JP7852382B2 - Solid electrolyte powder, fuel electrode components and solid electrolyte layer components for solid oxide electrolytic cells, and solid oxide electrolytic cells - Google Patents

Description

This invention relates to a solid electrolyte powder, a fuel electrode component and a solid electrolyte layer component for a solid oxide electrolytic cell, and a solid oxide electrolytic cell.

In recent years, solid oxide electrolytic cells (SOECs), which can electrolyze water vapor, carbon dioxide, or mixtures thereof to produce hydrogen and carbon monoxide, have attracted attention. An SOEC has a fuel electrode, an oxygen electrode, and a solid electrolyte layer between the two electrodes. It operates through the conduction of oxide ions within this solid electrolyte layer.

Typically, solid electrolytes such as yttria-stabilized zirconia (YSZ) are used in the solid electrolyte layer, while mixtures of Ni and YSZ are used in the fuel electrode.

Takahashi, T., Hara, H., and Ichimura, T., "Ionic conductivity of the solid solution CaTi1-xAlxO3-α based on calcium titanate," Electrochemistry and Industrial Physical Chemistry, Vol. 37, No. 12, pp. 857-862, 1962-12, The Electrochemical Society of Japan. F. M. Lea, C. H. Desch, The Chemistry of Cement and Concrete, 2nd ed. , p. 52, Edward Arnold & Co. , London, 1956

To achieve low-power operation of SOECs, it is necessary to increase the oxide ion conductivity of the materials contained in the fuel electrode and solid electrolyte layer. Therefore, research and development of alternative materials to YSZ is underway.

Non-patent document 1 describes, for example, that in a _CaTiO3 -based perovskite-type compound, substituting some of the Ti sites with Al improves the ionic conductivity in the high-temperature range.

However, according to Non-Patent Literature 1, CaTi _1-x Al _x O ₃ -type compounds exhibit a behavior in which the relationship between temperature and ionic conductivity changes at a certain temperature; that is, a "bend point" occurs in the relationship between temperature and ionic conductivity in the range of 800°C to 900°C. When such a "bend point" occurs in the relationship between temperature and ionic conductivity, there is a problem that the ionic conductivity of the material decreases significantly at low temperatures.

This invention has been made in view of the above background, and aims to provide a solid electrolyte powder that has significantly high ionic conductivity even at low temperatures. Furthermore, this invention aims to provide a fuel electrode component for a solid oxide electrolytic cell made from such a solid electrolyte powder. Furthermore, this invention aims to provide a solid electrolyte layer component for a solid oxide electrolytic cell composed of such a solid electrolyte powder. Finally, this invention aims to provide a solid oxide electrolytic cell having such a fuel electrode component and/or solid electrolyte layer component.

In this invention,
A solid electrolyte powder,
It contains compounds with a perovskite structure and compounds with a mayenite structure.
The compound having the perovskite structure comprises Ca and Ti,
The provided solid electrolyte powder has an Al content y (= Al / (Ti + Al)) relative to the total amount of Ti and Al that is 0.05 or more and less than 0.60 in atomic ratio.

Furthermore, in this invention,
A fuel electrode component for a solid oxide type electrolytic cell,
The fuel electrode component comprises a transition metal and a solid electrolyte.
The solid electrolyte comprises a compound with a perovskite structure and a compound with a mayenite structure.
The compound having the perovskite structure comprises Ca and Ti,
The provided solid electrolyte is a fuel electrode component in which the Al content y (= Al / (Ti + Al)) relative to the total amount of Ti and Al is 0.05 or more and less than 0.60 in atomic ratio.

Furthermore, in this invention,
A component for the solid electrolyte layer of a solid oxide type electrolytic cell,
The solid electrolyte layer member has a solid electrolyte,
The solid electrolyte comprises a compound with a perovskite structure and a compound with a mayenite structure.
The compound having the perovskite structure comprises Ca and Ti,
The provided solid electrolyte layer member has an Al content y (= Al / (Ti + Al)) relative to the total amount of Ti and Al, which is 0.05 or more and less than 0.60 in atomic ratio.

Furthermore, in the present invention,
Fuel electrode and
Oxygen electrode and
A solid electrolyte layer is placed between the fuel electrode and the oxygen electrode,
It has,
A solid oxide electrolytic cell is provided, comprising a fuel electrode member and/or a solid electrolyte layer member having the above-described characteristics.

The present invention provides a solid electrolyte powder that exhibits significantly high ionic conductivity even at low temperatures. Furthermore, the present invention provides a fuel electrode component for a solid oxide electrolytic cell made from such a solid electrolyte powder. The present invention also provides a solid electrolyte layer component for a solid oxide electrolytic cell composed of such a solid electrolyte powder. Moreover, the present invention provides a solid oxide electrolytic cell having such a fuel electrode and/or solid electrolyte layer.

