solid electrolyte layer contains a nickel component in addition to the metal oxide. However, in the first solid electrolyte layer, at least part of nickel exists in the form of a composite oxide containing nickel and a metal element that constitutes the metal oxide of the first solid electrolyte layer. For example, when the first solid electrolyte layer contains BZY, the first solid electrolyte layer may contain complex oxides such as BaY ₂ NiO ₅ and BaNiO ₂ . These composite oxides are stable compounds that are difficult to be reduced, and even if they come into contact with fuel gas (for example, hydrogen gas), Ni in the composite oxides is reduced and hardly changed to metallic nickel. Therefore, the volume change of the first solid electrolyte layer due to reduction treatment is smaller than that of the fuel electrode, which will be described later.

The thickness of the first solid electrolyte layer is, for example, 1 μm to 20 μm, preferably 2 μm to 10 μm.

(Second solid electrolyte layer)
The second solid electrolyte layer 4b constitutes at least part of the solid electrolyte layer 4 together with the first solid electrolyte layer 4a.
For the second solid electrolyte layer, the proton-conducting metal oxide having the perovskite structure described above for the first solid electrolyte layer can be used as the second solid electrolyte material. The composition of the metal oxide of the second solid electrolyte layer may be the same as or different from that of the metal oxide of the first solid electrolyte layer.

The second solid electrolyte layer is manufactured so as to contain substantially no nickel component. As a result, a fuel cell with excellent power generation performance can be obtained.

The thickness of the second solid electrolyte layer is, for example, 0.2 μm to 20 μm, preferably 0.2 μm to 10 μm. When the thickness of the second solid electrolyte layer is within this range, the resistance of the solid electrolyte layer can be kept low.

(fuel electrode)
At the fuel electrode 3 , a reaction (fuel oxidation reaction) proceeds by oxidizing the fuel gas (for example, hydrogen gas) introduced from the fuel flow channel to release protons and electrons.

For the fuel electrode, the proton-conducting metal oxide having the perovskite structure described above for the first solid electrolyte layer can be used as the third solid electrolyte material. The metal oxide of the fuel electrode may have the same or different metal oxide composition as the metal oxide of the first solid electrolyte layer or the metal oxide of the second solid electrolyte layer. The metal oxide of the first solid electrolyte layer (first solid electrolyte material), the metal oxide of the second solid electrolyte layer (second solid electrolyte material), and the metal oxide of the fuel electrode (third solid electrolyte material), In between, the metal elements entering the A site and B site of the perovskite structure may be the same. However, the composition ratio of the metal elements in each solid electrolyte material does not necessarily have to be the same, and may be different.

The fuel electrode contains a nickel component in addition to the above metal oxide. The nickel component is, for example, metallic nickel, and acts as a catalyst that promotes the hydrogen dissociation reaction.

The thickness of the fuel electrode can be appropriately determined, for example, from 10 μm to 2 mm, and may be from 10 μm to 100 μm.

(air electrode)
The air electrode 2 has a porous structure. When the second solid electrolyte layer 4b (solid electrolyte layer 4) has proton conductivity, in the air electrode 2, protons conducted through the second solid electrolyte layer 4b react with oxide ions (reduction of oxygen reaction) proceeds. Oxide ions are generated by dissociation of the oxidant (oxygen) introduced from the oxidant channel.

A known material can be used as the material of the air electrode. As the material for the air electrode, for example, compounds containing lanthanum and having a perovskite structure (ferrite, manganite, and/or cobaltite, etc.) are preferable, and among these compounds, those containing strontium are more preferable. Specifically, lanthanum strontium cobalt ferrite (LSCF, La _1-x1 Sr _x1 Fe _1-y1 Co _y1 O _3-δ1 , 0<x1<1, 0<y1<1, δ1 is the amount of oxygen deficiency), lanthanum strontium manganite (LSM, La _1-x2 Sr _x2 MnO _3-δ1 , 0<x2<1, δ1 is the amount of oxygen deficiency), lanthanum strontium cobaltite (LSC, La _1-x3 Sr _x3 CoO _3-δ1 , 0<x3≦1, and δ1 is the amount of oxygen deficiency). From the viewpoint of promoting the reaction between protons and oxide ions, the air electrode may contain a catalyst such as Pt. From the viewpoint of suppressing the diffusion of nickel into the second solid electrolyte layer, the air electrode is preferably formed at 850° C. or less.

