JP7719638B2 - Solid oxide electrochemical cell and its use - Google Patents

Description

This specification relates to solid oxide electrochemical cells and their uses.

Solid oxide electrochemical cells include solid oxide electrolysis cells (SOECs) and solid oxide fuel cells (SOFCs). It is known that the performance of these electrochemical cells is significantly affected not only by the properties of the electrode and electrolyte materials, but also by the resistive layer that can form at the interface between the electrode and electrolyte. It has been pointed out that in cells using a commonly used YSZ electrolyte and an LSCF ((LaSr)(CoFe)O _3-s ) oxygen electrode, highly resistive SrZrO ₃ is formed at the interface between the electrolyte and the oxygen electrode. For this reason, a ceria-based intermediate layer is introduced at the interface between the oxygen electrode and the electrolyte to prevent the reaction (Patent Document 1).

JP 2017-69214 A

However, even if an intermediate layer is introduced, highly resistive _SrZrO3 is formed at the interface between the intermediate layer and the electrolyte. Therefore, there is still a need to suppress the formation of a high-resistance layer in electrochemical cells.

This specification provides technology that can further suppress the formation of a high-resistance phase at the interface between the oxygen electrode and the electrolyte.

The present inventors investigated the reason why _SrZrO3 still forms even when a ceria-based interphase is present. As a result, they discovered that during heating, such as during cell firing, Sr diffuses from the oxygen electrode through the interphase, reaches the interface with the YSZ solid electrolyte, and reacts with Zr, which is highly reactive with Sr, to form _SrZrO3 . Therefore, the present inventors focused on Ti, which has a higher reactivity with Sr than Zr. They discovered that by preliminarily adding a Ti-based compound to the oxygen electrode, Ti can getter Sr to form _SrTiO3 during heating, etc., and thereby suppress the formation of _SrZrO3 at the YSZ interface. Based on these findings, this specification provides the following means.

[1] A solid oxide electrochemical cell,
an oxygen electrode containing titanium oxide and a strontium-containing composite oxide;
a solid electrolyte containing zirconium oxide;
A hydrogen electrode,
an intermediate layer containing rare earth-doped cerium oxide between the solid electrolyte and the oxygen electrode;
A cell comprising:
[2] The cell according to [1], wherein the strontium-containing composite oxide of the oxygen electrode is La1 _{- xSrxCoyFe1 -yO3 - σ} (0<x<1, 0<y≦1, and σ is a value determined so as to satisfy a charge neutrality condition).
[3] The cell according to [1] or [2], wherein the zirconium oxide of the solid electrolyte is rare earth-doped zirconium oxide.
[4] The cell according to any one of [1] to [3], wherein the rare earth-doped cerium oxide in the intermediate layer is at least one selected from the group consisting of gadolinium-doped cerium oxide, lanthanum-doped cerium oxide, samarium-doped cerium oxide, and yttrium-doped cerium oxide.
[5] The cell according to [2], wherein the zirconium oxide of the solid electrolyte is rare earth-doped zirconium oxide, and the rare earth-doped cerium oxide of the intermediate layer is gadolinium-doped cerium oxide.
[6] The cell according to any one of [1] to [5], wherein the oxygen electrode contains the titanium oxide in an amount effective to suppress thermal diffusion of strontium in the strontium-containing composite oxide relative to the strontium-containing composite oxide.
[7] The cell according to any one of [1] to [6], wherein the strontium-containing composite oxide of the oxygen electrode is La1 _{- xSrxCoyFe1 -yO3 - σ} (0<x<1, 0<y≦1, and σ is a value determined so as to satisfy a charge neutrality condition), and the oxygen electrode contains 8 mass % or less of the titanium oxide relative to the strontium-containing composite oxide.
[8] A solid oxide electrochemical device comprising the cell according to any one of [1] to [7].
[9] The solid oxide electrochemical device according to [8], which is a solid oxide fuel cell and/or a solid oxide electrolysis cell.
[10] An oxygen electrode material for a solid oxide electrochemical cell,
A material containing La1 _{- xSrxCoyFe1 -yO3 - σ} (0<x<1, 0<y≦1, and σ is a value determined so as to satisfy a charge neutrality condition), and titanium oxide in an amount of 1% by mass or more and 7% by mass or less relative to _{La1 - xSrxCoyFe1 -yO3 -σ} .
[11] The oxygen electrode material according to [10], which is a porous sintered body.
[12] A method for manufacturing a solid oxide electrochemical cell, comprising:
A method comprising the step of obtaining a cell comprising, in this order, an oxygen electrode layer containing titanium oxide and a strontium-containing composite oxide, an intermediate layer containing rare earth-doped cerium oxide, a solid electrolyte layer containing zirconium oxide, and a hydrogen electrode layer.

