阅读说明：本技术 固体碱性燃料电池 (Solid alkaline fuel cell ) 是由 武内幸久 菅博史 中村俊之 大森诚 于 2018-12-17 设计创作，主要内容包括：固体碱性燃料电池(10)具备被供给氧化剂的阴极(12)、被供给燃料的阳极(14)和具有氢氧化物离子传导性的无机固体电解质体(16)。无机固体电解质体(16)能够透过在阴极(12)处生成按阴极侧表面(16S)的每单位面积计算为0.04μmol/s·cm<Sup>2</Sup>～2.5μmol/s·cm<Sup>2</Sup>的二氧化碳的量的燃料。(A solid alkaline fuel cell (10) is provided with a cathode (12) to which an oxidizing agent is supplied, an anode (14) to which a fuel is supplied, and an inorganic solid electrolyte body (16) having hydroxide ion conductivity. The inorganic solid electrolyte body (16) is permeable to the electrolyte solution generated at the cathode (12) and has a thickness of 0.04 [ mu ] mol/S-cm calculated per unit area of the cathode-side surface (16S) 2 ～2.5μmol/s·cm 2 The amount of carbon dioxide.)

1. A solid alkaline fuel cell is provided with:

a cathode to which an oxidant containing oxygen is supplied,

An anode supplied with a fuel containing hydrogen atoms, and

an inorganic solid electrolyte body having hydroxide ion conductivity, disposed between the cathode and the anode,

the inorganic solid electrolyte body is permeable to the electrolyte solution generated at the cathode and has a surface area per unit area of 0.04 [ mu ] mol/s-cm²～2.5μmol/s·cm²The amount of carbon dioxide.

2. The solid alkaline fuel cell according to claim 1,

the inorganic solid electrolyte body is permeable to the electrolyte solution generated at the cathode and has a thickness of 0.15 [ mu ] mol/s-cm per unit area of the cathode-side surface²Fuel in the above amount of carbon dioxide.

3. The solid alkaline fuel cell according to claim 1,

the inorganic solid electrolyte body is permeable to the electrolyte solution generated at the cathode and has a thickness of 0.6 [ mu ] mol/s-cm per unit area of the cathode-side surface²Fuel in the above amount of carbon dioxide.

4. The solid alkaline fuel cell according to any one of claims 1 to 3,

the inorganic solid electrolyte body is permeableGenerated at the cathode at 1.7. mu. mol/s-cm per unit area of the cathode-side surface²The following amount of carbon dioxide.

Technical Field

The present invention relates to a solid alkaline fuel cell.

Background

As a fuel cell that operates at a relatively low temperature (e.g., 250 ℃ or lower), an Alkaline Fuel Cell (AFC) is known. Various liquid fuels or gaseous fuels can be used in AFC, and the following electrochemical reactions occur when methanol is used as a fuel, for example.

● anode: CH (CH)₃OH+6OH^-→6e^-+CO₂+5H₂O

● cathode: 3/2O₂+3H₂O+6e^-→6OH^-

● Overall: CH (CH)₃OH+3/2O₂→CO₂+2H₂O

Patent document 1 proposes a solid alkaline fuel cell using a layered Double Hydroxide (L DH: L hydrated Hydroxide) having no liquid permeability or air permeability as an inorganic solid electrolyte having Hydroxide ion conductivity.

L DH is represented by the general formula [ M: [ [ M ]²⁺ _1-xM³⁺ _x(OH)₂][A^n- _x/n·mH₂O](M²⁺Is a cation of valency 2, M³⁺Is a cation of valency 3, A^n-Is an n-valent anion. ) And (4) showing.

Patent document

Patent document 1: japanese patent laid-open publication No. 2016-

Disclosure of Invention

However, as shown in the above reaction formula, the solid alkaline fuel cell consumes oxygen (O) at the cathode₂) And water (H)₂O), it is necessary to supply an oxidizing agent (e.g., humidified air) containing oxygen and water to the cathode.

However, in order to supply the oxidizing agent containing water to the cathode, not only equipment for humidifying the oxidizing agent (e.g., a humidifier, a water tank, etc.) but also energy for humidifying the oxidizing agent is consumed.

Therefore, new solutions for efficiently supplying water to the cathode are desired.

The invention aims to provide a solid alkaline fuel cell capable of efficiently supplying water to a cathode.

