Solid oxide electrochemical cell and its use

Abstract

To provide a solid oxide electrochemical cell in which no high-resistance layer is formed at the interface between an electrolyte membrane and an oxygen electrode.SOLUTION: A solid oxide electrochemical cell includes 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-added cerium oxide between the solid electrolyte and the oxygen electrode, and the strontium-containing composite oxide of the oxygen electrode is La1-xSrxCoyFe1-yO3-σ(0<x<1, 0<y≤1, σ is a value that satisfies the charge neutrality condition.)SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present specification relates to a solid oxide electrochemical cell and its uses. [Background technology]

[0002] Solid oxide electrochemical cells include solid oxide electrolysis cells (SOECs) and solid oxide fuel cells (SOFCs). The performance of these electrochemical cells is known to be 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. The commonly used YSZ electrolyte and LSCF ((LaSr)(CoFe)O 3-s It has been pointed out that in cells using an oxygen electrode, highly resistive SrZrO3 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 this reaction (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-69214 Summary of the Invention [Problem to be solved by the invention]

[0004] However, even with the introduction of the intermediate layer, highly resistive SrZrO3 was formed at the interface between the intermediate layer and the electrolyte. Therefore, there is still a need to prevent the formation of this high-resistance layer in electrochemical cells.

[0005] The present specification provides a technology that can further suppress the formation of a high-resistance phase at the interface between the oxygen electrode and the electrolyte. [Means for solving the problem]

[0006] The inventors of the present invention examined the reason why SrZrO3 is still formed even when a ceria-based intermediate phase is arranged. As a result, it was found that during heating such as cell firing, Sr diffuses from the oxygen electrode through the intermediate phase, reaches the interface with YSZ which is a solid electrolyte, and reacts with Zr which is highly reactive with itself to form SrZrO3. Therefore, the inventors of the present invention focused on Ti whose reactivity with Sr is higher than that of Zr. And by previously causing a Ti-based compound to be present in the oxygen electrode, it was found that Ti can getter Sr to form SrTiO3 during heating or the like, and thereby the formation of SrZrO3 at the YSZ interface can be suppressed. This specification provides the following means based on these findings.

[0007] [1] A solid oxide fuel cell comprising: 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-added cerium oxide between the solid electrolyte and the oxygen electrode. A cell comprising the above. [2] The strontium-containing composite oxide of the oxygen electrode is La 1-x Sr x Co y Fe 1-y O 3-σ (0 < x < 1, 0 < y ≤ 1, and σ is a value determined so as to satisfy the charge neutrality condition.). The cell according to [1]. [3] The zirconium oxide of the solid electrolyte is rare earth-added zirconium oxide. The cell according to [1] or [2]. [4] The rare earth-added cerium oxide of the intermediate layer is at least one selected from the group consisting of gadolinium-added cerium oxide, lanthanum-added cerium oxide, samarium-added cerium oxide, and yttrium-added cerium oxide. The cell according to any one of [1] to [3]. [5] The zirconium oxide of the solid electrolyte is rare earth-added zirconium oxide, and the rare earth-added cerium oxide of the intermediate layer is gadolinium-added cerium oxide. The cell according to [2]. [6] The oxygen electrode of the cell according to any one of [1] to [5] contains the titanium oxide in an effective amount capable of suppressing the thermal diffusion of strontium in the strontium-containing composite oxide in the strontium-containing composite oxide. [7] The strontium-containing composite oxide of the oxygen electrode is La 1-x Sr x Co y Fe 1-y O 3-σ (where 0 < x < 1, 0 < y ≤ 1, and σ is a value determined to satisfy the charge neutrality condition), and the oxygen electrode contains 8% by mass or less of the titanium oxide with respect to the strontium-containing composite oxide. The cell according to any one of [1] to [6]. [8] A solid oxide type electrochemical device comprising the cell according to any one of [1] to [7]. [9] The solid oxide type 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 type electrochemical cell, La 1-x Sr x Co y Fe 1-y O 3-σ (where 0 < x < 1, 0 < y ≤ 1, and σ is a value determined to satisfy the charge neutrality condition), and 1% to 7% by mass of titanium oxide with respect to La 1-x Sr x Co y Fe 1-y O 3-σ And a material containing titanium oxide.