FIG. 1 is a diagram showing an outline of a laminate for an SOFC produced in Example 2. FIG. 10 shows the results of SEM/EDX (Sr, Co, Zr, Ti) analysis of a laminate for SOFC in which an LSCF containing TiO ₂ at various concentrations is used as the oxygen electrode. This figure shows the maximum power density at 700°C of SOFCs using LSCFs with various concentrations of _TiO2 added as the oxygen electrode. (A) shows the results for Production Examples 1 to 5 and Comparative Production Example 1, which include an intermediate layer (GDC), and (B) shows the results for Comparative Production Examples 2 to 6, which do not include an intermediate layer (GDC). This figure shows the maximum power density at 800°C of SOFCs using LSCFs with various concentrations of _TiO2 added as the oxygen electrode. (A) shows the results for Production Examples 1 to 5 and Comparative Production Example 1, which include an intermediate layer (GDC), and (B) shows the results for Comparative Production Examples 2 to 6, which do not include an intermediate layer (GDC).

The disclosure of this specification relates to solid oxide electrochemical cells and their uses.

The solid oxide electrochemical cell disclosed herein (hereinafter simply referred to as the cell) includes a ceria-based intermediate layer between an oxygen electrode and a solid electrolyte, and the oxygen electrode includes a composite oxide containing titanium oxide and at least strontium. Therefore, during heating, such as firing the oxygen electrode or co-firing the oxygen electrode, intermediate layer, and solid electrolyte, strontium in the oxygen electrode is gettered by titanium derived from the titanium oxide to form oxides such as _SrTiO3 , thereby suppressing thermal diffusion of strontium. As a result, the amount of strontium that thermally diffuses from the oxygen electrode through the intermediate layer to the solid electrolyte is reduced, and the formation of highly resistive _SrZrO3 at the interface between the solid electrolyte and the intermediate layer is suppressed.

By suppressing the formation of high-resistivity phases, efficient electrochemical reactions are achieved in both solid oxide electrolysis cells and solid oxide fuel cells.

Furthermore, the oxygen electrode material for solid oxide electrochemical cells disclosed in this specification can suppress the thermal diffusion of strontium, which causes the formation of a high-resistance phase even when an intermediate layer is provided. This makes it possible to suppress the formation of a high-resistance phase at the interface between the intermediate layer and the solid electrolyte.

Furthermore, the method for producing a solid oxide electrochemical cell disclosed in this specification includes a step of heating an oxygen electrode material layer containing titanium oxide and a strontium-containing composite oxide, and in this heating step, strontium reacts with titanium to produce _SrTiO3 . Therefore, in this heating step and also during other heating steps, strontium is prevented from migrating to the intermediate layer and solid electrolyte due to thermal diffusion. This makes it possible to prevent the formation of a high-resistance phase at the interface between the intermediate layer and the solid electrolyte layer.

In this specification, solid oxide electrochemical cells include solid oxide electrolysis cells (SOECs) and solid oxide fuel cells (SOFCs). Solid oxide electrochemical cells may be reversible between SOECs and SOFCs. In this specification, the term "oxygen electrode" refers to the electrode where oxygen is produced in SOECs, and the electrode (air electrode) to which oxygen (air) is supplied in SOFCs. Also, in this specification, the term "hydrogen electrode" refers to the electrode where water (water vapor) is supplied to produce hydrogen in SOECs, and the electrode (fuel electrode) to which hydrogen is supplied in SOFCs.

The following describes in detail embodiments of the solid oxide electrochemical cell, solid oxide electrochemical device, oxygen electrode material for the solid oxide electrochemical cell, and method for manufacturing the solid oxide electrochemical cell disclosed in this specification.

(Solid oxide electrochemical cell)
The solid oxide electrochemical cell can include an oxygen electrode, a solid electrolyte, a hydrogen electrode, and an intermediate layer disposed between the solid electrolyte and the oxygen electrode.