This figure shows the relationship between temperature and the logarithm of ionic conductivity in conventional CaTi _1-x Al _x O ₃ -type compounds. This figure schematically shows an example of a flow diagram for a method of producing solid electrolyte powder according to one embodiment of the present invention. This diagram schematically shows an example of the configuration of SOEC according to one embodiment of the present invention. This figure shows the X-ray diffraction pattern of a solid electrolyte powder (powder 1) according to one embodiment of the present invention. This figure shows the X-ray diffraction pattern of a solid electrolyte powder (powder 2) according to one embodiment of the present invention. This figure shows the X-ray diffraction pattern of a solid electrolyte powder (powder 3) according to one embodiment of the present invention. This graph shows the logarithmic temperature dependence of the ionic conductivity of a sintered body made from powder according to one embodiment of the present invention, along with the logarithmic temperature dependence of the ionic conductivity of conventional CaTi _1-x Al _x O ₃ -type compounds. This figure shows the activation energy value obtained from the slope of the straight line in Figure 7 for a sintered body made from powder according to one embodiment of the present invention.

The following describes one embodiment of the present invention with reference to the drawings.

In one embodiment of the present invention,
A solid electrolyte powder,
It contains compounds with a perovskite structure and compounds with a mayenite structure.
The compound having the perovskite structure comprises Ca and Ti,
The provided solid electrolyte powder has an Al content y (= Al / (Ti + Al)) relative to the total amount of Ti and Al that is 0.05 or more and less than 0.60 in atomic ratio.

A solid electrolyte powder according to one embodiment of the present invention contains a meienite compound with a C12A7 structure (Ca ₁₂ Al ₁₄ O ₃₃ ).

Mayenite compounds have a typical composition represented _by 12CaO· _7Al₂O₃ and possess a characteristic crystalline structure with three-dimensionally linked voids (cages) approximately 0.4 nm in diameter.

The framework constituting this cage is positively charged, forming 12 cages per unit cell. One-sixth of these cages are occupied by oxide ions to satisfy the electrical neutrality requirement of the crystal. However, these oxide ions within the cages have chemically distinct properties from the other oxygen ions constituting the framework; therefore, these oxide ions within the cages are specifically called free oxide ions.

Mayenite compounds are also represented by the chemical formula [Ca ₂₄ Al ₂₈ O ₆₄ ] ⁴⁺ (O ^2- ) ₂ (Non-patent Literature 2).

As mentioned above, the CaTi _1-x Al _x O ₃ compound described in Non-Patent Document 1 (hereinafter referred to as "conventional CaTi _1-x Al _x O ₃ compound") has the problem that the ionic conductivity of the material decreases significantly at low temperatures.

Figure 1 shows the relationship between temperature and ionic conductivity in conventional CaTi _1-x Al _x O ₃ compounds. Figure 1 shows the relationship between temperature and ionic conductivity for conventional CaTi _1-x Al _x O ₃ compounds when x = 0.1, 0.3, and 0.5.

Figure 1 shows that in each material, a "bend point" occurs in the temperature range of 800°C to 900°C, where the relationship between temperature and ionic conductivity changes.

For example, when x = 0.1, the slope of the line changes at approximately 839°C. Similarly, when x = 0.3, the slope changes at approximately 861°C. Likewise, when x = 0.5, the slope changes at approximately 838°C.

In the relationship between temperature and ionic conductivity, the occurrence of such a breakpoint presents a problem: the ionic conductivity of the material decreases significantly at low temperatures.

In contrast, the solid electrolyte powder according to one embodiment of the present invention contains a compound with a perovskite structure and a compound with a mayenite structure, and is characterized in that the Al content y (y = Al / (Ti + Al)) relative to the total amount of Ti and Al is 0.05 or more and less than 0.60 in atomic ratio. In particular, the weight abundance ratio of the mayenite structure compound relative to the total amount of the perovskite structure compound and the mayenite structure compound is preferably in the range of 0.1 wt% to 40 wt%.

In a solid electrolyte powder according to one embodiment of the present invention, by including a compound with a meienite-type structure within this range,
(i) In the relationship between temperature and ionic conductivity, no inflection point occurs in the temperature range of 800°C to 900°C.
(ii) The effect can be obtained in which the slope of the approximate straight line obtained from the relationship between temperature and ionic conductivity (activation energy in the diffusion of oxide ions) is small.

The effects described in (i) and (ii) above are thought to be due to the presence of both perovskite and mayenite-type compounds, which leads to the dominant diffusion of oxide ions at the interface between the perovskite and mayenite-type compounds.

Therefore, the solid electrolyte powder according to one embodiment of the present invention can maintain significantly high ionic conductivity even at low temperatures, such as 700°C or below.