[11] The oxygen electrode material according to

[10] , which is a porous sintered body.

[12] A method for manufacturing a solid oxide type electrochemical cell, A step of obtaining a cell including an oxygen electrode layer containing titanium oxide and a strontium-containing composite oxide, an intermediate layer containing rare earth-added cerium oxide, a solid electrolyte layer containing zirconium oxide, and a hydrogen electrode layer in this order.

Brief Description of the Drawings

[0008] [Figure 1] FIG. 1 is a diagram showing an outline of a laminate for SOFC produced in Example 2. [Figure 2] FIG. 1 shows the results of SEM / EDX (Sr, Co, Zr, Ti) analysis of SOFC laminates in which LSCFs containing TiO2 at various concentrations are used as the oxygen electrode. [Figure 3] 1 shows the maximum power density at 700°C of SOFCs using LSCFs with TiO added at various concentrations as the oxygen electrode, where (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). [Figure 4] 1 shows the maximum power density at 800°C of SOFCs using LSCFs with TiO added at various concentrations as the oxygen electrode, where (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). DETAILED DESCRIPTION OF THE INVENTION

[0009] The disclosure of the present specification relates to a solid oxide electrochemical cell and its uses.

[0010] 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 contains 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.

[0011] By suppressing the formation of a high-resistivity phase, efficient electrochemical reactions are achieved in both the solid oxide electrolysis cell and the solid oxide fuel cell.

[0012] Furthermore, the oxygen electrode material for a solid oxide electrochemical cell disclosed herein can suppress the thermal diffusion of strontium, which causes the formation of a high-resistance phase even when an intermediate layer is provided, thereby suppressing the formation of a high-resistance phase at the interface between the intermediate layer and the solid electrolyte.

[0013] Furthermore, the method for manufacturing a solid oxide electrochemical cell disclosed herein includes a step of heating an oxygen electrode material layer containing titanium oxide and a strontium-containing composite oxide. During this heating step, strontium reacts with titanium to produce SrTiO. Therefore, during this heating step and other heating steps, strontium is prevented from migrating to the intermediate layer and solid electrolyte due to thermal diffusion. This prevents the formation of a high-resistance phase at the interface between the intermediate layer and the solid electrolyte layer.

[0014] 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 oxygen electrode means the electrode where oxygen is produced in SOECs, and the electrode (air electrode) where oxygen (air) is supplied in SOFCs. In addition, in this specification, the hydrogen electrode means the electrode where water (water vapor) is supplied to produce hydrogen in SOECs, and the electrode (fuel electrode) where hydrogen is supplied in SOFCs.

[0015] Hereinafter, 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 will be described in detail.

[0016] (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.

[0017] (oxygen electrode) The oxygen electrode in 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 (La,Sr)(Co,Fe)O-based composite oxides containing La (lanthanum), Sr (strontium), Co (cobalt), and Fe (iron) (hereinafter referred to as "LSCF"); (La,Sr,Ca)MnO-based composite oxides containing La, Sr, Ca, and Mn (hereinafter referred to as "LSCM"); (La,Sr)CoO-based composite oxides containing La, Sr, and Co (hereinafter referred to as "LSC"); (La,Sr)MnO-based composite oxides containing La, Sr, and Mn (hereinafter referred to as "LSM"); and (Sr,Sm)CoO-based composite oxides containing Sr, Sm, and Co (hereinafter referred to as "SSC"). These can be used alone or in combination.

[0018] Among these, for example, (La,Sr)(Co,Fe)O3-based composite oxides, more specifically, La 1-x Sr x Co y Fe 1-y O 3-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. For example, x is, for example, 0.2 to 0.8, and for example, 0.3 to 0.7, and for example, 0.4. y is, for example, 0.05 to 0.65, and for example, 0.1 to 0.6, and for example, 0.2. Note that σ varies depending on the type of atom replacing a part of the perovskite structure, etc. Generally speaking, 0 ≤ σ < 1.