(oxygen electrode)
The oxygen electrode of the cell contains titanium oxide and a strontium-containing composite oxide. The strontium-containing composite oxide may be a composite oxide containing strontium and may be any known composite oxide used in SOECs and SOFCs. Examples of such composite oxides include compounds having a perovskite structure represented by the general formula _ABO3 . A contains at least Sr and is one or more elements selected from La and Ca, and B is one or more elements selected from Mn, Co, Fe, and Ni. More specifically, examples include a (La,Sr)(Co,Fe) _O3 -based composite oxide containing La (lanthanum), Sr (strontium), Co (cobalt), and Fe (iron) (hereinafter referred to as "LSCF"); a (La,Sr,Ca) _MnO3 -based composite oxide containing La, Sr, Ca, and Mn (hereinafter referred to as "LSCM"); a (La,Sr) _CoO3 -based composite oxide containing La, Sr, and Co (hereinafter referred to as "LSC"); a (La,Sr)MnO3- _based composite oxide containing La, Sr, and Mn (hereinafter referred to as "LSM"); and a (Sr,Sm) _CoO3 -based composite oxide containing Sr, Sm, and Co (hereinafter referred to as "SSC"). These can be used alone or in combination.

Among these, for example, (La,Sr)(Co,Fe) _O3 -based composite oxides, more specifically, La1 _{- xSrxCoyFe1 -yO3-σ (0<x<1, 0 < y} ≦1, and σ is a value determined to satisfy the charge neutrality condition) can be used. The values of x and y are not particularly limited, but x is, for example, 0.2 to 0.8, or for example, 0.3 to 0.7, or for example, 0.4. y is, for example, 0.05 to 0.65, or for example, 0.1 to 0.6, or for example, 0.2. Note that σ varies depending on the type of atom substituting a part of the perovskite structure, but in general, 0≦σ<1.

The oxygen electrode contains titanium oxide ( _TiO2 ). There are no particular limitations on the content of titanium oxide, and it is sufficient that the titanium oxide content is within a range that suppresses the thermal diffusion of the Sr-containing composite oxide used during heating, such as in the firing step during the production of a solid oxide electrochemical cell, i.e., an amount effective for suppressing thermal diffusion. The effective amount of titanium oxide can be easily determined by adding titanium oxide to the Sr-containing composite oxide to produce an SOEC or SOFC cell or a laminate that is a precursor thereof, which has a ceria-based intermediate layer between the oxygen electrode and the solid electrolyte, and then evaluating the thermal diffusion of Sr or evaluating the performance of the SOEC or SOFC.

The upper limit of the titanium oxide content is, for example, 15% by mass, 10% by mass, 9% by mass, 8% by mass, 7% by mass, 6% by mass, 5% by mass, or 4% by mass, based on the total amount of the Sr-containing composite oxide. The lower limit of the titanium oxide content is, for example, 0.1% by mass, 0.2% by mass, 0.4% by mass, 0.5% by mass, 0.6% by mass, 0.7% by mass, 0.8% by mass, 1% by mass, 1.2% by mass, 1.4% by mass, 1.6% by mass, 1.8% by mass, or 2% by mass, based on the total amount of the Sr-containing composite oxide. The range of titanium oxide content can be set to a suitable range for the cell element being used by selecting and combining any values from the upper and lower limits described above. For example, the range can be 0.5% by mass or more and 8% by mass or less, or 1% by mass or more and 7% by mass or less, or 2% by mass or more and 6% by mass or less, etc.

Such oxygen electrode materials can be synthesized by various known methods. For example, spray pyrolysis is a non-limiting example. Spray pyrolysis allows for control of shape and particle size, resulting in powder suitable for forming porous sintered bodies. For example, the average particle size of the oxygen electrode material powder is, for example, 20 μm or less, or, for example, 0.01 μm to 10 μm, or, for example, 0.05 μm to 10 μm, or, for example, 0.1 μm to 5 μm. The average particle size is measured using a particle size distribution analyzer based on laser scattering and diffraction, and refers to the particle size at 50% of the cumulative value in the volume-based particle size distribution.