The solid alkaline fuel cell of the present invention comprises: the fuel cell includes a cathode to which an oxidant containing oxygen is supplied, an anode to which a fuel containing hydrogen atoms is supplied, and an inorganic solid electrolyte having hydroxide ion conductivity and disposed between the cathode and the anode. The inorganic solid electrolyte body is permeable to the electrolyte solution generated at the cathode and has a thickness of 0.04. mu. mol/s-cm per unit area of the cathode side surface²～2.5μmol/s·cm²The amount of carbon dioxide.

According to the present invention, a solid alkaline fuel cell capable of efficiently supplying water to a cathode can be provided.

Drawings

Fig. 1 is a sectional view schematically showing the structure of a solid alkaline fuel cell.

Fig. 2 is an exploded perspective view of the solid alkaline fuel cell of the embodiment.

Detailed Description

(solid alkaline Fuel cell 10)

The solid alkaline fuel cell 10 is one of Alkaline Fuel Cells (AFC) that operate at a relatively low temperature. The operating temperature of the solid alkaline fuel cell 10 of the present embodiment is 50 to 250 ℃. The solid alkaline fuel cell 10 operates, for example, by methanol, and generates electricity by the following electrochemical reaction.

● cathode 12: 3/2O₂+3H₂O+6e^-→6OH^-

● anode 14: CH (CH)₃OH+6OH^-→6e^-+CO₂+5H₂O

● Overall: CH (CH)₃OH+3/2O₂→CO₂+2H₂O

Fig. 1 is a sectional view schematically showing the structure of a solid alkaline fuel cell 10. The solid alkaline fuel cell 10 includes a cathode 12, an anode 14, and an inorganic solid electrolyte body 16.

The cathode 12 is a positive electrode generally referred to as an air electrode. In the process of generating electricity in the solid alkaline fuel cell 10, oxygen (O) is supplied to the cathode 12 by the oxidizing agent supply mechanism 13₂) An oxidizing agent of (1). As the oxidizing agent, air may be used.

Here, the inorganic solid electrolyte body 16 of the present embodiment is configured such that: a part of the fuel supplied to the anode 14 can be permeated (crossover) to the cathode 12 side. At the cathode 12, the fuel permeated to the cathode 12 through the inorganic solid electrolyte body 16 reacts with oxygen contained in the oxidant, thereby generating carbon dioxide (CO)₂) And water (H)₂O). For example, in the case of using methanol as the fuel, the following reaction occurs at the cathode 12.

● cathode 12: CH (CH)₃OH+3/2O₂→CO₂+2H₂O

The water generated from the fuel that has permeated through the cathode 12 via the inorganic solid electrolyte body 16 in this manner is used for the electrochemical reaction at the cathode 12.

In the case where all of the water required for the electrochemical reaction at the cathode 12 is generated from the fuel, the oxidant supplied to the cathode 12 may contain substantially no water. In this case, it is not necessary to provide a device (e.g., a humidifier, a water tank, or the like) for humidifying the oxidizing agent, and in addition, there is no energy consumption for humidifying the oxidizing agent.

On the other hand, when only a part of the water required for the electrochemical reaction at the cathode 12 is generated from the fuel, the oxidizing agent supplied to the cathode 12 preferably contains water. In this case, although it is necessary to provide a device for humidifying the oxidizing agent, the device can be downsized, and the energy consumption for humidifying the oxidizing agent can be reduced. As the oxidizing agent containing oxygen and water, humidified air is preferable.

In the present specification, "water (H)" refers to water₂O) "may be any of water vapor in a gas state, moisture in a liquid state, and a gas-liquid mixture of water vapor and moisture.

The cathode 12 may contain a known cathode catalyst used in an alkaline fuel cell, and is not particularly limited. As cathode catalysisExamples of the agent include group 8 to 10 elements (elements belonging to groups 8 to 10 in the IUPAC periodic table) such as platinum group elements (Ru, Rh, Pd, Os, Ir, Pt), iron group elements (Fe, Co, Ni), group 11 elements (elements belonging to group 11 in the IUPAC periodic table) such as Cu, Ag, Au, rhodium phthalocyanine, tetraphenylporphyrin, Co-SA L EN, Ni-SA L EN (SA L EN ═ N, N' -bis (salicylidene) ethylenediamine), silver nitrate, and any combination thereof, the amount of the catalyst supported in the cathode 12 is not particularly limited, and is preferably 0.1 to 10mg/cm²More preferably 0.1 to 5mg/cm². The cathode catalyst is preferably supported on carbon. Preferred examples of the cathode 12 or the catalyst constituting the cathode 12 include platinum-supported carbon (Pt/C), palladium-supported carbon (Pd/C), rhodium-supported carbon (Rh/C), nickel-supported carbon (Ni/C), copper-supported carbon (Cu/C), and silver-supported carbon (Ag/C).