[0019] The oxygen electrode contains titanium oxide (TiO₂). The content of titanium oxide is not particularly limited, and as long as it contains an effective amount to suppress its thermal diffusion during heating such as in the firing process when manufacturing the solid oxide form electrochemical cell using the Sr-containing composite oxide, that is sufficient. The effective amount of titanium oxide can be easily determined by adding titanium oxide to the Sr-containing composite oxide, manufacturing a SOEC or SOFC cell or a laminate which is its precursor having a ceria-based intermediate layer between the oxygen electrode and the solid electrolyte, and evaluating the thermal diffusion of Sr or evaluating the performance of SOEC or SOFC.

[0020] The upper limit of the titanium oxide content is, for example, 15 mass%, 10 mass%, 9 mass%, 8 mass%, 7 mass%, 6 mass%, 5 mass%, or 4 mass%, relative to the total amount of the Sr-containing composite oxide. The lower limit of the titanium oxide content is, for example, 0.1 mass%, 0.2 mass%, 0.4 mass%, 0.5 mass%, 0.6 mass%, 0.7 mass%, 0.8 mass%, 1 mass%, 1.2 mass%, 1.4 mass%, 1.6 mass%, 1.8 mass%, or 2 mass%, relative to 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 to be 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.

[0021] Such an oxygen electrode material can be synthesized by various known methods. For example, it can be synthesized by spray pyrolysis, although this is not a limitation. Spray pyrolysis allows for control of the shape and particle size, making it possible to obtain powder suitable for forming a porous sintered body. Although not a limitation, 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 refers to the particle size measured by a particle size distribution analyzer based on the laser scattering / diffraction method, and is the particle size at 50% of the cumulative value in the volume-based particle size distribution.

[0022] The oxygen electrode can be obtained independently or as part of a cell by mixing these oxygen electrode materials and, if necessary, adding a solid electrolyte material described below, and further molding, forming a film, or laminating the mixture using a sintering aid, a pore-forming agent, etc., and then firing the mixture. The thickness of the oxygen electrode can be determined appropriately depending on the cell structure, etc., and is not particularly limited. For electrolyte-supported cells 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 firing step 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, and therefore, further explanation will be omitted.

[0023] (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. The metal doped to stabilize the zirconium oxide is not particularly limited, but examples thereof 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.

[0024] 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 and other factors, but 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 step 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.

[0025] (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 metal elements, such as nickel (Ni), copper (Cu), gold (Au), platinum (Pt), palladium (Pd), ruthenium (Ru), other platinum group elements, cobalt (Co), lanthanum (La), strontium (Sr), and titanium (Ti). These metal oxides can 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, can be mixed. The mass ratio of metal oxide to solid electrolyte can 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.

[0026] 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, pore-forming materials, etc., as needed, and then firing them. The thickness of the hydrogen electrode can be determined appropriately depending on the cell structure and other factors, 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, in terms of 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 firing step for sintering the hydrogen electrode are the same as those for the solid electrolyte. Methods for manufacturing laminates for solid oxide electrochemical cells are well known to those skilled in the art, so further explanation is omitted.

[0027] The cell may include an intermediate layer between the solid electrolyte and the oxygen electrode. The solid electrolyte may include, 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.

[0028] 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 a solid electrolyte, followed by firing. The thickness of the intermediate layer is not particularly limited and can be determined appropriately depending on the cell structure, etc., but 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, depending on durability, thermal expansion coefficient, etc. The heating temperature and time in the firing step 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 a detailed description will be omitted.

[0029] Typical embodiments of the cell include, for example, an oxygen electrode made of LSCF, LSCM, LSC, LSM, SSC, etc., a solid electrolyte made of rare earth-doped zirconium oxide such as YSZ, and an intermediate layer made of GDC.

[0030] Such cells can take various forms according to the intended form of SOEC or SOFC, such as cylindrical or flat plate. Usually, the cells are stacked in multiple layers through a known separator, and further equipped with various gas flow paths, current collectors, cooling devices, etc. to constitute SOEC or SOFC.