Furthermore, this demonstrates that the solid electrolyte powder according to one embodiment of the present invention can be significantly applied as a material for the solid electrolyte layer and fuel electrode of SOEC.

(Solid electrolyte powder according to one embodiment of the present invention)
Next, we will describe in more detail the solid electrolyte powder according to one embodiment of the present invention.

As described above, the solid electrolyte powder according to one embodiment of the present invention (hereinafter simply referred to as "the first powder") contains a compound with a perovskite-type structure and a compound with a mayenite-type structure.

Here, in the first powder, the compound with a perovskite structure is represented by the general formula _CaTiO3 . The compound with a perovskite structure may contain oxygen vacancies and is represented by CaTiO3 _-α , where 0 ≤ α ≤ 0.5. However, some of the Ti may be substituted with Al and is represented by CaTi1 _{- xAlxO3 -α} . α is an arbitrary value and depends on the atmosphere of the first powder, changing when some of the Ti is substituted with Al.

Furthermore, in the first powder, the compound with a meienite-type structure is represented by the compositional formula [Ca ₂₄ Al ₂₈ O ₆₄ ] ⁴⁺ (O ^2- ) _2. However, some of Ca and Al may be substituted with Ti or the like.

Furthermore, in one embodiment of the present invention, the Al content y (= Al / (Ti + Al)) relative to the total amount of Ti and Al contained in the first powder is 0.05 or more and less than 0.60 in atomic ratio.

In the first powder, the Al content y relative to the total amount of Ti and Al is preferably in the range of 0.06 ≤ y ≤ 0.55 in terms of atomic ratio, and more preferably in the range of 0.10 ≤ y ≤ 0.50.

By setting 0.10 ≤ y ≤ 0.50, it becomes possible to obtain an electrolyte that exhibits high ionic conductivity while keeping the activation energy low.

Here, in the first powder, the weight ratio of the meienite-type compound to the total weight of the perovskite-type compound and the meienite-type compound is, for example, in the range of 0.1 wt% to 40 wt%, and preferably in the range of 1.0 wt% to 35 wt%.

Furthermore, in this application, the content of meienite-type compounds in the powder can be determined from the X-ray diffraction results of the powder using the WPPF method.

As described above, in the first powder, some of the Ti sites of the perovskite-type compound may be substituted with Al. For example, the general formula of the perovskite-type compound may be represented as CaTi _1-x Al _x O _3. Here, for example, x = 0.07 to 0.53, and preferably x = 0.10 to 0.50.

Thus, by substituting some of the Ti sites in the perovskite-type compound with Al, the ionic conductivity of the first powder can be further increased.

Furthermore, in the first powder, the lattice constant of the perovskite-type compound is preferably in the range of 3.8020 Å to 3.8150 Å, more preferably in the range of 3.8030 Å to 3.8140 Å, and even more preferably in the range of 3.8040 Å to 3.8130 Å.

Furthermore, in the first powder, the crystal structure of the perovskite-type compound may be cubic.

(Fuel electrode component made from solid electrolyte powder according to one embodiment of the present invention)
Next, a fuel electrode component made from solid electrolyte powder according to one embodiment of the present invention will be described in more detail. The fuel electrode component may consist of a binder resin such as a green sheet, solid electrolyte powder, and powder of a transition metal or a compound of a transition metal, or it may be a substrate formed by sintering these powders. If it is a substrate, it is provided as a fuel electrode-supporting SOEC with the substrate as a support. Alternatively, it may be a fuel electrode component in which a fuel electrode is laminated on a porous support made of metal, ceramics, or a composite thereof.

(A component for a solid electrolyte layer made from solid electrolyte powder according to one embodiment of the present invention)
Next, a solid electrolyte layer member made from solid electrolyte powder according to one embodiment of the present invention will be described in more detail. The solid electrolyte layer member may be composed of a binder resin such as a green sheet and solid electrolyte powder, or it may be a substrate molded by sintering. If it is a substrate, it is provided as a solid electrolyte layer supporting SOEC with the substrate as a support. Alternatively, it may be a solid electrolyte layer member in which a solid electrolyte layer is laminated on the fuel electrode member described above.

(A solid oxide electrolytic cell made from solid electrolyte powder according to one embodiment of the present invention)
Next, a solid oxide type electrolytic cell made from solid electrolyte powder according to one embodiment of the present invention will be described in more detail. The solid oxide type electrolytic cell may be fuel electrode supported or solid electrolyte layer supported. If it is fuel electrode supported, a paste containing a solid electrolyte may be applied to a fuel electrode substrate and fired to form a solid electrolyte layer, or a green sheet containing a solid electrolyte may be laminated and fired to form it. If it is solid electrolyte layer supported, a paste containing powder for the fuel electrode may be applied to a solid electrolyte layer substrate and fired to form a fuel electrode, or a green sheet containing a fuel electrode member may be laminated and fired to form it.