The air electrode can be formed, for example, by applying raw materials of the above materials. If necessary, binders, additives, and/or dispersion media may be used together with the raw materials.
The thickness of the air electrode is not particularly limited, but can be appropriately determined, for example, from 5 μm to 2 mm, and may be about 5 μm to 40 μm.

1 and 2, the thickness of the fuel electrode 3 is made thicker than the thickness of the air electrode 2, and the fuel electrode 3 forms the solid electrolyte layer 4 (the first solid electrolyte layer 4a and the second solid electrolyte layer 4b) and thus the cell. It functions as a support that supports the structure 1 . The thickness of the fuel electrode 3 does not necessarily have to be thicker than that of the air electrode 2. For example, the thickness of the fuel electrode 3 may be approximately the same as the thickness of the air electrode 2.

(Oxidant channel and fuel channel)
The oxidant channel 23 has an oxidant inlet into which an oxidant flows and an oxidant outlet through which water generated by the reaction and unused oxidant are discharged (neither is shown). Oxidants include, for example, gases containing oxygen. The fuel flow path 53 has a fuel gas inlet into which fuel gas containing water vapor and hydrocarbon gas flows, and a fuel gas outlet through which unused fuel, H ₂ O, N ₂ , CO ₂ and the like generated by reactions are discharged. (none shown).

(separator)
When a fuel cell is configured by stacking a plurality of cell structures, for example, the cell structure 1, the air electrode side separator 22, and the fuel electrode side separator 52 can be stacked as one unit. A plurality of cell structures 1 may be connected in series by, for example, separators having gas channels (oxidant channel and fuel channel) on both sides.

Examples of materials for the separator include heat-resistant alloys such as stainless steel, nickel-based alloys, and chromium-based alloys in terms of electrical conductivity and heat resistance. Among them, stainless steel is preferable because it is inexpensive. In a proton conductive solid oxide fuel cell (PCFC), since the operating temperature is about 400° C. to 600° C., stainless steel can be used as the separator material.

(current collector)
The fuel cell 10 may include a fuel electrode side current collector 51 that is arranged between the fuel electrode 3 and the fuel electrode side separator 52 and is in contact with the fuel electrode 3 . The fuel electrode-side current collector 51 has a function of diffusing and supplying the fuel gas introduced from the fuel flow channel 53 to the fuel electrode 3 in addition to the current collecting function. The fuel cell 10 may also include an air electrode-side current collector 21 that is arranged between the air electrode 2 and the air electrode side separator 22 and that is in contact with the air electrode 2 . The air electrode-side current collector 21 has a function of diffusing and supplying the oxidant gas introduced from the oxidant flow path 23 to the air electrode 2 in addition to the current collecting function.
That is, the air electrode side current collector 21 forms at least part of the oxidant channel 23 , and the fuel electrode side current collector 51 forms at least part of the fuel channel 53 . Therefore, each current collector is preferably a structure having sufficient air permeability.

Examples of structures used for the air electrode side current collector and the fuel electrode side current collector include metal porous bodies containing silver, silver alloys, nickel, nickel alloys, etc., metal meshes, punched metals, expanded metals, and the like. be done. Among them, a metal porous body is preferable in terms of lightness and air permeability. In particular, a porous metal body having a three-dimensional network structure is preferred. A three-dimensional network structure refers to a structure in which rod-like or fibrous metals forming a metal porous body are connected to each other in a three-dimensional manner to form a network. Examples include a sponge-like structure and a non-woven fabric-like structure.

A metal porous body can be formed, for example, by coating a resin-made porous body having continuous voids with the above metal. After the metal coating treatment, when the resin inside is removed, a cavity is formed inside the skeleton of the metal porous body, making it hollow. As a commercially available metal porous body having such a structure, "Celmet" made of nickel manufactured by Sumitomo Electric Industries, Ltd. can be used.

A fuel cell can be manufactured by a known method except for using the cell structure described above.