[0031] (Oxygen electrode material of solid oxide type electrochemical cell) According to the present specification, a material containing titanium oxide and a strontium-containing composite oxide is provided as an oxygen electrode material of a solid oxide type electrochemical cell. More specifically, this oxygen electrode material contains a perovskite-type Sr-containing composite oxide such as La 1-x Sr x Co y Fe 1-y O 3-σ (where 0 < x < 1, 0 < y ≤ 1, and σ is a value determined to satisfy the charge neutrality condition.) and titanium oxide. Further, in this material, for example, it can contain 1 mass% or more and 7 mass% or less of titanium oxide with respect to the perovskite-type Sr-containing composite oxide such as LSCF.

[0032] The oxygen electrode material is a composition containing titanium oxide and a strontium-containing composite oxide, and as a form, it can take the form of a mixed powder of these. Also, the oxygen electrode material can take the form of a slurry for screen printing such mixed powder onto a solid electrolyte or the like. The slurry can contain a suitable solvent, sintering aid, pore-forming agent. Further, the oxygen electrode material can also take the form of a thin film or an unsintered molded body. Furthermore, the oxygen electrode material can also take the form of a porous sintered body itself.

[0033] (Manufacturing method of solid oxide type 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.

[0034] The order in which the oxygen electrode, intermediate layer, solid electrolyte, and hydrogen electrode are stacked and the preparation of each layer are not particularly limited, and the cell can be obtained according to a known method for manufacturing a solid electrolyte electrochemical cell.

[0035] This specification also provides a method for producing an SOEC or SOFC and a system including the same by applying a separator to one or more of the cells and further applying a gas flow path for hydrogen, oxygen, or water vapor, an electrode, or a current collector. Those skilled in the art can appropriately add these elements to a single cell to form an SOEC or SOFC, and then construct a system.

[0036] (Solid oxide electrochemical devices) 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 allows 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. [Example]

[0037] Examples will be described below as specific examples to more specifically explain the disclosure of this specification. The following examples are intended to illustrate the disclosure of this specification, but are not intended to limit the scope thereof. [Example]

[0038] (Preparation of raw material powder for cell elements) The raw material powders for the oxygen and hydrogen electrodes were synthesized as follows. The raw material powder for the intermediate layer was GDC (Ce 0.8 Gd 0.2 )O 2-x、 (Shin-Etsu Chemical Co., Ltd.), and TiO2 (Wako Pure Chemical Industries, Ltd.), the other raw material powder for the oxygen electrode, were prepared.

[0039] (Synthesis of raw material powder for oxygen electrode and hydrogen electrode) The raw material powders for the oxygen electrode and the hydrogen electrode were prepared by spray pyrolysis.

[0040] (Oxygen electrode raw material powder) As the raw material powder for the oxygen electrode, (La 0.6 Sr 0.4 )(Co 0.2 Fe 0.8 )O 3-x was synthesized by spray pyrolysis. 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.

[0041] <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 set inside the collector to collect the synthesized particles.

[0042] The spray pyrolysis synthesis conditions were as follows: the reaction tube temperatures were 200°C, 400°C, 800°C, and 1000°C from the side closest to the atomizer; the collector was kept at 100°C using a mantle heater to prevent condensation. 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.

[0043] (hydrogen electrode raw material powder) NiO-YSZ (ZrO2-8 mol% YO3) (NiO:YSZ = 6:4 (mass ratio)) was synthesized as the hydrogen electrode raw material powder by spray pyrolysis. A raw material solution was prepared by adding nickel acetate tetrahydrate, yttrium nitrate n-hydrate, and zirconium nitrate dihydrate to ion-exchanged water so that the nickel, yttrium, and zirconium content was as described above. 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 desired raw material powder. [Example]

[0044] (Fabrication 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. 0.6 Sr 0.4 )(Co 0.2 Fe 0.8 )O 3-xTo the powder, TiO2 was added in amounts of 0 mass %, 0.5 mass %, 1 mass %, 2 mass %, 5 mass %, and 10 mass %, and a number of slurries with different TiO2 contents were prepared in the same manner as above.