The oxygen electrode can be obtained independently or as part of a cell by mixing these oxygen electrode materials and, if necessary, adding the solid electrolyte material described below. The mixture is molded, film-formed, or laminated using sintering aids and pore-forming agents, and then sintered. The thickness of the oxygen electrode can be determined appropriately depending on the cell structure, but is not particularly limited. For electrolyte-supported or hydrogen-electrode-supported cells, the thickness is, for example, 5 μm to 200 μm, or, for example, 20 μm to 50 μm. For oxygen-electrode-supported cells, the thickness is, for example, 0.5 mm to 2 mm. For metal-supported cells, the thickness is, for example, 5 μm to 200 μm. The heating temperature in the sintering process for sintering the oxygen electrode is, for example, 650°C to 1350°C, or, for example, 1000°C to 1250°C. The heat treatment time is, for example, 0.5 hours to 24 hours, or, for example, 1 hour to 5 hours. Other methods for manufacturing laminates for solid oxide electrochemical cells are well known to those skilled in the art, so further explanation will be omitted.

(solid electrolyte)
The solid electrolyte contains zirconium oxide. The zirconium oxide is not particularly limited, but examples thereof include stabilized or partially stabilized zirconium oxide. Metals doped to stabilize zirconium oxide are not particularly limited, but examples include calcium (calcium oxide), magnesium (magnesium oxide), and rare earth elements such as yttrium (yttrium oxide) and scandium (scandium oxide). The doping amount is not particularly limited, but can be 6 mol % to 10 mol % of the metal oxide relative to the zirconia.

The solid electrolyte is provided as a dense sintered body. It can be obtained by molding, film-forming, and laminating zirconium oxide, followed by firing and sintering. The thickness of the solid electrolyte can be determined appropriately depending on the cell structure, etc., and is not particularly limited. For solid electrolyte-supported cells, the thickness is, for example, 0.1 mm to 1 mm. For oxygen electrode-supported cells or hydrogen electrode-supported cells, the thickness is, for example, 0.5 μm to 100 μm. The heating temperature and time in the firing process for sintering the solid electrolyte are, for example, 700°C to 1500°C, or, for example, 1200°C to 1450°C. The heat treatment time is, for example, 0.5 hours to 24 hours, or, for example, 1 hour to 6 hours. Other methods for manufacturing laminates for solid oxide electrochemical cells are well known to those skilled in the art, so further explanation is omitted.

(hydrogen electrode)
The hydrogen electrode contains materials conventionally known as hydrogen electrode materials for solid oxide electrochemical cells. Examples include metal oxides composed of one or more metals and/or metal elements, such as nickel (Ni), copper (Cu), gold (Au), platinum (Pt), palladium (Pd), ruthenium (Ru) and other platinum group elements, cobalt (Co), lanthanum (La), strontium (Sr), and titanium (Ti). These may be used singly or in combination. In addition to these catalytic metal oxides, a solid electrolyte material, such as stabilized or partially stabilized zirconia or rare-earth-doped ceria, may be mixed. While not particularly limited, the mass ratio of metal oxide to solid electrolyte may be, for example, 5/5 to 8/2. During operation as an SOEC or SOFC, the metal oxide is reduced to a metal at the hydrogen electrode.

The hydrogen electrode is provided as a porous sintered body. The hydrogen electrode can be obtained by mixing these hydrogen electrode materials, molding, film-forming, or laminating them using sintering aids and pore-forming agents, as necessary, and then sintering. The thickness of the hydrogen electrode can be determined appropriately depending on the cell structure, etc., and is not particularly limited. However, in the case of a solid electrolyte-supported cell or an oxygen electrode-supported cell, the thickness is, for example, 5 μm to 200 μm, or, for example, 20 μm to 50 μm, taking into account durability, thermal expansion coefficient, etc. Furthermore, in the case of a hydrogen electrode-supported cell, the thickness is, for example, 0.5 mm to 2 mm. The heating temperature and time in the sintering process for sintering the hydrogen electrode are the same as those for the solid electrolyte. Furthermore, methods for manufacturing laminates for solid oxide electrochemical cells are well known to those skilled in the art, so further explanation is omitted.

The cell may include an intermediate layer between the solid electrolyte and the oxygen electrode. The solid electrolyte may contain, for example, rare-earth-doped cerium oxide. Examples of rare-earth cerium oxides include, but are not limited to, gadolinium-doped cerium oxide (GDC), lanthanum-doped cerium oxide (LDC), samarium-doped cerium oxide (SDC), and yttrium-doped cerium oxide (YDC). These cerium oxides may be used alone or in combination.