(Fuel electrode-solid electrolyte layer composite member)
FIG. 3 is a schematic diagram showing a cross-sectional structure of a cell structure 1Z having a fuel electrode-solid electrolyte layer composite member used in the manufacturing process of the fuel cell shown in FIG. As shown in FIG. 3, the cell structure 1Z includes an air electrode (cathode) 2 and a fuel electrode-solid electrolyte layer composite member 5Z. A fuel electrode-solid electrolyte layer composite member 5Z is a laminate in which a fuel electrode 6a, a first solid electrolyte layer 6b, and a second solid electrolyte layer 6c are stacked in this order. A second solid electrolyte layer 6 c is in contact with the air electrode 2 . The fuel electrode 6a, the first solid electrolyte layer 6b, and the second solid electrolyte layer 6c are formed before the reduction treatment of the fuel electrode 3, the first solid electrolyte layer 4a, and the second solid electrolyte layer 4b shown in FIG. is in a state of

First solid electrolyte layer 6b includes nickel and a first solid electrolyte material. In the first solid electrolyte layer 6b, at least part of nickel exists in the form of a composite oxide with the metal element forming the first solid electrolyte material. The first solid electrolyte layer 6b can be formed, for example, by applying a paste containing powder of the first solid electrolyte material on the fuel electrode 6a and then drying it.

The second solid electrolyte layer 6c contains a second solid electrolyte material and does not substantially contain a nickel component. The second solid electrolyte layer 6c can be formed, for example, by a vapor phase method (eg, sputtering method). The deposition of the second solid electrolyte layer 6c is carried out at 850° C. or lower in order to suppress the diffusion of nickel from the first solid electrolyte layer 6b.

The fuel electrode 6a contains nickel oxide and a third solid electrolyte material. The fuel electrode 6a can be formed, for example, by putting a powder obtained by mixing nickel oxide and a third solid electrolyte material into a mold and molding the mixture under pressure.

The fuel electrode 6a and the first solid electrolyte layer 6b are preferably co-sintered. Co-sintering is performed at a high temperature of, for example, 1400° C. or higher. As a result, the first solid electrolyte layer 6b firmly adheres to the fuel electrode 6a. Also, the nickel element contained in the fuel electrode 6a diffuses into the first solid electrolyte layer 6b, forming a composite oxide in the first solid electrolyte layer 6b.

1 and 2, the fuel cell is assembled by replacing the cell structure 1 with the cell structure 1Z shown in FIG. After the fuel cell is assembled, fuel gas is supplied from the side of the fuel electrode 6a through the fuel flow path 53, whereby the nickel oxide in the fuel electrode 6a is reduced and changed to metallic nickel. At this time, the fuel electrode 6a shrinks as it changes to metallic nickel, and changes to a porous fuel electrode 3a. On the other hand, the composite oxide contained in the first solid electrolyte layer 6b is difficult to be reduced and hardly shrinks. Therefore, the fuel cell 10 shown in FIG. 1 can be manufactured.

As the fuel electrode 6a (3) shrinks, a shrinkage force is applied to the first solid electrolyte layer 6b (4a). However, co-sintering at a high temperature provides strong bonding between the fuel electrode 6a and the first solid electrolyte layer 6b. Therefore, the first solid electrolyte layer 4a after the reduction treatment is less likely to be cracked or peeled off. The stress associated with contraction is relieved within the first solid electrolyte layer 4a, and the stress transmitted to the second solid electrolyte layer 4b is reduced. Therefore, the second solid electrolyte layer 4b is less likely to be cracked or peeled off.

Therefore, by using the fuel electrode-solid electrolyte layer composite member 5Z, cracking and peeling of the fuel electrode-solid electrolyte layer composite 5 are suppressed. A fuel cell with a large output current can be easily realized. In addition, since the second solid electrolyte layer 4b of this fuel cell does not substantially contain a nickel component, the power generation efficiency is high.

EXAMPLES The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[Example 1]
(1) _Fabrication of _{fuel electrode} -solid electrolyte layer composite member active agent), and an appropriate amount of ethanol were mixed in a ball mill and granulated. At this time, NiO and BZY were mixed at a volume ratio of 70:30. The amounts of the binder and the surfactant were 10 parts by mass and 0.5 parts by mass, respectively, with respect to 100 parts by mass of the total amount of NiO and BZY. The obtained granules were uniaxially molded to obtain a molded body of the first precursor layer (diameter: 200 mm, thickness: 0.6 mm).