As materials for the oxygen electrode, for example, composite oxides such as La _0.4 Sr _0.6 Co _0.2 Fe _0.8 O ₃ (LSCF) and La _0.8 Sr _0.2 MnO ₃ (LSM), ceria oxides, and mixtures thereof can be used. Particularly preferable is the inclusion of a perovskite-type oxide containing two or more elements selected from the group consisting of La, Sr, Co, Fe, and Mn. In the case of a fuel electrode-supported type, the oxygen electrode may be formed by applying a paste containing oxygen electrode powder to a solid electrolyte layer and firing it. In the case of a solid electrolyte layer-supported type, the oxygen electrode may be formed by applying a paste containing oxygen electrode powder to a solid electrolyte substrate and firing it. A ceria-based electrolyte may be formed between the solid electrolyte layer and the oxygen electrode as a reaction prevention layer.

(Method for producing solid electrolyte powder according to one embodiment of the present invention)
Next, with reference to Figure 2, an example of a method for producing solid electrolyte powder according to one embodiment of the present invention will be described.

Figure 2 schematically shows an example of a flow chart for a method of producing solid electrolyte powder according to one embodiment of the present invention (hereinafter referred to as the "first manufacturing method").

As shown in Figure 2, the first manufacturing method is
(1) A step of mixing Ca source, Ti source, and Al source in predetermined proportions to obtain a mixed powder (step S110),
(2) A step of calcining the mixed powder to obtain calcined powder (step S120),
(3) A step of crushing the calcined powder (step S130),
It has.

The following explains each step of the process.

(Step S110)
First, a mixed powder is prepared. For this purpose, a Ca source, a Ti source, and an Al source are prepared.

The calcium source may be selected from, for example, metallic calcium, calcium carbonate, calcium oxide, calcium hydroxide, calcium nitrate, calcium sulfate, calcium fluoride, calcium chloride, calcium bromide, calcium iodide, and calcium carboxylate salts such as calcium acetate.

The Ti source may be selected from, for example, metallic Ti and/or oxides such as titanium(IV), titanium(III), and titanium(II) oxide, or titanium alkoxides such as titanium hydroxide, titanium fluoride, titanium chloride, titanium bromide, titanium iodide, titanium isopropoxide, and titanium butoxide. Titanium(IV) oxide may be either rutile or anatase form.

The Al source may be selected from, for example, metallic aluminum, α-alumina, γ-alumina, aluminum hydroxide, aluminum nitrate, aluminum sulfate, aluminum fluoride, aluminum chloride, aluminum bromide, aluminum iodide, and aluminum carboxylate salts such as aluminum acetate.

Each raw material is weighed and mixed to obtain a powder with the desired composition.

During mixing, it is preferable to use a ball mill, such as a planetary ball mill. For example, each raw material is wet-mixed with zirconia balls in the presence of an alcohol solvent such as isopropanol.

By using a ball mill, each raw material can be properly mixed without excessive mixing. Furthermore, using an alcohol solvent can suppress the decomposition of the raw materials in the solvent.

Subsequently, the slurry containing the raw materials is dried to remove the alcohol solvent. The drying temperature is not particularly limited, but is typically in the range of 80°C to 250°C.

This yields a dry mixed powder.

(Step S120)
Next, the mixed powder is calcined.

This process allows for the detachment of carbonate and nitrate rhizomes from the mixed powder, resulting in the formation of a mixture of perovskite-type and meienite-type compounds.

In the first manufacturing method, the resulting perovskite-type compound has some of the Ti sites replaced by Al, so its general formula is represented as CaTi _1-x Al _x O ₃ , where x = 0.07 to 0.53.

The calcination conditions are not particularly limited, but to obtain the desired mixture, a calcination temperature of 1000°C or higher is preferable. However, if the calcination temperature is too high, excessive sintering will occur in the mixed powder, making pulverization difficult. Therefore, a calcination temperature of 1450°C or lower is preferable.

The calcination time is typically around 5 to 24 hours. However, the calcination time also varies depending on the calcination temperature; the higher the calcination temperature, the shorter the calcination time.

(Step S130)
Next, the calcined flour is crushed.

This process forms a solid electrolyte powder.

The method for grinding the sintered body is not particularly limited, and conventional general grinding methods may be used.

Through the above steps, a solid electrolyte powder according to one embodiment of the present invention can be manufactured.

The first manufacturing method described above is merely an example, and the solid electrolyte powder according to one embodiment of the present invention may be manufactured by other methods.