The intermediate layer is provided as a dense sintered body or a porous sintered body. The intermediate layer can be obtained by molding rare earth cerium oxide, optionally with a sintering aid, or by forming or laminating it on the solid electrolyte and then firing it. The thickness of the intermediate layer can be determined appropriately depending on the cell structure, etc., and is not particularly limited. However, taking into account durability, thermal expansion coefficient, etc., it is, for example, 100 μm or less, or, for example, 1 μm to 50 μm, or, for example, 1 μm to 30 μm, or, for example, 1 μm to 20 μm. The heating temperature and time in the firing process for sintering the intermediate layer are the same as those for the hydrogen electrode, etc., and other methods for manufacturing laminates for solid oxide electrochemical cells are well known to those skilled in the art, so further explanation is omitted.

A typical embodiment of the cell is, for example, an oxygen electrode such as LSCF, LSCM, LSC, LSM, or SSC, a solid electrolyte such as rare earth-doped zirconium oxide such as YSZ, and an intermediate layer such as GDC.

These cells can take various forms, such as cylindrical or flat, depending on the intended form of the SOEC or SOFC. Typically, cells are stacked in multiple layers with known separators between them, and then various gas flow paths, current collectors, cooling devices, etc. are added to form the SOEC or SOFC.

(Oxygen electrode material for solid oxide electrochemical cells)
According to the present specification, a material containing titanium oxide and a strontium-containing composite oxide is provided as an oxygen electrode material for a solid oxide electrochemical cell. More specifically, this oxygen electrode material contains a perovskite-type Sr-containing composite oxide such as La1 _{- xSrxCoyFe1 -yO3 - σ} (0<x<1, 0<y≦1, and σ is a value determined so as to satisfy the charge neutrality condition), and titanium oxide. Furthermore, this material can contain, for example, 1% by mass or more and 7% by mass or less of titanium oxide relative to the perovskite-type Sr-containing composite oxide such as LSCF.

The oxygen electrode material is a composition containing titanium oxide and a strontium-containing composite oxide, and can take the form of a mixed powder of these. The oxygen electrode material can also take the form of a slurry for screen-printing this mixed powder onto a solid electrolyte or the like. The slurry can contain an appropriate solvent, sintering aid, and pore-forming material. Furthermore, the oxygen electrode material can also take the form of a thin film or an unsintered compact. Furthermore, the oxygen electrode material itself can take the form of a porous sintered body.

(Method for manufacturing a solid oxide electrochemical cell)
According to the present specification, there is provided a method comprising the step of obtaining a cell including an oxygen electrode containing titanium oxide and a strontium-containing composite oxide, an intermediate layer containing rare-earth-doped cerium oxide, a solid electrolyte containing zirconium oxide, and a hydrogen electrode. In this method, by obtaining a cell including an oxygen electrode and an intermediate layer having a predetermined composition, it is possible to suppress the generation of a high-resistance phase between the solid electrolyte and the intermediate layer due to thermal diffusion of Sr during one or more firing steps such as sintering in this obtaining step.

There are no particular limitations on the order in which the oxygen electrode, intermediate layer, solid electrolyte, and hydrogen electrode are stacked, or on the preparation of each layer, and the cell can be obtained using known methods for manufacturing solid electrolyte electrochemical cells.

This specification also provides a method for manufacturing an SOEC or SOFC, or a system including these, by applying a separator to one or more such cells, and further applying gas flow paths for hydrogen, oxygen, or water vapor, electrodes, and current collectors. Those skilled in the art can appropriately add these elements to a single cell to create an SOEC or SOFC, and then construct a system.

(Solid oxide electrochemical device)
According to the present specification, there is provided an electrochemical device including the solid oxide electrochemical cell disclosed herein. The cell suppresses thermal diffusion of Sr due to heating at least during cell fabrication or stack fabrication, thereby suppressing the formation of a high-resistivity phase between the solid electrolyte and the intermediate layer. This enables the device to operate efficiently as an electrochemical device. The device typically includes a stack of two or more cells stacked with a separator interposed therebetween. Examples of such devices include SOECs and SOFCs.

The following examples are provided as specific examples to more specifically explain the disclosure of this specification. The following examples are intended to illustrate the disclosure of this specification and are not intended to limit its scope.