By mixing BZY (BaZr _0.8 Y _0.2 O _2.9 ), a binder (ethyl cellulose), a surfactant (polycarboxylic acid-type surfactant), and an appropriate amount of butyl carbitol acetate, the first A paste of two precursor layers was prepared. The amounts of binder and surfactant were 6 parts by mass and 0.5 parts by mass, respectively, with respect to 100 parts by mass of BZY. The paste for the second precursor layer was applied to one surface of the compact by screen printing.

After forming the coating film, the molded body was heated at 750° C. for 10 hours to remove the binder. Next, the compact was fired at 1600° C. for 10 hours in an air atmosphere to obtain a laminate of the fuel electrode and the first solid electrolyte layer. The thickness of the second precursor layer (first solid electrolyte layer) after sintering was 5 μm.

Thereafter, BZY as a second solid electrolyte layer was deposited on the first solid electrolyte layer to a thickness of 5 μm by sputtering. The film formation temperature was 650°C. Thus, a fuel electrode-solid electrolyte layer composite member X1 was obtained.

(2) Reduction Treatment Subsequently, the fuel electrode-solid electrolyte layer composite member X1 was heated at 600° C. for 10 hours in a hydrogen atmosphere to reduce NiO contained in the fuel electrode to Ni. Thus, a fuel electrode-solid electrolyte layer composite was obtained.

(3) Fabrication of fuel cell Subsequently, LSCF (La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O _3-δ ) powder, which is the material of the air electrode, was applied to the surface of the second solid electrolyte layer. and an organic solvent (butyl carbitol acetate) were screen-printed and dried at 120° C. to form an air electrode. As a result, the cell structure shown in FIG. 2 was obtained.
The thickness of the air electrode was 10 μm.

A stainless steel anode-side separator having gas flow paths is laminated on the surface of the fuel electrode of the cell structure obtained above, and a stainless steel cathode-side separator having gas flow paths is laminated on the surface of the air electrode. were stacked to assemble the fuel cell Y1.
One end of the lead wire was joined to each of the anode-side separator and the cathode-side separator. The other end of each lead wire was pulled out of the fuel cell and connected to a measuring instrument so that the current value and voltage value between each lead wire could be measured.
(4) Evaluation The fuel cell was operated under operating conditions of 600°C. Hydrogen humidified to a dew point of 25 ° C. is supplied to the fuel electrode side at a flow rate of 1 L / min, and synthetic air (a mixture of only oxygen and nitrogen) having a dew point of −40 ° C. or less is supplied to the air electrode side at a flow rate of 1 L / min, OCV (open circuit voltage) was measured.

[Comparative Example 1]
NiO and BZY (BaZr _0.8 Y _0.2 O _2.9 ) powder are mixed in a ball mill with a binder (polyvinyl alcohol), a surfactant (polycarboxylic acid-type surfactant), and an appropriate amount of ethanol. and granulated. At this time, NiO and BZY were mixed at a volume ratio of 70:30. The amounts of the binder and the surfactant were 10 parts by mass and 0.5 parts by mass, respectively, with respect to 100 parts by mass of the total amount of NiO and BZY. The obtained granules were uniaxially molded to obtain a molded body of the first precursor layer (diameter: 200 mm, thickness: 0.6 mm). The compact was heated at 750° C. for 10 hours to remove the binder. Next, the molded body was fired at 1600° C. for 10 hours in an air atmosphere to obtain a sintered body of the fuel electrode.

Thereafter, BZY as a second solid electrolyte layer was deposited on the fuel electrode to a thickness of 10 μm by sputtering. The film formation temperature was 650°C. Thus, a fuel electrode-solid electrolyte layer composite member X2 was obtained.

Using the fuel electrode-solid electrolyte layer composite member X2, a fuel cell Y2 was produced in the same manner as in Example 1 and evaluated in the same manner.

[Comparative Example 2]
NiO and BZY (BaZr _0.8 Y _0.2 O _2.9 ) powder are mixed in a ball mill with a binder (polyvinyl alcohol), a surfactant (polycarboxylic acid-type surfactant), and an appropriate amount of ethanol. and granulated. At this time, NiO and BZY were mixed at a volume ratio of 70:30. The amounts of the binder and the surfactant were 10 parts by mass and 0.5 parts by mass, respectively, with respect to 100 parts by mass of the total amount of NiO and BZY. The obtained granules were uniaxially molded to obtain a molded body of the first precursor layer (diameter: 200 mm, thickness: 0.6 mm).