However, in the method described in Non-Patent Document 1, if the Al content y (= Al / (Ti + Al)) relative to the total amount of Ti and Al is less than 0.60 in atomic ratio, it is not possible to produce a compound with a perovskite structure and a compound with a meienite structure simultaneously (see Figure 1 in Non-Patent Document 1). Therefore, in order to obtain a solid electrolyte powder containing both a perovskite and a meienite structure, care must be taken in preparing the mixed powder in step S110, ensuring that the raw materials are not excessively mixed. In particular, it is difficult to obtain a compound with a meienite structure using the method described in Non-Patent Document 1, which involves adding a nitric acid solution to the raw materials to decompose calcium carbonate.

(An example of application of solid electrolyte powder according to one embodiment of the present invention)
Next, an example of the application of a solid electrolyte powder according to one embodiment of the present invention will be described. As shown below, the solid electrolyte powder according to one embodiment of the present invention ("first powder") can be applied to various components in various forms.

(Paste for solid electrolyte layer)
The first powder may be provided as a paste for the solid electrolyte layer of the SOEC.

Such a paste (hereinafter referred to as "the first paste") may be prepared by mixing a dispersion medium with the aforementioned first powder.

The dispersion medium is not particularly limited, but may be at least one of the following: water, alcohol, ketone, ester, ether, and hydrocarbon. Among these, one or more solvents such as terpene alcohols (e.g., terpineol and dihydroterpineol), polyhydric alcohols (e.g., ethylene glycol and propylene glycol), hydrocarbons (e.g., decane, toluene, and xylene), and ethers (e.g., ethyl carbitol and butyl carbitol) can be used individually or in combination.

The paste may contain a binder resin to adjust its viscosity and binding properties. Examples of binder resins include at least one of the following: acrylic resin, epoxy resin, phenolic resin, alkyd resin, polyester resin, rosin resin, polycarbonate resin, and cellulose resin. Of these, the inclusion of a cellulose-based polymer such as ethylcellulose is particularly preferred.

(Solid electrolyte layer)
The first powder may be applied to the solid electrolyte layer of the SOEC.

In that case, the first paste described above may be prepared from the first powder, and a solid electrolyte layer may be formed using this first paste.

When forming a solid electrolyte layer from the first paste, for example, the following steps may be performed.

First, the first paste is applied to the fuel electrode support to form a coating film. The application method is not particularly limited, and general methods such as screen printing, doctor blade application, or spin coating may be used.

Next, after drying the coating film, it may be heat-treated to form a solid electrolyte layer. The heat treatment temperature is, for example, in the range of 1000°C to 1450°C.

(Mixed powder for fuel electrodes)
The first powder may be applied to the mixed powder for the fuel electrode of SOEC.

In this case, the transition metal or transition metal compound powder may be mixed with the first powder. The transition metal or transition metal compound powder is, for example, a metal or oxide powder such as nickel, copper, iron, or cobalt (3d transition elements). The content of the first powder in the mixed powder is, for example, in the range of 20 wt% to 90 wt%. More preferably, it is in the range of 30 wt% to 80 wt%, and even more preferably, in the range of 30 wt% to 70 wt%.

(Paste for fuel electrodes)
The first powder may be provided as a paste for the SOEC fuel electrode.

Such a paste (hereinafter referred to as the "second paste") may be prepared by adding the aforementioned mixed powder for the fuel electrode to a dispersion medium.

The dispersion medium is not particularly limited, but the same dispersion medium or binder resin as in the first paste can be used.

(Fuel electrode)
The first powder may be applied to the fuel electrode of the SOEC.

In that case, the second paste described above may be prepared from the first powder, and the fuel electrode may be formed using this second paste.

When forming the fuel electrode from the second paste, for example, the following steps may be performed:

First, the second paste is applied onto the solid electrolyte support. The application method is not particularly limited, and common methods such as screen printing, doctor blade application, and spin coating may be used.

Next, after drying the second paste, it may be heat-treated to form the fuel electrode. The heat treatment temperature is, for example, in the range of 1000°C to 1450°C.

(SOEC)
In one embodiment of the present invention, the SOEC may be constructed using the first powder.

Figure 3 schematically shows one example of such an SOEC configuration.

As shown in Figure 3, this SOEC (hereinafter referred to as "single cell") 100 has an oxygen electrode 110, a fuel electrode 120, and a solid electrolyte layer 130 between the two electrodes.

Assuming that water vapor is electrolyzed, when a single cell 100 is connected to an external power supply 150, the following reaction occurs at the fuel electrode 120:

2H ₂ O+4e ⁻ →2H ₂ +2O ²⁻ (1) Formula

Furthermore, if we assume that carbon dioxide is electrolyzed, the following reaction will occur:

CO ₂ +2e-→CO+O ^2- (2) Formula

Oxide ions generated at the fuel electrode 120 pass through the solid electrolyte layer 130 and reach the oxygen electrode 110 on the opposite side.