The method for producing the cathode 12 is not particularly limited, and for example, the cathode can be formed by mixing a cathode catalyst and, if necessary, a carrier and a binder into a paste, and applying the paste mixture to one surface of the inorganic solid electrolyte body 16.

Anode 14 is a negative electrode commonly referred to as a fuel electrode. During the power generation of the solid alkaline fuel cell 10, a fuel containing hydrogen atoms (H) is supplied to the anode 14 by the fuel supply mechanism 15.

Fuel containing hydrogen atoms as long as it can react with hydroxide ions (OH) at the anode 14^-) It is sufficient that water is generated by reaction and reaction with oxygen at the cathode 12.

Such a fuel may be in the form of either a liquid fuel or a gaseous fuel. The liquid fuel may be a liquid fuel in which the fuel compound itself is liquid, or a liquid fuel in which a solid fuel compound is dissolved in a liquid such as water or alcohol.

Examples of the fuel compound include (i) hydrazine (NH)₂NH₂) Hydrazine hydrate (NH)₂NH₂·H₂O), hydrazine carbonate ((NH)₂NH₂)₂CO₂) Hydrazine sulfate (NH)₂NH₂·H₂SO₄) Monomethylhydrazine (CH)₃NHNH₂) Dimethylhydrazine ((CH)₃)₂NNH₂、CH₃NHNHCH₃) And carbohydrazide ((NHNH)₂)₂Hydrazines such as CO), and (ii) urea (NH)₂CONH₂) (iii) Ammonia (NH)₃) (iv) heterocyclic compounds such as imidazole, 1,3, 5-triazine and 3-amino-1, 2, 4-triazole, and (v) hydroxylamine (NH)₂OH), hydroxylamine sulfate (NH)₂OH·H₂SO₄) And the like and combinations thereof.

Among the above fuel compounds, compounds containing no carbon (i.e., hydrazine hydrate, hydrazine sulfate, ammonia, hydroxylamine sulfate, etc.) do not have a problem of catalyst poisoning by carbon monoxide, and therefore, durability can be improved, and not only can emission of carbon dioxide be avoided.

The fuel compound may be used as it is or in the form of a solution dissolved in water and/or an alcohol (e.g., a lower alcohol such as methanol, ethanol, propanol, or isopropanol). For example, among the above fuel compounds, hydrazine hydrate, monomethylhydrazine and dimethylhydrazine are liquid and therefore can be used as they are as liquid fuels. In addition, hydrazine carbonate, hydrazine sulfate, carbohydrazide, urea, imidazole, 3-amino-1, 2, 4-triazole and hydroxylamine sulfate are solid but soluble in water. The 1,3, 5-triazine and hydroxylamine are solids, but are soluble in alcohols. Ammonia is a gas, but soluble in water. As described above, the solid fuel compound can be dissolved in water or alcohol and used in the form of a liquid fuel. When the fuel compound is dissolved in water and/or alcohol for use, the concentration of the fuel compound in the solution is, for example, 1 to 90% by weight, preferably 1 to 30% by weight.

Further, a hydrocarbon-based liquid fuel containing alcohols such as methanol and ethanol, ethers, a hydrocarbon-based gas such as methane, pure hydrogen, or the like can be used as it is. Methanol is particularly preferable as the fuel used in the solid alkaline fuel cell 10 of the present embodiment. The methanol may be in any of a gas state, a liquid state, and a gas-liquid mixed state.

The anode 14 may contain a known anode catalyst used in an alkaline fuel cell, and is not particularly limited. Examples of the anode catalyst include metal catalysts such as Pt, Ni, Co, Fe, Ru, Sn, and Pd. The metal catalyst is preferably supported on a carrier such as carbon, and may be in the form of an organometallic complex having a metal atom of the metal catalyst as a central metal, or such an organometallic complex may be supported on a carrier. Further, a diffusion layer made of a porous material or the like may be disposed on the surface of the anode catalyst. Preferred examples of the anode 14 or the catalyst constituting the anode 14 include nickel, cobalt, silver, platinum-supported carbon (Pt/C), palladium-supported carbon (Pd/C), rhodium-supported carbon (Rh/C), nickel-supported carbon (Ni/C), copper-supported carbon (Cu/C), and silver-supported carbon (Ag/C).