(Preparation of raw material powder for cell elements)
The raw material powders for the oxygen electrode and the hydrogen electrode were synthesized as follows: GDC( _Ce0.8Gd0.2 )O2 _-x (Shin-Etsu Chemical Co., _Ltd. ) was prepared as the raw material powder for the intermediate layer, and _TiO2 (Wako Pure Chemical Industries, Ltd.) was prepared as the other raw material powder for the oxygen electrode.

(Synthesis of raw material powders for oxygen electrode and hydrogen electrode)
The raw material powders for the oxygen electrode and the hydrogen electrode were prepared by spray pyrolysis.

(Oxygen electrode raw material powder)
The oxygen electrode raw material powder was synthesized by spray pyrolysis using _{( La0.6Sr0.4} ) _{( Co0.2Fe0.8} )O3 _-x . A raw material solution was prepared using lanthanum nitrate hexahydrate, strontium nitrate, cobalt nitrate hexahydrate, and iron nitrate nonahydrate in ion-exchanged water so that the lanthanum, strontium, cobalt, and iron compositions were as described above. The total molar concentration of this raw material solution was 0.4 mol/L. This raw material solution was subjected to spray pyrolysis under the following conditions to obtain the target raw material powder.

<Spray pyrolysis conditions>
Spray pyrolysis was performed using a spray pyrolysis apparatus (manufactured by ON General Electric Co., Ltd.). This apparatus consists of a polyvinyl chloride resin atomizer, an alumina reaction tube (inner diameter 20 mmφ, outer diameter 25 mmφ, length 1500 mm), and a glass collector. The reaction tube is equipped with four independent heating furnaces (Kanthal heaters). A membrane filter (142 mmφ, pore size: 0.45 μm, Omnipore JHWP14225) is installed inside the collector to collect the synthesized particles.

The spray pyrolysis synthesis conditions were as follows: the reaction tube temperatures, from the side closest to the atomizer, were 200°C, 400°C, 800°C, and 1000°C; to prevent condensation, the collector was kept at 100°C using a mantle heater. The ultrasonic atomizer water bath temperature was 30°C, and the solution container temperature was 27°C. The carrier gas flow rate during synthesis was 3.0 L/min. Air was used as the carrier gas.

(Hydrogen electrode raw material powder)
NiO-YSZ (ZrO2 - 8 _mol % _Y2O3 ) ₍ NiO:YSZ = 6:4 (mass ratio)) was synthesized as the hydrogen electrode raw material powder by spray pyrolysis. A raw material solution was prepared using nickel acetate tetrahydrate, yttrium nitrate n-hydrate, zirconium nitrate dihydrate, and ion-exchanged water to achieve the above composition of nickel, yttrium, and zirconium. The total molar concentration of this raw material solution was 0.45 mol/L. This raw material solution was subjected to spray pyrolysis under the same conditions as above to obtain the target raw material powder.

(Production of a laminate for a single cell of a solid oxide fuel cell)
The raw material powders other than the oxygen electrode prepared in Example 1 were mixed with polyethylene glycol (degree of polymerization 400) in a mass ratio of 3:1 to prepare a slurry for _the hydrogen electrode and a slurry for the intermediate layer, respectively. For the oxygen electrode slurry, _TiO2 was mixed with ( _La0.6Sr0.4 ) _{( Co0.2Fe0.8} )O3 _-x so that the TiO2 contents were 0 mass%, 0.5 mass%, 1 mass%, 2 mass%, 5 mass%, and 10 mass%, and multiple slurries with different _TiO2 contents were prepared in the same manner as above.

The single cell laminate fabricated in this example is shown in Figure 1. The single cell was fabricated by _screen -printing a GDC intermediate layer slurry onto one side of a solid electrolyte disk (8YSZ ( _ZrO2-8 mol% _Y2O3 ), diameter 14 mm, thickness 200 μm, manufactured by Tosoh Corporation) so that the resulting diameter would be 9 mm and the resulting thickness would be 5 μm after firing. A hydrogen electrode slurry was screen-printed onto the other side so that the resulting diameter would be 6 mm and the resulting thickness would be 20 μm after firing, followed by firing in air at 1400°C for 2 hours. Furthermore, a oxygen electrode slurry was screen-printed onto the fired intermediate layer so that the resulting diameter would be 6 mm and the resulting thickness would be 20 μm after firing, followed by firing in air at 1150°C for 2 hours. In this way, six laminates of Production Examples 1 to 5 were prepared, each having an oxygen electrode derived from five slurries with different _TiO2 blending amounts (0.5 mass%, 1 mass%, 2 mass%, 5 mass%, and 10 mass%) as the oxygen electrode slurry, and a laminate of Comparative Production Example 1 was prepared, each having an oxygen electrode derived from a slurry that did not contain _TiO2 (0 mass%).