At the oxygen electrode 110, for example, the following reaction occurs:

2O ^2- →O ₂ +4e ^- Formula (3)

Therefore, the reactions in equations (1) to (3) allow for the electrolytic reaction of water vapor or carbon dioxide to proceed, producing hydrogen or carbon monoxide.

In such a single cell 100, a solid electrolyte powder according to one embodiment of the present invention can be applied to the solid electrolyte layer 130. For example, the solid electrolyte layer 130 is formed by heat-treating a first paste containing the aforementioned first powder.

In such a single cell 100, the solid electrolyte layer 130 has high oxide ion conductivity even at low temperatures, allowing the electrolysis voltage during electrolysis to be reduced even at low temperatures. Therefore, hydrogen and/or carbon monoxide can be produced with low power.

In addition to or separately from the above, a solid electrolyte powder according to one embodiment of the present invention may be applied to the fuel electrode 120 in the single cell 100. For example, the fuel electrode 120 may be formed by heat-treating a second paste containing the first powder described above.

The following describes embodiments of the present invention. In the following examples, Examples 1 to 3 are examples.

(Example 1)
A solid electrolyte powder was produced using the first manufacturing method described above.

First, we prepared 3.6807 g of _CaCO3 powder (manufactured by Kojunkagaku Co., Ltd.) as a Ca source, 2.6648 g of _TiO2 powder (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a Ti source, and 1.3919 g of Al( _NO3 ) ₃ · _9H2O powder (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as an Al source.

Next, these powders were mixed using a planetary ball mill and zirconia balls in the presence of a solvent. 10 g of 2-propanol was used as the solvent. The planetary ball mill was set to 300 rpm, and the processing time was 60 minutes.

Next, the resulting mixed powder was dried in air at a high temperature for two hours. The processing temperature was 140°C. This resulted in a dried mixed powder from which the solvent had been removed.

Next, the dried mixed powder was calcined in the air.

The processing temperature was set to 1400°C, and the processing time was set to 10 hours.

After cooling to room temperature, the resulting processed material was ground in a mortar to produce a powder.

The resulting powder is referred to as "Powder 1".

In powder 1, the Al content y (= Al / (Ti + Al)) relative to the total amount of Ti and Al was 0.1 in atomic ratio.

(Example 2)
The powder was produced using the same method as in Example 1. However, in Example 2, the amounts of Ca source, Ti source, and Al source contained in the raw materials were changed from those in Example 1.

The resulting powder is referred to as "Powder 2".

In powder 2, the Al content y (= Al / (Ti + Al)) relative to the total amount of Ti and Al was 0.3 in atomic ratio.

(Example 3)
The powder was produced using the same method as in Example 1. However, in Example 3, the amounts of Ca source, Ti source, and Al source contained in the raw materials were changed from those in Examples 1 and 2.

The resulting powder is referred to as "Powder 3".

In powder 2, the Al content y (= Al / (Ti + Al)) relative to the total amount of Ti and Al was 0.5 in atomic ratio.

(evaluation)
The following evaluations were conducted using powders 1 to 3.

(X-ray diffraction analysis)
X-ray diffraction analysis of powders 1 to 3 was performed using an X-ray diffractometer (Bruker D2PHASER).

The measurement results are shown in Figures 4 to 6. Figure 4 shows the X-ray diffraction pattern of powder 1, Figure 5 shows the X-ray diffraction pattern of powder 2, and Figure 6 shows the X-ray diffraction pattern of powder 3.

These results show that in all powders, diffraction peaks corresponding to _CaTiO3 and diffraction peaks corresponding to compounds with a mayenite-type structure appeared. Therefore, it was confirmed that powders 1 to 3 all contain CaTiO3 _- based perovskite-type compounds and compounds with a mayenite-type structure. Furthermore, the crystal structure of the _CaTiO3- based perovskite-type compounds in each powder was cubic.

Next, based on the obtained results, the weight ratio of the meienite-type compound to the total weight of the meienite-type compound and the lattice constant of the meienite-type compound were calculated using the WPPF method.

For the WPPF method, Rigaku's analysis software "PDXL2" was used. For _CaTiO3 , the diffraction pattern of PDF card number: 03-065-3287 was used for fitting, and for compounds with a meienite-type structure, the diffraction pattern of PDF card number: 01-076-5010 was used.

As a result, in powders 1 to 3, the weight abundance of the meienite-type compound relative to the total amount of the perovskite-type compound and the meienite-type compound was 2.0 wt%, 6.8 wt%, and 30.0 wt%, respectively. Furthermore, the lattice constants of the perovskite-type compound were 3.8120 Å, 3.8094 Å, and 3.8057 Å, respectively.