By mixing BZY (BaZr _0.8 Y _0.2 O _2.9 ), a binder (ethyl cellulose), a surfactant (polycarboxylic acid-type surfactant), and an appropriate amount of butyl carbitol acetate, the first A paste of two solid electrolyte layers was prepared. The amounts of binder and surfactant were 6 parts by mass and 0.5 parts by mass, respectively, with respect to 100 parts by mass of BZY. The paste was applied to one surface of the compact by screen printing.

After forming the coating film, the molded body was heated at 750° C. for 10 hours to remove the binder. Next, the molded body was fired at 1600° C. for 10 hours in an air atmosphere to obtain a sintered body of the fuel electrode and the second solid electrolyte layer. The thickness of the second solid electrolyte layer after sintering was 5 μm. Thus, a fuel electrode-solid electrolyte layer composite member X3 was obtained.

Using the fuel electrode-solid electrolyte layer composite member X3, a fuel cell Y3 was produced in the same manner as in Example 1 and evaluated in the same manner.

The fuel cell Y1 of Example 1 using the fuel electrode-solid electrolyte layer composite member X1 exhibited a high OCV of 1.05V. Further, when the fuel cell after evaluation was disassembled and the fuel electrode-solid electrolyte layer composite was taken out, cracks and peeling were not visually observed in the second solid electrolyte layer.

On the other hand, in the fuel cell Y2 of Comparative Example 1 using the fuel electrode-solid electrolyte layer composite member X2, the OCV was 0.3 V or less, and power generation was difficult. When the fuel cell after evaluation was disassembled and the fuel electrode-solid electrolyte layer composite was taken out, it was found that part of the second solid electrolyte layer was separated from the fuel electrode. Also, many cracks were visually observed in the second solid electrolyte layer.

Further, in the fuel cell Y3 of Comparative Example 2 using the fuel electrode-solid electrolyte layer composite member X3, the OCV was 0.96 V, which was lower than that of the fuel cell Y1 of Example 1. When the fuel cell after evaluation was disassembled and the fuel electrode-solid electrolyte layer composite was taken out, no cracks or peeling of the second solid electrolyte layer was visually observed. The reason why the OCV of the fuel cell Y3 is lower than that of the fuel cell Y1 is that the fuel electrode (first precursor layer) and the second solid electrolyte layer are co-sintered at a high temperature (1600° C.). part of the nickel contained in the diffusion into the second solid electrolyte layer, and the proton conductivity of the second solid electrolyte layer decreased.

The fuel electrode-solid electrolyte layer composite member and the fuel electrode-solid electrolyte layer composite according to the embodiments of the present disclosure are suitable for use in solid oxide fuel cells (SOFC), particularly in the medium temperature range of 400 ° C. to 600 ° C. Suitable for working SOFC.

1, 1Z: cell structure 2: air electrode 3: fuel electrode 4: solid electrolyte layer 4a: first solid electrolyte layer 4b: second solid electrolyte layer 5: fuel electrode-solid electrolyte layer composite 5Z: fuel electrode-solid Electrolyte layer composite member 6a: Fuel electrode 6b: First solid electrolyte layer 6c: Second solid electrolyte layer 10: Fuel cell 21, 51: Current collector 22, 52: Separator 23: Oxidant channel 53: Fuel channel

Claims (16)