The method for producing the anode 14 is not particularly limited, and for example, the anode can be formed by mixing an anode catalyst and, if necessary, a carrier and a binder into a paste, and applying the paste mixture to the surface of the inorganic solid electrolyte body 16 opposite to the cathode 12.

The inorganic solid electrolyte body 16 is disposed between the cathode 12 and the anode 14. The inorganic solid electrolyte body 16 has a cathode-side surface 16S and an anode-side surface 16T. The cathode-side surface 16S is a region of the outer surface of the inorganic solid electrolyte body 16 exposed to the space in which the cathode 12 is disposed, and faces the cathode 12. The anode-side surface 16T is a region of the outer surface of the inorganic solid electrolyte body 16 exposed to the space where the anode 14 is disposed, and faces the anode 14.

The inorganic solid electrolyte body 16 is a ceramic having hydroxide ion conductivity. The higher the hydroxide ion conductivity of the inorganic solid electrolyte body 16, the better, typically 10^-4～10^-1S/m。

The inorganic solid electrolyte 16 may be formed of a layered Double Hydroxide (L a layered Double Hydroxide, hereinafter referred to as "L DH"), and in this case, the inorganic solid electrolyte 16 exhibits superior heat resistance and durability compared to a case where an organic material such as AEM (anion exchange membrane) is used as an electrolyte.

L DH has the general formula [ M²⁺ _1-xM³⁺ _x(OH)₂][A^n- _x/n·mH₂O](in the formula, M²⁺A cation having a valence of 2，M³⁺Is a cation of valency 3, A^n-An anion having a valence of n, n is an integer of 1 or more, and x is 0.1 to 0.4).

In the above formula, M²⁺May be any cation having a valence of 2, and a preferable example thereof is Mg²⁺、Ca²⁺And Zn²⁺More preferably Mg²⁺。M³⁺Any cation having a valence of 3 may be used, and preferred examples thereof include Al³⁺Or Cr³⁺More preferably Al³⁺。A^n-May be any anion, and preferable examples thereof include OH^-And CO₃ ^2-。

Thus, in the above formula, it is particularly preferred: m²⁺Containing Mg²⁺，M³⁺Containing Al³⁺，A^n-Containing OH^-And/or CO₃ ^2-. n is an integer of 1 or more, preferably 1 or 2. x is 0.1 to 0.4, preferably 0.2 to 0.35. m is an arbitrary real number.

In addition, M may be represented by the above general formula³⁺In which a part or all of them are replaced with a cation having a valence of 4 or more, in this case, the anion A in the above general formula^n-The coefficient x/n of (2) can be changed as appropriate.

The inorganic solid electrolyte body 16 of the present embodiment is configured to: a part of the fuel supplied to the anode 14 can permeate the cathode 12. As described above, at the cathode 12, the fuel permeated from the anode 14 to the cathode 12 through the inorganic solid electrolyte body 16 reacts with oxygen contained in the oxidant, thereby generating carbon dioxide and water. Therefore, the fuel permeability (i.e., the degree of permeation of the fuel) of the inorganic solid electrolyte bodies 16 can be determined by the amount of carbon dioxide generated at the cathode 12. The amount of carbon dioxide generated at the cathode 12 may be specified as the amount of carbon dioxide generated per unit area of the cathode-side surface 16S.

Specifically, the inorganic solid electrolyte body 16 is permeable to the electrolyte solution generated at the cathode 12 and has a thickness of 0.04. mu. mol/S-cm per unit area of the cathode-side surface 16S²～2.5μmol/s·cm²Of carbon dioxideAnd (3) fuel.