Pure _CaTiO3 is orthorhombic, but the crystalline phases of powders 1 to 3 are cubic, and the lattice constant decreases as the Al content y increases relative to the total amount of Ti and Al.

From this, it is considered that the CaTiO3 _- based compounds contained in powders 1 to 3 have a structure of CaTi1 _{-xAlxO3 ,} in which some of the Ti sites are substituted with _Al .

Table 1 below summarizes the evaluation results obtained for each powder.

(Evaluation of ionic conductivity)
Next, sintered bodies were prepared using each powder, and the oxide ion conductivity was measured using the AC impedance method.

(Preparation of sample for measurement)
0.7 g of calcined powder was placed in a φ10 mm carbide die, and a compact was produced by uniaxial forming using a hydraulic press (NT-200H, manufactured by NPA Systems Co., Ltd.) with a pressure of 10 MPa. Further cold isostatic pressing was performed at 200 MPa. The compact was heat-treated in air at 1400°C for 10 hours to obtain a sintered body.

Both sides of the sintered body were polished smooth with sandpaper. Platinum paste (Tanaka Precious Metals: U-3401) was applied to both sides of the sintered body, and the body was heat-treated at 1000°C for 15 minutes in an air atmosphere to bake on the platinum electrodes.

(Measurement of AC impedance)
The sintered body was placed in an electric furnace (Nolex Probostat) under an atmospheric environment. The sintered body was sandwiched between platinum electrodes connected to platinum wires and connected to a potentiogalvanostat (Solartron Analytical 1260A). Impedance measurements were performed, and a Cole-Cole plot was obtained. The measurement frequency was 10 MHz to 100 mHz, and the modulation potential amplitude was 100 mV. The oxide ion conductivity was calculated by dividing the impedance value obtained from the measurement by the thickness of the sintered body.

Figure 7 shows the measurement results of ionic conductivity obtained for each powder.

In Figure 7, the horizontal axis represents the reciprocal of temperature (1/T) (unit: ^K⁻¹ ), and the vertical axis represents the logarithm of oxide ion conductivity (unit: S/cm). Figure 7 also shows the oxide ion conductivity of the CaTi _1-x Al _x O ₃ compound described in Non-Patent Document 1 shown in Figure 1.

Figure 7 shows that powders 1 to 3 do not exhibit the "bend point" observed in conventional CaTi _1-x Al _x O ₃ -type compounds. In other words, the temperature dependence of ionic conductivity for powders 1 to 3 was approximated by a single straight line.

Furthermore, the results showed that powders 1 to 3 exhibited higher oxide ion conductivity even at low temperatures below 700°C compared to conventional CaTi _1-x Al _x O ₃ -based compounds.

Figure 8 shows the activation energy values for each powder, obtained from the slope of the straight line in Figure 7. For reference, Figure 8 also shows the activation energy for conventional CaTi _1-x Al _x O ₃ -type compounds. Note that the activation energy for the conventional CaTi _1-x Al _x O ₃ -type compounds, where a "bend point" occurred, was calculated from the approximate straight line on the low-temperature side.

Figure 8 shows that powders 1 to 3 have significantly lower activation energies compared to conventional CaTi _1-x Al _x O ₃ -based compounds.

Thus, it was found that for powders 1 to 3, no inflection point in the relationship between temperature and ionic conductivity occurred in the range of 800°C to 900°C, and the activation energy was relatively small.

Therefore, powders 1 to 3 exhibit significantly higher ionic conductivity even at low temperatures below 700°C.