(Scanning electron microscope (SEM)/energy dispersive X-ray fluorescence analysis (EDX) of a cross section of a single cell)
For each of the laminates prepared in Example 2, cross sections in the lamination direction were observed using an SEM (HITACHI SU8000) at an accelerating voltage of 15 kV and a magnification of 5,000 to 10,000 times, and the distribution of elements (Sr, Co, Zr, Ti) in the cross sections was analyzed using an EDX (HORIBA X-max80). The results are shown in Figure 2.

Figure 2 shows SEM and EDX images of Comparative Production Example 1, followed by Production Examples 3 to 5 from the top. As shown in Figure 2, as the _TiO2 content increased, the amount of Sr at the interface between the intermediate layer (GDC) and the solid electrolyte (YSZ) decreased. In contrast, Co and Zr were retained in their respective layers, regardless of the _TiO2 content. Furthermore, Ti was present in the oxygen electrode (LCSF) as the _TiO2 content increased.

From the above, it was found that adding _TiO2 to the oxygen electrode (LSCF) clearly reduces the amount of Sr present between the solid electrolyte (YSZ) and the intermediate layer, i.e., reduces _SrZrO3 . Furthermore, the fact that Sr, Ti, and O were detected at the same location strongly suggests that Sr and Ti reacted to form _SrTiO3 in the oxygen electrode (LSCF).

(Evaluation of power generation characteristics of stack in SOFC mode)
The stack prepared in Example 2 was used as a single SOFC cell, and the maximum power density was measured at operating temperatures of 700°C and 800°C, with air supplied to the cathode side at 50 ^cm³ /min and H₂- ₃ % _H₂O supplied to the anode side at 50 ^cm³ /min. The maximum power density was also measured for Comparative Production Examples _{2 to} 6, which were prepared in the same manner as in Production Example 1, except that no intermediate layer was formed and the anode contained TiO₂ at concentrations of 0 mass%, 0.1 mass%, 0.25 mass%, 0.5 mass%, and 1.0 mass%. The results are shown in Figures 3 and 4.

Figure 3 shows the results at an operating temperature of 700°C. Figure 3(A) shows all Production Examples and Comparative Production Examples on the same scale, while Figure 3(B) shows only Comparative Production Examples 2 to 6 on an enlarged scale. As shown in Figure 3, among Production Examples 1 to 5 in which _TiO2 was added, Production Examples 1 to 4 showed a higher maximum power density than Comparative Production Example 1, which did not contain _TiO2 . Furthermore, Comparative Production Examples 2 to 6, which were SOFCs without an intermediate layer, showed significantly lower maximum power density, indicating that adding _TiO2 to the oxygen electrode (LSCF) had almost no effect.

Figure 4 shows the results at an operating temperature of 800°C. Figure 4(A) shows all Production Examples and Comparative Production Examples on the same scale, while Figure 4(B) shows only Comparative Production Examples 2 to 6 on an enlarged scale. As shown in Figure 4, among Production Examples 1 to 5 in which _TiO2 was added, Production Examples 1 to 4 showed a higher maximum power density than Comparative Production Example 1, which did not contain _TiO2 , as in the case of an operating temperature of 700°C. Furthermore, Comparative Production Examples 2 to 6, which were SOFCs without an intermediate layer, showed significantly lower maximum power density, indicating that adding _TiO2 to the oxygen electrode (LSCF) had almost no effect.

From the above, it was found that by adding _TiO2 to an oxygen electrode made of a composite oxide containing thermally diffusible Sr, it is possible to suppress the formation of _SrZrO3 between the solid electrolyte (YSZ) and the intermediate layer, and thereby improve the power generation characteristics in SOFC mode.

Furthermore, this shows that even when this cell is used as an SOEC, it is possible to suppress the formation of high-resistance phases and improve electrolysis efficiency.