The amount of carbon dioxide produced was set to 0.04. mu. mol/s-cm per unit area²As described above, since the water produced from the fuel having permeated through the inorganic solid electrolyte 16 can be supplied to the cathode 12, the rated load (0.3A/cm) is applied²Air utilization rate Ua 50%), the output of the solid alkaline fuel cell 10 can be maintained even if the humidifier output is reduced. The amount of carbon dioxide produced was set to 2.5. mu. mol/s.cm per unit area²Hereinafter, the rate of increase in the required fuel supply amount due to permeation of the fuel to the cathode 12 can be suppressed while maintaining the output of the solid alkaline fuel cell 10 by suppressing the deterioration of the characteristics of the inorganic solid electrolyte body 16.

The amount of carbon dioxide produced was set to 0.15. mu. mol/s-cm per unit area²As described above, the amount of carbon dioxide produced per unit area was 0.6. mu. mol/s-cm²As described above, even if the humidifier output is further reduced when power generation is performed at the rated load, the output of the solid alkaline fuel cell 10 can be maintained.

The amount of carbon dioxide produced was 1.7. mu. mol/s.cm per unit area²The amount of carbon dioxide produced was 1.7. mu. mol/s-cm per unit area²As described below, the deterioration of the characteristics of the inorganic solid electrolyte body 16 itself can be further suppressed, and the increase rate of the fuel supply amount can be further suppressed.

The amount of carbon dioxide generated from the fuel at the cathode 12 is obtained as follows: the amount of carbon dioxide [ μmol ] contained in the oxidant recovered in the entirety after passing through the cathode 12 is measured by a gas chromatograph apparatus, whereby the amount of carbon dioxide generated from the fuel at the cathode 12 is obtained. However, when the oxidizing agent itself supplied from the oxidizing agent supply means 13 contains carbon dioxide, the amount of carbon dioxide generated from the fuel can be accurately grasped by subtracting the amount of carbon dioxide contained in the oxidizing agent itself from the measured amount of carbon dioxide. Then, the amount of carbon dioxide generated from the fuel is divided by the area of the cathode side surface 16S and the operating time, thereby calculating the amount of carbon dioxide generated per unit area of the cathode side surface 16S.

In order to impart the fuel permeation function to the inorganic solid electrolyte bodies 16, for example, any of the following methods 1,2, or a combination of the methods 1 and 2 can be used.

The first method for imparting a fuel permeation function is a method of providing through holes in the inorganic solid electrolyte body 16. The through hole is formed as follows: the interior of the inorganic solid electrolyte body 16 penetrates from the anode side surface 16T to the cathode side surface 16S. The inner diameter and the number of the through-holes were 0.04. mu. mol/S-cm per unit area of the cathode-side surface 16S formed at the cathode 12²～2.5μmol/s·cm²The carbon dioxide of (2) may be appropriately set. The through-hole is preferably disposed in the vicinity of the supply port of the oxidizing agent supply mechanism 13 in the inorganic solid electrolyte body 16. This allows the water produced by the reaction between the fuel and oxygen flowing out of the through-holes to the cathode 12 to be distributed over the entire cathode 12 together with the oxidant.

The 2 nd method for imparting the fuel permeation function is a method of providing pores in the inorganic solid electrolyte body 16. The air holes are preferably formed as: the interior of the inorganic solid electrolyte body 16 is communicated from the anode-side surface 16T to the cathode-side surface 16S. The shape of the pores is not particularly limited, and may be an indefinite shape, a mesh shape, or the like. The pores may be formed over the entire inorganic solid electrolyte body 16, or may be formed only in a part of the inorganic solid electrolyte body 16. The inner diameter, length and number of pores were 0.04. mu. mol/s.cm per unit area of the cathode-side surface 16S generated at the cathode 12²～2.5μmol/s·cm²The carbon dioxide of (2) may be appropriately set.

However, when the inorganic solid electrolyte body 16 contains a substrate described later, the above-described method 2 (method of providing pores) can be employed only when the substrate is made of a material that can withstand a firing temperature (for example, 400 ℃. The method of manufacturing the inorganic solid electrolyte body 16 is described later.

The inorganic solid electrolyte body 16 may be composed of only a particle group containing an inorganic solid electrolyte having hydroxide ion conductivity, or may contain an auxiliary component that contributes to densification and solidification of the particle group.

The inorganic solid electrolyte 16 may be a composite of a porous body having open porosity as a base material and an inorganic solid electrolyte (for example, L DH) deposited and grown in the pores so as to fill the pores of the porous body.