(Aspects of the present invention)
The present invention may have the following embodiments:
(Aspect 1)
A solid electrolyte powder,
It contains compounds with a perovskite structure and compounds with a mayenite structure.
The compound having the perovskite structure comprises Ca and Ti,
The solid electrolyte powder is a solid electrolyte powder in which the Al content y (= Al / (Ti + Al)) relative to the total amount of Ti and Al is 0.05 or more and less than 0.60 in atomic ratio.
(Aspect 2)
The solid electrolyte powder according to embodiment 1, wherein the weight ratio of the mayenite compound to the total of the perovskite-type compound and the mayenite-type compound is in the range of 0.1 wt% to 40 wt%.
(Aspect 3)
A portion of the Ti site in the aforementioned perovskite-type compound is substituted with Al.
The solid electrolyte powder according to embodiment 1 or 2, wherein the lattice constant of the perovskite-type compound is in the range of 3.8020 Å to 3.8150 Å.
(Aspect 4)
The solid electrolyte powder according to any one of embodiments 1 to 3, wherein the crystal structure of the perovskite-type compound is cubic.
(Aspect 5)
A powder of a transition metal or a transition metal compound,
A solid electrolyte powder according to any one of embodiments 1 to 4,
A powder for fuel electrode material of a solid oxide type electrolytic cell, having the following properties.
(Aspect 6)
Dispersion medium and
The powder for the fuel electrode member described in embodiment 5,
A paste for the fuel electrode of a solid oxide electrolytic cell, having the following properties.
(Aspect 7)
Dispersion medium and
A solid electrolyte powder according to any one of embodiments 1 to 4,
A paste for the solid electrolyte layer of a solid oxide type electrolytic cell, having the following properties.
(Appendix 8)
A fuel electrode component for a solid oxide type electrolytic cell,
The fuel electrode component comprises a transition metal and a solid electrolyte.
The solid electrolyte comprises a compound with a perovskite structure and a compound with a mayenite structure.
The compound having the perovskite structure comprises Ca and Ti,
The solid electrolyte is a fuel electrode component in which the Al content y (= Al / (Ti + Al)) relative to the total amount of Ti and Al is 0.05 or more and less than 0.60 in atomic ratio.
(Aspect 9)
A component for the solid electrolyte layer of a solid oxide type electrolytic cell,
The solid electrolyte layer member has a solid electrolyte,
The solid electrolyte comprises a compound with a perovskite structure and a compound with a mayenite structure.
The compound having the perovskite structure comprises Ca and Ti,
The solid electrolyte is a component for a solid electrolyte layer, wherein the Al content y (= Al / (Ti + Al)) relative to the total amount of Ti and Al is 0.05 or more and less than 0.60 in atomic ratio.
(Aspect 10)
Fuel electrode and
Oxygen electrode and
A solid electrolyte layer is placed between the fuel electrode and the oxygen electrode,
It has,
A solid oxide electrolytic cell wherein the fuel electrode is composed of a fuel electrode member as described in embodiment 8, and/or the solid electrolyte layer is composed of a solid electrolyte layer member as described in embodiment 9.

100 SOEC
110 Oxygen electrode 120 Fuel electrode 130 Solid electrolyte layer 150 External power supply

Claims (10)

A solid electrolyte powder,
It contains compounds with a perovskite structure and compounds with a mayenite structure.
The compound having the perovskite structure comprises Ca , Ti , and Al .
The solid electrolyte powder is a solid electrolyte powder in which the Al content y (= Al / (Ti + Al)) relative to the total amount of Ti and Al is 0.05 or more and less than 0.60 in atomic ratio. The solid electrolyte powder according to claim 1, wherein the weight ratio of the meienite compound to the total of the perovskite-type compound and the meienite-type compound is in the range of 0.1 wt% to 40 wt%. A portion of the Ti site in the aforementioned perovskite-type compound is substituted with Al.
The solid electrolyte powder according to claim 1 or 2, wherein the lattice constant of the perovskite-type compound is in the range of 3.8020 Å to 3.8150 Å. The solid electrolyte powder according to claim 3, wherein the crystal structure of the perovskite-type compound is cubic. A powder of a transition metal or a transition metal compound,
The solid electrolyte powder according to claim 3,
A powder for fuel electrode material of a solid oxide type electrolytic cell, having the following properties. Dispersion medium and
The powder for the fuel electrode member according to claim 5,
A paste for the fuel electrode of a solid oxide electrolytic cell, having the following properties. Dispersion medium and
The solid electrolyte powder according to claim 3,
A paste for the solid electrolyte layer of a solid oxide type electrolytic cell, having the following properties. A fuel electrode component for a solid oxide type electrolytic cell,
The fuel electrode component comprises a transition metal and a solid electrolyte.
The solid electrolyte comprises a compound with a perovskite structure and a compound with a mayenite structure.
The compound having the perovskite structure comprises Ca , Ti , and Al .
The solid electrolyte is a fuel electrode component in which the Al content y (= Al / (Ti + Al)) relative to the total amount of Ti and Al is 0.05 or more and less than 0.60 in atomic ratio. A component for the solid electrolyte layer of a solid oxide type electrolytic cell,
The solid electrolyte layer member has a solid electrolyte,
The solid electrolyte comprises a compound with a perovskite structure and a compound with a mayenite structure.
The compound having the perovskite structure comprises Ca , Ti , and Al .
The solid electrolyte is a component for a solid electrolyte layer, wherein the Al content y (= Al / (Ti + Al)) relative to the total amount of Ti and Al is 0.05 or more and less than 0.60 in atomic ratio. Fuel electrode and
Oxygen electrode and
A solid electrolyte layer is placed between the fuel electrode and the oxygen electrode,
It has,
A solid oxide electrolytic cell wherein the fuel electrode is composed of the fuel electrode member described in claim 8, and/or the solid electrolyte layer is composed of the solid electrolyte layer member described in claim 9.