a porous fuel electrode;
a first solid electrolyte layer formed on the fuel electrode;
a second solid electrolyte layer having a porosity smaller than that of the fuel electrode, the second solid electrolyte layer being laminated on the opposite side of the first solid electrolyte layer from the fuel electrode;
The first solid electrolyte layer includes a first solid electrolyte material and a composite oxide containing a nickel element and a metal element constituting the first solid electrolyte material,
the second solid electrolyte layer contains a second solid electrolyte material and does not substantially contain nickel element;
The fuel electrode is a fuel electrode-solid electrolyte layer composite including a third solid electrolyte material and metallic nickel. 2. The fuel electrode-solid electrolyte layer composite according to claim 1, wherein the nickel content in said first solid electrolyte layer is smaller than the nickel content in said fuel electrode. 3. The fuel electrode-solid electrolyte layer composite according to claim 1, wherein said first solid electrolyte layer does not substantially contain metallic nickel. 4. The fuel electrode-solid electrolyte layer composite according to claim 1, wherein said first solid electrolyte layer does not substantially contain nickel oxide. 5. The fuel electrode-solid electrolyte layer composite according to claim 1, wherein the second solid electrolyte layer has a thickness of 0.2 μm to 20 μm. At least one of the first solid electrolyte material, the second solid electrolyte material, and the third solid electrolyte material has a perovskite structure, and the following formula (1):
A _x B _1-y M _y O _3-δ
Including a metal oxide represented by
Element A is at least one selected from the group consisting of Ba, Ca and Sr,
Element B is at least one selected from the group consisting of Ce and Zr,
element M is at least one selected from the group consisting of Y, Yb, Er, Ho, Tm, Gd, In and Sc;
6. The fuel electrode-solid electrolyte layer composite according to any one of claims 1 to 5, wherein δ is the amount of oxygen deficiency and satisfies 0.95≤x≤1 and 0<y≤0.5. A fuel electrode-solid electrolyte layer composite according to any one of claims 1 to 6 and an air electrode, wherein the second solid electrolyte layer is interposed between the fuel electrode and the air electrode a cell structure that
an oxidant channel for supplying an oxidant to the air electrode; and
A fuel cell comprising: a fuel channel for supplying fuel to the fuel electrode. a fuel electrode, a first solid electrolyte layer, and a second solid electrolyte layer laminated on the first solid electrolyte layer side of a laminate of the fuel electrode and the first solid electrolyte layer,
The first solid electrolyte layer includes a first solid electrolyte material and a composite oxide containing a nickel element and a metal element constituting the first solid electrolyte material,
the second solid electrolyte layer contains a second solid electrolyte material and does not substantially contain nickel element;
The fuel electrode is a fuel electrode-solid electrolyte layer composite member containing a third solid electrolyte material and nickel oxide. 9. The method according to claim 8, wherein said first solid electrolyte layer does not substantially contain nickel oxide, or the content of nickel oxide in said first solid electrolyte layer is lower than the content of nickel oxide in said fuel electrode. fuel electrode-solid electrolyte layer composite member. 10. The fuel electrode-solid electrolyte layer composite member according to claim 9, wherein said first solid electrolyte layer does not substantially contain nickel oxide. At least one of the first solid electrolyte material, the second solid electrolyte material, and the third solid electrolyte material has a perovskite structure, and the following formula (2):
A _x B _1-y M _y O _3-δ
Including a metal oxide represented by
Element A is at least one selected from the group consisting of Ba, Ca and Sr,
Element B is at least one selected from the group consisting of Ce and Zr,
element M is at least one selected from the group consisting of Y, Yb, Er, Ho, Tm, Gd, In and Sc;
11. The fuel electrode-solid electrolyte layer composite member according to any one of claims 8 to 10, wherein δ is the amount of oxygen deficiency and satisfies 0.95≤x≤1 and 0<y≤0.5. A laminate of a fuel electrode containing nickel oxide (NiO), a first solid electrolyte material, and a first solid electrolyte layer containing a composite oxide of nickel and a metal element constituting the first solid electrolyte material a process of obtaining
A second solid electrolyte layer containing a second solid electrolyte material and substantially free of nickel element is formed on the first solid electrolyte layer side of the laminate at 850° C. or less, and the fuel electrode-solid electrolyte layer composite obtaining a member;
forming an air electrode on the second solid electrolyte layer side of the fuel electrode-solid electrolyte layer composite member to obtain a cell structure. 13. The method of manufacturing a fuel cell according to claim 12, further comprising a reduction treatment step of reducing nickel oxide contained in said fuel electrode to metallic nickel. 14. The fuel according to claim 12 or 13, wherein in the step of obtaining the laminate, the first solid electrolyte layer does not substantially contain nickel oxide or has a nickel oxide content lower than that of the fuel electrode. Battery manufacturing method. The step of obtaining the laminate includes
forming a second precursor layer containing the first solid electrolyte material on a first precursor layer containing the third solid electrolyte material and nickel oxide;
The first precursor layer and the second precursor layer are heat-treated at 1400° C. or higher, and the fuel electrode corresponding to the first precursor layer and the first solid electrolyte layer corresponding to the second precursor layer 15. The method of manufacturing a fuel cell according to any one of claims 12 to 14, comprising the step of obtaining 16. The method of manufacturing a fuel cell according to claim 15, wherein said second precursor layer does not substantially contain nickel element.

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