The inorganic solid electrolyte body 16 may be in any form of a plate, a film, and a layer. When the inorganic solid electrolyte 16 is in the form of a film or a layer, the inorganic solid electrolyte 16 may be an inorganic solid electrolyte formed in the form of a film or a layer on or in a porous substrate. When the inorganic solid electrolyte body 16 is in the form of a film or a layer, the thickness of the inorganic solid electrolyte body 16 may be 100 μm or less, preferably 75 μm or less, more preferably 50 μm or less, still more preferably 25 μm or less, and particularly preferably 5 μm or less. By making the inorganic solid electrolyte body 16 thin, the resistance of the inorganic solid electrolyte body 16 can be reduced. The lower limit of the thickness of the inorganic solid electrolyte body 16 may be set according to the application, and is preferably 1 μm or more, and more preferably 2 μm or more, in order to ensure a certain degree of compactness. When the inorganic solid electrolyte body 16 is plate-shaped, the thickness of the inorganic solid electrolyte body 16 may be 0.01mm to 0.5mm, preferably 0.02mm to 0.2mm, and more preferably 0.05mm to 0.1 mm.

(method for producing inorganic solid electrolyte 16)

An example of a method for producing the inorganic solid electrolyte 16 will be described, in which L DH powder of L DH represented by hydrotalcite is molded and fired to prepare an oxide fired body, which is regenerated to L DH, and then excess water is removed, and in which a dense inorganic solid electrolyte 16 can be produced easily and stably.

Preparation of L DH powder

Prepared to have a structure represented by the general formula: [ M ] A²⁺ _1-xM³⁺ _x(OH)₂][A^n- _x/n·mH₂O](in the formula, M²⁺Is a cation of valency 2, M^{3 +}Is a cation of valency 3, A^n-L DH powder having a basic composition represented by n-valent anion, n is an integer of 1 or more, and x is 0.1 to 0.4) L DH powder may be a commercially available product or a raw material prepared by a known method such as a liquid phase synthesis method using nitrate or chloride.

L DH powder has a particle size not particularly limited, but the volume-based D50 average particle size is preferably 0.1 to 1.0. mu.m, more preferably 0.3 to 0.8. mu.m. if the particle size of L DH powder is too small, the powder is agglomerated, pores are likely to remain during molding, and if the particle size of L DH powder is too large, moldability is likely to deteriorate.

L DH powder can be made into oxide powder by calcination, the calcination temperature in this case may be set to a temperature range in which the particle size of the raw material does not change significantly, and is, for example, preferably 500 ℃ or less, more preferably 380 to 460 ℃.

2. Process for producing molded article

Then, L DH powder is molded to obtain a molded article, the molding is preferably performed by, for example, press molding in such a manner that the relative density of the molded article becomes 43% to 65%, more preferably 45% to 60%, and still more preferably 47% to 58%, and a known method such as uniaxial die pressing, Cold Isostatic Pressing (CIP), slip casting, or extrusion molding can be used for the press molding, but the method of preparing L DH powder into oxide powder by calcining is limited to dry molding.

When the fuel permeation function is imparted to the inorganic solid electrolyte body 16 by the method 2 (the method of providing pores), a pore-forming material (for example, an acrylic polymer, methyl cellulose, or the like) is added to the L DH powder to form a molded body, the pore-forming material is removed by firing in the firing step described later, pores are formed in the oxide fired body, and the inner diameter, length, and number of pores can be adjusted by the particle diameter and amount of the pore-forming material.

Since the weight of the molded article is affected by adsorbed moisture, it is preferable to measure the relative density of a molded article obtained by using L DH powder stored in a desiccator at room temperature and a relative humidity of 20% or less for 24 hours or more, or to measure the relative density of a molded article after storing the molded article under the above conditions.

However, when L DH powder was calcined to prepare oxide powder, the relative density of the molded article was 26% to 40%, more preferably 29% to 36%, and when oxide powder was used, the relative density was determined by calculating the converted density as a mixture of the respective oxides assuming that the respective metal elements constituting L DH were converted to the respective oxides by calcination, and using the converted density as a denominator.

3. Firing Process

Then, the molded body is fired to obtain an oxide fired body. The firing is preferably carried out in such a manner that the oxide fired body is 57 to 65% by weight of the molded body and/or 70 to 76% by volume of the molded body.