Claims (13)

1. A solid oxide electrochemical cell comprising:
an oxygen electrode containing titanium oxide and a strontium-containing composite oxide;
a solid electrolyte containing zirconium oxide;
A hydrogen electrode,
an intermediate layer including rare earth-doped cerium oxide disposed between the solid electrolyte and the oxygen electrode;
Equipped with
the oxygen electrode includes the titanium oxide so as to suppress thermal diffusion of Sr in the strontium-containing composite oxide at the oxygen electrode and to suppress formation of a high-resistance phase;
The strontium-containing composite oxide is a compound having a perovskite structure represented by the general formula ABO3 ₍ A contains at least Sr and represents one or more elements selected from La and Ca, and B represents one or more elements selected from Mn, Co, Fe, and Ni), and the cell contains the titanium oxide in an amount of 0.5% by mass or more and 8% by mass or less with respect to the total amount of the strontium-containing composite oxide . 2. The cell according to claim 1, wherein the titanium oxide is contained in an amount of 1.0 mass % to 5.0 mass % based on the total amount of the strontium-containing composite oxide. 3. The cell according to claim 1, wherein diffusion of Sr into the solid electrolyte and/or the intermediate layer is suppressed, and/or SrTiO3 is formed in the oxygen _electrode . The cell according to any one of claims 1 to 3, wherein the oxygen electrode does not have titanium oxide distributed at a higher concentration near a surface opposite to a surface facing the solid electrolyte in a thickness direction of the oxygen electrode. The cell according to any one of claims 1 to 4, wherein the strontium-containing composite oxide is La1-xSrxCoyFe1 _{- yO3 - σ (} 0.2≦x≦0.8, 0.05≦y≦0.65, and σ is a value determined so as to satisfy a charge neutrality condition). 6. The cell according to claim 1 , wherein the zirconium oxide of the solid electrolyte is rare earth-doped zirconium oxide. The cell according to any one of claims 1 to 6, wherein the rare earth-doped cerium oxide of the intermediate layer is at least one selected from the group consisting of gadolinium-doped cerium oxide, lanthanum-doped cerium oxide, samarium-doped cerium oxide, and yttrium-doped cerium oxide. 8. The cell according to claim 1, wherein the zirconium oxide of the solid electrolyte is rare earth-doped zirconium oxide, and the rare earth-doped cerium oxide of the intermediate layer is gadolinium-doped cerium oxide. A solid oxide electrochemical device comprising the cell described in any one of claims 1 to 8. 10. The solid oxide electrochemical device according to claim 9 , which is a solid oxide fuel cell and/or a solid oxide electrolysis cell. 1. A method for manufacturing a solid oxide electrochemical cell, comprising:
obtaining the solid oxide electrochemical cell comprising, in this order: an oxygen electrode containing titanium oxide and a strontium-containing composite oxide; a solid electrolyte containing zirconium oxide; a hydrogen electrode; and an intermediate layer containing rare earth-doped cerium oxide and disposed between the solid electrolyte and the oxygen electrode;
The strontium-containing composite oxide is a compound having a perovskite structure represented by the general formula ABO3 ₍ A contains at least Sr and represents one or more elements selected from La and Ca, and B represents one or more elements selected from Mn, Co, Fe, and Ni),
The method, wherein the step of obtaining the solid oxide electrochemical cell includes firing the strontium-containing composite oxide so as to suppress thermal diffusion of Sr in the strontium-containing composite oxide into the solid electrolyte and/or the intermediate layer . The step of obtaining the solid oxide electrochemical cell includes: ₃ The method of claim 11 , comprising forming: 1. A method for inhibiting the formation of a high-resistivity phase in a solid oxide electrochemical cell, comprising:
the solid oxide electrochemical cell comprises, in this order, an oxygen electrode containing titanium oxide and a strontium-containing composite oxide, a solid electrolyte containing zirconium oxide, a hydrogen electrode, and an intermediate layer containing rare earth-doped cerium oxide and disposed between the solid electrolyte and the oxygen electrode;
The strontium-containing composite oxide is a compound having a perovskite structure represented by the general formula ABO3 ₍ A contains at least Sr and represents one or more elements selected from La and Ca, and B represents one or more elements selected from Mn, Co, Fe, and Ni),
and/or sintering the cathode to inhibit thermal diffusion of Sr into the intermediate layer and/or the solid electrolyte and/or to form _SrTiO3 in the cathode.