[0045] The single cell laminate fabricated in this example is shown in Figure 1. The single cell was fabricated by screen-printing a GDC slurry for the intermediate layer onto one side of a solid electrolyte disk (8YSZ (ZrO2-8mol%Y2O3), 14mm diameter, 200µm thickness, manufactured by Tosoh Corporation) so that the resulting diameter would be 9mm and the thickness would be 5µm after firing. A slurry for the hydrogen electrode was screen-printed onto the other side so that the resulting diameter would be 6mm and the thickness would be 20µm after firing, followed by firing in air at 1400°C for 2 hours. Furthermore, a slurry for the oxygen electrode was screen-printed onto the fired intermediate layer so that the resulting diameter would be 6mm and the thickness would be 20µm after firing, followed by firing in air at 1150°C for 2 hours. In this way, six types of laminates (Production Examples 1 to 5) were produced, each having an oxygen electrode derived from five types of slurries with different TiO2 content amounts (0.5 mass%, 1 mass%, 2 mass%, 5 mass%, and 10 mass%) as the oxygen electrode slurry, and a laminate (Comparative Production Example 1) having an oxygen electrode derived from a slurry that did not contain TiO2 (0 mass%). [Example]

[0046] (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.

[0047] Figure 2 shows SEM images 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.

[0048] 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 detection of Sr, Ti, and O from the same location strongly suggests that Sr and Ti react to form SrTiO3 in the oxygen electrode (LSCF). [Example]

[0049] (Evaluation of power generation characteristics of stack in SOFC mode) The stack produced in Example 2 was used as a single cell of an SOFC, and air was supplied to the oxygen electrode side at 50 cm at operating temperatures of 700°C and 800°C. 3 / min, and 50 cm of H2-3% H2O was added to the hydrogen electrode side. 3 The maximum power density was measured by supplying gas at a rate of 1 / min. In this example, the maximum power density was also measured for Comparative Production Examples 2 to 6, which were prepared in the same manner as the Production Examples except that no intermediate layer was formed and the oxygen electrode 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.

[0050] 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 in which TiO2 was not added. Furthermore, Comparative Production Examples 2 to 6, which are SOFCs without an intermediate layer, showed significantly lower maximum power density, indicating that adding TiO2 to the oxygen electrode (LSCF) had almost no effect.

[0051] 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, as with the case of an operating temperature of 700°C, 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 in which TiO2 was not added. Furthermore, Comparative Production Examples 2 to 6, which are SOFCs without an intermediate layer, showed significantly lower maximum power density, indicating that adding TiO2 to the oxygen electrode (LSCF) had almost no effect.

[0052] 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, thereby improving the power generation characteristics in SOFC mode.

[0053] This also shows that when this cell is used as an SOEC, the formation of a high-resistance phase can be suppressed and the electrolysis efficiency can be improved.

Claims

1. 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 mass% to 8 mass% based on the total amount of the strontium-containing composite oxide.

2. A cell as described in claim 1, containing the titanium oxide in an amount of 1.0 mass% or more and 5.0 mass% or less relative to the total amount of the strontium-containing complex oxide.

3. A cell according to claim 1 or 2, wherein diffusion of Sr into the solid electrolyte and / or the intermediate layer is suppressed, and / or SrTiO 3 is formed at the oxygen electrode.

4. A cell described in any of claims 1 to 3, wherein the oxygen electrode does not have a higher concentration of titanium oxide distributed on the side opposite to the side facing the solid electrolyte in the thickness direction of the oxygen electrode.

5. The strontium-containing composite oxide is 1-x Sr x Co y Fe 1-y O 3-σ 5. The cell according to claim 1, wherein 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. 6. The cell according to claim 1, wherein the zirconium oxide of the solid electrolyte is rare earth-doped zirconium oxide.

7. 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. 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.

9. A solid oxide electrochemical device comprising the cell according to any one of claims 1 to 8.

10. 10. The solid oxide electrochemical device according to claim 9, which is a solid oxide fuel cell and / or a solid oxide electrolysis cell.

11. 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 ABO 3 (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.

12. The method of claim 11, wherein the step of obtaining the solid oxide electrochemical cell includes forming SrTiO 3 at the oxygen electrode.

13. 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 ABO 3 (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 further comprises sintering the cathode to suppress thermal diffusion of Sr into the intermediate layer and / or the solid electrolyte and / or to form SrTiO 3 in the cathode.

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