When the weight of the oxide fired body is 57% or more of the weight of the compact, a heterogeneous phase which cannot be regenerated in the subsequent step, i.e., when the regeneration is L DH, is not easily generated, and when the weight of the oxide fired body is 65% or less of the weight of the compact, the firing is sufficiently performed, and the subsequent step is sufficiently densified, and when the volume of the oxide fired body is 70% or more of the volume of the compact, a heterogeneous phase is not easily generated in the subsequent step, i.e., when the regeneration is L DH, and cracks are not easily generated, and when the volume of the oxide fired body is 76% or less of the volume of the compact, the firing is sufficiently performed, and the subsequent step is sufficiently densified.

However, when L DH powder is calcined to form oxide powder, it is preferable to calcine the oxide fired body to a volume of 85 to 95% by weight of the compact and/or 90% or more by volume of the compact.

Regardless of whether L DH powder is calcined, the calcination is preferably performed such that the relative density of the oxide calcined body is 20% to 40%, more preferably 20% to 35%, and still more preferably 20% to 30% in terms of oxide, and the relative density in terms of oxide is determined by using, as a denominator, the reduced density determined as a mixture of the oxides, assuming that each metal element constituting L DH is converted to its respective oxide by calcination.

The firing temperature of the molded article may be 400 to 850 ℃, and preferably 700 to 800 ℃. The firing step preferably includes a step of holding the firing temperature for 1 hour or more, preferably 3 hours to 10 hours. In order to prevent the molded article from being cracked by the release of water or carbon dioxide due to a rapid temperature rise, the temperature rise rate up to the above firing temperature is preferably 100 ℃/h or less, more preferably 5 ℃/h to 75 ℃/h, and still more preferably 10 ℃/h to 50 ℃/h. Therefore, the total firing time from the temperature rise to the temperature decrease (100 ℃ or less) is preferably 20 hours or more, more preferably 30 hours to 70 hours, and further preferably 35 hours to 65 hours.

In the above-described step of producing a molded article, when a pore-forming material is added to the molded article, the pore-forming material is removed by firing in the firing step, thereby forming pores in the oxide fired body.

4. Regeneration to L DH

Next, the oxide fired body is held in the above-mentioned anion (A) containing a valence of n^n-) L DH, thereby obtaining a L DH-enriched solidified body, i.e., a L DH-solidified body obtained by the method necessarily contains excess moisture.

The anion contained in the aqueous solution may be the same kind of anion as the anion contained in the L DH powder, or may be a different kind of anion.

The oxide fired body is preferably held in or directly above the aqueous solution in a closed vessel by hydrothermal synthesis. As an example of the closed container, a closed container made of teflon (registered trademark) is given. A jacket made of stainless steel or the like is preferably provided outside the sealed container.

L DH is preferably carried out by holding the oxide fired body at 20 ℃ or higher and less than 200 ℃ in a state where at least one surface of the oxide fired body is in contact with the aqueous solution, more preferably at 50 ℃ to 180 ℃, still more preferably at 100 ℃ to 150 ℃, and at such L DH temperature, the oxide sintered body is preferably held for 1 hour or more, more preferably 2 hours or more, still more preferably 5 hours or more, whereby the heterogeneous phase can be suppressed from remaining by sufficiently performing the regeneration into L DH.

When the hydrothermal treatment is performed in a closed vessel, the oxide fired body may be submerged in the aqueous solution, or the treatment may be performed in a state where at least one side is in contact with the aqueous solution using a jig.

When pores are formed in the oxide fired body, even after the regeneration step, the pores remain in the L DH solidified body.

5. Dehydration step

Next, the inorganic solid electrolyte 16 is obtained by removing excess water from L DH cured body, the step of removing excess water is preferably performed in an environment of 300 ℃ or lower and 25% or higher of the estimated relative humidity at the highest temperature of the removal step, and in order to prevent rapid evaporation of water from L DH cured body, it is preferably performed by sealing again in a closed container used in the step of regenerating to L DH at a temperature higher than room temperature, and in this case, the temperature is preferably 50 to 250 ℃, more preferably 100 to 200 ℃.

When the fuel permeation function is imparted to the inorganic solid electrolyte body 16 by the method 1 (method of providing through holes), through holes are directly formed in the inorganic solid electrolyte body 16 from which excess water has been removed. The through-holes can be formed by making holes in the thickness direction of the inorganic solid electrolyte body 16 using a laser. The inner diameter of the through hole can be adjusted by changing the laser output power and the irradiation time.